WEBVTT 00:00:00.000 --> 00:00:01.985 align:middle line:90% [SQUEAKING] 00:00:01.985 --> 00:00:03.965 align:middle line:90% [RUSTLING] 00:00:03.965 --> 00:00:06.935 align:middle line:90% [CLICKING] 00:00:06.935 --> 00:00:16.630 align:middle line:90% 00:00:16.630 --> 00:00:17.880 align:middle line:90% JUEJUN HU: OK, so let's start. 00:00:17.880 --> 00:00:19.480 align:middle line:84% So in the last lecture, we discussed 00:00:19.480 --> 00:00:22.560 align:middle line:84% about essentially glass manufacturing techniques, 00:00:22.560 --> 00:00:25.080 align:middle line:90% more for volume production. 00:00:25.080 --> 00:00:27.200 align:middle line:84% So we're going to switch gears a little bit. 00:00:27.200 --> 00:00:30.600 align:middle line:84% We're going to start by talking about caneworking, which 00:00:30.600 --> 00:00:34.120 align:middle line:90% is really more for artworks. 00:00:34.120 --> 00:00:35.265 align:middle line:90% People do this manually. 00:00:35.265 --> 00:00:36.640 align:middle line:84% It's more of a skill, rather than 00:00:36.640 --> 00:00:38.380 align:middle line:84% for any kind of industrial-scale production. 00:00:38.380 --> 00:00:40.755 align:middle line:84% This is how they actually make all kinds of beautiful art 00:00:40.755 --> 00:00:41.600 align:middle line:90% pieces out of glass. 00:00:41.600 --> 00:00:43.280 align:middle line:84% I want to mention that glass has always 00:00:43.280 --> 00:00:45.480 align:middle line:84% been a very important material for artists. 00:00:45.480 --> 00:00:48.400 align:middle line:84% It has many striking properties that make it very attractive. 00:00:48.400 --> 00:00:50.400 align:middle line:84% You can exhibit all kinds of colors. 00:00:50.400 --> 00:00:53.520 align:middle line:84% It can go from optically, perfectly transparent, 00:00:53.520 --> 00:00:55.480 align:middle line:84% all the way to opaque or translucent. 00:00:55.480 --> 00:00:59.080 align:middle line:84% Also, from the processing side, the fact 00:00:59.080 --> 00:01:01.960 align:middle line:84% that you have this continuous viscosity-temperature curve 00:01:01.960 --> 00:01:03.600 align:middle line:84% allows you to easily shape glasses 00:01:03.600 --> 00:01:06.040 align:middle line:84% into many different kinds of geometries that otherwise 00:01:06.040 --> 00:01:07.760 align:middle line:84% can be quite challenging, if you're trying to do 00:01:07.760 --> 00:01:09.140 align:middle line:90% it using crystalline materials. 00:01:09.140 --> 00:01:12.400 align:middle line:84% That's why, for a long time, back from ancient Romans 00:01:12.400 --> 00:01:14.640 align:middle line:84% to today, people have always been using glasses 00:01:14.640 --> 00:01:17.660 align:middle line:84% as one of the dominant materials for art pieces. 00:01:17.660 --> 00:01:21.600 align:middle line:84% So what I'm going to show you here is essentially a technique 00:01:21.600 --> 00:01:23.920 align:middle line:84% that people have been adopting to essentially make 00:01:23.920 --> 00:01:25.500 align:middle line:90% different kinds of glass pieces. 00:01:25.500 --> 00:01:28.170 align:middle line:90% It's called caneworking. 00:01:28.170 --> 00:01:29.920 align:middle line:84% And I'm showing you here, this is actually 00:01:29.920 --> 00:01:32.640 align:middle line:84% just a few photos of examples of artwork 00:01:32.640 --> 00:01:34.760 align:middle line:90% coming from caneworking there. 00:01:34.760 --> 00:01:37.340 align:middle line:84% You can notice the names here-- reticello, 00:01:37.340 --> 00:01:39.840 align:middle line:90% zanfirico, millefiori. 00:01:39.840 --> 00:01:42.867 align:middle line:90% These all have Italian origin. 00:01:42.867 --> 00:01:45.200 align:middle line:84% This is not surprising because a lot of these techniques 00:01:45.200 --> 00:01:48.120 align:middle line:84% were actually developed in medieval times 00:01:48.120 --> 00:01:51.160 align:middle line:84% by essentially glass workers in Venice. 00:01:51.160 --> 00:01:55.480 align:middle line:84% In fact, at the time, back in the 13th century, 00:01:55.480 --> 00:01:58.730 align:middle line:84% Venice actually had essentially grouped all the glass workers, 00:01:58.730 --> 00:02:01.497 align:middle line:84% put them on one isolated island, called Murano island. 00:02:01.497 --> 00:02:03.330 align:middle line:84% That's where they actually made the glasses. 00:02:03.330 --> 00:02:04.910 align:middle line:84% And the motivation is pretty clear. 00:02:04.910 --> 00:02:07.150 align:middle line:84% Firstly, glass-making is considered 00:02:07.150 --> 00:02:08.669 align:middle line:84% dangerous industry because of all 00:02:08.669 --> 00:02:10.009 align:middle line:90% the high-temperature furnaces. 00:02:10.009 --> 00:02:11.970 align:middle line:84% And trying to do that in wooden houses 00:02:11.970 --> 00:02:14.165 align:middle line:84% is not a very perfectly safe practice. 00:02:14.165 --> 00:02:16.290 align:middle line:84% So they figured that they should just isolate them, 00:02:16.290 --> 00:02:18.050 align:middle line:84% put them all in an island, so in case something happens, 00:02:18.050 --> 00:02:19.830 align:middle line:84% nothing's going to spread to [INAUDIBLE]. 00:02:19.830 --> 00:02:23.110 align:middle line:84% Second reason, glassmaking is actually 00:02:23.110 --> 00:02:27.190 align:middle line:84% one of the most profitable businesses at the time. 00:02:27.190 --> 00:02:29.830 align:middle line:84% So Venice were able to get lots of profit out of it 00:02:29.830 --> 00:02:31.790 align:middle line:84% through essentially, basically a monopoly. 00:02:31.790 --> 00:02:34.830 align:middle line:84% They keep all the secrets about glassmaking as trade secrets, 00:02:34.830 --> 00:02:38.990 align:middle line:84% so they can essentially have all the profits to their own. 00:02:38.990 --> 00:02:41.810 align:middle line:84% In fact, at the time, the glassmakers, 00:02:41.810 --> 00:02:43.930 align:middle line:84% they were actually not allowed to leave Venice. 00:02:43.930 --> 00:02:45.322 align:middle line:90% They had to stay on the island. 00:02:45.322 --> 00:02:47.030 align:middle line:84% So it makes sense to essentially put them 00:02:47.030 --> 00:02:49.110 align:middle line:90% all in one single island there. 00:02:49.110 --> 00:02:52.150 align:middle line:84% In compensation, they get lots of privileges. 00:02:52.150 --> 00:02:56.550 align:middle line:84% The glassmakers, they can actually wear swords. 00:02:56.550 --> 00:03:00.950 align:middle line:84% They don't get prosecuted by the republic. 00:03:00.950 --> 00:03:03.110 align:middle line:84% So they have lots of privileges [INAUDIBLE]. 00:03:03.110 --> 00:03:05.910 align:middle line:84% But anyways, over time, I mean, the technology eventually 00:03:05.910 --> 00:03:06.690 align:middle line:90% spread out. 00:03:06.690 --> 00:03:09.050 align:middle line:84% So now you see glass workshops across the world. 00:03:09.050 --> 00:03:12.070 align:middle line:84% But still, lots of techniques originally from those types, 00:03:12.070 --> 00:03:15.550 align:middle line:84% from essentially the glassworks in Venice. 00:03:15.550 --> 00:03:18.230 align:middle line:84% So now for caneworking, the whole idea of caneworking 00:03:18.230 --> 00:03:20.550 align:middle line:84% is that you can create essentially these long, thin 00:03:20.550 --> 00:03:22.670 align:middle line:90% glass rods called canes. 00:03:22.670 --> 00:03:24.890 align:middle line:84% They can have different kind of colors and patterns. 00:03:24.890 --> 00:03:26.973 align:middle line:84% You can then merge them together to form all kinds 00:03:26.973 --> 00:03:28.290 align:middle line:90% of beautiful appearances. 00:03:28.290 --> 00:03:30.810 align:middle line:84% There are two different ways we essentially 00:03:30.810 --> 00:03:32.550 align:middle line:90% still use these canes. 00:03:32.550 --> 00:03:34.670 align:middle line:84% Some of them, you can use them to essentially look 00:03:34.670 --> 00:03:35.930 align:middle line:90% at from the side. 00:03:35.930 --> 00:03:37.670 align:middle line:84% This is one example of zanfirico. 00:03:37.670 --> 00:03:40.150 align:middle line:84% You can see that these kind of twisted patterns, those 00:03:40.150 --> 00:03:41.890 align:middle line:84% are actually embedded in the glass case. 00:03:41.890 --> 00:03:43.890 align:middle line:84% And you're looking at them from the side. 00:03:43.890 --> 00:03:45.410 align:middle line:90% You have another example here. 00:03:45.410 --> 00:03:46.635 align:middle line:90% This one is millefiori. 00:03:46.635 --> 00:03:49.010 align:middle line:84% We're going to see a little video about how this is made. 00:03:49.010 --> 00:03:49.950 align:middle line:84% But you can see that there are actually 00:03:49.950 --> 00:03:51.390 align:middle line:84% many sections of canes, where you're actually 00:03:51.390 --> 00:03:53.750 align:middle line:84% looking at the cross-sectional patterns on the canes. 00:03:53.750 --> 00:03:56.140 align:middle line:84% So these are two primary ways how the canes 00:03:56.140 --> 00:03:59.260 align:middle line:90% can be used in decoration. 00:03:59.260 --> 00:04:01.460 align:middle line:84% Now, specifically, how you actually make a cane? 00:04:01.460 --> 00:04:03.540 align:middle line:84% So the way it works is that you start it 00:04:03.540 --> 00:04:06.540 align:middle line:84% out by using essentially a long steel 00:04:06.540 --> 00:04:10.700 align:middle line:84% rod to gather a gob of glass, a big chunk of glass 00:04:10.700 --> 00:04:11.560 align:middle line:90% from the furnace. 00:04:11.560 --> 00:04:13.860 align:middle line:90% So this is the goal. 00:04:13.860 --> 00:04:17.339 align:middle line:84% The large steel rod you use to actually gather the glass 00:04:17.339 --> 00:04:19.980 align:middle line:84% is called pontil, one of those terminologies 00:04:19.980 --> 00:04:21.459 align:middle line:90% specific for glassworking. 00:04:21.459 --> 00:04:23.860 align:middle line:84% So once you have that, what you do next is then 00:04:23.860 --> 00:04:28.420 align:middle line:84% you try to roll that piece of glass gob on a bench, 00:04:28.420 --> 00:04:31.620 align:middle line:84% workbench with a stainless steel flat surface. 00:04:31.620 --> 00:04:35.980 align:middle line:84% So that bench is called a marver. 00:04:35.980 --> 00:04:40.458 align:middle line:84% So you roll it until you get this kind of cylindrical shape. 00:04:40.458 --> 00:04:43.000 align:middle line:84% And then next thing is that you actually have another person, 00:04:43.000 --> 00:04:45.000 align:middle line:84% or sometimes you can do it yourself, essentially 00:04:45.000 --> 00:04:51.180 align:middle line:84% fit another pontil to the other end of this gob there. 00:04:51.180 --> 00:04:54.700 align:middle line:84% So then you essentially have this cylindrical shape 00:04:54.700 --> 00:04:57.780 align:middle line:84% of the glass now attached to two rods. 00:04:57.780 --> 00:05:00.062 align:middle line:84% You can then pull it on the two ends. 00:05:00.062 --> 00:05:01.520 align:middle line:84% This is usually done by two person, 00:05:01.520 --> 00:05:02.978 align:middle line:84% but you can also do it by yourself. 00:05:02.978 --> 00:05:07.140 align:middle line:84% So this glass can now actually deform viscously and then 00:05:07.140 --> 00:05:10.140 align:middle line:90% get extended into a thin strand. 00:05:10.140 --> 00:05:14.260 align:middle line:84% So once that thin strand cools down, this is your cane. 00:05:14.260 --> 00:05:17.020 align:middle line:84% So the typical cane has a diameter, 00:05:17.020 --> 00:05:20.380 align:middle line:84% I would say, maybe like five millimeters, give or take. 00:05:20.380 --> 00:05:23.060 align:middle line:84% And there are a lot of tricks you can actually do while you're 00:05:23.060 --> 00:05:24.145 align:middle line:90% actually creating a cane. 00:05:24.145 --> 00:05:25.520 align:middle line:84% You can essentially, for example, 00:05:25.520 --> 00:05:27.780 align:middle line:84% merge different kind of glasses and colored glasses 00:05:27.780 --> 00:05:29.260 align:middle line:90% into one single cane. 00:05:29.260 --> 00:05:31.860 align:middle line:84% You can also twist it while you're actually doing the cane 00:05:31.860 --> 00:05:34.080 align:middle line:84% joint, so you get these kind of twisted patterns, 00:05:34.080 --> 00:05:36.140 align:middle line:84% sort of like what you have here for zanfirico. 00:05:36.140 --> 00:05:39.860 align:middle line:84% And then in the end, you can further 00:05:39.860 --> 00:05:42.340 align:middle line:84% merge the canes together, stack them together, bundle them 00:05:42.340 --> 00:05:44.820 align:middle line:84% together, then do another cane joint process 00:05:44.820 --> 00:05:47.500 align:middle line:84% to get all the complex patterns, composite patterns. 00:05:47.500 --> 00:05:54.730 align:middle line:84% So for a long time, this kind of canemaking process 00:05:54.730 --> 00:05:57.170 align:middle line:84% is pretty much a trial-and-error process. 00:05:57.170 --> 00:05:59.570 align:middle line:84% People make somewhat informed guesses 00:05:59.570 --> 00:06:02.510 align:middle line:84% about what cane may be looking like after a certain process, 00:06:02.510 --> 00:06:04.450 align:middle line:84% but [INAUDIBLE] there's a lot of guessing and trial and error 00:06:04.450 --> 00:06:05.090 align:middle line:90% there. 00:06:05.090 --> 00:06:08.530 align:middle line:84% We are MIT, so we like to quantify things. 00:06:08.530 --> 00:06:12.370 align:middle line:84% So that's why, a few years back, the MIT Glass Lab actually 00:06:12.370 --> 00:06:14.770 align:middle line:84% developed this Virtual Glass software package 00:06:14.770 --> 00:06:17.410 align:middle line:84% that allows you to now actually mathematically model 00:06:17.410 --> 00:06:18.930 align:middle line:84% how the cane is going to come out, 00:06:18.930 --> 00:06:20.690 align:middle line:84% depending on processing parameters. 00:06:20.690 --> 00:06:24.010 align:middle line:84% So I'm going to show you a little video here. 00:06:24.010 --> 00:06:27.170 align:middle line:84% In the video, it is also going to show you how the canemaking 00:06:27.170 --> 00:06:28.570 align:middle line:90% process is actually done. 00:06:28.570 --> 00:06:31.430 align:middle line:84% So that helps explain a lot of things here. 00:06:31.430 --> 00:06:33.310 align:middle line:90% So let me just play this video. 00:06:33.310 --> 00:06:38.510 align:middle line:90% 00:06:38.510 --> 00:06:39.930 align:middle line:90% [VIDEO PLAYBACK] 00:06:39.930 --> 00:06:42.410 align:middle line:84% - The idea of glass cane is to heat and stretch 00:06:42.410 --> 00:06:45.850 align:middle line:84% colored glass into long rods that can, after cooling, be 00:06:45.850 --> 00:06:48.690 align:middle line:84% cut into shorter lengths, combined, and then reheated 00:06:48.690 --> 00:06:51.250 align:middle line:84% to make various geometric designs. 00:06:51.250 --> 00:06:54.210 align:middle line:84% The use of cane goes back far into the history of glass, 00:06:54.210 --> 00:06:57.050 align:middle line:84% at least 2,000 years, to Roman times. 00:06:57.050 --> 00:06:59.690 align:middle line:84% It is still one of the most popular methods of decoration 00:06:59.690 --> 00:07:02.010 align:middle line:90% used by glass artists today. 00:07:02.010 --> 00:07:04.770 align:middle line:84% One of the reasons for the continuing popularity of cane 00:07:04.770 --> 00:07:07.410 align:middle line:84% among glass artists is the almost endless variety 00:07:07.410 --> 00:07:11.030 align:middle line:84% of possibilities afforded by changing a few basic variables, 00:07:11.030 --> 00:07:14.630 align:middle line:84% such as color, the geometry of the design within each cane, 00:07:14.630 --> 00:07:17.010 align:middle line:84% and the way the cane is then put together and included 00:07:17.010 --> 00:07:18.890 align:middle line:90% in a finished glass piece. 00:07:18.890 --> 00:07:20.730 align:middle line:84% For many hundreds of years, the main way 00:07:20.730 --> 00:07:22.970 align:middle line:84% to find out what a new cane design might look like 00:07:22.970 --> 00:07:25.690 align:middle line:84% has been to go into the studio and try it, perhaps 00:07:25.690 --> 00:07:27.830 align:middle line:84% after sketching some ideas on paper. 00:07:27.830 --> 00:07:31.170 align:middle line:84% In other words, a lengthy process of trial and error. 00:07:31.170 --> 00:07:33.890 align:middle line:84% - Virtual Glass is a free, open-source software program 00:07:33.890 --> 00:07:36.010 align:middle line:84% that allows anyone, at any skill level, 00:07:36.010 --> 00:07:38.137 align:middle line:84% to explore the world of cane design. 00:07:38.137 --> 00:07:39.970 align:middle line:84% While ultimately there's still no substitute 00:07:39.970 --> 00:07:42.490 align:middle line:84% for trial and error in the studio as a way of proving what 00:07:42.490 --> 00:07:44.570 align:middle line:84% a design will actually look like in glass, 00:07:44.570 --> 00:07:46.850 align:middle line:84% Virtual Glass allows the user to rapidly try 00:07:46.850 --> 00:07:48.360 align:middle line:84% many different kinds of approaches 00:07:48.360 --> 00:07:51.140 align:middle line:84% to designing glass cane, all at the speed of thought, 00:07:51.140 --> 00:07:54.320 align:middle line:84% without having to spend hours manipulating and heating glass. 00:07:54.320 --> 00:07:57.060 align:middle line:84% Let's start with the creation and use of a simple white cane, 00:07:57.060 --> 00:07:59.980 align:middle line:84% alternating between the software where the cane is designed 00:07:59.980 --> 00:08:02.800 align:middle line:84% and the glass studio where the cane is made and used. 00:08:02.800 --> 00:08:05.920 align:middle line:84% First, we select the color from a library of colors produced 00:08:05.920 --> 00:08:08.080 align:middle line:90% by popular glass manufacturers. 00:08:08.080 --> 00:08:10.500 align:middle line:84% The selected color appears in the library on the left, 00:08:10.500 --> 00:08:13.520 align:middle line:84% under the New Color heading, ready to be used in cane. 00:08:13.520 --> 00:08:16.260 align:middle line:84% - When making cane in the glass studio, color, 00:08:16.260 --> 00:08:18.160 align:middle line:84% here in the concentrated bar form, 00:08:18.160 --> 00:08:20.960 align:middle line:84% is broken into appropriately sized chunks and then placed 00:08:20.960 --> 00:08:23.960 align:middle line:84% in the pickup oven, where it sits for about 15 minutes 00:08:23.960 --> 00:08:26.360 align:middle line:84% to come up to a working temperature of about 1,000 00:08:26.360 --> 00:08:28.400 align:middle line:90% degrees Fahrenheit. 00:08:28.400 --> 00:08:31.000 align:middle line:84% - In Virtual Glass, we create a cane by specifying its 00:08:31.000 --> 00:08:32.179 align:middle line:90% cross-section. 00:08:32.179 --> 00:08:34.000 align:middle line:84% First we select a template, in this case 00:08:34.000 --> 00:08:36.520 align:middle line:84% a colored core surrounded by clear glass. 00:08:36.520 --> 00:08:39.080 align:middle line:84% Then we drag a color into the cross-section from the library 00:08:39.080 --> 00:08:40.400 align:middle line:90% area on the left. 00:08:40.400 --> 00:08:42.440 align:middle line:84% Finally, we adjust the diameter of the colored 00:08:42.440 --> 00:08:45.140 align:middle line:84% core in proportion to the clear casing around it. 00:08:45.140 --> 00:08:46.960 align:middle line:84% - In the glass studio, the cane begins 00:08:46.960 --> 00:08:50.000 align:middle line:84% by picking up the color previously loaded into the oven 00:08:50.000 --> 00:08:51.940 align:middle line:90% onto a metal rod called a punty. 00:08:51.940 --> 00:08:55.130 align:middle line:84% The color gets further heated in the glory hole to nearly 2,000 00:08:55.130 --> 00:08:57.520 align:middle line:84% degrees Fahrenheit, allowing it to be shaped 00:08:57.520 --> 00:08:59.640 align:middle line:90% into a straight-sided cylinder. 00:08:59.640 --> 00:09:02.260 align:middle line:84% Next, we gather clear glass from the furnace, 00:09:02.260 --> 00:09:04.340 align:middle line:84% which is the start of the cased layer. 00:09:04.340 --> 00:09:07.360 align:middle line:90% 00:09:07.360 --> 00:09:09.080 align:middle line:84% We shape and cool the casing until we 00:09:09.080 --> 00:09:10.740 align:middle line:90% can add more clear glass. 00:09:10.740 --> 00:09:15.320 align:middle line:90% 00:09:15.320 --> 00:09:18.180 align:middle line:84% After a final shaping pass and heat adjustment, 00:09:18.180 --> 00:09:20.940 align:middle line:84% we attach another rod and start to pull the cane. 00:09:20.940 --> 00:09:25.440 align:middle line:90% 00:09:25.440 --> 00:09:31.000 align:middle line:84% We slowly stretch the glass, finally pulling it straight 00:09:31.000 --> 00:09:35.800 align:middle line:84% as the glass becomes rigid, and set it down when 00:09:35.800 --> 00:09:38.540 align:middle line:90% it is cool enough not to bend. 00:09:38.540 --> 00:09:40.040 align:middle line:84% - Next, let's combine the cane we've 00:09:40.040 --> 00:09:42.080 align:middle line:90% created into a finished piece. 00:09:42.080 --> 00:09:44.220 align:middle line:84% First, we select a template for a pickup. 00:09:44.220 --> 00:09:45.790 align:middle line:84% In this case, a simple arrangement 00:09:45.790 --> 00:09:48.590 align:middle line:84% that we adjust to contain 24 canes. 00:09:48.590 --> 00:09:51.530 align:middle line:84% Then we drag cane from the library area on the left, 00:09:51.530 --> 00:09:53.150 align:middle line:90% filling in the template. 00:09:53.150 --> 00:09:55.650 align:middle line:84% Once the first cane has been dragged into the template, 00:09:55.650 --> 00:09:58.110 align:middle line:84% subsequent canes can be added by dragging from the canes 00:09:58.110 --> 00:09:59.790 align:middle line:90% already in the template. 00:09:59.790 --> 00:10:02.350 align:middle line:84% The 3D visualization in the right window can be switched 00:10:02.350 --> 00:10:05.670 align:middle line:84% to several common forms, which can be altered by dragging 00:10:05.670 --> 00:10:07.110 align:middle line:90% control points. 00:10:07.110 --> 00:10:09.050 align:middle line:90% Here, we settle on a bowl shape. 00:10:09.050 --> 00:10:13.150 align:middle line:90% 00:10:13.150 --> 00:10:15.050 align:middle line:84% - To make the bowl in the studio, 00:10:15.050 --> 00:10:18.470 align:middle line:84% first we cut the cane to uniform lengths, 00:10:18.470 --> 00:10:21.850 align:middle line:84% and then we arrange it onto a pre-heated ceramic kiln shelf. 00:10:21.850 --> 00:10:25.910 align:middle line:90% 00:10:25.910 --> 00:10:28.790 align:middle line:84% Once the temperature of the cane and the shelf equalize, 00:10:28.790 --> 00:10:31.070 align:middle line:84% we heat the pickup further in the glory hole, where 00:10:31.070 --> 00:10:33.110 align:middle line:90% it fuses together into a sheet. 00:10:33.110 --> 00:10:35.390 align:middle line:84% And then we pick it up onto a blowpipe. 00:10:35.390 --> 00:10:39.710 align:middle line:84% We shape the pickup into a cylinder, 00:10:39.710 --> 00:10:45.310 align:middle line:84% close it off into a bubble, and then blow and shape it 00:10:45.310 --> 00:10:46.770 align:middle line:90% into the final piece. 00:10:46.770 --> 00:10:52.790 align:middle line:90% 00:10:52.790 --> 00:10:55.590 align:middle line:84% - Let's look at the creation of a more complex cane that uses 00:10:55.590 --> 00:10:56.930 align:middle line:90% two sub-canes. 00:10:56.930 --> 00:10:59.630 align:middle line:84% The first sub-cane is a transparent dark green cased 00:10:59.630 --> 00:11:01.550 align:middle line:84% in clear, and the second sub-cane 00:11:01.550 --> 00:11:04.950 align:middle line:84% is opaque white cased in transparent light green cased 00:11:04.950 --> 00:11:05.690 align:middle line:90% in clear. 00:11:05.690 --> 00:11:08.430 align:middle line:90% 00:11:08.430 --> 00:11:11.090 align:middle line:84% We arrange these two canes around a circular core, 00:11:11.090 --> 00:11:12.570 align:middle line:90% alternating light and dark. 00:11:12.570 --> 00:11:17.870 align:middle line:90% 00:11:17.870 --> 00:11:20.710 align:middle line:84% We color the core transparent yellow. 00:11:20.710 --> 00:11:22.950 align:middle line:84% We add some final clear casing to simulate 00:11:22.950 --> 00:11:25.450 align:middle line:84% the final gather of clear glass from the furnace. 00:11:25.450 --> 00:11:29.430 align:middle line:90% Finally, we twist the cane. 00:11:29.430 --> 00:11:31.950 align:middle line:84% - In the studio, we create this setup by preheating 00:11:31.950 --> 00:11:33.490 align:middle line:90% the sub-canes with a torch. 00:11:33.490 --> 00:11:37.030 align:middle line:90% 00:11:37.030 --> 00:11:39.690 align:middle line:84% Then roll them into the hot yellow core. 00:11:39.690 --> 00:11:42.910 align:middle line:90% 00:11:42.910 --> 00:11:47.110 align:middle line:84% After casing and shaping, the cane is ready to be pulled. 00:11:47.110 --> 00:11:49.910 align:middle line:84% We achieve the twist by constantly spinning the rods 00:11:49.910 --> 00:11:51.090 align:middle line:90% during the pull. 00:11:51.090 --> 00:12:00.430 align:middle line:90% 00:12:00.430 --> 00:12:02.110 align:middle line:90% Here is the final cane. 00:12:02.110 --> 00:12:04.950 align:middle line:84% The top is the virtual drawing from Virtual Glass, 00:12:04.950 --> 00:12:07.910 align:middle line:84% and the bottom is a photograph from the studio. 00:12:07.910 --> 00:12:11.590 align:middle line:84% We hope you enjoy using Virtual Glass to design your own cane. 00:12:11.590 --> 00:12:12.810 align:middle line:90% Thanks for watching. 00:12:12.810 --> 00:12:13.550 align:middle line:90% [END PLAYBACK] 00:12:13.550 --> 00:12:15.232 align:middle line:84% JUEJUN HU: Now, the cane you see there, 00:12:15.232 --> 00:12:17.690 align:middle line:84% that's actually one example of how you actually make canes. 00:12:17.690 --> 00:12:20.190 align:middle line:84% So actually, you can use the patterns by viewing essentially 00:12:20.190 --> 00:12:21.310 align:middle line:90% from the side of the cane. 00:12:21.310 --> 00:12:22.570 align:middle line:84% I want to show you another video. 00:12:22.570 --> 00:12:24.550 align:middle line:84% This actually shows the making of a millefiori, 00:12:24.550 --> 00:12:26.735 align:middle line:84% which essentially means 1,000 flowers. 00:12:26.735 --> 00:12:28.110 align:middle line:84% This is another classical example 00:12:28.110 --> 00:12:30.330 align:middle line:84% to show how to actually make different canes, 00:12:30.330 --> 00:12:33.070 align:middle line:84% and then use the cross-sectional patterns to actually decorate 00:12:33.070 --> 00:12:34.210 align:middle line:90% the final pieces. 00:12:34.210 --> 00:12:37.960 align:middle line:90% 00:12:37.960 --> 00:12:40.385 align:middle line:90% [VIDEO PLAYBACK] 00:12:40.385 --> 00:12:42.820 align:middle line:90% 00:12:42.820 --> 00:12:46.660 align:middle line:84% - This object is made by fusing millefiori canes 00:12:46.660 --> 00:12:51.020 align:middle line:84% into the surface of a rather thick bubble of glass. 00:12:51.020 --> 00:12:53.620 align:middle line:84% There are two types of canes, canes 00:12:53.620 --> 00:13:02.740 align:middle line:84% meant to be viewed from the side and canes meant 00:13:02.740 --> 00:13:05.140 align:middle line:90% to be viewed from the end. 00:13:05.140 --> 00:13:09.020 align:middle line:90% Millefiori canes are this type. 00:13:09.020 --> 00:13:12.340 align:middle line:84% They are usually cut into small sections. 00:13:12.340 --> 00:13:18.220 align:middle line:84% A millefiori cane can be cold-worked to reveal a chevron 00:13:18.220 --> 00:13:19.000 align:middle line:90% pattern. 00:13:19.000 --> 00:13:27.900 align:middle line:90% 00:13:27.900 --> 00:13:31.260 align:middle line:84% In this video, three colored glasses 00:13:31.260 --> 00:13:37.140 align:middle line:84% will be used to create a millefiori bead. 00:13:37.140 --> 00:13:41.260 align:middle line:90% The first is opaque white. 00:13:41.260 --> 00:13:44.540 align:middle line:84% Molten, the glass appears colorless. 00:13:44.540 --> 00:13:49.440 align:middle line:84% As the glass cools, crystals form, which create the opacity. 00:13:49.440 --> 00:13:52.620 align:middle line:90% 00:13:52.620 --> 00:13:56.420 align:middle line:84% This is an opaque red glass that similarly 00:13:56.420 --> 00:14:00.920 align:middle line:84% appears colorless and transparent when molten. 00:14:00.920 --> 00:14:04.500 align:middle line:90% 00:14:04.500 --> 00:14:11.620 align:middle line:84% The third is a transparent, intensely colored aqua. 00:14:11.620 --> 00:14:14.000 align:middle line:84% When the glass cools to room temperature, 00:14:14.000 --> 00:14:15.800 align:middle line:90% the colors reveal themselves. 00:14:15.800 --> 00:14:26.500 align:middle line:90% 00:14:26.500 --> 00:14:32.180 align:middle line:84% The first step is gathering glass on the end of a metal rod. 00:14:32.180 --> 00:14:37.530 align:middle line:84% To get a sufficient amount, this is done two times. 00:14:37.530 --> 00:14:39.370 align:middle line:84% The glass is rolled back and forth 00:14:39.370 --> 00:14:42.690 align:middle line:84% on the brass table called the marver. 00:14:42.690 --> 00:14:45.070 align:middle line:84% And this elongates the mass of glass. 00:14:45.070 --> 00:14:48.730 align:middle line:90% 00:14:48.730 --> 00:14:53.950 align:middle line:84% This is lowered into a different color, here opaque white. 00:14:53.950 --> 00:15:02.970 align:middle line:90% 00:15:02.970 --> 00:15:05.710 align:middle line:84% Marvering ensures an even coating. 00:15:05.710 --> 00:15:08.770 align:middle line:90% 00:15:08.770 --> 00:15:12.410 align:middle line:84% This is lowered into the transparent aqua glass. 00:15:12.410 --> 00:15:17.490 align:middle line:90% Excess is left to drip off. 00:15:17.490 --> 00:15:22.770 align:middle line:84% It's marvered, and the excess at the tip is cut away. 00:15:22.770 --> 00:15:27.690 align:middle line:84% The goal is to produce a rather thin layer of aqua. 00:15:27.690 --> 00:15:31.370 align:middle line:84% This is pressed firmly into the dip or optic mold 00:15:31.370 --> 00:15:33.890 align:middle line:90% to create ribs. 00:15:33.890 --> 00:15:37.530 align:middle line:84% And as soon as it hardens, it's lowered gradually 00:15:37.530 --> 00:15:40.630 align:middle line:84% into the pot of molten opaque white glass. 00:15:40.630 --> 00:15:52.930 align:middle line:90% 00:15:52.930 --> 00:15:55.510 align:middle line:84% Excess glass is trimmed free at the end. 00:15:55.510 --> 00:15:59.410 align:middle line:90% 00:15:59.410 --> 00:16:04.810 align:middle line:84% This is then pressed into a larger optic or dip mold. 00:16:04.810 --> 00:16:08.610 align:middle line:84% After slightly cooling, it's lowered gradually 00:16:08.610 --> 00:16:10.830 align:middle line:90% into the opaque red glass. 00:16:10.830 --> 00:16:17.930 align:middle line:90% 00:16:17.930 --> 00:16:21.350 align:middle line:84% After reheating, it goes into another mold. 00:16:21.350 --> 00:16:25.290 align:middle line:90% 00:16:25.290 --> 00:16:28.950 align:middle line:84% The final layer will be opaque white glass. 00:16:28.950 --> 00:16:34.040 align:middle line:90% 00:16:34.040 --> 00:16:36.220 align:middle line:84% This is pressed into the dip mold. 00:16:36.220 --> 00:16:41.240 align:middle line:90% 00:16:41.240 --> 00:16:45.500 align:middle line:84% And after reheating, the cane is pulled. 00:16:45.500 --> 00:17:06.599 align:middle line:90% 00:17:06.599 --> 00:17:09.300 align:middle line:84% No matter how long the cane is pulled, 00:17:09.300 --> 00:17:12.720 align:middle line:84% and no matter how small the diameter, the pattern 00:17:12.720 --> 00:17:14.380 align:middle line:90% will remain intact. 00:17:14.380 --> 00:17:22.280 align:middle line:90% 00:17:22.280 --> 00:17:27.460 align:middle line:84% A simple machine is used to cut the cane into thin slices. 00:17:27.460 --> 00:17:37.320 align:middle line:90% 00:17:37.320 --> 00:17:44.440 align:middle line:84% The ball is made by gathering clear glass, 00:17:44.440 --> 00:17:48.640 align:middle line:84% marvering it to make the glass even, 00:17:48.640 --> 00:17:57.160 align:middle line:84% blowing air into the pipe to create a bubble, 00:17:57.160 --> 00:18:02.780 align:middle line:84% and then rolling the bubble over the preheated millefiori slices. 00:18:02.780 --> 00:18:09.080 align:middle line:90% 00:18:09.080 --> 00:18:14.180 align:middle line:84% The glass is reheated and the process repeated. 00:18:14.180 --> 00:18:25.200 align:middle line:90% 00:18:25.200 --> 00:18:29.110 align:middle line:84% The glass is reheated and marvered to press the canes 00:18:29.110 --> 00:18:32.170 align:middle line:84% gently into the surface of the clear glass. 00:18:32.170 --> 00:18:41.750 align:middle line:90% 00:18:41.750 --> 00:18:44.890 align:middle line:84% Eventually, the surface becomes smooth. 00:18:44.890 --> 00:18:52.830 align:middle line:90% 00:18:52.830 --> 00:18:55.510 align:middle line:84% The goal is to completely cover the bubble 00:18:55.510 --> 00:18:59.250 align:middle line:84% with millefiori canes, so the process is repeated. 00:18:59.250 --> 00:19:09.430 align:middle line:90% 00:19:09.430 --> 00:19:12.590 align:middle line:84% The canes are embedded in clear glass, 00:19:12.590 --> 00:19:17.330 align:middle line:84% so a second gather of glass is made atop the millefiori canes. 00:19:17.330 --> 00:19:21.430 align:middle line:90% 00:19:21.430 --> 00:19:23.490 align:middle line:90% Glassblowing now begins. 00:19:23.490 --> 00:19:29.670 align:middle line:90% 00:19:29.670 --> 00:19:32.230 align:middle line:84% To separate the bubble from the blowpipe, 00:19:32.230 --> 00:19:35.130 align:middle line:84% it's necessary to make a constriction. 00:19:35.130 --> 00:19:41.390 align:middle line:90% 00:19:41.390 --> 00:19:43.810 align:middle line:84% Water is dropped on the constriction, 00:19:43.810 --> 00:19:47.370 align:middle line:84% the blowpipe tapped, and the ball breaks free. 00:19:47.370 --> 00:19:52.710 align:middle line:90% 00:19:52.710 --> 00:19:55.230 align:middle line:84% Only after cooling to room temperature 00:19:55.230 --> 00:19:58.936 align:middle line:90% do the colors reveal themselves. 00:19:58.936 --> 00:20:00.470 align:middle line:90% [END PLAYBACK] 00:20:00.470 --> 00:20:03.510 align:middle line:84% JUEJUN HU: So the cane join process has always 00:20:03.510 --> 00:20:05.260 align:middle line:90% been quite amazing to me. 00:20:05.260 --> 00:20:07.010 align:middle line:84% When I first saw it in the glass workshop, 00:20:07.010 --> 00:20:10.350 align:middle line:84% I see people pulling on these very long, thin canes. 00:20:10.350 --> 00:20:12.650 align:middle line:84% The immediate analogy that I have in my mind, 00:20:12.650 --> 00:20:14.150 align:middle line:84% from a material science perspective, 00:20:14.150 --> 00:20:18.750 align:middle line:84% is those tensile tests of materials. 00:20:18.750 --> 00:20:20.750 align:middle line:84% Now, you are all familiar with the tensile test. 00:20:20.750 --> 00:20:24.250 align:middle line:84% In tensile test, what usually happens with a very short, 00:20:24.250 --> 00:20:26.700 align:middle line:84% somewhat ductile material is that you get 00:20:26.700 --> 00:20:28.580 align:middle line:90% this phenomena called necking. 00:20:28.580 --> 00:20:30.440 align:middle line:84% Essentially, as you are pulling on the rod, 00:20:30.440 --> 00:20:32.580 align:middle line:84% as you increase the stress, due to some kind 00:20:32.580 --> 00:20:36.020 align:middle line:84% of inherent randomness or intrinsic non-uniformity, 00:20:36.020 --> 00:20:38.660 align:middle line:84% some part of the rod essentially becomes a little bit thinner. 00:20:38.660 --> 00:20:40.540 align:middle line:84% And now, when that happens, you actually 00:20:40.540 --> 00:20:43.500 align:middle line:84% get higher stress due to the smaller cross-section 00:20:43.500 --> 00:20:45.020 align:middle line:90% at that necking region. 00:20:45.020 --> 00:20:48.700 align:middle line:84% And then this essentially leads to accelerated deformation 00:20:48.700 --> 00:20:52.340 align:middle line:84% of that necking region, which eventually leads to breakage. 00:20:52.340 --> 00:20:54.940 align:middle line:84% Now, as you can see from the video there, 00:20:54.940 --> 00:20:56.723 align:middle line:84% cane join is pretty much a manual process. 00:20:56.723 --> 00:20:58.140 align:middle line:84% So there's really not much you can 00:20:58.140 --> 00:21:01.140 align:middle line:84% show about how uniform you apply the stress or strain 00:21:01.140 --> 00:21:02.740 align:middle line:90% across the process there. 00:21:02.740 --> 00:21:06.580 align:middle line:84% So now my question is that why you are not 00:21:06.580 --> 00:21:12.100 align:middle line:84% breaking the cane during this seemingly very crude process? 00:21:12.100 --> 00:21:16.060 align:middle line:84% Why they can actually maintain this stable, uniform diameter 00:21:16.060 --> 00:21:17.480 align:middle line:90% throughout this join process? 00:21:17.480 --> 00:21:18.360 align:middle line:90% 00:21:18.360 --> 00:21:22.620 align:middle line:84% AUDIENCE: Since in a glass you don't have dislocation plates? 00:21:22.620 --> 00:21:24.340 align:middle line:84% So plastic deformation generation 00:21:24.340 --> 00:21:28.873 align:middle line:84% is from the movement of dislocations? 00:21:28.873 --> 00:21:30.540 align:middle line:84% JUEJUN HU: OK, that's a very good guess. 00:21:30.540 --> 00:21:33.540 align:middle line:84% Indeed, glass doesn't have those kind of plastic deformation 00:21:33.540 --> 00:21:35.420 align:middle line:90% mechanisms as in like metals. 00:21:35.420 --> 00:21:37.900 align:middle line:84% But you can also get viscous flow. 00:21:37.900 --> 00:21:39.620 align:middle line:90% So glass is deformable. 00:21:39.620 --> 00:21:41.900 align:middle line:84% And naively, one would think if you actually 00:21:41.900 --> 00:21:44.772 align:middle line:84% have somewhere happen to get a little bit narrower, 00:21:44.772 --> 00:21:46.480 align:middle line:84% then it will, of course, get more stress. 00:21:46.480 --> 00:21:48.460 align:middle line:84% Then it will deform faster, then it will break. 00:21:48.460 --> 00:21:51.580 align:middle line:84% So something is actually preventing that. 00:21:51.580 --> 00:21:53.180 align:middle line:90% OK. 00:21:53.180 --> 00:21:55.140 align:middle line:84% Well, we can do some quantitative analysis 00:21:55.140 --> 00:21:56.992 align:middle line:90% to see what actually happens. 00:21:56.992 --> 00:21:58.700 align:middle line:84% To see that, the first thing I want to do 00:21:58.700 --> 00:22:02.100 align:middle line:84% is that I want to do a little bit of quick scaling analysis. 00:22:02.100 --> 00:22:04.420 align:middle line:84% This goes back to what I call the scale invariance 00:22:04.420 --> 00:22:06.100 align:middle line:90% of the viscous flow equation. 00:22:06.100 --> 00:22:08.960 align:middle line:84% If you recall the governing equation for viscous flow, 00:22:08.960 --> 00:22:12.620 align:middle line:84% it basically says that the strain rate 00:22:12.620 --> 00:22:16.237 align:middle line:84% is proportional to the shear stress, where 00:22:16.237 --> 00:22:17.820 align:middle line:84% the proportionality constant basically 00:22:17.820 --> 00:22:19.195 align:middle line:84% gives you by the viscosity if you 00:22:19.195 --> 00:22:20.780 align:middle line:90% assume it's a Newtonian fluid. 00:22:20.780 --> 00:22:22.420 align:middle line:84% Now, if you look at the equation, 00:22:22.420 --> 00:22:26.780 align:middle line:84% nowhere in the equation does any kind of dimensions or length 00:22:26.780 --> 00:22:28.460 align:middle line:90% appears in that equation. 00:22:28.460 --> 00:22:32.700 align:middle line:84% So what it means is that this a for viscous flow fluid system, 00:22:32.700 --> 00:22:36.340 align:middle line:84% it's supposed to be scale invariant. 00:22:36.340 --> 00:22:38.720 align:middle line:84% So what I mean by that is that if you think about, 00:22:38.720 --> 00:22:41.040 align:middle line:84% for example we have a section of the rod, 00:22:41.040 --> 00:22:44.460 align:middle line:84% you apply some stress on the n sigma, it's going to elongate, 00:22:44.460 --> 00:22:45.220 align:middle line:90% OK? 00:22:45.220 --> 00:22:47.840 align:middle line:84% And you have some kinetics of how fast it's going to deform. 00:22:47.840 --> 00:22:50.960 align:middle line:84% Now, if you scale the system size by lambda times, 00:22:50.960 --> 00:22:52.740 align:middle line:84% so all the linear dimensions essentially 00:22:52.740 --> 00:22:54.688 align:middle line:84% get multiplied by a factor of lambda, 00:22:54.688 --> 00:22:56.480 align:middle line:84% you still keep the same boundary condition, 00:22:56.480 --> 00:22:58.580 align:middle line:84% which means in this case, the same stress. 00:22:58.580 --> 00:23:01.940 align:middle line:84% The system is going to deform in exactly the same rate, meaning 00:23:01.940 --> 00:23:03.580 align:middle line:84% the strain rate is going to be exactly 00:23:03.580 --> 00:23:05.740 align:middle line:84% the same regardless of the size or the scaling 00:23:05.740 --> 00:23:08.320 align:middle line:90% factor of the system. 00:23:08.320 --> 00:23:08.820 align:middle line:90% OK? 00:23:08.820 --> 00:23:10.240 align:middle line:84% So that's pretty straightforward. 00:23:10.240 --> 00:23:16.083 align:middle line:84% It's just same stress gives you the same strain rate, right? 00:23:16.083 --> 00:23:18.000 align:middle line:84% So now we can take a look at now what happens. 00:23:18.000 --> 00:23:20.978 align:middle line:84% We can essentially look at two segments in the cane. 00:23:20.978 --> 00:23:22.770 align:middle line:84% Suppose there's some non-uniformity leading 00:23:22.770 --> 00:23:25.410 align:middle line:84% to a segment with slightly different diameter. 00:23:25.410 --> 00:23:30.325 align:middle line:84% And so for one of the canes, here we apply axial force of F. 00:23:30.325 --> 00:23:32.450 align:middle line:84% Now, because all the different segments essentially 00:23:32.450 --> 00:23:35.410 align:middle line:84% they are connected in series, so what's kept constant 00:23:35.410 --> 00:23:38.410 align:middle line:84% is actually the force rather than the stress. 00:23:38.410 --> 00:23:41.730 align:middle line:84% So when you increase the diameter of the cane 00:23:41.730 --> 00:23:44.890 align:middle line:84% locally, because the force is the same, 00:23:44.890 --> 00:23:48.210 align:middle line:84% it means that the stress, which is normalized by area, 00:23:48.210 --> 00:23:50.570 align:middle line:84% has to decrease by a factor of lambda 00:23:50.570 --> 00:23:53.890 align:middle line:90% squared in a scaled system. 00:23:53.890 --> 00:23:54.390 align:middle line:90% OK? 00:23:54.390 --> 00:23:56.910 align:middle line:84% So if the stress decreases by lambda squared, 00:23:56.910 --> 00:23:58.730 align:middle line:84% we know the strain rate must also decrease 00:23:58.730 --> 00:24:00.150 align:middle line:90% by a factor of lambda squared. 00:24:00.150 --> 00:24:05.690 align:middle line:84% So what it says is that if you have a larger rod, wider 00:24:05.690 --> 00:24:11.450 align:middle line:84% or thicker rod, you are going to have a slower deformation. 00:24:11.450 --> 00:24:14.470 align:middle line:84% So eventually, the thinner sections, it deforms faster. 00:24:14.470 --> 00:24:15.750 align:middle line:90% It gets even thinner. 00:24:15.750 --> 00:24:19.610 align:middle line:84% So it will break before the thicker sections do. 00:24:19.610 --> 00:24:21.770 align:middle line:90% OK? 00:24:21.770 --> 00:24:23.770 align:middle line:84% Now, it's actually pretty straightforward 00:24:23.770 --> 00:24:25.810 align:middle line:90% to show quantitatively. 00:24:25.810 --> 00:24:29.910 align:middle line:84% This can be easily shown like if you think about the strain rate, 00:24:29.910 --> 00:24:35.930 align:middle line:84% strain rate is basically given by how 00:24:35.930 --> 00:24:41.490 align:middle line:84% the linear dimensions like diameter, in this case 00:24:41.490 --> 00:24:44.330 align:middle line:84% D is basically diameter, so this gives you basically a strain 00:24:44.330 --> 00:24:44.830 align:middle line:90% rate. 00:24:44.830 --> 00:24:49.690 align:middle line:84% If we gauge this trend in terms of the change of the diameter. 00:24:49.690 --> 00:24:52.330 align:middle line:84% So we know that this strain rate, 00:24:52.330 --> 00:24:57.670 align:middle line:84% it must be proportional to, in this case, stress, right? 00:24:57.670 --> 00:25:03.490 align:middle line:84% And stress scaled with diameter essentially to the inverse 00:25:03.490 --> 00:25:04.290 align:middle line:90% squared. 00:25:04.290 --> 00:25:10.090 align:middle line:84% So therefore, this must scale with 1 over D squared. 00:25:10.090 --> 00:25:11.210 align:middle line:90% OK? 00:25:11.210 --> 00:25:13.170 align:middle line:84% So you can cancel out the 1 over D 00:25:13.170 --> 00:25:20.320 align:middle line:84% on both sides, which then gives you this very simple condition 00:25:20.320 --> 00:25:20.820 align:middle line:90% here. 00:25:20.820 --> 00:25:26.040 align:middle line:90% 00:25:26.040 --> 00:25:29.240 align:middle line:84% And if you don't want this cane to essentially break, 00:25:29.240 --> 00:25:33.920 align:middle line:84% you need to make sure that the strain rate essentially 00:25:33.920 --> 00:25:37.400 align:middle line:90% remains a constant, right? 00:25:37.400 --> 00:25:41.080 align:middle line:84% But that's obviously not the case here. 00:25:41.080 --> 00:25:42.920 align:middle line:84% What this analysis shows is essentially 00:25:42.920 --> 00:25:45.840 align:middle line:84% why necking happens in general materials because 00:25:45.840 --> 00:25:48.157 align:middle line:90% of stress concentration. 00:25:48.157 --> 00:25:50.240 align:middle line:84% However, one factor we have not taken into account 00:25:50.240 --> 00:25:52.282 align:middle line:84% here is that actually a proportionality constant, 00:25:52.282 --> 00:25:53.800 align:middle line:90% which is the viscosity eta. 00:25:53.800 --> 00:25:54.720 align:middle line:90% OK. 00:25:54.720 --> 00:25:58.380 align:middle line:84% So the larger the eta, the slower the deformation. 00:25:58.380 --> 00:26:02.800 align:middle line:90% 00:26:02.800 --> 00:26:06.920 align:middle line:84% So in order to reach stability, this factor, the strain rate, 00:26:06.920 --> 00:26:08.360 align:middle line:90% must be the same. 00:26:08.360 --> 00:26:12.440 align:middle line:84% So what it means, that you must have eta 00:26:12.440 --> 00:26:18.240 align:middle line:84% that essentially increases as the diameter gets smaller. 00:26:18.240 --> 00:26:21.040 align:middle line:84% You can already probably guess what's actually happening there. 00:26:21.040 --> 00:26:23.080 align:middle line:90% What does eta depend on? 00:26:23.080 --> 00:26:24.880 align:middle line:90% Eta depends on temperature. 00:26:24.880 --> 00:26:30.920 align:middle line:84% So thinner segments, the temperature drops faster. 00:26:30.920 --> 00:26:33.760 align:middle line:84% And then that leads to increase viscosity, which then eventually 00:26:33.760 --> 00:26:36.960 align:middle line:84% allows you to reach this stability condition there, 00:26:36.960 --> 00:26:41.760 align:middle line:84% where the strain rate becomes a constant, which, 00:26:41.760 --> 00:26:45.040 align:middle line:84% in this context, is basically the eta times the diameter 00:26:45.040 --> 00:26:46.260 align:middle line:90% squared, becomes a constant. 00:26:46.260 --> 00:26:48.040 align:middle line:84% That's basically stability theorem, 00:26:48.040 --> 00:26:52.720 align:middle line:84% where you have a constant strain rate across the entire rod. 00:26:52.720 --> 00:26:54.760 align:middle line:90% OK. 00:26:54.760 --> 00:26:58.640 align:middle line:84% So where might we want to be a quantitative? 00:26:58.640 --> 00:27:00.700 align:middle line:84% We want to see if that actually happens. 00:27:00.700 --> 00:27:02.720 align:middle line:84% So I did a little bit more analysis 00:27:02.720 --> 00:27:05.800 align:middle line:84% looking into essentially trying to model this process. 00:27:05.800 --> 00:27:11.000 align:middle line:84% So because our hypothesis is that thinner cane is going 00:27:11.000 --> 00:27:13.740 align:middle line:84% to have a faster heat dissipation, so as a result, 00:27:13.740 --> 00:27:14.690 align:middle line:90% it cools down faster. 00:27:14.690 --> 00:27:16.530 align:middle line:84% That's what prevents essentially breakage. 00:27:16.530 --> 00:27:19.780 align:middle line:84% We have to look into essentially the heat dissipation process. 00:27:19.780 --> 00:27:21.030 align:middle line:90% What are the mechanisms there? 00:27:21.030 --> 00:27:24.430 align:middle line:84% Generally, there are three kinds of heat dissipation mechanisms. 00:27:24.430 --> 00:27:25.977 align:middle line:90% You get conduction. 00:27:25.977 --> 00:27:28.310 align:middle line:84% Conduction means essentially heat directly pass from one 00:27:28.310 --> 00:27:29.750 align:middle line:90% solid to another solid. 00:27:29.750 --> 00:27:31.608 align:middle line:84% It's actually pretty negligible in this case 00:27:31.608 --> 00:27:33.150 align:middle line:84% because if you think about cane, it's 00:27:33.150 --> 00:27:36.510 align:middle line:84% a pretty long, elongated geometry, right? 00:27:36.510 --> 00:27:38.870 align:middle line:84% So the real contact, solid-to-solid contact 00:27:38.870 --> 00:27:40.445 align:middle line:84% happens at the end of the cane, which 00:27:40.445 --> 00:27:42.070 align:middle line:84% is much smaller compared to essentially 00:27:42.070 --> 00:27:44.190 align:middle line:90% the sidewall surfaces. 00:27:44.190 --> 00:27:46.510 align:middle line:84% So conduction is pretty much negligible. 00:27:46.510 --> 00:27:48.110 align:middle line:90% You also get convection. 00:27:48.110 --> 00:27:50.270 align:middle line:84% Convection is when you have air coming 00:27:50.270 --> 00:27:52.212 align:middle line:90% into contact with the rod. 00:27:52.212 --> 00:27:53.670 align:middle line:84% And then the heated air essentially 00:27:53.670 --> 00:27:55.790 align:middle line:84% gets essentially you get lighter, it moves away, 00:27:55.790 --> 00:27:57.010 align:middle line:90% where the cold air comes in. 00:27:57.010 --> 00:27:59.190 align:middle line:90% So this process continues. 00:27:59.190 --> 00:28:01.550 align:middle line:84% Air is not very good thermal conductor even 00:28:01.550 --> 00:28:03.510 align:middle line:84% with a pretty strong convective flow. 00:28:03.510 --> 00:28:06.770 align:middle line:84% And in this case, it turns out it's pretty negligible as well, 00:28:06.770 --> 00:28:08.390 align:middle line:90% the convective heat flow. 00:28:08.390 --> 00:28:10.070 align:middle line:84% The dominant heat transfer mechanism 00:28:10.070 --> 00:28:12.850 align:middle line:84% in this particular case is radiative heat transfer. 00:28:12.850 --> 00:28:14.540 align:middle line:84% Essentially due to blackbody radiation, 00:28:14.540 --> 00:28:16.790 align:middle line:84% anything when you heat up higher temperature, it emits 00:28:16.790 --> 00:28:20.803 align:middle line:84% infrared radiation that carries away energy from the hot body. 00:28:20.803 --> 00:28:22.470 align:middle line:84% General rule of thumb, if you're dealing 00:28:22.470 --> 00:28:25.830 align:middle line:84% with a hot body, a high temperature above a few hundred 00:28:25.830 --> 00:28:29.510 align:middle line:84% degrees Celsius, usually the dominant heat transfer mechanism 00:28:29.510 --> 00:28:32.550 align:middle line:90% becomes radiative heat transfer. 00:28:32.550 --> 00:28:36.230 align:middle line:84% So for radiative heat transfer, we have the Stefan-Boltzmann law 00:28:36.230 --> 00:28:40.470 align:middle line:84% which basically says here is the heat flux q is proportional to T 00:28:40.470 --> 00:28:41.910 align:middle line:90% to the 4th power. 00:28:41.910 --> 00:28:44.170 align:middle line:84% This explains what my conclusion, as I said, 00:28:44.170 --> 00:28:46.830 align:middle line:84% for high temperature bodies, usually radiative heat transfer 00:28:46.830 --> 00:28:50.750 align:middle line:84% dominates because the heat flux scales T to the 4th power. 00:28:50.750 --> 00:28:53.450 align:middle line:84% Versus convective and conductive heat flow, 00:28:53.450 --> 00:28:56.630 align:middle line:84% where the heat flux scales temperature difference linearly. 00:28:56.630 --> 00:28:58.510 align:middle line:84% So that's why eventually at high temperature, 00:28:58.510 --> 00:29:00.790 align:middle line:84% radiative heat transfer takes over. 00:29:00.790 --> 00:29:03.950 align:middle line:90% So e is the emissivity. 00:29:03.950 --> 00:29:06.110 align:middle line:90% It's a constant between 0 to 1. 00:29:06.110 --> 00:29:09.550 align:middle line:84% Sigma is what's called the Stefan-Boltzmann constant. 00:29:09.550 --> 00:29:11.300 align:middle line:84% So then if you have that, you can actually 00:29:11.300 --> 00:29:12.925 align:middle line:84% write the temperature churn rate if you 00:29:12.925 --> 00:29:14.780 align:middle line:84% think about one section of the cane 00:29:14.780 --> 00:29:20.220 align:middle line:84% there, with a volume V and the surface area S. 00:29:20.220 --> 00:29:22.720 align:middle line:84% So S would be the sidewall surface area, right? 00:29:22.720 --> 00:29:25.260 align:middle line:84% So then you can simplify this equation. 00:29:25.260 --> 00:29:26.760 align:middle line:84% I'm going to go through the details. 00:29:26.760 --> 00:29:27.640 align:middle line:90% It's pretty straightforward. 00:29:27.640 --> 00:29:30.182 align:middle line:84% It's basically about the heat removes lead to the temperature 00:29:30.182 --> 00:29:32.880 align:middle line:90% reduction of the rod. 00:29:32.880 --> 00:29:36.940 align:middle line:84% And finally, you can also model how the viscosity changes 00:29:36.940 --> 00:29:40.780 align:middle line:84% as a function of temperature by using this, basically, 00:29:40.780 --> 00:29:42.420 align:middle line:90% a Arrhenius equation. 00:29:42.420 --> 00:29:45.827 align:middle line:84% Now rigorously speaking, this delta E, activation energy, 00:29:45.827 --> 00:29:47.160 align:middle line:90% should be temperature-dependent. 00:29:47.160 --> 00:29:48.900 align:middle line:90% We already learned about it. 00:29:48.900 --> 00:29:51.775 align:middle line:84% But for now, for typical glasses, over temperature 00:29:51.775 --> 00:29:54.400 align:middle line:84% range we're thinking about here as a first-order approximation, 00:29:54.400 --> 00:29:56.940 align:middle line:90% let's treat that as a constant. 00:29:56.940 --> 00:29:58.820 align:middle line:84% So now we can actually do our model. 00:29:58.820 --> 00:30:01.400 align:middle line:84% So I actually put a code already on the Canvas website. 00:30:01.400 --> 00:30:04.020 align:middle line:84% I put a little Matlab code that actually did the calculation. 00:30:04.020 --> 00:30:05.460 align:middle line:84% I'm looking at a simplified case, 00:30:05.460 --> 00:30:08.860 align:middle line:84% where we look at essentially two connected sections. 00:30:08.860 --> 00:30:11.620 align:middle line:84% It has a slightly difference in diameter. 00:30:11.620 --> 00:30:14.220 align:middle line:84% They started out in terms of same temperature. 00:30:14.220 --> 00:30:15.767 align:middle line:84% And I made some assumptions here. 00:30:15.767 --> 00:30:18.100 align:middle line:84% I assumed that the temperature is uniform across the can 00:30:18.100 --> 00:30:22.000 align:middle line:84% cross-section, which for small k is pretty good approximation 00:30:22.000 --> 00:30:22.843 align:middle line:90% in any case. 00:30:22.843 --> 00:30:25.260 align:middle line:84% I assume there's no heat or mass exchange between the cane 00:30:25.260 --> 00:30:26.820 align:middle line:84% sections, which obviously is wrong. 00:30:26.820 --> 00:30:30.600 align:middle line:84% But if the cane is long enough, it's a decent approximation. 00:30:30.600 --> 00:30:33.380 align:middle line:84% And then I only consider radiative heat transfer 00:30:33.380 --> 00:30:34.500 align:middle line:90% as we have mentioned. 00:30:34.500 --> 00:30:37.020 align:middle line:84% And finally, I'm assuming a constant joint speed 00:30:37.020 --> 00:30:40.180 align:middle line:84% and hence, essentially, a constant force 00:30:40.180 --> 00:30:42.900 align:middle line:90% across the two rods, actually. 00:30:42.900 --> 00:30:44.840 align:middle line:84% So now if you look at the simulated results, 00:30:44.840 --> 00:30:47.420 align:middle line:84% what I'm plotting here is that both canes or both canes 00:30:47.420 --> 00:30:51.180 align:middle line:84% segments started out at the same temperature of 900C. 00:30:51.180 --> 00:30:54.720 align:middle line:84% But as you can see here, the smaller cross section 1, 00:30:54.720 --> 00:30:57.060 align:middle line:84% it actually decreases, temperature decreases faster 00:30:57.060 --> 00:30:58.220 align:middle line:90% than the thicker one. 00:30:58.220 --> 00:31:00.380 align:middle line:84% Basically, if you go back to equation, 00:31:00.380 --> 00:31:01.960 align:middle line:84% it goes back to this factor here. 00:31:01.960 --> 00:31:04.860 align:middle line:84% It's basically surface-to-volume ratio. 00:31:04.860 --> 00:31:07.783 align:middle line:84% If the thinner section you have more surface to volume 00:31:07.783 --> 00:31:09.950 align:middle line:84% and therefore, this kind of radiative heat transfer, 00:31:09.950 --> 00:31:12.410 align:middle line:84% which scales with surface area, becomes more efficient. 00:31:12.410 --> 00:31:15.330 align:middle line:84% So that's why it cools down faster. 00:31:15.330 --> 00:31:18.370 align:middle line:84% As it cools down faster, we expect its viscosity 00:31:18.370 --> 00:31:19.970 align:middle line:90% to increase. 00:31:19.970 --> 00:31:23.343 align:middle line:84% Once its viscosity increases, that resists this deformation, 00:31:23.343 --> 00:31:26.010 align:middle line:84% so that this becomes essentially this kind of self-feedback loop 00:31:26.010 --> 00:31:30.310 align:middle line:84% that prevents destabilization in the cane joining process. 00:31:30.310 --> 00:31:30.810 align:middle line:90% OK? 00:31:30.810 --> 00:31:33.310 align:middle line:84% So that's what I'm putting here thinner section faster, 00:31:33.310 --> 00:31:35.010 align:middle line:84% increasing viscosity, which then keeps 00:31:35.010 --> 00:31:38.123 align:middle line:84% you to damp out any kind of non-uniformity cane 00:31:38.123 --> 00:31:38.790 align:middle line:90% joining process. 00:31:38.790 --> 00:31:41.450 align:middle line:84% And that's why when you see the canes join, despite, 00:31:41.450 --> 00:31:43.490 align:middle line:84% people, essentially there's no control 00:31:43.490 --> 00:31:45.530 align:middle line:84% over the specific joint conditions there, 00:31:45.530 --> 00:31:47.907 align:middle line:84% they usually come up with very, very uniform diameters, 00:31:47.907 --> 00:31:49.990 align:middle line:84% except at the end when you're close to the pointy. 00:31:49.990 --> 00:31:52.530 align:middle line:90% OK 00:31:52.530 --> 00:31:53.150 align:middle line:90% OK? 00:31:53.150 --> 00:31:54.010 align:middle line:90% Make sense? 00:31:54.010 --> 00:31:56.770 align:middle line:84% Now, this same process, the same mechanism 00:31:56.770 --> 00:31:59.450 align:middle line:84% also applies to other cases when you're doing glass deformation 00:31:59.450 --> 00:32:01.410 align:middle line:84% as well, for example, when you're doing glass fiber joint. 00:32:01.410 --> 00:32:03.327 align:middle line:84% It's basically the same process but with a lot 00:32:03.327 --> 00:32:05.410 align:middle line:84% more control and going to much smaller diameter. 00:32:05.410 --> 00:32:07.090 align:middle line:84% But the same kind of stability criteria 00:32:07.090 --> 00:32:09.910 align:middle line:84% helps you prevent the breakage in that case as well. 00:32:09.910 --> 00:32:14.622 align:middle line:90% 00:32:14.622 --> 00:32:16.330 align:middle line:84% And that's shown in the simulation result 00:32:16.330 --> 00:32:19.630 align:middle line:84% here where the diameter of the two canes eventually converges. 00:32:19.630 --> 00:32:21.130 align:middle line:84% So any kind of initial difference, 00:32:21.130 --> 00:32:22.990 align:middle line:84% they will damp out in the process. 00:32:22.990 --> 00:32:26.170 align:middle line:90% 00:32:26.170 --> 00:32:27.010 align:middle line:90% OK. 00:32:27.010 --> 00:32:31.410 align:middle line:84% Questions about this, or this is all good? 00:32:31.410 --> 00:32:32.730 align:middle line:90% All right. 00:32:32.730 --> 00:32:35.295 align:middle line:84% So now next, besides caneworking, 00:32:35.295 --> 00:32:37.170 align:middle line:84% I also want to mention that people are always 00:32:37.170 --> 00:32:39.130 align:middle line:84% exploring new ways to actually create 00:32:39.130 --> 00:32:42.970 align:middle line:84% all kinds of innovative art structures. 00:32:42.970 --> 00:32:45.610 align:middle line:84% And this example, this also comes from MIT, 00:32:45.610 --> 00:32:46.970 align:middle line:90% actually comes from Media Lab. 00:32:46.970 --> 00:32:49.410 align:middle line:84% They now develop a way to essentially create different art 00:32:49.410 --> 00:32:50.990 align:middle line:90% pieces using 3D printing. 00:32:50.990 --> 00:32:52.850 align:middle line:90% OK. 00:32:52.850 --> 00:32:54.170 align:middle line:90% I will just show the video. 00:32:54.170 --> 00:32:57.170 align:middle line:90% It's pretty straightforward. 00:32:57.170 --> 00:32:58.661 align:middle line:90% [VIDEO PLAYBACK] 00:32:58.661 --> 00:33:02.637 align:middle line:90% [MUSIC PLAYING] 00:33:02.637 --> 00:34:03.768 align:middle line:90% 00:34:03.768 --> 00:34:04.840 align:middle line:90% [END PLAYBACK] 00:34:04.840 --> 00:34:07.520 align:middle line:84% So at the end of the video, that's 00:34:07.520 --> 00:34:09.159 align:middle line:84% actually a display that used to be 00:34:09.159 --> 00:34:11.820 align:middle line:84% in the lobby of the Media Lab, the new Media Lab building. 00:34:11.820 --> 00:34:14.540 align:middle line:84% I don't know if they still have it, but you can take a look. 00:34:14.540 --> 00:34:17.840 align:middle line:84% Also, if you go back a few years back when we actually 00:34:17.840 --> 00:34:19.360 align:middle line:84% do the glass lab demo, you actually 00:34:19.360 --> 00:34:22.880 align:middle line:84% get to see the printer right in the glass lab. 00:34:22.880 --> 00:34:24.133 align:middle line:90% Not anymore. 00:34:24.133 --> 00:34:25.800 align:middle line:84% They were doing the printing essentially 00:34:25.800 --> 00:34:28.100 align:middle line:84% inside the MIT Glass Lab for a few years, 00:34:28.100 --> 00:34:30.373 align:middle line:84% and then later on, they increased demand. 00:34:30.373 --> 00:34:31.540 align:middle line:90% So they decided to spin out. 00:34:31.540 --> 00:34:33.873 align:middle line:84% They actually started their own glass workshop somewhere 00:34:33.873 --> 00:34:35.020 align:middle line:90% in the vicinity here. 00:34:35.020 --> 00:34:36.620 align:middle line:84% So you don't get to see it anymore. 00:34:36.620 --> 00:34:40.514 align:middle line:84% That's why I'm playing a YouTube video here. 00:34:40.514 --> 00:34:42.639 align:middle line:84% But people are actually extending these techniques. 00:34:42.639 --> 00:34:44.659 align:middle line:84% Now, people will only do for oxide glass printing. 00:34:44.659 --> 00:34:46.800 align:middle line:84% People even do non-oxide glasses like chalcogenide. 00:34:46.800 --> 00:34:48.440 align:middle line:84% They essentially use the same technique 00:34:48.440 --> 00:34:52.560 align:middle line:84% to create all kinds of functional components. 00:34:52.560 --> 00:34:55.080 align:middle line:90% 00:34:55.080 --> 00:34:55.880 align:middle line:90% OK. 00:34:55.880 --> 00:34:59.065 align:middle line:84% So now comes back to more industrial scale process. 00:34:59.065 --> 00:35:00.440 align:middle line:84% I want to discuss about processes 00:35:00.440 --> 00:35:05.320 align:middle line:84% that people use to structure small glass pieces, especially 00:35:05.320 --> 00:35:07.520 align:middle line:90% on precision optical components. 00:35:07.520 --> 00:35:10.200 align:middle line:84% This is called a precision glass molding. 00:35:10.200 --> 00:35:12.220 align:middle line:84% The idea behind this is pretty straightforward. 00:35:12.220 --> 00:35:13.622 align:middle line:90% You have a two-piece mold. 00:35:13.622 --> 00:35:15.080 align:middle line:84% When you put them together, there's 00:35:15.080 --> 00:35:17.000 align:middle line:84% a cavity forming between the two. 00:35:17.000 --> 00:35:19.880 align:middle line:84% So if you put in some glasses, heat it up, press it, 00:35:19.880 --> 00:35:21.880 align:middle line:84% the glass will then viscously flow and then fill 00:35:21.880 --> 00:35:22.860 align:middle line:90% the entire cavity. 00:35:22.860 --> 00:35:24.420 align:middle line:84% So then when you actually release the mold, 00:35:24.420 --> 00:35:25.540 align:middle line:90% you can take out the piece. 00:35:25.540 --> 00:35:28.123 align:middle line:84% It will conform to the shape of the cavity to the first order. 00:35:28.123 --> 00:35:29.040 align:middle line:90% OK. 00:35:29.040 --> 00:35:31.440 align:middle line:90% AUDIENCE: --injection molding? 00:35:31.440 --> 00:35:33.080 align:middle line:90% JUEJUN HU: Great question. 00:35:33.080 --> 00:35:35.920 align:middle line:84% These are two slightly different processes. 00:35:35.920 --> 00:35:39.002 align:middle line:84% For glass, because we typically do a compression molding. 00:35:39.002 --> 00:35:40.460 align:middle line:84% This is called compression molding. 00:35:40.460 --> 00:35:42.560 align:middle line:84% Injection molding is a little bit different. 00:35:42.560 --> 00:35:46.400 align:middle line:84% The cavity or the mold resides in essentially one piece. 00:35:46.400 --> 00:35:49.668 align:middle line:84% You inject the liquid into that cavity to fill in. 00:35:49.668 --> 00:35:51.960 align:middle line:84% And then you eventually open up cavity and take it out. 00:35:51.960 --> 00:35:53.860 align:middle line:84% Versus in this case, you have two pieces. 00:35:53.860 --> 00:35:56.332 align:middle line:84% You use pressure to force the glass 00:35:56.332 --> 00:35:57.540 align:middle line:90% to conform to the two pieces. 00:35:57.540 --> 00:35:59.332 align:middle line:84% That's why it's called compression molding. 00:35:59.332 --> 00:36:01.870 align:middle line:90% It's very similar. 00:36:01.870 --> 00:36:04.030 align:middle line:84% If you go to polymer community, people actually 00:36:04.030 --> 00:36:06.910 align:middle line:84% can do both, either compression or injection. 00:36:06.910 --> 00:36:09.430 align:middle line:84% The difference is are somewhat minor. 00:36:09.430 --> 00:36:11.710 align:middle line:84% Compression molding is a bit easier to handle. 00:36:11.710 --> 00:36:13.990 align:middle line:90% The tooling is simpler. 00:36:13.990 --> 00:36:15.950 align:middle line:84% You can make large sheets and pieces, 00:36:15.950 --> 00:36:18.350 align:middle line:84% like flat-panel pieces with low aspect ratio easier 00:36:18.350 --> 00:36:19.610 align:middle line:90% using compression molding. 00:36:19.610 --> 00:36:21.870 align:middle line:84% Injection molding is more industrial-scale process, 00:36:21.870 --> 00:36:22.687 align:middle line:90% higher throughput. 00:36:22.687 --> 00:36:24.770 align:middle line:84% Eventually, you get lower cost with higher volume. 00:36:24.770 --> 00:36:26.970 align:middle line:90% So minor differences. 00:36:26.970 --> 00:36:28.830 align:middle line:84% But from a material perspective, they 00:36:28.830 --> 00:36:30.450 align:middle line:90% are pretty much very similar. 00:36:30.450 --> 00:36:31.950 align:middle line:84% They all rely on viscous deformation 00:36:31.950 --> 00:36:35.110 align:middle line:84% or viscoelastic deformation of the amorphous materials. 00:36:35.110 --> 00:36:35.630 align:middle line:90% Yes. 00:36:35.630 --> 00:36:39.680 align:middle line:84% AUDIENCE: So could you injection-mold glass? 00:36:39.680 --> 00:36:41.930 align:middle line:84% JUEJUN HU: Yes, I do think it's a very common process. 00:36:41.930 --> 00:36:43.847 align:middle line:84% People still typically do compression molding, 00:36:43.847 --> 00:36:46.110 align:middle line:84% but I believe it's definitely doable. 00:36:46.110 --> 00:36:48.110 align:middle line:84% In fact, we are going to see an example when 00:36:48.110 --> 00:36:50.590 align:middle line:90% we talk about amorphous metal. 00:36:50.590 --> 00:36:53.630 align:middle line:84% People do injection molding of amorphous metal, which is glass. 00:36:53.630 --> 00:36:55.430 align:middle line:90% So, yes, you can do it. 00:36:55.430 --> 00:36:58.370 align:middle line:84% AUDIENCE: --you just have to get a lot harder to get it back. 00:36:58.370 --> 00:37:01.477 align:middle line:84% JUEJUN HU: Injection molding requires lower viscosity 00:37:01.477 --> 00:37:02.810 align:middle line:90% compared to compression molding. 00:37:02.810 --> 00:37:05.510 align:middle line:84% I mean, if you look at compression molding here, 00:37:05.510 --> 00:37:07.550 align:middle line:84% the pressure range we are talking about here 00:37:07.550 --> 00:37:10.347 align:middle line:84% is actually well above the working range, 00:37:10.347 --> 00:37:12.430 align:middle line:84% because you essentially use pressure to accelerate 00:37:12.430 --> 00:37:13.930 align:middle line:90% the viscous flow process. 00:37:13.930 --> 00:37:17.030 align:middle line:84% Injection molding, you have to fill in essentially 00:37:17.030 --> 00:37:18.230 align:middle line:90% the whole cavity there. 00:37:18.230 --> 00:37:21.870 align:middle line:84% That's why it requires, essentially, lower viscosity. 00:37:21.870 --> 00:37:25.570 align:middle line:84% So it means that the material you are trying to mold here, 00:37:25.570 --> 00:37:28.172 align:middle line:84% you need to have sufficient resistance to crystallization, 00:37:28.172 --> 00:37:29.630 align:middle line:84% because injection molding, you need 00:37:29.630 --> 00:37:31.310 align:middle line:90% to raise to higher temperature. 00:37:31.310 --> 00:37:33.970 align:middle line:90% So a little caveat that. 00:37:33.970 --> 00:37:36.295 align:middle line:90% 00:37:36.295 --> 00:37:38.670 align:middle line:84% Maybe that's why people are doing more of the compression 00:37:38.670 --> 00:37:40.650 align:middle line:84% molding because it requires a lower temperature 00:37:40.650 --> 00:37:42.950 align:middle line:84% and it's easy, a bit easier in terms of all the wear and tear 00:37:42.950 --> 00:37:45.325 align:middle line:84% and everything, temperature tolerance and all that stuff. 00:37:45.325 --> 00:37:50.150 align:middle line:84% But, yeah, for glass, for inorganic like oxide type 00:37:50.150 --> 00:37:54.610 align:middle line:84% of glasses, compression molding is the more common process. 00:37:54.610 --> 00:37:58.260 align:middle line:84% So if you look at the typical compression molding 00:37:58.260 --> 00:38:00.760 align:middle line:84% process, what I'm showing on this plot here, 00:38:00.760 --> 00:38:03.500 align:middle line:84% this is how the force or the pressure you apply on the mold 00:38:03.500 --> 00:38:06.260 align:middle line:84% as the temperature evolves across the entire process. 00:38:06.260 --> 00:38:08.560 align:middle line:84% You start out with a purging step. 00:38:08.560 --> 00:38:10.833 align:middle line:84% This is optional if you're doing like oxide glasses. 00:38:10.833 --> 00:38:12.250 align:middle line:84% If you're doing non-oxide glasses, 00:38:12.250 --> 00:38:14.333 align:middle line:84% like chalcogenide, you don't want to get oxidized. 00:38:14.333 --> 00:38:16.640 align:middle line:84% You have to purge it with inert gas a bit. 00:38:16.640 --> 00:38:18.260 align:middle line:90% And then you start to heat it. 00:38:18.260 --> 00:38:20.100 align:middle line:84% During the heating process, you essentially 00:38:20.100 --> 00:38:22.480 align:middle line:84% ramp up the temperature and then you stay there for some time. 00:38:22.480 --> 00:38:23.897 align:middle line:84% You apply a very low pressure just 00:38:23.897 --> 00:38:25.220 align:middle line:90% to ensure the door is closed. 00:38:25.220 --> 00:38:28.060 align:middle line:84% And then you go to a pressing step, where you actually 00:38:28.060 --> 00:38:31.017 align:middle line:84% crank up the pressure, allow the things to deform. 00:38:31.017 --> 00:38:33.100 align:middle line:84% And then finally, you allow it to slowly cool down 00:38:33.100 --> 00:38:34.860 align:middle line:84% while you actually release the stress. 00:38:34.860 --> 00:38:37.140 align:middle line:90% So fairly simple process. 00:38:37.140 --> 00:38:40.540 align:middle line:84% Some of the key points here is that in order 00:38:40.540 --> 00:38:43.140 align:middle line:84% to improve the throughput and reduce any kind of damage 00:38:43.140 --> 00:38:46.420 align:middle line:84% of the mold so you can reuse it, essentially, 00:38:46.420 --> 00:38:48.940 align:middle line:84% you need to prevent any kind of mold sticking and damage. 00:38:48.940 --> 00:38:51.240 align:middle line:84% So that's why for a lot of these molds, 00:38:51.240 --> 00:38:53.580 align:middle line:84% people actually also put the low friction and also 00:38:53.580 --> 00:38:55.103 align:middle line:90% refractory coatings on top. 00:38:55.103 --> 00:38:56.520 align:middle line:84% Titanium nitride, silicon carbide, 00:38:56.520 --> 00:38:59.380 align:middle line:84% that's one very important parameter there. 00:38:59.380 --> 00:39:01.060 align:middle line:84% Also, you need to essentially prevent 00:39:01.060 --> 00:39:03.220 align:middle line:84% any kind of non-uniform temperature distribution 00:39:03.220 --> 00:39:05.980 align:middle line:84% in this process, because non-uniform temperature 00:39:05.980 --> 00:39:09.700 align:middle line:84% diffusion lead to variation in terms of viscosity, which 00:39:09.700 --> 00:39:12.420 align:middle line:90% is not desirable in this case. 00:39:12.420 --> 00:39:15.660 align:middle line:84% And variation of viscosity leads to a variation of strain rate. 00:39:15.660 --> 00:39:17.357 align:middle line:84% So that's why people don't like it. 00:39:17.357 --> 00:39:19.940 align:middle line:84% And finally, one very important part also want to mention here 00:39:19.940 --> 00:39:23.260 align:middle line:84% is that people develop very elaborate models, trying 00:39:23.260 --> 00:39:25.240 align:middle line:84% to essentially simulate this process, 00:39:25.240 --> 00:39:29.060 align:middle line:84% to predict any kind of a postmodern shape deformation. 00:39:29.060 --> 00:39:32.100 align:middle line:84% And that mostly come from essentially viscoelasticity 00:39:32.100 --> 00:39:32.707 align:middle line:90% of the glass. 00:39:32.707 --> 00:39:34.540 align:middle line:84% So we're going to talk about viscoelasticity 00:39:34.540 --> 00:39:35.623 align:middle line:90% in the next section there. 00:39:35.623 --> 00:39:39.500 align:middle line:84% But basically, a material during the glass transition temperature 00:39:39.500 --> 00:39:41.380 align:middle line:84% regime exhibits both elastic properties 00:39:41.380 --> 00:39:43.500 align:middle line:84% and also viscous flow properties. 00:39:43.500 --> 00:39:45.380 align:middle line:84% So a direct consequence of that is 00:39:45.380 --> 00:39:49.140 align:middle line:84% that the final geometry of the structure, now very sensitively 00:39:49.140 --> 00:39:52.315 align:middle line:84% depends on the temperature history. 00:39:52.315 --> 00:39:53.690 align:middle line:84% During this modeling process, you 00:39:53.690 --> 00:39:55.610 align:middle line:84% expect that you get lots of information. 00:39:55.610 --> 00:39:58.330 align:middle line:84% This actually leads to a lot of residual stress. 00:39:58.330 --> 00:40:02.770 align:middle line:84% So if you release the mold, now essentially, 00:40:02.770 --> 00:40:04.930 align:middle line:84% you allow the surface to freely deform. 00:40:04.930 --> 00:40:08.770 align:middle line:84% This residual stress is then going to lead to relaxation 00:40:08.770 --> 00:40:11.730 align:middle line:84% and eventually leading to a geometric deviation 00:40:11.730 --> 00:40:14.310 align:middle line:84% from your target mold structures. 00:40:14.310 --> 00:40:16.970 align:middle line:84% So that's something you have to very carefully model 00:40:16.970 --> 00:40:20.130 align:middle line:84% in order to prevent this kind of shape deformation there. 00:40:20.130 --> 00:40:21.850 align:middle line:84% So there are tons of papers looking 00:40:21.850 --> 00:40:23.810 align:middle line:84% into how to actually model this process 00:40:23.810 --> 00:40:27.890 align:middle line:84% to prevent any kind of a shape deformation. 00:40:27.890 --> 00:40:29.610 align:middle line:84% Now, why this is so important, why people 00:40:29.610 --> 00:40:32.010 align:middle line:84% care about it, because the most important application 00:40:32.010 --> 00:40:35.970 align:middle line:84% for this kind of modeling process is for optical elements. 00:40:35.970 --> 00:40:39.330 align:middle line:84% And for these optical surfaces, any kind of a shape deviation 00:40:39.330 --> 00:40:40.830 align:middle line:90% can be very harmful. 00:40:40.830 --> 00:40:43.170 align:middle line:84% It leads to aberrations, essentially blurs 00:40:43.170 --> 00:40:46.270 align:middle line:84% the image you get in your final camera products. 00:40:46.270 --> 00:40:49.470 align:middle line:84% So what I'm showing you here, this is actually a table. 00:40:49.470 --> 00:40:52.530 align:middle line:84% It's a bit old, but the general features are still there. 00:40:52.530 --> 00:40:54.490 align:middle line:84% It compares two common materials people 00:40:54.490 --> 00:40:56.530 align:middle line:84% use for essentially molding process, glass 00:40:56.530 --> 00:40:59.250 align:middle line:90% versus plastic or polymer. 00:40:59.250 --> 00:41:00.370 align:middle line:90% OK. 00:41:00.370 --> 00:41:04.970 align:middle line:84% So if you think about state-of-the-art consumer 00:41:04.970 --> 00:41:07.610 align:middle line:84% electronic devices like the phone in your pocket, 00:41:07.610 --> 00:41:10.910 align:middle line:84% these lenses here, a lot of the high-end cameras, 00:41:10.910 --> 00:41:14.830 align:middle line:84% they now use a mix of glass lenses plus polymer lenses. 00:41:14.830 --> 00:41:20.650 align:middle line:84% You sometimes see people seeing like a camera may have 1G6P 00:41:20.650 --> 00:41:23.290 align:middle line:90% or maybe like 7P8P. 00:41:23.290 --> 00:41:27.010 align:middle line:84% So essentially, what it means is that your camera lens 00:41:27.010 --> 00:41:31.530 align:middle line:84% contains one piece of glass lens and six pieces of plastic lens. 00:41:31.530 --> 00:41:33.530 align:middle line:84% Or you can also do like eight pieces of plastic 00:41:33.530 --> 00:41:36.210 align:middle line:90% or seven pieces of plastic. 00:41:36.210 --> 00:41:38.930 align:middle line:84% So previously, people pretty much 00:41:38.930 --> 00:41:42.490 align:middle line:90% just plastic only like this. 00:41:42.490 --> 00:41:44.530 align:middle line:84% Recently, people start to transition 00:41:44.530 --> 00:41:46.530 align:middle line:84% to this kind of hybrid lenses, where you combine 00:41:46.530 --> 00:41:47.970 align:middle line:90% both glass and plastics. 00:41:47.970 --> 00:41:51.430 align:middle line:84% The motivation behind that goes back to the properties here. 00:41:51.430 --> 00:41:55.195 align:middle line:84% So for glasses, you get huge amount 00:41:55.195 --> 00:41:56.570 align:middle line:84% of varieties where you can easily 00:41:56.570 --> 00:41:57.870 align:middle line:90% tailor optical properties. 00:41:57.870 --> 00:42:00.687 align:middle line:84% Most importantly, it goes back to this P number, 00:42:00.687 --> 00:42:02.770 align:middle line:84% which basically gives you the dispersion of glass. 00:42:02.770 --> 00:42:04.610 align:middle line:84% We're going to talk about that later on when we were talking 00:42:04.610 --> 00:42:05.870 align:middle line:90% about optical properties. 00:42:05.870 --> 00:42:09.870 align:middle line:84% But plastics tend to have very high dispersion. 00:42:09.870 --> 00:42:12.370 align:middle line:84% So it means that refractive index changes pretty drastically 00:42:12.370 --> 00:42:14.305 align:middle line:90% with wavelength. 00:42:14.305 --> 00:42:15.930 align:middle line:84% And that can be problematic when you're 00:42:15.930 --> 00:42:17.810 align:middle line:84% trying to focus all different colors of light 00:42:17.810 --> 00:42:20.570 align:middle line:84% into the same point to get a sharp image. 00:42:20.570 --> 00:42:23.570 align:middle line:84% So the way to correct for it is to find a material 00:42:23.570 --> 00:42:25.970 align:middle line:84% with different dispersion characteristics. 00:42:25.970 --> 00:42:28.630 align:middle line:84% And that's actually what exactly glass is actually good for. 00:42:28.630 --> 00:42:31.170 align:middle line:84% They can actually compensate, provide different dispersion 00:42:31.170 --> 00:42:33.370 align:middle line:84% characteristics to compensate the color performance 00:42:33.370 --> 00:42:34.270 align:middle line:90% of the cameras. 00:42:34.270 --> 00:42:37.180 align:middle line:90% 00:42:37.180 --> 00:42:38.850 align:middle line:84% And that's why, I mean if you also 00:42:38.850 --> 00:42:40.830 align:middle line:84% look at the specific parameters here, 00:42:40.830 --> 00:42:43.650 align:middle line:84% glass modeling also tend to be a bit more precise. 00:42:43.650 --> 00:42:45.750 align:middle line:84% So essentially you can use, for example, 00:42:45.750 --> 00:42:47.360 align:middle line:84% one piece of glass lenses potentially 00:42:47.360 --> 00:42:49.720 align:middle line:84% to replace two pieces of polymer lenses 00:42:49.720 --> 00:42:52.480 align:middle line:84% while not sacrificing any optical performance. 00:42:52.480 --> 00:42:53.780 align:middle line:90% Well, that may sound trivial. 00:42:53.780 --> 00:42:55.947 align:middle line:84% It actually gets important because people are always 00:42:55.947 --> 00:42:58.840 align:middle line:84% looking for something that's more compact so 00:42:58.840 --> 00:43:01.580 align:middle line:84% that you don't have this bump on the cell phone right there. 00:43:01.580 --> 00:43:03.920 align:middle line:84% So those are important considerations people 00:43:03.920 --> 00:43:04.860 align:middle line:90% are looking into that. 00:43:04.860 --> 00:43:08.240 align:middle line:84% The advantage of polymer is actually cost. 00:43:08.240 --> 00:43:11.680 align:middle line:84% Injection-molded polymer lenses are extremely cheap. 00:43:11.680 --> 00:43:15.320 align:middle line:84% They basically cost nothing practically. 00:43:15.320 --> 00:43:19.680 align:middle line:84% So while glasses, they still get more expensive compared 00:43:19.680 --> 00:43:21.120 align:middle line:90% to polymer lenses. 00:43:21.120 --> 00:43:23.600 align:middle line:84% So that's why you see essentially 00:43:23.600 --> 00:43:28.480 align:middle line:84% this kind of hybrid lenses mostly in high-end cell phone 00:43:28.480 --> 00:43:31.867 align:middle line:84% products like iPhone, iPhone Pro Max, something like that. 00:43:31.867 --> 00:43:34.200 align:middle line:84% That's where they actually use hybrid lenses to give you 00:43:34.200 --> 00:43:36.540 align:middle line:90% the ultimate imaging qualities. 00:43:36.540 --> 00:43:38.400 align:middle line:84% There are also other use cases where 00:43:38.400 --> 00:43:42.560 align:middle line:84% glasses is very important, for example in automotive industry. 00:43:42.560 --> 00:43:45.640 align:middle line:84% There are lots of cameras on the car. 00:43:45.640 --> 00:43:47.737 align:middle line:84% Both outside the car, outside the cabin, 00:43:47.737 --> 00:43:50.320 align:middle line:84% inside the cabin to either look at the surrounding environment 00:43:50.320 --> 00:43:53.880 align:middle line:84% or to monitor the occupants or drivers in the cabin. 00:43:53.880 --> 00:43:56.560 align:middle line:84% For those applications, it's really important 00:43:56.560 --> 00:43:58.240 align:middle line:84% that the material you use has to be 00:43:58.240 --> 00:44:01.170 align:middle line:84% compatible with the automotive regulations. 00:44:01.170 --> 00:44:02.920 align:middle line:84% Automotive regulations are quite stringent 00:44:02.920 --> 00:44:04.337 align:middle line:84% in terms of temperature excursion, 00:44:04.337 --> 00:44:07.440 align:middle line:84% in terms of saw, mist, dust, everything. 00:44:07.440 --> 00:44:11.080 align:middle line:84% So that's where glass actually excels compared to polymers. 00:44:11.080 --> 00:44:13.800 align:middle line:84% Polymers often have challenges, especially meeting 00:44:13.800 --> 00:44:15.620 align:middle line:90% those kinds of specifications. 00:44:15.620 --> 00:44:19.265 align:middle line:84% And that's why it's almost pretty much a mandated 00:44:19.265 --> 00:44:20.640 align:middle line:84% requirement that you actually use 00:44:20.640 --> 00:44:23.240 align:middle line:84% glass lenses on those automotive applications. 00:44:23.240 --> 00:44:27.880 align:middle line:84% So that's why the glass molding is really picking up 00:44:27.880 --> 00:44:31.120 align:middle line:84% in recent years because of the increasing use of, essentially, 00:44:31.120 --> 00:44:34.040 align:middle line:90% computer vision systems. 00:44:34.040 --> 00:44:37.080 align:middle line:84% All right, so these are four tiny little lenses, right? 00:44:37.080 --> 00:44:39.280 align:middle line:90% What about the huge ones? 00:44:39.280 --> 00:44:40.660 align:middle line:90% Telescope ones. 00:44:40.660 --> 00:44:42.160 align:middle line:84% So we're looking at telescopes here. 00:44:42.160 --> 00:44:43.535 align:middle line:84% I showed you this picture before. 00:44:43.535 --> 00:44:45.750 align:middle line:84% This is actually one of the large tactical mirrors 00:44:45.750 --> 00:44:47.430 align:middle line:90% made by Corning. 00:44:47.430 --> 00:44:51.550 align:middle line:84% This one has a diameter of 2.7 meters, which may appear big. 00:44:51.550 --> 00:44:53.430 align:middle line:84% But if you look at this big chart here, 00:44:53.430 --> 00:44:57.590 align:middle line:84% that actually shows all the telescopes in the world 00:44:57.590 --> 00:44:59.110 align:middle line:90% to scale. 00:44:59.110 --> 00:45:02.430 align:middle line:84% They also put, in this case, a tennis court and a basketball 00:45:02.430 --> 00:45:03.950 align:middle line:90% court to scale. 00:45:03.950 --> 00:45:07.030 align:middle line:84% So now if you look at this one, this one may seem very big. 00:45:07.030 --> 00:45:09.010 align:middle line:84% It's about the size of this Hooker Telescope. 00:45:09.010 --> 00:45:11.370 align:middle line:84% It's not the same one, but size-wise very similar. 00:45:11.370 --> 00:45:14.790 align:middle line:90% So this tiny little one. 00:45:14.790 --> 00:45:16.970 align:middle line:84% Now, if you look at this plot here, 00:45:16.970 --> 00:45:18.370 align:middle line:90% now I have a couple of things. 00:45:18.370 --> 00:45:20.270 align:middle line:84% I've a couple of observations I made. 00:45:20.270 --> 00:45:23.150 align:middle line:84% First thing is about that the astronomers 00:45:23.150 --> 00:45:24.910 align:middle line:84% don't seem very creative when it comes 00:45:24.910 --> 00:45:27.130 align:middle line:90% to naming because look at it. 00:45:27.130 --> 00:45:32.190 align:middle line:84% They have large telescope, very large telescope, 00:45:32.190 --> 00:45:35.168 align:middle line:84% extremely large telescope, overwhelmingly large telescope. 00:45:35.168 --> 00:45:37.210 align:middle line:84% AUDIENCE: They're like, no, no, no, it's too big. 00:45:37.210 --> 00:45:37.770 align:middle line:90% It's too big. 00:45:37.770 --> 00:45:38.437 align:middle line:90% We'll cancel it. 00:45:38.437 --> 00:45:39.271 align:middle line:90% [INTERPOSING VOICES] 00:45:39.271 --> 00:45:41.090 align:middle line:84% JUEJUN HU: They are smart people, right? 00:45:41.090 --> 00:45:42.950 align:middle line:84% I wish they come up with more creative names 00:45:42.950 --> 00:45:45.163 align:middle line:90% rather than that, but whatever. 00:45:45.163 --> 00:45:46.330 align:middle line:90% Now, that's the first thing. 00:45:46.330 --> 00:45:49.430 align:middle line:84% Second thing, look at these ones, these big mirrors. 00:45:49.430 --> 00:45:51.960 align:middle line:90% Do you notice something? 00:45:51.960 --> 00:45:53.972 align:middle line:90% AUDIENCE: [INAUDIBLE] 00:45:53.972 --> 00:45:55.430 align:middle line:84% JUEJUN HU: Yeah, that's because you 00:45:55.430 --> 00:45:58.055 align:middle line:84% need light waves to actually go through the camera in the back. 00:45:58.055 --> 00:45:59.370 align:middle line:90% Outside that, look at the size. 00:45:59.370 --> 00:46:01.390 align:middle line:90% You notice something there? 00:46:01.390 --> 00:46:03.590 align:middle line:84% They're all more or less the same size. 00:46:03.590 --> 00:46:06.750 align:middle line:84% In fact, they all have a maximum diameter of 8.4 meters. 00:46:06.750 --> 00:46:09.260 align:middle line:84% I mean, wonder where that number comes from. 00:46:09.260 --> 00:46:11.010 align:middle line:84% Because they all come from the same place. 00:46:11.010 --> 00:46:13.390 align:middle line:84% There's only one big furnace in the world that actually 00:46:13.390 --> 00:46:14.890 align:middle line:90% can make such huge mirrors. 00:46:14.890 --> 00:46:17.950 align:middle line:84% And the diameter of that furnace is 8.4 meters. 00:46:17.950 --> 00:46:20.472 align:middle line:90% This is all made in Arizona. 00:46:20.472 --> 00:46:21.930 align:middle line:84% If you go to University of Arizona, 00:46:21.930 --> 00:46:23.570 align:middle line:84% you go to their football stadium, 00:46:23.570 --> 00:46:26.530 align:middle line:84% this is under, essentially, audience seats. 00:46:26.530 --> 00:46:28.910 align:middle line:90% This is the mirror lab. 00:46:28.910 --> 00:46:32.750 align:middle line:84% All those mirrors are melted right there, that big furnace. 00:46:32.750 --> 00:46:33.510 align:middle line:90% OK. 00:46:33.510 --> 00:46:35.123 align:middle line:84% AUDIENCE: --just go into the furnace. 00:46:35.123 --> 00:46:35.950 align:middle line:90% [LAUGHTER] 00:46:35.950 --> 00:46:37.030 align:middle line:90% JUEJUN HU: There you go. 00:46:37.030 --> 00:46:38.655 align:middle line:84% They probably don't charge you a ticket 00:46:38.655 --> 00:46:39.970 align:middle line:90% anyway without hefty price. 00:46:39.970 --> 00:46:41.100 align:middle line:90% So maybe a good thing. 00:46:41.100 --> 00:46:43.640 align:middle line:84% OK, so now if you look inside this furnace, if you open up, 00:46:43.640 --> 00:46:45.140 align:middle line:84% this is actually what it looks like. 00:46:45.140 --> 00:46:47.060 align:middle line:84% You're going to pour molten glass into that. 00:46:47.060 --> 00:46:49.380 align:middle line:84% And then you see at the bottom here, 00:46:49.380 --> 00:46:51.980 align:middle line:84% this mirror is actually not a big solid piece. 00:46:51.980 --> 00:46:54.140 align:middle line:84% They usually put this kind of honeycomb structures 00:46:54.140 --> 00:46:55.075 align:middle line:90% at the bottom. 00:46:55.075 --> 00:46:57.700 align:middle line:84% This is similar to the kind of patterns, corrugated pattern you 00:46:57.700 --> 00:46:59.020 align:middle line:90% have on a waffle iron. 00:46:59.020 --> 00:47:01.560 align:middle line:84% So essentially, the created mirrors, 00:47:01.560 --> 00:47:03.060 align:middle line:84% instead of having a big solid piece, 00:47:03.060 --> 00:47:06.040 align:middle line:84% they are connected by ridges around this honeycomb pieces. 00:47:06.040 --> 00:47:08.540 align:middle line:84% And the point of that is that you want to reduce essentially 00:47:08.540 --> 00:47:11.620 align:middle line:84% the amount of material used to reduce weight, reduce 00:47:11.620 --> 00:47:14.340 align:middle line:84% the cooling time, and also maintain the mechanical stress 00:47:14.340 --> 00:47:15.960 align:middle line:90% using the honeycomb structures. 00:47:15.960 --> 00:47:16.860 align:middle line:90% Makes sense. 00:47:16.860 --> 00:47:17.780 align:middle line:90% Right. 00:47:17.780 --> 00:47:18.360 align:middle line:90% All right. 00:47:18.360 --> 00:47:20.820 align:middle line:84% Now, this mirror has a big parabolic 00:47:20.820 --> 00:47:23.540 align:middle line:84% surfaces so that you can focus light from distant stars 00:47:23.540 --> 00:47:24.720 align:middle line:90% into a spot. 00:47:24.720 --> 00:47:27.420 align:middle line:84% So now my question for you, how do you 00:47:27.420 --> 00:47:32.020 align:middle line:84% create these huge parabolic surfaces? 00:47:32.020 --> 00:47:33.620 align:middle line:84% If you're doing grinding and polishing 00:47:33.620 --> 00:47:35.780 align:middle line:90% that's going to take forever. 00:47:35.780 --> 00:47:37.400 align:middle line:90% Right, so what-- 00:47:37.400 --> 00:47:38.980 align:middle line:90% AUDIENCE: Stamping? 00:47:38.980 --> 00:47:40.380 align:middle line:90% JUEJUN HU: Stamping. 00:47:40.380 --> 00:47:41.160 align:middle line:90% Good guess. 00:47:41.160 --> 00:47:42.360 align:middle line:90% You need a huge stamp. 00:47:42.360 --> 00:47:43.780 align:middle line:90% It has to be very precise. 00:47:43.780 --> 00:47:44.440 align:middle line:90% Stamp it. 00:47:44.440 --> 00:47:48.060 align:middle line:84% AUDIENCE: Different cooling/heating rates 00:47:48.060 --> 00:47:50.640 align:middle line:84% JUEJUN HU: You get a parabolic shape. 00:47:50.640 --> 00:47:53.160 align:middle line:90% AUDIENCE: Maybe to like-- 00:47:53.160 --> 00:47:54.700 align:middle line:84% JUEJUN HU: Use your wildest guesses. 00:47:54.700 --> 00:47:57.860 align:middle line:84% AUDIENCE: Drip it like [INAUDIBLE]. 00:47:57.860 --> 00:47:59.500 align:middle line:90% JUEJUN HU: They spin it. 00:47:59.500 --> 00:48:00.200 align:middle line:90% There you go. 00:48:00.200 --> 00:48:00.722 align:middle line:90% Very good. 00:48:00.722 --> 00:48:02.180 align:middle line:84% Now they should hire you as their-- 00:48:02.180 --> 00:48:06.140 align:middle line:84% [LAUGHS] so the way they do it is essentially they 00:48:06.140 --> 00:48:08.300 align:middle line:84% spin it while the glass is melted. 00:48:08.300 --> 00:48:11.460 align:middle line:84% If you go ahead and calculate it, what you find out 00:48:11.460 --> 00:48:14.900 align:middle line:84% is that under gravitational force, if you spin a liquid, 00:48:14.900 --> 00:48:17.080 align:middle line:84% its surface obviously is going to rise on the edge. 00:48:17.080 --> 00:48:20.080 align:middle line:84% The center is going to sink because of centrifugal force. 00:48:20.080 --> 00:48:24.980 align:middle line:84% The surface exactly conforms to a parabolic shape. 00:48:24.980 --> 00:48:27.200 align:middle line:84% This is a homework assignment for you. 00:48:27.200 --> 00:48:28.160 align:middle line:90% AUDIENCE: [INAUDIBLE] 00:48:28.160 --> 00:48:29.660 align:middle line:84% JUEJUN HU: No, don't worry about it. 00:48:29.660 --> 00:48:30.480 align:middle line:90% But you can do it. 00:48:30.480 --> 00:48:32.369 align:middle line:90% It's exactly a parabolic shape. 00:48:32.369 --> 00:48:33.952 align:middle line:84% AUDIENCE: Is the question [INAUDIBLE]? 00:48:33.952 --> 00:48:34.380 align:middle line:90% JUEJUN HU: PSAT. 00:48:34.380 --> 00:48:35.713 align:middle line:90% I'm going to put it on the PSAT. 00:48:35.713 --> 00:48:37.050 align:middle line:90% You have to solve it exactly. 00:48:37.050 --> 00:48:39.570 align:middle line:84% This is actually one of the questions 00:48:39.570 --> 00:48:42.003 align:middle line:84% I recall when I was doing my Physics Olympiad and stuff. 00:48:42.003 --> 00:48:43.170 align:middle line:90% That's one of the questions. 00:48:43.170 --> 00:48:44.878 align:middle line:84% You have to actually prove it is actually 00:48:44.878 --> 00:48:47.550 align:middle line:84% a parabolic shape, which indeed a parabolic shape, by the way. 00:48:47.550 --> 00:48:50.010 align:middle line:84% OK, so you basically have that molten glass. 00:48:50.010 --> 00:48:50.910 align:middle line:90% It's cooling. 00:48:50.910 --> 00:48:53.450 align:middle line:84% We said that glass cooling has to go a long time because you 00:48:53.450 --> 00:48:54.510 align:middle line:90% need to release all the stress. 00:48:54.510 --> 00:48:55.843 align:middle line:90% So that's a pretty long process. 00:48:55.843 --> 00:48:58.410 align:middle line:84% Over the entire process, you have to spin and spin 00:48:58.410 --> 00:48:59.310 align:middle line:90% until it cools down. 00:48:59.310 --> 00:49:01.110 align:middle line:84% And actually, it's actually frozen into it. 00:49:01.110 --> 00:49:02.410 align:middle line:90% So it's pretty remarkable. 00:49:02.410 --> 00:49:07.170 align:middle line:84% Actually that huge, gigantic furnace is actually spinning. 00:49:07.170 --> 00:49:11.270 align:middle line:84% And at the end, you get this very nice parabolic shape. 00:49:11.270 --> 00:49:14.170 align:middle line:90% You do some fine-tuning. 00:49:14.170 --> 00:49:15.230 align:middle line:90% You do a little bit more. 00:49:15.230 --> 00:49:18.130 align:middle line:84% Essentially, you're milling and then polishing so that you get 00:49:18.130 --> 00:49:21.110 align:middle line:84% it down to a 25-nanometer accuracy, 00:49:21.110 --> 00:49:25.350 align:middle line:84% which is remarkable over that 8.4-meter diameter length. 00:49:25.350 --> 00:49:28.770 align:middle line:90% 00:49:28.770 --> 00:49:31.402 align:middle line:84% OK, so that's one more example where this kind of viscous flow 00:49:31.402 --> 00:49:33.610 align:middle line:84% properties can give you one way to actually structure 00:49:33.610 --> 00:49:35.730 align:middle line:90% these gigantic pieces. 00:49:35.730 --> 00:49:39.530 align:middle line:90% 00:49:39.530 --> 00:49:40.330 align:middle line:90% All right. 00:49:40.330 --> 00:49:42.330 align:middle line:84% Any more questions about these inorganic 00:49:42.330 --> 00:49:44.830 align:middle line:84% glasses before we move on to talk about metallic glasses? 00:49:44.830 --> 00:49:48.130 align:middle line:90% 00:49:48.130 --> 00:49:51.530 align:middle line:84% OK, so now, let's switch gears a little bit and talk 00:49:51.530 --> 00:49:53.832 align:middle line:84% about how you actually shape metallic glasses. 00:49:53.832 --> 00:49:55.290 align:middle line:84% We'll have one chapter specifically 00:49:55.290 --> 00:49:57.090 align:middle line:84% talking about structures and mechanical properties 00:49:57.090 --> 00:49:59.010 align:middle line:84% or mechanical glasses later after we talk 00:49:59.010 --> 00:50:00.230 align:middle line:90% about mechanical properties. 00:50:00.230 --> 00:50:02.772 align:middle line:84% But I want to give you a little preview about how we actually 00:50:02.772 --> 00:50:08.730 align:middle line:84% essentially produce all kinds of products with diverse geometries 00:50:08.730 --> 00:50:10.190 align:middle line:90% out of metallic glasses. 00:50:10.190 --> 00:50:11.047 align:middle line:90% So 00:50:11.047 --> 00:50:13.130 align:middle line:84% We have already talked about some basic attributes 00:50:13.130 --> 00:50:14.623 align:middle line:90% of bulk metallic glasses. 00:50:14.623 --> 00:50:17.290 align:middle line:84% We mentioned that you have this kind of random packing structure 00:50:17.290 --> 00:50:19.530 align:middle line:84% that's free from the typical crystalline defects 00:50:19.530 --> 00:50:21.572 align:middle line:84% you would see in a conventional metal, like grain 00:50:21.572 --> 00:50:25.130 align:middle line:84% boundaries or crystalline planes or dislocations. 00:50:25.130 --> 00:50:27.050 align:middle line:84% So one immediate consequence of that 00:50:27.050 --> 00:50:30.770 align:middle line:84% is that this amorphous metal tends 00:50:30.770 --> 00:50:33.880 align:middle line:84% to exhibit a much higher yield strength, 00:50:33.880 --> 00:50:37.520 align:middle line:84% because there's no way for them to easily deform plastically. 00:50:37.520 --> 00:50:39.640 align:middle line:84% In a conventional metal, plastic deformation 00:50:39.640 --> 00:50:41.980 align:middle line:84% usually takes place through a motion of dislocations. 00:50:41.980 --> 00:50:45.360 align:middle line:84% You get essentially slip or essentially a climb. 00:50:45.360 --> 00:50:47.500 align:middle line:84% So those macroscopic deformation, 00:50:47.500 --> 00:50:48.780 align:middle line:90% you don't have any of that. 00:50:48.780 --> 00:50:51.760 align:middle line:84% So that's why the lack of plastic deformation mechanism 00:50:51.760 --> 00:50:54.240 align:middle line:84% means that it has to deform elastically 00:50:54.240 --> 00:50:56.800 align:middle line:90% over a much wider stress range. 00:50:56.800 --> 00:51:01.640 align:middle line:84% So now, if you look at the definition of yield stress, 00:51:01.640 --> 00:51:06.277 align:middle line:84% you essentially put the stress versus strain. 00:51:06.277 --> 00:51:08.860 align:middle line:84% And typically, for material, it will look something like this. 00:51:08.860 --> 00:51:11.200 align:middle line:84% You get elastic range, the Hooke and range. 00:51:11.200 --> 00:51:13.160 align:middle line:84% And then it may deviate from that range 00:51:13.160 --> 00:51:15.640 align:middle line:84% and eventually, you start to deform plastically. 00:51:15.640 --> 00:51:18.080 align:middle line:84% If you're in a less range, if you remove the stress, 00:51:18.080 --> 00:51:20.680 align:middle line:84% this curve is going to come back exactly where I come from. 00:51:20.680 --> 00:51:23.540 align:middle line:84% But if it is going to a plastic range, 00:51:23.540 --> 00:51:27.200 align:middle line:84% then as you unload, then essentially, you come to a point 00:51:27.200 --> 00:51:29.640 align:middle line:84% where you leave some residual plastic deformation. 00:51:29.640 --> 00:51:33.840 align:middle line:84% So the point where this deformation gets to 0.2%, 00:51:33.840 --> 00:51:37.960 align:middle line:84% the corresponding stress is what we define as yield stress. 00:51:37.960 --> 00:51:40.040 align:middle line:84% Now, in amorphous metal, because it 00:51:40.040 --> 00:51:41.780 align:middle line:84% doesn't want to deform plastically, 00:51:41.780 --> 00:51:43.520 align:middle line:84% it means that this elastic range actually 00:51:43.520 --> 00:51:48.560 align:middle line:84% extends much beyond yield, therefore conventional method. 00:51:48.560 --> 00:51:53.360 align:middle line:84% So that's one reason people like this amorphous metal there. 00:51:53.360 --> 00:51:56.500 align:middle line:84% So what I'm putting on this plot on the right-hand side here, 00:51:56.500 --> 00:51:58.640 align:middle line:84% I'm basically comparing the strength 00:51:58.640 --> 00:52:01.340 align:middle line:84% of amorphous metal versus unconventional materials. 00:52:01.340 --> 00:52:04.200 align:middle line:84% I apologize, the fonts here are tiny. 00:52:04.200 --> 00:52:05.780 align:middle line:84% I don't think you can ever read it, 00:52:05.780 --> 00:52:07.300 align:middle line:84% but these are essentially magnesium. 00:52:07.300 --> 00:52:09.280 align:middle line:90% This is aluminum. 00:52:09.280 --> 00:52:10.420 align:middle line:90% This is titanium. 00:52:10.420 --> 00:52:11.420 align:middle line:90% This is stainless steel. 00:52:11.420 --> 00:52:13.800 align:middle line:84% So compared to conventional crystalline metal. 00:52:13.800 --> 00:52:16.320 align:middle line:84% What you see here is the strength of amorphous metal 00:52:16.320 --> 00:52:19.180 align:middle line:84% is much superior compared to all these conventional materials. 00:52:19.180 --> 00:52:23.600 align:middle line:84% Again, because you don't have a mechanism to deform plastically. 00:52:23.600 --> 00:52:26.322 align:middle line:84% And same thing applies to other things like harness, 00:52:26.322 --> 00:52:28.280 align:middle line:84% which is also a measure of how the material can 00:52:28.280 --> 00:52:29.600 align:middle line:90% resist deformation. 00:52:29.600 --> 00:52:36.200 align:middle line:84% So in terms of those metrics, amorphous metals always win. 00:52:36.200 --> 00:52:37.740 align:middle line:84% However, that also has a problem. 00:52:37.740 --> 00:52:40.120 align:middle line:84% If you now come back to processing and trying to use it 00:52:40.120 --> 00:52:41.400 align:middle line:90% as a mechanical component. 00:52:41.400 --> 00:52:43.580 align:middle line:84% If you are trying to process conventional metal, 00:52:43.580 --> 00:52:46.260 align:middle line:90% you typically do a co-working. 00:52:46.260 --> 00:52:47.260 align:middle line:90% You can roll it. 00:52:47.260 --> 00:52:48.300 align:middle line:90% You can extrude it. 00:52:48.300 --> 00:52:49.120 align:middle line:90% You can deform it. 00:52:49.120 --> 00:52:52.000 align:middle line:90% 00:52:52.000 --> 00:52:54.440 align:middle line:84% It's going to plastically deform. 00:52:54.440 --> 00:52:56.840 align:middle line:84% And in that process, the reason the conventional metal 00:52:56.840 --> 00:53:00.120 align:middle line:84% can be cold-worked is because of this attribute 00:53:00.120 --> 00:53:03.400 align:middle line:90% of so-called strain hardening. 00:53:03.400 --> 00:53:06.880 align:middle line:84% So when you are trying to plastically deform these metals, 00:53:06.880 --> 00:53:08.580 align:middle line:84% you actually generate more defects. 00:53:08.580 --> 00:53:10.180 align:middle line:84% You generate a lot more dislocations. 00:53:10.180 --> 00:53:14.020 align:middle line:84% And then these iterations, as they move around, 00:53:14.020 --> 00:53:15.900 align:middle line:84% they are going to interact with each other. 00:53:15.900 --> 00:53:18.560 align:middle line:84% And this interaction hampers the further movement 00:53:18.560 --> 00:53:20.240 align:middle line:90% of the dislocations. 00:53:20.240 --> 00:53:22.320 align:middle line:84% And as a result, the more cold work 00:53:22.320 --> 00:53:24.280 align:middle line:84% you put on a conventional metal, the higher 00:53:24.280 --> 00:53:27.420 align:middle line:90% the mechanical strength it gets. 00:53:27.420 --> 00:53:30.070 align:middle line:84% That's called a strain hardening. 00:53:30.070 --> 00:53:32.070 align:middle line:84% Now, why is strain hardening important? 00:53:32.070 --> 00:53:33.670 align:middle line:84% Strain hardening is the mechanism 00:53:33.670 --> 00:53:37.627 align:middle line:84% to prevent essentially localized deformation and failure. 00:53:37.627 --> 00:53:39.710 align:middle line:84% Think about the same example as like cane joining. 00:53:39.710 --> 00:53:41.877 align:middle line:84% If you're trying to essentially use cold working to, 00:53:41.877 --> 00:53:43.790 align:middle line:84% for example, pull a metal wire, if you 00:53:43.790 --> 00:53:45.910 align:middle line:84% have some non-uniformity such that locally you 00:53:45.910 --> 00:53:47.730 align:middle line:84% get some essentially smaller diameter, 00:53:47.730 --> 00:53:50.030 align:middle line:84% it means that you actually get more deformation there. 00:53:50.030 --> 00:53:52.990 align:middle line:84% More deformation lead to more strain hardening. 00:53:52.990 --> 00:53:54.570 align:middle line:90% So strength increases. 00:53:54.570 --> 00:53:56.710 align:middle line:84% This increased strength then prevents 00:53:56.710 --> 00:53:59.290 align:middle line:84% essentially catastrophic failure right at that point. 00:53:59.290 --> 00:53:59.790 align:middle line:90% OK? 00:53:59.790 --> 00:54:04.470 align:middle line:84% So that's why co-working is a viable way of processing 00:54:04.470 --> 00:54:06.190 align:middle line:90% conventional metals. 00:54:06.190 --> 00:54:08.390 align:middle line:84% Now, what about amorphous metals? 00:54:08.390 --> 00:54:10.710 align:middle line:84% So when amorphous metals-- if you apply lots of stress, 00:54:10.710 --> 00:54:13.030 align:middle line:84% it will start to deform at some point plastically. 00:54:13.030 --> 00:54:15.350 align:middle line:84% But when it deforms plastically, instead 00:54:15.350 --> 00:54:19.970 align:middle line:84% of relying on dislocations, what happens is that essentially, 00:54:19.970 --> 00:54:22.590 align:middle line:84% in an intuitive manner, the atomic clusters 00:54:22.590 --> 00:54:26.730 align:middle line:84% will have to move past each other directly. 00:54:26.730 --> 00:54:27.230 align:middle line:90% OK? 00:54:27.230 --> 00:54:29.550 align:middle line:84% So later on, we're going to talk about the specific mechanism 00:54:29.550 --> 00:54:29.810 align:middle line:90% there. 00:54:29.810 --> 00:54:31.090 align:middle line:90% And how this actually happens. 00:54:31.090 --> 00:54:33.310 align:middle line:84% But essentially, when you have these clusters move 00:54:33.310 --> 00:54:35.990 align:middle line:84% past each other, one thing that inevitably happens 00:54:35.990 --> 00:54:40.150 align:middle line:84% is it generates excess free volume. 00:54:40.150 --> 00:54:49.590 align:middle line:84% So speaking about free volume, where's the wipe? 00:54:49.590 --> 00:54:50.530 align:middle line:90% Forget about it. 00:54:50.530 --> 00:54:53.070 align:middle line:90% 00:54:53.070 --> 00:54:58.870 align:middle line:84% So if you look at the volume-temperature curve 00:54:58.870 --> 00:55:02.270 align:middle line:84% that you have seen many, many times, 00:55:02.270 --> 00:55:06.750 align:middle line:84% for a crystalline material, you get something like this. 00:55:06.750 --> 00:55:12.870 align:middle line:84% Amorphous material, it would be more like this. 00:55:12.870 --> 00:55:19.070 align:middle line:84% So if you allow the liquid to completely relax 00:55:19.070 --> 00:55:21.210 align:middle line:84% here, this dotted line, what I'm showing you here, 00:55:21.210 --> 00:55:23.810 align:middle line:84% this would be the supercooled liquid line. 00:55:23.810 --> 00:55:27.700 align:middle line:84% The definition of the glass says that the glass always 00:55:27.700 --> 00:55:30.540 align:middle line:84% try to relax towards the supercool liquid line. 00:55:30.540 --> 00:55:32.780 align:middle line:84% So the excess volume we're seeing 00:55:32.780 --> 00:55:38.160 align:middle line:84% here, this is what's called a free volume, this delta V here. 00:55:38.160 --> 00:55:40.820 align:middle line:90% 00:55:40.820 --> 00:55:42.820 align:middle line:84% Because the glass usually has a larger 00:55:42.820 --> 00:55:47.520 align:middle line:84% volume compared to its supercool liquid counterpart. 00:55:47.520 --> 00:55:51.260 align:middle line:84% Now, you can imagine that if you have an amorphous metal, if you 00:55:51.260 --> 00:55:53.580 align:middle line:84% start to have atom clusters move past each other, 00:55:53.580 --> 00:55:58.060 align:middle line:84% you need free volume to induce this kind of deformation. 00:55:58.060 --> 00:55:59.580 align:middle line:84% Also, the more information you bring 00:55:59.580 --> 00:56:04.860 align:middle line:84% into it, the more free volume you introduce into the system. 00:56:04.860 --> 00:56:08.740 align:middle line:84% You are deviating from this very close packed structure there. 00:56:08.740 --> 00:56:10.360 align:middle line:90% Now, this creates an issue here. 00:56:10.360 --> 00:56:12.340 align:middle line:90% This is called strain softening. 00:56:12.340 --> 00:56:15.900 align:middle line:84% The more you deform it, the more excess volume you generate, 00:56:15.900 --> 00:56:19.753 align:middle line:90% the more deformable it becomes. 00:56:19.753 --> 00:56:21.420 align:middle line:84% So the strength of the material actually 00:56:21.420 --> 00:56:25.320 align:middle line:84% decreases with increasing amount of strain in amorphous metal. 00:56:25.320 --> 00:56:29.020 align:middle line:90% 00:56:29.020 --> 00:56:30.900 align:middle line:84% And this is very problematic if you're 00:56:30.900 --> 00:56:33.820 align:middle line:84% trying to use do cold working on these metals here. 00:56:33.820 --> 00:56:36.860 align:middle line:84% You need to essentially shear, so-called shear localization 00:56:36.860 --> 00:56:38.580 align:middle line:90% and catastrophic failure. 00:56:38.580 --> 00:56:40.453 align:middle line:84% So what happens here, this is one example. 00:56:40.453 --> 00:56:42.120 align:middle line:84% This is, basically, amorphous metal rod. 00:56:42.120 --> 00:56:45.380 align:middle line:84% You're placing essentially axial compressive strain. 00:56:45.380 --> 00:56:48.680 align:middle line:84% And then what happens is that at some point, 00:56:48.680 --> 00:56:52.620 align:middle line:84% you start to get this deformation, plastic deformation 00:56:52.620 --> 00:56:54.300 align:middle line:90% along one of the planes here. 00:56:54.300 --> 00:56:56.820 align:middle line:84% Now, what happens is strain softens. 00:56:56.820 --> 00:56:58.440 align:middle line:84% So it becomes even more deformable. 00:56:58.440 --> 00:57:01.180 align:middle line:84% So this actually accelerates local deformation. 00:57:01.180 --> 00:57:03.020 align:middle line:84% So that if you look at the deformation, 00:57:03.020 --> 00:57:06.320 align:middle line:84% it all localizes in this kind of few localized bands, 00:57:06.320 --> 00:57:07.840 align:middle line:90% these lines here. 00:57:07.840 --> 00:57:11.280 align:middle line:84% And then it eventually breaks along one of them. 00:57:11.280 --> 00:57:13.157 align:middle line:84% So this is called a shear localization. 00:57:13.157 --> 00:57:14.740 align:middle line:84% Essentially, all the shear deformation 00:57:14.740 --> 00:57:17.100 align:middle line:84% is localized within a very narrow band. 00:57:17.100 --> 00:57:21.060 align:middle line:90% 00:57:21.060 --> 00:57:22.287 align:middle line:90% So there will be a problem. 00:57:22.287 --> 00:57:24.370 align:middle line:84% That means that you can no longer use cold working 00:57:24.370 --> 00:57:26.010 align:middle line:90% to process these materials. 00:57:26.010 --> 00:57:27.850 align:middle line:84% They are not stable against perturbations, 00:57:27.850 --> 00:57:30.890 align:middle line:90% against deformation. 00:57:30.890 --> 00:57:34.890 align:middle line:84% So that's why the way people used to actually process 00:57:34.890 --> 00:57:40.110 align:middle line:84% these small metallic glasses are two different methods. 00:57:40.110 --> 00:57:42.130 align:middle line:84% One is to essentially you try to heat it up 00:57:42.130 --> 00:57:43.850 align:middle line:90% to above the melting point. 00:57:43.850 --> 00:57:46.450 align:middle line:84% So you go to a liquid state, and then you cool it down. 00:57:46.450 --> 00:57:49.410 align:middle line:84% You're essentially casting it or essentially put the liquid 00:57:49.410 --> 00:57:51.530 align:middle line:84% into some kind of mold, allow it to cool down, 00:57:51.530 --> 00:57:54.110 align:middle line:84% and then that allows you to go to the final geometry. 00:57:54.110 --> 00:57:56.812 align:middle line:84% So this will be basically the casting process. 00:57:56.812 --> 00:57:58.270 align:middle line:84% And there are a few variants there. 00:57:58.270 --> 00:58:00.890 align:middle line:84% You can have a suction casting, which basically use vacuum 00:58:00.890 --> 00:58:02.510 align:middle line:84% to assist in the filling of the mold. 00:58:02.510 --> 00:58:03.830 align:middle line:90% Or you can do a die casting. 00:58:03.830 --> 00:58:07.090 align:middle line:84% But all those variants follow the same manner there. 00:58:07.090 --> 00:58:09.665 align:middle line:84% You go from liquid phase, pour into a mold, 00:58:09.665 --> 00:58:10.790 align:middle line:90% allow you to fill the mold. 00:58:10.790 --> 00:58:14.030 align:middle line:84% Eventually, you remove it from a piece. 00:58:14.030 --> 00:58:16.330 align:middle line:84% There is some advantage of doing casting 00:58:16.330 --> 00:58:18.770 align:middle line:84% of using metallic glasses compared to conventional metal 00:58:18.770 --> 00:58:19.270 align:middle line:90% there. 00:58:19.270 --> 00:58:21.690 align:middle line:84% The most important one being that the volume shrinkage 00:58:21.690 --> 00:58:23.250 align:middle line:90% is much smaller. 00:58:23.250 --> 00:58:25.890 align:middle line:84% So if you look at the volume change 00:58:25.890 --> 00:58:28.790 align:middle line:84% during the casting process, for crystalline material, 00:58:28.790 --> 00:58:30.730 align:middle line:84% you're essentially from liquid state right 00:58:30.730 --> 00:58:32.330 align:middle line:90% to go to the solid state. 00:58:32.330 --> 00:58:33.917 align:middle line:84% So the volume change is represented 00:58:33.917 --> 00:58:36.250 align:middle line:84% by this vertical line here, that's the first-order phase 00:58:36.250 --> 00:58:36.990 align:middle line:90% transition. 00:58:36.990 --> 00:58:39.850 align:middle line:84% So there's a certain volume from liquid to solid phase. 00:58:39.850 --> 00:58:42.130 align:middle line:90% Now versus glass. 00:58:42.130 --> 00:58:44.930 align:middle line:84% For glass, the liquid phase actually 00:58:44.930 --> 00:58:47.010 align:middle line:84% extends a little bit longer, right? 00:58:47.010 --> 00:58:50.270 align:middle line:84% Over this supercooled liquid regime, this is still liquid. 00:58:50.270 --> 00:58:53.490 align:middle line:84% It still has some viscous flow properties that 00:58:53.490 --> 00:58:54.830 align:middle line:90% can still conform to the mold. 00:58:54.830 --> 00:58:59.050 align:middle line:84% Also at the end, you see that because of the presence 00:58:59.050 --> 00:59:03.050 align:middle line:84% of the free volume, the final density of the amorphous metal 00:59:03.050 --> 00:59:05.090 align:middle line:84% also tend to be a little bit smaller compared 00:59:05.090 --> 00:59:06.690 align:middle line:90% to a crystalline metal. 00:59:06.690 --> 00:59:09.130 align:middle line:84% So these two factors combined together 00:59:09.130 --> 00:59:10.650 align:middle line:84% that this supercritical line extends 00:59:10.650 --> 00:59:12.370 align:middle line:84% to lower temperature and also the fact 00:59:12.370 --> 00:59:15.130 align:middle line:84% that you have free volume means that the net volume 00:59:15.130 --> 00:59:17.930 align:middle line:84% change during the casting process 00:59:17.930 --> 00:59:20.400 align:middle line:84% is much smaller for amorphous metal 00:59:20.400 --> 00:59:22.280 align:middle line:90% compared to a crystalline metal. 00:59:22.280 --> 00:59:24.920 align:middle line:90% Does that make sense? 00:59:24.920 --> 00:59:28.000 align:middle line:84% So this leads to this kind of process 00:59:28.000 --> 00:59:29.760 align:middle line:90% called a net shape forming. 00:59:29.760 --> 00:59:32.080 align:middle line:84% Essentially means that because the volume shrinkage is 00:59:32.080 --> 00:59:33.680 align:middle line:84% sufficiently small, it's about half 00:59:33.680 --> 00:59:35.500 align:middle line:84% a percent, versus conventional metal, 00:59:35.500 --> 00:59:37.280 align:middle line:84% which is typically a few percent, 00:59:37.280 --> 00:59:39.920 align:middle line:84% you don't have to do any kind of a further processing 00:59:39.920 --> 00:59:41.680 align:middle line:84% or shaping to fine-tune the shape. 00:59:41.680 --> 00:59:45.080 align:middle line:84% You get exactly what you want just from the mold geometry. 00:59:45.080 --> 00:59:47.140 align:middle line:84% So quantitatively, this is just one example, 00:59:47.140 --> 00:59:48.900 align:middle line:84% comparing this is amorphous metal, 00:59:48.900 --> 00:59:51.480 align:middle line:84% this is a volume shrinkage during casting compared 00:59:51.480 --> 00:59:53.900 align:middle line:84% to conventional metal, again, aluminum, titanium, steel, 00:59:53.900 --> 00:59:54.560 align:middle line:90% copper. 00:59:54.560 --> 00:59:56.018 align:middle line:84% You see that conventional metal has 00:59:56.018 --> 00:59:59.120 align:middle line:84% a few percent of volume change versus half 00:59:59.120 --> 01:00:00.620 align:middle line:90% a percent for amorphous metal. 01:00:00.620 --> 01:00:04.880 align:middle line:84% So that's one advantage for amorphous metal casting there. 01:00:04.880 --> 01:00:08.560 align:middle line:84% So the key process parameter you want to control in this process 01:00:08.560 --> 01:00:11.320 align:middle line:90% here again is the viscosity. 01:00:11.320 --> 01:00:14.200 align:middle line:84% You want to make sure it's induced sufficient viscous flow 01:00:14.200 --> 01:00:16.640 align:middle line:90% to completely fill the mold. 01:00:16.640 --> 01:00:19.680 align:middle line:84% Also, you are working against crystallization. 01:00:19.680 --> 01:00:21.920 align:middle line:90% The process cannot take forever. 01:00:21.920 --> 01:00:23.920 align:middle line:84% You have to essentially complete it 01:00:23.920 --> 01:00:25.480 align:middle line:84% with sufficiently fast cooling rate 01:00:25.480 --> 01:00:28.760 align:middle line:84% to bypass crystallization, which was indicated by this line here. 01:00:28.760 --> 01:00:32.000 align:middle line:84% You have to avoid this crystallization region in order 01:00:32.000 --> 01:00:33.680 align:middle line:90% to get amorphous metal. 01:00:33.680 --> 01:00:36.180 align:middle line:84% So this also limits essentially geometric dimensioning, 01:00:36.180 --> 01:00:40.280 align:middle line:84% if you remember, of the metal you can cast. 01:00:40.280 --> 01:00:41.520 align:middle line:90% So that's one way. 01:00:41.520 --> 01:00:44.640 align:middle line:84% Now, the second way of doing a bulk metallic glass shaping 01:00:44.640 --> 01:00:48.600 align:middle line:84% is to use a process called a thermoplastic forming. 01:00:48.600 --> 01:00:50.640 align:middle line:84% So this really derives from the processing 01:00:50.640 --> 01:00:53.400 align:middle line:90% of amorphous polymers. 01:00:53.400 --> 01:00:56.140 align:middle line:84% The idea is that you have a piece of polymer. 01:00:56.140 --> 01:00:58.522 align:middle line:84% You heat it up to above the glass transition temperature, 01:00:58.522 --> 01:01:00.480 align:middle line:84% where it becomes more or less a viscous liquid. 01:01:00.480 --> 01:01:03.360 align:middle line:84% You can then use all kinds of molding or deformation 01:01:03.360 --> 01:01:05.940 align:middle line:84% techniques to change it to a desired geometry 01:01:05.940 --> 01:01:07.960 align:middle line:84% and then you quit out so that you can freeze 01:01:07.960 --> 01:01:10.000 align:middle line:90% the final geometry there. 01:01:10.000 --> 01:01:13.060 align:middle line:84% You can do the same thing with bulk metallic glasses. 01:01:13.060 --> 01:01:15.890 align:middle line:84% And the thermal history is shown by this curve here. 01:01:15.890 --> 01:01:17.750 align:middle line:84% It's actually heat up to somewhere 01:01:17.750 --> 01:01:19.750 align:middle line:84% where you have low enough viscosity 01:01:19.750 --> 01:01:22.030 align:middle line:84% to allow you to deform it, and then you cool it down 01:01:22.030 --> 01:01:24.310 align:middle line:90% to freezing the structure. 01:01:24.310 --> 01:01:27.350 align:middle line:84% For this process, the key parameter 01:01:27.350 --> 01:01:32.950 align:middle line:84% we want to look at here, again, is crystallization kinetics. 01:01:32.950 --> 01:01:36.590 align:middle line:84% You want to make sure you pick a bulk metallic glass 01:01:36.590 --> 01:01:40.230 align:middle line:84% component where crystallization is sufficiently slow so that 01:01:40.230 --> 01:01:42.470 align:middle line:84% allows you enough time to do the molding 01:01:42.470 --> 01:01:44.455 align:middle line:90% or to do the geometric shaping. 01:01:44.455 --> 01:01:46.330 align:middle line:84% So just as one example here, I'm showing you, 01:01:46.330 --> 01:01:48.580 align:middle line:84% this is a typical plot people use to essentially gauge 01:01:48.580 --> 01:01:51.630 align:middle line:84% which metallic glass composition is suitable for some processing 01:01:51.630 --> 01:01:52.170 align:middle line:90% techniques. 01:01:52.170 --> 01:01:54.710 align:middle line:84% You essentially look at the essentially viscosity at one 01:01:54.710 --> 01:01:55.210 align:middle line:90% end. 01:01:55.210 --> 01:01:57.550 align:middle line:84% You have time to crystallization on the other axis. 01:01:57.550 --> 01:02:00.430 align:middle line:84% So based on your specific structuring techniques, 01:02:00.430 --> 01:02:02.990 align:middle line:84% you know your viscosity window, where 01:02:02.990 --> 01:02:04.250 align:middle line:90% your process to take place. 01:02:04.250 --> 01:02:07.330 align:middle line:84% You then look at what is the time to crystallization. 01:02:07.330 --> 01:02:09.990 align:middle line:84% And then you can tell for yourself whether or not 01:02:09.990 --> 01:02:12.470 align:middle line:84% this composition gives you enough time window 01:02:12.470 --> 01:02:14.190 align:middle line:90% to complete the process. 01:02:14.190 --> 01:02:20.270 align:middle line:84% So for example, actually here, this zirconium-based alloy 01:02:20.270 --> 01:02:23.310 align:middle line:84% obviously is a lot better than this palladium-based alloy 01:02:23.310 --> 01:02:24.810 align:middle line:84% in terms of this kind of processing. 01:02:24.810 --> 01:02:25.768 align:middle line:90% It's a lot more stable. 01:02:25.768 --> 01:02:29.980 align:middle line:84% Gives you more time to complete your process. 01:02:29.980 --> 01:02:31.050 align:middle line:90% The other factor. 01:02:31.050 --> 01:02:34.110 align:middle line:84% I also want to mention here is this phenomenon called 01:02:34.110 --> 01:02:35.990 align:middle line:90% thermal embrittlement. 01:02:35.990 --> 01:02:38.390 align:middle line:84% So thermal embrittlement essentially 01:02:38.390 --> 01:02:41.390 align:middle line:84% means that if you have a piece of bulk metallic glass, 01:02:41.390 --> 01:02:43.810 align:middle line:84% you go through this thermoplastic forming, 01:02:43.810 --> 01:02:46.590 align:middle line:84% it typically becomes more brittle. 01:02:46.590 --> 01:02:48.230 align:middle line:84% And the reason for that is because when 01:02:48.230 --> 01:02:50.570 align:middle line:84% you heat it up, reheat it up to glass transition, 01:02:50.570 --> 01:02:52.028 align:middle line:84% pass the glass transition region, 01:02:52.028 --> 01:02:54.070 align:middle line:84% you essentially introducing structural relaxation 01:02:54.070 --> 01:02:54.770 align:middle line:90% in the material. 01:02:54.770 --> 01:02:58.310 align:middle line:84% So any kind of glass is always trying 01:02:58.310 --> 01:03:01.230 align:middle line:84% to relax towards its corresponding supercooled liquid 01:03:01.230 --> 01:03:01.910 align:middle line:90% state. 01:03:01.910 --> 01:03:05.350 align:middle line:84% Now once it relaxes, it means that you actually decreasing 01:03:05.350 --> 01:03:07.230 align:middle line:90% the free volume there. 01:03:07.230 --> 01:03:09.870 align:middle line:84% In amorphous metal, you need free volume 01:03:09.870 --> 01:03:13.890 align:middle line:84% to essentially default to introducing information. 01:03:13.890 --> 01:03:16.070 align:middle line:84% So the fact that after the process 01:03:16.070 --> 01:03:19.110 align:middle line:84% you have less free volume means that the material essentially 01:03:19.110 --> 01:03:22.630 align:middle line:90% becomes more brittle. 01:03:22.630 --> 01:03:26.950 align:middle line:84% Its ability to deform plastically decreases. 01:03:26.950 --> 01:03:30.150 align:middle line:84% So that's one thing to keep into account that the material 01:03:30.150 --> 01:03:31.893 align:middle line:84% property after the thermoplastic forming 01:03:31.893 --> 01:03:33.810 align:middle line:84% could be different from the starting material. 01:03:33.810 --> 01:03:38.170 align:middle line:90% 01:03:38.170 --> 01:03:38.670 align:middle line:90% OK. 01:03:38.670 --> 01:03:41.670 align:middle line:84% Outside that, this process, you can essentially 01:03:41.670 --> 01:03:43.910 align:middle line:84% use almost any kind of techniques 01:03:43.910 --> 01:03:46.230 align:middle line:84% that people have developed for processing polymers 01:03:46.230 --> 01:03:48.210 align:middle line:84% and apply them to a bulk metallic glasses. 01:03:48.210 --> 01:03:52.790 align:middle line:84% It can be molding, extrusion, rolling, whatever. 01:03:52.790 --> 01:03:57.645 align:middle line:84% But one advantage of doing thermoplastic forming 01:03:57.645 --> 01:03:59.270 align:middle line:84% on these bulk metallic glasses compared 01:03:59.270 --> 01:04:01.530 align:middle line:84% to conventional polymers, I want to mention here, 01:04:01.530 --> 01:04:03.610 align:middle line:84% is that it has basically two advantages here. 01:04:03.610 --> 01:04:06.663 align:middle line:84% One, in terms of a liquid fragility. 01:04:06.663 --> 01:04:08.330 align:middle line:84% So what I'm plotting on this curve here, 01:04:08.330 --> 01:04:10.940 align:middle line:84% this is the Angell plot, now contains a lot of this bulk 01:04:10.940 --> 01:04:13.580 align:middle line:90% metallic glasses, these ones. 01:04:13.580 --> 01:04:16.760 align:middle line:84% Compared to this last one, these crosses, 01:04:16.760 --> 01:04:19.900 align:middle line:84% this is actually for a typical polymer or organic liquid. 01:04:19.900 --> 01:04:22.800 align:middle line:84% What you notice here is that these bulk metallic glasses, 01:04:22.800 --> 01:04:24.700 align:middle line:84% they are definitely somewhat fragile. 01:04:24.700 --> 01:04:26.660 align:middle line:84% They don't follow straight lines, 01:04:26.660 --> 01:04:30.900 align:middle line:84% but they are a lot closer to a strong liquid compared 01:04:30.900 --> 01:04:32.620 align:middle line:90% to organic fluids. 01:04:32.620 --> 01:04:35.860 align:middle line:84% So it means that they have a reduced fragility compared 01:04:35.860 --> 01:04:37.780 align:middle line:90% to typical polymers. 01:04:37.780 --> 01:04:40.140 align:middle line:84% As I mentioned before, reduced fragility 01:04:40.140 --> 01:04:42.023 align:middle line:84% is actually advantageous for processing 01:04:42.023 --> 01:04:43.940 align:middle line:84% because it means that its viscosity dependence 01:04:43.940 --> 01:04:46.220 align:middle line:90% on temperature is less. 01:04:46.220 --> 01:04:49.060 align:middle line:84% So it's more tolerant to any kind of temperature variations 01:04:49.060 --> 01:04:51.860 align:middle line:84% without causing too much viscosity excursion. 01:04:51.860 --> 01:04:52.360 align:middle line:90% OK? 01:04:52.360 --> 01:04:54.540 align:middle line:84% So that's an advantage for this process here. 01:04:54.540 --> 01:04:57.180 align:middle line:84% You have a better control over the viscosity. 01:04:57.180 --> 01:04:58.820 align:middle line:84% The second advantage that comes in 01:04:58.820 --> 01:05:01.440 align:middle line:84% is that these bulk metallic glasses, they are metal. 01:05:01.440 --> 01:05:03.740 align:middle line:84% So they are a lot more thermally conductive. 01:05:03.740 --> 01:05:05.540 align:middle line:84% So it means that temperature uniformity 01:05:05.540 --> 01:05:08.440 align:middle line:84% tend to be much better chemical polymers. 01:05:08.440 --> 01:05:09.940 align:middle line:84% And this could be useful if you want 01:05:09.940 --> 01:05:12.142 align:middle line:84% to prevent any kind of inhomogeneity 01:05:12.142 --> 01:05:14.600 align:middle line:84% in the temperature and viscosity developed in your process. 01:05:14.600 --> 01:05:19.120 align:middle line:90% 01:05:19.120 --> 01:05:21.468 align:middle line:84% So the next few slides is just a quick overview 01:05:21.468 --> 01:05:23.260 align:middle line:84% of some of the common techniques people use 01:05:23.260 --> 01:05:26.100 align:middle line:84% to structure bulk metallic glasses. 01:05:26.100 --> 01:05:30.580 align:middle line:84% They are all borrowed from the plastic processing community. 01:05:30.580 --> 01:05:32.240 align:middle line:90% You can do compression modeling. 01:05:32.240 --> 01:05:35.060 align:middle line:84% Same idea as to how you do the glass. 01:05:35.060 --> 01:05:38.060 align:middle line:84% The main difference here is that in the glass, 01:05:38.060 --> 01:05:41.940 align:middle line:84% you typically have basically like a parison or preform, 01:05:41.940 --> 01:05:43.900 align:middle line:84% essentially a big, single solid piece 01:05:43.900 --> 01:05:46.420 align:middle line:84% where you use to do the compression modeling. 01:05:46.420 --> 01:05:47.920 align:middle line:90% In bulk metallic glasses. 01:05:47.920 --> 01:05:52.620 align:middle line:84% Instead of using a parison, you actually use beads, small beads. 01:05:52.620 --> 01:05:55.120 align:middle line:84% When you apply pressure and heat it up, 01:05:55.120 --> 01:05:56.820 align:middle line:90% they essentially fuse together. 01:05:56.820 --> 01:05:59.780 align:middle line:84% So it's a slightly different way of doing the process there. 01:05:59.780 --> 01:06:01.940 align:middle line:84% Other than that, it's pretty similar. 01:06:01.940 --> 01:06:04.100 align:middle line:84% It's typically used to create open structures 01:06:04.100 --> 01:06:06.890 align:middle line:84% with relatively low aspect ratio, which also makes sense. 01:06:06.890 --> 01:06:10.290 align:middle line:84% Because you have two pieces, you cannot have, essentially, 01:06:10.290 --> 01:06:12.570 align:middle line:84% sealed cavity where you cannot take it out. 01:06:12.570 --> 01:06:15.150 align:middle line:84% So they typically are used to create large sheets, 01:06:15.150 --> 01:06:16.470 align:middle line:90% more like flat pieces. 01:06:16.470 --> 01:06:20.090 align:middle line:90% 01:06:20.090 --> 01:06:22.190 align:middle line:84% You have injection molding, as I promise you. 01:06:22.190 --> 01:06:24.610 align:middle line:84% [CHUCKLES] It's very, very similar to the process 01:06:24.610 --> 01:06:25.400 align:middle line:90% illustrated here. 01:06:25.400 --> 01:06:27.650 align:middle line:84% The main difference here being that essentially you're 01:06:27.650 --> 01:06:30.418 align:middle line:84% more essentially forms a cavity shape on one pieces. 01:06:30.418 --> 01:06:31.210 align:middle line:90% You have a plunger. 01:06:31.210 --> 01:06:34.610 align:middle line:84% You essentially put one piece of this liquid metal in there, 01:06:34.610 --> 01:06:37.370 align:middle line:84% amorphous metal in there and then deform it 01:06:37.370 --> 01:06:39.370 align:middle line:90% during the heating process. 01:06:39.370 --> 01:06:43.090 align:middle line:84% So I, again, have another quick video that shows you 01:06:43.090 --> 01:06:46.724 align:middle line:84% how this is actually implemented in industry. 01:06:46.724 --> 01:06:48.215 align:middle line:90% [VIDEO PLAYBACK] 01:06:48.215 --> 01:06:52.191 align:middle line:90% [MUSIC PLAYING] 01:06:52.191 --> 01:08:14.196 align:middle line:90% 01:08:14.196 --> 01:08:15.320 align:middle line:90% [END PLAYBACK] 01:08:15.320 --> 01:08:18.560 align:middle line:84% So fairly straightforward process. 01:08:18.560 --> 01:08:20.560 align:middle line:84% Same thing, this also applies to open structures 01:08:20.560 --> 01:08:22.080 align:middle line:84% because you need to be able to essentially take it out 01:08:22.080 --> 01:08:22.700 align:middle line:90% from the mode. 01:08:22.700 --> 01:08:24.825 align:middle line:84% So you need to be able to find a way to open it up. 01:08:24.825 --> 01:08:27.080 align:middle line:84% But as I said, this usually applies 01:08:27.080 --> 01:08:29.479 align:middle line:84% to typically with lower viscosity. 01:08:29.479 --> 01:08:31.520 align:middle line:84% So in terms of essentially glass stability, 01:08:31.520 --> 01:08:33.439 align:middle line:84% it places a more stringent requirement 01:08:33.439 --> 01:08:36.359 align:middle line:84% compared to if you do a compression model because 01:08:36.359 --> 01:08:40.520 align:middle line:84% of the high temperature processing temperature. 01:08:40.520 --> 01:08:42.465 align:middle line:84% Now, you can also do blow molding. 01:08:42.465 --> 01:08:43.840 align:middle line:84% In glasses, we mentioned that you 01:08:43.840 --> 01:08:46.340 align:middle line:84% can use this to create things like bottles. 01:08:46.340 --> 01:08:50.080 align:middle line:84% Same idea here, you can use compressed air 01:08:50.080 --> 01:08:53.620 align:middle line:84% to conform a piece of a parison into the final geometry. 01:08:53.620 --> 01:08:55.279 align:middle line:90% So this is actually one example. 01:08:55.279 --> 01:08:57.840 align:middle line:84% This is actually a starting preform or parison. 01:08:57.840 --> 01:08:59.060 align:middle line:90% This is the final shape. 01:08:59.060 --> 01:09:01.720 align:middle line:84% They essentially blow-mold it against the Chanel perfume 01:09:01.720 --> 01:09:02.560 align:middle line:90% bottle. 01:09:02.560 --> 01:09:04.439 align:middle line:84% So that's what it ended up being. 01:09:04.439 --> 01:09:05.890 align:middle line:84% The advantage of this blow molding 01:09:05.890 --> 01:09:07.640 align:middle line:84% is that it allows you to create structures 01:09:07.640 --> 01:09:09.920 align:middle line:84% with very high aspect ratio, essentially thin wall 01:09:09.920 --> 01:09:11.040 align:middle line:90% components. 01:09:11.040 --> 01:09:16.960 align:middle line:84% The challenge there is that because of the wall 01:09:16.960 --> 01:09:18.955 align:middle line:84% gets very thin, it means that it gets 01:09:18.955 --> 01:09:21.080 align:middle line:84% a lot more sensitive to any kind of non-uniformity. 01:09:21.080 --> 01:09:24.245 align:middle line:84% If a local stress concentrates, you may concentrate a strain 01:09:24.245 --> 01:09:25.620 align:middle line:84% and eventually leads to breakage. 01:09:25.620 --> 01:09:28.532 align:middle line:84% This is one example where if you don't have good control, 01:09:28.532 --> 01:09:29.740 align:middle line:90% that's what actually happens. 01:09:29.740 --> 01:09:32.654 align:middle line:84% So in this regard, if you compare plastic 01:09:32.654 --> 01:09:35.279 align:middle line:84% with bulk metallic glasses, this is where bulk metallic glasses 01:09:35.279 --> 01:09:37.840 align:middle line:84% has some advantage there because of their much higher 01:09:37.840 --> 01:09:39.904 align:middle line:90% thermal conductivity. 01:09:39.904 --> 01:09:42.279 align:middle line:84% So this leads to a more uniform temperature distribution, 01:09:42.279 --> 01:09:45.200 align:middle line:84% potentially less tendency for localized temperature 01:09:45.200 --> 01:09:46.020 align:middle line:90% variations. 01:09:46.020 --> 01:09:48.220 align:middle line:84% And then these are local failure. 01:09:48.220 --> 01:09:50.140 align:middle line:84% Another thing I also want to mention here, 01:09:50.140 --> 01:09:53.439 align:middle line:84% if you compare these two plots, is in terms of maximum strain. 01:09:53.439 --> 01:09:56.900 align:middle line:84% For plastics, the maximum strain is listed as infinity 01:09:56.900 --> 01:09:59.000 align:middle line:84% because they basically don't crystallize. 01:09:59.000 --> 01:10:02.575 align:middle line:84% They have very strong resistance to crystallization. 01:10:02.575 --> 01:10:03.950 align:middle line:84% So you can essentially stay there 01:10:03.950 --> 01:10:07.070 align:middle line:84% at this relatively low viscosity state for a very extended 01:10:07.070 --> 01:10:08.390 align:middle line:90% period of time. 01:10:08.390 --> 01:10:10.590 align:middle line:84% So you can get lots of deformation there. 01:10:10.590 --> 01:10:12.750 align:middle line:84% However, for bulk metallic glasses, 01:10:12.750 --> 01:10:14.930 align:middle line:84% they do crystallize at some point. 01:10:14.930 --> 01:10:17.390 align:middle line:84% So this eventually limits maximum strain 01:10:17.390 --> 01:10:19.650 align:middle line:90% and maximum deformation. 01:10:19.650 --> 01:10:22.230 align:middle line:84% So that's what limit the expiration we are actually 01:10:22.230 --> 01:10:28.030 align:middle line:84% showing here, crystallization or glass-forming ability. 01:10:28.030 --> 01:10:31.295 align:middle line:84% All right, so last quick piece, I just also want to mention here 01:10:31.295 --> 01:10:33.670 align:middle line:84% is that people can also do a 3D printing of bulk metallic 01:10:33.670 --> 01:10:35.910 align:middle line:90% glasses. 01:10:35.910 --> 01:10:39.110 align:middle line:84% There are lots of variants of this technique there. 01:10:39.110 --> 01:10:41.590 align:middle line:84% The example I'm giving here is called fused filament 01:10:41.590 --> 01:10:42.610 align:middle line:90% fabrication. 01:10:42.610 --> 01:10:45.250 align:middle line:90% It's fairly straightforward. 01:10:45.250 --> 01:10:48.070 align:middle line:84% You have essentially a filament of metallic glasses. 01:10:48.070 --> 01:10:51.290 align:middle line:84% It's essentially fed into this nozzle where it is heated. 01:10:51.290 --> 01:10:54.590 align:middle line:84% So it goes into this kind of molten state, glass 01:10:54.590 --> 01:10:55.670 align:middle line:90% forming liquid. 01:10:55.670 --> 01:10:58.750 align:middle line:84% You then apply a voltage across this nozzle 01:10:58.750 --> 01:11:00.950 align:middle line:90% and your conductive substrate. 01:11:00.950 --> 01:11:05.430 align:middle line:84% Now, this voltage drop mostly takes place at this nozzle 01:11:05.430 --> 01:11:07.882 align:middle line:84% right here because you have this reduced cross-section. 01:11:07.882 --> 01:11:10.090 align:middle line:84% So this is where you have most electrical resistance. 01:11:10.090 --> 01:11:12.730 align:middle line:84% So this is where all the voltage drop actually takes place. 01:11:12.730 --> 01:11:15.990 align:middle line:84% So all the heating is confined right in this little filament 01:11:15.990 --> 01:11:16.750 align:middle line:90% there. 01:11:16.750 --> 01:11:20.270 align:middle line:84% As soon as it comes into contact with the bulk piece, 01:11:20.270 --> 01:11:22.090 align:middle line:90% its cross-section increases. 01:11:22.090 --> 01:11:23.970 align:middle line:84% So it means that you have current spreading. 01:11:23.970 --> 01:11:25.790 align:middle line:84% This decreases the voltage drop, and therefore you 01:11:25.790 --> 01:11:27.070 align:middle line:90% get much less joule heating. 01:11:27.070 --> 01:11:30.590 align:middle line:84% Also, the heat dissipation becomes very efficient because 01:11:30.590 --> 01:11:32.570 align:middle line:90% of the bulk volume there. 01:11:32.570 --> 01:11:35.110 align:middle line:90% So it quickly solidifies. 01:11:35.110 --> 01:11:37.110 align:middle line:84% So using this, you can then essentially 01:11:37.110 --> 01:11:38.090 align:middle line:90% translating the nozzle. 01:11:38.090 --> 01:11:41.070 align:middle line:84% You can then print all kinds of geometries in this technique 01:11:41.070 --> 01:11:41.790 align:middle line:90% there. 01:11:41.790 --> 01:11:45.330 align:middle line:84% So that's the last slide I have here. 01:11:45.330 --> 01:11:48.490 align:middle line:84% Any more questions about shaping of amorphous materials? 01:11:48.490 --> 01:11:52.550 align:middle line:90% 01:11:52.550 --> 01:11:53.630 align:middle line:90% All good? 01:11:53.630 --> 01:11:54.670 align:middle line:90% All right. 01:11:54.670 --> 01:11:56.580 align:middle line:90% Thank you. 01:11:56.580 --> 01:12:56.000 align:middle line:90%