3.22 | Spring 2008 | Graduate
Mechanical Behavior of Materials
Projects

Role of Water in Accelerated Fracture of Fiber Optic Glass

Group Members

  • Matthew Smith
  • Sophie Poizeau
  • Michiel Vanhoutte
  • Noémie Chocat

Image removed due to copyright restrictions.
Please see: https://web.archive.org/web/20121213052722/http://www.rtcfiber.com/layout/multiflex3/images/fiber-optics.jpg

References

Kurkjian, C. R., J. T. Krause, and M. J. Matthewson. “Strength and Fatigue of Silica Optical Fibers.” Journal of Lightwave Technology 7 (1989): 1360-1370.

The above review article is a thorough review of the mechanics of silica optical fibers, but it was published in 1989. Here is a more recent but less focused review, in case 1989 is not sufficiently recent:

Suhir, E. “Fiber Optic: Structural Mechanics and Nanotechnology Based New Generation of Fiber Coatings.” Proceedings of the SPIE 6126 (2006): 612606.

Mauro do Nascimento, E., and C. M. Lepienski. “Mechanical Properties of Optical Glass Fibers Damaged by Nanoindentation and Water Ageing.” Journal of Non-Crystalline Solids 352 (2006): 3556-3560.

Michalske, T. A., and B. C. Bunker. “Slow Fracture Model Based on Strained Silicate Structures.” Journal of Applied Physics 56 (1984): 2686-2693.

Wiki Assignments

Problem Set 2

a) What are the (short-range ordered) structures and elastic moduli of E-glass (aluminum-barium borosilicate glass) and silica glass in the bulk form?

b) Would you expect the stiffness of these two types of glass to change as the physical dimensions were reduced to the diameters typical of current (2008) fiber optic applications? How about for nanoscale fibers? Why or why not? See also Silva, et al.

c) State the Cij matrix you feel best captures the elastic constants of these glasses, and justify your answer in terms of the material structure.

d) Kurkjian, et al. noted that Sakaguchi had intentionally added dust particles to increase the failure stress of such glass fibers. What would the impact on isotropic elastic properties be for the fibers Sakaguchi created, for the sizes and volume fractions of particles he used?

Problem Set 3

(b) Explain the physical mechanisms and mechanical consequences of aging in such fiber optic silica.

(c) Explain how do Nascimento and Lepienski calculated the fracture stress for glasses subjected to Berkovich indentation in Table 1. What was the point of using the indenter in this experiment? If they were instead to indent the fiber sufficiently to attain the fracture stress by loading the fiber surface with a Berkovich diamond indenter, state the corresponding indentation loads and depths for the pristine and maximally aged fibers.

(d) Graphically represent a cross-sectional view of this proposed fracture stress experiment on the fibers, considering the relative lengthscales of the fiber, the depth of indentation corresponding to fracture noted in your calculations for (c), and the finite radius of diamond Berkovich indenter probes.

Problem Set 5

(b) Michalske predicted that water molecules assisted bond breaking in silica long before it was observed directly in atomistic simulations. In his 1984 paper, Fig. 6 is a little hard to understand at first. Make this the inset in a larger figure that shows a macroscopic crack, the direction of loading to open that crack in Mode I, and the direction of propagation of that crack.

(c) Explain chemically assisted fracture so that anyone in 3.22 would understand it, using Michalske’s Fig. 7 type graphics to illustrate the interaction of water with silica at the molecular level.

(d) Michalske’s argument necessarily implies that the amount of chemical in the environment affects the speed of crack growth. Assume an initial, through-thickness crack of width 150 nm at the surface of a sheet of silica that is 1 cm thick. The crack is under Mode I loading. From Michalske’s Fig. 2, how long would it take for that crack to grow another 150 nm under an applied stress of 100 MPa in an environment of 100% water?

(e) At a partial pressure of 50%, how many water molecules would be sitting on the initial crack faces?

Final Presentation

“Water-ageing of Silica Optical Fibers.” (PDF)

Plasticity and fracture of microelectronic thin films/lines
Effects of multidimensional defects on III-V semiconductor mechanics
Defect nucleation in crystalline metals
Role of water in accelerated fracture of fiber optic glass | Problem Set 2 | Problem Set 3 | Problem Set 5
Carbon nanotube mechanics
Superelastic and superplastic alloys
Mechanical behavior of a virus
Effects of radiation on mechanical behavior of crystalline materials

Course Info
As Taught In
Spring 2008
Level
Learning Resource Types
theaters Simulation Videos
grading Exams with Solutions
group_work Projects
assignment_turned_in Problem Sets with Solutions