Hey Q&A expert I have this question about the difference between the Fracture To
ID: 1520483 • Letter: H
Question
Hey Q&A expert I have this question about the difference between the Fracture Toughness of glass and steel (KIc).
I know that glass has high yield strength giving it no way to relieve some form of crack stress by plastic flow. So the atomic bonds will tear apart with a small crack, allowing the crack to spread, carrying its stress field with it.
The real problem is that I have to formulate a good answer containing a bunch of terms and I hope you guys could help me out. The questions is written below:
Exercise 1
Why is the fracture toughness KIc of glass so much lower than of a metal like steel? Note that the following elements all play a role and thus have to be included in your answer: 1. Atomic bonding, 2. Atomic packing structure, 3. Dislocations (density and mobility), 4. Plasticity, 5. Stress concentrations.
Explanation / Answer
Fracture toughness is a quantitative way of expressing a material's resistance to brittle fracture when a crack is present. If a material has high fracture toughness it will probably undergo ductile fracture. Brittle fracture is very characteristic of materials with low fracture toughness.
=> elastic energy released = surface energy created.
If the elastic energy released is less than the critical value, then the crack will not grow; equality signifies neutral stability and if the strain energy release rate exceeds the critical value, the crack will start growing in an unstable manner. For ductile materials, energy associated with plastic deformation has to be taken into account.
This include crack deflection by secondary phases, crack bifurcation due to fine grain structure and modification to the grain boundaries, and crack meandering by pores in the material. Any alteration to the base material which increases its ductility can also be thought of as intrinsic toughening.