Fracture Mechanics

Question 1

What are the 3 modes of brittle fracture

Answer 1

Crack Opening from tension

Sliding mode due to in plane shear

Tearing mode due to out of plane shear

Question 2

What is K_0 and the eqn

Answer 2

Stress Intensity Factor (units: Pa*m^(1/2)

K_0=Sigmaroot(piea)

Where a is the half the distance of the crack

Question 3

What is brittle fracture

Answer 3

When strain failure is less or equal to 0.05%

Question 4

List the 5 common factors in a brittle failure

Answer 4

1. Its a sudden failure
2. Not much yeilding or plastic deformation
3. Below ductile-to-brittle temp
4. Not much pull-out on the fractal surface
5. Starts form a micro crack or scratch

Question 5

List the 4 common factor in a fatigue failure

Answer 5

1. Its subjected to cyclic or fluctuating stress
2. Occurs when applied stress is lower than static fracture strength
3. Its a slow process including crack initiation,propagation and finally fracture
4. Occurs at defects and stress raiser