Fracture

Question 1

what are the two methods of measuring crack growth

Answer 1

• Griffiths approach (energy)
• Stress Intensity approach

Question 2

what does a stable crack entail and is it associated with brittle or ductile fractures

Answer 2

• stable = propagates slowly with increasing stress, ductile fractures
• unstable = propagation continues without an increase in stress, brittle

Question 3

what happens with the stress reaches above the critical stress in a brittle fracture

Answer 3

• the crack propagates quickly through the lattice breaking one band at a time, fast fracture

Question 4

what is the difference between intergranular and transgranular

Answer 4

• intergranular, fracture travels along grain boundaries
• transgranular, fracture travels across grains

Question 5

what does the critical strain release rate tell us

Answer 5

how easily cracks can form

Question 6

Griffiths approach equation

Answer 6

σ = (EG/πa)^1/2

σ = critical value, applied stress
E = Youngs modulus
G = critical strain energy release rate

Question 7

Stress Intensity approach equation

Answer 7

K = Yσ*(πa)^1/2

K = Stress Intensity factor
Y = shape factor
σ = critical value, applied stress