Fatigue + surface engineering

Question 1

Typical fatigue crack growth behaviour in metals

A, B, C

Answer 1

A - When delta K = close to delta Kth, rate of crack growth is so slow = undetectable rate

∴ many cycles with no crack advances.

B - Paris Law can be applied

Question 2

Delta Kth

Answer 2

If rate of crack growth is 10^-8 mm/cycle or less, conditions = or below Kth