The specifications on a part specify that the part should be replaced when any crack reaches 25% of the critical crack length that will lead to fracture. We know that the part has an intial crack of length 0.02 mm, and that the fracture toughness is 55 MPA(m)^1/2
If the part is subject to cycle loading of 300 Mpa in tension and compression, calculate (assuming Y1.2, n = 3.4 and C = 2x10^-11 in units of Mpa m)
a-the critical crack length required to cause fracture
b-the number of cycles until the part needs replacing
c-how many cycles the part has left when it is being replaced and before it fails