# Why is Stress Intensity Factor a valid parameter for evaluating fatigue crack growth?

1. May 2, 2009

### bill nye scienceguy!

The best I can come up with is Paris' postulation that if SIF controls static fracture then it's reasonable that it should also control dynamic fracture, the fact that Paris' law 'works', and Swanson et al's experiment that proved that if SIF is kept const the fatigue crack will grow a t a constant velocuty.

Any input?

2. May 4, 2009

### Mapes

Re: Why is Stress Intensity Factor a valid parameter for evaluating fatigue crack gro

Yes, and also the interesting prediction (and experimental verification) that crack growth rate should decrease as crack length increases at constant stress. Also see Saxena et al, J Test Eval 6, 167 (1978) and the chapter "Fatigue Crack Propagation" in Hertzberg's Deformation and Fracture Mechanics of Engineering Materials.