Crack Tip Plastic Zone Effect on Fatigue Crack Propagation

The Paris-Erdogan equation can predict fatigue crack propagation only under particular conditions. It fails when R≠0 or under variable amplitude loads or with small cracks and cannot predict overload retardation etc. in all these cases fatigue crack propagation depends on what is actually happening at the crack tip in the plastic zone. Therefore, the study of the plastic zone behavior is fundamental to address the fatigue crack propagation issue and adjourn the Paris-Erdogan equation.