Plastic zones about fatigue cracks in metals

The plastic areas surrounding fatigue cracks produced by constant amplitude loading in various metallic materials have been studied by Moiré interferometry. Two distinct plastic zones have been identified and their sizes in the direction perpendicular to the crack plane correlated with previous theoretical and experimental results. Differences have been addressed referring to specimen geometry and mechanical properties of materials. Moiré interferometry has also been used to investigate the effect of overloads on plastic zone development. Once the monotonic and cyclic plastic zone evolutions were outlined, they favourably correlated with predictions according to Führing/Seeger's fatigue crack growth model.