Analysis of fatigue crack tip plasticity in Fe-2.6Si

Abstract

Saurface roughness analysis, etch-pit, and recrystallization techniques were employed to characterize the plastic deformation zones around fatigue cracks in Fe-2.6wt% Si. Both surface and sub-surface cross-sections are evaluated. The plastic zone size changes significantly in the surface layers. It is correlated with energy release rate, J, because of the elastoplastic nature of crack propagation and a linear correlation is found. The plastic deformation experienced inside the plastic zone is analysed and is reported in terms of equivalent tensile strains. The material in the immediate vicinity of the crack tip experiences large plastic strains under a steep gradient. This region, however, occupies a very small fraction of the plastic zone, the rest of which is deformed to less than 4% plastic strain. In the light of the experimental data, an attempt is made to identify potential sources for the variation in measured plastic zone parameters reported in the literature.