Failure initiation in unnotched specimens subjected to monotonic and cyclic loading

Abstract

Failure initiation in unnotched cylindrical bar specimens is predicted by application of the strain energy density theory. Maximum value of the local minimum strain energy density function is calculated, the critical value of which is assumed to coincide with failure by monotonic as well as cyclic uniaxial loading. Damage is accumulated in the specimen for each increment of monotonically rising load and each cycle of repeatedly applied load. Use is made of the incremental theory of plasticity to account for permanent deformation that is nonuniformly distributed throughout the cylindrical bar. Failure initiation site is found to occur at the center of the bar for monotonic loading where dilatation is dominant and near the specimen surface for fatigue loading where distortion is more significant. The results are consistent with the experimental observations without including microstructural effects. Nonhomogeneity caused by macro-dilatation and macro-distortion is also shown to play an important role in failure initation.