Cyclic deformation fields interactions between pores in cast high manganese steel

Abstract

Cast pores are known to cause stress/strain concentrations, facilitating the initiation of fatigue cracks and shortening the fatigue lifetime of cast materials; however, it is an open question regarding how the deformation fields generated by different pores interact each other and evolve with fatigue loading. The present study addresses the local deformation behavior in cast-pore containing high manganese steel during fatigue loading investigated using single- and multi-pore finite-element models. These models take into account the actual size, shape and distribution of pores based on X-ray computed tomography images and consider the actual material properties of the steel, i.e. the high strain-hardening rate, cyclic hardening law and Bauschinger effect using a viscoplastic constitutive model within the framework of Chaboche model. The results demonstrate that the local stress, strain and hysteresis loop energy around an actual pore evolve progressively with fatigue loading, and reach as large as 2 to 4, 2.5 to 8.5 and 6 to 30 times their corresponding far-field values at high fatigue cycles. More importantly, two different effects, i.e. "umbrella-like stress shielding" and "overlapping stress amplifying", are identified in the presence of multiple pores, due to the deformation fields interactions between pores. And, which of the two effects takes place or predominates depends on the specific location of concern and the spatial distribution of pores. These findings may be extended to provide some new insight into the fatigue damage micromechanisms in various cast-pore containing materials and to help understand the scatters of their fatigue lifetime in terms of the local deformation fields around pores and their interactions.