Micromechanical Simulation of Cyclic Plasticity at Inclusion Particles with Pre-Over Straining

Abstract

Understanding and quantifying correctly the effects of overload on the cyclic damage accumulation at a microscale discontinuity is essential for the development of a multstage fatigue model under variable loading. Micromechanical simulations were conducted on a 7075-T651 Al alloy to quantify the cyclic microplasticity induced by constant amplitude cyclic loads following a pre -overload. The initial overstraining amplitudes were selected in the region of limited macroscopic plastic deformation to account for both macroscopic and microscopi c plastic overloading effects. The nonlocal equivalent plastic strain at the micrometer-scale discontinuity showed the overload effects primarily in two forms: 1) the cyclic plastic dissipation is greater in the cycles following a pre -overstraining than that without a pre -overstraining; 2) the overtraining causes the nonlocal equivalent plastic strain to increase two times in a tensile loading step and three times in the compression loading steps, as compared to those without a pre -overstraining. The cyclic plastic zone at the microdiscontinuity corresponds to the maximum load in o verstraining. The micromechanical simulation results support a cyclic damage accumulation rule that captures the cyclic microplasticity accumulation induced by an overstraining for a high fidelity fatigue incubation model under variable amplitude loading.