Micromechanical simulation of cyclic plasticity at inclusion particles with pre-over-straining

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 microscopic 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 overstraining. 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.