Analysis of meso-inhomogeneous deformation on a metal material surface under low-cycle fatigue

A polycrystalline Voronoi aggregation with a free surface is applied as the representative volume element (RVE) of the nickel-based GH4169 superalloy. Considering the plastic deformation mechanism at the grain level and the Bauschinger effect, a crystal plasticity model reflecting the nonlinear kinematic hardening of crystal slipping system is applied. The microscopic inhomogeneous deformation during cyclic loading is calculated through numerical simulation of crystal plasticity. The deformation inhomogeneity on the free surface of the RVE under cyclic loading is described respectively by using the following parameters: standard deviation of the longitudinal strain in macro tensile direction, statistical average of first principal strains, and standard deviation of longitudinal displacement. The relationship between the fatigue cycle number and the evolution of inhomogeneous deformation of the material's free surface is investigated. This research finds that: (1) The inhomogeneous deformation of the material free surface is significantly higher than that of the RVE inside; (2) the increases of the characterization parameters of inhomogeneous deformation on the free surface with cycles reflect the local maximum deformation of the RVE growing during cyclic loading; (3) these parameters can be used as criteria to assess and predict the low-cycle fatigue life rationally.