Cyclic crystal plasticity analyses of stationary, microstructurally small surface cracks in ductile single phase polycrystals

Abstract

This paper explores the effects of microstructural heterogeneity on the cyclic crack tip opening and sliding displacements for stationary, microstructurally small transgranular surface cracks in a single phase metallic polycrystal using planar double slip crystal plasticity computations. Crack tip displacements are examined under plane strain conditions for stationary cracks of different lengths relative to grain size as a function of the applied nominal strain amplitude for tension‐compression and cyclic shear. Nominal strain amplitudes range from well below to slightly above the nominal cyclic yield strength for each type of loading condition. Results indicate the complex nature of the crack tip sliding and opening displacements as functions of nominal strain amplitude and orientation of the nearest neighbour grains, the influence of the free surface in promoting the cyclic opening displacement even for cracks in the first surface grain, the rather restricted limits of applicability of linear elastic fracture mechanics, and very interesting crack tip plasticity effects which include crack tip displacement ratcheting or progressive accumulation, even for completely reversed, proportional applied loading. Results are compared for cases with and without crack face friction.

Fatigue crack propagation under in‐phase and out‐of‐phase biaxial loading

“…Several theories have been proposed to predict the small Nomenclature: K I , = Mode I stress intensity factor; K II , = Mode II stress intensity factor; M R , = Mode-mixity ratio; θ, = Angle of crack propagation crack initiation under mixed-mode loading based on stress-strain, energy, and critical plane approaches. [9][10][11] A crystal plasticity micromechanical model embedded with finite elements was developed by Bennett and McDowell 12 and Zhang et al 13 to assess the effect of grain orientations on the crack initiation behaviour. Zhang et al 13 developed a physics-based multiscale damage criterion to predict the fatigue crack initiation life under in-plane biaxial Fighter Aircraft Loading STandard For Fatigue (FALSTAFF) loading.…”

Finite element simulation of surface deformation of polycrystal with a rough surface under repeated load

“…In the last ten years, the finite element (FE) simulations of fatigue problems using crystal plasticity have been carried out. Bennett and Mcdowell [9] assessed the effects of micro-structural heterogeneity on cyclic crack tip opening and sliding displacements for microstructurally small fatigue cracks extending from the surface. Xie et al [10] analyzed the material response of HSLA-50 steel using a rate dependent elastic crystal plasticity model.…”

Computational micromechanics of fatigue of microstructures in the HCF–VHCF regimes

“…Bennett and McDowell [30,31] and McDowell [27] introduced the notion of a range of FIPs that reflect in more explicit manner the relative roles of reversed and cumulative directional slip at the scale of individual grains or crystalline regions in polycrystals (i.e., microplasticity). For example, the Fatemi-Socie [32,33] shear-based FIP has been shown to correlate multiaxial fatigue crack initiation data very well in both LCF and HCF regimes at the grain scale and above [34,28,35].…”