Abstract
Slip band formation and crack initiation during cyclic fatigue were investigated by in-situ experiments and non-local CPFEM simulations systematically. Experimental techniques including EBSD, digital image correlation (DIC) and SEM have been used to obtain consistent grain orientations, local strains, as well as the locations where slip bands and micro-cracks form on the sample surface. The realistic microstructure based on the EBSD map has been generated and used for finite element modelling. An advanced non-local crystal plasticity model, which considers the isotropic and kinematic hardening of the plastic strain gradient, has been adopted. The simulation results match well the corresponding experimental results. It was found that total strain and averaged slip on all slip systems, combined with accumulated slip on specific slip planes help predict the location and orientation of slip bands and micro-crack initiation correctly. Furthermore, a fatigue indicating parameter based on competition between maximum slip and the total slip has been proposed to reproduce the experimental observations.
Highlights
The fatigue life of metallic materials usually goes through three main stages as crack initiation, crack propagation and failure
The different micro-crack locations infer that grain shape and grain orientation influence the crack initiation process strongly
Damage occurred away from the hole edge within the upper triangle area. This suggests that the strain magnitudes alone are not sufficient to predict crack initiation
Summary
The fatigue life of metallic materials usually goes through three main stages as crack initiation, crack propagation and failure. The local microstructural features of the material determine the location sites for the appearance of cracks, which usually take place in these regions such as triple points, particle-matrix interfaces, pores and so called weak grains. Crack initiation plays a dominant role in the whole process of fatigue, it has received relatively less attention than crack propagation. Many studies have been lately done in this field Various experiments have been conducted to observe how cracks formed in the material, and a large number of numerical models have been established to predict crack initiation in past decades. A large number of experiments with different materials under different loading conditions have been conducted through
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