An HR-EBSD and computational crystal plasticity investigation of microstructural stress distributions and fatigue hotspots in polycrystalline copper

Abstract

High resolution EBSD studies on a deformed copper polycrystal have been carried out to quantify the microstructural residual stress distributions, and those of stress state including triaxiality of importance in defect nucleation studies. Crystal plasticity analysis of a representative, similarly textured, model polycrystal has been carried out showing that the experimental distributions of microstructural residual stress components, effective stress, hydrostatic stress and stress triaxiality are well captured.The crystal model enables point-wise microstructural Schmid factors to be calculated both globally (ie with respect to the macroscopic remote loading) and locally from full knowledge of the grain-level stress state. Significant differences are demonstrated such that global Schmid analysis tends to overestimate slip activity and the frequency of high Schmid factors, indicating that the local microstructural heterogeneity is significant and caution is necessary in interpreting polycrystal behaviour using global Schmid factors. A stored energy criterion for fatigue crack nucleation indicates that preferential sites for fatigue crack nucleation are local to grain boundaries (as opposed to triple junctions), and that hard-soft grain interfaces where high GND densities develop are preferable.

Quantitative investigation of micro slip and localization in polycrystalline materials under uniaxial tension

“…The latter is calculated from the most active slip system such that the accumulated slip in that system is the highest, and the loading direction is affected by the local stress state. It is clear that the slip activation from the crystal plasticity modelling rightly depends on the microscale stress distribution, because the local stress state may be important in grain-level slip activation, and is often different to that assumed from the macroscale (Wan et al, 2016;Zhang et al, 2016a). Figure 6.…”

A Review of Damage, Void Evolution, and Fatigue Life Prediction Models

“…The third law 12 = [ 1 2 21 21 2 (1 − )] 21 (72) In unified mechanics the material is treated as a thermodynamic system. As a result, governing partial differential equations of any system automatically include energy loss, entropy generation and degradation of the system.…”

Combining microstructural characterization with crystal plasticity and phase-field modelling for the study of static recrystallization in pure aluminium

“…CPFE models can capture the activation of individual slip systems and the inhibition effect on slip due to the change of grain orientation, thus providing the full-field heterogeneous strain, dislocation density distributions and elastic stress in a grain structure [35]. The model that was used to simulate the deformation state is strain rate sensitive and was implemented in the user material subroutine UMAT using ABAQUS standard analysis [9,32,34,[38][39][40][41]. where is given as the sum of contributions to slip from the active slip systems following…”