A micromechanics study on strain-localization-induced fracture initiation in bending using crystal plasticity models

A crystal-plasticity-based computational micromechanics model is presented to study the localization and fracture initiation modes in bending of sheet materials. The model accounts for the orientation-dependent non-uniform de formation within each grain. Parameters evaluated include strain hardening, second-phase particle position and distribution, and crystallographic text ure. Surface roughening and localized deformation are found to result natur ally from orientation and slip geometry differences across neighbouring gra ins. Shear bands initiate on or near the outer surface and from the low poi nts of surface roughness. The maximum plastic strain may occur below the fr ee surface, which is different from the predictions based on continuum elas tic-plastic theories. Computational results also suggest that constituent p articles, especially near the free surface, can significantly increase the localization intensity and the surface roughening. Crystallographic texture s that contain high volume fractions of rolling texture components can incr ease the surface roughening significantly compared with a random texture. B ifurcation analysis results in further understanding of the different local ization modes between the tension and the compression sides of the bending specimen. These findings from the theoretical-computational study agree wel l with experimental observations. They give insights into improving the ben dability of aluminium sheet alloys.