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 deformation within each grain. Parameters evaluated include strain hardening, second-phase particle position and distribution, and crystallographic texture. Surface roughening and localized deformation are found to result naturally from orientation and slip geometry differences across neighbouring grains. Shear bands initiate on or near the outer surface and from the low points of surface roughness. The maximum plastic strain may occur below the free surface, which is different from the predictions based on continuum elastic-plastic theories. Computational results also suggest that constituent particles, especially near the free surface, can significantly increase the localization intensity and the surface roughening. Crystallographic textures that contain high volume fractions of rolling texture components can increase the surface roughening significantly compared with a random texture. Bifurcation analysis results in further understanding of the different localization modes between the tension and the compression sides of the bending specimen. These findings from the theoretical-computational study agree well with experimental observations. They give insights into improving the bendability of aluminium sheet alloys.