Orientation dependence of shear banding in fcc single crystals
N. Jia, P. Eisenlohr, F. Roters, D. Raabe
We present crystal plasticity finite element simulations of plane strain compression of α-brass single crystals with different initial orientations. The aim is to study the fundamentals of mesoscale structure and texture development in fcc metals with low stacking fault energy (SFE). Shear banding depends on the initial orientation of the crystals. In Copper and Brass-R oriented crystals which show the largest tendency to form shear bands, an inhomogeneous texture distribution induced by shear banding is observed. To also understand the influence of the micromechanical boundary conditions on shear band formation, simulations on Copper oriented single crystals with varying sample geometry and loading conditions are performed. We find that shear banding can be understood in terms of a mesoscopic softening mechanism. The predicted local textures and the shear banding patterns agree well with experimental observations in low SFE fcc crystals.
Keywords: fcc material; shear band; texture; crystal plasticity finite element analysis
Shear bands, in the form of non-crystallographic band-like regions of concentrated plastic flow, are one of the most frequently observed yet least understood microstructural features in plastically strained face-centered-cubic (fcc) metallic materials. They are characterized by massive collective dislocation activity in a narrow local deformation zone while the abutting matrix undergoes comparably homogeneous flow. Shear banding is promoted when homogeneous dislocation slip is inhibited. In such cases shear banding can act as an alternative and mesoscopically non-crystallographic deformation mode, often associated with a sudden drop in the local flow stress. The stacking fault energy (SFE) plays an important intrinsic role in that context as it influences the formation of strong obstacles.
In this study, the development of shear bands in a low SFE fcc material (α-Brass) is systematically studied as a function of orientation, constitutive behavior, and loading conditions. Plane strain compression of single crystal samples with different initial orientations is simulated using a crystal plasticity finite element (CPFE) model that incorporates the non-crystallographic shear banding mechanism in addition to dislocation slip and mechanical twinning. Our aim is to predict the structure and texture development of the material undergoing shear banding. We analyze the simulation results with respect to mechanical instability aspects, inhomogeneity of microstructures and plastic flow, orientation dependence, and effects of boundary conditions. More specifically, we conduct the following steps:
- By performing simulations with different constitutive models on differently oriented single crystals, the effects of initial orientation on shear banding are investigated.
- For each single crystal we analyze the resulting textures in regions of strain localization. Predictions of local texture evolution in Copper-oriented fcc crystals are compared in detail to published experiments.
- As Copper-oriented crystals have a strong tendency to form shear bands, systematic simulations for this orientation are performed on samples with varying aspect ratios and boundary condition.