Coupled texture and non-Schmid effects on yield surfaces of body-centered cubic polycrystals predicted by a crystal plasticity finite element approach

Understanding and modeling the plastic deformation of body-centered cubic (BCC) metals involves considering non-Schmid (NS) driving forces to move dislocations. Here, the deformation of individual single crystals results not only from the resolved shear stress along the direction of slip (Schmid law) but also from shear stresses resolved along directions orthogonal to the slip direction as well as the three normal stress components (NS effects). In this work, we develop a multiscale model, called non-Schmid crystal plasticity finite element (NS-CPFE), to calculate the elastic-plastic deformation response of BCC polycrystals. The model accounts for coupled Schmid and NS effects through the modification of the driving shear stresses for both the 〈11¯1〉{110} and 〈111¯〉{112} slip families. The model is validated using data from the literature and then applied to calculate polycrystalline yield surfaces through the finite element (FE) cell approach. Using the model, we perform an in-depth study of the relative importance of different terms taken in the NS contribution to the driving force for slip. Results show that for a random texture or relatively weak textures, the NS shear stress components acting normal to the Burgers vector have no effect on the polycrystalline yield surface. However, for a relatively strong transversely isotropic texture, we find an interesting result: NS shear and normal stress components can negate the effects of texture on asymmetry and plastic anisotropy. In particular, the calculations performed for the best-fit NS constants for Ta, Mo, and W show that disparate sets of NS constants for the same material coupled with preferred texture can significantly influence the shape of the polycrystalline yield surface.