Effect of uniaxial loading direction on mechanical responses and texture evolution in cold pilgered Zircaloy-4 tube: Experiments and modeling

Abstract

Mechanical responses of cold pilgered Zircaloy-4 (Zr-4) tubes are measured under different uniaxial (tension/compression) loading directions. Tensile tests were carried out along three directions: rolling direction (RD), transverse direction (TD) and 45° to the rolling direction (45RD) at quasi static strain rate. Compression test was also performed in the RD. Texture was characterized at intermediate strains with electron backscattered diffraction method. For different uniaxial loading conditions, anisotropic yield stress and strain hardening behavior can be observed. Such complex mechanical behavior is well explained with the variations in activation of deformation mechanisms predicted by the Schmid factor distribution and visco-plastic self-consistent (VPSC) model. In order to calibrate the VPSC model’s parameters more accurately, both mechanical responses and texture changes for four different directional tests are compared with VPSC simulations. The calculated Lankford coefficients are also calibrated with anisotropic tensile results. Furthermore, a deepening understanding of the texture evolution under different loading directions were disclosed based on VPSC method. The results indicate that the activity of deformation mechanisms changes significantly with different uniaxial loading directions. Non-prismatic slips with higher critical resolved shear stress, e.g. basal and pyramidal slip, make larger contributions to the yield and strengthening stress resulting in the highest stress in TD compared with RD and 45RD. Compression test along RD prefers the activation for tensile twinning (TTW). Meanwhile, TTW can be detected in 45RD and TD tension owing to the spread distribution of initial texture towards TD.