Effect of initial texture on the formability of Zircaloy-4 sheet in stamping with FEM-VPSC modeling

Abstract

Zircaloy-4 (Zr-4) sheets are widely used in nuclear industry as assembly structural parts due to its low neutron absorption cross, excellent corrosion resistance and mechanical properties. The initial texture of Zr-4 has great influence on the formability of the sheet. In this paper, the texture evolution with its related deformation mechanism have been analyzed for Zr-4 during stamping process. Finite element model (FEM) was built to achieve the strain path for various locations on the longitudinal section. Modeling accuracy has been validated with the comparison of crack location and experimental thickness distribution. The effect of initial texture on the mechanical property and forming limit curves were discussed. At last, FEM combined with visco-plastic self-consistent (VPSC) modeling was built to predict the effect of different initial texture on deformation modes for Zr-4 in sheet forming process. The results show that smaller initial Kearns factor in normal direction lead to lower stress-strain curves with higher hardening exponents (n value). The cracking strain path near punch corner followed at first plane strain path, then changing to biaxial stretching strain path. It went beyond the forming limit curves (FLC) firstly with normal Kearns factor of 0.71. With the initial normal Kearns factor decreasing to 0.68, the strain paths always remain in the safe region without exceeding FLC. Lower normal Kearns factor induced better formability for Zr-4 sheet with higher prismatic slip. It is expected that this investigation will be helpful to optimize the initial texture, which will be more appropriate for forming process.

Keywords

• Zircaloy-4
• Stamping
• Initial texture
• Formability
• Anisotropy
• Crystal plasticity