Forming Limit Diagrams of Zircaloy-4 and Zirlo Sheets for Stamping Process of Spacer Grids of Nuclear Fuel Rod

Abstract

We investigated the theoretical forming limit models for Zircaloy‐4 and Zirlo used for spacer grid of nuclear fuel rods. Tensile tests were performed to obtain stress‐strain curves and anisotropic coefficients, such as r‐values. The experimental forming limit diagrams (FLD) for two materials were obtained by dome stretching tests following the specification of NUMISHEET 96. Theoretical FLD depends on forming limit model and yield criterion. To obtain the right hand side of FLD, we applied the forming limit models (Swift’s diffuse necking, Marciniak‐Kuczynski damage defect, Storen‐Rice’s vertex theory) to Zircaloy‐4 and Zirlo sheets. Hill’s local necking theory was adopted for the left side of FLD. To consider the anisotropy of sheets, the yield criteria of Hill (1948) and Hosford (1979) were applied. Comparing the predicted curves with the experimental data, we found that the FLD for Zircaloy‐4 can be described by the Swift model with the Hill 48 yield criterion, while the FLD for Zirlo can be explained by the Storen‐Rice model and the Hosford yield criterion (a = 8).