Alternative characterization method for the failure behavior of sheet metals derived from Nakajima test

Abstract

One sustainability approach in sheet metal forming is to reduce costs by increasing the reliability of the forming process by applying numerical simulations. These are based upon the finite element analysis and require specific characteristic values of the material. To improve the accuracy of the numerical model regarding the failure behavior, forming limit curves (FLC) which display the conduct and failure boundaries of sheet metals are characterized. Optical measurement systems are used to analyze the strain distribution and to generate a material dependent FLC. To reduce the amount of testing, the tensile test, the plane-strain test and the hydraulic bulge test are combined to characterize the uniaxial, plane, and the biaxial strain area and the forming limit. The results are summarized in the presented FLC, which is consequently compared with results from the standardized Nakajima test. The method is validated with different materials to compare a ductile (DX54D), a brittle (DP800) and a lightweight sheet metal (AA5182). That approach is used for the validation of the alternative and cost-effective FLC characterization. This eliminates the need for the Nakajima testing facility and the high utilization of a testing machine can save costs and time in creating the specific material data.