Application of Ring Compression Test for Thin Sheet Metals

―Measurement Method for Flow Stress in Large Strain Range for Thin Sheet Metals (1st report)―

Abstract

Flow stress is commonly measured by tensile test in the strain range before necking appears. The equivalent strain given in sheet metal forming is higher than the strain measured by tensile test. Although flow stress strongly affects the accuracy of FEM simulation, particularly for fracture simulations in stretch forming, extrapolated flow stress is applied to a strain range higher than the measurable ones. The purpose of this study is to propose a measurement method for the flow stress of thin sheet metals in a wide strain range, using the ring compression test. By considering the strain distribution of the workpiece and the elastic deformation of dies through compression, as well as the friction between the workpiece and the dies, it is possible to measure the flow stress of thin sheet metals up to a strain of 1.0. The validation of the measured data by the ring compression test developed was also conducted. The measured data was compared with the data obtained by the tensile test and upsettability test with specimens cut from the same thick sheet metal. The data of the ring compression test developed corresponds to other two data sets.