Experimental Validation of Simplified Identification Method of Yield Function Using Circumscribing Polygon of Yield Locus and Its Application for Analysis of Sheet Metal Forming

In this study, a method to identify the yield surface by three types of simplified material tests is proposed. The uniaxial tensile test, hydraulic bulge test, and plane strain tensile test are used in this method. A polygon circumscribing the equal plastic work contour can be defined by assuming the associated flow rule on the direction of the plastic strain rate. The parameters of anisotropic yield function are identified as a smooth curve inscribed in this polygon. This paper describes the details of these material testing methods. The yield surface of the cold-rolled steel sheet (SPCE) is identified by the proposed method and modeled with Yld2000-2d yield function. The model is compared to the stress points which are measured by the biaxial stress tests using cruciform specimen. Both yield loci agree well. Moreover, the yield function identified by the proposed method is applied to two types of simple sheet metal forming problems, the hole expansion test and deep-drawing of cylindrical cup. The results of finite element analysis are compared with the experimental results in both problems. The thickness strain on the hole edge in the hole expansion test and the ear height of the deep-drawn cup are evaluated. The results of the analysis using the modeled yield function agree with the experimental results qualitatively.