INFLUENCE OF LIMIT STRESS STATES AND YIELD CRITERIA ON THE PREDICTIONOF FORMING LIMIT STRAINS IN SHEET METALS

Several researchers have proposed analytical methods for predicting th e forming limit curve (FLC), which has been successfully used as a dia gnostic tool in sheetmetal forming. However, these approaches lack eas e of adaptability to various situations and also involve considerable complexity. Sing and Rao proposed a new FLC modeling approach based on limit stress states derived from yield criterion and material propert ies from a simple tensile test. The first aspect of this study address es the influence of the shape of the forming limit stress curve (FLSC) upon the I;LC. The FLC modeled from a singly linear FLSC: exhibits go od agreement with the experimental curve, unlike those modeled from an elliptical or a piecewise linear FLSC. It is, thus, established that a linearized limit stress locus describes adequately the actual locali zed neck condition for the materials chosen in this study. Second, the study focuses on the suitability of the different cases of Hill's yie ld criterion for satisfactory prediction of FLCs. The FLCs predicted u sing different cases of Hill's criterion are compared with experimenta l FLCs in the case of steel and copper. Different cases of Hill's crit erion provide a wider choice for FLC modeling for different classes of materials. The sensitivity of Hill's stress:exponent is also thorough ly explored for achieving a close correspondence between the predicted and experimental FLCs.