The effects of Hosford, Hill's quadratic and non-quadratic yield criteria on prediction of forming limit diagrams based on M-K Model

One of the most important parameters in prediction of sheet metal forming process is the influence of yield criteria on prediction of forming limit strains. In this paper، the effects of normal anisotropy coefficient on the Hill’s (1948) quadratic، Hosford’s (1979) higher-order، Hill’s (1979) non-quadratic anisotropic yield criteria، with attention to plane strain location is studied. Also the effects of these yield criteria and normal anisotropy coefficient، strain rate sensitivity factor، strain hardening exponent and yield criterion exponent on the forming limit diagram based on the M-K model have been discussed. The different effects of normal anisotropy coefficient on the limit strains of three above criteria have a good agreement with the effect of normal anisotropy coefficient on the yield different surfaces. The comparison has been made between yield criterion exponent and normal anisotropy coefficient effect on the Hill’s non-quadratic yield criterion. The results show that the proper selection of yield criterion have a significant influence on the forming limit diagram.