Effect of deformation-dependent material parameters on forming limits of thin sheets

Material properties are deformation history dependent. To take this fact into consideration in forming limit analysis, the material parameters are defined as functions of strain using the Voce equation. These history-dependent material parameters are incorporated in the M–K analysis based on Hillʹs 1993 yield criterion in which all material parameters are independent, so that the effect of each of these history-dependent parameters on forming limits can be investigated individually. The analysis shows that history-dependent material properties have a significant influence on forming limits. An increasing r-value will increase the limit strain under plane strain (FLD0), which is different from the traditional M–K analysis. Comparison of predicted results with experimental data illustrates that the consideration of history-dependent material properties can improve forming limit predictions considerably.