Numerical and Experimental Investigations of Key Assumptions in Analytical Failure Models for Sheet Metal Forming.

In this paper, the key assumptions in the M-K and effective stress ratio models are investi-gated for Al SI 1018 steel specimens with a thickness of 0.78 mm using experimental and numerical data from Marciniak tests. The experimental procedure included Digital Imag-ing Correlation (DIC) to measure the major and minor in-plane strains. Strain compo-nents were obtained at points inside (i.e., the defect region) and adjacent (i.e., the safe regions) to the high strain concentrations for four different strain paths. In the numerical analysis, FEA simulations with Marc Mentat were performed with shell elements to investigate the four specimen geometries. The key assumptions of interest are the incre-mental major strain ratio from M-K model and the critical stress concentration factor from effective stress ratio model. Thus, the mechanics- and material-based failure phe-nomena in these two analytical models are examined in this paper to provide insight into the material behavior at failure. Also, data are presented that shows clearly the localiza-tion (both size and strain value) for the various strain paths. [ABSTRACT FROM AUTHOR]