Prediction of necking for two aluminum alloys under non-proportional loading by using an FE-based approach

Forming Limit Diagrams (FLDs) were found numerically for sheets under non-proportional loading by means of an FE-based Marciniak–Kuczynski (M-K) analysis. The material model used in the analysis includes two instability criteria; a non-local criterion to detect incipient localized necking and a through-thickness shear instability criterion. The objective was to study whether the effects of pre-straining on the FLD could be predicted by the chosen modeling approach, and compare the results from the two instability criteria. The results with the two criteria were different, but both criteria were able to capture the strong strain-path dependence of the FLDs as the governing phenomenon is plastic instability.