Experimental and Numerical Analysis of the Buckling and Post-Buckling Phenomenon in the Yoshida Test

Simulation-based Design and Manufacturing has shown its great effectiveness in shortening the design cycle. The objective of this work was to further increase the robustness of numerical prediction in capturing subtle wrinkling in sheet metal forming process. A stress-based wrinkling predictor is further developed to predict the initiation and wave mode of potential wrinkling in forming of flat sheet. The predictor is linked to the LS-DYNA commercial FEM package. Stress prediction from LS-DYNA was compared to the implicit code ABAQUS and satisfactory results were obtained. Hence, stress, nodal coordinates and connectivity information of the LS-DYNA simulation are fed into the predictor via an automatic interface program. A set of Yoshida buckling tests was used as a verification tool for the wrinkling predictor. 0.78mm thick 180B steel and 1.012mm thick 6111-T4P aluminum are tested. Through the comparison of the experiments and simulations, it shows that the wrinkling predictor is able to predict the initiation point and wave mode for the wrinkling accurately. In addition, post-buckling behavior in numerical simulations was captured through including initial imperfections following the wrinkling mode predicted. It was found that such a method provides more reliable results in terms of the post-buckling behavior than random imperfection.