Buckling of sheet metals in contact with tool surfaces

The buckling point detected at the Yoshida Buckling Test is at an extremely low strain level, which does not reflect the reality observed in stamping of complex parts. A new buckling test, "Contact Buckling Test", is proposed here with the thought that the delay of buckling in reality is due to the existence of sheet curvature and the contact support provided by tooling. Interesting buckling phenomena have been observed for both aluminum and steel sheets, including oil canning, buckling at the loading stage, and buckling at unloading. The fundamentals of these different buckling phenomena will be explained through a stress-based wrinkling predictor developed by the authors.