Physically-Based Methodology for the Characterization of Wrinkling Limit Curve Validated by Yoshida Tests

This paper presents a new experimental methodology for determining the formability limits by wrinkling in sheet metal forming using Yoshida buckling tests (YBTs). The YBT has been the most used formability test by the scientific community to determine the occurrence of wrinkling, on the one hand, due to its simple clamping configuration directly related to the kinematics of tensile tests. On the other hand, the formability test replicates the occurrence of wrinkling in deformation regions under tension, similar to the side wall wrinkling of a deep drawn part. The new physically-based methodology is built upon the direct analysis of the in-plane minor strain and its strain rate for a point located at the center of the YBT specimen. Application of the methodology in AA1050-O aluminium alloy sheets enabled the experimental determination of the onset of wrinkling. Results also showed that in contrast to conventional techniques, where the wrinkling prediction is based in a specified percentage of the initial thickness of the blank (5-10%), considering a physical wrinkle-triggering factor enables one to identify the precise moment at which wrinkling occurs. The proposed physically-based methodology provides a new level of understanding of the YBT behavior and the onset of wrinkling determination for sheet metal forming with a higher degree of accuracy.