Determining factors affecting sheet metal plastic wrinkling in response to nonuniform tension using wrinkling limit diagrams

In thin plate plastic forming, the efficient, accurate prediction and control of wrinkling is a basic requirement. Because there is no clear means of determining the main strain space curve (similar to the fracture forming limit diagram) when establishing the critical wrinkling state, this work used diagonal tensile plate tests to verify a numerical simulation of plastic wrinkling in thin plates. This model included a buckling mode obtained by an eigenvalue buckling analysis as the initial shape defect in a dynamic explicit numerical simulation of the plastic deformation of the test pieces. This permitted calculation of the true instability morphology of the test piece and avoided the difficulty associated with simulating plastic deformation wrinkling morphologies using existing static implicit or dynamic explicit numerical simulation algorithms. The morphology and characteristics of the critical wrinkling limit diagram (WLD) associated with nonuniform tension were investigated. The effect of the specimen thickness and boundary conditions on the WLD in the main strain space were also examined and the effects of various processing parameters on crease resistance were established. Finally, the effectiveness of the WLD established in this work was verified based on using non-contact full-field strain measurements to examine the plastic wrinkling of thin plates. This research provides a means of establishing the critical wrinkling line for various conditions.