Evaluation and optimization of wrinkle resistance in plastic forming of bimetal composite sheets under complex boundary conditions

Metal composite sheets are widely used in transportation and aerospace due to their comprehensive performance. However, given the property differences of heterogeneous metals, interlayer interactions, and complex forming boundary conditions, they are more prone to wrinkling than single-layer sheets, and their wrinkling mechanism is more complicated. To investigate this mechanism and propose an evaluation method for wrinkle resistance, this study conducts wrinkling tests on bimetal composite sheet wedges under complex boundary conditions. A simulation model for wedge wrinkling is developed using the Buckle-Dynamic algorithm with continuum shell elements in ABAQUS, and experimental results validate the model accuracy. The model is used to analyze the relationships between the stress–strain of each metal layer, the position of the stress-neutral layer, and the thickness direction displacement. Consequently, a method for judging the wrinkling of composite sheets is proposed, which takes the bifurcation time of the integral point strain path of the metal layer where the stress-neutral layer is located as the critical wrinkling time. Based on this, the critical wrinkling strain lines of the composite sheets are established, and their slopes are used to characterize and quantify the wrinkle resistance. Research shows that increasing the proportion of the material with lower hardness in the component layers of the composite sheet and the overall thickness of the sheet will both reduce the number of wrinkles, thereby enhancing wrinkle resistance. This study introduces a method for evaluating the wrinkle resistance of composite sheets under complex boundaries and guides the optimization of their performance in forming.