A forming limit prediction model based on tensile instability theory for orthotropic sheet metal considering distortion hardening

Abstract

The anisotropic nature and distortion hardening characteristics of inherent in rolled sheet metal pose challenges in accurately predicting forming limits. Anisotropy introduces variations in forming limit curves, while distortion hardening alters both the magnitude and scope of these curves. Neglecting these factors can lead to significant inaccuracies in forming limit predictions. In this study, an orthotropic model for predicting forming limits is proposed. Drawing from Swift's diffuse instability theory and Hill’s localized instability theory, the proposed model comprehensively incorporates the influences of anisotropy and distortion hardening. To validate the approach, Nakajima tests utilizing semi-circular rigid punches were conducted on DC06 deep-drawing steel and DP590 high-strength steel. The results demonstrate that the proposed model rectifies overstated limit strains, narrows the predicted range of theoretical forming limit diagrams, aligns theoretical predictions more closely with experimental data, and enhances overall prediction accuracy. This research contributes valuable theoretical insights into the sheet metal forming industry.