Experimental Researches on Nonlinear Strain Paths Forming for Dual Phase Steel
Strain paths during sheet metal forming are always complex and nonlinear. Forming limit diagram (FLD) is a common method to determine failure in the past decades. However, it is only suitable for linear strain path condition. Regarding dual phase steel DP780, a special experiment was designed and carried out on Zwick Cupping equipment to get nonlinear strain paths. And the strain status was analyzed in FLD. It was found that FLD cannot predict failure precisely in this case. A new approach proposed by Stoughton and Yoon which based on polar effective plastic strain was introduced to analyze this nonlinear strain paths condition, the result is in good agreement with experiment, which indicated that Polar Effective Plastic Strain Diagram was an effective and precise tool to determine failure especially for complex nonlinear strain paths forming.