EXPERIMENTAL, ANALYTICAL, AND FINITE ELEMENT STUDY OF THE BENDING AND SPRINGBACK BEHAVIOR OF DP780 AND DP90 STEEL SHEETS

Abstract

The bending and spring back behaviors of DP780 and DP980 were investigated using experiments, analytical models, and PEA. An PEA study using 3D shells was first performed of the work by Queener and DeAngelis (1968) and demonstrated that the 3D shell element behavior in bending and springback, is similar to that from simple bending theory. Experimental and FE studies were then performed using DP780 and DP980 steels under simple and general bending conditions. Simple bending conditions were studied in V -die bending. General bending was studied for DP780 using a commercial bending machine. The PEA examined the effect of element formulation and material hardening assumptions on springback, bending stresses, and the residual stress distributions after springback. Corresponding simple and general bending analytical models were also compared. The simple bending model was from Queener and DeAngelis ( 1968), and the general bending model was from Tan et al. ( 1995), modified for Ludwig hardening. Overall, the PEA predicted the springback magnitude in the order; 2D continuum >3D continuum> 3D shells, and kinematic hardening> mixed hardening> isotropic hardening. In the V -die bending study the 3D shell PEA, using a calibrated mixed hardening assumption, produced the most accurate results. The PEA using pure isotropic hardening demonstrated that bending and springback behaviors for both steels were consistent with that described by simple bending theory. The behaviors demonstrated by the FEA using mixed or pure kinematic hardening were not. In the general bending study, the 3D continuum element FEA using pure kinematic hardening was the most accurate. The 3D continuum element FEA captured the bending stress interaction with the hardening assumption as well as thinning deformation, in agreement with the analytical model and thinning measured experimentally. 3D Shell elements could not capture these behaviors and significantly under-predicted springback under the pure isotropic hardening assumption.