变弹性模量对高强钢辊弯成型回弹预测的影响

Springback prediction of DP980 steel considering nonlinear elastic modulus in cold roll forming

摘要:

为研究非线性弹性模量对高强钢辊弯成型回弹预测的影响，进行拉伸试验和连续循环加载卸载试验，分析DP980高强钢在不同预塑性应变下的非线性弹性模量.采用塑性屈服面法和弹性模量减少转化面法，建立DP980高强钢弦线模量数学模型.运用型钢成型COPRA RF专业软件和有限元MSC MARC商业软件，建立了八机架的连续辊弯三维有限元模型.采用连续辊弯汽车用高强钢薄壁结构件试验验证有限元模型的可靠性.结果表明：循环加载实验中，随着预塑性应变的增加，弹性模量出现初期迅速下降，其后保持几乎不变的趋势，且塑性应变为10%时，DP980高强钢弹性模量下降了25%；对比试验与仿真结果发现，变弹性模量模型比恒值弹性模量模型能更准确地预测回弹问题，且预测精度提高了20%以上.充分考虑高强钢在预应变下非线性弹性模量，能显著改善辊弯成型预测回弹的精度.

Abstract:

To accurately predict the springback of high strength steel and ultra high strength steel in cold roll forming, two mechanically-measured tests, uniaxial and loading-unloading-loading cycle tests, were introduced to determine the elastic modulus degradation of DP980 with the increase of plastic strain. Considering yield surface and elastic degradation surface, the chord modulus was developed in addition to elastic and plastic strain. The 3D finite element analysis models with eight stands were carried out by the professional COPPA RF and MSC MARC software. The simulation results achieved good agreement with experimental results observed in roll forming for thin cross-section automotive products. It is found that, with the increase of the plastic strain, the value of Young's modulus firstly reduces rapidly, and then slowly, finally tends to a steady value. Degradation of the Young's modulus is found to be 25% from the initial Young's modulus for the saturated value. Compared to the constant elastic modulus, the springback prediction result by using the variable elastic modulus is more accurate.