一种改进的Lemaitre断裂准则及其在弯曲成形裂纹预测中的应用

An Improved Lemaitre Fracture Criterion and Its Application to Crack Prediction in Bending Forming

摘要:

针对弯曲成形中的裂纹缺陷，应用Lemaitre韧性断裂准则，同时考虑应力三轴度，最大主应力比，以及塑性应变对损伤的影响，对Lemaitre准则进行改进，有效预测了弯曲成形中金属板料的成形极限。以7075-T6铝合金为研究对象，模拟得到该合金板材的裂纹产生条件，获取改进的Lemaitre准则材料参数，确定破裂阈值。对6 mm厚7075-T6铝合金板材进行三点弯曲实验，并观察其金相组织。对其产生裂纹时的压下量与断裂准则所得的理论压下量进行比较，验证了改进后断裂准则对裂纹预测的准确性。通过对比产生裂纹时的压下量，结果表明，改进后的Lemaitre断裂准则所得理论压下量为9.7 mm，与模拟和实验结果一致，证明改进后的Lemaitre准则对弯曲成形裂纹预测具有一定的准确性。

Abstract:

In order to predict the crack defects in sheet metal bending, an Lemaitre criterion was improved to effectively predict the forming limit in bending while considering the stress triaxiality , the maximum principal stress ratio , and the influence of plastic strain on the damage. Taking 7075-T6 aluminum alloy as the research object, the crack forming in sheet bending was simulated to obtain the criterion parameter so as to determine the cracking threshold. Three point bending test and metallographic test were carried out on 7075-T6 aluminum alloy sheet with 6 mm in thickness. The accuracy of the criterion for crack prediction was verified by comparing the press measure of experimental, simulation and theoretical values. The results show that the improved Lemaitre fracture criterion is 9.7 mm, which is consistent with the results of simulation and experiment. Therefore the improved Lemaitre fracture criterion has a certain accuracy in predicting the crack of bending forming.