基于韧性断裂准则的修正MK模型及其在充液热成形中的应用

摘要

将MK模型与韧性断裂准则相结合，提出预测不同温度下5A06-O铝合金板材成形极限的新模型。基于宽板弯曲试验，应用新的修正 MK 模型确定材料常数(C)和初始厚度不均度( f0)。通过提出的新模型计算得到20和200°C下的成形极限图。将板材厚度法向应力对成形极限的影响计入新模型，并嵌入Abaqus/Explicit中，进行筒形件充液成形并加以验证。结果表明：与传统MK模型对比可知，新模型预测的成形极限图与实验值更加接近；在20和200°C下，充液热成形模拟与实验之间的误差分别为8.23%和9.24%，验证了模型的有效性。%A modified MK model combined with ductile fracture criterion (DFC-MK model) is proposed to compute the forming limit diagrams (FLDs) of 5A06-O aluminum alloy sheet at different temperatures. The material constant (C) of ductile fracture criterion and initial thickness imperfection parameter (f0) at various temperatures are determined by using a new computing method based on wide sheet bending test. The FLDs at 20 and 200 °C are calculated through the DFC-MK model. The DFC-MK model, which includes the influence of through-thickness normal stress, is written into the subroutine VUMAT embedded in Abaqus/Explicit. The cylindrical cup hydroforming tests are carried out to verify the model. The results show that compared with experimental observations, the predicted FLDs based on DFC-MK model are more accurate than the conventional MK model;the errors between the simulations and experiments in warm hydroforming are 8.23%at 20 °C and 9.24%at 200 °C, which verify the effectiveness of the proposed model.