QP980板材边缘开裂的实验研究和数值模拟

目的 冲裁加工后的第3代先进高强钢QP980板材在成形中会因边缘开裂而显著影响汽车结构件安全性，针对这一问题，对QP980板材边缘开裂行为进行研究。方法 使用QP980板材通过钻孔和冲孔2种方法制备不同边缘状态的试样，并进行扩孔和中心孔拉伸试验。分析不同边缘状态试样的扩孔率和断裂应变演化规律。采用DF2015断裂模型对QP980板材的韧性断裂行为进行预测。结果 钻孔试样的扩孔率约为33%，冲孔试样的扩孔率约为24%。与钻孔试样的试验结果相比，DF2015断裂模型的模拟结果显示出了良好的预测性，但DF2015断裂模型无法准确预测冲孔试样的载荷–位移响应、扩孔率和断裂应变。结论 不同的预加工工艺导致QP980板材表现出不同的边缘开裂行为。中心孔拉伸试验结果与扩孔试验结果趋势一致，因此中心孔拉伸试验是研究边缘开裂的良好方法。钻孔预加工工艺可以保持板材的原始性能，而冲裁预加工工艺会导致板材边缘发生严重的预损伤。由于DF2015断裂模型未考虑预损伤，因此无法准确预测冲孔试样的边缘开裂行为。

Experimental Study and Numerical Simulation of Edge Fracture of QP980 Steel Sheet

The work aims to study the edge fracture of QP980 steel sheet to solve the problem that the edge fracture of QP980 AHSS sheet during stamping significantly affects the safety of automotive structural components after blanking process. Two types of specimens with different edge conditions (drilled and punched) were prepared and subject to hole expansion and center hole tensile tests. The evolution of hole expansion ratio (HER) and fracture strain of specimens with different edge conditions was analyzed. The DF2015 fracture model was used to characterize the ductile fracture behavior of QP980 steel sheets. The HER was approximately 33% in the drilled specimens and approximately 24% in the punched specimens. Compared with the test results of drilled specimens, the simulation results of DF2015 fracture model showed good predictability, but the DF2015 fracture model could not accurately predict the load-displacement response, HER, and fracture strain of the punched specimens. Different pre-processing techniques result in different edge fracture behaviors in QP980 steel sheets. The center hole tensile test results show the same trend as the hole expansion test results. The center hole tensile test is a good alternative for studying edge fracture. The drilled pre-processing technique can maintain the actual properties of the sheet, while the punching process introduces severe pre-damage to the sheet edge. The DF2015 fracture model does not consider the pre-damage during the punching process, and therefore can not accurately predict the edge fracture behavior of the punched specimens.