Q235B钢材考虑应力三轴度和Lode参数影响的断裂模型

Fracture Model of Q235B Steel Considering the Influence of Stress Triaxiality and Lode Parameter

Q235B钢材广泛应用在建筑钢结构中,目前的钢材延性断裂破坏准则主要考虑应力三轴度的影响,忽略了Lode参数对于钢材断裂准则的影响,为此,本文在微孔扩展模型(VGM模型)的基础上,提出了综合考虑应力三轴度和Lode参数影响的断裂模型(LVGM模型).加工了一批体现不同应力状态的Q235B钢材圆棒和板状试样,开展了试样的单调拉伸试验、断口的扫描电镜试验以及有限元分析.基于试验和有限元分析结果,标定了Q235B钢材的LVGM模型参数.应用LVGM模型预测了含初始裂缝试件的裂纹起始和断裂破坏过程,预测结果与试验结果吻合良好,并且与VGM模型的预测结果相比,LVGM模型具有更好的预测精度.最后得到了Q235B钢材临界等效塑性应变与应力三轴度和Lode参数的关系.

Q235 B steel is widely applied in building steel structures in China.Previous ductile fracture models for steel have indicated that the stress triaxiality is a key parameter controlling the ductility of steel,however,they neglect the effect of Lode parameter on the ductile fracture.A fracture model considering the influence of stress triaxiality and Lode parameter on the fracture failure is proposed based on the void growth model(VGM),which is namely as LVGM model.A series of round bar specimens and plate specimens of Q235 B steel were designed and prepared to vary the stress state,the tensile tests of the specimens were carried out,and scanning electron microscopic tests and finite element analyses were also conducted.The material parameters of LVGM for Q235 B steel are calibrated according to the test results and finite element calculation of tensile specimens.Then LVGM is applied to predict the crack initiation and fracture process of the specimens with initial crack,and the predicted results are consisted with experimental results.Compared with the numerical simulation based on VGM model,the numerical results from LVGM show better prediction accuracy.Finally,the relationship of equivalent plastic strain and stress triaxiality and Lode parameter is acquired.