6061-T6铝合金动态拉伸本构关系及失效行为

采用HMH-206高速材料试验机开展了6061-T6铝合金在0.001～100 s?1应变率范围内的静、动态拉伸力学性能实验，分析了其应力-应变响应特征和应变率敏感性，讨论了应变率对6061-T6铝合金流动应力和应变率敏感性指数的影响，并基于实验结果对Johnson-Cook本构模型进行了修正。结合缺口试件的实验结果和模拟数据，得到了材料的Johnson-Cook失效模型参数，并对模型的准确性和适用性进行了验证。结果表明，在拉伸载荷作用下，6061-T6铝合金表现出明显的应变硬化特征和应变率敏感性，其流动应力随应变率的升高而提高，修正的Johnson-Cook本构模型可以描述材料的动态塑性流动行为，建立的Johnson-Cook失效模型能够表征材料的断裂失效行为。

Dynamic tensile constitutive relationship and failure behavior of 6061-T6 aluminum alloy

The quasi-static and dynamic tensile mechanical properties of 6061-T6 aluminum alloy in a strain rate range from 0.001 s?1 to 100 s?1 were investigated by using a HMH-206 high-speed material testing machine. The stress-strain response characteristics and strain rate sensitivity of the 6061-T6 aluminum alloy were analyzed, and the effects of strain rate on the flow stress and strain rate sensitivity index were discussed. Based on the experimental results, the Johnson-Cook constitutive model was modified to describe the plastic flow characteristics of the 6061-T6 aluminum alloy under dynamic tensile loading. In addition, the relationship between the fracture strain and stress triaxiality of the notched specimens was established by experiments and simulations, and the values of the parameters in the Johnson-Cook failure model were obtained according to the experimental and simulation results. The results show that the 6061-T6 aluminum alloy exhibits obvious strain hardening characteristics and strain rate strengthening effects, and the flow stress increases with the increase of true strain and strain rate. The strain rate sensitivity index of the material is affected by the coupling effect of strain and strain rate. During the tensile process, the Mises stress of the notched specimens was symmetrically distributed about the minimum cross-section, and the stress triaxiality at the minimum cross-section was symmetrically distributed about the center line along the width and thickness directions. Furthermore, the fracture strain of the material decreases gradually with the increase of the stress triaxiality, and increases approximately linearly with the increasing dimensionless logarithmic strain rate. The plastic flow characteristics of the 6061-T6 aluminum alloy can be described by the modified Johnson-Cook constitutive model, and the parameters in the Johnson-Cook failure model of the material can be obtained by the experiments and simulations on the notched specimens. The verification results indicate that the established models can predict the tensile mechanical response and fracture failure behavior of the 6061-T6 aluminum alloy under a complex stress state.