金属材料在复杂应力状态下的塑性流动特性及本构模型^*

Metallic materials are widely used in automotive, aerospace, energy, national defense, and other important fields due to their excellent mechanical properties. During service periods, metallic materials are generally subjected to complex stress states. Recent researches reveal that the plastic behavior of materials is affected by the stress state. Therefore, to accurately describe the plastic flow behavior of materials under complex stress states, the influence of the stress state must be considered in the constitutive model. Under dynamic loading, however, the effects of strain rate and stress state are coupled, which makes it difficult to study the effect of stress state and to establish a stress-state-dependent constitutive model. In this work, mechanical tests were performed under various loading conditions including uniaxial compression, uniaxial tension, and simple shear using the MTS universal testing machine and the split Hopkinson bars technique. The stress-strain curves of Ti-6Al-4V were obtained over a wide range of strain rates and temperatures. It is observed that stress states have an obvious effect on the plastic flow properties and work-hardening characteristics of the material. Based on the experimental results, a new constitutive model that incorporates the influence of the stress triaxiality and the Lode angle parameter was proposed. Under tensile or compressive loading conditions, the flow stress determined by the J-C model is significantly lower than the test results, while the present model can predict the flow stress accurately. To check the applicability of the proposed model, the dynamic experiment of a specimen under the compression-shear combined load was simulated by both the J-C model and the proposed model implemented in the ABAQUS/Explicit software via the VUMAT user subroutine. The results show that the present model exhibits a higher accuracy in the prediction of the flow stress curves. Moreover, this model can predict both the transmitted pulse and the force-displacement curves more accurately. Therefore, the new model can describe the stress state effect successfully and predict the plastic behavior of the material under complex stress states more precisely.