金属材料在极端载荷条件下的塑性流变特性及三维应力效应研究

In the processes of explosion, impact, and penetration, metallic materials are subjected to extreme loading conditions such as high temperature, high strain rate, and large deformation, and at the same time the materials always have a complex three-dimensional (3D) stress state. It’s shown in recent research that the plastic and failure behaviors of materials are influenced evidently by the 3D stress state effect. However, due to the shortcomings in the dynamic loading techniques, it’s quite difficult to control precisely the stress state of the material under dynamic loading. Therefore, the study on the 3D stress effect of metallic materials under extreme loading conditions is still very deficient. In this work, the problem of quantitative control of the stress states in the materials under extreme loading conditions will be solved through the improvement of dynamic experimental techniques and loading methods, and hence the plastic and failure behaviors of metallic materials will be researched systematically under the conditions of high temperature, high strain rate, large deformation, and complex 3D stress state. Then, theoretical models of deformation and failure of materials with consideration of the effects of Lode angle parameter and stress triaxiality will be proposed based on the study of the micromechanism of plastic flow. In this work, a new experimental method will be developed for studying of material behaviors under extreme loading conditions and complex 3D stress states, and new theoretical models with the effect of 3D stress state will be established. Theoretical foundation and data support will be supplied for the design of advanced weapon systems and aerospace structures in our country.

金属材料在爆炸、冲击、侵彻等过程中不仅要承受高温、高应变率及大变形的极端载荷条件，而且材料通常处于复杂的三维应力状态。近期研究表明，材料的变形及失效行为均受到应力状态的显著影响。但是，由于动态加载技术所存在的弊端，目前很难在冲击载荷下对材料的应力状态进行精确控制，因而有关金属材料在极端载荷条件下的三维应力效应研究仍十分欠缺。本项目拟通过对动态实验技术和加载方法的改进，解决在极端载荷条件下对材料应力状态的定量控制难题，从而实现对金属材料在高温、高应变率、大变形及复杂应力状态条件下的塑性及失效行为的系统研究。在此基础上，结合对材料塑性流变行为的微观机理研究，提出考虑罗德角参数及应力三轴度的变形及失效理论模型。本项目将发展在极端载荷条件及复杂应力状态下对材料特性的新型实验方法，建立考虑三维应力效应的新型理论模型，为我国先进武器系统及航空航天结构的设计提供理论基础和数据支撑。

工程应用中，金属材料和结构往往处于复杂应力状态。现有研究表明，材料的塑性及失效行为会受到应力状态的影响，因此为精确描述材料在复杂应力状态下的塑性流动行为，必须在本构模型中考虑应力状态效应的影响。然而，由于在动态加载下材料的应变率和应力状态效应相互耦合、难以分离，给应力状态效应的研究和模型的建立造成很大困难。通过对Ti-6Al-4V合金在不同应力状态（单轴拉伸、压缩和简单剪切）、广泛的应变率（10-3s-1-6.5×103s-1）和温度（93K-1073K）下的塑性流动和微观机制进行一系列实验研究，提出了一个包含应力三轴度和Lode角参数影响的新型本构模型，并通过编写用户子程序VUMAT将其嵌入到ABAQUS/Explicit 软件中。分别采用新提出的塑性模型和 JC 模型对压剪复合试样的动态实验进行了数值模拟。结果表明，新模型不仅在对材料本构曲线的拟合方面具有较强的优势，而且由该模型所得到的透射脉冲和载荷-位移曲线均更加准确。因此，该模型能够更精确地描述和预测金属材料在复杂应力状态下的塑性流变行为。另外，设计了新型的剪切、拉剪和压剪试样以实现对应力状态的精确控制。同时，为了获得更为广泛的应力状态范围，光滑和缺口圆棒试样、平板槽口和圆柱压缩试样也被使用。采用实验和数值模拟相结合的方法得到了等效塑性应变、应力三轴度和Lode角参数三者之间的关系。结果表明，应力三轴度和断裂应变的关系是非单调的。随后，提出了一个考虑应力三轴度和Lode角参数影响的非耦合断裂模型，并验证了该模型的有效性。该模型能够准确描述金属材料在复杂应力状态下的延性行为。