Modeling and Characterization of Materials for Dynamic Metal Working Processes

诸如轧制、锻造和挤压等制造操作的特点是在高应变率（104sec-1）和高同源温度（0.5至0.9）下中断、非等温、大变形。很少有可用的试验数据来验证和/或完善描述这些加载条件下材料行为的本构关系。本研究的目的是在不同应变速率和不同同源温度下，对Fe-2% Si和Ti6A1-4V在分离式Hopkinson扭转棒上进行实验。这些测试数据和其他文献中可用的数据将用于划分本构关系的功能形式，也用于寻找材料参数的值。这些本构方程的预测能力将通过比较分析/计算结果与不同加载条件下的实验结果来确定，这些加载条件包括在与动态加载方向不同的方向上进行准静态预应变的试件的动加载。所建立的本构关系将用于分析挤压和热锻过程，以及加载速率和试样初始温度对锻造、扭转和复合加载中剪切带萌生和生长的影响。这项研究将结合彻底的理论/数值努力和仔细准确的实验调查。实验和理论工作之间的紧密协作和整合将有助于建立可靠的本构关系，可用于分析其他高应变率过程，如加工和快速移动穿透金属目标。

Manufacturing operations like rolling, forging, and extrusion are characterized by interrupted, non-isothermal, large deformations at high strain rates (104sec-1) and high homologous temperatures (0.5 to 0.9). There is very little test data available to validate and/or refine constitutive relations proposed to describe the material behavior under these loading conditions. The purpose of this research is to perform experiments on Fe-2% Si and Ti6A1-4V in a split Hopkinson torsion bar at different strain-rates and various values of the homologous temperature. These test data and others available in the literature will be used to delimit the functional forms of constitutive relations, and also to find values of material parameters. The predictive capability of these constitutive equations will be ascertained by comparing analytical/computed results with experimental findings under loading conditions different from those used to establish them, including dynamic loading of specimens pre-strained quasistatically in a direction different from that of dynamic loading. The developed constitutive relations will be used to analyze extrusion and hot forging processes, and the effect of loading rate and initial specimen temperature upon the initiation and growth of shear bands in forging, torsion, and combined loading. The study will combine a thorough theoretical/numerical effort with careful and accurate experimental investigation. The close collaboration and integration between the experimental and theoretical work should help formulate reliable constitutive relations that can be used to analyze other high strain-rate processes such as machining and penetration of metallic targets by fast moving penetrators.