Modeling and Characterization of Materials for Dynamic Metal Working Processes

轧制、锻造和挤压等制造操作的特点是在高应变率(104秒-1)和高相应温度(0.5到0.9)下出现间断、非等温、大变形。可用于验证和/或改进用于描述材料在这些加载条件下的行为的本构关系的试验数据非常少。本研究的目的是在分离式Hopkinson扭杆中对Fe-2%Si和Ti6Al-4V进行不同应变率和不同相对应温度下的实验。这些试验数据和文献中的其他数据将被用来划定本构关系的函数形式，并找出材料参数的值。这些本构方程的预测能力将通过将分析/计算结果与实验结果在不同于建立本构方程的加载条件下进行比较来确定，包括在与动态加载方向不同的方向上准静态预应变的试件的动态加载。建立的本构关系将用于分析挤压和热锻造过程，以及加载速率和初始试件温度对锻造、扭转和复合加载中剪切带的萌生和长大的影响。这项研究将把彻底的理论/数值努力与仔细和准确的实验研究结合起来。实验和理论工作之间的密切合作和结合将有助于建立可靠的本构关系，这些本构关系可用于分析其他高应变率过程，如快速弹丸对金属靶材的加工和侵彻。

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.