Modeling and Characterization of Materials for Dynamic Metal Working Processes

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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.