Development of a Multi-Scale Methodology for Prediction of the Microscopic Anisotropic Stress-Strain Response of Textured Metals under Dynamic Loading

This report documents a comprehensive experimental and theoretical investigation of the deformation behavior of high-purity, polycrystalline alpha-titanium. A series of monotonic uniaxial compression and tension tests were carried out at room temperature under quasi-static conditions to quantify the plastic anisotropy and the tension-compression asymmetry of this material. The evolution of microstructure and texture during deformation was studied using optical image microscopy (OIM) and neutron-diffraction techniques to elucidate the role of deformation twinning and its effect on the macroscopic response. To characterize the material's strain rate sensitivity, Split Hopkinson Pressure Bar tests at strain rates of 400 to 600 sec-1 were performed along the axes of symmetry of the material. The experimental activities were complemented with multi-scale model development in the framework of plasticity theory. To describe the quasi-static macroscopic response of the material, a new anisotropic elastic/plastic model was developed. Key in its formulation is a yield criterion that captures strength differential effects. Anisotropy was introduced through a linear transformation on the Cauchy stress tensor applied to the material. This integrated experimental-theoretical effort appears to have resulted in the description, for the first time, of the anisotropic stress-response of high-purity titanium at room temperature.