Massively parallel computations on shear bands and other phenomena

Shear localization phenomena have been simulated numerically on massively parallel computers. Dynamic viscoplastic constitutive laws are considered to investigate the strain rate and inertial effects on the formation of shear bands. Various types of imperfections, material defects, thickness inhomogeneties and nonhomogeneous deformation fields, have been considered. It is shown that all of these imperfections play an important part in triggering shear bands and the structure of the shear band. The influences of some aspects of material properties on shear band formation, like strain softening, vertex like yield surface and thermal softening, have also been examined through numerical simulation.; All of these computations have been performed on massively parallel computers, CM2 and CM200. A one-point quadrature quadrilateral element has been used in most computations as opposed to the crossed-triangular element commonly used by most researchers. From 65,536 to 262,144 elements were used in these computations, and the results show this element achieves good resolution of the shear band when the element size is smaller then the width of the shear band.; The algorithm proposed in this thesis is also applied to crystalline materials to study the shear band formation in these materials under dynamic loading conditions. Nonuniform thickness and grain boundaries have been introduced to trigger the shear bands in single crystal and polycrystals to study their effect on the stress-strain response.; The dynamic behavior of a stationary crack has also been studied by this method. The problem at hand is a brittle-ductile failure transition problem reported by Kalthoff (1987). The domain integral has been used to evaluate the response near the crack tip for both low and high impact velocities in conjunction a thermal-mechanical material model. The results show that at low impact velocities, shear bands do not form, and that brittle fracture is likely. At high velocities, a shear band forms, as is observed experimentally, but the computed shear band is shorter than observed experimentally.