Development of numerical and experimental capabilities for investigating large deformation elastic-plastic problems

A Lagrangian finite element code is developed which accounts for dynamic effects, heat conduction, contact with friction, and full thermo-mechanical coupling. The constitutive equations for finite deformation, isotropic, elastic-viscoplastic solids are formulated in the intermediate configuration within the framework of multiplicative plasticity. The formulation reduces to classical hyperelasticity in the absence of plastic deformations. The elastic response is formulated in non-rate hyperelastic form. As an application, the finite element code is employed to interpret plate-impact pressure-shear experiments involving dynamic friction under high slip speeds, high pressures and elevated temperatures. The plate-impact friction experiments represent a significant improvement over conventional dynamic friction experiments by allowing control of interfacial tractions with the use of combined pressure-shear loading waves instead of manipulating actuator motion. Also, by measuring the combined normal and transverse motion of the rear surface of the target plate, along with the finite element program presented here, critical frictional parameters such as the applied normal pressure, the interfacial slip resistance, and the interfacial slip speeds can be interpreted. In the present study, simulation of experiments are conducted on Carpenter-Hampden tool steel/Ti-6A1-4V and Carpenter-Hampden tool steel/7075-T6 aluminum alloy tribo-pairs are presented. The results of these experiments/finite element analysis provide some new insights into the evolution of interfacial sliding resistance with accumulated interfacial slip, and its dependence on slip velocity, normal pressure and the interfacial temperature.; Also, a new version of a moiré microscope is constructed to investigate large elastic-plastic quasi-static deformation which embodies the theory of optical moiré interferometry. In order to interrogate the deformed specimen grating the device utilizes a transmission diffraction grating, which allows for simple and quick change of the virtual reference grating vector, and hence the sensitivity of the device, without disturbing the optical alignment of the other components in the optical train. Moreover, an interactive fringe-processing program is developed to acquire the moiré interference fringe patterns and carry out the deformation analysis. The deformation analysis of the fringes is consistent with the continuum principles of finite deformation, and can be readily used to obtain the local micro-mechanical quantities of interest such as the local strains, stretches and rotations.