| Structural components which are subjected to severe loading conditions need reliability and performance analyses prior to production. The first step in these analyses is the inelastic analysis which provides information about stresses and strains during manufacturing and service time.; During manufacturing processes such as extrusion, metal forming, forging and deep drawing, the workpiece is subjected to large inelastic deformation. As a result of large inelastic deformation, an initially isotropic material becomes anisotropic. Mechanical material properties, for instance Young modulus (E), will depend on the direction. During the service time, in most cases, especially at high temperatures, inelastic deformation is inevitable: strain accumulation in pressure vessels, creep in turbine blades, stress relaxation in springs. For predicting the lifetime of structural components, the constitutive models have been developed over the years.; In this thesis, the viscoplasticity theory based on overstress (VBO) model which has been developed through the years by Krempl and his co-workers (1996) is modified to model non-proportional cyclic loading and deformation induced anisotropy. The room temperature ratcheting behavior of AISI 1026 carbon steel, see Hassan and Kyriakides (1992) and Hassan et al. (1992), under uniaxial and biaxial loading conditions is investigated. The response of convected and co-rotational objective rates for simple shear with various material laws is examined as well. |
