Date of Award
Doctor of Philosophy (PhD)
Civil and Environmental Engineering
George Z. Voyiadjis
A system of constitutive equations is proposed that describes the viscoplastic behavior of a class of metal alloys when subjected to large deformations. The model is purely elastic before the plastic state is reached, and becomes elastic/viscoplastic after the plastic state has been exceeded. Three main assumptions are made with regard to the strain-rate dependency in the proposed formulation. The inelastic strain rate tensor is assumed to be normal to each point of the rate dependent convex yield surface. The initial yield stress obtained from uniaxial tests is assumed to be dependent on the rate of strain loading. Finally, the hardening effect is due to isotropic and kinematic work hardening and due to the influence of the strain-rate effect. Uniaxial tests are conducted in this work on specimens made of commercially pure aluminum in order to check the validity of the proposed constitutive model and to determine the material parameters of the model. The uniaxial loading-reverse loading tests are conducted at five different constant strain-rate values in an effort to obtain a wide range of applicability of the proposed model. The material behavior is simulated numerically using the proposed constitutive model, and compared with the experimental results in order to check the accuracy of the proposed model. The applicability and effectiveness of the proposed constitutive model in solving complex (i.e., and shape and any deformation) finite deformation problems is demonstrated by the numerical simulation of a moderately thick plate. Experimental verification is provided for the bending of a thick plate. Creep and relaxation behavior of the commercially pure aluminum is also investigated.
Mohammad, Louay Nadhim, "Constitutive Equations for Large Deformation, Rate-Dependent Plasticity for Metal Alloys." (1989). LSU Historical Dissertations and Theses. 4863.