Date of Award

1996

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

First Advisor

George Z. Voyiadjis

Abstract

In this work, two backstress models and a modified yield criterion for crystalline materials are proposed. The proposed work is for the identification of texture development in metals when subjected to large deformation processes such as rolling, extrusion, stamping and deep drawing, etc. These models are incorporated into a numerical procedure similar to the approaches by Asaro (1983), Peirce et al. (1983), Nemat-Nasser (1983), and Rashid and Nemat-Nasser (1992). Also, similar to their approaches, a two-dimensional crystal structure is used for a feasibility study of the model by solving a simple shear problem. More importantly, the proposed formulations are strain rate independent expressions used to evaluate the plastic behavior and texture development in rate independent materials. This modification to the numerical procedure avoids the inconsistencies of mathematical manipulations by other approaches which use a strain rate dependent materials model to solve the problems of strain rate independent materials. Furthermore, the parameters in the proposed models are studied to evaluate their effects on the plastic behavior of the modeled materials. Numerical results showed that both backstress models are physically sound and feasible. The method in this work is quite flexible and can be used to model complex anisotropic behavior of the materials. This approach is also compared with the works by Zbib and Aifantis (1987) and Lamar (1989). It is noticed that the proposed method in this work has more advantages in physical process than the other compared approaches. Finally, a general form of yield surface in polycrystalline materials is proposed that incorporates the Tresca and von Mises and other models.

Pages

100

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