Date of Award

1996

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

First Advisor

George Z. Voyiadjis

Abstract

A new six parameter general anisotropic yield surface using a fourth order anisotropic tensor $M\sb{ijkl}$ has been proposed. This form has been derived based on the physical behavior observed for the material under consideration--directionally reinforced metal matrix composites. Its validity has been shown by proving its convexity and form under coordinate transformation. This form of the anisotropic yield function is general in nature which can be used for either pressure dependent or independent cases. The proposed surface compares well with the extensive experimental data of Dvorak et al. (1988) and Nigam et al. (1993) performed on boron-aluminum metal matrix composite. Based on a six parameter general anisotropic yield surface that has been proposed earlier, a cyclic plasticity model to model the behavior of directionally reinforced metal matrix composite, has been proposed here. Apart from being able to model different initial yielding behavior along different stress directions, a number of features have been incorporated into the plasticity model. They include the usage of a proposed non-associative flow rule, kinematic hardening rule of Phillips type, a modified form of the bounding surface model for modelling the cyclic behavior, and the usage of a proposed form for evaluating the plastic modulus for anisotropic materials. The stress-strain results generated from the model have then been compared with those from the experiments. A cyclic damage-plasticity model is then proposed for modeling the behavior of Metal-Matrix Composites (MMC's) under the behavior of cyclic multi-axial loading situations. Two different approaches to model the damage behavior are presented here and results are presented for both cases. The first approach is a 'continuum-damage' model and the other is a 'micromechanical-damage' model. Comparisons are made with experimental data in order for cyclic loading situations. Other results depicting the evolution of damage under cyclic loading are also presented.

Pages

145

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