Doctoral Dissertations

Donald Erdman

Date of Award

12-1995

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Engineering Science

Major Professor

Y. J. Weitsman

Committee Members

Marion Hansen, John Landes, Madhu Madhukar, Frank Swinson

Abstract

This work concerns the development of an analytic model to predict the stress-strain and damage behavior of ceramic matrix cross-ply laminates. The validity of the model is to be assessed by experimental observations. Major features of the analysis include : prediction of transverse matrix cracking in the 90° plies at each increment of applied stress utilizing a fracture criterion to determine the increase in crack density, prediction of interfacial slip zones between the 0° and 90° ply groups, and a bilinear constitutive formulation to account for the non-linear behavior of the 0° ply groups within the cross-ply composite. This work presents a novel approach to analyze cross-ply ceramic composites in a rational manner, while most other analyses of ceramic composites are confined to the simpler case of unidirectional reinforcement. The analysis employs basic concepts of fracture mechanics to establish criteria for the complex process of multiple crack formation within the laminate. The incorperation of the non-linearity associated with the 0° plies along with interfacial slippage between the 0° and 90° ply groups in the damage prediction, leads to the stress-strain response of the cross-ply lay-up. In this manner, the current approach enables the prediction of both damage states and the stress-strain behavior of the laminate. A comprehensive mechanical testing program which complements the analytical portion of this work, provides essential verification of stress-strain data for the unidirectional and cross-ply laminates, along with quantitative information concerning damage initiation, as well as interlaminar shear strength.

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