Date of Award

3-1996

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Aeronautics and Astronautics

First Advisor

Shankar Mall, PhD

Abstract

An analytic methodology is developed to model the response of fiber-reinforced ceramic matrix composites (CMOs) when subjected to monotonic and fatigue loadings. The analysis requires the formulation of (1) a micromechanics model which defines the laminate's geometry and constitutive relationship; (2) failure criteria which estimate the extent of microstructural damage, and, finally, (3) a means of analyzing frictional slip, fiber pull-out, interfacial wear and laminate failure. For the present study, the behavior of unidirectional and crossply CMOs is investigated using modified shear-lag theory in conjunction with a set of failure criteria with a minimum reliance on empirical data. The damage mechanisms considered are matrix cracking, fiber/matrix interfacial debonding and fiber fracture. The stress-strain response under monotonic tensile loading, and the fatigue life (S-N relationship) and stress-strain hysteresis under cyclic loading obtained from the present solution are compared with their experimental counterparts. They are in good agreement with one another. As expected, the assumed degradation in the frictional resistance along the constituent interface plays a dominant role in determining the material response.

AFIT Designator

AFIT-DS-ENY-96-2

DTIC Accession Number

ADA304782

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