A simplified approach for modeling fatigue of unidirectional ceramic matrix composites

An analytical methodology is developed to model the response of unidirectional ceramic matrix composites (CMCs) under monotonic and fatigue loadings at room temperature. The analysis is presented as a first step toward analyzing the fatigue behavior of CMCs at elevated temperatures. The laminate is modeled using a modified shear-lag analyses in which the microstructural damage is estimated using simple damage criteria. Moreover, the damage mechanisms considered in this study are matrix cracking, fiber/matrix interfacial debonding and slip, fiber fracture, and fiber pullout. A simple criterion for estimating the average matrix crack density is developed and compared with classical fracture mechanics techniques. Additionally, a formulation for modeling the fatigue response of ceramic composites including stress-strain hysteresis and strain ratchetting is presented. 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 analytical methodology are compared with their experimental counterparts. They are in good agreement with one another.