A SIMPLIFIED APPROACH FOR MODELING FATIGUE OF UNIDIRECTIONAL CERAMIC-MATRIX COMPOSITES

An analytical methodology is developed to model the response of unidir ectional ceramic matrix composites (CMCs) under monotonic and fatigue loadings at room temperature. The analysis is presented as a first ste p toward analyzing the fatigue behavior of CMCs at elevated temperatur es. The laminate is modeled using a modified shear-lag analyses in whi ch the microstructural damage is estimated using simple damage criteri a. 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 mat rix crack density is developed and compared with classical fracture me chanics techniques. Additionally, a formulation for modeling the fatig ue response of ceramic composites including stress-strain hysteresis a nd strain ratchetting is presented. The stress-strain response under m onotonic tensile loading, and the fatigue life (S-N relationship) and stress-strain hysteresis under cyclic loading obtained from the presen t analytical methodology are compared with their experimental counterp arts. They are in good agreement with one another.