A MICROMECHANIC MODEL FOR PREDICTION OF FAILURE MODES IN IN CERAMIC MATRIX COMPOSITES

A MICROMECHANICAL ANALYTICAL MODEL WILL BE DEVELOPED FOR PREDICTING THE FAILURE MODES IN A FIBER REINFORCED UNIDIRECTIONAL CERAMIC MATRIX COMPOSITE. THE PROPOSED MODELWILL BE BASED ON MODIFIED SHEAR-LAG THEORY THAT WOULD ACCOUNT FOR THE RELATIVELY LARGE MATRIX STIFFNESS, UP TO FIFTY PERCENT OF THE FIBER STIFFNESS. A COMBINATION OF STRESS INTENSITY FACTOR AND MICROMECHANICS APPROACHES WILL BE EMPLOYED IN DETERMINING THE CRITICAL CRACK LENGTH IN THE MATRIX. THE STRESSES IN THE MATRIX AND IN THE FIBERS BRIDGING THE MATRIX CRACK WILL BE ESTABLISHED AS A FUNCTION OF THE APPLIED STRESS, CRACK GEOMETRY AND MOST IMPORTANTLY THE MICROSTRUCTURAL PROPERTIES OF THE CONSTITUENTS AND THE FIBER-MATRIX INTERFACE. FROM THE PREDICTED STRESSES, THE MODE OF FAILURE WILL BE ESTABLISHED. THE ROLE OF MICRO-STRUCTURAL PROPERTIES, IN PARTICULAR THE ROLE OF THE FIBER-MATRIX INTERFACE, ON THE FAILURE MODE, ULTIMATE STRENGTH, AND THE FRACTURE TOUGHNESS IN THE PRESENCE OF RESIDUAL STRESSES WILL BE ASSESSED. A PARAMETRIC STUDY WILLBE CARRIED OUT USING THE MODEL TO ESTABLISH REGIONS OF NON-STEADY STATE CRACKING (STABLE CRACK GROWTH) IN A UNIDIRECTIONAL CERAMIC MATRIX COMPOSITE.