A FRACTURE-MECHANICS BASED NUMERICAL-ANALYSIS FOR PREDICTING OPTIMUM INTERFACE PROPERTIES IN A METAL-MATRIX COMPOSITE

The interface in continuous fiber reinforced composites governs the mo de and extent of load transfer between the fiber and the matrix. It al so affects the damage initiation and growth mechanisms. An additional feature of the interface is that it is strongly influenced by thermal residual stresses due to the processing history of the composite. The effect of residual stresses on the stress state of the interface near a crack tip might prove to be advantageous or detrimental to the globa l mechanical properties of the composite. These issues are of interest for a better understanding of the mechanics of fracture of composites , which in turn will lead to the development of composites with superi or properties. In this study, 2-D plane stress and axisymmetric residu al stress analyses are performed for a 37% volume fraction SiC fiber ( SCS-6) reinforced titanium (Ti-15V-3Cr-3Al-3Sn) composite plate with s ingle and multilayered interphases. ''Design plots'' for optimum utili zation of fiber and matrix strength properties are obtained. Initial d ebonding and subsequent debond growth at the fiber/interphase interfac e are predicted using quasistatic numerical analysis. The results sugg est that the composite retains sufficient load bearing capability upon initial debonding to allow a graceful failure. The residual stresses due to the coefficient of thermal expansion (CTE) mismatches between t he fiber and the matrix with single or multilayered interphases are al so compared with the help of axisymmetric analysis of the composite. T he use of the multilayered interphase effects a smooth transition of t he hoop stresses between the fiber and the matrix across the interphas e, thus reducing the propensity of interfacial cracking due to the res idual stresses caused by the CTE mismatch.