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AbstractÐFatigue crack initiation and multiplication of the unnotched SCS-6 silicon carbide ®ber-reinforced titanium matrix composites with dierent matrix and interfacial properties have been investigated experimentally and analytically. Ti±15V±3Al, Ti±6Al±4V, and Ti±22Al±23Nb were chosen as matrix materials. The initiation and propagation of each individual matrix crack as a function of fatigue cycles and applied stress levels were carefully monitored. The statistical distribution of crack growth rates in each composite has been constructed and analyzed. The evolution of normalized matrix crack density and stiness reduction of these composites under fatigue loading also has been characterized. A modi®ed shear-lag model, coupled with the strain-life equation and a ®ber bridging model were used to predict the fatigue crack initiation life, matrix crack growth rate, normalized matrix crack density, and residual stiness of the composites. The predicted fatigue properties correlated well with experimental results. #