Mesomechanics of nucleation and propagation of small fatigue cracks in metal matrix composites

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1. A new system for the fatigue tests of metal matrix composites in a scanning electron microscope was developed to conduct in-situ observation of initiation and propagation of small fatigue cracks.2. The stress intensity factor for a crack interacting with particles was determined by the finite element method, and used for the prediction of the crack propagation direction and the rate.3. The threshold condition of small fatigue crack propagation was given by the emission of a dislocation from the crack tip or the dislocation annihilation. The propagation behavior of a microstructurally small crack interacting with the grain boundaries was modeled on the basis of continuously distributed dislocation theory combined with the crack closure model. The propagation condition of mechanically small cracks was given by the resistance curve method.4. The published data on the fatigue limit, the threshold stress intensity factor and the effective threshold stress intensity factor of aluminum alloys reinforced and unreinforced by silicon carbide particles or whiskers were correlated to the tensile properties of materials. The reinforcement influenced the tensile strength and also the fatigue properties of materials.