Development of evaluation technique for fatigue strength in discontinuously reinforced composites

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1. For the case of fine particle-reinforced composites, crack initiation was associated with matrix slip in a particle-rich region. On the other hand, for the case of coarse particle-reinforced composites, cracks were mainly initiated by particle cracking under cyclic loading.2. For the case of fine particle-reinforced composites, the crack is decelerated when it hits the particle. When the crack becomes longer than about 150μm, the crack does not show large irregularity in the crack growth curve. For the case of coarse particle-reinforced composites, main crack propagated with coalescence with sub-cracks initiated from particle fracture ahead of a main crack.3. When compared at the same stress intensity range, crack propagation rate, da/dN, decreases with increasing volume fraction of SiC particle. SiC particles act as a resistance of crack propagation. For the case of a coarse particle composite, da/dN is lower than that of a fine particle composite for lower stress intensity range region. The crack closure increases with particle volume fraction, when compared at the same Kmax. Increase of the crack closure at threshold with volume fraction is mainly caused by the roughness of fracture surface.4. The fatigue strength of notched components increases with increasing volume fraction of SiC particle. The prediction method based on a resistance-curve was proposed.5. Model of fatigue crack interacting with the secondary phase and grain boundary was proposed to evaluate the fatigue limit of smooth specimen on the basis of plasticity induced crack closure model.