Fatigue crack growth behavior of the epoxy resin reinforced by silica particles was investigated at various temperatures below glass-transition temperature. K max versus da/dt crack growth curves showed the temperature dependence, where the crack growth resistance decreased with increasing temperature. On the other hand, ∆J versus da/dt crack growth curves showed two separated bands: one band corresponded to room temperature (22 o C) and the other corresponded to elevated temperatures (50, 80 o C). The hysteresis loops showed a clear nonlinear deformation behavior at elevated temperatures, while linear deformation behavior was found at room temperature. Fracture surface observations revealed two different crack growth mechanisms at each temperature. The crack propagated along the micro-cracks nucleated in the interface or in the matrix near the interface between matrix and fine particle and also propagated through pre-existing flaws in the coarse particles at room temperature. On the other hand, the crack propagated along the micro-cracks nucleated by debonding or pulling-out of fine particles and also propagated along the interface between matrix and coarse particle even if a pre-existing flaw would be in the particle at elevated temperatures. Nonlinear deformation behavior at elevated temperature would be attributed not only to matrix softening but also to debonding of particles.

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