Effects of stress ratio on fatigue crack growth of thermoset epoxy resin

The influences of stress ratio (R) on fatigue crack growth (FCG) of thermoset epoxy resin with polyamine hardener were investigated. The FCG growth rates (da/dN) have been correlated by the linear-elastic fracture mechanics parameters (ΔK and Kmax), and nonlinear-elastic fracture mechanics parameter (ΔJ). The effects of R on FCG were observed when the ΔK and ΔJ were used as fracture mechanics parameters for FCG. However, the Kmax successfully characterized FCG under cyclic-dependent condition (FCGs at R = 0.1 and 0.4); but it failed to characterize the FCG under time-dependent condition (FCG at R = 0.7). As a time-dependent fracture mechanics parameter, C* was applied to correlate the time-dependent FCG rate (da/dt). A reasonable agreement was obtained between time-dependent FCG (R = 0.7) and creep crack growth (CCG) results.