The effect of stress frequency on fatigue crack propagation in 99.5% pure titanium which has remarkable strain rate dependency in the plastic region was studied. Fatigue crack propagation tests were carried out under three kinds of stress frequencies (0.02, 0.2, 20Hz). FEM elasto/visco-plastic analysis of fatigue crack propagation was performed, and the comparison between the dependency of crack propagation rate on stess frequency and the strain behavior at the crack tip calculated by the analysis was made. The results obtained in this study are summarized as follows:
(1) It was found from the experiments that the crack propagation rate was approximately in inverse proportion to fn(n>0), where f is the stress frequency.
(2) The parameter closely related to the fatigue crack growth rate is the strain range Δεy or visco-plastic strain range Δεyvp at the crack tip.
(3) The effect of stress frequency on fatigue crack propagation rate may be explained by the variation of Δεy or Δεyvp based on the strain rate dependency of material.
