Effect of pre-strain on fatigue crack growth behavior for commercial pure titanium at ambient temperature

In this paper, the effects of pre-strain on fatigue crack growth rate are investigated considering wide ranges of load amplitudes and load ratios for commercial titanium alloy (CP-Ti). Considering the influences of load ratio and load amplitude, the effect of pre-strain on the strain energy and crack tip plastic zone size, and on the fatigue fracture mechanism have been clearly demonstrated. Besides these, how the pre-strain affects fatigue crack propagation, and therefore affects whole fatigue life have also been clearly stated. Results demonstrate that pre-strain may be more sensitive to the enhancement of fatigue crack growth resistance under high load ratio and high peak load conditions. Fatigue lives increase with increasing in the pre-strain level. With the increase of load ratio and load amplitude, pre-strain has more and more significant influence on the plastic strain energy of specimen. A high pre-strain level of 8% and a high load ratio of R = 0.8 are more sensitive to the fatigue life. Static load or static damage has the most significant contribution to the crack tip plastic deformation than fatigue load. The production of twin crystal and dislocation structure after pre-strain process will greatly ensure the enhancement of fatigue crack resistance under all loading conditions. This research will provide support to the insight of pre-strain effect on fatigue crack growth behavior of CP-Ti.