Study on the I-II mixed mode fatigue crack growth behavior of TC4 titanium alloy

This article focuses on investigating the influence of mixed mode loading and loading ratio on the fatigue crack growth (FCG) behaviors of TC4 titanium alloy . It reveals that there exists a transformation towards mode I dominant crack for mixed mode crack, while the existing mode II component at crack tip still has effects on FCG behavior, which causes a continuous change in the crack propagation path and a slower fatigue crack growth rate . During the crack propagation , the non-collinear loading has an important role on the stress intensity factor , which causes greater mode I and mode II stress intensity factors. The improved expressions of SIFs have been proposed taken the non-collinear loading into account. The effects of mixed mode loading and loading ratio on the crack tip fields were also discussed, where the SIF acting as the driving force was modified to be applicable to all the loading ratios. The FCGR curve with relationship of the equivalent SIF was proposed taking the compressive loading and mixed mode loading into consideration.