Quasistatic Tensile and Fatigue Performances of Titanium Alloy Open Hole Structures Strengthened by Different Cold Expansion Mandrel Front Cone Angles

ABSTRACT In this paper, the cold expansion test of titanium alloy open hole structures was conducted, and the fatigue performance was also assessed. A parametric study of the mandrel front cone angle revealed a correlation with the strengthening quality and fatigue performance evolution, providing valuable insight for optimization of open hole structure designs. The results showed that the strengthening resistance decreased and then increased with the increase of the front cone angle. The microhardness of the hole edge increased and exhibited obvious sensitivity to the mandrel front cone angle. As expected, the fatigue life of specimens increased after strengthening. The best fatigue life strengthening front cone angle was 15°. Although the front cone angle exhibited little influence on the location of the fatigue crack initiation zone and crack propagating direction, the crack extension rate and the stiffness degradation rate could be reduced by the proper mandrel front cone angle.