TC4 titanium alloy is the main material of aircraft landing frame and other structural parts. The study of its ultra-low cycle fatigue properties is essential for evaluating the reusability of aircraft structures that experience substantial loads. In this paper

the ultra-low cycle fatigue tests on TC4 titanium alloy at room temperature are conducted utilizing the axial strain control method and the fatigue fracture mechanism is analyzed. The alloy exhibits continuous cyclic softening behavior under significant heavy fatigue loading. The ultra-low cycle fatigue properties of TC4 titanium alloy are characterized respectively by the Coffin–Manson formula

the strain energy density-based model and the powerexponent function model

with the latter presenting better properties and precisions for fatigue life prediction under different strain ratios. Under different strain amplitudes

secondary cracks and holes appear in the materials

and as the strain amplitude increases

the fracture mode transitions from the normal fracture to the shear fracture.