A Gradient Cold Expansion Fatigue Strengthening Method of Titanium Alloy Open Hole Structures

ABSTRACT In this study, a gradient cold expansion (GCE) method was developed to enhance the fatigue life of open hole structures. The fatigue performance strengthening mechanism of the GCE method was investigated by theoretical modeling, numerical simulation, and experiment, respectively. The resistance force, hole diameter, bulge, residual stress, and tensile performance were all characterized. Moreover, the fatigue life of specimens after GCE and direct cold expansion (DCE) was assessed, and the fatigue failure mechanism was discussed. Results showed that the GCE method can reduce resistance force and generate a more uniform hole diameter and residual stress distribution along the hole axial direction. The tensile performance of GCE specimens was also better than those of DCE specimens. Specimens also exhibited longer fatigue life treated by GCE, which exhibited significant effects on fatigue crack initiation and growth of specimens.