Study on Cold Expansion Technology of Adjacent Hole ForceMate Bushings in TC4 Titanium Alloy

Abstract In aircraft, parts often have too closely spaced holes. Stress concentration around these holes can lead to crack initiation at the hole edges. Cold expansion technology can enhance the circumferential residual compressive stress around the hole edges, thereby improving the fatigue life of the part. However, current research on cold expansion of adjacent holes is limited, particularly for cases where two holes are expanded in the same direction. In this study, finite element simulation was used to simulate the cold expansion process of ForceMate bushings in TC4 titanium alloy lugs. The effects of hole spacing, interference level, and expansion direction on the residual stress distribution between the holes were investigated. The results show that expanding the two holes in opposite directions is more beneficial for the first expanded hole. When the hole spacing is greater than 3 times the hole diameter, the effect of cold expansion of adjacent holes on the residual stress distribution between the holes can be neglected.