Investigation on Residual Stress and Fatigue Properties of the Cold Hole Expansion Process in Titanium Alloy TC21 Plates

Abstract:

The perforated parts of damage tolerant titanium alloy TC21 in rear fuselage frame were easy to prematurely suffer fatigue crack in the service process. With the purpose of resolving the problem mentioned above, different expansion degrees were applied to the hole of plate specimens of TC21 in the split sleeve cold expansion experiment。The effect of expansion degree to fatigue life was achieved in the fatigue tests. By the method of 3D finite element simulation, the distribution regularity of residual stress was obtained around the hole after cold expansion. The surface feature of fatigue fracture has been observed and analyzed from macroscopic aspect and microscopic aspect with different expansion degree. The examination of fractured sections show that cold expansion can change fatigue crack initiation position around the hole surface, and extend the fatigue crack propagation life under cyclic loading. It was further show that fatigue life increase as expansion degree, furthermore, the fatigue life is increased more than 50%.