Experimental and numerical study on fillet rolling of a Ti6Al4V alloy aircraft bolt focusing on fatigue life

The fillet rolling process is experimentally and numerically studied to reveal the fatigue fracture at a Ti6Al4V alloy bolt's neck. The experiments show that the fatigue life remarkably increases after applying the fillet rolling to the critical bolt neck corner (CBNC). A practical full analysis model, based on an implicit elastoplastic finite element method (FEM), is presented to quantitatively explain the reason for the dramatic results of the fillet rolling. A finite element analysis of the fatigue test is also conducted. The accurate flow information obtained by the tensile test is employed, considerably influencing the finite element (FE)-predicted residual stresses. The validity of the analysis model is numerically verified. The FE predictions of the fillet rolling process show that the maximum effective plastic strain at the CBNC's center increases linearly with time. On the contrary, the maximum effective residual stress drastically increases in the early stroke, but the increasing rate becomes negligible afterward. The effect of the fillet rolling on the effective stresses during the fatigue test is quantitatively revealed.