Abstract: The results of research of the effects of combined process of hole cold expansion with interference-fit strengthening on improving fatigue life of TC-4(Ti-6Al-4v) titaninum alloy when bush is not used are presented. The experiment demonstrates that under the experimental conditions of this investigation the fatigue life improvement factor (LIf) is 13 for cold expanded TC-4 titaninum alloy's sheet coupon, and is 3 for interference-fit bolted joint. The fatigue life of cold expansion with interference-fit coupon is double of the value of interference-fit coupon. The results of analyzing fatigue fracture by electron metalloscope show that the initiation and growth of the crack on strengthened TC-4 titaninum alloy hole is similar to LY12-CZ aluminium alloy and 30CrMnSiA alloy steel, none of them shows typical corner-crack feature, i. e. there is an evident difference between the crack growth rates along sheet surface and the direction of thickness. Bushing cold expansion is more superior to cold expansion without bush on improving the fatigue property of TC-4 alloy.

Key words: hole cold eYransion, interference-fit strenrithcning, fatigue life