TEST RESEARCH ON FATIGUE LIFE ENHANCING EFFECT OF COLD-EXPANDING HOLE

Experimental research has been carried out to study the fatigue life enhancing effect of direct mandrel cold-expansion and split sleeve cold-expansion processes,and effect of the stress level.Adopting the widely used aluminum and titanium alloys in aircraft structure three kinds of specimens were designed,i.e.,the surfaces of the specimen's holes were of 3 different conditions including non-expanded(NE),direct mandrel cold-expanded(DMCE) and split sleeve cold-expanded(SSCE).The crack initiation,crack propagation and total lives of the specimen were obtained through constant amplitude fatigue test.Through comparing and statistic analyzing the entire test data,the difference in fatigue life enhancing effect between the direct mandrel and split sleeve cold-expanding processes was revealed,the effect of stress level on the life enhancing was also presented.And the life enhancing ratios in crack initiation and crack propagation stages were discussed.