Numerical study of double cold expansion of the hole at crack tip and the influence on the residual stresses field

Hole cold expansion (HCE) is an effective method to prolong the fatigue life of mechanical structures because it introduces residual compressive tangential stresses around the expanded hole. In the present work, experimental and numerical studies have been carried out in order to analyse the effect of the application of both single and double HCE procedures, on the subsequent fatigue life of 6082-T6 aluminium alloy. In the double HCE experiments, the second expansion was conducted both in the same direction (SESD) and in the opposite direction (SEOD) of the first expansion, employing a rigid ball of a diameter slightly larger than that used in the first expansion. The distribution of the residual tangential stresses resulting from the double expansion procedure is compared with that obtained after the application of a single expansion. The results obtained indicate that the SEOD method can give rise to an improvement in the fatigue life of the material.