Fatigue crack growth from plain and cold expanded holes in aluminium alloys

Fatigue crack growth in open holes in aluminium alloys 2024-T351 and 2650 was investigated. Tests were carried out using plates containing plain holes and cold expanded holes in aluminium. The tests explored the influence of the applied stress, the ratio of the minimum to the maximum applied stress, R, and crack closure. Longer fatigue lives of specimens with cold expanded holes were obtained provided that the applied load ratio was less than 0.7, and the maximum applied stress was less than 0.5 of the yield strength. The decrease in fatigue crack growth in cold-expanded specimens was related to higher crack opening stresses which is a consequence of the presence of compressive residual stresses arising from cold expansion. Fatigue crack growth rates were described as a function of an effective stress intensity factor, which was determined using measured crack opening stress. Measured crack opening stress was also compared with opening stress determined from fatigue crack growth rates.