The fatigue crack growth resistance was evaluated for several aluminum alloys, and the factors to influence it were examined. The results were compared with the opening and growth characteristics of an ideal crack.
The results obtained are as follows:
(1) The ratio of the striation spacing to the stretched zone width for the same J value is independent of material properties and becomes nearly constant. By using this value, it is possible to predict the effect of fatigue crack closure.
(2) The opening ratio, U, measured by ultrasonic technique is identical to that of the predicted value, although other conventional techniques have given higher values of U.
(3) The main fatigue crack growth controlling factor is the flow stress, σfs, except 7075-T6 alloy, or Young's modulus, E, except 2XXX alloys.
