The effects of environment and load frequency on the crack propagation law for macro fatigue crack growth in aluminium alloys

Abstract Data are presented for fatigue crack propagation of two aluminium alloys (2024-T3 Alclad-7075-T6 clad) in different environments and for several loading frequencies. Correlation of the data was attempted by the stress-intensity factor by application of the equation for crack growth proposed by Forman. The result was that the influence of the stress ratio on the crack growth was predicted by the equation in agreement with the test results but that the effects of the environment and the load frequency could not be coped with by changes in the constants of the equation. There may be a threshold level of the stress-intensity factor, strongly dependent on the environment and the alloy, in order to make the crack grow.