The Effect of Hydrogen and Mean Stress on Variable Amplitude Fatigue Crack Growth in Aluminium

Mean stress and hydrogen accelerate the rate at which fatigue cracks grow. Understanding these mechanisms can lead to better predictions of the safe life of aircraft. Experiments here show that the normal explanation of the mean stress effect was incorrect. Atomic simulations demonstrate that the mechanisms involved change with different levels of mean stress. Hydrogen increases the rate of crack growth at high mean stress and reduces the rate of growth at lower mean stress because of the different mechanisms operating.