The influence of mean stress and thickness on the fatigue crack growth behaviour of the aluminium alloy BS2L71

Abstract

A series of fatigue crack growth tests have been conducted on sheet specimens of thicknesses 3, 6, 16 and 22 mm. These tests have been under both random and constant amplitude loading for a number of different mean stress levels. The results from these tests have shown that the resistance to fatigue crack growth increases as the thickness increases at low growth rates. In contrast, at high growth rates this behaviour is reversed. Both random and constant amplitude data showed this feature. Crack-closure measurements have been used in an attempt to explain these differences in behaviour for high and low growth rates. The random and constant amplitude test results have been correlated successfully for square-mode growth, using a ‘weighted’ average range approach.