The material-dependent variability of fatigue crack growth rates of aluminium alloys in the Paris regime

Abstract Constant amplitude fatigue crack growth rates of a number of heat-treatable thin-sheet wrought aluminium alloys are presented in terms of the Paris equation with the stress intensity factor range normalized by a characteristic value, in the present case 10 MPa m 1/2 . There is a considerable overall variability of the crack growth rates at any given value of Δ K . It turned out that there are two markedly different groups of alloys. For the first group, the crack growth curves strongly focus at 10 MPa m 1/2 , whereas the Paris exponents vary considerably and are related to a material parameter obtained by dimensional analysis. For the second group, the crack growth rates at 10 MPa m 1/2 are found to be always less and vary much more than for the first group. The observed behaviour is discussed indicating that for the first group plasticity-induced crack closure should mainly be responsible for the observed material dependence, whereas for the second group roughness-induced crack closure also plays an important role.