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

Constant amplitude fatigue crack growth rates of a number of heat-treatable thin-sheet wrought aluminium alloys are presented in terms of the Paris eq uation with the stress intensity factor range normalized by a characteristi c 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 DeltaK. It tur ned out that there are two markedly different groups of alloys. For the fir st 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 paramet er 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 f or the first group plasticity-induced crack closure should mainly be respon sible for the observed material dependence, whereas for the second group ro ughness-induced crack closure also plays an important role. (C) 2001 Elsevi er Science Ltd. All rights reserved.