Crack growth behavior of 7075-T6 under biaxial tension-tension fatigue

Crack growth behavior of aluminum alloy 7075-T6 was investigated under in-plane biaxial tension-tension fatigue with stress ratio of 0.5. Two biaxiality ratios, lambda 2 (=1 and 1.5) were used. Cruciform specimens with a center hole, having a notch at 45 degrees to the specimen's arms, were tested in a biaxial fatigue test machine. Crack initiated and propagated coplanar with the notch for lambda = 1 in L-T orientation, while it was non-coplanar for lambda = 1.5 between L-T and T-L orientations. Uniaxial fatigue crack growth tests in L-T and T-L orientations were also conducted. Crack growth rate in region II was practically the same for biaxial fatigue with lambda = 1 in L-T orientation and for the uniaxial fatigue in L-T or T-L orientations, while it was faster for biaxial fatigue with lambda = 1.5 at a given crack driving force. However, fatigue damage mechanisms were quite different in each case. In region I, crack driving force at a given crack growth rate was smallest for biaxial fatigue with lambda = 1.5 and for uniaxial fatigue in T-L orientation, followed by biaxial fatigue with lambda = 1 and uniaxial fatigue in L-T orientation in ascending order at a given crack growth rate. Published by Elsevier Ltd.