Extended slip band mixed-mode fatigue crack growth in an AA8090 Al-Li alloy

摘要

The complexities of crack growth processes have been examined for various combinations of mode I and mode II loading of long cracks in the Al-Li alloy AA8090, for which shear crack growth processes can be dominant. An equivalent co-planar strain energy release rate formulation of crack driving force for mixed mode loading has been utilised, which, for a given R-ratio, provides a consistent interpretation of crack growth with respect to pure mode II loading; and also for the different R-ratios of 0.1 and 0.5, with the latter showing a factor of 10 increase in growth rates. The paper concludes by discussing shielding mechanisms, with contact shielding having only a limited influence when compared to previously reported mixed mode fatigue work. This is consistent with the unusually flat crack paths produced under mixed mode loading conditions in such strongly textured materials. The applicability of established sliding contact modelling approaches is discussed with respect to the present data.