On the crack growth behavior under simple compressive loads of 2024-T3 aluminium alloy

Abstract

In real life, many engineering components and structures are subjected to complex variable load conditions. Sudden changes in loading are known to significantly influence the fatigue behaviour of materials. However, simplified, constant amplitude data are usually altered in different ways and subsequently used in order to predict the variable amplitude fatigue. This practice is known to have its limitations when precision of predictions is concerned. Obviously, there is a great need for an increase in understanding of variable amplitude fatigue, re-evaluation of existing models and development of useful concepts for engineering practice. The results and observations obtained from the investigation of the crack growth behaviour of AA2024-T3 aluminium alloy are outlined in this paper. Specifically, the crack growth lives of samples loaded under simplified variable conditions containing constant amplitude and varying underload cycles are presented. The crack growth lives were shown to be very dependent on the underload magnitude (stress ratio) and on their occurrence (grouping) in the load sequence. Fractographic investigations show that crack growth lives affected by crack extension initiated by applied underloads rather than by crack propagation initiated by constant amplitude loading. Experimental observations on crack path changes and plastic deformation (related to crack wake closure) induced by selective variable amplitude loading is also presented and discussed with respect to crack growth life. © Springer Science+Business Media B.V. 2009.