R.J.H. Wanhill
Published: 2013-09-20
Total Pages: 40
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Most aluminium-lithium (Al–Li) alloy fatigue crack growth (FCG) data have been obtained for 2nd generation alloys, specifically under constant amplitude (CA) and constant stress ratio (CR) loading, and for long/large cracks. These data show the alloys in a favourable light, but this FCG ‘advantage’ essentially disappears under realistic flight simulation loading, and is also absent for short/small cracks. Furthermore, the FCG advantage is due to inhomogeneous plastic deformation, which has undesirable consequences for other important properties. These consequences have greatly restricted the use of 2nd generation alloys in aerospace structures. FCG data for 3rd generation Al–Li alloys are becoming more available. Many of the issues associated with 2nd generation alloys have been eliminated or greatly alleviated as a result of several changes, including reduced Li contents and innovative thermomechanical processing. Consequently, the FCG behaviour of 3rd generation alloys is more similar to that of conventional alloys. Nevertheless, the 3rd generation alloys tend to have better FCG properties than equivalent conventional alloys; and these and other improvements have already led to many aircraft applications.
