Fatigue crack growth and closure in fine-grained aluminium alloys

The effects of microstructure on fatigue crack growth rate and fracture mechanism have been examined for several relatively fine-grained/high dispersoid aluminium alloys. Particular attention has been paid to the behaviour of spraycast Al–Li alloys, as such materials may present novel property combinations for light weight structural aerospace applications, with extended conventional composition ranges. Fracture resistance has been assessed in terms of both intrinsic and extrinsic factors, including roughness induced closure (RICC). In these fine-grained/high dispersoid materials, high crack growth rates are typically seen in comparison to traditional DC cast alloys, consistent with low fracture surface roughness levels and correspondingly reduced levels of RICC. The competitive influence of shearable precipitates on crack roughness is however noted in a high-Li alloy variant. The effects of fracture surface roughness and closure levels on long crack fatigue crack growth rates have been compared with recent novel modelling of closure levels.