Fatigue crack propagation in aluminium alloy foams

The mode I fatigue crack propagation (FCP) response of the closed-cell aluminium alloy foams Alulight and Alporas have been measured for a relative density in the range 0.1 to 0.4. The validity of linear elastic fracture mechanics (LEFM) to characterise the fatigue crack propagation (FCP) response is demonstrated, and K-increasing and K-decreasing tests are used to determine the full shape of the FCP response. The classical sigmoidal variation of log da/dN with log DeltaK is evident, with a paris-law exponent m=20 for Alulight and m=25 for Alporas. The effects of relative density, mean stress and a single peak overload on the FCP response are investigated. The study concludes by analysing the mechanism of fatigue crack growth; it is suggested that the fatigue crack growth rate is controlled by the progressive degradation of crack bridging by fatigue failure of the cell edges behind the crack tip. (C) 2001 Elsevier Science Ltd. All rights reserved.