Fatigue crack propagation in aluminium alloy foams

The mode I fatigue crack propagation (FCP) response of the closed-cell alum inium alloy foams Alulight and Alporas have been measured for a relative de nsity in the range 0.1 to 0.4. The validity of linear elastic fracture mech anics (LEFM) to characterise the fatigue crack propagation (FCP) response i s demonstrated, and K-increasing and K-decreasing tests are used to determi ne 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 A lulight 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 suggest ed that the fatigue crack growth rate is controlled by the progressive degr adation of crack bridging by fatigue failure of the cell edges behind the c rack tip. (C) 2001 Elsevier Science Ltd. All rights reserved.