Predicting the Effects of Overloads on Fatigue Crack Growth in an Al-SiC MMC Using a Computational Model

Abstract

A defect tolerant approach to fatigue modeling for constant amplitude loading was developed by Bruzzi and McHugh (2002) and applied to two metal matrix composites: (1) a forged 2124 Al reinforced with 17 percent SiC particles and (2) a cast 359 Al reinforced with 20 percent SiC particles MMC in Bruzzi and McHugh (2003). In reality, however, engineering components are invariably subjected to varying cyclic stress amplitudes. In order to investigate the suitability of extending the fatigue modelling approach developed to variable amplitude loading, the effects of single and periodic peak tensile overloads are investigated in this work for the case of the Al 2124 MMC. The effects of overloads in causing significant changes to the level of closure in the wake of the crack tip, following the overload, in addition to changes in the nominally applied stress amplitude are firstly discussed in an overview. The quantification of the effects of overloads by use of experimental “resistance to crack growth curves” and the extension of the fatigue modeling approach to account for these effects are then described and investigated. Finally the predicted results of the impact of overloads on the short crack growth behavior of the Al 2124 MMC are presented and discussed. The extension of the fatigue modeling approach to account for the effects of overloads provides an additional means of validating the modelling approach developed by Bruzzi and McHugh (2002, 2003).