Methodology for Modelling the Short Crack Fatigue Behaviour of Al-SiC MMCs

摘要

The objective of this study is to develop a computational modelling methodology for the fatigue crack growth behaviour of: (1) a forged 2124 Al reinforced with 17% SiC particles and (2) a cast 359 Al reinforced with 20% SiC particles. In particular, the focus of this work is on correlating local crack tip driving force conditions of an initial short crack with an experimental long crack growth rate curve, using crack closure. A defect tolerant approach is assumed. The crack tip is modelled using the finite element method, and the correlating parameter, ΔJ_(eff) (the effective range of the J-integral), is calculated. The material is assumed to be homogenous with the macroscale properties of the metal matrix composite, (MMC), for modelling purposes. An effective crack growth rate curve is calculated, and the ΔJ is used to obtain the crack growth increment per cycle. The method is repeated with the new crack size until the entire crack growth rate curve for the initial short crack is obtained. Crack growth rate curves for different stress levels and initial defect sizes are presented. Predicted S-N curves, obtained from the crack growth rate curves for a loading ratio of R=0.1, are compared with experimental results for each of the particulate reinforced MMCs. A good agreement with experimental results is obtained for an appropriate choice of defect size. Finally the method was validated by comparing the results on a Kitagawa diagram with those of the R-curve method, for the Al 2124 MMC.