Fatigue behavior and life predictions of a particle-reinforced metal matrix composite at room and elevated temperatures

Experiments were performed to determine the monotonic, low cycle fatigue and fatigue crack growth behavior of a metal matrix composite, based on cast aluminum alloy A356 reinforced with 20 volume % SiC particles, at room temperature and 150{dollar}spcirc{dollar}C. Variable amplitude loading tests were also performed and the experimental fatigue lives were compared with calculations, based on the composite fatigue properties. A micromechanics composite material model was developed for the purposes of fatigue crack initiation life calculations.; The research has indicated that the composite strengths retained their values with increasing temperature much better than the unreinforced matrix, which gives a distinct advantage to the composite over the unreinforced matrix for high temperature applications. Also, the composite elastic modulus values were about 30% higher at both temperatures than the room temperature matrix value. Constant strain amplitude room temperature fatigue lives of the composite were shorter than the respective matrix values. The fatigue lives at high strain amplitudes were shorter at 150{dollar}spcirc{dollar}C than at room temperature, but the difference decreased with decreasing strain amplitude. Constant load amplitude fatigue crack growth rates were higher in the composite than in the matrix at room temperature by about an order of magnitude or less. Fatigue crack growth rates in the composite were similar at both temperatures. Variable amplitude loading fatigue crack initiation lives (formation of a 1.5 mm crack) accounted for more than 80% of the total lives at room temperature and more than 65% at 150{dollar}spcirc{dollar}C.; It was shown that reasonably reliable fatigue life calculations under variable amplitude loading at room temperature and 150{dollar}spcirc{dollar}C can be obtained for this composite material using common low cycle fatigue and fatigue crack growth approach, but with care. The empirical fatigue notch factor allows for better fatigue initiation life predictions at both room temperature and 150{dollar}spcirc{dollar}C, compared to the stress concentration factor. Reasonably conservative composite fatigue crack initiation life calculations can be obtained with the developed composite material model. The model applicability to other similar metal matrix composites needs to be verified through additional experiments.