Thermal stresses arise in compositematerials because of the difference in the thermalexpansion coefficient (α) of the reinforcementand that of the matrix. In metal metal matrixcomposites (MMCs), the matrix generally has ahigher α than the reinforcement (fiber orparticle). The magnitude of thermal stresses in ametal matrix can easily exceed its yield stresswhen the composite is heated or cooled. In thispaper we shall present results of thermal fatiguestudies in some fiber reinforced metal matrixcomposites, including microstructural changesresulting from thermal cycling and techniques forevaluating thermal fatigue damage. In particular,we have shown that changes in stiffness anddensity can be used as damage parameters to studydamage evolution as a function of thermal cyclesin an alumina fiber/magnesium alloy composite.
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