Fatigue of ceramic matrix composites: Damage mechanisms and fatigue life diagrams
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abstract
Ceramic matrix composites (CMCs) provide higher strength and toughness properties than are possible from monolithic ceramics, in addition to the high temperature resistance. The mechanisms of toughness of these materials have been treated extensively, although some confusion exists in characterizing this property, which has been recently addressed in a systematic manner (Sorensen and Talreja 1995). It is, however, of greater importance in most engineering applications that the long term behavior of CMCs remains in a safe regime. In particular, degradation of stiffness and strength under cyclic loading is a major concern. In contrast to monolithic materials, such as metals, the progression of fatigue in composites is governed by a multitude of mechanisms. The sequential or concurrent progression of the mechanisms, their driving forces and obstacles, and the modes of criticality render the study of fatigue in composites a challenging endeavor. It can be readily recognized that a conventional plotting of S-N curves would at best lead to qualitative assessment of relative goodness of given composite systems. Unless a proper understanding of the roles of the underlying mechanisms is generated, no real advance in modeling for life prediction can be expected. The fatigue behavior of polymer matrix composites (PMCs) has been studied extensively for over two decades. To facilitate interpretation of the underlying damage mechanisms and to guide the modeling efforts for fatigue in PMCs a conceptual framework called fatigue life diagrams was proposed by this author (Talreja 1981). Later, further considerations were made to use this framework for metal matrix composites (Talreja 1995).
