A new generation of relatively 'ductile' CMCs is being developed that expands the general utility of structural ceramic composites. These new materials rely on inelastic mechanisms such as interface failure, matrix cracking, fiber failure and fiber pullout to redistribute stress away from locations of stress concentration. The combined effect of these mechanisms can be summarized in three macroscopic damage classifications: Class I damage is the development of a single matrix crack bridged by fibers; Class II damage involves the development of multiple cracks in the matrix; and Class III damage involves the development of a shear damage zone. The operative damage mechanism depends upon the composite constituent properties, while the extent of stress redistribution depends upon the damage mechanism. Recent experiments have identified these damage mechanisms and have also quantified the effect of stress redistribution.
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