Abstract: A definition of central crack damaged zone (CCDZ) is introduced based on tension experiments of Ceramic Matrix Composites (CMCs). The width of the CCDZ is defined to equal the debond length and the effect of interface toughness is neglected. When the CMCs rupture, the stress carried by the fibers can be estimated by the mean fiber stress within the CCDZ. Furthermore, the rule of mixtures is modified. Considering that the interface properties control the fracture mode, two kinds of models are presented respectively for brittle and ductile fracture strength. The stress concentration factor and interface debond energy release rate are introduced and discussed. It indicates that both the above factors result in decline of the tensile strength as they increase. The predictions of the given formulae are in good agreement with experimental data.

Key words: interface properties, ceramic matrix composites, stress concentration, energy release rate, tensile strength