Microcracking behavior of particulate titanium diboride-silicon carbide composites and its influence on elastic properties

This study examines the microcracking behavior of particulate titanium diboride-silicon carbide composites, which tend to form microcracks at the particulate/matrix interface as a result of thermal expansion mismatch. The objectives of this investigation are to examine the second phase characteristics that affect the formation of microcracks and to quantify the influence of interfacial microcracks on composite properties.;The thermoelastic properties of two sources of composites studied were characterized at temperatures up to 1500;Residual stress calculations of this composite system emphasized the influence of crystal anisotropy and orientation. In particular, the possibility of preferential microcracking at a specific relative orientation between grains was studied. A bi-crystal model was proposed in order to examine the residual stress state at all possible relative orientations. The results showed that this system does not have strong dependence on crystal anisotropy and relative orientation, and therefore, preferential microcracking is likely to occur.;Models were established to quantify the influence of crack size and microcrack density on the elastic properties of a composite using a combination of theoretical and numerical techniques. Based on energy principles, the influence of a dilute concentration of interfacial microcracks was first studied. The case of finite concentration of microcracks was solved subsequently by combining the dilute concentration solutions and the differential scheme. The results of these models, for the first time, successfully predicted the effective elastic properties as functions of both crack size and microcrack density (titanium diboride debonded fraction).