The effect of inclusions in brittle material

Abstract

This thesis experimentally investigates the cracking behavior of brittle heterogeneous materials. Unconfined, uniaxial compression tests are conducted on prismatic gypsum specimens containing either one, or two, inclusions. These inclusions are of different strengths, stiffnesses, shapes, and sizes. Real-time video and high speed video (HSV) systems are used to capture the sequence of cracking events, such as initiation and propagation. The coalescence processes associated with the specimens containing an inclusion pair was also studied. In addition to examining the effects of shape, strength, and stiffness for an inclusion pair, the effect of the inclusion inclination angle on coalescence is also investigated. Some observations reported in this study compare well with those of other researchers, while other observations are quite different. In general, the overall cracking sequences are similar to those reported previously; on the other hand, the amount of debonding observed at the inclusion interface is significantly less. Moreover, the extent of shear crack growth at an inclusion boundary increased substantially in specimens containing two inclusions, compared to those with single inclusions. The coalescence patterns associated with specimens containing an inclusion pair is also compared to past work done by the MIT rock mechanics group on specimens containing double flaws. These results are found to be remarkably similar. In addition to studying cracking behavior, the goal of this study is to provide a database for future work in formulating predictive models on the behavior of materials with inclusions.