Toughening by continuous single fiber bridging in ceramic matrix composite

The crack bridging process of fiber-reinforced ceramic matrix composites has been studied using a model composite consisting of CVD-SiC fiber and borosilicate glass matrix. The crack growth resistance curve (R curve) of the model composite under a single fiber bridging condition was obtained. The crack bridging process, which governs the R curve behavior, was also observed in situ using a crosspolarized transmission photoelastic technique. Analysis of the toughening process showed them to be: (i) matrix crack bowing before the crack front approaches the fiber, (ii) fiber bridging with the interfacial sliding after the crack front has completely passed the fiber. The increase of the measured stress intensity factor was explained by a crack bowing model and fiber point bridging model that included the effect of a finite specimen size. The most efficient mechanism for the toughening was fiber bridging. The contribution of different toughening mechanism on the R curve of fiber-reinforced ceramics was discussed.