Dynamic Observation of Fracture Process in Laminated Ceramic Matrix Composites

Laminated ceramic composite is a new type of material developed in recent years to improve the mechanical properties of structural ceramics. Gel casting and hot-pressure sintering technologies were used to obtain the laminated SiC/BN-Al2O3 composite. Mechanical properties of the laminated composite and monolithic SiC ceramic were compared, and the fracture toughness of the laminated composite is nearly one times higher than that of the monolithic ceramic. Dynamic process of crack propagation in laminated composite was observed in situ by SEM. The interfacial crack initiate first in interlayer near to the notch tip, and then the through layer crack formed in matrix layer at the notch tip. After the through layer crack grows across the first matrix layer, it can be deflected by the interlayer and becomes an interfacial crack again. The through layer crack and the interfacial crack are generated alternately until the failure of the composite. The load / displacement plot of laminated material possess several peaks, and each peak is caused by one propagation of the through layer crack. Toughening mechanisms of the laminated composite include crack deflection, interfacial crack, through layer branch crack and parallel main crack.

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