The characterization and measurement of interfacial toughness for Si3N4/BN composites by the four-point bend test

The interfacial toughness of Si3N4/BN composites with different interphase compositions has been characterized. A single-inter-layer type of sandwich material Si3N4/BN/Si3N4, with one preset crack path connecting directly to the BN interphase in the center of one side of the Si3N4 matrix, was designed and fabricated. Sandwiched sample bars measuring 3 mmx4 mmx50 mm were cut and machined. The load-displacement curves for the samples were obtained using the four-point bend test, and the interfacial toughness was calculated, based on the model for a specimen with bimaterial interface. The interfacial toughness was measured for composites with interphases strengthened by Si3N4 or Al2O3 modifiers. The method was proved to be viable. The effectiveness of the method was further discussed and the reasons for its effectiveness explained. (C) 2003 Elsevier Ltd. All rights reserved.