Measurement and characterization of interfacial strain energy release rate of Si3N4/BN composites by four-point bending test

A new method was developed to measure the interfacial strain energy release rate of Si3N4/BN composites. A kind of sandwich material with a single interlayer was designed and prepared by using tape casting and hot press processing. The source of crack directly connecting the interface was preset on one of the Si3N4 matrices. The load-displacement curves were obtained by the four-point bending test and the interfacial toughness was calculated on the basis of the fracture model of laminated composites. The interfacial toughness of Si3N4/BN composites modified with Si3N4 and the interfacial toughness of Al2O3/BN composites modified with Al2O3 were measured and characterized respectively. The strain energy release rate of pure BN is 37.16 J/m2. For BN interphases modified by Si3N4 with the volume fraction of 15% and 25%, the strain energy release rates are 90.58 J/m2 and 117.76 J/m2 respectively. For BN interphases modified by Al2N3 with the volume fraction of 16%, 36% and 63%, the corresponding critical strain energy release rates are 53.95 J/m2, 71.86 J/m2 and 119.21 J/m2 respectively. The advantages and disadvantages of the new method in comparison with other methods are discussed.