INFLUENCE OF THE INTERFACE AND FIBER SPACING ON THE FRACTURE-BEHAVIOR OF GLASS MATRIX COMPOSITES

In this work, a nondestructive methodology is provided to determine the presence of microcracking in unidirectional SiC fiber reinforced brittle (borosilicate glass) matrix composites and to detect internal cracks in the composites that did not reach the surface of the specimen. The methodology is based on a combination of several ultrasonic techniques including shear back reflectivity (SBR), back-reflected surface wave imaging and acoustic microscopy. The composites used in this study were made with controlled fiber spacing consisting of regular arrays of either TiB2 coated SIGMA 1240 or carbon coated SCS-6 monofilament fibers in a series of borosilicate glasses. The combinations of different constituents provided composite samples with various fiber matrix interface properties. The composites were subjected to axial loading, and the stress in the composite when matrix cracking first occurs was determined and compared with theoretical values provided by a semi-empirical model which can assume either a completely bonded (i. e. perfect) or completely unbonded (i. e. pure slip) fibre-matrix interface. Results from the tensile data for different glass matrix composite systems were also compared with data of interface elastic property evaluation using ultrasonic SEX technique, allowing investigation of the influence of the fiber-matrix interface elastic property, the volume fraction of the fibers, and the state of radial residual stresses at the interface, on the fracture behavior of glass matrix composites.