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

In this work, a nondestructive methodology is provided to determine th e presence of microcracking in unidirectional SiC fiber reinforced bri ttle (borosilicate glass) matrix composites and to detect internal cra cks in the composites that did not reach the surface of the specimen. The methodology is based on a combination of several ultrasonic techni ques including shear back reflectivity (SBR), back-reflected surface w ave 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 f ibers in a series of borosilicate glasses. The combinations of differe nt constituents provided composite samples with various fiber matrix i nterface properties. The composites were subjected to axial loading, a nd the stress in the composite when matrix cracking first occurs was d etermined and compared with theoretical values provided by a semi-empi rical model which can assume either a completely bonded (i. e. perfect ) or completely unbonded (i. e. pure slip) fibre-matrix interface. Res ults from the tensile data for different glass matrix composite system s were also compared with data of interface elastic property evaluatio n using ultrasonic SEX technique, allowing investigation of the influe nce of the fiber-matrix interface elastic property, the volume fractio n of the fibers, and the state of radial residual stresses at the inte rface, on the fracture behavior of glass matrix composites.