Fracture toughness and work of fracture of SiC-fibre reinforced glass matrix composites: Assessment by means of the chevron-notch technique

The applicability of the chevron-notch flexural technique to determine the fracture toughness and work of fracture of fiber reinforced glass matrix co mposites was investigated. Borosilicate glass matrix composites containing SiC-Nicalon fiber reinforcement were considered in the as-received conditio n and after thermal aging. The thermal aging involved exposure of the sampl es to temperatures in the range 500-700 degrees C for up to 1000 hours in A rgon. To detect the onset of unstable microcracking during the chevron-notc h experiments, an acoustic emission technique was used. Except for the most severe conditions investigated (600 degrees C, 1000 hours and 700 degrees C, 100 hours), the values of the fracture toughness did not change signific antly, and they were in the range 19-26 MPa m(1/2), in agreement with liter ature results. The possible degradation mechanisms which may be activated d uring high-temperature aging are discussed.