Microcracking and Toughness of Ceramic-Fiber/Ceramic-Matrix Composites under High Temperature.

摘要

This report contains the results of the research project entitled: 'Microcracking and Toughness of Ceramic-Fiber/Ceramic-Matrix Composites Under High Temperature.' Microcracking mechanisms and toughness of Nicalon (Silicon carbide)/Silicon carbide composite at elevated temperature are studied analytically and experimentally. First the fiber distribution patterns in the ceramic composite are determined by observing the specimens under optical and scanning electron microscopes. Thus the effect of fibers and fiber interactions on the microcrack propagation are investigated analytically through the single-fiber, the two-fiber, and the ring models. Monolithic SiC specimens are tested under varying temperature to determine the effect of temperature on the toughness of the matrix material. The Nicalon/SiC composite specimens are then tested at various temperatures. The combined effect of temperature and fibers on the toughness of the matrix is expressed by introducing the concept of 'apparent fracture toughness.' The experimental results indicate that for the Nicalon/SiC composite the 'apparent fracture toughness' decreases with local volume fraction of fibers Volume fraction and temperature. Keywords: Composites; Ceramic; Fracture; High temperature; Microcracking; Materials; Fibers. (JG)