THERMAL RESIDUAL STRAINS AND STRESSES IN SILICON CARBIDE-FIBER-REINFORCED SILICON-NITRIDE COMPOSITES

Neutron diffraction was used to measure thermal residual strains in Si C-fiber-reinforced reaction-bonded silicon nitride composites as a fun ction of volume fraction of fibers. The measured values are in agreeme nt with those estimated by finite-element modeling. Due to the anisotr opy of the thermal expansion coefficient of SiC, residual axial strain (stress) is tensile and residual transverse strain (stress) is compre ssive in the fibers. The variation in the measured residual axial stra in in the matrix can be related to the density of the composite. In ad dition, neutron diffraction was used to study the effects of fiber coa tings and processing on the thermal residual strains.