Abstract
Tensile strength at temperatures between room temperature and 773K of the unidirectional Si-Ti-C-O fiber (Tyranno fiber) reinforced aluminum matrix composite produced by a squeeze casting method was investigated. The longitudinal strength decreased gradually with increasing temperature up to 673K, but then a rapid decrease was observed at the higher temperature. The transverse strength decreased larger than longitudinal one with increasing temperature. A drop of strength was observed at about 500 and also at 673K. In order to understand the temperature dependence of composite strength, temperature-dependence of matrix yield stress in the composite was deduced from thermal expansion curve. Using thus deduced matrix yield stress and temperature dependence of shear modulus of matrix taken from a literature, the stress concentration factor in the fibers adjacent to broken fibers and the critical length of broken fibers in the composite, which are representative strength-determining factors, were calculated for various temperatures by means of the shear lag analysis. The stress concentration factor decreased slightly, while the critical length increased much with increasing temperature. From the calculation, the decrease in longitudinal strength with increasing temperature could be attributed to the increase in critical length due to the softening of matrix. The reduction in transverse strength was caused directly by the softening of matrix.
