Dynamic and transient characterization of silicon carbide fibers at elevated temperatures

摘要

Ceramic fibers at elevated temperatures exhibit time or frequency dependent mechanical behavior, the most studied of which is creep. Several techniques for characterizing time dependent mechanical properties have been developed in this laboratory. Fibers studied to date include single crystal alumina, YAG, and seven compositions of SiC. Dynamic mechanical spectroscopy methods are used to examine short relaxation time processes associated with periodic deformation phenomena, and provide both dynamic modulus and loss factor versus temperature (to 1600 deg C) and frequency (from 0.1 to 25 Hz). Pulsed periodic creep and recovery tests are used to examine the longer relaxation time phenomena, and provide an accelerated means to identify and separate anelastic and inelastic creep rates. Taken together these methods provide a comprehensive understanding of the multiplicity of mechanisms and time scales that are relevant to the proper application and design of ceramic fiber reinforced composites.