Role of Microstructural Damage in the Thermal Diffusivity of Fiber- Reinforced Ceramic-Matrix Composites

摘要

A phase-sensitive photothermal technique for the determination of the thermal diffusivity of solids and the thermal, conductance of cracks and interfaces has been developed. The technique has been validated using a model systems comprising stainless steel disks, placed either in direct contact with each other or with thin polyethylene sheets between them. The corresponding heat flow analysis has also been developed. The technique has been used to study in detail the thermal conductance of delamination cracks in a unidirectionally reinforced ceramic composite, with measurements being made in situ under load. Special emphasis has been placed on the effects of the local crack opening displacement and fiber bridging. A model for the crack conductance that takes into account the contributions from both the air and the bridging fibers within the crack has been developed and validated by comparison with the measurements. Complementary studies have been performed of the effects of multiple matrix cracks on the in plane diffusivity of two unidirectional CMCs, with measurements being made in situ under uniaxial tensile loading. The effects of the cracks have been rationalized on the basis of a model that incorporates the matrix crack density, the crack opening displacement, and the Biot number associated with heat flow through the bridging fibers.