Effect of Micro-Cracking on Thermal Conductivity: Analysis and Experiment
High densities of micro-cracks can have a profound effect on the conduction of heat through materials. An analysis of this effect on thermal conductivity is presented. The variables which affect the formation of micro-cracks in brittle materials due to thermal expansion mismatches are discussed. It is shown that micro-cracking results in a “thermo-mechanically” coupled thermal conductivity which is a function of elastic properties, the coefficient of thermal expansion, fracture toughness, microstructural variables such as grain size, as well as the closure and healing of cracks at higher temperatures These effects are demonstrated by experimental data for the temperature dependence of the thermal diffusivity of polycrystalline iron titanate, magnesium dititanate, composites of alumina with silicon carbide, and a glass containing a dispersed phase of nickel.
KeywordsThermal Conductivity Thermal Diffusivity Brittle Material Crack Closure Thermal Expansion Mismatch
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