Factors Affecting Thermal Shock Resistance Of Polyphase Ceramic Bodies

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Report Number: WADD TR 60-749 Part II
Author(s): Shaffer, P. T. B., Hasselman, D. P. H.
Corporate Author(s): The Carborundum Company, Research and Development Division, Niagara Falls, N.Y.
Laboratory: Directorate of Materials and Processes
Date of Publication: 1962-04
Pages: 167
Contract: AF 33(616)-6806
DoD Project: 7350
DoD Task: 73500
Identifier: AD0277605

An investigation of the material properties which affect the thermal shock resistance of polyphase ceramic systems composed of a high Young's modulus continuous phase containing a low Young's modulus dispersed phase has been conducted using the model system zirconium carbide-graphite. The principal effect of the dispersed phase of graphite on the thermal shock resistance of the zirconium carbide is to reduce the degree of damage resulting from fracture by thermal shock. The presence of the graphite also causes a decrease in strength and Young's modulus of elasticity in such a manner as to decrease the elastic energy stored at fracture and at higher volume fractions graphite to increase the extensibility (i.e., strain at fracture). Suitable thermal shock damage resistance factors were derived. The coefficient of thermal expansion and Poisson's ratio to a first approximation were independent of graphite content. Due to the relative differences in thermal properties the graphite causes an increase in thermal conductivity, thermal diffusivity and emissivity. Porosity was found to be a major variable. Emissivity (absorptivity) was introduced as a variable affecting thermal shock resistance of ceramic materials. A quantitative theory of thermal shock by radiation was developed. Excellent agreement with experiment was show. Calculations were carried out of the transient temperatures and thermal stresses in a sphere subjected to thermal shock in a medium with constant surface heat transfer coefficient It was found that at the time of maximum stress the sphere is still close to its initial temperature. Using, these results thermal shock data in the literature were recalculated. Good agreement with experiment was shown.

Provenance: IIT

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