Approximate Theory of Thermal Stress Resistance of Brittle Ceramics Involving Creep

The effect of stress relaxation by creep on the thermal stress fracture of brittle ceramics at high temperature under conditions of quasi‐static heat flow is discussed. It is shown that, to a good approximation, thermal stress relaxation rates can be calculated on the basis of creep rates which correspond to the minimum temperature of the ceramic workpiece. For materials exhibiting linear stress‐creep rate dependence, expressions for the relaxation time and maximum temperature difference or heat flux to which ceramic bodies can be subjected are derived in terms of the material variables affecting thermal stress fracture and stress relaxation by creep. A numerical example shows that high‐temperature creep can materially affect the thermal stress behavior of brittle ceramics. Appropriate thermal stress parameters are proposed to form the basis of proper material selection for high‐temperature environments involving thermal stress and stress relaxation by creep. Conditions for which thermal stress calculations should be based on an elastic or viscoelastic analysis are outlined.