Analysis of thermal fatigue behaviour of brittle structural materials

Abstract

The effect of the level of maximum temperature (Tmax), the temperature range (ΔT) and the mode of convective heat transfer on the thermal fatigue resistance of brittle structural materials is analysed. Expressions are derived for the number of thermal cycles to failure in terms of the appropriate mechanical and thermal properties, crack growth parameter, ΔT andTmax. For simultaneous changes inTmax and ΔT commonly used in practice, the change in thermal fatigue life is governed by both the thermal stress intensity exponent (n) and the activation energy (Q) for subcritical crack growth, in contrast to the results of other studies. For constantTmax but variable ΔT, thermal fatigue life is affected byn only, whereas, for constant ΔT but variableTmax, the value ofQ alone governs changes in fatigue-life. Heat transfer by natural or forced convection will result in differences in thermal fatigue resistance. Recommendations are made for the design and analysis of thermal fatigue experiments. Figures-of-merit for the selection of materials with high thermal fatigue resistance are presented.