The application of thermal emission analysis to damage assessment and material characterisation

Thermal emission is the phenomenon of heat dissipation in crystalline materials undergoing deformation. Analysis of the thermal emission from materials subject to strain in the form of mechanical tests is possible by measuring the specimen temperature locally with high resolution temperature sensors. The mechanism of heat dissipation depends intrinsically on a material's mechanical properties and stress history. It is shown that analysis of the thermal emission response to deformation can quantify these properties and provide evidence of microstructural damage. A number of different materials have been studied, including steels, aluminium and nickel alloys, and a carbon/epoxy composite. Simple stress regimes were imposed on the specimens, e.g. creep, fatigue and impact damage, and their thermal emission characteristics were analysed during a following tensile test. It was found that the thermoelastic response of the materials was in some cases sensitive to the level of pre-stressing or damage. In addition information was often contained in the thermal emission responses which was not present or unclear in the stress and strain data. It is concluded that deformation mechanisms cannot be fully understood unless the complete thermomechanical process is examined, involving the measurement of temperature as well as the usual stress and strain. It is envisaged that thermal emission could be developed into a tool for non-destructive damage assessment operating as a complement for established techniques.