Residual stress measurement by means of the thermoelastic effect

Abstract

The term thermoelastic effect refers to the coupling between mechanical deformation and the change in thermal energy of an elastic material. The first theoretical treatment of this phenomenon is attributed to Lord Kelvin¹, and the resulting law states that the rate of change in temperature of a dynamically loaded body is directly related to the rate of change of the principal stress sum under adiabatic conditions. Although Kelvin's law has been well known for over a century, it is only in the past ten years that the thermoelastic effect has been exploited as a means for dynamic stress analysis. A system known as SPATE (stress pattern analysis by measurement of thermal emission) has been developed which can detect changes in infrared emission due to minute changes in the temperature of a dynamically stressed material. Recently it was discovered that the SPATE response or, more generally, the thermal response of a cyclically loaded body is not only a function of the dynamic part of the stress, but also of the static component². This finding has led to the suggestion that residual stresses within a material might be detected using this phenomenon, and here we present the first demonstration of such a means of residual stress measurement.