Thermoelasticity is based on temperature changes induced by expansion and compression of the test part. Although this coupling between mechanical deformation and thermal energy has been known for over a century, it has only been recently that this phenomenon has been exploited as a means of experimental stress analysis. The heat generated from the thermoelastic effect is small -- giving temperature excursions of 0.2 degrees Celcuis for mild steel just below its yielding point -- requiring thermoelastic stress analysis to be performed under a dynamic loading condition with synchronous averaging to increase the signal to noise ratio. Laboratory measurements are typically performed under time-harmonic loading of a sufficiently high frequency to maintain an effectively adiabatic state in the material. For practical thermoelastic measurements using infrared thermograph, the object under examination must also have a highly emissive surface. For objects with low emissivity, such as metallic surfaces, a coating must be added, such as flat black paint.
