If you exercise mechanical sresses on components it will effect different changes of temperature. In the one hand you will recognise a thermal change by mechanical hysteresis and on the other hand a will create a thermal change by the thermoelastic effect.

This means a change in the state of stress makes an impact on the temperature of a component. Thermoelastic stress analysis uses this effect and grabs this change of heat by an ir-camera and analyses the values in the same way like LockIn-thermography.