Based on the first law of thermodynamics

a theoretical model is developed in order to calculate the thermal energy dissipated per unit volume and per cycle

in which the cooling rate of the specimen is a parameter obtained from the test. According to the continuous noncontact measurement during the fatigue test of LY12CZ aluminum alloy by using infrared thermography

the surface temperature of material increases at the beginning of the test

then tends to a stationary value and rapidly increases till fracture finally. The surface temperature oscillates around the stationary value with small amplitude which increases with the increase of stress amplitude. The higher the stress amplitude applies

the higher the thermal energy dissipates per unit volume and per cycle.