Nondestructive Evaluation of Early Contact Fatigue Using Eddy Current Pulsed Thermography

Cyclic loading can lead to fatigue damage on the surface or subsurface of a gear tooth. In order to evaluate the contact fatigue damage, this paper applies eddy current pulsed thermography (ECPT) for fatigue damage characterization at different intervals of the loading cycle. The challenging task of fatigue evaluation is one of solving the qualitative microstructure state characterization before microcrack initiation. This paper proposes the thermooptical flow entropy tracking method to trace the heat flow and characterize the degree of fatigue damage while in this status no macrodefects appears using ECPT. In addition, the thermooptical flow is mathematically modeled to yield several desirable unique properties to evaluate minor variations in the microstructure of the material during the fatigue process. The nondestructive evaluation of fatigue damage with ECPT thermooptical flow is derived. The relationship between the entropy of thermooptical flow and the degree of contact fatigue at an early stage is established. The experimental study validates that the proposed method can detect and characterize the implicit damage and that the entropy of thermooptical flow is highly correlated with fatigue cycles which has the potential to evaluate the degree of fatigue damage.