High resolution mapping of thermal contact resistance using lock-in thermography

Abstract

This paper proposes a new thermal contact resistance distribution measurement method using a lock-in thermography. To evaluate two-dimensional local thermal contact resistance distribution, a uniform intensity laser heating system was developed, which has top-hat intensity distribution with a diameter of 30 mm. By combining this heat source and the lockin thermography, a new measurement instrument was developed, which can evaluate local temperature behavior in the frequency domain affected by the contact interface in high spatial resolution of about 70 micrometers. Additionally, a new thermal contact resistance measurement principle was constructed based on one-dimensional heat transfer equation in consideration of the reflected and transmitted temperature wave at the boundary and contact interface. The thermal contact resistance was acquired as a solution of the inverse problem of the temperature response by fitting analyses. The validation of this method was evaluated with a sample made of bonded two isotropic graphite plates. The sample has intentional defect area which has slightly higher thermal resistance. As the results, the validity of the measurement method was confirmed in comparison with the other validated method. Also, the defect area was quantitatively detected clearly as high thermal resistance region. Furthermore, the measurement method was applied for two different contact interface roughness sample consisting of aluminum alloys and thermal grease as a practical example. Consequently, it was revealed and visualized that the contact interface with rough surface has high thermal resistance spot.