Microscale mapping of thermal contact resistance using lock-in thermography

This paper proposes a new thermal contact resistance distribution measurement method using lock-in thermography. This method was used to evaluate a two-dimensional local thermal contact resistance distribution. To be able to measure the distribution, a uniform intensity laser heating system was developed. The developed system has a top-hat intensity distribution with a diameter of 30 mm. By combining this heat source and the lock-in thermography, a new measurement instrument was developed, which can evaluate local temperature behavior in the frequency domain, including the information of the contact interface in high spatial resolution of about 70 μm. Additionally, a new thermal contact resistance measurement principle was constructed based on a one-dimensional heat transfer equation that considers the reflected and transmitted temperature waves at the boundary and contact interface. The thermal contact resistance was acquired as a solution to the inverse problem of the temperature response done by fitting analyses. The validation of this method was performed quantitatively with two samples made of two bonded isotropic graphite plates. The one sample has an intentional defect area that has a slightly higher thermal resistance. The other sample has the known thermal contact resistance value measured with a validated method. Based on the results, the measurement value agreed with the referenced value. Also, the defect area was quantitatively detected clearly as a high thermal resistance region. Furthermore, as a practical example, the measurement method was applied for two different contact interface roughness samples consisting of aluminum alloys and thermal grease. Consequently, it was revealed and visualized that the contact interface with a rough surface has a high thermal resistance spot. •A new thermal contact resistance distribution measurement method was using lock-in thermography are proposed.•A new measurement device using a laser light source with a uniform intensity and lock-in thermograph is developed.•The differences in thermal contact resistance due to differences in surface roughness can be quantitatively visualized.