Analysis of Thermal Diffusivity of Metals using Lock-in Thermography

The thermal diffusivity, , is determined for sheets of different metals by means of an approach based on lock-in thermography in combination with periodical laser heating. Different lock-in frequencies are used to obtain the frequencydependent phase behavior of thermal waves generated by laser pulses. A subsequent curve fitting provides the coefficients required to determine the thermal diffusivity. To evaluate the effect of ambient conditions, the measurements are also performed in vacuum. A comparison with literature data substantiates that lock-in infrared thermography is a promising approach for the determination of the thermal diffusivity. An accurate knowledge of thermal material properties is important for various technical applications. The thermal diffusivity, , is a complex material parameter which depends on the thermal conductivity, k, the specific heat capacity, cp, as well as the mass density, . The infrared (IR) lock-in thermography approach is based on the generation of thermal waves in the material under investigation. The thermal response is then recorded by an IR camera and is analyzed for the amplitude and phase information of the thermal waves. This work focuses on the analysis of the thermal diffusivity of different metal samples of various thicknesses under periodical heating by laser pulses. Contact-free and non-destructive (active) IR lock-in thermography enables the detection of the amplitude and phase information by monitoring the temporal development of the surface temperature [1]. The measured phase data and lock-in frequency are fitted based on the three-dimensional heat equation and thereon, the thermal diffusivity is determined. A comparison between measurements under ambient conditions and in vacuum is also carried out. 2. Experimental details