研究目的
To propose a method, based on laser spot lock-in thermography to measure the thermal diffusivity of samples moving at constant speed, as it is the case of in-line production or in-line inspection in factories, where heterogeneities, i.e. local changes in the properties, must be detected in real time, without stopping the production chain.
研究成果
The proposed methods, based on simple linear relations, are effective for measuring the in-plane thermal diffusivity of samples moving at constant speed. Measurements on a wide range of materials confirm the validity of these methods, with results consistent with literature values.
研究不足
The method's reliability decreases as the dimensionless factor v2/Df increases, with an upper limit established at v2/Df < 25. For thermal insulators, it is difficult to work at speeds > 1 cm/s due to limited spatial resolution.
1：Experimental Design and Method Selection:
The methodology involves illuminating the sample surface by a modulated and focused laser beam and recording the surface temperature by an IR video camera. The surface temperature is analyzed using lock-in thermography to reduce noise and improve accuracy.
2：Sample Selection and Data Sources:
Samples covering a wide range of thermal diffusivities, from thermal insulators to good thermal conductors, were tested. The samples were opaque, semitransparent, thick, and thin.
3：List of Experimental Equipment and Materials:
A CW laser (532 nm, up to 6 W), a mechanical chopper, a 10 cm focal length lens, a Ge window, an IR video camera (FLIR, model SC7500), and an IR microscope lens were used.
4：Experimental Procedures and Operational Workflow:
The sample is moved at constant speed while illuminated by the modulated laser beam. The IR camera records the temperature field, and a lock-in module transforms the recorded film into an amplitude thermogram and a phase thermogram.
5：Data Analysis Methods:
The thermal diffusivity is retrieved from the linear behavior of the temperature profiles in the directions parallel and perpendicular to the sample motion.
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