Measurement of translucent coating thickness based on pulsed thermography

To measure the thickness of translucent coating quickly and accurately, the method based on pulse thermography was proposed. A simplified theoretical semi-infinite model of pulsed infrared heating conduction for translucent coating and a two-layer physical model of pulsed infrared heating for translucent coatings were established. The theoretical analysis and numerical results show that the thickness of the translucent coating is linearly proportional to the peak time of the surface temperature in logarithmic coordinates, through which the thickness of the translucent coating can be derived without spraying black ink on the surface of the sample to avoid the effect of translucency. A translucent coating specimen with continuously varying thickness was fabricated and tested with a flash thermographic system. The result of the measured thicknesses is within 5% of the actual values. It demonstrates that the technique has the potential for fast and non-contact measurement of the thickness for translucent coatings.