Nondestructive analysis of uneven paint coatings by dynamic heat conduction following flash heating

A method of assessing uneven paint coatings is described, wherein a painted surface is rapidly heated by a light flash and the subsequent surface temperature changes are monitored using thermography. This method exploits the differences in dynamic heat transport caused by variations in paint thickness, using thermographic observation to track differences in temperature related to thickness. During trials with intentionally uneven test specimens spray coated with blackbody paint or red, blue, and green acrylic lacquers, we determined that surfaces with thinner paint coatings exhibited lower temperatures. Based on our findings, this article also discusses the theoretical basis of the detection method. While this technique can detect uneven painting, it is difficult to determine a quantitative relationship between temperature variations in the coated surfaces and paint thickness, since the relationship is dependent not only on the particular substrate and paint, but also on the optical reflectance of the paint. We consider that the proposed method is currently capable of detecting uneven paint coatings with variations in thickness of approximately 20 μm, although improvements in detection resolution are possible. Although detection sensitivity is somewhat low, this technique allows rapid analysis of coatings to assess evenness through visual examination.