A SIMPLE METHOD FOR DETERMINING A THICKNESS OF METAL BASED ON LOCK-IN THERMOGRAPHY

The use of coatings is an important tool in the industry. It allows protecting against oxidation, corrosion and various types of fatigue. The coating thickness is an important characteristic that influences the quality and the performance of materials. In this paper, we develop a simple method of infrared lock-in thermography (LIT) to determine galvanizing coating thickness measurement, by using a sample multiple zinc layer with thickness ranging from 0.25 mm to 1.5 mm. The method has the particularity of taking a sinusoidal excitation heat flux which contributes with a heat exchange coefficient fixed at 10 w/m(2)k and a surface emissivity of about 0.1. The finite element method (FEM) is used to model and analyze the thermal response of studied structure. The metal substrate used in this study is a structural steel, covered with six zinc layers. The finite elements analysis allows us to determine the temperature evolution at different points on the specimen. The Fourier transform method is used on the Matlab software to determine the phase angle of the data found. A correlation between the coating thickness and the equivalent phase angle is defined, and the results deduced show that the estimated values are close to the actual coating thicknesses with a precision ranging from 0.029 mm to 0.011 mm.