Determination of Young's Modulus of Surface Coating Paint with Impulse Excitation Technique and Analysis of Laser Signals

Abstract

Polymer coatings of metallic surfaces offer them not only aesthetic value but at the same time provide anticorrosive protection or even improvement of some mechanical properties of the composite structure. The mechanical properties of paints are often negligible although the two aspects considered: aesthetics and durability are related to the mechanical properties of both the base material and the paint. The durability of the paint depends on how it adheres to the substrate, but at the same time a jump in the bending stress value occurs in the separation area of the two materials, which leads to the appearance of shear stress. The shear stress value depends on the ratio of the modulus of elasticity of the base material and the paint. In this paper it will follow, starting from the mechanical properties of the substrate, the metallic sheet in general, to determine the new properties of the assembly of substrate and the two painting layers, also the determination of mechanical properties of the layers. From the analysis of laser signals obtained by the impulse excitation of the samples, one can determine the elastic modulus. These results come to validate the results based on Finite Element Analysis (FEA) of the same samples. From the analysis of Bernoulli's equation for the two situations: the uncovered beam and the painted beam, the ratio of natural frequencies is determined as a function depending on the modulus of elasticity, density and geometric dimensions of the substrate, respectively the same elements of the coating paint. From this ratio, Young's modulus of the paint can be determined.