New analytical development to determine the elastic constants of thin films using impulse excitation technique

Abstract : Thin films are widely used in various applications to enhance the surface properties and characteristics of materials. Their physical properties differ from those of bulk materials and depend essentially on the technique of elaboration. So, in order to optimize the reliability and the performance of a coated component, the mechanical properties of films must be controlled. In the last two decades, many methods were developed to determine the elasticity constants of coated materials, which are classified into two groups: static and dynamic techniques. Our work will be focused on the characterization of the coating elasticity constants by dynamical resonant method also known as the impulse excitation technique (IET). It is non-destructive technique with high precision and with which the elasticity constants are easy to measure. In this work the analytical models developed to determine the film’s Young and shear moduli are reviewed. The models used to calculate the Young modulus are based on two different theories: the flexural rigidity of a composite beam and the classical laminated beam theory (CLBT). The problem is that the validity of these models depends on coating’s thickness and physical properties of both the coating and the substrate. A finite element model was developed with the ABAQUS software, and then the comparison with the analytical models allowed to identify the limits and drawbacks of each one. A new analytical model was developed to determine the coating shear modulus.