Nondestructive evaluation of coated structures using Lamb wave propagation

Abstract

Nondestructive evaluation (NDE) of the mechanical properties and thickness loss of coated structures is of great importance for health monitoring purposes. This study aimed to propose an NDE method based on the Lamb wave propagation for the inspection of coated structures. The inverse problem of Lamb wave propagation in coated structures was developed and solved. The dispersion curves for the fundamental antisymmetric Lamb wave mode were obtained analytically, considering different thicknesses and a range of material properties decay for the substrate and coating. To assess the proposed inverse wave propagation NDE method, four carbon steel specimens coated by composite materials were fabricated and underwent the Lamb wave propagation tests. The Lamb wave phase velocity was measured for the specimens. The elastic modulus and thickness of the carbon steel plate were estimated for each specimen using the measured phase velocities through the inverse solution of the developed Lamb wave propagation model. The estimated elastic modulus and thickness of the specimens were in good agreement with the actual ones. Therefore, the validity of the proposed nondestructive Lamb wave propagation method for the evaluation of coated structures was confirmed. Prospective applications of this method for the in-situ inspection of coated structures to assess the thickness loss and material decay are envisioned.