Nondestructive Evaluation of Clad Rods by Inversion of Acoustic Scattering Data

Abstract

In many engineering applications, it is important to know various characteristics of the materials including their elastic properties. For clad rods, especially those with small radii, such as fibres used in fibre-reinforced composites, it is extremely difficult to prepare test samples from the core and cladding materials. In this paper, we develop a novel nondestructive testing technique for measuring the elastic constants of both the core and cladding materials as well as the cladding thickness by solving an inverse problem. The clad rod is insonified by an acoustic wave in water and the scattered field from the sample is recorded. By using a theoretical model for the scattering process, an inverse problem is formed. The unknowns of this problem are the wave velocities of the core and cladding materials and the cladding thickness. This problem is then solved by using a genetic algorithm to find the unknown parameters. A perturbation study is also conducted to show the sensitivity of the resonance frequencies of the clad rod to changes in cladding thickness. The proposed approach shows very good convergence and the measured values agree very well with tabulated data. The proposed technique could be considered as a powerful nondestructive evaluation tool for characterizing clad rods.