Inversion of leaky Lamb wave data by simplex algorithm

Abstract

A numerical procedure is presented for the inversion of leaky Lamb wave (LLW) data to determine certain material properties of a waveguide, using a modified version of the simplex algorithm. The technique is capable of computing the parameter values that best fit a particular set of data, given an analytical model of the associated phenomenon containing any number of variables and parameters. The basic theoretical concepts involved are reviewed, and the versatility and simplicity of the method are illustrated by examples. The inversion scheme is used to estimate the elastic properties and thickness of an adhesive layer between two aluminum plates and the elastic constants of a unidirectional graphite/epoxy composite laminate. The limitations of the LLW data in the determination of the elastic constants of a composite are discussed.

Characterization of composite laminates using combined LLW and PBS methods

“…The computer program that was written to find the minima on the reflection spectrum is used to determine the dispersion curves along 0, 45, and 90 degrees for composite laminates or a single curve for a metallic bonded joint. The experimental dispersion curve is then processed by the Simplex inversion algorithm that was developed by the authors [5]. This algorithm determines the elastic properties that provide the best fit between the analysis and the experimental data.…”

“…The defects characterization is made by analyzing the reflection pattern, whereas the properties are determined using the Simplex inversion process that was recently developed by the authors [5]. Using this inversion process, five stiffness coefficients are determined representing the complete number of coefficients needed to characterize the laminate as a transversely isotropic material.…”

Leaky Lamb Waves (LLW) in Multiorientation Composite Laminates

“…This response was acquired by placing a tungsten film over the laminate and measuring the reflected spectra. Using the authors' new computer code based on the simplex algorithm [5,6] for data inversion, the following properties were determined for a unidirectional lamina:…”

“…Further, they have developed a data inversion technique for determining the elastic constants and interface properties of composite laminates [5,6]. This has led to better capability for comparing theoretical and experimental results for general laminates.…”

Ultrasonic nondestructive evaluation of cracked composite laminates

“…A major difficulty in inversion is that it requires the solution of a system of nonlinear equations, resulting in non-uniqueness [9]. In this study, a least squares method for the nonlinear, implicit model presented by Britt and Luecke [10] is applied to estimate the material properties of damaged composite laminates.…”