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The influence of damage on waves propagating in beam structures is investigated through a numerical model formulated by combining spectral finite elements and perturbation techniques. The resulting numerical tool allows for an efficient computation of the wave propagation response and the analysis of the effects of localized damages of various extents and locations. The dynamic behavior of damaged beams is described through a first-order model, which couples bending and axial behavior, thus allowing the prediction of mode conversion phenomena. Damage is modeled as a small, localized reduction of the beam thickness which, allows for an application of perturbation theory. Numerical examples in the time and frequency domains are presented to illustrate the model capabilities. Keywords: damaged beam, notched beam, spectral finite element method, perturbation techniques, first order beam theory

This paper presents a micromechanical analysis of the influence of fiber–matrix interface fracture properties on the transverse tensile response of fiber-reinforced composite. The method combines three-dimensional (3D) computational micromechanics and augmented finite element method to provide high-fidelity results of damage initiation and propagation. Random arrangement of fibers and normal distribution of interface toughness and strength are considered in representative volume elements to capture the stochastic behavior of the composite under loading. Sensitivity analysis with respect to the interface properties distribution, and shape and size of fibers on the representative volume element’s strength are performed. The effect of fiber volume fractions on the strength and elastic modulus of the composite is investigated. Failure path in different representative volume elements are compared. The results show that the response of a representative volume element with identical interface properties overestimates the composite’s transverse strength. It is also shown that the damage initiation and propagation locations are affected by the distributions of fracture properties, and the shape and size of fibers within the representative volume element. [ABSTRACT FROM AUTHOR]

The article presents techniques for localization and quantification of defects based on the evaluation of reflection, transmission, and conversion of Lamb wave modes and of the spatial evolution of their phase. Reflection, transmission, and conversion coefficients are estimated using mode separation and incident-wave removal procedures implemented in the frequency/wavenumber domain. The practical implementation of the concept relies on the availability of spatially refined measurements, as provided for example by a Scanning Doppler Laser Vibrometer. The application to simulated and experimental data illustrate the effectiveness of the proposed procedures. Specifically, a finite element model of a 2D elastic domain in plane strain featuring a notch is used to estimate the reflection, transmission, and conversion coefficients. Such procedures rely on the spatial integration of wave amplitudes in contrast to pointwise estimations, as a way to reduce the effect of noise. Likewise, the techniques are demonstrated on experimental data obtained using a Scanning Laser Doppler Vibrometer on an aluminum plate with a notch. [ABSTRACT FROM AUTHOR]

This study investigates several available sandwich beam theories for their suitability of application to one-dimensional sandwich plates with functionally graded core. Two equivalent single-layer theories based on assumed displacements, a higher-order theory, and the Fourier-Galerkin method are compared. The results are also compared with the finite element analysis. The core of the sandwich panel is functionally graded such that the density, and hence its stiffness, vary through the thickness. The variation of core Young's modulus is represented by a differentiable function in the thickness coordinate, but the Poisson's ratio is kept constant. A very good agreement is found among the Fourier-Galerkin method, the higher-order theory, and the finite element analysis. [ABSTRACT FROM AUTHOR]

A single head scanning laser Doppler vibrometer is used for the estimation of the polarization of the first symmetric (S(0)) and antisymmetric (A(0)) Lamb wave modes. The measurements at two known incidence angles are performed in order to resolve the two components of motion. Filtering in the frequency/wavenumber domain of the response recorded along a scan line separates the contributions from each mode and allows the evaluation of the corresponding elliptical trajectories of particle motion. Comparison between measured and analytically estimated trajectories validates the measurement technique and suggests its application for the development of material characterization and diagnostics tools.