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We investigate guided (Lamb) waves in a human cadaver skull through experiments and computational simulations. Ultrasonic wedge transducers and scanning laser Doppler vibrometry are used respectively to excite and measure Lamb waves propagating in the cranial bone of a degassed skull. Measurements are performed over a section of the parietal bone and temporal bone spanning the squamous suture. The experimental data are analyzed for the identification of wave modes and the characterization of dispersion properties. In the parietal bone, for instance, the A0 wave mode is excited between 200 and 600 kHz, and higher-order Lamb waves are excited from 1 to 1.8 MHz. From the experimental dispersion curves and average thickness extracted from the skull computed tomography scan, we estimate average isotropic material properties that capture the essential dispersion characteristics using a semi-analytical finite-element model. We also explore the leaky and non-leaky wave behavior of the degassed skull with water loading in the cranial cavity. Successful excitation of leaky Lamb waves is confirmed (for higher-order wave modes with phase velocity faster than the speed of sound in water) from 500 kHz to 1.5 MHz, which may find applications in imaging and therapeutics at the brain periphery or skull-brain interface (e.g., for metastases). The non-leaky A0 Lamb wave mode propagates between 200 and 600 kHz, with or without fluid loading, for potential use in skull-related diagnostics and imaging (e.g., for sutures). [ABSTRACT FROM AUTHOR]

Lamb wave propagating behavior in woven glass fiber reinforced epoxy (WGF/epoxy) composite laminates was studied by simulation and experiment. A 3D finite element (FE) model was built in Abaqus/Explicit software with the help of user material subroutine to capture the wave propagating features in WGF/epoxy composite plate. The Lamb wave tests were carried out by a non-circular array with 8 piezoelectric (PZT) wafers. A defect imaging algorithm was developed using MATLAB based on the ellipse theory in time-dependent domains. Two defect imaging cases were carried out in the WGF/epoxy composite plate to verify the feasibility of the proposed algorithm. A good agreement between the simulated waveforms and experimental data was achieved. This indicates a great potential of the proposed algorithm in the field of damage localization and identification for WGF/epoxy thin-walled laminates. [ABSTRACT FROM AUTHOR]

• A new finite element method reproduced the impact damage in composite laminate. • The model describes the geometric properties of the actual impact damage. • Simulation of acousto-ultrasonic sensing was conducted to manifest the change of the Lamb wave. • Investigating the change of the Lamb wave which interacts with impact damage. • The simulation results ware compared with another finite element method and validated by the experiment. It is difficult to investigate the interaction between the Lamb wave and impact damage within a composite laminate if the interfaces caused by impact-induced delamination and cracks are not modeled precisely. In this study, a novel finite element modeling method was proposed to virtually reproduce multiple damage after observing the distribution and form of different impacts in a cross-ply carbon fiber reinforced plastic laminate. Further, a numerical simulation of acousto-ultrasonic sensing was performed to manifest the tone-burst Lamb wave that propagated in the laminate. The calculated stress and displacement contours distinguished the dispersed modes and exhibited the wave attenuation after it interacted with multiple interfaces. The change in amplitude provided a reference for impact damage evaluation. The proposed method was compared with another existing modeling method and validated by the acousto-ultrasonic sensing experiment, which demonstrated its accuracy and capability to study the phenomena in acousto-ultrasonic sensing for low-velocity impact damage. [ABSTRACT FROM AUTHOR]

Abstract: The propagation of guided Lamb waves in metallic foam sandwich panels is described in this paper and analyzed numerically with a three-dimensional finite element simulation. The influence of geometrical properties of the foam sandwich plates (such as the irregularity of the foam structure, the relative density or the cover plate thickness) on the wave propagation is investigated in a parametric study. Open-cell and closed-cell structures are found to exhibit similar wave propagation behavior. In addition to the finite element model with fully resolved microstructure, a simplified, computationally cheaper model is also considered – there the porous core of the sandwich panel is approximated by a homogenized effective medium. The limitations of this homogenization approach are briefly pointed out. [Copyright &y& Elsevier]

Abstract: The paper aims to describe the guided Lamb wave propagation in honeycomb sandwich panels. The application of Lamb waves is a well-known method in modern online structural health monitoring techniques. To analyze the wave propagation in such a complicated geometry with an analytical solution is hardly possible; therefore a dimensional finite element simulation is used. A piezoelectric actuator is used to excite the waves on the sandwich panel surface. The extended model of the honeycomb sandwich panel is consisting of two plate layers and a mid-core layer. In addition, a simplified model is used to reduce the computing costs, where the mid-core of the sandwich panel is replaced by a homogeneous layer. The results from the extended model and the simplified model are in most cases in a good agreement; however the limitations of using the simplified model are discussed. A parametric study is used to show the influence of the geometrical properties of honeycomb plates, the material properties of the skin plates and the loading frequency on the group velocity, the wave length and the energy transmission. Each of these properties provides valuable information to design an efficient health monitoring system. Finally, an experimental test is presented. [Copyright &y& Elsevier]

Abstract: This paper deals with the investigation of the Lamb wave propagation in particle reinforced composites excited by piezoelectric patch actuators. A three-dimensional finite element method (FEM) modeling approach is set up to perform parameter studies in order to better understand how the Lamb wave propagation in particle reinforced composite plates is affected by change of central frequency of excitation signal, volume fraction of particles, size of particles and stiffness to density ratio of particles. Furthermore, the influence of different arrangements is investigated. Finally, the results of simplified models using material data obtained from numerical homogenization are compared to the results of models with heterogeneous build-up. The results show that the Lamb wave propagation properties are mainly affected by the volume fraction and ratio of stiffness to density of particles, whereas the particle size does not affect the Lamb wave propagation in the considered range. As the contribution of the stiffer material increases, the group velocity and the wave length also increase while the energy transmission reduces. Simplified models based on homogenization technique enabled a tremendous drop in computational costs and show reasonable agreement in terms of group velocity and wave length. [Copyright &y& Elsevier]

Abstract: In this study, the Lamb mode attenuation constants were derived in terms of the attenuation coefficient, group velocity and central frequency of excitation of the Lamb mode, using the Rayleigh damping model. Attenuation of Lamb waves, both fundamental symmetric and anti-symmetric modes, propagating through viscoelastic media (cross-ply glass/epoxy laminate) was modelled using the Finite Element Method. Numerically simulated attenuation of Lamb waves using Lamb mode attenuation constants was found to be in good agreement with the assumed attenuation. Experiments were performed on a quasi-isotropic laminate, employing air-coupled ultrasonic transducers, to measure the attenuation coefficient. Lamb mode attenuation constants, computed using the attenuation coefficient, were used to model the attenuation of the Lamb mode in quasi-isotropic laminates. Numerically simulated amplitude variation was found to be in good agreement with that computed from experiments. [Copyright &y& Elsevier]

Abstract: The mode selection of Lamb waves generated in thin aluminium plates by using 2-2 piezocomposites has been studied. In this paper, 2-2 piezocomposite square plates have been designed, made, and compared with standard piezoceramic plates to test the improvement on the generation and propagation of symmetric and antisymmetric Lamb modes. An optical interferometer was used to measure the out-of-plane displacement of the propagating Lamb wave modes generated with the piezoceramic plates. Different Finite Element Models, using a commercial simulation program (PZFlex) were also developed to calculate the displacement signals and to compare them with the experimental ones. Next, the same measurements were done with two different 2-2 piezocomposites to see the mode selection of the Lamb waves generated. Different excitation frequencies were used experimentally and implemented in PZFlex to calculate the displacement signals, verifying the mode cancellations. The experimental measurements show good agreement with the models. [Copyright &y& Elsevier]