Damage identification in various types of composite plates using guided waves excited by a piezoelectric transducer and measured by a laser vibrometer

Composite materials are widely used in the industry, and the interest of this material is growing rapidly, due to its light weight, strength and various other desired mechanical properties. However, composite materials are prone to production defects and other defects originated during exploitation, which may jeopardize the safety of such a structure. Thus, non-destructive evaluation methods that are material-independent and suitable for a wide range of defects identification are needed. In this paper, a technique for damage characterization in composite plates is proposed. In the presented non-destructive testing method, guided waves are excited by a piezoelectric transducer, attached to tested specimens, and measured by a scanning laser Doppler vibrometer in a dense grid of points. By means of signal processing, irregularities in wavefield images caused by any material defects are extracted and used for damage characterization. The effectiveness of the proposed technique is validated on four different composite panels: Carbon fiber-reinforced polymer, glass fiber-reinforced polymer, composite reinforced by randomly-oriented short glass fibers and aluminum-honeycomb core sandwich composite. Obtained results confirm its versatility and efficacy in damage characterization in various types of composite plates

Deep learning aided topology optimization of phononic crystals

In this work, a novel approach for the topology optimization of phononic crystals based on the replacement of the computationally demanding traditional solvers for the calculation of dispersion diagrams with a surrogate deep learning (DL) model is proposed. We show that our trained DL model is ultrafast in the prediction of the dispersion diagrams, and therefore can be efficiently used in the optimization framework

Wavefield analysis tools for wavenumber and velocities extraction in polar coordinates

Experimental characterization of Lamb waves in plate–like structures overcomes the intrinsic limits of a–priori Semi–Analytical Finite Elements simulations, where material inaccuracies and non–idealities can not be easily considered. Unfortunately, the experimental extraction of guided waves dispersion curves, and especially their polar representation along different directions of propagation at a given frequency, is not trivial. In non-isotropic materials, such analysis is a key aspect for a reliable and robust characterization of the waves behaviour. In this work, by exploiting Scanning Laser Doppler Vibrometer measurements with narrowband excitation, two different signal processing methods for the extraction of the wavenumber polar representation at the excitation frequency are investigated and characterized. The first method is based on a Distance Regularized Level Set algorithm, widely used in image processing and computer vision but, to the best of author’s knowledge, never used in the Lamb waves’ field. The second method is based on the two-dimensional sparse wavenumber analysis which exploits the wavefield sparse representation in the wavenumber domain. With a precise and reliable extraction of the wavenumber characteristic in the k–space, the polar representations at the excitation frequency of phase and group velocities can be estimated. The former, by exploiting the well-known wavenumber–frequency relation, the latter, instead, by computing numerical derivative among wavenumbers at multiple frequencies. The methodology has been validated on three different composite plates with different degrees of non-isotropy properties. The results show the effectiveness of the two methods, highlighting the advantages and disadvantages of both

Application of a Laser-Based Time Reversal Algorithm for Impact Localization in a Stiffened Aluminum Plate

Non-destructive testing and structural health monitoring (SHM) techniques using elastic guided waves are often limited by material inhomogeneity or geometrical irregularities of the tested parts. This is a severe restriction in many fields of engineering such as aerospace or aeronautics, where typically one needs to monitor composite structures with varying mechanical properties and complex geometries. This is particularly true in the case of multiscale composite materials, where anisotropy and material gradients may be present. Here, we provide an impact localization algorithm based on time reversal and laser vibrometry to cope with this type of complexity. The proposed approach is shown to be insensitive to local elastic wave velocity or geometrical features. The technique is based on the correlation of the measured impact response and a set of measured test data acquired at various grid points along the specimen surface, allowing high resolution in the determination of the impact point. We present both numerical finite element simulations and experimental measurements to support the proposed procedure, showing successful implementation on an eccentrically stiffened aluminum plate. The technique holds promise for advanced SHM, potentially in real time, of geometrically complex composite structures

Experimental full wavefield reconstruction and band diagram analysis in a single-phase phononic plate with internal

Research on phononic crystal architectures has produced many interesting designs in the past years, with useful wave manipulation properties. However, not all of the proposed designs can lead to convenient realizations for practical applications, and only a limited number of them have actually been tested experimentally to verify numerical estimations and demonstrate their feasibility. In this work, we propose a combined numerical-experimental procedure to characterize the dynamic behavior of metamaterials, starting from a simplied 2D design to a real 3D manufacturing structure. To do this, we consider a new simplified design of a resonator-type geometry for a phononic crystal, and verify its wave filtering properties in wave propagation experiments. The proposed geometry exploits a circular distribution of cavities in a homogeneous material, leading to a central resonator surrounded by thin ligaments and an external matrix. Parametric simulations are performed to determine the optimal thickness of this design leading to a large full band gap in the kHz range. Full field experimental characterization of the resulting phononic crystal using a scanning laser Doppler vibrometer is then performed, showing excellent agreement with numerically predicted band gap properties and with their resulting effects on propagating waves. The outlined procedure can serve as a useful step towards a standardization of metamaterial development and validation procedures