Elastic parameters characterization of multilayered structures by air-coupled ultrasonic transmission and genetic algorithm

Analysis of damage localisation results in GFRP panel for different configurations of air-coupled transducers

In this paper results of the damage assessment of fiber-reinforced composite panels using guided wave propagation phenomenon are presented. For this purpose, non-contact elastic wave generation based on an air-coupled transducer (ACT) is utilised. Elastic wave sensing was based on a scanning laser Doppler vibrometer (SLDV). The problem of ACT slope angle for the effectiveness of elastic wave modes generation is analysed. It was shown that for an excitation frequency of 40 kHz it is possible to generate A₀ wave mode. The authors also investigated the damage sensitivity related to panel coverage area by elastic waves with large energy. An artificial damage in the form of Teflon inserts was utilised. Moreover, the influence of single and multiple acoustic wave sources on artificial damage localisation results was investigated. For this purpose RMS wave energy maps, statistical parameters, and damage indices are utilised. Different locations of ACTs and their influence on damage localisation results are investigated. A damage imaging algorithm based on wavefield irregularity mapping (WIM) has been proposed. In this research low-cost and popular, low-frequency ACT was utilised giving the possibility of realisation of the non-contact damage localisation method.

Ultrasonic characterization of multi-layered porous lithium-ion battery structure for state of charge

A multi-layered porous finite element model of lithium-ion battery is proposed by using Voronoi polygons. The time domain simulation of ultrasonic transmission characteristics with different state of charge (SOC) are carried out, and the variation of acoustic parameters versus SOCs is explored. Then, in the experiment research, the ultrasonic transmission signals are obtained by employing piezoelectric ceramic transducers during the discharging step. By extracting the time domain characteristic parameters, it is discovered that the amplitude and time-of-flight (TOF) have a strong correlation with SOC, the slow pressure-wave (SPW) velocities of the experiments correspond well with the simulation results. In addition, the frequency domain analysis shows a linear link between the amplitude of the frequency spectrum and SOC. Moreover, via repeated experiments, it is found that the ultrasonic transmission method has good repeatability in probing the SOC, and the SPW velocities acquired by experiments can almost be covered by 95% confidence interval formed based on the results of the simulation. Furthermore, according to the results of the experiments, a gray model based on the particle swarm optimization-based-simulated annealing (GM-PSO-SA) is established, which realized the prediction of the SOC under the condition of small sample data. The research results can serve as a reference for creating a comprehensive finite element model of the multi-layered porous structure of lithium-ion battery. Meanwhile, it also provides a detection and evaluation tool for the monitoring of the SOC.

Correlation of Bone Material Model Using Voxel Mesh and Parametric Optimization

The authors present an algorithm for determining the stiffness of the bone tissue for individual ranges of bone density. The paper begins with the preparation and appropriate mechanical processing of samples from the bovine femur and their imaging using computed tomography and then processing DICOM files in the MIMICS system. During the processing of DICOM files, particular emphasis was placed on defining basic planes along the sides of the samples, which improved the representation of sample geometry in the models. The MIMICS system transformed DICOM images into voxel models from which the whole bone FE model was built in the next step. A single voxel represents the averaged density of the real sample in a very small finite volume. In the numerical model, it is represented by the HEX8 element, which is a cube. All voxels were divided into groups that were assigned average equivalent densities. Then, the previously prepared samples were loaded to failure in a three-point bending test. The force waveforms as a function of the deflection of samples were obtained, based on which the global stiffness of the entire sample was determined. To determine the stiffness of each averaged voxel density value, the authors used advanced optimization analyses, during which numerical analyses were carried out simultaneously, independently mapping six experimental tests. Ultimately, the use of genetic algorithms made it possible to select a set of stiffness parameters for which the error of mapping the global stiffness for all samples was the smallest. The discrepancies obtained were less than 5%, which the authors considered satisfactory by the authors for such a heterogeneous medium and for samples collected from different parts of the bone. Finally, the determined data were validated for the sample that was not involved in the correlation of material parameters. The stiffness was 7% lower than in the experimental test.

On the Identification of Orthotropic Elastic Stiffness Using 3D Guided Wavefield Data

Scanning laser Doppler vibrometry is a widely adopted method to measure the full-field out-of-plane vibrational response of materials in view of detecting defects or estimating stiffness parameters. Recent technological developments have led to performant 3D scanning laser Doppler vibrometers, which give access to both out-of-plane and in-plane vibrational velocity components. In the present study, the effect of using (i) the in-plane component; (ii) the out-of-plane component; and (iii) both the in-plane and out-of-plane components of the recorded vibration velocity on the inverse determination of the stiffness parameters is studied. Input data were gathered from a series of numerical simulations using a finite element model (COMSOL), as well as from broadband experimental measurements by means of a 3D infrared scanning laser Doppler vibrometer. Various materials were studied, including carbon epoxy composite and wood materials. The full-field vibrational velocity response is converted to the frequency-wavenumber domain by means of Fourier transform, from which complex wavenumbers are extracted using the matrix pencil decomposition method. To infer the orthotropic elastic stiffness tensor, an inversion procedure is developed by coupling the semi-analytical finite element (SAFE) as a forward method to the particle swarm optimizer. It is shown that accounting for the in-plane velocity component leads to a more accurate and robust determination of the orthotropic elastic stiffness parameters.

Identification of Material Properties of Elastic Plate Using Guided Waves Based on the Matrix Pencil Method and Laser Doppler Vibrometry

Ultrasonic based inspection of thin-walled structures often requires prior knowledge of their mechanical properties. Their accurate estimation could be achieved in a non-destructive manner employing, e.g., elastic guided waves. Such procedures require efficient approaches for experimental data extraction and processing, which is still a challenging task. An advanced automated technique for material properties identification of an elastic waveguide is proposed in this investigation. It relies on the information on dispersion characteristics of guided waves, which are extracted by applying the matrix pencil method to the measurements obtained via laser Doppler vibrometry. Two objective functions have been successfully tested, and the advantages of both approaches are discussed (accuracy vs. computational costs). The numerical analysis employing the synthetic data generated via the mathematical model as well as experimental data shows that both approaches are stable and accurate. The influence of the presence of various modes in the extracted data is investigated. One can conclude that the influence of the corruptions related to the extraction of dispersion curves is not critical if the majority of guided waves propagating in the considered frequency range are presented. Possible extensions of the proposed technique for damaged and multi-layered structures are also discussed.