Detection of double defects for plate-like structures based on a fuzzy c-means clustering algorithm

Deconvolution processing for improved acoustic wavefield imaging

Development of a linear array electromagnetic acoustic transducer for shear horizontal guided wave inspection

The identification of defects in plate-like structures has been successfully treated using both local guided ultrasonic waves and global modal quantities. Although there are many papers on these techniques, a lack of comparability between the two methods persists. This makes it difficult for users to identify the most appropriate method for the defect in question. This paper examines the effect of different parameterizations of a circular defect in a square aluminum plate on the system response in a case study. The measured local ultrasound signal from a propagating guided wave makes up the initial data set. The first method uses the entire waveform for the objective function of the optimization problem, while the second considers the velocity of the A0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$A_0$$\\end{document} mode. In the third and fourth methods, the first and second global natural frequencies of the plate modeled with free-free boundary conditions are investigated. The numerical models are validated experimentally through measurements with a laser Doppler vibrometer. This results in the qualitative and quantitative evaluation of the objective functions for all parameter combinations of the defect. The recommendation to sequentially employ modal analysis and then the ultrasound procedure is made for the defect type used in this study. The data gathered on the objective functions suggests that potential joint employment of the natural frequency and ultrasound methods may increase computational efficiency. For a specific case, the methods could also complement each other in terms of challenges such as local minima.

A numerical simulation method is adopted to analyze the effects of three types of defect geometries ((1) a single defect on the inner surface, (2) a single defect on the outer surface, and (3) double coaxial defects on the inner surface and the outer surface.) on the residual strength of corroded X60 steel pipelines and equivalent stress and plastic strain distribution of the local defect area. The results show that the defect geometry exerts obvious effects on stress–strain distribution. The earliest plastic deformation occurs at the edge of the inner surface defect (type 1), but it occurs on the central part of both the outer surface defect (type 2) and the double defects (type 3). The appearance of defects greatly weakens the stability of the pipeline. For equivalent sum total corrosion defect depth, a single defect is more harmful to the pipeline than double defects.

Factor VIII and von Willebrand factor changes after desmopressin and during pregnancy in type 2M von Willebrand disease Vicenza: a prospective study comparing patients with single (R1205H) and double (R1205H-M740I) defect.

In recent years, ultrasonic Lamb waves have been widely applied to the field of non-destructive testing of plate-like structures as they have outstanding advantages, such as low attenuation, high sensitivity, and wide detection range. Current studies about defect-detection of plate-like structures using Lamb waves mostly focus on non-weld plate-like structures, and defect-detection methods are based on baseline data. This paper proposes a novel baseline-free damage inspection method of welded plate-like structures, which is based on the principle of reciprocity loss and combines the OPTICS and K-means intelligent clustering algorithms to achieve accurate defect localization. In order to verify the location accuracy of the clustering defect localization algorithm, this paper performs comparative experiments between the ellipse imaging algorithm and the clustering algorithm, which use baseline data as health signals. The comparative experimental results show that the single-defect location accuracy of the clustering algorithm is greatly improved compared with the traditional ellipse algorithm. Moreover, in order to verify the validity and feasibility of the baseline-free method, this paper applies this method to obtain characteristic signals and combines the clustering algorithm to locate both single-defect and double-defects. The experimental result of baseline-free method shows that this method can successfully detect and locate multiple defects, which gets rid of the dependence of baseline data.

This paper presents an analytical investigation for a baseline-free imaging of a defect in plate-like structures using the time-reversal of Lamb waves. We first consider the flexural wave (A0 mode) propagation in a plate containing a defect, and reception and time reversal process of the output signal at the receiver. The received output signal is found t obe composed of two parts: a directly propagated wave and a scattered wave from the defect. The time reversal of these waves recovers the original input signal, and produces two additional sidebands that contain the time-of-flight information on the defect location. One of the side band signals is then extracted as a pure defect signal. A defect localization image is then constructed from a beamforming technique based on the time-frequency analysis of the side band signal for each transducer pair in a network of sensors. The simulation results show that the proposed scheme enables the accurate, baseline-free detection of a defect, so that experimental studies are needed to verify the proposed technique and to be applied to real structural health monitoring applications.

Fracture analysis of monolayer graphene sheets with double vacancy defects via MD simulation

Summary form only given, substantially as follows. Ultrasonic non-destructive inspection is today a routine method in industries for the detection, localization and sizing of surface and buried defects in engineering structures. However, the analysis of the huge amount of data obtained during an ultrasonic non-destructive inspection is not a simple task and is usually time consuming. This is why the data are displayed in the form of images in order to take advantage of the power of visual representation of information and image processing tools used so as to speed up the analysis problem. In ultrasonic non-destructive inspection the data are displayed in the form of mainly three types of images known as B-SCAN, C-SCAN and D-SCAN displays. Our work is concerned with the application of an image processing algorithm on B-SCAN displays in order to detect crack defects in thick engineering structures. This algorithm is based on the Hough transform in which a gradient analysis is performed during the computation of the Hough space. In order to decide whether a defect is present in the structure or not we need to set a threshold and analyze the Hough space. Any maximum in the Hough space which is greater than the threshold represents a defect in the structure. Due to the diversity of B-SCAN displays which may or may not contain defects, the threshold is not a fixed one and depends on the Hough space obtained.

Several previous studies have been dedicated to incorporating double defect modes of a phononic crystal (PnC) into piezoelectric energy harvesting (PEH) systems to broaden the bandwidth. However, these prior studies are limited to examining an identical configuration of the double defects. Therefore, this paper aims to propose a new design concept for PnCs that examines differently configured double defects for broadband elastic wave energy localization and harvesting. For example, a square-pillar-type unit cell is considered and a defect is considered to be a structure where one piezoelectric patch is bonded to a host square lattice in the absence of a pillar. When the double defects introduced in a PnC are sufficiently distant from each other to implement decoupling behaviors, each defect oscillates like a single independent defect. Here, by differentiating the geometric dimensions of two piezoelectric patches, the defects’ dissimilar equivalent inertia and stiffness contribute to individually manipulating defect bands that correspond to each defect. Hence, with adequately designed piezoelectric patches that consider both the piezoelectric effects on shift patterns of defect bands and the characteristics for the output electric power obtained from a single-defect case, we can successfully localize and harvest the elastic wave energy transferred in broadband frequencies.

Material defects localization in concrete plate-like structures – Experimental and numerical study

The effect of local molecular structural cavity defect on the atom frequencies of bonded atoms is investigated in this study. The molecular dynamic (MD) simulation method is used to simulate the variation of atom frequency near by the cavity defect in a carbon diamond structure. The potential energy model, i.e. the second-generation reactive empirical bond order (REBO) potential function, is employed to derive the dynamic interaction between bonded atoms. The effect of local defect on the vibration amplitude and the density of state (DOS) is studied. The simulated results indicate that the local defect may affect the dynamic behavior of atoms near the local cavity defect significantly.

A novel method for localization of the maximum glenoid bone defect during reverse shoulder arthroplasty

In order to more accurately grasp the exact shape, contour size and distribution of defects in the plate-like structures material and other detailed feature information, this paper designed the graphical user interface GUIGWT0.1, which is specifically used for ultrasonic guided wave imaging. This software integrates filtering back projection algorithm, damage probability reconstruction algorithm and diffraction tomography algorithm, which can image the plate-like structures structure as required, and develop the defect detection results to the visual direction. To investigate the validity of the interface, the projection data of lamb wave in the plate-like with a partial-thickness notch are numerically simulated by three-dimensional elastodynamic finite integration technique (EFIT). The resulting projected data is imported into the graphical user interface for imaging. For each existing reconstruction imaging, the result can be represented in terms of grayscale image of projected data, defect imaging, image color inversion and false color defect recognition. Through simple operation, reconstruction of image with defect of plate-like structure are obtained in the user interface.

The in-plane dynamic energy absorption of metal honeycombs with defects consisting of missing cells are analyzed using explicit dynamic finite element method. Two types of structural defects (a single defect located in the center of the model and a double defect) are firstly introduced. Then the influence of the defects and the impact velocities on the energy absorption abilities of metal honeycombs is investigated. Researches show that single and isolated defects reduce the absorbed energy of cellular materials. The separation distance between two defects has little effect on the dynamic energy absorption, while the size of the single defect has great influence on it. These results will provide some useful guides for the safety evaluation and the dynamic energy absorption design of metal honeycombs.