Detection Of Multiple Cracks Research Articles

Quantitative Crack Depth Monitoring Based on Traveling Wave at Millimeter-Wave Frequency

The electromagnetic (EM) resonator-based sensor has a well-known high sensitivity for crack inspection. The nonuniform field distribution inside the resonator, however, causes an associated position-dependent sensitivity phenomenon. This article is intended to address the accurate problem of EM resonator-based sensors. Instead, a methodology based on the traveling wave is first explored. A transmission line-based sensor is implemented for accurate crack depth evaluation. The sensitivity is maintained by tightly bounded the magnetic field in the cross Section of the transmission line through loading the high dielectric material. The accuracy is naturally improved by the uniform field distributed along the propagation direction. An equivalent circuit is modeled based on the transmission line theory to validate the sensing principle. For a wide range of crack width, both simulation and measurement results demonstrate that the detection sensitivity of crack depth is up to 1.893 GHz/mm. The error bar caused by the variation of crack position can be controlled in 0.166 GHz. The performance of multiple crack detection has been verified for the proposed transmission line-based sensor at the same time. This article paves a way to extend the local structural health monitoring based on EM resonators to the large area structural health monitoring.

Integrated pixel-level CNN-FCN crack detection via photogrammetric 3D texture mapping of concrete structures

Although multiple learning-based crack detection systems show promising results in detecting cracks with pixel accuracy on individual images, few effectively enable inspection of larger structures. This paper thereby proposes an advanced inspection reporting system based on an integrated CNN-FCN crack detection system applied on the texture space of a footing, enabling crack inspection and display for larger structures. The system, a Convolutional Neural Network (CNN) and a Fully Convolutional Network (FCN), segments cracks at the pixel-level on the texture space, acquired from a 3D model created with photogrammetry techniques. Firstly, the trained CNN is employed to detect crack patches, then imported to the trained FCN system to segment cracks at the pixel-level, and a crack map is then generated which is projected onto a 3D model. This system indicates promising results for footing textures as represented by: Accuracy (99.88%), Precision (82.2%), Recall (90.2%), and F1 Score (86.01%).

Multiple Crack Detection in Thick-walled Pipes Using Artificial Bee Colony Algorithm

An analytical method for diagnosis of cracks in thick-walled pipes with a circular hollow section is investigated in this study. In the proposed method, the defect is assumed to be a non-leaking crack, which is modeled by a massless linear spring with infinitesimal length at the crack location. In order to find the cracks in the pipe, the vibration-based method related to the modal properties of the pipe is utilized. In the modal analysis, the mass and stiffness matrices influence the dynamic properties of the pipe. It is assumed that the mass matrix remains unchanged after the crack initiation, while the corresponding stiffness matrix changes. The stiffness matrix of a cracked element can be formulated by the finite element method with two unknown parameters: location and depth of the crack. Using the eigensolution for an undamped dynamic system to formulate the objective function yields to a complicated optimization problem, which can be solved by an iterative numerical optimization method. Among the optimization approaches, the Artificial Bee Colony (ABC) algorithm is a simple and flexible technique for minimizing the objective function. In this paper, the analytical model is utilized to find the size and position of cracks in a pipe using the ABC algorithm and subsequently some numerical examples are examined in order to assess the accuracy of the method. The results show that the proposed method is able to acceptably estimate the location and depth of multiple cracks in the straight pipes as well as curved ones.

Inverse problem techniques for multiple crack detection in 2D elastic continua based on extended finite element concepts

Two efficient methods are presented to detect multiple cracks in 2D elastic bodies, based on the insights from Extended Finite Element. Adetection mesh is assigned to the cracked body and the responses are measured at the nodes. A finite element model with the same mesh is used to represent the uncracked state of the physical body. In the first method which is called Crack Detection based on Residual Error (CDRE), the residual error norm is calculated based on the uncracked body stiffness matrix and the cracked body responses. The contour of the error norm would show the crack pattern; the method is computationally efficient. In the second method that is coined as Crack Detection based on Stiffness Residual (CDSR), the crack locations are found based on the difference between the stiffness matrix of the cracked body and the uncracked body. The stiffness matrix of the cracked body is found by solving a dynamic inverse problem based on a modified Tikhonov regularization. The efficiency and accuracy of the identification method are enhanced by predicting the crack pattern by the CDRE method. Several examples are presented to show the accuracy and robustness of the methods in the presence of high noise levels.

A Novel Probe of DC Electromagnetic NDT Based on Drag Effect: Design and Application in Crack Characterization of High-Speed Moving Ferromagnetic Material

Electromagnetic nondestructive testing (NDT) of high-speed moving ferromagnetic material is a challenging topic; due to the relative motion between ferromagnetic material and detection devices, motion-induced eddy current (MIEC) will be generated and the drag effect will show up, which result in a more complex magnetic field distribution in the ferromagnetic material than static or quasi-static testing. Therefore, an electromagnetic NDT probe, which is suitable for multiple crack detection in high-speed moving ferromagnetic materials, is urgently required. In this article, a novel probe of dc electromagnetic NDT based on drag effect is designed considering the strength and sensitivity of the detection signal by experiment, and then it is applied to crack characterization of high-speed moving ferromagnetic material. After that, the measurement uncertainty of the detection signal based on a multiconvolutional approach is investigated and estimated. The investigation indicated that the proposed probe can quantitatively characterize the multiple cracks at 20 m/s within the relative error and standard deviation of 10% when the crack depth is deeper than 1.0 mm; furthermore, the deeper the crack, the higher the experimental repeatability. Accordingly, the proposed probe can be expected to detect the multiple cracks in high-speed moving ferromagnetic materials, such as rotating bearings, pipelines, and high-speed railway.

An h-version adaptive FEM for eigenproblems in system of second order ODEs: vector Sturm-Liouville problems and free vibration of curved beams

Purpose This study aims to overcome the involved challenging issues and provide high-precision eigensolutions. General eigenproblems in the system of ordinary differential equations (ODEs) serve as mathematical models for vector Sturm-Liouville (SL) and free vibration problems. High-precision eigenvalue and eigenfunction solutions are crucial bases for the reliable dynamic analysis of structures. However, solutions that meet the error tolerances specified are difficult to obtain for issues such as coefficients of variable matrices, coincident and adjacent approximate eigenvalues, continuous orders of eigenpairs and varying boundary conditions. Design/methodology/approach This study presents an h-version adaptive finite element method based on the superconvergent patch recovery displacement method for eigenproblems in system of second-order ODEs. The high-order shape function interpolation technique is further introduced to acquire superconvergent solution of eigenfunction, and superconvergent solution of eigenvalue is obtained by computing the Rayleigh quotient. Superconvergent solution of eigenfunction is used to estimate the error of finite element solution in the energy norm. The mesh is then, subdivided to generate an improved mesh, based on the error. Findings Representative eigenproblems examples, containing typical vector SL and free vibration of beams problems involved the aforementioned challenging issues, are selected to evaluate the accuracy and reliability of the proposed method. Non-uniform refined meshes are established to suit eigenfunctions change, and numerical solutions satisfy the pre-specified error tolerance. Originality/value The proposed combination of methodologies described in the paper, leads to a powerful h-version mesh refinement algorithm for eigenproblems in system of second-order ODEs, that can be extended to other classes of applications in damage detection of multiple cracks in structures based on the high-precision eigensolutions.

2D Digital Image Correlation and Region-Based Convolutional Neural Network in Monitoring and Evaluation of Surface Cracks in Concrete Structural Elements.

This paper shows how 2D digital image correlation (2D DIC) and region-based convolutional neural network (R-CNN) can be combined for image-based automated monitoring and assessment of surface crack development of concrete structural elements during laboratory quasi-static tests. In the presented approach, the 2D DIC-based monitoring enables estimation of deformation fields on the surface of the concrete element and measurements of crack width. Moreover, the R-CNN model provides unmanned simultaneous detection and localization of multiple cracks in the images. The results show that the automatic monitoring and evaluation of crack development in concrete structural elements is possible with high accuracy and reliability.

Nonlinear multiple breathing cracks detection using direct zeros estimation of higher-order frequency response function

On-board structures are currently submitted to high-level vibrations which may affect their integrity and operational lifetime. Structural health monitoring is then of great interest to avoid mechanical failures and to increase operational safety of mechanical systems. Indeed, in the case of cracked structures, the presence of cracks may affect the dynamic behavior. Thus, this paper focusses particularly on the detection and location of small cracks using the nonlinear response of cracked structures and more specifically using the zeros of the Higher-Order Frequency Response Function. The proposed method is based on the Direct Zeros Estimation algorithm to identify the antiresonances of the system. The locus of the identified antiresonances according to the crack location are discussed through numerical examples applied to the simplified nonlinear finite element model of a rectangular beam with multiple breathing cracks.

Mode shape curvature of multiple cracked beam and its use for crack identification in beam-like structures

The problem of using the modal curvature for crack detection is discussed in this paper based on an exact expression of mode shape and its curvature. Using the obtained herein exact expression for the mode shape and its curvature, it is demonstrated that the mode shape curvature is really more sensitive to crack than mode shape itself. Nevertheless, crack-induced change in the approximate curvature calculated from the exact mode shape by the central finite difference technique (Laplacian) is much greater in comparison with both the mode shape and curvature. It is produced by the fact, shown in this study, that miscalculation of the approximate curvature is straightforwardly dependent upon crack magnitude and resolution step of the finite difference approximation. Therefore, it can be confidently recommended to use the approximate curvature for multiple crack detection in beam by properly choosing the approximation mesh. The theoretical development has been illustrated by numerical results.

Detection of Multiple Cracks in Four-Point Bending Tests Using the Coda Wave Interferometry Method.

The enlargement of the cracks outside the permitted dimension is one of the main causes for the reduction of service life of Reinforced Concrete (RC) structures. Cracks can develop due to many causes such as dynamic or static load. When tensile stress exceeds the tensile strength of RC, cracks appear. Traditional techniques have limitations in early stage damage detection and localisation, especially on large-scale structures. The ultrasonic Coda Wave Interferometry (CWI) method using diffuse waves is one of the most promising methods to detect subtle changes in heterogeneous materials, such as concrete. In this paper, the assessment of the CWI method applied for multiple cracks opening detection on two specimens based on four-point bending test is presented. Both beams were monitored using a limited number of embedded Ultrasonic (US) transducers as well as other transducers and techniques (e.g., Digital Image Correlation (DIC), LVDT sensors, strain gauges, and Fiber Optics Sensor (FOS)). Results show that strain change and crack formation are successfully and efficiently detected by CWI method even earlier than by the other techniques. The CWI technique using embedded US transducers is undoubtedly a feasible, efficient, and promising method for long-term monitoring on real infrastructure.

Automatic detection and damage quantification of multiple cracks on concrete surface from video

Real-time automatic detection of multiple cracks from a video stream of a concrete surface is addressed in this paper. Robust principal component analysis is used to detect multiple cracks forming at different instances of time in an unsupervised manner using the Gini index as a metric to quantify the presence of an observable crack. The relative positions of the relevant pixels around the crack are monitored using the Kanade Lucas Tomasi feature tracking algorithm. Further, Hu's invariant moments of those pixel positions are computed which acts as a robust damage indicator even for breathing cracks under time-varying service loads. The proposed method is experimentally validated using two small scale under-reinforced beams undergoing three-point bending tests. The method successfully detects the onset of multiple cracks, at varied locations, at different time instants and further tracks their propagations.

Automatic detection and damage quantification of multiple cracks on concrete surface from video

Real-time automatic detection of multiple cracks from a video stream of a concrete surface is addressed in this paper. Robust principal component analysis is used to detect multiple cracks forming at different instances of time in an unsupervised manner using the Gini index as a metric to quantify the presence of an observable crack. The relative positions of the relevant pixels around the crack are monitored using the Kanade Lucas Tomasi feature tracking algorithm. Further, Hu's invariant moments of those pixel positions are computed which acts as a robust damage indicator even for breathing cracks under time-varying service loads. The proposed method is experimentally validated using two small scale under-reinforced beams undergoing three-point bending tests. The method successfully detects the onset of multiple cracks, at varied locations, at different time instants and further tracks their propagations.

An improved two-step method based on Kriging model for beam structures

An improved two-step method for multiple cracks detection in beam structures is presented in this paper. First, the crack locations are identified by the mode shape curvatures. Second, samples of v...

Distributed detection of microcracks by differential narrowing of FWHM in BFS

Brillouin scattering based optical fiber sensors provide the opportunity for distributed detection of multiple cracks in structures. Because of capability for making high spatial resolution measurements, pre-pump-pulse Brillouin optical time domain analysis (PPP-BOTDA) systems have been successful in detecting microcracks. Recent studies have shown that when the space between two neighboring microcracks is smaller than the full width at half maximum (FWHM) of the peaks in Brillouin frequency shift (BFS), the strain peaks in BFS interfere, and inhibit detection of multiple microcracks. The focus of the present study is to narrow the size of FWHM by computing the difference in BFS of the strain peaks at two slightly different spatial resolutions. The differential FWHM obtained in this manner is narrower than the original FWHM for single microcrack, as well as two neighboring microcracks. The efficiency of the proposed approach was tested through experiments. The results indicated that it was possible to reduce the FWHM for single cracks, and also to detect the presence of dual microcracks with crack spacing distances smaller than the FWHM. However, the effectiveness of the proposed approach is also dependent on the spatial resolution of measurements, and the signal to noise ratio of the measurement system. While higher spatial resolutions are required for effective narrowing of FWHM in differential approach, the measurement noise at higher spatial resolutions limited the applicability of the method for very small crack opening displacements.

Multiple crack detection in 3D using a stable XFEM and global optimization

A numerical scheme is proposed for the detection of multiple cracks in three dimensional (3D) structures. The scheme is based on a variant of the extended finite element method (XFEM) and a hybrid optimizer solution. The proposed XFEM variant is particularly well-suited for the simulation of 3D fracture problems, and as such serves as an efficient solution to the so-called forward problem. A set of heuristic optimization algorithms are recombined into a multiscale optimization scheme. The introduced approach proves effective in tackling the complex inverse problem involved, where identification of multiple flaws is sought on the basis of sparse measurements collected near the structural boundary. The potential of the scheme is demonstrated through a set of numerical case studies of varying complexity.

Closed-form solution based genetic algorithm software: Application to multiple cracks detection on beam structures by static tests

In this paper a procedure for the static identification and reconstruction of concentrated damage distribution in beam-like structures, implemented in a dedicated software, is presented. The proposed damage identification strategy relies on the solution of an optimisation problem, by means of a genetic algorithm, which exploits the closed form solution based on the distribution theory of multi-cracked beams subjected to static loads. Precisely, the adoption of the closed-form solution allows a straightforward evolution of an initial random population of chromosomes, representing different damage distributions along the beam axis, towards the fittest and selected as the sought solution. This method allows the identification of the position and intensity of an arbitrary number of cracks and is limited only by the amount of data experimentally measured. The proposed procedure, which has the great advantage of being robust and very fast, has been implemented in the powerful agent based software environment NetLogo, and is here presented and validated with reference to several benchmark cases of single and multi-cracked beams considering different load scenarios and boundary conditions. Sensitivity analyses to assess the influence of instrumental errors are also included in the study.

Experimental Investigation on the Detection of Multiple Surface Cracks Using Vibrothermography with a Low-Power Piezoceramic Actuator.

Vibrothermography often employs a high-power actuator to generate heat on a specimen to reveal damage, however, the high-power actuator brings inconvenience to the application and possibly introduces additional damage to the inspected objects. This study uses a low-power piezoceramic transducer as the actuator of vibrothermography and explores its ability to detect multiple surface cracks in a metal part. Experiments were conducted on a thin aluminum beam with three cracks in different orientations. Detailed analyses of both thermograms and temperature data are presented to validate the proposed vibrothermography method. To further investigate the performance of the proposed vibrothermography method, we experimentally studied the effects of several critical factors, including the amplitude of excitation signal, specimen constraints, relative position between the transducer and cracks (the transducer is mounted on the same or the opposite side with the cracks). The results demonstrate that all cracks can be detected conveniently and simultaneously by using the proposed low-power vibrothermography. We also found that the magnitude of excitation signal and the specimen constraints have a great influence on detection results. Combined with effective data processing methods, such as Fourier transformation employed in this study, the proposed method provides a promising potential to detect multiple cracks on a metal surface in a safe and effective manner.

Multiple Cracks Detection in Pipeline Using Damage Index Matrix Based on Piezoceramic Transducer-Enabled Stress Wave Propagation.

Cracks in oil and gas pipelines cause leakage which results in property damage, environmental pollution, and even personal injury or loss of lives. In this paper, an active-sensing approach was conducted to identify the crack damage in pipeline structure using a stress wave propagation approach with piezoceramic transducers. A pipeline segment instrumented with five distributed piezoceramic transducers was used as the testing specimen in this research. Four cracks were artificially cut on the specimen, and each crack had six damage cases corresponding to different crack depths. In this way, cracks at different locations with different damage degrees were simulated. In each damage case, one piezoceramic transducer was used as an actuator to generate a stress wave to propagate along the pipeline specimen, and the other piezoceramic transducers were used as sensors to detect the wave responses. To quantitatively evaluate the crack damage status, a wavelet packet-based damage index matrix was developed. Experimental results show that the proposed method can evaluate the crack severity and estimate the crack location in the pipeline structure based on the proposed damage index matrix. The sensitivity of the proposed method decreases with increasing distance between the crack and the mounted piezoceramic transducers.

Structural single and multiple crack detection in cantilever beams using a hybrid Cuckoo-Nelder-Mead optimization method

Abstract In this study, the number, location and depth of cracks created in several Euler-Bernoulli beams, such as a simple beam and a more complex multi-step beam are investigated. The location and depth of the created cracks are determined using the hybrid Cuckoo-Nelder-Mead Optimization Algorithm (COA-NM) with high accuracy. The natural frequencies of the cracked beams are determined by solving frequency response equations, and performing modal test experiments. Results of COA-NM show a higher accuracy and convergence speed compared with other methods such as GA-NM, PSO-NM, GA, PSO, COA and several previous studies. Amount of calculations performed by COA-NM to achieve this accuracy is much less compared to other methods.

Damage detection of pipeline multiple cracks using piezoceramic transducers

To study the feasibility of detecting pipeline multi-cracks damage using piezoceramic transducers, the electromechanical impedance method and the stress wave based active sensing method were used respectively to perform the damage detection of pipeline with multi-cracks. In this research, the lead zirconate titanate (PZT) type transducers were used due to its strong piezoelectric effect and low cost. During the experiments, two artificial cracks on the pipeline specimen were created, ranging from 0 mm to 9 mm, and seven different operating conditions were generated for each artificial crack. In the monitoring test, for the electromechanical impedance method, the damage index based on Root Mean Square Deviation (RMSD) was used, and for the active sensing method, the damage index based on Wavelet Packet Energy Loss (WPEL) was used. In addition, the relationship between the crack depth and RMSD as well as the relationship between the crack depth and location and WPEL were analyzed. The results show that RMSD and WPEL indices increase with the increase of the depth of pipeline cracks. In addition, the WPEL index increases with the appearance of new cracks. Quantitative analysis of pipeline crack damage can be realized by electromechanical impedance method, and localization analysis on the pipeline multi-cracks damage can be achieved by stress wave method based on sensor arrays.