Detection Of Multiple Cracks Research Articles

Detection of multiple thin surface cracks using vibrothermography with low-power piezoceramic-based ultrasonic actuator—a numerical study with experimental verification

Ultrasonic vibrations in cracked structures generate heat at the location of defects mainly due to frictional rubbing and viscoelastic losses at the defects. Vibrothermography is an effective nondestructive evaluation method which uses infrared imaging (IR) techniques to locate defects such as cracks and delaminations by detecting the heat generated at the defects. In this paper a coupled thermo-electro-mechanical analysis with the use of implicit finite element method was used to simulate a low power (10 W) piezoceramic-based ultrasonic actuator and the corresponding heat generation in a metallic plate with multiple surface cracks. Numerical results show that the finite element software Abaqus can be used to simultaneously model the electrical properties of the actuator, the ultrasonic waves propagating within the plate, as well as the thermal properties of the plate. Obtained numerical results demonstrate the ability of these low power transducers in detecting multiple cracks in the simulated aluminum plate. The validity of the numerical simulations was verified through experimental studies on a physical aluminum plate with multiple surface cracks while the same low power piezoceramic stack actuator was used to excite the plate and generate heat at the cracks. An excellent qualitative agreement exists between the experimental results and the numerical simulation’s results.

Multiple cracks detection and visualization using magnetic flux leakage and eddy current pulsed thermography

This paper investigates two non-destructive evaluation methods, magnetic flux leakage (MFL) and eddy current pulsed thermography (ECPT), for both artificial and natural multiple cracks (MC) detection and visualization. The detection capability and characteristics of MC visualization are verified and compared through simulations and experiments. Results show that, MFL testing reflects the surface shapes and orientations of MC by 3D magnetic field imaging. However, it is unable to evaluate the depth of artificial MC and detailed surface shapes of natural MC due to limitations of sensor array spatial resolution. ECPT shows more capability in MC visualization in detail from thermal images. The obtained thermal image sequences from ECPT demonstrate rich transient and pattern information to evaluate MC geometrical features. After discussion of the two methods with the probability of detection (POD) analysis, a promising new sensing structure which potentially combines both advantages of them is proposed to enhance the NDE performance for MC evaluation.

Experimental verification of detection and prediction of multiple cracks by vibrations, FEM and ANN

Purpose – The purpose of this paper is to address the determination of crack location and depth of multiple transverse cracks by monitoring natural frequency and its prediction using Artificial Neural Networks (ANN). An alternative to the existing NDTs is suggested. Design/methodology/approach – Modal analysis is performed to extract the natural frequency. Analysis is performed for two cases of cracks. In first case, both cracks are perpendicular to axis. In second case, both cracks are inclined to vertical plane and also inclined with each other. Finite element method (FEM) is performed using ANSYSTM software which is theoretical basis. Experimentation is performed using Fast Fourier Transform (FFT) analyzer on simply supported stepped rotor shaft and cantilever circular beam with two cracks each. Findings – The results of FEM and experimentation are validated and are in good agreement. The error in crack detection by FEM is in the range of 3-15 percent while 5-20 percent by experimentation. The database obtained by modal analysis is used to train the network of ANN which predicts crack characteristics. Validity of method is investigated by comparing the predictions of ANN with FEM and experimentation. The results are in good agreement with error of 7-16 percent between ANN and FEM while 9-21 percent between ANN and experimental analysis. Originality/value – It envisages that the method is capable. It is an effective as well as an alternate method of fault detection in beam/rotating element to the existing methods.

MRT detection of fretting fatigue cracks in a cableway locked coil rope

The Magnetic Rope Testing is a non-destructive method in use for the detection of flaws and cracks in steel wire ropes. Given the severe protocol of safety certification for in-service cableway ropes, a proper methodology operating in accordance with new European standard specifications is here presented. A relevant experience about detection of multiple cracks due to fretting fatigue on a peculiar locked coil structure rope is also shown and discussed.

Multiple crack damage detection of structures using the two crack transfer matrix

A damage detection scheme for multiple crack detection in beams is presented, based on a transfer matrix derived from beam element with two cracks. Based on fracture mechanics principles, a crack is modelled as a hinge, which provides an additional flexibility to the element. Each element is assumed to have two open-edge cracks and a new transfer matrix called two crack transfer matrix is developed using finite element method. Using an inverse approach, the transfer matrix is used to predict cracks in a beam. The state vector at a node includes displacements, forces and moments at that node; when it is multiplied with the transfer matrix, the state vector at the adjacent node can be obtained. The state vector formed at the starting node, known as initial state vector, needs to be estimated, from which state vectors at adjacent nodes are predicted using the transfer matrix. Displacement responses are measured at a few adjacent nodes in the structure. The mean square error between measured and predicted responses is minimized using a heuristic optimization algorithm, with crack depth and location in each element as the optimization variables. Two numerical examples, a cantilever and a sub-structure of a frame with nine members, are solved with two cracks in each element. The damage detection method is also validated experimentally by local identification of sub-structure of a fixed beam where the initial state vector is measured using strain gauges and accelerometers. Using this method, two cracks per single element were successfully identified. The two crack transfer matrix method is suitable for local damage identification in large structures.

Detection and localisation of multiple cracks in a shaft system: An experimental investigation

Experimental verification of an algorithm for detection and localisation of multiple cracks in a simple shaft system is presented. Cracks in a shaft cause the slope discontinuity in the shaft elastic line. The algorithm is based upon detecting the slope discontinuity due to cracks. Two simply supported non-rotating shafts are used for the experimentation. Both the shafts are tested with single as well as double artificially introduced open cracks. Transverse deflections of the shaft due to sine-sweep excitation force through an exciter are measured at regular axial locations of the shaft. The slope discontinuity is obtained by fitting shaft deflections at regular axial locations in a quadratic polynomial. The algorithm uses shaft deflections at several excitation frequencies to incorporate adequate modal information in the response to improve the crack identification. A scheme is proposed to improve the working of the algorithm in low signal to noise ratio conditions. The algorithm identifies the presence of crack and successfully locates the crack along the shaft length.

Detection of Cracks in Structures Using Two Crack Transfer Matrix

Abstract A novel damage detection scheme for multiple crack detection in a beam like structures is presented, based on a transfer matrix (TM) derived from the beam element with two cracks. Based on Linear Elastic Fracture Mechanics (LEFM) principles, a crack is modelled as a hinge which provides an additional flexibility to the element. Each element is assumed to have two open edge cracks and a new TM called Two Crack Transfer Matrix (TCTM) is developed using the Finite Element method. Using an inverse approach, the TCTM is used to predict cracks in a beam. The state vector at a node includes displacements, forces and moments at that node; when it is multiplied with the TM the state vector at the adjacent node can be obtained. The state vector formed at the starting node, known as initial state vector needs to be estimated, from which state vectors at adjacent nodes are predicted using the TM. Displacement responses are measured at a few adjacent nodes in the structure. The mean square error (MSE) between measured and predicted responses is minimized using a heuristic optimization algorithm, with crack depth and location in each element as the optimization variables. Two numerical examples, a cantilever and a sub-structure (SS) of a frame with nine members are solved with two cracks in each element. The damage detection method is also validated experimentally by local identification of a SS of a fixed beam where the initial state vector is measured using strain gauges and accelerometers. Using this method, maximum of two cracks per element were successfully identified. The TCTM method is suitable for local damage identification in large structures.

Multiple Crack Detection of Pipes Using PZT-Based Guided Waves

This paper focuses on the multiple crack detection of steel pipelines using PZT-based guided waves. Numerical simulations of cracked pipes based on ultrasonic guided-waves are conducted by using the ANSYS finite element software. Based on the analysis of the reflected signal, the arrival time of the crack reflection waves are determined and the crack positions are accurately evaluated by the calculation of the travel time and group velocity of the PZT-based guided waves. The crack parameters are numerically altered to determine how the parameters impact the sensitive degree of the pipe crack damage. To validate the efficiency of the numerical simulation, an experiment of the multiple crack detection for the same parameter pipe with the numerical model is performed in the laboratory, and the results match well with the numerical simulation.

Change in mode shape nodes of multiple cracked bar: I. The theoretical study

In present paper change in position of mode shape nodes induced by multiple cracks in bar is studied with purpose to use for the multiple crack detection from measured mode shape nodes. First, there is derived an explicit expression for natural modes in axial vibration of multiple cracked bar that allows obtaining exact positions of the node in the case of single and double crack. The change in mode shape nodes induced by multiple cracks provides an important indicator for crack localization in bar. Finally, a procedure for multiple crack detection by using mode shape nodes has been proposed and examined in an example of application.

Vibration based algorithm for crack detection in cantilever beam containing two different types of cracks

In this paper, a simple method for detection of multiple edge cracks in Euler–Bernoulli beams having two different types of cracks is presented based on energy equations. Each crack is modeled as a massless rotational spring using Linear Elastic Fracture Mechanics (LEFM) theory, and a relationship among natural frequencies, crack locations and stiffness of equivalent springs is demonstrated. In the procedure, for detection of m cracks in a beam, 3m equations and natural frequencies of healthy and cracked beam in two different directions are needed as input to the algorithm.The main accomplishment of the presented algorithm is the capability to detect the location, severity and type of each crack in a multi-cracked beam. Concise and simple calculations along with accuracy are other advantages of this method. A number of numerical examples for cantilever beams including one and two cracks are presented to validate the method.

Three-steps-meshing based multiple crack identification for structures and its experimental studies

Multiple crack identification plays an important role in vibration-based crack identification of structures. Traditional crack detection method of single crack is difficult to be used in multiple crack diagnosis. A three-step-meshing method for the multiple cracks identification in structures is presented. Firstly, the changes in natural frequency of a structure with various crack locations and depth are accurately obtained by means of wavelet finite element method, and then the damage coefficient method is used to determine the number and the region of cracks. Secondly, different regions in the cracked structure are divided into meshes with different scales, and then the small unit containing cracks in the damaged area is gradually located by iterative computation. Lastly, by finding the points of intersection of three frequency contour lines in the small unit, the crack location and depth are identified. In order to verify the effectiveness of the presented method, a multiple cracks identification experiment is carried out. The diagnostic tests on a cantilever beam under two working conditions show the accuracy of the proposed method: with a maximum error of crack location identification 2.7% and of depth identification 5.2%. The method is able to detect multiple crack of beam with less subdivision and higher precision, and can be developed as a multiple crack detection approach for complicated structures.

Multiple cracks detection in a beam subjected to a moving load using wavelet analysis combined with factorial design

Abstract In this paper, a new method of multiple cracks detection in a simply supported beam subjected to a moving load along the beam based on Continuous Wavelet Transform (CWT) combined with factorial design is presented. Deflection of the beam when the moving load passes the mid span of the beam is considered. Peaks in the CWT coefficient of data using Gaussian4 Wavelet show Cracks' location. The value of CWT coefficient at the points of cracks assumed as Damage Index (DI). A technique for defining the velocity of moving load and normalizing the deflection introduced which makes the DI independent from beam material parameters. The important parameters which affect the damage index are found using factorial design. By introducing a novel multivariable curve fitting approach, an explicit expression for the DI is developed which shows effect of all important parameters clearly. Applying factorial design, it is shown that the DI of one crack does not depend on the size and location of other cracks in a multiple cracked beam. Hence, the obtained expression for the DI can be used to find the size of each crack independently. The proposed damage index can detect the crack depths of more than 5% of beam's height and can predict the size of crack even in the case of noisy data. The effect of 10% noise level on the beam having three cracks was introduced and is shown this noise level does not affect the procedure of damage detection introduced in this paper. Each crack is modeled as a rotational spring whose stiffness is obtained from fracture mechanics. The modal expansion theory is used to obtain the response of the beam due to moving load.

On multiple crack detection in beam structures

This study presents an inverse procedure to identify multiple cracks in beams using an evolutionary algorithm. By considering the crack detection procedure as an optimization problem, an objective function can be constructed based on the change of the eigenfrequencies and some strain energy parameters. Each crack is modeled by a rotational spring. The changes in natural frequencies due to the presence of the cracks are related to a damage index vector. Then, the bees algorithm, a swarm-based evolutionary optimization technique, is used to optimize the objective function and find the damage index vector, whose positive components show the number and position of the cracks. A second objective function is also optimized to find the crack depths. Several experimental studies on cracked cantilever beams are conducted to ensure the integrity of the proposed method. The results show that the number of cracks as well as their sizes and locations can be predicted well through this method.

Evaluation of fatigue cracks using nonlinearities of acousto-ultrasonic waves acquired by an active sensor network

There has been increasing interest in using the nonlinear features of acousto-ultrasonic (AU) waves to detect damage onset (e.g., micro-fatigue cracks) due to their high sensitivity to damage with small dimensions. However, most existing approaches are able to infer the existence of fatigue damage qualitatively, but fail to further ascertain its location and severity. A damage characterization approach, in conjunction with the use of an active piezoelectric sensor network, was established, capable of evaluating fatigue cracks in a quantitative manner (including the co-presence of multiple fatigue cracks, and their individual locations and severities). Fundamental investigations, using both experiment and enhanced finite element analysis dedicated to the simulation of nonlinear AU waves, were carried out to link the accumulation of nonlinearities extracted from high-order AU waves to the characteristic parameters of a fatigue crack. A probability-based diagnostic imaging algorithm was developed, facilitating an intuitive presentation of identification results in images. The approach was verified experimentally by evaluating multi-fatigue cracks near rivet holes of a fatigued aluminum plate, showing satisfactory precision in characterizing real, barely visible fatigue cracks. Compared with existing methods, this approach innovatively (i) uses permanently integrated active sensor networks, conducive to automatic and online health monitoring; (ii) characterizes fatigue cracks at a quantitative level; (iii) allows detection of multiple fatigue cracks; and (iv) visualizes identification results in intuitive images.

Detection and localization of multiple cracks in a stepped shaft

ABSTRACTThe presence of a crack in a shaft causes a slope discontinuity in the elastic line of the shaft. There are crack detection techniques, available in the literature, exploiting the slope discontinuity arising because of the crack in the shaft. Steps present in a shaft are expected to interfere with the results obtained through these identification techniques based upon slope discontinuity. It would be even more difficult to identify a crack if it is near a step as both the step and the crack will cause slope discontinuities. A multi‐crack identification technique has been developed (Singh S. K. and Tiwari R. (2010). Mech. Machine Theory 45, 1813–1827; Singh S. K., Tiwari R. and Talukdar S. (2009). IUTAM Proc. in Recent Trends in Rotor Dynamics, March 23–26, IIT Delhi, India) which uses shaft‐forced responses at several frequencies to identify the number of cracks and their locations over the shaft. The algorithm uses normalization of quadratic coefficients obtained from measured responses of a cracked shaft and from simulated responses of the intact shaft for detecting the slope discontinuity. In the present work, the effect of steps in the shaft on crack identification has been analysed. Cracks are assumed to be both near the step and far from the step. The identification algorithm works well for both the simulation cases.

Sampling interval sensitivity analysis for crack detection by stationary wavelet transform

The purpose of this paper was to analyze the sampling interval sensitivity for crack detection by stationary wavelet transform (SWT) in order to facilitate the identification of crack locations in beam-like structures. SWT is a redundant transform that doubles the number of input samples at each iteration. It has been shown that the SWT decomposition detail coefficient of mode shapes of beam-like structure can provide sensitive crack indication that is useful for damage detection. However, the sampling interval is an important factor that affects the sensitivity of crack detection. Three SWT methods were analyzed, including the method using the SWT of the original mode shape (designated SWT-1), the method using the difference between the detail coefficients of the SWT of the left-half and the reconstructed right-half sets of the mode shapes (designated SWT-2), and the method using the difference between the detail coefficient of the left-half and right-half sets of the interpolated mode shapes (designated SWT-3). The modal responses of damaged beams with single and multiple cracks are computed using the finite element method. The curve of the peak value of SWT detail coefficient versus sampling interval was obtained using a fifth-order polynomial fit method. The effects of crack depth, crack width, and crack locations on the sensitivity of sampling interval on crack detection are investigated. SWT-2 method has a shortcoming in determining whether the cracks are located at the true crack location or its mirror image position at different sampling intervals. In order to overcome this shortcoming, two rules are proposed for the determination of true crack locations and the selection of sampling intervals for single crack or multiple crack detection.

Topological Sensitivity Analysis for Steady State Eddy Current Problems With an Application to Nondestructive Testing

This paper proposes a novel solution to the inverse problem of eddy current nondestructive testing (NDT) based on topological shape optimization. The topological gradient (TG) is derived for a steady state eddy current problem using a topological asymptotic expansion for the Maxwell equation of a time harmonic problem. TG provides information on where the objective function is most sensitive to topology changes and can be used as a fast identification of the locations of the defects in the test specimen. The proposed method has been applied to typical eddy current testing (ECT) problems such as buried crack reconstruction and the detection of multiple cracks. The reconstructed shape of the crack shows good agreement with the experimental data from TEAM workshop problem 15. A comparison of different ECT inverse analyses is also discussed.

Formulation of a Genetic Algorithm Based Methodology for Multiple Crack Detection in a Beam Structure

In the current analysis, the vibration characteristics of a cracked cantilever beam having different crack locations and depths have been studied. Numerical and finite element methods have been used to extract the diagnostic indices (natural frequencies, mode shapes) from the beam structure. An intelligent genetic algorithm based controller has been designed to automate the fault identification process. Single point crossover and mutation procedure have been followed to find out the optimal solution from the search space. The outcome from the developed controller shows that the system could not only detect the cracks but also predict their locations and severities.

Statistical detection of multiple cracks on thin plates utilizing dynamic response

This paper focuses on the development of a practice crack detection methodology for identifying cracks on thin plate structures utilizing measured dynamic responses on only a few points on the target plate. From the literature, most existing model-based methods target on the detection of single-crack (or multi-crack with a given crack number) on beams. Only very limited research works have been carried out for the detection of multiple cracks for plate-type structures following the model-based method. The proposed crack detection methodology consists of two phases. The number of cracks is first identified by adopting the Bayesian model class selection method in the first phase. In the second phase, the posterior (updated) probability density function (PDF) of the crack parameters, such as crack locations, lengths and depths are identified following the Bayesian statistical identification framework. This paper reports not only the theoretical development but also a comprehensive series of numerical case studies for illustrating and verifying the proposed methodology. The numerical case study results are encouraging showing that the proposed methodology can correctly identify the number of cracks, the corresponding crack parameters and the associated uncertainties. Different factors affecting the accuracy of the crack detection results are studied and discussed through the case studies.

Analytical Approach for Detection of Multiple Cracks in a Beam

An analytical approach for the detection of a beam with multiple cracks is presented in this article. The method is based on the bending vibration theory of Euler-Bernoulli beam and the cracks are treated as massless rotational springs, by which the cracked beam is separated into a number of segments of perfect beams. By using the nontrivial solution condition of the vibration mode of the beam elements, specially using the transfer matrix method for the multiple cracks detection, the crack identification equation of the cracked beam is obtained explicitly, which is a function of natural frequencies, the locations, and depths of the cracks. Since the natural frequencies of a cracked beam can be measured through many of the structural testing methods, then the relations of the locations and the depths of the cracks can be determined explicitly from the identification equation of a cracked beam which geometrical and physical parameters as well as the boundary conditions are given. The results of some examples are shown and the present method is validated with the existing and measured experimental data. The detection for other types of beams with different number of cracks and various boundary conditions can also be obtained by a similar procedure.