Crack Identification Method Research Articles

Wavelet-based crack identification of bridge beam from operational deflection time history

A new method for crack identification of bridge beam structures under a moving load based on wavelet analysis is presented. Crack is modeled through rotational springs whose compliance is evaluated using linear elastic fracture mechanics. Dynamic behavior of the cracked beam subject to moving load is analyzed using mode superposition. The response obtained at a single measuring point is analyzed using continuous wavelet transform and the location of the cracks is estimated. The locations of the cracks are determined from the sudden changes in the spatial variation of the transform responses. To estimate the relative depth of the cracks, a damage factor is established which relates the size of the cracks to the coefficients of the wavelet transform. The proposed method is validated by both simulation and experiment. Locations of multiple damages can be located accurately, and the results are not sensitive to measurement noise, speed and magnitude of moving load, measuring location, etc.

Variational formulation of a rod under torsional vibration for crack identification

A variational formulation is developed for the torsional vibration of a cylindrical shaft with a circumferential crack. The work is compared with existing methods. The Hu–Washizu–Barr variational formulation was used to develop the differential equation and the boundary conditions of the cracked rod. The general variational principle and the independent assumptions about the displacement, the momentum, the strain and the stress fields of the cracked rod, and the equations of motion for a uniform rod in torsional vibration, are derived. The crack was modelled as a continuous flexibility using the displacement field in the vicinity of the crack, found with fracture mechanics methods. Rayleigh quotient was used to approximate the natural frequencies of the cracked rod. Independent evaluations of crack identification methods in rotating shafts are reported and compared with methods using the continuous crack flexibility theory.

A model-based identification method of transverse cracks in rotating shafts suitable for industrial machines

This paper presents a model-based transverse crack identification method suitable for industrial machines. The method is validated by experimental results obtained on a large test rig, which was expressly designed for investigating the dynamical behaviour of cracked horizontal rotors. The identification method and the relative theory is briefly presented, while three different types of cracks are considered: the first is a slot, therefore not actually a crack since it has not the typical breathing behaviour, the second a small crack (14% of the diameter) and the third a deep crack (47% of the diameter). The excellent accuracy obtained in identifying position and depth of different cracks proves the effectiveness and reliability of the proposed method.

Gain-scheduled Control of a Smart Structure with Identification of a Crack

This paper deals with damage detection and vibration control of a smart structure. A finite element model of a cracked beam is established. This model is applied to a cantilever beam and the natural frequencies are determined for a different crack length and locations. This study proposes a method for the crack identification when the vibration of the beam is suppressed by using active control. Once cracks are present in structures, the control performance becomes worse. This is because both eigenvalue and eigenvector of the beam vary. So, in this study we design the gain-scheduled controller considering both the crack length and the location. To obtain the linear parameter-varying (LPV) model for controller design, its Frobenius norm is measured. The efficiencies of our crack identification method and the gain scheduled controller design are verified by simulation.

Determination of the Crack Configuration in an Anisotropic Elastic Medium

The problem of the identification of a single internal crack in an anisotropic elastic body is investigated. Using the dislocation theory approach, a system of boundary integral equations for the crack opening functions is constructed and studied by the boundary element method. A crack identification method is developed on the basis of the crack parametrization by a finite number of parameters, with their subsequent determination through the minimization of a certain nonquadratic residual functional. The problem of identifying a transverse tunnel crack in an orthotropic layer is solved for the cases of plane and antiplane deformations.

712 振動制御中の構造物に対するクラック推定とゲインスケジュールド制御

This paper deals with damage detection and vibration control of a smart structure. A finite element model of a cracked beam is established. This model is applied to a cantilever beam and the natural frequencies are determined for a different crack length and locations. This study proposes a method for the crack identification when the vibration of the beam is suppressed by using active control. Furthermore, we design the gain-scheduled controller considering both the crack length and the location. The efficiencies of our crack identification method and the gain-scheduled controller design are verified by simulation and experiment.

Crack Identification in Plates Using Genetic Algorithm

When a crack exists in a structural member, it leads to changes in natural frequencies. Therefore, cracks in structures can be detected by measuring the vibrations in the natural frequencies of appropriate vibration modes. In this paper a crack identification method for plates is presented using both a genetic algorithm (GA) and FEM. The FEM program is developed to calculate the natural frequencies of the cracked plates based on the BFM (Bogner, Fox and Schmidt) plate model since the accuracy of the forward solver is important. In the study, two types of cracks, i.e., internal and edge crack are considered. To identify the crack location and the depth from frequency measurements, the width and the position of the crack in a plate are coded into fixed-length binary digit string. By using GA, the square sum of residuals between the measured data and the dynamic response is minimized in the identification process and thus the crack is identified. To avoid a large number of calculation cost, Response Surface Method (RSM) is also adopted in the minimizing process. The combination of GA and RSM made the identification more effective ad robust. The availability of the proposed method is confirmed by -results of numerical simulation.

212 き裂を有するはりのGAによる逆解析 : 三次元P法FEMを用いたき裂の逆解析(関東支部 茨城講演会)

In this paper a crack identification method for beam is presented using both a genetic algorithm (GA) and FEM. To identify the crack location from frequency measurements, FEM program is also developed to calculate the natural frequencies of the cracked beam based on 8-node hexahedron element. The position of the crack in the beam are estimated by using these natural frequencies and the GA. The availability of the proposed method is confirmed by results of numerical simulation.

Crack identification in double-cracked beams using wavelet analysis

A method for crack identification in double-cracked beams based on wavelet analysis is presented. The fundamental vibration mode of a double-cracked cantilever beam is analyzed using continuous wavelet transform and both the location and depth of the cracks are estimated. The location of the cracks is determined by the sudden changes in the spatial variation of the transformed response. To estimate the relative depth of the cracks, an intensity factor is established which relates the size of the cracks to the coefficients of the wavelet transform. It is shown that the intensity factor follows definite trends and therefore can be used as an indicator for crack size. The proposed technique is validated both analytically and experimentally in case of a double-cracked cantilever beam having cracks of varying depth at different positions. In the light of the obtained results, the advantages and limitations of the method are presented and discussed.

Crack Identification of Curved Beam Using Frequency Change

In this paper a crack identification method for curved beams is presented using both genetic algorithm (GA) and FEM. The crack is simulated by an equivalent rotational spring model. On the basis of this approximate model, the stiffness matrices of a cracked element are derived employing the curved beam theory. In order to calculate the natural frequencies of the curved beam, which are required to identify of the crack location and the depth from frequency measurements, FEM program including the cracked element is developed. The depth and the position of the crack in the curved beam are estimated by using these natural frequencies and GA. The proposed method is verified by numerical simulation of some sample problems.

Crack identification in plates using wavelet analysis

In this paper, a method for crack identification in plates based on wavelet analysis is presented. The case of an all-over part-through crack parallel to one edge of the plate is considered. The vibration modes of the plate are analyzed using the continuous wavelet transform and both the location and depth of the crack are estimated. The position of the crack is determined by the sudden change in the spatial variation of the transformed displacement response. To estimate the depth of the crack, an intensity factor is defined which relates the depth of the crack to the coefficients of the wavelet transform. An intensity factor law is established which allows accurate prediction of crack depth. The viability of the proposed approach is demonstrated using simulation examples. In view of the obtained results, the advantages and limitations of the proposed approach as well as suggestions for future work are presented and discussed.

Crack identification in beams using wavelet analysis

In this paper a simple method for crack identification in beam structures based on wavelet analysis is presented. The fundamental vibration mode of a cracked cantilever beam is analyzed using continuous wavelet transform and both the location and size of the crack are estimated. The position of the crack is located by the sudden change in the spatial variation of the transformed response. To estimate the size of the crack, an intensity factor is defined which relates the size of the crack to the coefficients of the wavelet transform. An intensity factor law is established which allows accurate prediction of crack size. The viability of the proposed method is investigated both analytically and experimentally in case of a cantilever beam containing a transverse surface crack. In the light of the results obtained, the advantages and limitations of the proposed method as well as suggestions for future work are presented and discussed.

314 き裂を有する平板の効率的な逆解析 : 第三報内部き裂を有する場合の逆解析

In this paper a crack identification method for plates is presented using both a genetic algorithm (GA) and FEM. In addition to an edge crack, this paper is concerned with an internal crack of plates. To identify the crack location and the width from frequency measurements, FEM program is also developed to calculate the natural frequencies of the cracked plates. The width and the position of the crack in the plate are estimated by using these natural frequencies and the GA. The availability of the proposed method is confirmed by results of numerical simulation.

Operator controlled, vehicle-based highway crack-sealing machine

This paper presents a new heavy vehicle system developed for the automated sealing of cracks in highway pavement. The machine has been developed based on the authors' experience over the last twelve years building such machines. A special sealant applicator that deploys a pressurised reservoir was developed to allow for high-speed, automated sealing operations. A telescoping long-reach robotic arm was developed, which can position the sealing head mounted to its end in a 3.65 m (12 ft) by 4 m (13 ft) large workspace within 0.4 mm (1/64 in) at a traverse speed up to 1 m/s (3 ft/s). To ensure adequate sealant flow, a special electrically heated hose was developed. A control network of both fast 100 Mbps Ethernet and 10 Mbps Wireless allows for distributed real-time motion control, I/O control and machine vision. A fully object-oriented, multi-threaded and Internet-based software architecture allows reliable and efficient system integration and provides an interactive and responsive user interface for feature-rich and easy imaging, path planning and system control. An operator-assisted crack identification method is used and the path planning method is based on simulated annealing in order to optimally seal a network of cracks.

Genetic Algorithm Approach for Crack Identification of Plane Frame Structures by Timoshenko Beam Theory.

In this paper a crack identification method of plane frame is presented using both genetic algorithm (GA) and FEM. The crack is simulated by an equivalent rotational spring model. On the basis of this approximate model, the stiffness matrices of a cracked element are developed employing the Timoshenko beam thory. In order to calculate the natural frequencies of the frame, which are required to identify of the crack location and depth from frequency measurements, FEM program including the cracked element is written. The depth and the position of the crack in the plane frame are estimated by using these natural frequencies and GA. The proposed method is verified by numerical simulation of some sample problems.

Nondestructive identification of three-dimensional embedded cracks in finite bodies by inversion of surface displacements

A combined experimental and numerical investigation demonstrates the effectiveness of a nondestructive method for crack identification based on inversion of surface displacements. Holographic interferometry was used to measure displacements of transparent acrylic cubes containing pressurized cracks. Results compared favorably with those of a three-dimensional hybrid numerical model. A nonlinear inversion code, using Levenberg–Marquardt iterations, was developed in order to search for the fracture geometries which minimized the difference between the theoretical and experimental predictions of surface displacement. The resulting algorithm was able to distinguish clearly the specimen geometries. The requisite level of robustness was achieved by gradually relaxing the constraints on the fracture geometry.

Inverse Analysis of Cracked Frame Structures by Genetic Algorithm.

A crack in a structural member can change the eigenfrequencies of the undamaged structure. The magnitude of change in the eigenfrequencies is a function of the depth and the location of the crack. By relating the eigenfrequencies to the crack location and depth, we proposed a crack identification method for plane frame structures in present paper. In the FEM vibration analysis for the structures, the crack is simulated by an equivalent rotational spring, connecting the two segments of the beam. The matrix elements containing a crack are derived explicitly by combining both the transfer matrix method and the compatibility equation of each segment. The eigenfrequencies computed by FEM are then applied to studying the inverse problem-identification of crack location from frequency measurements. And the crack identification method is performed by using both the finlte element method and the genetic algorithm. In order to confirm the validity of the proposed method, several frame structures with a crack are analyzed.

Analytical and experimental crack identification of beam structures in air or in fluid

In this paper a new method for crack identification in beams is presented. The transverse surface crack is considered to remain always open. Using this method the crack location and depth can be determined. The method is based on the basic observation that the eigenmodes of any cracked structure are different from those of the uncracked one. The differences are due to the slope discontinuity of the vibration eigenmodes at the crack location. The basic idea in this paper is to correlate the mode differences with the crack depth and location. These correlated differences are chosen to be (a) the ratio of two amplitude measurements in two positions and (b) the distance of the node of the vibrating mode from the left end, while the structure is vibrating under harmonic excitation in resonant condition. The analytical results presented here are also experimentally proven. In a free-free beam the two first eigenmodes are measured and the node distance of the uncracked and the cracked beam are used in pre-plotted diagrams to verify the crack location and depth. Here, it is also theoretically proved that the above results for the beam are the same in both the air and the water. This is valid irrespective of whether the damping effect is taken into consideration or not.

An improved method for magnetic identification and localization of cracks in conductors: Wikswo, J.P.; Sepulveda, N.G.; Ma, Y.P.; Henry, W.P.; Staton, DJ.; Crum, D. Journal of Nondestructive Evaluation, Vol. 12, No. 2, pp. 109–119 (Jun. 1993

An improved method for magnetic identification and localization of cracks in conductors: Wikswo, J.P.; Sepulveda, N.G.; Ma, Y.P.; Henry, W.P.; Staton, DJ.; Crum, D. Journal of Nondestructive Evaluation, Vol. 12, No. 2, pp. 109–119 (Jun. 1993

A biem optimization method for fracture dynamics inverse problem

In the present paper, based on the theory of dynamic boundary integral equation, an optimization method for crack identification is set up in the Laplace frequency space, where the direct problem is solved by the author's new type boundary integral equations and a method for choosing the high sensitive frequency region is proposed. The results show that the method proposed is successful in using the information of boundary elastic wave and overcoming the ill-posed difficulties on solution, and helpful to improve the identification precision.