Crack Detection In Structures Research Articles

Multi crack detection in structures using artificial neural network

Cracks are one of the main causes of structural failure. The detection of cracks is broadly carried out using NDT methods, vibration-based methods, and various mathematical models. The detection of single crack has been widely and importantly studied in recent years. However, the diagnosis of multiple cracks is minimal. In this paper, an alternative way for detecting multiple cracks used is Artificial Neural Networks (ANN) based modeling which is a subfield of artificial intelligence. The evolutions in the ANN have brought up various new potential in the arena of complex problems. In ANN modeling, networks can be built directly from experimental data using its self-organizing capabilities which is the main advantage of using ANN. This paper tries to predict multiple cracks in cantilever beam using soft computing technique. The crack location and crack depth of two cracks are the output parameters and the first three relative natural frequencies are the input parameters to the neural network. The result sets obtained from the finite element analysis (FEA) are used to train the network and the simulated results are obtained. It has been found that the maximum error percentage between the analytical and the ANN outputs is very less which shows that the ANN can well build to predict the characteristics of the multiple crack. This paper proposes a good approach for multiple damage detection in cantilever beam.

Line Laser Image Processing for Automated Crack Detection of Concrete Structures

Line Laser Image Processing for Automated Crack Detection of Concrete Structures

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.

무인기 기반의 교량 균열 탐지를 위한 타당성 연구

This paper deals with the study of the detection and quantification of cracks in bridge structures using image data obtained by using unmanned aerial vehicle (UAV). In general, an UAV is influenced by fly environment such as a gust of wind and self-excitation during bridge inspection. Therefore, a feasibility study is required in order to verify the performance in dynamical environment. In this study, a 2D motion jig was fabricated to simulate the dynamical environment. And a steel and two concrete crack specimens were prepared. To detect crack of the specimens, improved image processing techniques (IPTs) are proposed. It is aimed to correct the image distortion due to the vibration that can occur in the appearance of the bridge using the drone. Performances of the technique were evaluated through lab-test. Finally, improved IPTs are applied to the detected regions to quantify cracks at 100 micrometers. The non-contact detection technology of bridge damage proposed in this study can be applied to the actual bridge inspection field and it is expected that the economic and technical efficiency will be high.

Automated crack detection in conductive smart-concrete structures using a resistor mesh model

Various nondestructive evaluation techniques are currently used to automatically detect and monitor cracks in concrete infrastructure. However, these methods often lack the scalability and cost-effectiveness over large geometries. A solution is the use of self-sensing carbon-doped cementitious materials. These self-sensing materials are capable of providing a measurable change in electrical output that can be related to their damage state. Previous work by the authors showed that a resistor mesh model could be used to track damage in structural components fabricated from electrically conductive concrete, where damage was located through the identification of high resistance value resistors in a resistor mesh model. In this work, an automated damage detection strategy that works through placing high value resistors into the previously developed resistor mesh model using a sequential Monte Carlo method is introduced. Here, high value resistors are used to mimic the internal condition of damaged cementitious specimens. The proposed automated damage detection method is experimentally validated using a mm3 reinforced cement paste plate doped with multi-walled carbon nanotubes exposed to 100 identical impact tests. Results demonstrate that the proposed Monte Carlo method is capable of detecting and localizing the most prominent damage in a structure, demonstrating that automated damage detection in smart-concrete structures is a promising strategy for real-time structural health monitoring of civil infrastructure.

Sweep excitation with order tracking: A new tactic for beam crack analysis

Crack detection in beams and beam-like structures is an important issue in industry and has attracted numerous investigations. A local crack leads to global system dynamics changes and produce non-linear vibration responses. Many researchers have studied these non-linearities for beam crack diagnosis. However, most reported methods are based on impact excitation and constant frequency excitation. Few studies have focused on crack detection through external sweep excitation which unleashes abundant dynamic characteristics of the system. Together with a signal resampling technique inspired by Computed Order Tracking, this paper utilize vibration responses under sweep excitations to diagnose crack status of beams. A data driven method for crack depth evaluation is proposed and window based harmonics extracting approaches are studied. The effectiveness of sweep excitation and the proposed method is experimentally validated.

Pharmacology of BMN 250 administered via intracerebroventricular infusion once every 2 weeks for twenty-six weeks or longer in a canine model of mucopolysaccharidosis type IIIB

An analytical method for determination of dimensions of longitudinal crack in monolithic beams, based on frequency measurements, has been extended to model L and inverted T cracks. Such cracks including longitudinal crack arise in beams made of layered isotropic or composite materials. A new formulation for modelling cracks in bi-material beams is presented. Longitudinal crack segment sizes, for L and inverted T cracks, varying from 2.7% to 13.6% of length of Euler-Bernoulli beams are considered. Both forward and inverse problems have been examined. In the forward problems, the analytical results are compared with finite element (FE) solutions. In the inverse problems, the accuracy of prediction of crack dimensions is verified using FE results as input for virtual testing. The analytical results show good agreement with the actual crack dimensions. Further, experimental studies have been done to verify the accuracy of the analytical method for prediction of dimensions of three types of crack in isotropic and bi-material beams. The results show that the proposed formulation is reliable and can be employed for crack detection in slender beam like structures in practice.

Application of ultrasonic waves towards the inspection of similar and dissimilar friction stir welded joints

Crack detection in welded structures of dissimilar material using guided waves is not well developed. This paper scrutinizes the effect of material discontinuity in plate structures and the excessive plastic deformation, within friction stir welded (FSW) joints, on the propagation behavior of guided waves toward their application in weld assessment. Quantifying the scattering, attenuation and group velocities of the guided waves when they propagate across different media, as well as determining the elastic properties of the material within the weld will provide rich information about the behavior of ultrasonic waves.Three pristine defect free friction stir welded plates were used in this study. The first specimen was a weld of dissimilar materials aluminum/magnesium alloy (AA6061-T6/AZ31B), the second was of dissimilar aluminum alloy grades (AA6060/AA7020-T651), and the third was of the same aluminum grade (AA7020-T651/AA7020-T651). The elastic properties across all the welds were extrapolated using nano-indentation technique. Ultrasonic guided waves were excited and measured using piezoelectric wafers and laser Doppler vibrometer (LDV). Additionally, a sensor network design was implemented on the three specimens using piezoelectric transducers.Wave reflections, based on the LDV results and the information collected from the sensor network, were observed at the weld zone of the AA6061-T6/AZ31B FSW plate, while no reflections were detected at the weld zones in the AA7020-T651/AA7020-T651 and AA6060/AA7020-T651 plates. The results were correlated with the measurements obtained from the nano-indentation experiment, where a sharp change in the elastic properties of the base metals in the AA6061-T6/AZ31B welded joint were detected, unlike the other two plates that showed constant elastic properties across the weld zones. The results showed that the amount of scattering at the joints is a function of the wave propagation direction. It was noticed that the average wave reflection generated when the wave crossed from the AZ31B to the AA6061-T6 base metal was around 35% of the incident signal, but it reduced to 25% when the wave propagation direction was reversed.Characterizing ultrasonic waves in FSWs and the behavior of the incident and reflected waves in the welded zones will further improve on the technology used for inspection and monitoring of solid state welded joints.

Identification of crack positions and crack loading quantities from strain gauge data by inverse problem solution

A method for the detection of cracks in finite and semi-infinite plane structures is presented. This allows both the identification of crack position parameters such as length, location and inclination angles with respect to a reference coordinate system and the calculation of stress intensity factors (SIFs). The method is based on strains measured at different locations on the surface of a structure and the application of the dislocation technique. Cracks and boundaries are modelled by continuous distributions of dislocation densities. This approach gives a set of singular integral equations with Cauchy kernels, which can be solved using Gauss-Chebyshev numerical quadrature [Erdogan et al. (1973)]. Once knowing the dislocation densities, the strain at an arbitrary point can be calculated. The crack parameters as well as external loads are parameters which are determined by solving the inverse problem with a genetic algorithm. Once knowing loading and crack parameters, the SIFs can be calculated.

Smart bricks for strain sensing and crack detection in masonry structures

The paper proposes the novel concept of smart bricks as a durable sensing solution for structural health monitoring of masonry structures. The term smart bricks denotes piezoresistive clay bricks with suitable electronics capable of outputting measurable changes in their electrical properties under changes in their state of strain. This feature can be exploited to evaluate stress at critical locations inside a masonry wall and to detect changes in loading paths associated with structural damage, for instance following an earthquake. Results from an experimental campaign show that normal clay bricks, fabricated in the laboratory with embedded electrodes made of a special steel for resisting the high baking temperature, exhibit a quite linear and repeatable piezoresistive behavior. That is a change in electrical resistance proportional to a change in axial strain. In order to be able to exploit this feature for strain sensing, high-resolution electronics are used with a biphasic DC measurement approach to eliminate any resistance drift due to material polarization. Then, an enhanced nanocomposite smart brick is proposed, where titania is mixed with clay before baking, in order to enhance the brick’s mechanical properties, improve its noise rejection, and increase its electrical conductivity. Titania was selected among other possible conductive nanofillers due to its resistance to high temperatures and its ability to improve the durability of construction materials while maintaining the aesthetic appearance of clay bricks. An application of smart bricks for crack detection in masonry walls is demonstrated by laboratory testing of a small-scale wall specimen under different loading conditions and controlled damage. Overall, it is demonstrated that a few strategically placed smart bricks enable monitoring of the state of strain within the wall and provide information that is capable of crack detection.

Numerical and experimental studies for crack detection of a beam-like structure using element stiffness index distribution method

In this paper, numerical and experimental studies for crack detection of structures using "element stiffness index distribution" are presented. The element stiffness index distribution is defined as a vector of norms of sub-matrices corresponding to element stiffness matrices calculated from the reconstructed global stiffness matrix of the beam. When there is a crack at an element, the element stiffness index of that element will be changed. By inspecting the change in the element stiffness index distribution, the crack can be detected. A significant peak in the element stiffness index distribution is the indicator of the crack existence. The crack location is determined by the location of the peak and the crack depth can be determined from the height of the peak. The global stiffness matrix is calculated from the measured frequency response functions instead of mode shapes to avoid limitations of the mode shape-based methods for crack detection. Numerical simulation results for the cases of beam-like structures are provided. The experiment is carried out to justify the efficiency of the proposed method.

Analytical and experimental studies on detection of longitudinal, L and inverted T cracks in isotropic and bi-material beams based on changes in natural frequencies

Abstract An analytical method for determination of dimensions of longitudinal crack in monolithic beams, based on frequency measurements, has been extended to model L and inverted T cracks. Such cracks including longitudinal crack arise in beams made of layered isotropic or composite materials. A new formulation for modelling cracks in bi-material beams is presented. Longitudinal crack segment sizes, for L and inverted T cracks, varying from 2.7% to 13.6% of length of Euler-Bernoulli beams are considered. Both forward and inverse problems have been examined. In the forward problems, the analytical results are compared with finite element (FE) solutions. In the inverse problems, the accuracy of prediction of crack dimensions is verified using FE results as input for virtual testing. The analytical results show good agreement with the actual crack dimensions. Further, experimental studies have been done to verify the accuracy of the analytical method for prediction of dimensions of three types of crack in isotropic and bi-material beams. The results show that the proposed formulation is reliable and can be employed for crack detection in slender beam like structures in practice.

Investigation of the Effect of Material on Undamped Free Vibration of Cantilever Beams with Uniform Single Surface Crack

Crack detection in structures is a critical area of research where the developments have been made out since decades. Various techniques are available for early identification and quantification of cracks to predict and prevent the unexpected sudden failure of structure and ensure uninterrupted service. Use of vibration analysis for detecting crack is one of the widely used techniques which offer lots of advantages over other like it is easier and less costly method and can be used for inaccessible components. The present work attempts to use modal analysis through FEA to investigate the effect of crack on natural frequency of vibration in beams of different materials, for three different crack location. From the result, it has been inferred that among Structural Steel (SS), Aluminium alloy (Al) and Gray Cast Iron (CI), the natural frequency is highest for Al beam and lowest for CI beam. Introduction of crack reduces the natural frequency of vibration, however, the effect of crack location on frequency is not uniform for different modes. Also, the trend is similar in beams of all the materials.

Image processing algorithms for crack detection in welded structures via pulsed eddy current thermal imaging

As the common metal structure type, welded structures are widely used in civil infrastructure, bridges, ships and engineering machinery. Fatigue cracks often originate in welds enduring intense stress concentration or in welding defects under long-term continuous alternating loading [1]. Once these cracks propagate to a critical length, the structural integrity will be challenged. As a result, welding cracks detection is significant in engineering applications.

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.

Bayesian approach to breathing crack detection in beam structures

In this paper, a Bayesian approach is developed to conduct uncertainty quantification on a single breathing crack in a beam structure using nonlinear forced responses. The proposed methodology not only determines the breathing crack characteristics but also quantifies associated uncertainties of the inferred values. Such information is important for fatigue crack monitoring and remaining life prediction in cracked beam structures. First, a single degree of freedom model is developed to characterize the nonlinear behavior of the cracked beam. The Modified Homotopy Perturbation Method (MHPM) is applied to determine analytical approximate solutions. Then, a Bayesian inference approach is proposed by applying Markov chain Monte Carlo (MCMC) technique, in which the Random Walk Metropolis algorithm is employed. The objective is to estimate crack size or location from the nonlinear vibration responses, in which noise is added to represent actual measurement data. Finally, the proposed probabilistic damage detection approach is successfully demonstrated and the breathing crack status is quantified with associated uncertainties. This leads to a new way of detecting a single breathing crack in beam structures.

Crack detection in hydraulic concrete structures using bending loss data of optical fiber

Due to low tensile strength of concrete, seasonal temperature, shrinkage of concrete, and so on, many of hydraulic concrete structures experience cracking. An optical fiber–based approach is introduced to implement the crack detection in hydraulic concrete structures. The experimental and theoretical investigations on bending loss and time-domain reflection behaviors of optical fiber are performed. According to the bending loss mechanism of optical fiber, the monitoring method of hydraulic concrete crack is presented. First, the effect of optical fiber bending radius on optical loss is analyzed. The mathematical model between bending radius and optical loss is established. Then, the identification principle of concrete crack using bending loss data of optical fiber is studied. Considering the crack characteristics of hydraulic concrete structure, the arrangement forms of optical fiber, which are used to monitor the tension crack and hybrid crack in hydraulic concrete structure, are proposed. Finally, the relationship between crack development and optical loss is investigated using laboratory experiments with optical fiber.

Crack detection of structures using modified extreme learning machine (MELM)

In this paper, crack detection and estimation method is presented in structures using modified extreme learning machine. For this purpose, extreme learning machine was modified using modified weights and biases. By using the first three frequencies and mode shapes as input, crack was detected as output. Performance of the proposed method was evaluated by using some numerical examples consisting of a simply supported beam, cantilever beam and fixed-simply supported beam. In addition, noise effect (3% noise level) on the measured frequencies and mode shapes have been investigated. In another work, a portal frame has been studied. The results indicated that the proposed method is effective and fast in crack detection and estimation of structures.

Detection of Cracks in Concrete Structure Using Microwave Imaging Technique

Cracks in concrete or cement based materials present a great threat to any civil structures; they are very dangerous and have caused a lot of destruction and damage. Even small cracks that look insignificant can grow and may eventually lead to severe structural failure. Besides manual inspection that is ineffective and time-consuming, several nondestructive evaluation techniques have been used for crack detection such as ultrasonic technique, vibration technique, and strain-based technique; however, some of the sensors used are either too large in size or limited in resolution. A high resolution microwave imaging technique with ultrawideband signal for crack detection in concrete structures is proposed. A combination of the delay-and-sum beamformer with full-view mounted antennas constitutes the image reconstruction algorithm. Various anomaly scenarios in cement bricks were simulated using FDTD, constructed, and measured in the lab. The reconstructed images showed a high similarity between the simulation and the experiment with a resolution of λ/14 which enables a detection of cracks as small as 5 mm in size.

Automatic Crack Detection and Measurement Based on Image Analysis

Crack detection and measurement in civil structures has been a constant field of research. Conventionally, a technician is responsible to detect and measure cracks in the field. In this paper, a system based on machine vision concepts has been developed with the goal to automate the crack measurement process. Using this method with only a single camera installed in a truck or even in a robot, a sequence of images is processed and the crack dimensions are estimated. The experimental results validate the application of the proposed method for real structures.