Crack Parameters Research Articles

Intelligent feature extraction, data fusion and detection of concrete bridge cracks: current development and challenges

As a common appearance defect of concrete bridges, cracks are important indices for bridge structure health assessment. Although there has been much research on crack identification, research on the evolution mechanism of bridge cracks is still far from practical applications. In this paper, the state-of-the-art research on intelligent theories and methodologies for intelligent feature extraction, data fusion and crack detection based on data-driven approaches is comprehensively reviewed. The research is discussed from three aspects: the feature extraction level of the multimodal parameters of bridge cracks, the description level and the diagnosis level of the bridge crack damage states. We focus on previous research concerning the quantitative characterization problems of multimodal parameters of bridge cracks and their implementation in crack identification, while highlighting some of their major drawbacks. In addition, the current challenges and potential future research directions are discussed.

Highly sensitive methods for vibration diagnostics of fatigue damage in structural elements of aircraft gas turbine engines

Vibration diagnostics of damage belongs to the class of non-destructive methods, which usually do not take long time. However, the main problem of vibration diagnostics is relatively low sensitivity to the critical damage of fatigue crack type, which arises because of long time accumulation of plastic deformation. To improve the sensitivity and reliability of vibration diagnostics of damage two methods were considered. The first method was based on the fact, that a characteristic feature of vibrations of structural elements with fatigue crack is the occurrence of non-linear resonances (sub- and super-harmonic) and significant non-linearity of vibration response at these resonances. The second one – on the fact, that quite noticeable in certain cases increase of damping characteristic caused by a crack can be observed. Analytical and experimental studies of these methods were carried out as applied to the blades of aircraft gas turbine engines. As a result of the studies, the intensity of change in parameter of super-harmonic resonance and in damping characteristics at different parameters of crack was determined. Besides, the experimental techniques for vibration testing of turbine blades were developed. There was demonstrated, that the sensitivity of both considered methods of vibration diagnostics is several orders of magnitude higher than the sensitivity of conventional methods based on the change in natural frequencies and mode shapes, and they can be effectively used for the diagnostics of blades on the stage of engine repair.

Analysis on Stop-hole Parameters for Fatigue Cracks at Arc Notch in Steel Bridge Deck

Two types of fatigue cracks at arc notch in steel bridge deck were repaired by drilling stop-holes. The effect of stop-holes with different diameters and positions was considered. Based on finite element models, the variation laws of stress distribution and the effects of stress concentration were compared for different stop-hole diameters and positions. Analysis results indicated that stop-hole can effectively improve the stress concentration at crack tip and the fatigue life of components can be considerably increased. The crack-stopping performance enhances with the increase of stop-hole diameter, but large stop-hole cannot effectively retard crack growth. The stop-hole performs well with the location at -0.5D∼0.5D. The maximum stress point still appears at crack tip when the stop-hole is outside or inside the crack. The stop-hole diameter has no effect on the stop-hole location.

Primena parisovog zakona u uslovima promenljivog opterećenja

The most important characteristics for service safety of welded joints are those describing crack initiation and growth caused by variable loading. Crack initiation and growth caused by variable loading is the subject of numerous investigations. This paper shows the determination of parameters of the fatigue crack for constituents of welded joints produced of high strength low alloyed steel. The crack growth law of Paris establishes the relation between the applied variable load quantity or the corresponding stress intensity factor range and crack growth per cycle. Results have shown that the position of the notch and crack initiation affect the values of the stress intensity range of fatigue threshold DKth and parameters in the Paris' equation.

Estimation of Fracture Mechanics Parameters and Inclined Angle of Crack Using Digital Image Correlation Method

Cracks in mechanical structures lead to serious destruction accidents. High precision detection of cracks and evaluation of mechanical parameter of crack are important issues in order to prevent destruction accidents. In this study, we developed a crack detection method by digital correlation method which can evaluate the strain distribution from the surface image. Using this method, the stress intensity factors for mode I and mode II can be evaluated from sample surface. It also can be used to evaluate the inclination angle of the cracks.

A study on J-integral and J-integral range ΔJ applicable to finite deformation elastic-plastic problems

This paper summarizes the formulations and some of the applications of the three-dimensional J-integral and J-integral range ΔJ that were proposed by the authors. The proposed crack parameters are evaluated by the domain integral method. Their values are guaranteed to be unconditionally independent of size and shape of integral domain by their formulation. The numerical examples demonstrate that the proposed crack parameters can characterize the severity of the crack tip deformation field. Hence, they can characterize the crack propagation behavior.

3D crack identification using the Nelder-Mead Simplex algorithm combined with a random generation of crack positions

In this paper, we present a scheme for cracks identification in three-dimensional linear elastic mechanical components. The scheme uses a boundary element method for solving the forward problem and the Nelder-Mead simplex numerical optimization algorithm coupled with a low discrepancy sequence in order to identify an embedded crack. The crack detection process is achieved through minimizing an objective function defined as the difference between measured strains and computed ones, at some specific sensors on the domain boundaries. Through the optimization procedure, the crack surface is modelled by geometrical parameters, which serve as identity variables. Numerical simulations are conducted to determine the identity parameters of an embedded elliptical crack, with measures randomly perturbed and the residual norm regularized in order to provide an efficient and numerically stable solution to measurement noise. The accuracy of this method is investigated in the identification of cracks over two examples. Through the treated examples, we showed that the method exhibits good stability with respect to measurement noise and convergent results could be achieved without restrictions on the selected initial values of the crack parameters.

Non-linear vibration analysis of specially orthotropic tapered micro-plates with arbitrary located crack: A non-classical analytical approach

The present work aims to study the non-linear vibrations in a cracked orthotropic tapered micro-plate. Linear and parabolic variation in the plate thickness is assumed in one as well as two directions. The partial crack is located in the centre, and it is continuous; this crack’s location is arbitrary and can be varied within the centre-line. Based on classical plate theory, the equilibrium principle is applied, and the governing equation of tapered orthotropic plate is derived. Additionally, the microstructure’s effect has been included in the governing equation using the non-classical modified couple stress theory. The simplified line spring model is used to consider the impact of partial crack on the plate dynamics and is incorporated using in-plane forces and bending moments. The introduction of Berger’s formulation brings the non-linearity in the model in terms of in-plane forces. Here, Galerkin’s method has been chosen for converting the derived governing equation into time-dependent modal coordinates, which uses an approximate solution technique to solve the non-linear Duffing equation. The crack is considered along the fibres and across the fibres to show the effect of orthotropy. Results are presented for an orthotropic cracked plate with non-uniform thickness. The effects of the variation of taper constants, crack location, crack length, internal material length scale parameter on the fundamental frequency are obtained for two different boundary conditions. The non-linear frequency response curves are plotted to show the effect of non-linearity on the system dynamics using the method of multiple scales, and the contribution of taper constants and crack parameters on non-linearity is shown with bending-hardening and bending-softening phenomenon. It has been found that vibration characteristics are affected by the taper parameters and fibre direction for a cracked orthotropic plate.

A Macro–Micro Damage Model for Rock under Compression Loading

Rock damage caused by its microcrack growth has a great influence on the deformation and strength properties of rock under compressive loading. Considering the interaction of wing cracks and the additional stress caused by rock bridge damage, a new calculation model for the mode-I stress intensity factor at wing crack tip was proposed in this study. The proposed calculation model for the stress intensity factor can not only accurately predict the cracking angle of wing crack, but can also simulate the whole range of variation of wing crack length from being extremely short to very long. Based on the modified stress intensity factor, a macro–micro damage model for rock materials was also established by combining the relationship between microcrack growth and macroscopic strain. The proposed damage model was verified with the results from the conventional triaxial compression test of sandstone sample. The results show that the proposed damage model can not only continuously simulate the stress-strain curves under different confining pressures, but also can better predict the peak strength. Furthermore, the sensitivities of initial crack size, crack friction coefficient, fracture toughness, initial damage and parameter m on the stress-strain relationship are discussed. The results can provide a theoretical reference for understanding the effect of microcrack growth on the progressive failure of rock under the compressive loading.

Crack identification in beam by antiresonant frequencies

The present paper deals with the concept of antiresonance in multiple cracked beams and application for multi-crack identification. First, governing equations for antiresonant frequency are conducted and used for both computing antiresonant frequencies versus crack parameters and measuring-loading colocation and identifying cracks by measured antiresonant frequencies. Then, a procedure is proposed for crack identification in cantilever beam by antiresonant frequencies based on the so-called crack scanning method. Theoretical development is illustrated by numerical examples.

Correlation between Rheological Fatigue Tests on Bitumen and Various Cracking Tests on Asphalt Mixtures.

Accurate characterisation and appropriate binder selection are essential to increase the load-induced cracking resistance of asphalt mixtures at an intermediate temperature. Hence, the primary goal of this study was to correlate the cracking resistance exerted by the binder with the cracking performance of asphalt mixtures. The laboratory-based experimental plan covered various types of laboratory tests specified by various agencies and road authorities to study the correlation of a neat bitumen and five polymer-modified binders with their corresponding asphalt mixtures. The fatigue life of the binders was assessed through a Linear Amplitude Sweep (LAS) test and statistically correlated with various load-induced cracking parameters from the indirect tensile test, semi-circular bending (SCB) test, and four points bending beam test (FPBB) of asphalt mixtures at 25 °C. Binders and mixes were further grouped depending on their polymeric family (i.e., modified with a particular type of polymer) to validate their statistical correlation. The indicator that mostly correlated the binder properties with the asphalt mixture properties is the secant modulus from the SCB test. Fatigue parameters obtained through LAS better explain the asphalt fatigue performance obtained through FPBB; specifically, asphalt tests at high strain levels (e.g., 400 micro strain) better correlate to the LAS fatigue parameter (Nf).

New non-destructive testing approach based on eddy current for crack orientation detection and parameter estimation

Crack orientation is a vital factor in the behavioral study of fractures, especially the study of crack propagation in structures that are under dynamic or fatigue loading. Indeed, many non-destructive testing (NDT) techniques have been developed recently for the detection of cracks such as the eddy current testing (ECT). However, the crack orientation has not been undertaken into consideration. In this paper, a NDT based on eddy current using 3D finite element modeling, is proposed for the determination of the crack orientation. The idea of this proposed technique benefits from the influences of crack orientation, which can be observed on the components of eddy current and the related magnetic flux density following the x, y axes, for the estimation of the crack angle orientation based on an interpolation criteria. The obtained results through the presented simulation prove the validity of the proposed technique for the detection of crack angle orientation.

A crack theory-based bonded-particle model for rock particles considering size effects

Particle breakage shows significant effect on the macroscopic behaviour of rock materials, and the discrete element method is a powerful tool to investigate the relationship between micro fracture and macro deformation and strength. In this study, the concept of crack is introduced into the bonded-particle model (BPM) to simulate the breakage behaviour of rockfill materials, with randomly placed weak bonds representing cracks. Different from traditional BPM, the number, position and strength of the weak bonds are directly related to the number, position and length of cracks. With a reasonable length distribution of cracks, the proposed model can successfully reflect both the crushing strength variation and size effects. A set of crack parameters including the crack density, minimum crack length, maximum crack length and fractal dimension, are suggested. The crushing characteristics of realistic rockfill particles with two typical shapes are simulated quantitatively and verified with test data. It is found that the proposed model with suggested crack parameters can give reasonable prediction on the Weibull's modulus and size effect of rockfill particles.

Reliable crack detection in a rotor system with uncertainties via advanced simulation models based on kriging and Polynomial Chaos Expansion

In this study the authors propose to take into account the nonlinear effects induced by the presence of a transverse crack to carry out vibratory monitoring and detect transverse cracks in rotating systems subject to model uncertainties. More precisely, we focus more particularly on the global complexity of the nonlinear dynamic behaviour of cracked rotors and the evolution of their harmonic components as a function of the parameters of a transverse breathing crack (its position and depth) when numerous uncertainties are considered. These random uncertainties correspond to random geometric imperfections (two disc thicknesses), random material properties (Young modulus and material density) and boundary conditions uncertainty (two bearing stiffnesses). The objective of the present work is to identify robust indicators capable of determining the presence of a crack and its status even though numerous uncertainties are present.To conduct such a study, an advanced surrogate modelling technique based on kriging and Polynomial Chaos Expansion (PCE) is proposed for the prediction of both the critical speeds and the harmonic components n× during passage through sub-critical resonances. An extensive study to ensure the validation of the surrogate models and a relevant choice of both the parametric and random Design of Experiments (i.e. kriging DoE and PCE DoE) is proposed. The proposed methodology is applied on a flexible rotor with a transverse breathing crack and subjected to random geometric imperfections and fluctuations in material properties of the rotor system.

Study on Crack Development and Micro-Pore Mechanism of Expansive Soil Improved by Coal Gangue under Drying-Wetting Cycles.

Expansive soil is prone to cracks under a drying–wetting cycle environment, which brings many disasters to road engineering. The main purpose of this study is use coal gangue powder to improve expansive soil, in order to reduce its cracks and further explore its micro-pore mechanism. The drying–wetting cycles test is carried out on the soil sample, and the crack parameters of the soil sample are obtained by Matlab and Image J software. The roughness and micro-pore characteristics of the soil samples are revealed by means of the Laser confocal 3D microscope and Mercury intrusion meter. The results show that coal gangue powder reduces the crack area ratio of expansive soil by 48.9%, and the crack initiation time is delayed by at least 60 min. Coal gangue powder can increase the internal roughness of expansive soil. The greater the roughness of the soil, the less cracks in the soil. After six drying–wetting cycles, the porosity and average pore diameter of the improved and expanded soil are reduced by 37% and 30%, respectively, as compared to the plain expansive soil. By analyzing the cumulative pore volume and cumulative pore density parameters of soil samples, it is found that the macro-cracks are caused by the continuous connection and fusion of micro-voids in soil. Coal gangue powder can significantly reduce the proportion of micro-voids, cumulative pore volume, and cumulative pore density in expansive soil, so as to reduce the macro-cracks.

Interaction integral method for crack-tip intensity factor evaluations of magneto-electro-elastic materials with residual strain

Magneto-electro-elastic (MEE) materials generally consist of piezoelectric and piezomagnetic constituent phases so that the residual strain often occurs during the manufacturing process. The distributed residual strain and complex interfaces between constituents cause a great challenge to the fracture analysis of MEE materials. Considering the effect of the residual strain, this paper develops an interaction integral (I-integral) method for the extraction of the fracture parameters of an impermeable crack in nonhomogeneous MEE materials. The I-integral method has several merits: 1) it can decouple stress intensity factors (SIFs), electric displacement intensity factor (EDIF) and magnetic induction intensity factor (MIIF); 2) the I-integral is independent of the size of the integration domain, even when the integration domain contains nonhomogeneous and discontinuous material properties. Combined with the extended finite element method (XFEM), the I-integral is adopted to investigate several crack problems subjected to homogeneous, nonhomogeneous and discontinuous residual strains. The I-integral values calculated by different integration domains agree well with each other (relative deviation < 1%) for nonhomogeneous and discontinuous MEE properties. Then, single-crack and multi-crack problems are studied to show the influences of residual strain distributions on the intensity factors. Homogeneous residual strain affects the SIFs dramatically but has a slight influence on the EDIF and MIIF. By comparison, nonhomogeneous residual strains affect the SIFs, EDIF and MIIF significantly. In addition, the residual strain gradients affect the variations of intensity factors with crack location extremely.

An effective crack position diagnosis method for the hollow shaft rotor system based on the convolutional neural network and deep metric learning

In recent years, the crack fault is one of the most common faults in the rotor system and it is still a challenge for crack position diagnosis in the hollow shaft rotor system. In this paper, a method based on the Convolutional Neural Network and deep metric learning (CNN-C) is proposed to effectively identify the crack position for a hollow shaft rotor system. Center-loss function is used to enhance the performance of neural network. Main contributions include: Firstly, the dynamic response of the dual-disks hollow shaft rotor system is obtained. The analysis results show that the crack will cause super-harmonic resonance, and the peak value of it is closely related to the position and depth of the crack. In addition, the amplitude near the non-resonant region also has relationship with the crack parameters. Secondly, we proposed an effective crack position diagnosis method which has the highest 99.04% recognition accuracy compared with other algorithms. Then, the influence of penalty factor on CNN-C performance is analyzed, which shows that too high penalty factor will lead to the decline of the neural network performance. Finally, the feature vectors are visualized via t-distributed Stochastic Neighbor Embedding (t-SNE). Naive Bayes classifier (NB) and K-Nearest Neighbor algorithm (KNN) are used to verify the validity of the feature vectors extracted by CNN-C. The results show that NB and KNN have more regular decision boundaries and higher recognition accuracy on the feature vectors data set extracted by CNN-C, indicating that the feature vectors extracted by CNN-C have great intra-class compactness and inter-class separability.

Modal analysis of cracked FGM beam with piezoelectric layer

The present paper addresses modal analysis of cracked Timoshenko beam bonded with piezoelectric layer. The host beam is made of functionally graded material with the power law and crack appeared in the host beam is modeled by a pair of axial and rotational springs with stiffness calculated from its depth. The piezoelectric layer is represented as a homogeneous Timoshenko beam. Governing equations and general solution for free vibration of the cracked double beam are conducted in the frequency domain. The obtained solution has been used for examining modal parameters of the coupled beam that include natural frequencies, mode shapes and so-called modal sensor charge in dependence on crack parameter, material gradient index and thickness of piezoelectric layer. Analysis of the modal sensor charge in dependence upon crack parameters provides a novel indicator that is expected to be more efficient than the traditional ones for crack detection in functionally graded beam using distributed smart sensors. The theoretical development is validated and illustrated by numerical analysis accomplished for simply supported beam.

Research on an image-based crack detection method for subway tunnels based on feature analysis

To effectively detect the surface cracks of subway tunnels, an automatic tunnel crack detection system based on machine vision is presented. Aiming at the problems of environmental complexity and low contrast in subway tunnels, the image texture feature is first enhanced by the methods of frequency domain filtering and spatial differencing. Then, depending on the characteristics of the tunnel cracks in question, the crack propagation method is used to extract the complete cracks. Finally, broken cracks are connected during processing, and the method of combining projection and threshold is used to determine the crack types. At the same time, characteristics such as the length, width, and area of the cracks are obtained. The experimental results show that the presented methods can effectively extract complete cracks in complex tunnel environments. The identification error of tunnel crack parameters meets the actual engineering requirements.

METHODS AND CRITERIA FOR ASSESSING THE CONDITION OF RIGID PAVEMENT CONTAINING CRACKS

Road agencies around the world note the aging of the national road network and the accelerated destruction of pavement during operation due to changes in the composition of the traffic. Many scientific studies have noted that cracks of various configurations, depths, origins are the most characteristic type of pavement damage, make up a significant part of the total area of destruction and are the main danger as the initial stage of more serious damage leading to loss of pavement distribution. Timely detection of hidden cracks in the coating layers and the base layers allows to prevent the destruction of pavement and significantly reduce the cost of road repairs. The purpose of the article is to analyze the methods and criteria for assessing the condition of non-rigid pavement, which contains hidden defects in its structural layers. The results of the analysis make it possible to take into account a particular type of defect when choosing a calculation scheme and the order of calculation of pavement. The analysis proved that the calculated schemes of pavement design do not allow to take into account such indicators of pavement condition as the number of cracks, their position, geometric parameters of hidden cracks, sizes of cracked base blocks, volumetric damage of the layer material. The assumptions and simplifications accepted in the normative documents actually make it impossible to assess the condition and predict the failure of the design of paved roads with cracks. Therefore, the assessment of the condition of non-rigid pavement should be based on probabilistic methods and criteria for assessing the condition of pavement, which allow to take into account the heterogeneity of pavement design, due, inter alia, the presence of cracks in layers of monolithic materials. The next stage of research is the analysis of existing probabilistic methods of designing and assessing the condition of pavement.