Crack Curving Research Articles

Segment-based pavement crack quantification

Abstract Accurate quantitative information of crack length and width is important for assessing the severity level of cracks and making accurate pavement maintenance decisions. Nevertheless, due to the noise and fluctuation at the crack edge of pavement image, itis difficult to precisely determine the edge correspondence of crack that is necessary for measuring the crack width at a specific pixel. Different automated or manually performed measurements are likely to yield different results at the same pixel. Instead of measuring the crack width on a pixel-by-pixel basis, this paper presents an accurate and robust segment-based method for measuring crack width. Firstly, based on the distinctive curved structure of pavement crack, a structured edge detector is trained to obtain the confidence map of crack edges. Secondly, with the crack edge map, the morphological operation is used to extract the crack skeleton which characterizes the propagation of the crack. Adaptive segmentation of the crack skeleton is performed to partition a crack curve into crack segments. Each crack segment has the same width because its edges become almost parallel after the segmentation. Finally, combining the structured edge confidence and grayscale contrast at crack edges, an enhanced edge map of crack is proposed to measure the width of each crack segment by translating the skeleton towards both edges. A large number of experiments taken on the synthetic and real-world pavement images demonstrate that the proposed method can accurately and robustly quantify various cracks with the average accuracy of 93.7% for crack width. It is promising for quantitative pavement condition assessment and maintenance.

On the connection between two equilibrium problems for cracked bodies in the cases of thin and volume rigid inclusions

We consider equilibrium problems for an inhomogeneous two-dimensional body with a crack and a rigid inclusion. The matrix of the body is assumed to be elastic. The boundary condition on the crack curve is an inequality describing mutual nonpenetration of the crack faces. We study two different equilibrium models. For the first model, we assume that a volume rigid inclusion is described by a domain. The second one describes a body containing a set of connected thin rigid inclusions, each corresponding to a curve. The crack is given by the same curve in both models. We prove that the solutions of equilibrium problems corresponding to the second model strongly converge to the problem solution for the first model as the number of inclusions tends to infinity.

Optimal radius of a rigid cylindrical inclusion in nonhomogeneous plates with a crack

We consider equilibrium problems for a cracked inhomogeneous plate with a rigid circular inclusion. Deformation of an elastic matrix is described by the Timoshenko model. The plate is assumed to have a through crack that reaches the boundary of the rigid inclusion. The boundary condition on the crack curve is given in the form of inequality and describes the mutual nonpenetration of the crack faces. For a family of corresponding variational problems, we analyze the dependence of their solutions on the radius of the rigid inclusion. We formulate an optimal control problem with a cost functional defined by an arbitrary continuous functional on the solution space, while the radius of the cylindrical inclusion is chosen as the control parameter. Existence of a solution to the optimal control problem and continuous dependence of the solutions with respect to the radius of the rigid inclusion are proved.

Dynamic Fracture Analysis of Functional Gradient Material Coating Based on the Peridynamic Method

Functional gradient materials (FGMs) have tremendous potential due to their characteristic advantage of asymptotic continuous variation of their properties. When an FGM is used as a coating material, damage and failure of the interface with the substrate component can be effectively inhibited. In order to study the dynamic crack propagation in FGM coatings, a new method, peridynamics (PD), was used in the present study to simulate dynamic fractures of FGM coatings bonded to a homogeneous substrate under dynamic loading. The bond-based PD theory was employed to study crack propagation and branching in the FGM coating. The influences of the coating gradient pattern, loading, and the geometry and size of the structure on crack curving and propagation under impact loading were investigated. The numerical results show that different forms of the elastic modulus of graded material, the geometry of the structure, and the loading conditions have considerate effects on crack propagation in FGM coatings, but a specific form of elastic modulus had a limited effect on the dynamic fracture of FGM coating.

Optimal Control of the Location of a Thin Rigid Inclusion in the Equilibrium Problem of an Inhomogeneous Two-Dimensional Body with a Crack

Under study is some two-dimensional model describing equilibriumof a composite solid with a thin rigid inclusion and a crack. A boundary condition of Signorini’s type is prescribed on the crack curve. For a family of corresponding variational problems, the dependence is analyzed of their solutions on the parameter characterizing the location of the rigid inclusion. The existence of solution of the optimal control problem is proved. For this problem, the quality functional is defined with the help of an arbitrary continuous functional on the solution space, while the location of the inclusion is chosen as the control parameter.

Crack Junction Detection in Pavement Image Using Correlation Structure Analysis and Iterative Tensor Voting

Crack junction is the crossing or branching point of different cracks in the pavement image. It represents the branch of transverse crack or longitudinal crack, and describes the interlaced network of alligator crack. It is a simple yet important factor to characterize the type and severity level of crack. This paper is motivated to robustly detect crack junctions of any type and size in pavement image, regardless of the pavement interferences. In this paper, the contrast between the crack junction and pavement background is first enhanced by removing the large interferences and background. Then, based on the structure characteristic of crack curves, correlation structure index is proposed to locate candidates of crack junctions. Actual junctions are extracted among the candidates with the unified ball tensor structure after the iterative tensor voting. The proposed method is tested with the concrete pavement images of public data set of SDNET2018 and asphalt pavement images collected by the unmanned aerial vehicle on the highway G45 in China. Experimental results demonstrate that the proposed method can detect crack junctions with the correctness of 0.891 and completeness of 0.887. It can be applied to junction detection on concrete and alligator pavement with different noise and interference, and is promising to classify the crack type and quantify the severity level.

О РЕГУЛЯРНОСТИ РЕШЕНИЯ В ЗАДАЧЕ О РАВНОВЕСИИ ПЛАСТИНЫ ТИМОШЕНКО, СОДЕРЖАЩЕЙ НАКЛОННУЮ ТРЕЩИНУ

Исследуется задача о равновесии упругой трансверсально-изотропной пластины (модели Тимошенко), содержащей сквозную наклонную трещину. Считается что трещина не выходит на внешнюю границу. В исходном состоянии предполагается, что противоположные берега соприкасаются друг с другом. При этом трещина описывается с помощью поверхности, которая удовлетворят определенным предположениям. На кривой, задающей трещину в срединной плоскости, ставится краевое условие в виде неравенства, описывающее непроникание противоположных берегов трещины. На внешней границе заданы однородные условия Дирихле. Установлена локальная дополнительная гладкость решения по сравнению с заданной в вариационной формулировке при определенных условиях на поверхность, задающую трещину. Доказана бесконечная дифференцируемость функции решения при дополнительных предположениях на функцию, задающую внешние нагрузки, а также на значения функций перемещений вблизи кривой, описывающей трещину. The equilibrium problem for an transversely isotropic elastic plate (Timoshenko model) with an inclined crack is studied. It is supposed that the crack does not touch the external boundary. For initial state, we assume that opposite crack faces are in contact with each other on a frictionless crack surface. Herewith, the crack is described with the use of a surface satisfying certain assumptions. On the crack curve defining the crack in the middle plane, we impose a nonlinear boundary condition as an inequality describing the nonpenetration of the opposite crack faces. It is assumed that on the exterior boundary of the cracked elastic plate the homogeneous Dirichlet boundary conditions are prescribed. We establish additional smoothness of the solution in comparison with that given in the variational statement. We prove that the solution functions are infinitely smooth under additional assumptions on the function of external loads and the functions of displacements near the curve describing the inclined crack.

Numerical simulation of crack propagation and branching in functionally graded materials using peridynamic modeling

In this study, a bond-based peridynamic (PD) model for functionally graded materials (FGMs) was introduced to simulate various dynamic brittle fractures in FGMs. The PD analyses of dynamic crack propagation and branching in FGMs were discussed, and the results of the two convergence studies under uniform grid refinement (m-convergence) and decreasing radius of PD horizon (δ-convergence) were presented. The influence of material gradient pattern on crack curving and branching in FGMs under dynamic loads was analyzed. In addition, the propagation of a single crack in FGMs subjected to dynamic biaxial loads was studied. The effects of loading conditions and gradient patterns of FGMs were investigated. The results of these investigations suggest that both the material gradient patterns and the loading conditions can affect the crack propagation in FGMs, whereas the influence of a specific form of elastic modulus on the fracture behavior of FGMs is limited.

Method for Detecting Micron Cracks on a Magnetic Rotor Surface Based on a Support Vector Machine

Micro-scale cracks on the surface of a magnetic rotor are difficult to detect because of the formation of stains. A method that is based on computer vision and a support vector machine (SVM) that can accurately and rapidly locate micro-scale cracks are proposed. To further highlight the cracks and reduce interference, the image is pre-processed using improved adaptive median filtering, image sharpening, extract feature point, and an expansion based on mathematical morphology. Next, the feature curves of cracks and stains are extracted as training samples using the feature curve extract algorithm and the region orientation algorithm (ROA) for continuous and discontinuous crack curves images, respectively. SVM is later used to distinguish between the two types of image sources. An improved region orientation algorithm (IROA) is proposed to increase the efficiency of discontinuous crack curves images through online detection. Experiment results show that the accuracy of crack detection using ROA is 97.9%, and the accuracy is 94.7% using IROA. However, the IROA algorithm execution time is 3% that of ROA, and IROA’s average crack detection time is shorter than that of ROA by 51%. The proposed method provides the basis for the automatic online detection of micro-scale cracks on a magnetic rotor surface and paves the way for the identification of cracks on complex morphologies, such as split cracks and circular cracks.

A novel underwater dam crack detection and classification approach based on sonar images.

Underwater dam crack detection and classification based on sonar images is a challenging task because underwater environments are complex and because cracks are quite random and diverse in nature. Furthermore, obtainable sonar images are of low resolution. To address these problems, a novel underwater dam crack detection and classification approach based on sonar imagery is proposed. First, the sonar images are divided into image blocks. Second, a clustering analysis of a 3-D feature space is used to obtain the crack fragments. Third, the crack fragments are connected using an improved tensor voting method. Fourth, a minimum spanning tree is used to obtain the crack curve. Finally, an improved evidence theory combined with fuzzy rule reasoning is proposed to classify the cracks. Experimental results show that the proposed approach is able to detect underwater dam cracks and classify them accurately and effectively under complex underwater environments.

Effect of rivet holes on calibration curves for edge cracks under various loading types in steel bridge structure

Attention has been paid to fatigue cracks in steel structures and bridges for a long time. In spite of efforts to eliminate the creation and propagation of fatigue cracks throughout the designed service life, cracks are still revealed during inspections. There is some limitation of crack sizes which are detectable on structure (from 2 up to 10 mm). Note that depending on the location of the initial crack, the crack may dominantly propagate from the edge or from the surface. The theoretical model of fatigue crack progress is based on linear elastic fracture mechanics. Steel specimens are subjected to various load types (tension, three- and four-point bending, pure bending etc.). The calibration functions for short edge cracks that are near the hole for a rivet or bolt are compared for various loads and the discrepancies are discussed.

Peridynamic modelling of impact damage in three-point bending beam with offset notch

The nonlocal peridynamic theory has been proven to be a promising method for the material failure and damage analyses in solid mechanics. Based upon the integrodifferential equations, peridynamics enables predicting the complex fracture phenomena such as spontaneous crack nucleation and crack branching, curving, and arrest. In this paper, the bond-based peridynamic approach is used to study the impact damage in a beam with an offset notch, which is widely used to investigate the mixed I-II crack propagation in brittle materials. The predictions from the peridynamic analysis agree well with available experimental observations. The numerical results show that the dynamic fracture behaviors of the beam under the impact load, such as crack initiation, curving, and branching, rely on the location of the offset notch and the impact speed of the drop hammer.

A new driving force parameter for fatigue growth of multiple cracks

In this paper, the 2060 Al-Li alloy specimens containing a single crack and multiple cracks were tested under fatigue load. The experimental results showed that the fatigue crack growth rates for multiple cracks deviated from the single crack when there is no interaction between multiple cracks. The results cannot be interpreted by the conventional Paris law using the crack tip stress intensity factor range ΔK calculated with the external applied nominal stress Δσ. At a given ΔK, the fatigue crack growth rates (da/dN) of different cracks for the same homogeneous material should be same based on the Paris law. Therefore, a new mechanical driving force parameter ΔKn that was calculated using the net section stress range Δσn was proposed to describe the single crack and collinear multiple cracks growth behavior under fatigue load. All da/dN vs ΔKn curves for collinear cracks of equal and unequal crack sizes were overlapped, and also overlapped with the single crack curve when no interaction occurred, showing that the ΔKn can be considered as a proper parameter to address the fatigue behavior of materials containing multi-cracks.

Thickness dependence of mode I interlaminar fracture toughness in a carbon fiber thermosetting composite

The relation of the non-singular opening stress component with apparent fracture toughness was investigated for unidirectional carbon-fiber laminates by means of double cantilever beam experiments in which laminate thickness was varied. It was found that a sample configuration with smaller thickness related to a higher apparent fracture toughness measurement. This result was explained by the presence of a negative non-singular opening stress component, which was found to decrease with thickness. The experimental procedure utilized first crack propagation from the initial polytetrafluoroethylene insert to avoid ambiguity of defining crack location due to crack curving, resulting in a wider crack front and fiber bridging. The two dimensional finite element analyses were used to calculate the corresponding singular and non-singular stress components and the energy release rates. Based on the experimental results a two parameter linear elastic fracture mechanics model was calibrated to incorporate the thickness dependence of the apparent fracture toughness.

Dynamic crack branching and curving in brittle polymers

This paper presents peridynamics simulation on crack branching and curving in a pre-existing center-notched brittle polymer. Fracturing patterns in brittle polymer under a biaxial tensile loading condition are compared with experimental observations for validation. Then, several numerical examples are conducted in order to investigate crack initiation and propagation of the pre-existing center notch under the effect of different loading ratios. Further to this, the crack development sequences of branching and curving are in detail discussed, and their underlying causes are identified through various perspectives including crack curving and branching angles, elastic strain energy, and branching damage patterns. The numerical results reasonably reflect the physical observations. This paper both complements the test results and provides insightful information for the prediction of crack branching and curving in brittle polymers.

Numerical simulation of crack curving and branching in brittle materials under dynamic loads using the extended non-ordinary state-based peridynamics

Abstract In this paper, the stress-based failure criteria are implemented into the extended non-ordinary state-based peridynamics (NOSB-PD). When the mean stresses between the interacting material points satisfy the stress-based failure criteria, the breakage of bonds between the interacting material points occurs. The phenomena of crack curving and branching in brittle materials subjected to dynamic loads are investigated using the proposed method. A benchmark example and the Kalthoff-Winkler experiment are firstly simulated to prove the ability and accuracy of the proposed numerical method. Then, one single crack curving and branching in brittle materials subjected to dynamic biaxial loads are also simulated. The effects of geometric and loading conditions on crack curving and branching are studied. The present numerical results are in good agreement with the previous experimental and numerical results. Finally, the phenomena of multiple crack propagation, branching and coalescence under biaxial dynamic loads are also investigated. The effects of non-overlapping length on crack propagation, branching and coalescence under biaxial dynamic loads are analyzed.

Vibration strength of structures based on the theory of cracking and fatigue curves

The algorithm for calculating a fatigue crack formed in force parts of structures under the harmonic vibration load has been presented. The source data for calculating an unknown quantity are fatigue curves in the material and the assumed linearity of the first section of the kinetic diagram of the fatigue fracture. All of the necessary parameters for describing the law of crack propagation in the form proposed by Paris are determined by the characteristics of the fatigue curve. This approach shows that the fracture of the thin-walled force parts of structures with a thickness of less than 2 mm (the size of a fatigue crack for which the fracture of samples is tested to develop the fatigue curve) occurs at a smaller number of cycles than that shown in the fatigue curve for the same stress amplitude.

Existence of an optimal size of a delaminated rigid inclusion embedded in the Kirchhoff-Love plate

We consider equilibrium problems for an inhomogeneous plate with a crack situated at the inclusion-matrix interface. The matrix of the plate is assumed to be elastic. The boundary condition on the crack curve are given in the form of inequalities and describes the mutual nonpenetration of the crack faces. We analyze the dependence of solutions on the size of rigid inclusion. The existence of the solution to the optimal control problem is proved. For that problem the cost functional characterizes the deviation of the displacement vector from a given function, while the size parameter of rigid inclusion is chosen as the control function.

Evaluation of Shear Capacity According to Transverse Spacing of Wide Beam Shear Reinforced with Steel Plate with Openings

Abstract In this paper, transverse shear spacing and effective depth of wide beams were considered as parameters to evaluate the shear capacity of wide beam according to transverse spacing of steel plates with openings in experimental way. The eight specimens were composed of: five specimens of shear reinforced by steel plates with openings and three non-reinforced specimens. Crack, failure mode, strain and load-displacement curve of specimens were analysed. Shear contribution of shear reinforcement is evaluated and maximum transverse spacing of shear reinforcement was proposed. Shear strength of the specimen that reinforced with three stirrup legs was higher than shear strength of the specimen that reinforced with two stirrup legs. And as the effective depth increased, shear strength was increased. Keywords :steel plate with openings, wide beam, shear reinforcement, transverse spacing, effective depth † Corresponding author: Tel: +82-31-201-2542; E-mail: kimhc@khu.ac.krReceived January 19 2015; Revised March 6 2015Accepted March 18 2015Ⓒ2015 by Computational Structural Engineering Institute of KoreaThis is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License(http://creativecommons. org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

A stereovision-based crack width detection approach for concrete surface assessment

To quantitatively evaluate crack width of concrete structures surface, this paper presents a stereovision-based crack width detection method. Compared with the traditional visual inspection with single camera, this approach uses a pair of cameras to capture cracks images for recovering 3D coordinates of crack edge, and does not needs scale attached to concrete surface for converting measurement unit. A novel Canny-Zernike combination algorithm is utilized to obtain the image coordinates of crack edge in the left crack image, this combination algorithm can achieve 0.02 subpixel precision. The 3D coordinates of crack edge are acquired by projecting crack edge curve on concrete surface where cracks are located. The crack width is assessed by the minimum distance between two sides of crack edge. The detection tests are conducted on three concrete beams destroyed in static test, and the crack width of two inspection zones on each beam is acquired. Experimental results indicate that the stereovision-based crack width detection approach can accurately measure the crack width compared with the crack width gauge or the vernier calliper. This verifies the proposed method is applicable and useful for assessing the crack width of concrete surface.