• Steel and Composite Structures
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• v.35 no.2
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• pp.215-235
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• 2020

Cracks and defects may occur anywhere in a plate under tension. Cracks can affect the buckling stability performance and even the failure mode of the plate. A search of the literature reveals that the reported research has mostly focused on the study of plates with central and small cracks. Considering the effectiveness of cracks on the buckling behavior of plates, this study intends to investigate the effects of some key parameters, i.e., crack size and location as well as the plate aspect ratio and support conditions, on the buckling behavior, stress intensity factor (SIF), and the failure mode (buckling or fracture) in cracked plates under tension. To this end, a sophisticated mathematical code was developed using MATLAB in the frame-work of extended finite element method (XFEM) in order to analyze the buckling stability and collapse of numerous plate models. The results and findings of this research endeavor show that, in addition to the plate aspect ratio and support conditions, careful consideration of the crack location and size can be quite effective in buckling behavior assessment and failure mode prediction as well as SIF evaluation of the cracked plates subjected to tensile loading.

• Structural Engineering and Mechanics
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• v.55 no.6
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• pp.1087-1097
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• 2015

In this paper, the effect of functionally graded material (FGM) coatings on the fracture behavior of semi-elliptical cracks in cylinders is assessed. The objective is to calculate the stress intensity factor (SIF) of a longitudinal semi-elliptical crack on the wall of an aluminum cylinder with FGM coating. A three-dimensional finite element method (FEM) is used for constructing the mechanical models and analyzing the SIFs of cracks. The effect of many geometrical parameters such as relative depth, crack aspect ratio, FG coating thickness to liner thickness as well as the mechanical properties of the FG coating on the SIF of the cracks is discussed. For a special case, the validity of the FE model is examined. The results indicated that there is a particular crack aspect ratio in which the maximum value of SIFs changes from the deepest point to the surface point of the crack. Moreover, it was found that the SIFs decrease by increasing the thickness ratio of the cylinder. But, the cylinder length has no effect on the crack SIFs.

• Smart Structures and Systems
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• v.22 no.6
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• pp.663-673
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• 2018

In this study, the effect of particle size on the cracks propagation and coalescence or cracking pattern of the edge notched disc specimens are investigated. Firstly, calibration of PFC3D was performed using Brazilian experimental test output. Then micro parameters were used to build edge notched disc specimen. The horizontal wall of the assembly is let to move downward with a standard low speed of 0.016 m/s. The numerical results show that the tensile cracks are dominant failure pattern for the modeled discs. These tensile cracks initiate from the pre-existing notch tip and propagate parallel to the loading direction then interact with the upper boundary of the modeled specimen. As the size of the balls (ball diameter) decrease the number of tensile cracks increase. The tensile fracture toughness of the samples also decreases as the particle size increases. Understanding the crack propagation and crack coalescence phenomena in brittle materials such as concretes and rocks is of paramount importance in the stability analyses for engineering structures such as rock slopes, underground structures and tunneling.

• Structural Engineering and Mechanics
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• v.71 no.3
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• pp.211-221
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• 2019

To study the eccentric compression behavior of ultra-high performance fiber reinforced concrete (UHPFRC) columns, six UHPFRC columns and one high-strength concrete (HSC) column were tested. Variation parameters include load eccentricity, volume of steel fibers and stirrup ratio. The crack pattern, failure mode, bearing capacity, and deformation of the specimens were studied. The results showed that the UHPFRC columns had different failure modes. The large eccentric compression failure mode was the longitudinal tensile reinforcements yielded and many horizontal cracks appeared in the tension zone. The small eccentric compression failure mode was the longitudinal compressive reinforcements yielded and vertical cracks appeared in the compressive zone. Because of the bridging effect of steel fibers, the number of cracks significantly increased, and the width of cracks decreased. The load-deflection curves of the UHPFRC columns showed gradually descending without sudden dropping, indicating that the specimens had better deformation. The finite element (FE) analysis was performed to stimulate the damage process of the specimens with monotonic loading. The concrete damaged plasticity (CDP) model was adopted to characterize the behaviour of UHPFRC. The contribution of the UHPFRC tensile strength was considered in the bearing capacity, and the theoretical calculation formulas were derived. The theoretical calculation results were consistent with the test results. This research can provide the experimental and theoretical basis for UHPFRC columns in engineering applications.

• Composites Research
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• v.13 no.3
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• pp.9-20
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• 2000

Free vibration characteristics of a cantilevered laminated composite beam with multiple non-propagating transverse open cracks are investigated. In the present analysis a special ply-angle distribution referred to as asymmetric stiffness configuration inducing the elastic coupling between chord-wise bending and extension is considered. The multiple open cracks are modelled as equivalent rotational springs whose spring constants are calculated based on the fracture mechanics of composite material structures. Governing equations of a composite beam with open cracks are derived via Hamilton's Principle and Timoshenko beam theory encompassing transverse shear and rotary inertia effect is adopted. The effects of various parameters such as the ply angle, fiber volume fraction, crack numbers, crack positions and crack depthes on the free vibration characteristics of the beam with multiple cracks are highlighted. The numerical results show that the existence of the multiple cracks in an anisotropic composite beam affects the free vibration characteristics in a more complex fashion compared with the beam with a single crack.

• Journal of the Korean GEO-environmental Society
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• v.22 no.10
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• pp.13-19
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• 2021

Cracks in asphalt pavement occur due to changes in weather or impact from vehicles, and if cracks are left unattended, the life of the pavement may be shortened, and various accidents may occur. Therefore, studies have been conducted to detect cracks through images in order to quickly detect cracks in the asphalt pavement automatically and perform maintenance activity. Recent studies adopt machine-learning models for detecting cracks in asphalt road pavement using a Convolutional Neural Network. However, their practical use is limited because they require high-performance computing power. Therefore, this paper proposes a framework for detecting cracks in asphalt road pavement by applying a small deep learning model applicable to mobile devices. The small deep learning model proposed through the case study was compared with general deep learning models, and although it was a model with relatively few parameters, it showed similar performance to general deep learning models. The developed model is expected to be embedded and used in mobile devices or IoT for crack detection in asphalt pavement.

• Computers and Concrete
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• v.10 no.3
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• pp.277-294
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• 2012

The aim of the study is to determine the modal parameters of a prototype damaged arch dam by operational modal analysis (OMA) method for some damage scenarios. For this purpose, a prototype arch dam-reservoir-foundation model is constructed under laboratory conditions. Ambient vibration tests on the arch dam model are performed to identify the modal parameters such as natural frequency, mode shape and damping ratio. The tests are conducted for four test-case scenarios: an undamaged dam with empty reservoir, two different damaged dams with empty reservoirs, and a damaged dam with full reservoir. Loading simulating random impact effects is applied on the dam to crack. Cracks and fractures occurred at the middle of the upper part of the dams and distributed through the abutments. Sensitivity accelerometers are placed on the dams' crests to collect signals for measurements. Operational modal analysis software processes the signals collected from the ambient vibration tests, and enhanced frequency domain decomposition and stochastic subspace identification techniques are used to estimate modal parameters of the dams. The modal parameters are obtained to establish a basis for comparison of the results of two techniques for each damage case. Results show that approximately 35-40% difference exists between the natural frequencies obtained from Case 1 and Case 4. The natural frequencies of the dam considerably decrease with increasing cracks. However, observation shows that the filled reservoir slightly affected modal parameters of the dam after severe cracking. The mode shapes obtained are symmetrical and anti-symmetrical. Apparently, mode shapes in Case 1 represent the probable responses of arch dams more accurately. Also, damping ratio show an increase when cracking increases.

• Journal of the Korean Geotechnical Society
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• v.17 no.6
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• pp.149-162
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• 2001

Longitudinal cracks have occurred on the crest of dams soon after their construction of two earth-rocfill dams located in Samlangjin. They are a pair of pumped storage dams constructed for generation of electrical power. The upper dam and lower dam are subjected to the variation of water level more than 10m once in a day alteratively. This paper deals with the finding of possible causes for longitudinal cracks about upper dam. The dominant cause was considered to be due to fluctuation of water load, for which numerical analysis was carried out using the hyperbolic model. In order to obtain parameters necessary to the analysis, a series of triaxial tests was performed for both core and rock material. Also dynamic triaxial test was performed to obtain dynamic properties of soils, which could be used as input data to simulate frequent variation of stress change due to the water fluctuation. It was known from the numerical analysis that the confining pressure of upper 4m from the top of the crest become negative after repeating of water load, meaning that tension cracks occurred in the top portion of the crest. The depth of longitudinal cracks has been investigated by digging test pit on the crest. This results agree with the field observation.

• Geomechanics and Engineering
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• v.24 no.2
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• pp.179-191
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• 2021

In this study, the strength and failure mechanism of red sandstones with combined defects were investigated by uniaxial compression tests on red sandstones with different crack angles using two-dimensional particle flow code numerical software, and their mechanical parameters and failure process were studied and analyzed. The results showed that the mechanical characteristics such as peak strength, peak strain, and elastic modulus of the samples with prefabricated combined defects were significantly inferior than those of the intact samples. With increasing crack angle from 15° to 60°, the weakening area of cracks increased, elastic modulus, peak strength, and peak strain gradually reduced, the total number of cracks increased, and more strain energy was released. In addition, the samples underwent initial brittle failure to plastic failure stage, and the failure form was more significant, leading to peeling phenomenon. However, with increasing crack angle from 75° to 90°, the crack-hole combination shared the stress concentration at the tip of the crack-crack combination, resulted in a gradual increase in elastic modulus, peak strain and peak strength, but a decrease in the number of total cracks, the release of strain energy reduced, the plastic failure state weakened, and the spalling phenomenon slowed down. On this basis, the samples with 30° and 45° crack-crack combination were selected for further experimental investigation. Through comparative analysis between the experimental and simulation results, the failure strength and final failure mode with cracks propagation of samples were found to be relatively similar.

• Journal of the Korean GEO-environmental Society
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• v.10 no.4
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• pp.65-71
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• 2009

Hydraulic fracturing technology has been widely applied in the industry for the recovery of the natural resources such as gas, oil and geothermal heat from hot dry rock. During hydraulic fracturing stimulation, multiple cracks are created resulting in mechanical interaction between cracks. Such an interaction influences obtaining hydraulic fracturing key parameters (crack opening, length, and borehole net pressure). The boundary collocation method (BCM) has been proved to be very effective in considering mechanical interaction. However, for better confidence, it needs to be verified by comparison with analytical solutions such as stress intensity factors. In this paper, three cases, single fracture in remote uniaxial tension, single fracture in remote shear stress field and two arbitrary segments in an infinite plane loaded at infinity are considered. As a result, the BCM is proved to be valid technique to consider mechanical interaction between cracks and can be used to estimate the hydraulic fracturing parameters such as opening of the fracture, and so on.