• Structural Engineering and Mechanics
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• v.68 no.4
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• pp.497-505
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• 2018

Three points bending flexural test was modeled numerically to study the crack propagation in the pre-cracked beams. The pre-existing edge cracks in the beam models were considered to investigate the crack propagation and coalescence paths within the modeled samples. The effects of particle size on the single edge-notched round bar in bending test were considered too. The results show that Failure pattern is constant by increasing the ball diameter. Tensile cracks are dominant mode of failure. These crack initiates from notch tip, propagate parallel to loading axis and coalescence with upper model boundary. Number of cracks increase by decreasing the ball diameter. Also, tensile fracture toughness was decreased with increasing the particle size. In the present study, the influences of particles sizes on the cracks propagations and coalescences in the brittle materials such as rocks and concretes are numerically analyzed by using a three dimensional particle flow code (PFC3D). These analyses improve the understanding of the stability of rocks and concretes structures such as rock slopes, tunnel constructions and underground openings.

• Computational Structural Engineering
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• v.8 no.4
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• pp.137-148
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• 1995

A new path independent contour integral formulus for the distinct calculation of mode I stress intensity factors in two dimensional linear elastic fracture mechanics problems is presented. This method is based on p-convergence concepts and can be easily appended to existing finite element computer codes. In this study, the stress state at crack tip has been investigated and the path independence of J-integral values has been tested with respect to different contours expressed by normalized distance apart from the crack tip. Numerical results by p-convergence for the problems such as centrally cracked panels, single and double edged cracks in rectangular panels have been compared with those by the conventional h-convergence. The comparison demonstrates the accuracy and stability of the proposed method.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.429-432
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• 2008

Large area members such as foundation concrete of underground structures in power plants have an effect on structural stability and durability of the structure due to danger of crack occurrence and shrinkage crack that occur owing to the difference of temperature by heat of hydration between inside and outside of the members at initial age. And a construction for waterproofness is performed additionally to protect marine structures from osmosis of seawater because the structures adjoin below the surface of sea. So, if a rise of the heat of hydration, crack, and corrosion of bars are controled effectively using a composite such as fluosilicate salt in concrete production process of a initial construction, expenses are cut down and construction hours are reduced by securing durability through improvement of watertightness. The property tests of adiabatic temperature by hydration are carried out at initial age about standard concrete and test concrete using a fluosilicate salt composite to evaluate an effect on improvement of watertightness for concrete structures in this study. And the experiments such as a permeability test of hardened concrete, a water absorption test, a compression strength test and a elongation test are carried out and the results from these are described.

• 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.

• Journal of the Korean Society of Safety
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• v.37 no.5
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• pp.7-13
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• 2022

Digital image correlation (DIC) is a method used to measure the displacement and strain of structures. It involves transforming and analyzing images before and after deformation using correlation coefficients from irregular light and shade on the surface of structures. In the present study, a microspeckle pattern was applied to the surface of a specimen to identify initial cracking. The test specimen constituted CFRP composites laminated on a curved Al liner The specimen was manufactured by stacking 100 ply of CFRP prepregs in the 0° and 90° directions in a three-point bending test. The equivalent strain was evaluated through DIC analysis after monitoring deformation using a CCD camera. Fracture shape was observed using a microscope. The equivalent strain contour distribution was checked until the maximum load fracture occurred at the center of the test specimen. Variations in the strain indicated the initial occurrence and progression of microcracks. These results can be used to improve the accuracy of detecting micro crack initiation and to achieve structural stability.

• Structural Engineering and Mechanics
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• v.66 no.5
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• pp.649-663
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• 2018

The scaled boundary finite element method is extended to evaluate the dynamic stress intensity factors and T-stress with a numerical procedure based on the improved continued-fraction. The improved continued-fraction approach for the dynamic stiffness matrix is introduced to represent the inertial effect at high frequencies, which leads to numerically better conditioned matrices. After separating the singular stress term from other high order terms, the internal displacements can be obtained by numerical integration and no mesh refinement is needed around the crack tip. The condition numbers of coefficient matrix of the improved method are much smaller than that of the original method, which shows that the improved algorithm can obtain well-conditioned coefficient matrices, and the efficiency of the solution process and its stability can be significantly improved. Several numerical examples are presented to demonstrate the increased robustness and efficiency of the proposed method in both homogeneous and bimaterial crack problems.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.301-308
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• 1999

With the shortage of the land and NIMBY syndrome, it is issued recently that the capacity of waste-landfill site is needed though the decreasing tendency of waste landfill. From this point, the stability is the most essential problem in the landfill that will be constructed. Advanced design and construction are most important for that. In this paper, for the study of desiccation, dry-shrinkage crack from drying and chemical reaction in cement hydration, which is occurred when the surface layer stabilization method is applied in wast landfill, laboratory test of the ground and specimen according to the mixture ratio of stabilizer is performed. From the result, it is notified that the uni-axial strength increases with the stabilizer, but dry-shrinkage increases too, therefore, it is important and the goal of this study to find the optimal mixture ratio of each stabilizer. Analysis of variance for regression with acting variables is performed to find optimal mixture ratio of each stabilizer.

• Journal of the Korean Society of Safety
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• v.14 no.2
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• pp.32-41
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• 1999

If the Leak-Before-Break (LBB) concept is applicable to the nuclear piping design, it is not necessary to consider the dynamic effect due to pipe rupture. Therefore, the construction cost can be significantly reduced by eliminating unnecessary pipe whip restraints and jet impingement devices. The objective of this paper is to develop the Piping Evaluation Diagram (PED) for efficient application of LBB concept to piping system at an initial piping design stage. For this purpose, the 3-D finite element analyses were performed to evaluate the crack stability. And the stress-strain curve based on the pipe material tests were used to calculate the detectable leakage crack length. Finally, the present PED which was composed as a function of NOP load and allowable SSE load, was developed for an application of LBB concept to the safety injection and shutdown cooling line in Korean Next Generation Reactor (KNGR).

• Journal of Ocean Engineering and Technology
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• v.23 no.6
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• pp.111-116
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• 2009

The cracking due to hydration heat in mass concrete must be resolved to improve the stability and durability of concrete structures. In this study, the economic efficiency was improved by replacing a copper pipe with a steel one for the heat pipe, and the heat pipe was standardized to significantly improve the operation efficiency, such as the processing, transport, assembly, and construction time. As a result of the experiment, the peak temperature of the ICSHP, ISSHP, and ISUHP specimens decreased by about $7.2{\sim}10.9^{\circ}C$ compared to the OPC specimen and the probability of a thermal crack being generated in the ICSHP, ISSHP, and ISUHP specimens decreased by up to 84~88%.

• International Journal of Precision Engineering and Manufacturing
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• v.1 no.2
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• pp.84-93
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• 2000

Computer simulations of the mechanical behavior of 3 point bend specimens with a quarter notch under impact load are performed. This validity is found to be identified by the experimental proof. The cases with various loading rates applied at the side of the specimen are considered. An elastoplastic von Mises material model is chosen. Gap opening displacement, reaction force, crack tip opening displacement and strain rate are also compared with rate dependent material(visco-plastic material). The stability during various dynamic load can be seen by using the simulation of this study. These differences of the cases with various loading rates are also investigated.