• Journal of Wind Energy
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• v.14 no.3
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• pp.83-90
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• 2023

The purpose of this study is to evaluate the inter-laminar fracture toughness characteristics of CFRP pultrusion spar cap materials reinforced with non-woven glass fabric. Test specimens were fabricated by the infusion technique. A non-woven glass fabric and artificial defects were embedded on the middle surface between two pultruded CFRP panels. Double cantilever beam (DCB) and End Notched Flexure (ENF) tests were performed according to ASTM standards. Fracture toughness and crack propagation characteristics were evaluated with load-displacement curves and delamination resistance curves (R-Curve). The fracture toughness results were calculated by compliance calibration (CC) method. The initiation and propagation values of Mode-I critical strain energy release rate value G_Ic were 1.357 kJ/m2 and 1.397 kJ/m2, respectively, and Mode-II critical strain energy release rate values G_IIc were 4.053 kJ/m2 for non-precracked test and 4.547 kJ/m2 for precracked test. It was found that the fracture toughness properties of the CFRP pultrusion spar-cap are influenced by the interface between the layers of CFRP and glass fiber non-woven.

• Restorative Dentistry and Endodontics
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• v.34 no.4
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• pp.324-332
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• 2009

The purpose of this study was to investigate the effect of rigidity of post core systems on stress distribution by the theoretical technique, finite element stress-analysis method. Three-dimensional finite element models simulating an endodontically treated maxillary central incisor restored with a zirconia ceramic crown were prepared and 1.5 mm ferrule height was provided. Each model contained cortical bone, trabecular bone, periodontal ligament, 4 mm apical root canal filling, and post-and-core. Six combinations of three parallel type post (zirconia ceramic, glass fiber, and stainless steel) and two core (Paracore and Tetric ceram) materials were evaluated, respectively. A 50 N static occlusal load was applied to the palatal surface of the crown with a $60^{\circ}$angle to the long axis of the tooth. The differences in stress transfer characteristics of the models were analyzed. von Mises stresses were chosen for presentation of results and maximum displacement and hydrostatic pressure were also calculated. An increase of the elastic modulus of the post material increased the stress, but shifted the maximum stress location from the dentin surface to the post material. Buccal side of cervical region (junction of core and crown) of the glass fiber post restored tooth was subjected to the highest stress concentration. Maximum von Mises stress in the remaining radicular tooth structure for low elastic modulus resin core (29.21 MPa) was slightly higher than that for high elastic modulus resin core (29.14 MPa) in case of glass fiber post. Maximum displacement of glass fiber post restored tooth was higher than that of zirconia ceramic or stainless steel post restored tooth.

• Journal of the Korean Arthroscopy Society
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• v.10 no.1
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• pp.45-52
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• 2006

Purpose: We evaluated the results of operative treatment of tibial plateau fractures using both arthroscopy and fluoroscopy. Materials and Methods: From May 1999 to February 2003, tibial plateau fractures were treated with arthroscopy. Tweenty seven patients are followed up over two years and the average follow-up period was fourty one months. We classified the fractures according to the Schatzker classification. We reduced the fracture over 2mm depression and displacement on articular surface in simple radiologic finding. Firstly, we treated the associated injuries and reduced the fractures using Steinmann pins. Then, we accomplished internal fixation or external fixation. Both the postoperative clinical and radiological results were evaluated by Rasmussen system. Results: In all tweenty seven cases, the fractures were healed completely in average fourty one months. According to Rasmussen classification, we obtained the excellent or good results in 23 cases. An average range of motion was between 2.5 degrees and 130 degrees. However, postoperative infection developed in one case and the other had loss of reduction. Conclusions: We consider that arthroscopically assisted operative treatment of tibial plateau fracture is a useful method. We can reduce joint surface correctly and treat associated injuries with arthroscopy. There are less complications.

• Journal of the Korean Geotechnical Society
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• v.34 no.10
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• pp.29-38
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• 2018

The slime formed at the bottom of the borehole causes the excessive displacement and loss of the bearing capacity of the drilled shaft. In this study, the slime meter is developed for the evaluation of the slime based on the electrical properties of the fluid and the slime in the borehole. The slime meter is composed of a probe instrumented with electrodes and temperature sensor and a frame with rotary encoder, so that the slime meter profiles the electrical resistivity compensated with temperature effect along the depth. For the application of the slime meter, three field tests are conducted at a borehole with a diameter of 3 m and a depth of 46.9 m with different testing time and locations. For all the tests, the experimental results show that while electrical resistivities are constantly measured in the fluid, the electrical resistivities sharply increase at the surface of the slime. Therefore, the slime thicknesses are estimated by the differences in the depths of the slime surface and the ground excavation. The experimental results obtained at the same testing point with different testing time show that the estimated thickness of the slime increases by the elapsed time. Also, the estimated slime at the side of the borehole is thicker than that at the center of the borehole. As the slime meter estimates the slime in the borehole by measuring the electrical resistivity with simple equipment, the slime meter may be effectively used for the evaluation of the slime formed at the bottom of the borehole.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.5
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• pp.653-660
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• 2007

Since the temperature of asphalt for deck plate of steel bridge during paying procedure is relatively high as $240^{\circ}C\;to\;260^{\circ}C$, the temperature of deck plate of bridge rises mere than $100^{\circ}C$ and excessive displacement and stress could occur. In order to avoid undesirable failure of base plate and determine the optimal pavement pattern, a thorough thermal analysis is needed. General structural model which is made of beam and plate element should be modified for transient heat transfer analysis; asphalt pavement material and convection effect on surface of structure need to be added. A new technique with the Equivalent Heat Source (EHS) for numerical thermal analysis for steel bridge under thermal load of Guss asphalt pavement is proposed. Since plate/beam elements which were generally used for structural analysis for bridge cannot explain convection effect easily on plate/beam surface, EHS which is determined based on calculated temperature with convection effect is used. To verify the EHS proposed in this study, numerical analyses with plate elements are performed and the results are compared with estimated temperatures. EHS might be used for other thermal analyses of steel bridge such as welding residual stress analysis and bridge fire analysis.

• The Journal of Korean Academy of Prosthodontics
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• v.31 no.1
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• pp.129-150
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• 1993

Since the restoration or masticatory function is the most important aim of implants, it should be substituted for the role of natural teeth and deliver the stress to the bone under the continous load during function. In natural teeth, stress distribution can be obtained through enamel, dentin and cementum and the elasticity of the periodontal ligament play a role of buffering action. In contrast, implant prosthesis has a very unique characteristics that it delvers the load directly to bone through the implant and superstructure. This fact arise the needs to evaluate the stress distribution of the implant in the mechnical aspects, which has a similar role of natural teeth but different pathway of stress. With 3 kinds of implant in prevalent use, 2 types of experimental PEA implant models were made, axisymmetric and 2-dimensional type. In axisymmetric model, the stiffness of the part including the prosthesis and implant which extrude out of bony surface could be calculated with displacement of the superstructure un er 100N vertical load and then damping effects could be determined through this stiffness. In axisymmetric FEA model, load to the bone could be deduced by evaluation the stress distribution of the designed surface under the 100N vertical force and in 2-dimensional model, 100N eccentric vertical load and 20N horizontal loda. The result are as follows. 1. In every implant, stress to the bone tends to be concenturated on the cortical bone. 2. Though the stress of the cancellous bone is larger at the apex of implants, it is less compared with cortical bone. 3. Under 20N horizontal load, stress of the left and right sides of implant shows a symmetrical pattern. But under 100N eccentric vertical load, loaded side shows much larger stress value. 4. In the 1mm interface, stress distribution among implants tend to have a similar pattern. But under 20N horizontal load apposite side of being loaded shows less stress in IMZ. 5. In the case of screw type implant, stress tends to vary along with screw shape. 6. According to the result determined with microstrain, cancellous bone id generally under the condition of overload, while cortical bone is usually within the limitation of physiologic load. 7. In the Branemark implant, maximum stress to the cortical bone is larger than any other implant except for the condition of 20N horizontal force and 0.05mm interface. 8. Damping effects of implants is maximum in IMZ.

• Journal of the Korean Geophysical Society
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• v.9 no.4
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• pp.377-386
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• 2006

There is an inseparable relation between human race and engineering work. As world developed into highly industrialized society, a diversity of large structures is being built up correspondently to limited topographical circumstance. Though large structures are national establishments which provide us with convenience of life, there are some disastrous possibilities which were never predicted such as ground subsidence and degradation. It is very difficult to analyze the volume of total metamorphosis with the relative displacement measurement system which is now used and it is impossible to know whether there is structural metamorphosis within a permissible range of design or not. In this research with an object of 13-year-old earthen dam, through generating point-cloud which has 3D spatial coordinates(x, y, z) of this dam by means of 3D Laser Scanning, we can get real configuration data of slanting surface of this dam with this method of getting a number of 3D spatial coordinates(x, y, z). It gives 3D spatial model to us and we can get various information of this dam such as the distance of slanting surface of dam, dimensions and cubic volume. It can be made full use of as important source material of reinforcement and maintenance works to detect previously the bulging of the dam through this research.

• Composites Research
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• v.27 no.6
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• pp.248-253
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• 2014

In this study, tapered double cantilever beam specimens are designed with the variable of angle to investigate the fracture property at the bonded surface of adjoint structure. These specimens are made with four kinds of models as the length of 200 mm and the slanted angles of bonded surfaces on specimens of $6^{\circ}$, $8^{\circ}$, $10^{\circ}$ and $12^{\circ}$. By investigating experiment and analysis result of these specimens, the maximum loads are happened at 120 N, 137 N, 154 N and 171 N respectively in cases of the specimens with slanted angles of $6^{\circ}$, $8^{\circ}$, $10^{\circ}$ and $12^{\circ}$. As the analysis result approach the experimental value, it is confirmed to have no much difference with the values of experiment and analysis. It is thought that the material property can be investigated effectively on shear behavior of the material composed of aluminum foam bonded with adhesive through simulation instead of experiment by applying this study method.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.541-548
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• 2009

A theoretical prediction model of fiber bridging curve was established based on the assumption that fibers are uniformly distributed on the crack surface. However, the distance between fibers and their orientation with respect to crack surface can greatly affect the prediction of fiber bridging curve. Since, the shape of fiber bridging curve is a critical factor for predicting the tensile stress-strain relationship of ECC, it is expected that the assumption of uniform distribution of fiber may cause a significant error when predicting the tensile behavior of ECC. To overcome this shortcoming, a new prediction method of stress-strain relation of ECC is proposed based on the modified fiber bridging curve. Only effective fibers are taken into account considering the effects of their orientation and distance between them. Moreover, the approach for formulating the tensile stress-strain relation is discussed, where a procedure is presented for obtaining important parameters, such as the first crack strength, the peak stress, the displacement at peak stress, tensile strain capacity, and the crack spacing. Subsequent uniaxial tensile tests were performed to validate the proposed method. It was found that the predicted stress-strain relations obtained based on the proposed modified fiber bridging curve exhibited a good agreement with experimental results.

• Tunnel and Underground Space
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• v.25 no.2
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• pp.155-167
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• 2015

The thermal-hydrological-mechanical (T-H-M) behavior of rock mass surrounding a high-temperature cavern thermal energy storage (CTES) operated for a period of 30 years has been investigated by TOUGH2-FLAC3D simulator. As a fundamental study for the development of prediction and control technologies for the environmental change and rock mass behavior associated with CTES, the key concerns were focused on the hydrological-thermal multiphase flow and the consequential mechanical behavior of the surrounding rock mass, where the insulator performance was not taken into account. In the present study, we considered a large-scale cylindrical cavern at shallow depth storing thermal energy of $350^{\circ}C$. The numerical results showed that the dominant heat transfer mechanism was the conduction in rock mass, and the mechanical behavior of rock mass was influenced by thermal factor (heat) more than hydrological factor (pressure). The effective stress redistribution, displacement and surface uplift caused by heating of rock and boiling of ground-water were discussed, and the potential of shear failure was quantitatively examined. Thermal expansion of rock mass led to the ground-surface uplift on the order of a few centimeters and the development of tensile stress above the storage cavern, increasing the potential of shear failure.