• International Journal of Highway Engineering
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• v.8 no.3 s.29
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• pp.143-153
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• 2006

The differences in the stress distribution and the critical stresses in concrete pavement systems were analyzed when the dual-wheel single-, tandem-, and tridem-axle loads were applied at the interior and the edge of the pavement. The effects of the concrete elastic modulus, slab thickness, foundation stiffness, and tire contact pressure were investigated. The stresses under the interior loads were calculated using the transformed field domain analysis and stresses under the edge loads were obtained using the finite element method. The critical stresses under the interior and the edge loads were compared with respect to various parameters and the equations to predict the ratio between the stresses under the edge and the interior loads were developed and verified. From this study, it was found that the trends of the changes in the critical concrete stresses under the interior and the edge loads were very similar and the critical stress locations under those loads were identical. The critical stress ratio, which was obtained by dividing the critical stress under the edge loads into that under the interior loads, decreased with increasing the number of axles. That ratio became larger as the concrete elastic modulus increased, the slab thickness increased, the foundation stiffness decreased, and the tire contact pressure increased.

• Journal of the Korean Vacuum Society
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• v.18 no.4
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• pp.245-253
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• 2009

For the growth optimization of InAs/GaSb (8/8-ML) strained-layer superlattice (SLS), the structure has been grown under various conditions and modes and characterized by the high-resolution x-ray diffraction (XRD) analysis. In this study, the strain modulation is induced by changing parameters and modes, such as the growth temperature, the ratio of V/III beam-equivalent-pressure (BEP), and the growth interruption (GI), and the strain variation is analyzed by measuring the angle separation of 0th-order satellite peak in XRD patterns. The XRD results reveal that the growth temperature and the V/III(Sb/Ga) ratio are major parameters to change the crystallineity and the strain modulation in SLS structures, respectively. We have observed that the SLS samples with compressive strain prepared in this study are show a transition to tensile strain with decreasing V/III(Sb/Ga) ratio, and the GI process is a sensitive factor giving rise to strain modulation. These results obtained in this study suggest that optimized growth temperature and V/III(Sb/Ga) ratio are $350^{\circ}C$ and 20, respectively, and the appropriate GI time is approximately 3 seconds just before InAs growth that the crystallineity is maximized and the strain relaxation is minimized.

• Tunnel and Underground Space
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• v.5 no.3
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• pp.230-239
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• 1995

암석의 인장강도 실험법의 하나로써 새롭게 개발된 Hoop Test에 대한 이론적 뒷받침을 하고자 유한요소법을 사용하여 응력분포를 해석하였다. 간단하며 사용하기 편리한 실험장치이지만 시료가공시 생길 수 있는 내부공의 지름에 대한 오차, 재부공벽면과 하중장치외벽과의 마찰 등이 있어 이들로부터 발생할 오차를 평가해 보았다. 또한 시료의 안지름과 바깥지름의 비율이 응력의 크기에 끼치는 영향을 조사하였다. 응력해석결과, 일반적인 시료준바에 필요한 주의만 기울이면 실험치에 별다른 영향을 주지않는 것으로 제안되었고 이는 그동안의 실험결과의 신뢰성을 이론적으로 보충해 주었다.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.695-702
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• 2006

The stress distribution and the critical stresses in concrete pavements were analyzed using formulations in the transformed field domains when dual-wheel single-, tandem-, and tridem-axle loads were applied. First the accuracy of the transformed field domain analysis results was verified by comparing with the finite element analysis results. Then, the stress distribution along the longitudinal and transverse directions was investigated, and the effects of slab thickness, concrete elastic modulus, and foundation stiffness on the stress distribution were studied. The effect of the tire contact pressure related to the tire print area was also studied, and the location of the critical stress occurrence in concrete pavements was finally investigated. From this study, it was found that the critical concrete stress due to multi-axle loads became larger as the concrete elastic modulus increased, the slab thickness increased, and the foundation stiffness decreased. The number of axles did not tend to affect the critical stress ratio except for a small foundation stiffness value with which the critical stress ratio became significantly larger as the number of axles increased. The critical stress location in the transverse direction tended to move into the interior as the tire contact pressure increased, the concrete elastic modulus increased, the slab thickness increased, and the foundation stiffness decreased. The critical stress location in the longitudinal direction was under the axle for single- and tandem-axle loads, but for tridem-axle loads, it tended to move under the middle axle from the outer axles as the concrete elastic modulus and/or slab thickness increased and the foundation stiffness decreased.

• The Journal of Engineering Geology
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• v.6 no.3
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• pp.111-118
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• 1996

In general, a three dimensional ground behaviour during tunneling is simulated by using two dimensional analysis programs in consideration of a certain ratio of stress or strain distribution to take into account the effect of construction stage by a tunnel face advance. A series of trree dimensional analyses was conducted to deduce a normalized displacement (surface or crown settlement) curve in longitudinal direction, of which curve is reflecting an effect of a tunnel advance under a various condition. And, by using try and error technique, two dimensional analyses were carried out to determine an optimum stress distribution ratio for a settiement curve coincided with the curve obtained by three dimensional analyses. Finally, monitored results from a subway tunnel were compared with two dimensional analysis results for varification of the deduced stress distribution ratio as well as the two dimensional analysis program employed in this study.

• Journal of Korean Society of Steel Construction
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• v.9 no.4 s.33
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• pp.489-500
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• 1997

The number of railway bridges in Korea reaches to about 3,000. Among them, the ratio of steel bridges is about 47%. Most of the long span railway bridges take the truss type, its number is 15 in Korea. These bridges have more than 30 years service life, it is expected that the damages of cracks and corrosion is going. Therefore, the estimation of fatigue life with random stress is considered as significant subject in maintenance. In this paper, the random stress was measured in bridges and counted the stress cycles using the rainflow counting method So, the stress range frequencies and their equivalent stress are obtained and the amplification factor for the span length, bridge types and traveling speed is assessed by the dynamic testing. From the results, the stress range of the stringer and the lower chord is higher than the other members and the characteristics of the stress histogram is varied to the loading system and the amount of the passing through trains. And the impact effects are depended on the traveling speed as well as the span length.

• The Journal of Korean Academy of Prosthodontics
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• v.32 no.1
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• pp.120-147
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• 1994

This study was performed for the purpose of evaluating the stress distribution around threaded type implants, cylindrical type implants and teeth connected with rigid or non-rigid connector. The stress distribution around the surrounding bone was analyzed by three-dimensional photoelastic method. Twelve mandibular photoelastic epoxy resin models and a circular polariscope were used to record the isochromatic fringes. After the stress distribution around the implant and tooth was observed, the results were as follows ; 1. In threaded type implants, stress concentrated patterns were observed at the neck either vertical or 25 degree lateral force. 2. The stress concentrated patterns were observed at the tooth apical portion and neck portions of the implant and tooth when a threaded implant was connected with the tooth by either a rigid or non-rigid connector. More force was generated at the tooth neck portion by a rigid connector and more force at the implant neck portion by a non-rigid connector. 3. The stress concentrated patterns were observed at the apical portion of the implant and tooth when a cylindrical type ,implant was connected with the tooth either by a rigid or non-rigid connector. More force was generated at the tooth apical portion by a rigid connector and more force at the neck portion of the tooth and implant by a non-rigid connector. 4. The stress around the tooth was more equally distributed in a threaded type implant than in a cylindrical implant when the tooth was connected with either a rigid or non-rigid connector. 5. The stress around a threaded type implant was progressively more equally distributed in the following order : 1) when used a single implant, 2) a non-rigid connection with the implant and tooth, 3) a rigid connection with the implant and tooth, 4) a rigid connection with two implant fixtures.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.5
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• pp.479-489
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• 2008

Statement of the problem: Under anatomical limitations on maxillary posterior region, a poor crown-to root ratio acting on dental implants can result in undesirable stress in surrounding bone, which in turn can cause bone defects and eventual failure of implants. Purpose: The purpose is to compare stress distribution due to different crown-root ratio and effect of splinting between natural teeth and implants in maxillary molar area under different loads. Material and methods: Analysis of stress arising supporting bone of the natural teeth and the implant was made with 3-dimensional finite element method. The model simulated naturel teeth was made with 2nd premolar and 1st molar in the maxillary molar region (Model T). The model simulated implants placed on same positions with two parallel implants of Straumann Dental Implant cemented abutment (Model I). Each model was designed in different crown-root ratio (0.7:1, 1:1, 1.25:1) and set cement type gold crown to make it non-splinted or splinted. After that, 300 N force was loaded to each model in five ways (Load 1: middle of occlusal table, Load 2: middle of buccal cusp, Load 3: middle of lingual cusp, Load 4: horizontal load to buccal cusp of anterior abutment only, Load 5: horizontal load to middle of buccal cusp of each abutment), and stress distribution was analyzed. Results and conclusion: On all occasions, stress was concentrated at the cervical region of the implant. Under load 1, 2 and 3, stress was not increased even when crown-root ratio increases, but under load 4 and 5, when crown-root ratio increases, stress also increased. There was difference in stress values between natural teeth and implants when crown-root ratio gradually increases; In case of natural teeth, splinting decreased stress under vertical and horizontal loads. In case of implants, splinting decreased stress under vertical loads 1,2 and 3, but increased maximal stress under loads 2 and 3. Under horizontal loads, splinting decreased stress, however the effect of splinting decreased under load 5 than load 4. Furthermore, the stress was increased, when crown-root ratio is 1.25:1. Clinical implications: This limited finite element study suggests that the stress on supporting bone may be increased under non-axial loads and poor crown-root ratio. Under poor crown-root ratio, excessive stress was generated at the cervical region of the implant, and decreased splinting effect for stress distribution, which can be related to clinical failure.

• Journal of Korean Society of Steel Construction
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• v.18 no.6
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• pp.747-758
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• 2006

With the growth of economy, the esthetic values of bridges become significant points in the decision process of a type of new bridges. So, it is common that a long-span bridge or a multi-purpose bridge are selected as the type of new bridges. Also, the economic growth derives increase in traffic and then the increased traffic derives multi purpose bridges from the decision process of bridge types. In the multi-purpose bridges with private fund, the construction cost is simply alloted to several organizations according to the percentage of participation and usage. But the allotment of the maintenance cost is not simple. Because the loads and safety factors in design are different between the criterion of design of highway bridges and that of railway bridges. In this study, we verify the possible problems in case of allotment method of maintenance cost in foreign examples as well as domestic example. As one of the method of determination of allotment ratio in maintenance cost, the method based on the stress of structural analysis is presented and it can be an example in the similar problem later.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.223.2-223.2
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• 2013

비정질 실리콘은 태양전지, 트랜지스터, 이미지 센서 등 다양한 분야에서 응용되고 있으며 새로운 박막 소자 개발을 위한 소재로서 많은 연구가 진행되고 있다. 하지만 소자개발에 있어 공정상에서 발생하는 비정질 실리콘 박막의 높은 응력(stress)은 소자의 특성을 떨어뜨리는 문제점을 갖는다. 따라서 우수한 특성의 소자 개발을 위해서는 보다 낮은 응력을 갖는 비정질 실리콘 박막 증착 및 공정 조건에 따른 응력 조절이 필요하다. 저응력의 비정질 실리콘 박막 증착은 보다 낮은 반응온도에서 증착속도를 최소로 하여 성장되어야 하는데 이는 플라즈마기상증착(Plasma enhanced chemical vapor deposition, PECVD) 시스템에 의해 가능하다. 따라서 본 연구에서는 PECVD 시스템을 사용하여 비정질 실리콘 박막을 증착하였고 그 특성을 분석하였다. 이 때 증착 온도, rf 파워, 공정 압력은 실험결과로부터 얻어진 낮은 박막 증착속도 하에서 안정적으로 증착이 가능한 조건으로 일정하게 유지하여 실험하였다. 공정 가스는 SiH4/He/N2의 혼합가스를 사용하였고 응력 조절을 위해 SiH4/He 가스비를 일정한 비율로 변화하여 비정질 실리콘 박막을 증착하였다. 증착된 박막의 두께 및 표면 특성은 field emission scanning electron microscopy 및 atomic force microscopy를 이용하여 분석하였고, energy dispersive X-ray 분석을 통하여 정량 및 정성적 분석을 수행하였다. 그리고 stress measurement system을 이용하여 박막의 응력을 측정하였고 X-ray diffraction 측정 및 ellipsometry 측정으로부터 증착된 박막의 결정성, 굴절률 및 oiptical bandgap을 분석하였다.