• Journal of Korean Society of Steel Construction
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• v.16 no.2 s.69
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• pp.257-265
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• 2004

The aim of this study is to investigate the inelastic buckling behavior of the beams under moment gradient using a line-type finite element method. The method is incorporated the non-uniform yielding of the cross-section caused by the presence of residual stress and accepted model of residual stress so called 'simplified' and 'polynomial' pattern is adopted in this study. The inelastic lateral-torsional buckling results obtained in this study is compared with the buckling results obtained from the design method based on the allowable stress method given in Korean Steel Designers Manual (KSDM 1995). This study have found that the design method in KSDM (1995) is conservative without and with intermediate bracing applied at the mid span of the beam, and there is some scope for improving the provisions of KSDM (1995)

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.44-44
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• 2011

현존하는 초경도 박막물질 중 입방정 질화붕소(cBN)은 철계 금속과의 반응안정성 및 낮은 온도에서의 합성가능성 등 많은 장점을 가지고 있다. 그러나 필수로 수반되는 이온충돌 효과로 인해 박막 내 높은 잔류응력으로 인한 박리 현상으로 응용이 어려운 실정에 있다. 현재까지 이를 개선하기 위해 수소를 첨가하여 박막의 잔류응력을 줄이는 연구, B4C 타겟을 이용하여 B-C-N 의 gradient layer를 설계하여 점진적으로 잔류응력을 감소시키는 연구 등 많은 연구들이 진행되고 있다. 본 연구에서는 MOCVD로 만들어진 NCD(Nano Crystalline Diamond) buffer layer 위에 RF-UBM(unbalanced magnetron) PVD를 이용하여 BN을 증착시켰다. hBN 타겟을 이용하여 2mTorr에서 400W 의 RF 파워를 사용하여 기판에 RF bias를 인가해 실험하였다. cBN 박막과 기판의 lattice mismatch 를 줄이기 위해서 본 연구소에서 제공되는 NCD 기판을 사용하였으며, 다이아몬드 기판과 cBN 박막의 1:1 에피성장을 이루기 위해 상온에서부터 800도까지 온도 변화를 주어 cBN을 증착시켰다. FTIR(Fourier transform infrared spectroscopy)로 $sp^2$구조인 hBN과 $sp^3$구조인 cBN의 성장유무를 확인하였으며, FTIR peak intensity 차이로 박막내 cBN의 함량을 계산하였고, Scratch test로 박막과 기판사이의 밀착력을 상대적으로 비교하였으며, 격자의 에픽성장을 확인하기 위해 FIB 의 작업을 거쳐 HRTEM 으로 각 위치별로 SAD pattern를 이용하여 성장거동을 확인하였다.

• Journal of Korean Association for Spatial Structures
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• v.11 no.4
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• pp.37-47
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• 2011

This article aims to analytically research for influence of residual stresses on bending moment responses against welded steel pipes subjected to quasi -static or dynamic loadings. The residual stresses of the welded steel pipe are computed by three-dimensional welding simulation. The bending moment responses of the welded and seamless steel pipes are determined by using three-dimensional dynamic elastoplastic FE analysis as a function of loading rate. It is seen from analytical results that the welded steel pipe shows lower moment response comparing to the seamless steel pipe, and moment difference between seamless and welded steel pipes tends to decrease as loading rate increases.

• Journal of the Korean GEO-environmental Society
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• v.6 no.1
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• pp.45-51
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• 2005

The distribution of shaft resistance is measured by the static load test with the strain gauge or stress gauge, so that the long-term load distribution must be considered for the pile design. However, the measurement by strain gauge generally assumes the 'zero reading', which is the reading taken at 'zero time' with 'zero' load and the residual stress, which is the negative skin friction(or the negative shaft resistance) caused by the pile construction, is neglected. Therefore, the measured value by strain gauge is different from the true load-distribution because residual stresses were neglected. In this study, the three drilled shafts were constructed, and the strain measurements were carried out just after shaft construction. As a result of this study, it is shown that the true load-distribution of drilled shaft is quite different with known load distribution and the true load-distribution of drilled shaft changed from the negative skin friction to the positive skin according to the load increment.

• Composites Research
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• v.37 no.1
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• pp.15-20
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• 2024

Since the residual stress of hydrogen tank is directly related to durability, it is very important to reduce it for safety. Type II~IV hydrogen tank are manufactured by the filament winding method, in which the fiber is impregnated with resin and wound around the liner. Residual stress in composite is affected by curing conditions and fiber tension etc. In this study, the effect of curing conditions on residual stress was analyzed when manufacturing a Type III hydrogen tank using carbon fiber filament winding process. First, the curing behavior of the epoxy resin was analyzed using a differential scanning calorimetry. Through this, the curing temperature was set to 140℃. During the same curing time, the specimens were cured under 2-stage curing condition that reached 140℃ earlier and a 4-stage curing condition that reached 140℃ later, respectively. After curing, the residual stress of the composite material was measured by the ring slitting method, and the experimental values were compared with numerical values. It was confirmed that there was a significant difference in residual stress according to the optimization of curing conditions.

• Journal of Korean Society of Steel Construction
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• v.10 no.3 s.36
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• pp.407-421
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• 1998

The purpose of this paper is to provide and verify an analytical method, based on the spline finite strip method, which can be used to investigate the buckling mode and stress of thin-walled steel sections. Geometric imperfection and initial stress of plates and plate assemblies, which are resulted from various preloadings and may cause prebuckling deformations before buckling, are included in the analysis. Material nonlinearity and residual stress are also considered. It can be applied to sections with simple or non-simple boundary conditions and arbitrary loading. The method has been applied to investigate the buckling behavior of plates and plate assemblies which are subjected to compression with initial imperfections and residual stresses.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.6 s.165
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• pp.943-951
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• 1999

The welded structure unnecessarily remains residual stress due to the very high heating of local region and lastly cooling. The residual stress sometimes causes fracture initiation of welded structures. In this paper, distribution and magnitude of tensile and compressive residual stresses in the TIG(Tungsten Inert Gas) welded aluminum alloy such as Al5083-H112 are measured by using the hole-drilling method. Furthermore, the effects of residual stresses in the TIG welded aluminum CCT(Center Crack Tension) and SEN(Single Edge Notched) Specimens on the fatigue crack propagation behavior are analyzed. The fatigue cracks initiated at residual stresses region are influnced by tensile and compressive residual stresses. However, the effects are found to be released fast for both cases according to the cyclic loads and extension of crack length.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.4
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• pp.75-82
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• 2001

Static loadings on ship structure induced either by water pressure before service such as a tank test and ballasting or by cargo pressure during first laden voyage cause relatively much greater stress than dynamic loadings induced by wave. With these static pre-loadings, the initial residual stresses around welded joint, where fatigue strength is concerned(in most cases, where stress concentration occurs) are expected to be shaken-down in a great extent by the elasto-plastic deformation behavior of material. Therefore, it is more resonable to assess the fatigue strength of ship structure with S-N data which have taken into account the effect of shaken-down residual stresses(re-distributed stresses) on the fatigue strength. In this research work, the re-distribution of residual stresses by the tensile pre-loading is measured using an ordinary sectioning method for specimens of padding plate weldment. Fatigue tests are performed also to evaluate the fatigue strength of the both as-welded and pre-loaded specimens.

• Journal of the Korean Institute of Gas
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• v.23 no.4
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• pp.65-73
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• 2019

A spiral steel pipe has been more used widely as a structural member as well as transport pipeline because the pipe can be manufactured continuously, consequently more economical than the conventional UOE pipe. As improved pipe manufacture technology makes spiral pipes to have high strength and to have larger diameters, the spiral pipes have been recently used as long distance transport pipeline with a large diameter and strain-based design is thus required to keep structural integrity and cost effectiveness of the spiral pipe. However, design codes of spiral pipe have not been completely established yet, and structural behaviors of a spiral pipe are not clearly understood for strain-based design. In this paper, the effects of residual stresses due to the spiral pipe manufacture process are investigated on the flexural behavior of the spiral pipe. Finite element analyses were conducted to estimate residual stresses due to the manufacturing process for the pipes which have different forming angle, thickness, and strength, respectively. After that, the results were used as initial conditions for flexural analysis of the pipe to numerically investigate its flexural behaviors.

• Journal of Korean Society of Steel Construction
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• v.20 no.3
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• pp.421-435
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• 2008

This paper presents an investigation on the ultimate behavior of a transmission tower using nonlinear analyses inconsideration of residual stress and initial imperfection. Main members, such as main post, horizontal member and diagonal member of the transmission tower were modeled using beam element. Moreover, submembers of the transmission tower were modeled using truss element. ABAQUS (2004) program was used to perform finite element analyses. Initial condition options of the ABAQUS program considering initial stress and imperfection were used in this study. Before performing the analysis of the total transmission tower, simple angle section models using beam or plate/shell element w ere investigated to verify the appropriateness of ABAQUS analysis models and options. According to the verification results, the beam element was used for nonlinear analyses of the transmission tower. From nonlinear analyses results, buckling failure was in the main member of the leg part because of ${P-{\triangle}}$ effect at that point. Also, this paper includes significant results to define real structural failure modes and quantitative values. This study should be used in the development of a reasonable and economic design method for transmission towers.