• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2012.03a
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• pp.86-86
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• 2012

고속방사소재는 연신공정이 없이 6,000m/min이상의 고속방사공정만이 있으므로 원가절감이 되고, 빠른 냉각, 높은 변형속도 등으로 섬유의 결정화도, 분자와 결정의 배향 및 모폴로지(morphology) 변화 등의 기계적 및 섬유상의 특성이 종래의 원사와는 다르게 된다. 방사속도가 증가함에 따라 배향도가 증가하면서 결정영역 또한 증가한다. 또한 기존 연신사에 비해 큰 결정크기를 갖는데 방사속도에 에 따른 방사응력의 증가가 응력유도 결정화도를 유발하여 결정크기 및 결정화도를 증가시키고,따라서 고분자의 용융점도를 고온측으로 이동시키는 현상을 나타내게 한다. 즉, 고속방사에 있어서는 연신에 필요한 임계응력 이상의 과도한 응력이 가해짐으로 인해 결정구조가 일반 연신사에 비해 현저히 발달한다는 것을 알 수 있다. 고속방사 원사를 통일한 조건으로 염색하는 경우 기존의 연신사보다 염착량이 많아 농색으로 염색이 가능하고 염착속도도 빠른 특징을 갖는 데이는 고속방사 원사의 비결정 배향이 낮고 느슨한 구조를 갖기 때문에 염료의 침투가 용이한 것으로 해석되고 있다. PET 섬유는 방사 후 형태안정성을 부여하기 위해서 염색 전처리 공정에서 열을 가하게 된다. 이런 과정에서 섬유의 미세구조가 변하게 되는데,특히 고속방사의 경우 섬유 형성과정이 연신사와는 다르므로 열에 의한 구조 변화와 이에 따른 염색성 변화에 대해 검토해 보는 것은 고속방사의 응용면에서 꼭 필요하다. 본 연구에서는 고속방사소재의 가장 단점인 잔류신도, 저수축현상, stiff감을 보완하면서 고속방사소재의 장점인 심색성을 부각시켜 차별화된 복합사 제조기술을 개발하기 위해 그 기술개발이 기초 연구로서 일반 일반 DTY사와 고속방사소재인 HOY사를 이용한 DTY사의 물성 및 염색 특성을 비교분석 하고자 한다.

• Analytical Science and Technology
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• v.7 no.2
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• pp.193-199
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• 1994

We have synthesized K-CFICs by the modified two-bulb method. These synthesized compound were analysed with X-ray diffractometer and UV/VIS spectrophotometer. According to X-ray diffraction analysis, the intercalation of potassium between the carbon layers of carbon fiber was better then other intercalants. From obtained data for this deintercalation process, we can see that a number of potassiums were presented as a residue between the carbon layers and this residue compounds had a stability for a long term. Therefore, it is appear that these compounds have a capability as new useful material. From UV/VIS spectrometry data, we can suppose that spectrum of K-CFICs synthesized at $250^{\circ}C$ had only a $R_{min}$, and spectra of any other compounds were not appeared charecteristic peaks because potassium ions were little affect the energy levels of original carbon fiber.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.4
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• pp.1889-1894
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• 2012

A small-scale chamber test laboratory for controlled low strength materials with bottom ash and recycled in-situ soil have been carried out. Laboratory test which was simulated during construction stage was conducted. The vertical deflection of 4.43mm to 6.6mm, and the horizontal deflection of 5.49mm to 15.9 mm were measured during backfilling. In case of loading, the vertical deflection of 2.41mm to 8.69mm, and the horizontal deflection of 1.66mm to 2.53mm were measured. Its residual deflections were 1.40mm to 5.93mm for vertical and 1.66mm to 2.53mm for lateral. The vertical and horizontal deflecto of controlled low strength materials were smaller than that of sand backfill. Also, it was same trend for the measured surface settlement.

• Korean Journal of Materials Research
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• v.5 no.1
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• pp.132-139
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• 1995

Tnermomechanical treatment consisting of homogenizing, hot and warm rolling were introduced to Al-MgCu-Mn alloys for obtaining superplasticity. The factors affecting the superplasticity of the alloys were investigated by optical and transmission electron microscopy. Large particles which had not been decomposed during homogenizing treatments remained stable in the hot and warm rolling processes. These particles were a source of cavitation and poor elongation in superplastic deformation. On the other hand, fine precipitates were produced during thermomechanical processing, and resulted in improvement of superplasticity by stabilizing microstructure. Two-step homogenizing and air cooling process was more effective than onestep homogenizing and furance cooling process in removing microsegregations and producing fine particles.

• Journal of Korean Society of Steel Construction
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• v.29 no.1
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• pp.73-80
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• 2017

In this study, cyclic loading analysis was conducted in order to understand the behavior of self-centering connections based on the number of PT(posttensioning) strands and initial posttensioning force. The initial posttensioning force needs to be above the yield moment of an angle for obtaining noticeable self-centering effect and it is proper that decompression moment ratio needs to be below 0.35 to minimize the residual displacement of major elements. As the number of PT strands increased, self-centering capacity also improved since initial posttensiong force in each PT strand has been decreased. It is also appropriate that initial posttensiong force needs to be less than or equal to 75% of yield strength of PT strands.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.6 no.3
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• pp.75-86
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• 1986

The welded joint of the rail of railroad had shown the complicated behaviour of fatigue crack growth due to the effect of low toughness, residual stress, welding stress and strain etc. resulting from welding. Also, the welding connection has been necessary as making longer the rail, thus fatique fracture has often occurred at welded joints. From above, in this paper, faigue test was done at base metal, gas pressure and thermit welded joints to give the basic data to construct S-N diagrams. From this, it was known that the base metal was better than welded joint and gas pressure better than thermit welded joints in the resistance against the behaviour of fatigue crack growth. And it was also found that it is very dangerous to control fracture only by the method of material mechanics.

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.173-181
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• 1999

To deepen the understanding of shear behaviour in beams without transverse reinforcement, the relative importance of five contributing factors to concrete shear resistance($v_c$), which are i)flexural compression zone, ii)friction at crack faces, iii)dowel action, iv)arch action and recently identified, v)residual tensile stresses across cracks, was explained physically using two analytical methods based on the truss concept. One is called "Modified Compression Field Theory(MCFT)" considering ii) and v) explicitly, and the other "Crack Friction Truss Model(CFTM)" more dominantly ii) in determining concrete resistance. To verify their effectiveness, the predictions using MCFT and CFTM were also made for twenty KAIST beam tests($f'_c$=53.7Mpa), designated more likely to the development of the size effect law based on the fracture mechanics concept. Experimental findings with varying of a/d, longitudinal reinforcement ratios, and obtained from MCFT enabled additional explanations for some phenomena which were difficult to measure in tests. However, MCFT seemed somewhat conservative for beams with higher longitudinal reinforcement, while somewhat unsafe for beams with larger depths. More tests are necessary leading to firm conclusions in these areas.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.83-93
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• 2003

This research, in order to study the effects of initial shear stress of anisotropically consolidated sand that has 0.558% fines, performed several undrained static and dynamic triaxial test. To simulate the real field conditions, loose and dense samples were prepared. Besides, the cyclic shear strength of Nakdong River sand under various combinations of initial static shear stress, stress path, pore water pressure and residual strength relationship was studied. By using Bolton's theory, peak internal friction angle at failure which has considerable effects on the relative density and mean effective stress was determined. In p'- q diagram, the phase transformation line moves closer to the failure line as the specimen's initial anistropical consolidation stress increases. Loose sands were more affected than dense sands. The increase of consolidation stress ratio from 1.4 to 1.8 had an effect on liquefaction resistance strength resulting from the increase of relativity density, and showed similar CSR values in dense specimen condition.

• The Journal of Korean Academy of Prosthodontics
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• v.27 no.2
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• pp.53-78
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• 1989

This study was taken to observe the changes of the residual stress in the alloy and to measure 3 dimensional distortions of the long span ceramo-metal bridge. The materials used in this study were Pors-on 4 (Pd-Ag alloy), and Ceramco and Vita VMK 68 powders. The residual stress of the alloy was measured on the six specimens (dia. 8m/m) by the X-ray diffraction stress analyzer according to the kind of ceramic powder and different measuring stages. And, for the measurement of the distortions, fifteen specimens of the anterior 8-unit ceramo-metal brige were fabricated and subjected to the 3-D coordinate measuring machine. Variables included the 2 kinds of a ceramic powder and the presence or absence of a splint bar at the cast metal framework. The measuring stages in both were after casting, after degassing and after glazing. The following conclusions were obtained : 1. The residual stress of the alloy showed increasing tendency for the tension by the ceramic fusing, but there was not significance. 2. The tendency of the distortions in the cast metal frameworks were decrease of the width, the anterior displacement and sagging. 3. The amount of the distortions at the degassing stage were greater than that at the ceramic fusing stage. 4. The splint bar was effective to control the distortion only at ceramic fusing stage. 5. The sagging distortion in the Ceramco firing were even through all measuring stages, but in the Vita firing, pronounced at degassing stage.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.1
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• pp.399-405
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• 2012

This paper investigates the characteristics of buckling loads for steel arches with new type cross section which is consisted of T-section and pipe-section. A general purpose finite-element program ABAQUS was used to evaluate the inelastic buckling strengths of the arches which included the influence of the geometric and material nonlinearity. According to the comparisons between earlier studies and results from finite-element analyses, new design equations should be developed for the new arches. New buckling factors were developed to consider influence of rise-to-span ratio and boundary conditions. It is found that the presented factors are sufficiently accurate to predict the inplane buckling loads of new type section steel arches subjected to uniformly distributed loading. The proposed equations can be used to investigate new type steel arches subjected to unsymmetrical loading and composited arches.