• 한국강구조학회 논문집
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• 제21권5호
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• pp.527-536
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• 2009

본 연구의 목적은 박판 탄소강 일면전단 2행 2열 볼트접합부의 블록전단파단거동과 면외변형의 영향을 조사하는 것이다. 하중직각 방향 연단거리, 볼트직경, 피치, 게이지 치수를 고정하고 블록전단파단이 발생하도록 실험체를 계획한다. 접합평판의 두께, 하중방향연단거리를 주요변수로 설정한다. 단순인장 실험을 실시하고 블록전단파단 양상, 최대내력을 현행의 설계기준식에 의한 예측치와 비교한다. 또한, 판 두께와 연단거리에 따른 하중방향과 직각방향으로 발생하는 면외변형의 발생조건을 조사하고 면외변형의 발생으로 인한 내력저하정도를 고찰한다.

• 한국항공우주학회지
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• 제41권8호
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• pp.665-672
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• 2013

적층된 복합재 구조물의 강도와 강성 저하를 발생시키는 중요원인 중의 하나는 복합재 층 사이에 발생하는 층간 분리이다. 적용되는 대부분의 복합재 구조물은 어느 정도 곡률을 가지고 있다. 만약 굽은 복합재 구조물이 굽힘 하중을 받게 되면 평평하게 되려는 현상 때문에 두께 방향의 수직응력이 발생하게 되며, 최대 응력이 발생되는 곳에서 층간 분리가 발생한다. 본 논문에서는 굽은 복합적층 보의 반경방향 응력을 결정하는 방법을 설명하고, 층간 분리 응력에 미치는 적층 순서의 영향을 검토하였다. 그리고 층간분리 응력의 크기와 위치를 이론적인 해와 유한요소 방법을 이용하여 해석하고 비교하였다.

• 한국음향학회지
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• 제36권3호
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• pp.158-164
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• 2017

수중에서 은밀하게 움직이는 표적을 조기에 탐지하기 위한 선배열센서에 적용되는 통상의 하이드로폰은 표적신호의 크기만 측정할 뿐, 외부에서 들어오는 음향신호의 방향은 파악할 수 없는 한계가 있다. 이에 본 연구에서는 표적으로부터의 음향신호의 크기와 방향을 동시에 탐지할 수 있는 관성형 벡터 하이드로폰의 기본 구성품으로 두께 전단형 진동자를 제안하였다. 외력에 대한 진동자의 출력 전압을 해석할 수 있는 수식을 유도하였으며, PMN-PT 단결정 진동자에 대한 유한요소해석을 통해 수식의 타당성을 검증하였다. 본 연구에서 얻어진 해석 결과는 향후 두께 전단형 진동자로 구성된 관성형 벡터 하이드로폰 설계에 활용될 것이다.

• 한국재료학회지
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• 제33권12호
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• pp.565-571
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• 2023

AA1050/AA6061/AA1050 layered sheet was fabricated by cold roll-bonding process and subsequently T4 and T6 aging-treated. Two commercial AA1050 sheets of 1 mm thickness and one AA6061 sheet of 2 mm thickness were stacked up so that an AA6061 sheet was located between two AA1050 sheets. After surface treatments such as degreasing and wire brushing, they were then roll-bonded to a thickness of 2 mm by cold rolling. The roll-bonded Al sheets were then processed by natural aging (T4) and artificial aging (T6) treatments. The as roll-bonded Al sheets showed a typical deformation structure, where the grains are elongated in the rolling direction. However, after the T4 and T6 aging treatments, the Al sheets had a recrystallized structure consisting of coarse grains in both the AA5052 and AA6061 regions with different grain sizes in each. In addition, the sheets showed an inhomogeneous hardness distribution in the thickness direction, with higher hardness in AA6061 than in AA1050 after the T4 and T6 age treatments. The tensile strength of the T6-treated specimen was higher than that of the T4-treated one. However, the strength-ductility balance was much better in the T4-treated specimen than the T6-treated one. The tensile properties of the Al sheets fabricated in the present study were compared with those in a previous study.

• Corrosion Science and Technology
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• 제13권1호
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• pp.20-27
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• 2014

The structures of reinforced concrete has been extensively increased with rapid development of industrial society. Futhermore, these reinforced concretes are easy to expose to severe corrosive environments such as sea water, contaminated water, acid rain and seashore etc.. Thus, corrosion problem of inner steel bar embedded in concrete is very important in terms of safety and economical point of view. In this study, multiple mortar test specimen(W/C:0.4) with six types having different cover thickness each other was prepared and was immerged in seawater solution for five years to evaluate the effect of cover thickness and immersion years to corrosion property of embedded steel bar. And the polarization characteristics of these embedded steel bars was investigated using electrochemical methods such as measuring corrosion potential, cathodic polarization curve, and cyclic voltammogram. At the beginning of immersion, the corrosion potentials exhibited increasingly nobler values with increasing cover thickness. However, after immersed for 5 years, the thicker cover of thickness, the corrosion potentials shifted in the negative direction, and the relationship between corrosion potential and cover thickness was not in good agreement with each other. Therefore, it is considered that the thinner cover of thickness, corrosive products deposited on the surface of the embedded steel bar plays the role as a resistance polarization which is resulted in decreasing the corrosion rate as well as shifting the corrosion potential in the positive direction. As a result, it seemed that the evaluation which corrosion possibility of the reinforced steel would be estimated by only measuring the corrosion potential may not be a completely desirable method. Therefore, it is suggested that we should take into account various parameters, including cover thickness, passed aged years as well as corrosion potential for more accurate assessment of corrosion possibility of reinforced steel which is exposed to partially or fully in marine environment for long years.

• 한국정밀공학회지
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• 제34권4호
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• pp.259-264
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• 2017

Spectrally resolved interferometry (SRI) is an attractive technique to measure absolute distances without any moving components. In the spectral interferogram obtained by a spectrometer, the optical path difference (OPD) can simply be extracted from the linear slope of the spectral phase. However, SRI has a fundamental measuring range limitation due to maximum and minimum measurable distances. In addition, SRI cannot distinguish the OPD direction because the spectral interferogram is in the form of a natural sinusoidal function. In this investigation, we describe a direction determining SRI and propose the optimal conditions for determining OPD direction. Spectral phase nonlinearity, caused by a dispersive material, effects OPD direction but deteriorates spectral interferogram visibility. In the experiment, various phase nonlinearities were measured by adjusting the dispersive material (BK7) thickness. We observed the interferogram visibility and the possibility of direction determination. Based on the experimental results, the optimal dispersion conditions are provided to distinguish OPD directions of SRI.

• 한국농공학회지
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• 제38권3호
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• pp.82-91
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• 1996

This is a basic study for the static and dynamic analysis on the elasto-plastic and elasto-viscoplastic of an axi-symmetric shell. The objective of this study was to investigate the mechanical characteristics of a nuclear reinforced concrete containment structure, which was selected as a model, by a numerical analysis using a finite element method. The structure was modeled with discrete ring elements of 8-noded isoparametric element rotating against the symmetrical axis, and the interaction between the foundation and the structure was modeled by Winkler's model. Also, the meridional tendon was modeled with 2-node truss elements, and the hoop tendon was done with point elements in two degrees of freedom. The effect of the tendon was considered without the increasement in total degree of freedom as the stiffness matrix of modeled tendon elements was assembled on the stiffness matrix of ring elements linked with the tendon. The results obtained from the analysis of an example were summarized as follows : 1. The stresses in the hoop direction on the interior and exterior surfaces of the structure were shown in changes of similar trend, and high stresses appeared on the structure wall 2. The stresses in the meridional direction on the interior and exterior surfaces were shown in change of different trend. Especially, the stresses at the junctions between the dome and the wall and between the wall and the bottom plate of the structure were very high, compared with those at other parts of the structure. 3. The stress changes in the direction of thickness on the crown of the dome were much linearly distributed. However, as the amount of tendon increased, the stresses in the upper and lower parts of the wall established with the tendon were shown stress concentration. 4. The stress changes in the direction of thickness on the center of the structure wall was linearly distributed in the all cases, and special stress due to the use of the tendon was not shown.

• 한국의상디자인학회지
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• 제24권2호
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• pp.1-10
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• 2022

The purpose of this study is to analyze the structural properties of 100% wool fabrics knitted with various stitch types and to evaluate dimensional stability from shrinkage in wet cleaning and drying. Materials were weft-knitted from twenty-four different stitches with 7 gauge using a computerized flatbed knitting machine. Weight, thickness, density, and length were measured. A domestic washing machine and a tumble dryer were used for the shrinkage test. The results are as follows: Knitted fabrics were divided into 3 groups based on weight per unit area. Porous knits show light weight whilst milano, pintuck, rib stitches belong to the heaviest group. A positive correlation between weight and thickness was found and the same result was obtained for wale density and weight. Dimensional shrinkage of knitted fabrics was increased during repetitive wet cleaning and drying regardless of knit stitches. Especially, fabrics knitted with float, tuck, cable, and links & links stitches samples were contracted more than 15% in the first treatment whereas 2x1 rib stitch showed 1% shrinkage rate. Fisherman and milano stitches contracted in both course and wale direction with similar shrinkage rates. However, porous knits with float and tuck stitches shrank in course direction by 20% as well as cable samples contracted from 5% to 20% after repeated washing and drying. On the other hand, 30% and 15% contraction of wale direction occurred in orderly float and links & links stitches, respectively. Machine dried knits have a higher shrinkage rate than air-dried knits, but the drying method did not affect to the direction of contraction. In conclusion, variations of knit, tuck, and float stitches affect knit construction and dimensional stability from shrinkage in wet cleaning and drying of wool knitted fabrics.

• 소성∙가공
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• 제28권6호
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• pp.328-335
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• 2019

Demand for ultra-thin materials is increasing due to their light-weight and versatile properties. In this work, the formability of the ultra-thin stainless steel sheets of various thicknesses in the incremental sheet forming (ISF) process is investigated. The effects of the thickness on formability were evaluated with forming experiments of the truncated cone shape with 10° intervals. As the thickness of the material decreased, the maximum forming angle decreased and wrinkles also occurred quickly. The maximum forming angles in the truncated cone shape without the wrinkles for the thickness of 0.05 mm, 0.08 mm, and 0.1mm were 30°, 40°, and 50°, respectively. Wrinkles occurred in a twisted shape along the moving direction of the tool. As the material thickness increased, the size of the wrinkles increased.

• Steel and Composite Structures
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• 제34권5호
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• pp.657-670
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• 2020

In this paper, vibration analysis of functionally graded nanoshell is studied based on the sinusoidal higher-order shear and normal deformation theory to account thickness stretching effect. To account size-dependency, Eringen nonlocal elasticity theory is used. For more accurate modeling the problem and corresponding numerical results, sinusoidal higher-order shear and normal deformation theory including out of plane normal strain is employed in this paper. The radial displacement is decomposed into three terms to show variation along the thickness direction. Governing differential equations of motion are derived using Hamilton's principle. It is assumed that the cylindrical shell is made of an arbitrary composition of metal and ceramic in which the local material properties are measured based on power law distribution. To justify trueness and necessity of this work, a comprehensive comparison with some lower order and lower dimension works and also some 3D works is presented. After presentation of comparative study, full numerical results are presented in terms of significant parameters of the problem such as small scale parameter, length to radius ratio, thickness to radius ratio, and number of modes.