• 한국해안·해양공학회논문집
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• 제23권4호
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• pp.285-291
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• 2011

이 연구에서는 신형소파블록을 대상으로 실험 및 수치해석을 수행하여 역학적 성능을 평가하고 적절한 보강재의 배근에 따른 구조성능 향상 효과를 검토하였다. 수치해석을 통하여 신형소파블록에 인장응력이 발생하는 위치와 크기를 예측하여 보강재를 설계하였다. 보강재로는 일반 철근 및 해양환경에 적합하도록 부식과 피로에 장점을 지닌 섬유보강재(FRP)를 사용하였다. 실험을 통하여 보강재가 없는 무근 신형소파블록의 파괴하중은 350 kN으로 소파블록의 자중에 비하여 6.2배로 나타났으며, 철근이나 FRP보로 보강한 실험체는 모두 실험의 최고하중인 900 kN 이상의 강도를 보였다. 위험단면을 통과하는 보강재의 개수는 시공의 편의를 위해서는 굵은 지름의 단일 보강재를 사용하는 것이 유리하지만 가는 지름의 보강재 여러 개를 사용하여 균열 폭을 감소시키는 것이 바람직하다는 결과를 얻었다.

• Design & Manufacturing
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• 제14권4호
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• pp.11-16
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• 2020

In this study, forming of carbon composite parts was performed using an injection/compression molding process. An impregnation of matrix is determined by ability of wet and flow rate between the matrix and reinforcement. The flow rate of matrix passing through the reinforcements is a function of permeability of reinforcement, a viscosity of matrix and pressure gradient on molding, and the viscosity of the matrix depends on the mold temperature, molding pressure and shear strain of matrix. Therefore, compression molding experiment was conducted using a heating mold in order to confirm the possibility of matrix impregnation. The impregnation of the matrix through the porosities between the woven yarns was confirmed by the cross-sectional SEM image of compression molded parts. An injection molding process was also performed at a short cycle time, high molding pressure and low mold temperature than those of compression experiment conditions. Deterioration of impregnation on the surface of molded parts were caused by these injection conditions and it could be the reason of decreasing the maximum tensile strength. In order to improve impregnation of matrix on the surface, injection/compression molding and insert-over molding were applied. As a result of applying injection/compression molding and insert-over molding, it was shown that the improvement of impregnation on the surface and the maximum tensile strength was increased about 2.8 times than the virgin matrix.

• 한국해양공학회지
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• 제35권4호
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• pp.266-272
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• 2021

Mooring systems are among the most important elements employed to control the motion of floating offshore structures on the sea. Considering the use of polymer material, a new method is proposed to address the creep characteristics rather than the method of using a tension load cell for measuring the tension of the mooring line. This study uses a synthetic mooring rope made from a polymer material, which usually consists of three parts: center, eye, and splice, and which makes a joint for two successive ropes. We integrate the optical sensor into the synthetic mooring ropes to measure the rope tension. The different structure of the mooring line in the longitudinal direction can be used to measure the loads with the entire mooring configuration in series, which can be defined as SMART (Smart Mooring and Riser Truncation) mooring. To determine the characteristics of the basic SMART mooring, a SMART mooring with a diameter of 3 mm made of three different polymer materials is observed to change the wavelength that responds as the length changes. By performing the longitudinal tension experiment using three different SMART moorings, it was confirmed that there were linear wavelength changes in the response characteristics of the 3-mm-diameter SMART moorings. A 54-mm-diameter SMART mooring is produced to measure the response of longitudinal tension on the center, eye, and splice of the mooring, and a longitudinal tension of 100 t in step-by-step applied for the Maintained Test and Fatigue Cycle Test is conducted. By performing a longitudinal tension experiment, wavelength changes were detected in the center, eye, and splice position of the SMART moorings. The results obtained from each part of the installed sensors indicated a different strain measurement depending on the position of the SMART moorings. The variation of the strain measurement with the position was more than twice the result of the difference measurement, while the applied external load increased step-by-step. It appears that there is a correlation with an externally generated longitudinal tensional force depending on the cross-sectional area of each part of the SMART mooring.

• 한국자동차공학회논문집
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• 제21권4호
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• pp.77-82
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• 2013

In this paper, the design of experiment with two-way factorial design was adopted and from that, optimum values of welding variables including the welding speed and rotation speed were found to improve the strength of AZ31 magnesium alloy sheets joined by the friction stir technique. Tool with shoulder diameter of 12 mm and pin diameter of 3.5 mm was used. Also the welding direction was aligned with the material rolling direction, and dimensions of the AZ31 magnesium alloy sheets were $100{\times}100{\times}2mm$. Conditions of rotation speed were 1000, 1100 and 1200 rpm and those of welding speed were 200, 300 and 400 mm/min. As far as this work is concerned, the optimal conditions for friction stir joint were predicted as the rotation speed of 1200 rpm and welding speed of 200 mm/min.

• 터널과지하공간
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• 제29권3호
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• pp.197-213
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• 2019

본 연구에서는 TOUGH-FLAC 연동해석기법을 이용하여 Mont Terri 지하연구시설에서 수행된 단층 내 물 주입시험을 수치적으로 모델링하고, 단층의 재활성과 수리역학적 거동 특성을 살펴보았다. TOUGH2 해석에서는 단층을 Darcy의 법칙과 삼승법칙(Cubic law)을 따르는 연속체 요소로 모델링하였으며, FLAC3D 해석에서는 미끄러짐과 개폐가 허용되는 불연속 인터페이스 요소를 통해 모사하였다. 현장에서 획득한 단층의 균열개방압력(fracture opening pressure), 주입율, 모니터링 압력, 변위 곡선 등을 바탕으로, 단층의 탄성적 변형과 파괴에 의한 수직팽창 특성을 반영할 수 있는 수리간극모델과 수리역학 커플링 관계를 해석모델에 반영하였다. 한편, 현지응력 조건, 단층의 강도 및 변형 특성에 따른 파라미터 해석을 실시하여 각 입력변수가 해석 결과에 미치는 영향을 분석하였으며, 이를 통해 현장시험 결과를 가장 잘 재현할 수 있는 파라미터 조합을 선정하였다. 해석 결과, 균열개방압력에서 단층의 주입율과 모니터링 압력이 크게 증가하는 현상을 합리적으로 재현할 수 있었다. 하지만, 동일한 입력 변수 조건에서 단층의 전단변위와 파괴영역의 범위는 현장시험 결과에 비해 과대평가되는 결과를 보였다. 이는 해석모델에서는 고압의 주입조건에서 단층의 지속적인 전단파괴가 유도되는 반면, 현장에서는 수리간극의 변화가 전단 미끄러짐보다는 인장력에 의한 단층면의 개방(tensile opening)에 크게 의존하는 것으로 추정되기 때문이다.

• Journal of Welding and Joining
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• 제26권1호
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• pp.69-75
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• 2008

Spot welding which use the main process for side block production of stainless steel railway vehicle is legged behind in laser welding about a quality and productivity. Although the laser welding has many potential advantages such as low heat input and aspect ratio of weld bead, its application to a new structural component still is required many engineering data including mechanical properties such as tensile, fatigue strength, etc on. Therefore, experimental analysis was carried out to understand the fatigue phenomena of different thickness stainless steel overlap joining panels by Nd:YAG laser welding. The fatigue life curves were obtained through fatigue tests with the various levels of applied load. The fatigue life is related with the parameters such as gap size and penetration depth through experiment. As the results, tensile strength and fatigue life were proportional in heat input level and gap was identified the major factor for fatigue life. Also we could know that deferent a-ferrite content at HAZ depend on welding heat input was important factor to determine a formation of initial crack and total fatigue life cycle.

• 한국생산제조학회지
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• 제21권4호
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• pp.613-618
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• 2012

The Ultrasonic metal welding is used in the solid-phase welding method at room temperature or low temperature state. In welding process, the high frequency vibration energy is delivered to the welding part under the constant pressure for welding. In this study, we aimed to design and manufacture a 40,000 Hz band horn through finite element analysis. By performing modal analysis and harmonic response analysis, the modal analysis result is that the horn frequency was 39,599Hz and the harmonic response result that the horn frequency was 39,533Hz. These results were similar. In order to observe the designed horn's performance, about 4,000 voltage data was obtained from a light sensor and was analyzed by FFT analysis using Origin Tool. The result RMS amplitude was approximately $8.5{\mu}m$ at 40,000Hz, and maximum amplitude was $12.3{\mu}m$. Using this manufactured horn along with an ultrasonic metal welder and tension tester, the weldability of Cu sheets was evaluated. The maximum tensile force was 66.53 N in the welding condition of 2.0 bar pressure, 60% amplitude, and 0.32 s welding time. In excessive welding conditions, it was revealed that weldability is influenced negatively.

• 한국생산제조학회지
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• 제22권1호
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• pp.173-177
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• 2013

The purpose of this paper is to investigate the influences on mechanical properties of two-stroke cycle motor pistons manufactured by casting, conventional forging and powder forging, through the comparison of characteristics, merits and disadvantages of each forming technology. For each forming technology, the optimal process parameters were determined through the experiments for several conditions, and microstructure, hardness, tensile strength and elongation of pistons are compared and analyzed. In conventional forging process, material temperature was $460^{\circ}C$ and the die temperature was $210^{\circ}C$ for the Al 4032. The optimal condition was found as solution treatment under $520^{\circ}C$ for 5 hours, quenching with $23^{\circ}C$ water, and aging under $190^{\circ}C$ for 5 hours. In powder forging process, the proper composition of material was determined and optimal sintering conditions were examined. From the experiment, 1.5% of Si contents on the total weight, $580^{\circ}C$ of sintering temperature, and 25 minutes of sintering time were determined as the optimal process condition. For the optimal condition, the pistons had 76.4~78.3 [HRB] of hardness, and 500 [MPa] of tensile strength after T6 heat treatment.

• 한국정밀공학회지
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• 제17권10호
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• pp.200-205
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• 2000

This paper presents the vibration characteristics of a rectangular plate with 45$^{\circ}$oblique crack and a smooth plate subjected to a uniaxial tension. The experiment is adopted by the time-average holography method. The natural frequency and mode shape are considered accurate according to the increasement of tensile load in the study. When tensile load is zero, the vibration modes are almost agreed with the smooth and the 45$^{\circ}$obliquely cracked plate. But since then, according to the increasement of load, it is shown that vibration modes are extremely varied. The effects of the crack length in the vibration characteristic are discussed in detail. It is indicated that the increase of the crack length makes the variation of the frequencies and modes complicate in the range of even a small load.

• 한국응용과학기술학회지
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• 제28권1호
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• pp.109-117
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• 2011

In this study, we experimented that how influence chain extension to waterborne urethane-epoxy hybrid resin for leather garment coatings. First of all, We had analyzed datas by FT-IR, SEM and machanical properties. By instruments analysis measurement we confirmed that synthesis of epoxy and hybrid resin. In this experiment we knew that polyurethane-epoxy hybrid resin have 5 grades of solvent resistance. Tensile strength measured in the polyurethane-epoxy resin(EDA 5.37g, 2.386 $kg_f/mm^2$) had the most strong strength.. Also polyurethane-epoxy hybrid resin had better result(EDA 5.37g. 37.4 mg. loss) than other hybrid resins. As hight proportion of EDA in hybid resin, we obtained low elongation and low flexibility. In this result, chain extension of waterborne polyurethane-epoxy hybrid resin showed that how effect in leather coating by ratio of EDA.