• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.21 no.1
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• pp.75-81
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• 1985

The tensile and dielctric strength of the epoxied resin with bi-directional woven glass fibers with a laminate of two layers(G-10) are studied, and the test parameter is the angle between fiber orientation and the tensile axis. The obtained results may be summaried as follows: 1) when the angle between fiber orientation and tensile axis was varied from 0$^{\circ}$ to 45$^{\circ}$ the yield and fracture stresses have a tendency to decrease with increase in the angle. Especially, the decrease rates in the yield and fracture stresses are changed remarkably in the range of 0$^{\circ}$ to 15$^{\circ}$. 2) The fracture strain has showed the maximum value when the angle between fiber orientation and tensile axis is 45$^{\circ}$, and showed the rapid rate of change from 15$^{\circ}$ to 45$^{\circ}$. 3) For the sample with same angle between fiber orientation and tensile axis the maximum dielectric strength under compressive stress is decreased with increase in tensile stress, when the compressive stress is increased as a parameter of tensile stress. 4) When the angle between fiber orientation and tensile axis is 45$^{\circ}$, the dielectric strength showed the worst value, as the mechanical strength did.

• Journal of Korean Tunnelling and Underground Space Association
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• v.3 no.2
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• pp.23-32
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• 2001

Rock masses are usually discontinuous in nature, as a result of various geological processes they have underdone and they contain rock joints and bridges. Crack propagation and coalescence processes mainly cause rock failures in tunnels. In this study, we focused on the crack initiation, propagation and coalescence process of rock materials containing two pre-existing open cracks arranged in different geometries. During uniaxial compression, wing crack initiation stress, wing crack propagation angle, and crack coalescence stress of Diastone gypsum and Yeosan Marble specimens were examined. And crack initiation, propagation, and coalescence processes were observed. Shear, tensile and mixed (shear+tensile) types of crack coalescence occurred. To compare the experimental results with Ashby & Hallam model, crack coalescence stress was normalized and it generally agreed with the experimental results.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.4
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• pp.393-399
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• 2017

In a reciprocating compressor, the piston and connecting rod are important parts. Excess mechanical stress on these parts may cause damage, and broken parts are expensive and difficult to replace. Therefore, it is necessary to analyze the mechanical stress affecting durability and longevity. The main purpose of this study was to identify locations of maximum stress on pistons and connecting rods. Based on dynamic calculation of the working process of a specific air compressor, an analysis of piston and connecting rod performance has been completed. A three-dimensional model for the air compressor's pistons and connecting rods was built separately, and FEM analysis of these components was carried out using a numerical method. The pistons were loaded by pressure which was changed according to crankshaft angle without thermal boundary conditions. The simulation results were used to predict and estimate stress concentration as well as the value of this stress on pistons and connecting rods. The maximum equivalent stress calculated are over 190 MPa on pistons and 123 MPa on connecting rods at crank angle $135^{\circ}$ and $225^{\circ}$ but these are under tensile yield strength. Besides, the calculated safety factors of connecting rods and pistons is higher than 1. Moreover, the results obtained can be used to provide manufacturers with references to optimize the design of pistons and connecting rods for reciprocating compressors.

• Composites Research
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• v.17 no.4
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• pp.1-6
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• 2004

In this paper, the importance of the size effects on the strength ratio is demonstrated by numerical results. The rate of decrease of tensile strength is for glass fiber, based on the experience of a composite manufacturing specialist. For other material, similar procedure may be used until detailed test result on such material is available. The strength criterion used is that of Tsai-Wu fur stress space. The factors influencing the ratio are, reducing the tensile strength alone or both tensile and compression strengths, selection of the normalized interaction term, that is, the generalized von Mises criterion or the Hill's criterion, and the status of applied stresses. Some of the numerical results are presented for a guideline for the future study.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1493_1494
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• 2009

초고압 전력 케이블용 도체 접속을 위한 접속방법으로 압축형(compressing type), 용접형(welding type), 압축-용접형(CW type; compressing-welding type)의 슬리브는 물론 동과 알루미늄의 이종(nonidentical materials) 접속을 위한 슬리브를 개발 하였으며, 전기적, 기계적으로 검증된 제품 개발을 위하여, 슬리브의 구조 변경과 접속 방법의 차이뿐 아니라 접속 전후의 응력 평가를 위해 슬리브 시편의 인장시험(tensile strength) 결과에 따른 슬리브 제작 및 시험을 진행하였다. 신뢰성 있는 제품 개발과 데이터를 얻기 위하여 초고압용 지중 고압 케이블을 시험 시료로 적용하여 시험 선로(test loop)를 구성하였으며, 이를 통하여 구조와 재질에 따른 접속 방법, 이상 온도 상승 또는 국부적인 고온 부위 발생 여부 등의 전기 시험 및 열싸이클 전압 시험(heating cycle voltage test) 조건을 설정하여 시험 전후의 열신축 등 전기적, 기계적 특성을 평가하였다. 접속 슬리브의 구조 및 재질에 따른 위치별 발열 양상을 체크하였으며, X-ray 장비를 이용하여 슬리브 내부의 압축 및 충진 정도를 점검함으로써 기존 접속 슬리브 보완은 물론 개발된 접속 슬리브의 설계 기준 및 안전율을 설정 할 수 있었다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.5A
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• pp.307-315
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• 2012

Recently, ultra high performance fiber reinforced concrete (UHPFRC) having over 180 MPa compressive strength and 10 MPa tensile strength has been developed in Korea. However, UHPFRC represents different material properties with normal concrete (NC) and conventional high performance concrete (HPC) such as a high early age autogenous shrinkage and a rapid dry on the surface, because it has a low water-binder ratio and high fineness admixtures without coarse aggregate. In this study, therefore, to propose suitable experimental methods and regulations, and to evaluate mechanical properties at a very early age for UHPFRC, setting, shrinkage and tensile tests were performed. From the setting test results, paraffin oil was an appropriate material to prevent drying effect on the surface, because if paraffin oil is applied on the surface, it can efficiently prevent the drying effect and does not disturb or catalyze the hydration of cement. From the ring-test results, it was defined that the shrinkage stress is generated at the time when the graph tendency of temperature and strain of inner steel ring is changed. By comparing with setting test result, the shrinkage stress was firstly occurred as the penetration resistance of 1.5 MPa was obtained, and it was about 0.6 and 2.1 hour faster than those of initial and final sets. So, the starting time of autogenous shrinkage measurement (time-zero) of UHPFRC was determined when the penetration resistance of 1.5 MPa was obtained. Finally, the tensile strength and elastic modulus of UHPFRC were measured from near initial setting time by using a very early age tensile test apparatus, and the prediction models for tensile strength and elastic modulus were proposed.

• 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 Wood Science and Technology
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• v.19 no.1
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• pp.31-63
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• 1991

It was proved that in conventional kiln drying of disks piling position in the kiln exerted a great influence on drying rates, and the larger the variation of disk diameter, the more undulating drying rates of disks. While in vacuum drying disks there was no influence on drying rates. By the end-wrapping treatments and the radial direction of disks tangential surface stresses in the core of disks were slightly compressive in three species. In control disks the drying stresses distributed into one step-style that compressive stresses in the pith side of 6cm from pith were larger than those in the bark side, while in the disks end-wrapped with Korean paper the drying stresses distributed uniformly, because flow rates of free water in disks had no difference between heart-and sap-wood by obstruction of evaporating water from surface of disks by end-wrapping with Korean paper. And end-wrapping with Korean paper considerably restrained those. Tangential differential shrinkage stresses developed the maximum tensile stress near the bark and with approaching the pith the stresses gradually reduced and changed into compressive stresses in near the pith. At the end of vacuum drying the maximum tangential tensile stresses of disks end-wrapped with Korean paper were smaller than those of control disks, and critical moisture contents causing the V-shaped crack of disks end-wrapped with Korean paper were lower than those of control disks because of the set by obstruction of evaporating water of end-wrapping with Korean paper. In the experiment of vacuum drying stress distribution the disks end-wrapped with Korean paper or aluminum foil in three species were free from V-shaped cracks and control disks were defected very slightly by V-shaped cracks. And also disks end-wrapped with Korean paper were free from heart checks in Alnus japonica and Juglans sinensis, and heart checks were occurred very slightly in others. Especially, not to speak of disks end-wrapped with Korean paper, vacuum drying of disks end-wrapped with aluminum foil prevented effectively drying defects, moreover drying times could be shortened, that is. Ginkgo biloba, Alnus japonica, and Juglans sinensis disks could be dried from green to in-use moisture content in 110 hours, 272 hours, and 407 hours, respectively.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.5
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• pp.453-458
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• 2011

We study the effect of mechanical machining and heat treatment on the surface residual stress of TP 316L stainless steel. Electrical discharge machining (EDM), milling and grinding were applied to TP 316L plate specimens. The residual stress and hardness were measured and the effect of heat treatment on the surface residual stress was examined. The residual stress was measured by the X-ray diffraction method, which showed that the surface residual stress was related only to the stress magnitude and was independent of the compressive or tensile component. The surface residual stress was greatly decreased by the heat treatment, but it was not removed completely.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.1
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• pp.38-44
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• 2004

An experimental study for a crane hook was performed to investigate the stress distribution along a certain line where the maximum and minimum stresses to be developed. On this line, the isoclinic fringe and/or principal stress direction is constant. The crane hook was modeled into a 2-dimensional plate made of urethane rubber called 'Photoflex' The Photoflex is very sensitive to a load and has low photoelastic fringe constant. The Tardy compensation method with the fringe sharpening process and the 4-step phase shifting method, was used for the photoelastic technique. Experimental results by photoelasticity were compared with the calculated stresses from the simple curved beam theory and tile finite element analysis. Ail the results were close to each other.