• Journal of Practical Engineering Education
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• v.6 no.2
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• pp.105-110
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• 2014

In this work, mechanical characteristics of titanium diaphragm have been studied as a potential robust substrate and a diaphragm material for automotive tire pressure sensor. Lamination process techniques combined with traditional micromachining processes have been adopted as suitable fabrication technologies. To illustrate these principles, capacitive pressure sensors based on titanium diaphragm have been designed, fabricated and characterized. The fabrication process for micromachined titanium devices keeps the membrane and substrate being at the environment of 20 MPa pressure and $200^{\circ}C$ for a half hour and then subsequently cooled to $24^{\circ}C$. Each sensor uses a stainless steel substrate, a laminated titanium film as a suspended movable plate and a fixed, surface micromachined back electrode of electroplated nickel. The finite element method is adopted to investigate residual stresses formed in the process. Besides, out-of-plane deflections are calculated under pressures on the diaphragm. The sensitivity of the fabricated device is $9.45ppm\;kPa^{-1}$ with a net capacitance change of 0.18 pF over a range 0-210 kPa.

• Journal of the Korea Society for Simulation
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• v.27 no.4
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• pp.69-77
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• 2018

Launching system is designed to store the payload, withstand the rigors, and prevent it from rusting and damaging. The behavior during initial deployment of the missile is determined by production, assembly and insertion condition of a launching tube and a missile. The purpose of this research is to confirm the safety of a launching tube by statistically analyzing behavior of the missile, during initial deployment stage. Error parameters which effect initial behavior of the missile are selected and analyzed through Monte-Carlo Simulation. Based on the result of simulation, tip-off and stress distribution between rail and shoe is predicted by using the commercial analysis program called Recurdyn. Lastly, the safety factor is calculated based on yield strength of the material and maximum stress of the rail during the process of launching. The safety of the launching system is verified from the result of the safety factors.

• Composites Research
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• v.34 no.2
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• pp.101-107
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• 2021

Composite structures have components and joints. Theses connections or joints can be potentially weak points in the structure. The failure mode of the composite bolted joint is designed as a bearing failure mode for structural safety. The load-displacement relation exhibits bearing failure mode shows a nonlinear behavior after the initial failure and progressive failure behavior. In order to accurately predict the failure behavior of composite bolted joints, this study modified the shear damage variable calculation process in the existing progressive failure analysis model. The results of the bearing stress-bearing strain of the composite bolted joint were predicted using the modified progressive failure analysis model, and the modified model was verified through comparison with the previous progressive analysis model.

• Journal of the Korean Geotechnical Society
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• v.25 no.4
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• pp.39-54
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• 2009

Large scale direct shear tests were carried out to analyze the shear behavior of crushed rocks at local representative quarries. Shear strength for each specimen was derived and the effects on shear behavior induced by the variation of factors such as particle size, water immersion, density, uniformity coefficient, and particle breakage were evaluated and quantitatively compared with previous studies. The opportunity was also taken to identify stress-dilatancy relation of crushed rocks following the energy-based theory and friction coefficients at critical state as well as peak friction angles and dilation angles were estimated. As a result of tests it was found that uniaxial compressive strength and particle breakage of the parent rocks have crucial effect on internal friction angles; in addition, dilatancy at the failure showed strong relationship as well.

• Journal of the Korean Geotechnical Society
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• v.22 no.10
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• pp.111-120
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• 2006

In this research, numerical simulations by PFC considering discrete element method are conducted to predict experimental results of large triaxial compression test with rockfill material for dam construction. For generation of compacted assembly with specific grain size distribution and initial material porosity, the clump logic method and expansion of generated particles are adapted. To predict stress-stain behavior of large triaxial test, discrete particle modelling is applied with micro parameters which are chosen by calibration process. It is expected that distinct particle modelling method could be used as a useful tool to investigate micro and macro behavior associated with geotechnical problems and develop a numerical laboratory.

• Journal of Korean Society of Steel Construction
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• v.25 no.2
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• pp.115-130
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• 2013

In this study, lateral-torsional buckling (LTB) strength of high-strength H-beams built up from 800MPa tensile-strength steel was experimentally and analytically evaluated according to current lateral stability provisions (KBC 2009, AISC-LRFD 2010). The motivation was to evaluate whether or not current LTB provisions, which were originally developed for ordinary steel with different stress-strain characteristics, are still applicable to high-strength steel. Two sets of compact-section specimens with relatively low (Set A) or high (Set B) warping stiffness were prepared and tested under uniform moment loading. Laterally unbraced lengths of the test specimens were controlled such that inelastic LTB could be induced. All specimens exhibited LTB strength exceeding the minimum limit required by current provisions by a sufficient margin. Moreover, some specimen in Set A reached a rotation capacity required for plastic design, although its laterally unbraced length belonged to the inelastic LTB range. All the test results indicated that extrapolation of current provisions to high-strength steel is conservative. In order to further analyze the test results, the relationship between inelastic moment and laterally unbraced length was also derived in explicit form for both ordinary- and high-strength steel based on the effective tangent modulus of inelastic section. The analytical relationship derived again showed that extrapolation of current laterally unbraced length limit leads to a conservative design in the case of high-strength steel and that the laterally unbraced length to control the inelastic LTB behavior of high-strength steel beam should be specified by including its unique post-yield strain-hardening characteristics.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.23 no.2
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• pp.61-65
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• 1987

In this study, the characteristics of TRC (tensile restraint crack) critical stress in the gravity type underwater wet welding process and in the in-air welding have been investigated for Y, y and 45$^{\circ}$r grooves using the KR Grade A-3 steel plates and the E4303 covered electrodes. The following results were obtained: (1) In the TRC tests, the initial critical stress of Y groove is higher than those of the 45$^{\circ}$r single bebel grooves in both in-air and underwater weldings, and the cold fracture sensitivity is higher in the underwater welding than in the in-air welding. (2) The hardness of underwater weld metal is the highest in heat affected zone is about Hk 365 in the in-air weld but Hk 670 in the underwater weld which is higher for cooling speed is more rapid, resulting in the lower critical stress by increase of fracture sensitivity. (3) The diffusible hydrogen quantity for 48 hours is about 18cc/100g-weld-metal in the in-air welding but 48cc/100g-weld-metal in the underwater welding. So that, in the case of underwater welding the diffusible hydrogen penetrates about 3 times more than that in the in-air welding.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.23 no.2
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• pp.15-15
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• 1987

In this study, the characteristics of TRC (tensile restraint crack) critical stress in the gravity type underwater wet welding process and in the in-air welding have been investigated for Y, y and 45°r grooves using the KR Grade A-3 steel plates and the E4303 covered electrodes. The following results were obtained: (1) In the TRC tests, the initial critical stress of Y groove is higher than those of the 45°r single bebel grooves in both in-air and underwater weldings, and the cold fracture sensitivity is higher in the underwater welding than in the in-air welding. (2) The hardness of underwater weld metal is the highest in heat affected zone is about Hk 365 in the in-air weld but Hk 670 in the underwater weld which is higher for cooling speed is more rapid, resulting in the lower critical stress by increase of fracture sensitivity. (3) The diffusible hydrogen quantity for 48 hours is about 18cc/100g-weld-metal in the in-air welding but 48cc/100g-weld-metal in the underwater welding. So that, in the case of underwater welding the diffusible hydrogen penetrates about 3 times more than that in the in-air welding.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.10
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• pp.1411-1417
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• 2010

CFRP (Carbon Fiber Reinforced Plastic) has received considerable attention in various fields as a structural material, because of its high specific strength, high specific stiffness, excellent design flexibility, favorable chemical properties, etc. Most products consisting of several parts are generally assembled by mechanical joining methods (using rivets, bolts, pins, etc.). Holes must be drilled in the parts to be joined, and the strength of the components subjected to static and fatigue loads caused by stress concentration must be decreased. In this study, we experimentally evaluated the variation in the residual strength of a holenotched CFRP plate subjected to fatigue load. We repeatedly subjected the hole-notched specimen to fatigue load for a certain number of cycles, and then we investigated the residual strength of the hole-notched specimen by performing the fracture test. From the results of the test, we can observe the initiation of a directional crack caused by the applied fatigue load. Further, we observed that the residual strength increases with a decrease in the notch effect due to this crack. It was evaluated that the residual strength increases to a certain level and subsequently decreases. This variation in the residual strength was represented by a simple equation by using a model of the decrease in residual strength for plain plate, which was developed by Reifsnider and a stress redistribution model for hole-notched plate, which was developed by Yip.

• Journal of Korean Society of Steel Construction
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• v.24 no.6
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• pp.671-682
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• 2012

The use of sinusoidal corrugated web girder for the box-type girders and gable steel main frames has recently been increasing very much. The reasons are that the thin web of the girder affords a significant weight reduction compared with rolled beam and welded built-up girder, and that corrugation prevents the buckling failure of the web. Improvements of the automatic fabrication process makes mass production of the corrugated web and unit possible, and applications of this girder have been extended considerably. Thus, the research for the optimum design processer considering the production data is needed practically. For doing this research, we develope the discrete optimum structural design program in consideration of production list data for the research, and the program apply to the single girder under the uniform load and the concentrated load as numerical example. We consider objective function as minimum weight of the girder, and use slenderness ratio, stress of flanges and corrugated web, and the girder deflection as the constraint functions. And also the Genetic Algorithms is adopted to search the global minimum point by using the production list as a discrete design variable. Finally, to verify the optimality of the design, we conduct a comparison of the results of the discrete optimum design with those of the continuous one, and also analyze the characteristics of the optimum cross-section.