• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1398-1401
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• 2003

Recently, The PolyPropylene(PP) Foam used as Bumper and Helmet is well known as a protective material for products. In this paper, the effect of the density of PP foams on the absorption of the impact energy is implemented. The result of the experiment has revealed that the effect of the high-density PP foams is remarkably increased compared with that of the low-density PP foams. And it also shows that the absorption of the impact energy of PP foams are greatly influenced by the density in impact velocity(220cm/s). These results are expected to be utilized for the technique of manufacturing a optimum impact structure.

• 한국가스학회지
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• 제12권1호
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• pp.42-47
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• 2008

환경친화적인 에너지원으로서 가스의 수요가 날로 급증하고 있다. 또한 가스의 수요와 더불어 가스사용이 늘어나면서 폭발과 화재에 의한 인명피해가 해마다 증가하고 있다. 따라서, 본 연구에 사용된 실험용 부스의 밀폐된 공간에서의 증기운폭발 과압의 피해를 Hopkinson의 삼승근법을 이용하여 계산하고, 인체에 미치는 영향을 프로빗 모델에 적용하여 피해예측을 평가하였다. 그 결과 프로빗 모델에 적용하여 계산하면 3 m 이격된 인체에는 손상가능성이 전혀 없는 0%로 나타났으며, 25 m 이격되면 고막파열 손상가능성이 전혀 없는 것으로 나타났다.

• 한국지반공학회논문집
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• 제22권12호
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• pp.33-43
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• 2006

직항타공법에서 사용되는 해머 쿠션의 재질 차이가 항타시 주변 지반의 진동과 발생 소음 및 에너지 전달효율에 미치는 영향을 실내 모형시험을 통해 평가하였다. 항타 과정을 모사할 수 있는 모델 말뚝과 항타시스템 및 스트레인 게이지와 홉킨슨 바(Hopkinson bar)를 이용한 에너지 전달효율 측정장치를 제작, 구성하였다. 해머 쿠션 재질로는 상용의 해머 쿠션재인 Micarta 이외, 현장에서 다수 사용하는 Plywood, Polyurethane, Rubber(SBR), Silicone rubber 등의 5가지 재료를 선정하여 항타시험을 실시하였다 항타시험결과 쿠션 재료별 에너지 전달효율은 (1)Micarta, (2)Polyurethane, (3)Plywood, (4)Rubber(SBR), (5)Silicone rubber의 순이었다. 또한 에너지 전달효율이 높은 쿠션재료가 음압레벨의 평균치 또한 높은 비례관계를 보였다. 항타 종료후 말뚝 정재하시험을 실시하여 말뚝의 지지력과 축하중전이 특성을 비교, 분석한 결과 Micarta와 Polyurethane이 다른 쿠션재료에 비해 높은 지지력 값을 보였다.

• 한국재료학회지
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• 제34권7호
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• pp.330-340
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• 2024

Al-Mg-Si alloys are light weight and have excellent corrosion resistance, and are attracting attention as a liner material for high-pressure hydrogen containers in hydrogen fuel cell vehicles. Because it has excellent plastic hardening properties, it is also applied to car body panel materials, but it is moderate in strength, so research to improve the strength by adding Si-rich or Cu is in progress. So far, the authors have conducted research on the intergranular fracture of alloys with excessive Si addition from the macroscopic mechanical point of view, such as specimen shape. To evaluate their impact tensile properties, the split-Hopkinson bar impact test was performed using thin plate specimens of coarse and fine grain alloys of Al-Mg-X (X = Cr,Si) alloy. The effect of the shape of the specimen on the characteristics was studied through finite element method (FEM) analysis. As a result, it was found that the intergranular fracture of the alloy with excessive Si depended on the specimen width (W)/grain size (d), which can be expressed by the specimen size and grain size. As W/d decreases, the intergranular fracture transforms into a transgranular fracture. As the strain rate increases, the fracture elongation decreases, and the fracture surface of the intergranular fracture becomes more brittle. It was confirmed that intergranular fracture occurred in the high strain rate region even in materials with small grain sizes.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.895-900
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• 2001

It is very important for impact analysis to reflect the dynamic characteristics of materials as well as the static characteristics. As the dynamic behavior of a material is different from the static(or quasi-static) one due to the inertia effect and the stress wave propagation, an adequate experimental technique has to be developed to obtain the dynamic responses for the corresponding level of the strain rate. To determine the dynamic characteristics of materials, the Hopkinson bar (compression type) experiment is carried out. For using dynamic material properties, Johnson-Cook model is applied in impact analysis with explicit finite element method

• Geomechanics and Engineering
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• 제13권2호
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• pp.333-352
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• 2017

A comparison study is made between the dynamic properties of an argillaceous siltstone and its grouting-reinforced body. The purpose is to investigate how grout injection can help repair broken soft rocks. A slightly weathered argillaceous siltstone is selected, and part of the siltstone is mechanically crushed and cemented with Portland cement to simulate the grouting-reinforced body. Core specimens with the size of $50mm{\times}38mm$ are prepared from the original rock and the grouting-reinforced body. Impact tests on these samples are then carried out using a Split Hopkinson Pressure Bar (SHPB) apparatus. Failure patterns are analyzed and geotechnical parameters of the specimens are estimated. Based on the experimental results, for the grouting-reinforced body, its shock resistance is poorer than that of the original rock, and most cracks happen in the cementation boundaries between the cement mortar and the original rock particles. It was observed that the grouting-reinforced body ends up with more fragmented residues, most of them have larger fractal dimensions, and its dynamic strength is generally lower. The mass ratio of broken rocks to cement has a significant effect on its dynamic properties and there is an optimal ratio that the maximum dynamic peak strength can be achieved. The dynamic strain-softening behavior of the grouting-reinforced body is more significant compared with that of the original rock. Both the time dependent damage model and the modified overstress damage model are equally applicable to the original rock, but the former performs much better compared with the latter for the grouting-reinforced body. In addition, it was also shown that water content and impact velocity both have significant effect on dynamic properties of the original rock and its grouting-reinforced body. Higher water content leads to more small broken rock pieces, larger fractal dimensions, lower dynamic peak strength and smaller elastic modulus. However, the water content plays a minor role in fractal dimensions when the impact velocity is beyond a certain value. Higher impact loading rate leads to higher degree of fragmentation and larger fractal dimensions both in argillaceous siltstone and its grouting-reinforced body. These results provide a sound basis for the quantitative evaluation on how cement grouting can contribute to the repair of broken soft rocks.

• 한국공작기계학회논문집
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• 제12권4호
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• pp.43-49
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• 2003

This research work has been carried out for finding J-integral in mode II of CFRP(carbon fiber reinforced plastics) laminate plates based on the classical bar theory in dynamic conditions with consideration of the effect of inertia forces, eventually to lead to finding the dynamic inter-layer fracture toughness. Dynamic inter-layer fracture toughness was found by a self-made ENF(End Notched Flexure) experimental apparatus using Split Hopkinson's Bar(SHPB), and also observed the variation of the fracture toughness haying different resin contents and fiber arrangements of CFRP specimen([$0_3^{\circ}/90_3^{\circ}/0_6^{\circ}/90_3^{\circ}/0_3^{\circ}$], [$0_{20}^{\circ}$], [$0_5^{\circ}/90_{10}^{\circ}/0_5^{\circ}$]). As an experimental result, in either cases of quasi-static or dynamic load condition, the critical load and the inter-layer fracture toughness increased sharply depending on the increase of resin contents. Therefore, it could, be concluded that the effect by resin contents is the major factor determining the inter-layer fracture toughness in the CFRP laminate plates.

• 한국가스학회지
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• 제19권2호
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• pp.12-19
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• 2015

CCS(Carbon Dioxide Capture and Storage)은 온실가스의 주원인 중 하나인 $CO_2$를 감축하기 위한 대안으로 발전, 시멘트 및 철강 산업 등에서 발생하는 대량의 $CO_2$를 포집, 압축 액화하여 저장소에 격리하는 일련의 전 과정을 말한다. 이때, 포집된 $CO_2$는 수송 과정 전 후에 임시저장소에 저장 하게 된다. $CO_2$는 일반적으로 비 가연성, 무독성 가스로 저장소에서 화학적 폭발을 일으킬 가능성이 희박한 가스지만, 임시로 저장되어 보관될 동안 100bar이상의 압력으로 보관되고 있으며, 포집된 가스에 포함된 불순물과 산화물 등에 의해 용기의 부식으로 인한 물리적 폭발이 일어날 가능성이 있다. 폭발 강도는 일반적으로 TNT 상당질량을 통해 계산할 수 있으며, $CO_2$ 임시 저장소는 대량의 $CO_2$를 보관하기 위한 시설로 용기의 용량을 100,000L(100톤)로 가정하여 계산하였다. 계산을 통하여 약 100bar로 압축되어 저장된 100톤의 임시저장소 1개가 폭발할 때의 폭발위력을 산출하면, 대략 2346 lb 이며, 이를 환산하면 약 1064 kg의 TNT가 폭발하는 위력과 동일한 것으로 계산된다. 폭발중심으로부터의 거리에 따른 과압은 환산법칙(scaling law)을 통해 계산하였다. 또한, 폭발과압으로 인한 인체 상해에 대해 폐출혈(Lung Haemorrhage)로 인한 사망과 고막파열 등의 상해를 고려하여 Probit 모델을 통하여 추정하였다.

• KIEAE Journal
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• 제12권5호
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• pp.77-84
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• 2012

Daylighting is the controlled admission of natural light into a space, reducing electric lighting and saving energy. By providing a direct link to the dynamic and perpetually evolving patterns of outdoor illumination, daylighting helps create a visually stimulating and comfort environment for building occupants, while reducing energy costs. Especially, however, glare is the most important factor in daylighting, which is issued by incoming direct sunlight into windows. This study analyzed the discomfort glare on a daylighting window by using Image processing methodology and found a solution to problems with glare source of occupants. There are several ways to evaluate discomfort glare such as UGR (Unified Glare Rating) of CIE, DGI (Daylight Glare Index, Hopkinson, 1972) and VCP (Visual Comfort Probability) of IES. These are used to apply to the relatively little artificial light source and they cannot cover discomfort glare from a real daylighting window. In this regarding, this paper aimed to calculate DGI index of the real daylighting window in a experimental space by using image processing methodology. The variables and outcomes are luminance distribution of non-shading window, effect of venetian blind installed on the window and locations related to position index of DGI.

• 대한기계학회논문집A
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• 제31권11호
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• pp.1093-1099
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• 2007

A compressive split Hopkinson pressure bar (SHPB) technique is used to investigate the dynamic behavior of SM45C at high temperature. A radiant heater, which consists of one ellipsoidal reflector and one halogen lamp, is used to heat the specimen. Specimens are tested from $600^{\circ}C$ to $1000^{\circ}C$ at intervals of $100^{\circ}C$ at a strain-rate ranging from 1100/s to 1150/s. A critical phenomenon occurs between $700^{\circ}C$ and $750^{\circ}C$ in SM45C. This phenomenon results in the drastic drop in a flow stress. In a modified Johnson-Cook constitutive equation, a reducer function is used to take into account for the effect of the drastic drop in a flow stress. A reducer function, which is dependant on the temperature as well as the strain, is introduced and the parameters of the modified Johnson-Cook constitutive equation are determined from test results.