• 한국군사과학기술학회지
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• 제23권5호
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• pp.444-451
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• 2020

This study was conducted to develop the hydraulic brake assembly for MUAV(Medium-altitude Unmanned Aerial Vehicle). The brake assembly has the self-gap adjuster which performs to maintain a constant gap between the piston and the disk, even if the friction pad wore down. The function of adjuster helps to keep the brake-reaction speed constant and prevent the unnecessary abrasion of the wear pad during the life of the brake assembly. The development of the aircraft hydraulic brake assembly with the self-gap-adjuster in this paper is the first ever in South Korea. The concept of the mechanism was defined and the formula which is necessary to calculate the friction force was set up in the paper. The tester was invented for the functional test and the proper operation of the self-gap-adjuster was confirmed through the test. Dynamo tests and flight tests were also carried out to verify the braking performance of the brake assembly.

• Advances in concrete construction
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• 제6권4호
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• pp.363-373
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• 2018

Portland cement pervious concrete (PCPC) is an effective pavement material to solve or reduce the urban waterlogging problems. The Mechanical properties, the permeability, the abrasion resistance and the frost resistance of PCPC without fine aggregate were investigated. The increase of porosity was achieved by fixing the dosage of coarse aggregate and reducing the amount of cement paste. The results show that the compressive strength and the flexural strength of PCPC decrease with the increase of porosity. The permeability coefficient and the wear loss of PCPC increase with the increase of the porosity. The compressive strength and the flexural strength of PCPC subjected to 25 freeze-thaw cycles are reduced by 13.7%-17.8% and 10.6%-18.3%, respectively. For PCPC subjected to the same freeze-thaw cycles, the mass loss firstly increases and then decreases with the increase of the porosity. The relative dynamic modulus elasticity decreases with the increase of freeze-thaw cycles. And the lower the PCPC porosity is, the more obvious the dynamic modulus elasticity decreases.

• 한국생산제조학회지
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• 제23권3호
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• pp.259-265
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• 2014

When the brakes of a vehicle are applied, large amounts of heat are generated on the surfaces of the brake discs owing to friction between the discs and the brake pads. A high temperature gradient on the disc surfaces leads to thermal deformation and severe disc abrasion. Ultimately, the thermal deformation and disc wear give rise to a thermal judder phenomenon, which has a major effect on the stability of the vehicle. To investigate and propose a solution to these problems, thermoelastic instabilities under applied thermal and mechanical loads were analyzed using the commercial finite element package ANSYS by considering the contact surfaces between the discs and pads. Direct-contact three-dimensional finite elements between the discs and pads were applied to investigate the disc friction temperature, thermal deformation, and contact stress so that the thermal judder phenomenon on the surface of the disc could be predicted.

• The Journal of Korean Physical Therapy
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• 제15권3호
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• pp.414-418
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• 2003

The purpose of this study is to investigate the sports injuries of korea women hockey players before and during the international KT Cup game This study was done by survey questions about injuries of 20 players. The results were as follows: 1. Before game types of injuries are muscular strain ($51\%$), ligament injury ($25\%$), contusion ($8\%$), fracture ($8\%$), abrasion ($8\%$). But the types during game appeared as contusion ($50\%$), ligament injury ($33.3\%$), muscular strain ($16.7\%$). 2. Before game regions of injuries are lower limbs ($45.5\%$), back/torso ($36.4\%$), upper limbs ($18.2\%$). But the regions during game appeared as upper limbs ($71.4\%$), lower limbs ($28.6\%$). 3. During the game, the injuries were caused by ball ($66\%$), collision ($17\%$), that fall ($17\%$). These results indicate the importance that players need enough stretching before they start exercise. Also, in order to protect their upper limbs, players must wear gloves before games

• Nuclear Engineering and Technology
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• 제52권3호
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• pp.647-653
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• 2020

Stainless steel is used commonly in nuclear applications for shielding radiation, so in this study, three different types of new stainless steel samples were designed and developed. New stainless steel compound ratios were determined by using Monte Carlo Simulation program Geant 4 code. In the sample production, iron (Fe), nickel (Ni), chromium (Cr), silicium (Si), sulphur (S), carbon (C), molybdenum (Mo), manganese (Mn), wolfram (W), rhenium (Re), titanium (Ti) and vanadium (V), powder materials were used with powder metallurgy method. Total macroscopic cross sections, mean free path and transmission number were calculated for the fast neutron radiation shielding by using (Geant 4) code. In addition to neutron shielding, the gamma absorption parameters such as mass attenuation coefficients (MACs) and half value layer (HVL) were calculated using Win-XCOM software. Sulfuric acid abrasion and compressive strength tests were carried out and all samples showed good resistance to acid wear and pressure force. The neutron equivalent dose was measured using an average 4.5 MeV energy fast neutron source. Results were compared to 316LN type stainless steel, which commonly used in shielding radiation. New stainless steel samples were found to absorb neutron better than 316LN stainless steel at both low and high temperatures.

• Journal of Welding and Joining
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• 제26권2호
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• pp.50-54
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• 2008

The wearplate with Cr-C has been used in condition of severe abrasion. Recently, the demand of wearplate made by hardfacing with Cr-C has increased in the world, but it is lack of supply and expensive due to low productivity. CMAW (Compound Metal Arc Welding) is very useful process of several welding methods to make wearplate. In this paper, twin torch CMAW to use twin torch at the same time was developed to improve productivity and to ensure quality of wear plate. When the distance between two touches was smaller than 30mm, arc blow was occurred. However when the distance was larger than 35mm, there was no arc blow any more. If the oscillation path of each torch was overlapped together, the melt through at the overlapped zone was occurred due to concentrated heat input in substrate. On the other hand, the turning point of each torch was open more than 5mm, separated bead was generated. Therefore twin torch CMAW which has adequate conditions was able to make wearplate having flatter surface at the bead connection than single torch.

• 한국레이저가공학회지
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• 제12권4호
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• pp.12-16
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• 2009

The engineering ceramic is one of the materials advantageous in various conditions with high strength, endurance at high temperature, abrasion resistance and corrosion resistance, etc. However, due to high strength and high brittleness, ceramic incurs high costs and long time on finishing process required after sintering. So a process for obtaining wanted measurements of them has been studied using the high temperature which makes ceramics softened and heat affected recently. This study makes an estimate of laser-assisted machining (LAM) if an economically practical process for manufacturing precision silicon nitride ceramic parts using laser beam. In this study, mechanical properties of silicon nitride at high temperature were observed. And during the LAM, it was observed that cutting force and tool wear were reduced and oxidation of machined surface was increased according to a increase of laser power.

• 한국자동차공학회논문집
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• 제10권6호
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• pp.171-177
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• 2002

Metal matrix composites had generated a lot of interest in recent times because of significant in specific properties, it was also highlighted as the material of frontier industry because strength, heat-resistant, corrosion-resistant and wear-resistant were superiored. In recent years, the study of metal matrix composite has increased by aluminum alloy. The study is based on the tribological properties of AC4CH that is a part of the mechanical property of metal matrix composites. Metal matrix composite that is produced from matrix material AC4CH and reinforcement SiO$_2$, Al$_2$O$_3$ and TiO$_2$ are added to the metal matrix composite fur strength so binding among the whisker can take place. Each metal matrix composite is produced using the squeeze casting method. To test for tribe a pin-on-disk machine and lubricant is used without paraffine 8.2CST at room temperature which is 40$\^{C}$. As the results of this study, the tribological properties of each specimen are more improved than AC4CH. The variation of coefficient resistance is more stable at the AC4CH and TiO$_2$, but the variation rates are higher at the inanimate binder.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2014년도 추계학술대회 논문집
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• pp.29-29
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• 2014

최근 화석에너지 고갈 및 에너지 수요의 폭발적 팽창을 해결하기 위하여 경량화와 내마모 측면에서 고효율 시스템을 적용한 자동차 및 각종 성형 기기들이 개발되고 있다. 특히 장치의 고성능화라는 요구조건을 충족시키기 위해서는 금속가공산업에서 표면개질의 중요성이 부각되고 있다. 이러한 표면개질에는 일반적으로 표면의 성질을 개선하여 마모(abrasion) 및 국부 압력(local stress) 또는 피로(fatigue), 마식(wear and corrosion)에 견디게 하여 부품의 수명증대와 제품의 소형화에 기여하고 있다. 이러한 표면개질법에는 경질의 물질을 표면에 코팅시켜 재료표면의 특성을 향상시키는 방법과 금속의 표면에 다른 원소를 침투 및 확산시키는 방법으로 나눌 수 있다. 확산방법으로 침탄, 질화, 보로나이징, 크마이징 처리 방법 등이 있다. 상업적으로 가장 많이 사용되는 표면 개질법은 침탄기술로서, 고온에서 짧은 시간내에 물성 향상이 가능하지만, 강의 변태점 이상의 온도에서 진행됨으로서, 변형에 따른 문제가 발생되어 후처리를 필요로 하는 문제점을 가지고 있다. 반면, 질화법은 변태점 이하의 저온에서 철강 표면에 N을 침투시켜 강을 경화시키는 특징을 가진다. 변형이 적고 질소원자가 강내에 침투함으로 인해 내마모성, 내피로성, 내식성 등의 물리적 성질을 향상시키는 점에서 유리하여 각종 정밀 부품 및 자동차 부품, 금형 등에 많이 사용된다. 또한, 경도 향상 및 결정구조의 영향으로 코팅처리시 모재와 코팅 층의 밀착력 향상을 가져오면 이러한 이유로 코팅 층의 하지 층으로써 각광 받고 있다. 본 발표에서는 플라즈마 질화의 이해를 높이기 위해 관련 기술에 대한 전반적인 소개와 향후 플라즈마 질화 기술의 적용이 기대되는 침탄대체 적용 가능 부품, 침류질화 기술, PECVD 공정과의 접목 등 산업적은 응용 측면에서 응용 분야에 대한 소개를 진행하고자 한다.

• Elastomers and Composites
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• 제54권4호
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• pp.330-334
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• 2019

Cryogenic crushing techniques have been employed for recycling waste rubber articles and for extracting residual organic additives present in rubber samples. Rubber particulate derived from tire tread abrasion is one of the key components of road dust. Therefore, in this work, we prepared rubber particulates using a cryogenic crusher and characterized their shapes as well as size distributions according to the type of rubber. The rubber particulates exhibited uneven surfaces with the presence of some small pieces. The order of the particle size distribution was observed to be: NR > BR > SBR. Subsequently, carbon black was added; this led to a decrease in the particle size and the shape becoming rougher. The crushed particulates of the carbon black-filled samples comprised agglomerated shapes of small pieces, which were similar in shape to that of wear debris in tire tread. It was discovered that crosslink density was one of the principal factors that led to the formation of small crushed particulates. The small particulates obtained by cryogenic crushing can be utilized as model rubber particulates for researching micro dust.