• 한국초전도ㆍ저온공학회논문지
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• 제17권4호
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• pp.1-7
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• 2015

This paper addresses technical problems of thermal contact conductance or resistance which inevitably occurs in most cryogenic engineering systems. The main focus of this paper is to examine what kind of physical factors primarily influences the thermal contact resistance and to suggest how it can be minimized. It is a good practical rule that the contact surface must have sub-micron roughness level with no oxide layer and be thinly covered by indium, gold, or Apiezon-N grease for securing sufficient direct contact area. The higher contact pressure, the lower the thermal contact resistance. The general description of this technique has been widely perceived and reasonable engineering results have been achieved in most applications. However, the detailed view of employing these techniques and their relative efficacies to reduce thermal contact resistances need to be thoroughly reviewed. We should consider specific thermal contact conditions, examine the engineering requirements, and execute each method with precautions to fulfil their maximum potentials.

• 전기학회논문지P
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• 제63권2호
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• pp.119-123
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• 2014

In this study, four kinds of specimens of PE(polyethylene)-based insulating materials were prepared for selecting the optimum insulation materials in a wet environment. The specimens were tested by various methods, the anti tracking test, the transmittance test in the water vapor transmittance(WVT) and the abrasion resistive test, etc. The HDPE(high-density polyethylene) specimen was showed excellent property in the tracking resistance test and the lowest transmittance in water vapor transmittance test. In the abrasion resistive test, the LLDPE(linear low-density polyethylene) and MDPE(medium-density Polyethylene) were showed excellent mechanical properties. The value of cut-through resistance for MDPE and HDPE were superior to that for LLDPE and LDPE(low-density polyethylene).

• 대한기계학회논문집A
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• 제29권8호
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• pp.1109-1117
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• 2005

To identify damage that develops in filament wound composite pressure vessels subjected to low velocity impact, a series of impact tests was performed on specimens cutting from the full scale pressure vessel. The resulting damages by the three different impactors were assessed by the scanning acoustic and metallurgical microscope. Based on the impact force history and damage, the resistance parameters were proposed and its validity in identifying the damage resistance of CFRP pressure vessel was reviewed. As the results, the impact resistance of the filament wound composites and its dependency on the impactor shape were estimated quantitatively.

• 대한기계학회논문집
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• 제10권6호
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• pp.898-905
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• 1986

본 논문에서는 강의 피로균열진전거동과 미시조직과의 관계를 밝히기 위한 연 구의 일환으로 제이상 마르텐사이트 중에 모상 페라이트가 존재하는 복합조직강을 준 비하여 이들 강의 제이상 경도변화에 따른 피로균열진전저항을 균열휨과 균열닫힘을 통하여 검토하였다.

• 대한치과기공학회지
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• 제21권1호
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• pp.43-53
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• 1999

The mechannical properties and corrosion resistance of alloy added commercially pure titanium for dental implants have been investigated. Ti, To-65Zr, Ti-10.1Ta and Ti-17Sn alloys were melthed in arc furnace and the corrosion resistance of Ti alloys was evaluated by anodic polarization test. The microstructure and mechanical properties of Ti alloy were analysed by optical micrograph. hardness tester and instron. In isothermal test, Ti-10.1Ta and Ti-17Sn alloys exhibited the best oxidation resistance below $1100^{\circ}C$. Ti65Zr, Ti-10.1Ta and Ti-17Sn alloys showed better rockwell hardness compared with commercially pure. Ti As the result of the anodic polarization test in 5%HCl, it 5%HCl, it was known knows that Ti-65Zr, alloy showed a rapid decrease in current density at higher potenial in comparision with other Ti alloys.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2002년도 추계학술대회 논문집
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• pp.205-208
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• 2002

Thermal design is required with considering thermal stability to verify the reliability of electric power device with using IGBT. Numerical analysis is performed to analyzed the change in thermal resistance with respect to the various thermal density of heating element. Correlations between thermal resistance and heat generation density are established. With using these correlations, performance curve is composed with respect to the change in thermal resistance of cooling conditions for natural convection and forced convection. Thermal fatigue is occurred at the Inside and outside of IGBT by repeated heat load. The crack is occurred between base plate and ceramic substrate for the inside. When the crack length is 4mm, the failure is occurred. Therefore, Thermal design method considering thermal density, thermal fatigue resistance is presented on this study and it is expected to thermal design with considering life prediction.

• Journal of Welding and Joining
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• 제23권6호
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• pp.55-60
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• 2005

In part 1. optimal process parameters such as thickness of stopper and welding time are achieved to produce high strength ISB(Inner Structured and Bonded) panels. Developed process is different from the usual resistance welding process in the number of points welded at a time. In part 2, Numerical modeling for this new process is proposed and the variation of contact area with respect to the gap of electrodes is studied through FE analyses, Besides, it is tried to figure out the welding nugget formation and proper distance between welding points. FE analytic results show that inner structures are melted more than skin plate, and current distribution between points to be welded can be controlled by distance welding points. Comparison of some FE analytic results with corresponding experimental results could confirm the validity of the proposed numerical modeling.

• 한국군사과학기술학회지
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• 제23권5호
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• pp.475-484
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• 2020

Individual curing process of each layer in two resin composites can be caused the separation between two layers. In this study, co-curing process for two resin composites is suggested to improve the inter-layer bonding. Glass fiber reinforced composites with phenolic and epoxy resins were manufactured by co-curing process, and several types of glass/phenolic composites were considered to confirm the application on two resin composites. Experiments for smoke resistance, scratch resistance and flexural strength were carried out to verify requirements corresponding to thermal and mechanical environments. It was validated that two resin composites with phenolic resin impregnated prepreg exhibits good thermal and mechanical characteristics, and it can serve as highly effective composite structures in aerospace and many industry areas.

• Journal of Welding and Joining
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• 제24권6호
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• pp.13-20
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• 2006

Resistance spot welding is widely used for joining sheet metals in the automotive manufacturing process. Recently, servo-gun is used to increase the productivity and precise control the acting force. However, force control mechanisms have not been investigated with servo-guns until now. In this paper, it is proved that servo-motor current is proportional to torque and by experiment, experimental equation between servo-motor current and electrode force was derived. Algorithm for feedback control of electrode force was suggested using current measurement. In addition, applying soft touch method to this system the impact between electrode and specimen, which is the problem of air gun, could be reduced. Indentation made the force decrease in holding time of resistance spot welding. In order to overcome this problem, force compensation using the servo gun was used and it improved weld strength in good welding current range.

• 한국기계가공학회지
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• 제15권4호
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• pp.93-100
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• 2016

The laser surface treatment of magnesium alloy was studied. $ZrO_2$ was used as sintering ceramics, and its corrosion resistance was verified. Appropriate laser parameters were proposed for homogeneous solidification of the sintered layer. The chemical compositions of the sintered layer were analyzed with laser-induced breakdown spectroscopy. $Na_2SO_4$ was used for a corrosion test, and the resistance of the sintered sample was confirmed. The microstructures of the sintered parts were also examined. The solidified grains on the top sintered surface were observed; however, reasonable fusion was obtained at the interface between the baseline and the ceramics. Laser surface treatment using $ZrO_2$ on magnesium alloy showed an improvement in corrosion resistance.