• 한국항행학회논문지
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• 제18권4호
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• pp.381-386
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• 2014

전기 커넥터에 영향을 주는 프레팅 부식 요인 중 하나인 접촉 부하의 영향을 조사하기 위하여, 프레팅 부식 표본 쌍을 두께 $3{\mu}m$의 두께를 갖는 주석으로 도금된 황동 표본을 사용하여 제조하였다. 접점의 전기저항은 프레팅 부식 시험 기간 동안 측정되었다. 프레팅 주기에서 저항은 증가하였다. 저항의 변화는 3단계로 나눌 수 있다. 첫 번째 단계는 미미하고 안정적인 저항을 나타내었다. 두 번째 단계는 저항이 꾸준한 증가를 보여 주었다. 그리고 세 번째 단계는 매우 높고 간헐적인 저항을 보여주었다. 실패주기(Nf)와 접촉력(P) 사이의 관계는 다음과 같이 표현될 수 있다. 각각의 하중, 변위, 온도 등 다양한 조건에서 프레팅 테스트를 통해 다양한 환경 조건 하에서 매우 높고 간헐적인 저항에 대응 전기 커넥터의 실패주기 예측공식의 표현이 가능할 것이다.

• 대한기계학회논문집A
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• 제28권9호
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• pp.1352-1358
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• 2004

The mechanical spring is one of widely used machine elements. Among various kinds, flat-type spring loaded by a rotating pin was studied. A flat spring was simplified to a cantilever beam, and numerical analysis was attempted. Since the loading pin rotates about a separate axis from the fixed spring or vice versa, the location, direction, and magnitude of the contact force including normal contact and friction loads vary accordingly. Meanwhile, the spring is deformed substantially as the relative motion progresses. Therefore, this problem needs to be formulated taking the follower loading characteristics and geometrical non-linearity into account. Derived nonlinear differential equation was solved to yield the spring deflection, contact force and the torque to rotate the pin, and the result was compared with a finite element solution. Also, the influences of principal design parameters were studied. The proposed methodology is expected to be useful for the design of pin-loaded flat spring and the prevention of mechanical failures in the form of yielding or fatigue failure of spring or severe wear of the components.

• 대한기계학회논문집A
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• 제36권11호
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• pp.1391-1397
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• 2012

하이포 트로코이드 기반의 CRG(Cam ring gear) 시스템은 핀 또는 롤러 치형을 가지는 기어와 공액인 캠 링기어로 구성된 내접기어 시스템이다. 본 논문에서는 CRG 시스템의 엄밀 치형설계를 바탕으로 기어 치면에서의 접촉특성을 분석하였으며 형상설계변수인 치형수정계수에 따른 기어의 내구수명을 검토하였다. 결과적으로 치형수정계수의 증가를 통해 기 설계된 CRG 시스템에 영향을 미치지 않으면서 기어의 접촉 피로수명을 향상시킬 수 있다.

• 소음진동
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• 제9권4호
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• pp.643-651
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• 1999

A brief description of the current technology (contact-start-stop) employed in most of today's hard disk drive is presented. The dynamics and head/disk interactions during a start/stop process are very complicated and no one has been able to accurately model the interactions. Thus, the head/disk interface that meets the start/stop durability and stiction requirements are always developed statistically. In arriving at a solution. many sets of statistical tests are run by varying several parameters. such as, the carbon overcoat thickness. lubricant thickness. disk surface roughness, etc. Consequently, the cost associated III developing an interface could be significant since the outcome is difficult to predict. An alternative method known as Load/Unload technology alters the problem set. such that. the start/stop performance can be designed in a predictable manner. Although this techno¬logy offers superior performance and significantly reduces statistical testing time, it also has some potential problems. However. contrary to the CSS technology. most of the problems can be solved by design and not by trial and error. One critical problem is that of head/disk contacts during the loading and unloading processes. These contact can cause disk and slider damage because the contacts are likely to occur at high disk speeds resulting in large friction forces. Use of glass substrate disks also may present problems if not managed correctly. Due to the low thermal conductivity of glass substrates. any head/disk contacts may result in erasure due to frictional heating of the head/disk interface. In spite of these and other potential problems. the advantage with L/UL system is that these events can be understood. analyzed. and solved in a deterministic manner.

• 한국안전학회지
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• 제2권1호
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• pp.31-41
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• 1987

The surface rolling method which is one of the plastic deformation processes increases the surface roughness with reduction of diameter and hardness. In this study, three NACHI 6000 ZZ bearing were used for surface rolling tool on a mild steel. The following results have been obtained with the mild steel. 1) The load is major factor in getting fine surface roughness of roller fininshing after grinding. The optimal surface roughness of SS40 steel can be obtained at the contact pressure of $210kgf/cm^2$. But, Better surface roughness can not be expected, Due to flaking phenomena at more than 300 kgf/cm of contact pressure. 2) At the contact pressure range of $200kgf/cm^2{\sim}210kgf/cm^2$ for optimal surface roughness, The surface hardness increased to Hv 200~Hv 240 from Hv 125 before surface rolling. 3) Within the diameter variation of $13{\mu}m$ the surface roughness and the surface hardness were increased, but out of variation of $14{\mu}m$. The surface roughness become worse and the surface hardness was increased.

• Tribology and Lubricants
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• 제20권2호
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• pp.51-57
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• 2004

Micro/nano adhesion and friction properties of mixed self-assembled monolayer (SAM) with different chain length for MEMS application were experimentally studied. Many kinds of SAM having different spacer chains(C6, C10 and C18) and their mixtures (1:1) were deposited onto Si-wafer, where the deposited SAM resulted in the hydrophobic nature. The adhesion and friction properties between tip and SAM surfaces under nano scale applied load were measured using an atomic force microscope (AFM) and under micro scale applied load were measured using ball-on-flat type micro-tribotester. Surface roughness and water contact angles were measured with SPM (scanning probe microscope) and contact anglemeter. Results showed that water contact angles of mixed SAMs were similar to those of pure SAMs. The morphology of coating surface was roughened as mixing of SAM. Nano adhesion and nano friction decreased as increasing of the spacer chain length and mixing of SAM. Micro friction was decreased as increasing of the spacer chain length, but micro friction of mixed SAM showed the value between pure SAMs. Nano adhesion and friction mechanism of mixed SAM was proposed in a view of stiffness of spacer chain modified chemically and topographically.

• 대한인간공학회지
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• 제29권4호
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• pp.639-646
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• 2010

The APAM's quantitative effectiveness and comparative study in preventing and treating pressure ulcer has not been sufficiently evaluated mainly because of uncertainty of pressure load input and lack of interpretation of dynamic perfusion recovery characteristics of soft tissue. The purpose of this paper was to quantify and analyze the alternating pressure characteristics of APAM as a preventive measure for pressure ulcers. To quantify the alternating load to human body, we introduced alternating pressure profile concept and developed parametric model of the profile. Regarding pressure level and cycle time, 3 global and 7 local periodic parameters were used to define the profile such as light, standard, typical and heavy duty profile shape. Pressure impulse ratio of light duty is the lowest but pressure fluctuation is significantly high. For the same duty shape, contact conditions are changed with alternating cycle time and more dramatically in shorter alternating cycle time conditions. We can conclude that if we use shorter alternating cycle time on APAM's operation we can get more positive effects regarding to inflated contact time condition. We proposed the quantitative methods on tissue viability study of external loading by simultaneous measurement of interface pressure and tissue perfusion with proper alternating pressure profile conditions.

• 한국세라믹학회지
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• 제35권5호
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• pp.429-436
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• 1998

The mechanical properties and damage mode of {{{{ {Y}_{2 } {O}_{3} }}-doped tetragonal (Y-TZP) can-didated as biomaterials were performed under indentation stress-strain curve critical load for yield and cracking strength degradation and fatigue behavior with Hertzian indentation tests. This material shows the brittle behavior which is confirmed by indentation stress-strain response. The critical load for cracking(Pc) is much higher than that for yields (Py) indicating crack resistance Strength were strongly dependant on contact area and there were no degradation when the indenter size was ${\gamma}$=3.18 mm suggesting that Y-TZP should be highly damage tolerant to the blunt contacts. Multi-cycle contact were found to be innocuous up to {{{{ {10 }^{6 } }} cycles at 500N and {{{{ {10 }^{5 } }} cycles at 1000N in water. On the other hand contacts at {{{{ {10 }^{6 } }} cycles at 1000 N in water did show some signs of incipient degradation. By contrast contacts with Vickers indenter pro-duced substantial strength losses at much lower loads suggesting that the mechanical integrity of this ma-terial would be compromised by inadvertent sharp contacts.

• Geomechanics and Engineering
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• 제14권1호
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• pp.51-60
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• 2018

The foundations are classified into shallow and deep, which have important differences: in terms of geometry, the behavior of the soil, its structural functionality, and its constructive systems. The shallow foundations may be of various types according to their function; isolated footings, combined footings, strip footings, and slabs foundation. The isolated footings are of the type rectangular, square and circular. The combined footing may be rectangular, trapezoidal or T-shaped in plan. This paper presents a new model for T-shaped combined footings to obtain the most economical contact surface on the soil (optimal dimensioning) to support an axial load and moment in two directions to each column. The new model considers the soil real pressure, i.e., the pressure varies linearly. The classical model uses the technique of test and error, i.e., a dimension is proposed, and subsequently, the equation of the biaxial bending is used to obtain the stresses acting on each vertex of the T-shaped combined footing, which must meet the conditions following: The minimum stress should be equal or greater than zero, and maximum stress must be equal or less than the allowable capacity that can withstand the soil. To illustrate the validity of the new model, numerical examples are presented to obtain the minimum area of the contact surface on the soil for T-shaped combined footings subjected to an axial load and moments in two directions applied to each column.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.523-528
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• 2001

In this study we tried to determine the work-hardening exponent using continuous indentation test. Work-hardening exponent, which was determined by Hollomon equation, in tensile test, is an important parameter to determine plastic deformation and brittle/ductile property of materials. For using Hollomon equation, true stress and true strain were defined by indentation depth and indentation load. Using them the new equation, which is constituted by indentation depth, indentation load and work-hardening exponent, was induced. Indentation depth was calibrated because of elastic deflection and pile-up/sink-in phenomena. Work-hardening exponents of various steels derived by it showed good agreement to the results of tensile tests. In addition to experiments, FEM simulation was accomplished to investigate changes of real contact depth with materials properties changes. Through this simulation it is concluded that the real contact depth is changed by Y/E value which affect the early stage of indentation, and work-hardening exponent which the latter stage.