• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.28-28
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• 2003

고온가압소결(Hot Pressing) 된 다이아몬드 공구용 Co-Fe, Co-Ni계 금속본드의 상온 건식 미끄럼 마멸시험을 행하고, 조성에 따른 각 본드의 마멸 특성을 비교하고 마멸 기구를 규명하였다. 미끄럼 마멸시험은 pin-on-disk 형태의 마멸시험기를 사용하여 각 조성의 성분, 적용하중 그리고 마멸상대재를 변수로 상온, 대기 중에서 실시되었다. 마멸속도는 마멸시험 전후의 시편의 무게 감량을 이론밀도와 거리로 나누어 계산되었다. 마멸기구의 규명을 위하여 시험된 시편의 마멸면과 마멸단면을 SEM과 EDS를 이용하여 분석하였다. 시험 결과 Co-Fe system의 경우 그 마멸속도는 마멸상대재의 영향보다는 Fe 첨가에 따른 시편의 미세조직과 기계적 성질의 차이에 따라 크게 변화하였다. 그러나 Co-Ni system의 마멸속도는 마멸 상대재에 따라 크게 변화하는 것이 관찰되었다. $Al_2$O$_3$를 상대재로 마멸된 경우에는 마멸속도가 시편/상대재 접촉면에서 형성되는 산화층의 영향을 크게 받았고, glass bead(83% SiO$_2$)를 상대재로 한 경우에는 시편의 경도와 마멸속도는 서로 반비례하였다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.26-26
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• 2003

본 연구에서는 누적압연접합공정(ARB)을 통하여 5052 알루미늄 합금의 결정립을 약 0.2$\mu\textrm{m}$ 크기로 미세화 하였다. 누적압연에 의한 변형량 증가에 따른 미세 조직 변화와 결정립 간의 상대적인 방위각 차이를 TEM을 이용하여 관찰하였다. 누적 변형량을 함수로 상온 인장특성을 분석하였고, 초미세립 소재를 후속 열처리한 후 미세 조직 변화를 관찰하여 제조된 초미세립 소재의 열적 안정성을 평가하였다. 상온 대기 중에서 pin-on-disk 형태의 마멸시험기를 사용하여 초미세립 소재의 미끄럼 마멸시험을 변형량과 하중을 변수로 행하였다. 강소성 변형에 의해 제조된 5052 알루미늄 합금 소재의 마멸저항성은 강소성 변형 전과 비교하여 소재의 경도가 크게 증가하였음에도 불구하고 오히려 감소하였다. 마멸시험 후 마멸면의 SEM, 마멸단면의 OM 관찰과 마멸면 직하의 깊이에 따른 경도측정을 통하여 초미세립 소재의 마멸기구를 분석하였고 마멸표면의 변형 층을 관찰하였다. 또한 마멸면 직하 조직의 TEM 관찰을 통해서 마멸시험 중의 미세 조직 변화를 연구하였다.

• Tribology and Lubricants
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• v.21 no.6
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• pp.272-277
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• 2005

Continuously variable transmission (CVT) of toroidal type has a elliptical shape of contact zone under the elastohydrodynamic lubrication (EHL) condition, where the power is transmitted only by shearing the lubricant. Due to the small contact area of elliptical shape, the traction of the shear behaviors of lubricant over the contact zone is under extremely high contact pressure over 1.0GPa. During the power transmission by shearing the fluid, many kinds of mechanical movements occur such as squeezing, sliding, rolling and spin. Among the movements, the spin effect that is the most undesirable contact behavior in transmitting the power frequently makes significant abnormal wear damage. In this work, the analysis of elliptical contact of EHL with spin effect is performed, which will give very useful information to understand the traction behaviors in toroidal type of CVT system.

• Tribology and Lubricants
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• v.18 no.3
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• pp.204-210
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• 2002

Automotive brake pads with four different sizes of zircon particles (average sizes of 1㎛, 6㎛, 75㎛, and 140㎛, respectively) were investigated to evaluate the size effect of abrasive particles on friction performance. Results showed that the brake pads with the larger size of zircon particles tend to show better frictional stability and low pad wear. However, the rotor surface was severely abraded in the case of using larger zircon particles. On the other hand, the small zircon particles in the pads showed the fast increase of the coefficient of friction with friction force oscillation and the tendency was pronounced at low sliding speeds. The brake pads with small particle sizes also exhibited strong fade phenomena at elevated temperatures.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.482-487
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• 2001

Leaf type foil bearings have been used successfully in many aerospace applications such as air cycle machines, turbocompressors and turboexpander. These applications are characterized by light loads, constant speeds and low to moderate temperatures. But, as system on start-up or shutdown, sliding contact between the shaft and foil surfaces cause wear. So, in present study, to understand pressure-flow characteristics and deformation of foil bearing, flow/structure interaction analysis was used. and using this method, 2D and 3D calculation was peformed for shape of foil bearing to know circumferential direction flow and leakage flow characteristics of axial direction.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.4
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• pp.39-43
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• 2006

A computer-controlled micro tribotester has been developed to investigate the friction and wear characteristics of thin coatings, which can be applied to silicon-based materials. In the developed system, a step motor gives a reciprocating movement and an electromagnet applies a load between a ball and a plate specimen. Test results confirmed that the application of load in the range of $0.03{\sim}1.8N$ and with a sliding speed of $4.44{\sim}7.70mm/s$ was successfully accomplished. Advantages of the developed micro tribotester are: (1) realization of micro load and displacement applicable to micro electromechanical systems(MEMS) using DC motor and electromagnet (2) continuously variable load and reciprocating speed; and (3) high reliability, which allows for unattended use for long periods.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.11a
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• pp.42-48
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• 1999

An experimental study was performed to discover the effect of environment on the tribological behavior of Si-incorporated diamond-like carbon(Si-DLC) film slid on a steel ball. The films were deposited on Si(100) wafers from radio-frequency glow discharge of mixtures of benzene and dilute silane gases. Experiments using a ball-on-disk test-rig was performed under vacuum, dry air and ambient air conditions. It was observed that coefficient of friction was decreased as the environmental condition changes from vacuum, to dry air. It was also observed that the coefficient of friction decreased with increasing silicon concentration in the film. Chemical analyses of debris suggested that the low and stable friction coefficient is closely related to the silicon rich oxide debris and the rolling action.

• Tribology and Lubricants
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• v.17 no.6
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• pp.417-426
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• 2001

The effect of silver particle introduction on the rolling friction of AISI 52100 steel pairs has been investigated. Experiments ware performed in dry conditions using a thrust bearing-type rolling test rig at a load range of 12-960 N and a sliding velocity range of 8-785 mm/sec with pure (99.99%) silver particles. Results showed that introduced silver particles formed transfer layers, which protected the virgin bearing surfaces and resulted in the low lolling friction. By changing the quantity of silver particles, transitions in the rolling friction were found. Results also showed that the variations in normal load and rolling speed also affected the rolling friction behavior. Analyses of SEM and EPMA showed that the formation the transfer layer was mainly governed by the silver particle quantity, normal load and rolling speed, and this resulted in the different behavior of rolling friction. In this study, it was found that the low and stable rolling friction was resulted from the, shakedown phenomena occurred at the silver transfer layer.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.27-34
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• 2001

A new functionally gradient metal coating method using an atomic mixing technique was developed. In this work the effect of silver atomic mixing on the tribological characteristics of silver$.$ films. has been investigated experimentally. Atomic mixing was implemented by using the, bombardment .of accelerated Ar ions during the thermal evaporation coating process of silver films. Experiments were performed in dry conditions using a ball-on-disk test rig at a load range of 19.6 mN - 17.64 N and a sliding velocity of 20 mm/sec. Results showed that the life of functionally gradient silver coating was enhanced about 100 times more than that of thermally evaporated silver coating and 2 times more than that of IBAD silver coating. The functionally gradient. film also showed low friction and wear compared to those of the evaporated silver and

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.310-315
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• 2001

The most general feature of contact zone among the mechanical components is elliptical circle. In particular, continuously variable transmission (CVT) of toroidal type has elliptical shape of contact zone under the elastohydrodynamic lubrication condition, where the power is transmitted by the shearing the efluid. Due to the traction of the shear behaviors of lubricant over the small elliptical contact zone, high power of torque is transmitted. During the power transmission, many kinds of mechanical movements occur such as squeezing, sliding, rolling and spinning. The spinning effect that is not common contact behavior in tribological components frequently makes significant abnormal wear damage. In this work, the analysis of elliptical contact of elastohydrodynamic lubrication with spin effect is performed, which will give very useful information to understand the traction behaviors in toroidal type of CVT system.