• Tribology and Lubricants
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• v.20 no.4
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• pp.177-182
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• 2004

In a turbopump cryogenic ball bearings are used to carry static and hydraulic loads, and these ball bearings must stand up to high load and speed in cryogenic circumstance. Verification of bearing performance is crucial to successful development of a turbopump. In this paper, focusing on the turbopump under developing by KARI, the performances of 203 and 207 bearings are verified through the series of tests simulating the real operating condition of turbopump.

• Tribology and Lubricants
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• v.7 no.2
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• pp.61-66
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• 1991

The frictional and wear characteristics of non-asbestos friction materials made of four different fibers (carbon, aramid, ceramic and glass) have been investigated at elevated temperature using High Frequency Friction Tester. On the basis of the experimental results, friction and wear phenomena of four different non-asbestos fibers were caused by lattice layer film of carbon, polymeric transfer film of aramid, abrasion of ceramic and adhesion of glass fiber under each contact junction. The surface analysis of the worn specimens and counter parts after tests were observed using Scanning Electron Microscope and Optical Microscope.

• Tribology and Lubricants
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• v.2 no.1
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• pp.39-45
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• 1986

Wear simulation test have been conducted in mild, severe and transient wear regions by a four-ball wear tester. Wear particles are separatively deposited by the RPD technique, and quantitatively analysed in terms of wear particles size distribution. Characteristics of the wear particle size distribution are compare to the results of wear tests through both weibull parameters and center moment method of the weibull distribution function.

• Tribology and Lubricants
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• v.24 no.1
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• pp.44-48
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• 2008

The wear characteristics of the gold alloy dental prosthesis have been investigated. The wear tests were performed by using a pin-on-disk wear tester at room temperature. Vickers hardness and fracture toughness measurement of dental materials were preformed. Microscopic observations on worn surfaces of specimens were conducted by microscope. The friction coefficient of the gold alloy dental prosthesis was investigated according to weight and slinging velocity. The hardness of the gold alloy dental prosthesis were similar and a half of the enamel of natural teeth.

• Tribology and Lubricants
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• v.15 no.1
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• pp.108-115
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• 1999

The electrical and frictional properties of oil-impregnated sintered-metal bearing (OSB) and herringbone-grooved fluid bearing (HFB) with varying loads and speeds were measured. OSB shows very good performance up to 20,000 rpm and 0.05 N, and HFB successfully works up to 35,000 rpm and 0.05 N. From the endurance tests on start-stop and continuous operation, it was confirmed that those bearings could be mass-produced fur use on scanner motor in a laser scanner unit.

• Tribology and Lubricants
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• v.16 no.5
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• pp.324-331
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• 2000

Wear characteristics of Plastic and Nylon pinions against steel gear were studied to gain a better understanding of their tribological behaviors. Wear tests were conducted with power circulating gear test rig under dry contact conditions. Specific wear rates were measured as a function of applied load and the number of revolution. The worn teeth surfaces were examined with a profile projector and a camera. Nylon pinion showed lower specific wear rates than acetal pinion, but suffered teeth breakage under high load per unit tooth width. The dominant wear mechanisms found were adhesion and abrasion.

• Tribology and Lubricants
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• v.13 no.2
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• pp.68-73
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• 1997

The adhesion between wheel and rail plays an important role in the braking performance of trains. Though there have been numerous studies on the characteristics of adhesion phenomenon, a general understanding from the physical point of view is still lacking. In this work, the adhesion mechanism between wheel and rail was investigated by studying the mechanisms of pure rolling and sliding experiments. Tests were performed under various conditions to determine the physical phenomenon responsible for adhesion between wheel and rail. The results of this study is expected to aid in improving the braking performance of trains.

• Tribology and Lubricants
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• v.16 no.6
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• pp.477-483
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• 2000

Rolling contact fatigue (RCF) tests were performed for two kinds of commercial silicon nitride balls using 4-Ball rolling contact fatigue life tester under EHL condition (Λ=8.9) and boundary lubrication condition (Λ=0.2). All the test balls were finished up to the dimensional accuracy of Grade 5 defined in KS B 2001 (Steel Balls for Ball Bearings) with a size of 8.731 mm. RCF tests were then conducted under the initial theoretical maximum contact stress 6.63 GPa and the spindle speed 10,000 rpm. All the test balls were not failed until 3.75 $\times$ 107 contact cycles and wear tracks of test balls were not conspicuous under EHL condition (Λ= 8.9). In the operations of low lambda regime (Λ= 0.2), all the test balls were surface damaged and high rolling wear resistance was achievable in fully densified using MgO 1 wt% and HIPed balls. Rolling wear of silicon nitride balls under boundary lubrication condition depend mainly on grain size and intergranular phase content of silicon nitride balls.

• Tribology and Lubricants
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• v.12 no.3
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• pp.33-38
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• 1996

High temperature wear behaviors of plasma-sprayed ZrO$_{2}$-$Y_{2}O_{3}$ composite coatings were investigated for high temperature wear resistance applications. The composite powders containing 20, 50, 80 vol% of alumina for plasma spray were made by spray drying method. Wear tests with composite coated specimens were performed at temperature ranges from room temperature to 800$^{\circ}$C. Wear tests were also carried out with heat treated specimens at room temperature. The microstructural change of coatings and the worn surface were examined by SEM and XRD. Sharp increase of wear loss at high temperature wear test was observed in specimens containing 50 and 80 vol% alumina. Similar trend was observed in the heat treated coatings. The measured residual stress was increased with increased alumina contents and heat treating temperatures. Residual stress induced during heat treatment appeared to be responsible to the observed harmful effect of alumina additions on the high temperature wear.

• Tribology and Lubricants
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• v.20 no.1
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• pp.7-13
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• 2004

High strength steels are widely used as tribo-materials in the field. Previous study revealed that for mild steel, the states of strain on the worn surface measured by X-ray diffraction has a good relationship with the state of wear. The objective of this study is to identify the relationship between the state of strain on the worn surface and the state of wear in high strength steels. Sliding wear tests were carried out using several hardened steels. X-ray diffraction tests were conducted to analyze the state of strain on the worn surface during wear. The experimental results indicated that the state of strain on worn surface in the hardened steel shows the same tendency as in the mild steel. It is clear that change of half value width on the worn surface as a function of sliding speeds is broadly similar in shape to wear characteristics curve and its magnitude has a good relationship with the wear rate at two different wear modes in the hardened steel.