• Tribology and Lubricants
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• v.38 no.6
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• pp.261-266
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• 2022

Notably, laser surface patterning facilitates tribological applications under lubricated sliding contacts. Consequently, a special pattern that can reduce the coefficient of friction under contact is considered necessary for improved machine efficiency. However, inappropriate pattern designs produce higher friction coefficients and cannot reduce friction. In this study, we use cast iron pins as specimens to investigate their friction and wear characteristics. Moreover, we experimentally investigate the correlation between the friction reduction effect and the design of groove crosshatch patterns fabricated with various angles and widths. We conduct a friction test using a pin-on-disc type tribometer under grease lubrication to study the friction reduction effect of the specimens, and we observe that the average coefficient of friction changes with the crosshatch angle and width. The experiment reveals that grooved crosshatch specimens with a crosshatch angle of 135°maximize friction reduction. The coefficient of friction of the groove specimens with a width of 120 ㎛ is lower than that of the specimens with a width of 200?. The friction reduction effect of the width of the groove is attributed to the density of the groove pattern. Thus, grooved crosshatch patterns can be designed to maximize friction reduction, and the friction property of a grooved crosshatch pattern is found to be related to its width and angle.

• Tribology and Lubricants
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• v.30 no.5
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• pp.278-283
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• 2014

Carbon nanotubes (CNTs) are used in various composite materials to enhance electrical, thermal and mechanical properties of composite materials. In this study, we investigate the wear characteristics of polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) blends containing multi-walled carbon nanotubes (MWCNTs). PC/ABS blends are commonly used in many industrial applications such as cellular phones and display cases and MWCNTs have been added to the PC/ABS blends to improve their electromagnetic interference shielding (EMS). We performed wear tests on PC/ABS blends containing MWCNTs under reciprocating linear sliding conditions with chrome steel balls as a counterpart material. The normal loads were 10, 30, 50, 70, 100 N, the sliding speed was 10 mm/s, the stroke length was 15 mm, and the tests lasted 900 s. The MWCNTs included in the PC/ABS blends lower the wear volume and friction coefficient of the composites. We analyzed the wear debris collected from the composites during the tests in terms of the MWCNT concentration using inductively coupled plasma optical emission spectroscopy. The results show that the quantity of MWCNTs in the debris is proportional to the concentration of MWCNTs in the composite, indicating that the exposure of the MWCNTs to environments by wear could be increased with their concentration in the composite.

• Journal of the Korean Ceramic Society
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• v.40 no.9
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• pp.881-885
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• 2003

Wear and friction properties of the alumina-glass dental ceramics were evaluated in exact in vitro environment (artificial saliva at 37$^{\circ}C$), using a ball-on-disc apparatus, at contact loads from 49 N to 196 N and with the disc rotating at 120 rpm up to 10$^{6}$ cycles to investigate the wear behavior. As the load increased from 49 N to 196 N, the friction coefficient of 0.025 was maintained, however, the volumetric wear rate rose from 2.18 ${\times}$10$^{-9}$TEX>$mm^{3}$/Nㆍm to 2.35 ${\times}$10$^{-6}$TEX>$mm^{3}$/Nㆍm. Experimental results indicated that the wear behavior of the alumina-glass composites with a sliding distance of 4.4 km was a typical adhesive wear, which was applicable for orthodontia ceramic brackets.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.11
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• pp.1349-1354
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• 2013

Sealing structure to prevent flowing hot gas into the driving device, located between the driving shaft and the liner of On-Off valve for controlling the hot gas flow path was studied. Wear occurs due to the constant movement of the driving shaft controlled by actuator on graphite as the sealing material. In this paper, the dynamic wear behavior in high temperature of graphite(HK-6) to be used as sealing material was evaluated. Reciprocating wear test was carried out for the graphite(HK-6) to the relative motion between shaft materials(W-25Re). The results of friction coefficient and specific wear rate according to contact load, sliding speed at room temperature and $485^{\circ}C$ considering the actual operating environment were evaluated. Through the SEM analysis of the worn surface, third body as lubricant films were observed and lubricant effect of third body was considered.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.6 s.165
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• pp.952-960
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• 1999

The effects of binder on the mechanical properties of the preforms and metal matrix composites (MMCs) were studied. Fibers were $9Al_2O_3{\cdot}2B_2O_3(Alborex)$, HTZ and $Al_2O_3$ fibers(Saffil) and binders were organic binder, inorganic binder, polyacrylamide under various PH conditions. Compressive strength of the preform increased with the addition of inorganic binder. The polyacrylamide did not improve the permeability of the preforms. PH of the slurry should be controlled because it affects the viscosity of the slurry. Good preforms were obtained under following conditions : 3 wt% inorganic binder, 0.1 wt% organic binder, 0.1 wt% polyacrylamide and PH 9. Tensile tests of MMCs were conducted at $20^{\circ}C,\;150^{\circ}C,\;250^{\circ}C,\;350^{\circ}C$ using MTS(100KN USA). Wear tests were conducted under various sliding speeds. High temperature($250^{\circ}C$) tensile strengths of Alborex/Saffil/AC8A and HTZ/AC8A are 80% and 75% of the room temperature tensile strengths respectively. The tensile and wear properties of the Alborex/Saffil/AC8A are superior to that of the HTZ/AC8A. The wear behavior of HTZ/AC8A shows more orthotropic characteristic than that of Alborex/Saffil/AC8A.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.5
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• pp.113-120
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• 2013

Graphite is commonly used as a solid lubricant leading to low friction coefficient and abrasion. In this study, wear behavior of sealing graphite(HK-6) at elevated temperature was evaluated. Reciprocating wear test was carried out as wear occurred graphite as a seal(HK-6) is positioned between the liner and driving shaft. Variables which are temperature, sliding speed and contact load are set. This study suggest optimized environment conditions through the wear properties of graphite.

• Structural Engineering and Mechanics
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• v.76 no.2
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• pp.153-162
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• 2020

Aiming at the mechanical and structural characteristics of the contact zone composite rock, the shear tests and numerical studies were carried out. The effects of the differences in mechanical properties of different materials and the normal stress on shear properties of contact zone composite samples were analyzed from a macro-meso level. The results show that the composite samples have high shear strength, and the interface of different materials has strong adhesion. The differences in mechanical properties of materials weakens the shear strength and increase the shear brittleness of the sample, while normal stress will inhibit these effect. Under low/high normal stress, the sample show two failure modes, at the meso-damage level: elastic-shearing-frictional sliding and elastic-extrusion wear. This is mainly controlled by the contact and friction state of the material after damage. The secondary failure of undulating structure under normal-shear stress is the nature of extrusion wear, which is positively correlated to the normal stress and the degree of difference in mechanical properties of different materials. The increase of the mechanical difference of the sample will enhance the shear brittleness under lower normal stress and the shear interaction under higher normal stress.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.2
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• pp.231-239
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• 1999

The microstructure of ceramic composite has been found to be governed by the type and amount of the secondary phase, the sintering aid, and the sintering conditions such as sintering temperature, pressure and holing time. Moreover, tribological properties are strongly dependent on microsturcture of composite and operating conditions. In this study, silicon nitride with various amount of magnesia as a sintering aid were prepared and sintered by a hot pressing (HP) technique. Microstructure, mechanical properties (hardness, strength, and fracture toughness), and tribological properties in different environments of $Si_{3}N_{4}$ (in air, water, and paraffine oil) were investigated as a function of MgO content in $Si_{3}N_{4}$. As increasing the amount of MgO in $Si_{3}N_{4}$, the glassy phase in the grain boundaries enlarged the $\beta$-phase elongated grains, and also degraded the Hertzian contact damage resistance. Tribological behaviors in air was seemed to be determined by fracture toughness of $Si_{3}N_{4}$, and those in water and paraffin oil was seemed to be determined by hardness as well as strength. Since glassy grain-boundary phase (MgO) in $Si_{3}N_{4}$ expected to be reacted with water during sliding, such tribochemical reaction reduced wear. In paraffin oil under a higher applied load, the initial sliding dominated wear rate because of Hertzian contact damage.

• Journal of Surface Science and Engineering
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• v.39 no.4
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• pp.179-189
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• 2006

High velocity oxygen fuel(HVOF) thermal spray coating of WC-Co powder is one of the most promising candidate for the replacement of the traditional hard chrome plating and ceramics coating because of the environmental problem of the very toxic $Cr^{6+}$ known as carcinogen and the brittleness of ceramics coating. WC-Co micron and nano powder were coated by HVOF thermal spraying method for the study of durability improvement of the high speed spindle. Coatings were planned by Taguchi program for the four spray parameters of spray distance, flow rates of hydrogen, oxygen and powder feed rate. Optimal coating process was obtained by the studies of coating properties such as porosity, surface roughness, micro hardness, and micro structure. WC-Co micron and nano powder were coated on the Inconel 718 substrate by the optimal coating process obtained in this study. The wear behaviors were studied by the sliding wear tester at room temperature and at an elevated temperature of $500^{\circ}C$ for the application to high speed spindle. Sliding wear test was carried out for four most promising hard coatings of chrome coating, ceramics coatings such as $A1_2O_3,\;Cr_2O_3$ and HVOF Co-alloy T800 for the comparison of their wear behaviors. HVOF WC-Co coating was better than other coatings showing highest micro hardness of 1400 Hv and comparable friction coefficients with others. HVOF WC-Co coating is a strong candidate for the replacement of the traditional hard chrome plating for the high speed spindle.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.1
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• pp.137-142
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• 2003

In automotive brake systems, the frictional heat generated can cause high temperature at the interface of rotor and pad which may deteriorate the material properties of the sliding parts and can result in brake fade. Conventionally, a pie-shaped 3-dimentional model is adopted to calculate temperature of ventilated disk using finite element method. To overcome the difficulties in preparing 3D finite element model and reduce the computational time required, the ventilated rotor is to be analyzed, in this study, as an axisymmetric finite element model in which, taking into considerations the effects of cooling passages, a homogenization technique is used to obtain the equivalent thermal properties and boundary conditions for the elements placed at the vent holes. Numerical tests show the proposed procedure can be successfully applied in practice, replacing 3-dimensional thermal analysis of ventilated disk.