• Journal of the Korean GEO-environmental Society
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• v.14 no.12
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• pp.23-30
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• 2013

Bearing capacity of pile is governed by only skin friction in frozen ground condition, while it is generally governed both by skin friction and end bearing capacity in typically unfrozen ground condition. Skin friction force, which arises from the interaction between pile and frozen soils, is defined as adfreeze bond strength, and adfreeze bond strength is one of the most important key parameters for design of pile in frozen soils. Many studies have been carried out in order to analyze adfreeze bond strength characteristics over the last fifty years. However, many studies for adfreeze bond strength have been conducted with limited circumstances, since adfreeze bond strength is sensitively affected by various influence factors such as intrinsic material properties, pile surface roughness, and externally imposed testing conditions. In this study, direct shear test is carried out inside of large-scaled freezing chamber in order to analyze the adfreeze bond strength characteristics with varying freezing temperature and normal stress. Also, the relationship between adfreeze bond strength and shear strength of the frozen soil obtained from previous study was analyzed. The coefficient of adfreeze bond strength was evaluated in order to predict adfreeze bond strength based on shear strength, and coefficients suggested from this and previous studies were compared.

• Korean Journal of Materials Research
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• v.10 no.1
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• pp.62-68
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• 2000

Ultra thin TiN films (50∼700nm thickness) were deposited on AISI 304 stainless steel substrates using a reactive DC magnetron sputtering deposition process to investigate their wear and friction properties. Dry sliding wear tests of the films were carried out against hardened steel and alumina counterparts using a pin-on-disk type wear tester at room temperature. Variation of friction coefficient was measured as a function of film thickness, load, sliding speed and roughness of the substrate. Worn surfaces of the film were examined by a scanning electron microscope. Wear resistance of the TiN film increased with the increase of the film thickness. The TiN film showed relatively high wear resistance in spite of its ultra thin thickness when it is mated by the steel counterpart, while it showed poor wear resistance with the alumina counterpart. The good wear resistance with the steel counterpart was explained by the formation of oxide layers on the film surface and sound interface character between the ultra thin film and the substrate.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.6
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• pp.740-750
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• 2006

Statement of problems. In an attempt to reduce screw loosening, dry lubricant coatings such as pure gold or tefron have been applied to the abutment screw. However, under repeated tightening and loosening procedures, low wear resistance and adhesion strength of coating material produced free particles on the surface of abutment screw and increased frictional resistance resulting in screw tightening problems. Purpose. The aim of this study was to compare friction coefficient, adhesion strength, vickers hardness and evaluate coating surface of titanium alloy specimens coated with TiN(titanium nitride), ZrN(zirconium nitride) and WC(tungsten carbide). Material and method. Titanium alloy(Ti-6Al-4V) discs of 12mm in diameter and 1mm in thickness divided into 4 groups. TiN, ZrN and WC was coated for the specimens of 3 groups respectively, and those of 1 group were not coated. Each group was made up of 4 specimens. In this study, sputtering method was used among the PVD(Physical Vapor Deposition) techniques available for TiN, ZrN and WC coatings. Friction coefficient, adhesion strength, vickers hardness and coating surface of 4 groups were measured. Results. 1. For all three coating conditions, friction coefficient was significantly decreased. Especially, ZrN coated surface showed the lowest value. $TiN(0.39{\pm}0.02)$, $ZrN(0.24{\pm}0.01)$, $WC(0.31{\pm}0.03)$. 2. TiN coating showed the highest adhesion strength, however ZrN coating had the lowest value. $TiN(25.3N{\pm}1.6)$, $ZrN(14.8N{\pm}0.6)$, $ WC(18.4N{\pm}0.7)$. 3. Vickers hardness of all three coatings was remarkably increased as compared with that of none coated specimen. TiN coating had the highest Vickers hardness, however WC coating showed the lowest value. $TiN(1865.2{\pm}33.8)$, $ZrN(1814.4{\pm}18.6)$, $WC(1008.5{\pm}35.9)$. 4. The ZrN or WC coated specimen showed a homogeneous and smooth surface, however the rough surface with defects was observed for TiN coating. Conclusions. When TiN, ZrN and WC coating applied to the abutment screw, frictional resistance would be reduced, as a result, the greater preload and prevention of the screw loosening could be expected.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.23-23
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• 2010

마찰교반접합(Friction Stir Welding)은 1991년 영국 TWI에서 개발된 접합 법으로서 일정한 속도로 회전하는 툴이 재료내부에 삽입 되면서 툴과 재료사이에서 마찰열이 발생하여 연화된 재료와 접합 툴 사이에서의 기계적 교반에 의해 소성변형이 일어남과 동시에 접합이 이루어진다. 마찰교반접합은 동적 재결정에 의한 접합부의 미세한 결정립 형성으로 인하여 기계적 특성이 향상되며 보호 가스가 필요 없어 친환경적임과 동시에 용융 용접 법에 비해 접합 시 에너지 소모가 적다는 장점이 있다. 마찰교반접합은 기존의 저융점 재료에 관한 접합을 넘어서 최근에는 철계 합금, 타이타늄 합금, 니켈계 합금 등 고융점 재료에서의 적용에 관한 연구가 이루어지고 있다. 하지만 마찰교반접합을 이용하여 위와 같은 강한 재료를 접합하기 위해서는 내구성이 갖추어진 툴이 반드시 수반된다. 슈퍼 오스테나이트계 스테인리스강은 염화물의 농도가 높은 부식 환경에 적용되는 소재로서, 공식(pitting corrosion) 및 틈부식 (crevice corrosion)에 대한 내식성을 높이기 위하여 Mo의 함량을 6%로 낮추고 20~25% Cr과 Ni을 첨가하여 사용된다. 이러한 고합금의 슈퍼 오스테나이트계 스테인리스강은 여타 내식성 합금에 비하여 내식성이 매우 우수한 것으로 알려져 있다. 최근 SO2 배출에 대하여 규제가 강화되면서 화력 발전소용 탈황 설비 중 일부 장비에서 6% Mo가 첨가된 슈퍼 오스테나이트계 스테인리스강의 사용이 늘어나고 있다. 본 연구에서는 $Si_3N_4$ 툴을 사용하여 Mo이 6% 첨가된 슈퍼 오스테나이트계 스테인리스강인 1925hMo강을 마찰교반접합하였다. 툴 회전속도 (200rpm, 300rpm, 460rpm, 700rpm)를 변수로 하여 접합을 실시하였다. 접합 후 외관상태를 점검하였으며 광학현미경 (optical microscope)과 주사전자현미경 (scanning electron microscope)을 사용하여 미세조직 관찰을 하였으며 경도 및 인장강도 측정 등의 실험을 통하여 접합부의 기계적 특성을 평가하였다. 그 후 이러한 결과를 통하여 미세조직과 기계적 특성과의 관련성을 조사하였다.

• Journal of the Korean Ceramic Society
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• v.42 no.2 s.273
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• pp.88-93
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• 2005

Ti-AI-Si-N coating layers were deposited on WC-Co substrates by a hybrid system of arc ion plating and sputtering techniques. The coatings were prepared with different Si contents to investigate the effect of Si content on their mechanical properties and microstructures. The dry sliding wear experiments were conducted on Ti-AI-Si-N coated WC-Co discs at constant load, 3N, and sliding speed, 0.1 m/s with two different counterpart materials such as steel ball and zirconia ball using a conventional ball-on-disc sliding wear apparatus. In the case of steel ball, the friction coefficient of Ti-AI-Si-N coating layers became lower than that of Ti-AI­N coating layers. The friction coefficient decreased with increasing of Si content due to adhesive wear behavior between coating layer and steel ball. On the contrary, in the case of zirconia ball, the friction coefficient increased with increasing of Si content, indicating that abrasive wear behavior was more dominant when the coating layers slid against zirconia ball.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.42-42
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• 2009

마찰교반접합 (Friction Stir Welding)은 1991년 영국 TWI에서 개발된 접합 법으로서 회전하는 툴이 재료내부에 삽입되면 툴과 재료사이에서 발생하는 마찰열에 의하여 온도가 상승하게 되어 재료는 연화되고, 이러한 재료 내부에서 회전하는 툴이 이동하게 되면 재료 내부는 기계적 교반에 의해 소성변형이 일어남과 동시에 접합이 이루어진다. 마찰교반접합은 동적 재결정에 의한 접합부의 미세한 결정립 형성으로 인하여 기계적 특성이 향상되며 보호 가스가 필요 없어 친환경적임과 동시에 용융 용접 법에 비해 접합 시 에너지 소모가 적으며 또한 접합 후 접합부에서의 변형이 상대적으로 적다는 장점이 있다. 이러한 장점을 가진 마찰교반접합은 알루미늄 합금, 마그네슘 합금 그리고 동 합금과 같은 저 융점 비철재료에 많은 연구와 적용 사례들이 있어왔다. 하지만 최근에는 일반 탄소강, 연강, 오스테나이트계 스테인리스강, 니켈 합금, 티타늄 합금과 같은 고융점 재료에도 연구 및 적용이 진행되고 있는 추세이다. 페라이트계 스테인리스강은 가격이 비싼 Ni을 함유하지 않아 오스테나이트계 스테인리스강에 비하여 강재의 가격은 낮으면서도 고온특성 및 내식성이 우수하여 건축용, 자동차 배기계용으로 널리 사용되고 있다. 하지만 이런 장점을 가진 페라이트계 스테인리스강을 기존의 용융 용접 법으로 접합 시 용접부 및 열영향부에서의 결정립의 조대화로 인한 인성 및 연성이 저하되며, 특히 예민화된 열영향부 입계 내에 Cr 탄화물이 석출되어 입계주변에 Cr 결핍 층을 형성되어 입계부식이 발생되는 문제점이 발생된다. 본 연구에서는 마찰교반접합을 이용하여 두께 3mm의 409 스테인리스강에 대해 맞대기 접합을 실시하였다. 접합 변수를 툴의 재료 (WC-12wt%Co, $Si_3N_4$)로 하여 접합을 실시하였고 접합 후 외관상태 점검, 광학 현미경과 주사 전자 현미경을 통하여 미세조직을 관찰하였으며 황산-황산동 부식 시험을 실시하여 접합부의 부식 특성을 평가하였다.

• Journal of Dental Rehabilitation and Applied Science
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• v.25 no.2
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• pp.157-169
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• 2009

The aim of this study was to evaluate effect of implant abutment screw coating treatment on joint stability, investigating mechanical properties of these. For this study used $ExFeel^{(R)}$ external hexed implant system and $15mm{\times}1mm$ discs. Experimental group was $1{\mu}m$ TiN, TiCN, TiC coated abutment screws and discs. To know mechanical property, i evaluated adhesion strength, surface hardness, using disc, corrosion test using screw. The results were as follows : rotation angle of coated screws increased than that of non-coated screw because of lower friction coefficient, especially TiC coated screw group had the largest value, but removal torque decreased in all coated screws (p<0.05). Torque loss before and after fatigue test was the smallest in TiC-coated screws, and the largest in non-coated screws (p<0.05), and there was no statistically significant difference between dry condition and wet condition of screws because of higher surface hardness and lower friction coefficient. From the above results, TiN, TiCN, TiC coating group had high abrasion resistance, especially TiC coated group which had low torque-consuming, high rotation angle as low friction coefficient will be considered to influence on implant abutment screw joint stability positively.

• Ocean and Polar Research
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• v.29 no.4
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• pp.283-295
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• 2007

We investigated the longitudinal variations in zooplankton abundances and their related physicochemical properties at nine stations located between $136^{\circ}W$ and $128^{\circ}W$ at $10.5^{\circ}N$ in the northeastern Pacific in summer 2004. Temperature, salinity, inorganic nutrients, chlorophyll-a (hereafter chl-a) and zooplankton ($>200\;{\mu}m$) were sampled within the depth from the surface to 200 m depth at $1^{\circ}$ longitude intervals. Zooplankton($>200\;{\mu}m$) samples were vertically collected at two depth intervals from surface to 200 m, consisting of surface mixed and lower layers (thermocline$\sim$200 m). Longitudinal distributional pattern of hydrological parameters (especially salinity) was physically influenced by the intensity of westward geostrophic current passage relating to the NEC (North Equatorial Current). Data from the longitudinal survey showed clear zonal distributions in the hydrological parameters(temperature, salinity and nutrients). However, spatial patterns of the chl-a concentrations and zooplankton abundances were mostly independent of the zonal distributions of hydrological parameters. The two peaks of zooplankton abundance in the surface mixed layer were characterized by different controlling factors such as bottom-up control from nutrients to zooplankton ($129^{\circ}W$) and accumulation by increment of friction force and taxonomic interrelationship ($133^{\circ}$ and $134^{\circ}W$). Divergence-related upwelling caused introduction of nutrients into surface waters leading to the increment of chl-a concentration and zooplankton abundances ($129^{\circ}W$). Increased friction force in relation to reduced flow rates of geostrophic currents caused accumulation of zooplankton drifting from eastern stations of study area($133^{\circ}$ and $134^{\circ}W$). Besides, high correlation between immature copepods and carnivorous groups such as chaetognaths and cyclopoids also possibly contributed to the enhanced total abundance of zooplankton in the surface mixed layer (p<0.05). Zooplankton community was divided into three groups (A, B, C) which consecutively included the eastern peak of zooplankton($129^{\circ}W$), the western peak($133^{\circ}$ and $134^{\circ}W$) and high nutrient but low chl-a concentration and zooplankton abundance ($136^{\circ}W$). Moreover, Group B corresponded to the westward movement of low saline waters(<33.6 psu) from 128 to $132^{\circ}W$. In summary, longitudinal distributions of zooplankton community was characterized by three different controlling factors: bottom-up control ($129^{\circ}W$), accumulation by increased friction force and relationships among zooplankton groups ($133^{\circ}$ and $134^{\circ}W$), and mismatch between hydrological parameters and zooplankton in the high nutrient low chlorophyll area ($136^{\circ}W$) during the study period.

• The Journal of Engineering Geology
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• v.31 no.3
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• pp.357-366
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• 2021

Shear behavior dependent on the shape and roughness of rock joints can greatly influence the stability of the ground and rock structures. The efficient design of rock structures requires understanding of the shear behavior due to joints and accurate calculation of the shear strength. This work reports numerical shear tests using PFC2D on No. 1 (JCR-1), with smooth joints, and No. 7 (JRC-7) and No. 9 (JRC-9), with relatively rough joints, for the 10 shapes of standard joint profiles proposed by Barton and Choubey (1977). The aim was to investigate the shear behavior of rock joints with respect to their roughness. The results show the maximum shear stress to be about 3.2 to 5.0 times greater in the rougher JRC-7 and JRC-9 joints than in smoother JRC-1. The maximum shear displacement was approximately 4.1 to 5.8 times greater at the first normal stress than at the second. The rougher joints showed friction angles of the rock joints that were approximately 1.8 to 3.9 times greater than that in the smooth joint. Overall, increasing the rock joint roughness increased the maximum shear stress and friction angle.

• Journal of Adhesion and Interface
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• v.24 no.4
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• pp.124-130
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• 2023

For automotive coating agents that require little change in characteristics due to changes in external temperature, changes in noise characteristics due to changes in the external environment are very important. Therefore, soft polyurethane with excellent cold resistance, weather resistance, and abrasion resistance, and polysiloxane whose -OH terminated and side chains are modified with amines, are widely used. In this study, coating agents was prepared by adding water-born polyurethane, polysiloxane, ultra high molecular weight polypropylene (UHMWPP) powder, carbon black, and a matting agent to determine the effect of each resin component on noise. To study the effect of each resin component on noise, a coating agent was prepared by adding water-born polyurethane, polysiloxane, UHMWPP powder, carbon black, and a matting agent. The hard/soft segment ratio of water-born polyurethane, the main component of the coating, was 27.1%/72.9%, and the ratio of amino siloxanes to hydroxy-terminated polysiloxane was 2:7, which produced the least noise. The difference in friction coefficient was large when the friction body moves at high speed. When UHMWPP powder replaced SiO₂, noise decreased and gloss also decreased.