• Tribology and Lubricants
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• 제33권3호
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• pp.98-105
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• 2017

A pin-on-disk test is performed to measure the wear volume of a ductile cast iron (DCI) roll when it wears down using a high carbon steel and two alloy steels at different sliding velocities between the roll and the material (steel). Normal pressure is set as constant and test temperatures are 400, 500 and $600^{\circ}C$. In addition, thermal softening behavior of the DCI roll is examined using a high-temperature micro-hardness tester and the surface hardness variation of the DCI roll is expressed in terms of temperature and heating time. Based on experimental data, a wear coefficient used in Archard's wear model for each material is obtained. The wear volume is clearly observed when the test temperature is $400^{\circ}C$ and sliding velocity varies. However, it is not measured at temperatures of $500^{\circ}C$ and $600^{\circ}C$ even with variations in sliding velocity. From the optical photographs of the pin and disk, the abrasive wear is observed at $400^{\circ}C$ clearly, but no at $500^{\circ}C$ and $600^{\circ}C$. At higher temperatures, the pin surface is not smooth and has many tiny caves distributed on it. It is found that wear volume is dependent on the carbon contents rather than alloy contents. Results also reveal that the variations of wear coefficients are almost linearly proportional to the carbon contents of the material.

• 한국지진공학회논문집
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• 제2권2호
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• pp.13-22
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• 1998

본 연구는 지진격리장치의 일종인 마찰 단진자 시스템(FPS)의 교량에의 적용에 관한 연구이다. FPS에 의하여 지진 격리된 교량과 지진 격리되지 않은 교량의 지진하중 작용시의 응답을 비교하기 위하여 축소모델 교량을 이용한 진동대 실험을 수행하였다. 연구결과, 본 장치를 설치한 경우 지진하중에 대한 지지능력이 향상하는 것으로 나타났다. 또한, 활동면 곡류반경에 의해 조절이 가능한 F.P.S 베어링의 강성은 입력된 kwlsfur의 강도와는 무관하며, 활동면의 마찰계수에 따라 속도가 변화하여 약진시에는 활동면에서의 속도가 작으므로 강진시와 비교하여 지진하중에 의하여 발생하는 마찰력도 감소하게 되었다. 한편 F.P.S 베어링의 마찰특성은 반복된 실험에서도 변화하지 않았고, 영구변형은 약적으로도 작았을 뿐만 아니라 누적되지도 않았다.

• 한국분말재료학회지
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• 제13권6호
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• pp.421-426
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• 2006

The microstructural and mechanical properties of Al-Si alloyed powder, prepared by gas atomization fallowed by hot extrusion, were studied by optical and scanning electron microscopies, hardness and wear testing. The gas atomized Al-Si alloy powder exhibited uniformly dispersed Si particles with particle size ranging from 5 to $8{\mu}m$. The hot extruded Al-Si alloy shows the average Si particle size of less than $1{\mu}m$. After heat-treatment, the average particle size was increased from 2 to $5{\mu}m$. Also, mechanical properties of extruded Al-Si alloy powder were analyzed before and after heat-treatment. As expected from the microstructural analysis, the heat-treated samples resulted in a decrease in the hardness and wear resistance due to Si particle growth. The friction coefficient of heat-treated Al-Si alloyed powder showed higher value tough all sliding speed. This behavior would be due to abrasive wear mechanism. As sliding speed increases, friction coefficient and depth and width of wear track increase. No significant changes occurred in the wear track shape with increased sliding speed.

• Tribology and Lubricants
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• 제17권4호
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• pp.267-275
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• 2001

Friction and wear properties of brake friction materials containing different metal fibers (Al, Cu or Steel fibers) were investigated. Based on a simple experimental formulation, friction materials with the same amount of metal fibers were tested using a pad-on-disk type friction tester. Two different materials (gray cast iron and aluminum metal matrix composite (MMC)) were used for disks rubbing against the friction materials. Results front ambient temperature tests revealed that the friction material containing Cu fibers sliding against gray cast iron disk showed a distinct negative $\mu$-v (friction coefficient vs. sliding velocity) relation implying possible stick-slip generation at low speeds. The negative $\mu$- v relation was not observed when the Cu-containing friction materials were rubbed against the Al-MMC counter surface. Elevated temperature tests showed that the friction level and the intensity of friction force oscillation were strongly affected by the thermal conductivity and melting temperature of metallic ingredients of the friction couple. Friction materials slid against cast iron disks exhibited higher friction coefficients than Al-MMC (metal matrix composite) disks during high temperature tests. On the other hand, high temperature test results suggested that copper fibers in the friction material improved fade resistance and that steel fibers were not compatible with Al-MMC disks showing severe material transfer and erratic friction behavior during sliding at elevated temperatures.

• 한국지반환경공학회 논문집
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• 제15권2호
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• pp.59-66
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• 2014

본 논문에서는 석션파일의 인발거동을 조사하기 위해 유한차분법 상용 프로그램인 FLAC3D를 이용하여 수치해석을 수행하였다. 석션파일의 인발지지력을 전통적인 지지력 식을 이용하여 구하고, 이 값을 파일의 직경, 길이, 그리고 주변 점토의 비배수 전단강도를 변수로 하는 수치해석을 통한 해석 값과 비교하였다. 총 24개의 수치해석 결과를 바탕으로 석션파일의 인발파괴는 석션파일의 배수조건뿐만 아니라 파일의 제원과 주변 지반의 물성값에 의해 형태가 결정되는 것으로 밝혀졌다. 수치해석 결과로부터 석션파일 내부 주면에 발현되는 전단응력을 구하여 활동파괴와 인장파괴 중 어떤 파괴가 발생할 것인지를 결정하는데 사용하였다. 외부주면의 전단응력과 관계없이 높은 내부 전단응력을 얻은 경우 수치해석 내에서 활동파괴가 발생하는 경우가 많았으며, 이는 전통적인 지지력 공식으로부터 얻은 예측과 잘 맞았다.

• Geomechanics and Engineering
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• 제31권6호
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• pp.599-614
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• 2022

One of the methods of stabilizing retaining walls, embankments, and deep excavations is the implementation of plate anchors (like the Geolock wall anchor systems). Back-to-back Mechanically Stabilized Earth (BBMSE) walls are common stabilized earth structures that can be used for bridge ramps. But so far, the analysis of the interactive behavior of two back-to-back anchored walls (BBAW) by double-plates anchors (constructed closely from each other and subjected to the limited-breadth vertical loading) including interference of their failure and sliding surfaces has not been the subject of comprehensive studies. Indeed, in this compound system, the interaction of sliding wedges of these two back-to-back walls considering the shear failure wedge of the foundation, significantly impresses on the foundation bearing capacity, adjacent walls displacements and deformations, and their stability. In this study, the effect of horizontal distance between two walls (W), breadth of loading plate (B), and position of vertical loading was investigated experimentally. In addition, the comparison of using single and equivalent double-plate anchors was evaluated. The loading plate bearing capacity and displacements, and deformations of BBAW were measured and the results are presented. To evaluate the shape, form, and how the critical failure surfaces of the soil behind the walls and beneath the foundation intersect with one another, the Particle Image Velocimetry (PIV) technique was applied. The experimental tests results showed that in this composite system (two adjacent-loaded BBAW) the effective distance of walls is about W = 2.5*H (H: height of walls) and the foundation effective breadth is about B = H, concerning foundation bearing capacity, walls horizontal displacements and their deformations. For more amounts of W and B, the foundation and walls can be designed and analyzed individually. Besides, in this compound system, the foundation bearing capacity is an exponential function of the System Geometry Variable (SGV) whereas walls displacements are a quadratic function of it. Finally, as an important achievement, doubling the plates of anchors can facilitate using concrete walls, which have limitations in tolerating curvature.

• 한국해양공학회지
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• 제21권6호
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• pp.7-15
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• 2007

A mechanical model was developed to predict the behavior of point-loaded RC slender beams (a/d > 2.5) without stirrups. It is commonly accepted by most researchers that a diagonal tension crack plays a predominant role in the failure mode of these beams, but the failure mechanism of these members is still debatable. In this paper, it was assumed that diagonal tension failure was triggered by the concrete cover splitting due to the dowel action at the initial location of diagonal tension cracks, which propagate from flexural cracks. When concrete cover splitting occurred, the shape of a diagonal tension crack was simultaneously developed, which can be determined from the principal tensile stress trajectory. This fictitious crack rotates onto the crack tip with load increase. During the rotation, all forces acting on the crack (i.e, dowel force of longitudinal bars, vertical component of concrete tensile force, shear force by aggregate interlock, shear force in compression zone) were calculated by considering the kinematical conditions such as crack width or sliding. These forces except for the shear force in the compression zone were uncoupled with respect to crack width and sliding by the proposed constitutive relations for friction along the crack. Uncoupling the shear forces along the crack was aimed at distinguishing each force from the total shear force and clarifying the failure mechanism of RC slender beams without stirrups. In addition, a proposed method deriving the dowel force of longitudinal bars made it possible to predict the secondary shear failure. The proposed model can be used to predict not only the entire behavior of point-loaded RC slender shear beams, but also the ultimate shear strength. The experiments used to validate the proposed model are reported in a companion paper.

• Earthquakes and Structures
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• 제17권3호
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• pp.245-256
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• 2019

An experimental study was conducted to evaluate the dynamic behavior of a free-standing frame equipped with a movable base system using cast iron and mortar as the bearing materials. The preliminary friction test indicated that a graphite layer developed on the interface and exhibited stable friction behavior. The friction coefficient ranged from 0.33 to 0.36 when the applied normal compression stress ranged from 2.6 to 5.2 MPa. The effect of the variation of normal compression stress would be small. Shaking table tests on the free-standing frame showed that rock, slide, and rock-slide responses occurred. The cumulative slide distance reached 381 mm under JMA Kobe wave excitation; however, only a few cyclic slides occurred at the same locations along the moving track. Most surfaces sustained single slides. Similar results can be observed in other shaking conditions. The insufficient cyclic sliding and significant rocking resulted in a few graphite layers on the mortar surfaces. Friction coefficients were generally similar to those obtained in the preliminary friction tests; however, the values fluctuated when the rocking became significant. The collisions due to rocking caused strong horizontal acceleration responses and resulted in high friction coefficient. In addition, the strong horizontal acceleration responses caused by the collisions made the freestanding specimen unable to reduce the input horizontal acceleration notably, even when slippage occurred. Compared with the counterpart fixed-base specimen, the specimen equipped with the iron-mortar base could reduce the horizontal acceleration amplification response and the structural deformation, whereas the vertical acceleration response was doubled due to collisions from rocking.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2000
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• pp.448-454
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• 2000

Piled multi-block system has been frequently adopted in the historic structures or monuments of cultural heritage. It is well known that such a structural system is very vulnerable to the earthquake shaking. If the structure is of slender type, then it may experience overturning at very low level intensity of ground shaking. One of the methods used to protect such structures from earthquake is seismic isolation system. But the behavior of multi-block systems mounted on the isolated basis is not well understood yet. In this paper we investigate the dynamic behavior of single slender rigid block mounted on the three different isolation systems, i.e., P-F system, FPS and LRB system. Sliding at the isolation interface of P-F system and FPS is formulated based on Coulomb friction. The mounted single block is assumed undergoing rocking or sticking only. Impacting of a single block is described using distinct element method (DEM). Free vibrations due to a prescribed initial conditions are studied. Responses to the harmonic excitation and earthquake motions are calculated

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제29회 춘계학술대회
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• pp.220-224
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• 1999

Sliding wear test was employed to determine the effect of whisker content and orientation on the firiction and wear behavior of SiC whisker reinforced alumina. Composites containing unidirectionally oriented whiskers were prepared by a modified tape casting followed by lamination, binder removal and hot pressing in order to align the whiskers in the tape casting direction. Wear coefficients on three directions were measured; parallel and normal to the tape casting direction on the tape casting surface and normal to lamination direction on surfnce normal to the tape casting direction. In the effect of whisker orientation, the highest wear rate was obtained in the direction parallel tape casting direction and the lowest in the direction normal to lamination direction at all temperatures. Silicon oxide layer amoothing the surface was detected by energy dispersive X-ray analysis on the worn surface.