• Journal of the Korean Geotechnical Society
• /
• v.26 no.8
• /
• pp.5-14
• /
• 2010

To simulate two-dimensional plane-strain conditions in the laboratory model test, the side frictional resistance between the soil and thick glass or plastic sheet of the soil container should be reduced as much as possible. However, in fact this side friction cannot be removed completely. In this paper, the ground model simulated as a multi-sized aluminium rod mixture was introduced to get rid of the side frictional resistance and applied to the laboratory shear box test. In addition, an application of the close range photogrammetric technique to the shear box test was validated. As a result, it was found that a mean value of dilation angle from the close range photogrammetry was close to the dilation angle defined by the curve of shear strain vs. volumetric strain.

• Journal of the Korean Society of Industry Convergence
• /
• v.21 no.5
• /
• pp.247-255
• /
• 2018

In this research, the effect of normal load, sliding velocity, and texture density on thefriction coefficient of surfaces micro-textured on AISI 4140 under paraffin oil lubrication were investigated. The predicted tribological behavior by numerical calculation can be serves as guidance for the designer during the machine development stage. Therefore, in this research friction coefficient prediction model based on response surface methodology (RSM), support vector machine (SVM), and artificial neural network (ANN) were developed. The experimental result shows that the variation of load, speed and texture density were influence the friction coefficient. The RSM, ANN and SVM model was successfully developed based on the experimental data. The ANN model can effectively predict the tribological characteristics of micro-textured AISI 4140 in paraffin oil lubrication condition compare to RSM and SVM.

• The Journal of Engineering Geology
• /
• v.32 no.4
• /
• pp.597-610
• /
• 2022

Knowledge of the failure behavior of friction materials considering their intermediate principal stress is related to an understanding of situations where these materials might be used: for example, the stability of deep-seated boreholes and fault slip analysis. This study designed equipment for physically implementing true triaxial compression and used it to assess specimens of plaster, a friction material. The material's mechanical behaviors are discussed based on the results. The applicability of the 3D failure criteria are also reviewed. The tested specimens were molded cuboids of width, length, and height 52, 52, and 104 mm, respectively. A total of 24 true triaxial compression tests were performed under various combinations of 𝜎₃ and 𝜎₂ conditions. Conventional uniaxial and triaxial compression tests were employed to estimate the mechanical properties of the plaster for use as parameters for 3D failure criteria. Examining the stress-strain relations of the plaster materials showed that a large difference between the intermediate principal stress and the minimum principal stress indicated strong brittle behavior. The mechanical behavior of the plaster used here reflects the change of intermediate principal stress. Nonlinear multiple regression analysis on the test data in the principal space showed that the modified Wiebols-Cook failure criterion and the modified Lade failure criterion were the most suitable 3D failure criteria for the tested plaster.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2016.05a
• /
• pp.166-166
• /
• 2016

국내에서는 기후변화로 인해 집중호우 및 태풍 발생이 증가하고 있으며, 이는 자연재해의 발생뿐만 아니라 차량 및 항공 운항의 어려움을 야기한다. 차량 및 항공 운항의 안정성 확보를 위해서는 노면의 마찰저항을 유지하는 것이 중요한데, 강수로 인해 형성되는 수막두께는 노면의 마찰저항을 감소시키므로 포장설계시 고려해야 할 주요소이다. 특히, 물적/인적 이동이 많은 공항은 기상조건에 더욱 취약하며, 기후변화로 인한 강수특성 변화로 활주로의 수막두께 증가 및 운항의 차질이 우려되고 있다. 따라서 본 연구에서는 과거 및 미래 강우조건에 따라 활주로 노면의 수막두께를 산정하고, 기후변화에 따른 수막두께의 변화를 평가하고자 한다. 과거 관측 및 기후변화 시나리오를 이용하여 강우자료를 생산하였고, 이를 강우-유출 모형의 강우 입력 자료로 활용하였다. 과거 강우자료는 인천지점의 기상청 관측자료를 수집하였으며, AR5 RCP 시나리오(RCP4.5, RCP8.5) 기반의 적정 GCMs 결과를 활용하여 미래 강우시나리오를 산정하였다. 강우의 재현기간 및 지속시간에 따른 수막두께의 변화를 분석하기 위해 인천지역의 과거 및 미래 확률강우량을 산정하였다. 수막두께를 산정하기 위해 활주로 폭, 경사 등 활주로 제원을 수집하고, 유출 모형의 입력자료를 구축하였다. 과거 및 미래 확률강우량을 SWMM 모형에 적용하여 유출량을 산정하였으며, 유속과 흐름폭으로 나누어 활주로의 수막두께를 산정하였다. 산정결과, 강우량이 증가함에 따라 수막두께는 증가하고, 강우의 지속시간이 증가함에 따라서는 감소하는 것으로 분석되었다. 미래의 경우, 기후변화의 영향에 따라 강수량이 증가하여 수막두께가 과거에 비해 증가하였다.

• Tribology and Lubricants
• /
• v.34 no.6
• /
• pp.262-269
• /
• 2018

In this work the friction and wear characteristics of the gray cast iron surface processed by broaching method, which is widely used in the machinery industry, were investigated. The broaching process is mainly used for mass production because it has high dimensional accuracy and processing speed, but the defects on surface can be easily generated. In order to improve the tribological characteristics, the approach was to reduce the roughness and hardness of the surface by adding a machining process to the broaching specimen. The secondary machining process using abrasive grains produces low roughness and hardness than broaching because it has high tool accuracy and removes the work hardened surface. The friction coefficient and the wear rate were assessed using a reciprocating-type tribotester to analyze the effects of surface finishing on the tribological properties. The friction tests were conducted under dry and lubricated conditions. The test results showed that the reduction of surface roughness and hardness through secondary machining process in lubricated condition improved the friction and wear characteristics. The reason why the same results did not appear in a dry condition was that wear occurred more rapidly than in lubricated condition. Thus, the positive effect of roughness and hardness of the surface obtained through the secondary machining process was not observed.

• Tribology and Lubricants
• /
• v.35 no.1
• /
• pp.24-29
• /
• 2019

In this work we investigated the friction and wear characteristics of a magnesium alloy, which has been receiving much attention as a light metal in industrial applications such as automobiles and aerospace. Magnesium is one of the lightest structural material that has high specific strength, lightweight, low density and good formability. However, current issue of using magnesium alloy is that magnesium has weakness against temperature. As the temperature increases, magnesium undergoes poor creep resistance and ease of softening, and therefore, its mechanical strength decreases sharply. To solve this issue, a new type of magnesium alloy that retains high strength at high temperature has been proposed. The tribological behavior of this alloy was investigated using a tribotester with reciprocating motion and heating plate. A stainless steel ball was used as a counter surface. Results showed that extrusion process has similar wear behavior to the commonly used casting process but retains good mechanical strength and durability. The presence of an alloying element enhanced the wear properties especially in high temperature. This study is expected to be utilized as fundamental data for the replacement of high density materials currently used in mechanical industries to a much lighter and durable heat-resistant materials.

• Journal of ILASS-Korea
• /
• v.27 no.3
• /
• pp.161-166
• /
• 2022

To measure the change in friction loss due to the control of fuel mass and oil temperature in a gasoline engine, the floating liner method was used to measure the friction generated by the piston of a single-cylinder engine. First, to check the effect of combustion pressure on friction, the friction loss was measured by adjusting the fuel mass. It was confirmed that the friction loss increased as the fuel mass increased under the same lubrication conditions. In addition, it was confirmed that the mechanical efficiency decreased as the fuel mass increased. Next, to check the effect of lubrication conditions on friction, the friction loss was measured by controlling the oil temperature. It was confirmed that friction loss increased as the oil temperature decreased at the same fuel mass. As the oil temperature decreases, the viscosity increases, resulting in decreased mechanical efficiency and increased friction loss.

• Journal of the Korean Geotechnical Society
• /
• v.27 no.10
• /
• pp.55-67
• /
• 2011

The shear load distribution and deformation of offshore friction piles are investigated using experimental tests and a numerical analysis. Special attention is given to the soil-pile interaction of axially loaded pile. A framework for determining the f-w curve is proposed based on both theoretical analysis and experimental load test data base. A numerical analysis that takes into account the proposed f-w curves was performed for major parameters on pile-soil interaction such as the pile diameter, the pile length, and the soil condition. Based on the analysis, it is shown that the proposed f-w method is capable of predicting the behavior of a friction pile in deep soft clay. Through comparisons with case histories and finite element results, it is found that the proposed f-w curves are more appropriate and realistic m representing the pile-soil interaction of axially loaded piles in deep soft clay than that of existing f-w method.

• Journal of the Korean Geotechnical Society
• /
• v.21 no.1
• /
• pp.93-103
• /
• 2005

Both static pile load test with load transfer measuring system and the pile dynamic load test are performed to estimate the skin friction and behavior characteristics of a large drilled shaft. And the numerical modeling of large drilled shaft is performed by applying the FDM program. Since the magnitude of friction resistance depends on the relative displacement between soil and shaft, load and displacement at the arbitrary depth along the large drilled shaft are estimated to analyze the correlation. According to the measuring results of load transfer, unit skin friction along the large drilled shaft was fully mobilized at gravel layer in the middle of shaft and the frictional resistance transmitted to bedrock was relatively small. Also, even for the same drilled shaft, the results of PDA and static load test are different with each other and the difference is discussed.

• Geotechnical Engineering
• /
• v.6 no.4
• /
• pp.7-18
• /
• 1990

To deal with the case of a rigid retaining wall built close to a stable rock face with cohesionless backfill, analytical solution methods Proposed by Spangler- Handy and Sokolovskii are modified. The modified solution methods, taking into account different friction angles along the wall and the rock face, can estimate the developed static or dynamic horizontal earth pressures behind vertical retaining walls experiencing various types of outward wall movements. The range of application of each proposed method, which is represented by the ratio of the distance between the wall and the rock face to the height of the wall, is compared with each other and also is examined for different wall friction angles as well as soil friction angles. Further, the result predicted by the modified Spangler - Handy solution method is compared with that from the experimental model test on sand. The comparison shows in general good agreements at various stages of retaining wall rotation about its toe. Finally results of analytical parametric study, together with the design charts, are presented to demonstrate the effects of wall friction angles and horizontal acceleration coefficients.