• Corrosion Science and Technology
• /
• 제11권2호
• /
• pp.48-55
• /
• 2012

Clamping force of a high strength bolt is reduced by a certain period of time after the initial set-up. In case of special treatments on faying surfaces such as protective coating, clamping force is relaxed more severely. Tests for slip critical joints subject to various faying surface parameters were conducted. Five different surface treatments were tested including mill scale surface, blast surface, rust surface and coated surfaces. Each specimen was composed of F10T M20 of high strength bolts and steel plates. Based on the result of slip coefficient test, blast treatment surface showed 0.59, rust treatment surface showed 0.54 and inorganic zinc treatment surface exhibited 0.44. Clean mill treatment surface and red lead paint treatment surface were 0.23, 0.21 respectively. It is identified that the slip coefficient in Korean structural design guide should be determined for various surface conditions. Subsequently from long term relaxation test of ASTM A 490 high strength bolts, relaxation of no-coated surfaces such as blast, clean mill, rust treatment, the loss of initial clamping load was 10.5%, 13.6% and 7.9% for 1,000 hours, while the loss of initial clamping force was reached as 15.0%, 18.7% more than the required redundancy 10% in case of inorganic zinc and red lead painted treatment. It is required that the limit of relaxation on coated faying surface should be established separately for various surfaces.

• 한국자동차공학회논문집
• /
• 제3권4호
• /
• pp.19-29
• /
• 1995

This paper discusses the stick-slip phenomenon of the driveline system of a vehicle in consideration of friction. Friction is operated on the between of flywheel and clutch disk. The expressions for obtaining the results have been derived from the equation of motion of a three degree of freedom frictional torsion vibration system which is made up driving part(engine, flywheel), driven part(clutch, transmission) and dynamic load part(vehicle body) by applying forth-order Rungekutta method. It was found that the great affect parameters of the stick-slip or stick motion were surface pressure force between flywheel and clutch disk, time decay parameter of surface pressure force and 1st torsional spring constant of clutch disk when driveline system had been affected by friction force. The results of this study can be used as basic design data of the clutch system for the ride quality improvement of a car.

• 터널과지하공간
• /
• 제30권4호
• /
• pp.404-416
• /
• 2020

2차원 응력조건에서 V형 암석노치의 파괴하중을 계산하는 해석적 절차를 slip-line 소성해석법 기반으로 개발하였다. 노치 주변의 암석이 소성상태에 있을 때 slip-line 중 하나인 α선이 암석 노치 면과 노치 외부 수평면을 연결한다는 사실과 α선을 따라서 변하지 않는 불변량이 존재한다는 이론적 사실이 해석적 절차 개발과정에서 핵심 아이디어로 활용되었다. 암석 노치 외부 수평면의 응력 경계조건을 알고 있으므로 불변량 방정식을 풀면 암석 노치 면에 작용하는 수직응력과 전단응력을 계산하는 것이 가능해진다. 노치 면에 작용하는 응력성분 값을 이용하여 쐐기에 의해 노치에 가해지는 파괴하중을 계산하였다. 개발된 해석적 절차를 적용하여 암석 노치파괴 해석을 수행하였다. 암석 노치의 파괴하중은 노치의 각도 및 노치 면의 마찰이 증가함에 따라 지수함수적 비선형성을 가지고 증가하는 특성이 있음을 해석결과는 보여주었다. 이 연구에서 개발한 해석적 절차는 쐐기형 노치 형성을 통한 암석균열 개시조건 연구, 암반 기초 지지력 계산, 암반사면 및 원형터널의 안전성 해석 등에 응용될 수 있을 것으로 기대된다.

• Tribology and Lubricants
• /
• 제34권6호
• /
• pp.279-283
• /
• 2018

In this study, we investigate the behavior of abrasive particles and change of the stick-slip pattern according to chemical mechanical polishing (CMP) process parameters when a large number of abrasive particles are fixed on a pad. The CMP process is simulated using the finite element method. In the simulation, the abrasive grains are composed of those used in the actual CMP process. Considering the cohesion of the abrasive grains with the start of the CMP process, abrasive particles with various sizes are fixed onto the pad at different intervals so that stick-slip could occur. In this analysis, we determine that when the abrasive particle size is relatively large, the stick-slip period does not change as the pressure increases while the moving speed is constant. However, if the size of the abrasive grains is relatively small, the amount of deformation of the grains increases due to the elasticity of the pad. Therefore, the stick-slip pattern may not be observed. As the number of abrasive particles increases, the stick-slip period and displacement decrease. This is consistent with the decrease in the von Mises yield stress value on the surface of the wafer as the number of abrasive grains increases. We determine that when the number of the abrasive grains increases, the polishing rate, and characteristics are improved, and scratches are reduced. Moreover, we establish that the period of stick-slip increases and the change of the stick-slip size was not large when the abrasive particle size was relatively small.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 1999년도 봄 학술발표회 논문집
• /
• pp.331-338
• /
• 1999

In the present study, a searching technique for critical slip surface in two dimensional slope stability analysis is proposed. The failure surface generation and analysis has been usually limited to simple geometric shapes. However, more random surfaces need to be examined for some particular ground conditions. For this purpose, random searching technique is developed using genetic algorithm. The generalized limit equilibrium method is employed as the method of stability analysis. Using this technique, the factor of safety is compared with the result by using simplified Bishop's method. In addition, the convergent trend of fitness value is analyzed.

• 한국해안·해양공학회논문집
• /
• 제29권2호
• /
• pp.67-76
• /
• 2017

본 연구에서는 케이슨 안벽의 뒷굽이 주동토압에 미치는 영향을 조사하였다. 한계해석법을 사용하여 뒷굽의 길이에 따라 벽면마찰력이 뒷굽 상부에서 발생하는 활동면의 경사각에 미치는 영향을 분석하였다. 분석결과 뒷굽의 길이가 짧을수록 내측 활동면의 경사각은 증가하나, 외측 활동면의 경사각은 일정하였다. 실제 케이슨 안벽에서 발생하는 파괴면에 작용하는 토압과 동일한 토압을 갖는 뒷굽 끝에서의 가상의 연직배면에 작용하는 토압에 대하여 뒷굽의 상대 길이-뒤채움 토사의 내부마찰각-벽면마찰각-가상의 연직배면에 작용하는 배면마찰각 등의 상관관계를 구하였다. 뒷굽이 짧을수록 케이슨 안벽에 작용하는 토압이 Rankine 토압보다는 작아지나 뒷굽의 길이를 고려하지 않은 Coulomb 토압보다는 항상 크게 나타났다.

• 한국구조물진단유지관리공학회 논문집
• /
• 제11권5호
• /
• pp.114-122
• /
• 2007

강구조물의 고력볼트 마찰접합부에 있어서 마찰면의 부식은 장기적으로 마찰력 감소와 접합부 내력저하를 초래한다. 본 연구는 고력볼트 접합부의 부식을 방지하고 소요 역학적 성질을 만족시키기 위해 접합부의 마찰면에 Zn/Al 금속용사 방청처리 한 고력볼트 접합부를 대상으로 마찰면의 표면처리방법과 피막두께를 주요 변수로 하여 인장시험을 실시하였고, 실험으로 부터 마찰면 표면거칠기와 미끄럼계수를 측정하였다. 무도장 샌드블라스트 처리한 접합부 및 샌드블라스트 처리 후 금속용사를 실시한 볼트 접합부의 미끄럼 계수는 국내 규준의 규정 값과 비교하여 동등 이상의 우수한 미끄럼계수 값을 나타냈다.

• Advances in concrete construction
• /
• 제15권5호
• /
• pp.303-312
• /
• 2023

The present study investigates the effects of Cattaneo-Christov thermal effects of stagnation point in Walters-B nanofluid flow through lubrication of power-law fluid by taking the slip at the interfacial condition. For the solution, the governing partial differential equation is transformed into a series of non-linear ordinary differential equations. With the help of hybrid homotopy analysis method; that consists of both the homotopy analysis and shooting method these equations can be solved. The influence of different involved constraints on quantities of interest are sketched and discussed. The viscoelastic parameter, slip parameters on velocity component and temperature are analyzed. The velocity varies by increase in viscoelastic parameter in the presence of slip parameter. The slip on the surface has major effect and mask the effect of stagnation point for whole slip condition and throughout the surface velocity remained same. Matched the present solution with previously published data and observed good agreement. It can be seen that the slip effects dominates the effects of free stream and for the large values of viscoelastic parameter the temperature as well as the concentration profile both decreases.

• Korea-Australia Rheology Journal
• /
• 제15권2호
• /
• pp.55-61
• /
• 2003

The steady shear flow properties of vaseline generally used as a base of the pharmaceutical dosage forms were studied in the consideration of wall slip phenomenon. The purpose of this study was to show that how slip may affect the experimental steady-state flow curves of semisolid ointment bases and to discuss the ways to eliminate (or minimize) wall slip effect in a rotational rheometer. Using both a strain-controlled ARES rheometer and a stress-controlled AR1000 rheometer, the steady shear flow behavior was investigated with various experimental conditions ; the surface roughness, sample preparation, plate diameter, gap size, shearing time, and loading methods were varied. A stress-controlled rheometer was suitable for investigating the flow behavior of semisolid ointment bases which show severe wall slip effects. In the conditions of parallel plates attached with sand paper, treated sample, smaller diameter fixture, larger gap size, shorter shearing time, and normal force control loading method, the wall slip effects could be minimized. A critical shear stress for the onset of slip was extended to above 10,000 dyne/$\textrm{cm}^2$. The wall slip effects could not be perfectly eliminated by any experimental conditions. However, the slip was delayed to higher value of shear stress by selecting proper fixture properties and experimental conditions.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
• /
• pp.643-648
• /
• 2011

Fatigue crack in most rails take place by rolling contact between wheel and rail in railway industry. Therefore, it is critical to understand the rolling contact phenomena, especially for the three-dimensional situation. In this paper the steady-state rolling contact problem of KTX wheel and rail (UIC60) has been studied with three-dimensional finite element analysis. The variation of contact pressure and contact stresses on rolling contact surface were obtained using the finite element method. The three-dimensional distribution of contact stresses on the contact surface are investigated. Results show that the distribution of shear stress and contact stress (von Mises) on the contact surface varies rapidly as a result of the variation of stick-slip region. The contact stress at the leading edge is greater than at the trailing edge because of stick and slip phenomena.