• Title/Summary/Keyword: Static Coefficient of Friction

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Performance evaluation of plasma nitrided 316L stainless steel during long term high temperature sodium exposure

  • Akash Singh;R. Thirumurugesan;S. Krishnakumar;Revati Rani;S. Chandramouli;P. Parameswaran;R. Mythili
    • Nuclear Engineering and Technology
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    • v.55 no.4
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    • pp.1468-1475
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    • 2023
  • Enhancement of wear resistance of components used in fast reactors is necessary for long service life of the components. Plasma nitriding is a promising surface modification technology to impart high hardness and improved wear resistance of various steel components. This study discusses the characterization of chrome nitrided SS316L casing ring used in secondary sodium pump of fast breeder reactor and its stability under long term sodium exposure. Microstructural and hardness analysis showed that stress relieved component could be chrome nitrided successfully to a thickness of about 100 ㎛. Assessment of in-sodium performance of the chrome nitrided casing ring subjected to long term exposure up to 5000h at 550℃, showed retention of chrome nitrided layer with a case depth almost similar to that before sodium exposure. A slight decrease in the hardness was observed due to prolonged high temperature sodium exposure. Tribological studies indicate very low coefficient of friction indicating the retention of good wear resistance of the coating even after long term sodium exposure.

Behaviour of a plane joint under horizontal cyclic shear loading

  • Dang, Wengang;Fruhwirt, Thomas;Konietzky, Heinz
    • Geomechanics and Engineering
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    • v.13 no.5
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    • pp.809-823
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    • 2017
  • This paper describes lab test results of artificial rock-like material samples having a plane joint. Cyclic shear tests were performed under different normal loads and different shear displacement amplitudes. For this purpose, multi-stage normal loading tests (30 kN, 60 kN, 90 kN, 180 kN, 360 kN and 480 kN) with cyclic excitation at frequency of 1.0 Hz and different shear displacement amplitudes (0.5 mm, 1.0 mm, 2.0 mm, 4.0 mm, 5.0 mm, and 8.0 mm) were conducted using the big shear box device GS-1000. Experimental results show, that shear forces increase with the increase of normal forces and quasi-static friction coefficient is larger than dynamic one. With the increase of normal loads, approaching the peak value of shear forces needs larger shear displacements. During each cycle the normal displacements increase and decrease (rotational behavior in every cycle). Peak angle of inclination increases with the increase of normal load. A phase shift between maximum shear displacement and maximum shear force is observed. The corresponding time shift decreases with increasing normal load and increases with increasing shear displacement amplitudes.

Partial safety factors for retaining walls and slopes: A reliability based approach

  • GuhaRay, Anasua;Baidya, Dilip Kumar
    • Geomechanics and Engineering
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    • v.6 no.2
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    • pp.99-115
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    • 2014
  • Uncertainties in design variables and design equations have a significant impact on the safety of geotechnical structures like retaining walls and slopes. This paper presents a possible framework for obtaining the partial safety factors based on reliability approach for different random variables affecting the stability of a reinforced concrete cantilever retaining wall and a slope under static loading conditions. Reliability analysis is carried out by Mean First Order Second Moment Method, Point Estimate Method, Monte Carlo Simulation and Response Surface Methodology. A target reliability index ${\beta}$ = 3 is set and partial safety factors for each random variable are calculated based on different coefficient of variations of the random variables. The study shows that although deterministic analysis reveals a safety factor greater than 1.5 which is considered to be safe in conventional approach, reliability analysis indicates quite high failure probability due to variation of soil properties. The results also reveal that a higher factor of safety is required for internal friction angle ${\varphi}$, while almost negligible values of safety factors are required for soil unit weight ${\gamma}$ in case of cantilever retaining wall and soil unit weight ${\gamma}$ and cohesion c in case of slope. Importance of partial safety factors is shown by analyzing two simple geotechnical structures. However, it can be applied for any complex system to achieve economization.

Evaluation of Portable Slipmeter using Human Perception (인간의 인지적 감각을 이용한 휴대용 미끄럼 측정기의 성능평가)

  • Choi, Hyung Jin;Kim, Jung Soo
    • Journal of the Korea Safety Management & Science
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    • v.16 no.3
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    • pp.267-271
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    • 2014
  • The objectives of this study were to evaluate the safe criteria of portable slipmeter using human perception onto the several different floor surfaces under contaminated conditions. It was difficult to find why many different slipmeters took there's own safe criteria. It is still unclear how thres hold values established in many literatures. Two different subjective slippery evaluating methods, AHP(Analytic Hierarchy Process) and Friedman test,were used to evaluate the perception of slipperiness of seven different floor surfaces under the contaminated condition with detergent solution. Twelve subjects worn same footwear and walked with self-selected step and cadence along the test floors. The SCOF(Static Coefficient of Friction) obtained for same test conditions with BOT-3000 was compared to perception of slipperiness to establish as a safe criteria. The very high significant correlation(r=0.97) was found between AHP and Friedman test. Also, The high significant correlation(r=0.96) was found between AHP and SCOF obtained with BOT-3000. The results suggested that the SCOF should be greater than 0.63 for safer walking. Perception rating obtained with AHP showed a high correlation with Friedman test and the SCOF obtained with BOT-3000 except for polished tile floor. The safe criteria obtained through this study were similar to ANSI/NFSIB101.1.

Analysis of Flexible Media Behavior by Dynamic Elastica (Dynamic Elastica에 의한 유연매체의 거동해석)

  • Hong, Sung-Kwon;Jee, Jung-Geun;Jang, Yong-Hoon;Park, No-Cheol;Park, Young-Pil
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.15 no.2 s.95
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    • pp.206-212
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    • 2005
  • In many machines handling lightweight and flexible media, such as magnetic tape drives, xerographic copiers and sewing machines, the media must transit an open space. It is important to predict the static and dynamic behavior of the sheets with a high degree of reliability. The nonlinear theory of the dynamic elastica has often been used to a nonlinear dynamic deflection model. In this paper, the governing equation is derived and simulated by the finite difference method. The parametric cubic curve is applied for defining the guide shape. The dynamic contact conditions suggested by Klarbring is used to predict the direction of the flexible media according to the initial velocity and the friction coefficient. The analysis is also compared to the conventional model, showing that after contacting a $45^{\circ}$ wall, the directions of flexible media of two models are different.

Analysis of Three-Pad Gas Foil Journal Bearing for Increasing Mechanical Preloads (3 패드 가스 포일 저널 베어링의 프리로드 증가에 따른 성능 해석)

  • Lee, Jong Sung;Kim, Tae Ho
    • Tribology and Lubricants
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    • v.30 no.1
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    • pp.1-8
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    • 2014
  • In this study, a three-pad gas foil journal bearing with a diameter of 40 mm and an axial length of 35 mm was modeled to predict the static and dynamic performances with regard to an increasing mechanical preload. The Reynolds equation for an isothermal and isoviscous ideal gas was coupled with a simple elastic foundation foil model to calculate the hydrodynamic pressure solution iteratively. In the prediction results, the journal eccentricity, journal attitude angle, and minimum film thickness decreased, but the friction torque increased with the preload. A quick comparison implied a lower load capacity but higher stability for a three-pad gas foil bearing compared to a one-pad gas foil journal bearing. The direct stiffness coefficients increased with the preload, but the cross-coupled stiffness coefficients decreased. The direct damping coefficient increased in the horizontal direction but decreased in the vertical direction as the preload increased. These model predictions will be useful as a benchmark against experimental test data.

Frictional responses of concrete-to-concrete bedding planes under complex loading conditions

  • Dang, Wengang;Konietzky, Heinz;Li, Xiang
    • Geomechanics and Engineering
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    • v.17 no.3
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    • pp.253-259
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    • 2019
  • Concrete-to-concrete bedding planes (CCBP) are observed from time to time due to the multistep hardening process of the concrete materials. In this paper, a series of direct/cyclic shear tests are performed on CCBP under static and dynamic normal load conditions to study the frictional behavior effect by the shear velocities, normal impact frequencies, horizontal shear frequencies, normal impact force amplitudes, horizontal shear displacement amplitudes and normal load levels. According to the experimental results, apparent friction coefficient k ($k=F_{Shear}/F_{Normal}$) shows different patterns under static and dynamic load conditions at the stable shear stage. k is nearly constant in direct shear tests under constant normal load conditions (DCNL), while it is cyclically changing with nearly constant peak value and valley value for the direct shear tests under dynamic normal load conditions (DDNL), where k increases with decreasing normal force and decreases with increasing normal force. Shear velocity has little influence on peak values of k for the DCNL tests, but increasing shear velocity leads to increasing valley values of k for DDNL tests. It is also found that, the valley values of k ascend with decreasing impact normal force amplitude in DDNL tests. The changing pattern of k for the cyclic shear tests under constant and dynamic normal load conditions (CCNL and CDNL tests) are similar, but the peak value of k is smaller in CDNL tests than that in CCNL tests. Normal load levels, shear displacement amplitudes, vertical impact frequencies, horizontal shear frequencies and normal impact force amplitudes have little influence on the changing pattern of k for the cyclic shear tests. The tests of this study provide useful data in understanding the frictional behavior of the CCBP under distinct loadings, and these findings are very important for analyzing the stability of the jointed geotechnical structures under complicated in situ stress conditions.

Evaluation of Landing Stability of Lunar Lander Considering Various Landing Conditions (다양한 착륙환경변수를 고려한 달착륙선 착륙안정성 평가)

  • Jeong, Hyun-Jae;Lim, Jae Hyuk;Kim, Jin-Won
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.46 no.2
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    • pp.124-132
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    • 2018
  • In this paper, landing stability evaluation of lunar lander considering various landing conditions was performed. The status of landing stability of the lunar lander is classified into stable landing, conditionally stable landing due to sliding and unstable landing due to tip-over. In particular, the quasi-static tip-over equation was rearranged considering the phenomena of lowering the center of gravity and extension of foot-pad interval of the landing gear. These results were compared by finite element model analysis results using a commercial software ABAQUS and its validity and accuracy were verified. The verified finite element model was used for examining the tendency of various environmental variables such as landing conditions, friction coefficient, lateral speed and slope of ground.

A Study on the Engineering Characteristic of scoria in Jeju-Do (제주도산 송이의 공학적 특성에 관한 연구)

  • Chun, Byung-Sik;Kim, Dong-Hoon;Kim, Young-Hun;Lee, Dong-Yeup
    • Proceedings of the Korean Geotechical Society Conference
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    • 2008.10a
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    • pp.1630-1637
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    • 2008
  • Jeju-do is a island formed by the volcanic activity and has more than 360 volcanic cones distributed widely along the long axis of the elliptically shaped island. The volcanic cones consist mainly of scoria, so called "Song-I" in the local dialect. In this study the chemical and soil mechanical properties of scoria being very different from those of the inland were investigated with the various tests. In the sieve-passing test the particle size of scoria had more than 10 of uniformity coefficient and gradation coefficient of 1 ~ 3, showing relatively homogenous distribution. Based on the uniformity classification, scoria was assorted into GW. In the large scale direct shear tested for measuring the mechanical strength of scoria the internal friction angle of red scoria was $37^{\circ}$ and that of black scoria was $36^{\circ}$. This indicated that there was no difference in the mechanical strength between two types of scoria. On the other hand, red and black scoria had $1.24{\times}10^{-3}$ to $3.55{\times}10^{-2}$ cm/sec of k values for the static water level permeability, thus being classified into a coarse or fine sand as compared with that representing the saturated soil. They also had 1.411 to $1.477\;g/cm^3$ of notably low $r_{dmax}$ values for the compaction test as compared with common soil, which was considered to be due to their low specific gravity and high porosity. In conclusion, the soil mechanic properties of scoria obtained from this study are thought to be very helpful for reducing lots of trial and error happening in the civil engineering construction.

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Earthquake-Resistant Design of Cantilever Retaining-Walls with Sloped Base (기초슬래브의 밑면이 경사진 캔티레바식 옹벽의 내진설계)

  • Kim, Hong Taek
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.10 no.3
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    • pp.87-98
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    • 1990
  • The present Study dealt with the earthquake-resistant design of cantilever retaining walls supporting cohesionless soils. With design examples of three different types of cantilever retaining walls, the factors of safety against sliding were computed at various values of horizontal acceleration coefficient and compared with each other. The horizontal inertia effect due to the weights of concrete wall itself and a portion of backfill was taken into account in the analyses, and also Mononobe-Okabe pseudo-static solution method was modified to deal with various states different from limiting equilibrium state. From the analyses of safety against sliding, it was found that a cantilever retaining wall with sloped base was the most efficient type in earthquake resistant design. It was also found that by sloping the base, the width of the base slab could be reduced, resulting in the least volume of concrete, excavation and backfill as compared to the other types of walls. In the case of a cantilever retaining wall with sloped feel, the efficiency similar to that of a wall with sloped base could be expected under static loading as well as at relatively low level of earthquake loading. However, this efficiency became vanished with the increase of horizontal acceleration coefficient, since the rate of reduction in developed earth pressures on the heel became smaller. In addition, the design charts with different soil friction angles as well as with different earthquake resistant design criteria of safety factor against sliding were presented for the design of cantilever retaining walls sith sloped base.

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