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Sample records for wall friction

  1. Shear localization and effective wall friction in a wall bounded granular flow

    Directory of Open Access Journals (Sweden)

    Artoni Riccardo

    2017-01-01

    Full Text Available In this work, granular flow rheology is investigated by means of discrete numerical simulations of a torsional, cylindrical shear cell. Firstly, we focus on azimuthal velocity profiles and study the effect of (i the confining pressure, (ii the particle-wall friction coefficient, (iii the rotating velocity of the bottom wall and (iv the cell diameter. For small cell diameters, azimuthal velocity profiles are nearly auto-similar, i.e. they are almost linear with the radial coordinate. Different strain localization regimes are observed : shear can be localized at the bottom, at the top of the shear cell, or it can be even quite distributed. This behavior originates from the competition between dissipation at the sidewalls and dissipation in the bulk of the system. Then we study the effective friction at the cylindrical wall, and point out the strong link between wall friction, slip and fluctuations of forces and velocities. Even if the system is globally below the sliding threshold, force fluctuations trigger slip events, leading to a nonzero wall slip velocity and an effective wall friction coefficient different from the particle-wall one. A scaling law was found linking slip velocity, granular temperature in the main flow direction and effective friction. Our results suggest that fluctuations are an important ingredient for theories aiming to capture the interface rheology of granular materials.

  2. Three measuring techniques for assessing the mean wall skin friction in wall-bounded flows

    Science.gov (United States)

    Zanoun, E.-S.; Jehring, L.; Egbers, C.

    2014-04-01

    The present paper aims at evaluating the mean wall skin friction data in laminar and turbulent boundary layer flows obtained from two optical and one thermal measuring techniques, namely, laser-Doppler anemometry (LDA), oil-film interferometry (OFI), and surface hot-film anemometry (SHFA), respectively. A comparison among the three techniques is presented, indicating close agreement in the mean wall skin friction data obtained, directly, from both the OFI and the LDA near-wall mean velocity profiles. On the other hand, the SHFA, markedly, over estimates the mean wall skin friction by 3.5-11.7% when compared with both the LDA and the OFI data, depending on the thermal conductivity of the substrate and glue material, probe calibration, probe contamination, temperature drift and Reynolds number. Satisfactory agreement, however, is observed among all three measuring techniques at higher Reynolds numbers, Re x >106, and within ±5% with empirical relations extracted from the literature. In addition, accurate velocity data within the inertial sublayer obtained using the LDA supports the applicability of the Clauser method to evaluate the wall skin friction when appropriate values for the constants of the logarithmic line are utilized.

  3. Contribution of velocity-vorticity correlations to the frictional drag in wall-bounded turbulent flows

    Science.gov (United States)

    Yoon, Min; Ahn, Junsun; Hwang, Jinyul; Sung, Hyung Jin

    2016-08-01

    The relationship between the frictional drag and the velocity-vorticity correlations in wall-bounded turbulent flows is derived from the mean vorticity equation. A formula for the skin friction coefficient is proposed and evaluated with regards to three canonical wall-bounded flows: turbulent boundary layer, turbulent channel flow, and turbulent pipe flow. The frictional drag encompasses four terms: advective vorticity transport, vortex stretching, viscous, and inhomogeneous terms. Drag-reduced channel flow with the slip condition is used to test the reliability of the formula. The advective vorticity transport and vortex stretching terms are found to dominate the contributions to the frictional drag.

  4. On Turbulent Contribution to Frictional Drag in Wall-Bounded Turbulent Flow

    Institute of Scientific and Technical Information of China (English)

    LI Feng-Chen; KAWAGUCHI Yasuo; HISHIDA Koichi; OSHIMA Marie

    2006-01-01

    @@ We propose a simple model for turbulent contribution to the frictional drag in a wall-bounded turbulent flow based on the characteristic parameters of turbulent bursting events. It is verified on water and drag-reducing surfactant solution flows investigated by particle image velocimetry in experiments. It is obtained that the turbulent contribution to the skin friction factor is linearly proportional to the product of the spatial frequency and strength of turbulent bursts originated from the wall.

  5. Rough-wall turbulent boundary layers with constant skin friction

    KAUST Repository

    Sridhar, A.

    2017-03-28

    A semi-empirical model is presented that describes the development of a fully developed turbulent boundary layer in the presence of surface roughness with length scale ks that varies with streamwise distance x . Interest is centred on flows for which all terms of the von Kármán integral relation, including the ratio of outer velocity to friction velocity U+∞≡U∞/uτ , are streamwise constant. For Rex assumed large, use is made of a simple log-wake model of the local turbulent mean-velocity profile that contains a standard mean-velocity correction for the asymptotic fully rough regime and with assumed constant parameter values. It is then shown that, for a general power-law external velocity variation U∞∼xm , all measures of the boundary-layer thickness must be proportional to x and that the surface sand-grain roughness scale variation must be the linear form ks(x)=αx , where x is the distance from the boundary layer of zero thickness and α is a dimensionless constant. This is shown to give a two-parameter (m,α) family of solutions, for which U+∞ (or equivalently Cf ) and boundary-layer thicknesses can be simply calculated. These correspond to perfectly self-similar boundary-layer growth in the streamwise direction with similarity variable z/(αx) , where z is the wall-normal coordinate. Results from this model over a range of α are discussed for several cases, including the zero-pressure-gradient ( m=0 ) and sink-flow ( m=−1 ) boundary layers. Trends observed in the model are supported by wall-modelled large-eddy simulation of the zero-pressure-gradient case for Rex in the range 108−1010 and for four values of α . Linear streamwise growth of the displacement, momentum and nominal boundary-layer thicknesses is confirmed, while, for each α , the mean-velocity profiles and streamwise turbulent variances are found to collapse reasonably well onto z/(αx) . For given α , calculations of U+∞ obtained from large-eddy simulations are streamwise

  6. Interface Friction of Double-Walled Carbon Nanotubes Investigated Using Molecular Dynamics †

    Directory of Open Access Journals (Sweden)

    Cheng-Da Wu

    2017-03-01

    Full Text Available The interface friction characteristics of double-walled carbon nanotubes (DWCNTs are studied using molecular dynamics simulations based on the Tersoff potential. The effects of the DWCNT type, outer shell diameter, and temperature are evaluated. The simulation results show that when an inner shell is being pulled out from a DWCNT, the friction force and normal force between shells increase with increasing the outer shell diameter. The noise of the friction force significantly increases with the increasing temperature. Zigzag@zigzag and armchair@armchair DWCNTs exhibit larger friction forces and smaller normal forces compared to those of chiral@chiral DWCNTs.

  7. Effect of frictions on cross section quality of thin-walled tube NC bending

    Institute of Scientific and Technical Information of China (English)

    YANG He; GU Rui-jie; ZHAN Mei; LI Heng

    2006-01-01

    The effect of frictions between dies and tube on the cross section quality of thin-walled tube numerical controlled(NC) bending was studied by numerical simulation method, combined with theoretical analysis and experiment. The results show that the frictions between mandrel, wiper, pressure die, bending die and tube have a significant and complicate effect on the section quality of thin-walled tube NC bending. To improve the section quality, frictions between mandrel, wiper and tube should be decreased, but the frictions between the pressure die, bending die and tube increase. The effect on the section distortion is more significant from mandrel, wiper, pressure die to bending die and the effect on the wall thinning more significant from mandrel, pressure die, wiper, to bending die. The effects of frictions between all dies and tube on wall thinning are smaller than their effects on section distortion.Mandrel and wiper should be lubricated well and drawing oil is used to lubricate them in actual production. The frictions between pressure die, bending die and tube should be increased and the dry friction is used between pressure die, bending die and tube in actual production.

  8. Numerical analysis of effect of friction between diaphragm wall and soil on braced excavation

    Institute of Scientific and Technical Information of China (English)

    刁钰; 郑刚

    2008-01-01

    A plane strain finite element model was established to investigate the effect of friction between diaphragm wall and soil on braced excavation. The behavior of interface between diaphragm wall and soil was simulated with the interface model of ABAQUS. Parametric studies were conducted with different diaphragm wall external friction angles δ. The results show that deflection of diaphragm wall and ground surface settlement decrease with the decrease of δ. However, the reduction effect on diaphragm wall deflection is the most significant at the depth where the maximum wall deflection occurs and can be neglected at the wall base. The ratio between wall deep inward component and wall cantilever component reaches its peak value 2.7 when δ=5°. The ratio of the maximum ground surface settlement to the maximum wall lateral deflection decreases at a reduced rate with the increase of δ. For excavation with braced diaphragm wall, the effect of friction between diaphragm and soil on the deflection of diaphragm wall and ground settlement, especially the distribution of ground surface settlement behind diaphragm, should be taken into account.

  9. A relation between velocity-vorticity correlations and skin friction in wall-bounded turbulent flows

    Science.gov (United States)

    Yoon, Min; Ahn, Junsun; Hwang, Jinyul; Sung, Hyung Jin

    2016-11-01

    The relationship between the skin friction and the velocity-vorticity correlations in wall-bounded turbulent flows is derived from the mean vorticity equation. A formula for the skin friction coefficient (Cf) is proposed and evaluated with regards to three canonical wall-bounded flows: turbulent boundary layer, turbulent channel flow, and turbulent pipe flow. The skin friction coefficient can be derived from the mean spanwise vorticity at the wall. Double integration with respect to the wall-normal direction (from 0 to y) is needed to derive Cf from the second derivative of the mean spanwise vorticity in the mean spanwise vorticity equation. One more integration is needed to find the contribution of each component to Cf from the wall to the boundary layer edge (from 0 to δ) . The present formula encompasses four terms: advective vorticity transport, vortex stretching, viscous, and inhomogeneous terms. Drag-reduced channel flow with the slip condition is used to test the reliability of the formula. The advective vorticity transport and vortex stretching terms are found to dominate the contributions to the frictional drag. This work was supported by the Creative Research Initiatives (No. 2016-004749) program of the National Research Foundation of Korea (MSIP).

  10. Fluid friction and wall viscosity of the 1D blood flow model

    CERN Document Server

    Wang, Xiao-Fei; Matsukawa, Mami; Ghigo, Arthur; Lagrée, Pierre-Yves; Fullana, Jose-Maria

    2015-01-01

    We study the behavior of the pulse waves of water into a flexible tube for application to blood flow simulations. In pulse waves both fluid friction and wall viscosity are damping factors, and difficult to evaluate separately. In this paper, the coefficients of fluid friction and wall viscosity are estimated by fitting a nonlinear 1D flow model to experimental data. In the experimental setup, a distensible tube is connected to a piston pump at one end and closed at another end. The pressure and wall displacements are measured simultaneously. A good agreement between model predictions and experiments was achieved. For amplitude decrease, the effect of wall viscosity on the pulse wave has been shown as important as that of fluid viscosity.

  11. Shear flow of dense granular materials near smooth walls. II. Block formation and suppression of slip by rolling friction.

    Science.gov (United States)

    Shojaaee, Zahra; Brendel, Lothar; Török, János; Wolf, Dietrich E

    2012-07-01

    The role of rotational degrees of freedom and of microscopic contact properties at smooth walls in two dimensional planar shear has been investigated by contact dynamics simulations of round hard frictional particles. Our default system setup consists of smooth frictional walls, giving rise to slip. We show that there exists a critical microscopic friction coefficient at the walls, above which they are able to shear the granular medium. We observe distinctive features at this critical point, which to our knowledge have not been reported before. Activating rolling friction at smooth walls reduces slip, leading to similar shear behavior as for rough walls (with particles glued on their surface). Our simulations with rough walls are in agreement with previous results, provided the roughness is strong enough. In the limit of small roughness amplitude, however, the distinctive features of shearing with smooth walls are confirmed.

  12. Simulation of die wall friction's effect on density distribution in metallic powder compaction

    Institute of Scientific and Technical Information of China (English)

    周照耀; 赵伟斌; 陈普庆; 陈维平; 邵明; 王郡文

    2002-01-01

    A computer simulation procedure for metal powder die compaction was described. Friction behavior of metal powder during cold compaction was simulated by the finite element method. The movement of powder relative to the die wall was taken into consideration by utilizing the shear friction model. Friction between the powder and the rigid die wall leads to inhomogeneous density distribution during the compaction process. The floating die technique and double punch pressing can attain more homogenous compacts than the fixed die technique can do. The results obtained from numerical analysis agree well with the experimental results. Simulation model was built in MSC.Mentat, and MSC.Marc software was used to calculate the powder compaction process.

  13. Structure and Properties of Thick-Walled Joints of Alloy 1570s Prepared by Friction Stir Welding

    Science.gov (United States)

    Velichko, O. V.; Ivanov, S. Yu.; Karkhin, V. A.; Lopota, V. A.; Makhin, I. D.

    2016-09-01

    The microstructure and mechanical properties of thick-walled joints of Al - Mg - Sc alloy 1570S, prepared by friction stir welding are studied. Joint microstructural and mechanical inhomogeneity are revealed.

  14. The effect of wall friction on the current-sheet speed of a magnetically driven shock tube

    DEFF Research Database (Denmark)

    Chang, C.T.

    1971-01-01

    The effect of wall friction on the current-sheet speed is examined by taking some plausible forms of the friction into consideration. The analysis shows that the current-sheet always attains a steady state regardless of the types of friction concerned. It further shows that the experimentally...... observed velocity limitation of the current-sheet at discharge conditions of high voltage and low pressure might be attributed to a friction drag varying linearly with the driving current and the current-sheet speed....

  15. Wall mass transfer and pressure gradient effects on turbulent skin friction

    Science.gov (United States)

    Watson, R. D.; Balasubramanian, R.

    1984-01-01

    The effects of mass injection and pressure gradients on the drag of surfaces were studied theoretically with the aid of boundary-layer and Navier-Stokes codes. The present investigation is concerned with the effects of spatially varying the injection in the case of flat-plate drag. Effects of suction and injection on wavy wall surfaces are also explored. Calculations were performed for 1.2 m long surfaces, one flat and the other sinusoidal with a wavelength of 30.5 cm. Attention is given to the study of the effect of various spatial blowing variations on flat-plate skin friction reduction, local skin friction coefficient calculated by finite difference boundary-layer code and Navier-Stokes code, and the effect of phase-shifting sinusoidal mass transfer on the drag of a sinusoidal surface.

  16. Investigation of the effect of wall friction on the flow rate in 2D and 3D Granular Flow

    Science.gov (United States)

    Carballo-Ramirez, Brenda; Pleau, Mollie; Easwar, Nalini; Birwa, Sumit; Shah, Neil; Tewari, Shubha

    We have measured the mass flow rate of spherical steel spheres under gravity in vertical, straight-walled 2 and 3-dimensional hoppers, where the flow velocity is controlled by the opening size. Our measurements focus on the role of friction and its placement along the walls of the hopper. In the 2D case, an increase in the coefficient of static friction from μ = 0.2 to 0.6 is seen to decrease the flow rate significantly. We have changed the placement of frictional boundaries/regions from the front and back walls of the 2D hopper to the side walls and floor to investigate the relative importance of the different regions in determining the flow rate. Fits to the Beverloo equation show significant departure from the expected exponent of 1.5 in the case of 2D flow. In contrast, 3D flow rates do not show much dependence on wall friction and its placement. We compare the experimental data to numerical simulations of gravity driven hopper granular flow with varying frictional walls constructed using LAMMPS*. *http://lammps.sandia.gov Supported by NSF MRSEC DMR 0820506.

  17. Bobbin-Tool Friction-Stir Welding of Thick-Walled Aluminum Alloy Pressure Vessels

    Energy Technology Data Exchange (ETDEWEB)

    Dalder, E C; Pastrnak, J W; Engel, J; Forrest, R S; Kokko, E; Ternan, K M; Waldron, D

    2007-06-06

    It was desired to assemble thick-walled Al alloy 2219 pressure vessels by bobbin-tool friction-stir welding. To develop the welding-process, mechanical-property, and fitness-for-service information to support this effort, extensive friction-stir welding-parameter studies were conducted on 2.5 cm. and 3.8 cm. thick 2219 Al alloy plate. Starting conditions of the plate were the fully-heat-treated (-T62) and in the annealed (-O) conditions. The former condition was chosen with the intent of using the welds in either the 'as welded' condition or after a simple low-temperature aging treatment. Since preliminary stress-analyses showed that stresses in and near the welds would probably exceed the yield-strength of both 'as welded' and welded and aged weld-joints, a post-weld solution-treatment, quenching, and aging treatment was also examined. Once a suitable set of welding and post-weld heat-treatment parameters was established, the project divided into two parts. The first part concentrated on developing the necessary process information to be able to make defect-free friction-stir welds in 3.8 cm. thick Al alloy 2219 in the form of circumferential welds that would join two hemispherical forgings with a 102 cm. inside diameter. This necessitated going to a bobbin-tool welding-technique to simplify the tooling needed to react the large forces generated in friction-stir welding. The bobbin-tool technique was demonstrated on both flat-plates and plates that were bent to the curvature of the actual vessel. An additional issue was termination of the weld, i.e. closing out the hole left at the end of the weld by withdrawal of the friction-stir welding tool. This was accomplished by friction-plug welding a slightly-oversized Al alloy 2219 plug into the termination-hole, followed by machining the plug flush with both the inside and outside surfaces of the vessel. The second part of the project involved demonstrating that the welds were fit for the intended

  18. Linear modeling of turbulent skin-friction reduction due to spanwise wall motion

    Science.gov (United States)

    Duque-Daza, Carlos; Baig, Mirza; Lockerby, Duncan; Chernyshenko, Sergei; Davies, Christopher; University of Warwick Team; Imperial College Team; Cardiff University Team

    2012-11-01

    We present a study on the effect of streamwise-travelling waves of spanwise wall velocity on the growth of near-wall turbulent streaks using a linearized formulation of the Navier-Stokes equations. The changes in streak amplification due to the travelling waves induced by the wall velocity are compared to published results of direct numerical simulation (DNS) predictions of the turbulent skin-friction reduction over a range of parameters; a clear correlation between these two sets of results is observed. Additional linearized simulations but at a much higher Reynolds numbers, more relevant to aerospace applications, produce results that show no marked differences to those obtained at low Reynolds number. It is also observed that a close correlation exists between DNS data of drag reduction and a very simple characteristic of the ``generalized'' Stokes layer generated by the streamwise-travelling waves. Carlos.Duque-Daza@warwick.ac.uk - School of Engineering, University of Warwick, Coventry CV4 7AL, UK caduqued@unal.edu.co - Department of Mechanical and Mechatronics Engineering, Universidad Nacional de Colombia.

  19. Analysis of flame acceleration induced by wall friction in open tubes

    CERN Document Server

    Akkerman, V'yacheslav; Bychkov, Vitaly; Eriksson, Lars-Erik; 10.1063/1.3425646

    2012-01-01

    Spontaneous flame acceleration leading to explosion triggering in open tubes/channels due to wall friction was analytically and computationally studied. It was first demonstrated that the acceleration is effected when the thermal expansion across the flame exceeds a critical value depending on the combustion configuration. For the axisymmetric flame propagation in cylindrical tubes with both ends open, a theory of the initial (exponential) stage of flame acceleration in the quasi-isobaric limit was developed and substantiated by extensive numerical simulation of the hydrodynamics and combustion with an Arrhenius reaction. The dynamics of the flame shape, velocity, and acceleration rate, as well as the velocity profile ahead and behind the flame, have been determined.

  20. Wall-Friction Support of Vertical Loads in Submerged Sand and Gravel Columns

    Energy Technology Data Exchange (ETDEWEB)

    Walton, O. R. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Vollmer, H. J. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Hepa, V. S. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2015-08-25

    Laboratory studies of the ‘floor-loads’ under submerged vertical columns of sand and/or gravel indicate that such loads can be approximated by a buoyancy-corrected Janssen-silo-theory-like relationship. Similar to conditions in storage silos filled with dry granular solids, most of the weight of the sand or gravel is supported by wall friction forces. Laboratory measurements of the loads on the floor at the base of the water-filled columns (up to 25-diameters tall) indicate that the extra floor-load from the addition of the granular solid never exceeded the load that would exist under an unsupported (wide) bed of submerged sand or gravel that has a total depth corresponding to only two column-diameters. The measured floorloads reached an asymptotic maximum value when the depth of granular material in the columns was only three or four pipe-diameters, and never increased further as the columns were filled to the top (e.g. up to heights of 10 to 25 diameters). The floor-loads were stable and remained the same for days after filling. Aggressive tapping (e.g. hitting the containing pipe on the outside, manually with a wrench up and down the height and around the circumference) could increase (and occasionally decrease) the floor load substantially, but there was no sudden collapse or slumping to a state without significant wall friction effects. Considerable effort was required, repeatedly tapping over almost the entire column wall periphery, in order to produce floor-loads that corresponded to the total buoyancy-corrected weight of granular material added to the columns. Projecting the observed laboratory behavior to field conditions would imply that a stable floor-load condition, with only a slightly higher total floor pressure than the preexisting hydrostatic-head, would exist after a water-filled bore-hole is filled with sand or gravel. Significant seismic vibration (either a large nearby event or many micro-seismic events over an extended period) would likely

  1. Validation of Wall Friction Model in SPACE-3D Module with Two-Phase Cross Flow Experiment

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Chi-Jin; Yang, Jin-Hwa; Cho, Hyoung-Kyu; Park, Goon-Cher [Seoul National University, Seoul (Korea, Republic of); Euh, Dong-Jin [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2015-10-15

    In this study, SPACE-3D was used to simulate the Yang's experiment, and obtained the local variables. Then, the wall friction model used in SPACE-3D was validated by comparing the two-phase cross flow experimental results with the calculated local variables. In this study, the two-phase cross flow experiment was modeled by SPACE-3D to validate the wall friction model in multi-dimensional module. Considering the realistic phenomena in the reactor, however, recent trends in safety analysis codes have tended to adopt multi-dimensional module to simulate the complex flow more accurately. Even though the module was applied to deal the multi-dimensional phenomena, implemented models in that are one-dimensional empirical models. Therefore, prior to applying the multi-dimensional module, the constitutive models implemented in the codes need to be validated. In the downcomer of Advanced Power Reactor 1400 (APR1400) which has direct vessel injection (DVI) lines as an emergency core cooling system, multi-dimensional two-phase flow may occur due to the Loss-of-Coolant-Accident (LOCA). The accurate prediction about that is high relevance to evaluation of the integrity of the reactor core. For this reason, Yang performed an experiment that was to investigate the two-dimensional film flow which simulated the two-phase cross flow in the upper downcomer, and obtained the local liquid film velocity and thickness data. From these data, it could be possible to validate the friction models in multi-dimensional module of system analysis codes. Compared with the experiment, SPACE-3D underestimated the liquid film velocity and overestimated the liquid film thickness. From these results, it was clarified that the Wallis correlation which is used as a wall friction model in SPACE-3D overestimates the wall friction. On the other hand, H.T.F.S. correlation which is used as the wall friction in MARS-multiD underestimates the wall friction.

  2. Effect of rolling friction on wall pressure, discharge velocity and outflow of granular material from a flat-bottomed bin

    Institute of Scientific and Technical Information of China (English)

    R.Balevi(c)ius; I.Sielamowicz; Z.Mróz; R.Ka(c)ianauskas

    2012-01-01

    The present paper provides both experimental and DEM analyses of the filling and discharge of pea grains from a 3D flat-bottomed bin.In the DEM model,the fixed mean values of the experimentally determined single particle data,such as the particle density,Young's modulus,Poisson's ratio as well as the sliding and rolling friction coefficients were incorporated to analyse their effects on the macroscale indicators,such as the wall pressure,discharge velocities and material outflow parameters.The effect of rolling friction was studied based on the experimentally measured single particle rolling friction coefficient.This analysis is aimed at the quantitative prediction of flow parameters as related to the identification of material parameters.

  3. Assessment of wall friction model in multi-dimensional component of MARS with air–water cross flow experiment

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Jin-Hwa [Nuclear Thermal-Hydraulic Engineering Laboratory, Seoul National University, Gwanak 599, Gwanak-ro, Gwanak-gu, Seoul 151-742 (Korea, Republic of); Korea Atomic Energy Research Institute, 989-111, Daedeok-daero, Yuseong-gu, Daejeon 305-600 (Korea, Republic of); Choi, Chi-Jin [Nuclear Thermal-Hydraulic Engineering Laboratory, Seoul National University, Gwanak 599, Gwanak-ro, Gwanak-gu, Seoul 151-742 (Korea, Republic of); Cho, Hyoung-Kyu, E-mail: chohk@snu.ac.kr [Nuclear Thermal-Hydraulic Engineering Laboratory, Seoul National University, Gwanak 599, Gwanak-ro, Gwanak-gu, Seoul 151-742 (Korea, Republic of); Euh, Dong-Jin [Korea Atomic Energy Research Institute, 989-111, Daedeok-daero, Yuseong-gu, Daejeon 305-600 (Korea, Republic of); Park, Goon-Cherl [Nuclear Thermal-Hydraulic Engineering Laboratory, Seoul National University, Gwanak 599, Gwanak-ro, Gwanak-gu, Seoul 151-742 (Korea, Republic of)

    2017-02-15

    Recently, high precision and high accuracy analysis on multi-dimensional thermal hydraulic phenomena in a nuclear power plant has been considered as state-of-the-art issues. System analysis code, MARS, also adopted a multi-dimensional module to simulate them more accurately. Even though it was applied to represent the multi-dimensional phenomena, but implemented models and correlations in that are one-dimensional empirical ones based on one-dimensional pipe experimental results. Prior to the application of the multi-dimensional simulation tools, however, the constitutive models for a two-phase flow need to be carefully validated, such as the wall friction model. Especially, in a Direct Vessel Injection (DVI) system, the injected emergency core coolant (ECC) on the upper part of the downcomer interacts with the lateral steam flow during the reflood phase in the Large-Break Loss-Of-Coolant-Accident (LBLOCA). The interaction between the falling film and lateral steam flow induces a multi-dimensional two-phase flow. The prediction of ECC flow behavior plays a key role in determining the amount of coolant that can be used as core cooling. Therefore, the wall friction model which is implemented to simulate the multi-dimensional phenomena should be assessed by multidimensional experimental results. In this paper, the air–water cross film flow experiments simulating the multi-dimensional phenomenon in upper part of downcomer as a conceptual problem will be introduced. The two-dimensional local liquid film velocity and thickness data were used as benchmark data for code assessment. And then the previous wall friction model of the MARS-MultiD in the annular flow regime was modified. As a result, the modified MARS-MultiD produced improved calculation result than previous one.

  4. The response of skin friction, wall heat transfer and pressure drop to wall waviness in the presence of buoyancy

    Directory of Open Access Journals (Sweden)

    C. N. B. Rao

    1982-01-01

    Full Text Available Laminar natural convection flow and heat transfer of a viscous incompressible fluid confined between two long vertical wavy walls has been analysed taking the fluid properties constant and variable. In particular, attention is restricted to estimate the effects of viscous dissipation and wall waviness on the flow and heat transfer characteristics. Use has been made of a linearization technique to simplify the governing equations and of Galerkin's method in the solution. The solutions obtained for the velocity and the temperature-fields hold good for all values of the Grashof number and wave number of the wavy walls.

  5. THE IMPACT OF WALL ROUGHNESS OF THE UNDERGROUND AIRWAYS ON THE VALUE OF HYDRAULIC FRICTION FACTOR

    Directory of Open Access Journals (Sweden)

    Vladimir Rendulić

    1991-12-01

    Full Text Available The studies of turbulent flows in round pipes resulted in many hydraulic formulas up to these days, which can also serve in projecting to calculate the resistance to the air flow in underground openings. The report discusses the way of establishing the hydraulic friction factor of untimbered underground workings when the value of equivalent roughness is obtained by measuring the ventilation parameters in a similar working of some other mine. A double reticular nomogram has been constructed for the fast determination of friction coefficient from the known roughness of an underground working (the paper is published in Croatian.

  6. Fabrication of Aluminum Foam-Filled Thin-Wall Steel Tube by Friction Welding and Its Compression Properties

    Directory of Open Access Journals (Sweden)

    Yoshihiko Hangai

    2014-09-01

    Full Text Available Aluminum foam has received considerable attention in various fields and is expected to be used as an engineering material owing to its high energy absorption properties and light weight. To improve the mechanical properties of aluminum foam, combining it with dense tubes, such as aluminum foam-filled tubes, was considered necessary. In this study, an aluminum foam-filled steel tube, which consisted of ADC12 aluminum foam and a thin-wall steel tube, was successfully fabricated by friction welding. It was shown that a diffusion bonding layer with a thickness of approximately 10 μm was formed, indicating that strong bonding between the aluminum foam and the steel tube was realized. By the X-ray computed tomography observation of pore structures, the fabrication of an aluminum foam-filled tube with almost uniform pore structures over the entire specimen was confirmed. In addition, it was confirmed that the aluminum foam-filled steel tube exhibited mechanical properties superior to those of the ADC12 aluminum foam and steel tube. This is considered to be attributed to the combination of the aluminum foam and steel tube, which particularly prevents the brittle fracture and collapse of the ADC12 foam by the steel tube, along with the strong metal bonding between the aluminum foam and the steel tube.

  7. Experimental investigation on friction and squeezing of roof structure key blocks corner upon long-wall face

    Institute of Scientific and Technical Information of China (English)

    Qingxiang Huang

    2005-01-01

    The coefficients of friction and squeezing of the key blocks corner in the roof structure of underground coalface are key factors to roof structure stability quantitative analysis. In this paper, through the special test of three-type corner friction and squeezing of real rock specimens, and physical simulation test on the roof key blocks of roof structure as well as the finite element calculation of the corner stress distribution and failure mechanism, the characteristics of friction and squeezing of the roof key blocks corner are revealed. It is found that the friction angle of the roof key blocks corner is the residual friction angle, and the frictional angle of the roof key blocks is 22-32° (average 27°), so the friction coefficient is determined as 0.5. It also found the squeezing strength is less than the uniaxial strength, and the squeezing coefficient of the roof blocks corner is determined as 0.4. Based on the results, the ground control theory can be updated from qualitative analysis to quantitative analysis.

  8. Numerical studies on the heat transfer and friction characteristics of the first wall inserted with the screw blade for water cooled ceramic breeder blanket of CFETR

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Kecheng [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031 (China); University of Science and Technology of China, Hefei, Anhui 230037 (China); Ma, Xuebin; Cheng, Xiaoman [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031 (China); Liu, Songlin, E-mail: slliu@ipp.ac.cn [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031 (China)

    2016-03-15

    Highlights: • Enhanced heat transfer and friction characteristics of the FW inserted with screw blade is investigated. • The screw blade structure optimization was done on the screw pitch and diameter. • Decreasing screw pitch and increasing screw diameter could further enhance heat transfer accompanied with increasing flow resistance. • Evaluate the overall enhanced heat performance by using the PEC value. - Abstract: The Water Cooled Ceramic Breeder (WCCB) blanket based on Pressurized Water Reactor (PWR) condition is one of the blanket candidates for Chinese Fusion Engineering Test Reactor (CFETR). The first wall (FW) which plays an important part in the blanket design must remove the high heat flux radiated from plasma and nuclear heat deposition on the structure in any operating conditions. In this paper, the characteristics of enhanced heat transfer and friction for the FW with the inserted screw blade are studied by the numerical method. After the comparison between the numerical and experimental results, the standard k–ε turbulent model is selected to do the numerical calculation. The numerical results show that the peak temperature of RAFM steel could be reduced by decreasing screw pitch or increasing screw diameter, while accompanied with ascending flow resistance. Besides, among all of the chosen calculation cases compared with the smooth channel, the maximum value of temperature reduction is 10 °C under the conditions of heat flux of 0.5 MW/m{sup 2} as well as screw pitch of 18 mm and screw diameter of 6 mm. The maximum increment ratio of the friction factor is 257% under the conditions of screw pitch of 10 mm and screw diameter of 4 mm. Furthermore, screw blade of 74 mm pitch and 4 mm diameter presents the highest overall performance evaluation criterion (PEC) value of 0.93 under Reynolds number of 270 000 conditions, and shows the best overall heat transfer enhancement performance.

  9. Interaction between a normal shock wave and a turbulent boundary layer at high transonic speeds. Part 1: Pressure distribution. Part 2: Wall shear stress. Part 3: Simplified formulas for the prediction of surface pressures and skin friction

    Science.gov (United States)

    Adamson, T. C., Jr.; Liou, M. S.; Messiter, A. F.

    1980-01-01

    An asymptotic description is derived for the interaction between a shock wave and a turbulent boundary layer in transonic flow, for a particular limiting case. The dimensionless difference between the external flow velocity and critical sound speed is taken to be much smaller than one, but large in comparison with the dimensionless friction velocity. The basic results are derived for a flat plate, and corrections for longitudinal wall curvature and for flow in a circular pipe are also shown. Solutions are given for the wall pressure distribution and the shape of the shock wave. Solutions for the wall shear stress are obtained, and a criterion for incipient separation is derived. Simplified solutions for both the wall pressure and skin friction distributions in the interaction region are given. These results are presented in a form suitable for use in computer programs.

  10. Drop Weight Impact Behavior of Al-Si-Cu Alloy Foam-Filled Thin-Walled Steel Pipe Fabricated by Friction Stir Back Extrusion

    Science.gov (United States)

    Hangai, Yoshihiko; Nakano, Yukiko; Utsunomiya, Takao; Kuwazuru, Osamu; Yoshikawa, Nobuhiro

    2017-02-01

    In this study, Al-Si-Cu alloy ADC12 foam-filled thin-walled stainless steel pipes, which exhibit metal bonding between the ADC12 foam and steel pipe, were fabricated by friction stir back extrusion. Drop weight impact tests were conducted to investigate the deformation behavior and mechanical properties of the foam-filled pipes during dynamic compression tests, which were compared with the results of static compression tests. From x-ray computed tomography observation, it was confirmed that the fabricated foam-filled pipes had almost uniform porosity and pore size distributions. It was found that no scattering of the fragments of collapsed ADC12 foam occurred for the foam-filled pipes owing to the existence of the pipe surrounding the ADC12 foam. Preventing the scattering of the ADC12 foam decreases the drop in stress during dynamic compression tests and therefore improves the energy absorption properties of the foam.

  11. Evidence of rare backflow and skin-friction critical points in near-wall turbulence using micropillar imaging

    OpenAIRE

    Brücker, C.

    2015-01-01

    © 2015 AIP Publishing LLC. The recent discovery of rare backflow events in turbulent boundary layer flows based on the analysis of simulation data has again raised the need of experimental visualizations of wall-shear stress fields in unsteady flows. The localization of critical points, which are thought to strongly correlate with large-scale events in the log-layer, is of importance. Up to now, there is no experimental proof of these rare events and their topological patterns. Their existenc...

  12. wall

    Directory of Open Access Journals (Sweden)

    Irshad Kashif

    2016-01-01

    Full Text Available Maintaining indoor climatic conditions of buildings compatible with the occupant comfort by consuming minimum energy, especially in a tropical climate becomes a challenging problem for researchers. This paper aims to investigate this problem by evaluating the effect of different kind of Photovoltaic Trombe wall system (PV-TW on thermal comfort, energy consumption and CO2 emission. A detailed simulation model of a single room building integrated with PV-TW was modelled using TRNSYS software. Results show that 14-35% PMV index and 26-38% PPD index reduces as system shifted from SPV-TW to DGPV-TW as compared to normal buildings. Thermal comfort indexes (PMV and PPD lie in the recommended range of ASHARE for both DPV-TW and DGPV-TW except for the few months when RH%, solar radiation intensity and ambient temperature were high. Moreover PVTW system significantly reduces energy consumption and CO2 emission of the building and also 2-4.8 °C of temperature differences between indoor and outdoor climate of building was examined.

  13. Financial Frictions

    DEFF Research Database (Denmark)

    Vestergaard Jensen, Mads

    frictions, a call option should never be exercised early, but only at expiration or just before the underlying stock pays a dividend. Chapter one of this thesis shows that suffciently severe frictions can make early exercise optimal. Short-sale costs especially represent an important driver of early...

  14. FEM simulation of friction testing method based on combined forward rod-backward can extrusion

    DEFF Research Database (Denmark)

    Nakamura, T; Bay, Niels; Zhang, Z. L

    1997-01-01

    A new friction testing method by combined forward rod-backward can extrusion is proposed in order to evaluate frictional characteristics of lubricants in forging processes. By this method the friction coefficient mu and the friction factor m can be estimated along the container wall and the conic...... in a mechanical press with aluminium alloy A6061 as the workpiece material and different kinds of lubricants. They confirm the analysis resulting in reasonable values for the friction coefficient and the friction factor....

  15. The Static Ladder Problem with Two Sources of Friction

    Science.gov (United States)

    Bennett, Jonathan; Mauney, Alex

    2011-01-01

    The problem of a ladder leaning against a wall in static equilibrium is a classic example encountered in introductory mechanics texts. Most discussions of this problem assume that the static frictional force between the ladder and wall can be ignored. A few authors consider the case where the static friction coefficients between ladder/wall…

  16. The Static Ladder Problem with Two Sources of Friction

    Science.gov (United States)

    Bennett, Jonathan; Mauney, Alex

    2011-01-01

    The problem of a ladder leaning against a wall in static equilibrium is a classic example encountered in introductory mechanics texts. Most discussions of this problem assume that the static frictional force between the ladder and wall can be ignored. A few authors consider the case where the static friction coefficients between ladder/wall…

  17. Acoustics of friction.

    Science.gov (United States)

    Akay, Adnan

    2002-04-01

    This article presents an overview of the acoustics of friction by covering friction sounds, friction-induced vibrations and waves in solids, and descriptions of other frictional phenomena related to acoustics. Friction, resulting from the sliding contact of solids, often gives rise to diverse forms of waves and oscillations within solids which frequently lead to radiation of sound to the surrounding media. Among the many everyday examples of friction sounds, violin music and brake noise in automobiles represent the two extremes in terms of the sounds they produce and the mechanisms by which they are generated. Of the multiple examples of friction sounds in nature, insect sounds are prominent. Friction also provides a means by which energy dissipation takes place at the interface of solids. Friction damping that develops between surfaces, such as joints and connections, in some cases requires only microscopic motion to dissipate energy. Modeling of friction-induced vibrations and friction damping in mechanical systems requires an accurate description of friction for which only approximations exist. While many of the components that contribute to friction can be modeled, computational requirements become prohibitive for their contemporaneous calculation. Furthermore, quantification of friction at the atomic scale still remains elusive. At the atomic scale, friction becomes a mechanism that converts the kinetic energy associated with the relative motion of surfaces to thermal energy. However, the description of the conversion to thermal energy represented by a disordered state of oscillations of atoms in a solid is still not well understood. At the macroscopic level, friction interacts with the vibrations and waves that it causes. Such interaction sets up a feedback between the friction force and waves at the surfaces, thereby making friction and surface motion interdependent. Such interdependence forms the basis for friction-induced motion as in the case of

  18. Friction enhancement in concertina locomotion of snakes.

    Science.gov (United States)

    Marvi, Hamidreza; Hu, David L

    2012-11-07

    Narrow crevices are challenging terrain for most organisms and biomimetic robots. Snakes move through crevices using sequential folding and unfolding of their bodies in the manner of an accordion or concertina. In this combined experimental and theoretical investigation, we elucidate this effective means of moving through channels. We measure the frictional properties of corn snakes, their body kinematics and the transverse forces they apply to channels of varying width and inclination. To climb channels inclined at 60°, we find snakes use a combination of ingenious friction-enhancing techniques, including digging their ventral scales to double their frictional coefficient and pushing channel walls transversely with up to nine times body weight. Theoretical modelling of a one-dimensional n-linked crawler is used to calculate the transverse force factor of safety: we find snakes push up to four times more than required to prevent sliding backwards, presumably trading metabolic energy for an assurance of wall stability.

  19. Friction enhancement in concertina locomotion of snakes

    Science.gov (United States)

    Marvi, Hamidreza; Hu, David L.

    2012-01-01

    Narrow crevices are challenging terrain for most organisms and biomimetic robots. Snakes move through crevices using sequential folding and unfolding of their bodies in the manner of an accordion or concertina. In this combined experimental and theoretical investigation, we elucidate this effective means of moving through channels. We measure the frictional properties of corn snakes, their body kinematics and the transverse forces they apply to channels of varying width and inclination. To climb channels inclined at 60°, we find snakes use a combination of ingenious friction-enhancing techniques, including digging their ventral scales to double their frictional coefficient and pushing channel walls transversely with up to nine times body weight. Theoretical modelling of a one-dimensional n-linked crawler is used to calculate the transverse force factor of safety: we find snakes push up to four times more than required to prevent sliding backwards, presumably trading metabolic energy for an assurance of wall stability. PMID:22728386

  20. Friction losses across pipe elements for coal-water slurries with wall-slip behavior%具有壁面滑移特性的水煤浆流经局部管件的阻力特性

    Institute of Scientific and Technical Information of China (English)

    陈良勇; 段钰锋; 刘猛; 赵长遂

    2009-01-01

    Experimental investigations were carried out on a pilot scale slurry transport apparatus to evaluate the friction losses across 90° bends, sudden contraction and sudden expansion for coal-water slurries with the presence of wall-slip behavior. The flow behavior (wall-slip behavior and rheological properties) of these slurries flowing in a straight pipe was determined to use as the baseline. Local resistance coefficients versus generalized Reynolds number correlations were established, in which the generalized Reynolds number (Re_g) well accounted for the wall-slip behavior and rheological properties of these slurries. Local energy losses in a series of bends were investigated as a function of ratio of bend to diameter, pipe diameter and generalized Reynolds number. For sudden expansion and sudden contraction, the effects of the flow behavior of the test slurries on local energy losses were determined. When Re_g was used as a parameter to represent the flow status, a high degree of overlap in local resistance coefficients of various slurries was observed for all test fittings except for sudden contraction. The trends of change in local resistance coefficients with Re_g showed obvious similarity for different bends. The measurements established that dynamic similarity could not be achieved in bends. With increasing Re_g, the resistance coefficients for sudden expansion decreased rapidly when Re_g350. At a high generalized Reynolds number, the resistance coefficient for sudden contraction became closely related to the flow behavior of the test slurries and increased with increasing solid concentration.%以水煤浆的流动特性(壁面滑移特性和流变特性)研究为基础,在中试规模的浆体输送装置上研究水煤浆流经90°弯管、突缩管和突扩管的阻力损失.以表征浆体流动特性的广义Reynolds数(Re_g)作为参数,建立了局部阻力系数关联式;考察了弯径比、管径和Re_g对弯管阻力损失的影响,分析了浆

  1. Experimental investigation of friction coefficient in tube hydroforming

    Institute of Scientific and Technical Information of China (English)

    Hyae Kyung YI; Hong Sup YIM; Gun Yeop LEE; Sung Mun LEE; Gi Suk CHUNG; Young-Hoon MOON

    2011-01-01

    The friction coefficient between tube and die in guide zone of tube hydroforming was obtained. In hydroforming, the tube is expanded by an internal pressure against the tool wall. By pushing the tube through tool, a friction force at the contact surface between the tube and the tool occurs. In guiding zone, the friction coefficients between tube and die can be estimated from the measured axial feeding forces. In expansion zone, the friction coefficients between tube and die can be evaluated from the measured geometries of expanded tubes and FE analysis.

  2. Fault rheology beyond frictional melting.

    Science.gov (United States)

    Lavallée, Yan; Hirose, Takehiro; Kendrick, Jackie E; Hess, Kai-Uwe; Dingwell, Donald B

    2015-07-28

    During earthquakes, comminution and frictional heating both contribute to the dissipation of stored energy. With sufficient dissipative heating, melting processes can ensue, yielding the production of frictional melts or "pseudotachylytes." It is commonly assumed that the Newtonian viscosities of such melts control subsequent fault slip resistance. Rock melts, however, are viscoelastic bodies, and, at high strain rates, they exhibit evidence of a glass transition. Here, we present the results of high-velocity friction experiments on a well-characterized melt that demonstrate how slip in melt-bearing faults can be governed by brittle fragmentation phenomena encountered at the glass transition. Slip analysis using models that incorporate viscoelastic responses indicates that even in the presence of melt, slip persists in the solid state until sufficient heat is generated to reduce the viscosity and allow remobilization in the liquid state. Where a rock is present next to the melt, we note that wear of the crystalline wall rock by liquid fragmentation and agglutination also contributes to the brittle component of these experimentally generated pseudotachylytes. We conclude that in the case of pseudotachylyte generation during an earthquake, slip even beyond the onset of frictional melting is not controlled merely by viscosity but rather by an interplay of viscoelastic forces around the glass transition, which involves a response in the brittle/solid regime of these rock melts. We warn of the inadequacy of simple Newtonian viscous analyses and call for the application of more realistic rheological interpretation of pseudotachylyte-bearing fault systems in the evaluation and prediction of their slip dynamics.

  3. Torsional friction damper optimization

    Science.gov (United States)

    Ye, Shaochun; Williams, Keith A.

    2006-06-01

    A new approach for the analysis of friction dampers is presented in this work. The exact form of the steady-state solution for a friction damper implemented on a primary system is developed and numerical solutions are used to determine the optimum friction in a friction damper applied to a specific primary system. When compared to classical results presented by earlier authors, the new approach provides a more optimal solution. In addition, viscous damping in the primary system may be included with the new analysis approach. The ability to optimize a friction damper when viscous damping is included in the primary system is a significant improvement over earlier methods and shows potential for serving as a guide to realizing a more accurate estimate of the optimal damping for friction dampers.

  4. Friction in orthodontics

    Science.gov (United States)

    Prashant, P. S.; Nandan, Hemant; Gopalakrishnan, Meera

    2015-01-01

    Conventional wisdom suggests that resistance to sliding (RS) generated at the wire-bracket interface has a bearing on the force transmitted to the teeth. The relative importance of static and kinetic friction and also the effect of friction on anchorage has been a topic of debate. Lot of research work has been done to evaluate the various factors that affect friction and thus purportedly retards the rate of tooth movement. However, relevancy of these studies is questionable as the methodology used hardly simulates the oral conditions. Lately studies have concluded that more emphasis should be laid on binding and notching of archwires as these are considered to be the primary factors involved in retarding the tooth movement. This article reviews the various components involved in RS and the factors affecting friction. Further, research work should be carried out to provide cost effective alternatives aimed at reducing friction. PMID:26538873

  5. Iliotibial band friction syndrome.

    Science.gov (United States)

    Lavine, Ronald

    2010-07-20

    Published articles on iliotibial band friction syndrome have been reviewed. These articles cover the epidemiology, etiology, anatomy, pathology, prevention, and treatment of the condition. This article describes (1) the various etiological models that have been proposed to explain iliotibial band friction syndrome; (2) some of the imaging methods, research studies, and clinical experiences that support or call into question these various models; (3) commonly proposed treatment methods for iliotibial band friction syndrome; and (4) the rationale behind these methods and the clinical outcome studies that support their efficacy.

  6. Polymer friction Molecular Dynamics

    DEFF Research Database (Denmark)

    Sivebæk, Ion Marius; Samoilov, Vladimir N.; Persson, Bo N. J.

    We present molecular dynamics friction calculations for confined hydrocarbon solids with molecular lengths from 20 to 1400 carbon atoms. Two cases are considered: a) polymer sliding against a hard substrate, and b) polymer sliding on polymer. In the first setup the shear stresses are relatively...... independent of molecular length. For polymer sliding on polymer the friction is significantly larger, and dependent on the molecular chain length. In both cases, the shear stresses are proportional to the squeezing pressure and finite at zero load, indicating an adhesional contribution to the friction force....

  7. Science 101: What Causes Friction?

    Science.gov (United States)

    Robertson, Bill

    2014-01-01

    Defining friction and asking what causes it might seem like a trivial question. Friction seems simple enough to understand. Friction is a force between surfaces that pushes against things that are moving or tending to move, and the rougher the surfaces, the greater the friction. Bill Robertson answers this by saying, "Well, not exactly".…

  8. Friction stir welding tool

    Science.gov (United States)

    Tolle; Charles R. , Clark; Denis E. , Barnes; Timothy A.

    2008-04-15

    A friction stir welding tool is described and which includes a shank portion; a shoulder portion which is releasably engageable with the shank portion; and a pin which is releasably engageable with the shoulder portion.

  9. Friction in volcanic environments

    Science.gov (United States)

    Kendrick, Jackie E.; Lavallée, Yan

    2016-04-01

    Volcanic landscapes are amongst the most dynamic on Earth and, as such, are particularly susceptible to failure and frictional processes. In rocks, damage accumulation is frequently accompanied by the release of seismic energy, which has been shown to accelerate in the approach to failure on both a field and laboratory scale. The point at which failure occurs is highly dependent upon strain-rate, which also dictates the slip-zone properties that pertain beyond failure, in scenarios such as sector collapse and pyroclastic flows as well as the ascent of viscous magma. High-velocity rotary shear (HVR) experiments have provided new opportunities to overcome the grand challenge of understanding faulting processes during volcanic phenomena. Work on granular ash material demonstrates that at ambient temperatures, ash gouge behaves according to Byerlee's rule at low slip velocities, but is slip-weakening, becoming increasingly lubricating as slip ensues. In absence of ash along a slip plane, rock-rock friction induces cataclasis and heating which, if sufficient, may induce melting (producing pseudotachylyte) and importantly, vesiculation. The viscosity of the melt, so generated, controls the subsequent lubrication or resistance to slip along the fault plane thanks to non-Newtonian suspension rheology. The shear-thinning behaviour and viscoelasticity of frictional melts yield a tendency for extremely unstable slip, and occurrence of frictional melt fragmentation. This velocity-dependence acts as an important feedback mechanism on the slip plane, in addition to the bulk composition, mineralogy and glass content of the magma, that all influence frictional behaviour. During sector collapse events and in pyroclastic density currents it is the frictional properties of the rocks and ash that, in-part, control the run-out distance and associated risk. In addition, friction plays an important role in the eruption of viscous magmas: In the conduit, the rheology of magma is integral

  10. Reflections on Friction in Quantum Mechanics

    Directory of Open Access Journals (Sweden)

    Yair Rezek

    2010-08-01

    Full Text Available Distinctly quantum friction effects of three types are surveyed: internalfriction, measurement-induced friction, and quantum-fluctuation-induced friction. We demonstrate that external driving will lead to quantum internal friction, and critique the measurement-based interpretation of friction. We conclude that in general systems will experience internal and external quantum friction over and beyond the classical frictional contributions.

  11. A general review of concepts for reducing skin friction, including recommendations for future studies

    Science.gov (United States)

    Fischer, M. C.; Ash, R. L.

    1974-01-01

    Four main concepts which have significantly reduced skin friction in experimental studies are discussed; suction, gaseous injection, particle additives, and compliant wall. It is considered possible that each of these concepts could be developed and applied in viable skin friction reduction systems for aircraft application. Problem areas with each concept are discussed, and recommendations for future studies are made.

  12. Wet Friction-Elements Boundary Friction Mechanism and Friction Coefficient Prediction

    Directory of Open Access Journals (Sweden)

    WANG Yanzhong

    2012-12-01

    Full Text Available The friction mechanism for the boundary friction course of friction elements engagement was explicitly expressed. The boundary friction model was built up by the surface topography. The model contained the effect of boundary film, adhesion, plough and lubrication. Based on the model, a coefficient for weakening plough for the lubrication was proposed. The modified model could fit for the working condition of wet friction elements. The friction coefficient as a function curve of rotating speed could be finally obtained by the data k and s/sm. The method provides a well interpretation of friction condition and friction coefficient prediction and the agreement between theoretical and experimental friction coefficients is reasonably good.

  13. Energy Balance of Friction and Friction Coefficient in Energetical Interpretation

    Directory of Open Access Journals (Sweden)

    S.V. Fedorov

    2015-09-01

    Full Text Available Sliding friction energy model is proposed. In this model, generalized mechanism of transformation and dissipation of energy under friction the model of elastic-plastic deformation and fracture contact volumes is considered. Energy model of the process of plastic deformation and destruction of solid bodies is based on the concept of ergodynamic of deformable bodies. Equations of energy balance of friction within the structural and energetic interpretation of deformation are proposed. The energy interpretation of the coefficient of friction is showed. From this position the friction coefficient is the most informative characteristic of the process. Experimental friction curves have been generalized. As a result of the energy analysis of friction, the energy diagram of the structural evolution of the friction surfaces is suggested.

  14. 器壁滑动摩擦力对受振颗粒体系中冲击力倍周期分岔过程的影响*%Effect of wall friction on subharmonic bifurcations of impact in vertically vibrated granular beds*

    Institute of Scientific and Technical Information of China (English)

    韩红; 姜泽辉†; 李翛然; 吕晶; 张睿; 任杰骥

    2013-01-01

      颗粒物质由离散的固体颗粒组成,受到周期性振动时可以表现出复杂的动力学行为。这些行为往往受众多因素的影响,如空气阻力和器壁摩擦力等。针对受振颗粒体系中冲击力的倍周期分岔现象,通过抽真空或将容器底镂空消除空气阻力,单独研究器壁滑动摩擦力的影响。结果表明在仅有器壁摩擦力作用的情况下,倍周期分岔过程仅受约化振动加速度的控制,与颗粒的尺寸、颗粒层数及振动频率无关。将器壁摩擦力处理成一个大小恒定、方向与颗粒和器壁相对速度反向的阻力,并包含到完全非弹性蹦球模型中,能够对所观察到的现象给出很好的解释。通过对倍周期分岔点测量平均值的拟合,得到器壁滑动摩擦力的大小约为颗粒总重量的10%。%Granular materials consist of a large number of discrete solid particles. When subjected to external vibrations, they exhibit various intricate dynamical behaviors, Which usually depend in a complicated way on many physical factors, such as air dragging, friction from the container wall and so forth. In this work, vertical vibrations are applied to a bed of stainless-steel spheres contained in a glass tube, and the subharmonic bifurcations of impact of particles on the container bottom are investigated. To eliminate the effects of air dragging, we evacuate the container or perforate the container bottom to make it quite permeable to the air. Experiments performed in such containers reveal that the impact bifurcations are controlled solely by the normalized vibration acceleration, but independent of the particle size, the filling height of particles, and the frequency of forced vibration. The sliding friction from the container wall is treated as a constant one with the direction opposite to the velocity relative to the container wall. By involving this damping term into the completely inelastic bouncing ball model, an

  15. Skin friction on a flat perforated acoustic liner

    Science.gov (United States)

    Boldman, D. R.; Brinich, P. F.

    1976-01-01

    The report concerns the measurement of friction coefficients of a typical perforated acoustic liner installed in the side of a wind tunnel. The results are compared with measured friction coefficients of a smooth hard wall for the same mean flow velocities in a wind tunnel. At a velocity of 61 m/sec, an increase in the local skin coefficient of only a few percent was observed, but at the highest velocity of 213 m/sec an increase of about 20% was obtained. This velocity is a realistic velocity for turbo-machinery components utilizing such liners, so a loss in performance is to be expected. Some tests were also performed to see if changes in the mean boundary layer induced by imposed noise would result in friction increase, but only at low velocity levels was such an increase in friction noted.

  16. Study on the cutting plane friction law of sandstone

    Institute of Scientific and Technical Information of China (English)

    ZHAI Ying-da (翟英达); KANG Li-xun(康立勋)

    2003-01-01

    The friction characteristics of rock damage plane have important impact on the stability of block structure formed after the stratum is broken. The mechanics properties of rock damage plane are described by parameters such as roughness coefficient, wall compress strength and basic friction angle. These three coefficients for fine grain sandstone and medium-granular sandstone and grit sandstone are test. The friction stress is researched at the condition of different normal compressive stress acting on the tension damage plane. The friction law of tension damage plane of sandstone abided by is summed up. This law will provide scientific basis for block structure stability judging in basic roof stratum and roof pressure intensity calculating.

  17. Influence of rolling friction on single spout fluidized bed simulation

    Institute of Scientific and Technical Information of China (English)

    Christoph Goniva; Christoph Kloss; Niels G. Deen; Johannes A. M. Kuipers; Stefan Pirker

    2012-01-01

    In this paper we study the effect of rolling friction on the dynamics in a single spout fluidized bed using Discrete Element Method (DEM) coupled to Computational Fluid Dynamics (CFD).In a first step we neglect rolling friction and show that the results delivered by the open source CFD-DEM framework applied in this study agree with previous simulations documented in literature.In a second step we include a rolling friction sub-model in order to investigate the effect of particle non-sphericity.The influence of particle-particle as well as particle-wall rolling friction on the flow in single spout fluidized bed is studied separately.Adequate rolling friction model parameters are obtained using first principle DEM simulations and data from literature.Finally,we demonstrate the importance of correct modelling of rolling friction for coupled CFD-DEM simulations of spout fluidized beds.We show that simulation results can be improved significantly when applying a rolling friction model,and that experimental data from literature obtained with Positron Emission Particle Tracking (PEPT) technique can be satisfactorily reproduced.

  18. Do Stops Slow Down Electroweak Bubble Walls?

    CERN Document Server

    John, P

    2001-01-01

    We compute the wall velocity in the MSSM. We therefore generalize the SMequations of motion for bubble walls moving through a hot plasma at theelectroweak phase transition and calculate the friction terms which describethe viscosity of the plasma. We give the general expressions and apply them toa simple model where stops, tops and W bosons contribute to the friction. In awide range of parameters including those which fulfil the requirements ofbaryogenesis we find a wall velocity of order v = 0.001-0.01 much below the SMvalue.

  19. A Typical Magnetohydrodynamic Flow of a Viscous Incompressible Fluid Between a Parallel Flat Wall and a Wavy Wall : Constant Suction Through the Former Wall

    Directory of Open Access Journals (Sweden)

    S. N. Maitra

    1986-01-01

    Full Text Available A magnetohydrodynamic flow of a viscous, incompressible and slightly conducting fluid is developed between a parallel flat wall and a wavy wall whereas at the same time fluid is continuously sucked through the flat wall with a constant suction velocity. The velocity and temperature distribution are determined alongwith the pressure gradient and co-efficient of skin friction.

  20. Internal friction and elastic softening in polycrystalline Nb3Sn

    Science.gov (United States)

    Bussière, J. F.; Faucher, B.; Snead, C. L., Jr.; Welch, D. O.

    1981-10-01

    The vibrating-reed technique was used to measure internal friction and Young's modulus of polycrystalline Nb3Sn in the form of composite Nb-Nb3Sn tapes from 6 to 300 K. In tapes with only small residual strain in the A 15 layers, a dramatic increase in internal friction with decreasing temperature is observed with an abrupt onset at ~48 K. The internal friction Q-1 between 6 and 48 K is believed to be associated with stress-induced motion of martensitic-domain walls. In this temperature range, Q-1 is approximately proportional to the square of the tetragonal strain of the martensitic phase; Q-1~(ca-1)2. With residual compressive strains of ~0.2%, the internal friction associated with domain-wall motion is considerably reduced. This is attributed to a biasing of domain-wall orientation with residual stress, which reduces wall motion induced by the (much smaller) applied stress. The transformation temperature, however, is unchanged (within +/- 1 K) by residual strains of up to 0.2%. Young's modulus exhibits substantial softening on cooling from 300 to 6 K. This softening is substantially reduced in the presence of small residual compressive strains, indicating a highly nonlinear stress-strain relationship as previously reported for V 3Si.

  1. Intelligent Flow Friction Estimation

    Directory of Open Access Journals (Sweden)

    Dejan Brkić

    2016-01-01

    Full Text Available Nowadays, the Colebrook equation is used as a mostly accepted relation for the calculation of fluid flow friction factor. However, the Colebrook equation is implicit with respect to the friction factor (λ. In the present study, a noniterative approach using Artificial Neural Network (ANN was developed to calculate the friction factor. To configure the ANN model, the input parameters of the Reynolds Number (Re and the relative roughness of pipe (ε/D were transformed to logarithmic scales. The 90,000 sets of data were fed to the ANN model involving three layers: input, hidden, and output layers with, 2, 50, and 1 neurons, respectively. This configuration was capable of predicting the values of friction factor in the Colebrook equation for any given values of the Reynolds number (Re and the relative roughness (ε/D ranging between 5000 and 108 and between 10−7 and 0.1, respectively. The proposed ANN demonstrates the relative error up to 0.07% which had the high accuracy compared with the vast majority of the precise explicit approximations of the Colebrook equation.

  2. Skin tribology: Science friction?

    NARCIS (Netherlands)

    Heide, van der E.; Zeng, X.; Masen, M.A.

    2013-01-01

    The application of tribological knowledge is not just restricted to optimizing mechanical and chemical engineering problems. In fact, effective solutions to friction and wear related questions can be found in our everyday life. An important part is related to skin tribology, as the human skin is fre

  3. Gravitomagnetic dynamical friction

    CERN Document Server

    Cashen, Benjamin; Kesden, Michael

    2016-01-01

    A supermassive black hole moving through a field of stars will gravitationally scatter the stars, inducing a backreaction force on the black hole known as dynamical friction. In Newtonian gravity, the axisymmetry of the system about the black hole's velocity $\\mathbf{v}$ implies that the dynamical friction must be anti-parallel to $\\mathbf{v}$. However, in general relativity the black hole's spin $\\mathbf{S}$ need not be parallel to $\\mathbf{v}$, breaking the axisymmetry of the system and generating a new component of dynamical friction similar to the Lorentz force $\\mathbf{F} = q\\mathbf{v} \\times \\mathbf{B}$ experienced by a particle with charge $q$ moving in a magnetic field $\\mathbf{B}$. We call this new force gravitomagnetic dynamical friction and calculate its magnitude for a spinning black hole moving through a field of stars with Maxwellian velocity dispersion $\\sigma$, assuming that both $v$ and $\\sigma$ are much less than the speed of light $c$. We use post-Newtonian equations of motion accurate to $...

  4. Quantum tunneling with friction

    Science.gov (United States)

    Tokieda, M.; Hagino, K.

    2017-05-01

    Using the phenomenological quantum friction models introduced by P. Caldirola [Nuovo Cimento 18, 393 (1941), 10.1007/BF02960144] and E. Kanai [Prog. Theor. Phys. 3, 440 (1948), 10.1143/ptp/3.4.440], M. D. Kostin [J. Chem. Phys. 57, 3589 (1972), 10.1063/1.1678812], and K. Albrecht [Phys. Lett. B 56, 127 (1975), 10.1016/0370-2693(75)90283-X], we study quantum tunneling of a one-dimensional potential in the presence of energy dissipation. To this end, we calculate the tunneling probability using a time-dependent wave-packet method. The friction reduces the tunneling probability. We show that the three models provide similar penetrabilities to each other, among which the Caldirola-Kanai model requires the least numerical effort. We also discuss the effect of energy dissipation on quantum tunneling in terms of barrier distributions.

  5. Friction in rail guns

    Science.gov (United States)

    Kay, P. K.

    1984-01-01

    The influence of friction is included in the present equations describing the performance of an inductively driven rail gun. These equations, which have their basis in an empirical formulation, are applied to results from two different experiments. Only an approximate physical description of the problem is attempted, in view of the complexity of details in the interaction among forces of this magnitude over time periods of the order of milisecs.

  6. Investigation for Transient Phenomena in Concentric Annular Turbulent Flow with Sudden Outer-Wall-Rotation

    OpenAIRE

    岡本, 正芳; 永江, 聡美; Masayoshi, OKAMOTO; Satomi, NAGAE; 静岡大工; 東北大流体研; Dept. of Mech. Eng., Shizuoka Univ.; Institute of Fluid Science, Tohoku Univ.

    2007-01-01

    Transient phenomena in turbulent concentric annular pipe flow with sudden outer-wall rotation were investigated by means of the direct numerical simulation (DNS). Due to the sudden rotation, the wall friction becomes small and the flow is stabilized. In the transient state, the axial mean velocity profile changes drastically and the Reynolds stresses vanish near the outer wall. When the wall friction increases suddenly, the vortex structures are invigorated.

  7. Theory of noncontact friction for atom-surface interactions

    CERN Document Server

    Jentschura, U D; DeKieviet, M

    2016-01-01

    The noncontact (van der Waals) friction is an interesting physical effect which has been the subject of controversial scientific discussion. The "direct" friction term due to the thermal fluctuations of the electromagnetic field leads to a friction force proportional to 1/Z^5 where Z is the atom-wall distance). The "backaction" friction term takes into account the feedback of thermal fluctuations of the atomic dipole moment onto the motion of the atom and scales as 1/Z^8. We investigate noncontact friction effects for the interactions of hydrogen, ground-state helium and metastable helium atoms with alpha-quartz (SiO_2), gold (Au) and calcium difluorite (CaF_2). We find that the backaction term dominates over the direct term induced by the thermal electromagnetic fluctuations inside the material, over wide distance ranges. The friction coefficients obtained for gold are smaller than those for SiO_2 and CaF_2 by several orders of magnitude.

  8. High Speed Friction Microscopy and Nanoscale Friction Coefficient Mapping

    OpenAIRE

    Bosse, James L.; Lee, Sungjun; Huey, Bryan D; Andersen, Andreas Sø; Sutherland, Duncan S

    2014-01-01

    As mechanical devices in the nano/micro length scale are increasingly employed, it is crucial to understand nanoscale friction and wear especially at technically relevant sliding velocities. Accordingly, a novel technique has been developed for Friction Coefficient Mapping (FCM), leveraging recent advances in high speed AFM. The technique efficiently acquires friction versus force curves based on a sequence of images at a single location, each with incrementally lower loads. As a result, true...

  9. A skin friction law for compressible turbulent flow

    Science.gov (United States)

    Barnwell, Richard W.; Wahls, Richard A.

    1989-01-01

    An algebraic skin friction law is derived for adiabatic, compressible, equilibrium, turbulent boundary layer flow. An outer solution in terms of the Clauser defect stream function is matched to an inner empirical expression composed of compressible laws of the wall and wake. The modified Crocco temperature-velocity relationship and the Clauser eddy viscousity model are used in the outer solution. The skin friction law pertains for all pressure gradients in the incompressible through supersonic range and for small pressure gradients in the hypersonic range. Excellent comparisons with experiment are obtained in the appropriate parameter ranges. The application to numerical computation is discussed.

  10. The effect of elastic modulus and friction coefficient on rubber tube sealing performance

    Science.gov (United States)

    Li, Zhimiao; Xu, Siyuan; Ren, Fushen; Liu, Jubao

    2015-03-01

    The packer is the key element in separating geosphere layers of water injection, water plugging and fracturing operations in the oilfield. The sealing ability of the packer is depending on the contact pressure between rubber tube and the casing. The circumferential strain of casing wall was tested by the strain gauge to get the contact pressure distribution along axial direction of the tube. The friction force between the casing and the rubber tube was taken by the pressure sensor in compression process. Under the 20,60 and 100 degrees Celsius conditions, the friction forces and the contact pressure distribution were taken in work condition of single rubber tube, double rubber tubes and combination rubber tubes after oil immersion .The result shows that elastic modulus of rubber tube has little effect on the friction force and contact pressure. With elastic modulus decreasing, the friction forces has gradually decreasing trend; The friction coefficient has much impact on friction force: the friction forces under the condition of dry friction and wet friction are respectively equivalent to 48.27% and 5.38% axial compression forces. At wet friction condition, the contact pressure distribution is more uniform and the sealing effect is better.

  11. Friction laws for lubricated nanocontacts

    Science.gov (United States)

    Buzio, R.; Boragno, C.; Valbusa, U.

    2006-09-01

    We have used friction force microscopy to probe friction laws for nanoasperities sliding on atomically flat substrates under controlled atmosphere and liquid environment, respectively. A power law relates friction force and normal load in dry air, whereas a linear relationship, i.e., Amontons' law, is observed for junctions fully immersed in model lubricants, namely, octamethylciclotetrasiloxane and squalane. Lubricated contacts display a remarkable friction reduction, with liquid and substrate specific friction coefficients. Comparison with molecular dynamics simulations suggests that load-bearing boundary layers at junction entrance cause the appearance of Amontons' law and impart atomic-scale character to the sliding process; continuum friction models are on the contrary of limited predictive power when applied to lubrication effects. An attempt is done to define general working conditions leading to the manifestation of nanoscale lubricity due to adsorbed boundary layers.

  12. Friction surfaced Stellite6 coatings

    Energy Technology Data Exchange (ETDEWEB)

    Rao, K. Prasad; Damodaram, R. [Department of Metallurgical and Materials Engineering - Indian Institute of Technology Madras, Chennai 600 036 (India); Rafi, H. Khalid, E-mail: khalidrafi@gmail.com [Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600 036 (India); Ram, G.D. Janaki [Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600 036 (India); Reddy, G. Madhusudhan [Metal Joining Group, Defence Metallurgical Research Laboratory (DMRL) Kanchanbagh, Hyderabad 500 058 (India); Nagalakshmi, R. [Welding Research Institute, Bharat Heavy Electricals Limited, Tiruchirappalli 620 014 (India)

    2012-08-15

    Solid state Stellite6 coatings were deposited on steel substrate by friction surfacing and compared with Stellite6 cast rod and coatings deposited by gas tungsten arc and plasma transferred arc welding processes. Friction surfaced coatings exhibited finer and uniformly distributed carbides and were characterized by the absence of solidification structure and compositional homogeneity compared to cast rod, gas tungsten arc and plasma transferred coatings. Friction surfaced coating showed relatively higher hardness. X-ray diffraction of samples showed only face centered cubic Co peaks while cold worked coating showed hexagonally close packed Co also. - Highlights: Black-Right-Pointing-Pointer Stellite6 used as coating material for friction surfacing. Black-Right-Pointing-Pointer Friction surfaced (FS) coatings compared with casting, GTA and PTA processes. Black-Right-Pointing-Pointer Finer and uniformly distributed carbides in friction surfaced coatings. Black-Right-Pointing-Pointer Absence of melting results compositional homogeneity in FS Stellite6 coatings.

  13. Solid friction between soft filaments

    CERN Document Server

    Ward, Andrew; Schwenger, Walter; Welch, David; Lau, A W C; Vitelli, Vincenzo; Mahadevan, L; Dogic, Zvonimir

    2015-01-01

    Any macroscopic deformation of a filamentous bundle is necessarily accompanied by local sliding and/or stretching of the constituent filaments. Yet the nature of the sliding friction between two aligned filaments interacting through multiple contacts remains largely unexplored. Here, by directly measuring the sliding forces between two bundled F-actin filaments, we show that these frictional forces are unexpectedly large, scale logarithmically with sliding velocity as in solid-like friction, and exhibit complex dependence on the filaments' overlap length. We also show that a reduction of the frictional force by orders of magnitude, associated with a transition from solid-like friction to Stokes' drag, can be induced by coating F-actin with polymeric brushes. Furthermore, we observe similar transitions in filamentous microtubules and bacterial flagella. Our findings demonstrate how altering a filament's elasticity, structure and interactions can be used to engineer interfilament friction and thus tune the prop...

  14. Micromechanical study of macroscopic friction and dissipation in idealised granular materials: the effect of interparticle friction

    NARCIS (Netherlands)

    Kruyt, N.P.; Rothenburg, L.; Gutkowski, Witold; Kowalewski, Tomasz A.

    2004-01-01

    Using Discrete Element Method (DEM) simulations with varying interparticle friction coefficient, the relation between interparticle friction coefficient and macroscopic continuum friction and dissipation is investigated. As expected, macroscopic friction and dilatancy increase with interparticle fri

  15. Friction and wear calculation methods

    CERN Document Server

    Kragelsky, I V; Kombalov, V S

    1981-01-01

    Friction and Wear: Calculation Methods provides an introduction to the main theories of a new branch of mechanics known as """"contact interaction of solids in relative motion."""" This branch is closely bound up with other sciences, especially physics and chemistry. The book analyzes the nature of friction and wear, and some theoretical relationships that link the characteristics of the processes and the properties of the contacting bodies essential for practical application of the theories in calculating friction forces and wear values. The effect of the environment on friction and wear is a

  16. FEM simulation of a friction testing method based on combined forward conical can-backward straight can extrusion

    DEFF Research Database (Denmark)

    Nakamura, T; Bay, Niels

    1998-01-01

    A new friction testing method based on combined forward conical can-backward straight can extrusion is proposed in order to evaluate friction characteristics in severe metal forming operations. By this method the friction coefficient along the conical punch surface is determined knowing...... the friction coefficient along the die wall. The latter is determined by a combined forward and backward can extrusion of straight cans. Calibration curves determining the relationship between punch travel, can heights, and friction coefficient for the two rests are calculated based on a rigid-plastic FEM...... analysis. Experimental friction tests are carried out in a mechanical press with aluminium alloy A6061 as the workpiece material and different kinds of lubricants. They confirm that the theoretical analysis results irt reasonable values for the friction coefficient....

  17. Friction or Closure

    DEFF Research Database (Denmark)

    Lundahl, Mikela

    2014-01-01

    . The anthropologist Anna Tsing has developed the concept-metaphor friction as a way to discuss the energy created when various actors narrate “the same” event(s) in different ways, and see the other participants’ accounts as fantasies or even fabrications. I will use my position as researcher and my relations...... is Stone Town in Zanzibar and the de-velopment and dissolution going on under the shadow of the UNESCO World Heritage flag; a growing tourism; a global and local increase in islamisation; and the political tension within the Tanzanian union. My main focus is narratives of the identity of Zanzibar since...

  18. Friction analysis of kinetic schemes : the friction coefficient

    NARCIS (Netherlands)

    Lolkema, Juke S.

    1995-01-01

    Friction analysis is proposed as the application of general control analysis to single enzymes to describe the control of elementary kinetic steps on the overall catalytic rate. For each transition, a friction coefficient is defined that measures the sensitivity of the turnover rate to the free ener

  19. FRICTION ANALYSIS OF KINETIC SCHEMES - THE FRICTION COEFFICIENT

    NARCIS (Netherlands)

    LOLKEMA, JS

    1995-01-01

    Friction analysis is proposed as the application of general control analysis to single enzymes to describe the control of elementary kinetic steps on the overall catalytic rate. For each transition, a friction coefficient is defined that measures the sensitivity of the turnover rate to the free ener

  20. Friction analysis of kinetic schemes : the friction coefficient

    NARCIS (Netherlands)

    Lolkema, Juke S.

    1995-01-01

    Friction analysis is proposed as the application of general control analysis to single enzymes to describe the control of elementary kinetic steps on the overall catalytic rate. For each transition, a friction coefficient is defined that measures the sensitivity of the turnover rate to the free ener

  1. Slow frictional waves

    Science.gov (United States)

    Viswanathan, Koushik; Sundaram, Narayan; Chandrasekar, Srinivasan

    Stick-slip, manifest as intermittent tangential motion between two dry solid surfaces, is a friction instability that governs diverse phenomena from automobile brake squeals to earthquakes. We show, using high-speed in situ imaging of an adhesive polymer interface, that low velocity stick-slip is fundamentally of three kinds, corresponding to passage of three different surface waves -- separation pulses, slip pulses and the well-known Schallamach waves. These waves, traveling much slower than elastic waves, have clear distinguishing properties. Separation pulses and Schallamach waves involve local interface separation, and propagate in opposite directions while slip pulses are characterized by a sharp stress front and do not display any interface detachment. A change in the stick-slip mode from separation to slip pulse is effected simply by increasing the normal force. Together, these three waves constitute all possible stick-slip modes in adhesive friction and are shown to have direct analogues in muscular locomotory waves in soft bodied invertebrates. A theory for slow wave propagation is also presented which is capable of explaining the attendant interface displacements, velocities and stresses.

  2. Friction Stir Welding

    Science.gov (United States)

    Nunes, Arthur C., Jr.

    2008-01-01

    Friction stir welding (FSW) is a solid state welding process invented in 1991 at The Welding Institute in the United Kingdom. A weld is made in the FSW process by translating a rotating pin along a weld seam so as to stir the sides of the seam together. FSW avoids deleterious effects inherent in melting and promises to be an important welding process for any industries where welds of optimal quality are demanded. This article provides an introduction to the FSW process. The chief concern is the physical effect of the tool on the weld metal: how weld seam bonding takes place, what kind of weld structure is generated, potential problems, possible defects for example, and implications for process parameters and tool design. Weld properties are determined by structure, and the structure of friction stir welds is determined by the weld metal flow field in the vicinity of the weld tool. Metal flow in the vicinity of the weld tool is explained through a simple kinematic flow model that decomposes the flow field into three basic component flows: a uniform translation, a rotating solid cylinder, and a ring vortex encircling the tool. The flow components, superposed to construct the flow model, can be related to particular aspects of weld process parameters and tool design; they provide a bridge to an understanding of a complex-at-first-glance weld structure. Torques and forces are also discussed. Some simple mathematical models of structural aspects, torques, and forces are included.

  3. Corrosion effects on friction factors

    Energy Technology Data Exchange (ETDEWEB)

    Magleby, H.L.; Shaffer, S.J.

    1996-03-01

    This paper presents the results of NRC-sponsored material specimen tests that were performed to determine if corrosion increases the friction factors of sliding surfaces of motor-operated gate valves, which could require higher forces to close and open safety-related valves when subjected to their design basis differential pressures. Friction tests were performed with uncorroded specimens and specimens subjected to accelerated corrosion. Preliminary tests at ambient conditions showed that corrosion increased the friction factors, indicating the need for additional tests duplicating valve operating parameters at hot conditions. The additional tests showed friction factors of corroded specimens were 0.1 to 0.2 higher than for uncorroded specimens, and that the friction factors of the corroded specimens were not very dependent on contact stress or corrosion film thickness. The measured values of friction factors for the three corrosion films tested (simulating three operating times) were in the range of 0.3 to 0.4. The friction factor for even the shortest simulated operating time was essentially the same as the others, indicating that the friction factors appear to reach a plateau and that the plateau is reached quickly.

  4. Elastic model of dry friction

    Energy Technology Data Exchange (ETDEWEB)

    Larkin, A. I.; Khmelnitskii, D. E., E-mail: dekl2@cam.ac.uk [Landau Institute for Theoretical Physics (Russian Federation)

    2013-09-15

    Friction of elastic bodies is connected with the passing through the metastable states that arise at the contact of surfaces rubbing against each other. Three models are considered that give rise to the metastable states. Friction forces and their dependence on the pressure are calculated. In Appendix A, the contact problem of elasticity theory is solved with adhesion taken into account.

  5. Friction in surface micromachined microengines

    Energy Technology Data Exchange (ETDEWEB)

    Miller, S.L.; Sniegowski, J.J.; LaVigne, G.; McWhorter, P.J.

    1996-03-01

    Understanding the frictional properties of advanced Micro-Electro- Mechanical Systems (MEMS) is essential in order to develop optimized designs and fabrication processes, as well as to qualify devices for commercial applications. We develop and demonstrate a method to experimentally measure the forces associated with sliding friction of devices rotating on a hub. The method is demonstrated on the rotating output gear of the microengine recently developed at Sandia National Laboratories. In-situ measurements of an engine running at 18300 rpm give a coefficient of friction of 0.5 for radial (normal) forces less than 4 {mu}N. For larger forces the effective coefficient of friction abruptly increases, suggesting a fundamental change in the basic nature of the interaction between the gear and hub. The experimental approach we have developed to measure the frictional forces associated with the microengine is generically applicable to other MEMS devices.

  6. Direct Numerical Simulation of Turbulent Couette-Poiseuille Flow With Zero Skin Friction

    Science.gov (United States)

    Coleman, Gary N.; Spalart, Philippe R.

    2015-01-01

    The near-wall scaling of mean velocity U(yw) is addressed for the case of zero skin friction on one wall of a fully turbulent channel flow. The present DNS results can be added to the evidence in support of the conjecture that U is proportional to the square root of yw in the region just above the wall at which the mean shear dU=dy = 0.

  7. Tactile friction of topical formulations.

    Science.gov (United States)

    Skedung, L; Buraczewska-Norin, I; Dawood, N; Rutland, M W; Ringstad, L

    2016-02-01

    The tactile perception is essential for all types of topical formulations (cosmetic, pharmaceutical, medical device) and the possibility to predict the sensorial response by using instrumental methods instead of sensory testing would save time and cost at an early stage product development. Here, we report on an instrumental evaluation method using tactile friction measurements to estimate perceptual attributes of topical formulations. Friction was measured between an index finger and an artificial skin substrate after application of formulations using a force sensor. Both model formulations of liquid crystalline phase structures with significantly different tactile properties, as well as commercial pharmaceutical moisturizing creams being more tactile-similar, were investigated. Friction coefficients were calculated as the ratio of the friction force to the applied load. The structures of the model formulations and phase transitions as a result of water evaporation were identified using optical microscopy. The friction device could distinguish friction coefficients between the phase structures, as well as the commercial creams after spreading and absorption into the substrate. In addition, phase transitions resulting in alterations in the feel of the formulations could be detected. A correlation was established between skin hydration and friction coefficient, where hydrated skin gave rise to higher friction. Also a link between skin smoothening and finger friction was established for the commercial moisturizing creams, although further investigations are needed to analyse this and correlations with other sensorial attributes in more detail. The present investigation shows that tactile friction measurements have potential as an alternative or complement in the evaluation of perception of topical formulations. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  8. Rolling Friction in Loose Media and its Role in Mechanics Problems

    Science.gov (United States)

    Klishin, S. V.; Revuzhenko, A. F.; Kazantsev, A. A.

    2016-08-01

    Rolling friction between particles is to be set in problems of granular material mechanics alongside with sliding friction. A classical problem of material passive lateral pressure on the retaining wall is submitted as a case in point. 3D method of discrete elements was employed for numerical analysis. Material is a universe of spherical particles with specified size distribution. Viscose-elastic properties of the material and surface friction are included, when choosing contact forces. Particles' resistance to rolling relative to other particles and to the boundary is set into the model. Kinetic patterns of medium deformations are given. It has been proved that rolling friction can significantly affect magnitude and nature of passive lateral pressure on the retaining wall.

  9. Student figures in friction

    DEFF Research Database (Denmark)

    Nielsen, Gritt B.

      This thesis analyses how ‘the student', as a contested figure, is negotiated and enacted in a period of extensive university reform in Denmark. Through a combination of historical and anthropological research, it focuses on students' changing participation in the shaping of Danish society......, students' room for participation in their own learning, influenced by demands for efficiency, flexibility and student-centred education. The thesis recasts the anthropological endeavour as one of ‘figuration work'. That is, ‘frictional events' are explored as moments when conflicting figures......, the university and their own education. Detailed studies explore, first, politically active students' various attempts to influence national educational policies; second, student participation in the development of the university, especially regarding debates over consumer conduct versus co-ownership; and third...

  10. Skin friction measurement on the NASA Common Research Model using global luminescent oil film skin friction meter

    Science.gov (United States)

    Rajendran, Lalit Kishore

    Accurate skin friction measurements are indispensable in the design of more efficient aerodynamic vehicles, and is also the controlling variable in closed loop flow control systems. Spatially and temporally resolved skin friction data is required to calibrate turbulence models used in Computational Fluid Dynamics analysis, and can also provide insight into the nature of near-wall turbulence. Luminescent oil film based techniques offer the ability to make distributed wall shear stress measurements with a relatively simple setup. The Global Luminescent Oil Film Skin Friction Meter (GLOSFM) technique involves calculating the shear stress based on observing the thickness of an oil film, which in turn is directly proportional to its luminescent intensity, provided the oil film is sufficiently thin. This technique is briefly reviewed, with some emphasis on uncertainty quantification, and the formation and propagation of ripples/surface waves on the oil film, as well as their impact on the shear stress measurement. Finally, this technique is used to measure the skin friction field on the wing and fuselage of the NASA Common Research Model, a passenger jet configuration. The issue of repeatability and the effects of tripping the flow are investigated, and the effect of flow parameters like the angle of attack and the Reynolds number are studied.

  11. Surface Hardness of Friction Stir Welded AA6063 Pipe

    OpenAIRE

    Ismail Azman; Awang Mokhtar

    2014-01-01

    The external surface hardness of friction stir welded aluminum alloy 6063 pipe joint was investigated in this paper. The 89mm of outside diameter pipe with 5mm of wall thickness was used as test pipe piece for this experiment on closed butt joint configuration by utilising Bridgeport 2216 CNC milling machine and orbital clamping unit specially designed to cater for this task and function. Several welded samples were produced on varying process parameters which were successfully joined by usin...

  12. Effect of electrostatic field on dynamic friction coefficient of pistachio

    Directory of Open Access Journals (Sweden)

    M. H Aghkhani

    2016-04-01

    25 mm and with wall thickness of 5 mm placed on trolleys. In the bottom of the container a separate aluminum plate was installed as the negative pole of the electric field. The friction plates as a positive pole placed on top of the sample. There were no contact between friction plates and walls of vessel (samples were about 2 to 3 mm higher from the edges of wall. Frictional force changes due to movement of table, measured and recorded by an accurate load cell. From force-displacement curves, the coefficient of dynamic friction and static coefficient of friction calculated. In general, according to the experimental design, 486 tests were performed. Results and Discussion: According to the results of statistical analysis, there is significant interaction affect between pistachios type and electrical field, as well as, the interaction between electrical field and speed, on dynamic coefficient of friction. It means two pistachio types can be separated by electrical charging. Different physical properties of surface of filled non-splits pistachio nuts (such as corners and edges and filled splits ones, caused differences in the distribution of electric charge and as a result, its interaction with the electric field were significant. Changes in dynamic coefficient of friction according to the electric field intensity at different levels of moisture content and speed on the friction surfaces of iron, aluminum and rubber, was drawn in Fig.4, 5 and 6, respectively. These figures reflected the reduction of dynamic coefficient of friction by increasing the movement speed of table. According to Fig.7, increasing the intensity of the electric field increases the dynamic coefficient of friction. Because this leads to build the opposition charge on samples and galvanized iron sheets, and with increase of electrical field, these charges will rise. Fig.9 shows different trends of variation of dynamic coefficient of friction against moisture on rubber surface. This chart shows the

  13. REDUCED ENGINE FRICTION AND WEAR

    Energy Technology Data Exchange (ETDEWEB)

    Ron Matthews

    2005-05-01

    This Final Technical Report discusses the progress was made on the experimental and numerical tasks over the duration of this project regarding a new technique for decreasing engine friction and wear via liner rotation. The experimental subtasks involved quantifying the reduction in engine friction for a prototype rotating liner engine relative to a comparable baseline engine. Both engine were single cylinder conversions of nominally identical production four-cylinder engines. Hot motoring tests were conducted initially and revealed that liner rotation decreased engine friction by 20% under motoring conditions. A well-established model was used to estimate that liner rotation should decrease the friction of a four-cylinder engine by 40% under hot motoring conditions. Hot motoring tear-down tests revealed that the crankshaft and valve train frictional losses were essentially the same for the two engines, as expected. However, the rotating liner engine had much lower (>70%) piston assembly friction compared to the conventional engine. Finally, we used the Instantaneous IMEP method to compare the crank-angle resolved piston assembly friction for the two engines. Under hot motoring conditions, these measurements revealed a significant reduction in piston assembly friction, especially in the vicinity of compression TDC when the lubrication regime transitions from hydrodynamic through mixed and into boundary friction. We have some remaining problems with these measurements that we expect to solve during the next few weeks. We will then perform these measurements under firing conditions. We also proposed to improve the state-of-the-art of numerical modeling of piston assembly friction for conventional engines and then to extend this model to rotating liner engines. Our research team first modeled a single ring in the Purdue ring-liner test rig. Our model showed good agreement with the test rig data for a range of speeds and loads. We then modeled a complete piston

  14. Frictional properties of confined polymers

    DEFF Research Database (Denmark)

    Sivebæk, Ion Marius; Samoilov, Vladimir N; Persson, Bo N J

    2008-01-01

    We present molecular dynamics friction calculations for confined hydrocarbon solids with molecular lengths from 20 to 1400 carbon atoms. Two cases are considered: a) polymer sliding against a hard substrate, and b) polymer sliding on polymer. In the first setup the shear stresses are relatively...... independent of molecular length. For polymer sliding on polymer the friction is significantly larger, and dependent on the molecular chain length. In both cases, the shear stresses are proportional to the squeezing pressure and finite at zero load, indicating an adhesional contribution to the friction force...

  15. Effects of third-order torque on frictional force of self-ligating brackets.

    Science.gov (United States)

    Muguruma, Takeshi; Iijima, Masahiro; Brantley, William A; Ahluwalia, Karamdeep S; Kohda, Naohisa; Mizoguchi, Itaru

    2014-11-01

    To investigate the effects of third-order torque on frictional properties of self-ligating brackets (SLBs). Three SLBs (two passive and one active) and three archwires (0.016 × 0.022-inch nickel-titanium, and 0.017 × 0.025-inch and 0.019 × 0.025-inch stainless steel) were used. Static friction was measured by drawing archwires though bracket slots with four torque levels (0°, 10°, 20°, 30°), using a mechanical testing machine (n  =  10). A conventional stainless-steel bracket was used for comparison. RESULTS were subjected to Kruskal-Wallis and Mann-Whitney U-tests. Contact between the bracket and wire was studied using a scanning electron microscope. In most bracket-wire combinations, increasing the torque produced a significant increase in static friction. Most SLB-wire combinations at all torques produced less friction than that from the conventional bracket. Active-type SLB-wire combinations showed higher friction than that from passive-type SLB-wire combinations in most conditions. When increasing the torque, more contact between the wall of a bracket slot and the edge of a wire was observed for all bracket types. Increasing torque when using SLBs causes an increase in friction, since contact between the bracket slot wall and the wire edge becomes greater; the design of brackets influences static friction.

  16. Spine growth mechanisms: friction and seismicity at Mt. Unzen, Japan

    Science.gov (United States)

    Hornby, Adrian; Kendrick, Jackie; Hirose, Takehiro; Henton De Angelis, Sarah; De Angelis, Silvio; Umakoshi, Kodo; Miwa, Takahiro; Wadsworth, Fabian; Dingwell, Don; Lavallee, Yan

    2014-05-01

    The final episode of dome growth during the 1991-1995 eruption of Mt. Unzen was characterised by spine extrusion accompanied by repetitive seismicity. This type of cyclic activity has been observed at several dome-building volcanoes and recent work suggests a source mechanism of brittle failure of magma in the conduit. Spine growth may proceed by densification and closure of permeable pathways within the uppermost conduit magma, leading to sealing of the dome and inflation of the edifice. Amplified stresses on the wall rock and plug cause brittle failure near the conduit wall once static friction forces are overcome, and during spine growth these fractures may propagate to the dome surface. The preservation of these features is rare, and the conduit is typically inaccessible; therefore spines, the extruded manifestation of upper conduit material, provide the opportunity to study direct evidence of brittle processes in the conduit. At Mt. Unzen the spine retains evidence for brittle deformation and slip, however mechanical constraints on the formation of these features and their potential impact on eruption dynamics have not been well constrained. Here, we conduct an investigation into the process of episodic spine growth using high velocity friction apparatus at variable shear slip rate (0.4-1.5 m.s-1) and normal stress (0.4-3.5 MPa) on dome rock from Mt. Unzen, generating frictional melt at velocity >0.4 m.s-1 and normal stress >0.7 MPa. Our results show that the presence of frictional melt causes a deviation from Byerlee's frictional rule for rock friction. Melt generation is a disequilibrium process: initial amphibole breakdown leads to melt formation, followed by chemical homogenization of the melt layer. Ultimately, the experimentally generated frictional melts have a similar final chemistry, thickness and comminuted clast size distribution, thereby facilitating the extrapolation of a single viscoelastic model to describe melt-lubricated slip events at Mt

  17. Slip versus Friction : Modifying the Navier condition

    Science.gov (United States)

    Kotsalis, Evangelos; Walther, Jens; Koumoutsakos, Petros

    2006-03-01

    The modeling of fluid-solid interfaces remains one of the key challenges in fluid mechanics. The prevailing model, attributed to Navier, defines the fluid ``slip'' velocity as proportional to the wall shear and a parameter defined as the slip length. Several works have in turn proposed models for this slip length but no universal model for the slip velocity has been accepted. We present results from large scale molecular dynamics simulations of canonical flow problems, indicating, that the inadequacy of this classic model, stems from not properly accounting for the pressure field. We propose and validate a new model, based on the fundamental observation that the finite ``slip'' velocity is a result of an imbalance between fluid and solid intermolecular forces. An excess force on the fluid elements will lead to their acceleration which in turn may result in a slip velocity at the interface. We formulate the slip velocity in terms of fluid-solid friction Ff and propose a generalized boundary condition: Ff= Fs+ Fp= λuus+ λpp where p denotes the pressure, and λuand λp the viscous and static friction coefficients, for which universal constants are presented. We demonstrate that the present model can overcome difficulties encountered by the classical slip model in canonical flow configurations.

  18. Multimodal Friction Ignition Tester

    Science.gov (United States)

    Davis, Eddie; Howard, Bill; Herald, Stephen

    2009-01-01

    The multimodal friction ignition tester (MFIT) is a testbed for experiments on the thermal and mechanical effects of friction on material specimens in pressurized, oxygen-rich atmospheres. In simplest terms, a test involves recording sensory data while rubbing two specimens against each other at a controlled normal force, with either a random stroke or a sinusoidal stroke having controlled amplitude and frequency. The term multimodal in the full name of the apparatus refers to a capability for imposing any combination of widely ranging values of the atmospheric pressure, atmospheric oxygen content, stroke length, stroke frequency, and normal force. The MFIT was designed especially for studying the tendency toward heating and combustion of nonmetallic composite materials and the fretting of metals subjected to dynamic (vibrational) friction forces in the presence of liquid oxygen or pressurized gaseous oxygen test conditions approximating conditions expected to be encountered in proposed composite material oxygen tanks aboard aircraft and spacecraft in flight. The MFIT includes a stainless-steel pressure vessel capable of retaining the required test atmosphere. Mounted atop the vessel is a pneumatic cylinder containing a piston for exerting the specified normal force between the two specimens. Through a shaft seal, the piston shaft extends downward into the vessel. One of the specimens is mounted on a block, denoted the pressure block, at the lower end of the piston shaft. This specimen is pressed down against the other specimen, which is mounted in a recess in another block, denoted the slip block, that can be moved horizontally but not vertically. The slip block is driven in reciprocating horizontal motion by an electrodynamic vibration exciter outside the pressure vessel. The armature of the electrodynamic exciter is connected to the slip block via a horizontal shaft that extends into the pressure vessel via a second shaft seal. The reciprocating horizontal

  19. A Pedagogical Model of Static Friction

    CERN Document Server

    Pickett, Galen T

    2015-01-01

    While dry Coulombic friction is an elementary topic in any standard introductory course in mechanics, the critical distinction between the kinetic and static friction forces is something that is both hard to teach and to learn. In this paper, I describe a geometric model of static friction that may help introductory students to both understand and apply the Coulomb static friction approximation.

  20. Friction Material Composites Materials Perspective

    CERN Document Server

    Sundarkrishnaa, K L

    2012-01-01

    Friction Material Composites is the first of the five volumes which strongly educates and updates engineers and other professionals in braking industries, research and test labs. It explains besides the formulation of design processes and its complete manufacturing input. This book gives an idea of mechanisms of friction and how to control them by designing .The book is  useful for designers  of automotive, rail and aero industries for designing the brake systems effectively with the integration of friction material composite design which is critical. It clearly  emphasizes the driving  safety and how serious designers should  select the design input. The significance of friction material component like brake pad or a liner as an integral part of the brake system of vehicles is explained. AFM pictures at nanolevel illustrate broadly the explanations given.

  1. Friction role in deformation behaviors of high-strength TA18 tubes in numerical control bending

    Science.gov (United States)

    Fang, Jun; Liang, Chuang; Lu, Shiqiang; Wang, Kelu; Zheng, Deliang

    2017-09-01

    In order to reveal the friction role in deformation behaviors of high-strength TA18 tubes in numerical control (NC) bending, a three dimensional (3D) elastic-plastic finite element (FE) model of high-strength TA18 tubes for whole process in NC bending was established based on ABAQUS code, and its reliability was validated by the experimental results in literature. Then, the bending deformation behaviors under different friction coefficients between tube and various dies were studied with respect to multiple defects such as wall thinning, wall thickening and cross section deformation. The results show that the wall thinning ratio and cross section deformation ratio increase with the increase of the friction coefficient between mandrel and tube f m or decrease of the friction coefficient between pressure die and tube f p, while the friction coefficient between bending die and tube f b has no obvious effect on these. The wall thickening ratio decreases with the increase of f b, f m or decrease of f p.

  2. Skin-friction measurements in a turbulent boundary layer under the influence of free-stream turbulence

    Science.gov (United States)

    Esteban, Luis Blay; Dogan, Eda; Rodríguez-López, Eduardo; Ganapathisubramani, Bharathram

    2017-09-01

    This experimental investigation deals with the influence of free-stream turbulence (FST) produced by an active grid on the skin friction of a zero-pressure-gradient turbulent boundary layer. Wall shear stress is obtained by oil-film interferometry. In addition, hot-wire anemometry was performed to obtain wall-normal profiles of streamwise velocity. This enables the skin friction to be deduced from the mean profile. Both methods show remarkable agreement for every test case. Although skin friction is shown to increase with FST, the trend with Reynolds number is found to be similar to cases without FST. Furthermore, once the change in the friction velocity is accounted for, the self-similarity of the logarithmic region and below (i.e. law of the wall) appears to hold for all FST cases investigated.

  3. Kinetic Friction Coefficient of Ice,

    Science.gov (United States)

    1985-03-01

    For the hardest ice tested (xi = 0.33 described by Rabinowicz (1965), where To is inter- mm, H, = 1525 kPa), the calculated values of a preted as...material with a low elastic pressures. The frictional force was measured at modulus ( Rabinowicz 1965). It has been observed the application point of...tion 10, pp. 8-16. Barnes, P. and D. Tabor (1966) Plastic flow and Rabinowicz , E. (1965) Friction and Wear of Mate- pressure melting in the deformation

  4. Peak mass and dynamical friction

    CERN Document Server

    Del Popolo, A

    1995-01-01

    We show how the results given by several authors relatively to the mass of a density peak are changed when small scale substructure induced by dynamical friction are taken into account. The peak mass obtained is compared to the result of Peacock \\& Heavens (1990) and to the peak mass when dynamical friction is absent to show how these effects conspire to reduce the mass accreted by the peak.

  5. Tire/runway friction interface

    Science.gov (United States)

    Yager, Thomas J.

    1990-01-01

    An overview is given of NASA Langley's tire/runway pavement interface studies. The National Tire Modeling Program, evaluation of new tire and landing gear designs, tire wear and friction tests, and tire hydroplaning studies are examined. The Aircraft Landing Dynamics Facility is described along with some ground friction measuring vehicles. The major goals and scope of several joint FAA/NASA programs are identified together with current status and plans.

  6. Labor Supply and Optimization Frictions

    DEFF Research Database (Denmark)

    Søgaard, Jakob Egholt

    2015-01-01

    In this paper I investigate the nature of optimization frictions by studying the labor market of Danish students. This particular labor market is an interesting case study as it features a range of special institutional settings that affect students’ incentive to earn income and comparing outcomes...... theory. More concretely I find the dominate optimization friction to be individuals’ inattention about their earnings during the year, while real adjustment cost and gradual learning appears to be of less importance....

  7. Frictional Effects on Gear Tooth Contact Analysis

    OpenAIRE

    Zheng Li; Ken Mao

    2013-01-01

    The present paper concentrates on the investigations regarding the situations of frictional shear stress of gear teeth and the relevant frictional effects on bending stresses and transmission error in gear meshing. Sliding friction is one of the major reasons causing gear failure and vibration; the adequate consideration of frictional effects is essential for understanding gear contact behavior accurately. An analysis of tooth frictional effect on gear performance in spur gear is presented us...

  8. Hydrodynamics of ultra-relativistic bubble walls

    Directory of Open Access Journals (Sweden)

    Leonardo Leitao

    2016-04-01

    Full Text Available In cosmological first-order phase transitions, gravitational waves are generated by the collisions of bubble walls and by the bulk motions caused in the fluid. A sizeable signal may result from fast-moving walls. In this work we study the hydrodynamics associated to the fastest propagation modes, namely, ultra-relativistic detonations and runaway solutions. We compute the energy injected by the phase transition into the fluid and the energy which accumulates in the bubble walls. We provide analytic approximations and fits as functions of the net force acting on the wall, which can be readily evaluated for specific models. We also study the back-reaction of hydrodynamics on the wall motion, and we discuss the extrapolation of the friction force away from the ultra-relativistic limit. We use these results to estimate the gravitational wave signal from detonations and runaway walls.

  9. Friction anisotropy in boronated graphite

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, N., E-mail: niranjan@igcar.gov.in [Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam (India); Radhika, R. [Crystal Growth Centre, Anna University, Chennai (India); Kozakov, A.T. [Research Institute of Physics, Southern Federal University, Rostov-on-Don (Russian Federation); Pandian, R. [Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam (India); Chakravarty, S. [UGC-DAE CSR, Kalpakkam (India); Ravindran, T.R.; Dash, S.; Tyagi, A.K. [Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam (India)

    2015-01-01

    Graphical abstract: - Highlights: • Friction anisotropy in boronated graphite is observed in macroscopic sliding condition. • Low friction coefficient is observed in basal plane and becomes high in prismatic direction. • 3D phase of boronated graphite transformed into 2D structure after friction test. • Chemical activity is high in prismatic plane forming strong bonds between the sliding interfaces. - Abstract: Anisotropic friction behavior in macroscopic scale was observed in boronated graphite. Depending upon sliding speed and normal loads, this value was found to be in the range 0.1–0.35 in the direction of basal plane and becomes high 0.2–0.8 in prismatic face. Grazing-incidence X-ray diffraction analysis shows prominent reflection of (0 0 2) plane at basal and prismatic directions of boronated graphite. However, in both the wear tracks (1 1 0) plane become prominent and this transformation is induced by frictional energy. The structural transformation in wear tracks is supported by micro-Raman analysis which revealed that 3D phase of boronated graphite converted into a disordered 2D lattice structure. Thus, the structural aspect of disorder is similar in both the wear tracks and graphite transfer layers. Therefore, the crystallographic aspect is not adequate to explain anisotropic friction behavior. Results of X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy shows weak signature of oxygen complexes and functional groups in wear track of basal plane while these species dominate in prismatic direction. Abundance of these functional groups in prismatic plane indicates availability of chemically active sites tends to forming strong bonds between the sliding interfaces which eventually increases friction coefficient.

  10. Friction factor of annular Poiseuille flow in a transitional regime

    Directory of Open Access Journals (Sweden)

    Takahiro Ishida

    2016-12-01

    Full Text Available Annular Poiseuille flows in a transitional regime were investigated by direct numerical simulations with an emphasis on turbulent statistics including the friction factor that are affected by the presence of large-scale transitional structures. Five different radius ratios in the range of 0.1–0.8 and several friction Reynolds numbers in the range of 48–150 were analyzed to consider various flow states accompanied by characteristic transitional structures. Three characteristic structures, namely, turbulent–laminar coexistence referred to as “(straight puff,”“helical puff,” and “helical turbulence” were observed. The selection of the structures depends on both the radius ratio and the Reynolds number. The findings indicated that despite the transitional state with a turbulent–laminar coexistence, the helical turbulence resulted in a friction factor that was as high as the fully turbulent value. In contrast, with respect to the occurrence of streamwise-finite transitional structures, such as straight/helical puffs, the friction factor decreased in a stepwise manner toward a laminar level. The turbulent statistics revealed asymmetric distributions with respect to the wall-normal direction wherein the profiles and magnitudes were significantly influenced by the occurrence of transitional structures.

  11. Versatile Friction Stir Welding/Friction Plug Welding System

    Science.gov (United States)

    Carter, Robert

    2006-01-01

    A proposed system of tooling, machinery, and control equipment would be capable of performing any of several friction stir welding (FSW) and friction plug welding (FPW) operations. These operations would include the following: Basic FSW; FSW with automated manipulation of the length of the pin tool in real time [the so-called auto-adjustable pin-tool (APT) capability]; Self-reacting FSW (SRFSW); SR-FSW with APT capability and/or real-time adjustment of the distance between the front and back shoulders; and Friction plug welding (FPW) [more specifically, friction push plug welding] or friction pull plug welding (FPPW) to close out the keyhole of, or to repair, an FSW or SR-FSW weld. Prior FSW and FPW systems have been capable of performing one or two of these operations, but none has thus far been capable of performing all of them. The proposed system would include a common tool that would have APT capability for both basic FSW and SR-FSW. Such a tool was described in Tool for Two Types of Friction Stir Welding (MFS- 31647-1), NASA Tech Briefs, Vol. 30, No. 10 (October 2006), page 70. Going beyond what was reported in the cited previous article, the common tool could be used in conjunction with a plug welding head to perform FPW or FPPW. Alternatively, the plug welding head could be integrated, along with the common tool, into a FSW head that would be capable of all of the aforementioned FSW and FPW operations. Any FSW or FPW operation could be performed under any combination of position and/or force control.

  12. Stress profile in a two-dimensional silo: Effects induced by friction mobilization

    Science.gov (United States)

    Vivanco, Francisco; Mercado, José; Santibáñez, Francisco; Melo, Francisco

    2016-08-01

    The effects of friction mobilization on the stress profile within a two-dimensional silo are investigated via simulations of discrete elements. Friction mobilization is driven by cyclic vertical displacement of the sidewalls. Two regimes have been observed for small filling height, with stress profiles identified as saturated (Janssen's profile) and exponentially growing. The transition between these regimes is denoted by an almost linear stress profile, similar to that of a hydrostatic system, with a significantly greater characteristic height compared to the height of the column of grains. For tall columns, the process of friction inversion is more complex. A partial inversion of friction mobilization is observed when the motion is reversed from upward to downward, which results in two coexisting zones of opposite mobilization. These zones are separated by a wide compaction front with a gradual upward progression sustained by the displacement of the walls. Conversely, if the motion is reversed, the two opposing friction mobilization zones retract, the transition zone becomes smooth, and the system rapidly transforms from two coexisting mobilization states to a Janssen-like regime. In both regimes, the general characteristics from the resulting stress profiles are depicted by generalizing Janssen's equation to include partial mobilization through the varying effective friction coefficient along the silo walls.

  13. Stress profile in a two-dimensional silo: Effects induced by friction mobilization.

    Science.gov (United States)

    Vivanco, Francisco; Mercado, José; Santibáñez, Francisco; Melo, Francisco

    2016-08-01

    The effects of friction mobilization on the stress profile within a two-dimensional silo are investigated via simulations of discrete elements. Friction mobilization is driven by cyclic vertical displacement of the sidewalls. Two regimes have been observed for small filling height, with stress profiles identified as saturated (Janssen's profile) and exponentially growing. The transition between these regimes is denoted by an almost linear stress profile, similar to that of a hydrostatic system, with a significantly greater characteristic height compared to the height of the column of grains. For tall columns, the process of friction inversion is more complex. A partial inversion of friction mobilization is observed when the motion is reversed from upward to downward, which results in two coexisting zones of opposite mobilization. These zones are separated by a wide compaction front with a gradual upward progression sustained by the displacement of the walls. Conversely, if the motion is reversed, the two opposing friction mobilization zones retract, the transition zone becomes smooth, and the system rapidly transforms from two coexisting mobilization states to a Janssen-like regime. In both regimes, the general characteristics from the resulting stress profiles are depicted by generalizing Janssen's equation to include partial mobilization through the varying effective friction coefficient along the silo walls.

  14. Wonderful Walls

    Science.gov (United States)

    Greenman, Jim

    2006-01-01

    In this article, the author emphasizes the importance of "working" walls in children's programs. Children's programs need "working" walls (and ceilings and floors) which can be put to use for communication, display, storage, and activity space. The furnishings also work, or don't work, for the program in another sense: in aggregate, they serve as…

  15. Ambiguous walls

    DEFF Research Database (Denmark)

    Mody, Astrid

    2012-01-01

    The introduction of Light Emitting Diodes (LEDs) in the built environment has encouraged myriad applications, often embedded in surfaces as an integrated part of the architecture. Thus the wall as responsive luminous skin is becoming, if not common, at least familiar. Taking into account how wall...

  16. The Reality of Casimir Friction

    Directory of Open Access Journals (Sweden)

    Kimball A. Milton

    2016-04-01

    Full Text Available For more than 35 years theorists have studied quantum or Casimir friction, which occurs when two smooth bodies move transversely to each other, experiencing a frictional dissipative force due to quantum electromagnetic fluctuations, which break time-reversal symmetry. These forces are typically very small, unless the bodies are nearly touching, and consequently such effects have never been observed, although lateral Casimir forces have been seen for corrugated surfaces. Partly because of the lack of contact with observations, theoretical predictions for the frictional force between parallel plates, or between a polarizable atom and a metallic plate, have varied widely. Here, we review the history of these calculations, show that theoretical consensus is emerging, and offer some hope that it might be possible to experimentally confirm this phenomenon of dissipative quantum electrodynamics.

  17. The Reality of Casimir Friction

    CERN Document Server

    Milton, K A; Brevik, I

    2015-01-01

    For more than 35 years theorists have studied quantum or Casimir friction, which occurs when two smooth bodies move transversely to each other, experiencing a frictional dissipative force due to quantum fluctuations. These forces are typically very small, unless the bodies are nearly touching, and consequently such effects have never been observed, although lateral Casimir forces have been seen for corrugated surfaces. Because of the lack of contact with phenomena, theoretical predictions for the frictional force between parallel plates, or between a polarizable atom and a metallic plate, have varied widely. Here we review the history of these calculations, show that theoretical consensus is emerging, and offer some hope that it might be possible to experimentally confirm this phenomenon of dissipative quantum electrodynamics.

  18. The microphysics of phyllosilicate friction

    Science.gov (United States)

    den Hartog, Sabine A. M.; Faulkner, Daniel R.; Spiers, Christopher J.

    2017-04-01

    Phyllosilicate-rich foliations in fault rocks are often thought to reduce overall fault strength and promote fault stability when forming an interconnected network. Indeed, laboratory measurements have shown that the average friction coefficient of dry phyllosilicates of 0.5 is reduced to 0.3 when wet or even 0.1 for smectite. A widely accepted interpretation of these observations is that the strength of phyllosilicates is controlled by breaking of interlayer bonds to form new cleavage surfaces when dry and by the low strength of surface-bound water films when wet. However, the correlation between phyllosilicate shear strength and interlayer bond strength, which formed the basis for this interpretation, was not reproduced in recent experiments (Behnsen and Faulkner, 2012) and is not supported by the latest calculations of the interlayer bond energies (Sakuma and Suehara, 2015). The accepted explanation for phyllosilicate friction also fails to account for the velocity dependence or (a-b) values, which decrease with temperature, reaching a minimum at intermediate temperatures, before increasing again at higher temperatures (Den Hartog et al., 2013, 2014). In this study, we developed a microphysical model for phyllosilicate friction, involving frictional sliding along atomically flat phyllosilicate grain interfaces, with overlapping grain edges forming barriers to sliding. Assuming that the amount of overlap is controlled by crystal plastic bending of grains into pores, together with rate-dependent edge-site cleavage, our model predicts most of the experimentally observed trends in frictional behaviour and provides a basis for extrapolation of laboratory friction data on phyllosilicates to natural conditions.

  19. Low temperature friction force microscopy

    Science.gov (United States)

    Dunckle, Christopher Gregory

    The application of friction force techniques within atomic force microscopy (AFM) allows for direct measurements of friction forces at a sliding, single-asperity interface. The temperature dependence of such single-asperity contacts provides key insight into the comparative importance of dissipative mechanisms that result in dry sliding friction. A variable temperature (VT), ultrahigh vacuum (UHV) AFM was used with an interface consisting of a diamond coated AFM tip and diamond-like carbon sample in a nominal sample temperature range of 90 to 275K. The results show that the coefficient of kinetic friction, mu k, has a linear dependence that is monotonically increasing with temperature varying from 0.28 to 0.38. To analyze this data it is necessary to correlate the sample temperature to the interface temperature. A detailed thermal model shows that the sample temperature measured by a macroscopic device can be very different from the temperature at the contact point. Temperature gradients intrinsic to the design of VT, UHV AFMs result in extreme, non-equilibrium conditions with heat fluxes on the order of gigawatts per squared meter through the interface, which produce a discontinuous step in the temperature profile due to thermal boundary impedance. The conclusion from this model is that measurements acquired by VT, UHV AFM, including those presented in this thesis, do not provide meaningful data on the temperature dependence of friction for single-asperities. Plans for future work developing an isothermal AFM capable of the same measurements without the introduction of temperature gradients are described. The experimental results and thermal analysis described in this thesis have been published in the Journal of Applied Physics, "Temperature dependence of single-asperity friction for a diamond on diamondlike carbon interface", J. App. Phys., 107(11):114903, 2010.

  20. Friction resistance for gas flow in smooth microtubes

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A new tube-cutting method was used to measure the pressure and Mach number distribution along a microtube of 108.3 μm. Experiments were also performed concerning the average Fanning friction factors of five kinds of microtubes whose diameters range from 80.0 to 166.6 μm. It is found that the pressure distribution in a microtube becomes nonlinear at a high Mach number and the product of measured average Fanning friction factors Cf and Reynolds number Re is higher than 16. Numerical results show that the gas compressibility leads to a variation of the velocity profile from parabolic, and results in a large velocity gradient at the tube inner wall surface. The transition from laminar to turbulence in microtubes also occurs at Re≈2 300, and the phenomenon of early transition is not observed in the experiments.

  1. Friction resistance for gas flow in smooth microtubes

    Institute of Scientific and Technical Information of China (English)

    杜东兴; 李志信; 过增元

    2000-01-01

    A new tube-cutting method was used to measure the pressure and Mach number distribution along a microtube of 108.3 μm. Experiments were also performed concerning the average Fanning friction factors of five kinds of microtubes whose diameters range from 80.0 to 166.6 μm. It is found that the pressure distribution in a microtube becomes nonlinear at a high Mach number and the product of measured average Fanning friction factors 75, and Reynolds number Re is higher than 16. Numerical results show that the gas compressibility leads to a variation of the velocity profile from parabolic, and results in a large velocity gradient at the tube inner wall surface. The transition from laminar to turbulence in microtubes also occurs at Re ≈ 2 300, and the phenomenon of early transition is not observed in the experiments.

  2. Entrance and exit region friction factor models for annular seal analysis. Ph.D. Thesis

    Science.gov (United States)

    Elrod, David Alan

    1988-01-01

    The Mach number definition and boundary conditions in Nelson's nominally-centered, annular gas seal analysis are revised. A method is described for determining the wall shear stress characteristics of an annular gas seal experimentally. Two friction factor models are developed for annular seal analysis; one model is based on flat-plate flow theory; the other uses empirical entrance and exit region friction factors. The friction factor predictions of the models are compared to experimental results. Each friction model is used in an annular gas seal analysis. The seal characteristics predicted by the two seal analyses are compared to experimental results and to the predictions of Nelson's analysis. The comparisons are for smooth-rotor seals with smooth and honeycomb stators. The comparisons show that the analysis which uses empirical entrance and exit region shear stress models predicts the static and stability characteristics of annular gas seals better than the other analyses. The analyses predict direct stiffness poorly.

  3. SURFACE DYNAMIC FRICTION OF POLYMER GELS

    Institute of Scientific and Technical Information of China (English)

    J.P.Gong; G.Kagata; Y.Iwasaki; Y.Osada

    2000-01-01

    The sliding friction of various kinds of hydrogels has been studied and it was found that the frictional behaviors of the hydrogels do not conform to Amonton's law F =μW which well describes the friction of solids. The frictional force and its dependence on the load are quite different depending on the chemical structures of the gels, surface properties of the opposing substrates, and the measurement condition. The gel friction is explained in terms of interfacial interaction, either attractive or repulsive, between the polymer chain and the solid surface. According to this model, the friction is ascribed to the viscous flow of solvent at the interface in the repulsive case. In the attractive case, the force to detach the adsorbing chain from the substrate appears as friction. The surface adhesion between glass particles and gels measured by AFM showed a good correlation with the friction, which supported the repulsion-adsorption model proposed by the authors.

  4. The Friction of Saline Ice on Aluminium

    Directory of Open Access Journals (Sweden)

    Christopher Wallen-Russell

    2016-01-01

    Full Text Available The friction of ice on other materials controls loading on offshore structures and vessels in the Arctic. However, ice friction is complicated, because ice in nature exists near to its melting point. Frictional heating can cause local softening and perhaps melting and lubrication, thus affecting the friction and creating a feedback loop. Ice friction is therefore likely to depend on sliding speed and sliding history, as well as bulk temperature. The roughness of the sliding materials may also affect the friction. Here we present results of a series of laboratory experiments, sliding saline ice on aluminium, and controlling for roughness and temperature. We find that the friction of saline ice on aluminium μice-al=0.1 typically, but that this value varies with sliding conditions. We propose physical models which explain the variations in sliding friction.

  5. DRA-10. Friction reducing additives: The activity 1987 - 1996; DRA-10. Friktionsnedsaettande tillsatser: Verksamheten 1987 - 1996

    Energy Technology Data Exchange (ETDEWEB)

    Bjurstroem, H. [AaF Energikonsult Stockholm AB (Sweden)

    1996-06-01

    The purpose of the work was to facilitate the introduction of the additives into Swedish district heating networks. R and D work has been performed in order to build up know-how that allows an assessment of the usefulness of the additives and to investigate questions that have not been treated in foreign programs, but are important in a Swedish context. The research has been focused on hydrodynamic problems and environmental questions. The influence of wall roughness has been investigated using three corrugated tubes as model rough-walled tubes. The turbulent flow is fully rough in one of the tubes: reduction deteriorates but the maximal shear stresses that can be withstood by the solution before friction reduction brakes down are increased. Flow in the other two tubes is transitionally rough and the wall structure does not affect friction reduction. In a naturally rough tube, reduction also deteriorates and critical shear stresses increase in spite of the flow being transitionally rough. The results are important for the design of heat exchangers. Pyranine, which is a leak tracing substance, reduces the domain of temperatures and mean wall shear stresses where friction reduction is obtained with cationic additive Habon-G. However, this effect may be overcome by increasing the additive concentration. Regarding environmental questions, only preliminary results are available and the main part of the work remains to be done. The information needs for an environmental assessment of the use of friction reducing additives has been defined. 27 refs

  6. Heat transfer and friction factors in the ribbed square convergent and divergent channels

    Science.gov (United States)

    Lee, M. S.; Ahn, S. W.

    2016-06-01

    Heat transfer and friction factors are reported for the measurements of turbulent flows in the convergent and divergent square channels with one-sided ribbed wall as well as two opposite in-line ribbed walls. The study covers three different hydraulic diameter ratios between inlet and exit at the test section such as Dho/Dhi = 0.75, 1.0, and 1.33 and Reynolds numbers in the range of 25,000-79,000. The channels, composing of ten isolated copper sections in the length of test section of 1 m, have the hydraulic diameter of 87.5 mm for the straight channel (Dho/Dhi = 1.0); the rib height-to-hydraulic diameter is 0.114; the rib pitch-to-height ratio equals 10. On the contrary to public opinion that the friction factor depends on the portion of the ribbed area, the total friction factor in the two opposite ribbed walls are lower than in the one-sided ribbed wall in the divergent channel of Dho/Dhi = 1.33 because the total pressure, summing positive dynamic and negative static pressures, is acted. The results show that the two opposite ribbed divergent channel of Dho/Dhi = 1.33 provides the best heat transfer enhancement and the two opposite ribbed convergent channel of Dho/Dhi = 0.75 provides the worst friction factor enhancement, and the ribbed divergent channels are generally recommended.

  7. Coordination Frictions and Job Heterogeneity

    DEFF Research Database (Denmark)

    Kennes, John; le Maire, Christian Daniel

    This paper develops and extends a dynamic, discrete time, job to worker matching model in which jobs are heterogeneous in equilibrium. The key assumptions of this economic environment are (i) matching is directed and (ii) coordination frictions lead to heterogeneous local labor markets. We de- rive...

  8. Frictional heating of tribological contacts

    NARCIS (Netherlands)

    Bos, Johannes

    1995-01-01

    Wherever friction occurs, mechanical energy is transformed into heat. The tem­ perature rise associated with this heating can have an important influence on the tribological behaviour of the contacting components. Apart from determining per­ formance, thermal phenomena affect reliability and may cau

  9. Friction Sensitivity of Primary Explosives

    Science.gov (United States)

    1982-09-01

    potassium dinitrobenzofuroxan none tetrazene 407913 tetrazene 7902454 The mixes which were tested are: NOL 130 (basic lead styphnate , barium nitrate, lead...azide, tetrazene, and antimony sulfide); PA 100 (normal lead styphnate , barium nitrate, tetrazene, lead dioxide, calcium silicide, and antimony...styuhnate, basic lead styphnate , potassium dinitrobenzofuroxan, and tetrazene were tested to determine the- 10% and 50% probability of friction

  10. Friction of atomically stepped surfaces

    Science.gov (United States)

    Dikken, R. J.; Thijsse, B. J.; Nicola, L.

    2017-03-01

    The friction behavior of atomically stepped metal surfaces under contact loading is studied using molecular dynamics simulations. While real rough metal surfaces involve roughness at multiple length scales, the focus of this paper is on understanding friction of the smallest scale of roughness: atomic steps. To this end, periodic stepped Al surfaces with different step geometry are brought into contact and sheared at room temperature. Contact stress that continuously tries to build up during loading, is released with fluctuating stress drops during sliding, according to the typical stick-slip behavior. Stress release occurs not only through local slip, but also by means of step motion. The steps move along the contact, concurrently resulting in normal migration of the contact. The direction of migration depends on the sign of the step, i.e., its orientation with respect to the shearing direction. If the steps are of equal sign, there is a net migration of the entire contact accompanied by significant vacancy generation at room temperature. The stick-slip behavior of the stepped contacts is found to have all the characteristic of a self-organized critical state, with statistics dictated by step density. For the studied step geometries, frictional sliding is found to involve significant atomic rearrangement through which the contact roughness is drastically changed. This leads for certain step configurations to a marked transition from jerky sliding motion to smooth sliding, making the final friction stress approximately similar to that of a flat contact.

  11. Rotary Engine Friction Test Rig Development Report

    Science.gov (United States)

    2011-12-01

    5  4.  Friction Rig Development 7  5.  AutoCAD ...Figure 4. Engine friction test rig AutoCAD model. ........................................................................8  Figure 5. Engine...top dead center. 8 5. AutoCAD Model Development A model of the rotary engine friction test rig was developed to determine the optimal

  12. Asbestos free friction composition for brake linings

    Indian Academy of Sciences (India)

    Arnab Ganguly; Raji George

    2008-02-01

    An asbestos free friction material composite for brake linings is synthesized containing fibrous reinforcing constituents, friction imparting and controlling additives, elastomeric additives, fire retarding components and a thermosetting resin. The composite shows exemplary friction characteristics and has great resistance to wear and shows good temperature stability.

  13. Multiscale friction modeling for sheet metal forming

    NARCIS (Netherlands)

    Hol, J.; Cid Alfaro, M.V.; de Rooij, Matthias B.; Meinders, Vincent T.; Felder, Eric; Montmitonnet, Pierre

    2010-01-01

    The most often used friction model for sheet metal forming simulations is the relative simple Coulomb friction model. This paper presents a more advanced friction model for large scale forming simulations based on the surface change on the micro-scale. The surface texture of a material changes when

  14. A thermodynamic model of sliding friction

    Directory of Open Access Journals (Sweden)

    Lasse Makkonen

    2012-03-01

    Full Text Available A first principles thermodynamic model of sliding friction is derived. The model predictions are in agreement with the observed friction laws both in macro- and nanoscale. When applied to calculating the friction coefficient the model provides a quantitative agreement with recent atomic force microscopy measurements on a number of materials.

  15. Wall Turbulence.

    Science.gov (United States)

    Hanratty, Thomas J.

    1980-01-01

    This paper gives an account of research on the structure of turbulence close to a solid boundary. Included is a method to study the flow close to the wall of a pipe without interferring with it. (Author/JN)

  16. Analysis of the moment caused by friction of cardan joint. Cardan joint no friction kishinryoku kaiseki

    Energy Technology Data Exchange (ETDEWEB)

    Ono, K.; Yagi, Shida, T. (Atsugi Unisia Corp., Kanagawa (Japan))

    1990-10-01

    Analyzing the vibromotive force, generated by the friction, in generation morphology, level, dynamical characteristics, etc., through measurement of joint unit friction simulation of frictional vibromotive force and on-platform measurement of propeller shaft in vibromotive force, the present report investigated the influence of friction on the vehicle in sound vibration performance. By a vibromotive force measurement system, internally equipped with a piezoelectric type force meter, frictional vibromotive force could be quantitatively grasped. The friction must be appropriately controlled, because the moment, generated by it, is expected to be put in the vehicle by intermediation of a supporting point and adversely influence the sound vibration performance. Apart from the above, elucidation was made of relation between the ordinal number components of rotation of vibromotive force and friction, calculation of reaction force at the supporting point by the frictional measurement, relation between the joint angle and frictional vibromotive force, second couple force due to the friction, etc. 3 refs., 15 figs.

  17. A One-Dimensional Global-Scaling Erosive Burning Model Informed by Blowing Wall Turbulence

    Science.gov (United States)

    Kibbey, Timothy P.

    2014-01-01

    A derivation of turbulent flow parameters, combined with data from erosive burning test motors and blowing wall tests results in erosive burning model candidates useful in one-dimensional internal ballistics analysis capable of scaling across wide ranges of motor size. The real-time burn rate data comes from three test campaigns of subscale segmented solid rocket motors tested at two facilities. The flow theory admits the important effect of the blowing wall on the turbulent friction coefficient by using blowing wall data to determine the blowing wall friction coefficient. The erosive burning behavior of full-scale motors is now predicted more closely than with other recent models.

  18. Deformation behaviors of 21-6-9 stainless steel tube numerical control bending under different friction conditions

    Institute of Scientific and Technical Information of China (English)

    方军; 鲁世强; 王克鲁; 姚正军

    2015-01-01

    For contact dominated numerical control (NC) bending process of tube, the effect of friction on bending deformation behaviors should be focused on to achieve precision bending forming. A three dimensional (3D) elastic-plastic finite element (FE) model of NC bending process was established under ABAQUS/Explicit platform, and its reliability was validated by the experiment. Then, numerical study on bending deformation behaviors under different frictions between tube and various dies was explored from multiple aspects such as wrinkling, wall thickness change and cross section deformation. The results show that the large friction of wiper die−tube reduces the wrinkling wave ratioη and cross section deformation degreeΔD and increases the wall thinning degreeΔt. The large friction of mandrel−tube causes largeη,Δt andΔD, and the onset of wrinkling near clamp die. The large friction of pressure die−tube reducesΔt andΔD, and the friction on this interface has little effect onη. The large friction of bending die−tube reducesη andΔD, and the friction on this interface has little effect onΔt. The reasonable friction coefficients on wiper die−tube, mandrel−tube, pressure die−tube and bending die−tube of 21-6-9 (0Cr21Ni6Mn9N) stainless steel tube in NC bending are 0.05−0.15, 0.05−0.15, 0.25−0.35 and 0.25−0.35, respectively. The results can provide a guideline for applying the friction conditions to establish the robust bending environment for stable and precise bending deformation of tube bending.

  19. Friction factor in smooth and rough gas pipelines. An experimental study

    Energy Technology Data Exchange (ETDEWEB)

    Sletfjerding, Elling

    1999-01-01

    Flow of high pressure natural gas in pipelines has been studied experimentally. Pipeline flow of natural gas is characterized by high Reynolds numbers due to the low viscosity and relatively high density of pressurized gas. Friction factor correlations for high Reynolds number flow in smooth and rough pipes were developed. To study the effect of wall roughness on pipe flow at high Reynolds numbers 8 test pipes with different wall roughness were fabricated. The wall roughness in 6 of the test pipes was varied by adding glass beads in an epoxy coating applied on the pipe wall. One test pipe was treated with a smooth epoxy coating and one was left untreated. The inner diameter of the test pipes was 150 mm. Measurements of the pressure drop in the pipes were made in a closed flow loop at line pressures of 25, 70, 95 and 120 bar. The Reynolds number of the flow was varied in the range 2-30 million. The wall roughness of the test pipes was measured with a stylus instrument. Correlations between the directly measured wall roughness and the friction factor at fully rough flow conditions were presented. To characterize the wall roughness of the test pipes a parameter combining a measure of the roughness height (R{sub q}) and the texture of the wall roughness was used. Due to the high Reynolds number of the flow, minute irregularities of the pipe wall had significant effect on the friction factor in the pipe. The measured wall roughness of the test pipes was in the range 1.4 < R{sub q} <31 (my)m. The flow experiments in test pipes was compared with data from operating pipelines in the North Sea. The offshore pipelines are coated with the same epoxy coating as used in the test pipes. The friction factor in coated offshore gas pipelines showed smooth behavior when the additional pressure drop due to welds were accounted for. The study of coated gas pipelines showed that the friction factor was significantly lower than predicted by standard correlations.

  20. PIV-based investigation of the skin friction of the flow over random fibrous media

    Science.gov (United States)

    Mirbod, Parisa; Gheisari, Reza

    2015-11-01

    Finite Reynolds number (Reflow over fibrous medium inside a rectangular duct was studied using a planar 2D PIV system. Three different fibrous materials with different porosities were used. Fibrous material lined the bottom wall of the duct along the length of the duct. The flow regime for all tests was laminar, and measurements were all done when the flow reached a steady state. Error and uncertainty sources in the experiments were also discussed. Shear rates were estimated at the surface of the fibrous media. As a conclusion to this study skin friction factor were calculated at the interface of all fibrous media at selected Reynolds number. Then using power function, curve fits with the Cf = a/Re form were found which could closely correlate skin friction and Reynolds number. To weaken the effect of near-wall errors in estimated shear rates and consequently skin friction, an average of shear rate estimation in a layer with thickness of 5 mm was calculated which was used to calculate an average skin friction. Correlations of average skin friction with average Reynolds number were also presented.

  1. Frictional energy barrier and blocking temperature in water molecules and carbon nanotubes system

    Science.gov (United States)

    Zhang, Jianwei; Li, Jiaxi; Li, Wenfeng

    2015-03-01

    Water transport through hydrophobic channels of single-walled carbon nanotubes has attracted a lot interests, especially, various potential applications of SWCNTs have been proposed for designing novel nanofluidic devices. By adopting Molecular dynamics method, we investigated mechanics and statistics properties of water molecules escaping from a confined single-walled carbon nanotube. From our numerical MD simulations and statistical model, we determined the friction energy barrier of water molecules in (10.10) SWCNT is 9.88 kcal/mol, and which is the minimal energy for flowing a water molecules in CNT. By only using friction energy barrier and relaxation time parameter, our model can fit all different situations MD simulation results. In order to describing the frictional lock behavior of water molecules, we introduced a new blocking temperature, below this temperature (391K for our system), water is locked in CNT due to friction energy barrier. We found that the blocking temperature is closely related to system response time, and it also shows a linear behavior to frictional energy barrier. Furthermore, we found several other interesting statistics results when a water molecules leaving SWCNTs. This work was supported by NSFC No. 11274240 and NO. 51471119.

  2. High temperature skin friction measurement

    Science.gov (United States)

    Tcheng, Ping; Holmes, Harlan K.; Supplee, Frank H., Jr.

    1989-01-01

    Skin friction measurement in the NASA Langley hypersonic propulsion facility is described. The sensor configuration utilized an existing balance, modified to provide thermal isolation and an increased standoff distance. For test run times of about 20 sec and ambient-air cooling of the test section and balance, the modified balance performed satisfactorily, even when it was subjected to acoustic and structural vibration. The balance is an inertially balanced closed-loop servo system where the current to a moving-coil motor needed to restore or null the output from the position sensor is a measure of the force or skin friction tending to displace the moving element. The accuracy of the sensor is directly affected by the position sensor in the feedback loop, in this case a linear-variable differential transformer which has proven to be influenced by temperature gradients.

  3. Thermodynamic aspects of rock friction

    CERN Document Server

    Mitsui, Noa

    2013-01-01

    Rate- and state-dependent friction law for velocity-step tests is analyzed from a thermodynamic point of view. A simple macroscopic non-equilibrium thermodynamic model with a single internal variable reproduces instantaneous jump and relaxation. Velocity weakening appears as a consequence of a plasticity related nonlinear coefficient. Permanent part of displacement corresponds to plastic strain, and relaxation effects are analogous to creep in thermodynamic rheology.

  4. Discrete Element study of granular material - Bumpy wall interface behavior

    Science.gov (United States)

    El Cheikh, Khadija; Rémond, Sébastien; Pizette, Patrick; Vanhove, Yannick; Djelal, Chafika

    2016-09-01

    This paper presents a DEM study of a confined granular material sheared between two parallel bumpy walls. The granular material consists of packed dry spherical particles. The bumpiness is modeled by spheres of a given diameter glued on horizontal planes. Different bumpy surfaces are modeled by varying diameter or concentration of glued spheres. The material is sheared by moving the two bumpy walls at fixed velocity. During shear, the confining pressure applied on each bumpy wall is controlled. The effect of wall bumpiness on the effective friction coefficient and on the granular material behavior at the bumpy walls is reported for various shearing conditions. For given bumpiness and confining pressure that we have studied, it is found that the shear velocity does not affect the shear stress. However, the effective friction coefficient and the behavior of the granular material depend on the bumpiness. When the diameter of the glued spheres is larger than about the average grains diameter of the medium, the latter is uniformly sheared and the effective friction coefficient remains constant. For smaller diameters of the glued spheres, the effective friction coefficient increases with the diameter of glued spheres. The influence of glued spheres concentration is significant only for small glued spheres diameters, typically half of average particle diameter of the granular material. In this case, increasing the concentration of glued spheres leads to a decrease in effective friction coefficient and to shear localization at the interface. For different diameters and concentrations of glued spheres, we show that the effect of bumpiness on the effective friction coefficient can be characterized by the depth of interlocking.

  5. Tripping Effects on the Friction Factor in Turbulent Pipe Flows

    Science.gov (United States)

    Al-Salaymeh, A.; Bayoumi, O. A.; Durst, F.; Gad-El-Hak, M.

    2004-11-01

    Tripping devices are usually installed at the entrance of laboratory-scale pipe test sections to obtain a fully developed turbulent flow sooner. The tripping of laminar flow to induce turbulence can be carried out in different ways, such as using cylindrical wires, sand papers, well-organized tape letters, fences, etc. Claims of tripping effects have been made periodically since the classical experiments of Nikuradse (1932), which covered a significant range of Reynolds numbers. NikuradseÂ's data have become the metric by which theories are established, and have also been the subject of intense scrutiny. Several subsequent experiments reported friction factors as much as 5% lower than those measured by Nikuradse, and the authors of those reports attributed the difference to tripping effects. In the present study, measurements with and without ring tripping devices of different blocking areas of 10%, 20%, 30% and 40% have been carried out to determine the effect of entrance condition on the developing flow field in pipes. Along with pressure drop measurements to compute the skin friction, both Pitot tube and hot-wire anemometry measurements have been used to accurately determine the mean velocity profile over the working test section at different Reynolds numbers in the range of 1× 10^5--4.5 × 10^5. The results we obtained suggest that the tripping technique has an insignificant effect on the wall friction factor, in agreement with Nikuradse's original data.

  6. Friction characteristics of floppy disks

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    This note presents the principle and structure of a tribological measure for floppy disks.The precision of the force measuring system is 1 mN in loading and 3×10-6 N in friction.The resolution of the film thickness between head and floppy disk is 0.5 nm in the vertical and 1.5 nm in the horizontal direction.In order to investigate the tribological characteristics of floppy disks,six types of floppy disks have been tested and the floating properties of these disks are also studied with film measuring system.The experimental results of the surface morphology and friction coefficient of these floppy disks using the atomic force microscope/friction force mcroscope (AFM/FFM) are in accordance with the conclusion made by our own measuring system.The experimental results show that the air film thickness between head and disk is of the same order as the surface roughness of floppy disks.

  7. Infrared thermography for monitoring heat generation in a linear friction welding process of Ti6Al4V alloy

    Science.gov (United States)

    Maio, L.; Liberini, M.; Campanella, D.; Astarita, A.; Esposito, S.; Boccardi, S.; Meola, C.

    2017-03-01

    The increasing use of titanium alloys in a wider range of applications requires the development of new techniques and processes capable to decrease production costs and manufacturing times. In this regard welding and other joining techniques play an important role. Today, solid state friction joining processes, such as friction stir welding, friction spot welding, inertia friction welding, continuous-drive friction welding and linear friction welding (LFW), represent promising methods for part manufacturing. They allow for joining at temperature essentially below the melting point of the base materials being joined, without the addition of filler metal. However, the knowledge of temperature is essential to understand and model the phenomena involved in metal welding. A global measured value represents only a clue of the heat generation during the process; while, a deep understanding of welding thermal aspects requires temperature field measurement. This paper is focused on the use of infrared thermography applied to the linear friction welding process of Ti6Al4V alloy. The attention is concentrated on thermal field that develops on the outer wall of the two parts to be joined (i.e. heat generated in the friction zone), and on the maximum temperature that characterizes the process before and after the flash formation.

  8. Physical model for turbulent friction on rough surfaces

    CERN Document Server

    Li, Zhuoqun

    2016-01-01

    We present an analytical expression for turbulent friction on rough surfaces with regularly distributed roughness elements. Wall shear stresses are expressed as functions of physical quantities. Surfaces with varying roughness densities and roughness elements with different aspect ratios are considered. As the drag on each roughness element decreases as roughness density increases, we propose a straight forward method based on momentum conservation to deduce drag on elements by expressing it as a function of the maximum drag on elements and drag reductions ratios. We proposed a drag reduction effect of momentum redistribution and studied the mutual sheltering effect. Reduction ratios for redistribution effect and mutual sheltering effect are deduced, for different rough surfaces. These two drag reduction mechanisms are significant for sparse and dense surfaces, respectively. The shear stress on elements and the total shear stress are obtained as the result of the drag analysis. The estimated wall shear stress...

  9. Wall Art

    Science.gov (United States)

    McGinley, Connie Q.

    2004-01-01

    The author of this article, an art teacher at Monarch High School in Louisville, Colorado, describes how her experience teaching in a new school presented an exciting visual challenge for an art teacher--monotonous brick walls just waiting for decoration. This school experienced only minimal instances of graffiti, but as an art teacher, she did…

  10. Analytical skin friction and heat transfer formula for compressible internal flows

    Science.gov (United States)

    Dechant, Lawrence J.; Tattar, Marc J.

    1994-01-01

    An analytic, closed-form friction formula for turbulent, internal, compressible, fully developed flow was derived by extending the incompressible law-of-the-wall relation to compressible cases. The model is capable of analyzing heat transfer as a function of constant surface temperatures and surface roughness as well as analyzing adiabatic conditions. The formula reduces to Prandtl's law of friction for adiabatic, smooth, axisymmetric flow. In addition, the formula reduces to the Colebrook equation for incompressible, adiabatic, axisymmetric flow with various roughnesses. Comparisons with available experiments show that the model averages roughly 12.5 percent error for adiabatic flow and 18.5 percent error for flow involving heat transfer.

  11. On the design of optimal compliant walls for turbulence control

    CERN Document Server

    Luhar, M; McKeon, B J

    2016-01-01

    This paper employs the theoretical framework developed by Luhar et al. (J. Fluid Mech., 768, 415-441) to consider the design of compliant walls for turbulent skin friction reduction. Specifically, the effects of simple spring-damper walls are contrasted with the effects of more complex walls incorporating tension, stiffness and anisotropy. In addition, varying mass ratios are tested to provide insight into differences between aerodynamic and hydrodynamic applications. Despite the differing physical responses, all the walls tested exhibit some important common features. First, the effect of the walls (positive or negative) is greatest at conditions close to resonance, with sharp transitions in performance across the resonant frequency or phase speed. Second, compliant walls are predicted to have a more pronounced effect on slower-moving structures because such structures generally have larger wall-pressure signatures. Third, two-dimensional (spanwise constant) structures are particularly susceptible to further...

  12. Friction and Wear in Timing Belt Drives

    Directory of Open Access Journals (Sweden)

    B. Stojanovic

    2010-09-01

    Full Text Available Timing belt tooth goes into contact with a drive pulley, stretched to the maximum, because of the previous tension. When the contact begins the peak of the belt tooth makes the contact with the outer surface of the pulley teeth. The process of the teeth entering into the contact zone is accompanied with the relative sliding of their side surfaces and appropriate friction force. The normal force value is changing with the parabolic function, which also leads to the changes of the friction force. The biggest value of the normal force and of the friction force is at the tooth root. Hollow between teeth and the tip of the pulley teeth are also in contact. Occasionally, the face surface of the belt and the flange are also in contact. The friction occurs in those tribomechanical systems, also. Values of these friction forces are lower compared with the friction force, which occurs at the teeth root.

  13. Static friction between rigid fractal surfaces.

    Science.gov (United States)

    Alonso-Marroquin, Fernando; Huang, Pengyu; Hanaor, Dorian A H; Flores-Johnson, E A; Proust, Gwénaëlle; Gan, Yixiang; Shen, Luming

    2015-09-01

    Using spheropolygon-based simulations and contact slope analysis, we investigate the effects of surface topography and atomic scale friction on the macroscopically observed friction between rigid blocks with fractal surface structures. From our mathematical derivation, the angle of macroscopic friction is the result of the sum of the angle of atomic friction and the slope angle between the contact surfaces. The latter is obtained from the determination of all possible contact slopes between the two surface profiles through an alternative signature function. Our theory is validated through numerical simulations of spheropolygons with fractal Koch surfaces and is applied to the description of frictional properties of Weierstrass-Mandelbrot surfaces. The agreement between simulations and theory suggests that for interpreting macroscopic frictional behavior, the descriptors of surface morphology should be defined from the signature function rather than from the slopes of the contacting surfaces.

  14. Friction coefficient dependence on electrostatic tribocharging

    Science.gov (United States)

    Burgo, Thiago A. L.; Silva, Cristiane A.; Balestrin, Lia B. S.; Galembeck, Fernando

    2013-08-01

    Friction between dielectric surfaces produces patterns of fixed, stable electric charges that in turn contribute electrostatic components to surface interactions between the contacting solids. The literature presents a wealth of information on the electronic contributions to friction in metals and semiconductors but the effect of triboelectricity on friction coefficients of dielectrics is as yet poorly defined and understood. In this work, friction coefficients were measured on tribocharged polytetrafluoroethylene (PTFE), using three different techniques. As a result, friction coefficients at the macro- and nanoscales increase many-fold when PTFE surfaces are tribocharged, but this effect is eliminated by silanization of glass spheres rolling on PTFE. In conclusion, tribocharging may supersede all other contributions to macro- and nanoscale friction coefficients in PTFE and probably in other insulating polymers.

  15. Friction tensor concept for textured surfaces

    Indian Academy of Sciences (India)

    K R Y Simha; Anirudhan Pottirayil; Pradeep L Menezes; Satish V Kailas

    2008-06-01

    Directionality of grinding marks influences the coefficient of friction during sliding. Depending on the sliding direction the coefficient of friction varies between maximum and minimum for textured surfaces. For random surfaces without any texture the friction coefficient becomes independent of the sliding direction. This paper proposes the concept of a friction tensor analogous to the heat conduction tensor in anisotropic media. This implies that there exists two principal friction coefficients $\\mu_{1,2}$ analogous to the principal conductivities $k_{1,2}$. For symmetrically textured surfaces the principal directions are orthogonal with atleast one plane of symmetry. However, in the case of polished single crystalline solids in relative sliding motion, crystallographic texture controls the friction tensor.

  16. Pyrometamorphism of Fault Zone Rocks Induced by Frictional Heating in High-velocity Friction Tests: Reliable Records of Seismic Slip?

    Science.gov (United States)

    Ree, J.; Ando, J.; Kim, J.; Han, R.; Shimamoto, T.

    2008-12-01

    Recognition of seismic slip zone is important for a better understanding of earthquake generation processes in fault zones and paleoseismology. However, there has been no reliable record of ancient seismic slip except pseudotachylyte. Recently, it has been suggested that decomposition (dehydration or decarbonation) products due to frictional heating can be used as a seismic slip record. The decomposition products, however, can be easily rehydrated or recarbonated with pervasive fluid migration in the fault zone after seismic slip, raising some question about their stability as a seismic slip record. Here, we review microstructural and mineralogical changes of the simulated fault zones induced by frictional heating (pyrometamorphism) from high-velocity friction tests (HVFT) on siltstone, sandstone and carbonates at seismic slip rates, and discuss on their stability after seismic slip. HVFT on siltstone generates pseuodotachylyte in the principal slip zone (0.30-0.75 mm thick) with 'damage' layer (0.1-0.2 mm thick) along its margins. Chlorite in the damage layer suffers an incipient dehydration with many voids (0.2-1.0 μm in diameter) in transmission electron microscopy (TEM), appearing as dark tiny spots both in plane-polarized light and back-scattered electron (BSE) photomicrographs. HVFT on brown sandstone induces a color change of wall rocks adjacent to the principal slip zone (brown to red) due to the dehydration of iron hydroxides with frictional heating. These dehydration products in siltstone and sandstone due to frictional heating may be unstable since they would be easily rehydrated with fluid infiltration after a seismic slip. HVFT on carbonates including Carrara marble and siderite-bearing gouges produces decarbonation products of nano-scale lime (CaO) and magnetite (Fe3O4), respectively. Lime is a very unstable phase whereas magnetite is a stable and thus may be used as an indicator of seismic slip. The simulated fault zones of Carrara marble contain

  17. Rubber friction on (apparently) smooth lubricated surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Mofidi, M; Prakash, B [Division of Machine Elements, Luleaa University of Technology, Luleaa SE-97187 (Sweden); Persson, B N J [IFF, FZ-Juelich, 52425 Juelich (Germany); Albohr, O [Pirelli Deutschland AG, 64733 Hoechst/Odenwald, Postfach 1120 (Germany)

    2008-02-27

    We study rubber sliding friction on hard lubricated surfaces. We show that even if the hard surface appears smooth to the naked eye, it may exhibit short-wavelength roughness, which may make the dominant contribution to rubber friction. That is, the observed sliding friction is mainly due to the viscoelastic deformations of the rubber by the counterface surface asperities. The results presented are of great importance for rubber sealing and other rubber applications involving (apparently) smooth surfaces.

  18. Low friction wear resistant graphene films

    Science.gov (United States)

    Sumant, Anirudha V.; Berman, Diana; Erdemir, Ali

    2017-02-07

    A low friction wear surface with a coefficient of friction in the superlubric regime including graphene and nanoparticles on the wear surface is provided, and methods of producing the low friction wear surface are also provided. A long lifetime wear resistant surface including graphene exposed to hydrogen is provided, including methods of increasing the lifetime of graphene containing wear surfaces by providing hydrogen to the wear surface.

  19. Rubber friction on (apparently) smooth lubricated surfaces

    Science.gov (United States)

    Mofidi, M.; Prakash, B.; Persson, B. N. J.; Albohr, O.

    2008-02-01

    We study rubber sliding friction on hard lubricated surfaces. We show that even if the hard surface appears smooth to the naked eye, it may exhibit short-wavelength roughness, which may make the dominant contribution to rubber friction. That is, the observed sliding friction is mainly due to the viscoelastic deformations of the rubber by the counterface surface asperities. The results presented are of great importance for rubber sealing and other rubber applications involving (apparently) smooth surfaces.

  20. Modelling cohesive, frictional and viscoplastic materials

    Science.gov (United States)

    Alehossein, Habib; Qin, Zongyi

    2016-06-01

    Most materials in mining and civil engineering construction are not only viscoplastic, but also cohesive frictional. Fresh concrete, fly ash and mining slurries are all granular-frictional-visco-plastic fluids, although solid concrete is normally considered as a cohesive frictional material. Presented here is both a formulation of the pipe and disc flow rates as a function of pressure and pressure gradient and the CFD application to fresh concrete flow in L-Box tests.

  1. The role of friction in orthodontics

    OpenAIRE

    Mariana Ribeiro Pacheco; Wellington Corrêa Jansen; Dauro Douglas de Oliveira

    2012-01-01

    INTRODUCTION: Sliding mechanics is widely used during orthodontic treatment. One of the disadvantages of this mechanics is the friction generated at the bracket/archwire interface, which may reduce the amount of desired orthodontic movement obtained. Due to the application and great acceptance of this type of mechanics, the role of friction in Orthodontics has been of interest for both clinicians and scientists. OBJECTIVE: Therefore, this article discussed how friction affects orthodontic too...

  2. How to teach friction: Experiments and models

    Science.gov (United States)

    Besson, Ugo; Borghi, Lidia; De Ambrosis, Anna; Mascheretti, Paolo

    2007-12-01

    Students generally have difficulty understanding friction and its associated phenomena. High school and introductory college-level physics courses usually do not give the topic the attention it deserves. We have designed a sequence for teaching about friction between solids based on a didactic reconstruction of the relevant physics, as well as research findings about student conceptions. The sequence begins with demonstrations that illustrate different types of friction. Experiments are subsequently performed to motivate students to obtain quantitative relations in the form of phenomenological laws. To help students understand the mechanisms producing friction, models illustrating the processes taking place on the surface of bodies in contact are proposed.

  3. Noise and vibration in friction systems

    CERN Document Server

    Sergienko, Vladimir P

    2015-01-01

    The book analyzes the basic problems of oscillation processes and theoretical aspects of noise and vibration in friction systems. It presents generalized information available in literature data and results of the authors in vibroacoustics of friction joints, including car brakes and transmissions. The authors consider the main approaches to abatement of noise and vibration in non-stationary friction processes. Special attention is paid to materials science aspects, in particular to advanced composite materials used to improve the vibroacoustic characteristics of tribopairs The book is intended for researchers and technicians, students and post-graduates specializing in mechanical engineering, maintenance of machines and transport means, production certification, problems of friction and vibroacoustics.

  4. Frictional Effects on Gear Tooth Contact Analysis

    Directory of Open Access Journals (Sweden)

    Zheng Li

    2013-01-01

    Full Text Available The present paper concentrates on the investigations regarding the situations of frictional shear stress of gear teeth and the relevant frictional effects on bending stresses and transmission error in gear meshing. Sliding friction is one of the major reasons causing gear failure and vibration; the adequate consideration of frictional effects is essential for understanding gear contact behavior accurately. An analysis of tooth frictional effect on gear performance in spur gear is presented using finite element method. Nonlinear finite element model for gear tooth contact with rolling/sliding is then developed. The contact zones for multiple tooth pairs are identified and the associated integration situation is derived. The illustrated bending stress and transmission error results with static and dynamic boundary conditions indicate the significant effects due to the sliding friction between the surfaces of contacted gear teeth, and the friction effect can not be ignored. To understand the particular static and dynamic frictional effects on gear tooth contact analysis, some significant phenomena of gained results will also be discussed. The potentially significant contribution of tooth frictional shear stress is presented, particularly in the case of gear tooth contact analysis with both static and dynamic boundary conditions.

  5. Friction Stir Processing of Cast Superalloys Project

    Data.gov (United States)

    National Aeronautics and Space Administration — This SBIR effort examines the feasibility of an innovative fabrication technology incorporating sand casting and friction stir processing (FSP) for producing...

  6. CLIMBING WALL

    CERN Multimedia

    1999-01-01

    The FIRE AND RESCUE Group of TIS Commission informs that the climbing wall in the yard of the Fire-fighters Station, is intended for the sole use of the members of that service, and recalls that access to this installation is forbidden for safety reasons to all persons not belonging to the Service.CERN accepts no liability for damage or injury suffered as a result of failure to comply with this interdiction.TIS/DI

  7. Job Heterogeneity and Coordination Frictions

    DEFF Research Database (Denmark)

    Kennes, John; le Maire, Daniel

    the job ladder, how the identification of assortative matching is fundamentally different in directed and undirected search models, how our theory accounts for business cycle facts related to inter-temporal changes in job offer distributions, and how our model could also be used to identify......We develop a new directed search model of a frictional labor market with a continuum of heterogenous workers and firms. We estimate two versions of the model - auction and price posting - using Danish data on wages and productivities. Assuming heterogenous workers with no comparative advantage, we...

  8. Friction of Plastic Rotating Bands

    Science.gov (United States)

    1984-11-01

    for speeds eve ., the rdnge: 10 - 300 cm/s. Overwhelming evidence was presented to support a melt phenomena. Melt depth of: polymer, pins on a glass disk...Polymers," Proc. Roy. Soc., (London),. A291 (1966), p. 186. 24. Rabinowicz , S., et al., "The Effect of Hydrostatic Pressure on the Shear Yield Behavior of...34 Proc. Roy.,Soc., (London), A269. (19620 p. 368. 51. Carignan, F. J., and Rabinowicz , E., "Friction and Wear at ligh Sliding Speeds," ASLE Trans., 24

  9. Fractional trajectories: Decorrelation versus friction

    Science.gov (United States)

    Svenkeson, A.; Beig, M. T.; Turalska, M.; West, B. J.; Grigolini, P.

    2013-11-01

    The fundamental connection between fractional calculus and subordination processes is explored and affords a physical interpretation of a fractional trajectory, that being an average over an ensemble of stochastic trajectories. Heretofore what has been interpreted as intrinsic friction, a form of non-Markovian dissipation that automatically arises from adopting the fractional calculus, is shown to be a manifestation of decorrelations between trajectories. We apply the general theory developed herein to the Lotka-Volterra ecological model, providing new insight into the final equilibrium state. The relaxation time to achieve this state is also considered.

  10. Investigation into Piston-Slap Force under Friction and Connecting Rod Effects of Diesel Engine

    Directory of Open Access Journals (Sweden)

    Fuadi Noor Balia

    2011-01-01

    Full Text Available In this paper, a dynamics analysis of diesel engine through investigation of the piston-slap force by considering the friction and connecting rod effects is presented. A single-cylinder of 500 cc Diesel Engine’s mechanism was examined. The position, velocity and acceleration of the pins and the center of mass for each linkage were calculated by using vector analysis principles. The governing equations of the forces and moments were derived based on the Cartesian coordinate principles, and solved by using Gauss elimination method. Hence, the piston-slap force onto the cylinder wall under friction and connecting rod effects were determined. Favourable comparison with previously published work was performed and excellent agreement between the results was obtained. The result shows that the friction and connecting rod effects significantly influence to the piston-slap force.

  11. Comparison of Frictional Heating Models

    Energy Technology Data Exchange (ETDEWEB)

    Davies, Nicholas R [ORNL; Blau, Peter Julian [ORNL

    2013-10-01

    The purpose of this work was to compare the predicted temperature rises using four well-known models for frictional heating under a few selected conditions in which similar variable inputs are provided to each model. Classic papers by Archard, Kuhlmann-Wilsdorf, Lim and Ashby, and Rabinowicz have been examined, and a spreadsheet (Excel ) was developed to facilitate the calculations. This report may be used in conjunction with that spreadsheet. It explains the background, assumptions, and rationale used for the calculations. Calculated flash temperatures for selected material combinations, under a range of applied loads and sliding speeds, are tabulated. The materials include AISI 52100 bearing steel, CDA 932 bronze, NBD 200 silicon nitride, Ti-6Al-4V alloy, and carbon-graphite material. Due to the assumptions made by the different models, and the direct way in which certain assumed quantities, like heat sink distances or asperity dimensions, enter into the calculations, frictional hearing results may differ significantly; however, they can be similar in certain cases in light of certain assumptions that are shared between the models.

  12. Rolling Friction on a Wheeled Laboratory Cart

    Science.gov (United States)

    Mungan, Carl E.

    2012-01-01

    A simple model is developed that predicts the coefficient of rolling friction for an undriven laboratory cart on a track that is approximately independent of the mass loaded onto the cart and of the angle of inclination of the track. The model includes both deformation of the wheels/track and frictional torque at the axles/bearings. The concept of…

  13. On the Blasius correlation for friction factors

    CERN Document Server

    Trinh, Khanh Tuoc

    2010-01-01

    The Blasius empirical correlation for turbulent pipe friction factors is derived from first principles and extended to non-Newtonian power law fluids. Two alternative formulations are obtained that both correlate well with the experimental measurements of Dodge, Bogue and Yoo. Key words: Blasius, turbulent friction factor, power law fluids

  14. FACTORS INFLUENCING FRICTION OF PHOSPHATE COATINGS,

    Science.gov (United States)

    surface roughness, crystalline structure , and velocity. The coefficients of friction for manganese phosphate coatings did not differ to any practical...The coefficient of friction was independent of the applied load. Velocity during dynamic testing, surface finish, and crystalline structure influenced

  15. Gimbaled-shoulder friction stir welding tool

    Science.gov (United States)

    Carter, Robert W. (Inventor); Lawless, Kirby G. (Inventor)

    2010-01-01

    A gimbaled-shoulder friction stir welding tool includes a pin and first and second annular shoulders coupled to the pin. At least one of the annular shoulders is coupled to the pin for gimbaled motion with respect thereto as the tool is rotated by a friction stir welding apparatus.

  16. The Gulf Stream: Inertia and friction

    OpenAIRE

    ASSAF, GAD

    2011-01-01

    The inertial theory of the Gulf Stream (Charney, 1955) is extended to include vertical friction in the cyclonic shear zone (the western side) of the stream. The vertical friction is assumed to be controlled by local Froude conditions.DOI: 10.1111/j.2153-3490.1977.tb00717.x

  17. Graphite friction coefficient for various conditions

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The friction coefficient the graphite used in the Tsinghua University 10MW High Tem-perature Gas-Cooled Reactor was analyzed for various conditions. The variation of the graphitefriction coefficient was measured for various sliding velocities, sliding distances, normal loads, en-vironments and temperatures. A scanning elector microscope (SEM) was used to analyze the fric-tion surfaces.

  18. Wiping Metal Transfer in Friction Stir Welding

    Science.gov (United States)

    Nunes, Arthur C., Jr.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Much evidence suggests that as the friction stir pin-tool moves along a weld seam the displacement of metal takes place by a wiping action at the surface of a plug of metal that rotates with the tool. The wiping model is explained and some consequences for the friction stir welding process are drawn.

  19. Heterogeneity in friction strength of an active fault by incorporation of fragments of the surrounding host rock

    Science.gov (United States)

    Kato, Naoki; Hirono, Tetsuro

    2016-07-01

    To understand the correlation between the mesoscale structure and the frictional strength of an active fault, we performed a field investigation of the Atera fault at Tase, central Japan, and made laboratory-based determinations of its mineral assemblages and friction coefficients. The fault zone contains a light gray fault gouge, a brown fault gouge, and a black fault breccia. Samples of the two gouges contained large amounts of clay minerals such as smectite and had low friction coefficients of approximately 0.2-0.4 under the condition of 0.01 m s-1 slip velocity and 0.5-2.5 MP confining pressure, whereas the breccia contained large amounts of angular quartz and feldspar and had a friction coefficient of 0.7 under the same condition. Because the fault breccia closely resembles the granitic rock of the hangingwall in composition, texture, and friction coefficient, we interpret the breccia as having originated from this protolith. If the mechanical incorporation of wall rocks of high friction coefficient into fault zones is widespread at the mesoscale, it causes the heterogeneity in friction strength of fault zones and might contribute to the evolution of fault-zone architectures.

  20. Trial manufacture of rotary friction tester and frictional force measurement of metals

    CERN Document Server

    Abe, T; Kanari, M; Tanzawa, S

    2002-01-01

    In the plasma confinement type fusion reactor, in-vessel structures such as a blanket module slide at the joints each other when plasma disruption occurs, and then frictional heat is generated there. Therefore, for the selection of material and the use as the design data, it is important to understand the frictional characteristics of metals and ceramic films in the vacuum. In the present study, we have manufactured a prototype of rotary friction tester and examined the performances of the tester. The frictional characteristics of metals in the room air was measured using the friction tester, and the results obtained are as follows. A drifting friction force for a constant time and a friction force during the idling were 98 mN and 225 mN, respectively. These values were sufficiently small as compared to pressing load (9.8 - 57.8 N) used in the friction test. In a friction force measurement of stainless steel, dynamic friction force obeyed Amontons' law which indicated that dynamic friction force is not depend...

  1. Velocity dependence of friction of confined polymers

    DEFF Research Database (Denmark)

    Sivebæk, Ion Marius; Samoilov, V.N.; Persson, B.N.J.

    2009-01-01

    We present molecular dynamics friction calculations for confined hydrocarbon solids with molecular lengths from 20 to 1400 carbon atoms. Two cases are considered: (a) polymer sliding against a hard substrate, and (b) polymer sliding on polymer. We discuss the velocity dependence of the frictional...... cases the frictional shear stress increases monotonically with the sliding velocity. For polymer sliding on polymer [case (b)] the friction is much larger, and the velocity dependence is more complex. For hydrocarbons with molecular lengths from 60 to 140 C-atoms, the number of monolayers of lubricant...... shows no dependence on the sliding velocity, and for the shortest hydrocarbon (20 C-atoms) the frictional shear stress increases nearly linearly with the sliding velocity....

  2. FRICTION-BOON OR BANE IN ORTHODONTICS

    Directory of Open Access Journals (Sweden)

    Sameer

    2015-11-01

    Full Text Available OBJECTIVE: Most fixed appliance techniques involve some degree of sliding between brackets and arch wires. A sound knowledge of the various factors affecting the magnitude of friction is of paramount importance to the clinician. The present study was performed to evaluate and compare the frictional resistance and characteristics between self-ligating brackets and pre-adjusted edgewise brackets with different types of ligation. MATERIALS AND METHODS: Tidy's frictional test design was used to simulate retraction of tooth along with artificial saliva to simulate wet conditions in oral cavity. The jig with this assembly was mounted on the Instron machine with the cross head moving upwards at a speed of 5mm/min. The movable bracket was suspended from the load cell of the testing machine, while the jig was mounted on cross head of machine and the load cell readings were recorded on digital display. Following wires are used 0.016 HANT, 0.019X 0.025HANT, 0.019X 0.025 SS, 0.021X 0.025 SS wires are used. The brackets used were 0.022 slot Damon, 0.022 Smart clip and 0.022 slot MBT system. RESULTS: Self ligating brackets were shown to produce lesser friction when compared to the conventional brackets used with modules, and stainless steel ligatures. Damon self-ligating brackets produce a least friction of all the brackets used in the study. Stainless steel ligatures produced the least friction compared to elastomeric. CONCLUSION: Self ligation brackets produce lesser friction than the conventional brackets ligated with elastomeric modules and stainless steel ligature. Damon self-ligating brackets produce a least friction of all the brackets used in the study width of the bracket was also found to be directly proportional to the friction produced 0.0016HANT with elastomeric modules produce more friction due increase in flexibility of wire.

  3. A preliminary study on the application of Friction Welding in structural repairs

    Energy Technology Data Exchange (ETDEWEB)

    Pauly, D.; Santos, J.F. dos [GKSS-Forschungszentrum Geesthacht GmbH (Germany). Inst. fuer Materialforschung; Blakemore, G.R. [Pressure Products Group, Aberdeen (United Kingdom); Gibson, D. [National Hyperbaric Centre, Aberdeen (United Kingdom)

    1998-11-01

    Friction Welding is characterised by the absence of a fusion zone associated with comparatively low temperatures in the weld. These features allow the application of this welding process in joining and repair of most engineering structures, especially in hazardous environments. This work presents a preliminary study on different friction welding processes, including the recently developed Friction Hydro-Pillar Processing (FHPP) and Friction Stitch Welding, as joining technologies for thick-walled structures. The use of these welding processes in different industrial applications, compared with the commonly used arc welding counterparts, as well as the influence of welding parameters on the weldment integrity are discussed. A brief description of a portable friction welding equipment and its possible implementation for FHPP are presented. Stud welds produced in the commissioning phase of this equipment have been analysed and tested to assess their quality. (orig.) [Deutsch] Da die Schweisszonentemperatur waehrend des Reibschweissvorganges vergleichsweise niedrig ist, bildet sich kein Schmelzbad aus. Anwendbar ist dieses Schweissverfahren zur Verbindung oder Reparatur der meisten Metallkonstruktionen, speziell in risikobehafteter Umgebung. Diese Arbeit enthaelt eine Vorstudie zu verschiedenen Reibschweissprozessen, einschliesslich der neu entwickelten Friction Hydro-Pillar Processing (FHPP)- und Friction Stitch Welding-Verfahren, als Fuegetechniken fuer dickwandige Strukturen. Die Anwendbarkeit dieser Schweissprozesse in verschiedenen Industrien, verglichen mit herkoemmlich verwendeten Lichtbogenschweissverfahren, sowie der Einfluss von Schweissparametern auf die Guete der Verbindung werden diskutiert. Praesentiert wird ausserdem eine tragbare Reibschweissmaschine und ihre moegliche Verwendung zum FHPP-Schweissen. Bolzenschweissungen, die waehrend der Inbetriebnahmephase dieser Maschine hergestellt wurden, sind zur Charakterisierung ihrer Qualitaet analysiert und

  4. Spectroscopic signatures of quantum friction

    Science.gov (United States)

    Klatt, Juliane; Bennett, Robert; Buhmann, Stefan Yoshi

    2016-12-01

    We present a formula for the spectroscopically accessible level shifts and decay rates of an atom moving at an arbitrary angle relative to a surface. Our Markov formulation leads to an intuitive analytic description whereby the shifts and rates are obtained from the coefficients of the Heisenberg equation of motion for the atomic flip operators but with complex Doppler-shifted (velocity-dependent) transition frequencies. Our results conclusively demonstrate that for the limiting case of parallel motion the shifts and rates are quadratic or higher in the atomic velocity. We show that a stronger, linear velocity dependence is exhibited by the rates and shifts for perpendicular motion, thus opening the prospect of experimentally probing the Markovian approach to the phenomenon of quantum friction.

  5. Friction Stir Welding and Processing

    Energy Technology Data Exchange (ETDEWEB)

    Hovanski, Yuri; Carsley, John; Clarke, Kester D.; Krajewski, Paul E.

    2015-05-01

    With nearly twenty years of international research and collaboration in friction stir welding (FSW) and processing industrial applications have spread into nearly every feasible market. Currently applications exist in aerospace, railway, automotive, personal computers, technology, marine, cutlery, construction, as well as several other markets. Implementation of FSW has demonstrated diverse opportunities ranging from enabling new materials to reducing the production costs of current welding technologies by enabling condensed packaging solutions for traditional fabrication and assembly. TMS has sponsored focused instruction and communication in this technology area for more than fifteen years, with leadership from the Shaping and Forming Committee, which organizes a biannual symposium each odd year at the annual meeting. A focused publication produced from each of these symposia now comprises eight volumes detailing the primary research and development activities in this area over the last two decades. The articles assembled herein focus on both recent developments and technology reviews of several key markets from international experts in this area.

  6. Mapping Instabilities in Polymer Friction

    Science.gov (United States)

    Rand, Charles; Crosby, Alfred

    2005-03-01

    Schallamach waves are instabilities that occur as interfaces between a soft elastomer and rigid surface slide past each other.(1) The presence of Schallamach waves can lead to drastic changes in frictional properties. Although the occurrence of Schallamach waves has been studied for the past several decades, a general map relating fundamental material properties, geometry, and operating conditions (i.e. speed and temperature) has not been established. Using a combinatorial approach, we illustrate the role of modulus, testing velocity and surface energetics of crosslinked poly(dimethyl siloxane) on the generation Schallamach waves. This knowledge will be used with polymer patterning processes to fabricate responsive coatings for applications such as anti-fouling coatings. (1)Schallamach, A.;Wear 1971,17, 301-312.

  7. Dynamical Friction on extended perturbers

    CERN Document Server

    Esquivel, O

    2008-01-01

    Following a wave-mechanical treatment we calculate the drag force exerted by an infinite homogeneous background of stars on a perturber as this makes its way through the system. We recover Chandrasekhar's classical dynamical friction (DF) law with a modified Coulomb logarithm. We take into account a range of models that encompasses all plausible density distributions for satellite galaxies by considering the DF exerted on a Plummer sphere and a perturber having a Hernquist profile. It is shown that the shape of the perturber affects only the exact form of the Coulomb logarithm. The latter converges on small scales, because encounters of the test and field stars with impact parameters less than the size of the massive perturber become inefficient. We confirm this way earlier results based on the impulse approximation of small angle scatterings.

  8. The influence of heat transfer and friction on the impulse of a detonation tube

    OpenAIRE

    Kawane, Ko; Shimada, Satoshi; Kasahara, Jiro; Matsuo, Akiko

    2011-01-01

    In the present study, we experimentally and numerically investigated the influence of heat transfer and friction on the performance of a single-shot detonation tube open at one end. Two kinds of specific impulse measurement were carried out with various tube lengths and levels of surface roughness, one by using a ballistic pendulum arrangement and the other by integrating the pressure history measured at the thrust wall. These measurements revealed the degree to which potential impulse can be...

  9. Temperature dependent effective friction coefficient estimation in friction stir welding with the bobbin tool

    Directory of Open Access Journals (Sweden)

    Mijajlović Miroslav M.

    2016-01-01

    Full Text Available The friction coefficient in many friction stir welding researches is generally used as an effective, constant value without concern on the adaptable and changeable nature of the friction during welding sequence. This is understandable because the main problem in analyzing friction in friction stir welding are complex nature of the friction processes, case-dependent and time dependent contact between the bodies, influence of the temperature, sliding velocity, etc. This paper is presenting a complex experimental-numerical-analytical model for estimating the effective friction coefficient on contact of the bobbin tool and welding plates during welding, considering the temperature at the contact as the most influencing parameter on friction. The estimation criterion is the correspondence of the experimental temperature and temperature from the numerical model. The estimation procedure is iterative and parametric - the heat transport parameters and friction coefficient are adapted during the estimation procedure in a realistic manner to achieve relative difference between experimental and model’s temperature lower than 3%. The results show that friction coefficient varies from 0.01 to 0.21 for steel-aluminium alloy contact and temperature range from 406°C to 22°C.

  10. Thermal activation in boundary lubricated friction

    Energy Technology Data Exchange (ETDEWEB)

    Michael, P.C. [Francis Bitter National Magnet Lab. and Dept. of Mechanical Engineering, Massachusetts Inst. of Tech., Cambridge, MA (United States); Rabinowicz, E. [Francis Bitter National Magnet Lab. and Dept. of Mechanical Engineering, Massachusetts Inst. of Tech., Cambridge, MA (United States); Iwasa, Y. [Francis Bitter National Magnet Lab. and Dept. of Mechanical Engineering, Massachusetts Inst. of Tech., Cambridge, MA (United States)

    1996-05-01

    The friction coefficients for copper pairs lubricated with fatty acids and fluorinated fatty acids have been measured over a wide range of sliding speeds and temperatures. Sliding speeds in the range 10{sup -7}-10{sup -2} m s{sup -1} and temperatures in the range 4.2-300 K were used. The friction coefficients near 300 K are generally low and increase with sliding speed, while the friction coefficients at low temperatures are markedly higher and relatively independent of velocity. Each lubricant`s friction vs. velocity behavior over the temperature range 150-300 K can be described by a friction-velocity master curve derived from a thermal activation model for the lubricant`s shear strength. The activation energies deduced from this friction model are identical to those obtained in the same temperature range for a vibrational mode associated with low temperature mechanical relaxations in similarly structured polymers. These results suggest that thermally activated interfacial shear is responsible for the fatty acids` positive-sloped friction vs. velocity characteristics at low sliding speeds near room temperature. (orig.)

  11. Load-Dependent Friction Hysteresis on Graphene.

    Science.gov (United States)

    Ye, Zhijiang; Egberts, Philip; Han, Gang Hee; Johnson, A T Charlie; Carpick, Robert W; Martini, Ashlie

    2016-05-24

    Nanoscale friction often exhibits hysteresis when load is increased (loading) and then decreased (unloading) and is manifested as larger friction measured during unloading compared to loading for a given load. In this work, the origins of load-dependent friction hysteresis were explored through atomic force microscopy (AFM) experiments of a silicon tip sliding on chemical vapor deposited graphene in air, and molecular dynamics simulations of a model AFM tip on graphene, mimicking both vacuum and humid air environmental conditions. It was found that only simulations with water at the tip-graphene contact reproduced the experimentally observed hysteresis. The mechanisms underlying this friction hysteresis were then investigated in the simulations by varying the graphene-water interaction strength. The size of the water-graphene interface exhibited hysteresis trends consistent with the friction, while measures of other previously proposed mechanisms, such as out-of-plane deformation of the graphene film and irreversible reorganization of the water molecules at the shearing interface, were less correlated to the friction hysteresis. The relationship between the size of the sliding interface and friction observed in the simulations was explained in terms of the varying contact angles in front of and behind the sliding tip, which were larger during loading than unloading.

  12. Assessment of semi-active friction dampers

    Science.gov (United States)

    dos Santos, Marcelo Braga; Coelho, Humberto Tronconi; Lepore Neto, Francisco Paulo; Mafhoud, Jarir

    2017-09-01

    The use of friction dampers has been widely proposed for a variety of mechanical systems for which applying viscoelastic materials, fluid based dampers or other viscous dampers is impossible. An important example is the application of friction dampers in aircraft engines to reduce the blades' vibration amplitudes. In most cases, friction dampers have been studied in a passive manner, but significant improvements can be achieved by controlling the normal force in the contact region. The aim of this paper is to present and study five control strategies for friction dampers based on three different hysteresis cycles by using the Harmonic Balance Method (HBM), a numerical and experimental analysis. The first control strategy uses the friction force as a resistance when the system is deviating from its equilibrium position. The second control strategy maximizes the energy removal in each harmonic oscillation cycle by calculating the optimal normal force based on the last displacement peak. The third control strategy combines the first strategy with the homogenous modulation of the friction force. Finally, the last two strategies attempt to predict the system's movement based on its velocity and acceleration and our knowledge of its physical properties. Numerical and experimental studies are performed with these five strategies, which define the performance metrics. The experimental testing rig is fully identified and its parameters are used for numerical simulations. The obtained results show the satisfactory performance of the friction damper and selected strategy and the suitable agreement between the numerical and experimental results.

  13. Hydrodynamic interactions of spherical particles in suspensions confined between two planar walls

    CERN Document Server

    Bhattacharya, S; Wajnryb, E

    2005-01-01

    Hydrodynamic interactions in a suspension of spherical particles confined between two parallel planar walls are studied under creeping-flow conditions. The many-particle friction matrix in this system is evaluated using our novel numerical algorithm based on transformations between Cartesian and spherical representations of Stokes flow. The Cartesian representation is used to describe the interaction of the fluid with the walls and the spherical representation is used to describe the interaction with the particles. The transformations between these two representations are given in a closed form, which allows us to evaluate the coefficients in linear equations for the induced-force multipoles on particle surfaces. The friction matrix is obtained from these equations, supplemented with the superposition lubrication corrections. We have used our algorithm to evaluate the friction matrix for a single sphere, a pair of spheres, and for linear chains of spheres. The friction matrix exhibits a crossover from a quasi...

  14. High Reynolds number rough-wall turbulent boundary layers

    Science.gov (United States)

    Squire, Dougal; Morrill-Winter, Caleb; Schultz, Michael; Hutchins, Nicholas; Klewicki, Joseph; Marusic, Ivan

    2015-11-01

    In his review of turbulent flows over rough-walls, Jimenez (2004) concludes that there are gaps in the current database of relevant experiments. The author calls for measurements in which δ / k and k+ are both large--low blockage, fully-rough flow--and where δ / k is large and k+ is small--low blockage, transitionally-rough flow--to help clarify ongoing questions regarding the physics of rough-wall-bounded flows. The present contribution details results from a large set of measurements carried out above sandpaper in the Melbourne Wind Tunnel. The campaign spans 45 rough-wall measurements using single and multiple-wire hot-wire anemometry sensors and particle image velocimetry. A floating element drag balance is employed to obtain the rough-wall skin friction force. The data span 20 friction Reynolds number range of 2800 < Reτ < 30000 , targeting areas in the parameter space identified by Jimenez (2004) as being sparsely populated by pre-existing data. Smooth-wall data are also obtained across a similar Reynolds number range to enable comparison of smooth- and rough-wall structural features. Generally, the data indicate similarity in the outer-layer of smooth- and fully-rough wall-bounded flows.

  15. Coordinated Water Under Confinement Eases Sliding Friction

    Science.gov (United States)

    Defante, Adrian; Dhopotkar, Nishad; Dhinojwala, Ali

    Water is essential to a number of interfacial phenomena such as the lubrication of knee joints, protein folding, mass transport, and adsorption processes. We have used a biaxial friction cell to quantify underwater friction between a hydrophobic elastomeric lens and a hydrophobic self-assembled monolayer in the presence of surfactant solutions. To gain an understanding of the role of water in these processes we have coupled this measurement with surface sensitive sum frequency generation to directly probe the molecular constitution of the confined contact interface. We observe that role of confined coordinated water between two hydrophobic substrates covered with surfactants is the key to obtaining a low coefficient of friction.

  16. An inquiry-based laboratory on friction

    CERN Document Server

    Montalbano, Vera

    2013-01-01

    Sliding friction is usually introduced in high school, but rarely through activities in laboratory. A qualitative introduction to friction is presented by proposing exploration of different kind of materials in order to suggest which aspects can be relevant and which interaction is involved. Different quantitative experiments are proposed for studying Leonardo's laws for friction. The learning path was tested with two high school classes during an instruction trip at department. Students were engaged in the inquiry-based introductory activity and seemed to realize with care the measurements. However, the analysis of their reports shows some learning difficulties.

  17. Methods and Devices used to Measure Friction

    DEFF Research Database (Denmark)

    Jeswiet, Jack; Arentoft, Mogens; Henningsen, Poul

    2004-01-01

    The physical condition at the work-piece/die boundary, in both bulk forming and sheet forming is, arguably, the single most important physical parameter influencing the processing of metals, yet it remains the least understood. Hence the need for basic research into metal-die interface mechanisms....... To gain a good understanding of the mechanisms at the interface and to be able to verify the friction and tribology models that exist, friction sensors are needed. Designing sensors to measure friction-stress in metal working has been pursued by many researchers. This paper surveys methods, which have...

  18. Quantized friction across ionic liquid thin films

    Science.gov (United States)

    Smith, Alexander M.; Lovelock, Kevin R. J.; Gosvami, Nitya Nand; Welton, Tom; Perkin, Susan

    Ionic liquids, salts in the liquid state under ambient conditions, are of great interest as precision lubricants. Ionic liquids form layered structures at surfaces, yet it is not clear how this nano-structure relates to their lubrication properties. We measured the friction force between atomically smooth solid surfaces across ionic liquid films of controlled thickness in terms of the number of ion layers. Multiple friction-load regimes emerge, each corresponding to a different number of ion layers in the film. In contrast to molecular liquids, the friction coefficients differ for each layer due to their varying composition.

  19. Forming of aluminium alloy friction stir welds

    Science.gov (United States)

    Bruni, Carlo

    2016-10-01

    The present paper aims at investigating, through analytical models, numerical models and experiments, the effect of the warm deformation phase, realised with an in temperature upsetting, on the weld previously performed by friction stir lap welding on aluminium alloy blanks. The investigation allows to show the deformation zones after upsetting that determine the homogenisation of the weld section. The analytical model allows to relate the friction factor with the upsetting load. The presence on the weld of not elevated friction factor values determines the deformation and localisation levels very useful for the weld. Such methodology allows to improve the weld itself with the forming phase.

  20. Study on the Friction Coefficient in Grinding

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The friction between the abrasive grains and workpi ec e is a crutial factor determining the main grinding output. Few studies have bee n carried out investigating the values of the friction coefficient in grinding, due to the difficulty of direct measurement. In this paper, a mathematical model of the friction coefficient in grinding has been established with the aid of a new grinding parameter C ge, which has close relations to wheel wear rate Z s, metal removal rate Z w, specific energy u and gr...

  1. Quantized friction across ionic liquid thin films.

    Science.gov (United States)

    Smith, Alexander M; Lovelock, Kevin R J; Gosvami, Nitya Nand; Welton, Tom; Perkin, Susan

    2013-10-07

    Ionic liquids - salts in the liquid state under ambient conditions - are of great interest as precision lubricants. Ionic liquids form layered structures at surfaces, yet it is not clear how this nano-structure relates to their lubrication properties. We measured the friction force between atomically smooth solid surfaces across ionic liquid films of controlled thickness in terms of the number of ion layers. Multiple friction-load regimes emerge, each corresponding to a different number of ion layers in the film. In contrast to molecular liquids, the friction coefficients differ for each layer due to their varying composition.

  2. Elastoplastic frictional contact problem study on interference fits of compressor

    Institute of Scientific and Technical Information of China (English)

    Hongwu ZHANG; Aihua LIAO; Changhua WU

    2008-01-01

    The FE parametric quadratic programming (PQP) method developed from the parametric variational principle (PVP) was used for the analysis of the stress distribution of the 3D elastoplastic frictional contact of an impeller-shaft sleeve-shaft. A locomotive-type turbo-charger compressor with 24 blades under combined cen-trifugal and interference-fit loading was considered in the numerical analysis. The solution of elastoplastic frictional contact problems belongs to unspecified boundary pro-blems where the interaction between two kinds of nonli-nearities should occur. To save time in the numerical computation, a multi-substructure technique was adopted in the structural modeling. The effect of fit tolerance, wall thickness of the shaft sleeve, and rotational speed on the contact stress was discussed in detail in the numerical computation. To decrease the difficulty of the assembly process and ensure the safety of the working state, the amount of interference between the shaft sleeve and shaft by press-fitting should be controlled strictly to avoid the rapid increase of contact stress. The numerical results show that the algorithm has high accuracy and good con-vergence. The study can be referred to in deciding the proper fit tolerance and improving the design and man-ufacturing technology of compressor impellers.

  3. A new skin friction balance and selected measurements

    Science.gov (United States)

    Vakili, A. D.

    1992-01-01

    A new skin friction balance with moving belt has been developed for measurement of the surface shear stress component in the direction of belt motion. The device is described in this paper with typical measurement results. This instrument is symmetric in design with small moving mass negligible internal friction. It is 3.8 cm high, 3.8 cm long and 2.1 cm wide, with the sensing surface 0.7 cm wide and 1.5 cm long, and it can be made in various sizes. The unique design of this instrument has reduced some of the errors associated with conventional floating-element balances. The instrument can use various sensing systems and the output signal is a linear function of the wall shear stress. Measurements show good agreement with data obtained by the floating element balances and flat plate prediction techniques. Dynamic measurements have been made in a limited range. The overall uncertainty of measurement is estimated to be +/- 2 percent.

  4. High friction and low wear properties of laser-textured ceramic surface under dry friction

    Science.gov (United States)

    Xing, Youqiang; Deng, Jianxin; Wu, Ze; Wu, Fengfang

    2017-08-01

    Two kinds of grooved textures with different spacing were fabricated on Al2O3/TiC ceramic surface by an Nd:YAG laser. The dry tribological properties of the textured samples were investigated by carrying out unidirectional rotary sliding friction and wear tests using a ball-on-disk tribometer. Results show that the laser textured samples exhibit higher friction coefficient and excellent wear resistance compared with the smooth sample under dry friction conditions. Furthermore, the texture morphology and spacing have a significant influence on the tribological properties. The sample with small texture spacing may be beneficial to increasing the friction coefficient, and the wavy-grooved sample exhibits the highest friction coefficient and shallowest wear depth. The increasing friction coefficient and anti-wear properties are attributed to the combined effects of the increased surface roughness, reduced real contact area, micro-cutting effect by the texture edges and entrapment of wear debris.

  5. Friction Stir Welding of ODS and RAFM Steels

    Science.gov (United States)

    Yu, Zhenzhen; Feng, Zhili; Hoelzer, David; Tan, Lizhen; Sokolov, Mikhail A.

    2015-09-01

    Advanced structural materials such as oxide dispersion strengthened steels and reduced-activation ferritic/martensitic steels are desired in fusion reactors as primary candidate materials for first wall and blanket structures, due to their excellent radiation and high-temperature creep resistance. However, their poor fusion weldability has been the major technical challenge limiting practical applications. For this reason, solid-state friction stir welding (FSW) has been considered for such applications. In this work, the effect of FSW parameters on joining similar and dissimilar advanced structural steels was investigated. Scanning electron microscopy and electron backscatter diffraction methods were used to reveal the effects of FSW on grain size, micro-texture distribution, and phase stability. Hardness mapping was performed to evaluate mechanical properties. Post weld heat treatment was also performed to tailor the microstructure in the welds in order to match the weld zone mechanical properties to the base material.

  6. Frictional Fluid Dynamics and Plug Formation in Multiphase Millifluidic Flow

    Science.gov (United States)

    Dumazer, Guillaume; Sandnes, Bjørnar; Ayaz, Monem; Mâløy, Knut Jørgen; Flekkøy, Eirik Grude

    2016-07-01

    We study experimentally the flow and patterning of a granular suspension displaced by air inside a narrow tube. The invading air-liquid interface accumulates a plug of granular material that clogs the tube due to friction with the confining walls. The gas percolates through the static plug once the gas pressure exceeds the pore capillary entry pressure of the packed grains, and a moving accumulation front is reestablished at the far side of the plug. The process repeats, such that the advancing interface leaves a trail of plugs in its wake. Further, we show that the system undergoes a fluidization transition—and complete evacuation of the granular suspension—when the liquid withdrawal rate increases beyond a critical value. An analytical model of the stability condition for the granular accumulation predicts the flow regime.

  7. Falling walls

    CERN Multimedia

    It was 20 years ago this week that the Berlin wall was opened for the first time since its construction began in 1961. Although the signs of a thaw had been in the air for some time, few predicted the speed of the change that would ensue. As members of the scientific community, we can take a moment to reflect on the role our field played in bringing East and West together. CERN’s collaboration with the East, primarily through links with the Joint Institute for Nuclear Research, JINR, in Dubna, Russia, is well documented. Less well known, however, is the role CERN played in bringing the scientists of East and West Germany together. As the Iron curtain was going up, particle physicists on both sides were already creating the conditions that would allow it to be torn down. Cold war historian Thomas Stange tells the story in his 2002 CERN Courier article. It was my privilege to be in Berlin on Monday, the anniversary of the wall’s opening, to take part in a conference entitled &lsquo...

  8. Frictional torque numbers for ball cup and journal bearings

    OpenAIRE

    Ligterink, D.J.

    1982-01-01

    Plastic bearing material wears in ball cup and journal bearings. Contact areas in the ball cup and the journal bearing increase. The frictional torque needed to rotate the ball or journal also increases. When the coefficient of friction is assumed to be constant during wearing out, the frictional torque increases to a maximum of 1.273 times the frictional torque at zero wear.

  9. Surface defects and temperature on atomic friction

    Energy Technology Data Exchange (ETDEWEB)

    Fajardo, O Y; Mazo, J J, E-mail: yovany@unizar.es [Departamento de Fisica de la Materia Condensada and Instituto de Ciencia de Materiales de Aragon, CSIC-Universidad de Zaragoza, 50009 Zaragoza (Spain)

    2011-09-07

    We present a theoretical study of the effect of surface defects on atomic friction in the stick-slip dynamical regime of a minimalistic model. We focus on how the presence of defects and temperature change the average properties of the system. We have identified two main mechanisms which modify the mean friction force of the system when defects are considered. As expected, defects change the potential profile locally and thus affect the friction force. But the presence of defects also changes the probability distribution function of the tip slip length and thus the mean friction force. We corroborated both effects for different values of temperature, external load, dragging velocity and damping. We also show a comparison of the effects of surface defects and surface disorder on the dynamics of the system. (paper)

  10. Shell Galaxies, Dynamical Friction, and Dwarf Disruption

    CERN Document Server

    Ebrova, Ivana; Canalizo, Gabriela; Bennert, Nicola; Jilkova, Lucie

    2009-01-01

    Using N-body simulations of shell galaxies created in nearly radial minor mergers, we investigate the error of collision dating, resulting from the neglect of dynamical friction and of gradual disruption of the cannibalized dwarf.

  11. Frictional Sliding without Geometrical Reflection Symmetry

    Science.gov (United States)

    Aldam, Michael; Bar-Sinai, Yohai; Svetlizky, Ilya; Brener, Efim A.; Fineberg, Jay; Bouchbinder, Eran

    2016-10-01

    The dynamics of frictional interfaces plays an important role in many physical systems spanning a broad range of scales. It is well known that frictional interfaces separating two dissimilar materials couple interfacial slip and normal stress variations, a coupling that has major implications on their stability, failure mechanism, and rupture directionality. In contrast, it is traditionally assumed that interfaces separating identical materials do not feature such a coupling because of symmetry considerations. We show, combining theory and experiments, that interfaces that separate bodies made of macroscopically identical materials but lack geometrical reflection symmetry generically feature such a coupling. We discuss two applications of this novel feature. First, we show that it accounts for a distinct, and previously unexplained, experimentally observed weakening effect in frictional cracks. Second, we demonstrate that it can destabilize frictional sliding, which is otherwise stable. The emerging framework is expected to find applications in a broad range of systems.

  12. Frictional sliding with geometrically broken reflection symmetry

    CERN Document Server

    Aldam, Michael; Svetlizky, Ilya; Brener, Efim A; Fineberg, Jay; Bouchbinder, Eran

    2016-01-01

    The dynamics of frictional interfaces play an important role in many physical systems spanning a broad range of scales. It is well-known that frictional interfaces separating two dissimilar materials couple interfacial slip and normal stress variations, a coupling that has major implications on their stability, failure mechanism and rupture directionality. In contrast, interfaces separating identical materials are traditionally assumed not to feature such a coupling due to symmetry considerations. We show, combining theory and experiments, that interfaces which separate bodies made of identical materials, but lack geometric reflection symmetry, generically feature such a coupling. We discuss two applications of this novel feature. First, we show that it accounts for a distinct and previously unexplained weakening effect in frictional cracks observed experimentally. Second, we demonstrate that it can destabilize frictional sliding which is otherwise stable. The emerging framework is expected to find applicatio...

  13. Permeability equipment for porous friction surfaces

    Science.gov (United States)

    Standiford, D. L.; Graul, R. A.; Lenke, L. R.

    1985-04-01

    Hydroplaning is the loss of traction between tires and pavement due to the presence of a layer of water. This loss of traction can result in loss of vehicle control. A porous friction surface (PFS) applied over an existing pavement permits the water to drain laterally and vertically away from the tire path, effectively lowering hydroplaning potential. Equipment used to measure pavement drainage (permeability) is discussed with respect to usage on porous friction surface. Background information on hydroplaning, flow theory, and PFS field performance as they are affected by permeability are also presented. Two dynamic test devices and four static devices are considered for measuring PFS permeability. Permeability tests are recommended to measure PFS permeability for maintenance purposes and construction control. Dynamic devices cited could possibly estimate hydroplaning potential; further research must be done to determine this. Permeability devices cannot be used to accurately estimate friction of a pavement surface, however, decreased permeability of a pavement infers a decrease in friction.

  14. Torque Control of Friction Stir Welding Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Longhurst Engineering, PLC and Vanderbilt University propose the innovation of torque control of friction stir welding (FSW) as a replacement to force control of...

  15. Transient effects in friction fractal asperity creep

    CERN Document Server

    Goedecke, Andreas

    2013-01-01

    Transient friction effects determine the behavior of a wide class of mechatronic systems. Classic examples are squealing brakes, stiction in robotic arms, or stick-slip in linear drives. To properly design and understand mechatronic systems of this type, good quantitative models of transient friction effects are of primary interest. The theory developed in this book approaches this problem bottom-up, by deriving the behavior of macroscopic friction surfaces from the microscopic surface physics. The model is based on two assumptions: First, rough surfaces are inherently fractal, exhibiting roughness on a wide range of scales. Second, transient friction effects are caused by creep enlargement of the real area of contact between two bodies. This work demonstrates the results of extensive Finite Element analyses of the creep behavior of surface asperities, and proposes a generalized multi-scale area iteration for calculating the time-dependent real contact between two bodies. The toolset is then demonstrated both...

  16. Friction Stir Processing of Cast Superalloys Project

    Data.gov (United States)

    National Aeronautics and Space Administration — This SBIR Phase I effort examines the feasibility of an innovative fabrication technology incorporating sand casting and friction stir processing (FSP) for producing...

  17. Composites materials for friction and braking application

    Science.gov (United States)

    Crăciun, A. L.; Pinca-Bretotean, C.; Birtok-Băneasă, C.; Josan, A.

    2017-05-01

    The brake pads are an important component in the braking system of automotive. Materials used for brake pads should have stable and reliable frictional and wear properties under varying conditions of load, velocity, temperature and high durability. These factors must be satisfied simultaneously which makes it difficult to select effective brake pads material. The paper presents the results of the study for characterisation of the friction product used for automotive brake pads. In the study it was developed four frictional composites by using different percentages of coconut fibres (0%, 5%, 10%, 15%) reinforcement in aluminium matrix. The new composites tested in the laboratory, modelling appropriate percentage ratio between matrix and reinforcement volume and can be obtained with low density, high hardness properties, good thermal stability, higher ability to hold the compressive force and have a stable friction coefficient. These characteristics make them useful in automotive industry.

  18. Friction and friction-generated temperature at a polymer-metal interface

    Science.gov (United States)

    Price, H. L.; Burks, H. D.

    1974-01-01

    Results of friction and thermal tests of molded polyimide and pyrrone polymers are presented. The coefficient of sliding friction up to surface velocities of 2 m/sec and the coefficient of thermal expansion from 300 to 500 K were measured. An apparatus was constructed to measure simultaneously the coefficient of sliding friction and the friction-generated temperature. Measurements were made at a nominal pressure-velocity product of 0.25 MN/msec and at temperatures between 300 and 500 K.

  19. Sliding without slipping under Coulomb friction: opening waves and inversion of frictional force

    CERN Document Server

    Yastrebov, Vladislav A

    2015-01-01

    An elastic layer slides on a rigid flat governed by Coulomb's friction law. We demonstrate that if the coefficient of friction is high enough, the sliding localizes within stick-slip pulses, which transform into opening waves propagating at intersonic speed in the direction of sliding or, for high Poisson's ratios, at supersonic speed in the opposite one. This sliding mode, characterized by small frictional dissipation, rapidly relaxes the shear elastic energy via stress waves and enables the contact surface slide ahead of the top one, resulting in inversion of the frictional force direction.

  20. A review of dynamics modelling of friction wedge suspensions

    Science.gov (United States)

    Wu, Qing; Cole, Colin; Spiryagin, Maksym; Sun, Yan Quan

    2014-11-01

    Three-piece bogies with friction wedge suspensions are the most widely used bogies in heavy haul trains. Fiction wedge suspensions play a key role in these wagon systems. This article reviews current techniques in dynamic modelling of friction wedge suspension with various motivations: to improve dynamic models of friction wedge suspensions so as to improve general wagon dynamics simulations; to seek better friction wedge suspension models for wagon stability assessments in complex train systems; to improve the modelling of other friction devices, such as friction draft gear. Relevant theories and friction wedge suspension models developed by using commercial simulation packages and in-house simulation packages are reviewed.

  1. Flexible Friction Stir Joining Technology

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Zhili [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Lim, Yong Chae [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Mahoney, Murray [MegaStir Technologies LLC, Orem, UT (United States); Sanderson, Samuel [MegaStir Technologies LLC, Orem, UT (United States); Larsen, Steve [MegaStir Technologies LLC, Orem, UT (United States); Steel, Russel [MegaStir Technologies LLC, Orem, UT (United States); Fleck, Dale [MegaStir Technologies LLC, Orem, UT (United States); Fairchild, Doug P [ExxonMobil, Upstream Research Company (URC), Houston, TX (United States); Wasson, Andrew J [ExxonMobil, Upstream Research Company (URC), Houston, TX (United States); Babb, Jon [MegaStir Technologies LLC, Orem, UT (United States); Higgins, Paul [MegaStir Technologies LLC, Orem, UT (United States)

    2015-07-23

    Reported herein is the final report on a U.S. Department of Energy (DOE) Advanced Manufacturing Office (AMO) project with industry cost-share that was jointly carried out by Oak Ridge National Laboratory (ORNL), ExxonMobil Upstream Research Company (ExxonMobil), and MegaStir Technologies (MegaStir). The project was aimed to advance the state of the art of friction stir welding (FSW) technology, a highly energy-efficient solid-state joining process, for field deployable, on-site fabrications of large, complex and thick-sectioned structures of high-performance and high-temperature materials. The technology innovations developed herein attempted to address two fundamental shortcomings of FSW: 1) the inability for on-site welding and 2) the inability to weld thick section steels, both of which have impeded widespread use of FSW in manufacturing. Through this work, major advance has been made toward transforming FSW technology from a “specialty” process to a mainstream materials joining technology to realize its pervasive energy, environmental, and economic benefits across industry.

  2. Linearization of friction effects in vibration of two rotating blades

    Directory of Open Access Journals (Sweden)

    Hajžman M.

    2013-06-01

    Full Text Available This paper is aimed at modelling of friction effects in blade shrouding which are realized by means of friction elements placed between blades. In order to develop a methodology of modelling, two blades with one friction element in between are considered only. Flexible blades fixed to a rotating disc are discretized by FEM using 1D Rayleigh beam elements derived in rotating space as well as the friction element modelled as a rigid body. The blades and the friction element are connected through two concurrent friction planes, where the friction forces arise on the basis of centrifugal force acting on the friction element. The linearization of friction is performed using the harmonic balance method to determine equivalent damping coefficients in dependence on the amplitudes of relative slip motion between the blades and the friction element. The methodology is applied to a model of two real blades and will be extended for the whole bladed disc with shrouding.

  3. Comparisons of friction models in bulk metal forming

    DEFF Research Database (Denmark)

    Tan, Xincai

    2002-01-01

    A friction model is one of the key input boundary conditions in finite element simulations. It is said that the friction model plays an important role in controlling the accuracy of necessary output results predicted. Among the various friction models, which one is of higher accuracy is still...... unknown and controversial. In this paper, finite element analyses applying five different friction models to experiments of upsetting of AA 6082 lubricated with four lubricants are presented. Frictional parameter values are determined by fitness of data of friction area ratio from finite element analysis...... to experimental results. It is found that calibration curves of the friction area ratio for all of the five chosen friction models used in the finite element simulation do fit the experimental results. Usually, calbration curves of the friction area ratio are more sensitive to friction at the tool...

  4. Comparing numerically exact and modelled static friction

    Directory of Open Access Journals (Sweden)

    Krengel Dominik

    2017-01-01

    Full Text Available Currently there exists no mechanically consistent “numerically exact” implementation of static and dynamic Coulomb friction for general soft particle simulations with arbitrary contact situations in two or three dimension, but only along one dimension. We outline a differential-algebraic equation approach for a “numerically exact” computation of friction in two dimensions and compare its application to the Cundall-Strack model in some test cases.

  5. THE FRICTION OF QUARTZ IN HIGH VACUUM

    Science.gov (United States)

    the effects of surface cleanliness . Ultra-high vacuums (to 10 to the minus 10th power torr) and high temperatures (to 350 deg C) were combined with...chemical cleaning and careful handling techniques to produce the maximum surface cleanliness . The coefficient of static friction under varying...on 30-40 mesh glass balls. The coefficient of friction of smooth quartz was found to vary from 0.1 to 1.0 depending on the surface cleanliness . The

  6. Frequency-dependent friction and its significance for liquid pipeline simulation; Influencia do fator de atrito com dependencia da frequencia na simulacao de transientes em oleodutos

    Energy Technology Data Exchange (ETDEWEB)

    Tepedino, Alexandre F. [TRANSPETRO - PETROBRAS Transporte S.A., Rio de Janeiro, RJ (Brazil); Rachid, Felipe B. Freitas [Universidade Federal Fluminense (UFF), Niteroi, RJ (Brazil). Programa de Pos-Graduacao em Engenharia Mecanica. Lab. de Transporte de Liquidos e Gases

    2008-07-01

    Unsteady liquid flow in pipelines is usually described by using one-dimensional models and, in a procedure referred to as quasi-steady approximation, friction losses are estimated by formulae derived for steady state flow conditions. The assumption is that the friction loss during transient flow conditions can be approximated by the friction loss obtained for a steady flow with the same average velocity. However, during unsteady flow conditions the velocity profile can be considerably different from the steady flow. The shear stress at the pipe wall and the mean velocity are not in phase. Therefore, friction losses computed according to the quasi-steady approximation are inaccurate. To overcome this, the concept of frequency-dependent friction was proposed, including the time history of the mean flow velocity and acceleration, resulting in better correlation to experimental data. This work presents an investigation of situations in which the use of a frequency-dependent friction model could bring additional improvement for the petroleum and products pipeline simulation. To do so, through computer simulations, the predictions of both quasi-steady and unsteady friction models, for short and long lines, operating under a range of Reynolds numbers, are compared and the significance of the friction model is evaluated. (author)

  7. Network-Configurations of Dynamic Friction Patterns

    CERN Document Server

    Ghaffari, H O

    2012-01-01

    The complex configurations of dynamic friction patterns-regarding real time contact areas- are transformed into appropriate networks. With this transformation of a system to network space, many properties can be inferred about the structure and dynamics of the system. Here, we analyze the dynamics of static friction, i.e. nucleation processes, with respect to "friction networks". We show that networks can successfully capture the crack-like shear ruptures and possible corresponding acoustic features. We found that the fraction of triangles remarkably scales with the detachment fronts. There is a universal power law between nodes' degree and motifs frequency (for triangles, it reads T(k)\\proptok{\\beta} ({\\beta} \\approx2\\pm0.4)). We confirmed the obtained universality in aperture-based friction networks. Based on the achieved results, we extracted a possible friction law in terms of network parameters and compared it with the rate and state friction laws. In particular, the evolutions of loops are scaled with p...

  8. Role of Friction in Cold Ring Rolling

    Institute of Scientific and Technical Information of China (English)

    He YANG; Lianggang GUO; Mei ZHAN

    2005-01-01

    Cold ring rolling is an advanced but complex metal forming process under coupled effects with multi-factors, such as geometry sizes of rolls and ring blank, material, forming process parameters and friction, etc. Among these factors,friction between rolls and ring blank plays animportant role in keeping the stable forming of cold ring rolling. An analytical method was firstly presented for proximately determining the critical friction coefficient of stable forming and then a method was proposed to determine thecritical friction coefficient by combining analytical method with numerical simulation. And the influence of friction coefficient on the quality of end-plane and side spread of ring,rolling force, rolling moment and metal flow characteristic in the cold ring rolling process have been explored using the three dimensional (3D) numerical simulation based on the elastic-plastic dynamic finite element method (FEM)under the ABAQUS software environment, and the results show that increasing the friction on the contact surfaces between rolls and ring blank is useful not only for improving the stability of cold ring rolling but also for improving the geometry and dimension precision of deformed ring.

  9. Frictional behavior of experimental faults during a simulated seismic cycle

    Science.gov (United States)

    Spagnuolo, Elena; Nielsen, Stefan; Violay, Marie; Di Felice, Fabio; Di Toro, Giulio

    2016-04-01

    Laboratory friction studies of earthquake mechanics aim at understanding complex phenomena either driving or characterizing the seismic cycle. Previous experiments were mainly conducted on bi-axial machines imposing velocity steps conditions, where slip and slip-rate are usually less than 10 mm and 1 mm/s, respectively. However, earthquake nucleation on natural faults results from the combination of the frictional response of fault materials and wall rock stiffness with complex loading conditions. We propose an alternative experimental approach which consists in imposing a step-wise increase in the shear stress on an experimental fault under constant normal stress. This experimental configuration allows us to investigate the relevance of spontaneous fault surface reworking in (1) driving frictional instabilities, (2) promoting the diversity of slip events including the eventual runaway, and (3) ruling weakening and re-strengthening processes during the seismic cycle. Using a rotary shear apparatus (SHIVA, INGV, Rome) with an on-purpose designed control system, the shear stress acting on a simulated fault can be increased step-wise while both slip and slip-rate are allowed to evolve spontaneously (the slip is namely infinite) to accommodate the new state of stress. This unconventional procedure, which we term "shear stress-step loading", simulates how faults react to either a remote tectonic loading or a sudden seismic or strain event taking place in the vicinity of a fault patch. Our experiments show that the spontaneous slip evolution results in velocity pulses whose shape and occurrence rate are controlled by the lithology and the state of stress. With increasing shear stress and cumulative slip, the experimental fault exhibits three frictional behaviors: (1) stable behavior or individual slip pulses up to few cm/s for few mm of slip in concomitance to the step-wise increase in shear stress; (2) unstable oscillatory slip or continuous slip but with abrupt changes

  10. Methods and devices used to measure friction in rolling

    DEFF Research Database (Denmark)

    Jeswiet, J.; Arentoft, Mogens; Henningsen, Poul

    2006-01-01

    a good understanding of the mechanisms at the interface and to be able to verify the friction and tribology models that exist, friction sensors are needed. Designing sensors to measure frictional stress in metal working has been pursued by many researchers. This paper surveys methods that have been used...... to measure friction in rolling in the past and discusses some of the recent sensor designs that can now be used to measure friction both in production situations and for research purposes....

  11. Numerical implementation of a state variable model for friction

    Energy Technology Data Exchange (ETDEWEB)

    Korzekwa, D.A. [Los Alamos National Lab., NM (United States); Boyce, D.E. [Cornell Univ., Ithaca, NY (United States)

    1995-03-01

    A general state variable model for friction has been incorporated into a finite element code for viscoplasticity. A contact area evolution model is used in a finite element model of a sheet forming friction test. The results show that a state variable model can be used to capture complex friction behavior in metal forming simulations. It is proposed that simulations can play an important role in the analysis of friction experiments and the development of friction models.

  12. Nano-Sized Grain Refinement Using Friction Stir Processing

    Science.gov (United States)

    2013-03-01

    friction stir weld is a very fine grain microstructure produced as a result of dynamic recrystallization. The friction stir ... Friction Stir Processing, Magnesium, Nano-size grains Abstract A key characteristic of a friction stir weld is a very fine grain microstructure...state process developed on the basis of the friction stir welding (FSW) technique invented by The Welding Institute (TWI) in 1991 [2]. During

  13. Wall to Wall Optimal Transport

    CERN Document Server

    Hassanzadeh, Pedram; Doering, Charles R

    2013-01-01

    The calculus of variations is employed to find steady divergence-free velocity fields that maximize transport of a tracer between two parallel walls held at fixed concentration for one of two constraints on flow strength: a fixed value of the kinetic energy or a fixed value of the enstrophy. The optimizing flows consist of an array of (convection) cells of a particular aspect ratio Gamma. We solve the nonlinear Euler-Lagrange equations analytically for weak flows and numerically (and via matched asymptotic analysis in the fixed energy case) for strong flows. We report the results in terms of the Nusselt number Nu, a dimensionless measure of the tracer transport, as a function of the Peclet number Pe, a dimensionless measure of the energy or enstrophy of the flow. For both constraints the maximum transport Nu_{MAX}(Pe) is realized in cells of decreasing aspect ratio Gamma_{opt}(Pe) as Pe increases. For the fixed energy problem, Nu_{MAX} \\sim Pe and Gamma_{opt} \\sim Pe^{-1/2}, while for the fixed enstrophy scen...

  14. Friction Stir Processing for Efficient Manufacturing

    Energy Technology Data Exchange (ETDEWEB)

    Mr. Christopher B. Smith; Dr. Oyelayo Ajayi

    2012-01-31

    Friction at contacting surfaces in relative motion is a major source of parasitic energy loss in machine systems and manufacturing processes. Consequently, friction reduction usually translates to efficiency gain and reduction in energy consumption. Furthermore, friction at surfaces eventually leads to wear and failure of the components thereby compromising reliability and durability. In order to reduce friction and wear in tribological components, material surfaces are often hardened by a variety of methods, including conventional heat treatment, laser surface hardening, and thin-film coatings. While these surface treatments are effective when used in conjunction with lubrication to prevent failure, they are all energy intensive and could potentially add significant cost. A new concept for surface hardening of metallic materials and components is Friction Stir Processing (FSP). Compared to the current surface hardening technologies, FSP is more energy efficient has no emission or waste by products and may result in better tribological performance. FSP involves plunging a rotating tool to a predetermined depth (case layer thickness) and translating the FSP tool along the area to be processed. This action of the tool produces heating and severe plastic deformation of the processed area. For steel the temperature is high enough to cause phase transformation, ultimately forming hard martensitic phase. Indeed, FSP has been used for surface modification of several metals and alloys so as to homogenize the microstructure and refine the grain size, both of which led to improved fatigue and corrosion resistance. Based on the effect of FSP on near-surface layer material, it was expected to have beneficial effects on friction and wear performance of metallic materials. However, little or no knowledge existed on the impact of FSP concerning friction and wear performance the subject of the this project and final report. Specifically for steel, which is the most dominant

  15. Effect of near-wall treatments on airflow simulations

    CERN Document Server

    Gharbi, Najla El; Benzaoui, Ahmed; Amara, E H

    2010-01-01

    Airflow simulation results depend on a good prediction of near wall turbulence. In this paper a comparative study between different near wall treatments is presented. It is applied to two test cases: (1) the first concerns the fully developed plane channel flow (i.e. the flow between two infinitely large plates). Simulation results are compared to direct numerical simulation (DNS) data of Moser et al. (1999) for $Re\\tau$ = 590 (where $Re\\tau$ denotes the friction Reynolds number defined by friction velocity $u\\tau$, kinematics viscosity $v$ and the channel half-width $\\delta$); (2) the second case is a benchmark test for room air distribution (Nielsen, 1990). Simulation results are compared to experimental data obtained with laser-doppler anemometry. Simulations were performed with the aid of the commercial CFD code Fluent (2005). Near wall treatments available in Fluent were tested: Standard Wall Functions, Non Equilibrium Wall Function and Enhanced Wall Treatment. In each case, suitable meshes with adequate...

  16. Frictional transfer and the self-organization phenomenon in the friction

    Science.gov (United States)

    Kolesnikov, I. V.; Manturov, D. S.

    2017-05-01

    The paper is devoted to the investigation of the mechanism and kinetics of the surface structures formation in the process of metal-polymer frictional contact. IR spectroscopy methods have showed that the formation kinetics of a frictionally transferred film is determined by the adhesion of the composite components and the direction of the electric field at the contact.

  17. Frictional stability-permeability relationships for fractures in shales: Friction-Permeability Relationships

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Yi [Department of Energy and Mineral Engineering, EMS Energy Institute, and G3 Center, Pennsylvania State University, University Park Pennsylvania USA; Elsworth, Derek [Department of Energy and Mineral Engineering, EMS Energy Institute, and G3 Center, Pennsylvania State University, University Park Pennsylvania USA; Department of Geosciences, EMS Energy Institute, and G3 Center, Pennsylvania State University, University Park Pennsylvania USA; Wang, Chaoyi [Department of Energy and Mineral Engineering, EMS Energy Institute, and G3 Center, Pennsylvania State University, University Park Pennsylvania USA; Ishibashi, Takuya [Department of Energy and Mineral Engineering, EMS Energy Institute, and G3 Center, Pennsylvania State University, University Park Pennsylvania USA; Fukushima Renewable Energy Institute, National Institute of Advanced Industrial Science and Technology, Koriyama Japan; Fitts, Jeffrey P. [Department of Civil and Environmental Engineering, Princeton University, Princeton New Jersey USA

    2017-01-01

    There is wide concern that fluid injection in the subsurface, such as for the stimulation of shale reservoirs or for geological CO2 sequestration (GCS), has the potential to induce seismicity that may change reservoir permeability due to fault slip. However, the impact of induced seismicity on fracture permeability evolution remains unclear due to the spectrum of modes of fault reactivation (e.g., stable versus unstable). As seismicity is controlled by the frictional response of fractures, we explore friction-stability-permeability relationships through the concurrent measurement of frictional and hydraulic properties of artificial fractures in Green River shale (GRS) and Opalinus shale (OPS). We observe that carbonate-rich GRS shows higher frictional strength but weak neutral frictional stability. The GRS fracture permeability declines during shearing while an increased sliding velocity reduces the rate of permeability decline. By comparison, the phyllosilicate-rich OPS has lower friction and strong stability while the fracture permeability is reduced due to the swelling behavior that dominates over the shearing induced permeability reduction. Hence, we conclude that the friction-stability-permeability relationship of a fracture is largely controlled by mineral composition and that shale mineral compositions with strong frictional stability may be particularly subject to permanent permeability reduction during fluid infiltration.

  18. Ultralow Friction in a Superconducting Magnetic Bearing

    Science.gov (United States)

    Bornemann, Hans J.; Siegel, Michael; Zaitsev, Oleg; Bareiss, Martin; Laschuetza, Helmut

    1996-01-01

    Passive levitation by superconducting magnetic bearings can be utilized in flywheels for energy storage. Basic design criteria of such a bearing are high levitation force, sufficient vertical and horizontal stability and low friction. A test facility was built for the measurement and evaluation of friction in a superconducting magnetic bearing as a function of operating temperature and pressure in the vacuum vessel. The bearing consists of a commercial disk shaped magnet levitated above single grain, melt-textured YBCO high-temperature superconductor material. The superconductor was conduction cooled by an integrated AEG tactical cryocooler. The temperature could be varied from 50 K to 80 K. The pressure in the vacuum chamber was varied from 1 bar to 10(exp -5) mbar. At the lowest pressure setting, the drag torque shows a linear frequency dependence over the entire range investigated (0 less than f less than 40 Hz). Magnetic friction, the frequency independent contribution, is very low. The frequency dependent drag torque is generated by molecular friction from molecule-surface collisions and by eddy currents. Given the specific geometry of the set-up and gas pressure, the molecular drag torque can be estimated. At a speed of 40 Hz, the coefficient of friction (drag-to-lift ratio) was measured to be mu = 1.6 x 10(exp -7) at 10(exp -5) mbar and T = 60 K. This is equivalent to a drag torque of 7.6 x 10(exp -10) Nm. Magnetic friction causes approx. 1% of the total losses. Molecular friction accounts for about 13% of the frequency dependent drag torque, the remaining 87% being due to eddy currents and losses from rotor unbalance. The specific energy loss is only 0.3% per hour.

  19. Gimballed Shoulders for Friction Stir Welding

    Science.gov (United States)

    Carter, Robert; Lawless, Kirby

    2008-01-01

    In a proposed improvement of tooling for friction stir welding, gimballed shoulders would supplant shoulders that, heretofore, have been fixedly aligned with pins. The proposal is especially relevant to self-reacting friction stir welding. Some definitions of terms, recapitulated from related prior NASA Tech Briefs articles, are prerequisite to a meaningful description of the proposed improvement. In friction stir welding, one uses a tool that includes (1) a rotating shoulder on top (or front) of the workpiece and (2) a pin that rotates with the shoulder and protrudes from the shoulder into the depth of the workpiece. In conventional friction stir welding, the main axial force exerted by the tool on the workpiece is reacted through a ridged backing anvil under (behind) the workpiece. When conventional friction stir welding is augmented with an auto-adjustable pin-tool (APT) capability, the depth of penetration of the pin into the workpiece is varied in real time by a position- or forcecontrol system that extends or retracts the pin as needed to obtain the desired effect. In self-reacting (also known as self-reacted) friction stir welding as practiced heretofore, there are two shoulders: one on top (or front) and one on the bottom (or back) of the workpiece. In this case, a threaded shaft protrudes from the tip of the pin to beyond the back surface of the workpiece. The back shoulder is held axially in place against tension by a nut on the threaded shaft. Both shoulders rotate with the pin and remain aligned coaxially with the pin. The main axial force exerted on the workpiece by the tool and front shoulder is reacted through the back shoulder and the threaded shaft into the friction-stir-welding machine head, so that a backing anvil is no longer needed. A key transmits torque between the bottom shoulder and the threaded shaft, so that the bottom shoulder rotates with the shaft. This concludes the prerequisite definitions of terms.

  20. New design and the manufacturing techniques of the main friction pair of frictional dampers

    Directory of Open Access Journals (Sweden)

    Aleksander GOLUBENKO

    2007-01-01

    Full Text Available The design of the main friction pair of the frictional oscillations damper of passenger car axle box stage suspension and its manufacturing techniques are described. The difference of the design of the main friction pair consists in replacement of a conicalcontact surface of the shpinton sleeve by a pyramidal surface as well as a cylindrical surface of the frictional slide block by a flat surface of the rectangular form. Technological ways of increase of strength and wear resistance were developed that allowed quantitatively to estimate a reserve of increase of strength and thermal wear resistance by methods of plastic deforming. With the purpose of increase of wear resistance and resource saving the new technology of producing the shpinton sleeve blank is offered by a method of cold die forging, and a frictional slide block – by hot dieforging.

  1. Skin friction measurements by a new nonintrusive double-laser-beam oil viscosity balance technique

    Science.gov (United States)

    Monson, D. J.; Higuchi, H.

    1980-01-01

    A portable dual-laser-beam interferometer that nonintrusively measures skin friction by monitoring the thickness change of an oil film subject to shear stress is described. The method is an advance over past versions in that the troublesome and error-introducing need to measure the distance to the oil leading edge and the starting time for the oil flow has been eliminated. The validity of the method was verified by measuring oil viscosity in the laboratory, and then using those results to measure skin friction beneath the turbulent boundary layer in a low-speed wind tunnel. The dual-laser-beam skin friction measurements are compared with Preston tube measurements, with mean velocity profile data in a 'law-of-the-wall' coordinate system, and with computations based on turbulent boundary-layer theory. Excellent agreement is found in all cases. This validation and the aforementioned improvements appear to make the present form of the instrument usable to measure skin friction reliably and nonintrusively in a wide range of flow situations in which previous methods are not practical.

  2. Determination of the Mechanical Properties of Friction Welded Tube Yoke and Tube Joint

    Directory of Open Access Journals (Sweden)

    Efe Işık

    2016-01-01

    Full Text Available This paper deals with the friction welding of the tube yoke and the tube of the drive shaft used in light commercial vehicles. Tube yoke made from hot forged microalloyed steel and the tube made from cold drawn steel, with a ratio (thickness/outside diameter ratio of less than 0.1, were successfully welded by friction welding method. Hardness distributions on both sides of the welded joint across the welding interface were determined and the microstructure of the joint was investigated. Furthermore, joint strength was tested under tensile, static torsional, and torsional fatigue loadings. The tested data were analyzed by Weibull distribution. The maximum hardness value along the welded joint was detected as 553 Hv1. The lowest detected tensile strength of the joint was 13% less than the base materials’ tensile strength. The torsional load carrying capacity of the friction welded thin walled tubular joint without any damage was obtained as 4.252,5 Nm in 95% confidence interval. After conducting fully reversed torsional fatigue tests, the fatigue life of friction welded tubular joints was detected as 220.066,3 cycles.

  3. Torsional Vibrations of a Cantilever with Lateral Friction in a Resonance Friction Microscope

    Institute of Scientific and Technical Information of China (English)

    CHEN Jian-Song; GE Yun; ZHANG Hui

    2012-01-01

    A model of fundamental torsional vibration of a cantilever with lateral friction is presented by using the harmonic balance method. The model demonstrates that the torsional vibration has close relations with the lateral friction threshold, the lateral contact stiffness and the torsional vibration amplitude of the cantilever. When the threshold is larger than a product of the stiffness and the vibration amplitude, the lateral friction is a linear force with the amplitude. If the lateral friction threshold is less than the product, the motions of the tip on the sample can be stick-slip or slip motions. The results are useful to optimize and to manipulate the fundamental flexural vibration of the piezo-cantilever, and give an insight into the tribological characterization of the interface in a resonance friction microscope.%A model of fundamental torsional vibration of a cantilever with lateral friction is presented by using the harmonic balance method.The model demonstrates that the torsional vibration has close relations with the lateral friction threshold,the lateral contact stiffness and the torsional vibration amplitude of the cantilever.When the threshold is larger than a product of the stiffness and the vibration amplitude,the lateral friction is a linear force with the amplitude.If the lateral friction threshold is less than the product,the motions of the tip on the sample can be stick-slip or slip motions.The results are useful to optimize and to manipulate the fundamental flexural vibration of the piezo-cantilever,and give an insight into the tribological characterization of the interface in a resonance friction microscope.

  4. Velocities, turbulence, and skin friction in a deep-sea logarithmic layer

    Science.gov (United States)

    Gust, Giselher; Weatherly, Georges L.

    1985-05-01

    Speed, turbulence, skin friction, and drag measurements made with metal-clad hot wires, epoxy-coated hot films, and Savonius rotors are reported for a deep-sea boundary layer at a water depth of ˜5000 m. They include data from heights z < 30 cm, a region hitherto only investigated in detail by Chriss and Caldwell (1982) for a shelf site. A mean speed logarithmic layer was observed at 3 < z < 200 cm. The difference between the friction velocity u*log determined from the speed profiles and the skin friction u*skin measured by flush-mounted hot films was statistically significant at the 95% level in five out of eight analyzed burst intervals. This result suggests form-drag influence on the vertical mean flow profile. Although identified from the mean speed data as a hydrodynamically rough boundary layer, the turbulence and bottom stress intensities at the deep-sea site were found to be reduced by more than 40% compared to smooth-wall open-channel flow and planetary boundary layers. Applicability of the universal law of the wall has not been confirmed for this deep-sea boundary layer.

  5. Time dependent friction in a free gas

    Science.gov (United States)

    Fanelli, Cristiano; Sisti, Francesco; Stagno, Gabriele V.

    2016-03-01

    We consider a body moving in a perfect gas, described by the mean-field approximation and interacting elastically with the body, we study the friction exerted by the gas on the body fixed at constant velocities. The time evolution of the body in this setting was studied in Caprino et al. [Math. Phys. 264, 167-189 (2006)], Caprino et al. [Math. Models Methods Appl. Sci. 17, 1369-1403 (2007)], and Cavallaro [Rend. Mat. Appl. 27, 123-145 (2007)] for object with simple shape; the first study where a simple kind of concavity was considered was in Sisti and Ricciuti [SIAM J. Math. Anal. 46, 3759-3611 (2014)], showing new features in the dynamic but not in the friction term. The case of more general shape of the body was left out for further difficulties, and we believe indeed that there are actually non-trivial issues to be faced for these more general cases. To show this and in the spirit of getting a more realistic perspective in the study of friction problems, in this paper, we focused our attention on the friction term itself, studying its behavior on a body with a more general kind of concavity and fixed at constant velocities. We derive the expression of the friction term for constant velocities, we show how it is time dependent, and we give its exact estimate in time. Finally, we use this result to show the absence of a constant velocity in the actual dynamic of such a body.

  6. Velocity Dependence of Friction of Confined Hydrocarbons

    DEFF Research Database (Denmark)

    Sivebæk, Ion Marius; Samoilov, Vladimir N.; Persson, Bo N. J.

    2010-01-01

    We present molecular dynamics friction calculations for confined hydrocarbon “polymer” solids with molecular lengths from 20 to 1400 carbon atoms. Two cases are considered: (a) polymer sliding against a hard substrate and (b) polymer sliding on polymer. We discuss the velocity dependence of the f......We present molecular dynamics friction calculations for confined hydrocarbon “polymer” solids with molecular lengths from 20 to 1400 carbon atoms. Two cases are considered: (a) polymer sliding against a hard substrate and (b) polymer sliding on polymer. We discuss the velocity dependence...... in the polymer film is always close to the thermostat temperature. In the first setup (a), for hydrocarbons with molecular lengths from 60 to 1400 carbon atoms, the shear stresses are nearly independent of molecular length, but for the shortest hydrocarbon C20H42 the frictional shear stress is lower. In all...... cases the frictional shear stress increases monotonically with the sliding velocity. For polymer sliding on polymer (case b) the friction is much larger, and the velocity dependence is more complex. For hydrocarbons with molecular lengths from 60 to 140 C atoms, the number of monolayers of lubricant...

  7. Friction characteristics of trocars in laparoscopic surgery.

    Science.gov (United States)

    Alazmani, Ali; Roshan, Rupesh; Jayne, David G; Neville, Anne; Culmer, Peter

    2015-04-01

    This article investigates the friction characteristics of the instrument-trocar interface in laparoscopic surgery for varying linear instrument velocities, trocar seal design and material, and trocar tilt. Furthermore, the effect of applying lubrication at the instrument-trocar seal interface on friction was studied. A friction testing apparatus was designed and built to characterise the resistance force at the instrument-trocar interface as a function of the instrument's linear movement in the 12-mm trocar (at constant velocity) for different design, seal material, and angle of tilt. The resistance force depended on the trocar seal design and material properties, specifically surface roughness, elasticity, hardness, the direction of movement, and the instrument linear velocity, and varied between 0.25 and 8 N. Lubricating the shaft with silicone oil reduced the peak resistance force by 75% for all trocars and eliminated the stick-slip phenomenon evident in non-lubricated cases. The magnitude of fluctuation in resistance force depends on the trocar design and is attributed to stick-slip of the sealing mechanism and is generally higher during retraction in comparison to insertion. Trocars that have an inlet seal made of rubber/polyurethane showed higher resistance forces during retraction. Use of a lubricant significantly reduced frictional effects. Comparisons of the investigated trocars indicate that a low friction port, providing the surgeon with improved haptic feedback, can be designed by improving the tribological properties of the trocar seal interface.

  8. Assessing the clarity of friction ridge impressions.

    Science.gov (United States)

    Hicklin, R Austin; Buscaglia, JoAnn; Roberts, Maria Antonia

    2013-03-10

    The ability of friction ridge examiners to correctly discern and make use of the ridges and associated features in finger or palm impressions is limited by clarity. The clarity of an impression relates to the examiner's confidence that the presence, absence, and attributes of features can be correctly discerned. Despite the importance of clarity in the examination process, there have not previously been standard methods for assessing clarity in friction ridge impressions. We introduce a process for annotation, analysis, and interchange of friction ridge clarity information that can be applied to latent or exemplar impressions. This paper: (1) describes a method for evaluating the clarity of friction ridge impressions by using color-coded annotations that can be used by examiners or automated systems; (2) discusses algorithms for overall clarity metrics based on manual or automated clarity annotation; and (3) defines a method of quantifying the correspondence of clarity when comparing a pair of friction ridge images, based on clarity annotation and resulting metrics. Different uses of this approach include examiner interchange of data, quality assurance, metrics, and as an aid in automated fingerprint matching.

  9. Modeling frictional melt injection to constrain coseismic physical conditions

    Science.gov (United States)

    Sawyer, William J.; Resor, Phillip G.

    2017-07-01

    Pseudotachylyte, a fault rock formed through coseismic frictional melting, provides an important record of coseismic mechanics. In particular, injection veins formed at a high angle to the fault surface have been used to estimate rupture directivity, velocity, pulse length, stress drop, as well as slip weakening distance and wall rock stiffness. These studies have generally treated injection vein formation as a purely elastic process and have assumed that processes of melt generation, transport, and solidification have little influence on the final vein geometry. Using a pressurized crack model, an analytical approximation of injection vein formation based on dike intrusion, we find that the timescales of quenching and flow propagation may be similar for a subset of injection veins compiled from the Asbestos Mountain Fault, USA, Gole Larghe Fault Zone, Italy, and the Fort Foster Brittle Zone, USA under minimum melt temperature conditions. 34% of the veins are found to be flow limited, with a final geometry that may reflect cooling of the vein before it reaches an elastic equilibrium with the wall rock. Formation of these veins is a dynamic process whose behavior is not fully captured by the analytical approach. To assess the applicability of simplifying assumptions of the pressurized crack we employ a time-dependent finite-element model of injection vein formation that couples elastic deformation of the wall rock with the fluid dynamics and heat transfer of the frictional melt. This finite element model reveals that two basic assumptions of the pressurized crack model, self-similar growth and a uniform pressure gradient, are false. The pressurized crack model thus underestimates flow propagation time by 2-3 orders of magnitude. Flow limiting may therefore occur under a wider range of conditions than previously thought. Flow-limited veins may be recognizable in the field where veins have tapered profiles or smaller aspect ratios than expected. The occurrence and

  10. Wall shear stress measurements using a new transducer

    Science.gov (United States)

    Vakili, A. D.; Wu, J. M.; Lawing, P. L.

    1986-01-01

    A new instrument has been developed for direct measurement of wall shear stress. This instrument is simple and symmetric in design with small moving mass and no internal friction. Features employed in the design of this instrument eliminate most of the difficulties associated with the traditional floating element balances. Vibration problems associated with the floating element skin friction balances have been found to be minimized by the design features and optional damping provided. The unique design of this instrument eliminates or reduces the errors associated with conventional floating-element devices: such as errors due to gaps, pressure gradient, acceleration, heat transfer and temperature change. The instrument is equipped with various sensing systems and the output signal is a linear function of the wall shear stress. Measurement made in three different tunnels show good agreement with theory and data obtained by the floating element devices.

  11. Friction and wear in polymer-based materials

    CERN Document Server

    Bely, V A; Petrokovets, M I

    1982-01-01

    Friction and Wear in Polymer-Based Materials discusses friction and wear problems in polymer-based materials. The book is organized into three parts. The chapters in Part I cover the basic laws of friction and wear in polymer-based materials. Topics covered include frictional interaction during metal-polymer contact and the influence of operating conditions on wear in polymers. The chapters in Part II discuss the structure and frictional properties of polymer-based materials; the mechanism of frictional transfer when a polymer comes into contact with polymers, metals, and other materials; and

  12. Benchmarking of direct and indirect friction tests in micro forming

    DEFF Research Database (Denmark)

    Eriksen, Rasmus Solmer; Calaon, Matteo; Arentoft, M.

    2012-01-01

    The sizeable increase in metal forming friction at micro scale, due to the existence of size effects, constitutes a barrier to the realization of industrial micro forming processes. In the quest for improved frictional conditions in micro scale forming operations, friction tests are applied...... to qualify the tribological performance of the particular forming scenario. In this work the application of a simulative sliding friction test at micro scale is studied. The test setup makes it possible to measure the coefficient of friction as a function of the sliding motion. The results confirm a sizeable...... increase in the coefficient of friction when the work piece size is scaled down. © (2012) Trans Tech Publications....

  13. A numerical modelling of non linear 2D-frictional multicontact problems: application to post-buckling in cellular media

    Science.gov (United States)

    Alart, P.; Barboteu, M.; Gril, J.

    2004-09-01

    In this paper a numerical modelling of non linear problems involving large deformations and frictional contact conditions is proposed. The motivation of this work comes from the study of the cellular materials (such as wood or foams) undergoing strong deformations. We restrict our study to a regular cellular network of hexagonal cells with thin walls. Strong loadings can generate at first buckling phenomena, then self-contact in the cell. Renouncing homogenization procedures, not always pertinent in this case, we have developed direct simulations. After giving the mechanical and mathematical formulations of the problem, we present two advanced numerical tools to solve large non linear frictional multicontact problems. This numerical modelling is based on an arc-length continuation method which permits to snap through singular points due to buckling phenomena and on an optimal domain decomposition method adapted to frictional contact problems. Finally, mechanical investigations of the contactless buckling and the post-buckling provide some pertinent parameters controlling the deformation process.

  14. Direct friction measurement in draw bead testing

    DEFF Research Database (Denmark)

    Olsson, David Dam; Bay, Niels; Andreasen, Jan Lasson

    2005-01-01

    The application of draw beads in sheet metal stamping ensures controlled drawing-in of flange parts. Lubrication conditions in draw beads are severe due to sliding under simultaneous bending. Based on the original draw bead test design by Nine [1] comprehensive studies of friction in draw beads...... have been reported in literature. A major drawback in all these studies is that friction is not directly measured, but requires repeated measurements of the drawing force with and without relative sliding between the draw beads and the sheet material. This implies two tests with a fixed draw bead tool...... and a freely rotating tool respectively, an approach, which inevitably implies large uncertainties due to scatter in the experimental conditions. In order to avoid this problem a new draw bead test is proposed by the authors measuring the friction force acting on the tool radius directly by a build...

  15. Hyperstaticity and loops in frictional granular packings

    Science.gov (United States)

    Tordesillas, Antoinette; Lam, Edward; Metzger, Philip T.

    2009-06-01

    The hyperstatic nature of granular packings of perfectly rigid disks is analyzed algebraically and through numerical simulation. The elementary loops of grains emerge as a fundamental element in addressing hyperstaticity. Loops consisting of an odd number of grains behave differently than those with an even number. For odd loops, the latent stresses are exterior and are characterized by the sum of frictional forces around each loop. For even loops, the latent stresses are interior and are characterized by the alternating sum of frictional forces around each loop. The statistics of these two types of loop sums are found to be Gibbsian with a "temperature" that is linear with the friction coefficient μ when μ<1.

  16. CAM/LIFTER forces and friction

    Science.gov (United States)

    Gabbey, D. J.; Lee, J.; Patterson, D. J.

    1992-02-01

    This report details the procedures used to measure the cam/lifter forces and friction. The present effort employed a Cummins LTA-10, and focuses on measurements and dynamic modeling of the injector train. The program was sponsored by the US Department of Energy in support of advanced diesel engine technology. The injector train was instrumented to record the instantaneous roller speed, roller pin friction torque, pushrod force, injector link force, and cam speed. These measurements, together with lift profiles for pushrod and injector link displacement, enabled the friction work loss in the injector train to be determined. Other significant design criteria such as camshaft roller follower slippage and maximum loads on components were also determined. Future efforts will concentrate on the dynamic model, with tests run as required for correlation.

  17. Physics of Friction in Disposable Plastic Syringes

    Science.gov (United States)

    Liebmann-Vinson, A.; Vogler, E. A.; Martin, D. A.; Montgomery, D. B.; Sugg, H. W.; Monahan, L. A.

    1997-03-01

    Nosocomial applications of disposable plastic syringes demand excellent frictional behavior with no stick-slip over a broad velocity range and, simultaneously, a tight seal between stopper and barrel. However, when used in syringe pumps at slow injection speeds, stick-slip motion is frequently observed and high "break-out" forces are often necessary to initiate plunger movement after extended storage times. We have traced this frictional behavior to a velocity-dependent interaction between the elastomeric stopper and the plastic syringe barrel mediated by the syringe lubricant, almost universally a polydimethyl siloxane fluid. Lubricant properties were altered by crosslinking the surface of the silicone oil in an oxygen plasma. Changes in surface chemistry and morphology of the crosslinked oil were correlated with changes in frictional performance.

  18. Direct friction measurement in draw bead testing

    DEFF Research Database (Denmark)

    Olsson, David Dam; Bay, Niels; Andreasen, Jan Lasson

    2005-01-01

    have been reported in literature. A major drawback in all these studies is that friction is not directly measured, but requires repeated measurements of the drawing force with and without relative sliding between the draw beads and the sheet material. This implies two tests with a fixed draw bead tool...... and a freely rotating tool respectively, an approach, which inevitably implies large uncertainties due to scatter in the experimental conditions. In order to avoid this problem a new draw bead test is proposed by the authors measuring the friction force acting on the tool radius directly by a build......-in piezoelectric torque transducer. This technique results in a very sensitive measurement of friction, which furthermore enables recording of lubricant film breakdown as function of drawing distance. The proposed test is validated in an experimental investigation of the influence of lubricant viscosity...

  19. Sensitivity to friction for primary explosives.

    Science.gov (United States)

    Matyáš, Robert; Šelešovský, Jakub; Musil, Tomáš

    2012-04-30

    The sensitivity to friction for a selection of primary explosives has been studied using a small BAM friction apparatus. The probit analysis was used for the construction of a sensitivity curve for each primary explosive tested. Two groups of primary explosives were chosen for measurement (a) the most commonly used industrially produced primary explosives (e.g. lead azide, tetrazene, dinol, lead styphnate) and (b) the most produced improvised primary explosives (e.g. triacetone triperoxide, hexamethylenetriperoxide diamine, mercury fulminate, acetylides of heavy metals). A knowledge of friction sensitivity is very important for determining manipulation safety for primary explosives. All the primary explosives tested were carefully characterised (synthesis procedure, shape and size of crystals). The sensitivity curves obtained represent a unique set of data, which cannot be found anywhere else in the available literature. Copyright © 2012 Elsevier B.V. All rights reserved.

  20. Static and dynamic friction of hierarchical surfaces

    Science.gov (United States)

    Costagliola, Gianluca; Bosia, Federico; Pugno, Nicola M.

    2016-12-01

    Hierarchical structures are very common in nature, but only recently have they been systematically studied in materials science, in order to understand the specific effects they can have on the mechanical properties of various systems. Structural hierarchy provides a way to tune and optimize macroscopic mechanical properties starting from simple base constituents and new materials are nowadays designed exploiting this possibility. This can be true also in the field of tribology. In this paper we study the effect of hierarchical patterned surfaces on the static and dynamic friction coefficients of an elastic material. Our results are obtained by means of numerical simulations using a one-dimensional spring-block model, which has previously been used to investigate various aspects of friction. Despite the simplicity of the model, we highlight some possible mechanisms that explain how hierarchical structures can significantly modify the friction coefficients of a material, providing a means to achieve tunability.

  1. Adhesion and friction of thin metal films

    Science.gov (United States)

    Buckley, D. H.

    1976-01-01

    Sliding friction experiments were conducted in vacuum with thin films of titanium, chromium, iron, and platinum sputter deposited on quartz or mica substrates. A single crystal hemispherically tipped gold slider was used in contact with the films at loads of 1.0 to 30.0 and at a sliding velocity of 0.7 mm/min at 23 C. Test results indicate that the friction coefficient is dependent on the adhesion of two interfaces, that between the film and its substrate and the slider and the film. There exists a relationship between the percent d bond character of metals in bulk and in thin film form and the friction coefficient. Oxygen can increase adhesive bonding of a metal film (platinum) to a substrate.

  2. Three-Dimensional Finite Element Based Numerical Simulation of Machining of Thin-Wall Components with Varying Wall Constraints

    Science.gov (United States)

    Joshi, Shrikrishna Nandkishor; Bolar, Gururaj

    2017-06-01

    Control of part deflection and deformation during machining of low rigidity thin-wall components is an important aspect in the manufacture of desired quality products. This paper presents a comparative study on the effect of geometry constraints on the product quality during machining of thin-wall components made of an aerospace alloy aluminum 2024-T351. Three-dimensional nonlinear finite element (FE) based simulations of machining of thin-wall parts were carried out by considering three variations in the wall constraint viz. free wall, wall constrained at one end, and wall with constraints at both the ends. Lagrangian formulation based transient FE model has been developed to simulate the interaction between the workpiece and helical milling cutter. Johnson-Cook material and damage model were adopted to account for material behavior during machining process; damage initiation and chip separation. A modified Coulomb friction model was employed to define the contact between the cutting tool and the workpiece. The numerical model was validated with experimental results and found to be in good agreement. Based on the simulation results it was noted that deflection and deformation were maximum in the thin-wall constrained at one end in comparison with those obtained in other cases. It was noted that three dimensional finite element simulations help in a better way to predict the product quality during precision manufacturing of thin-wall components.

  3. High fidelity frictional models for MEMS.

    Energy Technology Data Exchange (ETDEWEB)

    Carpick, Robert W. (University of Wisconsin, Madison, WI); Reedy, Earl David, Jr.; Bitsie, Fernando; de Boer, Maarten Pieter; Corwin, Alex David; Ashurst, William Robert (Auburn University, Auburn, AL); Jones, Reese E.; Subhash, Ghatu S. (Michigan Technological Institute, Houghton, MI); Street, Mark D. (University of Wisconsin, Madison, WI); Sumali, Anton Hartono; Antoun, Bonnie R.; Starr, Michael James; Redmond, James Michael; Flater, Erin E. (University of Wisconsin, Madison, WI)

    2004-10-01

    The primary goals of the present study are to: (1) determine how and why MEMS-scale friction differs from friction on the macro-scale, and (2) to begin to develop a capability to perform finite element simulations of MEMS materials and components that accurately predicts response in the presence of adhesion and friction. Regarding the first goal, a newly developed nanotractor actuator was used to measure friction between molecular monolayer-coated, polysilicon surfaces. Amontons law does indeed apply over a wide range of forces. However, at low loads, which are of relevance to MEMS, there is an important adhesive contribution to the normal load that cannot be neglected. More importantly, we found that at short sliding distances, the concept of a coefficient of friction is not relevant; rather, one must invoke the notion of 'pre-sliding tangential deflections' (PSTD). Results of a simple 2-D model suggests that PSTD is a cascade of small-scale slips with a roughly constant number of contacts equilibrating the applied normal load. Regarding the second goal, an Adhesion Model and a Junction Model have been implemented in PRESTO, Sandia's transient dynamics, finite element code to enable asperity-level simulations. The Junction Model includes a tangential shear traction that opposes the relative tangential motion of contacting surfaces. An atomic force microscope (AFM)-based method was used to measure nano-scale, single asperity friction forces as a function of normal force. This data is used to determine Junction Model parameters. An illustrative simulation demonstrates the use of the Junction Model in conjunction with a mesh generated directly from an atomic force microscope (AFM) image to directly predict frictional response of a sliding asperity. Also with regards to the second goal, grid-level, homogenized models were studied. One would like to perform a finite element analysis of a MEMS component assuming nominally flat surfaces and to include the

  4. Friction stir welding of single crystal aluminium

    DEFF Research Database (Denmark)

    Fonda, Richard Warren; Wert, John A.; Reynolds, A.P.

    2007-01-01

    Friction stir welds were prepared in different orientations in an aluminium single crystal. The welds were quenched to preserve the microstructure surrounding the tool and then electron backscattered diffraction was used to reveal the generation of grain boundaries and the evolution of crystallog......Friction stir welds were prepared in different orientations in an aluminium single crystal. The welds were quenched to preserve the microstructure surrounding the tool and then electron backscattered diffraction was used to reveal the generation of grain boundaries and the evolution...

  5. Ratchet device with broken friction symmetry

    DEFF Research Database (Denmark)

    Norden, Bengt; Zolotaryuk, Yaroslav; Christiansen, Peter Leth

    2002-01-01

    An experimental setup (gadget) has been made for demonstration of a ratchet mechanism induced by broken symmetry of a dependence of dry friction on external forcing. This gadget converts longitudinal oscillating or fluctuating motion into a unidirectional rotation, the direction of which is in ac......An experimental setup (gadget) has been made for demonstration of a ratchet mechanism induced by broken symmetry of a dependence of dry friction on external forcing. This gadget converts longitudinal oscillating or fluctuating motion into a unidirectional rotation, the direction of which...

  6. Analysis of nonlinear channel friction inverse problem

    Institute of Scientific and Technical Information of China (English)

    CHENG Weiping; LIU Guohua

    2007-01-01

    Based on the Backus-Gilbert inverse theory, the singular value decomposition (SVD) for general inverse matrices and the optimization algorithm are used to solve the channel friction inverse problem. The resolution and covari- ance friction inverse model in matrix form is developed to examine the reliability of solutions. Theoretical analyses demonstrate that the convergence rate of the general Newton optimization algorithm is in the second-order. The Wiggins method is also incorporated into the algorithm. Using the method, noise can be suppressed effectively, and the results are close to accurate solutions with proper control parameters. Also, the numerical stability can be improved.

  7. Design of Piston Ring Friction Tester Apparatus

    DEFF Research Database (Denmark)

    Klit, Peder

    2006-01-01

    the frictional behavior of a piston ring correctly is knowledge about the amount of lubricant present. For piston rings the external load may be established by measuring the pressure distribution, i.e. the pressure drop in the piston ring package. Speed and temperature may also be established. The amount...... and forces on piston rod. Since the frictional forces are small compared to the rest of the acting forces the main design idea is to fix the piston, while the cylinder liner moves. This approach makes it simple to measure the parameters mentioned above by putting the instrumentation in the piston....

  8. Frictional coupling between sliding and spinning motion

    CERN Document Server

    Farkas, Z; Unger, T; Wolf, D E; Farkas, Zeno; Bartels, Guido; Unger, Tamas; Wolf, Dietrich E.

    2002-01-01

    We show that the friction force and torque, acting at a dry contact of two objects moving and rotating relative to each other, are inherently coupled. As a simple test system, a sliding and spinning disk on a horizontal flat surface is considered. We calculate, and also measure, how the disk is slowing down, and find that it always stops its sliding and spinning motion at the same moment. We discuss the impact of this coupling between friction force and torque on the physics of granular materials.

  9. Monomeric Friction Coefficient of Metalnanodispersible Polymeric Systems

    Directory of Open Access Journals (Sweden)

    B.B. Kolupayev

    2016-12-01

    Full Text Available Influence of a nanodispersible metal excipient in number of 0    5,0 vol.% Cu for the size of a monomeric friction coefficient of polyvinylchloride (PVC systems in temperature range 298  Т  (Tg + 10 K is investigated. It is shown that various types of coordination movements of building blocks are described by a friction coefficient which serves as a measure of influence of external fields and ingredients on viscoelastic behavior of a composite. The analysis of processes of a relaxation on the basis of the theory of flexible chains taking into account power and entropic factors is carried out.

  10. Experimental study on steam-water two-phase flow frictional pressure drops in helical coils

    Institute of Scientific and Technical Information of China (English)

    1997-01-01

    Experiments of steam-water two-phase flow frictional pressure drop in a vertical helical coil were carried out in the high-pressure water test loop of Xi'an jiaotong University,The coil is made of stainless steel tube with an inner diameter of 16mm,the helix diameter measured from tube axis to tube axis is 1.3m,and helix angle of the coil is 3.65°,The experimental conditions are:pressurep=4-18MPa,mass velocity G=400-1400kg/(m2.s),inner wall heat flux q=100-700kW/m2,Based on these data,a correlation for predicting the steam-water two-phase flow frictional pressure drop was derived,it can be used for the design of steam generator of HTGR.

  11. Effects of forming parameters on temperature in frictional stir incremental sheet forming

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jin; Jiang, Husen [Qingdao Technological University, Qingdao (China); Li, Lihua [Qingdao University, Qingdao (China)

    2016-05-15

    Frictional stir Incremental sheet forming (ISF) is a new technology used to fabricate parts of hard-to-form materials without using heating equipment. Thus far, limited information is known about the effects of main forming parameters, except spindle speed of the tool, on the temperature of formed sheet in friction-stir ISF. The effects of six forming parameters, namely, sheet thickness, tool vertical step, tool diameter, spindle speed, feed rate, and wall angle of the formed part, were identified using the design of experiment of orthogonal array, analysis of response tables and graphs, and analysis of variance. Results show that spindle speed, feed rate, sheet thickness, and tool vertical step significantly affect the temperature of the sheet. In addition, the temperature of the sheet is significantly increased by increasing sheet thickness, tool vertical step, and spindle speed but significantly decreased with increasing tool feed rate.

  12. Studies in molecular dynamics of the friction coefficient and the Lorentz gas

    Energy Technology Data Exchange (ETDEWEB)

    Alley, W.E.

    1979-06-01

    The thesis consists of three hard-sphere molecular dynamics studies. The first describes a modification of Fick's diffusion law, required whenever long-time correlations are present. The second study concerns the mass and size dependence of the friction coefficient as well as its dependence on boundary conditions. The study presents a molecular dynamics method which calculates the infinite-mass friction coefficient of finite size hard-sphere particles. The third study presents the applicability of hydrodynamics to describe fluctuations in fluids on the molecular level. This study shows that the fluctuations present in a system of hard spheres when placed between closely spaced parallel hard walls lead to an acoustical resonance for those wavelengths which correspond to the spacing, or integer fractions thereof.

  13. Bifurcations in Systems with Friction : Basic Models and Methods

    NARCIS (Netherlands)

    Ivanov, A. P.

    2009-01-01

    Examples of irregular behavior of dynamical systems with dry friction are discussed. A classification of frictional contacts with respect to their dimensionality, associativity, and the possibility of interruptions is proposed and basic models showing typical features are stated. In particular,

  14. Micromechanisms of friction and wear introduction to relativistic tribology

    CERN Document Server

    Lyubimov, Dmitrij; Pinchuk, Leonid

    2013-01-01

    The modern vision of the micromechanism of friction and wear is explored, from the examination of ideal and real crystal structure and adhesion properties to the dynamics of solid frictional interaction. The fundamental quantum-mechanical and relativity principles of particle interaction are considered as basis of friction micro-process examination. The changes in solid structure originated from the influence of different kinds of force fields are considered. The principal possibility of relativity effect manifestation by friction is explained. The critical state of friction – triboplasma – was studied. Structural peculiarities of triboplasma, the kinetics of its transformation during frictional interaction as well as the influence of plasma and postplasma processes on tribojunction friction characteristics and complex formation by friction were examined. The book addresses to tribology researchers.

  15. Assessing slipperiness in fast-food restaurants in the USA using friction variation, friction level and perception rating.

    Science.gov (United States)

    Chang, Wen-Ruey; Huang, Yueng-Hsiang; Way Li, Kai; Filiaggi, Alfred; Courtney, Theodore K

    2008-05-01

    Although friction variation is speculated to be a significant contributor to slip and fall incidents, it has not been related to a measurement of slipperiness in the literature. This field study investigated the relationship among multiple friction variations, friction levels and the perception ratings of slipperiness in six major working areas of 10 fast-food restaurants in the USA. The mean perception rating score for each working area was correlated with various friction reduction variables across all the restaurants in comparison with its correlation with the mean friction coefficient of each working area. The results indicated that the absolute and relative reductions in friction over the whole working area, among 12 friction reduction variables evaluated, could have a slightly better correlation with the perception rating score (r=0.34 and 0.37, respectively) than the mean friction coefficient of each working area (0.33). However, in friction measurements, more effort and time are needed to quantify friction variations than to obtain the mean friction coefficient. The results of the multiple regression model on the perception rating indicated that adding friction reduction variables into the regression model, in addition to the mean friction coefficient, did not make a significant impact on the outcomes. The results further indicated a statistically significant correlation between the mean friction coefficient and the maximum relative friction reduction over the whole area in each working area across all the restaurants evaluated (r=0.80). Despite a slightly lower correlation with perception rating than the friction variation, the mean friction coefficient of an area is still a reasonably good indicator of slipperiness.

  16. Approximate Augmentation of Turbulent Law-of-the-Wall by Periodic Free-Stream Disturbances

    Energy Technology Data Exchange (ETDEWEB)

    Dechant, Lawrence J. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-12-01

    We examine the role of periodic sinusoidal free-stream disturbances on the inner law law-of-the-wall (log-law) for turbulent boundary layers. This model serves a surrogate for the interaction of flight vehicles with atmospheric disturbances. The approximate skin friction expression that is derived suggests that free-stream disturbances can cause enhancement of the mean skin friction. Considering the influence of grid generated free stream turbulence in the laminar sublayer/log law region (small scale/high frequency) the model recovers the well-known shear layer enhancement suggesting an overall validity for the approach. The effect on the wall shear associated with the lower frequency due to the passage of the vehicle through large (vehicle scale) atmospheric disturbances is likely small i.e. on the order 1% increase for turbulence intensities on the order of 2%. The increase in wall pressure fluctuation which is directly proportional to the wall shear stress is correspondingly small.

  17. An empirical model for friction in cold forging

    DEFF Research Database (Denmark)

    Bay, Niels; Eriksen, Morten; Tan, Xincai

    2002-01-01

    With a system of simulative tribology tests for cold forging the friction stress for aluminum, steel and stainless steel provided with typical lubricants for cold forging has been determined for varying normal pressure, surface expansion, sliding length and tool/work piece interface temperature...... of normal pressure and tool/work piece interface temperature. The model is verified by process testing measuring friction at varying reductions in cold forward rod extrusion. KEY WORDS: empirical friction model, cold forging, simulative friction tests....

  18. Low-impact friction materials for brake pads

    OpenAIRE

    2016-01-01

    State-of-the-art friction materials for applications in disc brake systems are constituted by composite materials, specifically formulated to ensure proper friction and wear performances, under the sliding contact conditions of braking events. The bases of typical friction compound formulations usually include 10 to 30 different components bonded with a polymeric binder cross-linked in situ. Main requests to be fulfilled during braking are an adequate friction efficiency and enough mechanical...

  19. Interfacial Friction and Adhesion of Polymer Brushes

    KAUST Repository

    Landherr, Lucas J. T.

    2011-08-02

    A bead-probe lateral force microscopy (LFM) technique is used to characterize the interfacial friction and adhesion properties of polymer brushes. Our measurements attempt to relate the physical structure and chemical characteristics of the brush to their properties as thin-film, tethered lubricants. Brushes are synthesized at several chain lengths and surface coverages from polymer chains of polydimethylsiloxane (PDMS), polystyrene (PS), and a poly(propylene glycol)-poly(ethylene glycol) block copolymer (PPG/PEG). At high surface coverage, PDMS brushes manifest friction coefficients (COFs) that are among the lowest recorded for a dry lubricant film (μ ≈ 0.0024) and close to 1 order of magnitude lower than the COF of a bare silicon surface. Brushes synthesized from higher molar mass chains exhibit higher friction forces than those created using lower molar mass polymers. Increased grafting density of chains in the brush significantly reduces the COF by creating a uniform surface of stretched chains with a decreased surface viscosity. Brushes with lower surface tension and interfacial shear stresses manifest the lowest COF. In particular, PDMS chains exhibit COFs lower than PS by a factor of 3.7 and lower than PPG/PEG by a factor of 4.7. A scaling analysis conducted on the surface coverage (δ) in relation to the fraction (ε) of the friction force developing from adhesion predicts a universal relation ε ∼ δ4/3, which is supported by our experimental data. © 2011 American Chemical Society.

  20. Multiscaling behavior of atomic-scale friction

    Science.gov (United States)

    Jannesar, M.; Jamali, T.; Sadeghi, A.; Movahed, S. M. S.; Fesler, G.; Meyer, E.; Khoshnevisan, B.; Jafari, G. R.

    2017-06-01

    The scaling behavior of friction between rough surfaces is a well-known phenomenon. It might be asked whether such a scaling feature also exists for friction at an atomic scale despite the absence of roughness on atomically flat surfaces. Indeed, other types of fluctuations, e.g., thermal and instrumental fluctuations, become appreciable at this length scale and can lead to scaling behavior of the measured atomic-scale friction. We investigate this using the lateral force exerted on the tip of an atomic force microscope (AFM) when the tip is dragged over the clean NaCl (001) surface in ultra-high vacuum at room temperature. Here the focus is on the fluctuations of the lateral force profile rather than its saw-tooth trend; we first eliminate the trend using the singular value decomposition technique and then explore the scaling behavior of the detrended data, which contains only fluctuations, using the multifractal detrended fluctuation analysis. The results demonstrate a scaling behavior for the friction data ranging from 0.2 to 2 nm with the Hurst exponent H =0.61 ±0.02 at a 1 σ confidence interval. Moreover, the dependence of the generalized Hurst exponent, h (q ) , on the index variable q confirms the multifractal or multiscaling behavior of the nanofriction data. These results prove that fluctuation of nanofriction empirical data has a multifractal behavior which deviates from white noise.

  1. Modelling and Testing of Friction in Forging

    DEFF Research Database (Denmark)

    Bay, Niels

    2007-01-01

    Knowledge about friction is still limited in forging. The theoretical models applied presently for process analysis are not satisfactory compared to the advanced and detailed studies possible to carry out by plastic FEM analyses and more refined models have to be based on experimental testing...

  2. [Penis friction edema: not a venereal disease

    NARCIS (Netherlands)

    Erceg, A.; Verlind, J.; Berretty, P.J.

    2003-01-01

    A 35-year-old man presented with a local swelling of the penis, which increased until the entire penis was thick and swollen. After infectious and obstructive causes had been eliminated, a diagnosis of 'penis friction oedema' was made. The swelling disappeared during several weeks of abstinence from

  3. Friction welding thermal and metallurgical characteristics

    CERN Document Server

    Yilbas, Bekir Sami

    2014-01-01

    This book provides insight into the thermal analysis of friction welding incorporating welding parameters such as external, duration, breaking load, and material properties. The morphological and metallurgical changes associated with the resulting weld sites are analysed using characterization methods such as electron scanning microscope, energy dispersive spectroscopy, X-ray Diffraction, and Nuclear reaction analysis.

  4. Ratchet due to broken friction symmetry

    DEFF Research Database (Denmark)

    Norden, Bengt; Zolotaryuk, Yaroslav; Christiansen, Peter Leth

    2002-01-01

    A ratchet mechanism that occurs due to asymmetric dependence of the friction of a moving system on its velocity or a driving force is reported. For this kind of ratchet, instead of a particle moving in a periodic potential, the dynamics of which have broken space-time symmetry, the system must...

  5. Sensitivity to friction for primary explosives

    Energy Technology Data Exchange (ETDEWEB)

    Matyas, Robert, E-mail: robert.matyas@upce.cz [Institute of Energetic Materials, Faculty of Chemical Technology, University of Pardubice, Pardubice 532 10 (Czech Republic); Selesovsky, Jakub; Musil, Tomas [Institute of Energetic Materials, Faculty of Chemical Technology, University of Pardubice, Pardubice 532 10 (Czech Republic)

    2012-04-30

    Highlights: Black-Right-Pointing-Pointer The friction sensitivity of 14 samples of primary explosives was determined. Black-Right-Pointing-Pointer The same apparatus (small scale BAM) and the same method (probit analysis) was used. Black-Right-Pointing-Pointer The crystal shapes and sizes were documented with microscopy. Black-Right-Pointing-Pointer Almost all samples are less sensitive than lead azide, which is commercially used. Black-Right-Pointing-Pointer The organic peroxides (TATP, DADP, HMTD) are not as sensitive as often reported. - Abstract: The sensitivity to friction for a selection of primary explosives has been studied using a small BAM friction apparatus. The probit analysis was used for the construction of a sensitivity curve for each primary explosive tested. Two groups of primary explosives were chosen for measurement (a) the most commonly used industrially produced primary explosives (e.g. lead azide, tetrazene, dinol, lead styphnate) and (b) the most produced improvised primary explosives (e.g. triacetone triperoxide, hexamethylenetriperoxide diamine, mercury fulminate, acetylides of heavy metals). A knowledge of friction sensitivity is very important for determining manipulation safety for primary explosives. All the primary explosives tested were carefully characterised (synthesis procedure, shape and size of crystals). The sensitivity curves obtained represent a unique set of data, which cannot be found anywhere else in the available literature.

  6. On the superradiance-tidal friction correspondence

    CERN Document Server

    Glampedakis, K; Kennefick, D

    2013-01-01

    Since the work of Hartle in the 1970s, and the subsequent development of the the Membrane Paradigm approach to black hole physics it has been widely accepted that superradiant scattering of gravitational waves bears strong similarities with the phenomenon of ``tidal friction'' (well-known from Newtonian gravity) operating in binary systems of viscous material bodies. In this paper we revisit the superradiance-tidal friction analogy within the context of ultracompact relativistic bodies. We advocate that as long as these bodies have non-zero viscosity they should undergo tidal friction that can be construed as a kind of superradiant scattering from the point of view of the dynamics of an orbiting test-body. In addition we consider the presence of anisotropic matter, which is required for at least some ultracompact bodies, if they are to sustain a radius very close to the gravitational radius. We find that the tidal friction/superradiance output is enhanced with increasing anisotropy and that strongly anisotrop...

  7. Rolling Friction on a Wheeled Laboratory Cart

    Science.gov (United States)

    2012-01-01

    by gravity, and a vehicle (such as a car or bicycle ) accelerating along a level road is driven by a motor or by pedalling. In such cases, static...continuously roll. Consider a cart of mass m that is free rolling up an incline, as sketched in figure 1. The total frictional force f on the cart

  8. Friction Stir Welding of Aluminum Alloys

    Institute of Scientific and Technical Information of China (English)

    FU Zhi-hong; HE Di-qiu; WANG Hong

    2004-01-01

    Friction stir welding(FSW), a new solid-state welding technology invited in the early 1990s,enables us weld aluminum alloys and titanium alloys etc. The processing of FSW, the microstructure in FSW alloysand the factors influencing weld quality are introduced. The complex factors affecting the properties are researched.

  9. Frictional Dermatosis in a Courier Driver

    Directory of Open Access Journals (Sweden)

    Uwe Wollina

    2017-07-01

    Full Text Available Frictional hypermelanosis is an uncommon finding in Caucasians. We report the unusual case of 56-year-old male courier driver who developed linear and patchy hypermelanosis of the back caused by the driver's seat. Histology has included other pathologies. Treatment of the asymptomatic hyper pigmentation was not warranted.

  10. Validation of measured friction by process tests

    DEFF Research Database (Denmark)

    Eriksen, Morten; Henningsen, Poul; Tan, Xincai;

    The objective of sub-task 3.3 is to evaluate under actual process conditions the friction formulations determined by simulative testing. As regards task 3.3 the following tests have been used according to the original project plan: 1. standard ring test and 2. double cup extrusion test. The task ...

  11. Frictional Torque on a Rotating Disc

    Science.gov (United States)

    Mungan, Carl E.

    2012-01-01

    Resistance to motion often includes a dry frictional term independent of the speed of an object and a fluid drag term varying linearly with speed in the viscous limit. (At higher speeds, quadratic drag can also occur.) Here, measurements are performed for an aluminium disc mounted on bearings that is given an initial twist and allowed to spin…

  12. Friction Force: From Mechanics to Thermodynamics

    Science.gov (United States)

    Ferrari, Christian; Gruber, Christian

    2010-01-01

    We study some mechanical problems in which a friction force is acting on a system. Using the fundamental concepts of state, time evolution and energy conservation, we explain how to extend Newtonian mechanics to thermodynamics. We arrive at the two laws of thermodynamics and then apply them to investigate the time evolution and heat transfer of…

  13. Tribology: Friction, lubrication, and wear technology

    Science.gov (United States)

    Blau, Peter J.

    1993-01-01

    The topics are presented in viewgraph form and include the following: introduction and definitions of terms; friction concepts; lubrication technology concepts; wear technology concepts; and tribological transitions. This document is designed for educators who seek to teach these concepts to their students.

  14. [Penis friction edema: not a venereal disease

    NARCIS (Netherlands)

    Erceg, A.; Verlind, J.; Berretty, P.J.

    2003-01-01

    A 35-year-old man presented with a local swelling of the penis, which increased until the entire penis was thick and swollen. After infectious and obstructive causes had been eliminated, a diagnosis of 'penis friction oedema' was made. The swelling disappeared during several weeks of abstinence from

  15. Fibre Distribution in Friction-spun Yarns

    Institute of Scientific and Technical Information of China (English)

    Eric Oyondi Nganyi; YU Chong-wen

    2006-01-01

    According to the yarn forming characteristics in friction spinning, the arrangement of fed sliver is designed, to get the desired fiber distribution in the resultant yarn. On the base of that, the relation between the theoretical fibre distribution and the actual fibre distribution is analyzed by use of electron microscope.

  16. Simulations of atomic-scale sliding friction

    DEFF Research Database (Denmark)

    Sørensen, Mads Reinholdt; Jacobsen, Karsten Wedel; Stoltze, Per

    1996-01-01

    Simulation studies of atomic-scale sliding friction have been performed for a number of tip-surface and surface-surface contacts consisting of copper atoms. Both geometrically very simple tip-surface structures and more realistic interface necks formed by simulated annealing have been studied. Ki...

  17. Comparative study of Trombe wall, water wall and trans wall

    Energy Technology Data Exchange (ETDEWEB)

    Sodha, M.S.; Bansal, N.K.; Singh, S.; Ram, S.; Annamalai, M.; Iyer, M.V.; Nirmala, K.A.; Venkatesh, P.; Prasad, C.R.; Subramani, C.

    1982-01-01

    The thermal performances of three systems viz. Trombe wall: (1) without; and (2) with vents (forced air circulation), water wall and Transwall have been studied analytically interms of heat flux entering the living space (Maintained at 20/sup 0/C) corresponding to the meteriological data on January 19, 1981 at New Delhi (India), a typical cold winter day. Subsequent parametric studies using the simulation indicated that the Transwall system is the more efficient system for the passive heating of buildings.

  18. 30 CFR 57.19008 - Friction hoist synchronizing mechanisms.

    Science.gov (United States)

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Friction hoist synchronizing mechanisms. 57... MINES Personnel Hoisting Hoists § 57.19008 Friction hoist synchronizing mechanisms. Where creep or slip may alter the effective position of safety devices, friction hoists shall be equipped with...

  19. 30 CFR 56.19008 - Friction hoist synchronizing mechanisms.

    Science.gov (United States)

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Friction hoist synchronizing mechanisms. 56... Personnel Hoisting Hoists § 56.19008 Friction hoist synchronizing mechanisms. Where creep or slip may alter the effective position of safety devices, friction hoists shall be equipped with synchronizing...

  20. 30 CFR 56.19014 - Friction hoist overtravel protection.

    Science.gov (United States)

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Friction hoist overtravel protection. 56.19014 Section 56.19014 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND... Hoisting Hoists § 56.19014 Friction hoist overtravel protection. In a friction hoist installation, tapered...

  1. 30 CFR 57.19014 - Friction hoist overtravel protection.

    Science.gov (United States)

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Friction hoist overtravel protection. 57.19014 Section 57.19014 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND... Hoisting Hoists § 57.19014 Friction hoist overtravel protection. In a friction hoist installation, tapered...

  2. Atomic-scale friction : thermal effects and capillary condensation

    NARCIS (Netherlands)

    Jinesh, Kochupurackal Balakrishna Pillai

    2006-01-01

    This work entitled as "Atomic-scale friction: thermal effects and capillary condensation" is a study on the fundamental aspects of the origin of friction from the atomic-scale. We study two realistic aspects of atomic-scale friction, namely the effect of temperature and the effect of relative humidi

  3. Investigation of Friction-induced Damage to the Pig Cornea

    NARCIS (Netherlands)

    da Cruz Barros, Raquel; Van Kooten, Theo G.; Veeregowda, Deepak Halenahally

    2015-01-01

    Mechanical friction causes damage to the cornea. A friction measurement device with minimal intervention with the pig cornea tear film revealed a low friction coefficient of 0.011 in glycerine solution. Glycerine molecules presumably bind to water, mucins, and epithelial cells and therewith improve

  4. Milled Die Steel Surface Roughness Correlation with Steel Sheet Friction

    DEFF Research Database (Denmark)

    Berglund, J.; Brown, C.A.; Rosén, B.-G.

    2010-01-01

    This work investigates correlations between the surface topography ofmilled steel dies and friction with steel sheet. Several die surfaces were prepared by milling. Friction was measured in bending under tension testing. Linear regression coefficients (R2) between the friction and texture...

  5. Investigation of Friction-induced Damage to the Pig Cornea

    NARCIS (Netherlands)

    da Cruz Barros, Raquel; Van Kooten, Theo G.; Veeregowda, Deepak Halenahally

    2015-01-01

    Mechanical friction causes damage to the cornea. A friction measurement device with minimal intervention with the pig cornea tear film revealed a low friction coefficient of 0.011 in glycerine solution. Glycerine molecules presumably bind to water, mucins, and epithelial cells and therewith improve

  6. Frictional torque numbers for ball cup and journal bearings

    NARCIS (Netherlands)

    Ligterink, D.J.

    1982-01-01

    Plastic bearing material wears in ball cup and journal bearings. Contact areas in the ball cup and the journal bearing increase. The frictional torque needed to rotate the ball or journal also increases. When the coefficient of friction is assumed to be constant during wearing out, the frictional t

  7. Observing the Forces Involved in Static Friction under Static Situations

    Science.gov (United States)

    Kaplan, Daniel

    2013-01-01

    Static friction is an important concept in introductory physics. Later in the year students apply their understanding of static friction under more complex conditions of static equilibrium. Traditional lab demonstrations in this case involve exceeding of the maximum level of static friction, resulting in the "onset of motion." (Contains…

  8. The Investigation with ANSYS of Stress Changes on Silo Wall According to Different Standards

    OpenAIRE

    KİBAR, Hakan; Öztürk,Turgut

    2013-01-01

    In this study, the optimal dimensions of the silo were investigated for barrel-type cylinder, conical outlet, steel construction silo which used in Tombul hazelnut storage in the Giresun province conditions. 10, 11, 12, 13, 14, 15 ve 20 mm wall thickness for 1635 tons storage capacity silo were examined in the study. For this purpose, pressure loads acting on the silo wall surface (vertical, horizontal, friction traction pressure load) using Eurocode 1 and Australian standards were calculated...

  9. THE STRUCTURAL ANALYSIS OF STEEL SILOS WITH CYLINDRICAL-WALL BEARING AND PROFILE-STEEL BEARING

    OpenAIRE

    Zhengjun Tang; Daibiao Zhou; Chenwei Peng; Wenping Wu

    2015-01-01

    The silos are widely used in bulk material in many fields such as agriculture, mining, chemical, electric power storage, etc. Thin metal cylindrical silo shells are vulnerable to buckling failure caused by the compressive wall friction force. In this paper, the structural analysis of two types of steel silo with cylindrical-wall bearing and profile-steel bearing is implemented by Abaqus finite element analysis. The results indicate that under the same loading conditions, steel silos with prof...

  10. A Microphysical Model for Phyllosilicate Friction

    Science.gov (United States)

    Den Hartog, S. A. M.; Faulkner, D.; Spiers, C. J.

    2016-12-01

    Phyllosilicate-rich foliations in fault rocks are often thought to reduce overall fault strength and promote fault stability when forming an interconnected network. Indeed, laboratory measurements have shown that the average friction coefficient of dry phyllosilicates of 0.5 is reduced to 0.3 when wet or even 0.1 for smectite. A widely accepted interpretation of these observations is that the strength of phyllosilicates is controlled by breaking of interlayer bonds to form new cleavage surfaces when dry and by the low strength of surface-bound water films when wet. However, the correlation between phyllosilicate shear strength and interlayer bond strength, which formed the basis for this interpretation, was not reproduced in recent experiments (Behnsen and Faulkner, 2012) and is not supported by the latest calculations of the interlayer bond energies (Sakuma and Suehara, 2015). The accepted explanation for phyllosilicate friction also fails to account for the velocity dependence or (a-b) values, which decrease with temperature, reaching a minimum at intermediate temperatures, before increasing again at higher temperatures (Den Hartog et al., 2013, 2014). In this study, we developed a microphysical model for phyllosilicate friction, involving frictional sliding along atomically flat phyllosilicate grain interfaces, with overlapping grain edges forming barriers to sliding. Assuming that the amount of overlap is controlled by crystal plastic bending of grains into pores, together with rate-dependent edge-site cleavage, our model predicts the experimentally observed temperature dependence of (a-b) and provides a basis for extrapolation of laboratory friction data on phyllosilicates to natural conditions.

  11. The carreau-yasuda fluids: a skin friction equation for turbulent flow in pipes and kolmogorov dissipative scales

    OpenAIRE

    ANDRADE, Luiz Claudio Fialho; PETRONÍLIO, Jamilson A.; MANESCHY, Carlos Edilson de Almeida; CRUZ, Daniel Onofre de Almeida

    2007-01-01

    In this work the turbulent flow of the Non-Newtonian Carreau-Yasuda fluid will be studied. A skin friction equation for the turbulent flow of Carreau-Yasuda fluids will be derived assuming a logarithmic behavior of the turbulent mean velocity for the near wall flow out of the viscous sub layer. An alternative near wall characteristic length scale which takes into account the effects of the relaxation time will be introduced. The characteristic length will be obtained through the analysis of v...

  12. Effect of pressure upon wall-to-wall polymerization contraction of a chemically-cured resin.

    Science.gov (United States)

    Hansen, E K

    1983-02-01

    The marginal gaps of 105 Silar fillings were measured after application of a load between zero and 100 N on the matrix during the initial polymerization. The fillings were placed in non-etched dentin cavities in extracted human teeth. The dentin surrounding the cavities was either roughened with carborundum paper No. 220 or polished with Alfa Micropolish 1 micron before the cavities were filled. When load was applied to the matrix, no effect was found of the roughness surrounding the cavities, but without load the wall-to-wall contraction was significantly greater in cavities where the surrounding dentin surfaces had been polished with Alfa Micropolish. Apparently the effect of load was related to friction during the polymerization between filling surplus and the dentin surrounding the cavities and not to load per se.

  13. Domain Walls on Singularities

    CERN Document Server

    Halyo, Edi

    2009-01-01

    We describe domain walls that live on $A_2$ and $A_3$ singularities. The walls are BPS if the singularity is resolved and non--BPS if it is deformed and fibered. We show that these domain walls may interpolate between vacua that support monopoles and/or vortices.

  14. The Lamportian cell wall

    Energy Technology Data Exchange (ETDEWEB)

    Keiliszewski, M.; Lamport, D. (Michigan State Univ. Plant Research Lab., East Lansing (United States))

    1991-05-01

    The Lamportian Warp-Weft hypothesis suggests a cellulose-extensin interpenetrating network where extensin mechanically couples the load-bearing cellulose microfibrils in a wall matrix that is best described as a microcomposite. This model is based on data gathered from the extensin-rich walls of tomato and sycamore cell suspension culture, wherein extensin precursors are insolubilized into the wall by undefined crosslinks. The authors recent work with cell walls isolated from intact tissue as well as walls from suspension cultured cells of the graminaceous monocots maize and rice, the non-graminaceous monocot asparagus, the primitive herbaceous dicot sugar beet, and the gymnosperm Douglas Fir indicate that although extensins are ubiquitous to all plant species examined, they are not the major structural protein component of most walls examined. Amino acid analyses of intact and HF-treated walls shows a major component neither an HRGP, nor directly comparable to the glycine-rich wall proteins such as those associated with seed coat walls or the 67 mole% glycine-rich proteins cloned from petunia and soybean. Clearly, structural wall protein alternatives to extensin exist and any cell wall model must take that into account. If we assume that extracellular matrices are a priori network structures, then new Hypless' structural proteins in the maize cell wall raise questions about the sort of network these proteins create: the kinds of crosslinks involved; how they are formed; and the roles played by the small amounts of HRGPs.

  15. Halogenation of microcapsule walls

    Science.gov (United States)

    Davis, T. R.; Schaab, C. K.; Scott, J. C.

    1972-01-01

    Procedure for halogenation of confining walls of both gelatin and gelatin-phenolic resin capsules is similar to that used for microencapsulation. Ten percent halogen content renders capsule wall nonburning; any higher content enhances flame-retardant properties of selected internal phase material. Halogenation decreases permeability of wall material to encapsulated materials.

  16. Measurement of friction coefficient in aluminum sheet warm forming

    Institute of Scientific and Technical Information of China (English)

    GUO Zheng-hua; LI Zhi-gang; HUANG Chong-jiu; DONG Xiang-huai

    2005-01-01

    Aluminum alloy sheets are used more and more to manufacture auto panels. Because the friction behavior is very complicated, it is necessary to study the friction during the aluminum sheet warm forming process. The author has designed a new probe sensor based on an online tribotest method which directly measures friction coefficient in the forming process. Experiments of cup drawing have been conducted and the friction coefficients under different forming conditions have been measured. The results indicate that the forming parameters, such as forming temperature, blankholding force and lubrication status have great effect upon the friction coefficient.

  17. A Damping Characteristics Calculation Method of Metal Dry Friction Isolators

    Institute of Scientific and Technical Information of China (English)

    JIANG Hong-yuan; HAO De-gang; XIA Yu-hong; ULANOV A M; PONOMAREV Yu K

    2008-01-01

    The dry friction ring-type vibration isolator is considered as an isotropic continuous medium. A method of dry friction hysteresis loop calculation is proposed based on friction force analysis of contact beam. The friction force is modeled as an equivalent distributed moment to use the finite element method (FEM) to calculate the dry friction vibration isolator hysteresis loop, so the damping characteristics can be obtained. A comparison of the hysteresis loop calculation results and the experimental results shows the average relative error is 2.7%, it proves the calculation method is feasible.

  18. Measurement of Normal and Friction Forces in a Rolling Process

    DEFF Research Database (Denmark)

    Henningsen, Poul; Arentoft, Mogens; Wanheim, Tarras

    2004-01-01

    by the fric-tion conditions. To achieve this important informa-tion, measurements of the normal pressure and friction stresses in the deformation zone are re-quested. The direction of the friction stresses is changing during the rolling gap. At the entrance of the de-formation zone, the peripherical velocity...... of the roll is higher than for the incoming material, which causes frictional stresses at the material acting in the rolling direction. At the outlet of the rolling gap, the velocity of the deformed material exceeds the velocity of the roll, generating frictional stresses contrary to the direction of rolling...

  19. Friction Effects in Pedestrian Headform Impacts with Engine Hoods

    Institute of Scientific and Technical Information of China (English)

    LIU Qi; XIA Yong; ZHOU Qing

    2009-01-01

    In the pedestrian headform impact test mandated by the European pedestrian safety requirements, the contact friction between the headform and the engine hood affects the headform kinematics and head injury criterion (HIC) to some extent. This study shows that the friction effect is more significant with child headform impact than with adult headform impact and the relative angle between the headform impact di-rection and the hood surface greatly affects the headform impact sensitivity to the friction coefficient. The sensitivity of the headform kinematics to the friction coefficient is also analyzed. The results show that ac-curate friction coefficients are needed to improve predictions of pedestrian headform impacts with hoods.

  20. Ferrous friction stir weld physical simulation

    Science.gov (United States)

    Norton, Seth Jason

    2006-04-01

    Traditional fusion welding processes have several drawbacks associated with the melting and solidification of metal. Weld defects associated with the solidification of molten metal may act as initiation sites for cracks. Segregation of alloying elements during solidification may cause local changes in resistance to corrosion. The high amount of heat required to produce the molten metal in the weld can produce distortion from the intended position on cooling. The heat from the electric arc commonly used to melt metal in fusion welds may also produce metal fumes which are a potential health hazard. Friction stir welding is one application which has the potential to make full thickness welds in a single pass, while eliminating fume, reducing distortion, and eliminating solidification defects. Currently the friction stir welding process is used in the aerospace industry on aluminum alloys. Interest in the process by industries which rely on iron and its alloys for structural material is increasing. While friction stir welding has been shown to be feasible with iron alloys, the understanding of friction stir welding process effects on these materials is in its infancy. This project was aimed to better that understanding by developing a procedure for physical simulation of friction stir welding. Friction stir weld material tracer experiments utilizing stainless steel markers were conducted with plates of ingot iron and HSLA-65. Markers of 0.0625" diameter 308 stainless steel worked well for tracing the end position of material moved by the friction stir welding tool. The markers did not produce measurable increases in the loading of the tool in the direction of travel. Markers composed of 0.25" diameter 304 stainless steel did not perform as well as the smaller markers and produced increased loads on the friction stir welding tool. The smaller markers showed that material is moved in a curved path around the tool and deposited behind the tool. Material near the surface

  1. Friction Reduction for Microhole CT Drilling

    Energy Technology Data Exchange (ETDEWEB)

    Ken Newman; Patrick Kelleher; Edward Smalley

    2007-03-31

    The objective of this 24 month project focused on improving microhole coiled tubing drilling bottom hole assembly (BHA) reliability and performance, while reducing the drilling cost and complexity associated with inclined/horizontal well sections. This was to be accomplished by eliminating the need for a downhole drilling tractor or other downhole coiled tubing (CT) friction mitigation techniques when drilling long (>2,000 ft.) of inclined/horizontal wellbore. The technical solution to be developed and evaluated in this project was based on vibrating the coiled tubing at surface to reduce the friction along the length of the downhole CT drillstring. The Phase 1 objective of this project centered on determining the optimum surface-applied vibration system design for downhole CT friction mitigation. Design of the system would be based on numerical modeling and laboratory testing of the CT friction mitigation achieved with various types of surface-applied vibration. A numerical model was developed to predict how far downhole the surface-applied vibration would travel. A vibration test fixture, simulating microhole CT drilling in a horizontal wellbore, was constructed and used to refine and validate the numerical model. Numerous tests, with varying surface-applied vibration parameters were evaluated in the vibration test fixture. The data indicated that as long as the axial force on the CT was less than the helical buckling load, axial vibration of the CT was effective at mitigating friction. However, surface-applied vibration only provided a small amount of friction mitigation as the helical buckling load on the CT was reached or exceeded. Since it would be impractical to assume that routine field operations be conducted at less than the helical buckling load of the CT, it was determined that this technical approach did not warrant the additional cost and maintenance issues that would be associated with the surface vibration equipment. As such, the project was

  2. Fault Wear and Friction Evolution: Experimental Analysis

    Science.gov (United States)

    Boneh, Y.; Chang, J. C.; Lockner, D. A.; Reches, Z.

    2011-12-01

    Wear is an inevitable product of frictional sliding of brittle rocks as evidenced by the ubiquitous occurrence of fault gouge and slickenside striations. We present here experimental observations designed to demonstrate the relationship between wear and friction and their governing mechanisms. The experiments were conducted with a rotary shear apparatus on solid, ring-shaped rock samples that slipped for displacements up to tens of meters. Stresses, wear and temperature were continuously monitored. We analyzed 86 experiments of Kasota dolomite, Sierra White granite, Pennsylvania quartzite, Karoo gabbro, and Tennessee sandstone at slip velocities ranging from 0.002 to 0.97 m/s, and normal stress from 0.25 to 6.9 MPa. We conducted two types of runs: short slip experiments (slip distance mechanisms; and long slip experiments (slip distance > 3 m) designed to achieve mature wear conditions and to observe the evolution of wear and friction as the fault surfaces evolved. The experiments reveal three wear stages: initial, running-in, and steady-state. The initial stage is characterized by (1) discrete damage striations, the length of which is comparable to total slip , and local pits or plow features; (2) timing and magnitude of fault-normal dilation corresponds to transient changes of normal and shear stresses; and (3) surface roughness increasing with the applied normal stress. We interpret these observations as wear mechanisms of (a) plowing into the fresh rock surfaces; (b) asperity breakage; and (c) asperity climb. The running-in stage is characterized by (1) intense wear-rate over a critical wear distance of Rd = 0.3-2 m; (2) drop of friction coefficient over a weakening distance of Dc = 0.2-4 m; (3) Rd and Dc display positive, quasi-linear relation with each other. We interpret these observations as indicating the organizing of newly-created wear particles into a 'three-body' structure that acts to lubricate the fault (Reches & Lockner, 2010). The steady

  3. On Surface Structure and Friction Regulation in Reptilian Limbless Locomotion

    CERN Document Server

    Abdel-Aal, Hisham A

    2012-01-01

    One way of controlling friction and associated energy losses is to engineer a deterministic structural pattern on the surface of the rubbing parts (i.e., texture engineering). Custom texturing enhances the quality of lubrication, reduces friction, and allows the use of lubricants of lower viscosity. To date, a standardized procedure to generate deterministic texture constructs is virtually non-existent. Many engineers, therefore, study natural species to explore surface construction and to probe the role surface topography assumes in friction control. Snakes offer rich examples of surfaces where topological features allow the optimization and control of frictional behavior. In this paper, we investigate the frictional behavior of a constrictor type reptile, Python regius. The study employed a specially designed tribo-acoustic probe capable of measuring the coefficient of friction and detecting the acoustical behavior of the skin in vivo. The results confirm the anisotropy of the frictional response of snakesk...

  4. Friction material composites copper-metal-free material design perspective

    CERN Document Server

    Sundarkrishnaa, K L

    2015-01-01

    This book examines material composites used in connection with brake friction, their design and safety. To aid in understanding, the essentials of friction are explained. This second edition was extended to include friction material composites without copper, as they offer an environmentally friendlier option. The second edition is intended to support beginners by offering insights into the essentials of friction material composites, helping them to develop a broader understanding of brake friction materials. Friction materials find wide-ranging applications in household and industrial appliances, brake pads for automotive applications, rail brake friction pads and composition brake blocks. This second edition is an introductory volume to a set of related books, and is based on the author’s experience and expertise with various material manufacturers, brake manufacturers, vehicle manufacturers, researchers and testing labs around the world with which the author has been associated for the past 28 years.

  5. Device for Measuring Sliding Friction on Highloft Nonwovens

    Directory of Open Access Journals (Sweden)

    Stephen Michielsen

    2006-08-01

    Full Text Available When measuring the sliding friction on highly compliant materials such as fabric batting and foam rubber, a substantial portion of the apparent friction is due to the deformation of the substrate. A new friction instrument consisting of a sled within a sled has been developed that eliminates the contribution of this deformation and provides the true sliding friction as well as the force required to deform the substrate. The friction coefficient as measured using a conventional steel sled sliding on high loft polyester batts increased as the number of polyester batts increased. Using the new, guarded friction sled, the friction coefficient was independent of the number of supporting batts, thus separating the deformation forces from the sliding forces.

  6. Formation and rupture of capillary bridges in atomic scale friction

    Science.gov (United States)

    Barel, Itay; Filippov, Aleksander E.; Urbakh, M.

    2012-10-01

    While formation of capillary bridges significantly contributes to the adhesion and friction at micro- and nanoscales, many key aspects of dynamics of capillary condensation and its effect on friction forces are still not well understood. Here, by analytical model and numerical simulations, we address the origin of reduction of friction force with velocity and increase of friction with temperature, which have been experimentally observed under humid ambient conditions. These observations differ significantly from the results of friction experiments carried out under ultrahigh vacuum, and disagree with predictions of thermal Prandtl-Tomlinson model of friction. Our calculations demonstrate what information on the kinetics of capillary condensation can be extracted from measurements of friction forces and suggest optimal conditions for obtaining this information.

  7. Friction drive of an SAW motor. Part II: analyses.

    Science.gov (United States)

    Shigematsu, Takashi; Kurosawa, Minoru Kuribayashi

    2008-09-01

    The mechanics of the friction drive of a surface acoustic wave motor were investigated by means of contact mechanics theory. As a means to control the contact condition, the motor's slider had projections on its frictional surface. Assuming the projection was a rigid circular punch and the slider body was an elastic half-space allowed application of contact mechanics formulae to the analyses of the friction drive. Because the projection contacted the Rayleigh wave vibration, the projection's responses were considered dynamic; thus, the dynamics were also analyzed in the same framework of contact mechanics formulae. Moreover, the analyses were applied to measurements of the projection's displacement to examine the detailed mechanics during the friction drive. We calculated the contact/frictional forces based on the measurement and indicated the necessity of further investigation of the surface acoustic wave motor's friction drive, because the usual friction law was unable to explain the measurement.

  8. Mixed Convection in a Composite System Bounded by Vertical Walls

    Directory of Open Access Journals (Sweden)

    N. Srivastava

    2010-01-01

    Full Text Available A combined convection process between two parallel vertical infinite walls, containing an incompressible viscous fluid layer and a fluid saturated porous layer has been presented analytically. There is a vertical axial variation of temperature in the upward direction along the walls. The Brinkman extended Darcy model is applied to describe the momentum transfer in the porous region. The viscosity of the fluid layer and the effective viscosity of the porous layer are assumed to be different. Also the thermal conductivities of both fluid and porous layers are assumed to be different. The graphs and tables have been used to distinguish the influence of distinct parameters on the velocity and skin-friction. It is determined that the velocity is intensified on making greater the temperature difference between the walls while increment in the viscosity ratio (porous/fluid parameter diminishes the velocity of the fluid. It has been observed that the numerical values of the skin-frictions have an increasing tendency with the increment in the values of temperature difference between the walls while decreasing tendency with the increment in the viscosity ratio parameter (porous/fluid.

  9. Effect of ZrSiO4 on the Friction Performance of Automotive Brake Friction Materials

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Friction-wear properties of the ZrSiO4 reinforced samples were measured and compared with those of plain bronze based ones. For this purpose, density, hardness, friction coefficient wear behaviour of the samples were tested. Microstructures of samples before and after sintering and worn surfaces were also investigated by scanning electron microscopy (SEM), and the wear types were determined. The optimum friction-wear behaviour was obtained in the sample compacted at 500 MPa and sintered at 820℃. Density of the final samples decreased with increasing the amount of reinforcing elements (ZrSiO4) before pre-sintering. However after sintering, there is no change in density of the samples including reinforcing elements (ZrSiO4). With increasing friction surface temperature, a reduction in the friction coefficient of the samples was observed.However, the highest reductions in the friction coefficients were observed in the as-received samples containing 0,5% reinforced ZrSiO4. The SEM images of the sample indicated that while bronze-based break lining material without ZrSiO4 showed abrasive wear behaviour, increasing the amount of ZrSiO4 resulted a change in abrasive to adhesive wear mechanism. All samples exhibited friction-wear values, which were within the values shown in SAE-J661 standard. With increasing the amount of reinforcing ZrSiO4, wear resistance of the samples was increased. However samples reinforced with 5% and 6% ZrSiO4 showed the best results.

  10. Control of friction at the nanoscale

    Science.gov (United States)

    Barhen, Jacob; Braiman, Yehuda Y.; Protopopescu, Vladimir

    2010-04-06

    Methods and apparatus are described for control of friction at the nanoscale. A method of controlling frictional dynamics of a plurality of particles using non-Lipschitzian control includes determining an attribute of the plurality of particles; calculating an attribute deviation by subtracting the attribute of the plurality of particles from a target attribute; calculating a non-Lipschitzian feedback control term by raising the attribute deviation to a fractionary power .xi.=(2m+1)/(2n+1) where n=1, 2, 3 . . . and m=0, 1, 2, 3 . . . , with m strictly less than n and then multiplying by a control amplitude; and imposing the non-Lipschitzian feedback control term globally on each of the plurality of particles; imposing causes a subsequent magnitude of the attribute deviation to be reduced.

  11. Frictional Impact Modeling of a Cereal Thresher

    Directory of Open Access Journals (Sweden)

    Christian O. Osueke

    2011-01-01

    Full Text Available Problem statement: There is no point producing cereal threshing models that cannot replicate its performance on the field. The frictional impact that occurs between the crop surface and threshing cylinder has been often neglected by most researchers in cereal threshing. Approach: Study proffers a solution to this issue by developing a model for threshing which in-cooperate friction. This was done by analyzing the crop/threshing cylinder behavior, hence establishing mathematical sub-models to characterize the performance of this model. Results: The model was further packaged with computer aided software based on visual basic programming language and finally applied. Conclusion: Upon application, it was discovered that at a moisture content of 15% v = 9 m sec-1, Q = 0.18 kg sec-1 the model yielded performance characteristics as Eff = 88.22%, TNL = 11.78% and CAPTH = 211.52 kg h-1.

  12. Mars - Wind friction speeds for particle movement

    Science.gov (United States)

    Greeley, R.; Leach, R.; White, B.; Iversen, J.; Pollack, J.

    1976-01-01

    Wind friction threshold speeds for particle movement were determined in a low pressure boundary layer wind tunnel at an atmospheric pressure of 5.3 mb. The results imply that for comparable pressures on Mars, the minimum wind friction threshold speed is about 2.5 m/sec, which would require free-stream winds of 50 to 135 m/sec, depending on the character of the surface and the atmospheric conditions. The corresponding wind speeds at the height of the Viking lander meteorology instrument would be about a factor of two less than the free-stream wind speed. The particle size most easily moved by winds on Mars is about 160 microns; particles both larger and smaller than this (at least down to about 5 microns) require stronger winds to initiate movement.

  13. Friction Experiments for Dynamical Coefficient Measurement

    Directory of Open Access Journals (Sweden)

    J. J. Arnoux

    2011-01-01

    Full Text Available An experimental study, including three experimental devices, is presented in order to investigate dry friction phenomena in a wide range of sliding speeds for the steel on steel contact. A ballistic setup, with an air gun launch, allows to estimate the friction coefficient between 20 m/s and 80 m/s. Tests are completed by an adaptation of the sensor on a hydraulic tensile machine (0.01 m/s to 3 m/s and a pin-on-disk tribometer mounted on a CNC lathe (1 to 30 m/s. The interactions at the asperity scale are characterized by a white light interferometer surface analysis.

  14. Network Theory, Cracking and Frictional Sliding

    CERN Document Server

    Ghaffari, H O

    2012-01-01

    We have developed different network approaches to complex patterns of frictional interfaces (contact areas developments). Here, we analyze the dynamics of static friction. We found, under the correlation measure, the fraction of triangles correlates with the detachment fronts. Also, for all types of the loops (such as triangles), there is a universal power law between nodes' degree and motifs where motifs frequency follow a power law. This shows high energy localization is characterized by fast variation of the loops fraction. Also, this proves that the congestion of loops occurs around hubs. Furthermore, the motif distributions and modularity space of networks -in terms of within-module degree and participation coefficient- show universal trends, indicating an in common aspect of energy flow in shear ruptures. Moreover, we confirmed that slow ruptures generally hold small localization, while regular ruptures carry a high level of energy localization. We proposed that assortativity, as an index to correlation...

  15. Frictional Coulomb drag in strong magnetic fields

    DEFF Research Database (Denmark)

    Bønsager, Martin Christian; Flensberg, Karsten; Hu, Ben Yu-Kuang;

    1997-01-01

    A treatment of frictional Coulomb drag between two two-dimensional electron layers in a strong perpendicular magnetic field, within the independent electron picture, is presented. Assuming fully resolved Landau levels, the linear response theory expression for the transresistivity rho(21) is eval......A treatment of frictional Coulomb drag between two two-dimensional electron layers in a strong perpendicular magnetic field, within the independent electron picture, is presented. Assuming fully resolved Landau levels, the linear response theory expression for the transresistivity rho(21......) is evaluated using diagrammatic techniques. The transresistivity is given by an integral over energy and momentum transfer weighted by the product of the screened interlayer interaction and the phase space for scattering events. We demonstrate, by a numerical analysis of the transresistivity, that for well...

  16. Friction boosted by spontaneous epitaxial rotations

    Science.gov (United States)

    Mandelli, Davide; Vanossi, Andrea; Manini, Nicola; Tosatti, Erio

    2015-03-01

    It is well known in surface science that incommensurate adsorbed monolayers undergo a spontaneous, energy-lowering epitaxial rotation from aligned to misaligned relative to a periodic substrate. We show first of all that a model 2D colloidal monolayer in an optical lattice, of recent importance as a frictional model, also develops in full equilibrium a small rotation angle, easy to detect in the Moiré pattern. The colloidal monolayer misalignment is then shown by extensive sliding simulations to increase the dynamic friction by a considerable factor over the aligned case. More generally, this example suggests that spontaneous rotations are rather ubiquitous and should not be ignored in all tribological phenomena between mismatched lattices. This work was mainly supported by the ERC Advanced Grant No. 320796-MODPHYSFRICT, and partly by SINERGIA contract CRSII2 136287, by PRIN/COFIN Contract 2010LLKJBX 004, by COST Action MP1303.

  17. Uniform Design of Optimizing Formulation of Friction Materials with Composite Mineral Fiber (CMF) and Their Friction and Wear Behavior

    Science.gov (United States)

    Yang, Yazhou; Jiang, Man; Xu, Jie; Ma, Yunhai; Tong, Jin

    2012-04-01

    In this work, the uniform design method was applied to arrange the experimental scheme for optimizing formulation of friction materials. The friction and wear of the friction materials based on the optimized formulation was carried out on a constant speed friction tester (JF150D-II), using pad-on-disc contact mode against gray cast iron disc. The worn surfaces of the friction materials were examined by scanning electron microscopy (JSM5310) and the friction mechanism was discussed. The results showed that the uniform design method was appropriate for finding the optimum formulation of the friction materials with better properties. Compared with two conventional friction materials, the friction materials based on the optimized formulation possessed higher and stable friction coefficient and higher wear resistance, even at the disc temperature of 350°C. The adhesion, strain fatigue and abrasive wear were the main wear mechanisms of the friction materials. Tribo-chemical phenomenon and plastic deformation existed on the worn surface layer.

  18. Direct measurements of wall shear stress by buried wire gages in a shock-wave boundary-layer interaction region

    Science.gov (United States)

    Murthy, V. S.; Rose, W. C.

    1977-01-01

    Detailed measurements of wall shear stress (skin friction) were made with specially developed buried wire gages in the interaction regions of a Mach 2.9 turbulent boundary layer with externally generated shocks. Separation and reattachment points inferred by these measurements support the findings of earlier experiments which used a surface oil flow technique and pitot profile measurements. The measurements further indicate that the boundary layer tends to attain significantly higher skin-friction values downstream of the interaction region as compared to upstream. Comparisons between measured wall shear stress and published results of some theoretical calculation schemes show that the general, but not detailed, behavior is predicted well by such schemes.

  19. Abdominal wall fat pad biopsy

    Science.gov (United States)

    Amyloidosis - abdominal wall fat pad biopsy; Abdominal wall biopsy; Biopsy - abdominal wall fat pad ... method of taking an abdominal wall fat pad biopsy . The health care provider cleans the skin on ...

  20. Fundamental Mechanisms Affecting Friction Welding under Vacuum

    Science.gov (United States)

    1991-06-01

    z Professor Koichi Masubuchi Ocean Engineering Dept., Thesis Supervisor ~Certified by - CProfessor Ltmest Rabinowicz Mechanical Engineering Dept...welding and oxide layer affects. 60 REFERENCES 1. Rabinowicz ,E., "Friction and Wear of Materials", Wiley, 1964 2. SmithM., "Effect of Vacuum on the...Professor ELnest Rabinowicz Mechanical Engineering Dept., Thesis Reader Accepted by- 14,~/G 1, ~ Z a- ’A. Douglas Carn-chtir,-hirman Departmental Graduate

  1. Aftershocks in a frictional earthquake model.

    Science.gov (United States)

    Braun, O M; Tosatti, Erio

    2014-09-01

    Inspired by spring-block models, we elaborate a "minimal" physical model of earthquakes which reproduces two main empirical seismological laws, the Gutenberg-Richter law and the Omori aftershock law. Our point is to demonstrate that the simultaneous incorporation of aging of contacts in the sliding interface and of elasticity of the sliding plates constitutes the minimal ingredients to account for both laws within the same frictional model.

  2. Thermal modelling of friction stir welding

    DEFF Research Database (Denmark)

    Schmidt, Henrik Nikolaj Blicher; Hattel, Jesper Henri

    2008-01-01

    The objective of the present work is to present the basic elements of the thermal modelling of friction stir welding as well as to clarify some of the uncertainties in the literature regarding the different contributions to the heat generation. Some results from a new thermal pseudomechanical model...... in which the temperature-dependent yield stress of the weld material controls the heat generation are also presented....

  3. Biotribology :articular cartilage friction, wear, and lubrication

    OpenAIRE

    Schroeder, Matthew O

    1995-01-01

    This study developed, explored, and refined techniques for the in vitro study of cartilage-on-cartilage friction, deformation, and wear. Preliminary results of in vitro cartilage-on- cartilage experiments with emphasis on wear and biochemistry are presented. Cartilage-bone specimens were obtained from the stifle joints of steers from a separate controlled study. The load, sliding speed, and traverse of the lower specimens were held constant as lubricant and test length were varied. Lubric...

  4. Frictional cooling of positively charged particles

    Directory of Open Access Journals (Sweden)

    Daniel Greenwald

    2012-02-01

    Full Text Available One of the focuses of research and development towards the construction of a muon collider is muon beam preparation. Simulation of frictional cooling shows that it can achieve the desired emittance reduction to produce high-luminosity muon beams. We show that for positively charged particles, charge-exchange interactions necessitate significant changes to schemes previously developed for negatively charged particles. We also demonstrate that foil-based schemes are not viable for positive particles.

  5. Managing Friction Blisters of the Feet.

    Science.gov (United States)

    Ramsey, M L

    1992-01-01

    In brief Active people often develop friction blisters on their feet. Although such blisters rarely create significant medical problems, they can be quite painful and can hinder athletic performance. People can decrease the chance of blister formation by wearing properly fitting shoes, doubling up on socks, and applying dressings or lubricants. If lesions do develop, conservative treatment will speed healing and lessen pain and disability.

  6. Simulating frictional contact in smoothed particle hydrodynamics

    Institute of Scientific and Technical Information of China (English)

    WANG; Jian; WU; Hao; GU; ChongShi; HUA; Hui

    2013-01-01

    Smoothed Particle Hydrodynamics (SPH) is a powerful tool for large deformation computation of soil flow. However, the method to simulate frictional contact in the framework of SPH is still absent and needs to be developed. This paper presents an algorithm to simulate frictional contact between soil and rigid or deformable structure in the framework of SPH. In this algo-rithm, the computational domain is divided into several sub-domains according to the existing contact boundaries, and contact forces are used as bridges of these sub-domains to fulfill problem solving. In the process of the SPH discretization for govern-ing equation of each sub-domain, the inherent problem of boundary deficiency of SPH is handled properly. Therefore, the par-ticles located at contact boundary can have precise acceleration, which is critical for contact detection. Then, based on the as-sumption that the SPH particle of soil can slightly penetrate into the structure, the contact forces along normal and tangential directions of the contact surface are computed by momentum principle, and the frictional force is modified if sliding occurs.Compared with previous methods, in which only particle-to-particle contact is considered or frictional sliding is just ignored,the method proposed in this study is more efficient and accurate, and is suitable for simulating interaction between soft materi-als and rigid or deformable structures, which are very common in geotechnical engineering. A number of numerical tests have been carried out to verify the accuracy and stability of the proposed algorithm, and the results have been compared with ana-lytical solutions or FEM results. The consistency obtained from these comparisons indicates that the algorithm is robust and can enhance the computing capability of SPH.

  7. Welding defects at friction stir welding

    Directory of Open Access Journals (Sweden)

    P. Podržaj

    2015-04-01

    Full Text Available The paper presents an overview of different types of defects at friction stir welding. In order to explain the reasons for their occurrence a short theoretical background of the process is given first. The main emphasis is on the parameters that influence the process. An energy supply based division of defects into three disjoint groups was used. The occurring defects are demonstrated on various materials.

  8. Ramsey monetary policy with labour market frictions

    OpenAIRE

    Faia, Ester

    2007-01-01

    This paper studies the design of optimal monetary policy (in terms of unconstrained Ramsey allocation) in a framework with sticky prices and matching frictions. Furthermore I consider the role of real wage rigidities. Optimal policy features significant deviations from price stability in response to various shocks. This is so since search externalities generate an unemployment/inflation trade-off. In response to productivity shocks optimal policy is pro-cyclical when the worker’s bargaining p...

  9. Rubber friction: comparison of theory with experiment.

    Science.gov (United States)

    Lorenz, B; Persson, B N J; Dieluweit, S; Tada, T

    2011-12-01

    We have measured the friction force acting on a rubber block slid on a concrete surface. We used both unfilled and filled (with carbon black) styrene butadiene (SB) rubber and have varied the temperature from -10 °C to 100 °C and the sliding velocity from 1 μm/s to 1000 μm/s. We find that the experimental data at different temperatures can be shifted into a smooth master-curve, using the temperature-frequency shifting factors obtained from measurements of the bulk viscoelastic modulus. The experimental data has been analyzed using a theory which takes into account the contributions to the friction from both the substrate asperity-induced viscoelastic deformations of the rubber, and from shearing the area of real contact. For filled SB rubber the frictional shear stress σ(f) in the area of real contact results mainly from the energy dissipation at the opening crack on the exit side of the rubber-asperity contact regions. For unfilled rubber we instead attribute σ(f) to shearing of a thin rubber smear film, which is deposited on the concrete surface during run in. We observe very different rubber wear processes for filled and unfilled SB rubber, which is consistent with the different frictional processes. Thus, the wear of filled SB rubber results in micrometer-sized rubber particles which accumulate as dry dust, which is easily removed by blowing air on the concrete surface. This wear process seams to occur at a steady rate. For unfilled rubber a smear film forms on the concrete surface, which cannot be removed even using a high-pressure air stream. In this case the wear rate appears to slow down after some run in time period.

  10. Friction and adhesion of hierarchical carbon nanotube structures for biomimetic dry adhesives: multiscale modeling.

    Science.gov (United States)

    Hu, Shihao; Jiang, Haodan; Xia, Zhenhai; Gao, Xiaosheng

    2010-09-01

    With unique hierarchical fibrillar structures on their feet, gecko lizards can walk on vertical walls or even ceilings. Recent experiments have shown that strong binding along the shear direction and easy lifting in the normal direction can be achieved by forming unidirectional carbon nanotube array with laterally distributed tips similar to gecko's feet. In this study, a multiscale modeling approach was developed to analyze friction and adhesion behaviors of this hierarchical fibrillar system. Vertically aligned carbon nanotube array with laterally distributed segments at the end was simulated by coarse grained molecular dynamics. The effects of the laterally distributed segments on friction and adhesion strengths were analyzed, and further adopted as cohesive laws used in finite element analysis at device scale. The results show that the laterally distributed segments play an essential role in achieving high force anisotropy between normal and shear directions in the adhesives. Finite element analysis reveals a new friction-enhanced adhesion mechanism of the carbon nanotube array, which also exists in gecko adhesive system. The multiscale modeling provides an approach to bridge the microlevel structures of the carbon nanotube array with its macrolevel adhesive behaviors, and the predictions from this modeling give an insight into the mechanisms of gecko-mimicking dry adhesives.

  11. Development of FDR-AF (Frictional Drag Reduction Anti-Fouling) Marine Coating

    Science.gov (United States)

    Lee, Inwon; Park, Hyun; Chun, Ho Hwan; GCRC-SOP Team

    2013-11-01

    In this study, a novel skin-friction reducing marine paint has been developed by mixing fine powder of PEO(PolyEthyleneOxide) with SPC (Self-Polishing Copolymer) AF (Anti-Fouling) paint. The PEO is well known as one of drag reducing agent to exhibit Toms effect, the attenuation of turbulent flows by long chain polymer molecules in the near wall region. The frictional drag reduction has been implemented by injecting such polymer solutions to liquid flows. However, the injection holes have been a significant obstacle to marine application. The present PEO-containing marine paint is proposed as an alternative to realize Toms effect without any hole on the ship surface. The erosion mechanism of SPC paint resin and the subsequent dissolution of PEO enable the controlled release of PEO solution from the coating. Various tests such as towing tank drag measurement of flat plate and turbulence measurement in circulating water tunnel demonstrated over 10% frictional drag reduction compared with conventional AF paint. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) through GCRC-SOP(No. 2011-0030013).

  12. Fabrication of Aluminum Tubes Filled with Aluminum Alloy Foam by Friction Welding

    Directory of Open Access Journals (Sweden)

    Yoshihiko Hangai

    2015-10-01

    Full Text Available Aluminum foam is usually used as the core of composite materials by combining it with dense materials, such as in Al foam core sandwich panels and Al-foam-filled tubes, owing to its low tensile and bending strengths. In this study, all-Al foam-filled tubes consisting of ADC12 Al-Si-Cu die-cast aluminum alloy foam and a dense A1050 commercially pure Al tube with metal bonding were fabricated by friction welding. First, it was found that the ADC12 precursor was firmly bonded throughout the inner wall of the A1050 tube without a gap between the precursor and the tube by friction welding. No deformation of the tube or foaming of the precursor was observed during the friction welding. Next, it was shown that by heat treatment of an ADC12-precursor-bonded A1050 tube, gases generated by the decomposition of the blowing agent expand the softened ADC12 to produce the ADC12 foam interior of the dense A1050 tube. A holding time during the foaming process of approximately tH = 8.5 min with a holding temperature of 948 K was found to be suitable for obtaining a sound ADC12-foam-filled A1050 tube with sufficient foaming, almost uniform pore structures over the entire specimen, and no deformation or reduction in the thickness of the tube.

  13. Silo with a Corrugated Sheet Wall

    Science.gov (United States)

    Németh, Csaba; Brodniansky, Ján

    2013-09-01

    Silos and tanks are currently being used to create reserves of stored materials. Their importance is based on balancing the production and consumption of bulk materials to establish an adequate reserve throughout the year. The case study introduced within the framework of this paper focuses on thin-walled silos made of corrugated sheets and on an approach for designing these types of structures. The storage of bulk materials causes compression or tensile stresses in the walls of a silo structure. The effect of a frictional force in the silo walls creates an additional bending moment in a wave, which ultimately affects the resulting bending moments. Several mathematical and physical models were used in order to examine various types of loading and their effects on a structure. Subsequently, the accuracy of the computational models was verified by experimental measurements on a grain silo in Bojničky, Slovakia. A comparison of the experimental and mathematical models shows a reasonable match and confirms the load specifications, while indicating that the mathematical model was correct.

  14. Partial squeeze film levitation modulates fingertip friction.

    Science.gov (United States)

    Wiertlewski, Michaël; Fenton Friesen, Rebecca; Colgate, J Edward

    2016-08-16

    When touched, a glass plate excited with ultrasonic transverse waves feels notably more slippery than it does at rest. To study this phenomenon, we use frustrated total internal reflection to image the asperities of the skin that are in intimate contact with a glass plate. We observed that the load at the interface is shared between the elastic compression of the asperities of the skin and a squeeze film of air. Stroboscopic investigation reveals that the time evolution of the interfacial gap is partially out of phase with the plate vibration. Taken together, these results suggest that the skin bounces against the vibrating plate but that the bounces are cushioned by a squeeze film of air that does not have time to escape the interfacial separation. This behavior results in dynamic levitation, in which the average number of asperities in intimate contact is reduced, thereby reducing friction. This improved understanding of the physics of friction reduction provides key guidelines for designing interfaces that can dynamically modulate friction with soft materials and biological tissues, such as human fingertips.

  15. Friction and wear of human hair fibres

    Science.gov (United States)

    Bowen, James; Johnson, Simon A.; Avery, Andrew R.; Adams, Michael J.

    2016-06-01

    An experimental study of the tribological properties of hair fibres is reported, and the effect of surface treatment on the evolution of friction and wear during sliding. Specifically, orthogonally crossed fibre/fibre contacts under a compressive normal load over a series of 10 000 cycle studies are investigated. Reciprocating sliding at a velocity of 0.4 mm s-1, over a track length of 0.8 mm, was performed at 18 °C and 40%-50% relative humidity. Hair fibres retaining their natural sebum were studied, as well as those stripped of their sebum via hexane cleaning, and hair fibres conditioned using a commercially available product. Surface topography modifications resulting from wear were imaged using scanning electron microscopy and quantified using white light interferometry. Hair fibres that presented sebum or conditioned product at the fibre/fibre junction exhibited initial coefficients of friction at least 25% lower than those that were cleaned with hexane. Coefficients of friction were observed to depend on the directionality of sliding for hexane cleaned hair fibres after sufficient wear cycles that cuticle lifting was present, typically on the order 1000 cycles. Cuticle flattening was observed for fibre/fibre junctions exposed to 10 mN compressive normal loads, whereas loads of 100 mN introduced substantial cuticle wear and fibre damage.

  16. Controlling vortex motion and vortex kinetic friction

    Science.gov (United States)

    Nori, Franco; Savel'ev, Sergey

    2006-05-01

    We summarize some recent results of vortex motion control and vortex kinetic friction. (1) We describe a device [J.E. Villegas, S. Savel'ev, F. Nori, E.M. Gonzalez, J.V. Anguita, R. Garcìa, J.L. Vicent, Science 302 (2003) 1188] that can easily control the motion of flux quanta in a Niobium superconducting film on an array of nanoscale triangular magnets. Even though the input ac current has zero average, the resulting net motion of the vortices can be directed along either one direction, the opposite direction, or producing zero net motion. We also consider layered strongly anisotropic superconductors, with no fixed spatial asymmetry, and show [S. Savel'ev, F. Nori, Nature Materials 1 (2002) 179] how, with asymmetric drives, the ac motion of Josephson and/or pancake vortices can provide a net dc vortex current. (2) In analogy with the standard macroscopic friction, we present [A. Maeda, Y. Inoue, H. Kitano, S. Savel'ev, S. Okayasu, I. Tsukada, F. Nori , Phys. Rev. Lett. 94 (2005) 077001] a comparative study of the friction force felt by vortices in superconductors and charge density waves.

  17. Theory of friction based on brittle fracture

    Science.gov (United States)

    Byerlee, J.D.

    1967-01-01

    A theory of friction is presented that may be more applicable to geologic materials than the classic Bowden and Tabor theory. In the model, surfaces touch at the peaks of asperities and sliding occurs when the asperities fail by brittle fracture. The coefficient of friction, ??, was calculated from the strength of asperities of certain ideal shapes; for cone-shaped asperities, ?? is about 0.1 and for wedge-shaped asperities, ?? is about 0.15. For actual situations which seem close to the ideal model, observed ?? was found to be very close to 0.1, even for materials such as quartz and calcite with widely differing strengths. If surface forces are present, the theory predicts that ?? should decrease with load and that it should be higher in a vacuum than in air. In the presence of a fluid film between sliding surfaces, ?? should depend on the area of the surfaces in contact. Both effects are observed. The character of wear particles produced during sliding and the way in which ?? depends on normal load, roughness, and environment lend further support to the model of friction presented here. ?? 1967 The American Institute of Physics.

  18. Friction and Wear Behaviors of Nanostructured Metals

    Institute of Scientific and Technical Information of China (English)

    Zhong HAN; Yusheng ZHANG; Ke LU

    2008-01-01

    Nanostructured (ns) materials, i.e., polycrystalline materials with grain sizes in the nanometer regime (typically below 100 nm), have drawn considerable attention in the past decades due to their unique properties such as high strength and hardness. Wear resistance of ns materials, one of the most important properties for engineering materials, has been extensively investigated in the past decades. Obvious differences have been identified in friction and wear behaviors Between the ns materials and their corresponding coarse-grained (cg) counterparts, consistently correlating with their unique structure characteristics and mechanical properties. On the other hand, the superior tribological properties of ns materials illustrate their potential applications under contact loads. The present overview will summarize the important progresses achieved on friction and wear behaviors of ns metallic materials, including ultrafine-grained (ufg) materials in recent years. Tribological properties and effects on friction and wear behaviors of ns materials will be discussed under different wear conditions including abrasive wear, sliding wear, and fretting wear. Their correlations with mechanical properties will be analyzed. Perspectives on development of this field will be highlighted as well.

  19. Friction, force chains, and falling fruit

    Science.gov (United States)

    Krim, Jacqueline; Behringer, Robert

    2010-03-01

    Friction is of great concern from both a national security and quality-of-life point of view, and the economic impact of energy efficiency, wear, and manufacturing cannot be underestimated. Theorists have always believed that friction plays a great role in avalanche-like collapse of a granular piles, but the predictions have proven difficult to test. We devised an experimentally controlled way to prove it, accessible to all who dare try, and report on it here [1,2]. With the aid of a middle school assistant, we studied and filmed piles of apples, oranges, and onions as one or more pieces of fruit were removed. Among other things, we discovered that increasing the friction of the onions (by peeling them) vastly decreased the likelihood of collapse. Our work includes videos written by, produced, and starring our seventh grade assistant, some of which are posted on the Physics Today YouTube channel [1] and featured in the Sept. 2009 issue of Physics Today [2]. [4pt] [1] Youtube.com, keywords ``unpeeled onions'', with full set at www.dukefruit.info. [0pt] [2] J. Krim and R.P. Berhinger, Physics Today (Sept., 2009) volume 62, pp.66-67

  20. Friction Modeling in Concentric Tube Robots.

    Science.gov (United States)

    Lock, Jesse; Dupont, Pierre E

    2011-01-01

    Concentric tube robots are a novel class of continuum robots that are constructed by combining pre-curved elastic tubes such that the overall shape of the robot is a function of the relative rotations and translations of the constituent tubes. Frictionless kinematic and quasistatic force models for this class of robots have been developed that incorporate bending and twisting of the tubes. Experimental evaluation of these models has revealed, however, a directional dependence of tube rotation on robot shape that is not predicted by these models. To explain this behavior, this paper models the contributions of friction arising from two sources: the distributed forces of contact between the tubes along their length and the concentrated bending moments generated at discontinuities in curvature and at the boundaries. It is shown that while friction due to distributed forces is insufficient to explain the experimentally observed tube twisting, a simple model of frictional torque arising from concentrated moments provides a good match with the experimental data.

  1. Markov state modeling of sliding friction

    Science.gov (United States)

    Pellegrini, F.; Landes, François P.; Laio, A.; Prestipino, S.; Tosatti, E.

    2016-11-01

    Markov state modeling (MSM) has recently emerged as one of the key techniques for the discovery of collective variables and the analysis of rare events in molecular simulations. In particular in biochemistry this approach is successfully exploited to find the metastable states of complex systems and their evolution in thermal equilibrium, including rare events, such as a protein undergoing folding. The physics of sliding friction and its atomistic simulations under external forces constitute a nonequilibrium field where relevant variables are in principle unknown and where a proper theory describing violent and rare events such as stick slip is still lacking. Here we show that MSM can be extended to the study of nonequilibrium phenomena and in particular friction. The approach is benchmarked on the Frenkel-Kontorova model, used here as a test system whose properties are well established. We demonstrate that the method allows the least prejudiced identification of a minimal basis of natural microscopic variables necessary for the description of the forced dynamics of sliding, through their probabilistic evolution. The steps necessary for the application to realistic frictional systems are highlighted.

  2. Dry friction avalanches: Experiment and theory

    Science.gov (United States)

    Buldyrev, Sergey V.; Ferrante, John; Zypman, Fredy R.

    2006-12-01

    Experimental evidence and theoretical models are presented supporting the conjecture that dry friction stick-slip is described by self-organized criticality. We use the data, obtained with a pin-on-disk tribometer set to measure lateral force, to examine the variation of the friction force as a function of time. We study nominally flat surfaces of matching aluminum and steel. The probability distribution of force drops follows a negative power law with exponents μ in the range 3.2-3.5. The frequency power spectrum follows a 1/fα pattern with α in the range 1-1.8. We first compare these experimental results with the well-known Robin Hood model of self-organized criticality. We find good agreement between theory and experiment for the force-drop distribution but not for the power spectrum. We explain this on a physical basis and propose a model which takes explicitly into account the stiffness and inertia of the tribometer. Specifically, we numerically solve the equation of motion of a block on a friction surface pulled by a spring and show that for certain spring constants the motion is characterized by the same power law spectrum as in experiments. We propose a physical picture relating the fluctuations of the force drops to the microscopic geometry of the surface.

  3. Development of a Constitutive Friction Law based on the Frictional Interaction of Rough Surfaces

    Directory of Open Access Journals (Sweden)

    F. Beyer

    2015-12-01

    Full Text Available Friction has a considerable impact in metal forming. This is in particular true for sheet-bulk metal-forming (SBMF in which local highly varying contact loads occur. A constitutive friction law suited to the needs of SBMF is necessary, if numerical investigations in SBMF are performed. The identification of the friction due to adhesion and ploughing is carried out with an elasto-plastic half-space model. The normal contact is verified for a broad range of normal loads. In addition, the model is used for the characterization of the occurring shear stress. Ploughing is determined by the work which is necessary to plastically deform the surface asperities of the new area that gets into contact during sliding. Furthermore, the surface patches of common half-space models are aligned orthogonally to the direction in which the surfaces approach when normal contact occurs. For a better reflection of the original surfaces, the element patches become inclined. This leads to a geometric share of lateral forces which also contribute to friction. Based on these effects, a friction law is derived which is able to predict the contact conditions especially for SBMF.

  4. Development and Optimization of Hybrid Friction Materials Consisting of Nanoclay and Carbon Nanotubes by using Analytical Hierarchy Process (AHP and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS under Fuzzy Atmosphere

    Directory of Open Access Journals (Sweden)

    Tej SINGH

    2013-07-01

    Full Text Available The tribo-performance of nanoclay and multi-walled carbon nanotube (MWNT filled and graphite lubricated phenolic composites, reinforced with a combination of lapinus and kevlar fibers, have been evaluated on a Kraus friction testing machine. The combined fuzzy analytical hierarchy process (FAHP and fuzzy technique for order preference by similarity to ideal solution (FTOPSIS approach, taking into account performance defining attributes (PDAs such as friction performance, wear, friction-fade, friction-recovery, stability coefficient, variability coefficient, friction fluctuations and temperature rise of the disc, was used for the performance assessment of fabricated friction composite materials. The weight of different PDAs were evaluated by FAHP; μ-performance (0.144, 0.255, 0.435, wear (0.144, 0.255, 0.435, fade-% (0.073, 0.15, 0.307, recovery-% (0.063, 0.126, 0.268, stability coefficient (0.037, 0.075, 0.156, variability coefficient (0.032, 0.063, 0.136, frictional fluctuations (0.023, 0.037, 0.069, and DTR (0.023, 0.037, 0.069 respectively.  FTOPSIS was employed to determine the optimal ranking of the friction composite materials as NC-7>NC-8>NC-6>NC-5>NC-3>NC-4>NC-2>NC-1. The alternative with kevlar: lapinus, 2.5:27.5 wt-% and graphite: nanoclay: carbon nanotube, 2.25:2.75 wt-% exhibits the optimal properties.

  5. Improved engine wall models for Large Eddy Simulation (LES)

    Science.gov (United States)

    Plengsaard, Chalearmpol

    Improved wall models for Large Eddy Simulation (LES) are presented in this research. The classical Werner-Wengle (WW) wall shear stress model is used along with near-wall sub-grid scale viscosity. A sub-grid scale turbulent kinetic energy is employed in a model for the eddy viscosity. To gain better heat flux results, a modified classical variable-density wall heat transfer model is also used. Because no experimental wall shear stress results are available in engines, the fully turbulent developed flow in a square duct is chosen to validate the new wall models. The model constants in the new wall models are set to 0.01 and 0.8, respectively and are kept constant throughout the investigation. The resulting time- and spatially-averaged velocity and temperature wall functions from the new wall models match well with the law-of-the-wall experimental data at Re = 50,000. In order to study the effect of hot air impinging walls, jet impingement on a flat plate is also tested with the new wall models. The jet Reynolds number is equal to 21,000 and a fixed jet-to-plate spacing of H/D = 2.0. As predicted by the new wall models, the time-averaged skin friction coefficient agrees well with experimental data, while the computed Nusselt number agrees fairly well when r/D > 2.0. Additionally, the model is validated using experimental data from a Caterpillar engine operated with conventional diesel combustion. Sixteen different operating engine conditions are simulated. The majority of the predicted heat flux results from each thermocouple location follow similar trends when compared with experimental data. The magnitude of peak heat fluxes as predicted by the new wall models is in the range of typical measured values in diesel combustion, while most heat flux results from previous LES wall models are over-predicted. The new wall models generate more accurate predictions and agree better with experimental data.

  6. Liquid Wall Chambers

    Energy Technology Data Exchange (ETDEWEB)

    Meier, W R

    2011-02-24

    The key feature of liquid wall chambers is the use of a renewable liquid layer to protect chamber structures from target emissions. Two primary options have been proposed and studied: wetted wall chambers and thick liquid wall (TLW) chambers. With wetted wall designs, a thin layer of liquid shields the structural first wall from short ranged target emissions (x-rays, ions and debris) but not neutrons. Various schemes have been proposed to establish and renew the liquid layer between shots including flow-guiding porous fabrics (e.g., Osiris, HIBALL), porous rigid structures (Prometheus) and thin film flows (KOYO). The thin liquid layer can be the tritium breeding material (e.g., flibe, PbLi, or Li) or another liquid metal such as Pb. TLWs use liquid jets injected by stationary or oscillating nozzles to form a neutronically thick layer (typically with an effective thickness of {approx}50 cm) of liquid between the target and first structural wall. In addition to absorbing short ranged emissions, the thick liquid layer degrades the neutron flux and energy reaching the first wall, typically by {approx}10 x x, so that steel walls can survive for the life of the plant ({approx}30-60 yrs). The thick liquid serves as the primary coolant and tritium breeding material (most recent designs use flibe, but the earliest concepts used Li). In essence, the TLW places the fusion blanket inside the first wall instead of behind the first wall.

  7. Energy based optimization of viscous-friction dampers on cables

    Science.gov (United States)

    Weber, F.; Boston, C.

    2010-04-01

    This investigation optimizes numerically a viscous-friction damper connected to a cable close to one cable anchor for fastest reduction of the total mechanical cable energy during a free vibration decay test. The optimization parameters are the viscous coefficient of the viscous part and the ratio between the friction force and displacement amplitude of the friction part of the transverse damper. Results demonstrate that an almost pure friction damper with negligibly small viscous damping generates fastest cable energy reduction over the entire decay. The ratio between the friction force and displacement amplitude of the optimal friction damper differs from that derived from the energy equivalent optimal viscous damper. The reason for this is that the nonlinearity of the friction damper causes energy spillover from the excited to higher modes of the order of 10%, i.e. cables with attached friction dampers vibrate at several frequencies. This explains why the energy equivalent approach does not yield the optimal friction damper. Analysis of the simulation data demonstrates that the optimally tuned friction damper dissipates the same energy per cycle as if each modal component of the cable were damped by its corresponding optimal linear viscous damper.

  8. Comparative Frictional Analysis of Automobile Drum and Disc Brakes

    Directory of Open Access Journals (Sweden)

    H.P. Khairnar

    2016-03-01

    Full Text Available In the present work, a comparative frictional behaviour of drum brakes and disc brakes in automobiles has been investigated. The influential factors; contact force and friction radius were modeled for the estimation of the friction coefficient for drum as well as disc brakes. The effect of contact force and friction radius is studied with varying conditions of parameters; longitudinal force, caliper force and torque on piston side as well as non-piston side. The numerical results obtained have been compared with the similar obtained from virtual Matlab/Simulink models for drum and disc brakes. The results evidenced that friction radius predominantly affects brake pressure and thus the friction coefficient, also the increase in contact force resulted with decrease in friction coefficient both for drum and disc brakes. Further it has been found that disc brakes exhibit gradual decrease of friction coefficient due to the equitable distribution of braking effort while drum brake presents sudden variations in friction coefficient. It can be revealed that frictional behaviour of disc brake is more consistent than drum brake.

  9. General Friction Model Extended by the Effect of Strain Hardening

    DEFF Research Database (Denmark)

    Nielsen, Chris V.; Martins, Paulo A.F.; Bay, Niels

    2016-01-01

    An extension to the general friction model proposed by Wanheim and Bay [1] to include the effect of strain hardening is proposed. The friction model relates the friction stress to the fraction of real contact area by a friction factor under steady state sliding. The original model for the real co...... of friction in metal forming, where the material generally strain hardens. The extension of the model to cover strain hardening materials is validated by comparison to previously published experimental data.......An extension to the general friction model proposed by Wanheim and Bay [1] to include the effect of strain hardening is proposed. The friction model relates the friction stress to the fraction of real contact area by a friction factor under steady state sliding. The original model for the real......-ideally plastic material, and secondly, to extend the solution by the influence of material strain hardening. This corresponds to adding a new variable and, therefore, a new axis to the general friction model. The resulting model is presented in a combined function suitable for e.g. finite element modeling...

  10. PREFACE: The International Conference on Science of Friction

    Science.gov (United States)

    Miura, Kouji; Matsukawa, Hiroshi

    2007-07-01

    The first international conference on the science of friction in Japan was held at Irago, Aichi on 9-13 September 2007. The conference focused on the elementary process of friction phenomena from the atomic and molecular scale view. Topics covered in the conference are shown below.: Superlubricity and friction Electronic and phononic contributions to friction Friction on the atomic and molecular scales van der Waals friction and Casimir force Molecular motor and friction Friction and adhesion in soft matter systems Wear and crack on the nanoscale Theoretical studies on the atomic scale friction and energy dissipation Friction and chaos Mechanical properties of nanoscale contacts Friction of powder The number of participants in the conference was approximately 100, registered from 11 countries. 48 oral and 29 poster talks were presented at the conference. This volume of Journal of Physics: Conference Series includes 23 papers devoted to the above topics of friction. The successful organization of the conference was made possible by the contribution of the members of the Organizing Committee and International Advisory Committee. The conference was made possible thanks to the financial support from Aichi University of Education and the Taihokogyo Tribology Research Foundation (TTRF), and moreover thanks to the approval societies of The Physical Society of Japan, The Surface Science Society of Japan, The Japanese Society of Tribologists and Toyota Physical and Chemical Research Institute. The details of the conference are available at http://www.science-of-friction.com . Finally we want to thank the speakers for the high quality of their talks and all participants for coming to Irago, Japan and actively contributing to the conference. Kouji Miura and Hiroshi Matsukawa Editors

  11. TMD FRICTION - a company profile; TMD FRICTION - ein Unternehmen stellt sich vor

    Energy Technology Data Exchange (ETDEWEB)

    Bauer, E.

    2000-07-01

    TMD FRICTION came into existence in August 2000 by separation of the friction material sector from BBA PLC. This transaction was supported by HSBC PE, the private equity branch of HSBC, the third largest bank world-wide. This report shall give some market background, the current position of the company and information about the strategic orientation of the new group regarding R and D and production - especially against the background of our customers' global activities. (orig.) [German] TMD FRICTION entstand im August 2000 durch Ausgliederung des Reibbelag-Bereichs aus der BBA PLC. Diese Transaktion wurde unterstuetzt durch HSBC, PE, dem Private Equity-Zweig von HSBC, der drittgroessten Bank weltweit. Der Bericht erlaeutert Markthintergruende, die aktuelle Positionierung des Unternehmens und gibt Hinweise auf die strategische Ausrichtung der neuen Gruppierung im Bereich Entwicklung und Produktion - insbesondere vor dem Hintergrund der globalen Ausrichtung unserer Kunden. (orig.)

  12. Dynamic friction of self-affine surfaces

    Science.gov (United States)

    Schmittbuhl, Jean; Vilotte, Jean-Pierre; Roux, Stéphane

    1994-02-01

    We investigate the velocity dependence of the friction between two rigid blocks limited by a self-affine surface such as the one generated by a crack. The upper solid is subjected either to gravity or to an external elastic stiffness, and is driven horizontally at constant velocity, V, while the lower solid is fixed. For low velocities, the apparent friction coefficient is constant. For high velocities, the apparent friction is shown to display a velocity weakening. The weakening can be related to the variation of the mean contact time due to the occurrence of jumps during the motions. The cross-over between these two regimes corresponds to a characteristic velocity which depends on the geometry of the surfaces and on the mean normal force. In the case of simple gravity loading, the velocity dependence of the apparent friction at high velocities is proportional to 1/V^2 where V is the imposed tangential velocity. In the case of external elastic stiffness, two velocity weakening regimes can be identified, the first is identical to the gravity case with a 1/V^2 dependence, the second appears at higher velocities and is characterized by a 1/V variation. The characteristic velocity of this second cross-over depends on the roughness and the elastic stiffness. The statistical distribution of ballistic flight distances is analysed, and is shown to reveal in all cases the self-affinity of the contacting surfaces. Nous analysons la dépendence en vitesse du frottement entre deux solides limités par une surface rugueuse auto-affine comme celle d'une surface de fracture. Le solide supérieur est soumis soit à la gravité, soit à une raideur élastique externe, et est entraîné à vitesse horizontale constante V sur le solide inférieur fixe. A faible vitesse, le coefficient de friction apparent, est constant. A forte vitesse, le coefficient de friction apparent devient inversement proportionnel à la vitesse. Cette dépendance peut être reliée à la variation du temps

  13. Solar heating wall

    Energy Technology Data Exchange (ETDEWEB)

    Schoenfelder, J.L.

    1983-08-16

    A solar heating wall is disclosed including a water pipe circulation system having a plurality of separate tubes, each formed as a loop, connected between a water supply and a return. The separate tubes are arranged in a single vertical plane at the approximate center of the wall. The wall is formed within a frame which is packed with a material suited for use as a thERMAL RESERVOIR, SUCH AS concrete. The frame provides extra support by having a series of horizontally disposed cross supports on one surface of the wall and a series of vertically disposed cross supports on the opposite surface A pressure relief valve may be provided between the water supply to the separate tubes and the water supply to the building or structure containing the solar wall, so that the solar wall can be adapted for use with a city water system.

  14. SIMULATION OF SUDDEN-EXPANSION AND SWIRLING GAS-PARTICLE FLOWS USING A TWO-FLUID PARTICLE-WALL COLLISION MODEL WITH CONSIDERATION OF THE WALL ROUGHNESS

    Institute of Scientific and Technical Information of China (English)

    ZHOU Lixing; ZHANG Xia

    2004-01-01

    A two-fluid particle-wall collision model with consideration of wall roughness is proposed. It takes into account the effects of the friction, restitution and in particular the wall roughness,and hence the redistribution of Reynolds stress in different directions, the absorption of turbulent energy from the mean motion and the attenuation of particle motion by the wall. The proposed model is used to simulate sudden-expansion and swirling gas-particle flows and is validated by comparing with experimental results. The results show that the proposed model gives better results than those obtained by the presently used zero-gradient condition. Hence, it is suggested that the proposed model should be used as the wall boundary condition for the particle phase in place of the presently used boundary condition.

  15. Cell Wall Proteome

    OpenAIRE

    Boudart, Georges; Minic, Zoran; Albenne, Cécile; Canut, Hervé; Jamet, Elisabeth; Pont-Lezica, Rafael F

    2007-01-01

    In this chapter, we will focus on the contribution of proteomics to the identification and determination of the structure and function of CWPs as well as discussing new perspectives in this area. The great variety of proteins found in the plant cell wall is described. Some families, such as glycoside hydrolases, proteases, lectins, and inhibitors of cell wall modifying enzymes, are discussed in detail. Examples of the use of proteomic techniques to elucidate the structure of various cell wall...

  16. Staggered domain wall fermions

    CERN Document Server

    Hoelbling, Christian

    2016-01-01

    We construct domain wall fermions with a staggered kernel and investigate their spectral and chiral properties numerically in the Schwinger model. In some relevant cases we see an improvement of chirality by more than an order of magnitude as compared to usual domain wall fermions. Moreover, we present first results for four-dimensional quantum chromodynamics, where we also observe significant reductions of chiral symmetry violations for staggered domain wall fermions.

  17. Green walls in Vancouver

    Energy Technology Data Exchange (ETDEWEB)

    Sharp, R. [Sharp and Diamond Landscape Architecture Inc., Vancouver, BC (Canada)

    2007-07-01

    With the renewed interest in design for microclimate control and energy conservation, many cities are implementing clean air initiatives and sustainable planning policies to mitigate the effects of urban climate and the urban heat island effect. Green roofs, sky courts and green walls must be thoughtfully designed to withstand severe conditions such as moisture stress, extremes in temperature, tropical storms and strong desiccating winds. This paper focused on the installation of green wall systems. There are 2 general types of green walls systems, namely facade greening and living walls. Green facades are trellis systems where climbing plants can grow vertically without attaching to the surface of the building. Living walls are part of a building envelope system where plants are actually planted and grown in a wall system. A modular G-SKY Green Wall Panel was installed at the Aquaquest Learning Centre at the Vancouver Aquarium in Stanley Park in September 2006. This green wall panel, which was originally developed in Japan, incorporates many innovative features in the building envelope. It provides an exterior wall covered with 8 species of plants native to the Coastal Temperate Rain Forest. The living wall is irrigated by rainwater collected from the roof, stored in an underground cistern and fed through a drip irrigation system. From a habitat perspective, the building imitates an escarpment. Installation, support systems, irrigation, replacement of modules and maintenance are included in the complete wall system. Living walls reduce the surface temperature of buildings by as much as 10 degrees C when covered with vegetation and a growing medium. The project team is anticipating LEED gold certification under the United States-Canada Green Building Council. It was concluded that this technology of vegetated building envelopes is applicable for acoustical control at airports, biofiltration of indoor air, greywater treatment, and urban agriculture and vertical

  18. Adhesion, friction and wear on the nanoscale of MWNT tips and SWNT and MWNT arrays.

    Science.gov (United States)

    Bhushan, Bharat; Galasso, Barbara; Bignardi, Cristina; Nguyen, Cattien V; Dai, Liming; Qu, Liangti

    2008-03-26

    The nanotribological characterization of carbon nanotubes is fundamental for the exploration of new sliding applications. In this study, a comprehensive investigation of adhesion, friction and wear of a multiwalled nanotube (MWNT) tip, and SWNT (single-walled nanotube) and MWNT arrays has been carried out. A nonlinear response of the MWNT tip is observed when the tip is brought into and out of contact with various surfaces. A nonlinear response occurs due to the buckling of the nanotube and its subsequent sliding on the surface. In addition to the role of surface chemistry, it can also explain the relatively high value of the coefficient of friction obtained on different surfaces, as compared to that of Si and Si(3)N(4) tips. The adhesion and friction studies carried out on SWNT and MWNT arrays using Si tips show that SWNT arrays, compared to MWNT arrays, exhibit lower values, possibly due to lower van der Waals forces as a result of lower packing density and higher flexibility. The wear tests conducted with the MWNT tip and a Si tip on a gold film, at two normal loads, show less damage of the surface when the MWNT tip is used because of the MWNT acting as a compliant spring, absorbing part of the load. Wear tests conducted with a Si tip on SWNT and MWNT arrays show that the arrays do not wear. The tip wear and the friction force in the SWNT array are lower, because of lower adhesion and higher flexibility of the SWNTs, which causes less opposition to the motion of the tip.

  19. Adhesion, friction and wear on the nanoscale of MWNT tips and SWNT and MWNT arrays

    Energy Technology Data Exchange (ETDEWEB)

    Bhushan, Bharat [Nanotribology Laboratory for Information Storage and MEMS/NEMS, 201 West 19th Avenue, Ohio State University, Columbus, OH 43210-1142 (United States); Galasso, Barbara; Bignardi, Cristina [Politecnico di Torino, Dipartimento di Meccanica, Corso Duca degli Abruzzi 24, 10129 Torino (Italy); Nguyen, Cattien V [ELORET NASA Ames Research Center, MS 229-1, Moffet Field, CA 94035 (United States); Dai Liming; Qu Liangti [Department of Chemical and Materials Engineering, University of Dayton Research Institute, 300 College Park, Dayton, OH 45469 (United States)

    2008-03-26

    The nanotribological characterization of carbon nanotubes is fundamental for the exploration of new sliding applications. In this study, a comprehensive investigation of adhesion, friction and wear of a multiwalled nanotube (MWNT) tip, and SWNT (single-walled nanotube) and MWNT arrays has been carried out. A nonlinear response of the MWNT tip is observed when the tip is brought into and out of contact with various surfaces. A nonlinear response occurs due to the buckling of the nanotube and its subsequent sliding on the surface. In addition to the role of surface chemistry, it can also explain the relatively high value of the coefficient of friction obtained on different surfaces, as compared to that of Si and Si{sub 3}N{sub 4} tips. The adhesion and friction studies carried out on SWNT and MWNT arrays using Si tips show that SWNT arrays, compared to MWNT arrays, exhibit lower values, possibly due to lower van der Waals forces as a result of lower packing density and higher flexibility. The wear tests conducted with the MWNT tip and a Si tip on a gold film, at two normal loads, show less damage of the surface when the MWNT tip is used because of the MWNT acting as a compliant spring, absorbing part of the load. Wear tests conducted with a Si tip on SWNT and MWNT arrays show that the arrays do not wear. The tip wear and the friction force in the SWNT array are lower, because of lower adhesion and higher flexibility of the SWNTs, which causes less opposition to the motion of the tip.

  20. Frictional melting dynamics in the upper conduit: A chemical answer to a complex physical question

    Science.gov (United States)

    Henton De Angelis, S.; Lavallee, Y.; Kendrick, J. E.; Hornby, A.; von Aulock, F. W.; Clesham, S.; Hirose, T.; Perugini, D.

    2013-12-01

    During volcanic eruptions the generation of frictional heat along the walls of the shallow conduit leads to melting of the rocks along the slip interface. Frictional melting has previously been described as a process out of thermodynamic equilibrium, but upon slip and mingling of the melt batches, homogeneity can be achieved, and may have an h important rheological control on the dynamics of slip. To test melt homogenization in the frictional melt zones of volcanic conduits we performed constant-rate slip experiments under controlled stress conditions using a high-velocity rotary shear apparatus. Volcanic dome samples from three different volcanoes (Volcán De Colima, Soufrière Hills Volcano and Santiaguito Volcano) were investigated. Each sample was subjected to a stress of 1 MPa and slip rate of 1 m/s. For each sample set 5 experiments were conducted: 1) experiment stopped at the onset of melting; 2) experiment stopped on the formation of a full melt layer; 3) experiment stopped after 5m of slip at steady state conditions; 4) experiment stopped after 10m of slip at steady state conditions; 5) experiment stopped after 15m of slip at steady state conditions. We analyzed the resulting proto-melt zones using micron sized X-ray spectroscopy in the high-brightness synchrotron beamline I18 (at Diamond Light Source UK). Particular focus was given to the concentration variance analysis of Rare Earth Elements as their mobilities can be used to precisely quantify the degree and timescale of homogenisation involved during frictional melting. This study refines our understanding of the chemical process of melting and mixing which carry important consequences for the rheological control on the physical dynamics of slip.

  1. Atomic-Scale Friction and Microfriction of Graphite and Diamond Using Friction Force Microscopy

    Science.gov (United States)

    1993-10-07

    19), 2642-2645 (1991). 21 [12] R. M. Overney, E. Meyer, J. Frommer , D. Brodbeck, R. Luithi, L. Howald, H. -J. GUntherodt, M. Fuji.,La, H. Takano, and Y...Meyer, R. Overney, D. Brodbeck, L. Howard, R. Luithi, J. Frommer , and H. -J. Guntherodt, "Friction and Wear of Langmuir-Blodgett Films Observed by...Friction Force Microscopy", Phys. Rev. Lett., Vol. 69(12), 1777-1780 (1992). [14] E. Meyer, R. Overney, R. Luthi, D. Brodbeck, L. Howald, J. Frommer , H

  2. On the nature of the static friction, kinetic friction and creep

    DEFF Research Database (Denmark)

    Persson, B. N. J.; Albohr, O.; Mancosu, F.

    2003-01-01

    In this paper, we discuss the nature of the static and kinetic friction, and of (thermally activated) creep.We focus on boundary lubrication at high confining pressure (∼1GPa), as is typical for hard solids, where one or at most two layers of confined molecules separates the sliding surfaces. We...... may depend linearly on ln (v/v0), as usually observed experimentally, rather than non-linearly [−ln (v/v0)]2/3 as predicted by a simple theory of activated processes. We also discuss the role of elasticity at stop and start. We show that for "simple" rubber (at low start velocity), the static friction...

  3. Analysis and Comparison of Friction Stir Welding and Laser Assisted Friction Stir Welding of Aluminum Alloy

    OpenAIRE

    Sabina Luisa Campanelli; Giuseppe Casalino; Caterina Casavola; Vincenzo Moramarco

    2013-01-01

    Friction Stir Welding (FSW) is a solid-state joining process; i.e., no melting occurs. The welding process is promoted by the rotation and translation of an axis-symmetric non-consumable tool along the weld centerline. Thus, the FSW process is performed at much lower temperatures than conventional fusion welding, nevertheless it has some disadvantages. Laser Assisted Friction Stir Welding (LAFSW) is a combination in which the FSW is the dominant welding process and the laser pre-heats the we...

  4. Road Friction Coefficient Real-Time Identification Based on the Tire Dynamic Friction Model

    Institute of Scientific and Technical Information of China (English)

    FAN Xiao-bin; DENG Pan; JIANG Yu; FAN Bing-xu

    2013-01-01

    Road friction coefficient real-time estimation methods is an important issue and problem in automotive active safety con-trol system development. First a fixed feedback gain sliding mode observer of road adhesion coefficient is designed through the es-tablishment of tire/road dynamic friction model in this article. The simulation results shows that the observer can well real-time iden-tify the current road adhesion characteristics. And more importantly, the observer only need wheel speed signal and the braking torque (brake pressure) signal, so the system is low cost, and its adaptability is good. There is no doubt this estimation method has a good application prospect.

  5. Reynolds-dependence of turbulent skin-friction drag reduction induced by spanwise forcing

    CERN Document Server

    Gatti, Davide

    2015-01-01

    This paper examines how increasing the value of the Reynolds number $Re$ affects the ability of spanwise-forcing techniques to yield turbulent skin-friction drag reduction. The control strategy is the streamwise-travelling waves of spanwise wall velocity (Quadrio {\\em et al. J. Fluid Mech.}, vol. 627, 2009, pp. 161--178). The study builds upon an extensive drag-reduction database created with Direct Numerical Simulation of a turbulent channel flow for two, 5-fold separated values of $Re$, namely $Re_\\tau=200$ and $Re_\\tau=1000$. The sheer size of the database, which for the first time systematically addresses the amplitude of the forcing, allows a comprehensive view of the drag-reducing characteristics of the traveling waves, and enables a detailed description of the changes occurring when $Re$ increases. The effect of using a viscous scaling based on the friction velocity of either the non-controlled flow or the drag-reduced flow is described. In analogy with other wall-based drag reduction techniques, like ...

  6. Velocity tuning of friction with two trapped atoms

    CERN Document Server

    Gangloff, Dorian; Counts, Ian; Jhe, Wonho; Vuletić, Vladan

    2015-01-01

    Friction is the basic, ubiquitous mechanical interaction between two surfaces that results in resistance to motion and energy dissipation. In spite of its technological and economic significance, our ability to control friction remains modest, and our understanding of the microscopic processes incomplete. At the atomic scale, mismatch between the two contacting crystal lattices can lead to a reduction of stick-slip friction (structural lubricity), while thermally activated atomic motion can give rise to a complex velocity dependence, and nearly vanishing friction at sufficiently low velocities (thermal lubricity). Atomic force microscopy has provided a wealth of experimental results, but limitations in the dynamic range, time resolution, and control at the single-atom level have hampered a full quantitative description from first principles. Here, using an ion-crystal friction emulator with single-atom, single substrate-site spatial resolution and single-slip temporal resolution, we measure the friction force...

  7. Friction laws from dimensional-analysis point of view

    CERN Document Server

    Hatano, Takahiro

    2015-01-01

    Friction laws, which are a key to the understanding of the diversity of earthquakes, are considered theoretically. Using dimensional analysis, the logarithmic dependence of the friction coefficient on the slip velocity and the state variable is derived without any knowledge of the underlying physical processes on the frictional surface. This is based on a simple assumption that the friction coefficient is expressed as the difference from a reference state. Therefore, the functional form of the rate and state dependent friction law itself does not necessarily mean that thermal activation processes dominate friction. It is also shown that, if there are two (or more) state variables having the same dimension, we need not assume the logarithmic dependence on the state variables.

  8. Variables influencing the frictional behaviour of in vivo human skin.

    Science.gov (United States)

    Veijgen, N K; Masen, M A; van der Heide, E

    2013-12-01

    In the past decades, skin friction research has focused on determining which variables are important to affect the frictional behaviour of in vivo human skin. Until now, there is still limited knowledge on these variables. This study has used a large dataset to identify the effect of variables on the human skin, subject characteristics and environmental conditions on skin friction. The data are obtained on 50 subjects (34 males and 16 females). Friction measurements represent the friction between in vivo human skin and an aluminium sample, assessed on three anatomical locations. The coefficient of friction increased significantly (pskin and the height of the subject. Other outcome variables in this study were the hydration of the skin and the skin temperature.

  9. Anomalous friction of graphene nanoribbons on waved graphenes

    Directory of Open Access Journals (Sweden)

    Jun Fang

    2015-11-01

    Full Text Available Friction plays a critical role in the function and maintenance of small-scale structures, where the conventional Coulomb friction law often fails. To probe the friction at small scales, here we present a molecular dynamics study on the process of dragging graphene nanoribbons on waved graphene substrates. The simulation shows that the induced friction on graphene with zero waviness is ultra-low and closely related to the surface energy barrier. On waved graphenes, the friction generally increases with the amplitude of the wave at a fixed period, but anomalously increases and then decreases with the period at a fixed amplitude. These findings provide insights into the ultra-low friction at small scales, as well as some guidelines into the fabrication of graphene-based nano-composites with high performance.

  10. Friction related size-effect in microforming – a review

    Directory of Open Access Journals (Sweden)

    Wang Chunju

    2014-01-01

    Full Text Available This paper presents a thorough literature review of the size effects of friction in microforming. During miniaturization, the size effects of friction occur clearly. The paper first introduces experimental research progress on size effects of friction in both micro bulk and sheet forming. The effects of several parameters are discussed. Based on the experimental results, several approaches have been performed to develop a model or functions to analyse the mechanism of size effects of friction, and simulate the micro deep drawing process by integrating them into an FE program. Following this, surface modification, e.g. a DLC film and a micro structure/textured surface, as a method to reduce friction are presented. Finally, the outlook for the size effect of friction in the future is assessed, based on the understanding of the current research progress.

  11. Friction Model for FEM Simulation of Sheet Metal Forming Operations

    Science.gov (United States)

    Keum, Y. T.; Wagoner, R. H.; Lee, J. K.

    2004-06-01

    In order to find the effect of frictional characteristics, lubricant viscosity, tool geometry, and forming speed on the sheet metal forming, a friction tester was designed and manufactured. Friction tests were performed using drawing oils, various tool radii and forming speeds for aluminum alloy sheets, galvanized steels sheets and cold rolled steel sheets. From the experimental observation, the mathematical friction model considering lubricant viscosity, sheet surface roughness and hardness, punch corner radii, and punch speed is developed. By comparing the punch load found by FEM using the proposed friction model with that of experimental measurement when the steel sheets are formed in 2-D geometry in dry and lubricating conditions, the validity and accuracy of the mathematical friction model are demonstrated.

  12. Frictional forces between hydrophilic and hydrophobic particle coated nanostructured surfaces

    DEFF Research Database (Denmark)

    Hansson, Petra M; Claesson, Per M.; Swerin, Agne;

    2013-01-01

    by utilizing the atomic force microscope (AFM). The chemistry of the surfaces and the probe was varied between hydrophilic silica and hydrophobized silica. For hydrophilic silica surfaces, the friction coefficient was significantly higher for the particle coated surfaces than on the flat reference surface. All...... the particle coated surfaces exhibited similar friction coefficients, from which it may be concluded that the surface geometry, and not the roughness amplitude per se, influenced the measured friction. During measurements with hydrophobic surfaces, strong adhesive forces related to the formation of a bridging...... air cavity were evident from both normal force and friction force measurements. In contrast to the frictional forces between the hydrophilic surfaces, the friction coefficient for hydrophobic surfaces was found to depend on the surface structure and we believe that this dependence is related...

  13. The Frictional Coefficient of Bovine Knee Articular Cartilage

    Institute of Scientific and Technical Information of China (English)

    Qian Shan-hua; Ge Shi-rong; Wang Qing-liang

    2006-01-01

    The normal displacement of articular cartilage was measured under load and in sliding, and the coefficient of friction during sliding was measured using a UMT-2 Multi-Specimen Test System. The maximum normal displacement under load and the start-up frictional coefficient have similar tendency of variation with loading time. The sliding speed does not significantly influence the frictional coefficient of articular cartilage.

  14. Paradoxical stabilization of forced oscillations by strong nonlinear friction

    Science.gov (United States)

    Esirkepov, Timur Zh.; Bulanov, Sergei V.

    2017-08-01

    In a dissipative dynamic system driven by an oscillating force, a strong nonlinear highly oscillatory friction force can create a quasi-steady tug, which is always directed opposite to the ponderomotive force induced due to a spatial inhomogeneity of oscillations. When the friction-induced tug exceeds the ponderomotive force, the friction stabilizes the system oscillations near the maxima of the oscillation spatial amplitude of the driving force.

  15. Self-Organization during Friction of Slide Bearing Antifriction Materials

    Directory of Open Access Journals (Sweden)

    Iosif S. Gershman

    2015-12-01

    Full Text Available This article discusses the peculiarities of self-organization behavior and formation of dissipative structures during friction of antifriction alloys for slide bearings against a steel counterbody. It shows that during self-organization, the moment of friction in a tribosystem may be decreasing with the load growth and in the bifurcations of the coefficient of friction with respect to load. Self-organization and the formation of dissipative structures lead to an increase in the seizure load.

  16. Friction Buttering: A New Technique for Dissimilar Welding

    Science.gov (United States)

    Karthik, G. M.; Mastanaiah, P.; Janaki Ram, G. D.; Kottada, Ravi Sankar

    2017-02-01

    This work offers a fresh perspective on buttering, a technique often considered for fusion welding of dissimilar metals. For the first time, buttering was attempted in solid state using friction deposition. Using this new "friction buttering" technique, fusion welding of two different dissimilar metal pairs (austenitic stainless steel/borated stainless steel and Al-Cu-Mg/Al-Zn-Mg-Cu) was successfully demonstrated. The results show that friction buttering can simplify a tough dissimilar welding problem into a routine fusion welding task.

  17. PROGRAM-PATTERN MULTIPOLE BOUNDARY ELEMENT METHOD FOR FRICTIONAL CONTACT

    Institute of Scientific and Technical Information of China (English)

    Yu Chunxiao; Shen Guangxian; Liu Deyi

    2005-01-01

    A mathematical program is proposed for the highly nonlinear problem involving frictional contact. A program-pattern using the fast multipole boundary element method (FMBEM) is given for 3-D elastic contact with friction to replace the Monte Carlo method. A new optimized generalized minimal residual (GMRES) algorithm is presented. Numerical examples demonstrate the validity of the program-pattern optimization model for node-to-surface contact with friction. The GMRES algorithm greatly improves the computational efficiency.

  18. Mathematical Programming Solution for the Frictional Contact Multipole BEM

    Institute of Scientific and Technical Information of China (English)

    YU Chunxiao; SHEN Guangxian; LIU Deyi

    2005-01-01

    This paper presents a new mathematical model for the highly nonlinear problem of frictional contact. A programming model, multipole boundary element method (BEM), was developed for 3-D elastic contact with friction to replace the Monte Carlo method. A numerical example shows that the optimization programming model for the point-to-surface contact with friction and the fast optimization generalized minimal residual algorithm (GMRES(m)) significantly improve the analysis of such problems relative to the conventional BEM.

  19. Classical shear cracks drive the onset of dry frictional motion.

    Science.gov (United States)

    Svetlizky, Ilya; Fineberg, Jay

    2014-05-08

    Frictional processes entail the rupture of the ensemble of discrete contacts defining a frictional interface. There are a variety of views on how best to describe the onset of dry frictional motion. These range from modelling friction with a single degree of freedom, a 'friction coefficient', to theoretical treatments using dynamic fracture to account for spatial and temporal dynamics along the interface. We investigated the onset of dry frictional motion by performing simultaneous high-speed measurements of the real contact area and the strain fields in the region surrounding propagating rupture tips within the dry (nominally flat) rough interfaces formed by brittle polymer blocks. Here we show that the transition from 'static' to 'dynamic' friction is quantitatively described by classical singular solutions for the motion of a rapid shear crack. We find that these singular solutions, originally derived to describe brittle fracture, are in excellent agreement with the experiments for slow propagation, whereas some significant discrepancies arise as the rupture velocity approaches the Rayleigh wave speed. In addition, the energy dissipated in the fracture of the contacts remains nearly constant throughout the entire range in which the rupture velocity is less than the Rayleigh wave speed, whereas the size of the dissipative zone undergoes a Lorentz-like contraction as the rupture velocity approaches the Rayleigh wave speed. This coupling between friction and fracture is critical to our fundamental understanding of frictional motion and related processes, such as earthquake dynamics.

  20. Friction Joint Between Basalt-Reinforced Composite and Aluminum

    DEFF Research Database (Denmark)

    Costache, Andrei; Glejbøl, Kristian; Sivebæk, Ion Marius

    2015-01-01

    The purpose of this study was to anchor basalt-reinforced polymers in an aluminum grip using dry friction. Dry friction clamping is considered the optimal solution for post-mounting of load-bearing terminations on composite structures. A new test method is presented for characterizing the frictio......The purpose of this study was to anchor basalt-reinforced polymers in an aluminum grip using dry friction. Dry friction clamping is considered the optimal solution for post-mounting of load-bearing terminations on composite structures. A new test method is presented for characterizing...

  1. Microstructure analysis in friction welding of copper and aluminum

    Science.gov (United States)

    Wibowo, A. G. Wahyu; Ismail, Rifky; Jamari, J.

    2016-04-01

    The Friction welding is a welding method with utilizing heat generated due to friction. Surfaces of two materials to be joined, one rotates the other being idle, is contacted by a pressure force. Friction on the second contact surface is done continuously so that the heat generated by the continuous friction will continue to rise. With the heat and the pressure force on the second surface to the second meeting of the material reaches its melting temperature then there is the process of welding. This paper examines the influence of the pressure force, rotational speed and contact time on friction welding of Aluminum (Al) and Copper (Cu) to the quality of welded joints. Friction welding process is performed on a friction welding machine that is equipped with the loading mechanism. The parameters used are the pressure force, rotational speed and friction time. Determination of the quality of welding is done by testing the tensile strength, hardness, and micro structure on the weld joint areas. The results showed that the friction welding quality is very good, this is evidenced by the results of a tensile strength test where the fault occurs outside the weld joint and increased violence in the weld joint. On the results visually cuts the welding area did not reveal any porosity so that it can be concluded that each metal contacts have melted perfectly and produce a connection with good quality.

  2. Friction Properties of Inkjet and Flexographic Prints on Different Papers

    Directory of Open Access Journals (Sweden)

    Simona Grigaliūnienė

    2015-03-01

    Full Text Available Friction between different papers, inkjet and flexographic prints has been experimentally investigated. Flexographic prints have been made using an anilox roller, and inkjet prints have been produced covering paper with one and four toner layers. Static (SCOF and kinetic (KCOF friction coefficients between paper and paper, paper and prints, prints and prints have been determined. Friction properties have been discovered to be different in flexographic and laser prints. The dependence of SCOF and KCOF on pressure (both decrease together with roughness measurements enables to conclude that the friction of prints is mainly governed by adhesion forces.

  3. Friction Compensation in the Upsetting of Cylindrical Test Specimens

    DEFF Research Database (Denmark)

    Christiansen, Peter; Martins, P. A. F.; Bay, Niels Oluf

    2016-01-01

    This manuscript presents a combined numerical andexperimental methodology for determining the stress-straincurve of metallic materials from the measurements of forceand displacement obtained in the axial compression of cylindrical test specimens with friction between the specimens and the platens...... model or combined friction models are utilized .Experimental results obtained from cylindrical and Rastegaev test specimens with different lubricants combined with the experimental determination of friction by means of ring compression tests allows compensating the effect of friction...... Appendix is provided for those readers interested in utilizing the associated numerical algorithm for determining the stress straincurves of metallic materials....

  4. MODIFICATION OF FLAKE REINFORCED FRICTION BRAKE COMPOSITE MATERIAL

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    According to the recent development trend and need of the friction brake material, the flake reinforced friction brake material has been made out by adjusting the recipe and techniques. The two-dimensional flake vermiculite is selected as the reinforced stuffing of the material; the modified resin is used as the basal bed of the material. The tests manifest that the properties of mechanics are high, the friction coefficients are suitable and stable,and especially in high temperatures the wear is low. It is an excellent friction brake material.

  5. Methods and devices used to measure friction in rolling

    DEFF Research Database (Denmark)

    Jeswiet, J.; Arentoft, Mogens; Henningsen, Poul

    2006-01-01

    Friction at the workpiece-die boundary, in both bulk forming and sheet forming is, arguably, the single most important physical parameter influencing the processing of metals; yet it remains the least understood. Hence there is a need for basic research into metal-die interface mechanisms. To gain...... a good understanding of the mechanisms at the interface and to be able to verify the friction and tribology models that exist, friction sensors are needed. Designing sensors to measure frictional stress in metal working has been pursued by many researchers. This paper surveys methods that have been used...

  6. Association between friction and wear in diarthrodial joints lacking lubricin

    Science.gov (United States)

    Jay, Gregory D; Torres, Jahn R; Rhee, David K; Helminen, Heikki J; Hytinnen, Mika M; Cha, Chung-Ja; Elsaid, Khaled; Kim, Kyung-Suk; Cui, Yajun; Warman, Matthew L

    2007-01-01

    Objective The glycoprotein lubricin (encoded by the gene Prg4) is secreted by surface chondrocytes and synovial cells, and has been shown to reduce friction in vitro. In contrast to man-made bearings, mammalian diarthrodial joints must endogenously produce friction-reducing agents. This study was undertaken to investigate whether friction is associated with wear. Methods The lubricating ability of synovial fluid (SF) samples from humans with genetic lubricin deficiency was tested in vitro. The coefficient of friction in the knee joints of normal and lubricin-null mice was measured ex vivo; these joints were also studied by light and electron microscopy. Atomic force microscopy was used to image and measure how lubricin reduces friction in vitro. Results SF lacking lubricin failed to reduce friction in the boundary mode. Joints of lubricin-null mice showed early wear and higher friction than joints from their wild-type counterparts. Lubricin self-organized and reduced the work of adhesion between apposing asperities. Conclusion These data show that friction is coupled with wear at the cartilage surface in vivo. They imply that acquired lubricin degradation occurring in inflammatory joint diseases predisposes the cartilage to damage. Lastly, they suggest that lubricin, or similar biomolecules, will have applications in man-made devices in which reducing friction is essential. PMID:17968947

  7. Skin friction related behaviour of artificial turf systems.

    Science.gov (United States)

    Tay, Sock Peng; Fleming, Paul; Hu, Xiao; Forrester, Steph

    2017-08-01

    The occurrence of skin friction related injuries is an issue for artificial turf sports pitches and remains a barrier to their acceptance. The purpose of this study was to evaluate the current industry standard Securisport® Sports Surface Tester that measures skin surface related frictional behaviour of artificial turf. Little research has been published about the device and its efficacy, despite its widespread use as a standard FIFA test instrument. To achieve a range of frictional behaviours, several "third generation" (3G) carpet and infill combinations were investigated; friction time profiles throughout the Securisport rotations were assessed in combination with independent measurements of skin roughness before and after friction testing via 3D surface scanning. The results indicated that carpets without infill had greatest friction (coefficients of friction 0.97-1.20) while those completely filled with sand or rubber had similar and lower values independent of carpet type (coefficient of friction (COF) ≈0.57). Surface roughness of a silicone skin (s-skin) decreased after friction testing, with the largest change on sand infilled surfaces, indicating an "abrasive" polishing effect. The combined data show that the s-skin is damaged in a surface-specific manner, thus the Securisport COF values appear to be a poor measure of the potential for skin abrasion. It is proposed that the change in s-skin roughness improves assessment of the potential for skin damage when players slide on artificial turf.

  8. Tool For Friction Stir Tack Welding of Aluminum Alloys

    Science.gov (United States)

    Bjorkman, Gerald W.; Dingler, Johnny W.; Loftus, Zachary

    2003-01-01

    A small friction-stir-welding tool has been developed for use in tack welding of aluminum-alloy workpieces. It is necessary to tack-weld the workpieces in order to hold them together during friction stir welding because (1) in operation, a full-size friction-stir-welding tool exerts a large force that tends to separate the workpieces and (2) clamping the workpieces is not sufficient to resist this force. It is possible to tack the pieces together by gas tungsten arc welding, but the process can be awkward and time-consuming and can cause sufficient damage to necessitate rework. Friction stir tack welding does not entail these disadvantages. In addition, friction stir tack welding can be accomplished by use of the same automated equipment (except for the welding tool) used in subsequent full friction stir welding. The tool for friction stir tack welding resembles the tool for full friction stir welding, but has a narrower shoulder and a shorter pin. The shorter pin generates a smaller workpiece-separating force so that clamping suffices to keep the workpieces together. This tool produces a continuous or intermittent partial-penetration tack weld. The tack weld is subsequently consumed by action of the larger tool used in full friction stir welding tool.

  9. Progress and development in thermodynamic theory of friction and wear

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Tribology theory lags well behind engineering needs because of those complex and multi-dimensional characteristics associated with friction and wear. The mechanism of friction is reviewed and discussed from a static thermodynamics perspective; research methods on the process of friction and wear and thermodynamic studies within the field of tribology are also reviewed. We propose that entropy can be a critical parameter in describing the evolution of friction and wear, and the entropy balance equation could be considered as a fundamental cornerstone for a systematic tribology theory. Applications of irreversible thermodynamic theory of tribology to various fields are reviewed.

  10. Progress and development in thermodynamic theory of friction and wear

    Institute of Scientific and Technical Information of China (English)

    DAI ZhenDong; XUE QunJi

    2009-01-01

    Tribology theory lags well behind engineering needs because of those complex and multi-dimensional characteristics associated with friction and wear. The mechanism of friction is reviewed end discussed from a static thermodynamics perspective; research methods on the process of friction and wear and thermodynamic studies within the field of tribology are also reviewed. We propose that entropy can be a critical parameter in describing the evolution of friction and wear, and the entropy balance equation could be considered as a fundamental cornerstone for a systematic tribology theory. Applications of irreversible thermodynamic theory of tribology to various fields are reviewed.

  11. Electrochemical Studies of Passive Film Formation and Corrosion of Friction Stir Processed Nickel Aluminum Bronze

    Science.gov (United States)

    2011-06-01

    friction stir welding (FSW) but is used for the purpose of refining...mechanical properties [11]. C. FRICTION STIR WELDING AND PROCESSING Friction Stir Processing (FSP) is derived from Friction Stir Welding (FSW) which was...Temple-Smith, and C. Dawes, Friction - stir butt welding , GB Patent No. 9125978.8, International patent application No. PCT/GB92/02203, 1991. [4

  12. Finite Element Modeling and Analysis of Nonlinear Impact and Frictional Motion Responses Including Fluid—Structure Coupling Effects

    Directory of Open Access Journals (Sweden)

    Yong Zhao

    1997-01-01

    Full Text Available A nonlinear three dimensional (3D single rack model and a nonlinear 3D whole pool multi-rack model are developed for the spent fuel storage racks of a nuclear power plant (NPP to determine impacts and frictional motion responses when subjected to 3D excitations from the supporting building floor. The submerged free standing rack system and surrounding water are coupled due to hydrodynamic fluid-structure interaction (FSI using potential theory. The models developed have features that allow consideration of geometric and material nonlinearities including (1 the impacts of fuel assemblies to rack cells, a rack to adjacent racks or pool walls, and rack support legs to the pool floor; (2 the hydrodynamic coupling of fuel assemblies with their storing racks, and of a rack with adjacent racks, pool walls, and the pool floor; and (3 the dynamic motion behavior of rocking, twisting, and frictional sliding of rack modules. Using these models 3D nonlinear time history dynamic analyses are performed per the U.S. Nuclear Regulatory Commission (USNRC criteria. Since few such modeling, analyses, and results using both the 3D single and whole pool multiple rack models are available in the literature, this paper emphasizes description of modeling and analysis techniques using the SOLVIA general purpose nonlinear finite element code. Typical response results with different Coulomb friction coefficients are presented and discussed.

  13. Hydrothermal frictional strengths of rock and mineral samples relevant to the creeping section of the San Andreas Fault

    Science.gov (United States)

    Moore, Diane E.; Lockner, David A.; Hickman, Stephen H.

    2016-01-01

    We compare frictional strengths in the temperature range 25–250 °C of fault gouge from SAFOD (CDZ and SDZ) with quartzofeldspathic wall rocks typical of the central creeping section of the San Andreas Fault (Great Valley sequence and Franciscan Complex). The Great Valley and Franciscan samples have coefficients of friction, μ > 0.35 at all experimental conditions. Strength is unchanged between 25° and 150 °C, but μ increases at higher temperatures, exceeding 0.50 at 250 °C. Both samples are velocity strengthening at room temperature but show velocity-weakening behavior beginning at 150 °C and stick-slip motion at 250 °C. These rocks, therefore, have the potential for unstable seismic slip at depth. The CDZ gouge, with a high saponite content, is weak (μ = 0.09–0.17) and velocity strengthening in all experiments, and μ decreases at temperatures above 150 °C. Behavior of the SDZ is intermediate between the CDZ and wall rocks: μ < 0.2 and does not vary with temperature. Although saponite is probably not stable at depths greater than ∼3 km, substitution of the frictionally similar minerals talc and Mg-rich chlorite for saponite at higher temperatures could potentially extend the range of low strength and stable slip down to the base of the seismogenic zone.

  14. International Divider Walls

    NARCIS (Netherlands)

    Kruis, A.; Sneller, A.C.W.(L.)

    2013-01-01

    The subject of this teaching case is the Enterprise Resource Planning (ERP) system implementation at International Divider Walls, the world market leader in design, production, and sales of divider walls. The implementation in one of the divisions of this multinational company had been successful, a

  15. Domain wall filters

    CERN Document Server

    Bär, O; Neuberger, H; Witzel, O; Baer, Oliver; Narayanan, Rajamani; Neuberger, Herbert; Witzel, Oliver

    2007-01-01

    We propose using the extra dimension separating the domain walls carrying lattice quarks of opposite handedness to gradually filter out the ultraviolet fluctuations of the gauge fields that are felt by the fermionic excitations living in the bulk. This generalization of the homogeneous domain wall construction has some theoretical features that seem nontrivial.

  16. Thin Wall Iron Castings

    Energy Technology Data Exchange (ETDEWEB)

    J.F. Cuttino; D.M. Stefanescu; T.S. Piwonka

    2001-10-31

    Results of an investigation made to develop methods of making iron castings having wall thicknesses as small as 2.5 mm in green sand molds are presented. It was found that thin wall ductile and compacted graphite iron castings can be made and have properties consistent with heavier castings. Green sand molding variables that affect casting dimensions were also identified.

  17. International Divider Walls

    NARCIS (Netherlands)

    Kruis, A.; Sneller, A.C.W.(L.)

    2013-01-01

    The subject of this teaching case is the Enterprise Resource Planning (ERP) system implementation at International Divider Walls, the world market leader in design, production, and sales of divider walls. The implementation in one of the divisions of this multinational company had been successful,

  18. Measuring Search Frictions Using Japanese Microdata

    DEFF Research Database (Denmark)

    Sasaki, Masaru; Kohara, Miki; Machikita, Tomohiro

    2013-01-01

    This paper estimates individual-level matching functions to measure search frictions in the Japanese labour market and presents the determinants of search duration. We employ administrative microdata that track the job search process of job seekers who left or lost their job in August 2005...... and subsequently registered at their local public employment service. Our finding is that the matching function exhibits decreasing rather than constant returns-to-scale for job seekers and vacancies. We also find that after controlling for the benefits period, job seekers who lost their job involuntarily were...

  19. Measuring Search Frictions Using Japanese Microdata

    DEFF Research Database (Denmark)

    Sasaki, Masaru; Kohara, Miki; Machikita, Tomohiro

    This paper estimates matching functions to measure search frictions in the Japanese labor market and presents determinants of search duration to explain the effect of unemployment benefits on a job seeker’s behavior. We employ administrative micro data that track the job search process...... unemployment benefits lengthen (shorten) the duration of job search for job seekers who voluntarily (involuntarily) leave employment....... of individuals who left or lost their job in August 2005 and subsequently registered at their local public employment service. Our finding is that the matching function would exhibit decreasing returns-to-scale for job seekers and vacancies, rather than constant return-to-scale. We also find that generous...

  20. Inverse Faraday Effect driven by Radiation Friction

    CERN Document Server

    Liseykina, T V; Macchi, A

    2015-01-01

    In the interaction of extremely intense ($>10^{23}~\\mbox{W cm}^{-2}$), circularly polarized laser pulses with thick targets, theory and simulations show that a major fraction of the laser energy is converted into incoherent radiation because of collective electron motion during the "hole boring" dynamics. The effective dissipation due to radiative losses allows the absorption of electromagnetic angular momentum, which in turn leads to the generation of an axial magnetic field of tens of gigagauss value. This peculiar "inverse Faraday effect" is demonstrated in three-dimensional simulations including radiation friction.

  1. Bioeconomy, Moral Friction and Symbolic Law

    DEFF Research Database (Denmark)

    Hoeyer, Klaus

    2016-01-01

    ‘symbolic’, treaties aimed at protecting the body are symbols with great impact. Similarly, the material preparation of body parts as tradable grafts involves symbolic work and this symbolism is an essential part of making a ‘market’. I argue that instances of ‘symbolic law’ can reflect situations in which...... several competing agendas are at play and to understand the effects, we therefore need to investigate empirically what emerges through this friction between competing governmental ambitions. My discussion is based on studies of tissue exchange in Europe and seeks to integrate theories of symbolic law...

  2. Deformation Characterization of Friction-Stir-Welded Tubes by Hydraulic Bulge Testing

    Science.gov (United States)

    Pang, Q.; Hu, Z. L.; Pan, X.; Zuo, X. Q.

    2014-10-01

    In this article, the large-diameter thin-walled aluminum alloy tubes were produced using a hybrid process combining friction-stir welding (FSW) and spinning. For this novel process, rolled aluminum alloy sheets with a thickness about 2-3 times the wall thickness of target tube, were FSW to form cylinders, and then the cylinders were subjected to spinning to get thin-walled aluminum alloy tubes. Both experimental and simulation study were conducted to investigate the deformation characterization of the FSW tube during hydraulic bulge testing, and the stress and strain states and thickness distribution of the FSW tube were investigated. It was found that the common defects of FSW tube can be significantly improved by specific welding devices. The ductility of the tube is considerably improved with nearly two times higher bulge ratio than as-spun tube after annealing treatment at 300°C. But the annealed tube still shows a high nonuniform wall thickness distribution due to the inhomogeneous deformation characteristics. With increasing deformation of the tube, the gap between the hoop and axial stress for the weld and base metal (BM) decreases. However, the hoop and axial stress of the weld are always greater than those of the BM at the same pressure.

  3. An Alternative Frictional Boundary Condition for Computational Fluid Dynamics Simulation of Friction Stir Welding

    Science.gov (United States)

    Chen, Gaoqiang; Feng, Zhili; Zhu, Yucan; Shi, Qingyu

    2016-09-01

    For better application of numerical simulation in optimization and design of friction stir welding (FSW), this paper presents a new frictional boundary condition at the tool/workpiece interface for computational fluid dynamics (CFD) modeling of FSW. The proposed boundary condition is based on an implementation of the Coulomb friction model. Using the new boundary condition, the CFD simulation yields non-uniform distribution of contact state over the tool/workpiece interface, as validated by the experimental weld macrostructure. It is found that interfacial sticking state is present over large area at the tool-workpiece interface, while significant interfacial sliding occurs at the shoulder periphery, the lower part of pin side, and the periphery of pin bottom. Due to the interfacial sticking, a rotating flow zone is found under the shoulder, in which fast circular motion occurs. The diameter of the rotating flow zone is smaller than the shoulder diameter, which is attributed to the presence of the interfacial sliding at the shoulder periphery. For the simulated welding condition, the heat generation due to friction and plastic deformation makes up 54.4 and 45.6% of the total heat generation rate, respectively. The simulated temperature field is validated by the good agreement to the experimental measurements.

  4. Frictional behavior of carbon fiber tows: a contact mechanics model of tow–tow friction

    NARCIS (Netherlands)

    Cornelissen, Bo; Rooij, de Matthijn B.; Rietman, Bert; Akkerman, Remko

    2014-01-01

    Composite-forming processes involve mechanical interactions at the ply, tow, and filament level. The deformations that occur during forming processes are governed by friction between the contacting tows on the mesoscopic level and consequently between filaments on the microscopic level. A thorough u

  5. Hard and soft walls

    CERN Document Server

    Milton, Kimball A

    2011-01-01

    In a continuing effort to understand divergences which occur when quantum fields are confined by bounding surfaces, we investigate local energy densities (and the local energy-momentum tensor) in the vicinity of a wall. In this paper, attention is largely confined to a scalar field. If the wall is an infinite Dirichlet plane, well known volume and surface divergences are found, which are regulated by a temporal point-splitting parameter. If the wall is represented by a linear potential in one coordinate $z$, the divergences are softened. The case of a general wall, described by a potential of the form $z^\\alpha$ for $z>0$ is considered. If $\\alpha>2$, there are no surface divergences, which in any case vanish if the conformal stress tensor is employed. Divergences within the wall are also considered.

  6. Scale dependence of rock friction at high work rate.

    Science.gov (United States)

    Yamashita, Futoshi; Fukuyama, Eiichi; Mizoguchi, Kazuo; Takizawa, Shigeru; Xu, Shiqing; Kawakata, Hironori

    2015-12-10

    Determination of the frictional properties of rocks is crucial for an understanding of earthquake mechanics, because most earthquakes are caused by frictional sliding along faults. Prior studies using rotary shear apparatus revealed a marked decrease in frictional strength, which can cause a large stress drop and strong shaking, with increasing slip rate and increasing work rate. (The mechanical work rate per unit area equals the product of the shear stress and the slip rate.) However, those important findings were obtained in experiments using rock specimens with dimensions of only several centimetres, which are much smaller than the dimensions of a natural fault (of the order of 1,000 metres). Here we use a large-scale biaxial friction apparatus with metre-sized rock specimens to investigate scale-dependent rock friction. The experiments show that rock friction in metre-sized rock specimens starts to decrease at a work rate that is one order of magnitude smaller than that in centimetre-sized rock specimens. Mechanical, visual and material observations suggest that slip-evolved stress heterogeneity on the fault accounts for the difference. On the basis of these observations, we propose that stress-concentrated areas exist in which frictional slip produces more wear materials (gouge) than in areas outside, resulting in further stress concentrations at these areas. Shear stress on the fault is primarily sustained by stress-concentrated areas that undergo a high work rate, so those areas should weaken rapidly and cause the macroscopic frictional strength to decrease abruptly. To verify this idea, we conducted numerical simulations assuming that local friction follows the frictional properties observed on centimetre-sized rock specimens. The simulations reproduced the macroscopic frictional properties observed on the metre-sized rock specimens. Given that localized stress concentrations commonly occur naturally, our results suggest that a natural fault may lose its

  7. Science friction: data, metadata, and collaboration.

    Science.gov (United States)

    Edwards, Paul N; Mayernik, Matthew S; Batcheller, Archer L; Bowker, Geoffrey C; Borgman, Christine L

    2011-10-01

    When scientists from two or more disciplines work together on related problems, they often face what we call 'science friction'. As science becomes more data-driven, collaborative, and interdisciplinary, demand increases for interoperability among data, tools, and services. Metadata--usually viewed simply as 'data about data', describing objects such as books, journal articles, or datasets--serve key roles in interoperability. Yet we find that metadata may be a source of friction between scientific collaborators, impeding data sharing. We propose an alternative view of metadata, focusing on its role in an ephemeral process of scientific communication, rather than as an enduring outcome or product. We report examples of highly useful, yet ad hoc, incomplete, loosely structured, and mutable, descriptions of data found in our ethnographic studies of several large projects in the environmental sciences. Based on this evidence, we argue that while metadata products can be powerful resources, usually they must be supplemented with metadata processes. Metadata-as-process suggests the very large role of the ad hoc, the incomplete, and the unfinished in everyday scientific work.

  8. Molecular friction in an actomyosin molecular machine.

    Science.gov (United States)

    Suda, H

    1990-10-07

    In muscle contraction, it has been widely recognized that a binding state exists between myosin and actin in the presence of Mg-ATP. To estimate the magnitude of binding strength, I introduce a concept of frictional phenomena which occurs between two sliding bodies in contact each other. In such cases, the sliding speed can be formulated as a function of the actin-myosin bond strength. In order to validate this, the present theory is applied for the two movement assay systems with no external load; one movement assay of Phalloidin Rhodamine bound F-actin on a myosin coated hydrophobic cover glass and another assay of myosin coated beads along actin cables of Nitella. If a coefficient of 0.005 is applied to the kinetic friction, 1pN for the sliding force per cross-bridge and 10 microns sec-1 for the sliding speed, it is found that the bond strength between actin and one myosin head is about 200 pN in the contracting state.

  9. A frictional sliding algorithm for liquid droplets

    Science.gov (United States)

    Sauer, Roger A.

    2016-12-01

    This work presents a new frictional sliding algorithm for liquid menisci in contact with solid substrates. In contrast to solid-solid contact, the liquid-solid contact behavior is governed by the contact line, where a contact angle forms and undergoes hysteresis. The new algorithm admits arbitrary meniscus shapes and arbitrary substrate roughness, heterogeneity and compliance. It is discussed and analyzed in the context of droplet contact, but it also applies to liquid films and solids with surface tension. The droplet is modeled as a stabilized membrane enclosing an incompressible medium. The contact formulation is considered rate-independent such that hydrostatic conditions apply. Three distinct contact algorithms are needed to describe the cases of frictionless surface contact, frictionless line contact and frictional line contact. For the latter, a predictor-corrector algorithm is proposed in order to enforce the contact conditions at the contact line and thus distinguish between the cases of advancing, pinning and receding. The algorithms are discretized within a monolithic finite element formulation. Several numerical examples are presented to illustrate the numerical and physical behavior of sliding droplets.

  10. Origins of Shear Jamming for Frictional Grains

    Science.gov (United States)

    Wang, Dong; Zheng, Hu; Ren, Jie; Dijksman, Joshua; Bares, Jonathan; Behringer, Robert

    2016-11-01

    Granular systems have been shown to be able to behave like solids, under shear, even when their densities are below the critical packing fraction for frictionless isotropic jamming. To understand such a phenomena, called shear jamming, the question we address here is: how does shear bring a system from a unjammed state to a jammed state, where the coordination number, Z, is no less than 3, the isotropic jamming point for frictional grains? Since Z can be used to distinguish jammed states from unjammed ones, it is vital to understand how shear increases Z. We here propose a set of three particles in contact, denoted as a trimer, as the basic unit to characterize the deformation of the system. Trimers, stabilized by inter-grain friction, fail under a certain amount of shear and bend to make extra contacts to regain stability. By defining a projection operator of the opening angle of the trimer to the compression direction in the shear, O, we see a systematically linear decrease of this quantity with respect to shear strain, demonstrating the bending of trimers as expected. In addition, the average change of O from one shear step to the next shows a good collapse when plotted against Z, indicating a universal behavior in the process of shear jamming. We acknowledge support from NSF DMR1206351, NASA NNX15AD38G, the William M. Keck Foundation and a RT-MRSEC Fellowship.

  11. Thermomechanical Modelling of Friction Stir Welding

    DEFF Research Database (Denmark)

    Hattel, Jesper Henri; Schmidt, Henrik Nikolaj Blicher; Tutum, Cem Celal

    2009-01-01

    Friction Stir Welding (FSW) is a fully coupled thermomechanical process and should in general be modelled as such. Basically, there are two major application areas of thermomechanical models in the investigation of the FSW process: i) Analysis of the thermomechanical conditions such as e.g. heat ...... together with selected modelling results including prediction of material flow during welding, prediction of heat generation with the thermal-pseudo mechanical model as well as residual stress and deformation analysis combined with in-service loads.......Friction Stir Welding (FSW) is a fully coupled thermomechanical process and should in general be modelled as such. Basically, there are two major application areas of thermomechanical models in the investigation of the FSW process: i) Analysis of the thermomechanical conditions such as e.g. heat......, typically on a local scale, the latter will very often be based on a semi-coupled, global procedure where the transient temperatures drive the stresses but not vice-versa. However, in the latter, prior knowledge about the heat generation must be obtained somehow, and if experimental data are not available...

  12. Numerical simulation of friction stir welding

    Directory of Open Access Journals (Sweden)

    Mijajlović Miroslav

    2014-01-01

    Full Text Available Friction stir welding is a solid-state welding technique that utilizes thermo-mechanical influence of the rotating welding tool on parent material resulting with monolith joint-weld. On the contact of welding tool and parent material, significant stirring and deformation of parent material appears, and during this process mechanical energy is partially transformed into heat. The paper describes the software for the numerical simulation of friction stir welding developed at Mechanical Engineering Faculty, University of Nis. Numerical solution for estimation of welding plates temperature is estimated using finite difference method-explicit scheme with adaptive grid, considering influence of temperature on material's conductivity, contact conditions between welding tool and parent material, material flow around welding tool etc. The calculated results are in good agreement with the experimental results. [Projekat Ministarstva nauke Republike Srbije, br. TR35034: The research of modern non-conventional technologies application in manufacturing companies with the aim of increase efficiency of use, product quality, reduce of costs and save energy and materials

  13. Monte Carlo simulation of a complex fluid confined to a pore with nanoscopically rough walls

    Science.gov (United States)

    Porcheron, Fabien; Schoen, Martin; Fuchs, Alain H.

    2002-04-01

    Understanding the properties of fluid films of nanometer scale thickness confined between two solid substrates is of fundamental interest as well as of practical importance for engineering applications such as lubrication, adhesion, and friction. We address here the question of the effect of the wall corrugation on the confined fluid structure. We report configurational bias grand canonical Monte Carlo simulations for model butane confined between planar and nonplanar walls. Furrowed walls have been used to model surface roughness effects on the nanometer length scale, while the confining walls remain smooth on the atomic scale. It is shown that the fluid confined between planar walls exhibits a damped oscillatory solvation pressure profile. A transition from an oscillatory to a nonoscillatory behavior is observed when the characteristic length of the furrow reaches the typical dimensions of a butane molecule. It is inferred from these simulations that disrupted oscillatory forces observed in the experiments may reflect the coupling between molecular and nanoscopic roughness length scales.

  14. Design and manufacture of intelligent Cu-based wet friction materials

    Institute of Scientific and Technical Information of China (English)

    丁华东; 韩文政; 傅苏黎; 杜建华; 遇元宏

    2004-01-01

    The friction sheets working process was analyzed. It is found that its characteristic is microregion instantaneous high temperature and the current cooling method, making the sheets cooled by the lubricating oil flowing through the friction surface, is not very efficient. Then, intelligent materials concept was introduced, the component and microstructure of intelligent Cu-based friction materials were designed, and the intelligent Cu-based wet friction materials as well as sheets were manufactured. And the intelligent friction materials working principle, i.e. the materials cooling the friction microregion in real time or the friction sheets cutting the peak value of microregion instantaneous high temperature during friction process, was given depending on the characteristics of the materials' and friction sheets' working process. Finally, it is indicated that the intelligent friction sheets excell the currently used friction sheets in properties, including anti-heating property, anti-wearing property as well as friction characteristic.

  15. Influence of friction on sampling disturbance of lunar surface in direct push sampling method based on DEM

    Science.gov (United States)

    Gao, Xingwen; Tang, Dewei; Yue, Honghao; Jiang, Shengyuan; Deng, Zongquan

    2017-06-01

    The direct push sampling method is one of the most commonly used sampling methods in lunar regolith exploration. However, the disturbance of in situ bedding information during the sampling process has remained an unresolved problem. In this paper, the discrete element method is used to establish a numerical lunar soil simulant basing on the Hertz-Mindlin contact model. The result of simulated triaxial test shows that the macro mechanical parameters of the simulant accurately simulate most known lunar soil samples. The friction coefficient between the simulant and the wall of the sampling tube is also tested and used as the key variable in the following simulation and study. The disturbance phenomenon is evaluated by the displacement of marked layers, and a swirling structure is observed. The changing trend of the friction coefficient on the soil simulant void ratio and stress distribution is also determined.

  16. Lubrication approximation for micro-particles moving along parallel walls

    CERN Document Server

    Ekiel-Jezewska, M L; Blawzdziewicz, J; Feuillebois, F

    2008-01-01

    Lubrication expressions for the friction coefficients of a spherical particle moving in a fluid between and along two parallel solid walls are explicitly evaluated in the low-Reynolds-number regime. They are used to determine lubrication expression for the particle free motion under an ambient Poiseuille flow. The range of validity and the accuracy of the lubrication approximation is determined by comparing with the corresponding results of the accurate multipole procedure. The results are applicable for thin, wide and long microchannels, or quasi-two-dimensional systems.

  17. Low-drag events in transitional wall-bounded turbulence

    Science.gov (United States)

    Whalley, Richard D.; Park, Jae Sung; Kushwaha, Anubhav; Dennis, David J. C.; Graham, Michael D.; Poole, Robert J.

    2017-03-01

    Intermittency of low-drag pointwise wall shear stress measurements within Newtonian turbulent channel flow at transitional Reynolds numbers (friction Reynolds numbers 70 - 130) is characterized using experiments and simulations. Conditional mean velocity profiles during low-drag events closely approach that of a recently discovered nonlinear traveling wave solution; both profiles are near the so-called maximum drag reduction profile, a general feature of turbulent flow of liquids containing polymer additives (despite the fact that all results presented are for Newtonian fluids only). Similarities between temporal intermittency in small domains and spatiotemporal intermittency in large domains is thereby found.

  18. A Split Forcing Technique to Reduce Log-layer Mismatch in Wall-modeled Turbulent Channel Flows

    Science.gov (United States)

    Deleon, Rey; Senocak, Inanc

    2016-11-01

    The conventional approach to sustain a flow field in a periodic channel flow seems to be the culprit behind the log-law mismatch problem that has been reported in many studies hybridizing Reynolds-averaged Navier-Stokes (RANS) and large-eddy simulation (LES) techniques, commonly referred to as hybrid RANS-LES. To address this issue, we propose a split-forcing approach that relies only on the conservation of mass principle. We adopt a basic hybrid RANS-LES technique on a coarse mesh with wall-stress boundary conditions to simulate turbulent channel flows at friction Reynolds numbers of 2000 and 5200 and demonstrate good agreement with benchmark data. We also report a duality in velocity scale that is a specific consequence of the split forcing framework applied to hybrid RANS-LES. The first scale is the friction velocity derived from the wall shear stress. The second scale arises in the core LES region, a value different than at the wall. Second-order turbulence statistics agree well with the benchmark data when normalized by the core friction velocity, whereas the friction velocity at the wall remains the appropriate scale for the mean velocity profile. Based on our findings, we suggest reevaluating more sophisticated hybrid RANS-LES approaches within the split-forcing framework. Work funded by National Science Foundation under Grant No. 1056110 and 1229709. First author acknowledges the University of Idaho President's Doctoral Scholars Award.

  19. Effect of friction at the walls of MHD channel on the flow for finite Rm

    Energy Technology Data Exchange (ETDEWEB)

    Lavrent' ev, I.V.; Sidorenkov, S.I.

    1986-10-01

    A method to prove the fact that the string tension sigma in strongly coupled lattice gauge theories is of the form sigma = -log ..beta..+sigma is an analytic function of the inverse coupling ..beta.. = 1/g/sup 2/, is presented. Its relation to random surface methods, in particular to the work of Debrushin and Holicky-acute-accent, Kotecky-acute-accent, and Zahradnik, is discussed.

  20. Boundary Behavior of Viscous Fluids: Influence of Wall Roughness and Friction-driven Boundary Conditions

    Science.gov (United States)

    Bucur, Dorin; Feireisl, Eduard; Nečasová, Šárka

    2010-07-01

    We consider a family of solutions to the evolutionary Navier-Stokes system supplemented with the complete slip boundary conditions on domains with rough boundaries. We give a complete description of the asymptotic limit by means of Γ-convergence arguments, and identify a general class of boundary conditions.

  1. Friction reduction using discrete surface textures: principle and design

    Science.gov (United States)

    Hsu, Stephen M.; Jing, Yang; Hua, Diann; Zhang, Huan

    2014-08-01

    There have been many reports on the use of dimples, grooves, and other surface textures to control friction in sliding interfaces. The effectiveness of surface textures in friction reduction has been demonstrated in conformal contacts under high speed low load applications such as mechanical seals and automotive water pump seals, etc., resulting in reduced friction and longer durability. For sliding components with higher contact pressures or lower speeds, conflicting results were reported. Reasons for the inconsistency may be due to the differences in texture fabrication techniques, lack of dimple size and shape uniformity, and different tester used. This paper examines the basic principles on which surface textural patterns influence friction under the three principle lubrication regimes: hydrodynamic, elastohydrodynamic, and boundary lubrication regimes. Our findings suggest that each regime requires specific dimple size, shape, depth, and areal density to achieve friction reduction. Control experiments were also conducted to explore mechanisms of friction reduction. The dimple geometric shape and the dimple's orientation with respect to the sliding direction influence friction significantly. The underlying mechanisms for friction control via textures are discussed.

  2. Friction at seismic slip rates: testing thermal weakening models experimentally

    Science.gov (United States)

    Nielsen, S. B.; Spagnuolo, E.; Violay, M.; Di Toro, G.

    2013-12-01

    Recent experiments systematically explore rock friction under crustal earthquake conditions (fast slip rate 1desing an efficient and accurate wavenumber approximation for a solution of the temperature evolution on the fault. Finally, we propose a compact and paractical model based on a small number of memory variables for the implementation of thermal weakening friction in seismic fault simulations.

  3. Biomechanics of iliotibial band friction syndrome in runners.

    Science.gov (United States)

    Orchard, J W; Fricker, P A; Abud, A T; Mason, B R

    1996-01-01

    We propose a biomechanical model to explain the pathogenesis of iliotibial band friction syndrome in distance runners. The model is based on a kinematic study of nine runners with iliotibial band friction syndrome, a cadaveric study of 11 normal knees, and a literature review. Friction (or impingement) occurs near footstrike, predominantly in the foot contact phase, between the posterior edge of the iliotibial band and the underlying lateral femoral epicondyle. The study subjects had an average knee flexion angle of 21.4 degrees +/- 4.3 degrees at footstrike, with friction occurring at, or slightly below, the 30 degrees of flexion traditionally described in the literature. In the cadavers we examined, there was substantial variation in the width of the iliotibial bands. This variation may affect individual predisposition to iliotibial band friction syndrome. Downhill running predisposes the runner to iliotibial band friction syndrome because the knee flexion angle at footstrike is reduced. Sprinting and faster running on level ground are less likely to cause or aggravate iliotibial band friction syndrome because, at footstrike, the knee is flexed beyond the angles at which friction occurs.

  4. Microstructure Evolution during Friction Stir Spot Welding of TRIP Steel

    DEFF Research Database (Denmark)

    Lomholt, Trine Colding; Pantleon, Karen; Somers, Marcel A. J.

    2010-01-01

    In this study, the feasibility of friction stir spot welding of TRIP steel is investigated. In addition to manufacturing successful welds, the present study aims at a fundamental understanding of the mechanisms occurring at the (sub)micron scale during friction stir spot welding. As one of the main...

  5. Scale effects in metal-forming friction and lubrication

    DEFF Research Database (Denmark)

    Nielsen, Peter Søe; Paldan, Nikolas Aulin; Calaon, Matteo

    2011-01-01

    equipment is developed for studies of the size effect in metal-forming friction in the range from macro-to microscale. Investigations confirm a significant friction increase when downscaling. Visual inspection of the workpieces shows this to be explained by the amount of open and closed lubricant pockets....

  6. Associated computational plasticity schemes for nonassociated frictional materials

    DEFF Research Database (Denmark)

    Krabbenhoft, K.; Karim, M. R.; Lyamin, A. V.;

    2012-01-01

    A new methodology for computational plasticity of nonassociated frictional materials is presented. The new approach is inspired by the micromechanical origins of friction and results in a set of governing equations similar to those of standard associated plasticity. As such, procedures previously...

  7. Apparatus Measures Friction In Vacuum Or Pressurized Gas

    Science.gov (United States)

    Trevathan, Joseph R.

    1996-01-01

    Friction-testing apparatus in small test chamber contains special atmosphere, which could include vacuum or pressurized gas. Provides readings indicative of friction between pin specimen and plate specimen sliding under pin in reciprocating linear motion. Pin and plate specimens made of same or different material.

  8. The role of friction in perceived oral texture

    NARCIS (Netherlands)

    Wijk, R.A. de; Prinz, J.F.

    2005-01-01

    Instrumentally measured in vitro friction in semi-solid foods was related to oral texture sensations. Increased fat content resulted in lower sensations of roughness, higher sensations of creaminess, and lower friction, suggesting that lubrication is the mechanism by which fat affects oral texture

  9. Measurements of Normal and Friction Forces in a Rolling Process

    DEFF Research Database (Denmark)

    Henningsen, Poul; Arentoft, Mogens; Wanheim, Tarras

    2004-01-01

    To improve the quality of frictional data and to validate the simulations in rolling, a load transducer for measuring normal and friction stresses in the deformation zone has been developed. The transducer consists of a strain gauge equipped insert embedded in the surface of the roll. The length ...

  10. Statistical analysis of friction sleeve length effects on soil classification

    Science.gov (United States)

    Saussus, D. R.; Frost, J. D.; Dejong, J. T.

    2004-10-01

    The cone penetration test (CPT) provides profiles of the tip resistance, sleeve friction, and pore water pressure encountered while penetrating the subsurface. These parameters are used either directly or indirectly to classify the soil types present and to obtain geotechnical design parameters. However, fundamental discrepancies exist in the manner by which these parameters are measured. This paper describes the results of a study that shows the sleeve friction measurement introduces unnecessary redundancy due to the length of the standard friction sleeve compared to the measurement increment. Further, the high sleeve length to measurement increment ratio results in filtering and smoothing of the friction data, thereby causing the variability of the friction between the soil and the cone sleeve to be underestimated. The importance of understanding the role of the sleeve length on measurements is demonstrated using synthetically generated friction profiles and estimating the profiles that would be measured using sleeves of different lengths. Differences in how the soils are classified as a function of the sleeve length used to obtain each profile are illustrated. Solutions are presented to validate the synthetic sleeve friction profiles, to demonstrate the filtering and smoothing effects of the friction sleeve on the data, and to explain the implications of the sleeve length on soil classification. Copyright

  11. Friction and stick-slip in a telescope construction

    NARCIS (Netherlands)

    Hammerschlag, R.H.

    1986-01-01

    Stick-slip in high resolution telescopes should be avoided. The contact places where stick-slip can occur are described. Some contact places require a high friction coefficient, others a low friction coefficient. Some experiments have been carried out to find lubricants for contact places which comb

  12. Variables influencing the frictional behaviour of in vivo human skin

    NARCIS (Netherlands)

    Veijgen, N.K.; Masen, M.A.; Heide, van der E.

    2013-01-01

    In the past decades, skin friction research has focused on determining which variables are important to affect the frictional behaviour of in vivo human skin. Until now, there is still limited knowledge on these variables. This study has used a large dataset to identify the effect of variables on t

  13. Variables influencing the frictional behaviour of in vivo human skin

    NARCIS (Netherlands)

    Veijgen, N.K.; Masen, M.A.; Heide, E. van der

    2013-01-01

    In the past decades, skin friction research has focused on determining which variables are important to affect the frictional behaviour of in vivo human skin. Until now, there is still limited knowledge on these variables.This study has used a large dataset to identify the effect of variables on the

  14. Synovial sarcoma presenting as iliotibial band friction syndrome.

    Science.gov (United States)

    Mesiha, Mena; Bauer, Thomas; Andrish, Jack

    2009-10-01

    Iliotibial band friction syndrome is a common entity that is often quickly diagnosed in orthopedic clinics. However, synovial sarcoma is an elusive clinical entity that appears around many joints with variable presentations. This case report is an example of a patient with a classic presentation of iliotibial band friction syndrome that was diagnosed as a synovial sarcoma on further investigation.

  15. Shearing Nanometer-Thick Confined Hydrocarbon Films: Friction and Adhesion

    DEFF Research Database (Denmark)

    Sivebæk, I. M.; Persson, B. N. J.

    2016-01-01

    We present molecular dynamics (MD) friction and adhesion calculations for nanometer-thick confined hydrocarbon films with molecular lengths 20, 100 and 1400 carbon atoms. We study the dependency of the frictional shear stress on the confining pressure and sliding speed. We present results...

  16. A lubrication approach to friction in thermoplastic composites forming processes

    NARCIS (Netherlands)

    Thije, ten R.H.W.; Akkerman, R.; Ubbink, M.P.; Meer, van der L.

    2011-01-01

    Friction is an important phenomenon that can dominate the resulting product geometry of thermoplastic composites upon forming. A model was developed that predicts the friction between a thermoplastic laminate and a rigid tool. The model is based on the Reynolds equation for thin film lubrication and

  17. Optimizing snake locomotion in the plane. II. Large transverse friction

    CERN Document Server

    Alben, Silas

    2013-01-01

    We determine analytically the form of optimal snake locomotion when the coefficient of transverse friction is large, the typical regime for biological and robotic snakes. We find that the optimal snake motion is a retrograde traveling wave, with a wave amplitude that decays as the -1/4 power of the coefficient of transverse friction. This result agrees well with our numerical computations.

  18. Influence of Friction Condition on Cold Upsetting of Tube Flange

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    FEM is used to analyze the influence of interface friction on the material flow and the cause of forming defect in the cold upsetting of tube flange. Based on the FEM simulation results, the relationships between flange width and the extreme friction factors are established. The concept of forming limit diagram for cold upsetting of tube flange is presented.

  19. Numerical simulation and experimental observations of initial friction transients

    Energy Technology Data Exchange (ETDEWEB)

    Hughes, D.A.; Weingarten, L.I.; Dawson, D.B.

    1995-07-01

    Experiments were performed to better understand the sliding frictional behavior between metals under relatively high shear and normal forces. Microstructural analyses were done to estimate local near-surface stress and strain gradients. The numerical simulation of the observed frictional behavior was based on a constitutive model that uses a state variable approach.

  20. The role of friction in perceived oral texture

    NARCIS (Netherlands)

    Wijk, R.A. de; Prinz, J.F.

    2005-01-01

    Instrumentally measured in vitro friction in semi-solid foods was related to oral texture sensations. Increased fat content resulted in lower sensations of roughness, higher sensations of creaminess, and lower friction, suggesting that lubrication is the mechanism by which fat affects oral texture i

  1. Frictional properties of single crystals HMX, RDX and PETN explosives.

    Science.gov (United States)

    Wu, Y Q; Huang, F L

    2010-11-15

    The frictional properties of single crystals of cyclotetramethylene tetranitramine (HMX), cyclotrimethylene trinitramine (RDX) and pentaerythritol tetranitrate (PETN) secondary explosives are examined using a sensitive friction machine. The explosive crystals used for the measurements are at least 3.5 mm wide. The friction coefficients between crystals of the same explosive (i.e., HMX on HMX, etc.), crystals of different explosives (i.e., HMX on RDX, etc.), and each explosive and a well-polished gauge steel surface are determined. The frictional surfaces are also studied under an environmental scanning electron microscope (ESEM) to analyze surface microstructural changes under increasing loading forces. The friction coefficients vary considerably with increasing normal loading forces and are particularly sensitive to slider shapes, crystal roughness and the mechanical properties of both the slider and the sample. With increasing loading forces, most friction experiments show surface damage, consisting of grooves, debris, and nano-particles, on both the slider and sample. In some cases, a strong evidence of a localized molten state is found in the central region of the friction track. Possible mechanisms that affect the friction coefficient are discussed based on microscopic observations. Copyright © 2010 Elsevier B.V. All rights reserved.

  2. Effect of energetic dissipation processes on the friction unit tribological

    Directory of Open Access Journals (Sweden)

    Moving V. V.

    2007-01-01

    Full Text Available In article presented temperature influence on reological and fric-tion unit coefficients cast iron elements. It has been found that surface layer formed in the temperature friction has good rub off resistance. The surface layer structural hardening and capacity stress relaxation make up.

  3. Friction Stir Welding Technology: Adapting NASA's Retractable Pin Tool

    OpenAIRE

    ECT Team, Purdue

    2007-01-01

    In late 1991, The Welding Institute (TWI), a British research and technology organization, invented and patented a welding process named Friction Stir Welding (FSW). Friction Stir Welding is a highly significant advancement in aluminum welding technology that can produce stronger, lighter, and more efficient welds than any previous process.

  4. Cladding of Advanced Al Alloys Employing Friction Stir Welding

    NARCIS (Netherlands)

    Stelt, van der A.A.; Bor, T.C.; Geijselaers, H.J.M.; Akkerman, R.; Boogaard, van den A.H.

    2013-01-01

    In this paper an advanced solid state cladding process, based on Friction Stir Welding, is presented. The Friction Surface Cladding (FSC) technology enables the deposition of a solid-state coating using filler material on a substrate with good metallurgical bonding. A relatively soft AA1050 filler m

  5. Damage Tolerance Behavior of Friction Stir Welds in Aluminum Alloys

    Science.gov (United States)

    McGill, Preston; Burkholder, Jonathan

    2012-01-01

    Friction stir welding is a solid state welding process used in the fabrication of various aerospace structures. Self-reacting and conventional friction stir welding are variations of the friction stir weld process employed in the fabrication of cryogenic propellant tanks which are classified as pressurized structure in many spaceflight vehicle architectures. In order to address damage tolerance behavior associated with friction stir welds in these safety critical structures, nondestructive inspection and proof testing may be required to screen hardware for mission critical defects. The efficacy of the nondestructive evaluation or the proof test is based on an assessment of the critical flaw size. Test data describing fracture behavior, residual strength capability, and cyclic mission life capability of friction stir welds at ambient and cryogenic temperatures have been generated and will be presented in this paper. Fracture behavior will include fracture toughness and tearing (R-curve) response of the friction stir welds. Residual strength behavior will include an evaluation of the effects of lack of penetration on conventional friction stir welds, the effects of internal defects (wormholes) on self-reacting friction stir welds, and an evaluation of the effects of fatigue cycled surface cracks on both conventional and selfreacting welds. Cyclic mission life capability will demonstrate the effects of surface crack defects on service load cycle capability. The fracture data will be used to evaluate nondestructive inspection and proof test requirements for the welds.

  6. Damage Tolerance Assessment of Friction Pull Plug Welds

    Science.gov (United States)

    McGill, Preston; Burkholder, Jonathan

    2012-01-01

    Friction stir welding is a solid state welding process developed and patented by The Welding Institute in Cambridge, England. Friction stir welding has been implemented in the aerospace industry in the fabrication of longitudinal welds in pressurized cryogenic propellant tanks. As the industry looks to implement friction stir welding in circumferential welds in pressurized cryogenic propellant tanks, techniques to close out the termination hole associated with retracting the pin tool are being evaluated. Friction pull plug welding is under development as a one means of closing out the termination hole. A friction pull plug weld placed in a friction stir weld results in a non-homogenous weld joint where the initial weld, plug weld, their respective heat affected zones and the base metal all interact. The welded joint is a composite, plastically deformed material system with a complex residual stress field. In order to address damage tolerance concerns associated with friction plug welds in safety critical structures, such as propellant tanks, nondestructive inspection and proof testing may be required to screen hardware for mission critical defects. The efficacy of the nondestructive evaluation or the proof test is based on an assessment of the critical flaw size in the test or service environments. Test data relating residual strength capability to flaw size in two aluminum alloy friction plug weld configurations is presented.

  7. Frictional characteristics of the newer orthodontic elastomeric ligatures

    Directory of Open Access Journals (Sweden)

    A V Arun

    2011-01-01

    Full Text Available Introduction: Elastomeric ligatures reduce chairside time but increase friction. Polymeric coatings and 45° angulations have been introduced to the ligature modules to combat its disadvantages and reduce friction. This in vitro study compared the frictional characteristics of six different types of the most commonly used elastomeric modules. Materials and Methods: Thecoefficient of friction for six ligation methods: the non-coated Mini Stix† and coated Super Slick Mini Stix™ (TP Orthodontics, 45° angulated but non-coated Alastik Easy-To-Tie™ (3M Unitek elastomerics and non-angulated non-coated Alastik QuiK-StiK FNx01 , 0.110′- and 0.120′-diameter elastomerics™ (Reliance Orthodontics were measured in dry conditions utilizing a jig according to the protocol of Tidy. Results: A significant difference was observed between the various types of elastomeric ligatures (P<.01. Among the six types of elastomeric ligatures, the 45° angulated elastomeric ligatures produced the least friction, followed by the coated Super Slick† elastomers. No difference in the friction was noted when the diameter of the elastomeric ligatures was varied. Conclusions: Polymeric surface coatings and introduction of angulations into elastomeric ligatures reduce the friction during sliding; however, the diameter of the ligature made no difference to sliding friction.

  8. Static friction in elastic adhesive MEMS contacts, models and experiment

    NARCIS (Netherlands)

    Tas, Niels Roelof; Gui, C.; Elwenspoek, Michael Curt

    2000-01-01

    Static friction in shearing mode can be expressed as the product of the shear strength of the interface and the real contact area. The influence of roughness on friction in elastic adhesive contact is analyzed. Special attention is paid to low loading conditions, in which the number of contact

  9. Bifurcations in Systems with Friction : Basic Models and Methods

    NARCIS (Netherlands)

    Ivanov, A. P.

    2009-01-01

    Examples of irregular behavior of dynamical systems with dry friction are discussed. A classification of frictional contacts with respect to their dimensionality, associativity, and the possibility of interruptions is proposed and basic models showing typical features are stated. In particular, bifu

  10. Frictional Forces Required for unrestrained locomotion in dairy cattle

    NARCIS (Netherlands)

    Tol, van der P.P.J.; Metz, J.H.M.; Noordhuizen-Stassen, E.N.; Back, W.; Braam, C.R.

    2005-01-01

    Most free-stall housing systems in the Netherlands are equipped with slatted or solid concrete floors with manure scrapers. A slipping incident occurs when the required coefficient of friction (RCOF) exceeds the coefficient of friction (COF) at the claw–floor interface. An experiment was conducted t

  11. Friction and wear behavior of carbon fiber reinforced brake materials

    Institute of Scientific and Technical Information of China (English)

    Du-qing CHENG; Xue-tao WANG; Jian ZHU; Dong-bua QIU; Xiu-wei CHENG; Qing-feng GUAN

    2009-01-01

    A new composite brake material was fabri-cated with metallic powders, barium sulphate and modified phenolic resin as the matrix and carbon fiber as the reinforced material. The friction, wear and fade character-istics of this composite were determined using a D-MS friction material testing machine. The surface structure of carbon fiber reinforced friction materials was analyzed by scanning electronic microscopy (SEM). Glass fiber-reinforced and asbestos fiber-reinforced composites with the same matrix were also fabricated for comparison. The carbon fiber-reinforced friction materials (CFRFM) shows lower wear rate than those of glass fiber- and asbestos fiber-reinforced composites in the temperature range of 100℃-300℃. It is interesting that the frictional coefficient of the carbon fiber-reinforced friction materials increases as frictional temperature increases from 100℃ to 300℃, while the frictional coefficients of the other two composites decrease during the increasing temperatures. Based on the SEM observation, the wear mechanism of CFRFM at low temperatures included fiber thinning and pull-out. At high temperature, the phenolic matrix was degraded and more pull-out enhanced fiber was demonstrated. The properties of carbon fiber may be the main reason that the CFRFM possess excellent tribological performances.

  12. Measurements of normal and frictional forces in a rolling process

    DEFF Research Database (Denmark)

    Henningsen, Poul; Arentoft, Mogens; Wanheim, Tarras

    2006-01-01

    To improve the quality of frictional data and to validate the simulations in rolling, a load transducer for measuring normal and frictional stresses in the deformation zone has been developed. The transducer consists of a strain-gauge-equipped insert embedded in the surface of the roll. The length...

  13. Contact mechanics, friction and adhesion with application to quasicrystals

    DEFF Research Database (Denmark)

    Persson, Bo; Carbone, Giuseppe; Samoilov, Vladimir N.;

    2015-01-01

    We discuss the origin of friction and adhesion between hard solids such as quasicrystals. We emphasize the fundamental role of surface roughness in many contact mechanics problems, in particular for friction and adhesion between solid bodies. The most important property of rough surfaces is the s...

  14. Predicting vibration-induced displacement for a resonant friction slider

    DEFF Research Database (Denmark)

    Fidlin, A.; Thomsen, Jon Juel

    2001-01-01

    A mathematical model is set up to quantify vibration-induced motions of a slider, sandwiched between friction layers with different coefficients of friction, and equipped with an imbedded resonator that oscillates at high frequency and small amplitude. This model is highly nonlinear, involving non...

  15. A lubrication approach to friction in thermoplastic composites forming processes

    NARCIS (Netherlands)

    ten Thije, R.H.W.; Akkerman, Remko; Ubbink, M.P.; van der Meer, L.

    2011-01-01

    Friction is an important phenomenon that can dominate the resulting product geometry of thermoplastic composites upon forming. A model was developed that predicts the friction between a thermoplastic laminate and a rigid tool. The model is based on the Reynolds equation for thin film lubrication and

  16. Certification of a weld produced by friction stir welding

    Science.gov (United States)

    Obaditch, Chris; Grant, Glenn J

    2013-10-01

    Methods, devices, and systems for providing certification of friction stir welds are disclosed. A sensor is used to collect information related to a friction stir weld. Data from the sensor is compared to threshold values provided by an extrinsic standard setting organizations using a certification engine. The certification engine subsequently produces a report on the certification status of the weld.

  17. "I Climbed the Great Wall"

    Institute of Scientific and Technical Information of China (English)

    1996-01-01

    I finally climbed the Great Wall, A dream of my childhood; my heart is filled with pleasure at the indescribable beauty of the Wall. China’s ancient civilization is best documented by the grandeur of the Wall.

  18. Characterization of Friction Stir Welded Tubes by Means of Tube Bulge Test

    Science.gov (United States)

    D'Urso, G.; Longo, M.; Giardini, C.

    2011-05-01

    Mechanical properties of friction stir welded joints are generally evaluated by means of conventional tensile test. This testing method might provide insufficient information because maximum strain obtained in tensile test before necking is small; moreover, the application of tensile test is limited when the joint path is not linear or even when the welds are executed on curved surfaces. Therefore, in some cases, it would be preferable to obtain the joints properties from other testing methods. Tube bulge test can be a valid solution for testing circumferential or longitudinal welds executed on tubular workpieces. The present work investigates the mechanical properties and the formability of friction stir welded tubes by means of tube bulge tests. The experimental campaign was performed on tubular specimens having a thickness of 3 mm and an external diameter of 40 mm, obtained starting from two semi-tubes longitudinally friction stir welded. The first step, regarding the fabrication of tubes, was performed combining a conventional forming process and friction stir welding. Sheets in Al-Mg-Si-Cu alloy AA6060 T6 were adopted for this purpose. Plates having a dimension of 225×60 mm were bent (with a bending axis parallel to the main dimension) in order to obtain semi-tubes. A particular care was devoted to the fabrication of forming devices (punch and die) in order to minimize the springback effects. Semi-tubes were then friction stir welded by means of a CNC machine tool. Some preliminary tests were carried out by varying the welding parameters, namely feed rate and rotational speed. A very simple tool having flat shoulder and cylindrical pin was used. The second step of the research was based on testing the welded tubes by means of tube bulge test. A specific equipment having axial actuators with a conical shape was adopted for this study. Some analyses were carried out on the tubes bulged up to a certain pressure level. In particular, the burst pressure and the

  19. Weldability of AISI 304 to copper by friction welding

    Energy Technology Data Exchange (ETDEWEB)

    Kirik, Ihsan [Batman Univ. (Turkey); Balalan, Zulkuf [Firat Univ., Elazig (Turkey)

    2013-06-01

    Friction welding is a solid-state welding method, which can join different materials smoothly and is excessively used in manufacturing industry. Friction welding method is commonly used in welding applications of especially cylindrical components, pipes and materials with different properties, for which other welding methods remain incapable. AISI 304 stainless steel and a copper alloy of 99.6 % purity were used in this study. This couple was welded in the friction welding machine. After the welding process, samples were analyzed macroscopically and microscopically, and their microhardness was measured. Tensile test was used to determine the bond strength of materials that were joined using the friction welding method. At the end of the study, it was observed that AISI 304 stainless steel and copper could be welded smoothly using the friction welding method and the bond strength is close to the tensile strength of copper. (orig.)

  20. Influence of shear velocity on frictional characteristics of rock surface

    Indian Academy of Sciences (India)

    T N Singh; A K Verma; Tanmay Kumar; Avi Dutt

    2011-02-01

    Understanding the fundamental issues related with the effect of shear velocity on frictional characteristics at the interface of rock surfaces is an important issue. In this paper, strain-rate dependence on friction is investigated in relation to sliding behaviour under normal load. The phenomenon of stick-slip of granite and shaly sandstone with a tribometer at constant rate of strain under normal loads was observed. Friction at the interface of the rock samples was developed by increasing shear strain at a constant rate by applying constant velocity using the tribometer. For shaly sandstone, state parameters ( and ) played a major role in determining the friction values and roughness of the contact surfaces as well. Higher values of for shaly sandstone may be attributed to the fact that its surface had a greater number of pronounced asperities. Rubbing between the surfaces does not mean that surface becomes smoother. This is because of variation of friction between surfaces.

  1. Method for Investigation of Frictional Properties at Impact Loading

    Science.gov (United States)

    Sundin, K. G.; Åhrström, B. O.

    1999-05-01

    In the assessment of lubricant performance and also in various other contact applications it is of importance to know the frictional qualities of a surface. Under quasi-static conditions, normal and frictional forces are measured using force transducers but the task is more difficult when loads are transient. The experimental method presented in this paper is based on the analysis of propagating waves in a beam, due to an impact on the end surface. The impact is oblique and therefore a transverse as well as a normal force is generated. The normal force history is measured from the axial non-dispersive wave using strain gauges. Transverse force and bending moment both generate dispersive flexural waves. From the FFT of two transverse acceleration histories, the frictional force at the end of the rod is evaluated using beam theory. The relation between normal and frictional force histories displays the frictional properties at the impact. Preliminary results are presented.

  2. Friction Modelling In Connection With Cold Forming Processes

    DEFF Research Database (Denmark)

    Tan, Xincai

    soap or molybdenum disulphide. As processes testing friction sensitive flow, the ring-compression tests and the double cup extrusion tests are carried out. An absolute constant friction model has been proposed to separate the influence of strain hardening from friction. This model has been applied...... in the FEM analyses of the process tests. In the simulative testing, the compression-twist tests in open die and closed die are carried out to measure friction stress directly at varying normal pressure, surface expansion, sliding length and tool temperature etc. It is found that normal pressure...... differences in the results. New empirical friction models have therefore been developed, based on the results of the simulative tests. Applying these models in the FEM simulations shows that they are acceptable for direct applications. In direct process testing, the forward rod extrusion test is investigated...

  3. A review of dynamics modelling of friction draft gear

    Science.gov (United States)

    Wu, Qing; Cole, Colin; Luo, Shihui; Spiryagin, Maksym

    2014-06-01

    Longer and heavier trains mean larger in-train forces and more complicated force patterns. Practical experience indicates that the development of fatigue failure of coupling systems in long heavy trains may differ from conventional understanding. The friction-type draft gears are the most widely used draft gears. The ever developing heavy haul transport environment requires further or new understanding of friction draft gear behaviour and its implications for train dynamics as well as fatigue damage of rolling stock. However, modelling of friction draft gears is a highly nonlinear question. Especially the poor predictability, repeatability and the discontinuity of friction make this task more challenging. This article reviews current techniques in dynamics modelling of friction draft gears to provide a starting point that can be used to improve existing or develop new models to achieve more accurate force amplitude and pattern predictions.

  4. On Sliding Friction of PEEK Based Composite Coatings

    Institute of Scientific and Technical Information of China (English)

    H. Liao; G. Zhang; C. Mateus; H. Li; C. Coddet

    2004-01-01

    Polyetheretherketone (PEEK) based composite materials become of great interest to applications as bearing and slider materials due to their excellent tribological performance. In present work, graphite and MoS2 (7%, wt) filled PEEK coatings were prepared using serigraph technique. Employing a uniform design experiment, the friction behavior of the composite coatings was systematically investigated under dry sliding conditions on a ball-on-disc arrangement. The evolution mechanism of coating friction coefficient was discussed. Correlation of coatings friction coefficient with sliding velocity and applied load was accomplished usingstepwise regression method. The results indicate that friction coefficients of PEEK + MoS2 and PEEK + graphite coating decrease while increasing applied load. Moreover, friction coefficient of PEEK + MoS2 coating increases with increasing sliding velocity.

  5. On Sliding Friction of PEEK Based Composite Coatings

    Institute of Scientific and Technical Information of China (English)

    H.Liao; G.Zhang; C.Mateus; H.Li; C.Coddet

    2004-01-01

    Polyetheretherketone (PEEK) based composite materials become of great interest to applications as bearing and slider materials due to their excellent tribological performance. In present work, graphite and MoS2(7%,wt) filled PEEK coatings were prepared using serigraph technique. Employing a uniform design experiment, the friction behavior of the composite coatings was systematically investigated under dry sliding conditions on a ball-on-disc arrangement. The evolution mechanism of coating friction coefficient was discussed. Correlation of coatings friction coefficient with sliding velocity and applied load was accomplished using stepwise regression method. The results indicate that friction coefficients of PEEK+MoS2 and PEEK+graphite coating decrease while increasing applied load. Moreover, friction coefficient of PEEK+MoS2 coating increases with increasing sliding velocity.

  6. Measurement of Normal and Friction Forces in a Rolling Process

    DEFF Research Database (Denmark)

    Henningsen, Poul; Arentoft, Mogens; Wanheim, Tarras

    2004-01-01

    For the rolling process, knowledge about interface conditions is important since it directly influences the maximum reduction ratio and thereby the num-ber of steps required for a given reduction. The mechanical properties of the produced sheet and the surface quality of it are also influenced...... by the fric-tion conditions. To achieve this important informa-tion, measurements of the normal pressure and friction stresses in the deformation zone are re-quested. The direction of the friction stresses is changing during the rolling gap. At the entrance of the de-formation zone, the peripherical velocity...... of the roll is higher than for the incoming material, which causes frictional stresses at the material acting in the rolling direction. At the outlet of the rolling gap, the velocity of the deformed material exceeds the velocity of the roll, generating frictional stresses contrary to the direction of rolling...

  7. Friction behavior of Al-Cu-Fe-B polycrystalline quasicrystals

    Institute of Scientific and Technical Information of China (English)

    周细应; 李培耀; 罗军明; 钱士强; 童建华

    2004-01-01

    Dry sliding friction between the polycrystalline Al59 Cu25.5 Fe12.5 B3 quasicrystals(QCs) and coating of thediamond-like carbon(DLC) was carried out by self-made tribometer under different conditions. The influences of four parameters(temperature, sliding velocity, applied load, atmosphere) on friction of quasicrystal surface were studied. Microstructure of quasicrystal, morphology of worn surface, and wear debris were observed by scanning electron microscope(SEM). The results show that for QCs, the friction coefficient and the roughness of worn surface is influenced by the parameters, especially greatly by the temperature. With increasing the applied load and sliding velocity, the friction coefficient decreases. The dominant wear mechanism at 350 ℃ is delamination for QCs. The cracks forms on the worn surface during friction. Moreover, phase transformation is not observed on worn surface of QCs at 350 ℃.

  8. Friction Properties of Bio-mimetic Nano-fibrillar Arrays

    Institute of Scientific and Technical Information of China (English)

    CHEN Shao-Hua; MI Chun-Hui

    2009-01-01

    Nano-fibrillar arrays are fabricated using polystyrene materials. The average diameter of each fiber is about 300 nm.Experiments show that such a fibrillar surface possesses a relatively hydrophobic feature with a water contact angle of 142°.Nanoscale friction properties are mainly focused on.It is found that the friction force of polystyrene nano-fibrillar surfaces is obviously enhanced in contrast to polystyrene smooth surfaces.The apparent coefficient of friction increases with the applied load, but is independent of the scanning speed.An interesting observation is that the friction force increases almost linearly with the real contact area, which abides by the fundamental Bowden-Tabor law of nano-scale friction.

  9. Effect of friction on the motion of plasma filaments

    DEFF Research Database (Denmark)

    Garcia, Odd Erik; Madsen, Jens; Naulin, Volker

    is influenced by the collisional friction with the neutral gas fluid. In magnetically confined plasmas, the motion of filamentary structures in the edge region can be influenced by parallel dynamics in a manner that resembles an effective friction. In the presence of strong ballooning, such a frictional...... response may take place in both the electrostatic and the electromagnetic regimes. Results are presented from two-dimensional numerical simulations of an isolated blob structure in a non-uniform magnetic field [1,2]. The effect of a linear damping term in the vorticity equation, which describes...... an effective friction, is investigated. In the inertial regime the radial filament velocity scales as the square root of its size. In the limit of strong friction regime the velocity scales as the inverse of the structure size. A discussion of these results will be given in the context of irregularities...

  10. Friction Compensation in the Upsetting of Cylindrical Test Specimens

    DEFF Research Database (Denmark)

    Christiansen, Peter; Martins, P. A. F.; Bay, Niels Oluf

    2016-01-01

    This manuscript presents a combined numerical andexperimental methodology for determining the stress-straincurve of metallic materials from the measurements of forceand displacement obtained in the axial compression of cylindrical test specimens with friction between the specimens and the platens...... model or combined friction models are utilized .Experimental results obtained from cylindrical and Rastegaev test specimens with different lubricants combined with the experimental determination of friction by means of ring compression tests allows compensating the effect of friction...... in the determination of the material flow curve. Comparison with the flow curves determined without friction compensation shows the viability of the proposed methodology. The proposed methodology is a simple and effective alternative to other solutions available in the literature and the pseudo-code supplied inthe...

  11. Friction measurement in MEMS using a new test structure

    Energy Technology Data Exchange (ETDEWEB)

    Crozier, B.T.; De Boer, M.P.; Redmond, J.M.; Bahr, D.F.; Michalske, T.A.

    1999-12-09

    A MEMS test structure capable of measuring friction between polysilicon surfaces under a variety of test conditions has been refined from previous designs. The device is applied here to measuring friction coefficients of polysilicon surfaces under different environmental, loading, and surface conditions. Two methods for qualitatively comparing friction coefficients ({mu}) using the device are presented. Samples that have been coated with a self-assembled monolayer of the lubricating film perfluorinated-decyltrichorosilane (PFTS) have a coefficient of friction that is approximately one-half that of samples dried using super-critical CO{sub 2} (SCCO{sub 2}) drying. Qualitative results indicate that {mu} is independent of normal pressure. Wear is shown to increase {mu} for both supercritically dried samples and PFTS coated samples, though the mechanisms appear to be different. Super critically dried surfaces appear to degrade continuously with increased wear cycles, while PFTS coated samples reach a steady state friction value after about 10{sup 4} cycles.

  12. Friction Coefficient of UHMWPE During Dry Reciprocating Sliding

    Directory of Open Access Journals (Sweden)

    F. Zivic

    2014-09-01

    Full Text Available This paper deals with the friction coefficient behaviour during dry reciprocating sliding of UHMWPE in contact with alumina (Al2O3, within a range of velocities typical for hip implants. Five values of normal force (100 - 1000 mN and three values of sliding speed (4 - 12 mm/s have been observed. Real time diagrams of the friction coefficient as a function of the sliding cycles were recorded for each test. Dynamic friction coefficient curves exhibited rather uniform behavior for all test conditions. Somewhat larger values of friction coefficient could be observed during the running-in period in case of low loads (100 - 250 mN and the lowest velocity (4 mm/s. In case of high loads and speeds, friction coefficient reached steady state values shortly after the beginning of the test.

  13. The behaviour of molybdenum dialkyldithiocarbamate friction modifier additives

    CERN Document Server

    Graham, J C H

    2001-01-01

    In recent years there has been growing concern to produce energy-efficient lubricated components and modem engine oil specifications require lubricants to demonstrate fuel efficiency in standardised engine tests. One important method of producing low friction and thus fuel-efficient lubricants is to use oil-soluble, molybdenum-containing, friction modifier additives. In optimal conditions these additives are able to produce very low friction coefficients, in the range 0.045 to 0.075 in boundary lubrication conditions. Very little is known about the chemical and physical mechanisms by which oil soluble molybdenum additives form low friction films in tribological contacts. Information about their activity could lead to optimal use of these additives in lubricants and, therefore, more efficient engine running. The work outlined in this thesis investigated the behaviour of oil-soluble molybdenum additives and showed that these additives were able to effectively reduce friction in the absence of other additives su...

  14. Advanced walling systems

    CSIR Research Space (South Africa)

    De Villiers, A

    2010-01-01

    Full Text Available The question addressed by this chapter is: How should advanced walling systems be planned, designed, built, refurbished, and end their useful lives, to classify as smart, sustainable, green or eco-building environments?...

  15. Static and kinetic friction characteristics of nanowire on different substrates

    Science.gov (United States)

    Kim, Hyun-Joon; Nguyen, Gia Hau; Ky, Dinh Le Cao; Tran, Da Khoa; Jeon, Ki-Joon; Chung, Koo-Hyun

    2016-08-01

    Friction characteristics of nanowires (NWs), which may be used as building blocks for nano-devices, are crucial, especially for cases where contact sliding occurs during the device operation. In this work, the static and kinetic friction characteristics of oxidized Si NWs deposited on thermally grown SiO2 and chemical vapor-deposited single layer graphene were investigated using an atomic force microscope (AFM). Kinetic friction between the oxidized Si NWs and the substrates was directly measured by the AFM. Static friction was also obtained from the most bent state of the NWs using the individually determined elastic moduli of the NWs from kinetic friction experiments based on elastic beam theory. Furthermore, the shear stress between the oxidized Si NWs and the substrates was estimated based on adhesive contact theory. It was found that both static and kinetic friction increased as the radius of the NWs increased. The friction of the oxidized Si NWs on the graphene substrate was found to be smaller than that on the SiO2 substrate, which suggests that chemical vapor-deposited graphene can be used as a lubricant or as a protective layer in nano-devices to reduce friction. The shear stress estimated from the kinetic friction data between the oxidized Si NWs and the SiO2 substrate ranged from 7.5 to 12.3 MPa while that between the oxidized Si NWs and the graphene substrate ranged from 4.7 to 7.0 MPa. The result also indicated that the dependence of shear stress on the radius of the NWs was not significant. These findings may provide insight into the friction characteristics of NWs.

  16. Dynamic non-equilibrium wall-modeling for large eddy simulation at high Reynolds numbers

    Science.gov (United States)

    Kawai, Soshi; Larsson, Johan

    2013-01-01

    A dynamic non-equilibrium wall-model for large-eddy simulation at arbitrarily high Reynolds numbers is proposed and validated on equilibrium boundary layers and a non-equilibrium shock/boundary-layer interaction problem. The proposed method builds on the prior non-equilibrium wall-models of Balaras et al. [AIAA J. 34, 1111-1119 (1996)], 10.2514/3.13200 and Wang and Moin [Phys. Fluids 14, 2043-2051 (2002)], 10.1063/1.1476668: the failure of these wall-models to accurately predict the skin friction in equilibrium boundary layers is shown and analyzed, and an improved wall-model that solves this issue is proposed. The improvement stems directly from reasoning about how the turbulence length scale changes with wall distance in the inertial sublayer, the grid resolution, and the resolution-characteristics of numerical methods. The proposed model yields accurate resolved turbulence, both in terms of structure and statistics for both the equilibrium and non-equilibrium flows without the use of ad hoc corrections. Crucially, the model accurately predicts the skin friction, something that existing non-equilibrium wall-models fail to do robustly.

  17. Comparative evaluation of frictional characteristics of coated low friction ligatures - Super Slick Ties™ with conventional uncoated ligatures

    Directory of Open Access Journals (Sweden)

    Deepu Leander

    2011-01-01

    Conclusions: SST produced lower levels of friction (11% for all archwire materials when compared to conventional uncoated ligatures (Dispense-A-Stix and both conventional uncoated ligatures and coated ligatures gave a rank order of coefficient of kinetic friction (μkf among archwires, with stainless steel archwires exhibiting the least and TMA TM showing the highest.

  18. Conducting Wall Hall Thrusters

    Science.gov (United States)

    Goebel, Dan M.; Hofer, Richard R.; Mikellides, Ioannis G.; Katz, Ira; Polk, James E.; Dotson, Brandon

    2013-01-01

    A unique configuration of the magnetic field near the wall of Hall thrusters, called Magnetic Shielding, has recently demonstrated the ability to significantly reduce the erosion of the boron nitride (BN) walls and extend the life of Hall thrusters by orders of magnitude. The ability of magnetic shielding to minimize interactions between the plasma and the discharge chamber walls has for the first time enabled the replacement of insulating walls with conducting materials without loss in thruster performance. The boron nitride rings in the 6 kW H6 Hall thruster were replaced with graphite that self-biased to near the anode potential. The thruster efficiency remained over 60% (within two percent of the baseline BN configuration) with a small decrease in thrust and increase in Isp typical of magnetically shielded Hall thrusters. The graphite wall temperatures decreased significantly compared to both shielded and unshielded BN configurations, leading to the potential for higher power operation. Eliminating ceramic walls makes it simpler and less expensive to fabricate a thruster to survive launch loads, and the graphite discharge chamber radiates more efficiently which increases the power capability of the thruster compared to conventional Hall thruster designs.

  19. Creep motion of a model frictional system

    CERN Document Server

    Blanc, Baptiste; Géminard, Jean-Christophe

    2011-01-01

    We report on the dynamics of a model frictional system submitted to minute external perturbations. The system consists of a chain of sliders connected through elastic springs that rest on an incline. By introducing cyclic expansions and contractions of the springs we observe a reptation of the chain. We account for the average reptation velocity theoretically. The velocity of small systems exhibits a series of plateaus as a function of the incline angle. Due to elastic e ects, there exists a critical amplitude below which the reptation is expected to cease. However, rather than a full stop of the creep, we observe in numerical simulations a transition between a continuous-creep and an irregular-creep regime when the critical amplitude is approached. The latter transition is reminiscent of the transition between the continuous and the irregular compaction of granular matter submitted to periodic temperature changes.

  20. Frictional granular mechanics: A variational approach

    Energy Technology Data Exchange (ETDEWEB)

    Holtzman, R.; Silin, D.B.; Patzek, T.W.

    2009-10-16

    The mechanical properties of a cohesionless granular material are evaluated from grain-scale simulations. Intergranular interactions, including friction and sliding, are modeled by a set of contact rules based on the theories of Hertz, Mindlin, and Deresiewicz. A computer generated, three-dimensional, irregular pack of spherical grains is loaded by incremental displacement of its boundaries. Deformation is described by a sequence of static equilibrium configurations of the pack. A variational approach is employed to find the equilibrium configurations by minimizing the total work against the intergranular loads. Effective elastic moduli are evaluated from the intergranular forces and the deformation of the pack. Good agreement between the computed and measured moduli, achieved with no adjustment of material parameters, establishes the physical soundness of the proposed model.