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Sample records for static friction kinetic

  1. Comments on Static vs Kinetic Friction

    NASA Astrophysics Data System (ADS)

    Kessler, Gabriel

    2009-09-01

    I'm writing to comment on the article published in the March edition of The Physics Teacher titled "Choose Wisely: Static or Kinetic Friction—The Power of Dimensionless Plots." As I was reading the article, something caught my eye that I couldn't reconcile with. It was the phrase on page 160 in the first column near the bottom. The statement was that the experimental value for the coefficient of kinetic friction was "unexpectedly greater than the coefficient of static friction!"

  2. Static and kinetic friction of granite at high normal stress

    USGS Publications Warehouse

    Byerlee, J.D.

    1970-01-01

    Frictional sliding on ground surfaces of granite, angle of sliding planes 30?? and 45??, was investigated as a function of confining pressure. Over the normal stress range of 2-12 kb, the static frictional shear stress ??s follows the relationship ??s = 0??5 + 0?? ??n and the kinetic frictional shear stress ??k was calculated to be ??k = 0??25 + 0??47 ??n. ?? 1970.

  3. Static and kinetic friction characteristics of nanowire on different substrates

    NASA Astrophysics Data System (ADS)

    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.

  4. Choose Wisely: Static or Kinetic Friction--The Power of Dimensionless Plots

    ERIC Educational Resources Information Center

    Ludwigsen, Daniel; Svinarich, Kathryn

    2009-01-01

    Consider a problem of sliding blocks, one stacked atop the other, resting on a frictionless table. If the bottom block is pulled horizontally, nature makes a choice: if the applied force is small, static friction between the blocks accelerates the blocks together, but with a large force the blocks slide apart. In that case, kinetic friction still…

  5. Choose Wisely: Static or Kinetic Friction-The Power of Dimensionless Plots

    NASA Astrophysics Data System (ADS)

    Ludwigsen, Daniel; Svinarich, Kathryn

    2009-03-01

    Consider a problem of sliding blocks, one stacked atop the other, resting on a frictionless table. If the bottom block is pulled horizontally, nature makes a choice: if the applied force is small, static friction between the blocks accelerates the blocks together, but with a large force the blocks slide apart. In that case, kinetic friction still forces the upper block forward but with less acceleration than the lower block. The choice, then, lies in the relative terms—what is meant by small and large? After a confusing experience during a recent exam, we've found a demonstration and graphical presentation that can help clarify the distinction between static and kinetic friction.

  6. Static and kinetic friction force and surface roughness of different archwire-bracket sliding contacts.

    PubMed

    Carrion-Vilches, Francisco J; Bermudez, María-Dolores; Fructuoso, Paula

    2015-01-01

    The aim of this study was to determine the static and kinetic friction forces of the contact bracket-archwire with different dental material compositions in order to select those materials with lower resistance to sliding. We carried out sliding friction tests by means of a universal testing machine following an experimental procedure as described in ASTM D1894 standard. We determined the static and kinetic friction forces under dry and lubricating conditions using an artificial saliva solution at 36.5ºC. The bracket-archwire pairs studied were: stainless steel-stainless steel; stainless steel-glass fiber composite; stainless steel-Nitinol 60; sapphire-stainless steel; sapphire-glass fiber composite; and sapphire-Nitinol 60. The best performance is obtained for Nitinol 60 archwire sliding against a stainless steel bracket, both under dry and lubricated conditions. These results are in agreement with the low surface roughness of Nitinol 60 with respect to the glass fiber composite archwire. The results described here contribute to establishing selection criteria for materials for dental archwire-brackets. PMID:26438988

  7. Size Scaling of Static Friction

    NASA Astrophysics Data System (ADS)

    Braun, O. M.; Manini, Nicola; Tosatti, Erio

    2013-02-01

    Sliding friction across a thin soft lubricant film typically occurs by stick slip, the lubricant fully solidifying at stick, yielding and flowing at slip. The static friction force per unit area preceding slip is known from molecular dynamics (MD) simulations to decrease with increasing contact area. That makes the large-size fate of stick slip unclear and unknown; its possible vanishing is important as it would herald smooth sliding with a dramatic drop of kinetic friction at large size. Here we formulate a scaling law of the static friction force, which for a soft lubricant is predicted to decrease as fm+Δf/Aγ for increasing contact area A, with γ>0. Our main finding is that the value of fm, controlling the survival of stick slip at large size, can be evaluated by simulations of comparably small size. MD simulations of soft lubricant sliding are presented, which verify this theory.

  8. PEBBLES Simulation of Static Friction and New Static Friction Benchmark

    SciTech Connect

    Joshua J. Cogliati; Abderrafi M. Ougouag

    2010-05-01

    Pebble bed reactors contain large numbers of spherical fuel elements arranged randomly. Determining the motion and location of these fuel elements is required for calculating certain parameters of pebble bed reactor operation. This paper documents the PEBBLES static friction model. This model uses a three dimensional differential static friction approximation extended from the two dimensional Cundall and Strack model. The derivation of determining the rotational transformation of pebble to pebble static friction force is provided. A new implementation for a differential rotation method for pebble to container static friction force has been created. Previous published methods are insufficient for pebble bed reactor geometries. A new analytical static friction benchmark is documented that can be used to verify key static friction simulation parameters. This benchmark is based on determining the exact pebble to pebble and pebble to container static friction coefficients required to maintain a stable five sphere pyramid.

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

    ERIC Educational Resources Information Center

    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…

  10. Device measures static friction of magnetic tape

    NASA Technical Reports Server (NTRS)

    Cole, P. T.

    1967-01-01

    Device measures the coefficient of static friction of magnetic tape over a range of temperatures and relative humidities. It uses a strain gage to measure the force of friction between a reference surface and the tape drawn at a constant velocity of approximately 0.0001 inch per second relative to the reference surface.

  11. The Static Ladder Problem with Two Sources of Friction

    ERIC Educational Resources Information Center

    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…

  12. Novel Friction Law for the Static Friction Force based on Local Precursor Slipping

    PubMed Central

    Katano, Yu; Nakano, Ken; Otsuki, Michio; Matsukawa, Hiroshi

    2014-01-01

    The sliding of a solid object on a solid substrate requires a shear force that is larger than the maximum static friction force. It is commonly believed that the maximum static friction force is proportional to the loading force and does not depend on the apparent contact area. The ratio of the maximum static friction force to the loading force is called the static friction coefficient µM, which is considered to be a constant. Here, we conduct experiments demonstrating that the static friction force of a slider on a substrate follows a novel friction law under certain conditions. The magnitude of µM decreases as the loading force increases or as the apparent contact area decreases. This behavior is caused by the slip of local precursors before the onset of bulk sliding and is consistent with recent theory. The results of this study will develop novel methods for static friction control. PMID:25205283

  13. Static friction between rigid fractal surfaces

    NASA Astrophysics Data System (ADS)

    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. Determination of the static friction coefficient from circular motion

    NASA Astrophysics Data System (ADS)

    Molina-Bolívar, J. A.; Cabrerizo-Vílchez, M. A.

    2014-07-01

    This paper describes a physics laboratory exercise for determining the coefficient of static friction between two surfaces. The circular motion of a coin placed on the surface of a rotating turntable has been studied. For this purpose, the motion is recorded with a high-speed digital video camera recording at 240 frames s-1, and the videos are analyzed using Tracker video-analysis software, allowing the students to dynamically model the motion of the coin. The students have to obtain the static friction coefficient by comparing the centripetal and maximum static friction forces. The experiment only requires simple and inexpensive materials. The dynamics of circular motion and static friction forces are difficult for many students to understand. The proposed laboratory exercise addresses these topics, which are relevant to the physics curriculum.

  15. Static Friction Unsung Hero of Everyday Introductory Biomechanics

    NASA Astrophysics Data System (ADS)

    Beverly, Nancy

    2006-12-01

    The ability of static friction to accelerate systems does not usually get the attention it deserves in introductory physics. Everyday human contexts abound in our grasp of objects to move them, in our being moved as passengers, and in our own locomotion. Student laboratory, classroom and homework activities have been developed which enable students to explore the vital role of static friction in various biomechanical contexts. Examples will be demonstrated.

  16. Slipping and Tipping: Measuring Static Friction with a Straightedge

    ERIC Educational Resources Information Center

    Dietz, Eric; Aguilar, Isaac

    2012-01-01

    Following a discussion of forces, torques, and the conditions for static equilibrium, I tell my introductory mechanics class that I will show them how to measure the coefficient of static friction, us, between the surfaces of a block and the front bench using "nothing but a straightedge". After a few seconds of hushed anticipation, I nudge the…

  17. Static friction between silicon nanowires and elastomeric substrates.

    PubMed

    Qin, Qingquan; Zhu, Yong

    2011-09-27

    This paper reports the first direct measurements of static friction force and interfacial shear strength between silicon (Si) nanowires (NWs) and poly(dimethylsiloxane) (PDMS). A micromanipulator is used to manipulate and deform the NWs under a high-magnification optical microscope in real time. The static friction force is measured based on "the most-bent state" of the NWs. The static friction and interface shear strength are found to depend on the ultraviolet/ozone (UVO) treatment of PDMS. The shear strength starts at 0.30 MPa without UVO treatment, increases rapidly up to 10.57 MPa at 60 min of treatment and decreases for longer treatment. Water contact angle measurements suggest that the UVO-induced hydrophobic-to-hydrophilic conversion of PDMS surface is responsible for the increase in the static friction, while the hydrophobic recovery effect contributes to the decrease. The static friction between NWs and PDMS is of critical relevance to many device applications of NWs including NW-based flexible/stretchable electronics, NW assembly and nanocomposites (e.g., supercapacitors). Our results will enable quantitative interface design and control for such applications. PMID:21815652

  18. Determination of the Static Friction Coefficient from Circular Motion

    ERIC Educational Resources Information Center

    Molina-Bolívar, J. A.; Cabrerizo-Vílchez, M. A.

    2014-01-01

    This paper describes a physics laboratory exercise for determining the coefficient of static friction between two surfaces. The circular motion of a coin placed on the surface of a rotating turntable has been studied. For this purpose, the motion is recorded with a high-speed digital video camera recording at 240 frames s[superscript-1], and the…

  19. Single-asperity friction during quasi-static sliding

    NASA Astrophysics Data System (ADS)

    Sharp, Tristan; Pastewka, Lars; Robbins, Mark

    2015-03-01

    The static friction of an asperity is investigated using atomic-scale simulations. We explore scale effects by varying the sphere radius R and the contact radius a from nanometers to micrometers. We first consider commensurate contact between bare lattices with repulsive interactions across the interface. In small contacts, all contacting atoms move coherently and the friction coefficient μ is independent of contact radius and load. In larger contacts, interfacial slip is mediated by localized dislocations, and the static friction coefficient μ ~ (Ra0/a2) 2 / 3 , where a0 is the nearest-neighbor spacing. In very large contacts μ stops decreasing and begins to increase with a, at fixed R. The results are in sharp contrast to Cattaneo-Mindlin continuum theory where μ is independent of contact size. Separate simulations are performed to connect the results to the dislocation-based models of contact-size effects due to Hurtado and Kim, and Gao, which assume adhesive interactions between surfaces and find μ ~ (a0/a)1/2. Simulations for incommensurate contacts show a transition from superlubricity for rigid contacts to a finite friction associated with the Peierls stress in very large contacts. Support from: DMR-1006805; NSF IGERT-0801471; OCI-0963185; CMMI-0923018

  20. Static and Dynamic Friction Behavior of Candidate High Temperature Airframe Seal Materials

    NASA Technical Reports Server (NTRS)

    Dellacorte, C.; Lukaszewicz, V.; Morris, D. E.; Steinetz, B. M.

    1994-01-01

    The following report describes a series of research tests to evaluate candidate high temperature materials for static to moderately dynamic hypersonic airframe seals. Pin-on-disk reciprocating sliding tests were conducted from 25 to 843 C in air and hydrogen containing inert atmospheres. Friction, both dynamic and static, was monitored and serves as the primary test measurement. In general, soft coatings lead to excessive static friction and temperature affected friction in air environments only.

  1. Universal Aging Mechanism for Static and Sliding Friction of Metallic Nanoparticles

    NASA Astrophysics Data System (ADS)

    Feldmann, Michael; Dietzel, Dirk; Tekiel, Antoni; Topple, Jessica; Grütter, Peter; Schirmeisen, André

    2016-07-01

    The term "contact aging" refers to the temporal evolution of the interface between a slider and a substrate usually resulting in increasing friction with time. Current phenomenological models for multiasperity contacts anticipate that such aging is not only the driving force behind the transition from static to sliding friction, but at the same time influences the general dynamics of the sliding friction process. To correlate static and sliding friction on the nanoscale, we show experimental evidence of stick-slip friction for nanoparticles sliding on graphite over a wide dynamic range. We can assign defined periods of aging to the stick phases of the particles, which agree with simulations explicitly including contact aging. Additional slide-hold-slide experiments for the same system allow linking the sliding friction results to static friction measurements, where both friction mechanisms can be universally described by a common aging formalism.

  2. Universal Aging Mechanism for Static and Sliding Friction of Metallic Nanoparticles.

    PubMed

    Feldmann, Michael; Dietzel, Dirk; Tekiel, Antoni; Topple, Jessica; Grütter, Peter; Schirmeisen, André

    2016-07-01

    The term "contact aging" refers to the temporal evolution of the interface between a slider and a substrate usually resulting in increasing friction with time. Current phenomenological models for multiasperity contacts anticipate that such aging is not only the driving force behind the transition from static to sliding friction, but at the same time influences the general dynamics of the sliding friction process. To correlate static and sliding friction on the nanoscale, we show experimental evidence of stick-slip friction for nanoparticles sliding on graphite over a wide dynamic range. We can assign defined periods of aging to the stick phases of the particles, which agree with simulations explicitly including contact aging. Additional slide-hold-slide experiments for the same system allow linking the sliding friction results to static friction measurements, where both friction mechanisms can be universally described by a common aging formalism. PMID:27447515

  3. Slipping and Tipping: Measuring Static Friction with a Straightedge

    NASA Astrophysics Data System (ADS)

    Dietz, Eric; Aguilar, Isaac

    2012-11-01

    Following a discussion of forces, torques, and the conditions for static equilibrium, I tell my introductory mechanics class that I will show them how to measure the coefficient of static friction, μs, between the surfaces of a block and the front bench using nothing but a straightedge. After a few seconds of hushed anticipation, I nudge the block in Fig. 1 (a) gently with the straightedge, applying a horizontal force F that gradually increases from zero to a value that either causes the object to slip (Fs) or to tip (Ft). Which of these happens first depends on μs, the depth D of the block, and on h, the height above the bench surface at which F is applied. Starting at the bottom of the block, it tends to slip before tipping, but there is a critical height hc above which the block tips before slipping. The value of hc at which this transition occurs is then used to produce a value of μs for these surfaces.

  4. Kinetics of a Frictional Granular Motor

    NASA Astrophysics Data System (ADS)

    Talbot, J.; Wildman, R. D.; Viot, P.

    2011-09-01

    Within the framework of a Boltzmann-Lorentz equation, we analyze the dynamics of a granular rotor immersed in a bath of thermalized particles in the presence of a frictional torque on the axis. In numerical simulations of the equation, we observe two scaling regimes at low and high bath temperatures. In the large friction limit, we obtain the exact solution of a model corresponding to asymptotic behavior of the Boltzmann-Lorentz equation. In the limit of large rotor mass and small friction, we derive a Fokker-Planck equation for which the exact solution is also obtained.

  5. Friction in macroscopic thermodynamics: A kinetic point of view

    NASA Astrophysics Data System (ADS)

    Bizarro, João P. S.

    2015-12-01

    To provide a solid support to a macroscopic framework developed to explicitly account for friction in thermodynamics, a kinetic description of frictional dissipation is developed. Using either a dissipative Fokker-Planck equation for Brownian motion or a Boltzmann equation with a friction-force term added, it is shown that both approaches lead to the emergence of the macroscopic thermodynamic relations that state the first and second laws with friction. The analysis is directly applied to the problem of determining the minimum amount of heating generated by memory erasure, known in computer science as Landauer's bound, and leads to a better understanding of the energetics behind the latter. A generalisation of Boltzmann's H theorem to include friction explicitly is also recovered, and the thermodynamics of granular rotators acted by a frictional torque and of radio-frequency (RF) current drive of fusion plasmas, in which collisional drag is present, are addressed as well. Various physics results are revisited employing the first and second laws with friction that have been derived from the appropriate dissipative kinetic equations, lower bounds for entropy production rates being derived both for granular rotators and for RF current drive.

  6. Comparison of static friction with self-ligating, modified slot design and conventional brackets

    PubMed Central

    CASTRO, Raquel Morais; SMITH NETO, Perrin; HORTA, Martinho Campolina Rebello; PITHON, Matheus Melo; OLIVEIRA, Dauro Douglas

    2013-01-01

    Objective To compare the static frictional forces generated at the bracket/wire interface of stainless steel brackets with different geometries and angulations, combined with orthodontic wires of different diameters. Material and Methods The frictional forces were evaluated with three different types of metal brackets: a passive self-ligating (SmartClipTM, 3M/Unitek, Monrovia, USA), with a modified slot design (Mini Uni TwinTM, 3M/Unitek, Monrovia, USA) and conventional (Kirium, Abzil, São José do Rio Preto, Brazil). The samples were mounted in a testing device with three different angulations and tested with 0.014" and 0.018" stainless steel wires (American Orthodontics, Sheboygan, USA). The static frictional force was measured using a universal testing machine (DL 500, EMIC®, São José dos Pinhais, Brazil) with a crosshead speed of 1 mm/min. Statistical analysis was performed by two-way ANOVA followed by Bonferroni's post hoc test. Results There was a significant difference (p<0.05) in static friction when the three types of brackets were tested with the same wire size. The wire diameter influenced friction only when the brackets had a 10º angulation (p<0.05). The angulation influenced friction (p<0.05) when the brackets were associated with a 0.018" wire. Conclusion Brackets with a modified slot design showed intermediate static frictional force values between the conventional and self-ligating brackets tested. PMID:24037069

  7. The effect of substrate roughness on the static friction of CuO nanowires

    NASA Astrophysics Data System (ADS)

    Polyakov, Boris; Vlassov, Sergei; Dorogin, Leonid M.; Kulis, Peteris; Kink, Ilmar; Lohmus, Rynno

    2012-09-01

    The dependence of static friction on surface roughness was measured for copper oxide nanowires on silicon wafers coated with amorphous silicon. The surface roughness of the substrate was varied to different extent by the chemical etching of the substrates. For friction measurements, the nanowires (NWs) were pushed by an atomic-force microscope (AFM) tip at one end of the NW until complete displacement of the NW was achieved. The elastic bending profile of a NW during this manipulation process was used to calculate the ultimate static friction force. A strong dependence of static friction on surface roughness was demonstrated. The real contact area and interfacial shear strength were estimated using a multiple elastic asperity model, which is based on the Derjaguin-Muller-Toporov (DMT) contact mechanics. The model included vertical elastic flexure of NW rested on high asperities due to van der Waals force.

  8. A Tactile Sensor Using Piezoresistive Beams for Detection of the Coefficient of Static Friction

    PubMed Central

    Okatani, Taiyu; Takahashi, Hidetoshi; Noda, Kentaro; Takahata, Tomoyuki; Matsumoto, Kiyoshi; Shimoyama, Isao

    2016-01-01

    This paper reports on a tactile sensor using piezoresistive beams for detection of the coefficient of static friction merely by pressing the sensor against an object. The sensor chip is composed of three pairs of piezoresistive beams arranged in parallel and embedded in an elastomer; this sensor is able to measure the vertical and lateral strains of the elastomer. The coefficient of static friction is estimated from the ratio of the fractional resistance changes corresponding to the sensing elements of vertical and lateral strains when the sensor is in contact with an object surface. We applied a normal force on the sensor surface through objects with coefficients of static friction ranging from 0.2 to 1.1. The fractional resistance changes corresponding to vertical and lateral strains were proportional to the applied force. Furthermore, the relationship between these responses changed according to the coefficients of static friction. The experimental result indicated the proposed sensor could determine the coefficient of static friction before a global slip occurs. PMID:27213374

  9. A Tactile Sensor Using Piezoresistive Beams for Detection of the Coefficient of Static Friction.

    PubMed

    Okatani, Taiyu; Takahashi, Hidetoshi; Noda, Kentaro; Takahata, Tomoyuki; Matsumoto, Kiyoshi; Shimoyama, Isao

    2016-01-01

    This paper reports on a tactile sensor using piezoresistive beams for detection of the coefficient of static friction merely by pressing the sensor against an object. The sensor chip is composed of three pairs of piezoresistive beams arranged in parallel and embedded in an elastomer; this sensor is able to measure the vertical and lateral strains of the elastomer. The coefficient of static friction is estimated from the ratio of the fractional resistance changes corresponding to the sensing elements of vertical and lateral strains when the sensor is in contact with an object surface. We applied a normal force on the sensor surface through objects with coefficients of static friction ranging from 0.2 to 1.1. The fractional resistance changes corresponding to vertical and lateral strains were proportional to the applied force. Furthermore, the relationship between these responses changed according to the coefficients of static friction. The experimental result indicated the proposed sensor could determine the coefficient of static friction before a global slip occurs. PMID:27213374

  10. The effects of static friction and backlash on extended physiological proprioception control of a powered prosthesis.

    PubMed

    Farrell, Todd R; Weir, Richard F; Heckathorne, Craig W; Childress, Dudley S

    2005-01-01

    In general, externally powered prostheses do not provide proprioceptive feedback and thus require the user to rely on cognitively expensive visual feedback to effectively control the prosthesis. Applying the concept of extended physiological proprioception (EPP) to externally powered prostheses provides direct feedback to the user's proprioceptive system regarding the position, velocity, and forces applied to the prosthesis. However, electric elbows with EPP controllers developed at the Northwestern University Prosthetics Research Laboratory have exhibited unexplained "jerky" behavior in both clinical fittings and bench-top operation. In addition, the development of limit cycles, a specific type of constant-amplitude oscillation, had been observed in bench-top use of these elbows. Backlash and static friction within the EPP system were found to be primarily responsible for the development of limit cycles. Reducing static friction and backlash improved the system's performance. These results suggest that to most effectively implement EPP, prosthesis manufacturers should design prosthetic components that minimize static friction and backlash. PMID:16187245

  11. Bridging in grafted layers : Statics and kinetics

    NASA Astrophysics Data System (ADS)

    Johner, A.

    We discuss bridging between a grafted layer and an opposing plate which adsorbs the polymer. The case of end adsorption is considered, as well as the case where all monomers adsorb. We predict that with increasing adsorption an exclusion zone grows in the vicinity of the adsorbing plate, this slows down the kinetics. For end adsorption we study the kinetics and argue that two main processes are involved: the exploration of the brush by a free end and its adsorption through the exclusion zone.

  12. Chemical kinetics computer program for static and flow reactions

    NASA Technical Reports Server (NTRS)

    Bittker, D. A.; Scullin, V. J.

    1972-01-01

    General chemical kinetics computer program for complex gas mixtures has been developed. Program can be used for any homogeneous reaction in either one dimensional flow or static system. It is flexible, accurate, and easy to use. It can be used for any chemical system for which species thermodynamic data and reaction rate constant data are known.

  13. Concurrent parametrization against static and kinetic information leads to more robust coarse-grained force fields

    NASA Astrophysics Data System (ADS)

    Rudzinski, J. F.; Bereau, T.

    2016-07-01

    The parametrization of coarse-grained (CG) simulation models for molecular systems often aims at reproducing static properties alone. The reduced molecular friction of the CG representation usually results in faster, albeit inconsistent, dynamics. In this work, we rely on Markov state models to simultaneously characterize the static and kinetic properties of two CG peptide force fields—one top-down and one bottom-up. Instead of a rigorous evolution of CG dynamics (e.g., using a generalized Langevin equation), we attempt to improve the description of kinetics by simply altering the existing CG models, which employ standard Langevin dynamics. By varying masses and relevant force-field parameters, we can improve the timescale separation of the slow kinetic processes, achieve a more consistent ratio of mean-first-passage times between metastable states, and refine the relative free-energies between these states. Importantly, we show that the incorporation of kinetic information into a structure-based parametrization improves the description of the helix-coil transition sampled by a minimal CG model. While structure-based models understabilize the helical state, kinetic constraints help identify CG models that improve the ratio of forward/backward timescales by effectively hindering the sampling of spurious conformational intermediate states.

  14. Monte Carlo simulations of the static friction between two grafted polymer brushes.

    PubMed

    Mendonça, Ana C F; Goujon, Florent; Malfreyt, Patrice; Tildesley, Dominic J

    2016-02-17

    A configurational bias Monte Carlo method has been developed to study the static friction between grafted polymers immersed in a good solvent. Simple models using the soft quadratic potential from a dissipative particle dynamics study have been used to model polyzwitterionic brushes at physiological pressures (up to 7.5 MPa). Three models of decreasing rigidity have been used to model the friction between the brushes by calculating the tangential component of the pressure induced by a mismatch in the registry of the two grafting surfaces. The static friction coefficient can be calculated for three model systems and the slip between the layers occurs at a much lower values of shear force for the more flexible polymer layer. A moderate increase in the flexibility of the chains reduces the friction coefficient by a factor of ca. 20. Tilting the layer directors of the brushes also increases the static friction between the layer when the top, tilted layer is displaced in the direction away from the tilt. Non-equilibrium dynamics techniques for the same model were performed using dissipative particle dynamics and the limiting extremes of the Stribeck curve corresponding to the boundary lubrication regime and the hydrodynamic lubrication regime were observed for these flat surfaces. As expected, μk is significantly lower than μs for the same system. The dynamical friction coefficients in the model are in good agreement with those observed in the experiment and the ratio of μk/μs of between 0.11 and 0.5 observed in the simulations is in reasonable agreement with the value of 0.5 normally observed for these seen for these systems. PMID:26847471

  15. Development and assessment of atomistic models for predicting static friction coefficients

    NASA Astrophysics Data System (ADS)

    Jahangiri, Soran; Heverly-Coulson, Gavin S.; Mosey, Nicholas J.

    2016-08-01

    The friction coefficient relates friction forces to normal loads and plays a key role in fundamental and applied areas of science and technology. Despite its importance, the relationship between the friction coefficient and the properties of the materials forming a sliding contact is poorly understood. We illustrate how simple relationships regarding the changes in energy that occur during slip can be used to develop a quantitative model relating the friction coefficient to atomic-level features of the contact. The slip event is considered as an activated process and the load dependence of the slip energy barrier is approximated with a Taylor series expansion of the corresponding energies with respect to load. The resulting expression for the load-dependent slip energy barrier is incorporated in the Prandtl-Tomlinson (PT) model and a shear-based model to obtain expressions for friction coefficient. The results indicate that the shear-based model reproduces the static friction coefficients μs obtained from first-principles molecular dynamics simulations more accurately than the PT model. The ability of the model to provide atomistic explanations for differences in μs amongst different contacts is also illustrated. As a whole, the model is able to account for fundamental atomic-level features of μs, explain the differences in μs for different materials based on their properties, and might be also used in guiding the development of contacts with desired values of μs.

  16. Static friction threshold effects on hysteresis and frequency spectra in rocks

    SciTech Connect

    Kadish, A.

    1999-06-01

    Static friction in rocks is modeled as a threshold phenomenon. An inverse problem in ground motion is analyzed for propagation in a medium with an arbitrary number of fractures at which static friction thresholds determine the onset of slippage. It is shown that seismic source dynamics inferred from surface motion is unique. This result is used to show that the threshold property of static friction is not a mechanism for hysteresis in rocks. The coda for the surface motion is shown, in the case of a single fracture and a deep source of finite duration, to be either a periodic function in time, or to asymptote in time to such a function, depending on an algebraic relation between ground and fracture parameters. The fundamental period of the coda is independent of the source time series and is equal to four times the signal transit time between the single fracture and ground surface. Only odd harmonics of the fundamental frequency are present in a Fourier series of these periodic functions. {copyright} {ital 1999 Acoustical Society of America.}

  17. An alternative formulation for quasi-static frictional and cohesive contact problems

    NASA Astrophysics Data System (ADS)

    Areias, P.; Pinto da Costa, A.; Rabczuk, T.; Queirós de Melo, F. J. M.; Dias-da-Costa, D.; Bezzeghoud, Mourad

    2014-04-01

    It is known by Engineering practitioners that quasi-static contact problems with friction and cohesive laws often present convergence difficulties in Newton iteration. These are commonly attributed to the non-smoothness of the equilibrium system. However, non-uniqueness of solutions is often an obstacle for convergence. We discuss these conditions in detail and present a general algorithm for 3D which is shown to have quadratic convergence in the Newton-Raphson iteration even for parts of the domain where multiple solutions exist. Chen-Mangasarian replacement functions remove the non-smoothness corresponding to both the stick-slip and normal complementarity conditions. Contrasting with Augmented Lagrangian methods, second-order updating is performed for all degrees-of-freedom. Stick condition is automatically selected by the algorithm for regions with multiple solutions. The resulting Jacobian determinant is independent of the friction coefficient, at the expense of an increased number of nodal degrees-of-freedom. Aspects such as a dedicated pivoting for constrained problems are also of crucial importance for a successful solution finding. The resulting 3D mixed formulation, with 7 degrees-of-freedom in each node (displacement components, friction multiplier, friction force components and normal force) is tested with representative numerical examples (both contact with friction and cohesive force), which show remarkable robustness and generality.

  18. Friction

    NASA Astrophysics Data System (ADS)

    Matsuo, Yoshihiro; Clarke, Daryl D.; Ozeki, Shinichi

    Friction materials such as disk pads, brake linings, and clutch facings are widely used for automotive applications. Friction materials function during braking due to frictional resistance that transforms kinetic energy into thermal energy. There has been a rudimentary evolution, from materials like leather or wood to asbestos fabric or asbestos fabric saturated with various resins such as asphalt or resin combined with pitch. These efforts were further developed by the use of woven asbestos material saturated by either rubber solution or liquid resin binder and functioned as an internal expanding brake, similar to brake lining system. The role of asbestos continued through the use of chopped asbestos saturated by rubber, but none was entirely successful due to the poor rubber heat resistance required for increased speeds and heavy gearing demands of the automobile industry. The use of phenolic resins as binder for asbestos friction materials provided the necessary thermal resistance and performance characteristics. Thus, the utility of asbestos as the main friction component, for over 100 years, has been significantly reduced in friction materials due to asbestos identity as a carcinogen. Steel and other fibrous components have displaced asbestos in disk pads. Currently, non-asbestos organics are the predominate friction material. Phenolic resins continue to be the preferred binder, and increased amounts are necessary to meet the requirements of highly functional asbestos-free disk pads for the automotive industry. With annual automobile production exceeding 70 million vehicles and additional automobile production occurring in developing countries worldwide and increasing yearly, the amount of phenolic resin for friction material is also increasing (Fig. 14.1). Fig. 14.1 Worldwide commercial vehicle production Reduction in static friction by deposition of a homogeneous diamond-like carbon (DLC) coating on orthodontic brackets.

    PubMed

    Akaike, Shun; Hayakawa, Tohru; Kobayashi, Daishiro; Aono, Yuko; Hirata, Atsushi; Hiratsuka, Masanori; Nakamura, Yoshiki

    2015-01-01

    In orthodontics, a reduction in static friction between the brackets and wire is important to enable easy tooth movement. The aim of this study was to examine the effects of a homogeneous diamond-like carbon (DLC) coating on the whole surfaces of slots in stainless steel orthodontic brackets on reducing the static friction between the brackets and the wire. The DLC coating was characterized using Raman spectroscopy, surface roughness and contact angle measurements, and SEM observations. Rectangular stainless steel and titanium-molybdenum alloy wires with two different sizes were employed, and the static friction between the brackets and wire was measured under dry and wet conditions. The DLC coating had a thickness of approximately 1.0 μm and an amorphous structure was identified. The results indicated that the DLC coating always led to a reduction in static friction. PMID:26632239

  19. Austenite Static Recrystallization Kinetics in Microalloyed B Steels

    NASA Astrophysics Data System (ADS)

    Larrañaga-Otegui, Ane; Pereda, Beatriz; Jorge-Badiola, Denis; Gutiérrez, Isabel

    2016-04-01

    Boron is added to steels to increase hardenability, substituting of more expensive elements. Moreover, B acts as a recrystallization delaying element when it is in solid solution. However, B can interact with N and/or C to form nitrides and carbides at high temperatures, limiting its effect on both phase transformation and recrystallization. On the other hand, other elements like Nb and Ti are added due to the retarding effect that they exert on the austenite softening processes, which results in pancaked austenite grains and refined room microstructures. In B steels, Nb and Ti are also used to prevent B precipitation. However, the complex interaction between these elements and its effect on the austenite microstructure evolution during hot working has not been investigated in detail. The present work is focused on the effect the B exerts on recrystallization when added to microalloyed steels. Although B on its own leads to retarded static recrystallization kinetics, when Nb is added a large delay in the static recrystallization times is observed in the 1273 K to 1373 K (1000 °C to 1100 °C) temperature range. The effect is larger than that predicted by a model developed for Nb-microalloyed steels, which is attributed to a synergistic effect of both elements. However, this effect is not so prominent for Nb-Ti-B steels. The complex effect of the composition on recrystallization kinetics is explained as a competition between the solute drag and precipitation pinning phenomena. The effect of the microalloying elements is quantified, and a new model for the predictions of recrystallization kinetics that accounts for the B and Nb+B synergetic effects is proposed.

  1. Austenite Static Recrystallization Kinetics in Microalloyed B Steels

    NASA Astrophysics Data System (ADS)

    Larrañaga-Otegui, Ane; Pereda, Beatriz; Jorge-Badiola, Denis; Gutiérrez, Isabel

    2016-06-01

    Boron is added to steels to increase hardenability, substituting of more expensive elements. Moreover, B acts as a recrystallization delaying element when it is in solid solution. However, B can interact with N and/or C to form nitrides and carbides at high temperatures, limiting its effect on both phase transformation and recrystallization. On the other hand, other elements like Nb and Ti are added due to the retarding effect that they exert on the austenite softening processes, which results in pancaked austenite grains and refined room microstructures. In B steels, Nb and Ti are also used to prevent B precipitation. However, the complex interaction between these elements and its effect on the austenite microstructure evolution during hot working has not been investigated in detail. The present work is focused on the effect the B exerts on recrystallization when added to microalloyed steels. Although B on its own leads to retarded static recrystallization kinetics, when Nb is added a large delay in the static recrystallization times is observed in the 1273 K to 1373 K (1000 °C to 1100 °C) temperature range. The effect is larger than that predicted by a model developed for Nb-microalloyed steels, which is attributed to a synergistic effect of both elements. However, this effect is not so prominent for Nb-Ti-B steels. The complex effect of the composition on recrystallization kinetics is explained as a competition between the solute drag and precipitation pinning phenomena. The effect of the microalloying elements is quantified, and a new model for the predictions of recrystallization kinetics that accounts for the B and Nb+B synergetic effects is proposed.

  2. Velocity Dependence of the Kinetic Friction of Nanoparticles

    NASA Astrophysics Data System (ADS)

    Dietzel, Dirk; Feldmann, Michael; Schirmeisen, Andre

    2010-03-01

    The velocity dependence of interfacial friction is of high interest to unveil the fundamental processes in nanoscopic friction. So far, different forms of velocity dependence have been observed for contacts between friction force microscope (FFM) tips and a substrate surface. In this work we present velocity-dependent friction measurements performed by nanoparticle manipulation of antimony nanoparticles on atomically flat HOPG substrates under UHV conditions. This allows to analyze interfacial friction for very well defined and clean surface contacts. A novel approach to nanoparticle manipulation, the so called 'tip-on-top' technique [1], made it possible to manipulate the same particle many times while varying the velocity. The antimony particles exhibit a qualitatively different velocity dependence on friction in comparison to direct tip-HOPG contacts. A characteristic change in velocity dependence was observed when comparing freshly prepared particles to contaminated specimen, which were exposed to air before the manipulation experiments. [1] Dietzel et al., Appl. Phys. Lett. 95, 53104 (2009)

  3. Using Models at the Mesoscopic Scale in Teaching Physics: Two Experimental Interventions in Solid Friction and Fluid Statics

    ERIC Educational Resources Information Center

    Besson, Ugo; Viennot, Laurence

    2004-01-01

    This article examines the didactic suitability of introducing models at an intermediate (i.e. mesoscopic) scale in teaching certain subjects, at an early stage. The design and evaluation of two short sequences based on this rationale will be outlined: one bears on propulsion by solid friction, the other on fluid statics in the presence of gravity.…

  4. Experimental Measurement of the Static Coefficient of Friction at the Ti-Ti Taper Connection in Total Hip Arthroplasty.

    PubMed

    Bitter, T; Khan, I; Marriott, T; Schreurs, B W; Verdonschot, N; Janssen, D

    2016-03-01

    The modular taper junction in total hip replacements has been implicated as a possible source of wear. The finite-element (FE) method can be used to study the wear potential at the taper junction. For such simulations it is important to implement representative contact parameters, in order to achieve accurate results. One of the main parameters in FE simulations is the coefficient of friction. However, in current literature, there is quite a wide spread in coefficient of friction values (0.15 - 0.8), which has a significant effect on the outcome of the FE simulations. Therefore, to obtain more accurate results, one should use a coefficient of friction that is determined for the specific material couple being analyzed. In this study, the static coefficient of friction was determined for two types of titanium-on-titanium stem-adaptor couples, using actual cut-outs of the final implants, to ensure that the coefficient of friction was determined consistently for the actual implant material and surface finish characteristics. Two types of tapers were examined, Biomet type-1 and 12/14, where type-1 has a polished surface finish and the 12/14 is a microgrooved system. We found static coefficients of friction of 0.19 and 0.29 for the 12/14 and type-1 stem-adaptor couples, respectively. PMID:26747129

  5. STATIC AND KINETIC SITE-SPECIFIC PROTEIN-DNA PHOTOCROSSLINKING: ANALYSIS OF BACTERIAL TRANSCRIPTION INITIATION COMPLEXES

    PubMed Central

    Naryshkin, Nikolai; Druzhinin, Sergei; Revyakin, Andrei; Kim, Younggyu; Mekler, Vladimir; Ebright, Richard H.

    2009-01-01

    Static site-specific protein-DNA photocrosslinking permits identification of protein-DNA interactions within multiprotein-DNA complexes. Kinetic site-specific protein-DNA photocrosslinking--involving rapid-quench-flow mixing and pulsed-laser irradiation--permits elucidation of pathways and kinetics of formation of protein-DNA interactions within multiprotein-DNA complexes. We present detailed protocols for application of static and kinetic site-specific protein-DNA photocrosslinking to bacterial transcription initiation complexes. PMID:19378179

  6. Static friction force between catalyst layer and micro porous layer and its effect on deformations of membrane electrode assemblies under swelling

    NASA Astrophysics Data System (ADS)

    Uchiyama, Tomoaki; Kumei, Hideyuki; Yoshida, Toshihiko; Ishihara, Kazuhiko

    2014-12-01

    Membrane electrode assemblies (MEAs) composed of a Nafion membrane and heat-transferred catalyst layers (CLs) were employed in this study. The deformation of MEAs between micro porous layers (MPLs)/gas diffusion layers (GDLs) was investigated in response to humidity cycles. The MEA deformed into wrinkle shapes at lower contact pressures and exhibited bulge deformation at higher contact pressures. Wrinkles were generated by large in-plane swelling after buckling when swelling could not be restricted by the friction force from MPLs. Next, the static friction coefficient between the MEA and MPL was measured, and a friction mechanism was investigated. The static friction coefficient was 0.43 at the contact pressure of 0.22 MPa between the MEA and MPL and increased with the increase in the contact pressure. The surface observation of the MPL after the friction test indicated that a static friction was generated by the contact of the convex MPL and flat CL surface. The static friction force and swelling force were calculated to investigate the effect of the static friction force on the MEA deformation. The static friction force, which was more than 12% of the swelling force, could prevent wrinkles in 33 μm thick MEA.

  7. Kinetic Friction of Non-Coalescing and Non- Wetting Drops

    NASA Technical Reports Server (NTRS)

    Neitzel, G. paul

    2004-01-01

    This project has focused on the experimental determination of the frictional forces associated with noncoalescing and nonwetting systems. In particular, the focus has been on friction associated with an isothermal nonwetting droplet sliding on a solid surface. The nonwetting phenomenon is driven by the establishment of a thin (of order microns in thickness) layer of lubricating gas that is swept by viscous action into the space between the liquid and solid, preventing them from coming into contact. The mechanism has been described in the review article by Neitzel & Dell'Aversana (2002). The work performed under this NASA GSRP sponsorship extends work done by Dell'Aversana & Neitzel (2004) on the load-carrying capacities of thermocapillary nonwetting droplets for a given relative displacement of the two surfaces in question.

  8. Being Careful with PASCO's Kinetic Friction Experiment: Uncovering Pre-Sliding Displacement?

    ERIC Educational Resources Information Center

    Lawlor, T. M.

    2008-01-01

    The widely used PASCO laboratory equipment is an excellent way to introduce students to many topics in physics. In one case, PASCO's equipment may be too good! Various experiments exist for calculating the kinetic coefficient of friction by measuring the acceleration of a sliding object under some constant force. With ever more accurate equipment,…

  9. Fluctuations in a kinetic transport model for quantum friction

    NASA Astrophysics Data System (ADS)

    Bauerschmidt, Roland; de Roeck, Wojciech; Fröhlich, Jürg

    2014-07-01

    We study a linear Boltzmann equation describing the effective dynamics of a quantum particle moving through an ideal Bose gas at zero temperature. The particle emits sound waves into the Bose gas, a process causing it to slow down. This mechanism for friction is akin to one exhibited by a charged particle travelling through an optically dense medium at a speed larger than the speed of light and hence emitting Čerenkov radiation. We study the spatial trajectory of the Markov process corresponding to the Boltzmann equation and prove that this process converges to a multiple of Brownian motion after an exponential rescaling of time. We also show that the asymptotic position of the particle remains finite on average, but that its absolute value diverges logarithmically. Our unusual exponential rescaling of time is appropriate for a description of friction at zero temperature and is distinct from diffusive scaling appropriate at positive temperature. It is also shown that if random fluctuations of the particle position were neglected the latter would turn out to diverge.

  10. The Effects of In-Office Reconditioning on the Slot Dimensions and Static Frictional Resistance of Stainless Steel Brackets

    PubMed Central

    Nellore, Chaitanya; Karnati, Praveen Kumar Reddy; Thalapaneni, Ashok Kumar; Myla, Vijay Bhaskar; Ramyasree, Konda; Prasad, Mandava

    2016-01-01

    Introduction Orthodontists are commonly faced with the decision of what to do with loose brackets, and with inaccurately located brackets that need repositioning during treatment. One solution is to recycle the brackets. The potential effects of reconditioning a bracket are dependent upon many factors which may result in physical changes like alteration in slot tolerance, which may influence sliding mechanics by affecting frictional resistance. Aim To study and compare the dimensional changes in the bracket slot width and depth in reconditioned brackets from unused brackets under scanning electronic microscope and to study and compare any consequent effects on the static frictional resistance of stainless steel brackets after reconditioning and in unused brackets. Materials and Methods Dentarum manufactured 90 stainless steel central incisors edgewise brackets of size 0.22 X 0.030″ inch and 0° tip and 0°angulation were taken. 60 samples for measuring frictional resistance and 30 samples for measuring slot dimensions. Ortho organizers manufactured stainless steel arch wires 0.019 X 0.025″ straight lengths 60 in number were considered for measuring static frictional resistance. Results The mean slot width and depth of new brackets were 0.0251″ and 0.0471″, which exceeded the manufacturers reported nominal size of 0.022″ X 0.030″, by 0.003″ and 0.017″. The reconditioned brackets demonstrated a further increase in mean slot width and depth to 0.028″ and 0.0518″ that is by 0.0035″ and 0.0047″ which is statistically significant (p=0.001, 0.002). The mean static frictional forces of the reconditioned brackets was nearly similar to that of new brackets that is 0.3167N for reconditioned brackets and 0.2613 N for new brackets. Conclusion Although the reconditioning process results in physical changes to bracket structure this does not appear to result in significant effect on ex-vivo static frictional resistance. PMID:26894182

  11. Transition from Static to Dynamic Macroscopic Friction in the Framework of the Frenkel-Kontorova Model (aplication to Crustal Earthquake)

    NASA Astrophysics Data System (ADS)

    Gershenzon, N. I.; Bambakidis, G.

    2011-12-01

    A new generation of experiments on dry macroscopic friction [1-4] has revealed that the transition from static to dynamic friction is essentially a spatially and temporally nonuniform process, initiated by a rupture-like detachment front. We show the suitability of the Frenkel-Kontorova model for describing this transition. The model developed predicts the existence of two types of detachment fronts, explaining both the variability and abrupt change of the velocity observed in experiments. The quantitative relation obtained between the velocity of the detachment front and the ratio of shear to normal stress is consistent with experiments (see Figure 1). The model provides a functional dependence (algebraic relations) between slip velocity and shear stress, and predicts that slip velocity is independent of normal stress. Paradoxically transition from static to dynamic friction does not depend explicitly on both static and dynamic friction coefficients even so the beginning and termination of transition process are controlled by those coefficients. In the proposed model, friction occurs due to movement of a certain type of defect (i.e. a dislocation or slip pulse) nucleated on the frictional surfaces by the presence of asperities. This constitutes a fundamental distinction between our approach to macro-friction and the approaches of others such as the Burridge-Knopoff and rate-and-state types of models. The model is suitable to describe quantitatively the relations between kinematic and dynamic parameters of the rupture process during a crustal earthquake [5]. These relations will be demonstrated on 2004 Parkfield earthquake. [1] S. M. Rubinstein, G. Cohen, and J. Fineberg, Nature (London) 430, 1005 (2004) [2] S. M. Rubinstein, G. Cohen, and J. Fineberg, Phys. Rev. Lett. 98, 226103 (2007) [3] O. Ben-David, S.M. Rubinstein and J. Fineberg, Nature 463, 76 (2010) [4] O. Ben-David, G. Cohen, J. Fineberg, Science 330, 211 (2010), DOI: 10.1126/science.1194777 [5] N

  12. On the limits of quasi-static analysis for a simple Coulomb frictional oscillator in response to harmonic loads

    NASA Astrophysics Data System (ADS)

    Papangelo, A.; Ciavarella, M.

    2015-03-01

    Due to the nonlinearity of the Coulomb friction law, even the simplest models of interfaces in contact show a very rich dynamic solution. It is often desirable, especially if the frequency of loading is only a fraction of the first natural frequency of the system, to replace a full dynamic analysis with a quasi-static one, which obviously is much simpler to obtain. In this work, we study a simple Coulomb frictional oscillator with harmonic tangential load, but with constant normal load. It is found that the quasi-static solution (which has only 2 stops) captures approximately the displacement peak as long as the forcing frequency is low enough for the dynamic solution to have 2 or, even better, more than 2 stops. Instead, the velocity peak is not correctly estimated, since the velocity becomes highly irregular due to the stick-slip stops, whose number increases without limit for zero frequency. In this sense, the classical quasi-static solution, obtaining by cancelling inertia terms in the equilibrium equations, does not coincide with the limit of the full dynamic solution at low frequencies. The difference is not eliminated by adding a small amount of viscous damping, as only with critical damping, the dynamic solution is very close to the quasi-static one. Additional discrepancies arise above a limit frequency whose value depends on the ratio of the tangential load to the limit one for sliding, and correspond to when the dynamic solution turns from 2 to 0 stop per cycle.

  13. Nanoscale wear and kinetic friction between atomically smooth surfaces sliding at high speeds

    SciTech Connect

    Rajauria, Sukumar Canchi, Sripathi V. Schreck, Erhard; Marchon, Bruno

    2015-02-23

    The kinetic friction and wear at high sliding speeds is investigated using the head-disk interface of hard disk drives, wherein the head and the disk are less than 10 nm apart and move at sliding speeds of 5–10 m/s relative to each other. While the spacing between the sliding surfaces is of the same order of magnitude as various AFM based fundamental studies on friction, the sliding speed is nearly six orders of magnitude larger, allowing a unique set-up for a systematic study of nanoscale wear at high sliding speeds. In a hard disk drive, the physical contact between the head and the disk leads to friction, wear, and degradation of the head overcoat material (typically diamond like carbon). In this work, strain gauge based friction measurements are performed; the friction coefficient as well as the adhering shear strength at the head-disk interface is extracted; and an experimental set-up for studying friction between high speed sliding surfaces is exemplified.

  14. Coulomb frictional contact by explicit projection in the cone for finite displacement quasi-static problems

    NASA Astrophysics Data System (ADS)

    Areias, P.; Rabczuk, T.; de Melo, F. J. M. Queirós; de Sá, J. César

    2015-01-01

    We propose, in this paper, a distinct perspective on the solution of the Coulomb frictional contact problem. By combining the prediction/correction method for the contact force vector with the correction step being a cone projection and writing the friction cone surface in the quadratic form, we directly calculate the contact force. The distance along the friction cone normal is determined by solving a nonlinear problem in closed form. Numerical advantages of this projection are apparent for large values of friction coefficient. Six problems previously indicated as difficult to solve by the node-to-segment discretization and the operator split algorithm are here solved with the new projection algorithm. Discretization follows node-to segment and node-to-face derivations with gap vector defined in a global frame (without tangential and normal decomposition). In addition, we provide source codes for the 2D and 3D contact cases.

  15. Friction in orthodontics

    PubMed Central

    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

  16. General chemical kinetics computer program for static and flow reactions, with application to combustion and shock-tube kinetics

    NASA Technical Reports Server (NTRS)

    Bittker, D. A.; Scullin, V. J.

    1972-01-01

    A general chemical kinetics program is described for complex, homogeneous ideal-gas reactions in any chemical system. Its main features are flexibility and convenience in treating many different reaction conditions. The program solves numerically the differential equations describing complex reaction in either a static system or one-dimensional inviscid flow. Applications include ignition and combustion, shock wave reactions, and general reactions in a flowing or static system. An implicit numerical solution method is used which works efficiently for the extreme conditions of a very slow or a very fast reaction. The theory is described, and the computer program and users' manual are included.

  17. Constitutive equation of friction based on the subloading-surface concept

    PubMed Central

    Ueno, Masami; Kuwayama, Takuya; Suzuki, Noriyuki; Yonemura, Shigeru; Yoshikawa, Nobuo

    2016-01-01

    The subloading-friction model is capable of describing static friction, the smooth transition from static to kinetic friction and the recovery to static friction after sliding stops or sliding velocity decreases. This causes a negative rate sensitivity (i.e. a decrease in friction resistance with increasing sliding velocity). A generalized subloading-friction model is formulated in this article by incorporating the concept of overstress for viscoplastic sliding velocity into the subloading-friction model to describe not only negative rate sensitivity but also positive rate sensitivity (i.e. an increase in friction resistance with increasing sliding velocity) at a general sliding velocity ranging from quasi-static to impact sliding. The validity of the model is verified by numerical experiments and comparisons with test data obtained from friction tests using a lubricated steel specimen. PMID:27493570

  18. A simple criterion for determining the static friction force between nanowires and flat substrates using the most-bent-state method.

    PubMed

    Hou, Lizhen; Wang, Shiliang; Huang, Han

    2015-04-24

    A simple criterion was developed to assess the appropriateness of the currently available models that estimate the static friction force between nanowires and substrates using the 'most-bent-state' method. Our experimental testing of the static friction force between Al2O3 nanowires and Si substrate verified our theoretical analysis, as well as the establishment of the criterion. It was found that the models are valid only for the bent nanowires with the ratio of wire length over the minimum curvature radius [Formula: see text] no greater than 1. For the cases with [Formula: see text] greater than 1, the static friction force was overestimated as it neglected the effect of its tangential component. PMID:25815772

  19. PROPERTIES OF CP: COEFFICIENT OF THERMAL EXPANSION, DECOMPOSITION KINETICS, AND REACTION TO SPARK, FRICTION AND IMPACT

    SciTech Connect

    Weese, R K; Burnham, A K

    2005-09-28

    The properties of pentaamine (5-cyano-2H-tetrazolato-N2) cobalt (III) perchlorate (CP), which was first synthesized in 1968, continues to be of interest for predicting behavior in handling, shipping, aging, and thermal cook-off situations. We report coefficient of thermal expansion (CTE) values over four specific temperature ranges, decomposition kinetics using linear and isothermal heating, and the reaction to three different types of stimuli: impact, spark, and friction. The CTE was measured using a Thermal Mechanical Analyzer (TMA) for samples that were uniaxially compressed at 10,000 psi and analyzed over a dynamic temperature range of -20 C to 70 C. Differential scanning calorimetry, DSC, was used to monitor CP decomposition at linear heating rates of 1-7 C min{sup -1} in perforated pans and of 0.1-1.0 C min{sup -1} in sealed pans. The kinetic triplet was calculated using the LLNL code Kinetics05, and predictions for 210 and 240 C are compared to isothermal thermogravimetric analysis (TGA) experiments. Values are also reported for spark, friction, and impact sensitivity.

  20. Mechanical behaviour of a friction stir spot welding lap under static loading

    NASA Astrophysics Data System (ADS)

    Herbelot, C.; Hoang, T. Dang; Imad, A.; Benseddiq, N.

    2011-01-01

    Friction stir spot welding (FSSW) is a recent welding method which takes advantage of being performed in the solid state and presents many benefits such as a lower heat-input, a reduction of residual stresses and an elimination of the solidification defects for example. The present study investigates, for fixed process parameters and tool geometry, the fracture and damage of a single-lap friction stir spot welding joints formed from thin sheets of aluminum alloy 6082 T6. An experimental approach was carried out in order to analyze the sequence of damage mechanisms using acoustic emission (A.E.) and measurement of fields by digital image correlation (D.I.C.) techniques simultaneously. The A.E. technique allows the monitoring of the evolution of acoustic activities by taking into account energy of the events. The D.I.C. technique confirms the damage scenarios after the treatment of strain field at any point near the fastener and especially between the exit hole and the shoulder footprint. The coupling of those two techniques allows to identify characteristic points and a breakdown of the load displacement curve in phases.

  1. Growth kinetics of Al–Fe intermetallic compounds during annealing treatment of friction stir lap welds

    SciTech Connect

    Movahedi, M.; Kokabi, A.H.; Seyed Reihani, S.M.; Najafi, H.; Farzadfar, S.A.; Cheng, W.J.; Wang, C.J.

    2014-04-01

    In this study, we explored the growth kinetics of the Al–Fe intermetallic (IM) layer at the joint interface of the St-12/Al-5083 friction stir lap welds during post-weld annealing treatment at 350, 400 and 450 °C for 30 to 180 min. Optical microscope (OM), field emission gun scanning electron microscope (FEG-SEM) and transmission electron microscope (TEM) were employed to investigate the structure of the weld zone. The thickness and composition of the IM layers were evaluated using image analysis system and electron back-scatter diffraction (EBSD), respectively. Moreover, kernel average misorientation (KAM) analysis was performed to evaluate the level of stored energy in the as-welded state. The results showed that the growth kinetics of the IM layer was not governed by a parabolic diffusion law. Presence of the IM compounds as well as high stored energy near the joint interface of the as-welded sample was recognized to be the origin of the observed deviation from the parabolic diffusion law. - Highlights: • This work provided a new insight into growth kinetics of Al–Fe IM thickness. • The growth kinetics of IM layer was not governed by a parabolic diffusion law. • IM near the joint interface was the origin of deviation from the parabolic law. • High stored energy at joint interface was origin of deviation from parabolic law.

  2. Numerical analysis of static performance comparison of friction stir welded versus riveted 2024-T3 aluminum alloy stiffened panels

    NASA Astrophysics Data System (ADS)

    Shao, Qing; He, Yuting; Zhang, Teng; Wu, Liming

    2014-07-01

    Most researches on the static performance of stiffened panel joined by friction stir welding(FSW) mainly focus on the compression stability rather than shear stability. To evaluate the potential of FSW as a replacement for traditional rivet fastening for stiffened panel assembly in aviation application, finite element method(FEM) is applied to compare compression and shear stability performances of FSW stiffened panels with stability performances of riveted stiffened panels. FEMs of 2024-T3 aluminum alloy FSW and riveted stiffened panels are developed and nonlinear static analysis method is applied to obtain buckling pattern, buckling load and load carrying capability of each panel model. The accuracy of each FEM of FSW stiffened panel is evaluated by stability experiment of FSW stiffened panel specimens with identical geometry and boundary condition and the accuracy of each FEM of riveted stiffened panel is evaluated by semi-empirical calculation formulas. It is found that FEMs without considering weld-induced initial imperfections notably overestimate the static strengths of FSW stiffened panels. FEM results show that, buckling patterns of both FSW and riveted compression stiffened panels represent local buckling of plate between stiffeners. The initial buckling waves of FSW stiffened panel emerge uniformly in each plate between stiffeners while those of riveted panel mainly emerge in the mid-plate. Buckling patterns of both FSW and riveted shear stiffened panels represent local buckling of plate close to the loading corner. FEM results indicate that, shear buckling of FSW stiffened panel is less sensitive to the initial imperfections than compression buckling. Load carrying capability of FSW stiffened panel is less sensitive to the initial imperfections than initial buckling. It can be concluded that buckling loads of FSW panels are a bit lower than those of riveted panels whereas carrying capabilities of FSW panels are almost equivalent to those of riveted

  3. Internal friction study of decomposition kinetics of SAF 2507 type duplex stainless steel

    SciTech Connect

    Smuk, O.; Smuk, S.; Hanninen, H.; Jagodzinski, Yu.; Tarasenko, O.

    1999-01-08

    During the last decade, super duplex stainless steels (DSSs) with increased nitrogen content have been an object of intensive studies. Present work is devoted to the study of the peculiarities of {delta}-ferrite decomposition in SAF 2507 type duplex steel, and redistribution of nitrogen between ferrite and austenite phases in a wide temperature range by means of internal fraction (IF). Unlike local methods of electron microscopy or engineering methods of hardness or impact toughness testing, which give basically information on the formation of brittle intermetallic phases, the internal friction technique allows to study the state of solid solution and kinetics of changes in the relative amounts of ferrite and austenite phases during thermal treatment.

  4. Characterising the nanoscale kinetic friction using force-equilibrium and energy-conservation models with optical manipulation

    NASA Astrophysics Data System (ADS)

    Xie, Hongtao; Wang, Shiliang; Huang, Han

    2016-02-01

    SiC nanowires were manipulated under an optic microscope to investigate the nanoscale friction between nanowires and a flat substrate. The deflection of the nanowires was modeled as that of an Euler-Bernoulli beam subjected to a uniformly distributed load. A simple formula was developed to calculate the kinetic friction from the normalized deflections at the two ends of a nanowire. The frictional force per unit area determined ranges from 0.18-0.51 MPa. Both experimental and simulated results demonstrated that the proposed approach was reliable. The results were also compared with those estimated using an energy-conservation model, which produced a frictional force ranging from 0.21-0.62 MPa. The results obtained from the two different methods are in excellent agreement.

  5. Characterising the nanoscale kinetic friction using force-equilibrium and energy-conservation models with optical manipulation.

    PubMed

    Xie, Hongtao; Wang, Shiliang; Huang, Han

    2016-02-12

    SiC nanowires were manipulated under an optic microscope to investigate the nanoscale friction between nanowires and a flat substrate. The deflection of the nanowires was modeled as that of an Euler-Bernoulli beam subjected to a uniformly distributed load. A simple formula was developed to calculate the kinetic friction from the normalized deflections at the two ends of a nanowire. The frictional force per unit area determined ranges from 0.18-0.51 MPa. Both experimental and simulated results demonstrated that the proposed approach was reliable. The results were also compared with those estimated using an energy-conservation model, which produced a frictional force ranging from 0.21-0.62 MPa. The results obtained from the two different methods are in excellent agreement. PMID:26762859

  6. Friction between silicon and diamond at the nanoscale

    NASA Astrophysics Data System (ADS)

    Bai, Lichun; Sha, Zhen-Dong; Srikanth, Narasimalu; Pei, Qing-Xiang; Wang, Xu; Srolovitz, David J.; Zhou, Kun

    2015-06-01

    This work investigates the nanoscale friction between diamond-structure silicon (Si) and diamond via molecular dynamics simulation. The interaction between the interfaces is considered as strong covalent bonds. The effects of load, sliding velocity, temperature and lattice orientation are investigated. Results show that the friction can be divided into two stages: the static friction and the kinetic friction. During the static friction stage, the load, lattice orientation and temperature dramatically affects the friction by changing the elastic limit of Si. Large elastic deformation is induced in the Si block, which eventually leads to the formation of a thin layer of amorphous Si near the Si-diamond interface and thus the beginning of the kinetic friction stage. During the kinetic friction stage, only temperature and velocity have an effect on the friction. The investigation of the microstructural evolution of Si demonstrated that the kinetic friction can be categorized into two modes (stick-slip and smooth sliding) depending on the temperature of the fracture region.

  7. A STUDY OF THE PROPERTIES OF CP: COEFFICIENT OF THERMAL EXPANSION, DECOMPOSITION KINETICS AND REACTION TO SPARK, FRICTION AND IMPACT

    SciTech Connect

    Weese, R K; Burnham, A K; Fontes, A T

    2005-03-30

    The properties of pentaamine (5-cyano-2H-tetrazolato-N2) cobalt (III) perchlorate (CP), which was first synthesized in 1968, continues to be of interest for predicting behavior in handling, shipping, aging, and thermal cook-off situations. We report coefficient of thermal expansion (CTE) values over four specific temperature ranges, decomposition kinetics using linear heating rates, and the reaction to three different types of stimuli: impact, spark, and friction. The CTE was measured using a Thermal Mechanical Analyzer (TMA) for samples that were uniaxially compressed at 10,000 psi and analyzed over a dynamic temperature range of -20 C to 70 C. Using differential scanning calorimetry, DSC, CP was decomposed at linear heating rates of 1, 3, and 7 C/min and the kinetic triplet calculated using the LLNL code Kinetics05. Values are also reported for spark, friction, and impact sensitivity.

  8. Material properties of commonly-used interface materials and their static coefficients of friction with skin and socks.

    PubMed

    Sanders, J E; Greve, J M; Mitchell, S B; Zachariah, S G

    1998-06-01

    Compressive stiffness (CS) of different supporting materials used in prosthetics and orthotics and their static coefficients of friction (COF) with skin and socks were characterized. Materials tested included Spenco, Poron, nylon-reinforced silicone, Soft Pelite, Medium Pelite, Firm Plastazote, Regular Plastazote, and Nickelplast. A displacement-controlled testing device was constructed to assess the CS of 11.1 mm diameter material specimens under cyclic loading (1 Hz) to 220 kPa over 10- and 60-min periods. Results demonstrated local CS ranging from 687 kPa (Poron) to 3,990 kPa (Soft Pelite). To fit the cyclic stress-strain (S-S) data within an error of 4.0 percent full-scale output, the minimum order of fit required for Spenco, Poron, and nylon-reinforced silicone was a third-order polynomial; for Soft Pelite, Medium Pelite, Firm Plastazote, and Regular Plastazote, a second-order polynomial; and for Nickelplast, a linear fit. For all materials, the nonrecovered strains were related to loading time using an exponential fit. A biaxial force-controlled load applicator device was used to assess COF at skin-material, sock-material, and skin-sock interfaces for shear forces of 1 to 4 N applied to a 10.2 x 7.8 mm loading pad. COFs ranged from 0.48 (+/- 0.05) to 0.89 (+/- 0.09). COFs at skin-material interfaces were significantly (p < 0.05) higher than those at skin-sock interfaces. There was a trend of a higher COF at sock-material interfaces than at skin-sock interfaces. These data are of potential utility in finite element modeling sensitivity analysis of residual limb-prosthetic socket systems or body-orthosis systems to characterize effects of material features on interface pressure and shear stress distributions. PMID:9651888

  9. Evaluation of Static Friction of Polycrystalline Ceramic Brackets after Conditioning with Different Powers of Er:YAG Laser.

    PubMed

    Arash, Valiollah; Javanmard, Saeed; Eftekhari, Zeinab; Rahmati-Kamel, Manouchehr; Bahadoram, Mohammad

    2015-01-01

    This research aimed to reduce the friction between the wire and brackets by Er:YAG laser. To measure the friction between the wires and brackets in 0° and 10° of wire angulations, 40 polycrystalline ceramic brackets (Hubit, South Korea) were divided into 8 study groups and irradiated by 100, 200, and 300 mj/s of Er:YAG laser power. Two groups of brackets were not irradiated. The friction between the wires and brackets was measured with universal testing machine (SANTAM) with a segment of .019 × .025 SS wire pulled out of the slot of bracket. ANOVA and t-test were used for analyzing the results. To evaluate the effect of the laser on surface morphology of the bracket, SEM evaluations were carried out. The mean frictional resistances between the brackets and wires with 0° of angulation by increasing the laser power decreased compared with control group, but, in 10° of angulation, the friction increased regardless of the laser power and was comparable to the friction of nonirradiated brackets. Furthermore, with each laser power, frictional resistance of brackets in 10° of angulation was significantly higher than 0° of angulation. These results were explained by SEM images too. PMID:26491447

  10. Evaluation of Static Friction of Polycrystalline Ceramic Brackets after Conditioning with Different Powers of Er:YAG Laser

    PubMed Central

    Arash, Valiollah; Javanmard, Saeed; Eftekhari, Zeinab; Rahmati-Kamel, Manouchehr; Bahadoram, Mohammad

    2015-01-01

    This research aimed to reduce the friction between the wire and brackets by Er:YAG laser. To measure the friction between the wires and brackets in 0° and 10° of wire angulations, 40 polycrystalline ceramic brackets (Hubit, South Korea) were divided into 8 study groups and irradiated by 100, 200, and 300 mj/s of Er:YAG laser power. Two groups of brackets were not irradiated. The friction between the wires and brackets was measured with universal testing machine (SANTAM) with a segment of .019 × .025 SS wire pulled out of the slot of bracket. ANOVA and t-test were used for analyzing the results. To evaluate the effect of the laser on surface morphology of the bracket, SEM evaluations were carried out. The mean frictional resistances between the brackets and wires with 0° of angulation by increasing the laser power decreased compared with control group, but, in 10° of angulation, the friction increased regardless of the laser power and was comparable to the friction of nonirradiated brackets. Furthermore, with each laser power, frictional resistance of brackets in 10° of angulation was significantly higher than 0° of angulation. These results were explained by SEM images too. PMID:26491447

  11. Kinetics of Static Strain Aging in Polycrystalline NiAl-based Alloys

    NASA Technical Reports Server (NTRS)

    Weaver, M. L.; Kaufman, M. J.; Noebe, R. D.

    1996-01-01

    The kinetics of yield point return have been studied in two NiAl-based alloys as a function of aging time at temperatures between 300 and 700 K. The results indicate that the upper yield stress increment, Delta sigma(sub u) (i.e., stress difference between the upper yield point and the final flow stress achieved during prestraining), in conventional purity (CP-NiAl) and in high purity carbon-doped (NiAl-C) material first increased with a t(exp 2/3) relationship before reaching a plateau. This behavior suggests that a Cottrell locking mechanism is the cause for yield points in NiAl. In addition, positive y-axis intercepts were observed in plots of Delta sigma(sub u) versus t(exp 2/3) suggesting the operation of a Snoek mechanism. Analysis according to the Cottrell Bilby model of atmosphere formation around dislocations yields an activation energy for yield point return in the range 70 to 76 kJ/mol which is comparable to the activation energy for diffusion of interstitial impurities in bcc metals. It is, thus, concluded that the kinetics of static strain aging in NiAl are controlled by the locking of dislocations by Cottrell atmospheres of carbon atoms around dislocations.

  12. Using a Geophysical Model to Estimate the Static Coefficient of Friction and Cohesion on a Central Portion of the North Anatolian Fault East of the Marmara Sea

    NASA Astrophysics Data System (ADS)

    Karimi, B.; McQuarrie, N.

    2012-12-01

    were assigned using this database, which were used to calculate S-wave velocity, shear modulus, bulk modulus, Young's modulus, Poisson's ratio, and Lamé's first parameter for potential use in processing the mesh model. We evaluate the range of permissible fault friction coefficients for the regions' recurrence interval by running a simulation for increasing values of static fault friction. Starting from a position of zero-stress, the blocks are pushed at their respective velocities to see how much time passes until the static fault friction is overcome to allow for steady-state slip greater than 1-cm/y. Several iterations were performed with increasing cohesion to determine the change in permissible fault friction coefficients as cohesion increased. Initial simulations allow for static fault friction coefficients between 0.4 and 0.6 at 0-MPa cohesion. Resulting values for static fault friction coefficients and cohesion will be used in experiments to determine the dynamic friction coefficients and slip-weakening parameters along the faults in the research area. This approach allows for a greater understanding of the dynamics controlling the NAF in the highly seismically active study area.

  13. Modeling of Kashmir Aftershock Decay Based on Static Coulomb Stress Changes and Laboratory-Derived Rate-and-State Dependent Friction Law

    NASA Astrophysics Data System (ADS)

    Javed, F.; Hainzl, S.; Aoudia, A.; Qaisar, M.

    2016-05-01

    We model the spatial and temporal evolution of October 8, 2005 Kashmir earthquake's aftershock activity using the rate-and-state dependent friction model incorporating uncertainties in computed coseismic stress perturbations. We estimated the best possible value for frictional resistance " Aσ n", background seismicity rate " r" and coefficient of stress variation "CV" using maximum log-likelihood method. For the whole Kashmir earthquake sequence, we measure a frictional resistance Aσ n ~ 0.0185 MPa, r ~ 20 M3.7+ events/year and CV = 0.94 ± 0.01. The spatial and temporal forecasted seismicity rate of modeled aftershocks fits well with the spatial and temporal distribution of observed aftershocks that occurred in the regions with positive static stress changes as well as in the apparent stress shadow region. To quantify the effect of secondary aftershock triggering, we have re-run the estimations for 100 stochastically declustered catalogs showing that the effect of aftershock-induced secondary stress changes is obviously minor compared to the overall uncertainties, and that the stress variability related to uncertain slip model inversions and receiver mechanisms remains the major factor to provide a reasonable data fit.

  14. Friction testing of a new ligature

    NASA Astrophysics Data System (ADS)

    Mantel, Alison R.

    Objective. To determine if American Orthodontics' (AO) new, experimental ligature demonstrates less friction in vitro when compared to four other ligatures on the market. Methods. Four brackets were mounted on a custom metal fixture allowing an 0.018-in stainless steel wire attached to an opposite fixture with one bracket to be passively centered in the bracket slot. The wire was ligated to the bracket using one of five types of ligatures including the low friction test ligatures (AO), conventional ligatures (AO), Sili-Ties(TM) Silicone Infused Ties (GAC), SynergyRTM Low-Friction Ligatures (RMO), and SuperSlick ligatures (TP Orthodontics). Resistance to sliding was measured over a 7 mm sliding distance using a universal testing machine (Instron) with a 50 Newton load cell and a crosshead speed of 5 mm/min. The initial resistance to sliding (static) was determined by the peak force needed to initiate movement and the kinetic resistance to sliding was taken as the force at 5 mm of wire/bracket sliding. Fifteen unique tests were run for each ligature group in both dry and wet (saliva soaked for 24 hours with one drop prior to testing) conditions. Results. In the dry state, the SuperSlick ligature demonstrated more static friction than all of the other ligatures, while SuperSlick and Sili-Ties demonstrated more kinetic friction than the AO conventional, AO experimental and Synergy ligatures. In the wet condition, SuperSlick and the AO experimental ligature demonstrated the least static friction, followed by the AO conventional and Sili-Ties. The most static friction was observed with the Synergy ligatures. In the wet condition, the SuperSlick, AO experimental and AO conventional exhibited less kinetic friction than the Sili-Ties and Synergy ligatures. Conclusions. AO's experimental ligature exhibits less friction in the wet state than conventional ligatures, Sili-Ties and Synergy and is comparable to the SuperSlick ligature. These preliminary results suggest that the

  15. Comparison of direct and quasi-static methods for neutron kinetic calculations with the EDF R and D COCAGNE code

    SciTech Connect

    Girardi, E.; Guerin, P.; Dulla, S.; Nervo, M.; Ravetto, P.

    2012-07-01

    Quasi-Static (QS) methods are quite popular in the reactor physics community and they exhibit two main advantages. First, these methods overcome both the limits of the Point Kinetic (PK) approach and the issues of the computational effort related to the direct discretization of the time-dependent neutron transport equation. Second, QS methods can be implemented in such a way that they can be easily coupled to very different external spatial solvers. In this paper, the results of the coupling between the QS methods developed by Politecnico di Torino and the EDF R and D core code COCAGNE are presented. The goal of these activities is to evaluate the performances of QS methods (in term of computational cost and precision) with respect to the direct kinetic solver (e.g. {theta}-scheme) already available in COCAGNE. Additionally, they allow to perform an extensive cross-validation of different kinetic models (QS and direct methods). (authors)

  16. A comprehensive method to identify the kinetics of static recrystallization using the hot torsion test results with an inverse solution

    NASA Astrophysics Data System (ADS)

    Khoddam, S.; Hodgson, P. D.

    2014-12-01

    Many difficulties exist in directly following the static recrystallization of metals, particularly during hot working. Indirect measurement of static recrystallization has been extensively performed in the literature where, for example, the recrystallization behavior of austenite in steels has commonly been measured indirectly using the fractional softening method. This method relies on the yield stress changes during recrystallization which are physically simulated by hot torsion or compression tests. However, the inherent heterogeneity of deformation during a mechanical test leads to a non-uniform static recrystallization distribution in the test sample. This, in turn, poses a serious question concerning the reliability of the measurement since the stress calculation techniques during recrystallization are not adequately developed in the existing literature. This paper develops a computer-based method to account for heterogeneous deformation during fractional softening measurements based on the hot torsion test data. The importance of the fractional softening gradient in determining the kinetics is emphasized and deficiencies in our understanding of the basic mechanisms are highlighted. A computer-based method is introduced to generate the experimental and computational components in a cost function. The cost function is then utilized by an inverse solution to calibrate the design parameters in a static recrystallization model.A

  17. Kinetics of thermolysis of lanthanum nitrate with hexamethylenetetramine: Crystal structure, TG-DSC, impact and friction sensitivity studies, Part-96

    NASA Astrophysics Data System (ADS)

    Nibha; Baranwal, B. P.; Singh, Gurdip; Singh, C. P.; Daniliuc, Constantin G.; Soni, P. K.; Nath, Yogeshwar

    2014-11-01

    The development of high energetic materials includes process ability and the ability to attain insensitive munitions (IM). This paper investigates the preparation of lanthanum metal nitrate complex of hexamethylenetetramine in water at room temperature. This complex of molecular formulae [La (NO3)2(H2O)6] (2HMTA) (NO3-) (H2O) was characterized by X-ray crystallography. Thermal decomposition was investigated using TG, TG-DSC and ignition delay measurements. Kinetic analysis of isothermal TG data has been investigated using model fitting methods as well as model free isoconversional methods. The sensitivity measurements towards mechanical destructive stimuli such as impact and friction were carried out and the complex was found to be insensitive. In order to identify the end product of thermolysis, X-ray diffraction patterns of end product was carried out which proves the formation of La2O3.

  18. Role of the static and dynamic aging of dislocations in the kinetics of deformation of doped crystals

    NASA Astrophysics Data System (ADS)

    Petukhov, B. V.

    2014-06-01

    A method has been developed for calculating yield stresses in doped crystals and solid solutions with inclusion of the static and dynamic aging of dislocations. An analytical description of the kinetics of deformation of these materials in the vicinity of the upper yield stress has been proposed. The stage character of stress-strain curves due to the dislocation immobilization by impurity atmospheres formed around dislocations has been demonstrated. The theory is applicable to the calculation of the impurity and solid solution hardening of semiconductors, metals with body-centered cubic (bcc) structure, intermetallic compounds, and other materials.

  19. A hybrid computer program for rapidly solving flowing or static chemical kinetic problems involving many chemical species

    NASA Technical Reports Server (NTRS)

    Mclain, A. G.; Rao, C. S. R.

    1976-01-01

    A hybrid chemical kinetic computer program was assembled which provides a rapid solution to problems involving flowing or static, chemically reacting, gas mixtures. The computer program uses existing subroutines for problem setup, initialization, and preliminary calculations and incorporates a stiff ordinary differential equation solution technique. A number of check cases were recomputed with the hybrid program and the results were almost identical to those previously obtained. The computational time saving was demonstrated with a propane-oxygen-argon shock tube combustion problem involving 31 chemical species and 64 reactions. Information is presented to enable potential users to prepare an input data deck for the calculation of a problem.

  20. Time-lapse nanoscopy of friction in the non-Amontons and non-Coulomb regime.

    PubMed

    Ishida, Tadashi; Sato, Takaaki; Ishikawa, Takahiro; Oguma, Masatsugu; Itamura, Noriaki; Goda, Keisuke; Sasaki, Naruo; Fujita, Hiroyuki

    2015-03-11

    Originally discovered by Leonard da Vinci in the 15th century, the force of friction is directly proportional to the applied load (known as Amontons' first law of friction). Furthermore, kinetic friction is independent of the sliding speed (known as Coulomb's law of friction). These empirical laws break down at high normal pressure (due to plastic deformation) and low sliding speed (in the transition regime between static friction and kinetic friction). An important example of this phenomenon is friction between the asperities of tectonic plates on the Earth. Despite its significance, little is known about the detailed mechanism of friction in this regime due to the lack of experimental methods. Here we demonstrate in situ time-lapse nanoscopy of friction between asperities sliding at ultralow speed (∼0.01 nm/s) under high normal pressure (∼GPa). This is made possible by compressing and rubbing a pair of nanometer-scale crystalline silicon anvils with electrostatic microactuators and monitoring its dynamical evolution with a transmission electron microscope. Our analysis of the time-lapse movie indicates that superplastic behavior is induced by decrystallization, plastic deformation, and atomic diffusion at the asperity-asperity interface. The results hold great promise for a better understanding of quasi-static friction under high pressure for geoscience, materials science, and nanotechnology. PMID:25330166

  1. Kinetics of thermolysis of ring-substituted arylammonium nitrates: 2 -- TG, DTA, impact, and friction sensitivity studies

    SciTech Connect

    Singh, G.; Kapoor, I.P.S.; Mannan, S.M. . Dept. of Chemistry); Agrawal, J.P. )

    1994-06-01

    Interest is growing in oxidizers that might replace ammonium perchlorate (AP) and ammonium nitrate (AN) in solid propellants and explosives. Thermolysis of ring-substituted arylammonium nitrates (RSAN) has been carried out by TG, DTA, impact, and friction sensitivity measurements. Although the kinetics of thermal decomposition of these salts was evaluated by fitting TG data in nine mechanism-based kinetic models, the contracting envelopes and Avrami-Erofeev gave the best fit. The activation energies for decomposition (E[sub d]), exothermic decomposition temperatures (T[sub d]) (from DTA curves), and impact sensitivity data are found to be linearly related to the Hammett substituent constant ([sigma]) and dissociation exponent (pK[sub a]) of the corresponding arylamine. The mechanism of thermolysis of these salts has also been suggested, based on the formation of reaction intermediates during decomposition. A reaction scheme, accounting for the products, is proposed that involves proton transfer, leading to the formation of an arylamine and HNO[sub 3] and oxidation of the arylamine by decomposition products of HNO[sub 3]. The oxidation-reduction reactions, near the surface of the thermolysing material (RSAN), are responsible for the decomposition.

  2. Kinetic versus Static Visuals for Facilitating College Students' Understanding of Organic Reaction Mechanisms in Chemistry

    ERIC Educational Resources Information Center

    Aldahmash, Abdulwali H.; Abraham, Michael R.

    2009-01-01

    Using animated computer-generated graphics to assist instruction has recently attracted the attention of educators and educational researchers. The specific focus of this study is to compare the influence of animated visuals with static visuals on college students' understanding of organic reaction mechanisms in chemistry. This study also focuses…

  3. Statistics of frictional families.

    PubMed

    Shen, Tianqi; Papanikolaou, Stefanos; O'Hern, Corey S; Shattuck, Mark D

    2014-09-19

    We develop a theoretical description for mechanically stable frictional packings in terms of the difference between the total number of contacts required for isostatic packings of frictionless disks and the number of contacts in frictional packings, m=Nc0 - Nc. The saddle order m represents the number of unconstrained degrees of freedom that a static packing would possess if friction were removed. Using a novel numerical method that allows us to enumerate disk packings for each m, we show that the probability to obtain a packing with saddle order m at a given static friction coefficient μ, Pm(μ), can be expressed as a power series in μ. Using this form for Pm(μ), we quantitatively describe the dependence of the average contact number on the friction coefficient for static disk packings obtained from direct simulations of the Cundall-Strack model for all μ and N. PMID:25279647

  4. Some aspects of the damage kinetics at static loading of a heterogeneous solid under the conditions of constrained deformation

    NASA Astrophysics Data System (ADS)

    Leksovskii, A. M.; Baskin, B. L.; Yakushev, P. N.

    2015-12-01

    The damaging kinetics of a composite system subjected to static loading, which simulates an inhomogeneous body with microductility, and of D16T-B(43%) composite simulating a quasi-brittle solid is analyzed with the acoustic emission method. By using laser interferometry, it is shown on a model sample that mesocracking may cause a short-term change in the plastic strain rate, which two or more orders of magnitude exceeds the change in the creep rate during the usual supramolecular structure reconfiguration. Whether the object will remain functional or acquire damage of the next scale after being subjected to such local "impact" loading depends on the ability of its immediate environment to absorb released energy.

  5. Nuclear reactor transient analysis via a quasi-static kinetics Monte Carlo method

    NASA Astrophysics Data System (ADS)

    Jo, YuGwon; Cho, Bumhee; Cho, Nam Zin

    2015-12-01

    The predictor-corrector quasi-static (PCQS) method is applied to the Monte Carlo (MC) calculation for reactor transient analysis. To solve the transient fixed-source problem of the PCQS method, fission source iteration is used and a linear approximation of fission source distributions during a macro-time step is introduced to provide delayed neutron source. The conventional particle-tracking procedure is modified to solve the transient fixed-source problem via MC calculation. The PCQS method with MC calculation is compared with the direct time-dependent method of characteristics (MOC) on a TWIGL two-group problem for verification of the computer code. Then, the results on a continuous-energy problem are presented.

  6. Nuclear reactor transient analysis via a quasi-static kinetics Monte Carlo method

    SciTech Connect

    Jo, YuGwon; Cho, Bumhee; Cho, Nam Zin

    2015-12-31

    The predictor-corrector quasi-static (PCQS) method is applied to the Monte Carlo (MC) calculation for reactor transient analysis. To solve the transient fixed-source problem of the PCQS method, fission source iteration is used and a linear approximation of fission source distributions during a macro-time step is introduced to provide delayed neutron source. The conventional particle-tracking procedure is modified to solve the transient fixed-source problem via MC calculation. The PCQS method with MC calculation is compared with the direct time-dependent method of characteristics (MOC) on a TWIGL two-group problem for verification of the computer code. Then, the results on a continuous-energy problem are presented.

  7. A model for the kinetics of homotypic cellular aggregation under static conditions

    NASA Technical Reports Server (NTRS)

    Neelamegham, S.; Munn, L. L.; Zygourakis, K.; McIntire, L. V. (Principal Investigator)

    1997-01-01

    We present the formulation and testing of a mathematical model for the kinetics of homotypic cellular aggregation. The model considers cellular aggregation under no-flow conditions as a two-step process. Individual cells and cell aggregates 1) move on the tissue culture surface and 2) collide with other cells (or aggregates). These collisions lead to the formation of intercellular bonds. The aggregation kinetics are described by a system of coupled, nonlinear ordinary differential equations, and the collision frequency kernel is derived by extending Smoluchowski's colloidal flocculation theory to cell migration and aggregation on a two-dimensional surface. Our results indicate that aggregation rates strongly depend upon the motility of cells and cell aggregates, the frequency of cell-cell collisions, and the strength of intercellular bonds. Model predictions agree well with data from homotypic lymphocyte aggregation experiments using Jurkat cells activated by 33B6, an antibody to the beta 1 integrin. Since cell migration speeds and all the other model parameters can be independently measured, the aggregation model provides a quantitative methodology by which we can accurately evaluate the adhesivity and aggregation behavior of cells.

  8. Showing Area Matters: A Work of Friction

    ERIC Educational Resources Information Center

    Van Domelen, David

    2010-01-01

    Typically, we teach the simplified friction equation of the form F[subscript s] = [mu][subscript s]N for static friction, where F[subscript s] is the maximum static friction, [mu][subscript s] is the coefficient of static friction, and "N" is the normal force pressing the surfaces together. However, this is a bit too simplified, and doesn't work…

  9. Friction-formed liquid droplets

    NASA Astrophysics Data System (ADS)

    Lockwood, A. J.; Anantheshwara, K.; Bobji, M. S.; Inkson, B. J.

    2011-03-01

    The formation of nanoscale liquid droplets by friction of a solid is observed in real-time. This is achieved using a newly developed in situ transmission electron microscope (TEM) triboprobe capable of applying multiple reciprocating wear cycles to a nanoscale surface. Dynamical imaging of the nanoscale cyclic rubbing of a focused-ion-beam (FIB) processed Al alloy by diamond shows that the generation of nanoscale wear particles is followed by a phase separation to form liquid Ga nanodroplets and liquid bridges. The transformation of a two-body system to a four-body solid-liquid system within the reciprocating wear track significantly alters the local dynamical friction and wear processes. Moving liquid bridges are observed in situ to play a key role at the sliding nanocontact, interacting strongly with the highly mobile nanoparticle debris. In situ imaging demonstrates that both static and moving liquid droplets exhibit asymmetric menisci due to nanoscale surface roughness. Nanodroplet kinetics are furthermore dependent on local frictional temperature, with solid-like surface nanofilaments forming on cooling. TEM nanotribology opens up new avenues for the real-time quantification of cyclic friction, wear and dynamic solid-liquid nanomechanics, which will have widespread applications in many areas of nanoscience and nanotechnology.

  10. Coherent Raman spectroscopy: From statics to dynamics and kinetics, progress in nonlinear methods

    NASA Astrophysics Data System (ADS)

    Akhmanov, S. A.

    1987-12-01

    In spite of its 60-year history Raman spectroscopy is still progressing nowadays. Highly stable lasers and short pulse oscillators, perfect electronic data acquisition systems, new nonlinear optical approaches created new exciting perspectives for Raman spectroscopy. One of the most important tendencies is Raman spectroscopy application for studying nonequilibrium states, fast dynamics and kinetics of atoms, molecules and condensed matter. All these problems were until recently regarded as inaccessible for optical spectroscopy. Nonlinear optical techniques of Coherent Anti-Stokes Raman Scattering (CARS) and modulation spectroscopy appeared to be most effective and provided important real-time information on molecular excitation and dissociation dynamics, deep cooling of molecules in a supersonic jet, short laser pulse induced phase transitions at semiconductor interface and so on. Problems yet to be solved include direct measurement of intramolecular vibrational relaxation, conformations in biomolecules, optical “oscilloscopy” of molecular vibrations.

  11. Micromachine friction test apparatus

    DOEpatents

    deBoer, Maarten P.; Redmond, James M.; Michalske, Terry A.

    2002-01-01

    A microelectromechanical (MEM) friction test apparatus is disclosed for determining static or dynamic friction in MEM devices. The friction test apparatus, formed by surface micromachining, is based on a friction pad supported at one end of a cantilevered beam, with the friction pad overlying a contact pad formed on the substrate. A first electrostatic actuator can be used to bring a lower surface of the friction pad into contact with an upper surface of the contact pad with a controlled and adjustable force of contact. A second electrostatic actuator can then be used to bend the cantilevered beam, thereby shortening its length and generating a relative motion between the two contacting surfaces. The displacement of the cantilevered beam can be measured optically and used to determine the static or dynamic friction, including frictional losses and the coefficient of friction between the surfaces. The test apparatus can also be used to assess the reliability of rubbing surfaces in MEM devices by producing and measuring wear of those surfaces. Finally, the friction test apparatus, which is small in size, can be used as an in situ process quality tool for improving the fabrication of MEM devices.

  12. The dissociation kinetics of NO on Rh(111) as studied by temperature programmed static secondary ion mass spectrometry and desorption

    NASA Astrophysics Data System (ADS)

    Borg, H. J.; Reijerse, J. F. C.-J. M.; van Santen, R. A.; Niemantsverdriet, J. W.

    1994-12-01

    Temperature programmed static secondary ion mass spectrometry (TPSSIMS) and temperature programmed desorption (TPD) have been used to study the kinetics of adsorption, dissociation, and desorption of NO on Rh(111). At 100 K, NO adsorption is molecular and proceeds via mobile precursor state kinetics with a high initial sticking probability. SSIMS indicates the presence of two distinct NO adsorption states, indicative of threefold adsorption at low coverage, and occupation of bridge sites at higher coverages. Three characteristic coverage regimes appear with respect to NO dissociation. At low coverages θNO<0.25 ML, NO dissociates completely at temperatures between 275 and 340 K. If we neglect lateral interactions and assume pure first order dissociation kinetics, we find effective values for the activation barrier and preexponential factor of 40±6 kJ/mol and 106±1 s-1 for the dissociation of 0.15-0.20 ML NO. However, if we assume that a NO molecule needs an ensemble of three to four vacant sites in order to dissociate, the preexponential factor and activation energy are ˜1011 s-1 and 65 kJ/mol, in better agreement with transition state theory expectations. The Nads and Oads dissociation products desorb as N2 and O2, respectively, with desorption parameters Edes=118±10 kJ/mol and νdes=1010.1±1.0 s-1 for N2 in the zero coverage limit. At higher coverages, the desorption kinetics of N2 is strongly influenced by the presence of coadsorbed oxygen. In the medium coverage range 0.25<θNO<0.50 ML, part of the NO desorbs molecularly, with an estimated desorption barrier of 113±10 kJ/mol and a preexponential of 1013.5±1.0 s-1. Dissociation of NO becomes progressively inhibited due to site blocking, the onset shifting from 275 K at 0.25 ML to 400 K, coinciding with the NO desorption temperature, at a coverage of 0.50 ML. The accumulation of nitrogen and oxygen atoms on the highly covered surface causes a destabilization of the nitrogen atoms, which results in an

  13. The influence of fault geometry and frictional contact properties on slip surface behavior and off-fault damage: insights from quasi-static modeling of small strike-slip faults from the Sierra Nevada, CA

    NASA Astrophysics Data System (ADS)

    Ritz, E.; Pollard, D. D.

    2011-12-01

    Geological and geophysical investigations demonstrate that faults are geometrically complex structures, and that the nature and intensity of off-fault damage is spatially correlated with geometric irregularities of the slip surfaces. Geologic observations of exhumed meter-scale strike-slip faults in the Bear Creek drainage, central Sierra Nevada, CA, provide insight into the relationship between non-planar fault geometry and frictional slip at depth. We investigate natural fault geometries in an otherwise homogeneous and isotropic elastic material with a two-dimensional displacement discontinuity method (DDM). Although the DDM is a powerful tool, frictional contact problems are beyond the scope of the elementary implementation because it allows interpenetration of the crack surfaces. By incorporating a complementarity algorithm, we are able to enforce appropriate contact boundary conditions along the model faults and include variable friction and frictional strength. This tool allows us to model quasi-static slip on non-planar faults and the resulting deformation of the surrounding rock. Both field observations and numerical investigations indicate that sliding along geometrically discontinuous or irregular faults may lead to opening of the fault and the formation of new fractures, affecting permeability in the nearby rock mass and consequently impacting pore fluid pressure. Numerical simulations of natural fault geometries provide local stress fields that are correlated to the style and spatial distribution of off-fault damage. We also show how varying the friction and frictional strength along the model faults affects slip surface behavior and consequently influences the stress distributions in the adjacent material.

  14. Comparison of frictional forces between aesthetic orthodontic coated wires and self-ligation brackets

    PubMed Central

    Kim, Yunmi; Cha, Jung-Yul; Hwang, Chung-Ju; Tahk, Seon Gun

    2014-01-01

    Objective The purpose of this study was to evaluate the clinical efficacy of polymer- and rhodium-coated wires compared to uncoated wires by measuring the frictional forces using self-ligation brackets. Methods 0.016-inch nickel titanium (NiTi) wires and 0.017 × 0.025-inch stainless steel (SS) wires were used, and the angulations between the brackets and wires were set to 0°, 5°, and 10°. Upper maxillary premolar brackets (Clippy-C®) with a 0.022-inch slot were selected for the study and a tensile test was performed with a crosshead speed of 5 mm/min. The maximum static frictional forces and kinetic frictional forces were recorded and compared. Results The maximum static frictional forces and the kinetic frictional forces of coated wires were equal to or higher than those of the uncoated wires (p < 0.05). The maximum static frictional forces of rhodium-coated wires were significantly higher than those of polymer-coated wires when the angulations between the brackets and wires were set to (i) 5° in the 0.016-inch NiTi wires and (ii) all angulations in the 0.017 × 0.025-inch SS wires (p < 0.05). The kinetic frictional forces of rhodium-coated wires were higher than those of polymer-coated wires, except when the angulations were set to 0° in the 0.016-inch NiTi wires (p < 0.05). Conclusions Although the frictional forces of the coated wires with regards to aesthetics were equal to or greater than those of the uncoated wires, a study under similar conditions regarding the oral cavity is needed in order to establish the clinical implications. PMID:25133130

  15. Is internal friction friction?

    USGS Publications Warehouse

    Savage, J.C.; Byerlee, J.D.; Lockner, D.A.

    1996-01-01

    Mogi [1974] proposed a simple model of the incipient rupture surface to explain the Coulomb failure criterion. We show here that this model can plausibly be extended to explain the Mohr failure criterion. In Mogi's model the incipient rupture surface immediately before fracture consists of areas across which material integrity is maintained (intact areas) and areas across which it is not (cracks). The strength of the incipient rupture surface is made up of the inherent strength of the intact areas plus the frictional resistance to sliding offered by the cracked areas. Although the coefficient of internal friction (slope of the strength versus normal stress curve) depends upon both the frictional and inherent strengths, the phenomenon of internal friction can be identified with the frictional part. The curvature of the Mohr failure envelope is interpreted as a consequence of differences in damage (cracking) accumulated in prefailure loading at different confining pressures.

  16. Engineering mechanics: statics and dynamics. [Textbook

    SciTech Connect

    Sandor, B.I.

    1983-01-01

    The purpose of this textbook is to provide engineering students with basic learning material about statics and dynamics which are fundamental engineering subjects. The chapters contain information on: an introduction to engineering mechanics; forces on particles, rigid bodies, and structures; kinetics of particles, particle systems, and rigid bodies in motion; kinematics; mechanical vibrations; and friction, work, moments of inertia, and potential energy. Each chapter contains introductory material, the development of the essential equations, worked-out example problems, homework problems, and, finally, summaries of the essential methods and equations, graphically illustrated where appropriate. (LCL)

  17. Reducing Sliding Friction with Liquid-Impregnated Surfaces

    NASA Astrophysics Data System (ADS)

    Habibi, Mohammad; Collier, C. Patrick; Boreyko, Jonathan; Nature Inspired Fluids; Interfaces Team; CenterNanophase Materials Sciences Team

    2015-11-01

    Liquid-impregnated surfaces are fabricated by infusing a lubricating liquid into the micro/nano roughness of a textured substrate, such that the surface is slippery for any deposited liquid immiscible with the lubricant. To date, liquid-impregnated surfaces have almost exclusively focused on repelling liquids by minimizing the contact angle hysteresis. Here, we demonstrate that liquid-impregnated surfaces are also capable of reducing sliding friction for solid objects. Ordered arrays of silicon micropillars were infused with lubricating liquids varying in viscosity by two orders of magnitude. Five test surfaces were used: two different micropillared surfaces with and without liquid infusion and a smooth, dry control surface. The static and kinetic coefficients of friction were measured using a polished aluminum cube as the sliding object. Compared to the smooth control surface, the sliding friction was reduced by at least a factor of two on the liquid-impregnated surfaces.

  18. Preface: Friction at the nanoscale

    NASA Astrophysics Data System (ADS)

    Fusc, Claudio; Smith, Roger; Urbakh, Michael; Vanossi, Andrea

    2008-09-01

    Interfacial friction is one of the oldest problems in physics and chemistry, and certainly one of the most important from a practical point of view. Everyday operations on a broad range of scales, from nanometer and up, depend upon the smooth and satisfactory functioning of countless tribological systems. Friction imposes serious constraints and limitations on the performance and lifetime of micro-machines and, undoubtedly, will impose even more severe constraints on the emerging technology of nano-machines. Standard lubrication techniques used for large objects are expected to be less effective in the nano-world. Novel methods for control and manipulation are therefore needed. What has been missing is a molecular level understanding of processes occurring between and close to interacting surfaces to help understand, and later manipulate friction. Friction is intimately related to both adhesion and wear, and all three require an understanding of highly non-equilibrium processes occurring at the molecular level to determine what happens at the macroscopic level. Due to its practical importance and the relevance to basic scientific questions there has been major increase in activity in the study of interfacial friction on the microscopic level during the last decade. Intriguing structural and dynamical features have been observed experimentally. These observations have motivated theoretical efforts, both numerical and analytical. This special issue focusses primarily on discussion of microscopic mechanisms of friction and adhesion at the nanoscale level. The contributions cover many important aspects of frictional behaviour, including the origin of stick-slip motion, the dependence of measured forces on the material properties, effects of thermal fluctuations, surface roughness and instabilities in boundary lubricants on both static and kinetic friction. An important problem that has been raised in this issue, and which has still to be resolved, concerns the

  19. Organic thermal maturity as a proxy for frictional fault heating: experimental constraints on biomarker kinetics at earthquake timescales

    NASA Astrophysics Data System (ADS)

    Sheppard, R. E.; Polissar, P. J.; Savage, H. M.

    2013-12-01

    The temperature rise during an earthquake is a reliable indicator of shear strength and localization along faults. We examined the thermal alteration of organic compounds in fault zones. Methylphenanthrenes are a type of organic molecule whose chemical alteration when exposed to heat is the basis for the established methylphenanthrene index MPI-1, which is correlated to vitrinite reflectance. However, previous experiments examining the kinetics of these reactions were conducted at longer time periods than suitable for the duration of temperature rise during an earthquake. We conducted twelve hydrous pyrolysis experiments in a small, low-thermal inertia stainless steel reactor to study how methylphenanthrenes change under controlled conditions at short timescales. Experiments were conducted with Woodford Shale, a well-studied benchmark for organic thermal maturity, under hydrous anoxic conditions. From each experiment, phenanthrenes were analyzed in the solid residue (the rock sample that would be taken from an exhumed fault) and the expelled liquid (pyrolyzate, the mixture of water and expelled oil). These experiments sought to determine the changes in MPI-1 that result from controlled periods of heating at various temperatures (unheated and 265-345°C) and durations (15-160 minutes for the heated samples). Our results demonstrate that methylphenanthrenes are sensitive to minutes of heating, and are thus effective paleothermometers for fault zones. The change in methylphenanthrenes with time and temperature allowed us to determine the activation energy and pre-exponential factor for the MPI-1 alteration, allowing temperatures during earthquakes to be constrained from the biomarker data. As methylphenanthrenes are consistently found in faults shallower than 4 km, this method will allow for more accurate estimation of the maximum temperature rise that occurred during slip on previously studied faults. Our kinetics were applied to estimate the temperature rises of the

  20. Machine tests slow-speed sliding friction in high vacuum

    NASA Technical Reports Server (NTRS)

    Skyrus, J.; Wilkinson, C.

    1967-01-01

    Testing machine that operates without any lubrication of the machine elements within the vacuum chamber measures static friction and sliding friction at very low speeds. Moving parts are held to a minimum to simplify operation in the vacuum chamber.

  1. Required coefficient of friction during turning at self-selected slow, normal, and fast walking speeds

    PubMed Central

    Fino, Peter; Lockhart, Thurmon

    2014-01-01

    This study investigated the relationship of required coefficient of friction to gait speed, obstacle height, and turning strategy as participants walked around obstacles of various heights. Ten healthy, young adults performed 90° turns around corner pylons of four different heights at their self selected normal, slow, and fast walking speeds using both step and spin turning strategies. Kinetic data was captured using force plates. Results showed peak required coefficient of friction (RCOF) at push off increased with increased speed (slow µ= 0.38, normal µ=0.45, fast µ=0.54). Obstacle height had no effect on RCOF values. The average peak RCOF for fast turning exceeded the OSHA safety guideline for static COF of µ>0.50, suggesting further research is needed into the minimum static COF to prevent slips and falls, especially around corners. PMID:24581815

  2. The stretching of single poly-ubiquitin molecules: Static versus dynamic disorder in the non-exponential kinetics of chain unfolding

    NASA Astrophysics Data System (ADS)

    Chatterjee, Debarati; Cherayil, Binny J.

    2011-04-01

    Static disorder has recently been implicated in the non-exponential kinetics of the unfolding of single molecules of poly-ubiquitin under a constant force [Kuo, Garcia-Manyes, Li, Barel, Lu, Berne, Urbakh, Klafter, and Fernández, Proc. Natl. Acad. Sci. U.S.A. 107, 11336 (2010), 10.1073/pnas.1006517107]. In the present paper, it is suggested that dynamic disorder may provide a plausible, alternative description of the experimental observations. This suggestion is made on the basis of a model in which the barrier to chain unfolding is assumed to be modulated by a control parameter r that evolves in a parabolic potential under the action of fractional Gaussian noise according to a generalized Langevin equation. The treatment of dynamic disorder within this model is pursued using Zwanzig's indirect approach to noise averaging [Acc. Chem. Res. 23, 148 (1990)]. In conjunction with a self-consistent closure scheme developed by Wilemski and Fixman [J. Chem. Phys. 58, 4009 (1973), 10.1063/1.1679757; ibid. 60, 866 (1974), 10.1063/1.1681162], this approach eventually leads to an expression for the chain unfolding probability that can be made to fit the corresponding experimental data very closely.

  3. Contact and friction of nanoasperities: effects of adsorbed monolayers.

    PubMed

    Cheng, Shengfeng; Luan, Binquan; Robbins, Mark O

    2010-01-01

    Molecular dynamics simulations are used to study contact between a rigid, nonadhesive, and spherical tip with radius of order 30 nm and a flat elastic substrate covered with a fluid monolayer of adsorbed chain molecules. Previous studies of bare surfaces showed that the atomic scale deviations from a sphere that are present on any tip constructed from discrete atoms lead to significant deviations from continuum theory and dramatic variability in friction forces. Introducing an adsorbed monolayer leads to larger deviations from continuum theory but decreases the variations between tips with different atomic structure. Although the film is fluid, it remains in the contact and behaves qualitatively like a thin elastic coating except for certain tips at high loads. Measures of the contact area based on the moments or outer limits of the pressure distribution and on counting contacting atoms are compared. The number of tip atoms making contact during a time interval Deltat grows as a power of Deltat when the film is present and as the logarithm of Deltat for bare surfaces. Friction is measured by displacing the tip at a constant velocity or pulling the tip with a spring. Both static and kinetic friction rise linearly with load at small loads. Transitions in the state of the film lead to nonlinear behavior at large loads. The friction is less clearly correlated with contact area than load. PMID:20365427

  4. Listening in on Friction: Stick-Slip Acoustical Signatures in Velcro

    NASA Astrophysics Data System (ADS)

    Hurtado Parra, Sebastian; Morrow, Leslie; Radziwanowski, Miles; Angiolillo, Paul

    2013-03-01

    The onset of kinetic friction and the possible resulting stick-slip motion remain mysterious phenomena. Moreover, stick-slip dynamics are typically accompanied by acoustic bursts that occur temporally with the slip event. The dry sliding dynamics of the hook-and-loop system, as exemplified by Velcro, manifest stick-slip behavior along with audible bursts that are easily micrphonically collected. Synchronized measurements of the friction force and acoustic emissions were collected as hooked Velcro was driven at constant velocity over a bed of looped Velcro in an anechoic chamber. Not surprising, the envelope of the acoustic bursts maps well onto the slip events of the friction force time series and the intensity of the bursts trends with the magnitude of the difference of the friction force during a stick-slip event. However, the analysis of the acoustic emission can serve as a sensitive tool for revealing some of the hidden details of the evolution of the transition from static to kinetic friction. For instance, small acoustic bursts are seen prior to the Amontons-Coulomb threshold, signaling precursor events prior to the onset of macroscopically observed motion. Preliminary spectral analysis of the acoustic emissions including intensity-frequency data will be presented.

  5. Frictional and mechanical properties of diamond-like carbon-coated orthodontic brackets.

    PubMed

    Muguruma, Takeshi; Iijima, Masahiro; Brantley, William A; Nakagaki, Susumu; Endo, Kazuhiko; Mizoguchi, Itaru

    2013-04-01

    This study investigated the effects of a diamond-like carbon (DLC) coating on frictional and mechanical properties of orthodontic brackets. DLC films were deposited on stainless steel brackets using the plasma-based ion implantation/deposition (PBIID) method under two different atmospheric conditions. As-received metal brackets served as the control. Two sizes of stainless steel archwires, 0.018 inch diameter and 0.017 × 0.025 inch cross-section dimensions, were used for measuring static and kinetic friction by drawing the archwires through the bracket slots, using a mechanical testing machine (n = 10). The DLC-coated brackets were observed with a scanning electron microscope (SEM). Values of hardness and elastic modulus were obtained by nanoindentation testing (n = 10). Friction forces were compared by one-way analysis of variance and the Scheffé test. The hardness and elastic modulus of the brackets were compared using Kruskal-Wallis and Mann-Whitney U-tests. SEM photomicrographs showed DLC layers on the bracket surfaces with thickness of approximately 5-7 μm. DLC-coated brackets deposited under condition 2 showed significantly less static frictional force for the stainless steel wire with 0.017 × 0.025 inch cross-section dimensions than as-received brackets and DLC-coated brackets deposited under condition 1, although both DLC-coated brackets showed significantly less kinetic frictional force than as-received brackets. The hardness of the DLC layers was much higher than that of the as-received bracket surfaces. In conclusion, the surfaces of metal brackets can be successfully modified by the PBIID method to create a DLC layer, and the DLC-coating process significantly reduces frictional forces. PMID:21934113

  6. Friction welding.

    NASA Technical Reports Server (NTRS)

    Moore, T. J.

    1972-01-01

    Results of an exploratory study of the structure and properties of friction welds in Udimet 700 (U-700) and TD-nickel (TD-Ni) bar materials, as well as dissimilar U-700/TD-Ni friction welds. Butt welds were prepared by friction welding 12.7-mm-diam U-700 bars and TD-Ni bars. Specimens for elevated temperature tensile and stress rupture testing were machined after a postweld heat treatment. Friction welding of U-700 shows great potential because the welds were found to be as strong as the parent metal in stress rupture and tensile tests at 760 and 980 C. In addition, the weld line was not detectable by metallographic examination after postheating. Friction welds in TD-Ni or between U-700 and TD-Ni were extremely weak at elevated temperatures. The TD-Ni friction welds could support only 9% as much stress as the base metal for 10-hour stress rupture life at 1090 C. The U-700/TD-Ni weld could sustain only 15% as much stress as the TD-Ni parent metal for a 10-hour stress rupture life at 930 C. Thus friction welding is not a suitable joining method for obtaining high-strength TD-Ni or U-700/TD-Ni weldments.

  7. General theory of frictional heating with application to rubber friction

    NASA Astrophysics Data System (ADS)

    Fortunato, G.; Ciaravola, V.; Furno, A.; Lorenz, B.; Persson, B. N. J.

    2015-05-01

    The energy dissipation in the contact regions between solids in sliding contact can result in high local temperatures which may strongly effect friction and wear. This is the case for rubber sliding on road surfaces at speeds above 1 mm s-1. We derive equations which describe the frictional heating for solids with arbitrary thermal properties. The theory is applied to rubber friction on road surfaces and we take into account that the frictional energy is partly produced inside the rubber due to the internal friction of rubber and in a thin (nanometer) interfacial layer at the rubber-road contact region. The heat transfer between the rubber and the road surface is described by a heat transfer coefficient which depends on the sliding speed. Numerical results are presented and compared to experimental data. We find that frictional heating results in a kinetic friction force which depends on the orientation of the sliding block, thus violating one of the two basic Leonardo da Vinci ‘laws’ of friction.

  8. Interplay of non-Markov and internal friction effects in the barrier crossing kinetics of biopolymers: Insights from an analytically solvable model

    NASA Astrophysics Data System (ADS)

    Makarov, Dmitrii E.

    2013-01-01

    Conformational rearrangements in biomolecules (such as protein folding or enzyme-ligand binding) are often interpreted in terms of low-dimensional models of barrier crossing such as Kramers' theory. Dimensionality reduction, however, entails memory effects; as a result, the effective frictional drag force along the reaction coordinate nontrivially depends on the time scale of the transition. Moreover, when both solvent and "internal" friction effects are important, their interplay results in a highly nonlinear dependence of the effective friction on solvent viscosity that is not captured by common phenomenological models of barrier crossing. Here, these effects are illustrated using an analytically solvable toy model of an unstructured polymer chain involved in an inter- or intramolecular transition. The transition rate is calculated using the Grote-Hynes and Langer theories, which—unlike Kramers' theory—account for memory. The resulting effective frictional force exerted by the polymer along the reaction coordinate can be rationalized in terms of the effective number of monomers engaged in the transition. Faster transitions (relative to the polymer reconfiguration time scale) involve fewer monomers and, correspondingly, lower friction forces, because the polymer chain does not have enough time to reconfigure in response to the transition.

  9. Internal rotor friction instability

    NASA Technical Reports Server (NTRS)

    Walton, J.; Artiles, A.; Lund, J.; Dill, J.; Zorzi, E.

    1990-01-01

    The analytical developments and experimental investigations performed in assessing the effect of internal friction on rotor systems dynamic performance are documented. Analytical component models for axial splines, Curvic splines, and interference fit joints commonly found in modern high speed turbomachinery were developed. Rotor systems operating above a bending critical speed were shown to exhibit unstable subsynchronous vibrations at the first natural frequency. The effect of speed, bearing stiffness, joint stiffness, external damping, torque, and coefficient of friction, was evaluated. Testing included material coefficient of friction evaluations, component joint quantity and form of damping determinations, and rotordynamic stability assessments. Under conditions similar to those in the SSME turbopumps, material interfaces experienced a coefficient of friction of approx. 0.2 for lubricated and 0.8 for unlubricated conditions. The damping observed in the component joints displayed nearly linear behavior with increasing amplitude. Thus, the measured damping, as a function of amplitude, is not represented by either linear or Coulomb friction damper models. Rotordynamic testing of an axial spline joint under 5000 in.-lb of static torque, demonstrated the presence of an extremely severe instability when the rotor was operated above its first flexible natural frequency. The presence of this instability was predicted by nonlinear rotordynamic time-transient analysis using the nonlinear component model developed under this program. Corresponding rotordynamic testing of a shaft with an interference fit joint demonstrated the presence of subsynchronous vibrations at the first natural frequency. While subsynchronous vibrations were observed, they were bounded and significantly lower in amplitude than the synchronous vibrations.

  10. Rate-dependent frictional adhesion in natural and synthetic gecko setae

    PubMed Central

    Gravish, Nick; Wilkinson, Matt; Sponberg, Simon; Parness, Aaron; Esparza, Noe; Soto, Daniel; Yamaguchi, Tetsuo; Broide, Michael; Cutkosky, Mark; Creton, Costantino; Autumn, Kellar

    2010-01-01

    Geckos owe their remarkable stickiness to millions of dry, hard setae on their toes. In this study, we discovered that gecko setae stick more strongly the faster they slide, and do not wear out after 30 000 cycles. This is surprising because friction between dry, hard, macroscopic materials typically decreases at the onset of sliding, and as velocity increases, friction continues to decrease because of a reduction in the number of interfacial contacts, due in part to wear. Gecko setae did not exhibit the decrease in adhesion or friction characteristic of a transition from static to kinetic contact mechanics. Instead, friction and adhesion forces increased at the onset of sliding and continued to increase with shear speed from 500 nm s−1 to 158 mm s−1. To explain how apparently fluid-like, wear-free dynamic friction and adhesion occur macroscopically in a dry, hard solid, we proposed a model based on a population of nanoscopic stick–slip events. In the model, contact elements are either in static contact or in the process of slipping to a new static contact. If stick–slip events are uncorrelated, the model further predicted that contact forces should increase to a critical velocity (V*) and then decrease at velocities greater than V*. We hypothesized that, like natural gecko setae, but unlike any conventional adhesive, gecko-like synthetic adhesives (GSAs) could adhere while sliding. To test the generality of our results and the validity of our model, we fabricated a GSA using a hard silicone polymer. While sliding, the GSA exhibited steady-state adhesion and velocity dependence similar to that of gecko setae. Observations at the interface indicated that macroscopically smooth sliding of the GSA emerged from randomly occurring stick–slip events in the population of flexible fibrils, confirming our model predictions. PMID:19493896

  11. Friction microprobe investigation of particle layer effects on sliding friction

    SciTech Connect

    Blau, P.J.

    1993-01-01

    Interfacial particles (third-bodies), resulting from wear or external contamination, can alter and even dominate the frictional behavior of solid-solid sliding in the absence of effective particle removal processes (e.g., lubricant flow). A unique friction microprobe, developed at Oak Ridge National Laboratory, was used to conduct fine- scale friction studies using 1.0 mm diameter stainless steel spheres sliding on several sizes of loose layers of fine aluminum oxide powders on both aluminum and alumina surfaces. Conventional, pin-on-disk experiments were conducted to compare behavior with the friction microprobe results. The behavior of the relatively thick particle layers was found to be independent of the nature of underlying substrate, substantiating previous work by other investigators. The time-dependent behavior of friction, for a spherical macrocontact starting from rest, could generally be represented by a series of five rather distinct phases involving static compression, slider breakaway, transition to steady state, and dynamic layer instability. A friction model for the steady state condition, which incorporates lamellar powder layer behavior, is described.

  12. Electrostatic chucking of EUVL masks: coefficients of friction

    NASA Astrophysics Data System (ADS)

    Kalkowski, Gerhard; Semmler, Christian; Risse, Stefan; Peschel, Thomas; Damm, Christoph; Müller, Sandra; Bauer, René

    2010-04-01

    In extreme ultraviolet lithography (EUVL), the mask hangs on an electrostatic chuck and is moved laterally during exposition. For proper control of the chucked mask under corresponding inertial forces, static friction of the mask on the chuck is critical and an important input parameter for reliable theoretical modelling. To determine static and dynamic friction values, measurements were performed in vacuum on a mask blank with a test chuck, smaller than a real EUVL mask chuck, but otherwise nearly identical in its characteristics. Experimental results were obtained at various voltages for a materials combination of Low Thermal Expansion Glass (LTEM) for the pin chuck surface and a mask blank with a chromium metal backside metallisation, respectively. Dynamic friction was found to be only marginally smaller than static friction and values in the range from 0.27 to 0.33 were determined for the static friction coefficient under vacuum conditions.

  13. Thermodynamics of a Block Sliding across a Frictional Surface

    ERIC Educational Resources Information Center

    Mungan, Carl E.

    2007-01-01

    The following idealized problem is intended to illustrate some basic thermodynamic concepts involved in kinetic friction. A block of mass m is sliding on top of a frictional, flat-topped table of mass M. The table is magnetically levitated, so that it can move without thermal contact and friction across a horizontal floor. The table is initially…

  14. Effect of friction on shear jamming

    NASA Astrophysics Data System (ADS)

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

    Shear jamming of granular materials was first found for systems of frictional disks, with a static friction coefficient μ ~ 0 . 6 (Bi et al. Nature (2011)). Jamming by shear is obtained by starting from a zero-stress state with a packing fraction ϕ between ϕJ (isotropic jamming) and a lowest ϕS for shear jamming. This phenomenon is associated with strong anisotropy in stress and the contact network in the form of force chains, which are stabilized and/or enhanced by the presence of friction. Whether shear jamming occurs for frictionless particles is under debate. The issue we address experimentally is how changing friction affects shear jamming. By applying a homogeneous simple shear, we study the effect of friction by using photoelastic disks either wrapped with Teflon to reduce friction or with fine teeth on the edge to increase friction. Shear jamming is still observed; however, the difference ϕJ -ϕS is smaller with lower friction. We also observe larger fluctuations due to initial configurations both at the lowest and the highest friction systems studied. Ongoing work is to use particles made of gelatin to reduce the friction coefficient to the order of 0.01. We acknowledge support from NSF Grant DMR1206351, NASA Grant NNX15AD38G and the William M. Keck Foundation.

  15. Effect of friction on shear jamming

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    Shear jamming of granular materials was first found for systems of frictional disks, with a static friction coefficient μ ~ 0 . 6. Jamming by shear is obtained by starting from a zero-stress state with a packing fraction ϕ between ϕJ (isotropic jamming) and a lowest ϕS for shear jamming. This phenomenon is associated with strong anisotropy in stress and the contact network in the form of force chains, which are stabilized and/or enhanced by the presence of friction. Whether shear jamming occurs for frictionless particles is under debate. The issue we address experimentally is how changing friction affects shear jamming. By applying a homogeneous simple shear, we study the effect of friction by using photoelastic disks either wrapped with Teflon to reduce friction or with fine teeth on the edge to increase friction. Shear jamming is still observed; however, the difference ϕJ -ϕS is smaller with lower friction. We also observe larger fluctuations due to initial configurations both at the lowest and the highest friction systems studied. Ongoing work is to characterize response from different friction systems under shear with information at local scale. We acknowledge support from NSF-DMR1206351, NASA NNX15AD38G and W.M. Keck Foundation.

  16. Structure and friction of stearic acid and oleic acid films adsorbed on iron oxide surfaces in squalane.

    PubMed

    Doig, Michael; Warrens, Chris P; Camp, Philip J

    2014-01-14

    The structure and friction of fatty acid surfactant films adsorbed on iron oxide surfaces lubricated by squalane are examined using large-scale molecular dynamics simulations. The structures of stearic acid and oleic acid films under static and shear conditions, and at various surface coverages, are described in detail, and the effects of unsaturation in the tail group are highlighted. At high surface coverage, the measured properties of stearic acid and oleic acid films are seen to be very similar. At low and intermediate surface coverages, the presence of a double bond, as in oleic acid, is seen to give rise to less penetration of lubricant in to the surfactant film and less layering of the lubricant near to the film. The kinetic friction coefficient is measured as a function of shear rate within the hydrodynamic (high shear rate) lubrication regime. Lubricant penetration and layering are observed to be correlated with friction coefficient. The friction coefficient with oleic acid depends only weakly on surface coverage, while stearic acid admits more lubricant penetration, and its friction coefficient increases significantly with decreasing surface coverage. Connections between film structure and friction are discussed. PMID:24364665

  17. Frictional ageing from interfacial bonding and the origins of rate and state friction.

    PubMed

    Li, Qunyang; Tullis, Terry E; Goldsby, David; Carpick, Robert W

    2011-12-01

    Earthquakes have long been recognized as being the result of stick-slip frictional instabilities. Over the past few decades, laboratory studies of rock friction have elucidated many aspects of tectonic fault zone processes and earthquake phenomena. Typically, the static friction of rocks grows logarithmically with time when they are held in stationary contact, but the mechanism responsible for this strengthening is not understood. This time-dependent increase of frictional strength, or frictional ageing, is one manifestation of the 'evolution effect' in rate and state friction theory. A prevailing view is that the time dependence of rock friction results from increases in contact area caused by creep of contacting asperities. Here we present the results of atomic force microscopy experiments that instead show that frictional ageing arises from the formation of interfacial chemical bonds, and the large magnitude of ageing at the nanometre scale is quantitatively consistent with what is required to explain observations in macroscopic rock friction experiments. The relative magnitude of the evolution effect compared with that of the 'direct effect'--the dependence of friction on instantaneous changes in slip velocity--determine whether unstable slip, leading to earthquakes, is possible. Understanding the mechanism underlying the evolution effect would enable us to formulate physically based frictional constitutive laws, rather than the current empirically based 'laws', allowing more confident extrapolation to natural faults. PMID:22139421

  18. Friction compensation strategies in large telescopes

    NASA Astrophysics Data System (ADS)

    Smith, David R.; Souccar, Kamal

    2010-07-01

    For large telescopes, management of axis friction presents a significant challenge. In some cases, this is avoided or minimized in the design stage by employing hydrostatic bearings. However, the main axis servo systems of many large telescopes must cope with bearing or wheel friction. This friction affects or limits servo control performance in several ways. The most obvious is the stick-slip limit cycle that is characteristic of trying to hold position with an integrating control system in the presence of friction. If it is not taken into account, friction also introduces effects into the state estimation in model-based controllers. There are several standard approaches to friction compensation. These include dithering (introducing a noise signal to the drive motors), direct Coulomb friction compensation (sending an additional torque based on the rate command), and adaptive techniques based on monitoring of the final drive velocities. In this work, we experimentally compare different friction compensation approaches on the static positioning performance of the Large Millimeter Telescope/Gran Telescopio Milimetrico (LMT). Single and double integrator systems are investigated, as well as direct Coulomb friction compensation.

  19. Static penetration resistance of soils

    NASA Technical Reports Server (NTRS)

    Durgunoglu, H. T.; Mitchell, J. K.

    1973-01-01

    Model test results were used to define the failure mechanism associated with the static penetration resistance of cohesionless and low-cohesion soils. Knowledge of this mechanism has permitted the development of a new analytical method for calculating the ultimate penetration resistance which explicitly accounts for penetrometer base apex angle and roughness, soil friction angle, and the ratio of penetration depth to base width. Curves relating the bearing capacity factors to the soil friction angle are presented for failure in general shear. Strength parameters and penetrometer interaction properties of a fine sand were determined and used as the basis for prediction of the penetration resistance encountered by wedge, cone, and flat-ended penetrometers of different surface roughness using the proposed analytical method. Because of the close agreement between predicted values and values measured in laboratory tests, it appears possible to deduce in-situ soil strength parameters and their variation with depth from the results of static penetration tests.

  20. The Load and Time Dependence of Chemical Bonding-Induced Frictional Ageing of Silica at the Nanoscale

    NASA Astrophysics Data System (ADS)

    Tian, K.; Gosvami, N. N.; Goldsby, D. L.; Carpick, R. W.

    2015-12-01

    Rate and state friction (RSF) laws are empirical relationships that describe the frictional behavior of rocks and other materials in experiments, and reproduce a variety of observed natural behavior when employed in earthquake models. A pervasive observation from rock friction experiments is the linear increase of static friction with the log of contact time, or 'ageing'. Ageing is usually attributed to an increase in real area of contact associated with asperity creep. However, recent atomic force microscopy (AFM) experiments demonstrate that ageing of nanoscale silica-silica contacts is due to progressive formation of interfacial chemical bonds in the absence of plastic deformation, in a manner consistent with the multi-contact ageing behavior of rocks [Li et al., 2011]. To further investigate chemical bonding-induced ageing, we explored the influence of normal load (and thus contact normal stress) and contact time on ageing. Experiments that mimic slide-hold-slide rock friction experiments were conducted in the AFM for contact loads and hold times ranging from 23 to 393 nN and 0.1 to 100 s, respectively, all in humid air (~50% RH) at room temperature. Experiments were conducted by sequentially sliding the AFM tip on the sample at a velocity V of 0.5 μm/s, setting V to zero and holding the tip stationary for a given time, and finally resuming sliding at 0.5 μm/s to yield a peak value of friction followed by a drop to the sliding friction value. Chemical bonding-induced ageing, as measured by the peak friction minus the sliding friction, increases approximately linearly with the product of normal load and the log of the hold time. Theoretical studies of the roles of reaction energy barriers in nanoscale ageing indicate that frictional ageing depends on the total number of reaction sites and the hold time [Liu & Szlufarska, 2012]. We combine chemical kinetics analyses with contact mechanics models to explain our results, and develop a new approach for curve

  1. Time-dependent friction and the mechanics of stick-slip

    USGS Publications Warehouse

    Dieterich, J.H.

    1978-01-01

    Time-dependent increase of static friction is characteristic of rock friction undera variety of experimental circumstances. Data presented here show an analogous velocity-dependent effect. A theor of friction is proposed that establishes a common basis for static and sliding friction. Creep at points of contact causes increases in friction that are proportional to the logarithm of the time that the population of points of contact exist. For static friction that time is the time of stationary contact. For sliding friction the time of contact is determined by the critical displacement required to change the population of contacts and the slip velocity. An analysis of a one-dimensional spring and slider system shows that experimental observations establishing the transition from stable sliding to stick-slip to be a function of normal stress, stiffness and surface finish are a consequence of time-dependent friction. ?? 1978 Birkha??user Verlag.

  2. Kalker's algorithm Fastsim solves tangential contact problems with slip-dependent friction and friction anisotropy

    NASA Astrophysics Data System (ADS)

    Piotrowski, J.

    2010-07-01

    This paper presents two extensions of Kalker's algorithm Fastsim of the simplified theory of rolling contact. The first extension is for solving tangential contact problems with the coefficient of friction depending on slip velocity. Two friction laws have been considered: with and without recuperation of the static friction. According to the tribological hypothesis for metallic bodies shear failure, the friction law without recuperation of static friction is more suitable for wheel and rail than the other one. Sample results present local quantities inside the contact area (division to slip and adhesion, traction) as well as global ones (creep forces as functions of creepages and rolling velocity). For the coefficient of friction diminishing with slip, the creep forces decay after reaching the maximum and they depend on the rolling velocity. The second extension is for solving tangential contact problems with friction anisotropy characterised by a convex set of the permissible tangential tractions. The effect of the anisotropy has been shown on examples of rolling without spin and in the presence of pure spin for the elliptical set. The friction anisotropy influences tangential tractions and creep forces. Sample results present local and global quantities. Both extensions have been described with the same language of formulation and they may be merged into one, joint algorithm.

  3. Effect of Friction on Shear Jamming

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    Shear jamming of granular materials was first found for systems of frictional disks, with a static friction coefficient μ ~ 0 . 6 (Bi et al. Nature (2011)). Jamming by shear is obtained by starting from a zero-stress state with a packing fraction ϕ between ϕJ (isotropic jamming) and a lowest ϕS for shear jamming. This phenomenon is associated with strong anisotropy in stress and the contact network in the form of force chains, which are stabilized and/or enhanced by the presence of friction. Whether shear jamming occurs for frictionless particles is under debate. The issue we address experimentally is how reducing friction affects shear jamming. We put the Teflon-wrapped photoelastic disks, lowering the friction substantially from previous experiments, in a well-studied 2D shear apparatus (Ren et al. PRL (2013)), which provides a uniform simple shear. Shear jamming is still observed; however, the difference ϕJ -ϕS is smaller with lower friction. We also observe larger anisotropies in fragile states compared to experiments with higher friction particles at the same density. In ongoing work we are studying systems using photoelastic disks with fine gears on the edge to generate very large effective friction. We acknowledge support from NSF Grant DMR1206351, NSF Grant DMS-1248071, NASA Grant NNX10AU01G and William M. Keck Foundation.

  4. Effect of friction on shear jamming

    NASA Astrophysics Data System (ADS)

    Wang, Dong; Ren, Jie; Dijksman, Joshua; Behringer, Robert

    2014-11-01

    Shear Jamming of granular materials was first found for systems of frictional disks, with a static friction coefficients μs ~= 0 . 6 . Jamming by shear is obtained by starting from a zero-stress state with a packing fraction ϕS <= ϕ <=ϕJ between ϕJ (isotropic jamming) and a lowest ϕS for shear jamming. This phenomenon is associated with strong anisotropy in stress and the contact network in the form of ``force chains,'' which are stabilized and/or enhanced by the presence of friction. The issue that we address experimentally is how reducing friction affects shear jamming. We use photoelastic disks that have been wrapped with Teflon, lowering the friction coefficient substantially from previous experiments. The Teflon-wrapped disks were placed in a well-studied 2D shear apparatus (Ren et al., PRL, 110, 018302 (2013)), which provides uniform simple shear without generating shear bands. Shear jamming is still observed, but the difference ϕJ -ϕS is smaller than for higher friction particles. With Teflon-wrapped disks, we observe larger anisotropies compared to the previous experiment with higher friction particles at the same packing fraction, which indicates force chains tending to be straight in the low friction system. We acknowledge support from NSF Grant No. DMR12-06351, ARO Grant No. W911NF-1-11-0110, and NASA Grant No. NNX10AU01G.

  5. Friction of different monolayer lubricants in MEMs interfaces.

    SciTech Connect

    Carpick, Robert W. (University of Wisconsin, Madison, WI); Street, Mark D.; Ashurst, William Robert; Corwin, Alex David

    2006-01-01

    This report details results from our last year of work (FY2005) on friction in MEMS as funded by the Campaign 6 program for the Microscale Friction project. We have applied different monolayers to a sensitive MEMS friction tester called the nanotractor. The nanotractor is also a useful actuator that can travel {+-}100 {micro}m in 40 nm steps, and is being considered for several MEMS applications. With this tester, we can find static and dynamic coefficients of friction. We can also quantify deviations from Amontons' and Coulomb's friction laws. Because of the huge surface-to-volume ratio at the microscale, surface properties such as adhesion and friction can dominate device performance, and therefore such deviations are important to quantify and understand. We find that static and dynamic friction depend on the monolayer lubricant applied. The friction data can be modeled with a non-zero adhesion force, which represents a deviation from Amontons' Law. Further, we show preliminary data indicating that the adhesion force depends not only on the monolayer, but also on the normal load applied. Finally, we also observe slip deflections before the transition from static to dynamic friction, and find that they depend on the monolayer.

  6. A comparative study to evaluate the effects of ligation methods on friction in sliding mechanics using 0.022" slot brackets in dry state: An In-vitro study

    PubMed Central

    Vinay, K; Venkatesh, M J; Nayak, Rabindra S; Pasha, Azam; Rajesh, M; Kumar, Pradeep

    2014-01-01

    Background: Friction between archwires and brackets is assuming greater importance for finishing with increased use of sliding mechanics in orthodontics as friction impedes the desired tooth movement. The following study is conducted to compare and evaluate the effect of ligation on friction in sliding mechanics using 0.022" slot bracket in dry condition. Materials & Methods: In the study 48 combinations of brackets, archwires and different ligation techniques were tested in order to provide best combination that offers less friction during sliding mechanics. Instron- 4467 machine was used to evaluate static and kinetic friction force values and the results were subjected to Statistical Analysis and Anova test. Results: The results of the study showed that 0.022" metal brackets, Stainless steel wires and Slick modules provided the optimum frictional resistance to sliding mechanics. It is observed that frictional forces of 0.019" x 0.025" were higher when compared with 0.016" x 0.022" Stainless steel archwire due to the increase in dimension. Self-ligating brackets offered least friction followed by mini twin, variable force, regular stainless steel, ceramic with metal insert bracket and ceramic brackets. The stainless steel ligature offered less resistance than slick and grey modules, and TMA wires recorded maximum friction. Conclusion: The stainless steel archwire of 0.019" x 0.025" dimension are preferred during sliding mechanics, these archwires with variable force brackets ligated with Slick Modules offer decreased friction and is cost effective combination which can be utilized during sliding mechanics. How to cite the article: Vinay K, Venkatesh MJ, Nayak RS, Pasha A, Rajesh M, Kumar P. A comparative study to evaluate the effects of ligation methods on friction in sliding mechanics using 0.022" slot brackets in dry state: An In-vitro study. J Int Oral Health 2014;6(2):76-83. PMID:24876706

  7. Active Dynamic Frictional Probes

    NASA Astrophysics Data System (ADS)

    Steimel, Joshua; Aragones, Juan; Alexander-Katz, Alfredo

    2015-03-01

    In biological systems there are a myriad of interactions occurring instantaneously and these interactions can vary drastically in the strength of the interaction, the speed at which this interaction occurs, and the duration of the interaction. When multiple interactions occur any of these factors can determine which particular interaction is dominant. However, currently it is extremely difficult to measure binding affinity, Kon, and Koff rates in a relatively high throughput manner. Here we propose a novel and versatile system that will be able to detect differences in binding affinity of wide range of transient interactions and will be able to extract the relevant time scales of these interactions. Our system will utilize ferromagnetic particles that can be easily functionalized with a receptor of interest and the substrate will be coated in the corresponding ligand. A rotating magnetic field will cause particles, henceforth referred to as rollers, to rotate and this rotational motion will be converted into translational motion via the effective frictional force induced by interaction that is being probed. By measuring the translation of the rollers to a baseline, where only hydrodynamic friction occurs, we can measure the relative strength of the interactions. We can also potentially measure kinetic information by changing the frequency at which the magnetic field rotates, since changing the frequency at which the bead rotates is akin to changing the time allowed for bond formation. We will measure a wide range of interaction including ionic, metal-ion coordination, IgG-Protein A complex, and biotin-streptavidin complex.

  8. Breakdown of Amontons' Law of Friction in Sheared-Elastomer with Local Amontons' Friction

    NASA Astrophysics Data System (ADS)

    Matsukawa, Hiroshi; Otsuki, Michio

    2012-02-01

    It is well known that Amontons' law of friction i.e. the frictional force against the sliding motion of solid object is proportional to the loading force and not dependent on the contact area, holds well for various systems. Here we show, however, the breakdown of the Amontons' law for the elastic object which have local friction obeying Amontons' law and is under uniform pressure by FEM calculation The external shearing force applied to the trailing edge of the sample induces local slip. The range of the slip increases with the increasing external force adiabatically at first. When the range reaches the critical magnitude, the slips moves rapidly and reaches the leading edge of the sample then the whole system slides. These behaviors are consistent with the experiment by Rubinstein et.al. (Phys. Rev. Lett. 98, 226103). The static frictional coefficient, the ratio between the static frictional force for the whole system and the loading force, decreases with the increasing pressure. This means the breakdown of Amontons' law. The pressure dependence of the frictional coefficient is caused by the change of the critical length of the local slip. The behaviors of the local slip and the frictional coefficient are well explained by the 1 dimensional model analytically.

  9. Adjustments to Local Friction in Multifinger Prehension

    PubMed Central

    Aoki, Tomoko; Latash, Mark L.; Zatsiorsky, Vladimir M.

    2010-01-01

    The authors studied the effects of surface friction at the digit–object interface on digit forces and moments when 12 participants statically held an object in a 5-digit grasp. The authors changed low-friction contact (LFC) with rayon and high-friction contact (HFC) with sandpaper independently for each digit in all 32 possible combinations. Normal forces of the thumb and virtual finger (VF), an imagined finger with a mechanical effect equal to that of the 4 fingers, increased with the thumb at LFC or with an increase in the number of fingers at LFC. When the thumb was at LFC, the thumb tangential force decreased. The VF tangential force decreased when the number of fingers at LFC increased. The interaction of the local responses to friction and the synergic responses necessary to maintain the equilibrium explain the coordination of individual digit forces. PMID:17664170

  10. Friction Forces in General Relativity

    NASA Astrophysics Data System (ADS)

    Bini, D.; Gregoris, D.; Rosquist, K.

    2015-01-01

    Friction forces play an important role in a wide class of phenomena both in the contexts of classical mechanics and general relativity. This paper discusses the Poynting-Robertson approach to the description of the motion of a massive test particle inside a perfect fluid undergoing dissipative effects in curved space. Specific cases of motions 1) inside a photon gas near a Schwarzschild black hole; 2) inside a photon gas in the Tolman metric are then discussed with applications to models of accretion disks of a black hole and to motion inside a static radiation dominated Universe.

  11. On the dependency of friction on load: Theory and experiment

    NASA Astrophysics Data System (ADS)

    Braun, O. M.; Steenwyk, B.; Warhadpande, A.; Persson, B. N. J.

    2016-03-01

    In rubber friction studies it is often observed that the kinetic friction coefficient depends on the nominal contact pressure. This is usually due to frictional heating, which softens the rubber, increases the area of contact, and (in most cases) reduces the viscoelastic contribution to the friction. In this paper we present experimental results showing that the rubber friction also depends on the nominal contact pressure at such low sliding speed that frictional heating is negligible. This effect has important implications for rubber sliding dynamics, e.g., in the context of the tire-road grip. We attribute this effect to the viscoelastic coupling between the macroasperity contact regions, and present a simple earthquakelike model and numerical simulations supporting this picture. The mechanism for the dependency of the friction coefficient on the load considered is very general, and is relevant for non-rubber materials as well.

  12. Frictional Resistance of Three Types of Ceramic Brackets

    PubMed Central

    Williams, Claire L

    2013-01-01

    ABSTRACT Objectives To investigate the static frictional resistance at the bracket/archwire interface in two recently introduced bracket systems and compare them to conventional ceramic and conventional metal bracket systems. Three variables were considered including the bracket system, archwire type and archwire angulation. Material and Methods Four bracket systems were tested in vitro: Self ligating ceramic, ceramic with metal slot and module, conventional ceramic with module and conventional metal with module. A specially constructed jig and an Instron testing machine were used to measure the static frictional resistance for 0.014 inches round and 0.018 x 0.025 inches rectangular stainless steel wires at 0° and 7° angulations. Main outcome measures: static frictional force at the bracket/archwire interface; recorded and measured in units of force (Newtons). Results Self ligating ceramic and metal slot ceramic bracket systems generated significantly less static frictional resistance than conventional ceramic bracket systems with the wire at both angulations (P < 0.05). Changing the wire from 0.014 round to 0.018 x 0.025 rectangular wire significantly increased frictional forces for metal slot ceramic and conventional metal bracket systems (P < 0.01). Increasing wire angulation significantly increased frictional resistance at the bracket/archwire interface for all four types of bracket systems tested (P < 0.001). Conclusions Compared to conventional ceramic, self ligating ceramic and metal slot ceramic bracket systems should give improved clinical performance, matching that of conventional metal brackets. PMID:24478913

  13. Onset of frictional sliding of rubber–glass contact under dry and lubricated conditions

    PubMed Central

    Tuononen, Ari J.

    2016-01-01

    Rubber friction is critical in many applications ranging from automotive tyres to cylinder seals. The process where a static rubber sample transitions to frictional sliding is particularly poorly understood. The experimental and simulation results in this paper show a completely different detachment process from the static situation to sliding motion under dry and lubricated conditions. The results underline the contribution of the rubber bulk properties to the static friction force. In fact, simple Amontons’ law is sufficient as a local friction law to produce the correct detachment pattern when the rubber material and loading conditions are modelled properly. Simulations show that micro-sliding due to vertical loading can release initial shear stresses and lead to a high static/dynamic friction coefficient ratio, as observed in the measurements. PMID:27291939

  14. Onset of frictional sliding of rubber–glass contact under dry and lubricated conditions

    NASA Astrophysics Data System (ADS)

    Tuononen, Ari J.

    2016-06-01

    Rubber friction is critical in many applications ranging from automotive tyres to cylinder seals. The process where a static rubber sample transitions to frictional sliding is particularly poorly understood. The experimental and simulation results in this paper show a completely different detachment process from the static situation to sliding motion under dry and lubricated conditions. The results underline the contribution of the rubber bulk properties to the static friction force. In fact, simple Amontons’ law is sufficient as a local friction law to produce the correct detachment pattern when the rubber material and loading conditions are modelled properly. Simulations show that micro-sliding due to vertical loading can release initial shear stresses and lead to a high static/dynamic friction coefficient ratio, as observed in the measurements.

  15. Onset of frictional sliding of rubber-glass contact under dry and lubricated conditions.

    PubMed

    Tuononen, Ari J

    2016-01-01

    Rubber friction is critical in many applications ranging from automotive tyres to cylinder seals. The process where a static rubber sample transitions to frictional sliding is particularly poorly understood. The experimental and simulation results in this paper show a completely different detachment process from the static situation to sliding motion under dry and lubricated conditions. The results underline the contribution of the rubber bulk properties to the static friction force. In fact, simple Amontons' law is sufficient as a local friction law to produce the correct detachment pattern when the rubber material and loading conditions are modelled properly. Simulations show that micro-sliding due to vertical loading can release initial shear stresses and lead to a high static/dynamic friction coefficient ratio, as observed in the measurements. PMID:27291939

  16. Emergent friction in two-dimensional Frenkel-Kontorova models

    NASA Astrophysics Data System (ADS)

    Norell, Jesper; Fasolino, Annalisa; de Wijn, Astrid S.

    2016-08-01

    Simple models for friction are typically one-dimensional, but real interfaces are two-dimensional. We investigate the effects of the second dimension on static and dynamic friction by using the Frenkel-Kontorova (FK) model. We study the two most straightforward extensions of the FK model to two dimensions and simulate both the static and dynamic properties. We show that the behavior of the static friction is robust and remains similar in two dimensions for physically reasonable parameter values. The dynamic friction, however, is strongly influenced by the second dimension and the accompanying additional dynamics and parameters introduced into the models. We discuss our results in terms of the thermal equilibration and phonon dispersion relations of the lattices, establishing a physically realistic and suitable two-dimensional extension of the FK model. We find that the presence of additional dissipation channels can increase the friction and produces significantly different temperature dependence when compared to the one-dimensional case. We also briefly study the anisotropy of the dynamic friction and show highly nontrivial effects, including that the friction anisotropy can lead to motion in different directions depending on the value of the initial velocity.

  17. Effect of friction on shear jamming

    NASA Astrophysics Data System (ADS)

    Wang, Dong; Ren, Jie; Dijksman, Joshua; Behringer, Robert

    2014-03-01

    Shear Jamming of granular materials was first found for systems of frictional disks, with a static friction coefficients μs ~= 0 . 6 . Jamming by shear is obtained by starting from a zero-stress state with a packing fraction ϕS <= ϕ <=ϕJ between ϕJ (isotropic jamming) and a lowest ϕS for shear jamming. This phenomenon is associated with strong anisotropy in stress and the contact network in the form of ``force chains,'' which are stabilized and/or enhanced by the presence of friction. We address experimentally how reducing friction affects shear jamming by using either teflon disks of teflon wrapped photoelastic particles. The teflon disks were placed in a wall driven 2D shear apparatus, in which we can probe shear stresses mechanically. Teflon-wrapped disks were placed in a bottom driven 2D shear apparatus (Ren et al., PRL 2013). Both apparatuses provide uniform simple shear. In all low- μ experiments, the shear jamming occurred, as observed through stress increases on the packing. However, the low- μ differences observed for ϕJ -ϕS were smaller than for higher friction particles. Ongoing work is studying systems using hydrogel disks, which have a lower friction coefficient than teflon. We acknowledge support from NSF Grant No. DMR12-06351, ARO Grant No. W911NF-1-11-0110, and NASA Grant No. NNX10AU01G.

  18. Frictional Characteristics of graphene

    NASA Astrophysics Data System (ADS)

    Lee, Changgu; Carpick, Robert; Hone, James

    2009-03-01

    The frictional characteristics of graphene were characterized using friction force microscopy (FFM). The frictional force for monolayer graphene is more than twice that of bulk graphite, with 2,3, and 4 layer samples showing a monotonic decrease in friction with increasing sample thickness. Measurements on suspended graphene membranes show identical results, ruling out substrate effects as the cause of the observed variation. Likewise, the adhesion force is identical for all samples. The frictional force is independent of load within experimental uncertainty, consistent with previous measurements on graphite. We consider several possible explanations for the origin of the observed thickness dependence.

  19. Nanotribology and Nanoscale Friction

    SciTech Connect

    Guo, Yi; Qu, Zhihua; Braiman, Yehuda; Zhang, Zhenyu; Barhen, Jacob

    2008-01-01

    Tribology is the science and technology of contacting solid surfaces in relative motion, including the study of lubricants, lubrication, friction, wear, and bearings. It is estimated that friction and wear cost the U.S. economy 6% of the gross national product (Persson, 2000). For example, 5% of the total energy generated in an automobile engine is lost to frictional resistance. The study of nanoscale friction has a technological impact in reducing energy loss in machines, in microelectromechanical systems (MEMS), and in the development of durable, low-friction surfaces and ultra-thin lubrication films.

  20. Friction drive characterization breadboard: test results

    NASA Astrophysics Data System (ADS)

    Sedghi, B.; Lucuix, C.; Tortolani, J. M.; Brunetto, E.; Delrez, C.; Gabriel, E.

    2010-07-01

    The drive and bearing technologies have a major impact on the static and dynamic performance of steerable structures such as telescope and dome. Merging drive and bearing system into friction drive mechanical devices (bogie) can reduce the complexity and cost of the design. In the framework of ELT design study (European FP6) a breadboard test setup was realized to test and evaluate the static and dynamic behavior of such bogies. In this paper some of the characterization test results are presented. Characterization of the bogies and the setup structure in the frequency domain, quantification and measure of the most important parameters of the friction forces, the control of the bogies and the tracking performance of the test setup are among the main results discussed in this paper.

  1. Friction mediated by redox-active supramolecular connector molecules.

    PubMed

    Bozna, B L; Blass, J; Albrecht, M; Hausen, F; Wenz, G; Bennewitz, R

    2015-10-01

    We report on a friction study at the nanometer scale using atomic force microscopy under electrochemical control. Friction arises from the interaction between two surfaces functionalized with cyclodextrin molecules. The interaction is mediated by connector molecules with (ferrocenylmethyl)ammonium end groups forming supramolecular complexes with the cyclodextrin molecules. With ferrocene connector molecules in solution, the friction increases by a factor of up to 12 compared to control experiments without connector molecules. The electrochemical oxidation of ferrocene to ferrocenium causes a decrease in friction owing to the lower stability of ferrocenium-cyclodextrin complex. Upon switching between oxidative and reduction potentials, a change in friction by a factor of 1.2-1.8 is observed. Isothermal titration calorimetry reveals fast dissociation and rebinding kinetics and thus an equilibrium regime for the friction experiments. PMID:26367352

  2. Dynamic measurements of gear tooth friction and load

    NASA Technical Reports Server (NTRS)

    Rebbechi, Brian; Oswald, Fred B.; Townsend, Dennis P.

    1991-01-01

    As part of a program to study fundamental mechanisms of gear noise, static and dynamic gear tooth strain measurements were made on the NASA gear-noise rig. Tooth-fillet strains from low-contact ratio-spur gears were recorded for 28 operating conditions. A method is introduced whereby strain gage measurements taken from both the tension and compression sides of a gear tooth can be transformed into the normal and frictional loads on the tooth. This technique was applied to both the static and dynamic strain data. The static case results showed close agreement with expected results. For the dynamic case, the normal-force computation produced very good results, but the friction results, although promising, were not as accurate. Tooth sliding friction strongly affected the signal from the strain gage on the tensionside of the tooth. The compression gage was affected by friction to a much lesser degree. The potential of the method to measure friction force was demonstrated, but further refinement will be required before this technique can be used to measure friction forces dynamically with an acceptable degree of accuracy.

  3. Frictional coefficients of ion-implanted alumina against ion-implanted beta-titanium in the low load, low velocity, single pass regime.

    PubMed

    Kusy, R P; Tobin, E J; Whitley, J Q; Sioshansi, P

    1992-05-01

    The frictional coefficients were measured for four wire alloys against the flats of polycrystalline alumina cylinders using a low load, low velocity, single pass device. Ion-implantations of titanium into polycrystalline alumina flats and nitrogen into beta-titanium wires reduced the static and kinetic coefficients from 0.50 and 0.44 before implantation to 0.20 and 0.25 after implantation, respectively. These results are similar in magnitude to frictional coefficients for unimplanted, control couples of stainless steel, cobalt-chromium, and nickel titanium wires against polycrystalline alumina flats. For orthodontic applications, we conclude that more efficient and reproducible appliances can be engineered for tooth movement if ion-implantation is used to reduce the abrasion of beta-titanium by polycrystalline alumina. PMID:1521704

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

    PubMed

    Svetlizky, Ilya; Fineberg, Jay

    2014-05-01

    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. PMID:24805344

  5. A hinged-pad test structure for sliding friction measurement in micromachining

    SciTech Connect

    Boer, M.P. de; Redmond, J.M.; Michalske, T.A.

    1998-08-01

    The authors describe the design, modeling, fabrication and initial testing of a new test structure for friction measurement in MEMS. The device consists of a cantilevered forked beam and a friction pad attached via a hinge. Compared to previous test structures, the proposed structure can measure friction over much larger pressure ranges, yet occupies one hundred times less area. The placement of the hinge is crucial to obtaining a well-known and constant pressure distribution in the device. Static deflections on the device were measured and modeled numerically, Preliminary results indicate that friction pad slip is sensitive to friction pad normal force.

  6. Temperature dependence of nanoscale friction for Fe on YBCO

    NASA Astrophysics Data System (ADS)

    Altfeder, Igor; Krim, Jacqueline

    2012-05-01

    A magnetic probe microscopy study of levitation and atomic-scale friction is reported for Fe on YBCO (Tc = 92.5 K) in the temperature range 65-293 K. Below Tc, the friction coefficient is constant and exhibits no correlation with the strength of superconducting levitation forces. Above Tc, the friction coefficient increases progressively, and nearly doubles between Tc and room temperature. The results are discussed within the context of the underlying atomic-scale electronic and phononic mechanisms that give rise to friction, and it is concluded that contact electrification and static electricity may play a significant role in the non-superconducting phase. Given that the properties of YBCO can be finely tuned, the results point the way to a variety of interesting studies of friction and superconductors.

  7. Enhanced friction of elastomer microfiber adhesives with spatulate tips

    NASA Astrophysics Data System (ADS)

    Kim, Seok; Aksak, Burak; Sitti, Metin

    2007-11-01

    Previous studies have demonstrated that gecko foot-hair inspired elastomer microfibers with spatulate tips have significant adhesion enhancement compared to the flat elastomer surface. In this study, we report the friction enhancement of these highly adhesive fibers and analyze the relation between adhesion and friction of elastomer microfiber arrays with spatulate tips. Fabricated polyurethane fiber arrays with spatulate tips demonstrate macroscale static friction pressures up to 41N/cm2 for a preload pressure of 1.5N/cm2 on a 6mm diameter smooth glass hemisphere.

  8. The friction and wear of TPS fibers

    NASA Technical Reports Server (NTRS)

    Bascom, W. D.; Wong, S.

    1987-01-01

    The sliding friction behavior of single filaments of SiO2, SiC, and an aluminoborosilicate has been determined. These fibers are used in thermal protection systems (TPS) and are subject to damage during weaving and aero-maneuvering. All fibers exhibited stick-slip friction indicating the successive formation and rupture of strong junctions between the contacting filaments. The static frictional resistance of the sized SiC filament was 4X greater than for the same filament after heat cleaning. This result suggests that the sizing is an organic polymer with a high shear yield strength. Heat cleaning exposes the SiC surface and/or leaves an inorganic residue so that the adhesional contact between filaments has a low fracture energy and frictional sliding occurs by brittle fracture. The frictional resistances of the sized and heat cleaned SiO2 and glass filaments were all comparable to that of the heat cleaned SiC. It would appear that the sizings as well as the heat cleaned surfaces of the silica and glass have low fracture energies so that the sliding resistance is determined by brittle fracture.

  9. Dependence of friction on roughness, velocity, and temperature

    NASA Astrophysics Data System (ADS)

    Sang, Yi; Dubé, Martin; Grant, Martin

    2008-03-01

    We study the dependence of friction on surface roughness, sliding velocity, and temperature. Expanding on the classic treatment of Greenwood and Williamson, we show that the fractal nature of a surface has little influence on the real area of contact and the static friction coefficient. A simple scaling argument shows that the static friction exhibits a weak anomaly μ˜A0-χ/4 , where A0 is the apparent area and χ is the roughness exponent of the surface. We then develop a method to calculate atomic-scale friction between a microscopic asperity, such as the tip of a friction force microscope (FFM) and a solid substrate. This method, based on the thermal activation of the FFM tip, allows a quantitative extraction of all the relevant microscopic parameters and reveals a universal scaling behavior of atomic friction on velocity and temperature. This method is extended to include a soft atomic substrate in order to simulate FFM scans more realistically. The tip is connected with the support of the cantilever by an ideal spring and the substrate is simulated with a ball-spring model. The tip and substrate are coupled with repulsive potentials. Simulations are done at different temperatures and scanning velocities on substrates with different elastic moduli. Stick-slip motion of the tip is observed, and the numerical results of the friction force and distribution of force maxima match the theoretical framework.

  10. A comparative study of frictional force in self-ligating brackets according to the bracket-archwire angulation, bracket material, and wire type

    PubMed Central

    Lee, Souk Min

    2015-01-01

    Objective This study aimed to compare the frictional force (FR) in self-ligating brackets among different bracket-archwire angles, bracket materials, and archwire types. Methods Passive and active metal self-ligating brackets and active ceramic self-ligating brackets were included as experimental groups, while conventional twin metal brackets served as a control group. All brackets were maxillary premolar brackets with 0.022 inch [in] slots and a -7° torque. The orthodontic wires used included 0.018 round and 0.019 × 0.025 in rectangular stainless steel wires. The FR was measured at 0°, 5°, and 10° angulations as the wire was drawn through the bracket slots after attaching brackets from each group to the universal testing machine. Static and kinetic FRs were also measured. Results The passive self-ligating brackets generated a lower FR than all the other brackets. Static and kinetic FRs generally increased with an increase in the bracket-archwire angulation, and the rectangular wire caused significantly higher static and kinetic FRs than the round wire (p < 0.001). The metal passive self-ligating brackets exhibited the lowest static FR at the 0° angulation and a lower increase in static and kinetic FRs with an increase in bracket-archwire angulation than the other brackets, while the conventional twin brackets showed a greater increase than all three experimental brackets. Conclusions The passive self-ligating brackets showed the lowest FR in this study. Self-ligating brackets can generate varying FRs in vitro according to the wire size, surface characteristics, and bracket-archwire angulation. PMID:25667913

  11. Friction of rocks

    USGS Publications Warehouse

    Byerlee, J.

    1978-01-01

    Experimental results in the published literature show that at low normal stress the shear stress required to slide one rock over another varies widely between experiments. This is because at low stress rock friction is strongly dependent on surface roughness. At high normal stress that effect is diminished and the friction is nearly independent of rock type. If the sliding surfaces are separated by gouge composed of Montmorillonite or vermiculite the friction can be very low. ?? 1978 Birkha??user Verlag.

  12. Preventing Friction Induced Chondrocyte Apoptosis: A Comparison of Human Synovial Fluid and Hylan G-F 20

    PubMed Central

    Waller, Kimberly A; Zhang, Ling X; Fleming, Braden C; Jay, Gregory D

    2013-01-01

    Objectives Symptomatic osteoarthritis (OA) is a common painful disease with limited treatment options. A rising number of OA patients have been treated with intraarticular injections of hyaluronic acid, including the high molecular weight hylan G-F 20, which is injected following arthrocentesis. This study investigated the effectiveness of hylan G-F 20 to lower coefficient of friction (COF) and prevent chondrocyte apoptosis in vitro. Methods A disc-on-disc bovine cartilage bearing was used to measure the static and kinetic COF when lubricated with hylan G-F 20, human synovial fluid (HSF) and phosphate buffered saline (PBS). Following friction testing, we stained paraffin embedded sections of these cartilage bearings for activated caspase-3, a marker of apoptosis. Results Bearings lubricated with hylan G-F 20 had kinetic COF values that were similar to bearings lubricated with PBS, but significantly higher than those lubricated with HSF. There were no significant differences in static COF values in bearings lubricated with hylan G-F 20 as compared to PBS or HSF. However, bearings lubricated with HSF had a significantly lower static COF values compared to bearings lubricated with PBS. The mean percentage of caspase-3 positive chondrocytes in the superficial and upper intermediate zones of bearings lubricated with hylan G-F 20 were significantly higher when compared to bearings lubricated with HSF or unloaded controls, but significantly lower than those lubricated with PBS. Conclusion These findings indicate that joint lubrication may prevent chondrocyte apoptosis by lowering the COF. Furthermore, removal of synovial fluid prior to hylan G-F 20 injection may be detrimental to cartilage health. PMID:22660808

  13. Friction and nonlinear dynamics

    NASA Astrophysics Data System (ADS)

    Manini, N.; Braun, O. M.; Tosatti, E.; Guerra, R.; Vanossi, A.

    2016-07-01

    The nonlinear dynamics associated with sliding friction forms a broad interdisciplinary research field that involves complex dynamical processes and patterns covering a broad range of time and length scales. Progress in experimental techniques and computational resources has stimulated the development of more refined and accurate mathematical and numerical models, capable of capturing many of the essentially nonlinear phenomena involved in friction.

  14. Friction and nonlinear dynamics.

    PubMed

    Manini, N; Braun, O M; Tosatti, E; Guerra, R; Vanossi, A

    2016-07-27

    The nonlinear dynamics associated with sliding friction forms a broad interdisciplinary research field that involves complex dynamical processes and patterns covering a broad range of time and length scales. Progress in experimental techniques and computational resources has stimulated the development of more refined and accurate mathematical and numerical models, capable of capturing many of the essentially nonlinear phenomena involved in friction. PMID:27249652

  15. Friction plug welding

    NASA Technical Reports Server (NTRS)

    Takeshita, Riki (Inventor); Hibbard, Terry L. (Inventor)

    2001-01-01

    Friction plug welding (FPW) usage is advantageous for friction stir welding (FSW) hole close-outs and weld repairs in 2195 Al--Cu--Li fusion or friction stir welds. Current fusion welding methods of Al--Cu--Li have produced welds containing varied defects. These areas are found by non-destructive examination both after welding and after proof testing. Current techniques for repairing typically small (<0.25) defects weaken the weldment, rely heavily on welders' skill, and are costly. Friction plug welding repairs increase strength, ductility and resistance to cracking over initial weld quality, without requiring much time or operator skill. Friction plug welding while pulling the plug is advantageous because all hardware for performing the weld can be placed on one side of the workpiece.

  16. Smart friction driven systems

    NASA Astrophysics Data System (ADS)

    Nitsche, Rainer; Gaul, Lothar

    2005-02-01

    Vibration properties of most assembled mechanical systems depend on frictional damping in joints. The nonlinear transfer behavior of the frictional interfaces often provides the dominant damping mechanism in a built-up structure and plays an important role in the vibratory response of the structure (Gaul and Nitsche 2001 Appl. Mech. Rev. 54 93-105). For improving the performance of systems, many studies have been carried out to predict, measure and/or enhance the energy dissipation of friction. To enhance the friction damping in joint connections a semi-active joint is investigated. A rotational joint connection is designed and manufactured such that the normal force in the friction interface can be influenced with a piezoelectric stack disc. With the piezoelectric device the normal force and thus the friction damping in the joint connection can be controlled. A control design method, namely semi-active control, is investigated. The recently developed LuGre friction model is used to describe the nonlinear transfer behavior of joints. This model is based on a bristle model and turns out to be highly suitable for systems assembled by such smart joints. Those systems can also be regarded as friction driven systems, since the energy flow is controlled by smart joints. The semi-active method is well suited for large space structures since the friction damping in joints turned out to be a major source of damping. To show the applicability of the proposed concept to large space structures a two-beam system representing a part of a large space structure is considered. Two flexible beams are connected with a semi-active joint connection. It can be shown that the damping of the system can be improved significantly by controlling the normal force in the semi-active joint connection. Experimental results validate the damping improvement due to the semi-active friction damping.

  17. The effect of ligation method on friction in sliding mechanics.

    PubMed

    Hain, Max; Dhopatkar, Ashish; Rock, Peter

    2003-04-01

    During orthodontic tooth movement with the preadjusted edgewise system, friction generated at the bracket/archwire interface tends to impede the desired movement. The method of ligation is an important contributor to this frictional force. This in vitro study investigated the effect of ligation method on friction and evaluated the efficacy of the new slick elastomeric modules from TP Orthodontics (La Porte, Ind), which are claimed to reduce friction at the module/wire interface. Slick modules were compared with regular nonslick modules, stainless steel ligatures, and the SPEED self-ligating bracket system (Strite Industries, Cambridge, Ontario, Canada). The effect of using slick modules with metal-reinforced ceramic (Clarity, 3M Unitek, Monrovia, Calif) and miniature brackets (Minitwin, 3M Unitek) was also examined. Results showed that, when considering tooth movement along a 0.019 x 0.025-in stainless steel archwire, saliva-lubricated slick modules can reduce static friction at the module/archwire interface by up to 60%, regardless of the bracket system. The SPEED brackets produced the lowest friction compared with the 3 other tested bracket systems when regular modules were used. The use of slick modules, however, with all of the ligated bracket types tested significantly reduced friction to below the values recorded in the SPEED groups. Loosely tied stainless steel ligatures were found to generate the least friction. PMID:12695769

  18. Confinement-dependent friction in peptide bundles.

    PubMed

    Erbaş, Aykut; Netz, Roland R

    2013-03-19

    Friction within globular proteins or between adhering macromolecules crucially determines the kinetics of protein folding, the formation, and the relaxation of self-assembled molecular systems. One fundamental question is how these friction effects depend on the local environment and in particular on the presence of water. In this model study, we use fully atomistic MD simulations with explicit water to obtain friction forces as a single polyglycine peptide chain is pulled out of a bundle of k adhering parallel polyglycine peptide chains. The whole system is periodically replicated along the peptide axes, so a stationary state at prescribed mean sliding velocity V is achieved. The aggregation number is varied between k = 2 (two peptide chains adhering to each other with plenty of water present at the adhesion sites) and k = 7 (one peptide chain pulled out from a close-packed cylindrical array of six neighboring peptide chains with no water inside the bundle). The friction coefficient per hydrogen bond, extrapolated to the viscous limit of vanishing pulling velocity V → 0, exhibits an increase by five orders of magnitude when going from k = 2 to k = 7. This dramatic confinement-induced friction enhancement we argue to be due to a combination of water depletion and increased hydrogen-bond cooperativity. PMID:23528088

  19. Is frictional healing slip-dependent?

    NASA Astrophysics Data System (ADS)

    Bhattacharya, P.; Rubin, A. M.; Ryan, K. L.; Riviere, J. V.; Marone, C.

    2015-12-01

    Frictional re-strengthening of bare rock surfaces at very low stresses and near zero slip rate, as observed in the laboratory, is traditionally interpreted as showing support for purely time-dependent healing as embodied in the Aging law. However, while slide-hold-slide experiments on bare surfaces do show an apparent (purely) time-dependent increase in the static friction upon reslide, we show that the stress minima attained during the preceding holds show a strong slip-dependence which contradict the Aging law. A velocity strengthening Slip law explains such data much better. We also show that, large velocity step decreases, which drive the system far below steady state just like long holds, clearly support the slip-dependent response of the Slip law over the time-dependent healing contained in the Aging law. But, while time-dependent healing has an intuitive physical picture in terms of growth of the 'real contact area' with time, it is more difficult to ascribe one to slip-dependent healing. Here, we explore the possibility that the slip-dependence arises out of an interplay between contact `quality' and `quantity' at the scale of the asperity contacts. First, to further study the slip-dependence of healing, we carry out large velocity step decreases and sequences of long slide-hold-slides on both bare rock and gouge. Secondly, to probe the micro-mechanical origins of healing, we complement our mechanical data with amplitudes and travel time data of ultrasonic P- and S- waves transmitted across the sliding interface. While ultrasonic P-wave transmissivity has been used as a proxy for 'real contact area' in friction experiments by Nagata et al. (2012, 2014) before, the simultaneous use of P- and S-phases in our experiments is designed specifically to probe contact rheology. Initial results show strong correlations between changes in friction, transmitted wave amplitudes and travel times in response to changes in slip rate. We also observe important differences

  20. Friction and Surface Damage of Several Corrosion-resistant Materials

    NASA Technical Reports Server (NTRS)

    Peterson, Marshall B; Johnson, Robert L

    1952-01-01

    Friction and surface damage of several materials that are resistant to corrosion due to liquid metals was studied in air. The values of kinetic friction coefficient at low sliding velocities and photomicrographs of surface damage were obtained. Appreciable surface damage was evident for all materials tested. The friction coefficients for the combinations of steel, stainless steel, and monel sliding against steel, stainless steel, nickel, Iconel, and Nichrome ranged from 0.55 for the monel-Inconel combination to 0.97 for the stainless-steel-nickel combination; for steel, stainless steel, monel, and tungsten carbide against zirconium, the friction coefficient was approximately 0.47. Lower coefficients of friction (0.20 to 0.60) and negligible surface failure at light loads were obtained with tungsten carbide when used in combination with various plate materials.

  1. Scalar model for frictional precursors dynamics.

    PubMed

    Taloni, Alessandro; Benassi, Andrea; Sandfeld, Stefan; Zapperi, Stefano

    2015-01-01

    Recent experiments indicate that frictional sliding occurs by nucleation of detachment fronts at the contact interface that may appear well before the onset of global sliding. This intriguing precursory activity is not accounted for by traditional friction theories but is extremely important for friction dominated geophysical phenomena as earthquakes, landslides or avalanches. Here we simulate the onset of slip of a three dimensional elastic body resting on a surface and show that experimentally observed frictional precursors depend in a complex non-universal way on the sample geometry and loading conditions. Our model satisfies Archard's law and Amontons' first and second laws, reproducing with remarkable precision the real contact area dynamics, the precursors' envelope dynamics prior to sliding, and the normal and shear internal stress distributions close to the interfacial surface. Moreover, it allows to assess which features can be attributed to the elastic equilibrium, and which are attributed to the out-of-equilibrium dynamics, suggesting that precursory activity is an intrinsically quasi-static physical process. A direct calculation of the evolution of the Coulomb stress before and during precursors nucleation shows large variations across the sample, explaining why earthquake forecasting methods based only on accumulated slip and Coulomb stress monitoring are often ineffective. PMID:25640079

  2. Scalar model for frictional precursors dynamics

    PubMed Central

    Taloni, Alessandro; Benassi, Andrea; Sandfeld, Stefan; Zapperi, Stefano

    2015-01-01

    Recent experiments indicate that frictional sliding occurs by nucleation of detachment fronts at the contact interface that may appear well before the onset of global sliding. This intriguing precursory activity is not accounted for by traditional friction theories but is extremely important for friction dominated geophysical phenomena as earthquakes, landslides or avalanches. Here we simulate the onset of slip of a three dimensional elastic body resting on a surface and show that experimentally observed frictional precursors depend in a complex non-universal way on the sample geometry and loading conditions. Our model satisfies Archard's law and Amontons' first and second laws, reproducing with remarkable precision the real contact area dynamics, the precursors' envelope dynamics prior to sliding, and the normal and shear internal stress distributions close to the interfacial surface. Moreover, it allows to assess which features can be attributed to the elastic equilibrium, and which are attributed to the out-of-equilibrium dynamics, suggesting that precursory activity is an intrinsically quasi-static physical process. A direct calculation of the evolution of the Coulomb stress before and during precursors nucleation shows large variations across the sample, explaining why earthquake forecasting methods based only on accumulated slip and Coulomb stress monitoring are often ineffective. PMID:25640079

  3. Science 101: What Causes Friction?

    ERIC Educational Resources Information Center

    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".…

  4. Scale effects in single-asperity friction

    NASA Astrophysics Data System (ADS)

    Robbins, Mark O.; Sharp, Tristan; Ligneres, Vincent; Pastewka, Lars

    2014-03-01

    Simulations are used to examine the static friction in model single-asperity contacts between a sphere and a flat elastic substrate. The two surfaces have the same crystalline structure. The radius R of the sphere and a of the contact are varied from nanometers to micrometers. For small contacts the atoms move coherently and the coefficient of friction μ is independent of load. As contact size increases, μ begins to drop. Results from a wide range of systems can be collapsed when μ is plotted against a2 / Ra0 where a0 nearest-neighbor spacing. The results are compared to Cattaneo-Mindlin continuum theory and dislocation-based models of contact-size effects from Hurtado and Kim and Gao. Supported by National Science Foundation Grant DMR 1006805 and IGERT 0801471.

  5. Friction stir welding tool

    DOEpatents

    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.

  6. Friction loss in straight pipes of unplasticized polyvinyl chloride.

    PubMed

    Iwasaki, T; Ojima, J

    1996-01-01

    In order to design proper ductwork for a local exhaust system, airflow characteristics were investigated in straight pipes of unplasticized polyvinyl chloride (PVC). A linear decrease in static pressure was observed downstream at points from the opening of the VU pipes (JIS K 6741) located at distances greater than 10 times the pipe diameter, for velocities ranging between 10.18-36.91 m/s. Roughness inside pipes with small diameters was found to be 0.0042-0.0056 mm and the friction factor was calculated on the basis of Colebrook's equation for an airflow transition zone. An extended friction chart was then constructed on the basis of the roughness value and the friction factor. This chart can be applied when designing a local exhaust system with the ducts of diameters ranging from 40 to 900 mm. The friction loss of the PVC pipe was found to be approximately 2/3 of that of a galvanized steel pipe. PMID:8768669

  7. Friction stir weld tools

    NASA Technical Reports Server (NTRS)

    Carter, Robert W. (Inventor); Payton, Lewis N. (Inventor)

    2007-01-01

    A friction stir weld tool sleeve is supported by an underlying support pin. The pin material is preferably selected for toughness and fracture characteristics. The pin sleeve preferably has a geometry which employs the use of an interrupted thread, a plurality of flutes and/or eccentric path to provide greater flow through. Paddles have been found to assist in imparting friction and directing plastic metal during the welding process.

  8. Friction Stir Weld Tools

    NASA Technical Reports Server (NTRS)

    Carter, Robert W. (Inventor); Payton, Lewis N. (Inventor)

    2007-01-01

    A friction stir weld tool sleeve is supported by an underlying support pin. The pin material is preferably selected for toughness and fracture characteristics. The pin sleeve preferably has a geometry which employs the use of an interrupted thread, a plurality of flutes and/or eccentric path to provide greater flow through. Paddles have been found to assist in imparting friction and directing plastic metal during the welding process.

  9. Rotor internal friction instability

    NASA Technical Reports Server (NTRS)

    Bently, D. E.; Muszynska, A.

    1985-01-01

    Two aspects of internal friction affecting stability of rotating machines are discussed. The first role of internal friction consists of decreasing the level of effective damping during rotor subsynchronous and backward precessional vibrations caused by some other instability mechanisms. The second role of internal frication consists of creating rotor instability, i.e., causing self-excited subsynchronous vibrations. Experimental test results document both of these aspects.

  10. Finite element modelling of frictional instability between deformable rocks

    NASA Astrophysics Data System (ADS)

    Xing, H. L.; Makinouchi, A.

    2003-10-01

    Earthquakes are recognized as resulting from a stick-slip frictional instability along faults. Based on the node-to-point contact element strategy (an arbitrarily shaped contact element strategy applied with the static-explicit algorithm for modelling non-linear frictional contact problems proposed by authors), a finite element code for modelling the 3-D non-linear friction contact between deformable bodies has been developed and extended here to analyse the non-linear stick-slip frictional instability between deformable rocks with a rate- and state-dependent friction law. A typical fault bend model is taken as an application example to be analysed here. The variations of the normal contact force, the frictional force, the transition of stick-slip instable state and the related relative slip velocity along the fault between the deformable rocks and the stress evolution in the total bodies during the different stages are investigated, respectively. The calculated results demonstrate the usefulness of this code for simulating the non-linear frictional instability between deformable rocks. Copyright

  11. Internal friction in Cu-Ti glass

    SciTech Connect

    Moorthy, S.A.; Baburaj, E.G.; Dey, G.K. . Metallurgy Division)

    1994-12-01

    Internal friction in solids is highly structure-sensitive and can be an effective means of studying the kinetics of atomic rearrangements associated with structural relaxation and crystallization in metallic glasses. Though a very large number of studies have been carried out on the crystallization behavior of metallic glasses, studies on structural relaxation, particularly the atomic rearrangement mechanism during structural relaxation, are few in comparison. Internal friction technique is a very useful method of studying thermally activated relaxation in an amorphous structure. Earlier studies have shown that metallic glasses exhibit a considerable amount of internal friction, particularly above 473 K, which besides being markedly reducible by structural relaxation, increases exponentially with increasing temperature, reaching a maximum during crystallization and then falls rapidly to a very low value at the completion of crystallization. In the present investigation, internal friction behavior of Cu[sub 49.5]Ti[sub 50.5] glass is studied in the temperature range covering both structural relaxation and crystallization. The glass transition temperature T[sub g] as well as crystallization temperature T[sub p] are determined and the distribution spectrum of activation energies for structural relaxation is discussed. Some comparisons are made with the DSC results and also with the results obtained in the case of Zr[sub 76]Ni[sub 24] glass.

  12. Laboratory manual for static pressure drop experiments in LMFBR wire wrapped rod bundles

    SciTech Connect

    Burns, K.J.; Todreas, N.E.

    1980-07-01

    Purpose of this experiment is to determine both interior and edge subchannel axial pressure drops for a range of Reynolds numbers. The subchannel static pressure drop is used to calculate subchannel and bundle average friction factors, which can be used to verify existing friction factor correlations. The correlations for subchannel friction factors are used as input to computer codes which solve the coupled energy, continuity, and momentum equations, and are also used to develop flow split correlations which are needed as input to codes which solve only the energy equation. The bundle average friction factor is used to calculate the overall bundle pressure drop, which determines the required pumping power.

  13. Method of generating and measuring static small force using down-slope component of gravity

    NASA Astrophysics Data System (ADS)

    Fujii, Yusaku

    2007-06-01

    A method of generating and measuring static small forces at the micro-Newton level is proposed. In the method, the down-slope component of gravity acting on a mass on an inclined plane is used as a static force. To realize a linear motion of the mass with a small friction, an aerostatic linear bearing is used. The forces acting on the mass, such as the down-slope component of gravity and the dynamic frictional force, are determined by the levitation mass method. In an experiment, a static small force of approximately 183μN is generated and measured with a standard uncertainty of approximately 2μN.

  14. Solvent fluctuations in hydrophobic cavity–ligand binding kinetics

    PubMed Central

    Setny, Piotr; Baron, Riccardo; Michael Kekenes-Huskey, Peter; McCammon, J. Andrew; Dzubiella, Joachim

    2013-01-01

    Water plays a crucial part in virtually all protein–ligand binding processes in and out of equilibrium. Here, we investigate the role of water in the binding kinetics of a ligand to a prototypical hydrophobic pocket by explicit-water molecular dynamics (MD) simulations and implicit diffusional approaches. The concave pocket in the unbound state exhibits wet/dry hydration oscillations whose magnitude and time scale are significantly amplified by the approaching ligand. In turn, the ligand’s stochastic motion intimately couples to the slow hydration fluctuations, leading to a sixfold-enhanced friction in the vicinity of the pocket entrance. The increased friction considerably decelerates association in the otherwise barrierless system, indicating the importance of molecular-scale hydrodynamic effects in cavity–ligand binding arising due to capillary fluctuations. We derive and analyze the diffusivity profile and show that the mean first passage time distribution from the MD simulation can be accurately reproduced by a standard Brownian dynamics simulation if the appropriate position-dependent friction profile is included. However, long-time decays in the water–ligand (random) force autocorrelation demonstrate violation of the Markovian assumption, challenging standard diffusive approaches for rate prediction. Remarkably, the static friction profile derived from the force correlations strongly resembles the profile derived on the Markovian assumption apart from a simple shift in space, which can be rationalized by a time–space retardation in the ligand’s downhill dynamics toward the pocket. The observed spatiotemporal hydrodynamic coupling may be of biological importance providing the time needed for conformational receptor–ligand adjustments, typical of the induced-fit paradigm. PMID:23297241

  15. Skin friction balance

    NASA Technical Reports Server (NTRS)

    Ping, Tcheng (Inventor); Supplee, Frank H., Jr. (Inventor)

    1989-01-01

    A skin friction balance uses a parallel linkage mechanism to avoid inaccuracies in skin friction measurement attributable to off-center normal forces. The parallel linkage mechanism includes a stationary plate mounted in a cage, and an upper and lower movable plate which are linked to each other and to the stationary plate throught three vertical links. Flexure pivots are provided for pivotally connecting the links and the plates. A sensing element connected to the upper plate moves in response to skin friction, and the lower plate moves in the opposite direction of the upper plate. A force motor maintains a null position of the sensing element by exerting a restoring force in response to a signal generated by a linear variable differential transformer (LVDT).

  16. LLNL small-scale static spark machine: static spark sensitivity test

    SciTech Connect

    Foltz, M F; Simpson, L R

    1999-08-23

    Small-scale safety testing of explosives and other energetic materials is done in order to determine their sensitivity to various stimuli, such as friction, static spark, and impact. Typically this testing is done to discover potential handling problems that may exist for either newly synthesized materials of unknown behavior, or materials that have been stored for long periods of time. This report describes the existing ''Static Spark Test Apparatus'' at Lawrence Livermore National Laboratory (LLNL), as well as the method used to evaluate the relative static spark sensitivity of energetic materials. The basic design, originally developed by the Picatinny Arsenal in New Jersey, is discussed. The accumulated data for the materials tested to date is not included here, with the exception of specific examples that have yielded interesting or unusual results during the tests.

  17. Overflow: Facts on Friction

    NASA Technical Reports Server (NTRS)

    Lawrence, Scott

    1999-01-01

    This paper presents results of three minor studies into the behavior of the OVERFLOW with respect to the prediction of skin friction drag on wing bodies at cruise Mach number and wind tunnel Reynolds number. The studies include a preliminary assessment of the behavior of the two new 2-equation turbulence models introduced with the latest version of OVERFLOW (v. 1.8f), an investigation into potential improvements in the matrix dissipation scheme currently implemented in OVERFLOW, and an analysis of the observed sensitivity of the code's skin friction predictions to grid stretching at solid surface boundaries.

  18. Effect of normal load variation on the frictional behavior of a simple Coulomb frictional oscillator

    NASA Astrophysics Data System (ADS)

    Papangelo, A.; Ciavarella, M.

    2015-07-01

    Various authors have studied the frictional contact problem for a simple concentrated mass under periodic forcing terms. In this paper, we give some additional closed form results for this problem for both the quasi-static limit and the full dynamic regime. We find in particular the regime where normal load is high enough to obtain a bounded displacement at all frequencies, which is of particular interest for "optimal" damping: in this case, the dynamic solution involves 2 stops of finite time. Contrary to the quasi-static prediction, the effect of normal load variation can decrease the peak displacement amplitude for in-phase loading up to the 80 percent. Moreover, similar to the quasi-static prediction, it can lead to a very large increase (up to more than 200 percent) for quadrature loading. Similar pattern is found for the frictional dissipation per cycle. For in-phase loading, therefore, the vibratory motion is damped more effectively, with additional beneficial effects on joint lifetime.

  19. Coupling Boltzmann and Navier-Stokes equations by friction

    SciTech Connect

    Bourgat, J.F.; Le Tallec, P. |; Tidriri, M.D.

    1996-09-01

    The aim of this paper is to introduce and validate a coupled Navier-Stokes Boltzman approach for the calculation of hypersonic rarefied flows around maneuvering vehicles. The proposed strategy uses locally a kinetic model in the boundary layer coupled through wall friction forces to a global Navier-Stokes solver. Different numerical experiments illustrate the potentialities of the method. 29 refs., 24 figs.

  20. Magnetic Low-Friction Track

    NASA Astrophysics Data System (ADS)

    Paetkau, Mark; Bahniwal, Manpreet; Gamblen, James

    2008-05-01

    The standard low-friction tracks used to test Newton's laws are the air track and the low-friction cart track. Both are commercially available and provide low-friction environments to test various physics concepts. At a recent science fair, one of the authors (JG) presented a magnetically levitated cart and track. A literature search found no previous testing of magnetically levitated carts. This paper compares a magnetically levitated cart against the two standard low-friction tracks.

  1. Friction induced skin tags.

    PubMed

    Allegue, Francisco; Fachal, Carmen; Pérez-Pérez, Lidia

    2008-01-01

    Skin tags are common benign neoplasm located predominantly in intertriginous skin. Generally of cosmetic concern, they can be easily treated with cryotherapy, electrodessication or snip-excision. Despite their high incidence data about their etiopathogenesis are scarce in the medical literature. We describe a patient who developed multiple skin tags arranged in a linear fashion suggesting an etiopathogenic role for friction. PMID:18627719

  2. Quantum theory of friction

    SciTech Connect

    Barnett, Stephen M.; Cresser, James D.

    2005-08-15

    We present a Markovian quantum theory of friction. Our approach is based on the idea that collisions between a Brownian particle and single molecules of the surrounding medium constitute, as far as the particle is concerned, instantaneous simultaneous measurements of its position and momentum.

  3. Intelligent Flow Friction Estimation

    PubMed Central

    Brkić, Dejan; Ćojbašić, Žarko

    2016-01-01

    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. PMID:27127498

  4. Intelligent Flow Friction Estimation.

    PubMed

    Brkić, Dejan; Ćojbašić, Žarko

    2016-01-01

    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 10(8) 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. PMID:27127498

  5. Friction-Testing Machine

    NASA Technical Reports Server (NTRS)

    Benz, F. J.; Dixon, D. S.; Shaw, R. C.

    1986-01-01

    Testing machine evaluates wear and ignition characteristics of materials in rubbing contact. Offers advantages over other laboratory methods of measuring wear because it simulates operating conditions under which material will actually be used. Machine used to determine wear characteristics, rank and select materials for service with such active oxidizers as oxygen, halogens, and oxides of nitrogen, measure wear characteristics, and determine coefficients of friction.

  6. A new algorithm for modeling friction in dynamic mechanical systems

    NASA Technical Reports Server (NTRS)

    Hill, R. E.

    1988-01-01

    A method of modeling friction forces that impede the motion of parts of dynamic mechanical systems is described. Conventional methods in which the friction effect is assumed a constant force, or torque, in a direction opposite to the relative motion, are applicable only to those cases where applied forces are large in comparison to the friction, and where there is little interest in system behavior close to the times of transitions through zero velocity. An algorithm is described that provides accurate determination of friction forces over a wide range of applied force and velocity conditions. The method avoids the simulation errors resulting from a finite integration interval used in connection with a conventional friction model, as is the case in many digital computer-based simulations. The algorithm incorporates a predictive calculation based on initial conditions of motion, externally applied forces, inertia, and integration step size. The predictive calculation in connection with an external integration process provides an accurate determination of both static and Coulomb friction forces and resulting motions in dynamic simulations. Accuracy of the results is improved over that obtained with conventional methods and a relatively large integration step size is permitted. A function block for incorporation in a specific simulation program is described. The general form of the algorithm facilitates implementation with various programming languages such as FORTRAN or C, as well as with other simulation programs.

  7. Influence of snow properties on dense avalanche friction parameters

    NASA Astrophysics Data System (ADS)

    Mohamed, Naaim

    2013-04-01

    The values of the Voellmy friction parameters of 735 historical avalanches that occurred along 26 paths in the Chamonix valley since 1958 are back-analysed with a depth-averaged hydraulic model including sub models for erosion, entrainment and deposition. For each path, the longitudinal and crosswise topographic profiles were derived from a high resolution digital elevation model acquired by laser scanning. The initial snow depth and snow cohesion, as well as various physical properties of snow, were computed from numerical simulations of the detailed snowpack model Crocus fed by the SAFRAN meteorological analysis. For each event, the full ranges of the two friction parameters were scanned and the pairs of friction parameters for which the run-out altitude is found close enough to the observed one (with an uncertainty of 5m), were retained. Statistical class analysis was used to investigate the correlation between the obtained friction coefficients and the snow physical properties. Concerning the inertial friction coefficient, no evident trend with the snow parameters was found. For the static friction coefficient, an increasing trend with the temperature and the density was observed, as well as a decreasing trend with the liquid water content and the initial snow depth.

  8. Friction in modern total hip arthroplasty bearings: Effect of material, design, and test methodology.

    PubMed

    Scholl, Laura; Longaray, Jason; Raja, Lokesh; Lee, Reginald; Faizan, Ahmad; Herrera, Lizeth; Thakore, Mayur; Nevelos, Jim

    2016-01-01

    The purpose of this study was to characterize the effect of a group of variables on frictional torque generated by acetabular components as well as to understand the influence of test model. Three separate test models, which had been previously used in the literature, were used to understand the effect of polyethylene material, bearing design, head size, and material combinations. Each test model differed by the way it simulated rotation of the head, the type of frictional torque value it reported (static vs. dynamic), and the type of motion simulated (oscillating motion vs. continuous motion). It was determined that not only test model may impact product ranking of fictional torque generated but also static frictional torque may be significantly larger than a dynamic frictional torque. In addition to test model differences, it was discovered that the frictional torque values for conventional and highly cross-linked polyethylenes were not statistically significantly different in the more physiologically relevant test models. With respect to bearing design, the frictional torque values for mobile bearing designs were similar to the 28-mm diameter inner bearing rather than the large diameter outer liner. Testing with a more physiologically relevant rotation showed that frictional torque increased with bearing diameter for the metal on polyethylene and ceramic on polyethylene bearings but remained constant for ceramic on ceramic bearings. Finally, ceramic on ceramic bearings produced smaller frictional torque values when compared to metal on polyethylene and ceramic on polyethylene groups. PMID:26721426

  9. Finger pad friction and its role in grip and touch

    PubMed Central

    Adams, Michael J.; Johnson, Simon A.; Lefèvre, Philippe; Lévesque, Vincent; Hayward, Vincent; André, Thibaut; Thonnard, Jean-Louis

    2013-01-01

    Many aspects of both grip function and tactile perception depend on complex frictional interactions occurring in the contact zone of the finger pad, which is the subject of the current review. While it is well established that friction plays a crucial role in grip function, its exact contribution for discriminatory touch involving the sliding of a finger pad is more elusive. For texture discrimination, it is clear that vibrotaction plays an important role in the discriminatory mechanisms. Among other factors, friction impacts the nature of the vibrations generated by the relative movement of the fingertip skin against a probed object. Friction also has a major influence on the perceived tactile pleasantness of a surface. The contact mechanics of a finger pad is governed by the fingerprint ridges and the sweat that is exuded from pores located on these ridges. Counterintuitively, the coefficient of friction can increase by an order of magnitude in a period of tens of seconds when in contact with an impermeably smooth surface, such as glass. In contrast, the value will decrease for a porous surface, such as paper. The increase in friction is attributed to an occlusion mechanism and can be described by first-order kinetics. Surprisingly, the sensitivity of the coefficient of friction to the normal load and sliding velocity is comparatively of second order, yet these dependencies provide the main basis of theoretical models which, to-date, largely ignore the time evolution of the frictional dynamics. One well-known effect on taction is the possibility of inducing stick–slip if the friction decreases with increasing sliding velocity. Moreover, the initial slip of a finger pad occurs by the propagation of an annulus of failure from the perimeter of the contact zone and this phenomenon could be important in tactile perception and grip function. PMID:23256185

  10. Quantum friction and fluctuation theorems

    NASA Astrophysics Data System (ADS)

    Intravaia, F.; Behunin, R. O.; Dalvit, D. A. R.

    2014-05-01

    We use general concepts of statistical mechanics to compute the quantum frictional force on an atom moving at constant velocity above a planar surface. We derive the zero-temperature frictional force using a nonequilibrium fluctuation-dissipation relation, and we show that in the large-time, steady-state regime, quantum friction scales as the cubic power of the atom's velocity. We also discuss how approaches based on Wigner-Weisskopf and quantum regression approximations fail to predict the correct steady-state zero-temperature frictional force, mainly due to the low-frequency nature of quantum friction.

  11. Four great challenges confronting our understanding and modeling of sliding friction

    SciTech Connect

    Blau, P.J.

    1997-08-01

    This paper addresses four challenges whose solutions may together enable significant progress in the predication and control of friction for energy conservation. Posed as questions these are: (1) how can materials with greatly different properties and compositions produce similar kinetic friction coefficients when tested under comparable conditions; (2) how is it possible that the kinetic friction coefficient for the same materials pair can differ greatly when it is slid in different tribosystems; (3) how can frictional phenomena at different size scales be reconciled; and (4) how can the effects of the machine, the materials (including lubricants) and the environment be successfully incorporated into quantitative and predictive friction models? Examples related to these four challenges are provided, as are possible approaches for attacking them in future research efforts.

  12. LLNL Small-Scale Friction sensitivity (BAM) Test

    SciTech Connect

    Simpson, L.R.; Foltz, M.F.

    1996-06-01

    Small-scale safety testing of explosives, propellants and other energetic materials, is done to determine their sensitivity to various stimuli including friction, static spark, and impact. Testing is done to discover potential handling problems for either newly synthesized materials of unknown behavior, or materials that have been stored for long periods of time. This report describes the existing {open_quotes}BAM{close_quotes} Small-Scale Friction Test, and the methods used to determine the friction sensitivity pertinent to handling energetic materials. The accumulated data for the materials tested is not listed here - that information is in a database. Included is, however, a short list of (1) materials that had an unusual response, and (2), a few {open_quotes}standard{close_quotes} materials representing the range of typical responses usually seen.

  13. Analytical comparison of effects of solid-friction and viscous structural damping on panel flutter

    NASA Technical Reports Server (NTRS)

    Cunningham, H. J.

    1976-01-01

    A Galerkin modal analysis is presented that accounts for the effects of both solid friction and viscous structural damping on panel flutter, based on unsteady aerodynamic forces from supersonic potential flow. The eigensolutions are made by complex eigenvalue computer routines. Markedly different effects on the flutter boundary of the two types of structural damping are obtained. This result establishes that there is not, in general, an "equivalent viscous" damping for solid-friction damping. For the limiting case of the static-aerodynamic approximation, a substantially different flutter dynamic pressure is obtained for solid friction identically zero compared with solid friction approaching zero as a limit. Use of the quasi-static aerodynamic approximation eliminates that difference.

  14. Friction at small displacement.

    NASA Technical Reports Server (NTRS)

    Campbell, W. E.; Aronstein, J.

    1972-01-01

    Low contact resistance between metal surfaces is often observed in spite of interposed lubricant and/or oxide films. To study this effect an apparatus is used with which normal force and tangential microdisplacement are applied between a small lead rider and a gold flat with various surface film conditions. Under nonoxidized and nonlubricated conditions, and with either oxide or stearic acid lubricant film alone, friction is high and contact resistance is low. With oxide and lubricant together, friction is much lower and slide is smooth, but contact resistance remains low and Ohm's law is obeyed. The results are consistent with Greenwood's theory of contact resistance for a cluster of minute metallic contact spots within the load-supporting area. The contact resistance of such a cluster is indistinguishable, for practical purposes, from that given by complete metallic contact.

  15. Noncontact Friction and Force Fluctuations between Closely Spaced Bodies

    SciTech Connect

    Stipe, B. C.; Mamin, H. J.; Stowe, T. D.; Kenny, T. W.; Rugar, D.

    2001-08-27

    Noncontact friction between a Au(111) surface and an ultrasensitive gold-coated cantilever was measured as a function of tip-sample spacing, temperature, and bias voltage using observations of cantilever damping and Brownian motion. The importance of the inhomogeneous contact potential is discussed and comparison is made to measurements over dielectric surfaces. Using the fluctuation-dissipation theorem, the force fluctuations are interpreted in terms of near-surface fluctuating electric fields interacting with static surface charge.

  16. Friction and Wear

    NASA Technical Reports Server (NTRS)

    Pomey, Jacques

    1952-01-01

    From the practical point of view, this analysis shows that each problem of friction or wear requires its particular solution. There is no universal solution; one or other of the factors predominates and defines the choice of the solution. In certain cases, copper alloys of great thermal conductivity are preferred; in others, plastics abundantly supplied with water. Sometimes, soft antifriction metals are desirable to distribute the load; at other times, hard metals with high resistance to abrasion or heat.

  17. Friction in rail guns

    NASA Technical Reports Server (NTRS)

    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.

  18. Magnetized static black Saturn

    SciTech Connect

    Yazadjiev, Stoytcho S.

    2008-06-15

    We present a new static solution to the 5D Einstein-Maxwell equations describing a static black hole surrounded by a nonrotating dipole black ring. The configuration is kept in equilibrium by an external magnetic field interacting with the dipole charge of the black ring. The properties of the black Saturn-like configuration are studied and the basic physical quantities are calculated. The solution demonstrates 2-fold continuous nonuniqueness of the 5D magnetized static neutral black objects for fixed total mass and Melvin background.

  19. Rectifier cabinet static breaker

    DOEpatents

    Costantino, Jr, Roger A.; Gliebe, Ronald J.

    1992-09-01

    A rectifier cabinet static breaker replaces a blocking diode pair with an SCR and the installation of a power transistor in parallel with the latch contactor to commutate the SCR to the off state. The SCR serves as a static breaker with fast turnoff capability providing an alternative way of achieving reactor scram in addition to performing the function of the replaced blocking diodes. The control circuitry for the rectifier cabinet static breaker includes on-line test capability and an LED indicator light to denote successful test completion. Current limit circuitry provides high-speed protection in the event of overload.

  20. Rectifier cabinet static breaker

    SciTech Connect

    Costantino, R.A. Jr; Gliebe, R.J.

    1992-09-01

    A rectifier cabinet static breaker replaces a blocking diode pair with an SCR and the installation of a power transistor in parallel with the latch contactor to commutate the SCR to the off state. The SCR serves as a static breaker with fast turnoff capability providing an alternative way of achieving reactor scram in addition to performing the function of the replaced blocking diodes. The control circuitry for the rectifier cabinet static breaker includes on-line test capability and an LED indicator light to denote successful test completion. Current limit circuitry provides high-speed protection in the event of overload. 7 figs.

  1. Static and dynamic theoretical analyses of a scanning tip on suspended graphene surface

    NASA Astrophysics Data System (ADS)

    Yu, Yan-Zi; Guo, Jian-Gang

    2016-08-01

    Recent research progress shows that graphene exhibits distinct adhesion and friction behaviors. In the paper, the static and dynamic analyses of a diamond tip sliding on suspended graphene surface are conducted via theoretical and numerical research methods, and the adhesion and friction properties between them are investigated. The analytical expression of interaction potential between a diamond tip and graphene surface is derived based on the interatomic pairwise potential, and then, the lateral and normal interaction forces are calculated. The equilibrium heights and adhesion energy of the diamond tip are calculated on three particular sites of graphene surface. The influence of vertical distance between the tip and graphene surface is studied on the maximum static frictional force and initial velocity of tip. What is more, the influence of scanning velocity and damping are also analyzed on the frictional force and dynamic behaviors of the scanning tip, and the "stick-slip" phenomenon is observed and discussed by the numerical calculation.

  2. Discovery in Statics

    NASA Astrophysics Data System (ADS)

    Makarov, Sergey

    2013-11-01

    This article described the opening of a new law in fundamental physics, namely the law of the formation of an endless series of suspension (cable-stayed) networks coatings. Opening relates to the mechanics, section of statics.

  3. Dynamic friction and the origin of the complexity of earthquake sources.

    PubMed Central

    Madariaga, R; Cochard, A

    1996-01-01

    We study a simple antiplane fault of finite length embedded in a homogeneous isotropic elastic solid to understand the origin of seismic source heterogeneity in the presence of nonlinear rate- and state-dependent friction. All the mechanical properties of the medium and friction are assumed homogeneous. Friction includes a characteristic length that is longer than the grid size so that our models have a well-defined continuum limit. Starting from a heterogeneous initial stress distribution, we apply a slowly increasing uniform stress load far from the fault and we simulate the seismicity for a few 1000 events. The style of seismicity produced by this model is determined by a control parameter associated with the degree of rate dependence of friction. For classical friction models with rate-independent friction, no complexity appears and seismicity is perfectly periodic. For weakly rate-dependent friction, large ruptures are still periodic, but small seismicity becomes increasingly nonstationary. When friction is highly rate-dependent, seismicity becomes nonperiodic and ruptures of all sizes occur inside the fault. Highly rate-dependent friction destabilizes the healing process producing premature healing of slip and partial stress drop. Partial stress drop produces large variations in the state of stress that in turn produce earthquakes of different sizes. Similar results have been found by other authors using the Burridge and Knopoff model. We conjecture that all models in which static stress drop is only a fraction of the dynamic stress drop produce stress heterogeneity. PMID:11607670

  4. Strongly Modulated Friction of a Film-Terminated Ridge-Channel Structure

    NASA Astrophysics Data System (ADS)

    He, Zhenping; Hui, Chung-Yuen; Levrard, Benjamin; Bai, Ying; Jagota, Anand

    2016-05-01

    Natural contacting surfaces have remarkable surface mechanical properties, which has led to the development of bioinspired surface structures using rubbery materials with strongly enhanced adhesion and static friction. However, sliding friction of structured rubbery surfaces is almost always significantly lower than that of a flat control, often due to significant loss of contact. Here we show that a film-terminated ridge-channel structure can strongly enhance sliding friction. We show that with properly chosen materials and geometrical parameters the near surface structure undergoes mechanical instabilities along with complex folding and sliding of internal interfaces, which is responsible for the enhancement of sliding friction. Because this structure shows no enhancement of adhesion under normal indentation by a sphere, it breaks the connection between energy loss during normal and shear loading. This makes it potentially interesting in many applications, for instance in tires, where one wishes to minimize rolling resistance (normal loading) while maximizing sliding friction (shear loading).

  5. Strongly Modulated Friction of a Film-Terminated Ridge-Channel Structure.

    PubMed

    He, Zhenping; Hui, Chung-Yuen; Levrard, Benjamin; Bai, Ying; Jagota, Anand

    2016-01-01

    Natural contacting surfaces have remarkable surface mechanical properties, which has led to the development of bioinspired surface structures using rubbery materials with strongly enhanced adhesion and static friction. However, sliding friction of structured rubbery surfaces is almost always significantly lower than that of a flat control, often due to significant loss of contact. Here we show that a film-terminated ridge-channel structure can strongly enhance sliding friction. We show that with properly chosen materials and geometrical parameters the near surface structure undergoes mechanical instabilities along with complex folding and sliding of internal interfaces, which is responsible for the enhancement of sliding friction. Because this structure shows no enhancement of adhesion under normal indentation by a sphere, it breaks the connection between energy loss during normal and shear loading. This makes it potentially interesting in many applications, for instance in tires, where one wishes to minimize rolling resistance (normal loading) while maximizing sliding friction (shear loading). PMID:27226233

  6. Strongly Modulated Friction of a Film-Terminated Ridge-Channel Structure

    PubMed Central

    He, Zhenping; Hui, Chung-Yuen; Levrard, Benjamin; Bai, Ying; Jagota, Anand

    2016-01-01

    Natural contacting surfaces have remarkable surface mechanical properties, which has led to the development of bioinspired surface structures using rubbery materials with strongly enhanced adhesion and static friction. However, sliding friction of structured rubbery surfaces is almost always significantly lower than that of a flat control, often due to significant loss of contact. Here we show that a film-terminated ridge-channel structure can strongly enhance sliding friction. We show that with properly chosen materials and geometrical parameters the near surface structure undergoes mechanical instabilities along with complex folding and sliding of internal interfaces, which is responsible for the enhancement of sliding friction. Because this structure shows no enhancement of adhesion under normal indentation by a sphere, it breaks the connection between energy loss during normal and shear loading. This makes it potentially interesting in many applications, for instance in tires, where one wishes to minimize rolling resistance (normal loading) while maximizing sliding friction (shear loading). PMID:27226233

  7. Observation of charge separation and gas discharge during sliding friction between metals and insulators

    NASA Astrophysics Data System (ADS)

    Miura, T.

    2015-10-01

    Charge generation due to friction between stainless steel and fused quartz in a vacuum was measured, and it was found that the density of the charge separation at the friction contact was 4×10-4 C/m2 In experiments in ambient gas, reduction of the separated charge caused by microgap gas discharge was observed. The residual rate of the charge, which is the ratio of charge accumulation in an ambient gas to that in a vacuum, in argon ambient gas was small, and it seemed to be effective for the relaxation of generated static electricity due to friction between solids.

  8. Solid friction between soft filaments

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    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’s 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 properties of fibrous composite materials.

  9. Friction surfaced Stellite6 coatings

    SciTech Connect

    Rao, K. Prasad; Damodaram, R.; Rafi, H. Khalid; Ram, G.D. Janaki; Reddy, G. Madhusudhan; Nagalakshmi, R.

    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.

  10. Solid friction between soft filaments.

    PubMed

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

    2015-06-01

    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's 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 properties of fibrous composite materials. PMID:25730393

  11. The Friction of Piston Rings

    NASA Technical Reports Server (NTRS)

    Tischbein, Hans W

    1945-01-01

    The coefficient of friction between piston ring and cylinder liner was measured in relation to gliding acceleration, pressure, temperature, quantity of oil and quality of oil. Comparing former lubrication-technical tests, conclusions were drawn as to the state of friction. The coefficients of friction as figured out according to the hydrodynamic theory were compared with those measured by tests. Special tests were made on "oiliness." The highest permissible pressure was measured and the ratio of pressure discussed.

  12. Fluctuations and friction

    NASA Astrophysics Data System (ADS)

    Raine, Derek

    2005-11-01

    Einstein's 1905 (Einstein 1905 Ann. Phys. 17 549) paper on Brownian motion is his most cited work, yet in terms of the scope of its application, apparently the least understood. In this brief note, I look at some examples of problems involving frictional forces that have puzzled school teachers, university lecturers and students, all of which can be understood from a proper appreciation of the relation between fluctuations and dissipation. For completeness I shall first give a simple derivation of a fluctuation-dissipation theorem, followed by three examples.

  13. Improved Skin Friction Interferometer

    NASA Technical Reports Server (NTRS)

    Westphal, R. V.; Bachalo, W. D.; Houser, M. H.

    1986-01-01

    An improved system for measuring aerodynamic skin friction which uses a dual-laser-beam oil-film interferometer was developed. Improvements in the optical hardware provided equal signal characteristics for each beam and reduced the cost and complexity of the system by replacing polarization rotation by a mirrored prism for separation of the two signals. An automated, objective, data-reduction procedure was implemented to eliminate tedious manual manipulation of the interferometry data records. The present system was intended for use in two-dimensional, incompressible flows over a smooth, level surface without pressure gradient, but the improvements discussed are not limited to this application.

  14. Frictional granular mechanics: A variational approach

    SciTech Connect

    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.

  15. Tidal friction in rotating turbulent convectivestellar and planetary regions

    NASA Astrophysics Data System (ADS)

    Mathis, S.; Auclair-Desrotour, P.; Guenel, M.; Le Poncin-Lafitte, C.

    2014-12-01

    Turbulent friction in stellar and planetary convection zones is one of the key physical mechanisms that drive the dissipation of the kinetic energy of tidal flows in stars and planets hosting companions. This friction acting both on the equilibrium tide and on tidal inertial waves thus deeply impacts the dynamics of the spin of the host star/planet and the orbital architecture of the surrounding system. It is thus very important to obtain robust prescription for this friction. In the current state-of-the-art, it is modeled by a turbulent viscosity coefficient using mixing-length theory. However, none of the existing prescriptions take into account the action of the possibly rapid rotation that strongly affects convective flows. In this work, we propose such a new prescription that takes into account rotation and discuss the possible implication for tidal dissipation in rotating stars and planets.

  16. The Schroedinger equation with friction from the quantum trajectory perspective

    SciTech Connect

    Garashchuk, Sophya; Dixit, Vaibhav; Gu Bing; Mazzuca, James

    2013-02-07

    Similarity of equations of motion for the classical and quantum trajectories is used to introduce a friction term dependent on the wavefunction phase into the time-dependent Schroedinger equation. The term describes irreversible energy loss by the quantum system. The force of friction is proportional to the velocity of a quantum trajectory. The resulting Schroedinger equation is nonlinear, conserves wavefunction normalization, and evolves an arbitrary wavefunction into the ground state of the system (of appropriate symmetry if applicable). Decrease in energy is proportional to the average kinetic energy of the quantum trajectory ensemble. Dynamics in the high friction regime is suitable for simple models of reactions proceeding with energy transfer from the system to the environment. Examples of dynamics are given for single and symmetric and asymmetric double well potentials.

  17. Slow frictional waves

    NASA Astrophysics Data System (ADS)

    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.

  18. Friction Stir Welding

    NASA Technical Reports Server (NTRS)

    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.

  19. Orbital friction stir weld system

    NASA Technical Reports Server (NTRS)

    Ding, R. Jeffrey (Inventor); Carter, Robert W. (Inventor)

    2001-01-01

    This invention is an apparatus for joining the ends of two cylindrical (i.e., pipe-shaped) sections together with a friction stir weld. The apparatus holds the two cylindrical sections together and provides back-side weld support as it makes a friction stir weld around the circumference of the joined ends.

  20. Friction in a Moving Car

    ERIC Educational Resources Information Center

    Goldberg, Fred M.

    1975-01-01

    Describes an out-of-doors, partially unstructured experiment to determine the coefficient of friction for a moving car. Presents the equation which relates the coefficient of friction to initial velocity, distance, and time and gives sample computed values as a function of initial speed and tire pressure. (GS)

  1. Corrosion effects on friction factors

    SciTech Connect

    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.

  2. Theoretical analysis of the dynamic behavior of presliding rolling friction via skeleton technique

    NASA Astrophysics Data System (ADS)

    Tjahjowidodo, T.

    2012-05-01

    Depending on the application, friction in mechanical systems can be a desirable or an undesirable thing. In order to optimally utilize or compensate for the frictional effect in the system, characterization of the frictional behavior is a crucial task. Unfortunately, friction force exhibits strong (hysteretic) nonlinear relationship with sliding velocity, displacement and time, which makes the characterization to become a difficult task to fulfill. The classical Coulomb friction has been widely used, especially in the field of control engineering to compensate for the static force in a system. However, despite its simplicity, the effectiveness of the Coulomb model in capturing the frictional behavior of friction in the presliding regime is very low. This paper deals with the derivation of equivalent modal parameters, namely the stiffness and damping elements, to represent the hysteresis friction element on mechanical systems. The analysis is carried out using the skeleton technique, which employs the instantaneous amplitude and frequency of the excitation input and the response of the system. Subsequently, the dynamic analysis is performed on the equivalent system and the result is compared to that of the original system. The results show good agreement between the equivalent system and the original system for wide range of excitation.

  3. Fundamental deformation processes controlling nanoscale friction and wear

    NASA Astrophysics Data System (ADS)

    Gotsmann, Bernd

    2010-03-01

    Thermally activated processes are often responsible for the kinetics of deformation and can control tribological performance. In this contribution two such processes are discussed in combination with nanoscale tribology experiments using atomic force microscopy (AFM). The first process describes single asperity wear as an atom-by-atom loss process driven by frictional shear stresses an interface. The wear rate is described by a thermally activated bond breaking process in which the energy barrier is reduced by the frictional shear stress. This leads to dramatic deviations from Archard's wear law which is commonly used to described macroscopic wear. Experimental confirmation of an atom-by-atom wear process is given by AFM wear experiments using different material combinations of tips sliding on surfaces [1]. The second process relates fundamental rearranging processes in polymers to friction. As an example, data of sliding friction between a silicon tip and a highly cross-linked polyaryletherketone film using friction force microscopy are presented. Energy dissipation into so-called molecular relaxations (alpha and beta relaxations) is identified as distinctive maxima of the friction force as a function of temperature between 150 and 500 K. A strong shift of such peak temperatures as a function of applied load is observed. Again, a model with an Arrhenius activation modulated by the applied shear stress describes experimental results quantitatively. The effect of the stress-shifted relaxation on friction-versus-load experiments is discussed [2]. Both processes will be discussed in the context of technological applications. [4pt] [1] B. Gotsmann and M. A. Lantz, Phys. Rev. Lett. 101, 125501 (2008) [0pt] [2] L. Jansen et al. Phys. Rev. Lett. 102, 236101 (2009)

  4. Friction between Archwire of Different Sizes, Cross Section, Alloy and Brackets Ligated with Different Brands of Low Friction Elastic Ligatures- An Invitro Study

    PubMed Central

    Patil, Bhushan; Patil, Neeraj Suresh; Kerudi, Veerendra Virupaxappa; Chitko, Shrikant Shrinivas; Maheshwari, Amit Ratanlal; Pekhale, Nikhita Popatrao; Tekale, Pawankumar Dnyandeo

    2016-01-01

    Introduction Friction in orthodontic treatment does exist and is thought to reduce the efficiency of orthodontic appliances during sliding mechanics. During sliding mechanics, a friction force is produced at the bracket archwire-ligature unit which tends to counteract the applied force and in turn resists the desired movement. Aim The aim of this invitro study was to determine the friction between archwire of different sizes, cross section, alloy and brackets ligated with different brands of low friction elastic ligatures. Materials and Methods An 0.022-in slot, 10 stainless steel brackets and various orthodontic archwires which were ligated with low-friction ligatures and subjected to evaluate frictional resistance i.e. static friction and dynamic friction. The archwires of 0.014″ and 0.016″ nickel titanium (NiTi), 0.016 × 0.022″ stainless steel (SS), 0.017 × 0.025″ NiTi, 0.017 × 0.025″ SS, 0.017 × 0.025″ titanium molybdenum alloy (TMA), 0.019 × 0.025″ SS were used. Each bracket/archwire combination was evaluated 10 times at room temperature of 27 ± 2°C. The study groups included Group I of conventional round shape module with reduced friction coating i.e. super slick and synergy and Group II contained figure of “8” shape module i.e. Octavia ties and Slide ligature. Result The mean static friction force and dynamic friction force for all 7 types of wires was lower in Group II (C, D) combined compared to Group I (A, B) and the difference was statistically very highly significant (p<0.001). Conclusion Super slick and synergy can be used in the initial and final phase of treatment when full engagement of archwire in the bracket slot is necessary for proper tip and torque expression. Slide and Octavia ties modules can be used in the premolar brackets during en mass retraction when using friction mechanics. PMID:27190944

  5. Rolling friction robot fingers

    NASA Technical Reports Server (NTRS)

    Vranish, John M. (Inventor)

    1992-01-01

    A low friction, object guidance, and gripping finger device for a robotic end effector on a robotic arm is disclosed, having a pair of robotic fingers each having a finger shaft slideably located on a gripper housing attached to the end effector. Each of the robotic fingers has a roller housing attached to the finger shaft. The roller housing has a ball bearing mounted centering roller located at the center, and a pair of ball bearing mounted clamping rollers located on either side of the centering roller. The object has a recess to engage the centering roller and a number of seating ramps for engaging the clamping rollers. The centering roller acts to position and hold the object symmetrically about the centering roller with respect to the X axis and the clamping rollers act to position and hold the object with respect to the Y and Z axis.

  6. Eliminating friction with friction: 2D Janssen effect in a friction-driven system.

    PubMed

    Karim, M Yasinul; Corwin, Eric I

    2014-05-01

    The Janssen effect is a unique property of confined granular materials experiencing gravitational compaction in which the pressure at the bottom saturates with an increasing filling height due to frictional interactions with side walls. In this Letter, we replace gravitational compaction with frictional compaction. We study friction-compacted 2D granular materials confined within fixed boundaries on a horizontal conveyor belt. We find that even with high-friction side walls the Janssen effect completely vanishes. Our results demonstrate that gravity-compacted granular systems are inherently different from friction-compacted systems in at least one important way: vibrations induced by sliding friction with the driving surface relax away tangential forces on the walls. Remarkably, we find that the Janssen effect can be recovered by replacing the straight side walls with a sawtooth pattern. The mechanical force introduced by varying the sawtooth angle θ can be viewed as equivalent to a tunable friction force. By construction, this mechanical friction force cannot be relaxed away by vibrations in the system. PMID:24856724

  7. Eliminating Friction with Friction: 2D Janssen Effect in a Friction-Driven System

    NASA Astrophysics Data System (ADS)

    Karim, M. Yasinul; Corwin, Eric I.

    2014-05-01

    The Janssen effect is a unique property of confined granular materials experiencing gravitational compaction in which the pressure at the bottom saturates with an increasing filling height due to frictional interactions with side walls. In this Letter, we replace gravitational compaction with frictional compaction. We study friction-compacted 2D granular materials confined within fixed boundaries on a horizontal conveyor belt. We find that even with high-friction side walls the Janssen effect completely vanishes. Our results demonstrate that gravity-compacted granular systems are inherently different from friction-compacted systems in at least one important way: vibrations induced by sliding friction with the driving surface relax away tangential forces on the walls. Remarkably, we find that the Janssen effect can be recovered by replacing the straight side walls with a sawtooth pattern. The mechanical force introduced by varying the sawtooth angle θ can be viewed as equivalent to a tunable friction force. By construction, this mechanical friction force cannot be relaxed away by vibrations in the system.

  8. Why Static Clings

    ERIC Educational Resources Information Center

    Naab, Laurie; Henry, David

    2009-01-01

    Using Wiggins and McTighe's (1998) concept of Big Ideas, the authors planned and designed an electricity investigation to address common student misconceptions about static electricity. With Styrofoam plates and transparent tape, elementary students investigated many properties of electrically charged and uncharged objects in a 5E learning cycle…

  9. I.1. Statics.

    PubMed

    Verkerke, Gijsbertus J; Lee, T Clive

    2010-01-01

    The forces that act on an object determine its dynamic behaviour and defromation. Analysis of all forces and moments is essential. A free-body diagram summarizes all forces and moments that act on an object. To calculate the magnitude of the forces we can use the static equilibrium of forces and moments. PMID:20407182

  10. Static & Dynamic Response of 2D Solids

    Energy Science and Technology Software Center (ESTSC)

    1996-07-15

    NIKE2D is an implicit finite-element code for analyzing the finite deformation, static and dynamic response of two-dimensional, axisymmetric, plane strain, and plane stress solids. The code is fully vectorized and available on several computing platforms. A number of material models are incorporated to simulate a wide range of material behavior including elasto-placicity, anisotropy, creep, thermal effects, and rate dependence. Slideline algorithms model gaps and sliding along material interfaces, including interface friction, penetration and single surfacemore » contact. Interactive-graphics and rezoning is included for analyses with large mesh distortions. In addition to quasi-Newton and arc-length procedures, adaptive algorithms can be defined to solve the implicit equations using the solution language ISLAND. Each of these capabilities and more make NIKE2D a robust analysis tool.« less

  11. Development and validation of a new method for measuring friction between skin and nonwoven materials.

    PubMed

    Cottenden, A M; Wong, W K; Cottenden, D J; Farbrot, A

    2008-07-01

    A new method for measuring the coefficient of friction between nonwoven materials and the curved surface of the volar forearm has been developed and validated. The method was used to measure the coefficient of static friction for three different nonwoven materials on the normal (dry) and over-hydrated volar forearms of five female volunteers (ages 18-44). The method proved simple to run and had good repeatability: the coefficient of variation (standard deviation expressed as a percentage of the mean) for triplets of repeat measurements was usually (80 per cent of the time) less than 10 per cent. Measurements involving the geometrically simpler configuration of pulling a weighted fabric sample horizontally across a quasi-planar area of volar forearm skin proved experimentally more difficult and had poorer repeatability. However, correlations between values of coefficient of static friction derived using the two methods were good (R = 0.81 for normal (dry) skin, and 0.91 for over-hydrated skin). Measurements of the coefficient of static friction for the three nonwovens for normal (dry) and for over-hydrated skin varied in the ranges of about 0.3-0.5 and 0.9-1.3, respectively. In agreement with Amontons' law, coefficients of friction were invariant with normal pressure over the entire experimental range (0.1-8.2 kPa). PMID:18756696

  12. Dynamic instabilities of frictional sliding at a bimaterial interface

    NASA Astrophysics Data System (ADS)

    Brener, Efim A.; Weikamp, Marc; Spatschek, Robert; Bar-Sinai, Yohai; Bouchbinder, Eran

    2016-04-01

    obtained in the quasi-static regime appear relevant only within a narrow region of the parameter space. Finally, we show that a finite-time regularized response to normal stress variations, within the framework of generalized rate-and-state friction models, tends to promote stability. The relevance of our results to the rupture of bi-material interfaces is briefly discussed.

  13. Modeling of Instabilities and Self-organization at the Frictional Interface

    NASA Astrophysics Data System (ADS)

    Mortazavi, Vahid

    frictional surface to exhibit "self-protection" and "self-healing" properties. Hence, this research is dealing with the fundamental concepts that allow the possibility of the development of a new generation of tribosystem and materials that reinforce such properties. In chapter 2, we investigate instabilities due to the temperature-dependency of the coefficient of friction. The temperature-dependency of the coefficient of friction can have a significant effect on the frictional sliding stability, by leading to the formation of "hot" and "cold" spots on the contacting surfaces. We formulate a stability criterion and perform a case study of a brake disk. In chapter 3, we study frictional running-in. Running-in is a transient period on the onset of the frictional sliding, in which friction and wear decrease to their stationary values. In this research, running-in is interpreted as friction-induced self-organization process. We introduce a theoretical model of running-in and investigate rough profile evolution assuming that its kinetics is driven by two opposite processes or events, i.e., smoothening which is typical for the deformation-driven friction and wear, and roughening which is typical for the adhesion-driven friction and wear. In chapter 4, we investigate the possibility of the so-called Turing-type pattern formation during friction. Turing or reaction-diffusion systems describe variations of spatial concentrations of chemical components with time due to local chemical reactions coupled with diffusion. During friction, the patterns can form at the sliding interface due to the mass transfer (diffusion), heat transfer, various tribochemical reactions, and wear. In chapter 5, we investigate how interfacial patterns including propagating trains of stick and slip zones form due to dynamic sliding instabilities. These can be categorized as self-organized patterns. We treat stick and slip as two phases at the interface, and study the effects related to phase transitions. Our

  14. Frictionless bead packs have macroscopic friction, but no dilatancy.

    PubMed

    Peyneau, Pierre-Emmanuel; Roux, Jean-Noël

    2008-07-01

    The statement of the title is shown by numerical simulation of homogeneously sheared assemblies of frictionless, nearly rigid beads in the quasistatic limit. Results coincide for steady flows at constant shear rate gamma[over ] in the limit of small gamma[over ] and static approaches, in which packings are equilibrated under growing deviator stresses. The internal friction angle phi , equal to 5.76 degrees +/-0.22 degrees in simple shear, is independent of average pressure P in the rigid limit and stems from the ability of stable frictionless contact networks to form stress-induced anisotropic fabrics. No enduring strain localization is observed. Dissipation at the macroscopic level results from repeated network rearrangements, similar to the effective friction of a frictionless slider on a bumpy surface. Solid fraction Phi remains equal to the random close packing value approximately 0.64 in slowly or statically sheared systems. Fluctuations of stresses and volume are observed to regress in the large system limit. Defining the inertial number as I=gamma radical m/(aP), with m the grain mass and a its diameter, both internal friction coefficient mu*=tan phi and volume 1/Phi increase as powers of I in the quasistatic limit of vanishing I , in which all mechanical properties are determined by contact network geometry. The microstructure of the sheared material is characterized with a suitable parametrization of the fabric tensor and measurements of coordination numbers. PMID:18763948

  15. Friction and wear of tin and tin alloys from minus 100 C to 150 C

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.

    1975-01-01

    Sliding friction experiments were conducted with an iron (110) single-crystal pin sliding on single and polycrystalline tin and tin alloys. Specimens were examined at various ambient temperatures from -100 to 150 C. Applied loads varied from 1 to 50 grams, and sliding velocity was constant at 0.7 mm/min. Results indicate that the crystal transformation of tin influences the friction coefficient. Friction was higher for the diamond structure (gray tin) than it was for the body-centered tetragonal structure (white tin). Bismuth arrested the crystal transformation, which resulted in constant friction over the temperature range -100 to 150 C. Both copper and aluminum enhanced the kinetics of transformation, with aluminum producing a nearly twofold change in friction with the crystal transformation.

  16. Singular Elasto-Static Field Near a Fault Kink

    NASA Astrophysics Data System (ADS)

    Arias, Rodrigo; Madariaga, Raúl; Adda-Bedia, Mokhtar

    2011-12-01

    We study singular elastic solutions at an angular corner left by a crack that has kinked. We have in mind a geophysical context where the faults on either side of the kink are under compression and are ready to slip, or have already slipped, under the control of Coulomb friction. We find separable static singular solutions that are matched across the sides of the corner by applying appropriate boundary conditions. In our more general solution we assume that one of the sides of the corner is about to slide, i.e. it is just contained by friction, and the other may be less pressured. Our solutions display power law behaviour with real exponents that depend continuously on the angle of the corner, the coefficient of static friction and the difference of shear load on both sides of the corner. When friction is the same on both sides of the kink, the solutions split into a symmetric and an antisymmetric solution. The antisymmetric solution corresponds to the simple shear case; while the symmetric solution appears when the kink is loaded by uniaxial stress along the bisector of the kink. The antisymmetric solution is ruled out under this model with contact since the faults cannot sustain tension. When one side of the corner is less pressured one can also distinguish modes with contact overall from others that must open up on one side. These solutions provide an insight into the stress distributions near fault kinks, they can also be used as tools for improving the numerical calculation of kinks under static or dynamic loads.

  17. Nanoscale friction and wear properties of silicon wafer under different lubrication conditions

    NASA Astrophysics Data System (ADS)

    Chen, Xiaochun; Zhao, Yongwu; Wang, Yongguang; Zhou, Hailan; Ni, Zhifeng; An, Wei

    2013-10-01

    The nanoscale friction and wear properties of single crystal silicon wafer under different lubrication conditions are studied in this paper. The experiments were performed with Si3N4 ball sliding on the surface of silicon wafer under four different lubrication conditions: dry friction, water lubrication, hydrogen peroxide lubrication and the static hydrogen peroxide dry friction. The results from the experiments have been analyzed showing the different friction and wear properties of the silicon wafer in different lubrication conditions. It is concluded that the wear rates under the water lubrication and under the hydrogen peroxide lubrication are both small, the chemical reactions are facilitated by the mechanical processes when the load and the sliding speed reach certain levels. This is mainly resulted by the enhanced lubricant performance with the formed silicon hydroxide Si(OH)4 film. Under the water lubrication, the wear is found in a way of material removed in molecule scale. Under the hydrogen peroxide lubrication, the wear is mainly caused by the spalling of micro-cracks. Under the dry friction condition, the wear is found being adhesive wear. And under the static peroxide dry friction, the wear is prevailing adhesive wear. These results are essential and valuable to the development of the efficient and environmental-friendly slurry for the chemical mechanical polishing (CMP) process.

  18. On laminar and turbulent friction

    NASA Technical Reports Server (NTRS)

    Von Karman, TH

    1946-01-01

    Report deals, first with the theory of the laminar friction flow, where the basic concepts of Prandtl's boundary layer theory are represented from mathematical and physical points of view, and a method is indicated by means of which even more complicated cases can be treated with simple mathematical means, at least approximately. An attempt is also made to secure a basis for the computation of the turbulent friction by means of formulas through which the empirical laws of the turbulent pipe resistance can be applied to other problems on friction drag. (author)

  19. REDUCED ENGINE FRICTION AND WEAR

    SciTech Connect

    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

  20. Flow Friction or Spontaneous Ignition?

    NASA Technical Reports Server (NTRS)

    Stoltzfus, Joel M.; Gallus, Timothy D.; Sparks, Kyle

    2012-01-01

    "Flow friction," a proposed ignition mechanism in oxygen systems, has proved elusive in attempts at experimental verification. In this paper, the literature regarding flow friction is reviewed and the experimental verification attempts are briefly discussed. Another ignition mechanism, a form of spontaneous combustion, is proposed as an explanation for at least some of the fire events that have been attributed to flow friction in the literature. In addition, the results of a failure analysis performed at NASA Johnson Space Center White Sands Test Facility are presented, and the observations indicate that spontaneous combustion was the most likely cause of the fire in this 2000 psig (14 MPa) oxygen-enriched system.

  1. Flexure Bearing Reduces Startup Friction

    NASA Technical Reports Server (NTRS)

    Clingman, W. Dean

    1991-01-01

    Design concept for ball bearing incorporates small pieces of shim stock, wire spokes like those in bicycle wheels, or other flexing elements to reduce both stiction and friction slope. In flexure bearing, flexing elements placed between outer race of ball bearing and outer ring. Elements flex when ball bearings encounter small frictional-torque "bumps" or even larger ones when bearing balls encounter buildups of grease on inner or outer race. Flexure of elements reduce high friction slopes of "bumps", helping to keep torque between outer ring and inner race low and more nearly constant. Concept intended for bearings in gimbals on laser and/or antenna mirrors.

  2. Friction and morphology of pleural mesothelia.

    PubMed

    Pecchiari, Matteo; Sartori, Patrizia; Conte, Vincenzo; D'Angelo, Edgardo; Moscheni, Claudia

    2016-01-01

    To verify the hypothesis that by enmeshing lubricants, microvilli reduce the coefficient of kinetic friction (μ) of pleural mesothelium, μ was measured during reciprocating sliding of rabbit's visceral against parietal pleura before and after addition of hyaluronan, and related to the morphological features of the microvillar network. Because no relation was found between μ or μ changes after hyaluronan and microvillar characteristics, the latter are not determinants of the frictional forces which oppose sliding of normal mesothelial surfaces under physiological conditions, nor of the effects of hyaluronan. Addition of hyaluronan increased μ slightly but significantly in normal specimens, probably by altering the physiological mix of lubricants, but decreased μ of damaged mesothelia, suggesting protective, anti-abrasion properties. Indeed, while sliding of an injured against a normal pleura heavily damaged the latter and increased μ when Ringer was interposed between the surfaces, both effects were limited or prevented when hyaluronan was interposed between the injured and normal pleura before onset of sliding. PMID:26376001

  3. Friction and adhesion mediated by supramolecular host-guest complexes.

    PubMed

    Guerra, Roberto; Benassi, Andrea; Vanossi, Andrea; Ma, Ming; Urbakh, Michael

    2016-04-01

    The adhesive and frictional response of an AFM tip connected to a substrate through supramolecular host-guest complexes is investigated by dynamic Monte Carlo simulations. Here, the variation of the pull-off force with the unloading rate recently observed in experiments is unraveled by evidencing simultaneous (progressive) breaking of the bonds at fast (slow) rates. The model reveals the origin of the observed plateaus in the retraction force as a function of the tip-surface distance, showing that they result from the tip geometrical features. In lateral sliding, the model exhibits a wide range of dynamic behaviors ranging from smooth sliding to stick-slip at different velocities, with the average friction force determined by the characteristic formation/rupture rates of the complexes. In particular, it is shown that for some molecular complexes friction can become almost constant over a wide range of velocities. Also, we show the possibility of exploiting the ageing effect through slide-hold-slide experiments, in order to infer the characteristic formation rate. Finally, our model predicts a novel "anti-ageing" effect which is characterized by a decrease of the static friction force with the hold time. Such an effect is explained in terms of enhancement of adhesion during sliding, especially observed at high driving velocities. PMID:26975343

  4. Polymer Chain Reinforcement across Narrow Interfaces: Entanglements Versus Chain Friction

    NASA Astrophysics Data System (ADS)

    Benkoski, Jason J.; Fredrickson, Glenn H.; Kramer, Edward J.

    2002-03-01

    It is widely believed that entangled chains that bridge a glassy polymer/polymer interface solely determine its fracture energy (G_c). However, experiments show that while Gc increases with interfacial width (w), Gc vs. w/d_t, where dt is the tube diameter of the melt, is not universal. For some polymer pairs Gc increases dramatically even when w << d_t, while for others Gc does not increase until w >= d_t. We demonstrate that the friction stress for polymer loop pull-out from the interface is given by f_monoρ_merw/2 where f_mono is the static friction coefficient per mer and ρ_mer is the mer number density. Unlike interfaces with short block copolymers, where the friction stress for block pull-out is limited by a maximum areal density of block copolymer, the polymer/polymer friction stress grows linearly with w. For interfaces as narrow as 3 nm, it can be large enough to induce crazing. A model that includes both loop pull-out and chain entanglement shows that modest changes in f_mono can account for the fact that Gc versus w/dt is non-universal. A high areal density of bridging, entangled chains is therefore sufficient, but not necessary, to reinforce polymer interfaces.

  5. Multimodal Friction Ignition Tester

    NASA Technical Reports Server (NTRS)

    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

  6. Static cylindrically symmetric spacetimes

    NASA Astrophysics Data System (ADS)

    Fjällborg, Mikael

    2007-05-01

    We prove the existence of static solutions to the cylindrically symmetric Einstein Vlasov system, and we show that the matter cylinder has finite extension in two of the three spatial dimensions. The same results are also proved for a quite general class of equations of state for perfect fluids coupled to the Einstein equations, extending the class of equations of state considered by Bicak et al (2004 Class. Quantum Grav.21 1583). We also obtain this result for the Vlasov Poisson system.

  7. Precursor events and the onset of frictional sliding

    NASA Astrophysics Data System (ADS)

    Libal, Andras; Robbins, Mark

    2008-03-01

    The precursor events leading to steady state sliding friction are investigated using a simple two-dimensional model of a rectangular block on a flat surface. As in experiments[1], a succession of cracks nucleates from the rear of the block. Each propagates rapidly and then arrests after a distance that scales with the height at which the lateral force is applied to the block. The propagation distance grows with each successive crack until a steady sliding state is attained. The distribution of local shear stress at the interface can be obtained directly in our simulations. The relation between this stress distribution, the static friction, the normal load, and the nucleation and propagation of successive cracks will be discussed. [1] S.M. Rubinstein, G. Cohen and J. Fineberg, PRL 98, 226103 (2007)

  8. Rubber friction and tire dynamics.

    PubMed

    Persson, B N J

    2011-01-12

    We propose a simple rubber friction law, which can be used, for example, in models of tire (and vehicle) dynamics. The friction law is tested by comparing numerical results to the full rubber friction theory (Persson 2006 J. Phys.: Condens. Matter 18 7789). Good agreement is found between the two theories. We describe a two-dimensional (2D) tire model which combines the rubber friction model with a simple mass-spring description of the tire body. The tire model is very flexible and can be used to accurately calculate μ-slip curves (and the self-aligning torque) for braking and cornering or combined motion (e.g. braking during cornering). We present numerical results which illustrate the theory. Simulations of anti-blocking system (ABS) braking are performed using two simple control algorithms. PMID:21406818

  9. Rubber friction and tire dynamics

    NASA Astrophysics Data System (ADS)

    Persson, B. N. J.

    2011-01-01

    We propose a simple rubber friction law, which can be used, for example, in models of tire (and vehicle) dynamics. The friction law is tested by comparing numerical results to the full rubber friction theory (Persson 2006 J. Phys.: Condens. Matter 18 7789). Good agreement is found between the two theories. We describe a two-dimensional (2D) tire model which combines the rubber friction model with a simple mass-spring description of the tire body. The tire model is very flexible and can be used to accurately calculate μ-slip curves (and the self-aligning torque) for braking and cornering or combined motion (e.g. braking during cornering). We present numerical results which illustrate the theory. Simulations of anti-blocking system (ABS) braking are performed using two simple control algorithms.

  10. Force fluctuations while pressing and moving against high- and low-friction touch screen surfaces.

    PubMed

    Joshi, Mukta N; Keenan, Kevin G

    2016-07-01

    The purpose of this study was to identify the influence of a high- and low-friction surface on the ability to maintain a steady downward force during an index finger pressing and moving task. Fifteen right-handed subjects (24-48 years) performed a static force pressing task and a hybrid pressing and moving task on the surface of an iPad mini while holding a steady 2-N force on high- and low-friction surfaces. Variability of force was quantified as the standard deviation (SD) of normal force (F z) and shear force (F xy) across friction conditions and tasks. The SD of F z was 227 % greater during the hybrid task as compared to the static task (p < .001) and was 19 % greater for the high- versus low-friction condition (p = .033). There were positive correlations between SD of F z and F xy during the hybrid force/motion tasks on the high- and low-friction conditions (r (2) = 0.5 and 0.86, respectively), suggesting significant associations between normal and shear forces for this hybrid task. The correlation between the SD of F z for static and hybrid tasks was r (2) = 0.44, indicating that the common practice of examining the control of static tasks may not sufficiently explain performance during hybrid tasks, at least for the young subjects tested in the current study. As activities of daily living frequently require hybrid force/motion tasks (e.g., writing, doing the dishes, and cleaning counters), the results of this study emphasize the need to study motor performance during hybrid tasks in addition to static force tasks. PMID:26898313

  11. Normal faults, normal friction?

    NASA Astrophysics Data System (ADS)

    Collettini, Cristiano; Sibson, Richard H.

    2001-10-01

    Debate continues as to whether normal faults may be seismically active at very low dips (δ < 30°) in the upper continental crust. An updated compilation of dip estimates (n = 25) has been prepared from focal mechanisms of shallow, intracontinental, normal-slip earthquakes (M > 5.5; slip vector raking 90° ± 30° in the fault plane) where the rupture plane is unambiguously discriminated. The dip distribution for these moderate-to-large normal fault ruptures extends from 65° > δ > 30°, corresponding to a range, 25° < θr < 60°, for the reactivation angle between the fault and inferred vertical σ1. In a comparable data set previously obtained for reverse fault ruptures (n = 33), the active dip distribution is 10° < δ = θr < 60°. For vertical and horizontal σ1 trajectories within extensional and compressional tectonic regimes, respectively, dip-slip reactivation is thus restricted to faults oriented at θr ≤ 60° to inferred σ1. Apparent lockup at θr ≈ 60° in each dip distribution and a dominant 30° ± 5° peak in the reverse fault dip distribution, are both consistent with a friction coefficient μs ≈ 0.6, toward the bottom of Byerlee's experimental range, though localized fluid overpressuring may be needed for reactivation of less favorably oriented faults.

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

    NASA Technical Reports Server (NTRS)

    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.

  13. Comprehensive parameter identification of feed servo systems with friction based on responses of the worktable

    NASA Astrophysics Data System (ADS)

    Liu, Lilan; Wu, Ziying

    2015-12-01

    A comprehensive identification method for structure and friction parameters of feed servo systems is put forward. A motor direct-connected feed system with Stribeck friction law is investigated. The relation between the critical stick-slip velocity of the worktable and the structure parameters as well as the difference between the static and Coulomb friction coefficient is derived first. Then, according to the data of critical stick-slip velocities at different feed positions, the structural parameters (such as diameter, lead and bearing length of the ball screw) are estimated using the nonlinear least square method. Furthermore, based on the stick-slip displacement response of the worktable, the Stribeck friction parameters are obtained using the direct graphical registration method. The feasibility and validity of the presented identification method is verified by numerical simulation. All the work can provide a theoretical reference for the comprehensive parameters identification of feed systems.

  14. An asymmetric dimer in a periodic potential: a minimal model for friction of graphene flakes

    NASA Astrophysics Data System (ADS)

    Hens, Remco; Fasolino, Annalisa

    2016-07-01

    We discuss the friction and motion of a model of a dimer with asymmetric interactions with a substrate potential. Starting from the consideration that a rigid dimer with spacing equal to half of the period of the potential has exactly zero static friction like the infinite incommensurate Frenkel Kontorova model, we show how stick-slip behaviour and friction arise as a function of asymmetry. We argue that this model can yield a simple yet insightful description of the frictional behaviour of graphene flakes on graphite and of superlubricity. The results can also be of interest for diatomic molecules on surfaces. Supplementary material in the form of three mp4 files available from the Journal web page at http://dx.doi.org/10.1140/epjb/e2016-70273-5

  15. Non-monotonic dependence of the friction coefficient on heterogeneous stiffness

    PubMed Central

    Giacco, F.; Ciamarra, M. Pica; Saggese, L.; de Arcangelis, L.; Lippiello, E.

    2014-01-01

    The complexity of the frictional dynamics at the microscopic scale makes difficult to identify all of its controlling parameters. Indeed, experiments on sheared elastic bodies have shown that the static friction coefficient depends on loading conditions, the real area of contact along the interfaces and the confining pressure. Here we show, by means of numerical simulations of a 2D Burridge-Knopoff model with a simple local friction law, that the macroscopic friction coefficient depends non-monotonically on the bulk elasticity of the system. This occurs because elastic constants control the geometrical features of the rupture fronts during the stick-slip dynamics, leading to four different ordering regimes characterized by different orientations of the rupture fronts with respect to the external shear direction. We rationalize these results by means of an energetic balance argument. PMID:25345800

  16. Rolling-Friction Robotic Gripper

    NASA Technical Reports Server (NTRS)

    Vranish, John M.

    1992-01-01

    Robotic gripper using rolling-friction fingers closes in on object with interface designed to mate with rollers somewhat misaligned initially, aligns object with respect to itself, then holds object securely in uniquely determined position and orientation. Operation of gripper causes minimal wear and burring of gripper and object. Exerts minimal friction forces on object when grasping and releasing. Releases object easily and reliably even when side forces and torques are between itself and object.

  17. Tire/runway friction interface

    NASA Technical Reports Server (NTRS)

    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.

  18. Experiment study on friction drive

    NASA Astrophysics Data System (ADS)

    Wang, Guomin; Ma, Lisheng; Yao, Zhengqiu; Li, Guoping

    2004-09-01

    In the past years, friction drive was developed to overcome the inherent deficiencies in both worm drive and gear drive. No periodical error and free of backlash are the main advantages of friction drive. With the trend towards bigger and bigger aperture of the optical telescopes, there are some reports about friction drive employed to drive the telescopes. However friction drive has its own deficiencies, such as slippage and creepage. This report here describes the study on the friction drive finished in an experiment arranged by LAMOST project. It comprises three main parts. First, it introduces the experiment apparatus and proposes a new kind of measurement and adjustment mechanisms. Secondly, the report gives the analysis of friction drive characteristics theoretically, such as slippage, creepage and gives the results of corresponding experiments. The experiment shows that the lowest stable speed reaches 0.05″/s with precision of 0.009″(RMS), the preload has little influence on the drive precision in the case of constant velocity and the variable velocity when the angle acceleration is less than 5″/s2 with close loop control and the creepage velocity of this experiment system is 1.47″/s. Lastly, the analysis in the second section lists some measures to improve the precision and stability further. These measures have been actually conducted in the testing system and proved to be reliable.

  19. Solid friction between soft filaments

    PubMed Central

    Ward, Andrew; Hilitski, Feodor; 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 filaments1,2. 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’s 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 properties of fibrous composite materials. PMID:25730393

  20. Characterization of Friction Joints Subjected to High Levels of Random Vibration

    NASA Technical Reports Server (NTRS)

    deSantos, Omar; MacNeal, Paul

    2012-01-01

    This paper describes the test program in detail including test sample description, test procedures, and vibration test results of multiple test samples. The material pairs used in the experiment were Aluminum-Aluminum, Aluminum- Dicronite coated Aluminum, and Aluminum-Plasmadize coated Aluminum. Levels of vibration for each set of twelve samples of each material pairing were gradually increased until all samples experienced substantial displacement. Data was collected on 1) acceleration in all three axes, 2) relative static displacement between vibration runs utilizing photogrammetry techniques, and 3) surface galling and contaminant generation. This data was used to estimate the values of static friction during random vibratory motion when "stick-slip" occurs and compare these to static friction coefficients measured before and after vibration testing.

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

    NASA Astrophysics Data System (ADS)

    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

  2. The Effect of Friction on Penetration in Friction Stir Welding

    NASA Technical Reports Server (NTRS)

    Rapp, Steve

    2002-01-01

    "Friction stir butt welding," as it was originally termed by Wayne Thomas and Christopher Dawes, in the early 1990s, but now commonly called "friction stir welding," has made great progress as a new welding technique. Marshall Space Flight Center has been investigating the use of FSW for assembly of the Shuttle's external fuel tank since the late 1990s and hopes to have the process in use by the summer of 2002. In FSW, a cylindrical pin tool of hardened steel, is rotated and plunged into the abutting edges of the parts to be joined. The tool is plunged into the weldment to within about .050 in of the bottom to assure full penetration. As the tool moves along the joint, the tool shoulder helps produce frictional heating, causing the material to plasticize. The metal of the two abutting plates flows from the front of the tool to the back where it cools and coalesces to form a weld in the solid phase. One quarter inch thick plates of aluminum alloy 2219 were used in this study. Two samples, each consisting of two 4 in x 12 in plates, were friction stir welded. The anvil for one sample was coated with molybdenum sulfide, while for the other sample a sheet of roughened stainless steel was placed between the anvil and the sample. The retractable pin tool was used so that the depth of the pin tool penetration could be varied. As welding proceeded, the length of the pin tool was gradually increased from the starting point. The purpose of this investigation is to find out at what point, in the down ramp, penetration occurs. Differences in root structure of the friction stir weld due to differences in anvil friction will be observed. These observations will be analyzed using friction stir weld theory.

  3. History-dependent friction and slow slip from time-dependent microscopic junction laws studied in a statistical framework.

    PubMed

    Thøgersen, Kjetil; Trømborg, Jørgen Kjoshagen; Sveinsson, Henrik Andersen; Malthe-Sørenssen, Anders; Scheibert, Julien

    2014-05-01

    To study how macroscopic friction phenomena originate from microscopic junction laws, we introduce a general statistical framework describing the collective behavior of a large number of individual microjunctions forming a macroscopic frictional interface. Each microjunction can switch in time between two states: a pinned state characterized by a displacement-dependent force and a slipping state characterized by a time-dependent force. Instead of tracking each microjunction individually, the state of the interface is described by two coupled distributions for (i) the stretching of pinned junctions and (ii) the time spent in the slipping state. This framework allows for a whole family of microjunction behavior laws, and we show how it represents an overarching structure for many existing models found in the friction literature. We then use this framework to pinpoint the effects of the time scale that controls the duration of the slipping state. First, we show that the model reproduces a series of friction phenomena already observed experimentally. The macroscopic steady-state friction force is velocity dependent, either monotonic (strengthening or weakening) or nonmonotonic (weakening-strengthening), depending on the microscopic behavior of individual junctions. In addition, slow slip, which has been reported in a wide variety of systems, spontaneously occurs in the model if the friction contribution from junctions in the slipping state is time weakening. Next, we show that the model predicts a nontrivial history dependence of the macroscopic static friction force. In particular, the static friction coefficient at the onset of sliding is shown to increase with increasing deceleration during the final phases of the preceding sliding event. We suggest that this form of history dependence of static friction should be investigated in experiments, and we provide the acceleration range in which this effect is expected to be experimentally observable. PMID:25353806

  4. Single-crystal-silicon-based microinstrument to study friction and wear at MEMS sidewall interfaces

    NASA Astrophysics Data System (ADS)

    Ansari, N.; Ashurst, W. R.

    2012-02-01

    Since the advent of microelectromechanical systems (MEMS) technology, friction and wear are considered as key factors that determine the lifetime and reliability of MEMS devices that contain contacting interfaces. However, to date, our knowledge of the mechanisms that govern friction and wear in MEMS is insufficient. Therefore, systematically investigating friction and wear at MEMS scale is critical for the commercial success of many potential MEMS devices. Specifically, since many emerging MEMS devices contain more sidewall interfaces, which are topographically and chemically different from in-plane interfaces, studying the friction and wear characteristics of MEMS sidewall surfaces is important. The microinstruments that have been used to date to investigate the friction and wear characteristics of MEMS sidewall surfaces possess several limitations induced either by their design or the structural film used to fabricate them. Therefore, in this paper, we report on a single-crystal-silicon-based microinstrument to study the frictional and wear behavior of MEMS sidewalls, which not only addresses some of the limitations of other microinstruments but is also easy to fabricate. The design, modeling and fabrication of the microinstrument are described in this paper. Additionally, the coefficients of static and dynamic friction of octadecyltrichlorosilane-coated sidewall surfaces as well as sidewall surfaces with only native oxide on them are also reported in this paper.

  5. Fundamental mechanisms of interfacial friction. 2. Stick-slip friction of spherical and chain molecules

    SciTech Connect

    Yoshizawa, Hisae; Israelachvili, J. )

    1993-10-28

    The friction and rheological properties of molecularly thin films of hexadecane between two shearing mica surfaces were measured under different conditions of load or applied pressure, film thickness, sliding velocity, temperature, and time or previous history. The aim was to investigate the tribological and rheological properties of ultrathin liquid films composed of chain molecules and to compare these properties with those of spherical molecules. The differences were found to be more quantitative than qualitative, and the results therefore provide insights into the general properties of liquids in thin films. The results show that during steady-state sliding between two solid crystalline surfaces, a liquid film may be considered to be in a one-phase or two-phase dynamic regime. In the two-phase regime, the film undergoes periodic [open quotes]stick-slip[close quotes] transitions between a solidlike and a liquidlike state. However, especially in the case of chain molecules such as hexadecane, the liquidlike state is very different from the bulk liquid. The frequency of transitions between the two dynamic states determines the static and dynamic friction forces and other dynamic properties of a shearing film. The effects produced by changing the load, temperature, sliding velocity, stopping time, etc., were found to be highly correlated. 49 refs., 21 figs., 3 tabs.

  6. In-Flight Capability for Evaluating Skin-Friction Gages and Other Near-Wall Flow Sensors

    NASA Technical Reports Server (NTRS)

    Bui, Trong T.; Pipitone, Brett J.; Krake, Keith L.; Richwine, Dave (Technical Monitor)

    2003-01-01

    An 8-in.-square boundary-layer sensor panel has been developed for in-flight evaluation of skin-friction gages and other near-wall flow sensors on the NASA Dryden Flight Research Center F-15B/Flight Test Fixture (FTF). Instrumentation on the sensor panel includes a boundary-layer rake, temperature sensors, static pressure taps, and a Preston tube. Space is also available for skin-friction gages or other near-wall flow sensors. Pretest analysis of previous F-15B/FTF flight data has identified flight conditions suitable for evaluating skin-friction gages. At subsonic Mach numbers, the boundary layer over the sensor panel closely approximates the two-dimensional (2D), law-of-the-wall turbulent boundary layer, and skin-friction estimates from the Preston tube and the rake (using the Clauser plot method) can be used to evaluate skin-friction gages. At supersonic Mach numbers, the boundary layer over the sensor panel becomes complex, and other means of measuring skin friction are needed to evaluate the accuracy of new skin-friction gages. Results from the flight test of a new rubber-damped skin-friction gage confirm that at subsonic Mach numbers, nearly 2D, law-of-the-wall turbulent boundary layers exist over the sensor panel. Sensor panel data also show that this new skin-friction gage prototype does not work in flight.

  7. High speed friction microscopy and nanoscale friction coefficient mapping

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    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 maps of the coefficient of friction can be uniquely calculated for heterogeneous surfaces. These parameters are determined at a scan velocity as fast as 2 mm s-1 for microfabricated SiO2 mesas and Au coated pits, yielding results that are identical to traditional speed measurements despite being ~1000 times faster. To demonstrate the upper limit of sliding velocity for the custom setup, the friction properties of mica are reported from 200 µm s-1 up to 2 cm s-1. While FCM is applicable to any AFM and scanning speed, quantitative nanotribology investigations of heterogeneous sliding or rolling components are therefore uniquely possible, even at realistic velocities for devices such as MEMS, biological implants, or data storage systems.

  8. Track-train dynamic analysis and test program. Barber S-2 static test

    NASA Technical Reports Server (NTRS)

    Abbott, P. W.

    1976-01-01

    The results of a static test of a Barber S-2 freight truck conducted to measure the stiffness and friction parameters of the modes of deformation which are being used in various mathematical models in the railroad industry were presented. Some difficulty was first experienced with the truck hardware since it was in an essentially new condition with many high spots causing interference. No difficulty was experienced once the interference was removed. The characteristics of the Barber S-2 are very similar to the ASF ride control truck. The major difference between the two trucks is the amount of friction between the bolster and side frames in both the vertical and lateral directions. The Barber S-2 has approximately twice the friction the ASF ride control truck has in the fully loaded condition. This does not necessarily imply that all trucks will have this same ratio of friction.

  9. Static elastica formulations of a pine conveying fluid

    NASA Astrophysics Data System (ADS)

    Thompson, J. M. T.; Lunn, T. S.

    1981-07-01

    An elastic pipe in an equilibrium configuration of arbitrary large deflection discharging fluid from its end experiences static centrifugal and frictional drag forces along its complete length. These are, however, entirely equivalent to an end follower force of magnitude ρ AV2. This equivalence is examined in detail by using the intrinsic field equations which are suitable for closed form solutions in terms of elliptic integrals. Once the pipe moves it also experiences gyroscopic Coriolis forces along its length, but these are not considered in this static examination. It is shown in detail how a discharging pipe with end forces and moments is statically equivalent to a beam or strut with the same end forces and moments plus the reversed momentum vector ρ AV2. It is seen that a cantilevered pipe with a free end can have no statical equilibrium states at all, at either large or small deflections, while pipes with constrained ends have large static deflections identical to those of the equivalent struts.

  10. The role of friction in the mechanism of retaining the partial removable dentures with double crown system.

    PubMed

    Dąbrowa, Tomasz; Dobrowolska, Anna; Wieleba, Wojciech

    2013-01-01

    Cylindrical telescopic crowns belong to bolt dentures, because their adhesion strength is based on the friction force. The magnitude of static and slide friction forces depends on the strain within the contact area and properties of materials employed. Friction force value between telescope elements declines in the first phase of wearing period and, subsequently, maintains particular constant value of 8 to 10 N. In the telescopic technique, homo and heterogenic joints are used. The following prosthodontic materials have been examined: goldbase alloys (Degudent Kiss, Degulor M), cobalt-base alloy (Brealloy 270), ceramics (Zircon Oxide, Zirconia) during tribological investigations on FGP composite resin. The cooperating surfaces were moistened with synthetic saliva. The research confirmed the dependence of the static friction coefficient on the contact pressure for the analyzed pairs of materials used in prosthodontics. The biggest effect of the contact pressure on the coefficient of friction value occurs when the ceramic rubs on FGP composite resin. The most stable friction coefficient in the context of contact pressure changes as well as life has been found in the case of the cobalt alloy Brealloy 270. An interesting material is a gold alloy Degulor M, for which the coefficient of friction varies only slightly with pressure in the range of 0.6 to 0.9 MPa. PMID:24479667

  11. Method of generating and measuring static small force using down-slope component of gravity.

    PubMed

    Fujii, Yusaku

    2007-06-01

    A method of generating and measuring static small forces at the micro-Newton level is proposed. In the method, the down-slope component of gravity acting on a mass on an inclined plane is used as a static force. To realize a linear motion of the mass with a small friction, an aerostatic linear bearing is used. The forces acting on the mass, such as the down-slope component of gravity and the dynamic frictional force, are determined by the levitation mass method. In an experiment, a static small force of approximately 183 microN is generated and measured with a standard uncertainty of approximately 2 microN. PMID:17614648

  12. A simple approach for calculating pile skin friction in clays

    SciTech Connect

    Mirza, U.A.A.

    1995-12-31

    A simple method is presented for calculating static shaft resistance of a pile driven into clay. The method is based on correlations established for North Sea clays between index properties and strengths. Application of the method to half a dozen full scale pile load tests which are part of the API RP2A`s data base and include a wide range of plasticity properties, overconsolidation ratios and strengths, is described. Except for short piles in very stiff to hard clays, the predictions agree very well with the measurements. The correlations presented allows an assessment of residual skin friction and indicate the importance of the liquidity index of the clay in static capacity calculations.

  13. Static Scale Conversion (SSC)

    SciTech Connect

    2007-01-19

    The Static Scale Conversion (SSC) software is a unique enhancement to the AIMVEE system. It enables a SSC to weigh and measure vehicles and cargo dynamically (i.e., as they pass over the large scale. Included in the software is the AIMVEE computer code base. The SSC and AIMVEE computer system electronically continue to retrieve deployment information, identify vehicle automatically and determine total weight, individual axle weights, axle spacing and center-of-balance for any wheeled vehicle in motion. The AIMVEE computer code system can also perform these functions statically for both wheel vehicles and cargo with information. The AIMVEE computer code system incorporates digital images and applies cubing algorithms to determine length, width, height for cubic dimensions of both vehicle and cargo. Once all this information is stored, it electronically links to data collection and dissemination systems to provide “actual” weight and measurement information for planning, deployment, and in-transit visibility.

  14. Static Scale Conversion (SSC)

    Energy Science and Technology Software Center (ESTSC)

    2007-01-19

    The Static Scale Conversion (SSC) software is a unique enhancement to the AIMVEE system. It enables a SSC to weigh and measure vehicles and cargo dynamically (i.e., as they pass over the large scale. Included in the software is the AIMVEE computer code base. The SSC and AIMVEE computer system electronically continue to retrieve deployment information, identify vehicle automatically and determine total weight, individual axle weights, axle spacing and center-of-balance for any wheeled vehicle inmore » motion. The AIMVEE computer code system can also perform these functions statically for both wheel vehicles and cargo with information. The AIMVEE computer code system incorporates digital images and applies cubing algorithms to determine length, width, height for cubic dimensions of both vehicle and cargo. Once all this information is stored, it electronically links to data collection and dissemination systems to provide “actual” weight and measurement information for planning, deployment, and in-transit visibility.« less

  15. Instantaneous engine frictional torque, its components and piston assembly friction

    SciTech Connect

    Nichols, F.A. ); Henein, N.A. . Center for Automotive Research)

    1992-05-01

    The overall goal of this report is to document the work done to determine the instantaneous frictional torque of internal combustion engine by using a new approach known as (P-[omega]) method developed at Wayne State University. The emphasis has been to improve the accuracy of the method, and apply it to both diesel and gasoline engines under different operating conditions. Also work included an investigation to determine the effect of using advanced materials and techniques to coat the piston rings on the instantaneous engine frictional torque and the piston assembly friction. The errors in measuring the angular velocity, [omega], have been determined and found to be caused by variations in the divisions within one encoder, encoder-to-encoder variations, misalignment within the encoder itself and misalignment between the encoder and crankshaft. The errors in measuring the cylinder gas pressure, P, have been determined and found to be caused by transducer-to-transducer variations, zero drift, thermal stresses and lack of linearity. The ability of the (P-[omega]) method in determining the frictional torque of many engine components has been demonstrated. These components include valve train, fuel injection pump with and without fuel injection, and piston with and without different ring combinations. The emphasis in this part of the research program has been on the piston-ring assembly friction. The effects of load and other operating variables on IFT have been determined. The motoring test, which is widely used in industry to measure engine friction has been found to be inaccurate. The errors have been determined at different loads.

  16. Versatile Friction Stir Welding/Friction Plug Welding System

    NASA Technical Reports Server (NTRS)

    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.

  17. Mesh Size Control of Friction

    NASA Astrophysics Data System (ADS)

    Pitenis, Angela; Uruena, Juan Manuel; Schulze, Kyle D.; Cooper, Andrew C.; Angelini, Thomas E.; Sawyer, W. Gregory

    Soft, permeable sliding interfaces in aqueous environments are ubiquitous in nature but their ability to maintain high lubricity in a poor lubricant (water) has not been well understood. Hydrogels are excellent materials for fundamental soft matter and biotribology studies due to their high water content. While mesh size controls the material and transport properties of a hydrogel, its effects on friction were only recently explored. Polyacrylamide hydrogels slid in a Gemini (self-mated) interface produced low friction under low speeds, low pressures, macroscopic contact areas, and room temperature aqueous environments. The friction coefficients at these interfaces are lowest at low speeds and are speed-independent. This behavior is due to thermal fluctuations at the interface separating the surfaces, with water shearing in this region being the main source of dissipation. We found that mesh size had an inverse correlation with friction. We further investigated a transition from this behavior at higher speeds, and found that the transition speed correlated with the mesh size and relaxation time of the polymer network. Very soft and correspondingly large mesh size Gemini hydrogels show superlubricity under specific conditions with friction being less than 0.005.

  18. Fundamentals of friction stir spot welding

    NASA Astrophysics Data System (ADS)

    Badarinarayan, Harsha

    The recent spike in energy costs has been a major contributor to propel the use of light weight alloys in the transportation industry. In particular, the automotive industry sees benefit in using light weight alloys to increase fuel efficiency and enhance performance. In this context, light weight design by replacing steel with Al and/or Mg alloys have been considered as promising initiatives. The joining of structures made of light weight alloys is therefore very important and calls for more attention. Friction Stir Spot Welding (FSSW) is an evolving technique that offers several advantages over conventional joining processes. The fundamentals aspects of FSSW are systematically studied in this dissertation. The effects and influence of process inputs (weld parameters and tool geometry) on the process output (weld geometry and static strength) is studied. A Design of Experiments (DoE) is carried out to identify the effect of each process parameter on weld strength. It is found that the tool geometry, and in particular the pin profile has a significant role in determining the weld geometry (hook, stir zone size etc.) which in turn influences the failure mode and weld strength. A novel triangular pin tool geometry is proposed that suppresses the hook formation and produces welds with twice the static strength as those produced with conventional cylindrical pin tools. An experimental and numerical approach is undertaken to understand the effect of pin geometry on the material flow and failure mechanism of spot welds. In addition, key practical issues have been addressed such as quantification of tool life and a methodology to control tool plunge depth during welding. Finally, by implementing the findings of this dissertation, FSSW is successfully performed on a closure panel assembly for an automotive application.

  19. Effect of passive self-ligating bracket placement on the posterior teeth on reduction of frictional force in sliding mechanics

    PubMed Central

    Kim, Kyu-Ry

    2016-01-01

    Objective The purpose of this study was to investigate the static (SFF) and kinetic frictional forces (KFF) in sliding mechanics of hybrid bracket systems that involve placing a conventional bracket (CB) or active self-ligating bracket (ASLB) on the maxillary anterior teeth (MXAT) and a passive SLB (PSLB) on the maxillary posterior teeth (MXPT). Methods The samples consisted of two thoroughbred types (group 1, anterior-CB + posterior-CB; group 2, anterior-ASLB + posterior-ASLB) and four hybrid types (group 3, anterior-CB + posterior-PSLB-type 1; group 4, anterior-CB + posterior-PSLB-type 2; group 5, anterior-ASLB + posterior-PSLB-type 1; group 6, anterior-ASLB + posterior-PSLB-type 2) (n = 13 per group). After maxillary dentition alignment and maxillary first premolars removal in the stereolithographically-made typodont system, a 0.019 × 0.025-inch stainless steel wire was drawn through the right quadrant of the maxillary arch at 0.5 mm/min for 5 min. The SFF and KFF were measured with a mechanical testing machine and statistical analyses were performed. Results Four different categories of SFF and KFF were observed among all groups (all p < 0.001). Group 1 demonstrated the highest SFF and KFF; groups 4 and 3 were second and third highest, respectively. The fourth category included groups 2, 5, and 6. Placing PSLBs on the MXPT resulted in significant SFF and KFF reductions in cases with CBs on the MXAT, but not in cases with ASLBs on the MXAT. Conclusions These data might aid in the development of a hybrid bracket system that enables low-friction sliding of an archwire through the MXPT. PMID:27019821

  20. The effect of zinc oxide nanoparticles deposition for friction reduction on orthodontic wires

    PubMed Central

    Kachoei, Mojghan; Eskandarinejad, Faranak; Divband, Baharak; Khatamian, Masumeh

    2013-01-01

    Background: In the sliding technique, the reduced frictional forces are associated with rapid tooth movements and better control of the anchorage. Recently, wire coating with different nanoparticles has been proposed to decrease frictional forces. This in vitro study was carried out to coat stainless steel (SS) wires with zinc oxide (ZnO) nanoparticles in order to determine the effect of this coating on friction between wires and orthodontic brackets. Materials and Methods: Eighty 0.016 inch and 0.019 inch × 0.025 inch SS wires with and without ZnO nanoparticles were used in 80 orthodontic brackets (0.018 and 0.022 systems). The coated wires were analyzed by SEM and X-Ray diffraction (XRD) observations. Kinetic friction between the wires and orthodontic brackets were calculated using a universal testing machine. Frictional forces were statistically analyzed using three-way ANOVA, one-way ANOVA, Student's t-test and Tukey multiple comparison tests. Results: Coating with ZnO nanoparticles significantly influenced frictional force values (P < 0.0001). In 0.019 inch × 0.025 inch wires, the frictional forces were 1.6912 ± 0.18868 and 3.4485 ± 0.32389 N in the coated and uncoated wires respectively, (51% reductions). In the 0.016 inch wires, the friction values were estimated to be 1.5668 ± 0.10703 and 2.56 ± 0.34008 N in the coated and uncoated conditions, respectively, (39% reductions). Conclusion: Due to the positive effects of ZnO nanoparticle coating on decreasing frictional forces, these nanoparticles might offer a novel opportunity to significantly reduce friction during tooth movement. PMID:24130586

  1. Direct Measurements of Skin Friction

    NASA Technical Reports Server (NTRS)

    Dhawan, Satish

    1953-01-01

    A device has been developed to measure local skin friction on a flat plate by measuring the force exerted upon a very small movable part of the surface of the flat plate. These forces, which range from about 1 milligram to about 100 milligrams, are measured by means of a reactance device. The apparatus was first applied to measurements in the low-speed range, both for laminar and turbulent boundary layers. The measured skin-friction coefficients show excellent agreement with Blasius' and Von Karman's results. The device was then applied to high-speed subsonic flow and the turbulent-skin-friction coefficients were determined up to a Mach number of about 0.8. A few measurements in supersonic flow were also made. This paper describes the design and construction of the device and the results of the measurements.

  2. Frictional processes in volcanic conduits

    NASA Astrophysics Data System (ADS)

    Lavallee, Y.; Kendrick, J. E.; Petrakova, L.; Mitchell, T. M.; Heap, M. J.; Hirose, T.; Di Toro, G.; Hess, K.; Dingwell, D. B.

    2012-12-01

    The ascent of high-viscosity magma in upper conduits proceeds via the development of shear zones, which commonly fracture, producing fault surfaces that control the last hundreds of meters of ascent by frictional slip. Frictional slip in conduits may occur along magma-rock, rock-rock and magma-magma interfaces, with or without the presence of gouge material. During slip, frictional work is converted to heat, which may result in strong geochemical disequilibria as well as rheological variations, with important consequences on the dynamics of magma ascent. Here, we present a thermo-mechanical study on the ability of volcanic rocks (with different proportions of interstitial glass, crystals and vesicles) to sustain friction, and in some cases to melt, using a high-velocity rotary apparatus. The friction experiments were conducted at a range of slip velocities (1.3 mm/s to 1.3 m/s) along a (fault) plane subjected to different normal stresses (0.5-10 MPa). We observe that the behaviour of volcanic rocks during slip events varies remarkably. Frictional slip along dense crystal-rich rocks is characterized by the occurrence of comminution, commonly followed by melting. In contrast, slip along dense glass rocks rarely proceeds along a discrete plane - a glass subjected to slip tends to shatter as temperature enters the glass transition interval. Alternatively, glass can be slipped against a crystalline material. In the case of porous material, slip generally results in rapid abrasion of the porous material, producing a high amount of ash particles. The inability of the material to preserve its slip surface inhibits the generation of significant heat. Finally, during experiments in which ash gouge occupies the slip zone, friction generates a modest amount of heat and does not induce significant comminution along the slip plane. Mechanically, the frictional coefficients of the tested volcanic material vary significantly, depending whether the material may sustain slip (and

  3. Friction and Adhesion Forces of Bacillus thuringiensis Spores on Planar Surfaces in Atmospheric Systems

    SciTech Connect

    Kweon, Hyojin; Yiacoumi, Sotira; Tsouris, Costas

    2011-01-01

    The kinetic friction force and the adhesion force of Bacillus thuringiensis spores on planar surfaces in atmospheric systems were studied using atomic force microscopy. The influence of relative humidity (RH) on these forces varied for different surface properties including hydrophobicity, roughness, and surface charge. The friction force of the spore was greater on a rougher surface than on mica, which is atomically flat. As RH increases, the friction force of the spores decreases on mica whereas it increases on rough surfaces. The influence of RH on the interaction forces between hydrophobic surfaces is not as strong as for hydrophilic surfaces. The friction force of the spore is linear to the sum of the adhesion force and normal load on the hydrophobic surface. The poorly defined surface structure of the spore and the adsorption of contaminants from the surrounding atmosphere are believed to cause a discrepancy between the calculated and measured adhesion forces.

  4. Kinetic Demonstration.

    ERIC Educational Resources Information Center

    Burgardt, Erik D.; Ryan, Hank

    1996-01-01

    Presents a unit on chemical reaction kinetics that consists of a predemonstration activity, the demonstration, and a set of postdemonstration activities that help students transfer the concepts to actual chemical reactions. Simulates various aspects of chemical reaction kinetics. (JRH)

  5. Kinetic Atom.

    ERIC Educational Resources Information Center

    Wilson, David B.

    1981-01-01

    Surveys the research of scientists like Joule, Kelvin, Maxwell, Clausius, and Boltzmann as it comments on the basic conceptual issues involved in the development of a more precise kinetic theory and the idea of a kinetic atom. (Author/SK)

  6. Friction and Hydration Repulsion Between Hydrogen-Bonding Surfaces

    NASA Astrophysics Data System (ADS)

    Netz, Roland

    2012-02-01

    The dynamics and statics of polar surfaces are governed by the hydrogen-bonding network and the interfacial water layer properties. Insight can be gained from all-atomistic simulations with explicit water that reach the experimentally relevant length and time scales. Two connected lines of work will be discussed: 1) On surfaces, the friction coefficient of bound peptides is very low on hydrophobic substrates, which is traced back to the presence of a depletion layer between substrate and water that forms a lubrication layer. Conversely, friction forces on hydrophilic substrates are large. A general friction law is presented and describes the dynamics of hydrogen-bonded matter in the viscous limit. 2) The so-called hydration repulsion between polar surfaces in water is studied using a novel simulation technique that allows to efficiently determine the interaction pressure at constant water chemical potential. The hydration repulsion is shown to be caused by a mixture of water polarization effects and the desorption of interfacial water.

  7. Granular friction: Triggering large events with small vibrations

    PubMed Central

    Lastakowski, Henri; Géminard, Jean-Christophe; Vidal, Valérie

    2015-01-01

    Triggering large-scale motion by imposing vibrations to a system can be encountered in many situations, from daily-life shaking of saltcellar to silo unclogging or dynamic earthquakes triggering. In the well-known situation of solid or granular friction, the acceleration of imposed vibrations has often been proposed as the governing parameter for the transition between stick-slip motion and continuous sliding. The threshold acceleration for the onset of continuous slip motion or system unjamming is usually found of the order of the gravitational acceleration. These conclusions are mostly drawn from numerical studies. Here, we investigate, in the laboratory, granular friction by shearing a layer of grains subjected to horizontal vibrations. We show that, in contrast with previous results, the quantity that controls the frictional properties is the characteristic velocity, and not the acceleration, of the imposed mechanical vibrations. Thus, when the system is statically loaded, the typical acceleration of the vibrations which trigger large slip events is much smaller than the gravitational acceleration. These results may be relevant to understand dynamic earthquake triggering by small ground perturbations. PMID:26334133

  8. Enzyme Kinetics.

    ERIC Educational Resources Information Center

    Moe, Owen; Cornelius, Richard

    1988-01-01

    Conveys an appreciation of enzyme kinetic analysis by using a practical and intuitive approach. Discusses enzyme assays, kinetic models and rate laws, the kinetic constants (V, velocity, and Km, Michaels constant), evaluation of V and Km from experimental data, and enzyme inhibition. (CW)

  9. Systematic assessment of the static stress triggering hypothesis using interearthquake time statistics

    NASA Astrophysics Data System (ADS)

    Nandan, Shyam; Ouillon, Guy; Woessner, Jochen; Sornette, Didier; Wiemer, Stefan

    2016-03-01

    A likely source of earthquake clustering is static stress transfer between individual events. Previous attempts to quantify the role of static stress for earthquake triggering generally considered only the stress changes caused by large events and often discarded data uncertainties. We conducted a robust twofold empirical test of the static stress change hypothesis by accounting for all events of magnitude M ≥ 2.5 and their location and focal mechanism uncertainties provided by catalogs for Southern California between 1981 and 2010, first after resolving the focal plane ambiguity and second after randomly choosing one of the two nodal planes. For both cases, we find compelling evidence supporting the static triggering with stronger evidence after resolving the focal plane ambiguity above significantly small (about 10 Pa) but consistently observed stress thresholds. The evidence for the static triggering hypothesis is robust with respect to the choice of the friction coefficient, Skempton's coefficient, and magnitude threshold. Weak correlations between the Coulomb index (fraction of earthquakes that received positive Coulomb stress change) and the coefficient of friction indicate that the role of normal stress in triggering is rather limited. Last but not the least, we determined that the characteristic time for the loss of the stress change memory of a single event is nearly independent of the amplitude of the Coulomb stress change and varies between ~95 and ~180 days implying that forecasts based on static stress changes will have poor predictive skills beyond times that are larger than a few hundred days on average.

  10. Joint Winter Runway Friction Program Accomplishments

    NASA Technical Reports Server (NTRS)

    Yager, Thomas J.; Wambold, James C.; Henry, John J.; Andresen, Arild; Bastian, Matthew

    2002-01-01

    The major program objectives are: (1) harmonize ground vehicle friction measurements to report consistent friction value or index for similar contaminated runway conditions, for example, compacted snow, and (2) establish reliable correlation between ground vehicle friction measurements and aircraft braking performance. Accomplishing these objectives would give airport operators better procedures for evaluating runway friction and maintaining acceptable operating conditions, providing pilots information to base go/no go decisions, and would contribute to reducing traction-related aircraft accidents.

  11. Apparatus for measurement of coefficient of friction

    NASA Technical Reports Server (NTRS)

    Slifka, A. J.; Siegwarth, J. D.; Sparks, L. L.; Chaudhuri, Dilip K.

    1990-01-01

    An apparatus designed to measure the coefficient of friction in certain controlled atmospheres is described. The coefficient of friction observed during high-load tests was nearly constant, with an average value of 0.56. This value is in general agreement with that found in the literature and also with the initial friction coefficient value of 0.67 measured during self-mated friction of 440C steel in an oxygen environment.

  12. Low-Friction Joint for Robot Fingers

    NASA Technical Reports Server (NTRS)

    Ruoff, C. F.

    1985-01-01

    Mechanical linkage allows adjacent parts to move relative to each other with low friction and with no chatter, slipping, or backlash. Low-friction joint of two surfaces in rolling contact, held in alinement by taut flexible bands. No sliding friction or "stick-slip" motion: Only rolling-contact and bending friction within bands. Proposed linkage intended for finger joints in mechanical hands for robots and manipulators.

  13. Deformation During Friction Stir Welding

    NASA Technical Reports Server (NTRS)

    White, Henry J.

    2002-01-01

    Friction Stir Welding (FSW) is a solid state welding process that exhibits characteristics similar to traditional metal cutting processes. The plastic deformation that occurs during friction stir welding is due to the superposition of three flow fields: a primary rotation of a radially symmetric solid plug of metal surrounding the pin tool, a secondary uniform translation, and a tertiary ring vortex flow (smoke rings) surrounding the tool. If the metal sticks to the tool, the plug surface extends down into the metal from the outer edge of the tool shoulder, decreases in diameter like a funnel, and closes up beneath the pin. Since its invention, ten years have gone by and still very little is known about the physics of the friction stir welding process. In this experiment, an H13 steel weld tool (shoulder diameter, 0.797 in; pin diameter, 0.312 in; and pin length, 0.2506 in) was used to weld three 0.255 in thick plates. The deformation behavior during friction stir welding was investigated by metallographically preparing a plan view sections of the weldment and taking Vickers hardness test in the key-hole region.

  14. Critical Length Limiting Superlow Friction

    NASA Astrophysics Data System (ADS)

    Ma, Ming; Benassi, Andrea; Vanossi, Andrea; Urbakh, Michael

    2015-02-01

    Since the demonstration of superlow friction (superlubricity) in graphite at nanoscale, one of the main challenges in the field of nano- and micromechanics was to scale this phenomenon up. A key question to be addressed is to what extent superlubricity could persist, and what mechanisms could lead to its failure. Here, using an edge-driven Frenkel-Kontorova model, we establish a connection between the critical length above which superlubricity disappears and both intrinsic material properties and experimental parameters. A striking boost in dissipated energy with chain length emerges abruptly due to a high-friction stick-slip mechanism caused by deformation of the slider leading to a local commensuration with the substrate lattice. We derived a parameter-free analytical model for the critical length that is in excellent agreement with our numerical simulations. Our results provide a new perspective on friction and nanomanipulation and can serve as a theoretical basis for designing nanodevices with superlow friction, such as carbon nanotubes.

  15. Improved Coulomb-Friction Damper

    NASA Technical Reports Server (NTRS)

    Campbell, G. E.

    1985-01-01

    Equal damping provided on forward and reverse strokes. Improved damper has springs and wedge rings symmetrically placed on both ends of piston wedge, so friction force same in both directions of travel. Unlike conventional automotive shock absorbers, they resemble on outside, both versions require no viscous liquid and operate over wide temperature range.

  16. Turbine blade friction damping study

    NASA Technical Reports Server (NTRS)

    Dominic, R. J.

    1985-01-01

    A lumped parameter method, implemented on a VAX 11/780 computer shows that the primary parameters affecting the performance of the friction damper of the first stage turbine of the SSME high pressure fuel pump are: the damper-blade coefficient of friction; the normal force applied to the friction interface; the amplitude of the periodic forcing function; the relative phase angle of the forcing functions for adjacent blades bridged by a damper (effectively, the engine order of the forcing function); and the amount of hysteretic damping that acts to limit the vibration amplitude of the blade in its resonance modes. The low order flexural resonance vibration modes of HPFTP blades without dampers, with production dampers, and with two types of lightweight experimental dampers were evaluated in high speed spin pit tests. Results agree with those of the analytical study in that blades fitted with production friction dampers experienced the airfoil-alone flexural resonance mode, while those without dampers or with lighter weight dampers did not. No blades fitted with dampers experienced the whole blade flexural resonance mode during high speed tests, while those without dampers did.

  17. Tool Wear in Friction Drilling

    SciTech Connect

    Miller, Scott F; Blau, Peter Julian; Shih, Albert J.

    2007-01-01

    This study investigated the wear of carbide tools used in friction drilling, a nontraditional hole-making process. In friction drilling, a rotating conical tool uses the heat generated by friction to soften and penetrate a thin workpiece and create a bushing without generating chips. The wear of a hard tungsten carbide tool used for friction drilling a low carbon steel workpiece has been investigated. Tool wear characteristics were studied by measuring its weight change, detecting changes in its shape with a coordinate measuring machine, and making observations of wear damage using scanning electron microscopy. Energy dispersive spectroscopy was applied to analyze the change in chemical composition of the tool surface due to drilling. In addition, the thrust force and torque during drilling and the hole size were measured periodically to monitor the effects of tool wear. Results indicate that the carbide tool is durable, showing minimal tool wear after drilling 11000 holes, but observations also indicate progressively severe abrasive grooving on the tool tip.

  18. Dynamical friction in cuspy galaxies

    SciTech Connect

    Arca-Sedda, M.; Capuzzo-Dolcetta, R.

    2014-04-10

    In this paper, we treat the problem of the dynamical friction decay of a massive object moving in an elliptical galaxy with a cuspidal inner distribution of the mass density. We present results obtained by both self-consistent, direct summation, N-body simulations, as well as by a new semi-analytical treatment of dynamical friction valid in such cuspy central regions of galaxies. A comparison of these results indicates that the proposed semi-analytical approximation is the only reliable one in cuspy galactic central regions, where the standard Chandrasekhar's local approximation fails and also gives estimates of decay times that are correct at 1% with respect to those given by N-body simulations. The efficiency of dynamical friction in cuspy galaxies is found definitively higher than in core galaxies, especially on more radially elongated satellite orbits. As another relevant result, we find a proportionality of the dynamical friction decay time to the –0.67 power of the satellite mass, M, shallower than the standardly adopted M {sup –1} dependence.

  19. Measuring Adhesion And Friction Forces

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa

    1991-01-01

    Cavendish balance adapted to new purpose. Apparatus developed which measures forces of adhesion and friction between specimens of solid materials in vacuum at temperatures from ambient to 900 degrees C. Intended primarily for use in studying adhesion properties of ceramics and metals, including silicon carbide, aluminum oxide, and iron-base amorphous alloys.

  20. Initial Friction Compensation by Disturbance Observer Based on Rolling Friction Model

    NASA Astrophysics Data System (ADS)

    Maeda, Yoshihiro; Iwasaki, Makoto

    This paper presents a rolling friction model-based initial friction compensation (IFC) by a disturbance observer for the fast and precise positioning of ball-screw-driven table systems. The effects of rolling friction in mechanisms should be suppressed in order to the achieve required control performance. In this study, therefore, a rolling friction model is adopted to compensate for the initial friction, so that delay-free friction estimation becomes possible. The proposed initial friction compensation method has been verified experimentally by using a prototype of industrial positioning devices.

  1. Properties of Broezel static probe

    NASA Astrophysics Data System (ADS)

    Gašparovič, Peter; Semrád, Karol; Cúttová, Miroslava

    2016-03-01

    The properties of flat static probe designed by Broezel and used in sailplanes are investigated for its planned use in low speed tunnel. Both the numerical CFD model and experiment in low speed wind tunnel confirm yaw insensitivity of the static pressure measured by the probe. The results indicate that the probe is sufficiently accurate for its planned use in wind tunnel measurements.

  2. Semiconductor ac static power switch

    NASA Technical Reports Server (NTRS)

    Vrancik, J.

    1968-01-01

    Semiconductor ac static power switch has long life and high reliability, contains no moving parts, and operates satisfactorily in severe environments, including high vibration and shock conditions. Due to their resistance to shock and vibration, static switches are used where accidental switching caused by mechanical vibration or shock cannot be tolerated.

  3. Practical considerations of joint friction and backlash in large ground-based telescope secondary optic positioning systems

    NASA Astrophysics Data System (ADS)

    Cash, Michael; Bruch, Daniel; Jahn, Bernie; Keas, Paul

    2008-07-01

    Secondary mirrors and lenses in several planned ground-based telescopes have masses on the order of 5000 kg and require a positioning system that is repeatable to one-tenth the pixel size of the optical sensors, nominally 10 micrometers or less. Hexapods, or Stewart Platforms, are frequently integrated into the support structure as six degree of freedom parallel positioning and alignment systems. These systems are limited in resolution by friction in the 36 kinematic degrees of freedom (DOF) necessary for properly constrained motion of the platform. The 30 passive DOF, typically implemented with one 3-DOF and one 2-DOF joint on each hexapod leg, introduce unwanted friction and/or backlash into the positioning system. Backlash is generally unacceptable and elimination requires significant preloading of the joints, which in turn increases joint friction. This paper will: review various joint types including rolling element, plain bearing (sliding), and flexure; examine the backlash and friction tradeoffs involved in selecting joint type including unwanted deflections due to joint moments, static position resolution limitations, dynamic positioning settling time effects, self-locking mechanisms, and power dissipation; compare with experimental data and previously published results; present methods for modeling both static and dynamic effects of friction; and suggest recommendations for general positioning system design. Considerations for both equatorial and altitude-azimuth telescopes will be discussed, along with variation of effects due to telescope positioning. Analyses will be reinforced with friction and backlash measurements made on several physical joints.

  4. Pressure and Friction Injuries in Primary Care.

    PubMed

    Phillips, Shawn; Seiverling, Elizabeth; Silvis, Matthew

    2015-12-01

    Pressure and friction injuries are common throughout the lifespan. A detailed history of the onset and progression of friction and pressure injuries is key to aiding clinicians in determining the underlying mechanism behind the development of the injury. Modifying or removing the forces that are creating pressure or friction is the key to both prevention and healing of these injuries. Proper care of pressure and friction injuries to the skin is important to prevent the development of infection. Patient education on positioning and ergonomics can help to prevent recurrence of pressure and friction injuries. PMID:26612376

  5. In vivo friction properties of human skin.

    PubMed

    Zhang, M; Mak, A F

    1999-08-01

    In vivo frictional properties of human skin and five materials, namely aluminium, nylon, silicone, cotton sock, Pelite, were investigated. Normal and untreated skin over six anatomic regions of ten normal subjects were measured under a controlled environment. The average coefficient of friction for all measurements is 0.46+/-0.15 (p<0.05). Among all measured sites, the palm of the hand has the highest coefficient of friction (0.62+/-0.22). For all the materials tested, silicone has the highest coefficient of friction (0.61+/-0.21), while nylon has the lowest friction (0.37+/-0.09). PMID:10493141

  6. Single and reciprocal friction testing of micropatterned surfaces for orthopedic device design.

    PubMed

    Mitchell, N; Eljach, C; Lodge, B; Sharp, J L; Desjardins, J D; Kennedy, M S

    2012-03-01

    The use of micropatterning to create uniform surface morphologies has been cited as yielding improvements in the coefficient of friction during high velocity sliding contact. Studies have not been preformed to determine if these micropatterns could also be useful in biomedical applications, such as total joint replacement surfaces, where the lower sliding velocities are used. In addition, other factors such as lubricant viscosities and materials used are more tightly constrained. In this study, the effect of pattern geometry, feature size and lubricant on contact friction and surface damage was investigated using 316L steel in sliding contact with a stainless steel and polyethylene pins. Using a novel proprietary forming process that creates millions of microstructures in parallel, a variety of micropatterned surfaces were fabricated to study the influence of shape (oval, circular, square), geometry (depressions, pillars) and feature size (10, 50 and 100 mm) on both contact friction and surface damage. All samples were 316L stainless steel and the static and dynamic coefficients of friction when in contact with either a stainless steel or polyethylene counterface were measured in dry and lubricated conditions. All samples were characterized for surface uniformity and pattern aspect ratio using white light interferometry and optical microscope image analysis, and the coefficients of friction were measured for each surface/lubricant/pin system using a CETR scratch testing system. Results showed that round depressions with diameters of 10 μm had a significantly lower steady state coefficient of friction than the non-patterned substrates or substrates with greater diameter depression patterns. In addition, our results showed that the single-pass coefficient of friction measurements were not good predictors of the steady state coefficient of friction values measured. PMID:22340690

  7. Viscosity calculated in simulations of strongly coupled dusty plasmas with gas friction

    SciTech Connect

    Feng Yan; Goree, J.; Liu Bin

    2011-05-15

    A two-dimensional strongly coupled dusty plasma is modeled using Langevin and frictionless molecular dynamical simulations. The static viscosity {eta} and the wave-number-dependent viscosity {eta}(k) are calculated from the microscopic shear in the random motion of particles. A recently developed method of calculating the wave-number-dependent viscosity {eta}(k) is validated by comparing the results of {eta}(k) from the two simulations. It is also verified that the Green-Kubo relation can still yield an accurate measure of the static viscosity {eta} in the presence of a modest level of friction as in dusty plasma experiments.

  8. Apparatus for measuring internal friction Q factors in brittle materials. [applied to lunar samples

    NASA Technical Reports Server (NTRS)

    Tittmann, B. R.; Curnow, J. M.

    1976-01-01

    A flexural analog of the torsion pendulum for measuring the Young's modulus and the internal friction Q factor of brittle materials has been developed for Q greater than 10 to the 3rd measurements at a zero static stress and at 10 to the -7th strains of brittle materials in the Hz frequency range. The present design was motivated by the desire to measure Q in fragile lunar return samples at zero static stress to shed light on the anomalously low attenuation of seismic waves on the moon. The use of the apparatus is demonstrated with data on fused silica and on a terrestrial analog of lunar basalt.

  9. Observation of Aubry-type transition in finite atom chains via friction.

    PubMed

    Bylinskii, Alexei; Gangloff, Dorian; Counts, Ian; Vuletić, Vladan

    2016-07-01

    The highly nonlinear many-body physics of a chain of mutually interacting atoms in contact with a periodic substrate gives rise to complex static and dynamical phenomena, such as structural phase transitions and friction. In the limit of an infinite chain incommensurate with the substrate, Aubry predicted a transition with increasing substrate potential, from the chain's intrinsic arrangement free to slide on the substrate, to a pinned arrangement favouring the substrate pattern. So far, the Aubry transition has not been observed. Here, using spatially resolved position and friction measurements of cold trapped ions in an optical lattice, we observed a finite version of the Aubry transition and the onset of its hallmark fractal atomic arrangement. Notably, the observed critical lattice depth for few-ion chains agrees well with the infinite-chain prediction. Our results elucidate the connection between competing ordering patterns and superlubricity in nanocontacts-the elementary building blocks of friction. PMID:26998915

  10. Quantum Otto cycle with inner friction: finite-time and disorder effects

    NASA Astrophysics Data System (ADS)

    Alecce, A.; Galve, F.; Lo Gullo, N.; Dell'Anna, L.; Plastina, F.; Zambrini, R.

    2015-07-01

    The concept of inner friction, by which a quantum heat engine is unable to follow adiabatically its strokes and thus dissipates useful energy, is illustrated in an exact physical model where the working substance consists of an ensemble of misaligned spins interacting with a magnetic field and performing the Otto cycle. The effect of this static disorder under a finite-time cycle gives a new perspective of the concept of inner friction under realistic settings. We investigate the efficiency and power of this engine and relate its performance to the amount of friction from misalignment and to the temperature difference between heat baths. Finally we propose an alternative experimental implementation of the cycle where the spin is encoded in the degree of polarization of photons.

  11. Friction in debris flows: inferences from large-scale flume experiments

    USGS Publications Warehouse

    Iverson, Richard M.; LaHusen, Richard G.

    1993-01-01

    A recently constructed flume, 95 m long and 2 m wide, permits systematic experimentation with unsteady, nonuniform flows of poorly sorted geological debris. Preliminary experiments with water-saturated mixtures of sand and gravel show that they flow in a manner consistent with Coulomb frictional behavior. The Coulomb flow model of Savage and Hutter (1989, 1991), modified to include quasi-static pore-pressure effects, predicts flow-front velocities and flow depths reasonably well. Moreover, simple scaling analyses show that grain friction, rather than liquid viscosity or grain collisions, probably dominates shear resistance and momentum transport in the experimental flows. The same scaling indicates that grain friction is also important in many natural debris flows.

  12. High temperature skin friction measurement

    NASA Technical Reports Server (NTRS)

    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.

  13. Computational Methods for Frictional Contact With Applications to the Space Shuttle Orbiter Nose-Gear Tire

    NASA Technical Reports Server (NTRS)

    Tanner, John A.

    1996-01-01

    A computational procedure is presented for the solution of frictional contact problems for aircraft tires. A Space Shuttle nose-gear tire is modeled using a two-dimensional laminated anisotropic shell theory which includes the effects of variations in material and geometric parameters, transverse-shear deformation, and geometric nonlinearities. Contact conditions are incorporated into the formulation by using a perturbed Lagrangian approach with the fundamental unknowns consisting of the stress resultants, the generalized displacements, and the Lagrange multipliers associated with both contact and friction conditions. The contact-friction algorithm is based on a modified Coulomb friction law. A modified two-field, mixed-variational principle is used to obtain elemental arrays. This modification consists of augmenting the functional of that principle by two terms: the Lagrange multiplier vector associated with normal and tangential node contact-load intensities and a regularization term that is quadratic in the Lagrange multiplier vector. These capabilities and computational features are incorporated into an in-house computer code. Experimental measurements were taken to define the response of the Space Shuttle nose-gear tire to inflation-pressure loads and to inflation-pressure loads combined with normal static loads against a rigid flat plate. These experimental results describe the meridional growth of the tire cross section caused by inflation loading, the static load-deflection characteristics of the tire, the geometry of the tire footprint under static loading conditions, and the normal and tangential load-intensity distributions in the tire footprint for the various static vertical loading conditions. Numerical results were obtained for the Space Shuttle nose-gear tire subjected to inflation pressure loads and combined inflation pressure and contact loads against a rigid flat plate. The experimental measurements and the numerical results are compared.

  14. Collective behavior of asperities as a model for friction and adhesion

    NASA Astrophysics Data System (ADS)

    Hulikal, Srivatsan

    Understanding friction and adhesion in static and sliding contact of surfaces is important in numerous physical phenomena and technological applications. Most surfaces are rough at the microscale, and thus the real area of contact is only a fraction of the nominal area. The macroscopic frictional and adhesive response is determined by the collective behavior of the population of evolving and interacting microscopic contacts. This collective behavior can be very different from the behavior of individual contacts. It is thus important to understand how the macroscopic response emerges from the microscopic one. In this thesis, we develop a theoretical and computational framework to study the collective behavior. Our philosophy is to assume a simple behavior of a single asperity and study the collective response of an ensemble. Our work bridges the existing well-developed studies of single asperities with phenomenological laws that describe macroscopic rate-and-state behavior of frictional interfaces. We find that many aspects of the macroscopic behavior are robust with respect to the microscopic response. This explains why qualitatively similar frictional features are seen for a diverse range of materials. We first show that the collective response of an ensemble of one-dimensional independent viscoelastic elements interacting through a mean field reproduces many qualitative features of static and sliding friction evolution. The resulting macroscopic behavior is different from the microscopic one: for example, even if each contact is velocity-strengthening, the macroscopic behavior can be velocity-weakening. The framework is then extended to incorporate three-dimensional rough surfaces, long- range elastic interactions between contacts, and time-dependent material behaviors such as viscoelasticity and viscoplasticity. Interestingly, the mean field behavior dominates and the elastic interactions, though important from a quantitative perspective, do not change the

  15. Friction Stir Process Mapping Methodology

    NASA Technical Reports Server (NTRS)

    Kooney, Alex; Bjorkman, Gerry; Russell, Carolyn; Smelser, Jerry (Technical Monitor)

    2002-01-01

    In FSW (friction stir welding), the weld process performance for a given weld joint configuration and tool setup is summarized on a 2-D plot of RPM vs. IPM. A process envelope is drawn within the map to identify the range of acceptable welds. The sweet spot is selected as the nominal weld schedule. The nominal weld schedule is characterized in the expected manufacturing environment. The nominal weld schedule in conjunction with process control ensures a consistent and predictable weld performance.

  16. Fault rheology beyond frictional melting.

    PubMed

    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. PMID:26124123

  17. Fault rheology beyond frictional melting

    PubMed Central

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

    2015-01-01

    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. PMID:26124123

  18. Chandrasekhar's dynamical friction and non-extensive statistics

    NASA Astrophysics Data System (ADS)

    Silva, J. M.; Lima, J. A. S.; de Souza, R. E.; Del Popolo, A.; Le Delliou, Morgan; Lee, Xi-Guo

    2016-05-01

    The motion of a point like object of mass M passing through the background potential of massive collisionless particles (m ll M) suffers a steady deceleration named dynamical friction. In his classical work, Chandrasekhar assumed a Maxwellian velocity distribution in the halo and neglected the self gravity of the wake induced by the gravitational focusing of the mass M. In this paper, by relaxing the validity of the Maxwellian distribution due to the presence of long range forces, we derive an analytical formula for the dynamical friction in the context of the q-nonextensive kinetic theory. In the extensive limiting case (q = 1), the classical Gaussian Chandrasekhar result is recovered. As an application, the dynamical friction timescale for Globular Clusters spiraling to the galactic center is explicitly obtained. Our results suggest that the problem concerning the large timescale as derived by numerical N-body simulations or semi-analytical models can be understood as a departure from the standard extensive Maxwellian regime as measured by the Tsallis nonextensive q-parameter.

  19. Test and analysis of the stability of friction drive of the vertical axis of the 1.2 m alt-az telescope.

    NASA Astrophysics Data System (ADS)

    Feng, Hesheng; Jiang, Chongguo; Wu, Wang; Wang, Jinso; Zhang, Yuncheng; Xiong, Yaoheng; Yang, Wanjiang; Niu, Xin

    The test and analysis of the static and dynamic stability of friction drive of the vertical axis of the 1.2 m alt-az telescope at Yunnan Observatory are carried out. The actual velocities and accelerations to be needed for tracking the Moon and the Lageos satellite are simulated. The tested results show that the stability of friction drive system can meet the needs of the ±1″tracking accuracy.

  20. Oxidation Effects on the Friction of Lubricants and Self-Lubricating Materials in the Enduring Stockpile

    SciTech Connect

    Dugger, M.T.; Peebles, D.E.; Ohlhausen, J.A.; Robinson, J.A.; Sorroche, E.H.; Fanska, J.

    1999-03-18

    Predictive models of solid lubricant performance are needed to determine the dynamic behavior of electromechanical devices after long periods of storage. X-ray photoelectron spectroscopy has been used to determine the kinetics of oxidation and sulfate formation for solid lubricants and self-lubricating materials containing MoS{sub 2}, exposed to a variety of oxidation conditions. The frictional performance of the lubricant has then been determined as a fi.mction of its surface chemistry and the ambient environment in which sliding takes place. Results indicate that surface sulfate formation governs the initial or start-up friction coefficient of MoS{sub 2}-containing films, while the composition of the ambient gas determines the steady-state friction coefficient. The dependence of the steady-state friction coefficient on the environment in which sliding takes place has been examined, and the results show that dynamic oxidation of surfaces having exposed metal has a major impact on friction. Surface oxidation is also shown to influence the frictional behavior of a self-lubricating composite material containing MoS{sub 2}.

  1. Effect of adsorbed films on friction of Al2O3-metal systems

    NASA Technical Reports Server (NTRS)

    Pepper, S. V.

    1976-01-01

    The kinetic friction of polycrystalline Al2O3 sliding on Cu, Ni, and Fe in ultrahigh vacuum was studied as a function of the surface chemistry of the metal. Clean metal surfaces were exposed to O2, Cl2, C2H4, and C2H3Cl, and the change in friction due to the adsorbed species was observed. Auger electron spectroscopy assessed the elemental composition of the metal surface. It was found that the systems exposed to Cl2 exhibited low friction, interpreted as the van der Waals force between the Al2O3 and metal chloride. The generation of metal oxide by oxygen exposures resulted in an increase in friction, interpreted as due to strong interfacial bonds established by reaction of metal oxide with Al2O3 to form the complex oxide (spinel). The only effect of C2H4 was to increase the friction of the Fe system, but C2H3Cl exposures decreases friction in both Ni and Fe systems, indicating the dominance of the chlorine over the ethylene complex on the surface

  2. Static Analysis of C Programs

    NASA Technical Reports Server (NTRS)

    Venet, Arnaud; Brat, Guillaume

    2003-01-01

    Contents include the following: Motivation. Cost of losing missions. Introduction to Static Analysis:definition, defect classes, applicability issues, specialization, analysis of MPF. C Global Surveyor (CGS): fact sheet, CGS phases, example. Conclusions.

  3. A quasi-static model of wheel-tissue interaction for surgical robotics.

    PubMed

    Wang, Xin; Sliker, Levin J; Qi, H Jerry; Rentschler, Mark E

    2013-09-01

    Wheel-driven mobile in vivo robotic devices can provide an unconstrained platform for visualization and task performance. Careful understanding of the wheel-tissue interaction is necessary to predict in vivo performance of medical mobility systems. Here, an analytical study of the friction involving rolling contact of a surgical wheel, moving at constant velocities over soft tissue, is presented and verified. A quasi-static frictionless solution is first derived from existing theory, and newly developed theory considering frictional effects is later introduced. In this analysis, the effect of friction on wheel mobility over a viscoelastic substrate is analyzed with wheel velocity as the only changing variable. The analytical model is later verified by experiments and Finite Element Method (FEM) simulations. A simple application of this model to help design a surgical robot is also presented. Additional results indicate that the resistance force, which arises from the tissue viscosity, approaches zero for small and very large wheel velocities. PMID:23582337

  4. Megathrust Friction in the Maule Earthquake Area in Relation to Forearc Morphology and Mechanical Stability, and to Earthquake Rupture Dynamics

    NASA Astrophysics Data System (ADS)

    Cubas, N.; Avouac, J.; Lapusta, N.

    2011-12-01

    Determining the spatio-temporal variations of frictional properties is a key issue in order to advance our understanding of earthquake dynamics. This study aims to characterize these variations for the 2010 Maule Mw 8.8 earthquake area based on the analysis of the forearc morphology and dynamic earthquake simulation. Two different mechanical approaches are applied to determine static and dynamic frictions. The first one relies on the critical taper theory and allows to constrain basal and internal frictions as well as the internal pore fluid pressure. The forearc above aseismic slipping areas of the Megathrust appear to be at critical mechanical state as evidenced from its morphology and indices of active deformation. Aseismic areas updip of the Maule Earthquake rupture area, where the forearc consists of a recently accreted sedimentary prism, show a moderate basal friction (0.17 - 0.21) and an internal pore fluid pressure close to hydrostatic conditions. Aseismic areas downdip of the Maule Earthquake rupture and beneath the Arauco peninsula, known to be a recurrent barrier to earthquake propagation, have higher basal friction (0.4). By contrast the forerarc above the seismogenic zone is observed to be mechanically stable, all the deformation being accommodated by slip along the Megathrust. We use the limit analysis approach to constrain the dynamic friction of the seismogenic zone as the critical taper theory provides only limited insight in this case. We determine spatial variations of the basal friction from the position of active faults. We focus on the Santa Maria island cross-section where an active backthrust splays from the megathrust near the transition from seismic sliding to aseismic sliding. A low basal friction in the seismogenic zone (< 0.1) is required for this splay fault to be active. These frictional properties are then integrated in a three-dimensional earthquake sequence model to investigate whether the low friction in the seismogenic zone is

  5. Economics of static VAR compensation

    SciTech Connect

    Alvarado, F.L.; DeMarco, C.; Jung, T.H. . Dept. of Electrical and Computer Engineering)

    1992-09-01

    This project was initiated in anticipation of widened use of static VAR (volt-ampere-reactive) compensation on US bulk-power transmission systems to increase levels of secure power transfer. Project objectives were to deten-nine power system cost savings and reliability benefits resulting from such use. System operating cost and stability probabilities were compared with and without static VAR compensation, applying simulation techniques. For the particular system model studied, there was a 21.4 percent reduction in operating costs taking into account losses added by the static VAR compensator. A procedure was developed to compare instability probabilities for various loadings and static VAR compensator sizes on a power system. For the particular system model studied, the static VAR compensator provided a significant increase in stability but over a narrow range of loading. Static VAR compensation is one of a number of promising FACTS (Flexible AC Transmission System) technologies for handling the demands of increased power transfers on power systems where transmission lines cannot be built or as a short-term altemative to building additional lines.

  6. Comparison of frictional resistance of esthetic and semi-esthetic self-ligating brackets

    PubMed Central

    Kannan, M. S.; Murali, R. V.; Kishorekumar, S.; Gnanashanmugam, K.; Jayanth, V.

    2015-01-01

    Aim: The frictional resistance encountered during sliding mechanics has been well established in the orthodontic literature, and it consists of complex interactions between the bracket, archwire, and method of ligation the claim of reduced friction with self-ligating brackets is often cited as a primary advantage over conventional brackets. This study was done to compare and evaluate the frictional forces generated between fully esthetic brackets and semi-aesthetic self-ligating brackets, which are of passive form and SEM (scanning electron microscope) study of the Brackets after Frictional evaluation. Materials and Methods: Two types of self-ligating esthetic brackets, Damon clear (Ormco) made of fully ceramic and Opal (Ultradent Products, USA) and, Two types of self-ligating semi-esthetic brackets, Clarity SL (3M Unitek) and Damon 3 (Ormco) both of which are made of ceramic with metal slot. Arch wires with different dimensions and quality 17 × 25, 19 × 25 Titanium Molybdenum Alloy (TMA) and 17 × 25, 19 × 25 stainless steel that came from plain strands of wire were used for frictional comparison test. The brackets used in this study had 0.022 × 0.028 inch slot. Results: The statistical tests showed significantly smaller amount of kinetic frictional forces is generated by Damon 3 (semi-esthetic self-ligating brackets). For each wire used, Damon 3 displayed significantly lower frictional forces (P ≤ 0.05) than any of the self-ligating system, followed by Opal (fully esthetic self-ligating brackets) which generated smaller amount of frictional forces but relatively on the higher side when compared with Damon 3. Damon clear (fully esthetic self-ligating brackets) generated the maximum amount of kinetic forces with all types of wire dimensions and properties when compared to the other three types of self-ligating system. Clarity SL (semi-esthetic self-ligating brackets) generated smaller amount of frictional forces when compared with Damon clear and relatively

  7. Friction coefficient dependence on electrostatic tribocharging

    PubMed Central

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

    2013-01-01

    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. PMID:23934227

  8. Friction Anisotropy with Respect to Topographic Orientation

    PubMed Central

    Yu, Chengjiao; Wang, Q. Jane

    2012-01-01

    Friction characteristics with respect to surface topographic orientation were investigated using surfaces of different materials and fabricated with grooves of different scales. Scratching friction tests were conducted using a nano-indentation-scratching system with the tip motion parallel or perpendicular to the groove orientation. Similar friction anisotropy trends were observed for all the surfaces studied, which are (1) under a light load and for surfaces with narrow grooves, the tip motion parallel to the grooves offers higher friction coefficients than does that perpendicular to them, (2) otherwise, equal or lower friction coefficients are found under this motion. The influences of groove size relative to the diameter of the mating tip (as a representative asperity), surface contact stiffness, contact area, and the characteristic stiction length are discussed. The appearance of this friction anisotropy is independent of material; however, the boundary and the point of trend transition depend on material properties. PMID:23248751

  9. SRM propellant, friction/ESD testing

    NASA Technical Reports Server (NTRS)

    Campbell, L. A.

    1989-01-01

    Following the Pershing 2 incident in 1985 and the Peacekeeper ignition during core removal in 1987, it was found that propellant can be much more sensitive to Electrostatic Discharges (ESD) than ever before realized. As a result of the Peacekeeper motor near miss incident, a friction machine was designed and fabricated, and used to determine friction hazards during core removal. Friction testing with and electrical charge being applied across the friction plates resulted in propellant ignitions at low friction pressures and extremely low ESD levels. The objective of this test series was to determine the sensitivity of solid rocket propellant to combined friction pressure and electrostatic stimuli and to compare the sensitivity of the SRM propellant to Peacekeeper propellant. The tests are fully discussed, summarized and conclusions drawn.

  10. Friction coefficient of faults inferred from earthquake focal mechanisms

    NASA Astrophysics Data System (ADS)

    Viganò, Alfio; Ranalli, Giorgio; Andreis, Daniele; Martin, Silvana; Rigon, Riccardo

    2013-04-01

    In earthquake mechanics and structural geology the static friction coefficient is usually assumed to have the laboratory value (μ = 0.6-0.8) according to the Coulomb-Byerlee's law. Estimates from deep boreholes and/or natural faults generally confirm this hypothesis but in some cases friction coefficients can be significantly lower, suggesting the existence of weak faults able to be activated by lower effective stress than theoretically expected. We apply a modified version of the method proposed by Yin and Ranalli (1995, Journal of Structural Geology, vol. 17, pp. 1327-1335), where the average friction coefficient of a set of n faults is estimated. This method is based on minimization of the sum of squares of the misfit ratios, where the misfit ratio of each fault is given dividing the misfit stress difference (i.e. the misfit between normalized stress difference and average normalized stress difference) by the average normalized stress difference. The normalized stress difference is defined as the critical stress difference divided by the effective overburden pressure, while the average stress difference is obtained considering the entire fault dataset. Input data are (i) the orientation of faults, (ii) the stress field orientation, and (iii) the stress ratio. The latter two must be independently estimated. A uniform stress field and a similar normalized critical stress difference for the fault dataset are assumed. The procedure has been extended to apply to fault plane solutions by considering both nodal planes of a set of n focal mechanisms and estimating the range of acceptable average friction coefficients from all possible combination of planes (2n number of combinations). The amount of calculation can be considerably reduced if independent information makes it possible to select which one of the nodal planes of each focal mechanism is the true fault plane (for example when aftershocks delineate the fault geometry at depth), resulting in only n combinations

  11. On the modelling of Coulomb friction

    NASA Astrophysics Data System (ADS)

    Cull, S. J.; Tucker, R. W.

    1999-03-01

    This paper analyses two different representations of Coulomb friction in the context of a dynamic simulation of the torsional vibrations of a driven drill-string. A simple model is used to compare the relative merits of a piecewise analytic approach using a discontinuous friction profile to a numerical integration using a smooth nonlinear representation of the Coulomb friction. In both cases the effects of viscous damping on the excitation of torsional relaxation oscillations are exhibited.

  12. Modelling cohesive, frictional and viscoplastic materials

    NASA Astrophysics Data System (ADS)

    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.

  13. Investigation of squeal noise under positive friction characteristics condition provided by friction modifiers

    NASA Astrophysics Data System (ADS)

    Liu, Xiaogang; Meehan, Paul A.

    2016-06-01

    Field application of friction modifiers on the top of rail has been shown to effectively curb squeal and reduce lateral forces, but performance can be variable, according to other relevant research. Up to now, most investigations of friction modifiers were conducted in the field, where it is difficult to control or measure important parameters such as angle of attack, rolling speed, adhesion ratio etc. In the present investigation, the effect of different friction modifiers on the occurrence of squeal was investigated on a rolling contact two disk test rig. In particular, friction-creep curves and squeal sound pressure levels were measured under different rolling speeds and friction modifiers. The results show friction modifiers can eliminate or reduce the negative slope of friction-creep curves, but squeal noise still exists. Theoretical modelling of instantaneous creep behaviours reveals a possible reason why wheel squeal still exists after the application of friction modifiers.

  14. Fault Friction and Physics: Lessons from SAFOD (Invited)

    NASA Astrophysics Data System (ADS)

    Carpenter, B. M.; Marone, C.; Saffer, D. M.; Lockner, D. A.; Morrow, C. A.; Hickman, S. H.; French, M. E.; Chester, J. S.; Chester, F. M.

    2013-12-01

    Sampling and down-hole measurements of active faults at seismogenic depths have produced significant advances in our knowledge of fault zone evolution, structure, composition and mechanical behavior. The San Andreas Fault Observatory at Depth (SAFOD), located in central California along a section of the San Andreas Fault (SAF) that is slipping through a combination of fault creep and repeating microearthquakes, has greatly increased our understanding of the mechanical behavior of plate-boundary faults. In this talk, we summarize results from studies of SAFOD core recovered from the creeping SAF at seismogenic depths (~2.7 km), focusing on the frictional strength and sliding stability of the fault, as well as deformation processes occurring within the active fault at depth. Ongoing laboratory investigations of SAFOD core continue to advance our understanding of frictional strength, slip stability, poromechanical properties, and their coupling in active fault zones. Fault slip is localized within two actively deforming gouge-filled zones (1.6 m and 2.6 m wide), which were identified on the basis of casing deformation prior to SAFOD coring (see Zoback et al., 2011, Scientific Drilling, No. 11). Friction experiments performed on fault gouge from these two deforming zones at near in-situ conditions have shown that material from the actively creeping SAF is remarkably weak (coefficient of friction as low as ~0.1), and exhibits little to no frictional restrengthening. Laboratory results further show that gouge from the creeping section is both statically and dynamically weak, and indicate that the shallow portion (< 4km) of this mature plate-boundary fault is weak over earthquake and geologic timescales. The laboratory data are consistent with constraints on the SAF's shear strength inferred from heat flow and stress orientation data, and with frictional constitutive properties deduced from post-seismic surface deformation and seismic behavior. Microstructural studies of

  15. A microphysical model explains rate-and-state friction

    NASA Astrophysics Data System (ADS)

    Chen, Jianye; Spiers, Christopher J.

    2015-04-01

    The rate-and-state friction (RSF) laws were originally developed as a phenomenological description of the frictional behavior observed in lab experiments. In previous studies, the empirical RSF laws have been extensively and quite successfully applied to fault mechanisms. However, these laws can not readily be envisioned in terms of the underlying physics. There are several critical discrepancies between seismological constraints on RSF behavior associated with earthquakes and lab-derived RSF parameters, in particular regarding the static stress drop and characteristic slip distance associated with seismic events. Moreover, lab friction studies can address only limited fault topographies, displacements, experimental durations and P-T conditions, which means that scale issues, and especially processes like dilatation and fluid-rock interaction, cannot be fully taken into account. Without a physical basis accounting for such effects, extrapolation of lab-derived RSF data to nature involves significant, often unknown uncertainties. In order to more reliably apply experimental results to natural fault zones, and notably to extrapolate lab data beyond laboratory pressure, temperature and velocity conditions, an understanding of the microphysical mechanisms governing fault frictional behavior is required. Here, following some pioneering efforts (e.g. Niemeijer and Spiers, 2007; Den Hartog and Spiers, 2014), a mechanism-based microphysical model is developed for describing the frictional behavior of carbonate fault gouge, assuming that the frictional behavior seen in lab experiments is controlled by competing processes of intergranular slip versus contact creep by pressure solution. The model basically consists of two governing equations derived from energy/entropy balance considerations and the kinematic relations that apply to a granular fault gouge undergoing shear and dilation/compaction. These two equations can be written as ˙τ/K = Vimp- Lt[λ˙γsbps +(1-

  16. Frictional melt and seismic slip

    NASA Astrophysics Data System (ADS)

    Nielsen, S.; di Toro, G.; Hirose, T.; Shimamoto, T.

    2008-01-01

    Frictional melt is implied in a variety of processes such as seismic slip, ice skating, and meteorite combustion. A steady state can be reached when melt is continuously produced and extruded from the sliding interface, as shown recently in a number of laboratory rock friction experiments. A thin, low-viscosity, high-temperature melt layer is formed resulting in low shear resistance. A theoretical solution describing the coupling of shear heating, thermal diffusion, and extrusion is obtained, without imposing a priori the melt thickness. The steady state shear traction can be approximated at high slip rates by the theoretical form τss = σn1/4 (A/?) ? under a normal stress σn, slip rate V, radius of contact area R (A is a dimensional normalizing factor and W is a characteristic rate). Although the model offers a rather simplified view of a complex process, the predictions are compatible with experimental observations. In particular, we consider laboratory simulations of seismic slip on earthquake faults. A series of high-velocity rotary shear experiments on rocks, performed for σn in the range 1-20 MPa and slip rates in the range 0.5-2 m s-1, is confronted to the theoretical model. The behavior is reasonably well reproduced, though the effect of radiation loss taking place in the experiment somewhat alters the data. The scaling of friction with σn, R, and V in the presence of melt suggests that extrapolation of laboratory measures to real Earth is a highly nonlinear, nontrivial exercise.

  17. Measurement of Gear Tooth Dynamic Friction

    NASA Technical Reports Server (NTRS)

    Rebbechi, Brian; Oswald, Fred B.; Townsend, Dennis P.

    1996-01-01

    Measurements of dynamic friction forces at the gear tooth contact were undertaken using strain gages at the root fillets of two successive teeth. Results are presented from two gear sets over a range of speeds and loads. The results demonstrate that the friction coefficient does not appear to be significantly influenced by the sliding reversal at the pitch point, and that the friction coefficient values found are in accord with those in general use. The friction coefficient was found to increase at low sliding speeds. This agrees with the results of disc machine testing.

  18. Effect of grafted oligopeptides on friction.

    PubMed

    Iarikov, Dmitri D; Ducker, William A

    2013-05-14

    Frictional and normal forces in aqueous solution at 25 °C were measured between a glass particle and oligopeptide films grafted from a glass plate. Homopeptide molecules consisting of 11 monomers of either glutamine, leucine, glutamic acid, lysine, or phenylalanine and one heteropolymer were each "grafted from" an oxidized silicon wafer using microwave-assisted solid-phase peptide synthesis. The peptide films were characterized using X-ray photoelectron spectroscopy and secondary ion mass spectrometry. Frictional force measurements showed that the oligopeptides increased the magnitude of friction compared to that on a bare hydrophilic silicon wafer but that the friction was a strong function of the nature of the monomer unit. Overall we find that the friction is lower for more hydrophilic films. For example, the most hydrophobic monomer, leucine, exhibited the highest friction whereas the hydrophilic monomer, polyglutamic acid, exhibited the lowest friction at zero load. When the two surfaces had opposite charges, there was a strong attraction, adhesion, and high friction between the surfaces. Friction for all polymers was lower in phosphate-buffered saline than in pure water, which was attributed to lubrication via hydrated salt ions. PMID:23594080

  19. Friction measurement in a hip wear simulator.

    PubMed

    Saikko, Vesa

    2016-05-01

    A torque measurement system was added to a widely used hip wear simulator, the biaxial rocking motion device. With the rotary transducer, the frictional torque about the drive axis of the biaxial rocking motion mechanism was measured. The principle of measuring the torque about the vertical axis above the prosthetic joint, used earlier in commercial biaxial rocking motion simulators, was shown to sense only a minor part of the total frictional torque. With the present method, the total frictional torque of the prosthetic hip was measured. This was shown to consist of the torques about the vertical axis above the joint and about the leaning axis. Femoral heads made from different materials were run against conventional and crosslinked polyethylene acetabular cups in serum lubrication. Regarding the femoral head material and the type of polyethylene, there were no categorical differences in frictional torque with the exception of zirconia heads, with which the lowest values were obtained. Diamond-like carbon coating of the CoCr femoral head did not reduce friction. The friction factor was found to always decrease with increasing load. High wear could increase the frictional torque by 75%. With the present system, friction can be continuously recorded during long wear tests, so the effect of wear on friction with different prosthetic hips can be evaluated. PMID:27160557

  20. Hydrodynamic skin-friction reduction

    NASA Astrophysics Data System (ADS)

    Reed, Jason C.; Bushnell, Dennis M.; Weinstein, Leonard M.

    1989-10-01

    A process for reducing skin friction, inhibiting the effects of liquid turbulence, and decreasing heat transfer in a system involving flow of a liquid along a surface of a body includes applying a substantially integral sheet of a gas, e.g., air, immediately adjacent to the surface of the body; a marine vehicle, which has a longitudinally grooved surface in proximity with the liquid and with a surface material having high contact angle between the liquid and said wall to reduce interaction of the liquid; water, with the surface of the body; and the hull of the marine vehicle.

  1. Hydrodynamic skin-friction reduction

    NASA Technical Reports Server (NTRS)

    Reed, Jason C. (Inventor); Bushnell, Dennis M. (Inventor); Weinstein, Leonard M. (Inventor)

    1991-01-01

    A process for reducing skin friction, inhibiting the effects of liquid turbulence, and decreasing heat transfer in a system involving flow of a liquid along a surface of a body includes applying a substantially integral sheet of a gas, e.g., air, immediately adjacent to the surface of the body, e.g., a marine vehicle, which has a longitudinally grooved surface in proximity with the liquid and with a surface material having high contact angle between the liquid and said wall to reduce interaction of the liquid, e.g., water, with the surface of the body, e.g., the hull of the marine vehicle.

  2. Fractional trajectories: Decorrelation versus friction

    NASA Astrophysics Data System (ADS)

    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.

  3. Influence of vanadium on static recrystallization in warm worked microalloyed steels

    SciTech Connect

    Garcia-Mateo, C.; Lopez, B.; Rodriguez-Ibabe, J.M.

    1999-12-31

    Warm forging of steels, in the range from 600 to 900 C, offers some important advantages over traditional forging procedures, with a better dimensional accuracy as well as surface quality in comparison with hot forging, and lower flow stress and therefore lower press loads in comparison with cold forging. It is well established that in hot working of V microalloyed steels, the vanadium in solid solution has a little effect on the static recrystallization kinetics between passes. In contrast, if strain induced precipitation takes place the static recrystallization is notably modified. The objective of this work is to study the effects that the application of warm working can have on the austenite static recrystallization process of vanadium microalloyed steels, considering a range of temperatures in which different precipitate volume fractions can remain undissolved in the austenite prior to deformation. The static recrystallization kinetics were determined by stress relaxation tests following the deformation by plain strain compression.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    Dumazer, Guillaume; Sandnes, Bjørnar; Ayaz, Monem; Måløy, 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. PMID:27447527

  6. Frictional property comparisons of conventional and self-ligating lingual brackets according to tooth displacement during initial leveling and alignment: an in vitro mechanical study

    PubMed Central

    Kim, Do-Yoon; Lim, Bum-Soon

    2016-01-01

    Objective We evaluated the effects of tooth displacement on frictional force when conventional ligating lingual brackets (CL-LBs), CL-LBs with a narrow bracket width, and self-ligating lingual brackets (SL-LBs) were used with initial leveling and alignment wires. Methods CL-LBs (7th Generation), CL-LBs with a narrow bracket width (STb), and SL-LBs (In-Ovation L) were tested under three tooth displacement conditions: no displacement (control); a 2-mm palatal displacement (PD) of the maxillary right lateral incisor (MXLI); and a 2-mm gingival displacement (GD) of the maxillary right canine (MXC) (nine groups, n = 7 per group). A stereolithographic typodont system and artificial saliva were used. Static and kinetic frictional forces (SFF and KFF, respectively) were measured while drawing a 0.013-inch copper-nickel-titanium archwire through brackets at 0.5 mm/min for 5 minutes at 36.5℃. Results The In-Ovation L exhibited lower SFF under control conditions and lower KFF under all displacement conditions than the 7th Generation and STb (all p < 0.001). No significant difference in SFF existed between the In-Ovation L and STb for a 2-mm GD of the MXC and 2-mm PD of the MXLI. A 2-mm GD of the MXC produced higher SFF and KFF than a 2-mm PD of the MXLI in all brackets (all p < 0.001). Conclusions CL-LBs with narrow bracket widths exhibited higher KFF than SL-LBs under tooth displacement conditions. CL-LBs and ligation methods should be developed to produce SFF and KFF as low as those in SL-LBs during the initial and leveling stage. PMID:27019823

  7. A comparison of Coulomb and pseudo-Coulomb friction implementations: Application to the table contact phase of gymnastics vaulting.

    PubMed

    Jackson, M I; Hiley, M J; Yeadon, M R

    2011-10-13

    In the table contact phase of gymnastics vaulting both dynamic and static friction act. The purpose of this study was to develop a method of simulating Coulomb friction that incorporated both dynamic and static phases and to compare the results with those obtained using a pseudo-Coulomb implementation of friction when applied to the table contact phase of gymnastics vaulting. Kinematic data were obtained from an elite level gymnast performing handspring straight somersault vaults using a Vicon optoelectronic motion capture system. An angle-driven computer model of vaulting that simulated the interaction between a seven segment gymnast and a single segment vaulting table during the table contact phase of the vault was developed. Both dynamic and static friction were incorporated within the model by switching between two implementations of the tangential frictional force. Two vaulting trials were used to determine the model parameters using a genetic algorithm to match simulations to recorded performances. A third independent trial was used to evaluate the model and close agreement was found between the simulation and the recorded performance with an overall difference of 13.5%. The two-state simulation model was found to be capable of replicating performance at take-off and also of replicating key contact phase features such as the normal and tangential motion of the hands. The results of the two-state model were compared to those using a pseudo-Coulomb friction implementation within the simulation model. The two-state model achieved similar overall results to those of the pseudo-Coulomb model but obtained solutions more rapidly. PMID:21889150

  8. Kinetics of atoms in a bichromatic field

    SciTech Connect

    Prudnikov, O. N.; Baklanov, A. S.; Taichenachev, A. V.; Tumaikin, A. M.; Yudin, V. I.

    2013-08-15

    The kinetics of atoms in a bichromatic field is considered. Analytic solutions are obtained for the force, friction coefficient, and diffusion coefficient in the model of a two-level atom without limitations imposed on the intensity of light fields. This effect is observed in the domain of global minima and maxima of the optical potential (i.e., at points where the relative phase of two standing waves is Greek-Phi-Symbol = 0, {pi}/2.

  9. The frictional properties of faults at shallow depths: implications for rupture propagation.

    NASA Astrophysics Data System (ADS)

    De Paola, N.; Bullock, R. J.; Holdsworth, R.

    2015-12-01

    Following the surge of great earthquakes from 2004-2014, revised synoptic models have been proposed, where 2D spatial heterogeneity in frictional properties of continental and subduction fault zones is invoked to explain earthquake behaviours. However, none of the proposed models accounts for the changes in frictional properties that past ruptures may have caused on the rupture zones of recent events. We performed velocity step friction experiments at sub-seismic slip rates (10-100 mm/s) on dry, water- and brine-saturated granite and calcite rocks (continental crust) showing that velocity strengthening behaviour evolves to velocity-neutral/-weakening behaviour after critical displacements of a few tens to hundreds of mm. Dry, water- and brine-saturated gabbros (oceanic crust) show velocity-weakening behaviour and slip localization for any applied displacement and normal stress. Dry, water- and brine-saturated phyllosilicate-rich gouges (typical of subduction zones and continental sedimentary deposits) show velocity-strengthening behaviour for any applied displacements and normal loads. Cyclic slide-hold-slide experiments show that, after sliding at sub-seismic slip rates, static friction increases with time according to a logarithmic relationship (fault healing) for almost all tested materials under dry, water- and brine-saturated conditions. The only exceptions are organic-rich black shales, which show a decrease in static fault friction with time (negative fault healing). The positive and negative healing rates tend to increase under water- and brine-saturated conditions, respectively. After sliding at seismic velocities (1 m/s), granite, calcite and phyllosilicate-rich gouges show an evolution toward less velocity strengthening to velocity-weakening behaviour, as opposed to grabbros gouges showing an evolution towards velocity strengthening behaviour. Our experimental results suggest that patches of small and large seismic slip of past events are critical in

  10. Applicability of Macroscopic Wear and Friction Laws on the Atomic Length Scale

    NASA Astrophysics Data System (ADS)

    Eder, S. J.; Feldbauer, G.; Bianchi, D.; Cihak-Bayr, U.; Betz, G.; Vernes, A.

    2015-07-01

    Using molecular dynamics, we simulate the abrasion process of an atomically rough Fe surface with multiple hard abrasive particles. By quantifying the nanoscopic wear depth in a time-resolved fashion, we show that Barwell's macroscopic wear law can be applied at the atomic scale. We find that in this multiasperity contact system, the Bowden-Tabor term, which describes the friction force as a function of the real nanoscopic contact area, can predict the kinetic friction even when wear is involved. From this the Derjaguin-Amontons-Coulomb friction law can be recovered, since we observe a linear dependence of the contact area on the applied load in accordance with Greenwood-Williamson contact mechanics.

  11. A frictional population model of seismicity rate change

    USGS Publications Warehouse

    Gomberg, J.; Reasenberg, P.; Cocco, M.; Belardinelli, M.E.

    2005-01-01

    We study models of seismicity rate changes caused by the application of a static stress perturbation to a population of faults and discuss our results with respect to the model proposed by Dieterich (1994). These models assume distribution of nucleation sites (e.g., faults) obeying rate-state frictional relations that fail at constant rate under tectonic loading alone, and predicts a positive static stress step at time to will cause an immediate increased seismicity rate that decays according to Omori's law. We show one way in which the Dieterich model may be constructed from simple general idead, illustratted using numerically computed synthetic seismicity and mathematical formulation. We show that seismicity rate change predicted by these models (1) depend on the particular relationship between the clock-advanced failure and fault maturity, (2) are largest for the faults closest to failure at to, (3) depend strongly on which state evolution law faults obey, and (4) are insensitive to some types of population hetrogeneity. We also find that if individual faults fail repeatedly and populations are finite, at timescales much longer than typical aftershock durations, quiescence follows at seismicity rate increase regardless of the specific frictional relations. For the examined models the quiescence duration is comparable to the ratio of stress change to stressing rate ????/??,which occurs after a time comparable to the average recurrence interval of the individual faults in the population and repeats in the absence of any new load may pertubations; this simple model may partly explain observations of repeated clustering of earthquakes. Copyright 2005 by the American Geophysical Union.

  12. Inverse Kinetics

    Energy Science and Technology Software Center (ESTSC)

    2000-03-20

    Given the space-independent, one energy group reactor kinetics equations and the initial conditions, this prgram determines the time variation of reactivity required to produce the given input of flux-time data.

  13. Speed of fast and slow rupture fronts along frictional interfaces

    NASA Astrophysics Data System (ADS)

    Trømborg, Jørgen Kjoshagen; Sveinsson, Henrik Andersen; Thøgersen, Kjetil; Scheibert, Julien; Malthe-Sørenssen, Anders

    2015-07-01

    The transition from stick to slip at a dry frictional interface occurs through the breaking of microjunctions between the two contacting surfaces. Typically, interactions between junctions through the bulk lead to rupture fronts propagating from weak and/or highly stressed regions, whose junctions break first. Experiments find rupture fronts ranging from quasistatic fronts, via fronts much slower than elastic wave speeds, to fronts faster than the shear wave speed. The mechanisms behind and selection between these fronts are still imperfectly understood. Here we perform simulations in an elastic two-dimensional spring-block model where the frictional interaction between each interfacial block and the substrate arises from a set of junctions modeled explicitly. We find that material slip speed and rupture front speed are proportional across the full range of front speeds we observe. We revisit a mechanism for slow slip in the model and demonstrate that fast slip and fast fronts have a different, inertial origin. We highlight the long transients in front speed even along homogeneous interfaces, and we study how both the local shear to normal stress ratio and the local strength are involved in the selection of front type and front speed. Last, we introduce an experimentally accessible integrated measure of block slip history, the Gini coefficient, and demonstrate that in the model it is a good predictor of the history-dependent local static friction coefficient of the interface. These results will contribute both to building a physically based classification of the various types of fronts and to identifying the important mechanisms involved in the selection of their propagation speed.

  14. Frictional behavior of large displacement experimental faults

    USGS Publications Warehouse

    Beeler, N.M.; Tullis, T.E.; Blanpied, M.L.; Weeks, J.D.

    1996-01-01

    The coefficient of friction and velocity dependence of friction of initially bare surfaces and 1-mm-thick simulated fault gouges (400 mm at 25??C and 25 MPa normal stress. Steady state negative friction velocity dependence and a steady state fault zone microstructure are achieved after ???18 mm displacement, and an approximately constant strength is reached after a few tens of millimeters of sliding on initially bare surfaces. Simulated fault gouges show a large but systematic variation of friction, velocity dependence of friction, dilatancy, and degree of localization with displacement. At short displacement (<10 mm), simulated gouge is strong, velocity strengthening and changes in sliding velocity are accompanied by relatively large changes in dilatancy rate. With continued displacement, simulated gouges become progressively weaker and less velocity strengthening, the velocity dependence of dilatancy rate decreases, and deformation becomes localized into a narrow basal shear which at its most localized is observed to be velocity weakening. With subsequent displacement, the fault restrengthens, returns to velocity strengthening, or to velocity neutral, the velocity dependence of dilatancy rate becomes larger, and deformation becomes distributed. Correlation of friction, velocity dependence of friction and of dilatancy rate, and degree of localization at all displacements in simulated gouge suggest that all quantities are interrelated. The observations do not distinguish the independent variables but suggest that the degree of localization is controlled by the fault strength, not by the friction velocity dependence. The friction velocity dependence and velocity dependence of dilatancy rate can be used as qualitative measures of the degree of localization in simulated gouge, in agreement with previous studies. Theory equating the friction velocity dependence of simulated gouge to the sum of the friction velocity dependence of bare surfaces and the velocity

  15. Comparison of Frictional Heating Models

    SciTech Connect

    Davies, Nicholas R; Blau, Peter Julian

    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.

  16. Quantum Friction in Different Regimes

    NASA Astrophysics Data System (ADS)

    Klatt, Juliane; Buhmann, Stefan

    2015-03-01

    Quantum friction is the velocity-dependent force between two polarizable objects in relative motion, resulting from field-fluctuation mediated transfer of energy and momentum between them. Due to its short-ranged nature it has proven difficult to observe experimentally. Theoretical attempts to determine the precise velocity-dependence of the quantum drag experienced by a polarizable atom moving parallel to a surface arrive at contradicting results. Scheel and Barton predict a force linear in relative velocity v - the former using the quantum regression theorem and the latter employing time-dependent perturbation theory. Intravaia, however, predicts a v3 power-law starting from a non-equilibrium fluctuation-dissipation theorem. In order to learn where exactly the above approaches part, we set out to perform all three calculations within one and the same framework: macroscopic QED. In addition, we include contributions to quantum friction from Doppler shift and Röntgen interaction, which play a role for perpendicular motion and retarded distances, respectively, and consider non-stationary states of atom and field. DFG Emmy-Noether Program.

  17. Kozai Cycles and Tidal Friction

    SciTech Connect

    L, K; P.P., E

    2009-07-17

    Several studies in the last three years indicate that close binaries, i.e. those with periods of {approx}< 3 d, are very commonly found to have a third body in attendance. We argue that this proves that the third body is necessary in order to make the inner period so short, and further argue that the only reasonable explanation is that the third body causes shrinkage of the inner period, from perhaps a week or more to the current short period, by means of the combination of Kozai cycles and tidal friction (KCTF). In addition, once KCTF has produced a rather close binary, magnetic braking also combined with tidal friction (MBTF) can decrease the inner orbit further, to the formation of a contact binary or even a merged single star. Some of the products of KCTF that have been suggested, either by others or by us, are W UMa binaries, Blue Stragglers, X-ray active BY Dra stars, and short-period Algols. We also argue that some components of wide binaries are actually merged remnants of former close inner pairs. This may include such objects as rapidly rotating dwarfs (AB Dor, BO Mic) and some (but not all) Be stars.

  18. Static heterogeneities in liquid water

    NASA Astrophysics Data System (ADS)

    Stanley, H. Eugene; Buldyrev, Sergey V.; Giovambattista, Nicolas

    2004-10-01

    The thermodynamic behavior of water seems to be closely related to static heterogeneities. These static heterogeneities are related to the local structure of water molecules, and when properly characterized, may offer an economical explanation of thermodynamic data. The key feature of liquid water is not so much that the existence of hydrogen bonds, first pointed out by Linus Pauling, but rather the local geometry of the liquid molecules is not spherical or oblong but tetrahedral. In the consideration of static heterogeneities, this local geometry is critical. Recent experiments suggested more than one phase of amorphous solid water, while simulations suggest that one of these phases is metastable with respect to another, so that in fact there are only two stable phases.

  19. "Frictional processes" in carbonate-bearing rocks at seismic deformation conditions

    NASA Astrophysics Data System (ADS)

    Di Toro, G.; Spagnuolo, E.; Violay, M.; Rempe, M.; Smith, S. A. F.; Nielsen, S. B.; Fondriest, M.; Plumper, O.

    2015-12-01

    Moderate to large earthquakes often rupture and propagate along faults in carbonate-bearing rocks (dolostones, limestones, marbles, etc.). Compared to silicate-bearing rocks, which melt, weaken and wear when sheared at seismic slip rates (ca. 1 m/s), carbonate-bearing rocks do not melt, the minimum friction coefficient can be much lower (down to 5% of static friction) and the wear rate is negligible at seismic slip rates. In cohesive carbonate-bearing rocks, experiments simulating seismic deformation conditions and stopped at slip initiation (< 5 mm) suggest that initial frictional decay down to 50% of static friction is associated with CO2 emission plus formation of nanograins and amorphous carbon. Experiments stopped at larger slips (< 5 mm) show that the slipping zone consists of a foam-like sintered surface overlying a microporous fabric made of calcite and lime (plus periclase in the case of dolomite) nanograins. In non-cohesive rocks (e.g. gouges) a similar evolution is observed after an initial period of strengthening and strain localization. Experiments with pressurized H2O show that the contribution of thermal and thermochemical pressurization is negligible in cohesive and questionable in non-cohesive carbonate-bearing rocks. We propose that initial frictional weakening is due to the formation of patches of amorphous carbon (solid lubricant) at asperity contacts. With progressive slip and bulk temperature increase, nanograins accommodate large strain rates (ca. 104 s-1) by grain boundary sliding as suggested by several authors. The presence of a microporous fabric boosts pore-controlled diffusive process propelled by CO2 gas exhaust due to decarbonation. Enhanced pore-controlled diffusive processes allow (1) efficient mass transfer during grain boundary sliding and (2) sintering of the nanograins into a foam-like slip surface at the end of the experiment.

  20. Quasi-Static Hydrodynamic Limits

    NASA Astrophysics Data System (ADS)

    De Masi, Anna; Olla, Stefano

    2015-12-01

    We consider hydrodynamic limits of interacting particles systems with open boundaries, where the exterior parameters change in a time scale slower than the typical relaxation time scale. The limit deterministic profiles evolve quasi-statically. These limits define rigorously the thermodynamic quasi static transformations also for transitions between non-equilibrium stationary states. We study first the case of the symmetric simple exclusion, where duality can be used, and then we use relative entropy methods to extend to other models like zero range systems. Finally we consider a chain of anharmonic oscillators in contact with a thermal Langevin bath with a temperature gradient and a slowly varying tension applied to one end.

  1. Static Fourier transform infrared spectrometer.

    PubMed

    Schardt, Michael; Murr, Patrik J; Rauscher, Markus S; Tremmel, Anton J; Wiesent, Benjamin R; Koch, Alexander W

    2016-04-01

    Fourier transform spectroscopy has established itself as the standard method for spectral analysis of infrared light. Here we present a robust and compact novel static Fourier transform spectrometer design without any moving parts. The design is well suited for measurements in the infrared as it works with extended light sources independent of their size. The design is experimentally evaluated in the mid-infrared wavelength region between 7.2 μm and 16 μm. Due to its large etendue, its low internal light loss, and its static design it enables high speed spectral analysis in the mid-infrared. PMID:27137061

  2. Voltage Sensors Monitor Harmful Static

    NASA Technical Reports Server (NTRS)

    2009-01-01

    A tiny sensor, small enough to be worn on clothing, now monitors voltage changes near sensitive instruments after being created to alert Agency workers to dangerous static buildup near fuel operations and avionics. San Diego s Quasar Federal Systems received a Small Business Innovation Research (SBIR) contract from Kennedy Space Center to develop its remote voltage sensor (RVS), a dime-sized electrometer designed to measure triboelectric changes in the environment. One of the unique qualities of the RVS is that it can detect static at greater distances than previous devices, measuring voltage changes from a few centimeters to a few meters away, due to its much-improved sensitivity.

  3. Sensitivities of Tropical Cyclones to Surface Friction and the Coriolis Parameter in a 2-D Cloud-Resolving Model

    NASA Technical Reports Server (NTRS)

    Chao, Winston C.; Chen, Baode; Tao, Wei-Kuo; Lau, William K. M. (Technical Monitor)

    2002-01-01

    The sensitivities to surface friction and the Coriolis parameter in tropical cyclogenesis are studied using an axisymmetric version of the Goddard cloud ensemble model. Our experiments demonstrate that tropical cyclogenesis can still occur without surface friction. However, the resulting tropical cyclone has very unrealistic structure. Surface friction plays an important role of giving the tropical cyclones their observed smaller size and diminished intensity. Sensitivity of the cyclogenesis process to surface friction. in terms of kinetic energy growth, has different signs in different phases of the tropical cyclone. Contrary to the notion of Ekman pumping efficiency, which implies a preference for the highest Coriolis parameter in the growth rate if all other parameters are unchanged, our experiments show no such preference.

  4. ANALYSIS OF THE MAGNETIZED FRICTION FORCE.

    SciTech Connect

    FEDOTOV, A.V.; BRUHWILER, D.L.; SIDORIN, A.O.

    2006-05-29

    A comprehensive examination of theoretical models for the friction force, in use by the electron cooling community, was performed. Here, they present their insights about the models gained as a result of comparison between the friction force formulas and direct numerical simulations, as well as studies of the cooling process as a whole.

  5. Internally architectured materials with directionally asymmetric friction.

    PubMed

    Bafekrpour, Ehsan; Dyskin, Arcady; Pasternak, Elena; Molotnikov, Andrey; Estrin, Yuri

    2015-01-01

    Internally Architectured Materials (IAMs) that exhibit different friction forces for sliding in the opposite directions are proposed. This is achieved by translating deformation normal to the sliding plane into a tangential force in a manner that is akin to a toothbrush with inclined bristles. Friction asymmetry is attained by employing a layered material or a structure with parallel 'ribs' inclined to the direction of sliding. A theory of directionally asymmetric friction is presented, along with prototype IAMs designed, fabricated and tested. The friction anisotropy (the ξ-coefficient) is characterised by the ratio of the friction forces for two opposite directions of sliding. It is further demonstrated that IAM can possess very high levels of friction anisotropy, with ξ of the order of 10. Further increase in ξ is attained by modifying the shape of the ribs to provide them with directionally dependent bending stiffness. Prototype IAMs produced by 3D printing exhibit truly giant friction asymmetry, with ξ in excess of 20. A novel mechanical rectifier, which can convert oscillatory movement into unidirectional movement by virtue of directionally asymmetric friction, is proposed. Possible applications include locomotion in a constrained environment and energy harvesting from oscillatory noise and vibrations. PMID:26040634

  6. Shaft Coupler With Friction and Spline Clutches

    NASA Technical Reports Server (NTRS)

    Thebert, Glenn W.

    1987-01-01

    Coupling, developed for rotor of lift/cruise aircraft, employs two clutches for smooth transmission of power from gas-turbine engine to rotor. Prior to ascent, coupling applies friction-type transition clutch that accelerates rotor shaft to speeds matching those of engine shaft. Once shafts synchronized, spline coupling engaged and friction clutch released to provide positive mechanical drive.

  7. Internally architectured materials with directionally asymmetric friction

    PubMed Central

    Bafekrpour, Ehsan; Dyskin, Arcady; Pasternak, Elena; Molotnikov, Andrey; Estrin, Yuri

    2015-01-01

    Internally Architectured Materials (IAMs) that exhibit different friction forces for sliding in the opposite directions are proposed. This is achieved by translating deformation normal to the sliding plane into a tangential force in a manner that is akin to a toothbrush with inclined bristles. Friction asymmetry is attained by employing a layered material or a structure with parallel ‘ribs’ inclined to the direction of sliding. A theory of directionally asymmetric friction is presented, along with prototype IAMs designed, fabricated and tested. The friction anisotropy (the ξ-coefficient) is characterised by the ratio of the friction forces for two opposite directions of sliding. It is further demonstrated that IAM can possess very high levels of friction anisotropy, with ξ of the order of 10. Further increase in ξ is attained by modifying the shape of the ribs to provide them with directionally dependent bending stiffness. Prototype IAMs produced by 3D printing exhibit truly giant friction asymmetry, with ξ in excess of 20. A novel mechanical rectifier, which can convert oscillatory movement into unidirectional movement by virtue of directionally asymmetric friction, is proposed. Possible applications include locomotion in a constrained environment and energy harvesting from oscillatory noise and vibrations. PMID:26040634

  8. Taylor series to solve friction problems

    NASA Astrophysics Data System (ADS)

    Béchet, Fabien; Lejeune, Arnaud; Potier-Ferry, Michel

    2010-06-01

    Thin metallic sheet transportation appears in numerous manufacturing processes such as continuous annealing, levelling or galvanization. It involves various nonlinear phenomena and, in particular, contact with friction. We develop a numerical method to solve this kind of mechanical problem, using shell finite elements and the Asymptotic Numerical Method (ANM). This article focuses on the treatment of the friction equations with ANM.

  9. Friction brake cushions acceleration and vibration loads

    NASA Technical Reports Server (NTRS)

    Fraser, G. F.; Zawadski, G. Z.

    1966-01-01

    Friction brake cushions an object in a vehicle from axially applied vibration and steady-state acceleration forces. The brake incorporates a doubly tapered piston that applies a controlled radial force to friction brake segments bearing against the walls of a cylinder.

  10. Gimbaled-shoulder friction stir welding tool

    NASA Technical Reports Server (NTRS)

    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.

  11. Wiping Metal Transfer in Friction Stir Welding

    NASA Technical Reports Server (NTRS)

    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.

  12. Studying the Frictional Force Directions via Bristles

    ERIC Educational Resources Information Center

    Prasitpong, S.; Chitaree, R.; Rakkapao, S.

    2010-01-01

    We present simple apparatus designed to help Thai high school students visualize the directions of frictional forces. Bristles of toothbrushes, paintbrushes and scrubbing brushes are used to demonstrate the frictional forces acting in a variety of situations. These demonstrations, when followed by discussion of free-body diagrams, were found to be…

  13. Instrument Measures Airflow Friction Without Contact

    NASA Technical Reports Server (NTRS)

    Monson, D. J.

    1983-01-01

    Dual beam laser interferometer determines airflow friction against body by measuring time-varying thickness of wind sheared oil film. Measurements yield skin friction between film and airstream. Errors from prerun oil flow, tunnel starting transients, and initial surface waves therefore eliminated.

  14. ABL and BAM Friction Analysis Comparison

    DOE PAGESBeta

    Warner, Kirstin F.; Sandstrom, Mary M.; Brown, Geoffrey W.; Remmers, Daniel L.; Phillips, Jason J.; Shelley, Timothy J.; Reyes, Jose A.; Hsu, Peter C.; Reynolds, John G.

    2014-12-29

    Here, the Integrated Data Collection Analysis (IDCA) program has conducted a proficiency study for Small-Scale Safety and Thermal (SSST) testing of homemade explosives (HMEs). Described here is a comparison of the Alleghany Ballistic Laboratory (ABL) friction data and Bundesanstalt fur Materialforschung und -prufung (BAM) friction data for 19 HEM and military standard explosives.

  15. Friction, wear, and lubrication in vacuum

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.

    1971-01-01

    A review of studies and observations on the friction, wear, and lubrication behavior of materials in a vacuum environment is presented. The factors that determine and influence friction and wear are discussed. They include topographical, physical, mechanical, and the chemical nature of the surface. The effects of bulk properties such as deformation characteristics, fracture behavior, and structure are included.

  16. On a model of frictional sliding

    NASA Astrophysics Data System (ADS)

    Estrin, Y.; Bréchet, Y.

    1996-10-01

    A model of frictional sliding with an N-shaped curve for the sliding velocity dependence of the coefficient of friction is considered. This type of friction law is shown to be related to dynamic i.e., velocity dependent ‘ageing’ of asperity junctions. Mechanisms of ‘ageing’ for ductile (Bowden-Tabor) and brittle (Byerlee) materials, though different in nature, lead to qualitatively similar N-shaped velocity dependencies of the coefficient of friction. Estimates for the velocities limiting the range of negative velocity sensitivity of the coefficient of friction are obtained for the ductile case and—albeit with a lesser degree of reliability—for the brittle one. It is shown by linear stability analysis that discontinuous sliding (stick-slip) is associated with the descending portion of the N-shaped curve. An instability criterion is obtained. An expression for the period of the attendant relaxation oscillations of the sliding velocity is given in terms of the calculated velocity dependence of the coefficient of friction. It is suggested that the micromechanically motivated friction law proposed should be used in models of earthquakes due to discontinuous frictional sliding on a crustal fault.

  17. Rolling Friction on a Wheeled Laboratory Cart

    ERIC Educational Resources Information Center

    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…

  18. Friction forces on phase transition fronts

    SciTech Connect

    Mégevand, Ariel

    2013-07-01

    In cosmological first-order phase transitions, the microscopic interaction of the phase transition fronts with non-equilibrium plasma particles manifests itself macroscopically as friction forces. In general, it is a nontrivial problem to compute these forces, and only two limits have been studied, namely, that of very slow walls and, more recently, ultra-relativistic walls which run away. In this paper we consider ultra-relativistic velocities and show that stationary solutions still exist when the parameters allow the existence of runaway walls. Hence, we discuss the necessary and sufficient conditions for the fronts to actually run away. We also propose a phenomenological model for the friction, which interpolates between the non-relativistic and ultra-relativistic values. Thus, the friction depends on two friction coefficients which can be calculated for specific models. We then study the velocity of phase transition fronts as a function of the friction parameters, the thermodynamic parameters, and the amount of supercooling.

  19. [Static disorders in hereditary ataxias].

    PubMed

    Badalian, L O; Lebedeva, N N; Sidorova, O P

    1987-01-01

    Static disorders elicited by the adequate methods of the assessment of equilibrium (stabilography) and gait (plantography) in hereditary ataxias have been analyzed. These techniques of examination make it possible to quantitatively estimate motor disorders, supplement clinical findings and provide an opportunity for objective evaluation of the efficacy of the conducted therapy. PMID:3115017

  20. FORTRAN Static Source Code Analyzer

    NASA Technical Reports Server (NTRS)

    Merwarth, P.

    1984-01-01

    FORTRAN Static Source Code Analyzer program, SAP (DEC VAX version), automatically gathers statistics on occurrences of statements and structures within FORTRAN program and provides reports of those statistics. Provisions made for weighting each statistic and provide an overall figure of complexity.

  1. FORTRAN Static Source Code Analyzer

    NASA Technical Reports Server (NTRS)

    Merwarth, P.

    1982-01-01

    FORTRAN Static Source Code Analyzer program (SAP) automatically gathers and reports statistics on occurrences of statements and structures within FORTRAN program. Provisions are made for weighting each statistic, providing user with overall figure of complexity. Statistics, as well as figures of complexity, are gathered on module-by-module basis. Overall summed statistics are accumulated for complete input source file.

  2. Static and dynamic characteristics of parallel-grooved seals

    NASA Technical Reports Server (NTRS)

    Iwatsubo, Takuzo; Yang, Bo-Suk; Ibaraki, Ryuji

    1987-01-01

    Presented is an analytical method to determine static and dynamic characteristics of annular parallel-grooved seals. The governing equations were derived by using the turbulent lubrication theory based on the law of fluid friction. Linear zero- and first-order perturbation equations of the governing equations were developed, and these equations were analytically investigated to obtain the reaction force of the seals. An analysis is presented that calculates the leakage flow rate, the torque loss, and the rotordynamic coefficients for parallel-grooved seals. To demonstrate this analysis, we show the effect of changing number of stages, land and groove width, and inlet swirl on stability of the boiler feed water pump seals. Generally, as the number of stages increased or the grooves became wider, the leakage flow rate and rotor-dynamic coefficients decreased and the torque loss increased.

  3. A microphysical interpretation of rate- and state-dependent friction for fault gouge

    NASA Astrophysics Data System (ADS)

    Ikari, Matt J.; Carpenter, Brett M.; Marone, Chris

    2016-05-01

    The evolution of fault strength during the seismic cycle plays a key role in the mode of fault slip, nature of earthquake stress drop, and earthquake nucleation. Laboratory-based rate- and state-dependent friction (RSF) laws can describe changes in fault strength during slip, but the connections between fault strength and the mechanisms that dictate the mode of failure, from aseismic creep to earthquake rupture, remain poorly understood. The empirical nature of RSF laws remains a drawback to their application in nature. Here we analyze an extensive data set of friction constitutive parameters with the goal of illuminating the microphysical processes controlling RSF. We document robust relationships between: (1) the initial value of sliding (or kinetic) friction, (2) RSF parameters, and (3) the time rates of frictional strengthening (aging). We derive a microphysical model based on asperity contact mechanics and show that these relationships are dictated by: (1) an activation energy that controls the rate of asperity growth by plastic creep, and (2) an inverse relationship between material hardness and the activation volume of plastic deformation. Collectively, our results illuminate the physics expressed by the RSF parameters, and which describe the absolute value of frictional strength and its dependence on time and slip rate. Moreover, we demonstrate that seismogenic fault behavior may be dictated by the interplay between grain properties and ambient conditions controlling the local shear strength of grain-scale asperity contacts.

  4. Impact comminution of solids due to local kinetic energy of high shear strain rate: I. Continuum theory and turbulence analogy

    NASA Astrophysics Data System (ADS)

    Bažant, Zdeněk P.; Caner, Ferhun C.

    2014-03-01

    The modeling of high velocity impact into brittle or quasibrittle solids is hampered by the unavailability of a constitutive model capturing the effects of material comminution into very fine particles. The present objective is to develop such a model, usable in finite element programs. The comminution at very high strain rates can dissipate a large portion of the kinetic energy of an impacting missile. The spatial derivative of the energy dissipated by comminution gives a force resisting the penetration, which is superposed on the nodal forces obtained from the static constitutive model in a finite element program. The present theory is inspired partly by Grady's model for expansive comminution due to explosion inside a hollow sphere, and partly by analogy with turbulence. In high velocity turbulent flow, the energy dissipation rate gets enhanced by the formation of micro-vortices (eddies) which dissipate energy by viscous shear stress. Similarly, here it is assumed that the energy dissipation at fast deformation of a confined solid gets enhanced by the release of kinetic energy of the motion associated with a high-rate shear strain of forming particles. For simplicity, the shape of these particles in the plane of maximum shear rate is considered to be regular hexagons. The particle sizes are assumed to be distributed according to the Schuhmann power law. The condition that the rate of release of the local kinetic energy must be equal to the interface fracture energy yields a relation between the particle size, the shear strain rate, the fracture energy and the mass density. As one experimental justification, the present theory agrees with Grady's empirical observation that, in impact events, the average particle size is proportional to the (-2/3) power of the shear strain rate. The main characteristic of the comminution process is a dimensionless number Ba (Eq. (37)) representing the ratio of the local kinetic energy of shear strain rate to the maximum possible

  5. Reflection type skin friction meter

    NASA Technical Reports Server (NTRS)

    Bandyopadhyay, Promode R. (Inventor); Weinstein, Leonard M. (Inventor)

    1993-01-01

    A housing block is provided having an upper surface conforming to the test surface of a model or aircraft. An oil film is supplied upstream of a transparent wedge window located in this upper surface by an oil pump system located external to the housing block. A light source located within the housing block supplies a light beam which passes through this transparent window and is reflected back through the transparent window by the upper surface of the oil film to a photo-sensitive position sensor located within the housing. This position sensor allows the slope history of the oil film caused by and aerodynamic flow to be determined. The skin friction is determined from this slope history. Internally located mirrors augment and sensitize the reflected beam as necessary before reaching the position sensor. In addition, a filter may be provided before this sensor to filter the beam.

  6. Macrostructure of Friction Stir Welds

    NASA Technical Reports Server (NTRS)

    Aloor, S.; Nowak, B.; Vargas, R.; McClure, J. C.; Murr, L. E.; Nunes, A. C.; Munafo, Paul M. (Technical Monitor)

    2002-01-01

    This paper will discuss two of the well know large scale features of friction stir welds: the "onion rings" seen in transverse sections, and the striations on the surface of the work piece. It will be shown that the surface features (sometimes called "tool marks") are the result of irregularities on the rotating shoulder of the pin tool and disappear when the shoulder is polished. The "onion ring" structure seen in transverse cross sections is formed by parts of the "carousel", the zone of material adjacent to and rotating with the pin tool, that are shed off in each rotation. The relation between the carousel and the "ring vortex", a rotational flow extending both in and out of the carousel and resembling a smoke-ring with the hole centered on the pin tool, will be discussed.

  7. Stabilizing Stick-Slip Friction

    NASA Astrophysics Data System (ADS)

    Fineberg, J.; Urbakh, M.; Rubinstein, S. M.

    2011-12-01

    Even the most regular stick-slip frictional sliding is always stochastic, with irregularity in both the intervals between slip events and the sizes of the associated stress drops. Applying small-amplitude oscillations to the shear force, we show, experimentally and theoretically, that the stick-slip periods synchronize. We further show that this phase locking is related to the inhibition of slow rupture modes which forces a transition to fast rupture, providing a possible mechanism for observed remote triggering of earthquakes. Such manipulation of collective modes may be generally relevant to extended nonlinear systems driven near to criticality. Reference: Rosario Capozza, Shmuel M. Rubinstein, Itay Barel, Michael Urbakh, and Jay Fineberg, Physical Review Letters 107, 024301 (2011).

  8. Friction Stir Welding and Processing

    SciTech Connect

    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.

  9. A molecular dynamics study of dielectric friction

    SciTech Connect

    Kurnikova, M.G.; Waldeck, D.H.; Coalson, R.D.

    1996-07-01

    A molecular dynamics study of the friction experienced by the dye molecule resorufamine rotating in a polar solvent is performed. The validity of simple continuum theories of dielectric friction is tested. It is found that the Alavi{endash}Waldeck theory gives reasonable results for the zero frequency dielectric friction coefficient while the Nee{endash}Zwanzig theory requires an unphysically small cavity radius. A procedure for evaluating the time dependent friction kernel from torques and angular velocities, which enables the contributions to the friction from the van der Waals and Coulomb forces to be evaluated separately, is suggested. This study of a realistic system shows that electrostatic interactions can enhance friction by at least two physical mechanisms. First is a contribution to the friction which arises solely from retardation of the solvent reaction field. Second is a contribution arising from local structural changes of the solvent which are driven by the electrostatic field, i.e., a change in the local viscosity. {copyright} {ital 1996 American Institute of Physics.}

  10. Friction of Compression-ignition Engines

    NASA Technical Reports Server (NTRS)

    Moore, Charles S; Collins, John H , Jr

    1936-01-01

    The cost in mean effective pressure of generating air flow in the combustion chambers of single-cylinder compression-ignition engines was determined for the prechamber and the displaced-piston types of combustion chamber. For each type a wide range of air-flow quantities, speeds, and boost pressures was investigated. Supplementary tests were made to determine the effect of lubricating-oil temperature, cooling-water temperature, and compression ratio on the friction mean effective pressure of the single-cylinder test engine. Friction curves are included for two 9-cylinder, radial, compression-ignition aircraft engines. The results indicate that generating the optimum forced air flow increased the motoring losses approximately 5 pounds per square inch mean effective pressure regardless of chamber type or engine speed. With a given type of chamber, the rate of increase in friction mean effective pressure with engine speed is independent of the air-flow speed. The effect of boost pressure on the friction cannot be predicted because the friction was decreased, unchanged, or increased depending on the combustion-chamber type and design details. High compression ratio accounts for approximately 5 pounds per square inch mean effective pressure of the friction of these single-cylinder compression-ignition engines. The single-cylinder test engines used in this investigation had a much higher friction mean effective pressure than conventional aircraft engines or than the 9-cylinder, radial, compression-ignition engines tested so that performance should be compared on an indicated basis.

  11. Load-Dependent Friction Hysteresis on Graphene.

    PubMed

    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. PMID:27110836

  12. EFFECT OF DYNAMIC LOADING ON THE FRICTIONAL RESPONSE OF BOVINE ARTICULAR CARTILAGE

    PubMed Central

    Krishnan, Ramaswamy; Mariner, Elise N.; Ateshian, Gerard A.

    2014-01-01

    Summary The objective of this study was to test the hypotheses that (1) the steady-state friction coefficient of articular cartilage is significantly smaller under cyclical compressive loading than the equilibrium friction coefficient under static loading, and decreases as a function of loading frequency; (2) the steady-state cartilage interstitial fluid load support remains significantly greater than zero under cyclical compressive loading and increases as a function of loading frequency. Unconfined compression tests with sliding of bovine shoulder cartilage against glass in saline were carried out on fresh cylindrical plugs (n=12), under three sinusoidal loading frequencies (0.05 Hz, 0.5 Hz and 1 Hz) and under static loading; the time-dependent friction coefficient μeff was measured. The interstitial fluid load support was also predicted theoretically. Under static loading μeff increased from a minimum value (μmin=0.005±0.003) to an equilibrium value (μeq=0.153±0.032). In cyclical compressive loading tests μeff similarly rose from a minimum value (μmin=0.004±0.002, 0.003±0.001 and 0.003±0.001 at 0.05, 0.5 and 1 Hz) and reached a steady-state response oscillating between a lower-bound (μlb=0.092±0.016, 0.083±0.019 and 0.084±0.020) and upper bound (μub=0.382±0.057, 0.358±0.059, and 0.298±0.061). For all frequencies it was found that and μub> μeq and μlb < μeq (p<0.05). Under cyclical compressive loading the interstitial fluid load support was found to oscillate above and below the static loading response, with suction occurring over a portion of the loading cycle at steady-state conditions. All theoretical predictions and most experimental results demonstrated little sensitivity to loading frequency. On the basis of these results, both hypotheses were rejected. Cyclical compressive loading is not found to promote lower frictional coefficients or higher interstitial fluid load support than static loading. PMID:15958224

  13. Eigenmodes of quasi-static magnetic islands in current sheet

    SciTech Connect

    Li Yi; Cai Xiaohui; Chai Lihui; Wang Shui; Zheng Huinan; Shen Chao

    2011-12-15

    As observation have shown, magnetic islands often appear before and/or after the onset of magnetic reconnections in the current sheets, and they also appear in the current sheets in the solar corona, Earth's magnetotail, and Earth's magnetopause. Thus, the existence of magnetic islands can affect the initial conditions in magnetic reconnection. In this paper, we propose a model of quasi-static magnetic island eigenmodes in the current sheet. This model analytically describes the magnetic field structures in the quasi-static case, which will provide a possible approach to reconstructing the magnetic structures in the current sheet via observation data. This model is self-consistent in the kinetic theory. Also, the distribution function of charged particles in the magnetic island can be calculated.

  14. General static spherically symmetric solutions in Horava gravity

    SciTech Connect

    Capasso, Dario; Polychronakos, Alexios P.

    2010-04-15

    We derive the equations describing a general static spherically symmetric configuration for the softly broken Horava gravity introduced by A. Kehagias and K. Sfetsos with nonzero shift field and no-projectability condition. These represent 'hedgehog' versions of black holes with radial 'hair' arising from the shift field. For the case of the standard de Witt kinetic term ({lambda}=1) there is an infinity of solutions that exhibit a deformed version of reparametrization invariance away from the general relativistic limit. Special solutions also arise in the anisotropic conformal point {lambda}=(1/3). Moreover we obtain an implicit general expression for the solutions with N{sub r}=0 and generic {lambda}. In this context we study the presence of horizons for standard matter and the related Hawking temperature, generalizing the corresponding relations in the usual static spherically symmetric case.

  15. Internal Friction And Instabilities Of Rotors

    NASA Technical Reports Server (NTRS)

    Walton, J.; Artiles, A.; Lund, J.; Dill, J.; Zorzi, E.

    1992-01-01

    Report describes study of effects of internal friction on dynamics of rotors prompted by concern over instabilities in rotors of turbomachines. Theoretical and experimental studies described. Theoretical involved development of nonlinear mathematical models of internal friction in three joints found in turbomachinery - axial splines, Curvic(TM) splines, and interference fits between smooth cylindrical surfaces. Experimental included traction tests to determine the coefficients of friction of rotor alloys at various temperatures, bending-mode-vibration tests of shafts equipped with various joints and rotordynamic tests of shafts with axial-spline and interference-fit joints.

  16. Lateral-deflection-controlled friction force microscopy

    NASA Astrophysics Data System (ADS)

    Fukuzawa, Kenji; Hamaoka, Satoshi; Shikida, Mitsuhiro; Itoh, Shintaro; Zhang, Hedong

    2014-08-01

    Lateral-deflection-controlled dual-axis friction force microscopy (FFM) is presented. In this method, an electrostatic force generated with a probe-incorporated micro-actuator compensates for friction force in real time during probe scanning using feedback control. This equivalently large rigidity can eliminate apparent boundary width and lateral snap-in, which are caused by lateral probe deflection. The method can evolve FFM as a method for quantifying local frictional properties on the micro/nanometer-scale by overcoming essential problems to dual-axis FFM.

  17. Coordinated Water Under Confinement Eases Sliding Friction

    NASA Astrophysics Data System (ADS)

    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.

  18. Entropy production in irreversible processes with friction.

    PubMed

    Bizarro, João P S

    2008-08-01

    Established expressions for entropy production in irreversible processes are generalized to include friction explicitly, as a source of irreversibility in the interaction between a system and its surroundings. The net amount of heat delivered to the system does not come now only from the reservoir, but may have an additional component coming from the work done against friction forces and dissipated as heat. To avoid ambiguities in interpreting the different contributions to entropy increase, the latter is also written in terms of the heat directly exchanged between the system and surroundings and of the fraction of frictional work that is lost in the system. PMID:18850816

  19. Quantized friction across ionic liquid thin films.

    PubMed

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

    2013-10-01

    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. PMID:23942943

  20. Frictional effects near a metal surface

    SciTech Connect

    Dou, Wenjie; Subotnik, Joseph E.; Nitzan, Abraham

    2015-08-07

    When a classical master equation (CME) is used to describe the nonadiabatic dynamics of a molecule at metal surfaces, we show that in the regime of reasonably strong molecule-metal couplings, the CME can be reduced to a Fokker-Planck equation with an explicit form of electronic friction. For a single metal substrate at thermal equilibrium, the electronic friction and random force satisfy the fluctuation-dissipation theorem. When we investigate the time scale for an electron transfer (ET) event between the molecule and metal surface, we find that the ET rates show a turnover effect (just as in Kramer’s theory) as a function of frictional damping.

  1. Frictional effects near a metal surface.

    PubMed

    Dou, Wenjie; Nitzan, Abraham; Subotnik, Joseph E

    2015-08-01

    When a classical master equation (CME) is used to describe the nonadiabatic dynamics of a molecule at metal surfaces, we show that in the regime of reasonably strong molecule-metal couplings, the CME can be reduced to a Fokker-Planck equation with an explicit form of electronic friction. For a single metal substrate at thermal equilibrium, the electronic friction and random force satisfy the fluctuation-dissipation theorem. When we investigate the time scale for an electron transfer (ET) event between the molecule and metal surface, we find that the ET rates show a turnover effect (just as in Kramer's theory) as a function of frictional damping. PMID:26254638

  2. Skin-Friction Measurements in Incompressible Flow

    NASA Technical Reports Server (NTRS)

    Smith, Donald W.; Walker, John H.

    1959-01-01

    Experiments have been conducted to measure the local surface-shear stress and the average skin-friction coefficient in Incompressible flow for a turbulent boundary layer on a smooth flat plate having zero pressure gradient. Data were obtained for a range of Reynolds numbers from 1 million to 45 million. The local surface-shear stress was measured by a floating-element skin-friction balance and also by a calibrated total head tube located on the surface of the test wall. The average skin-friction coefficient was obtained from boundary-layer velocity profiles.

  3. NASA tire/runway friction projects

    NASA Technical Reports Server (NTRS)

    Yager, Thomas J.

    1995-01-01

    The paper reviews several aspects of NASA Langley Research Center's tire/runway friction evaluations directed towards improving the safety and economy of aircraft ground operations. The facilities and test equipment used in implementing different aircraft tire friction studies and other related aircraft ground performance investigations are described together with recent workshop activities at NASA Wallops Flight Facility. An overview of the pending Joint NASA/Transport Canada/FM Winter Runway Friction Program is given. Other NASA ongoing studies and on-site field tests are discussed including tire wear performance and new surface treatments. The paper concludes with a description of future research plans.

  4. Skin friction measuring device for aircraft

    NASA Technical Reports Server (NTRS)

    Montoya, L. C.; Bellman, D. R. (Inventor)

    1980-01-01

    A skin friction measuring device for measuring the resistance of an aerodynamic surface to an airstream is described. It was adapted to be mounted on an aircraft and is characterized by a friction plate adapted to be disposed in a flush relationship with the external surface of the aircraft and be displaced in response to skin friction drag. As an airstream is caused to flow over the surface, a potentiometer connected to the plate for providing an electrical output indicates the magnitude of the drag.

  5. The mystery of Coulomb friction in sediment transport

    NASA Astrophysics Data System (ADS)

    Pähtz, Thomas; Duran, Orencio

    Nearly all analytical models of sediment transport in Newtonian fluid (e.g., air or water) are based on Bagnold's assumption of a constant Coulomb friction coefficient (particle-shear-pressure-ratio, μ) at the interface (zb) between sediment bed and transport layer. In fact, this assumption is the main reason why these models predict the sediment load (and subsequently the sediment transport rate) to be proportional to the excess shear stress (τ -τt), a scaling which has been confirmed in many wind-tunnel and flume experiments. Attempts to explain why μ (zb) is constant have usually been based on the sliding-friction analogy or rheology arguments. However, here we analytically derive μ (zs) √{ 3} - 1 , where zs is the location at which the production rate of particle fluctuation energy is maximal. Our derivation is based on the assumption that the rate of collisional transfer of horizontal into vertical kinetic energy is typically much larger than the rate of energy dissipation. Using state-of-the-art numerical simulations of sediment transport in Newtonian fluid, we validate all assumptions and approximation involved in our derivation. Interestingly, the location zs can significantly deviate from zb depending on the simulated conditions. We acknowledge support from grants National Natural Science Foundation of China (Nos. 1151101041 and 41376095) and Natural Science Foundation of Zhejiang Province (No. LR16E090001).

  6. Friction and shear fracture of an adhesive contact under torsion

    NASA Astrophysics Data System (ADS)

    Chateauminois, Antoine; Fretigny, Christian; Olanier, Ludovic

    2010-02-01

    The shear failure or stiction of an adhesive contact between a poly(dimethylsiloxane) (PDMS) rubber and a glass lens has been investigated using a torsional contact configuration. As compared to linear sliding, torsion presents the advantage of inducing a shear failure under a pure mode III condition, while preserving the cylindrical symmetry of the contact. The surface of the transparent PDMS substrate was marked using a network of dots in order to monitor continuously the in-plane surface displacements during the stiction process. Using a previously developed inversion procedure (A. Chateauminois and C. Fretigny, Eur. Phys. J. E 27, 221 (2008)), the corresponding surface shear stress distributions were obtained from the displacement fields. Stiction was found to involve the progressive shrinkage of a central adhesive zone surrounded by an annular microslip region. Adhesion effects were especially evidenced from a stress overshoot at the boundary of the adhesive zone. The experimental data were analysis using an extension to torsional contact of the Maugis-Dugdale approach’s to adhesive contacts which takes into account frictional effects. This model allowed to extract an effective adhesion energy in the presence of friction, which dependence on kinetics effect is briefly discussed.

  7. Transition from stick to slip in Hertzian contact with ``Griffith'' friction: The Cattaneo-Mindlin problem revisited

    NASA Astrophysics Data System (ADS)

    Ciavarella, M.

    2015-11-01

    Classically, the transition from stick to slip is modelled with Amonton-Coulomb law, leading to the Cattaneo-Mindlin problem, which is amenable to quite general solutions using the idea of superposing normal contact pressure distributions - in particular superposing the full sliding component of shear with a corrective distribution in the stick region. However, faults model in geophysics and recent high-speed measurements of the real contact area and the strain fields in dry (nominally flat) rough interfaces at macroscopic but laboratory scale, all suggest that the transition from 'static' to 'dynamic' friction can be described, rather than by Coulomb law, by classical fracture mechanics singular solutions of shear cracks. Here, we introduce an 'adhesive' model for friction in a Hertzian spherical contact, maintaining the Hertzian solution for the normal pressures, but where the inception of slip is given by a Griffith condition. In the slip region, the standard Coulomb law continues to hold. This leads to a very simple solution for the Cattaneo-Mindlin problem, in which the "corrective" solution in the stick area is in fact similar to the mode II equivalent of a JKR singular solution for adhesive contact. The model departs from the standard Cattaneo-Mindlin solution, showing an increased size of the stick zone relative to the contact area, and a sudden transition to slip when the stick region reaches a critical size (the equivalent of the pull-off contact size of the JKR solution). The apparent static friction coefficient before sliding can be much higher than the sliding friction coefficient and, for a given friction fracture "energy", the process results in size and normal load dependence of the apparent static friction coefficient. Some qualitative agreement with Fineberg's group experiments for friction exists, namely the stick-slip boundary quasi-static prediction may correspond to the arrest of their slip "precursors", and the rapid collapse to global

  8. Adhesion and friction properties of polymer brushes: fluoro versus nonfluoro polymer brushes at varying thickness.

    PubMed

    Bhairamadgi, Nagendra S; Pujari, Sidharam P; Leermakers, Frans A M; van Rijn, Cees J M; Zuilhof, Han

    2014-03-01

    A series of different thicknesses of fluoro poly(2,2,2-trifluoroethyl methacrylate) and its analogous nonfluoro poly(ethyl methacrylate) polymer brushes were prepared via surface-initiated ATRP (SI-ATRP) on Si(111) surfaces. The thiol-yne click reaction was used to immobilize the SI-ATRP initiator with a high surface coverage, in order to achieve denser polymer brushes (grafting density from ~0.1 to 0.8 chains/nm(2)). All polymer brushes were characterized by static water contact angle measurements, infrared absorption reflection spectroscopy, and X-ray photoelectron spectroscopy. Adhesion and friction force measurements were conducted with silica colloidal probe atomic force microscopy (CP-AFM) under ambient and dry (argon) conditions. The fluoro poly(2,2,2-trifluoroethyl methacrylate) polymer showed a decrease in adhesion and friction with increasing thickness. The analogous nonfluoro poly(ethyl methacrylate) polymer brushes showed high adhesion and friction under ambient conditions. Friction coefficients down to 0.0057 (ambient conditions) and 0.0031 (dry argon) were obtained for poly(2,2,2-trifluoroethyl methacrylate) polymer brushes with 140 nm thickness, which are the lowest among these types of polymer brushes. PMID:24555721

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

    NASA Astrophysics Data System (ADS)

    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.

  10. Static behaviour of induced seismicity

    NASA Astrophysics Data System (ADS)

    Mignan, A.

    2015-12-01

    The standard paradigm to describe seismicity induced by fluid injection is to apply nonlinear diffusion dynamics in a poroelastic medium. I show that the spatiotemporal behaviour and rate evolution of induced seismicity can, instead, be expressed by geometric operations on a static stress field produced by volume change at depth. I obtain laws similar in form to the ones derived from poroelasticity while requiring a lower description length. Although fluid flow is known to occur in the ground, it is not pertinent to the behaviour of induced seismicity. The proposed model is equivalent to the static stress model for tectonic foreshocks generated by the Non-Critical Precursory Accelerating Seismicity Theory. This study hence verifies the explanatory power of this theory outside of its original scope.

  11. Static Detection of Disassembly Errors

    SciTech Connect

    Krishnamoorthy, Nithya; Debray, Saumya; Fligg, Alan K

    2009-10-13

    Static disassembly is a crucial first step in reverse engineering executable files, and there is a consider- able body of work in reverse-engineering of binaries, as well as areas such as semantics-based security anal- ysis, that assumes that the input executable has been correctly disassembled. However, disassembly errors, e.g., arising from binary obfuscations, can render this assumption invalid. This work describes a machine- learning-based approach, using decision trees, for stat- ically identifying possible errors in a static disassem- bly; such potential errors may then be examined more closely, e.g., using dynamic analyses. Experimental re- sults using a variety of input executables indicate that our approach performs well, correctly identifying most disassembly errors with relatively few false positives.

  12. Water cooled static pressure probe

    NASA Technical Reports Server (NTRS)

    Lagen, Nicholas T. (Inventor); Eves, John W. (Inventor); Reece, Garland D. (Inventor); Geissinger, Steve L. (Inventor)

    1991-01-01

    An improved static pressure probe containing a water cooling mechanism is disclosed. This probe has a hollow interior containing a central coolant tube and multiple individual pressure measurement tubes connected to holes placed on the exterior. Coolant from the central tube symmetrically immerses the interior of the probe, allowing it to sustain high temperature (in the region of 2500 F) supersonic jet flow indefinitely, while still recording accurate pressure data. The coolant exits the probe body by way of a reservoir attached to the aft of the probe. The pressure measurement tubes are joined to a single, larger manifold in the reservoir. This manifold is attached to a pressure transducer that records the average static pressure.

  13. Note: A rigid piezo motor with large output force and an effective method to reduce sliding friction force

    SciTech Connect

    Guo, Ying; Lu, Qingyou; Hou, Yubin

    2014-05-15

    We present a completely practical TunaDrive piezo motor. It consists of a central piezo stack sandwiched by two arm piezo stacks and two leg piezo stacks, respectively, which is then sandwiched and spring-clamped by a pair of parallel polished sapphire rods. It works by alternatively fast expanding and contracting the arm/leg stacks while slowly expanding/contracting the central stack simultaneously. The key point is that sufficiently fast expanding and contracting a limb stack can make its two sliding friction forces well cancel, resulting in the total sliding friction force is <10% of the total static friction force, which can help increase output force greatly. The piezo motor's high compactness, precision, and output force make it perfect in building a high-quality harsh-condition (vibration resistant) atomic resolution scanning probe microscope.

  14. Surface roughness and friction coefficient in peened friction stir welded 2195 aluminum alloy

    NASA Astrophysics Data System (ADS)

    Hatamleh, Omar; Smith, James; Cohen, Donald; Bradley, Robert

    2009-05-01

    The tribological properties of friction stir welded 2195 aluminum alloy joints were investigated for several laser- and shot-peened specimens. The first portion of this study assessed the surface roughness changes at different regions of the weld resulting from the various peening processes and included an atomic force microscopy (AFM) study to reveal fine structures. The second portion investigated the friction characteristics for various conditions when slid against a 440C ball slider. Shot peening resulted in significant surface roughness when compared to the unpeened and laser-peened samples. The initial friction for all types of specimens was highly variable. However, long-term friction was shown to be lowest for samples with no peening treatment. Laser peening caused the friction to increase slightly. The shot peening process on the other hand resulted in an increase of the long-term friction effects on both sides of the weld.

  15. Architectures for statically scheduled dataflow

    SciTech Connect

    Lee, E.A.; Bier, J.C. )

    1990-12-01

    When dataflow program graphs can be statically scheduled, little run-time overhead (software or hardware) is necessary. This paper describes a class of parallel architectures consisting of von Neumann processors and one or more shared memories, where the order of shared- memory access is determined at compile time and enforced at run time. The architecture is extremely lean in hardware, yet for a set of important applications it can perform as well as any shared-memory architecture. Dataflow graphs can be mapped onto it statically. Furthermore, it supports shared data structures without the run-time overhead of I-structures. A software environment has been constructed that automatically maps signal processing applications onto a simulation of such an architecture, where the architecture is implemented using Motorola DSP96002 microcomputers. Static (compile-time) scheduling is possible for a subclass of dataflow program graphs where the firing pattern of actors is data independent. This model is suitable for digital signal processing and some other scientific computation. It supports recurrences, manifest iteration, and conditional assignment. However, it does not support true recursion, data-dependent iteration, or conditional evaluation. An effort is under way to weaken the constraints of the model to determine the implications for hardware design.

  16. Spectral domains for bosonic pair creation in static electromagnetic fields

    NASA Astrophysics Data System (ADS)

    Lv, Q. Z.; Li, Y. J.; Grobe, R.; Su, Q.

    2016-04-01

    We study the emission spectrum of bosons created from the vacuum by combined static electric and magnetic fields. Depending on the spatial extension of the magnetic field, we find four regimes of pair creation, characterized by different growth behaviors of the number of the produced particles. We show that these regimes manifest themselves in the eigenenergy spectrum of the Klein-Gordon Hamiltonian. The regimes also lead to rather different kinetic energy spectra of the emitted bosons, whose peak positions can be obtained from a generalized Fano-like perturbative approach.

  17. Friction and wear characteristics of carbon steels in vacuum

    NASA Technical Reports Server (NTRS)

    Verkin, B. I.; Lyubarskiy, I. M.; Udovenko, V. F.; Guslyakov, A. A.

    1974-01-01

    The nature of carbon steel friction and wear under vacuum conditions is described within the framework of general friction and wear theory. Friction is considered a dynamic process and wear is considered to be the result of a continuous sequence of transitions of the friction surface material from one state into another.

  18. Three Inexpensive Static-Electricity Demonstrations.

    ERIC Educational Resources Information Center

    Gore, Gordon R.; Gregg, William R.

    1992-01-01

    Describes demonstrations to (1) construct an inexpensive static electricity detector; (2) obtain an abundant supply of either negative or positive charge using household items; and (3) create static electricity using a Tesla coil or Van de Graaff generator. (MDH)

  19. Role of interfacial friction for flow instabilities in a thin polar-ordered active fluid layer.

    PubMed

    Sarkar, Niladri; Basu, Abhik

    2015-11-01

    We construct a generic coarse-grained dynamics of a thin inflexible planar layer of polar-ordered suspension of active particles that is frictionally coupled to an embedding isotropic passive fluid medium with a friction coefficient Γ. Being controlled by Γ, our model provides a unified framework to describe the long-wavelength behavior of a variety of thin polar-ordered systems, ranging from wet to dry active matter and free-standing active films. Investigations of the linear instabilities around a chosen orientationally ordered uniform reference state reveal generic moving and static instabilities in the system that can depend sensitively on Γ. Based on our results, we discuss estimation of bounds on Γ in experimentally accessible systems. PMID:26651694

  20. Role of interfacial friction for flow instabilities in a thin polar-ordered active fluid layer

    NASA Astrophysics Data System (ADS)

    Sarkar, Niladri; Basu, Abhik

    2015-11-01

    We construct a generic coarse-grained dynamics of a thin inflexible planar layer of polar-ordered suspension of active particles that is frictionally coupled to an embedding isotropic passive fluid medium with a friction coefficient Γ . Being controlled by Γ , our model provides a unified framework to describe the long-wavelength behavior of a variety of thin polar-ordered systems, ranging from wet to dry active matter and free-standing active films. Investigations of the linear instabilities around a chosen orientationally ordered uniform reference state reveal generic moving and static instabilities in the system that can depend sensitively on Γ . Based on our results, we discuss estimation of bounds on Γ in experimentally accessible systems.

  1. Rheological effects on friction in elastohydrodynamic lubrication

    NASA Technical Reports Server (NTRS)

    Trachman, E. G.; Cheng, H. S.

    1973-01-01

    An analytical and experimental investigation is presented of the friction in a rolling and sliding elastohydrodynamic lubricated contact. The rheological behavior of the lubricant is described in terms of two viscoelastic models. These models represent the separate effects of non-Newtonian behavior and the transient response of the fluid. A unified description of the non-Newtonian shear rate dependence of the viscosity is presented as a new hyperbolic liquid model. The transient response of viscosity, following the rapid pressure rise encountered in the contact, is described by a compressional viscoelastic model of the volume response of a liquid to an applied pressure step. The resulting momentum and energy equations are solved by an iterative numerical technique, and a friction coefficient is calculated. The experimental study was performed, with two synthetic paraffinic lubricants, to verify the friction predictions of the analysis. The values of friction coefficient from theory and experiment are in close agreement.

  2. Nuclear Fuel Plate Fabrication Employing Friction Welding

    SciTech Connect

    Douglas E. Burkes; Neil P. Hallinan; Curtis R. Clark

    2008-09-01

    This paper provides an overview of the friction bonding process, a novel modification of the more conventional friction stir welding process. The process has been modified to enable the fabrication of plate-type nuclear fuels for the conversion of research and test reactors currently operating using highly enriched uranium to low-enriched uranium. Discussions related to the specific modifications of the friction bonding process have been provided, in addition to challenges associated with these modifications. Progression of the process and solutions to the challenges are provided so that users of the friction stir welding process and those investigating fabrication of other laminar composites, where joining of one or more layers is essential, might draw from the authors’ experiences discussed in this paper.

  3. Sliding friction on wet and dry sand.

    PubMed

    Fall, A; Weber, B; Pakpour, M; Lenoir, N; Shahidzadeh, N; Fiscina, J; Wagner, C; Bonn, D

    2014-05-01

    We show experimentally that the sliding friction on sand is greatly reduced by the addition of some-but not too much-water. The formation of capillary water bridges increases the shear modulus of the sand, which facilitates the sliding. Too much water, on the other hand, makes the capillary bridges coalesce, resulting in a decrease of the modulus; in this case, we observe that the friction coefficient increases again. Our results, therefore, show that the friction coefficient is directly related to the shear modulus; this has important repercussions for the transport of granular materials. In addition, the polydispersity of the sand is shown to also have a large effect on the friction coefficient. PMID:24836256

  4. Special cases of friction and applications

    NASA Technical Reports Server (NTRS)

    Litvin, F. L.; Coy, J. J.

    1983-01-01

    Two techniques for reducing friction forces are presented. The techniques are applied to the generalized problem of reducing the friction between kinematic pairs which connect a moveable link to a frame. The basic principles are: (1) Let the moveable link be supported by two bearings where the relative velocities of the link with respect to each bearing are of opposite directions. Thus the resultant force (torque) of friction acting on the link due to the bearings is approximately zero. Then, additional perturbation of motion parallel to the main motion of the moveable link will require only a very small force; (2) Let the perturbation in motion be perpendicular to the main motion. Equations are developed which explain these two methods. The results are discussed in relation to friction in geared couplings, gyroscope gimbal bearings and a rotary conveyor system. Design examples are presented.

  5. Laser surface conditioning of semimetallic friction materials

    SciTech Connect

    Patten, D.T.

    1986-01-01

    Surface conditioning is one way of reducing the duration and magnitude of the initial transients occurring in friction materials. In developing a laser searing system for semimetallic materials the changes occurring on the surface were characterized as a function of the power density. Excessive power melted the surface of the lining and produced an undesirable microstructure, while too little power did not produce the changes desired. The changes produced by laser searing were found to be similar to the changes produced by other types of surface conditioning. The friction and wear performance was studied for linings seared with different power densities. Laser searing primarily increased the low speed, low temperature, pre-burnish friction level. The amount of increase was proportional to the amount of searing. After burnishing the searing did not effect the friction level of the lining. Excessive power densities produced undesirable surface microstructures and persistent rotor scoring.

  6. Extended ion pumped vacuum friction test

    NASA Technical Reports Server (NTRS)

    Hammel, R. L.

    1971-01-01

    Boundary layer friction data under ion pumped vacuum was taken for sixteen material couples. The test series was an extension of a previous study of the effects of modified ion pumped environments. Sliding distances imposed in the present effort greatly exceeded any studied in the previous contiguous, flight or ground tests. Wear out of specific couples, in particular, thin film lubricants was noted. The behavior of the test hardware including wear out of the mechanisms was noted. As a result, the impact of test interruption was observed for several test couples. Recovery of the friction upon re-establishing sliding in vacuum was generally rapid. The results of the extended sliding study reinforce the previous conclusion that sliding distance (mechanical history) is the primary factor in establishing the force limiting boundary layer friction. General friction value under the extended sliding confirm those observed in previous orbital and the related ground test studies.

  7. Anomalously Weak Dynamical Friction in Halos

    NASA Astrophysics Data System (ADS)

    Sellwood, J. A.; Debattista, Victor P.

    A bar rotating in a pressure-supported halo generally loses angular momentum and slows down due to dynamical friction. Valenzuela & Klypin report a counter-example of a bar that rotates in a dense halo with little friction for several Gyr, and argue that their result invalidates the claim by Debattista & Sellwood that fast bars in real galaxies require a low halo density. We show that it is possible for friction to cease for a while should the pattern speed of the bar fluctuate upward. The reduced friction is due to an anomalous gradient in the phase-space density of particles at the principal resonance created by the earlier evolution. The result obtained by Valenzuela & Klypin is probably an artifact of their adaptive mesh refinement method, but anyway could not persist in a real galaxy. The conclusion by Debattista & Sellwood still stands.

  8. Friction and Wear on the Atomic Scale

    NASA Astrophysics Data System (ADS)

    Gnecco, Enrico; Bennewitz, Roland; Pfeiffer, Oliver; Socoliuc, Anisoara; Meyer, Ernst

    Friction is an old subject of research: the empirical da Vinci-Amontons laws are common knowledge. Macroscopic experiments systematically performed by the school of Bowden and Tabor have revealed that macroscopic friction can be related to the collective action of small asperities. During the last 15 years, experiments performed with the atomic force microscope gave new insight into the physics of single asperities sliding over surfaces. This development, together with complementary experiments by means of surface force apparatus and quartz microbalance, established the new field of nanotribology. At the same time, increasing computing power allowed for the simulation of the processes in sliding contacts consisting of several hundred atoms. It became clear that atomic processes cannot be neglected in the interpretation of nanotribology experiments. Experiments on even well-defined surfaces directly revealed atomic structures in friction forces. This chapter will describe friction force microscopy experiments that reveal, more or less directly, atomic processes in the sliding contact.

  9. Suppression of friction by mechanical vibrations.

    PubMed

    Capozza, Rosario; Vanossi, Andrea; Vezzani, Alessandro; Zapperi, Stefano

    2009-08-21

    Mechanical vibrations are known to affect frictional sliding and the associated stick-slip patterns causing sometimes a drastic reduction of the friction force. This issue is relevant for applications in nanotribology and to understand earthquake triggering by small dynamic perturbations. We study the dynamics of repulsive particles confined between a horizontally driven top plate and a vertically oscillating bottom plate. Our numerical results show a suppression of the high dissipative stick-slip regime in a well-defined range of frequencies that depends on the vibrating amplitude, the normal applied load, the system inertia and the damping constant. We propose a theoretical explanation of the numerical results and derive a phase diagram indicating the region of parameter space where friction is suppressed. Our results allow to define better strategies for the mechanical control of friction. PMID:19792738

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

    NASA Technical Reports Server (NTRS)

    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.

  11. Effects of shear load on frictional healing

    NASA Astrophysics Data System (ADS)

    Ryan, K. L.; Marone, C.

    2014-12-01

    During the seismic cycle of repeated earthquake failure, faults regain strength in a process known as frictional healing. Laboratory studies have played a central role in illuminating the processes of frictional healing and fault re-strengthening. These studies have also provided the foundation for laboratory-derived friction constitutive laws, which have been used extensively to model earthquake dynamics. We conducted laboratory experiments to assess the affect of shear load on frictional healing. Frictional healing is quantified during slide-hold-slide (SHS) tests, which serve as a simple laboratory analog for the seismic cycle in which earthquakes (slide) are followed by interseismic quiescence (hold). We studied bare surfaces of Westerly granite and layers of Westerly granite gouge (thickness of 3 mm) at normal stresses from 4-25 MPa, relative humidity of 40-60%, and loading and unloading velocities of 10-300 μm/s. During the hold period of SHS tests, shear stress on the sample was partially removed to investigate the effects of shear load on frictional healing and to isolate time- and slip-dependent effects on fault healing. Preliminary results are consistent with existing works and indicate that frictional healing increases with the logarithm of hold time and decreases with normalized shear stress τ/τf during the hold. During SHS tests with hold periods of 100 seconds, healing values ranged from (0.013-0.014) for τ/τf = 1 to (0.059-0.063) for τ/τf = 0, where τ is the shear stress during the hold period and τf is the shear stress during steady frictional sliding. Experiments on bare rock surfaces and with natural and synthetic fault gouge materials are in progress. Conventional SHS tests (i.e. τ/τf = 1) are adequately described by the rate and state friction laws. However, previous experiments in granular quartz suggest that zero-stress SHS tests are not well characterized by either the Dieterich or Ruina state evolution laws. We are investigating

  12. Flexible Friction Stir Joining Technology

    SciTech Connect

    Feng, Zhili; Lim, Yong Chae; Mahoney, Murray; Sanderson, Samuel; Larsen, Steve; Steel, Russel; Fleck, Dale; Fairchild, Doug P; Wasson, Andrew J; Babb, Jon; Higgins, Paul

    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.

  13. REDUCED ENGINE FRICTION AND WEAR

    SciTech Connect

    Ron Matthews

    2003-07-08

    Progress was made on experimental and numerical subtasks during the second 6-month period of this project. One of the experimental subtasks scheduled for completion during the first 6 months was delayed due to a delay in receiving the prototype RLE face seal from the vendor. This component was acquired and testing was completed during the second 6 months. The test results indicate that this face seal fulfills the engineering objectives. The other experimental subtask scheduled for completion during the second 6-month period was final assembly of the prototype rotating liner engine. This subtask was completed on schedule. No results from this subtask were scheduled for this reporting period. One numerical subtask, development of the governing equations, was scheduled for completion during the first 6-month period but was completed during the second 6 months. However, we expect to re-explore these as we learn more throughout the course of the project. Two other numerical subtasks were scheduled to begin during the second 6 months: formulating the numerical equations governing piston assembly friction and coding/testing the resulting model. These subtasks were not scheduled for completion during this reporting period. Satisfactory progress was made.

  14. A review of dynamics modelling of friction wedge suspensions

    NASA Astrophysics Data System (ADS)

    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.

  15. Comparative Tests of Pitot-static Tubes

    NASA Technical Reports Server (NTRS)

    Merriam, Kenneth G; Spaulding, Ellis R

    1935-01-01

    Comparative tests were made on seven conventional Pitot-static tubes to determine their static, dynamic, and resultant errors. The effect of varying the dynamic opening, static opening, wall thickness, and inner-tube diameter was investigated. Pressure-distribution measurements showing stem and tip effects were also made. A tentative design for a standard Pitot-static tube for use in measuring air velocity is submitted.

  16. EXPERIMENTAL BENCHMARKING OF THE MAGNETIZED FRICTION FORCE.

    SciTech Connect

    FEDOTOV, A.V.; GALNANDER, B.; LITVINENKO, V.N.; LOFNES, T.; SIDORIN, A.O.; SMIRNOV, A.V.; ZIEMANN, V.

    2005-09-18

    High-energy electron cooling, presently considered as essential tool for several applications in high-energy and nuclear physics, requires accurate description of the friction force. A series of measurements were performed at CELSIUS with the goal to provide accurate data needed for the benchmarking of theories and simulations. Some results of accurate comparison of experimental data with the friction force formulas are presented.

  17. Experimental research on the friction of pivots

    NASA Technical Reports Server (NTRS)

    Jaquerod, A; Defossez, L; Mugeli, H

    1930-01-01

    In horology the friction between solids is of the greatest importance; one limited, however, to the application of the laws of Coulomb which, do not at all correspond with reality. This report presents a review of the subject and some general conclusions. The choice of lubricant is discussed as well as the pressure between frictional surfaces. The gears in a watch are used extensively as examples.

  18. Friction of Materials for Automotive Applications

    SciTech Connect

    Blau, Peter Julian

    2013-01-01

    This brief overview of friction-related issues in materials for automobiles is invited for a special issue on automotive materials in the ASM journal AM&P. It describes a range of areas in a ground vehicle in which friction must be controlled or minimized. Applications range from piston rings to tires, and from brakes to fuel injector components. A perspective on new materials and lubricants, and the need for validation testing is presented.

  19. Athletic skin injuries: combating pressure and friction.

    PubMed

    Basler, Rodney S W; Hunzeker, Christopher M; Garcia, Michael A

    2004-05-01

    Because the skin is the athlete's first line of defense, it is exposed to friction and pressure in nearly every athletic setting. Whether applied acutely or chronically, friction and pressure often cause skin trauma, such as abrasions, chafing, calluses, blisters, talon noir (black heel), and acne mechanica. Sports medicine clinicians, who regularly see skin injuries, can speed healing by making a timely diagnosis, recommending effective treatment, and discussing prevention strategies. PMID:20086411

  20. Friction analysis between tool and chip

    NASA Astrophysics Data System (ADS)

    Wang, Min; Xu, Binshi; Zhang, Jiaying; Dong, Shiyun

    2010-12-01

    The elastic-plasticity mechanics are applied to analyze the friction between tool and chip. According to the slip-line field theory, a series of theoretical formula and the friction coefficient is derived between the tool and chip. So the cutting process can be investigated. Based on the Orthogonal Cutting Model and the Mohr's circle stress, the cutting mechanism of the cladding and the surface integrity of machining can be studied.

  1. Friction analysis between tool and chip

    NASA Astrophysics Data System (ADS)

    Wang, Min; Xu, Binshi; Zhang, Jiaying; Dong, Shiyun

    2011-05-01

    The elastic-plasticity mechanics are applied to analyze the friction between tool and chip. According to the slip-line field theory, a series of theoretical formula and the friction coefficient is derived between the tool and chip. So the cutting process can be investigated. Based on the Orthogonal Cutting Model and the Mohr's circle stress, the cutting mechanism of the cladding and the surface integrity of machining can be studied.

  2. Frictional behavior of talc-calcite mixtures

    NASA Astrophysics Data System (ADS)

    Giorgetti, C.; Carpenter, B. M.; Collettini, C.

    2015-09-01

    Faults involving phyllosilicates appear weak when compared to the laboratory-derived strength of most crustal rocks. Among phyllosilicates, talc, with very low friction, is one of the weakest minerals involved in various tectonic settings. As the presence of talc has been recently documented in carbonate faults, we performed laboratory friction experiments to better constrain how various amounts of talc could alter these fault's frictional properties. We used a biaxial apparatus to systematically shear different mixtures of talc and calcite as powdered gouge at room temperature, normal stresses up to 50 MPa and under different pore fluid saturated conditions, i.e., CaCO3-equilibrated water and silicone oil. We performed slide-hold-slide tests, 1-3000 s, to measure the amount of frictional healing and velocity-stepping tests, 0.1-1000 µm/s, to evaluate frictional stability. We then analyzed microstructures developed during our experiments. Our results show that with the addition of 20% talc the calcite gouge undergoes a 70% reduction in steady state frictional strength, a complete reduction of frictional healing and a transition from velocity-weakening to velocity-strengthening behavior. Microstructural analysis shows that with increasing talc content, deformation mechanisms evolve from distributed cataclastic flow of the granular calcite to localized sliding along talc-rich shear planes, resulting in a fully interconnected network of talc lamellae from 20% talc onward. Our observations indicate that in faults where talc and calcite are present, a low concentration of talc is enough to strongly modify the gouge's frictional properties and specifically to weaken the fault, reduce its ability to sustain future stress drops, and stabilize slip.

  3. Experimental Benchmarking of the Magnetized Friction Force

    SciTech Connect

    Fedotov, A. V.; Litvinenko, V. N.; Galnander, B.; Lofnes, T.; Ziemann, V.; Sidorin, A. O.; Smirnov, A. V.

    2006-03-20

    High-energy electron cooling, presently considered as essential tool for several applications in high-energy and nuclear physics, requires accurate description of the friction force. A series of measurements were performed at CELSIUS with the goal to provide accurate data needed for the benchmarking of theories and simulations. Some results of accurate comparison of experimental data with the friction force formulas are presented.

  4. Parameter tuning method for dither compensation of a pneumatic proportional valve with friction

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Song, Yang; Huang, Leisheng; Fan, Wei

    2016-04-01

    In the practical application of pneumatic control devices, the nonlinearity of a pneumatic control valve become the main factor affecting the control effect, which comes mainly from the dynamic friction force. The dynamic friction inside the valve may cause hysteresis and a dead zone. In this paper, a dither compensation mechanism is proposed to reduce negative effects on the basis of analyzing the mechanism of friction force. The specific dither signal (using a sinusoidal signal) was superimposed on the control signal of the valve. Based on the relationship between the parameters of the dither signal and the inherent characteristics of the proportional servo valve, a parameter tuning method was proposed, which uses a displacement sensor to measure the maximum static friction inside the valve. According to the experimental results, the proper amplitude ranges are determined for different pressures. In order to get the optimal parameters of the dither signal, some dither compensation experiments have been carried out on different signal amplitude and gas pressure conditions. Optimal parameters are determined under two kinds of pressure conditions. Using tuning parameters the valve spool displacement experiment has been taken. From the experiment results, hysteresis of the proportional servo valve is significantly reduced. And through simulation and experiments, the cut-off frequency of the proportional valve has also been widened. Therefore after adding the dither signal, the static and dynamic characteristics of the proportional valve are both improved to a certain degree. This research proposes a parameter tuning method of dither signal, and the validity of the method is verified experimentally.

  5. Parameter tuning method for dither compensation of a pneumatic proportional valve with friction

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Song, Yang; Huang, Leisheng; Fan, Wei

    2016-05-01

    In the practical application of pneumatic control devices, the nonlinearity of a pneumatic control valve become the main factor affecting the control effect, which comes mainly from the dynamic friction force. The dynamic friction inside the valve may cause hysteresis and a dead zone. In this paper, a dither compensation mechanism is proposed to reduce negative effects on the basis of analyzing the mechanism of friction force. The specific dither signal (using a sinusoidal signal) was superimposed on the control signal of the valve. Based on the relationship between the parameters of the dither signal and the inherent characteristics of the proportional servo valve, a parameter tuning method was proposed, which uses a displacement sensor to measure the maximum static friction inside the valve. According to the experimental results, the proper amplitude ranges are determined for different pressures. In order to get the optimal parameters of the dither signal, some dither compensation experiments have been carried out on different signal amplitude and gas pressure conditions. Optimal parameters are determined under two kinds of pressure conditions. Using tuning parameters the valve spool displacement experiment has been taken. From the experiment results, hysteresis of the proportional servo valve is significantly reduced. And through simulation and experiments, the cut-off frequency of the proportional valve has also been widened. Therefore after adding the dither signal, the static and dynamic characteristics of the proportional valve are both improved to a certain degree. This research proposes a parameter tuning method of dither signal, and the validity of the method is verified experimentally.

  6. 30 CFR 18.26 - Static electricity.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Static electricity. 18.26 Section 18.26 Mineral... § 18.26 Static electricity. Nonmetallic rotating parts, such as belts and fans, shall be provided with a means to prevent an accumulation of static electricity....

  7. 30 CFR 18.26 - Static electricity.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Static electricity. 18.26 Section 18.26 Mineral... § 18.26 Static electricity. Nonmetallic rotating parts, such as belts and fans, shall be provided with a means to prevent an accumulation of static electricity....

  8. 30 CFR 18.26 - Static electricity.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Static electricity. 18.26 Section 18.26 Mineral... § 18.26 Static electricity. Nonmetallic rotating parts, such as belts and fans, shall be provided with a means to prevent an accumulation of static electricity....

  9. 30 CFR 18.26 - Static electricity.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Static electricity. 18.26 Section 18.26 Mineral... § 18.26 Static electricity. Nonmetallic rotating parts, such as belts and fans, shall be provided with a means to prevent an accumulation of static electricity....

  10. 30 CFR 18.26 - Static electricity.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Static electricity. 18.26 Section 18.26 Mineral... § 18.26 Static electricity. Nonmetallic rotating parts, such as belts and fans, shall be provided with a means to prevent an accumulation of static electricity....

  11. 14 CFR 31.61 - Static discharge.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Static discharge. 31.61 Section 31.61... STANDARDS: MANNED FREE BALLOONS Design Construction § 31.61 Static discharge. Unless shown not to be... gas as a lifting means to ensure that the effects of static discharges will not create a hazard....

  12. 14 CFR 31.61 - Static discharge.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Static discharge. 31.61 Section 31.61... STANDARDS: MANNED FREE BALLOONS Design Construction § 31.61 Static discharge. Unless shown not to be... gas as a lifting means to ensure that the effects of static discharges will not create a hazard....

  13. In-Flight Pitot-Static Calibration

    NASA Technical Reports Server (NTRS)

    Foster, John V. (Inventor); Cunningham, Kevin (Inventor)

    2016-01-01

    A GPS-based pitot-static calibration system uses global output-error optimization. High data rate measurements of static and total pressure, ambient air conditions, and GPS-based ground speed measurements are used to compute pitot-static pressure errors over a range of airspeed. System identification methods rapidly compute optimal pressure error models with defined confidence intervals.

  14. Dependence of Internal Friction on Folding Mechanism

    PubMed Central

    2016-01-01

    An outstanding challenge in protein folding is understanding the origin of “internal friction” in folding dynamics, experimentally identified from the dependence of folding rates on solvent viscosity. A possible origin suggested by simulation is the crossing of local torsion barriers. However, it was unclear why internal friction varied from protein to protein or for different folding barriers of the same protein. Using all-atom simulations with variable solvent viscosity, in conjunction with transition-path sampling to obtain reaction rates and analysis via Markov state models, we are able to determine the internal friction in the folding of several peptides and miniproteins. In agreement with experiment, we find that the folding events with greatest internal friction are those that mainly involve helix formation, while hairpin formation exhibits little or no evidence of friction. Via a careful analysis of folding transition paths, we show that internal friction arises when torsion angle changes are an important part of the folding mechanism near the folding free energy barrier. These results suggest an explanation for the variation of internal friction effects from protein to protein and across the energy landscape of the same protein. PMID:25721133

  15. A frictional law for volcanic ash gouge

    NASA Astrophysics Data System (ADS)

    Lavallée, Y.; Hirose, T.; Kendrick, J. E.; De Angelis, S.; Petrakova, L.; Hornby, A. J.; Dingwell, D. B.

    2014-08-01

    Volcanic provinces are structurally active regions - undergoing continual deformation along faults. Within such fault structures, volcanic ash gouge, containing both crystalline and glassy material, may act as a potential fault plane lubricant. Here, we investigate the frictional properties of volcanic ash gouges with varying glass fractions using a rotary shear apparatus at a range of slip rates (1.3-1300 mm/s) and axial stresses (0.5-2.5 MPa). We show that the frictional behaviour of volcanic ash is in agreement with Byerlee's friction law at low slip velocities, irrespective of glass content. The results reveal a common non-linear reduction of the friction coefficient with slip velocity and yield a frictional law for fault zones containing volcanic ash gouge. Textural analysis reveals that strain localisation and the development of shear bands are more prominent at higher slip velocities (>10 mm/s). The textures observed here are similar to those recorded in ash gouge at the surface of extrusive spines at Mount St. Helens (USA). We use the rate-weakening component of the frictional law to estimate shear-stress-resistance reductions associated with episodic seismogenic slip events that accompany magma ascent pulses. We conclude that the internal structure of volcanic ash gouge may act as a kinematic marker of exogenic dome growth.

  16. Analysis of operation of new construction of the frictional joint with the resistance wedge / Analiza pracy nowej konstrukcji złącza ciernego z klinem oporowym

    NASA Astrophysics Data System (ADS)

    Brodny, Jarosław

    2012-10-01

    Frictional joint is the basic part of the friction props and yielding steel frames of dog headings. It constitutes a constructional connection and have decisive influence on the basic operational parameters of the steel frames and props, i.e. their loading capacity and yielding capacity. Currently applied constructions of frictional joints characterize with low loading capacity and unstable operation. In order to improve their operational parameters a new constructional solution of frictional joint, consisting on the application of resistance wedge assembled between the cooperating sections, was developed. Application of the resistance wedge caused an increase of resistances to motion in the frictional joint, what influenced on the increase of its loading capacity and on the increase of values of axial forces in the bolts of stirrups. In the paper results of stand tests of frictional joints with the resistance wedge, subjected to the static axial compression and impact of freely falling mass, were presented. In order to determine the influence of the resistance wedge on the operational parameters of the frictional joint, obtained results were compared with the results of studies of the frictional joints without the resistance wedge. On the basis of stand tests a physical and mathematical models of the frictional joint with the resistance wedge, were developed, and utilized to simulation analysis of its operation at impulse loading. On the basis of conducted tests and analysis one can state, that application of the resistance wedge influences on the enhancement of loading capacity, improves the state of loading the bolts in stirrups, and creates possibility of regulation of operational characteristics of the frictional joints

  17. What causes frictional behavior in fluid-mediated sediment transport?

    NASA Astrophysics Data System (ADS)

    Pähtz, Thomas; Duran, Orencio

    2016-04-01

    Bagnoldian analytical models of sediment transport in Newtonian fluid (e.g., air or water) are based on Bagnold's assumption of a constant friction coefficient (particle-shear-pressure ratio, μ) at the interface (z = zb) between sediment bed and transport layer. In fact, this assumption is the main reason why these models predict the sediment load (which is the ratio between sediment transport rate and average particle velocity) to be proportional to the excess shear stress (τ ‑ τt), a scaling that has been confirmed in many wind-tunnel and flume experiments. Here, using numerical simulations with the coupled DEM/RANS model of sediment transport in Newtonian fluid by Duran et al. (POF, 103306, 2012), we investigate the physical reasons for this frictional behavior. In the case of subaqueous transport, we find that a local rheology μ(I), where I is the viscous number, can explain most of the simulation data. However, this rheology breaks down for aeolian transport. In an attempt to unify these transport regimes, we propose a novel characterization of frictional behavior through the dimensionless parameter ζ = ⟨Fxcvx ‑ Fzcvz⟩/⟨Fzcvx ‑ Fxcvz⟩, where Fc is the contact force, v the particle velocity, and ⟨ṡ⟩ a local ensemble average. We analytically derive ζ ≈√3 ‑ 1 for locations within the transport layer and slightly within the particle bed, where each derivation step and the final result are consistent with our numerical simulations throughout all simulated conditions. Our derivation is mainly based on the assumption that the conversion of horizontal kinetic particle energy into vertical kinetic particle energy in low-angle particle-bed impacts is the predominant collisional energy transformation process occurring in sediment transport. We then show that ζ(zs) ≈ μ(zs), where zs is the location at which the local production rate of particle fluctuation energy is maximal, and thus μ(zs) ≈√3- ‑ 1. This final result, which

  18. Numerical implementation of a state variable model for friction

    SciTech Connect

    Korzekwa, D.A.; Boyce, D.E.

    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.

  19. Structure-property relationships of dissimilar friction stir welded aluminum alloys

    NASA Astrophysics Data System (ADS)

    Quinones, Rogie Irwin Rodriguez

    In this work, the relationship between microstructure and mechanical properties of dissimilar friction stir welded AA6061-to-AA7050 aluminum alloys were evaluated. Experimental results from this study revealed that static strength increased with the tool rotational speed and was correlated with the material intermixing. Fully-reversed low cycle fatigue experimental results showed an increase in the strain hardening properties as well as the number of cycles-to-failure as the tool rotational speed was increased. Furthermore, under both static and cyclic loading, fracture of the joint was dominated by the AA6061 alloy side of the weld. In addition, inspection of the fatigue surfaces revealed that cracks initiated from intermetallic particles located near the surface. In order to determine the corrosion resistance of the dissimilar joint, corrosion defects were produced on the crown surface of the weld by static immersion in 3.5% NaCl for various exposure times. Results revealed localized corrosion damage in the thermo-mechanically affected and heat affected zones. Results demonstrated a decrease in the fatigue life, with evidence of crack initiation at the corrosion defects; however, the fatigue life was nearly independent of the exposure time. This can be attributed to total fatigue life dominated by incubation time. Furthermore, two types of failure were observed: fatigue crack initiation in the AA6061 side at high strain amplitudes (>0.3%); and fatigue crack initiation in the AA7050 side at low strain amplitudes (<0.2%). Lastly, a microstructure-sensitive model based on a multi-stage fatigue damage concept was extended to the dissimilar friction stir welded joints in order to capture the crack initiation and propagation in as-welded and pre-corroded conditions. Good correlation between experimental fatigue results and the model was achieved based on the variation in the initial defect size, microstructure, and mechanical properties of the dissimilar friction stir

  20. Breakway friction and dynamic friction/wear measurements of various ceramic materials from 25 C (75 F) to 650 C (1200 F)

    NASA Technical Reports Server (NTRS)

    Boes, D. J.

    1984-01-01

    This report describes the results of a program designed to evaluate the breakaway friction and dynamic friction/wear characteristics of materials having potential for use as load bearing components in a high-performance high-temperature heavy duty diesel engine. Ten candidate materials were selected, six of which were evaluated under all possible material combinations as both stationary as well as moving breakaway specimens. The remaining materials were evaluated either in the static mode against themselves and all other materials, or against themselves only. Experiments were performed at five temperatures up to 650 C (1200 F) and unit pressures of 700 kPa (100 lb/sq in.), 3500 kPa (500 lb/sq in.), and 7000 kPa (1000 lb/sq in.). Experimental results indicate that under dynamic conditions, four of the ten materials exhibited good to excellent friction/wear characteristics in various material combinations. These materials were: titanium carbide, silicon nitride, silicon carbide (reaction sintered), and Refel (SiC).

  1. Ice friction: Role of non-uniform frictional heating and ice premelting

    NASA Astrophysics Data System (ADS)

    Persson, B. N. J.

    2015-12-01

    The low friction of ice is usually attributed to the formation of a thin water film due to melting of ice by frictional heating. Melting of ice is a first order phase transition where physical quantities like mass density, the elastic modulus or the shear strength changes abruptly at the transition temperature. Thus, one may expect the friction coefficient to change abruptly at some characteristic sliding speed, when the melt water film is produced. We show that taking into account that, due to non-uniform frictional heating, melting does not occur simultaneously in all the ice contact regions, the transition is not abrupt but still more rapid (as a function of sliding speed) than observed experimentally. The slower than expected drop in the friction with increasing sliding speed may be a consequence of the following paradoxical phenomena: before the melt-water film is formed, the friction of ice is high and a large frictional heating occur which may result in the melting of the ice. If a thin (nanometer) water film would form, the friction becomes low which results in small frictional heating and the freezing of the water film. This suggests a region in sliding speed where a thin (nanometer) surface layer of the ice may be in a mixed state with small ice-like and water-like domains, which fluctuate rapidly in space and time. Alternatively, and more likely, heat-softening of the ice may occur resulting in a thin, statistically homogeneous (in the lateral direction) layer of disordered ice, with a shear strength which decreases continuously as the ice surface temperature approaches the bulk melting temperature. This layer could be related to surface premelting of ice. Using a phenomenological expression for the frictional shear stress, I show that the calculated ice friction is in good agreement with experimental observations.

  2. Stress propagation and Arching in Static Sandpiles

    NASA Astrophysics Data System (ADS)

    Wittmer, J. P.; Cates, M. E.; Claudin, P.

    1997-01-01

    We present a new approach to the modelling of stress propagation in static granular media, focussing on the conical sandpile constructed from a point source. We view the medium as consisting of cohesionless hard particles held up by static frictional forces; these are subject to microscopic indeterminacy which corresponds macroscopically to the fact that the equations of stress continuity are incomplete no strain variable can be defined. We propose that in general the continuity equations should be closed by means of a constitutive relation (or relations) between different components of the (mesoscopically averaged) stress tensor. The primary constitutive relation relates radial and vertical shear and normal stresses (in two dimensions, this is all one needs). We argue that the constitutive relation(s) should be local, and should encode the construction history of the pile: this history determines the organization of the grains at a mesoscopic scale, and thereby the local relationship between stresses. To the accuracy of published experiments, the pattern of stresses beneath a pile shows a scaling between piles of different heights (RSF scaling) which severely limits the form the constitutive relation can take; various asymptotic features of the stress patterns can be predicted on the basis of this scaling alone. To proceed further, one requires an explicit choice of constitutive relation; we review some from the literature and present two new proposals. The first, the FPA (fixed principal axes) model, assumes that the eigendirections (but not the eigenvalues) of the stress tensor are determined forever when a material element is first buried. (This assumes, among other things, that subsequent loadings are not so large as to produce slip deep inside the pile.) A macroscopic consequence of this mesoscopic assumption is that the principal axes have fixed orientation in space: the major axis everywhere bisects the vertical and the free surface. As a result of this

  3. Friction Stir Processing for Efficient Manufacturing

    SciTech Connect

    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

  4. Static feed water electrolysis module

    NASA Technical Reports Server (NTRS)

    Powell, J. D.; Schubert, F. H.; Jensen, F. C.

    1974-01-01

    An advanced static feed water electrolysis module (SFWEM) and associated instrumentation for generating breathable O2 was developed. The system also generates a H2 byproduct for use in an air revitalization system for O2 recovery from metabolic CO2. Special attention was given to: (1) eliminating water feed compartment degassing, (2) eliminating need for zero gravity condenser/separators, (3) increasing current density capability, and (4) providing a self contained module so that operation is independent of laboratory instrumentation and complicated startup/shutdown procedures.

  5. High-velocity drag friction in granular media near the jamming point.

    PubMed

    Takehara, Yuka; Okumura, Ko

    2014-04-11

    Drag friction that acts on a disk in a two-dimensional granular medium is studied at high packing fractions. We concentrate on a high-velocity region, in which the dynamic component of the force, obtained as an average of a strongly fluctuating force, clearly scales with velocity squared. We find that the total force composed of dynamic and static components, as well as its fluctuation, diverges with practically the same exponent as the packing fraction approaches the jamming point. To explain the critical behavior, we propose a simple theory equipped with a diverging length scale, which agrees well with the data and elucidates physical pictures for the divergence. PMID:24766018

  6. The obstacle block as a device to measure turbulent skin friction in compressible flow

    NASA Technical Reports Server (NTRS)

    Elfstrom, G. M.; Kostopoulos, C.; Peake, D. J.; Fisher, D. F.

    1982-01-01

    The obstacle block, developed as an alternative to the Preston tube for indirectly measuring skin friction on smooth surfaces in incompressible flows, is examined as a device for compressible flows as well. The block, which is congruent with a surface static pressure orifice, has a geometry which is easily specified and thus has a universal calibration. Data from two independent studies are used to establish such a calibration using 'wall' variables, valid for Mach numbers up to about 3. Various aspects concerning practical application of the device are examined, such as sensitivity to yaw and the minimum permissible axial spacing between blocks. Several examples showing the utility of the device are given.

  7. Frictional temperature rise in a sliding physisorbed monolayer of Kr/graphene

    NASA Astrophysics Data System (ADS)

    Walker, M.; Jaye, C.; Krim, J.; Cole, Milton W.

    2012-10-01

    A quartz crystal microbalance (QCM) with a graphene/Ni(111) electrode has been used to probe frictional heating effects in Kr monolayers sliding on the microbalance electrode in response to its oscillatory motion. The temperatures of the sliding Kr monolayers are observed to rise approximately 13 K higher than their static counterparts, but show surprisingly little dependence on oscillation amplitude. Although counterintuitive, the observation can be explained by noting that the Kr surface residence times are limited, which effectively caps how much the temperature can rise.

  8. Static and transient modeling of fast moving ball actuator as a display device

    NASA Astrophysics Data System (ADS)

    Lee, Jongmo; Yoon, Ho Won; Hong, MunPyo; Jhun, Chul Gyu; Bae, Byung Seong; Han, Seungoh

    2016-04-01

    FMBA(Fast Moving Ball Actuator), developed as novel electronic-paper display, has already proven its operability and functionality. However, optimization issues related with low operating voltage, high refresh rate, fine pixel and higher display resolution, etc. are still remaining to be improved for a successful commercialization. In order to optimize such issues effectively, static and transient model were developed and verified by comparing the calculated results to the measured. The static model is based on the force balancing equation between the driving and the holding forces while the transient model is developed from Newton's 2nd law by adding the inertia as well as the resistive damping forces caused by the surroundings. With the simplified static model, driving voltage of 30.71 V was obtained, which is reasonably matched to the measured voltage of 40 V. Based on the transient model, also, the transient response of the device can be estimated within reasonable margin. Considering the absence of reliable key parameters of surface roughness, static and dynamic frictional coefficient, and refractive indices, the developed static and transient models account well the experimental results and thus they are expected to contribute further improvements in FMBA.

  9. Measurement of static pressure on aircraft

    NASA Technical Reports Server (NTRS)

    Gracey, William

    1958-01-01

    Existing data on the errors involved in the measurement of static pressure by means of static-pressure tubes and fuselage vents are presented. The errors associated with the various design features of static-pressure tubes are discussed for the condition of zero angle of attack and for the case where the tube is inclined to flow. Errors which result from variations in the configuration of static-pressure vents are also presented. Errors due to the position of a static-pressure tube in the flow field of the airplane are given for locations ahead of the fuselage nose, ahead of the wing tip, and ahead of the vertical tail fin. The errors of static-pressure vents on the fuselage of an airplane are also presented. Various methods of calibrating static-pressure installations in flight are briefly discussed.

  10. First arrival time surface, estimation of statics

    SciTech Connect

    Chun, J.H.; Jacewitz, C.A.

    1983-09-05

    The problem of obtaining surface consistent statics using first arrival refractions has several phases. To begin with, the first arrivals must be picked in some reasonable, consistent fashion. Next, appropriate techniques must be used to solve for surface-consistent statics. Finally, the interpreter must be provided with an evaluation of the quality of the estimated statics. First arrival refractions are part of reflection seismic data. Early seismic reflection work used first arrival refractions for weathering static corrections. With the advent of the common midpoint (CMP) method, first arrivals lost their predominance in statics to correlation techniques within CMP gathers. However, the increasing use of a large number of receivers and a small group interval has made first arrival statics more reliable. In addition, recent work has helped to revitalize interest in the use of first arrival refractions for surface-consistent static corrections.

  11. Status of Stellite 6 friction testing

    SciTech Connect

    Watkins, J.C.; DeWall, K.G.; Weidenhamer, G.H.

    1998-06-01

    For the past several years, researchers at the Idaho National Engineering and Environmental Laboratory, under the sponsorship of the US Nuclear Regulatory Commission, Office of Nuclear Regulatory Research, have been investigating the performance of motor-operated valves subjected to design basis flow and pressure loads. Part of this research addresses the friction that occurs at the interface between the valve disc and the valve body seats during operation of a gate valve. In most gate valves, these surfaces are hardfaced with Stellite 6, a cobalt-based alloy. Analytical methods exist for predicting the thrust needed to operate these valves at specific pressure conditions. To produce accurate valve thrust predictions, the analyst must have a reasonably accurate, though conservative, estimate of the coefficient of friction at the disc-to-seat interface. One of the questions that remains to be answered is whether, and to what extent, aging of the disc and seat surfaces effects the disc-to-seat coefficient of friction. Specifically, does the environment in a nuclear plants piping system cause the accumulation of an oxide film on these surfaces that increases the coefficient of friction; and if so, how great is the increase? This paper presents results of specimen tests addressing this issue, with emphasis on the following: (1) the characteristics and thickness of the oxide film that develops on Stellite 6 as it ages; (2) the change in the friction coefficient of Stellite 6 as it ages, including the question of whether the friction coefficient eventually reaches a plateau; and (3) the effect in-service cycling has on the characteristics and thickness of the oxide film and on the friction coefficient.

  12. Mechanisms of friction in diamondlike nanocomposite coatings

    SciTech Connect

    Scharf, T. W.; Ohlhausen, J. A.; Tallant, D. R.; Prasad, S. V.

    2007-03-15

    Diamondlike nanocomposite (DLN) coatings (C:H:Si:O) processed from siloxane precursors by plasma enhanced chemical vapor deposition are well known for their low friction and wear behaviors. In the current study, we have investigated the fundamental mechanisms of friction and interfacial shear strength in DLN coatings and the roles of contact stress and environment on their tribological behavior. Friction and wear measurements were performed from 0.25 to 0.6 GPa contact pressures in three environments: dry (<1% RH) nitrogen, dry (<1% RH) air, and humid (50% RH) air, with precise control of dew point and oxygen content. At 0.3 GPa contact stress, the coefficient of friction (COF) in dry nitrogen was extremely low, {approx}0.02, whereas in humid air it increased to {approx}0.2, with minimal amount of wear in both environments. The coatings also exhibited non-Amontonian friction behavior, with COF decreasing with an increase in Hertzian contact stress. The main mechanism responsible for low friction and wear under varying contact stresses and environments is governed by the interfacial sliding between the DLN coating and the friction-induced transfer film adhered to the ball counterface. This interfacial shear strength, computed from COF-inverse Hertzian contact stress plots, was found to be 9 MPa in dry nitrogen and 78 MPa in humid air. Time-of-flight secondary ion mass spectroscopy analysis of the interfaces (wear tracks and transfer films) was used to explain the tribochemical effects in both environments. The transfer films generated in humid air were found to be enriched with SiO{sub 2} containing fragments, whereas those formed in dry nitrogen had hydrogenated and long range ordered carbons with practically no SiO{sub 2} fragments, ultimately resulting in much lower interfacial shear strength and COF.

  13. Gimballed Shoulders for Friction Stir Welding

    NASA Technical Reports Server (NTRS)

    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.

  14. Ultralow Friction in a Superconducting Magnetic Bearing

    NASA Technical Reports Server (NTRS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  16. Effect of sliding friction on the dynamics of spur gear pair with realistic time-varying stiffness

    NASA Astrophysics Data System (ADS)

    He, Song; Gunda, Rajendra; Singh, Rajendra

    2007-04-01

    The chief objective of this article is to propose a new method of incorporating the sliding friction and realistic time-varying stiffness into an analytical (multi-degree-of-freedom) spur gear model and to evaluate their effects. An accurate finite element/contact mechanics analysis code is employed, in the "static" mode, to compute the mesh stiffness at every time instant under a range of loading conditions. Here, the time-varying stiffness is calculated as an effective function which may also include the effect of profile modifications. The realistic mesh stiffness is then incorporated into the linear time-varying spur gear model with the contributions of sliding friction. Proposed methods are illustrated via two spur gear examples and validated by using the finite element in the "dynamic" mode as experimental results. A key question whether the sliding friction is indeed the source of the off-line-of-action forces and motions is then answered by our analytical model. Finally, the effect of the profile modification on the dynamic transmission error has been analytically examined under the influence of sliding friction. For instance, the linear tip relief introduces an amplification in the off-line-of-action forces and motions due to an out of phase relationship between the normal load and friction forces.

  17. Static behaviour of induced seismicity

    NASA Astrophysics Data System (ADS)

    Mignan, Arnaud

    2016-04-01

    The standard paradigm to describe seismicity induced by fluid injection is to apply non-linear diffusion dynamics in a poroelastic medium. I show that the spatio-temporal behaviour and rate evolution of induced seismicity can, instead, be expressed by geometric operations on a static stress field produced by volume change at depth. I obtain laws similar in form to the ones derived from poroelasticity while requiring a lower description length. Although fluid flow is known to occur in the ground, it is not pertinent to the geometrical description of the spatio-temporal patterns of induced seismicity. The proposed model is equivalent to the static stress model for tectonic foreshocks generated by the Non-Critical Precursory Accelerating Seismicity Theory. This study hence verifies the explanatory power of this theory outside of its original scope and provides an alternative physical approach to poroelasticity for the modelling of induced seismicity. The applicability of the proposed geometrical approach is illustrated for the case of the 2006, Basel enhanced geothermal system stimulation experiment. Applicability to more problematic cases where the stress field may be spatially heterogeneous is also discussed.

  18. Electrowetting -- from statics to dynamics.

    PubMed

    Chen, Longquan; Bonaccurso, Elmar

    2014-08-01

    More than one century ago, Lippmann found that capillary forces can be effectively controlled by external electrostatic forces. As a simple example, by applying a voltage between a conducting liquid droplet and the surface it is sitting on we are able to adjust the wetting angle of the drop. Since Lippmann's findings, electrocapillary phenomena - or electrowetting - have developed into a series of tools for manipulating microdroplets on solid surfaces, or small amounts of liquids in capillaries for microfluidic applications. In this article, we briefly review some recent progress of fundamental understanding of electrowetting and address some still unsolved issues. Specifically, we focus on static and dynamic electrowetting. In static electrowetting, we discuss some basic phenomena found in DC and AC electrowetting, and some theories about the origin of contact angle saturation. In dynamic electrowetting, we introduce some studies about this rather recent area. At last, we address some other capillary phenomena governed by electrostatics and we give an outlook that might stimulate further investigations on electrowetting. PMID:24268972

  19. Static-field-induced states

    NASA Astrophysics Data System (ADS)

    Gets, Artem V.; Tolstikhin, Oleg I.

    2013-01-01

    Considering an electron interacting with an atomic or molecular potential and an external static electric field, one usually focuses on narrow resonances at negative energies originating from the bound states in the absence of the field; we call them tunneling states (TSs). Meanwhile, there also exist relatively broad resonances at positive energies having no counterparts in the absence of the field; we call them static-field-induced states (SFISs). In this paper, the recently developed weak-field asymptotic theory of TSs [O. I. Tolstikhin , Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.84.053423 84, 053423 (2011)] is extended to SFISs. An asymptotic quantization condition defining the energies of SFISs in an arbitrary potential in the three-dimensional case is derived. The parabolic scattering amplitudes appearing in this quantization condition are defined. The theory is illustrated by calculations for the zero-range and Coulomb potentials. The SFISs in these potentials are found and their energies are shown to be in good agreement with the asymptotic results over a wide interval of the values of the field.

  20. Busulfan kinetics.

    PubMed

    Ehrsson, H; Hassan, M; Ehrnebo, M; Beran, M

    1983-07-01

    Busulfan kinetics were studied in patients with chronic myelocytic leukemia after oral doses of 2, 4, and 6 mg. The plasma concentration-time data could be fitted to a zero-order absorption one-compartment open model. The elimination rate constant averaged 0.27 +/- 0.05 hr-1 (SD). The plasma AUC was linearly related to the dose. The lag time for the start of absorption, the time absorption ends, and the absorption rate constant showed some interindividual variations. About 1% of busulfan is excreted unchanged in urine over 24 hr. PMID:6574831

  1. Texture and grain evolutions in a 2195 friction stire weld

    SciTech Connect

    Fonda, R. W.; Bingert, J. F.; Colligan, K. J.

    2004-01-01

    Variations in microstructure, crystallographic texture, and grain distributions were determined in a conventional transverse cross section of the deposited weld and in a planview cross section around the embedded welding tool in an Al 2195 friction stir weld that had been prepared to preserve a static representation of the dynamic deformation field surrounding the tool. These results reveal important new details about the development of grain structure and crystallographic texture around the FSW tool that cannot be determined from observations on the transverse cross section alone. Two orthogonal views of a friction stir weld were analyzed to determine the microstructure, crystallographic texture, and grain structure of the deposited weld and how these characteristics initially developed in the vicinity of the weld tool. The transverse cross section reveals many interesting features. There is a complex precipitation sequence across the different weld regions. The strengthening precipitates from the matrix become coarsened across the HAZ, then are gradually replaced by a separate precipitate distribution, which forms during cooling of the weld, in the TMAZ. A third precipitate distribution that includes the equilibrium T{sub B} phase is observed in the weld nugget and is responsible for the lower microhardness of that region. A coarsening of grains is observed in the TMAZ adjacent to the weld nugget, accompanied by an in-plane rotation of the grains towards <110>{parallel} welding direction. The latter observation suggests that this texture evolution is primarily in response to a simple-shear deformation field surrounding the tool. A plan-view section through the embedded FSW tool of this stop-action weld was prepared to reveal the initial development and evolution of the grain structure and crystallographic texture during friction stir welding. This analysis revealed bands of refined grains developing ahead of the fully refined region, likely reflecting different

  2. Low-Temperature Friction-Stir Welding of 2024 Aluminum

    NASA Technical Reports Server (NTRS)

    Benavides, S.; Li, Y.; Murr, L. E.; Brown, D.; McClure, J. C.

    1998-01-01

    Solid state friction-stir welding (FSW) has been demonstrated to involve dynamic recrystallization producing ultra-fine, equiaxed grain structures to facilitate superplastic deformation as the welding or joining mechanism. However, the average residual, equiaxed, grain size in the weld zone has ranged from roughly 0.5 micron to slightly more than 10 micron, and the larger weld zone grain sizes have been characterized as residual or static grain growth as a consequence of the temperatures in the weld zone (where center-line temperatures in the FSW of 6061 Al have been shown to be as high as 480C or -0.8 T(sub M) where T(sub M) is the absolute melting temperature)). In addition, the average residual weld zone grain size has been observed to increase near the top of the weld, and to decrease with distance on either side of the weld-zone centerline, an d this corresponds roughly to temperature variations within the weld zone. The residual grain size also generally decreases with decreasing FSW tool rotation speed. These observations are consistent with the general rules for recrystallization where the recrystallized grain size decreases with increasing strain (or deformation) at constant strain rate, or with increasing strain-rate, or with increasing strain rate at constant strain; especially at lower ambient temperatures, (or annealing temperatures). Since the recrystallization temperature also decreases with increasing strain rate, the FSW process is somewhat complicated because the ambient temperature, the frictional heating fraction, and the adiabatic heating fraction )proportional to the product of strain and strain-rate) will all influence both the recrystallization and growth within the FSW zone. Significantly reducing the ambient temperature of the base metal or work pieces to be welded would be expected to reduce the residual weld-zone grain size. The practical consequences of this temperature reduction would be the achievement of low temperature welding. This

  3. Friction drive and bogies for OWL's main axes, technological step backwards or cost effective alternative?

    NASA Astrophysics Data System (ADS)

    Brunetto, Enzo; Koch, Franz; Biancat Marchet, F.; Dimmler, Martin

    2003-01-01

    The drive and bearing technologies have a major impact on the static and dynamic performances of a steerable telescope. The costs related to the complexity of the design and its Reliability, Availability, Maintainability and Safety (RAMS) are not negligible. The design constraints of Extremely Large Telescopes (ELT) depart from those applicable to the current generation of 8 to 10 meter class telescopes, thus suggesting that alternative solutions should be investigated. This paper discusses the feasibility of implementing a design based on friction drives and bogies, tailored to OWL"s azimuthal and altitude degrees of freedom. The estimated static and dynamic performance of the mechanical structure, the achievable angular resolution, the optimal distribution of loads and stresses, the RAMS performance and finally its cost efficiency, make this solution particularly attractive.

  4. Assessment of Local Friction in Protein Folding Dynamics Using a Helix Cross-Linker

    PubMed Central

    Markiewicz, Beatrice N.; Jo, Hyunil; Culik, Robert M.; DeGrado, William F.; Gai, Feng

    2013-01-01

    Internal friction arising from local steric hindrance and/or the excluded volume effect plays an important role in controlling not only the dynamics of protein folding but also conformational transitions occurring within the native state potential well. However, experimental assessment of such local friction is difficult because it does not manifest itself as an independent experimental observable. Herein, we demonstrate, using the miniprotein trp-cage as a testbed, that it is possible to selectively increase the local mass density in a protein and hence the magnitude of local friction, thus making its effect directly measureable via folding kinetic studies. Specifically, we show that when a helix cross-linker, m-xylene, is placed near the most congested region of the trp-cage it leads to a significant decrease in both the folding rate (by a factor of 3.8) and unfolding rate (by a factor of 2.5 at 35 °C), but has little effect on protein stability. Thus, these results, in conjunction with those obtained with another cross-linked trp-cage and two uncross-linked variants, demonstrate the feasibility of using a non-perturbing cross-linker to help quantify the effect of internal friction. In addition, we estimate that an m-xylene cross-linker could lead to an increase in the roughness of the folding energy landscape by as much as 0.4-1.0kBT. PMID:24205975

  5. Static and flowing regions in granular collapses down channels: Insights from a sedimenting shallow water model

    NASA Astrophysics Data System (ADS)

    Doyle, Emma E.; Huppert, Herbert E.; Lube, Gert; Mader, Heidy M.; Sparks, R. Stephen J.

    2007-10-01

    A two layer model for the collapse and spreading of a granular column is presented. This model builds upon that of Larrieu et al. [J. Fluid Mech. 554, 669 (2006)] where the free fall collapse of the column and subsequent flow of material onto a plane is represented by a "raining" mass source term into a thin flowing layer of constant density. These modified shallow water equations with Coulomb friction capture the free surface of the flows and key scaling laws for initial sand columns of aspect ratios up to a <10. However, unrealistically high coefficients of friction of μ =0.9 are required to reproduce run-outs observed. Key scaling laws for high aspect ratio columns are also not captured. We thus extend the model of Larrieu (2006) to include an estimation for the interface between the static and flowing regions observed within granular collapses in the laboratory by Lube et al. [Phys. Fluids 19, 043301 (2007)]. An empirical sedimentation term Ls and the instantaneous removal of a static deposit wedge, seen in the laboratory, are incorporated into the "raining" shallow water model. The growing static deposit surface provides a basal topography for the flowing layer. For a constant empirical sedimentation rate of Ls=0.20m/s, a coefficient of friction of μ =0.4 simulates comparable run-outs to laboratory observations. The correct run-out dependence of a2/3 for columns of aspect ratio a >3 is also captured. Simulating this behavior for values of a above 10 has not been possible with previous continuum models. In addition, this model captures the correct dependence of final run-out time upon a0.5. The application of this extends beyond observed and simulated collapses, to sedimenting highly concentrated debris flows, useful in the development of large mechanistic numerical models utilized in hazard assessment.

  6. β-Relaxation of PMMA: Tip Size and Stress Effects in Friction Force Microscopy.

    PubMed

    Sondhauss, Johannes; Lantz, Mark; Gotsmann, Bernd; Schirmeisen, André

    2015-05-19

    The kinetic signature of the β-relaxation of poly(methyl methacrylate) (PMMA) is investigated by friction force microscopy. The variation in friction force was measured as a function of scan velocity, temperature (300 K-410 K), and applied load using both sharp and blunt probe tips. The friction data show distinct maxima, which can be ascribed to the β-relaxation of PMMA. The contact area was varied over the ranges of approximately 20 to 70 nm(2) and 12,000 to 43,000 nm(2) through the use of probe tips with radii of approximately 15, 18, 1350, and 2650 nm. Kinetic analysis shows that the apparent activation energy of the β-relaxation decreases with the tip radius. Accompanying finite element simulations indicate that for the sharp tips a substantial subvolume of the polymer underneath the tip exceeds the yield stress of PMMA. This suggests that for small contact sizes and high stresses the activation barrier of the β-process decreases through the activation of the α-process by material yielding. PMID:25927251

  7. Spatial Heterogeneity Induces Scale Dependent Rock Friction

    NASA Astrophysics Data System (ADS)

    Yamashita, F.; Fukuyama, E.; Xu, S.; Takizawa, S.; Mizoguchi, K.; Kawakata, H.; Passelègue, F. X.; Schubnel, A.

    2014-12-01

    We carried out large-scale biaxial friction experiments (Fukuyama et al., 2012; 2014) using a pair of meter-sized Indian gabbro as specimens, whose contacting area was 1.5 × 0.1 m2, normal stress was up to 6.7 MPa and loading velocity was up to 3 × 10-2 m/s. After each experiment, we found localized damages (i.e. grooves) were generated on the fault surface and gouges were distributed around them. We confirmed work rate dependency of rock friction as revealed by centimeter-sized rock samples (Di Toro et al., 2011), but further found that the meter-sized rock friction starts to decrease at one order of magnitude smaller work rate than that of the centimeter sized rock (Yamashita et al., 2013, AGU fall meeting). Here, we concluded that this difference is caused by stress localization and associated increase in heterogeneity on the fault as shown by: 1) Total amount of deviations of each local shear stress from the average, which were monitored by strain gauge array, increased with the decrease in friction. 2) Friction coefficients were negatively correlated with degree of spatial heterogeneity evaluated from the distribution of grooves and gouges. 3) Melt textures were found in the collected gouges by microscopic observation using HRSEM. Based on these observations, we propose a stress localization model; the fault surfaces are composed of patched and non-patched areas with high and low normal stress, respectively. The high normal stress patch leads to high shear stress, high mechanical work and thus production of much wear material (gouge), which further causes additional increase in normal stress. Assuming that the local friction follows the results by centimeter-sized gabbro experiments, we numerically simulated a slip-dependent friction for both patched and non-patched areas, and successively reproduced a weakening in macroscopic friction. We confirmed that the work rate dependency of simulated friction was consistent with that of biaxial experiments (Fig. 1

  8. Microblowing Technique Demonstrated to Reduce Skin Friction

    NASA Technical Reports Server (NTRS)

    Hwang, Danny P.; Biesiadny, Tom J.

    1998-01-01

    One of the most challenging areas of research in aerodynamics is the reduction of skin friction, especially for turbulent flow. Reduced skin friction means less drag. For aircraft, less drag can lead to less fuel burned or to a greater flight range for a fixed amount of fuel. Many techniques and methods have been tried; however, none of them has significantly reduced skin friction in the flight environment. An innovative skin-friction reduction technique, the Microblowing Technique (MBT), was invented in 1993. This is a unique concept in which an extremely small amount of air is blown vertically at a surface through very small holes. It can be used for aircraft or marine vehicles, such as submarines (where water is blown through the holes instead of air). As shown in the figure, the outer layer, which controls vertical flow, is a plate with high-vertical holes. The inner layer, which produces evenly distributed flow, is a low-permeability porous plate. Microblowing reduces the surface roughness and changes the flow velocity profile on the surface, thereby reducing skin friction.

  9. Assessing the clarity of friction ridge impressions.

    PubMed

    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. PMID:23313600

  10. Time dependent friction in a free gas

    NASA Astrophysics Data System (ADS)

    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.

  11. Friction characteristics of trocars in laparoscopic surgery.

    PubMed

    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. PMID:25825419

  12. Friction and Wear on the Atomic Scale

    NASA Astrophysics Data System (ADS)

    Gnecco, Enrico; Bennewitz, Roland; Pfeiffer, Oliver; Socoliuc, Anisoara; Meyer, Ernst

    Friction has long been the subject of research: the empirical da Vinci-Amontons friction laws have been common knowledge for centuries. Macroscopic experiments performed by the school of Bowden and Tabor revealed that macroscopic friction can be related to the collective action of small asperities. Over the last 15 years, experiments performed with the atomic force microscope have provided new insights into the physics of single asperities sliding over surfaces. This development, together with the results from complementary experiments using surface force apparatus and the quartz microbalance, have led to the new field of nanotribology. At the same time, increasing computing power has permitted the simulation of processes that occur during sliding contact involving several hundreds of atoms. It has become clear that atomic processes cannot be neglected when interpreting nanotribology experiments. Even on well-defined surfaces, experiments have revealed that atomic structure is directly linked to friction force. This chapter will describe friction force microscopy experiments that reveal, more or less directly, atomic processes during sliding contact.

  13. Tolrestat kinetics

    SciTech Connect

    Hicks, D.R.; Kraml, M.; Cayen, M.N.; Dubuc, J.; Ryder, S.; Dvornik, D.

    1984-10-01

    The kinetics of tolrestat, a potent inhibitor of aldose reductase, were examined. Serum concentrations of tolrestat and of total /sup 14/C were measured after dosing normal subjects and subjects with diabetes with /sup 14/C-labeled tolrestat. In normal subjects, tolrestat was rapidly absorbed and disappearance from serum was biphasic. Distribution and elimination t 1/2s were approximately 2 and 10 to 12 hr, respectively, after single and multiple doses. Unchanged tolrestat accounted for the major portion of /sup 14/C in serum. Radioactivity was rapidly and completely excreted in urine and feces in an approximate ratio of 2:1. Findings were much the same in subjects with diabetes. In normal subjects, the kinetics of oral tolrestat were independent of dose in the 10 to 800 mg range. Repetitive dosing did not result in unexpected cumulation. Tolrestat was more than 99% bound to serum protein; it did not compete with warfarin for binding sites but was displaced to some extent by high concentrations of tolbutamide or salicylate.

  14. Quasi-static analysis of foil journal bearings for a Brayton cycle turboalternator

    NASA Technical Reports Server (NTRS)

    Eshel, A.

    1974-01-01

    A quasi-static analysis is presented for foil journal bearings designed for a NASA Brayton Cycle Turboalternator. Included in the analysis are effects of 'slack' (due to flexural rigidity of the foil), of frictionally restrained extension of the foil-length in contact with cylindrical guides, of fluid inertia and compressibility, and of thermal expansion of rotor, foil and supporting structure. Comparisons are made with results of early experiments performed by Licht (1968, 1969) and recent data of Licht and Branger (1973). Variatons of film thickness, foil tension and bearing stiffness are presented graphically as functions of pertinent parameters for the case of operation in zero-gravity environment.

  15. A Method to Apply Friction Modifier in Railway System

    NASA Astrophysics Data System (ADS)

    Matsumoto, Kosuke; Suda, Yoshihiro; Iwasa, Takashi; Fujii, Takeshi; Tomeoka, Masao; Tanimoto, Masuhisa; Kishimoto, Yasushi; Nakai, Takuji

    Controlling the friction between wheel and rail is direct and very effective measures to improve the curving performances of bogie trucks, because the curving performances of bogie truck depend much on friction characteristics. Authors have proposed a method, “friction control”, which utilizes friction modifier (KELTRACKTM HPF) with onboard spraying system. With the method, not only friction coefficient, but also friction characteristics are able to be controlled as expected. In this paper, results of fundamental experiments are reported which play an important role to realize the new method.

  16. Are there reliable constitutive laws for dynamic friction?

    PubMed

    Woodhouse, Jim; Putelat, Thibaut; McKay, Andrew

    2015-09-28

    Structural vibration controlled by interfacial friction is widespread, ranging from friction dampers in gas turbines to the motion of violin strings. To predict, control or prevent such vibration, a constitutive description of frictional interactions is inevitably required. A variety of friction models are discussed to assess their scope and validity, in the light of constraints provided by different experimental observations. Three contrasting case studies are used to illustrate how predicted behaviour can be extremely sensitive to the choice of frictional constitutive model, and to explore possible experimental paths to discriminate between and calibrate dynamic friction models over the full parameter range needed for real applications. PMID:26303920

  17. Static Response of Neutron Matter.

    PubMed

    Buraczynski, Mateusz; Gezerlis, Alexandros

    2016-04-15

    We generalize the problem of strongly interacting neutron matter by adding a periodic external modulation. This allows us to study from first principles a neutron system that is extended and inhomogeneous, with connections to the physics of both neutron-star crusts and neutron-rich nuclei. We carry out fully nonperturbative microscopic quantum Monte Carlo calculations of the energy of neutron matter at different densities, as well as different strengths and periodicities of the external potential. In order to remove systematic errors, we examine finite-size effects and the impact of the wave function ansatz. We also make contact with energy-density functional theories of nuclei and disentangle isovector gradient contributions from bulk properties. Finally, we calculate the static density-density linear response function of neutron matter and compare it with the response of other physical systems. PMID:27127963

  18. Static Response of Neutron Matter

    NASA Astrophysics Data System (ADS)

    Buraczynski, Mateusz; Gezerlis, Alexandros

    2016-04-01

    We generalize the problem of strongly interacting neutron matter by adding a periodic external modulation. This allows us to study from first principles a neutron system that is extended and inhomogeneous, with connections to the physics of both neutron-star crusts and neutron-rich nuclei. We carry out fully nonperturbative microscopic quantum Monte Carlo calculations of the energy of neutron matter at different densities, as well as different strengths and periodicities of the external potential. In order to remove systematic errors, we examine finite-size effects and the impact of the wave function ansatz. We also make contact with energy-density functional theories of nuclei and disentangle isovector gradient contributions from bulk properties. Finally, we calculate the static density-density linear response function of neutron matter and compare it with the response of other physical systems.

  19. Static mixer improves desalting efficiency

    SciTech Connect

    Not Available

    1983-10-01

    An in-line static mixer has increased salt removal from crude oil at a large West Coast refinery, says the mixer supplier, Komax Systems Inc. The mixer was installed at a 150,000 b/d crude distillation unit's desalter. Crude at this refinery is a mixture of local production and imports from Indonesia and Alaska. In the past, the refiner used a typical globe-type mix valve to mix fresh water with crude at the desalters. The crude is heated to 300/sup 0/F., mixed with 5% fresh water, and then fed to the desalters. Chemical and electrostatic treatment is used in the desalters to remove salt and water from the crude.

  20. Static latching arrangement and method

    DOEpatents

    Morrison, Larry

    1988-01-01

    A latching assembly for use in latching a cable to and unlatching it from a given object in order to move an object from one location to another is disclosed herein. This assembly includes a weighted sphere mounted to one end of a cable so as to rotate about a specific diameter of the sphere. The assembly also includes a static latch adapted for connection with the object to be moved. This latch includes an internal latching cavity for containing the sphere in a latching condition and a series of surfaces and openings which cooperate with the sphere in order to move the sphere into and out of the latching cavity and thereby connect the cable to and disconnect it from the latch without using any moving parts on the latch itself.