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. 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…

  4. On the origin of why static or breakloose friction is larger than kinetic friction, and how to reduce it: the role of aging, elasticity and sequential interfacial slip.

    PubMed

    Lorenz, B; Persson, B N J

    2012-06-06

    We discuss the origin of static friction and show how it can be reduced towards kinetic friction by the appropriate design of the sliding system. The basic idea is to use elastically soft solids and apply the external forces in such a way that different parts of the contacting interface start to slip at different times during the (tangential) loading process. In addition, the local slip must be large enough in order to result in a strong drop in the static friction force. We illustrate the theoretical predictions with the results of a simple model experiment.

  5. 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…

  6. Static and kinetic frictional forces of silica-insert ceramic brackets with coated archwires in artificial saliva.

    PubMed

    Shahabi, Mostafa; Salari, Soheil; Poosti, Maryam; Abtahi, Mostafa

    2017-01-01

    During sliding mechanics, the frictional force (FF) is an important counterforce to orthodontic tooth movement. The purpose of this in vitro study was to investigate the static and kinetic FFs of S silica-insert ceramic (SIC) brackets with Teflon-coated (TC) and conventional S stainless steel (SS) archwires. The target group of this study included 80 maxillary canine 0.022 inch slot SIC brackets. Forty SS brackets were used as the control. TC and conventional uncoated SS archwires of different dimensions (0.016, 0.018, 0.016 × 0.022, and 0.018 × 0.025 inch) were examined. All tests were carried out under artificial saliva injected condition. Scanning Electron Micrographs were prepared for two samples of coated and uncoated archwires. Analysis of variance and Tukey post hoc tests were used for statistical purposes (level of significance P < 0.05). SIC brackets showed significantly lower levels of FFs than SS brackets. TC archwires had greater frictional values than conventional uncoated ones. They also exhibited an unusual behavior of increasing kinetic FFs with time. Indentation and delamination of coating were obvious under scanning electron microscopy observations. From the standpoint of friction, SIC brackets may serve well, even better than SS brackets, in sliding mechanics. The coating layer of the archwires may delaminate and lost, causing an impediment to tooth movement.

  7. Static and kinetic frictional forces of silica-insert ceramic brackets with coated archwires in artificial saliva

    PubMed Central

    Shahabi, Mostafa; Salari, Soheil; Poosti, Maryam; Abtahi, Mostafa

    2017-01-01

    Background: During sliding mechanics, the frictional force (FF) is an important counterforce to orthodontic tooth movement. The purpose of this in vitro study was to investigate the static and kinetic FFs of S silica-insert ceramic (SIC) brackets with Teflon-coated (TC) and conventional S stainless steel (SS) archwires. Materials and Methods: The target group of this study included 80 maxillary canine 0.022 inch slot SIC brackets. Forty SS brackets were used as the control. TC and conventional uncoated SS archwires of different dimensions (0.016, 0.018, 0.016 × 0.022, and 0.018 × 0.025 inch) were examined. All tests were carried out under artificial saliva injected condition. Scanning Electron Micrographs were prepared for two samples of coated and uncoated archwires. Analysis of variance and Tukey post hoc tests were used for statistical purposes (level of significance P < 0.05). Results: SIC brackets showed significantly lower levels of FFs than SS brackets. TC archwires had greater frictional values than conventional uncoated ones. They also exhibited an unusual behavior of increasing kinetic FFs with time. Indentation and delamination of coating were obvious under scanning electron microscopy observations. Conclusion: From the standpoint of friction, SIC brackets may serve well, even better than SS brackets, in sliding mechanics. The coating layer of the archwires may delaminate and lost, causing an impediment to tooth movement. PMID:29238380

  8. 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.

  9. An eight-legged tactile sensor to estimate coefficient of static friction.

    PubMed

    Wei Chen; Rodpongpun, Sura; Luo, William; Isaacson, Nathan; Kark, Lauren; Khamis, Heba; Redmond, Stephen J

    2015-08-01

    It is well known that a tangential force larger than the maximum static friction force is required to initiate the sliding motion between two objects, which is governed by a material constant called the coefficient of static friction. Therefore, knowing the coefficient of static friction is of great importance for robot grippers which wish to maintain a stable and precise grip on an object during various manipulation tasks. Importantly, it is most useful if grippers can estimate the coefficient of static friction without having to explicitly explore the object first, such as lifting the object and reducing the grip force until it slips. A novel eight-legged sensor, based on simplified theoretical principles of friction is presented here to estimate the coefficient of static friction between a planar surface and the prototype sensor. Each of the sensor's eight legs are straight and rigid, and oriented at a specified angle with respect to the vertical, allowing it to estimate one of five ranges (5 = 8/2 + 1) that the coefficient of static friction can occupy. The coefficient of friction can be estimated by determining whether the legs have slipped or not when pressed against a surface. The coefficients of static friction between the sensor and five different materials were estimated and compared to a measurement from traditional methods. A least-squares linear fit of the sensor estimated coefficient showed good correlation with the reference coefficient with a gradient close to one and an r(2) value greater than 0.9.

  10. The Indeterminate Case of Classical Static Friction When Coupled with Tension

    ERIC Educational Resources Information Center

    Hahn, Kenneth D.; Russell, Jacob M.

    2018-01-01

    It has been noted that the static friction force poses challenges for students and, at times, even their instructors. Unlike the gravitational force, which has a precise and unambiguous magnitude (F[subscript G] = mg), the magnitude and direction of the static friction force depend on other forces at play. Friction can be understood rather well in…

  11. The Indeterminate Case of Classical Static Friction When Coupled with Tension

    NASA Astrophysics Data System (ADS)

    Hahn, Kenneth D.; Russell, Jacob M.

    2018-02-01

    It has been noted that the static friction force poses challenges for students and, at times, even their instructors. Unlike the gravitational force, which has a precise and unambiguous magnitude (FG = mg), the magnitude and direction of the static friction force depend on other forces at play. Friction can be understood rather well in terms of complicated atomic-scale interactions between surfaces. Ringlein and Robbins survey aspects of the atomic origins of friction, and Folkerts explores factors that affect the value of static friction. However, what students typically encounter in an introductory course ignores the atomic origins of friction (beyond perhaps a brief overview of the atomic model). The rules of dry friction (i.e., non-lubricated surfaces in contact) taught in introductory physics were originally published in 1699 by Guillaume Amontons. Amontons's first law states that the force of friction is directly proportional to the applied load, i.e., f = μFN, where FN is the normal force and μ is the coefficient of friction. His second law states that the force of friction is independent of the macroscopic area of contact. These laws were verified by Coulomb in 1781.

  12. Static friction boost in edge-driven incommensurate contacts

    NASA Astrophysics Data System (ADS)

    Mandelli, Davide; Guerra, Roberto; Ouyang, Wengen; Urbakh, Michael; Vanossi, Andrea

    2018-04-01

    We present a numerical investigation of the size scaling of static friction in incommensurate two-dimensional contacts performed for different lateral loading configurations. Results of model simulations show that both the absolute value of the force Fs and the scaling exponent γ strongly depend on the loading configuration adopted to drive the slider along the substrate. Under edge loading, a sharp increase of static friction is observed above a critical size corresponding to the appearance of a localized commensurate dislocation. Noticeably, the existence of sublinear scaling, which is a fingerprint of superlubricity, does not conflict with the possibility to observe shear-induced localized commensurate regions at the contact interface. Atomistic simulations of gold islands sliding over graphite corroborate these findings, suggesting that similar elasticity effects should be at play in real frictional contacts.

  13. 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

  14. A study of kinetic friction: The Timoshenko oscillator

    NASA Astrophysics Data System (ADS)

    Henaff, Robin; Le Doudic, Gabriel; Pilette, Bertrand; Even, Catherine; Fischbach, Jean-Marie; Bouquet, Frédéric; Bobroff, Julien; Monteverde, Miguel; Marrache-Kikuchi, Claire A.

    2018-03-01

    Friction is a complex phenomenon that is of paramount importance in everyday life. We present an easy-to-build and inexpensive experiment illustrating Coulomb's law of kinetic friction. The so-called friction, or Timoshenko, oscillator consists of a plate set into periodic motion through the competition between gravity and friction on its rotating supports. The period of such an oscillator gives a measurement of the coefficient of kinetic friction μk between the plate and the supports. Our prototype is mainly composed of a motor, LEGO blocks, and a low-cost microcontroller, but despite its simplicity, the results obtained are in good agreement with values of μk found in the literature (enhanced online).

  15. 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

  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. Dynamics of static friction between steel and silicon

    PubMed Central

    Yang, Zhiping; Zhang, H. P.; Marder, M.

    2008-01-01

    We conducted experiments in which steel and silicon or quartz are clamped together. Even with the smallest tangential forces we could apply, we always found reproducible sliding motions on the nanometer scale. The velocities we study are thousands of times smaller than in previous investigations. The samples first slide and then lock up even when external forces hold steady. One might call the result “slip-stick” friction. We account for the results with a phenomenological theory that results from considering the rate and state theory of dynamic friction at low velocities. Our measurements lead us to set the instantaneous coefficient of static friction that normally enters rate and state theories to zero. PMID:18768792

  18. 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

  19. Friction between various self-ligating brackets and archwire couples during sliding mechanics.

    PubMed

    Stefanos, Sennay; Secchi, Antonino G; Coby, Guy; Tanna, Nipul; Mante, Francis K

    2010-10-01

    The aim of this study was to evaluate the frictional resistance between active and passive self-ligating brackets and 0.019 × 0.025-in stainless steel archwire during sliding mechanics by using an orthodontic sliding simulation device. Maxillary right first premolar active self-ligating brackets In-Ovation R, In-Ovation C (both, GAC International, Bohemia, NY), and SPEED (Strite Industries, Cambridge, Ontario, Canada), and passive self-ligating brackets SmartClip (3M Unitek, Monrovia, Calif), Synergy R (Rocky Mountain Orthodontics, Denver, Colo), and Damon 3mx (Ormco, Orange, Calif) with 0.022-in slots were used. Frictional force was measured by using an orthodontic sliding simulation device attached to a universal testing machine. Each bracket-archwire combination was tested 30 times at 0° angulation relative to the sliding direction. Statistical comparisons were performed with 1-way analysis of variance (ANOVA) followed by Dunn multiple comparisons. The level of statistical significance was set at P <0.05. The Damon 3mx brackets had significantly the lowest mean static frictional force (8.6 g). The highest mean static frictional force was shown by the SPEED brackets (83.1 g). The other brackets were ranked as follows, from highest to lowest, In-Ovation R, In-Ovation C, SmartClip, and Synergy R. The mean static frictional forces were all statistically different. The ranking of the kinetic frictional forces of bracket-archwire combinations was the same as that for static frictional forces. All bracket-archwire combinations showed significantly different kinetic frictional forces except SmartClip and In-Ovation C, which were not significantly different from each other. Passive self-ligating brackets have lower static and kinetic frictional resistance than do active self-ligating brackets with 0.019 × 0.025-in stainless steel wire. Copyright © 2010 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.

  20. 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.

  1. Comparison of friction force between corroded and noncorroded titanium nitride plating of metal brackets.

    PubMed

    Kao, Chia-Tze; Guo, Jia-Uei; Huang, Tsui-Hsien

    2011-05-01

    Titanium nitride (TiN) plating is a method to prevent metal corrosion and can increase the surface smoothness. The purpose of this study was to evaluate the friction forces between the orthodontic bracket, with or without TiN plating, and stainless steel wire after it was corroded in fluoride-containing solution. In total, 540 metal brackets were divided into a control group and a TiN-coated experimental group. The electrochemical corrosion was performed in artificial saliva with 1.23% acidulated phosphate fluoride (APF) as the electrolytes. Static and kinetic friction were measured by an EZ-test machine (Shimadazu, Tokyo, Japan) with a crosshead speed of 10 mm per minute over a 5-mm stretch of stainless steel archwire. The data were analyzed by using unpaired t test and analysis of variance (ANOVA). Both the control and TiN-coated groups' corrosion potential was higher with 1.23% APF solution than with artificial solution (P <0.05). In brackets without corrosion, both the static and kinetic friction force between the control and TiN-coated brackets groups showed a statistically significant difference (P <0.05). In brackets with corrosion, the control group showed no statistical difference on kinetic or static friction. The TiN-coated brackets showed a statistical difference (P <0.05) on kinetic and static friction in different solutions. TiN-coated metal brackets, with corrosion or without corrosion, cannot reduce the frictional force. Copyright © 2011 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.

  2. Static and dynamic friction in sliding colloidal monolayers

    PubMed Central

    Vanossi, Andrea; Manini, Nicola; Tosatti, Erio

    2012-01-01

    In a pioneer experiment, Bohlein et al. realized the controlled sliding of two-dimensional colloidal crystals over laser-generated periodic or quasi-periodic potentials. Here we present realistic simulations and arguments that besides reproducing the main experimentally observed features give a first theoretical demonstration of the potential impact of colloid sliding in nanotribology. The free motion of solitons and antisolitons in the sliding of hard incommensurate crystals is contrasted with the soliton–antisoliton pair nucleation at the large static friction threshold Fs when the two lattices are commensurate and pinned. The frictional work directly extracted from particles’ velocities can be analyzed as a function of classic tribological parameters, including speed, spacing, and amplitude of the periodic potential (representing, respectively, the mismatch of the sliding interface and the corrugation, or “load”). These and other features suggestive of further experiments and insights promote colloid sliding to a unique friction study instrument. PMID:23019582

  3. 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…

  4. Prediction of static friction coefficient in rough contacts based on the junction growth theory

    NASA Astrophysics Data System (ADS)

    Spinu, S.; Cerlinca, D.

    2017-08-01

    The classic approach to the slip-stick contact is based on the framework advanced by Mindlin, in which localized slip occurs on the contact area when the local shear traction exceeds the product between the local pressure and the static friction coefficient. This assumption may be too conservative in the case of high tractions arising at the asperities tips in the contact of rough surfaces, because the shear traction may be allowed to exceed the shear strength of the softer material. Consequently, the classic frictional contact model is modified in this paper so that gross sliding occurs when the junctions formed between all contacting asperities are independently sheared. In this framework, when the contact tractions, normal and shear, exceed the hardness of the softer material on the entire contact area, the material of the asperities yields and the junction growth process ends in all contact regions, leading to gross sliding inception. This friction mechanism is implemented in a previously proposed numerical model for the Cattaneo-Mindlin slip-stick contact problem, which is modified to accommodate the junction growth theory. The frictionless normal contact problem is solved first, then the tangential force is gradually increased, until gross sliding inception. The contact problems in the normal and in the tangential direction are successively solved, until one is stabilized in relation to the other. The maximum tangential force leading to a non-vanishing stick area is the static friction force that can be sustained by the rough contact. The static friction coefficient is eventually derived as the ratio between the latter friction force and the normal force.

  5. An automated high throughput tribometer for adhesion, wear, and friction measurements

    NASA Astrophysics Data System (ADS)

    Kalihari, Vivek; Timpe, Shannon J.; McCarty, Lyle; Ninke, Matthew; Whitehead, Jim

    2013-03-01

    Understanding the origin and correlation of different surface properties under a multitude of operating conditions is critical in tribology. Diverse tribological properties and a lack of a single instrument to measure all make it difficult to compare and correlate properties, particularly in light of the wide range of interfaces commonly investigated. In the current work, a novel automated tribometer has been designed and validated, providing a unique experimental platform capable of high throughput adhesion, wear, kinetic friction, and static friction measurements. The innovative design aspects are discussed that allow for a variety of probes, sample surfaces, and testing conditions. Critical components of the instrument and their design criteria are described along with examples of data collection schemes. A case study is presented with multiple surface measurements performed on a set of characteristic substrates. Adhesion, wear, kinetic friction, and static friction are analyzed and compared across surfaces, highlighting the comprehensive nature of the surface data that can be generated using the automated high throughput tribometer.

  6. Static-dynamic friction transition of FRP esthetic orthodontic wires on various brackets by suspension-type friction test.

    PubMed

    Suwa, N; Watari, F; Yamagata, S; Iida, J; Kobayashi, M

    2003-11-15

    A new testing apparatus for the measurement of frictional properties was designed and the frictional coefficients were obtained and compared with each other in various combinations of brackets and orthodontic wires, including esthetic fiber-reinforced plastic (FRP) wire that was especially designed and manufactured. Three kinds of wires (stainless steel, nickel-titanium, and FRP) and four brackets (single-crystal alumina, polycrystalline alumina, polycarbonate, and stainless steel) were used. The testing was done under dry and wet conditions. The friction testing equipment was designed to attach the bracket to a C-shaped bar suspended with a variable mass, and sliding along a fixed wire. The transition between static and dynamic friction was measured as a breakaway force, with the use of a universal test machine. In addition to material properties, this testing fixture eliminates geometrical factors, such as the rotational moment at the edge of the bracket slot, deflection of the orthodontic wire, and tension of the ligature wire. Nearly ideal frictional properties between materials are obtained. The frictional properties of FRP wire were similar to those of metal wires on all brackets, except the polycrystalline alumina bracket. The frictional coefficient between the polycrystalline ceramic bracket and FRP wire was larger than that of other combinations. There was little difference in frictional coefficients between dry and wet conditions. Copyright 2003 Wiley Periodicals, Inc.

  7. Parameter Identification of Static Friction Based on An Optimal Exciting Trajectory

    NASA Astrophysics Data System (ADS)

    Tu, X.; Zhao, P.; Zhou, Y. F.

    2017-12-01

    In this paper, we focus on how to improve the identification efficiency of friction parameters in a robot joint. First, the static friction model that has only linear dependencies with respect to their parameters is adopted so that the servomotor dynamics can be linearized. In this case, the traditional exciting trajectory based on Fourier series is modified by replacing the constant term with quintic polynomial to ensure the boundary continuity of speed and acceleration. Then, the Fourier-related parameters are optimized by genetic algorithm(GA) in which the condition number of regression matrix is set as the fitness function. At last, compared with the constant-velocity tracking experiment, the friction parameters from the exciting trajectory experiment has the similar result with the advantage of time reduction.

  8. Steady and transient sliding under rate-and-state friction

    NASA Astrophysics Data System (ADS)

    Putelat, Thibaut; Dawes, Jonathan H. P.

    2015-05-01

    The physics of dry friction is often modelled by assuming that static and kinetic frictional forces can be represented by a pair of coefficients usually referred to as μs and μk, respectively. In this paper we re-examine this discontinuous dichotomy and relate it quantitatively to the more general, and smooth, framework of rate-and-state friction. This is important because it enables us to link the ideas behind the widely used static and dynamic coefficients to the more complex concepts that lie behind the rate-and-state framework. Further, we introduce a generic framework for rate-and-state friction that unifies different approaches found in the literature. We consider specific dynamical models for the motion of a rigid block sliding on an inclined surface. In the Coulomb model with constant dynamic friction coefficient, sliding at constant velocity is not possible. In the rate-and-state formalism steady sliding states exist, and analysing their existence and stability enables us to show that the static friction coefficient μs should be interpreted as the local maximum at very small slip rates of the steady state rate-and-state friction law. Next, we revisit the often-cited experiments of Rabinowicz (J. Appl. Phys., 22:1373-1379, 1951). Rabinowicz further developed the idea of static and kinetic friction by proposing that the friction coefficient maintains its higher and static value μs over a persistence length before dropping to the value μk. We show that there is a natural identification of the persistence length with the distance that the block slips as measured along the stable manifold of the saddle point equilibrium in the phase space of the rate-and-state dynamics. This enables us explicitly to define μs in terms of the rate-and-state variables and hence link Rabinowicz's ideas to rate-and-state friction laws. This stable manifold naturally separates two basins of attraction in the phase space: initial conditions in the first one lead to the block

  9. Kinetic theory for identical, frictional, nearly elastic disks

    NASA Astrophysics Data System (ADS)

    Yoon, David K.; Jenkins, James T.

    2005-08-01

    We develop kinetic theory for slightly frictional and nearly elastic disks. The tangential interaction is modeled by two parameters: a Coulomb friction coefficient and a tangential restitution coefficient. Assuming Maxwellian velocity distribution functions for both translational and rotational velocities, we derive exact expressions for the rates of dissipation of translational and rotational fluctuation energies per unit area. Setting the rotational dissipation rate to zero, as in a steady, homogeneous shearing flow, we find the ratio of the rotational temperature to the translational. In the case of small friction, this is used to determine an effective coefficient of normal restitution. In this way, the effects of small friction can be incorporated into the theory, thereby dispensing with the need to separately consider the complete balances for the momentum and the energy of the rotational motion.

  10. Bioinspired orientation-dependent friction.

    PubMed

    Xue, Longjian; Iturri, Jagoba; Kappl, Michael; Butt, Hans-Jürgen; del Campo, Aránzazu

    2014-09-23

    Spatular terminals on the toe pads of a gecko play an important role in directional adhesion and friction required for reversible attachment. Inspired by the toe pad design of a gecko, we study friction of polydimethylsiloxane (PDMS) micropillars terminated with asymmetric (spatular-shaped) overhangs. Friction forces in the direction of and against the spatular end were evaluated and compared to friction forces on symmetric T-shaped pillars and pillars without overhangs. The shape of friction curves and the values of friction forces on spatula-terminated pillars were orientation-dependent. Kinetic friction forces were enhanced when shearing against the spatular end, while static friction was stronger in the direction toward the spatular end. The overall friction force was higher in the direction against the spatula end. The maximum value was limited by the mechanical stability of the overhangs during shear. The aspect ratio of the pillar had a strong influence on the magnitude of the friction force, and its contribution surpassed and masked that of the spatular tip for aspect ratios of >2.

  11. 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.

  12. Friction phenomena and phase transition in the underdamped two-dimensional Frenkel-Kontorova model

    NASA Astrophysics Data System (ADS)

    Yang, Yang; Duan, Wen-Shan; Chen, Jian-Min; Yang, Lei; Tekić, Jasmina; Shao, Zhi-Gang; Wang, Cang-Long

    2010-11-01

    Locked-to-sliding phase transition has been studied in the driven two-dimensional Frenkel-Kontorova model with the square symmetric substrate potential. It is found that as the driving force increases, the system transfers from the locked state to the sliding state where the motion of particles is in the direction different from that of driving force. With the further increase in driving force, at some critical value, the particles start to move in the direction of driving force. These two critical forces, the static friction or depinning force, and the kinetic friction force for which particles move in the direction of driving force have been analyzed for different system parameters. Different scenarios of phase transitions have been examined and dynamical phases are classified. In the case of zero misfit angle, the analytical expressions for static and kinetic friction force have been obtained.

  13. Disk in a groove with friction: An analysis of static equilibrium and indeterminacy

    NASA Astrophysics Data System (ADS)

    Donolato, Cesare

    2018-05-01

    This note studies the statics of a rigid disk placed in a V-shaped groove with frictional walls and subjected to gravity and a torque. The two-dimensional equilibrium problem is formulated in terms of the angles that contact forces form with the normal to the walls. This approach leads to a single trigonometric equation in two variables whose domain is determined by Coulomb's law of friction. The properties of solutions (existence, uniqueness, or indeterminacy) as functions of groove angle, friction coefficient and applied torque are derived by a simple geometric representation. The results modify some of the conclusions by other authors on the same problem.

  14. Static coefficient of friction between stainless steel and PMMA used in cemented hip and knee implants.

    PubMed

    Nuño, N; Groppetti, R; Senin, N

    2006-11-01

    Design of cemented hip and knee implants, oriented to improve the longevity of artificial joints, is largely based on numerical models. The static coefficient of friction between the implant and the bone cement is necessary to characterize the interface conditions in these models and must be accurately provided. The measurement of this coefficient using a repeatable and reproducible methodology for materials used in total hip arthroplasty is missing from the literature. A micro-topographic surface analysis characterized the surfaces of the specimens used in the experiments. The coefficient of friction between stainless steel and bone cement in dry and wet conditions using bovine serum was determined using a prototype computerized sliding friction tester. The effects of surface roughness (polished versus matt) and of contact pressure on the coefficient of friction have also been investigated. The serum influences little the coefficient of friction for the matt steel surface, where the mechanical interactions due to higher roughness are still the most relevant factor. However, for polished steel surfaces, the restraining effect of proteins plays a very relevant role in increasing the coefficient of friction. When the coefficient of friction is used in finite element analysis, it is used for the debonded stem-cement situation. It can thus be assumed that serum will propagate between the stem and the cement mantle. The authors believe that the use of a static coefficient of friction of 0.3-0.4, measured in the present study, is appropriate in finite element models.

  15. Nonlinear friction dynamics on polymer surface under accelerated movement

    NASA Astrophysics Data System (ADS)

    Aita, Yuuki; Asanuma, Natsumi; Takahashi, Akira; Mayama, Hiroyuki; Nonomura, Yoshimune

    2017-04-01

    Nonlinear phenomena on the soft material surface are one of the most exciting topics of chemical physics. However, only a few reports exist on the friction phenomena under accelerated movement, because friction between two solid surfaces is considered a linear phenomenon in many cases. We aim to investigate how nonlinear accelerated motion affects friction on solid surfaces. In the present study, we evaluate the frictional forces between two polytetrafluoroethylene (PTFE) resins using an advanced friction evaluation system. On PTFE surfaces, the normalized delay time δ, which is the time lag in the response of the friction force to the accelerated movement, is observed in the pre-sliding friction process. Under high-velocity conditions, kinetic friction increases with velocity. Based on these experimental results, we propose a two-phase nonlinear model including a pre-sliding process (from the beginning of sliding of a contact probe to the establishment of static friction) and a kinetic friction process. The present model consists of several factors including velocity, acceleration, stiffness, viscosity, and vertical force. The findings reflecting the viscoelastic properties of soft material is useful for various fields such as in the fabrication of clothes, cosmetics, automotive materials, and virtual reality systems as well as for understanding friction phenomena on soft material surfaces.

  16. 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.

  17. Kinetic-energy absorber employs frictional force between mating cylinders

    NASA Technical Reports Server (NTRS)

    Conrad, E. W.

    1964-01-01

    A kinetic energy absorbing device uses a series of coaxial, mating cylindrical surfaces. These surfaces have high frictional resistance to relative motion when axial impact forces are applied. The device is designed for safe deceleration of vehicles impacting on landing surfaces.

  18. Evaluation of frictional resistance and surface characteristics after immersion of orthodontic brackets and wire in different chemical solutions: A comparative in vitrostudy.

    PubMed

    Nanjundan, Kavitha; Vimala, G

    2016-01-01

    To evaluate the changes of static and kinetic frictional forces between the brackets and wires following exposure to a soft drink, acidic food ingredient, and acidulated fluoride prophylactic agents. Two types of Roth prescription mandibular incisor brackets were used: 3M Unitek Victory stainless steel (SS) brackets (n = 40) and Transcend 6000 polycrystalline alumina (PCA) brackets (n = 40) as well as eighty 0.019 × 0.025" dimension ortho technology SS wires of 50 mm length each. Subsequently, brackets tied with SS wires divided into eight subgroups (n = 10) and were immersed in vinegar (pH = 3.5 ± 0.5), Pepsi ® (pH = 2.46), Colgate Phos-Flur mouth rinse (pH = 5.1), and artificial saliva (control group pH = 7) for 24 h. Changes in surface morphology under scanning electron microscope ×1000, surface roughness (Ra) with surface profilometer (single bracket and single wire from each subgroup), and frictional resistance using universal testing machine were evaluated. Highest mean (standard deviation) static frictional force of 2.65 (0.25) N was recorded in Pepsi ® followed by 2.57 (0.25) N, 2.40 (0.22) N, and 2.36 (0.17) N for Vinegar, Colgate Phos-Flur mouth rinse, and artificial saliva groups, respectively. In a similar order, lesser mean kinetic frictional forces obtained. PCA brackets revealed more surface deterioration and higher frictional force values than SS brackets. A significant positive correlation was observed between frictional forces and bracket slot roughness (r = 0.861 and 0.802, respectively, for static and kinetic frictional forces, p < 0.001 for both) and wire roughness (r = 0.243 and 0.242, respectively, for static and kinetic frictional forces, p < 0.05 for both). Findings may have long-term implications when acidic food substances are used during fixed orthodontic treatment. Further, in vivo studies are required to analyze the clinical effect of acidic mediums in the oral environment during orthodontic treatment.

  19. Analysis of the behavior of a wiper blade around the reversal in consideration of dynamic and static friction

    NASA Astrophysics Data System (ADS)

    Unno, M.; Shibata, A.; Yabuno, H.; Yanagisawa, D.; Nakano, T.

    2017-04-01

    Reducing noise generated by automobile windshield wipers during reversals is a desirable feature. For this purpose, details of the behavior of the wiper blade need to be ascertained. In this study, we present theoretical and experimental clarification of this behavior during reversals. Using simulation algorithms to consider exactly the effects of dynamic and static friction, we determined theoretical predictions for the vibrational response caused by friction and the response frequency and compared these results with experimental ones obtained from a mock-up incorporating an actual wiper blade. We introduce an analytical link model with two degrees of freedom and consider two types of states at the blade tip. In the stick and the slip states, static friction and dynamic friction, respectively, act on the blade tip. In the theoretical approach, the static friction is expressed by a set-valued function. The transition between the two states is repeated and an evaluation of an exact transition time leads to an accurate prediction of the behavior of the wiper system. In the analysis, the slack variable method is used to find the exact transition time. Assuming low blade speeds during reversal, a parameter study indicates that the blade tip transitions between slip and stick states and the frequency of the vibration caused by this transitions is close to the natural frequency of the neck of the wiper blade. The theoretical predictions are in good agreement with experimental observations.

  20. The kinetic friction of ZnO nanowires on amorphous SiO2 and SiN substrates

    NASA Astrophysics Data System (ADS)

    Roy, Aditi; Xie, Hongtao; Wang, Shiliang; Huang, Han

    2016-12-01

    ZnO nanowires were bent on amorphous SiO2 and SiN substrates in an ambient atmosphere using optical nanomanipulation. The kinetic friction between the nanowires and substrate was determined from the bent shape of the nanowires. The kinetic friction force per unit area, i.e. frictional shear stress, for the ZnO/SiO2 and ZnO/SiN nanowire/substrate systems being measured were 1.05 ± 0.28 and 2.08 ± 0.33 MPa, respectively. The surface roughness and the Hamaker constant of SiO2 and SiN substrates had significant effect on the frictional stresses.

  1. 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

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

    PubMed

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

    2016-01-01

    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. 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. 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. 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. 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.

  3. Determination of the frictional coefficient of the implant-antler interface: experimental approach.

    PubMed

    Hasan, Istabrak; Keilig, Ludger; Staat, Manfred; Wahl, Gerhard; Bourauel, Christoph

    2012-10-01

    The similar bone structure of reindeer antler to human bone permits studying the osseointegration of dental implants in the jawbone. As the friction is one of the major factors that have a significant influence on the initial stability of immediately loaded dental implants, it is essential to define the frictional coefficient of the implant-antler interface. In this study, the kinetic frictional forces at the implant-antler interface were measured experimentally using an optomechanical setup and a stepping motor controller under different axial loads and sliding velocities. The corresponding mean values of the static and kinetic frictional coefficients were within the range of 0.5-0.7 and 0.3-0.5, respectively. An increase in the frictional forces with increasing applied axial loads was registered. The measurements showed an evidence of a decrease in the magnitude of the frictional coefficient with increasing sliding velocity. The results of this study provide a considerable assessment to clarify the suitable frictional coefficient to be used in the finite element contact analysis of antler specimens.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. Chemical origins of frictional aging.

    PubMed

    Liu, Yun; Szlufarska, Izabela

    2012-11-02

    Although the basic laws of friction are simple enough to be taught in elementary physics classes and although friction has been widely studied for centuries, in the current state of knowledge it is still not possible to predict a friction force from fundamental principles. One of the highly debated topics in this field is the origin of static friction. For most macroscopic contacts between two solids, static friction will increase logarithmically with time, a phenomenon that is referred to as aging of the interface. One known reason for the logarithmic growth of static friction is the deformation creep in plastic contacts. However, this mechanism cannot explain frictional aging observed in the absence of roughness and plasticity. Here, we discover molecular mechanisms that can lead to a logarithmic increase of friction based purely on interfacial chemistry. Predictions of our model are consistent with published experimental data on the friction of silica.

  9. 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…

  10. 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.

  11. 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.

  12. Pleural liquid and kinetic friction coefficient of mesothelium after mechanical ventilation.

    PubMed

    Bodega, Francesca; Sironi, Chiara; Porta, Cristina; Zocchi, Luciano; Agostoni, Emilio

    2015-01-15

    Volume and protein concentration of pleural liquid in anesthetized rabbits after 1 or 3h of mechanical ventilation, with alveolar pressure equal to atmospheric at end expiration, were compared to those occurring after spontaneous breathing. Moreover, coefficient of kinetic friction between samples of visceral and parietal pleura, obtained after spontaneous or mechanical ventilation, sliding in vitro at physiological velocity under physiological load, was determined. Volume of pleural liquid after mechanical ventilation was similar to that previously found during spontaneous ventilation. This finding is contrary to expectation of Moriondo et al. (2005), based on measurement of lymphatic and interstitial pressure. Protein concentration of pleural liquid after mechanical ventilation was also similar to that occurring after spontaneous ventilation. Coefficient of kinetic friction after mechanical ventilation was 0.023±0.001, similar to that obtained after spontaneous breathing. Copyright © 2014 Elsevier B.V. All rights reserved.

  13. Rate and State Friction Relation for Nanoscale Contacts: Thermally Activated Prandtl-Tomlinson Model with Chemical Aging

    NASA Astrophysics Data System (ADS)

    Tian, Kaiwen; Goldsby, David L.; Carpick, Robert W.

    2018-05-01

    Rate and state friction (RSF) laws are widely used empirical relationships that describe macroscale to microscale frictional behavior. They entail a linear combination of the direct effect (the increase of friction with sliding velocity due to the reduced influence of thermal excitations) and the evolution effect (the change in friction with changes in contact "state," such as the real contact area or the degree of interfacial chemical bonds). Recent atomic force microscope (AFM) experiments and simulations found that nanoscale single-asperity amorphous silica-silica contacts exhibit logarithmic aging (increasing friction with time) over several decades of contact time, due to the formation of interfacial chemical bonds. Here we establish a physically based RSF relation for such contacts by combining the thermally activated Prandtl-Tomlinson (PTT) model with an evolution effect based on the physics of chemical aging. This thermally activated Prandtl-Tomlinson model with chemical aging (PTTCA), like the PTT model, uses the loading point velocity for describing the direct effect, not the tip velocity (as in conventional RSF laws). Also, in the PTTCA model, the combination of the evolution and direct effects may be nonlinear. We present AFM data consistent with the PTTCA model whereby in aging tests, for a given hold time, static friction increases with the logarithm of the loading point velocity. Kinetic friction also increases with the logarithm of the loading point velocity at sufficiently high velocities, but at a different increasing rate. The discrepancy between the rates of increase of static and kinetic friction with velocity arises from the fact that appreciable aging during static contact changes the energy landscape. Our approach extends the PTT model, originally used for crystalline substrates, to amorphous materials. It also establishes how conventional RSF laws can be modified for nanoscale single-asperity contacts to provide a physically based friction

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    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.

  15. Influence of long-term in vivo exposure, debris accumulation and archwire material on friction force among different types of brackets and archwires couples.

    PubMed

    Mezeg, Uroš; Primožic, Jasmina

    2017-11-30

    The aim was to assess the influence of long-term in vivo exposure, debris accumulation and archwire material on static and kinetic friction force among different types of brackets and archwires couples. Friction testing was performed among four lower incisors' brackets, conventional and self-ligating (SL), coupled with either nickel-titanium or stainless steel archwires, as-received and in vivo exposed in 18 subjects. The friction testing was performed for a sliding distance of 14 mm at a speed of 10 mm/min, with a starting force of 0.2 N. Wear and quantitative assessment of debris accumulation was performed on pictures of brackets obtained using a scanning electron microscope. Non parametric tests were used for statistical analysis. Only bracket type, but not exposure duration, amount of debris accumulation, archwire material or their manufacturer, was significantly correlated with both static (rho = 0.602, P < 0.001) and kinetic (rho = 0.584, P < 0.001) friction force. Within each bracket type no significant difference was observed between as-received and in vivo exposed brackets for any friction parameter except for the SL brackets in which significantly higher static and kinetic (P = 0.001, at least) friction forces were seen in in vivo exposed SL brackets (164.9 cN and 217.63 cN, respectively) in comparison with as-received SL brackets (19.69 cN and 55.72 cN, respectively). The frictional testing was performed in the dry condition which might have influenced the results. A significant correlation was seen between friction force and bracket type, while treatment duration, amount of debris accumulation, archwire material or their manufacturer was not significantly correlated to it. Nevertheless, higher friction forces were measured among in vivo aged SL brackets in comparison with as-received ones. © The Author 2017. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: journals.permissions@oup.com

  16. Control of Reaction Kinetics During Friction Stir Processing

    DOE PAGES

    Das, Shamiparna; Martinez, Nelson Y.; Mishra, Rajiv S.; ...

    2017-02-17

    Friction stir processing (FSP) was used to successfully embed galfenol particles into aluminum (AA 1100 Al) matrix uniformly. But, intermetallic layer of Al 3Fe was formed around the galfenol particles. We estimated the activation energy for Al 3Fe formation during FSP, and attempts were made to minimize the Al 3Fe layer thickness. By changing the processing conditions, FSP successfully eliminated the intermetallic layer. Therefore, FSP, in addition to microstructural control, can successfully fabricate intermetallic-free embedded regions by controlling the reaction kinetics.

  17. Switchable static friction of piezoelectric composite—silicon wafer contacts

    NASA Astrophysics Data System (ADS)

    van den Ende, D. A.; Fischer, H. R.; Groen, W. A.; van der Zwaag, S.

    2013-04-01

    The meso-scale surface roughness of piezoelectric fiber composites can be manipulated by applying an electric field to a piezocomposite with a polished surface. In the absence of an applied voltage, the tips of the embedded piezoelectric ceramic fibers are below the surface of the piezocomposite and a silicon wafer counter surface rests solely on the matrix region of the piezocomposite surface. When actuated, the piezoelectric ceramic fibers protrude from the surface and the wafer rests solely on these protrusions. A threefold decrease in engineering static friction coefficient upon actuation of the piezocomposite was observed: from μ* = 1.65 to μ* = 0.50. These experimental results could be linked to the change in contact surface area and roughness using capillary adhesion theory, which relates the adhesive force to the number and size of the contacting asperities for the different surface states.

  18. 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,…

  19. Study of the effect of static/dynamic Coulomb friction variation at the tape-head interface of a spacecraft tape recorder by non-linear time response simulation

    NASA Technical Reports Server (NTRS)

    Mukhopadhyay, A. K.

    1978-01-01

    A description is presented of six simulation cases investigating the effect of the variation of static-dynamic Coulomb friction on servo system stability/performance. The upper and lower levels of dynamic Coulomb friction which allowed operation within requirements were determined roughly to be three times and 50% respectively of nominal values considered in a table. A useful application for the nonlinear time response simulation is the sensitivity analysis of final hardware design with respect to such system parameters as cannot be varied realistically or easily in the actual hardware. Parameters of the static/dynamic Coulomb friction fall in this category.

  20. Probing static disorder in Arrhenius kinetics by single-molecule force spectroscopy.

    PubMed

    Kuo, Tzu-Ling; Garcia-Manyes, Sergi; Li, Jingyuan; Barel, Itay; Lu, Hui; Berne, Bruce J; Urbakh, Michael; Klafter, Joseph; Fernández, Julio M

    2010-06-22

    The widely used Arrhenius equation describes the kinetics of simple two-state reactions, with the implicit assumption of a single transition state with a well-defined activation energy barrier DeltaE, as the rate-limiting step. However, it has become increasingly clear that the saddle point of the free-energy surface in most reactions is populated by ensembles of conformations, leading to nonexponential kinetics. Here we present a theory that generalizes the Arrhenius equation to include static disorder of conformational degrees of freedom as a function of an external perturbation to fully account for a diverse set of transition states. The effect of a perturbation on static disorder is best examined at the single-molecule level. Here we use force-clamp spectroscopy to study the nonexponential kinetics of single ubiquitin proteins unfolding under force. We find that the measured variance in DeltaE shows both force-dependent and independent components, where the force-dependent component scales with F(2), in excellent agreement with our theory. Our study illustrates a novel adaptation of the classical Arrhenius equation that accounts for the microscopic origins of nonexponential kinetics, which are essential in understanding the rapidly growing body of single-molecule data.

  1. Engineering mechanics: statics and dynamics. [Textbook

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    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)

  2. Detection of Visual Field Loss in Pituitary Disease: Peripheral Kinetic Versus Central Static

    PubMed Central

    Rowe, Fiona J.; Cheyne, Christopher P.; García-Fiñana, Marta; Noonan, Carmel P.; Howard, Claire; Smith, Jayne; Adeoye, Joanne

    2015-01-01

    Abstract Visual field assessment is an important clinical evaluation for eye disease and neurological injury. We evaluated Octopus semi-automated kinetic peripheral perimetry (SKP) and Humphrey static automated central perimetry for detection of neurological visual field loss in patients with pituitary disease. We carried out a prospective cross-sectional diagnostic accuracy study comparing Humphrey central 30-2 SITA threshold programme with a screening protocol for SKP on Octopus perimetry. Humphrey 24-2 data were extracted from 30-2 results. Results were independently graded for presence/absence of field defect plus severity of defect. Fifty patients (100 eyes) were recruited (25 males and 25 females), with mean age of 52.4 years (SD = 15.7). Order of perimeter assessment (Humphrey/Octopus first) and order of eye tested (right/left first) were randomised. The 30-2 programme detected visual field loss in 85%, the 24-2 programme in 80%, and the Octopus combined kinetic/static strategy in 100% of eyes. Peripheral visual field loss was missed by central threshold assessment. Qualitative comparison of type of visual field defect demonstrated a match between Humphrey and Octopus results in 58%, with a match for severity of defect in 50%. Tests duration was 9.34 minutes (SD = 2.02) for Humphrey 30-2 versus 10.79 minutes (SD = 4.06) for Octopus perimetry. Octopus semi-automated kinetic perimetry was found to be superior to central static testing for detection of pituitary disease-related visual field loss. Where reliant on Humphrey central static perimetry, the 30-2 programme is recommended over the 24-2 programme. Where kinetic perimetry is available, this is preferable to central static programmes for increased detection of peripheral visual field loss. PMID:27928344

  3. Evolution of real contact area under shear and the value of static friction of soft materials.

    PubMed

    Sahli, R; Pallares, G; Ducottet, C; Ben Ali, I E; Al Akhrass, S; Guibert, M; Scheibert, J

    2018-01-16

    The frictional properties of a rough contact interface are controlled by its area of real contact, the dynamical variations of which underlie our modern understanding of the ubiquitous rate-and-state friction law. In particular, the real contact area is proportional to the normal load, slowly increases at rest through aging, and drops at slip inception. Here, through direct measurements on various contacts involving elastomers or human fingertips, we show that the real contact area also decreases under shear, with reductions as large as 30[Formula: see text], starting well before macroscopic sliding. All data are captured by a single reduction law enabling excellent predictions of the static friction force. In elastomers, the area-reduction rate of individual contacts obeys a scaling law valid from micrometer-sized junctions in rough contacts to millimeter-sized smooth sphere/plane contacts. For the class of soft materials used here, our results should motivate first-order improvements of current contact mechanics models and prompt reinterpretation of the rate-and-state parameters.

  4. 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.

  5. 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

  6. 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.

  7. 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.…

  8. Investigation of kinetic friction using an iPhone

    NASA Astrophysics Data System (ADS)

    Baldock, Clive; Johnson, Roger

    2016-11-01

    The iPhone is particularly suitable for mechanics experiments using the in-built acceleration sensor or accelerometer in-conjunction with the on-board data collection facility and a downloadable so-called ‘app’. In this work the iPhone has been used to investigate the acceleration due to gravity and determine the coefficient of kinetic friction, μ k of the iPhone as an object sliding down an inclined plane. This method is more accurate than that usually employed in the laboratory where the ‘fits and starts’ of the block sliding down the inclined plane potentially invalidate the required assumption that the velocity is constant. In its simplest form the measurement of acceleration is required to be undertaken for only 2 angles.

  9. 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.

  10. 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.

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

    PubMed

    Fino, Peter; Lockhart, Thurmon E

    2014-04-11

    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, and 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. Copyright © 2014 Elsevier Ltd. All rights reserved.

  12. 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.

  13. 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.

  14. Analyzing the Molecular Kinetics of Water Spreading on Hydrophobic Surfaces via Molecular Dynamics Simulation.

    PubMed

    Zhao, Lei; Cheng, Jiangtao

    2017-09-07

    In this paper, we report molecular kinetic analyses of water spreading on hydrophobic surfaces via molecular dynamics simulation. The hydrophobic surfaces are composed of amorphous polytetrafluoroethylene (PTFE) with a static contact angle of ~112.4° for water. On the basis of the molecular kinetic theory (MKT), the influences of both viscous damping and solid-liquid retarding were analyzed in evaluating contact line friction, which characterizes the frictional force on the contact line. The unit displacement length on PTFE was estimated to be ~0.621 nm and is ~4 times as long as the bond length of C-C backbone. The static friction coefficient was found to be ~[Formula: see text] Pa·s, which is on the same order of magnitude as the dynamic viscosity of water, and increases with the droplet size. A nondimensional number defined by the ratio of the standard deviation of wetting velocity to the characteristic wetting velocity was put forward to signify the strength of the inherent contact line fluctuation and unveil the mechanism of enhanced energy dissipation in nanoscale, whereas such effect would become insignificant in macroscale. Moreover, regarding a liquid droplet on hydrophobic or superhydrophobic surfaces, an approximate solution to the base radius development was derived by an asymptotic expansion approach.

  15. Relating stick-slip friction experiments to earthquake source parameters

    USGS Publications Warehouse

    McGarr, Arthur F.

    2012-01-01

    Analytical results for parameters, such as static stress drop, for stick-slip friction experiments, with arbitrary input parameters, can be determined by solving an energy-balance equation. These results can then be related to a given earthquake based on its seismic moment and the maximum slip within its rupture zone, assuming that the rupture process entails the same physics as stick-slip friction. This analysis yields overshoots and ratios of apparent stress to static stress drop of about 0.25. The inferred earthquake source parameters static stress drop, apparent stress, slip rate, and radiated energy are robust inasmuch as they are largely independent of the experimental parameters used in their estimation. Instead, these earthquake parameters depend on C, the ratio of maximum slip to the cube root of the seismic moment. C is controlled by the normal stress applied to the rupture plane and the difference between the static and dynamic coefficients of friction. Estimating yield stress and seismic efficiency using the same procedure is only possible when the actual static and dynamic coefficients of friction are known within the earthquake rupture zone.

  16. An in vitro Evaluation of Friction Characteristics of Conventional Stainless Steel and Self-ligating Stainless Steel Brackets with different Dimensions of Archwires in Various Bracket-archwire Combination.

    PubMed

    Sridharan, K; Sandbhor, Shailesh; Rajasekaran, U B; Sam, George; Ramees, M Mohamed; Abraham, Esther A

    2017-08-01

    The purpose of this research is to compare the frictional attributes of stainless steel conventional brackets and self-ligating stainless steel brackets with different dimensions of archwires. The test was carried with two sets of maxillary brackets: (1) Conventional stainless steel (Victory Series), (2) stainless steel self-ligating (SmartClip) without first premolar brackets. Stainless steel, nickel-titanium (NiTi), and beta-Ti which are the types of orthodontic wire alloys were tested in this study. To monitor the frictional force, a universal testing machine (Instron 33R 4467) that comprises 10 kg tension load cell was assigned on a range of 1 kg and determined from 0 to 2 kg, which allows moving of an archwire along the brackets. One-way analysis of variance was used to test the difference between groups. To analyze the statistical difference between the two groups, Student's t-test was used. For Victory Series in static friction, p-value was 0.946 and for kinetic friction it was 0.944; at the same time for SmartClip, the p value for static and kinetic frictional resistance was 0.497 and 0.518 respectively. Hence, there was no statistically significant difference between the NiTi and stainless steel archwires. It is concluded that when compared with conventional brackets with stainless steel ligatures, self-ligating brackets can produce significantly less friction during sliding. Beta-Ti archwires expressed high amount of frictional resistance and the stainless steel archwires comprise low frictional resistance among all the archwire materials. In orthodontics, frictional resistance has always had a major role. Its ability to impair tooth movement leads to the need for higher forces to move the teeth and it extends the treatment time which results in loss of posterior anchorage. Friction in orthodontics is related with sliding mechanics when a wire is moving through one or a series of bracket slots.

  17. Comparison of quasi-static and dynamic squats: a three-dimensional kinematic, kinetic and electromyographic study of the lower limbs.

    PubMed

    Clément, Julien; Hagemeister, Nicola; Aissaoui, Rachid; de Guise, Jacques A

    2014-01-01

    Numerous studies have described 3D kinematics, 3D kinetics and electromyography (EMG) of the lower limbs during quasi-static or dynamic squatting activities. One study compared these two squatting conditions but only at low speed on healthy subjects, and provided no information on kinetics and EMG of the lower limbs. The purpose of the present study was to contrast simultaneous recordings of 3D kinematics, 3D kinetics and EMG of the lower limbs during quasi-stat ic and fast-dynamic squats in healthy and pathological subjects. Ten subjects were recruited: five healthy and five osteoarthritis subjects. A motion-capture system, force plate, and surface electrodes respectively recorded 3D kinematics, 3D kinetics and EMG of the lower limbs. Each subject performed a quasi-static squat and several fast-dynamic squats from 0° to 70° of knee flexion. The two squatting conditions were compared for positions where quasi-static and fast-dynamic knee flexion-extension angles were similar. Mean differences between quasi-static and fast-dynamic squats were 1.5° for rotations, 1.9 mm for translations, 2.1% of subjects' body weight for ground reaction forces, 6.6 Nm for torques, 11.2 mm for center of pressure, and 6.3% of maximum fast-dynamic electromyographic activities for EMG. Some significant differences (p<0.05) were found in internal rotation, anterior translation, vertical force and EMG. All differences between quasi-static and fast-dynamic squats were small. 69.5% of compared data were equivalent. In conclusion, this study showed that quasi-static and fast-dynamic squatting activities are comparable in terms of 3D kinematics, 3D kinetics and EMG, although some reservations still remain. Copyright © 2014 Elsevier B.V. All rights reserved.

  18. On kinetics of a dynamically unbalanced rotator with sliding friction in supports

    NASA Astrophysics Data System (ADS)

    Chistyakov, Viktor V.

    2018-05-01

    The dynamics is analytically and numerically modelled for both free and forced rotations of a rigid body around the central but non-principal vertical axis Oz under action of dry friction forces in plain bearings and heel supports in combination with other dissipative and conservative axial torques. The inertia forces due to D'Alembert principle cause the supports' reactions and hence the decelerating friction torque depending on not only angular speed but acceleration too. This dependence makes the dynamical equations not resolved with regard to the senior derivative and ambiguous, and being thus resolved they have an irrational or singular right hand side. This irrationality/singularity results in their featured solutions or paradoxical absence of those in frames of absolutely rigid body approach. The kinetics obtained is analyzed and compared with the standard ones of rotation under action of conservative elastic and drag torques.

  19. Friction between Polymer Brushes

    NASA Astrophysics Data System (ADS)

    Sokoloff, Jeffrey

    2006-03-01

    A polymer brush consists of a surface with a fairly concentrated coating of polymer chains, each one of which has one of its ends tightly bound to the surface. They serve as extremely effective lubricant, producing friction coefficients as low as 0.001 or less! Polymer brushes are a promising way to reduce friction to extremely low values. They have the disadvantage, however, that they must be immersed in a liquid solvent in order to function as a lubricant. The presence of a solvent is believed to result in osmotic pressure which partially supports the load. The density profile of a polymer brush (i.e., the density of monomers as a function of distance from the surface to which the polymers are attached) is well established. What is not understood is how the interaction of polymer brush coated surfaces in contact with each other is able to account for the details of the observed low friction. For example, molecular dynamics studies generally do not predict static friction, whereas surface force apparatus measurements due to Tadmor, et. al., find that there is static friction. This is the topic of the present presentation.

  20. Linear complementarity formulation for 3D frictional sliding problems

    USGS Publications Warehouse

    Kaven, Joern; Hickman, Stephen H.; Davatzes, Nicholas C.; Mutlu, Ovunc

    2012-01-01

    Frictional sliding on quasi-statically deforming faults and fractures can be modeled efficiently using a linear complementarity formulation. We review the formulation in two dimensions and expand the formulation to three-dimensional problems including problems of orthotropic friction. This formulation accurately reproduces analytical solutions to static Coulomb friction sliding problems. The formulation accounts for opening displacements that can occur near regions of non-planarity even under large confining pressures. Such problems are difficult to solve owing to the coupling of relative displacements and tractions; thus, many geomechanical problems tend to neglect these effects. Simple test cases highlight the importance of including friction and allowing for opening when solving quasi-static fault mechanics models. These results also underscore the importance of considering the effects of non-planarity in modeling processes associated with crustal faulting.

  1. Experience-based learning on determining the frictional coefficients of thermoset polymers incorporated with silicon carbide whiskers and chopped carbon fibers at different temperatures

    NASA Astrophysics Data System (ADS)

    Harrison, Edward; Alamir, Mohammed; Alzahrani, Naif; Asmatulu, Ramazan

    2017-04-01

    High temperature applications of materials have been increasing for various industrial applications, such as automobile brakes, clutches and thrust pads. The big portion of these materials are made out of the polymeric materials with various reinforcements. In the present study, high temperature polymeric materials were incorporated with SiC whiskers and chopped carbon fibers at 0, 5, 10 and 20wt.% and molded into desired size and shape prior to the curing process. These inclusions were selected because of their high mechanical strengths and thermal conductivity values to easily dissipate the frictional heat energy and sustain more external loads. The method of testing involves a metal ramp with an adjustable incline to find the coefficients of static and kinetic frictions by recording time and the angle of movement at various temperatures (e.g., -10°C and 50°C). The test results indicated that increasing the inclusions made drastic improvements on the coefficients of static and kinetic frictions. The undergraduate students were involved in the project and observed all the details of the process during the laboratory studies, as well as data collection, analysis and presentation. This study will be useful for the future trainings of the undergraduate engineering students on the composite, automobile and other manufacturing industries.

  2. 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

  3. Stick-slip chaos in a mechanical oscillator with dry friction

    NASA Astrophysics Data System (ADS)

    Kousaka, Takuji; Asahara, Hiroyuki; Inaba, Naohiko

    2018-03-01

    This study analyzes a forced mechanical dynamical system with dry friction that can generate chaotic stick-slip vibrations. We find that the dynamics proposed by Yoshitake et al. [Trans. Jpn. Soc. Mech. Eng. C 61, 768 (1995)] can be expressed as a nonautonomous constraint differential equation owing to the static friction force. The object is constrained to the surface of a moving belt by a static friction force from when it sticks to the surface until the force on the object exceeds the maximal static friction force. We derive a 1D Poincaré return map from the constrained mechanical system, and prove numerically that this 1D map has an absolutely continuous invariant measure and a positive Lyapunov exponent, providing strong evidence for chaos.

  4. Frictional `non-aging' of fault mirror surfaces?: Insight from friction experiments on Carrara marble

    NASA Astrophysics Data System (ADS)

    Park, Y.; Ree, J. H.; Hirose, T.

    2016-12-01

    Mirror-like fault surfaces (or fault mirror: FM) have recently been suggested as a precursor of unstable slip (thus indicative of seismic slip). Frictional aging of fault surfaces (increase in static friction during interseismic period) is a common phenomenon of fault surfaces, resulting from increase in contact area or in bond strength between asperities with time. Despite the importance of FM in earthquake faulting, the frictional-aging behavior of FM has never been studied. To understand the frictional-aging behavior of FM, slide-hold-slide friction experiments were done on carbonate FM and powdered gouge of former carbonate FM (PG hereafter) using low-to-high-velocity-rotary-shear apparatus, at a slip rate of 1 μm s-1 a normal stress of 1.5 MPa, room temperature and room humidity condition. The sheared PG specimens showed a logarithmic positive relationship between static friction and holding time, consistent with Dieterich-type healing behavior. In contrast, the sheared FM specimens showed little effect of holding time on static friction. The slip surface of FM specimens consists of densely-packed and sintered nano-particles while that of PG specimens is composed of loose nano-particles. It has been known that yield strength of a material increases dramatically with size-decreasing grains being nano-particles. Since FM is a layer of densely-packed and sintered nanoparticles, enhanced strength of FM may inhibit growth of real contact area of fault surfaces during hold time. Furthermore, sintered particles composing FM have less pore space than loose gouge layer, and thus there would be a less chance of strengthening by pore space reduction, inter-particle meniscus formation or water adsorption onto the particles surface in the FM layer. Our preliminary result suggests that carbonate FM's may impede the recovery of fault strength during interseismic period, resulting in less possibility of earthquake nucleation. Reduced frictional healing may be a common

  5. 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)

  6. Role of friction in vertically oscillated granular materials

    NASA Astrophysics Data System (ADS)

    Moon, Sung Joon; Swift, J. B.; Swinney, Harry L.

    2002-11-01

    We use a previously validated molecular dynamics simulation of vertically oscillated granular layers to study how the contact friction affects standing wave patterns. Our collision model follows Walton(O. R. Walton, in Particulate Two-Phase Flow), edited by M. C. Roco (Butterworth-Heinemann, Boston, 1993), p. 884.: Dissipation in the normal component of colliding velocity is characterized by the normal coefficient of restitution e (0<= e < 1), and interaction in the tangential component by the tangential coefficient of restitution β = β(μ,e,Φ), where -1<= β <= β_0, μ is the static coefficient of friction on the surface of grains, Φ is the collision angle, and β0 corresponds to the crossover between static and sliding friction. We varied the above parameters independently for the grain-grain collisions and for the grain-wall collisions. The grain-grain friction changes the phase diagram of patterns significantly, and the patterns become fuzzy as the friction is decreased. The grain-wall friction is necessary to stabilize the patterns.

  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. Perception and Haptic Rendering of Friction Moments.

    PubMed

    Kawasaki, H; Ohtuka, Y; Koide, S; Mouri, T

    2011-01-01

    This paper considers moments due to friction forces on the human fingertip. A computational technique called the friction moment arc method is presented. The method computes the static and/or dynamic friction moment independent of a friction force calculation. In addition, a new finger holder to display friction moment is presented. This device incorporates a small brushless motor and disk, and connects the human's finger to an interface finger of the five-fingered haptic interface robot HIRO II. Subjects' perception of friction moment while wearing the finger holder, as well as perceptions during object manipulation in a virtual reality environment, were evaluated experimentally.

  9. The coefficient of friction, particularly of ice

    NASA Astrophysics Data System (ADS)

    Mills, Allan

    2008-07-01

    The static and dynamic coefficients of friction are defined, and values from 0.3 to 0.6 are quoted for common materials. These drop to about 0.15 when oil is added as a lubricant. Water ice at temperatures not far below 0 °C is remarkable for low coefficients of around 0.05 for static friction and 0.04-0.02 for dynamic friction, but these figures increase as the temperature diminishes. Reasons for the slipperiness of ice are summarized, but they are still not entirely clear. One hypothesis suggests that it is related to the transient formation of a lubricating film of liquid water produced by frictional heating. If this is the case, some composition melting a little above ambient temperatures might provide a skating rink that did not require expensive refrigeration. Various compositions have been tested, but an entirely satisfactory material has yet to be found.

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

    PubMed

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

    2015-05-08

    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.

  11. In-Vivo Human Skin to Textiles Friction Measurements

    NASA Astrophysics Data System (ADS)

    Pfarr, Lukas; Zagar, Bernhard

    2017-10-01

    We report on a measurement system to determine highly reliable and accurate friction properties of textiles as needed for example as input to garment simulation software. Our investigations led to a set-up that allows to characterize not just textile to textile but also textile to in-vivo human skin tribological properties and thus to fundamental knowledge about genuine wearer interaction in garments. The method of test conveyed in this paper is measuring concurrently and in a highly time resolved manner the normal force as well as the resulting shear force caused by a friction subject intending to slide out of the static friction regime and into the dynamic regime on a test bench. Deeper analysis of various influences is enabled by extending the simple model following Coulomb's law for rigid body friction to include further essential parameters such as contact force, predominance in the yarn's orientation and also skin hydration. This easy-to-use system enables to measure reliably and reproducibly both static and dynamic friction for a variety of friction partners including human skin with all its variability there might be.

  12. Discrete dislocation plasticity analysis of loading rate-dependent static friction.

    PubMed

    Song, H; Deshpande, V S; Van der Giessen, E

    2016-08-01

    From a microscopic point of view, the frictional force associated with the relative sliding of rough surfaces originates from deformation of the material in contact, by adhesion in the contact interface or both. We know that plastic deformation at the size scale of micrometres is not only dependent on the size of the contact, but also on the rate of deformation. Moreover, depending on its physical origin, adhesion can also be size and rate dependent, albeit different from plasticity. We present a two-dimensional model that incorporates both discrete dislocation plasticity inside a face-centred cubic crystal and adhesion in the interface to understand the rate dependence of friction caused by micrometre-size asperities. The friction strength is the outcome of the competition between adhesion and discrete dislocation plasticity. As a function of contact size, the friction strength contains two plateaus: at small contact length [Formula: see text], the onset of sliding is fully controlled by adhesion while for large contact length [Formula: see text], the friction strength approaches the size-independent plastic shear yield strength. The transition regime at intermediate contact size is a result of partial de-cohesion and size-dependent dislocation plasticity, and is determined by dislocation properties, interfacial properties as well as by the loading rate.

  13. 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

  14. The amazing cases of motion with friction

    NASA Astrophysics Data System (ADS)

    Grech, Dariusz; Mazur, Zygmunt

    2001-07-01

    The paper describes the behaviour of a simple mechanical system, which should help students (or teachers) to understand and clarify the importance of relative motion of two surfaces when kinetic friction is present. We show that despite the simplicity of this system, the peculiar interplay between friction forces, tension forces and gravity leads to physical solutions exceeding in many cases most intuitive expectations. These are discussed in detail. The problem is intended to be solved in a theoretical framework as an example, which helps to understand better the physical background of kinetic friction phenomena.

  15. The Influence of Friction Between Football Helmet and Jersey Materials on Force: A Consideration for Sport Safety

    PubMed Central

    Rossi, Anthony M.; Claiborne, Tina L.; Thompson, Gregory B.; Todaro, Stacey

    2016-01-01

    Context: The pocketing effect of helmet padding helps to dissipate forces experienced by the head, but if the player's helmet remains stationary in an opponent's shoulder pads, the compressive force on the cervical spine may increase. Objective: To (1) measure the coefficient of static friction between different football helmet finishes and football jersey fabrics and (2) calculate the potential amount of force on a player's helmet due to the amount of friction present. Design: Cross-sectional study. Setting: Laboratory. Patients or Other Participants: Helmets with different finishes and different football jersey fabrics. Main Outcome Measure(s): The coefficient of friction was determined for 2 helmet samples (glossy and matte), 3 football jerseys (collegiate, high school, and youth), and 3 types of jersey numbers (silkscreened, sublimated, and stitched on) using the TAPPI T 815 standard method. These measurements determined which helmet-to-helmet, helmet-to-jersey number, and helmet-to-jersey material combination resulted in the least amount of static friction. Results: The glossy helmet versus glossy helmet combination produced a greater amount of static friction than the other 2 helmet combinations (P = .013). The glossy helmet versus collegiate jersey combination produced a greater amount of static friction than the other helmet-to-jersey material combinations (P < .01). The glossy helmet versus silkscreened numbers combination produced a greater amount of static friction than the other helmet-to-jersey number combinations (P < .01). Conclusions: The force of static friction experienced during collisions can be clinically relevant. Conditions with higher coefficients of static friction result in greater forces. In this study, the highest coefficient of friction (glossy helmet versus silkscreened number) could increase the forces on the player's helmet by 3553.88 N when compared with other helmet-to-jersey combinations. Our results indicate that the makeup of

  16. The Influence of Friction Between Football Helmet and Jersey Materials on Force: A Consideration for Sport Safety.

    PubMed

    Rossi, Anthony M; Claiborne, Tina L; Thompson, Gregory B; Todaro, Stacey

    2016-09-01

    The pocketing effect of helmet padding helps to dissipate forces experienced by the head, but if the player's helmet remains stationary in an opponent's shoulder pads, the compressive force on the cervical spine may increase. To (1) measure the coefficient of static friction between different football helmet finishes and football jersey fabrics and (2) calculate the potential amount of force on a player's helmet due to the amount of friction present. Cross-sectional study. Laboratory. Helmets with different finishes and different football jersey fabrics. The coefficient of friction was determined for 2 helmet samples (glossy and matte), 3 football jerseys (collegiate, high school, and youth), and 3 types of jersey numbers (silkscreened, sublimated, and stitched on) using the TAPPI T 815 standard method. These measurements determined which helmet-to-helmet, helmet-to-jersey number, and helmet-to-jersey material combination resulted in the least amount of static friction. The glossy helmet versus glossy helmet combination produced a greater amount of static friction than the other 2 helmet combinations (P = .013). The glossy helmet versus collegiate jersey combination produced a greater amount of static friction than the other helmet-to-jersey material combinations (P < .01). The glossy helmet versus silkscreened numbers combination produced a greater amount of static friction than the other helmet-to-jersey number combinations (P < .01). The force of static friction experienced during collisions can be clinically relevant. Conditions with higher coefficients of static friction result in greater forces. In this study, the highest coefficient of friction (glossy helmet versus silkscreened number) could increase the forces on the player's helmet by 3553.88 N when compared with other helmet-to-jersey combinations. Our results indicate that the makeup of helmet and uniform materials may affect sport safety.

  17. Modifying friction between ultra-high molecular weight polyethylene (UHMWPE) yarns with plasma enhanced chemical vapour deposition (PCVD)

    NASA Astrophysics Data System (ADS)

    Chu, Yanyan; Chen, Xiaogang; Tian, Lipeng

    2017-06-01

    Ultra-high molecular weight polyethylene (UHMWPE) yarns are widely used in military applications for protection owing to its high modulus and high strength; however, the friction between UHMWPE yarns is too small, which is a weakness for ballistic applications. The purpose of current research is to increase the friction between UHMWPE yarns by plasma enhanced chemical vapour deposition (PCVD). The changes of morphology and chemical structure were characterised by SEM and FTIR individually. The coefficients of friction between yarns were tested by means of Capstan method. Results from tests showed that the yarn-yarn coefficient of static friction (CSF) has been improved from 0.12 to 0.23 and that of kinetic friction (CSF) increased from 0.11 to 0.19, as the samples exposure from 21 s to 4 min. The more inter-yarn friction can be attributed to more and more particles and more polar groups deposited on the surfaces of yarns, including carboxyl, carbonyl, hydroxyl and amine groups and compounds containing silicon. The tensile strength and modulus of yarns, which are essential to ballistic performance, keep stable and are not affected by the treatments, indicating that PCVD treatment is an effective way to improve the inter-yarn friction without mechanical property degradation.

  18. A multivariable model for predicting the frictional behaviour and hydration of the human skin.

    PubMed

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

    2013-08-01

    The frictional characteristics of skin-object interactions are important when handling objects, in the assessment of perception and comfort of products and materials and in the origins and prevention of skin injuries. In this study, based on statistical methods, a quantitative model is developed that describes the friction behaviour of human skin as a function of the subject characteristics, contact conditions, the properties of the counter material as well as environmental conditions. Although the frictional behaviour of human skin is a multivariable problem, in literature the variables that are associated with skin friction have been studied using univariable methods. In this work, multivariable models for the static and dynamic coefficients of friction as well as for the hydration of the skin are presented. A total of 634 skin-friction measurements were performed using a recently developed tribometer. Using a statistical analysis, previously defined potential influential variables were linked to the static and dynamic coefficient of friction and to the hydration of the skin, resulting in three predictive quantitative models that descibe the friction behaviour and the hydration of human skin respectively. Increased dynamic coefficients of friction were obtained from older subjects, on the index finger, with materials with a higher surface energy at higher room temperatures, whereas lower dynamic coefficients of friction were obtained at lower skin temperatures, on the temple with rougher contact materials. The static coefficient of friction increased with higher skin hydration, increasing age, on the index finger, with materials with a higher surface energy and at higher ambient temperatures. The hydration of the skin was associated with the skin temperature, anatomical location, presence of hair on the skin and the relative air humidity. Predictive models have been derived for the static and dynamic coefficient of friction using a multivariable approach. These

  19. Kinetic theory of dark solitons with tunable friction.

    PubMed

    Hurst, Hilary M; Efimkin, Dmitry K; Spielman, I B; Galitski, Victor

    2017-05-01

    We study controllable friction in a system consisting of a dark soliton in a one-dimensional Bose-Einstein condensate coupled to a noninteracting Fermi gas. The fermions act as impurity atoms, not part of the original condensate, that scatter off of the soliton. We study semiclassical dynamics of the dark soliton, a particlelike object with negative mass, and calculate its friction coefficient. Surprisingly, it depends periodically on the ratio of interspecies (impurity-condensate) to intraspecies (condensate-condensate) interaction strengths. By tuning this ratio, one can access a regime where the friction coefficient vanishes. We develop a general theory of stochastic dynamics for negative-mass objects and find that their dynamics are drastically different from their positive-mass counterparts: they do not undergo Brownian motion. From the exact phase-space probability distribution function (i.e., in position and velocity), we find that both the trajectory and lifetime of the soliton are altered by friction, and the soliton can undergo Brownian motion only in the presence of friction and a confining potential. These results agree qualitatively with experimental observations by Aycock et al. [Proc. Natl. Acad. Sci. USA 114 , 2503 (2017)] in a similar system with bosonic impurity scatterers.

  20. Kinetic theory of dark solitons with tunable friction

    PubMed Central

    Hurst, Hilary M.; Efimkin, Dmitry K.; Spielman, I. B.; Galitski, Victor

    2018-01-01

    We study controllable friction in a system consisting of a dark soliton in a one-dimensional Bose-Einstein condensate coupled to a noninteracting Fermi gas. The fermions act as impurity atoms, not part of the original condensate, that scatter off of the soliton. We study semiclassical dynamics of the dark soliton, a particlelike object with negative mass, and calculate its friction coefficient. Surprisingly, it depends periodically on the ratio of interspecies (impurity-condensate) to intraspecies (condensate-condensate) interaction strengths. By tuning this ratio, one can access a regime where the friction coefficient vanishes. We develop a general theory of stochastic dynamics for negative-mass objects and find that their dynamics are drastically different from their positive-mass counterparts: they do not undergo Brownian motion. From the exact phase-space probability distribution function (i.e., in position and velocity), we find that both the trajectory and lifetime of the soliton are altered by friction, and the soliton can undergo Brownian motion only in the presence of friction and a confining potential. These results agree qualitatively with experimental observations by Aycock et al. [Proc. Natl. Acad. Sci. USA 114, 2503 (2017)] in a similar system with bosonic impurity scatterers. PMID:29744482

  1. Friction is Fracture: a new paradigm for the onset of frictional motion

    NASA Astrophysics Data System (ADS)

    Fineberg, Jay

    Friction is generally described by a single degree of freedom, a `friction coefficient'. We experimentally study the space-time dynamics of the onset of dry and lubricated frictional motion when two contacting bodies start to slide. We first show that the transition from static to dynamic sliding is governed by rupture fronts (closely analogous to earthquakes) that break the contacts along the interface separating the two bodies. Moreover, the structure of these ''laboratory earthquakes'' is quantitatively described by singular solutions originally derived to describe the motion of rapid cracks under applied shear. We demonstrate that this framework quantitatively describes both earthquake motion and arrest. This framework also providing a new window into the hidden properties of the micron thick interface that governs a body's frictional properties. Using this window we show that lubricated interfaces, although ``slippery'', actually becomes tougher; lubricants significantly increase dissipated energy during rupture. The results establish a new (and fruitful) paradigm for describing friction. Israel Science Foundation, ERC.

  2. Load and Time Dependence of Interfacial Chemical Bond-Induced Friction at the Nanoscale.

    PubMed

    Tian, Kaiwen; Gosvami, Nitya N; Goldsby, David L; Liu, Yun; Szlufarska, Izabela; Carpick, Robert W

    2017-02-17

    Rate and state friction (RSF) laws are widely used empirical relationships that describe the macroscale frictional behavior of a broad range of materials, including rocks found in the seismogenic zone of Earth's crust. A fundamental aspect of the RSF laws is frictional "aging," where friction increases with the time of stationary contact due to asperity creep and/or interfacial strengthening. Recent atomic force microscope (AFM) experiments and simulations found that nanoscale silica contacts exhibit aging due to the progressive formation of interfacial chemical bonds. The role of normal load (and, thus, normal stress) on this interfacial chemical bond-induced (ICBI) friction is predicted to be significant but has not been examined experimentally. Here, we show using AFM that, for nanoscale ICBI friction of silica-silica interfaces, aging (the difference between the maximum static friction and the kinetic friction) increases approximately linearly with the product of the normal load and the log of the hold time. This behavior is attributed to the approximately linear dependence of the contact area on the load in the positive load regime before significant wear occurs, as inferred from sliding friction measurements. This implies that the average pressure, and thus the average bond formation rate, is load independent within the accessible load range. We also consider a more accurate nonlinear model for the contact area, from which we extract the activation volume and the average stress-free energy barrier to the aging process. Our work provides an approach for studying the load and time dependence of contact aging at the nanoscale and further establishes RSF laws for nanoscale asperity contacts.

  3. Load and Time Dependence of Interfacial Chemical Bond-Induced Friction at the Nanoscale

    NASA Astrophysics Data System (ADS)

    Tian, Kaiwen; Gosvami, Nitya N.; Goldsby, David L.; Liu, Yun; Szlufarska, Izabela; Carpick, Robert W.

    2017-02-01

    Rate and state friction (RSF) laws are widely used empirical relationships that describe the macroscale frictional behavior of a broad range of materials, including rocks found in the seismogenic zone of Earth's crust. A fundamental aspect of the RSF laws is frictional "aging," where friction increases with the time of stationary contact due to asperity creep and/or interfacial strengthening. Recent atomic force microscope (AFM) experiments and simulations found that nanoscale silica contacts exhibit aging due to the progressive formation of interfacial chemical bonds. The role of normal load (and, thus, normal stress) on this interfacial chemical bond-induced (ICBI) friction is predicted to be significant but has not been examined experimentally. Here, we show using AFM that, for nanoscale ICBI friction of silica-silica interfaces, aging (the difference between the maximum static friction and the kinetic friction) increases approximately linearly with the product of the normal load and the log of the hold time. This behavior is attributed to the approximately linear dependence of the contact area on the load in the positive load regime before significant wear occurs, as inferred from sliding friction measurements. This implies that the average pressure, and thus the average bond formation rate, is load independent within the accessible load range. We also consider a more accurate nonlinear model for the contact area, from which we extract the activation volume and the average stress-free energy barrier to the aging process. Our work provides an approach for studying the load and time dependence of contact aging at the nanoscale and further establishes RSF laws for nanoscale asperity contacts.

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

    PubMed

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

    2011-11-30

    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.

  5. Investigation of the Maximum Spin-Up Coefficients of Friction Obtained During Tests of a Landing Gear Having a Static-Load Rating of 20,000 Pounds

    NASA Technical Reports Server (NTRS)

    Batterson, Sidney A.

    1959-01-01

    An experimental investigation was made at the Langley landing loads track to obtain data on the maximum spin-up coefficients of friction developed by a landing gear having a static-load rating of 20,000 pounds. The forward speeds ranged from 0 to approximately 180 feet per second and the sinking speeds, from 2.7 feet per second to 9.4 feet per second. The results indicated the variation of the maximum spin-up coefficient of friction with forward speed and vertical load. Data obtained during this investigation are also compared with some results previously obtained for nonrolling tires to show the effect of forward speed.

  6. 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

  7. 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

  8. The Effect of Prestrain Temperature on Kinetics of Static Recrystallization, Microstructure Evolution, and Mechanical Properties of Low Carbon Steel

    NASA Astrophysics Data System (ADS)

    Akbari, Edris; Karimi Taheri, Kourosh; Karimi Taheri, Ali

    2018-05-01

    In this research, the samples of a low carbon steel sheet were rolled up to a thickness prestrain of 67% at three different temperatures consisted of room, blue brittleness, and subzero temperature. Microhardness, SEM, and tensile tests were carried out to evaluate the static recrystallization kinetics defined by the Avrami equation, microstructural evolution, and mechanical properties. It was found that the Avrami exponent is altered with change in prestrain temperature and it achieves the value of 1 to 1. 5. Moreover, it was indicated that prestraining at subzero temperature followed by annealing at 600 °C leads to considerable enhancement in tensile properties and kinetics of static recrystallization compared to room and blue brittleness temperatures. The prestraining at blue brittleness temperature followed by annealing treatment caused, however, a higher strength and faster kinetics compared with that at room temperature. It was concluded that although from the steel ductility point of view, the blue brittleness temperature is called an unsuitable temperature, but it can be used as prestraining temperature to develop noticeable combination of strength and ductility in low carbon steel.

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

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    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 inmore » 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.« less

  10. 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…

  11. 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.

  12. 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.

  13. 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.

  14. Rolling Friction on a Wheeled Laboratory Cart

    DTIC Science & Technology

    2012-01-01

    by gravity, and a vehicle (such as a car or bicycle) accelerating along a level road is driven by a motor or by pedalling. In such cases, static...is slowing down, its acceleration a points downhill). The normal force N, frictional force f and axle torque four wheels. θ υ N a θ ω τ ƒ mg...friction force pointed backward (to translationally decelerate the object), then it would simultaneously rotationally accelerate the cylinder about its

  15. The evolving quality of frictional contact with graphene.

    PubMed

    Li, Suzhi; Li, Qunyang; Carpick, Robert W; Gumbsch, Peter; Liu, Xin Z; Ding, Xiangdong; Sun, Jun; Li, Ju

    2016-11-24

    Graphite and other lamellar materials are used as dry lubricants for macroscale metallic sliding components and high-pressure contacts. It has been shown experimentally that monolayer graphene exhibits higher friction than multilayer graphene and graphite, and that this friction increases with continued sliding, but the mechanism behind this remains subject to debate. It has long been conjectured that the true contact area between two rough bodies controls interfacial friction. The true contact area, defined for example by the number of atoms within the range of interatomic forces, is difficult to visualize directly but characterizes the quantity of contact. However, there is emerging evidence that, for a given pair of materials, the quality of the contact can change, and that this can also strongly affect interfacial friction. Recently, it has been found that the frictional behaviour of two-dimensional materials exhibits traits unlike those of conventional bulk materials. This includes the abovementioned finding that for few-layer two-dimensional materials the static friction force gradually strengthens for a few initial atomic periods before reaching a constant value. Such transient behaviour, and the associated enhancement of steady-state friction, diminishes as the number of two-dimensional layers increases, and was observed only when the two-dimensional material was loosely adhering to a substrate. This layer-dependent transient phenomenon has not been captured by any simulations. Here, using atomistic simulations, we reproduce the experimental observations of layer-dependent friction and transient frictional strengthening on graphene. Atomic force analysis reveals that the evolution of static friction is a manifestation of the natural tendency for thinner and less-constrained graphene to re-adjust its configuration as a direct consequence of its greater flexibility. That is, the tip atoms become more strongly pinned, and show greater synchrony in their stick

  16. 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 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.

  17. Fracture and Friction

    NASA Astrophysics Data System (ADS)

    Gerde, Eric; Marder, Michael

    2001-03-01

    We present an atomic scale description of a self-healing crack steadily traveling along a compressed interface between dissimilar solids. The motion is similar to the wrinkle-like Weertman pulse observed by Anooshehpoor in recent foam-rubber sliding experiments. In contrast to the theoretical models of Weertman and Adams, and the numerical calculations of Andrews and Ben-Zion, we do not employ a frictional constitutive law on the interface. Yet the restrictive conditions under which these cracks can propagate make the interface appear to have a static coefficient of friction. By analytically linking atomic and continuum fields, we are able to efficiently and exhaustively explore the conditions under which self-healing cracks can propagate. To a good approximation, they are sustainable only when the interfacial shear stresses are 0.4 times the compressive stresses.

  18. 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.

  19. 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.

  1. A Theoretical Investigation of Longitudinal Stability of Airplanes with Free Controls Including Effect of Friction in Control System

    NASA Technical Reports Server (NTRS)

    Greenberg, Harry; Sternfield, Leonard

    1944-01-01

    The relation between the elevator hinge moment parameters and the control forces for changes in forward speed and in maneuvers is shown for several values of static stability and elevator mass balance. The stability of the short period oscillations is shown as a series of boundaries giving the limits of the stable regions in terms of the elevator hinge moment parameters. The effects of static stability, elevator moment of inertia, elevator mass unbalance, and airplane density are also considered. Dynamic instability is likely to occur if there is mass unbalance of the elevator control system combined with a small restoring tendency (high aerodynamic balance). This instability can be prevented by a rearrangement of the unbalancing weights which, however, involves an increase of the amount of weight necessary. It can also be prevented by the addition of viscous friction to the elevator control system provided the airplane center of gravity is not behind a certain critical position. For high values of the density parameter, which correspond to high altitudes of flight, the addition of moderate amounts of viscous friction may be destabilizing even when the airplane is statically stable. In this case, increasing the viscous friction makes the oscillation stable again. The condition in which viscous friction causes dynamic instability of a statically stable airplane is limited to a definite range of hinge moment parameters. It is shown that, when viscous friction causes increasing oscillations, solid friction will produce steady oscillations having an amplitude proportional to the amount of friction.

  2. Experimental evidence for dynamic friction on rock fractures from frequency-dependent nonlinear hysteresis and harmonic generation

    NASA Astrophysics Data System (ADS)

    Saltiel, Seth; Bonner, Brian P.; Mittal, Tushar; Delbridge, Brent; Ajo-Franklin, Jonathan B.

    2017-07-01

    Frictional properties affect the propagation of high-amplitude seismic waves across rock fractures and faults. Laboratory evidence suggests that these properties can be measured in active seismic surveys, potentially offering a route to characterizing friction in situ. We present experimental results from a subresonance torsional modulus and attenuation apparatus that utilizes micron-scale sinusoidal oscillations to probe the nonlinear stress-strain relation at a range of strain amplitudes and rates. Nonlinear effects are further quantified using harmonic distortion; however, time series data best illuminate underlying physical processes. The low-frequency stress-strain hysteretic loops show stiffening at the sinusoid's static ends, but stiffening is reduced above a threshold frequency. This shape is determined by harmonic generation in the strain; the stress signal has no harmonics, confirming that the fractured sample is the source of the nonlinearity. These qualitative observations suggest the presence of rate-dependent friction and are consistent between fractures in three different rock types. We propose that static friction at the low strain rate part of the cycle, when given sufficient "healing" time at low oscillation frequencies, causes this stiffening cusp shape in the hysteresis loop. While rate-and-state friction is commonly used to represent dynamic friction, it cannot capture static friction or negative slip velocities. So we implement another dynamic friction model, based on the work of Dahl, which describes this process and produces similar results. Since the two models have a similar form, parameterizations of field data could constraint fault model inputs, such as specific location velocity strengthening or weakening properties.

  3. Influence of ligation method on friction resistance of lingual brackets with different second-order angulations: an in vitro study.

    PubMed

    Pereira, Graziane Olímpio; Gimenez, Carla Maria Melleiro; Prieto, Lucas; Prieto, Marcos Gabriel do Lago; Basting, Roberta Tarkany

    2016-01-01

    To evaluate stainless steel archwire static friction in active and passive self-ligating lingual and conventional brackets with second-order angulations. Two conventional lingual brackets for canines (STb light/Ormco; PSWb/Tecnident), and two self-ligating brackets, one active (In-Ovation L/GAC) and the other passive (3D/ Forestadent), were evaluated. A stainless steel archwire was used at 0°, 3° and 5° angulations. Metal ligatures, conventional elastic ligatures, and low friction elastic ligatures were also tested. A universal testing machine applied friction between brackets and wires, simulating sliding mechanics, to produce 2-mm sliding at 3 mm/minute speed. Two-way analysis of variance demonstrated a significant effect of the interaction between brackets and angulations (p < 0.001). Tukey test indicated that the highest frictional resistance values were observed at 5° angulation for In-Ovation L, PSWb bracket with non conventional ligature, and STb bracket with metal ligature. As for 3D, PSWb with conventional or metal ligatures, and STb brackets with non conventional ligature, showed significantly lower static frictional resistance with 0° angulation. At 0° angulation, STb brackets with metal ties, In-Ovation L brackets and 3D brackets had the lowest frictional resistance. As the angulation increased from 0° to 3°, static friction resistance increased. When angulation increased from 3° to 5°, static friction resistance increased or remained the same. Self-ligating 3D and In-Ovation L brackets, as well as conventional STb brackets, seem to be the best option when sliding mechanics is used to perform lingual orthodontic treatment.

  4. Influence of ligation method on friction resistance of lingual brackets with different second-order angulations: an in vitro study

    PubMed Central

    Pereira, Graziane Olímpio; Gimenez, Carla Maria Melleiro; Prieto, Lucas; Prieto, Marcos Gabriel do Lago; Basting, Roberta Tarkany

    2016-01-01

    ABSTRACT Objective: To evaluate stainless steel archwire static friction in active and passive self-ligating lingual and conventional brackets with second-order angulations. Methods: Two conventional lingual brackets for canines (STb light/Ormco; PSWb/Tecnident), and two self-ligating brackets, one active (In-Ovation L/GAC) and the other passive (3D/ Forestadent), were evaluated. A stainless steel archwire was used at 0°, 3° and 5° angulations. Metal ligatures, conventional elastic ligatures, and low friction elastic ligatures were also tested. A universal testing machine applied friction between brackets and wires, simulating sliding mechanics, to produce 2-mm sliding at 3 mm/minute speed. Results: Two-way analysis of variance demonstrated a significant effect of the interaction between brackets and angulations (p < 0.001). Tukey test indicated that the highest frictional resistance values were observed at 5° angulation for In-Ovation L, PSWb bracket with non conventional ligature, and STb bracket with metal ligature. As for 3D, PSWb with conventional or metal ligatures, and STb brackets with non conventional ligature, showed significantly lower static frictional resistance with 0° angulation. At 0° angulation, STb brackets with metal ties, In-Ovation L brackets and 3D brackets had the lowest frictional resistance. Conclusions: As the angulation increased from 0° to 3°, static friction resistance increased. When angulation increased from 3° to 5°, static friction resistance increased or remained the same. Self-ligating 3D and In-Ovation L brackets, as well as conventional STb brackets, seem to be the best option when sliding mechanics is used to perform lingual orthodontic treatment. PMID:27653262

  5. 14 CFR 23.173 - Static longitudinal stability.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Static longitudinal stability. 23.173 Section 23.173 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... airplane trimmed as indicated, the characteristics of the elevator control forces and the friction within...

  6. 14 CFR 23.173 - Static longitudinal stability.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Static longitudinal stability. 23.173 Section 23.173 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... airplane trimmed as indicated, the characteristics of the elevator control forces and the friction within...

  7. 14 CFR 23.173 - Static longitudinal stability.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Static longitudinal stability. 23.173 Section 23.173 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... airplane trimmed as indicated, the characteristics of the elevator control forces and the friction within...

  8. 14 CFR 23.173 - Static longitudinal stability.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Static longitudinal stability. 23.173 Section 23.173 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... airplane trimmed as indicated, the characteristics of the elevator control forces and the friction within...

  9. 14 CFR 23.173 - Static longitudinal stability.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Static longitudinal stability. 23.173 Section 23.173 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... airplane trimmed as indicated, the characteristics of the elevator control forces and the friction within...

  10. Effect of friction on anodic polarization properties of metallic biomaterials.

    PubMed

    Okazaki, Yoshimitsu

    2002-05-01

    The effect of friction on the anodic polarization properties of metallic biomaterials in a physiological saline solution was investigated. The current density during friction becomes higher than during the static condition. The fluctuation range of the current density caused by the destruction and formation of passive film was observed. For SUS316L stainless steel and Co-Cr-Mo casting alloy, the fluctuation range was observed in the passivity zone. Otherwise, for Ti alloys, the fluctuation range was observed in both the activity and passivity zones. The decrease of the corrosion potential for Ti alloys due to friction was much larger than that of SUS316L stainless steel and Co-Cr-Mo casting alloy. From this result, it was considered that in a the frictional environment, the stressing zone turned anodic and its periphery cathodic, and corrosion tended to progress more than in the static environment. The effect of wear on the anodic polarization curves also changed depending on the frictional load, potential zone and the pH of the solution. A rapid increase in current density due to corrosion starting from the frictional area was found in the Ti-6Al-4V and Ti-15Mo-5Zr-3Al alloys containing Al. However, for the new Ti-15Zr-4Nb-4Ta alloy, this rapid increase was not seen in the high-potential region. The effect of the lateral reciprocal speed was also negligible for the new Ti alloy. It was found that the new Ti-15Zr-4Nb-4Ta alloy exhibited excellent corrosion resistance under friction.

  11. Three-dimensional friction measurement during hip simulation.

    PubMed

    Sonntag, Robert; Braun, Steffen; Al-Salehi, Loay; Reinders, Joern; Mueller, Ulrike; Kretzer, J Philippe

    2017-01-01

    Wear of total hip replacements has been the focus of many studies. However, frictional effects, such as high loading on intramodular connections or the interface to the bone, as well as friction associated squeaking have recently increased interest about the amount of friction that is generated during daily activities. The aim of this study was thus to establish and validate a three-dimensional friction setup under standardized conditions. A standard hip simulator was modified to allow for high precision measurements of small frictional effects in the hip during three-dimensional hip articulation. The setup was verified by an ideal hydrostatic bearing and validated with a static-load physical pendulum and an extension-flexion rotation with a dynamic load profile. Additionally, a pendulum model was proposed for screening measurement of frictional effects based on the damping behavior of the angular oscillation without the need for any force/moment transducer. Finally, three-dimensional friction measurements have been realized for ceramic-on-polyethylene bearings of three different sizes (28, 36 and 40 mm). A precision of less than 0.2 Nm during three-dimensional friction measurements was reported, while increased frictional torque (resultant as well as taper torque) was measured for larger head diameters. These effects have been confirmed by simple pendulum tests and the theoretical model. A comparison with current literature about friction measurements is presented. This investigation of friction is able to provide more information about a field that has been dominated by the reduction of wear. It should be considered in future pre-clinical testing protocols given by international organizations of standardization.

  12. One-step global parameter estimation of kinetic inactivation parameters for Bacillus sporothermodurans spores under static and dynamic thermal processes.

    PubMed

    Cattani, F; Dolan, K D; Oliveira, S D; Mishra, D K; Ferreira, C A S; Periago, P M; Aznar, A; Fernandez, P S; Valdramidis, V P

    2016-11-01

    Bacillus sporothermodurans produces highly heat-resistant endospores, that can survive under ultra-high temperature. High heat-resistant sporeforming bacteria are one of the main causes for spoilage and safety of low-acid foods. They can be used as indicators or surrogates to establish the minimum requirements for heat processes, but it is necessary to understand their thermal inactivation kinetics. The aim of the present work was to study the inactivation kinetics under both static and dynamic conditions in a vegetable soup. Ordinary least squares one-step regression and sequential procedures were applied for estimating these parameters. Results showed that multiple dynamic heating profiles, when analyzed simultaneously, can be used to accurately estimate the kinetic parameters while significantly reducing estimation errors and data collection. Copyright © 2016 Elsevier Ltd. All rights reserved.

  13. 14 CFR 25.173 - Static longitudinal stability.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Static longitudinal stability. 25.173 Section 25.173 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... forces (including friction) must be as follows: (a) A pull must be required to obtain and maintain speeds...

  14. 14 CFR 25.173 - Static longitudinal stability.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Static longitudinal stability. 25.173 Section 25.173 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... forces (including friction) must be as follows: (a) A pull must be required to obtain and maintain speeds...

  15. 14 CFR 25.173 - Static longitudinal stability.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Static longitudinal stability. 25.173 Section 25.173 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... forces (including friction) must be as follows: (a) A pull must be required to obtain and maintain speeds...

  16. 14 CFR 25.173 - Static longitudinal stability.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Static longitudinal stability. 25.173 Section 25.173 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... forces (including friction) must be as follows: (a) A pull must be required to obtain and maintain speeds...

  17. 14 CFR 25.173 - Static longitudinal stability.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Static longitudinal stability. 25.173 Section 25.173 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... forces (including friction) must be as follows: (a) A pull must be required to obtain and maintain speeds...

  18. Solution procedure of dynamical contact problems with friction

    NASA Astrophysics Data System (ADS)

    Abdelhakim, Lotfi

    2017-07-01

    Dynamical contact is one of the common research topics because of its wide applications in the engineering field. The main goal of this work is to develop a time-stepping algorithm for dynamic contact problems. We propose a finite element approach for elastodynamics contact problems [1]. Sticking, sliding and frictional contact can be taken into account. Lagrange multipliers are used to enforce non-penetration condition. For the time discretization, we propose a scheme equivalent to the explicit Newmark scheme. Each time step requires solving a nonlinear problem similar to a static friction problem. The nonlinearity of the system of equation needs an iterative solution procedure based on Uzawa's algorithm [2][3]. The applicability of the algorithm is illustrated by selected sample numerical solutions to static and dynamic contact problems. Results obtained with the model have been compared and verified with results from an independent numerical method.

  19. Biomechanics of ant adhesive pads: frictional forces are rate- and temperature-dependent.

    PubMed

    Federle, Walter; Baumgartner, Werner; Hölldobler, Bert

    2004-01-01

    Tarsal adhesive pads enable insects to hold on to smooth plant surfaces. Using a centrifuge technique, we tested whether a "wet adhesion" model of a thin film of liquid secreted between the pad and the surface can explain adhesive and frictional forces in Asian Weaver ants (Oecophylla smaragdina). When forces are acting parallel to the surface, pads in contact with the surface can slide smoothly. Force per unit pad contact area was strongly dependent on sliding velocity and temperature. Seemingly consistent with the effect of a thin liquid film in the contact zone, (1) frictional force linearly increased with sliding velocity, (2) the increment was greater at lower temperatures and (3) no temperature dependence was detected for low-rate perpendicular detachment forces. However, we observed a strong, temperature-independent static friction that was inconsistent with a fully lubricated contact. Static friction was too large to be explained by the contribution of other (sclerotized) body parts. Moreover, the rate-specific increase of shear stress strongly exceeded predictions derived from estimates of the adhesive liquid film's thickness and viscosity. Both lines of evidence indicate that the adhesive secretion alone is insufficient to explain the observed forces and that direct interaction of the soft pad cuticle with the surface ("rubber friction") is involved.

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

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    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 ofmore » (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.« less

  1. Numerical Modeling Describing the Effects of Heterogeneous Distributions of Asperities on the Quasi-static Evolution of Frictional Slip

    NASA Astrophysics Data System (ADS)

    Selvadurai, P. A.; Parker, J. M.; Glaser, S. D.

    2017-12-01

    A better understanding of how slip accumulates along faults and its relation to the breakdown of shear stress is beneficial to many engineering disciplines, such as, hydraulic fracture and understanding induced seismicity (among others). Asperities forming along a preexisting fault resist the relative motion of the two sides of the interface and occur due to the interaction of the surface topographies. Here, we employ a finite element model to simulate circular partial slip asperities along a nominally flat frictional interface. Shear behavior of our partial slip asperity model closely matched the theory described by Cattaneo. The asperity model was employed to simulate a small section of an experimental fault formed between two bodies of polymethyl methacrylate, which consisted of multiple asperities whose location and sizes were directly measured using a pressure sensitive film. The quasi-static shear behavior of the interface was modeled for cyclical loading conditions, and the frictional dissipation (hysteresis) was normal stress dependent. We further our understanding by synthetically modeling lognormal size distributions of asperities that were randomly distributed in space. Synthetic distributions conserved the real contact area and aspects of the size distributions from the experimental case, allowing us to compare the constitutive behaviors based solely on spacing effects. Traction-slip behavior of the experimental interface appears to be considerably affected by spatial clustering of asperities that was not present in the randomly spaced, synthetic asperity distributions. Estimates of bulk interfacial shear stiffness were determined from the constitutive traction-slip behavior and were comparable to the theoretical estimates of multi-contact interfaces with non-interacting asperities.

  2. 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.

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

    NASA Astrophysics Data System (ADS)

    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.

  4. 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.

  5. Three-dimensional friction measurement during hip simulation

    PubMed Central

    Braun, Steffen; Al-Salehi, Loay; Reinders, Joern; Mueller, Ulrike; Kretzer, J. Philippe

    2017-01-01

    Objectives Wear of total hip replacements has been the focus of many studies. However, frictional effects, such as high loading on intramodular connections or the interface to the bone, as well as friction associated squeaking have recently increased interest about the amount of friction that is generated during daily activities. The aim of this study was thus to establish and validate a three-dimensional friction setup under standardized conditions. Materials and methods A standard hip simulator was modified to allow for high precision measurements of small frictional effects in the hip during three-dimensional hip articulation. The setup was verified by an ideal hydrostatic bearing and validated with a static-load physical pendulum and an extension-flexion rotation with a dynamic load profile. Additionally, a pendulum model was proposed for screening measurement of frictional effects based on the damping behavior of the angular oscillation without the need for any force/moment transducer. Finally, three-dimensional friction measurements have been realized for ceramic-on-polyethylene bearings of three different sizes (28, 36 and 40 mm). Results A precision of less than 0.2 Nm during three-dimensional friction measurements was reported, while increased frictional torque (resultant as well as taper torque) was measured for larger head diameters. These effects have been confirmed by simple pendulum tests and the theoretical model. A comparison with current literature about friction measurements is presented. Conclusions This investigation of friction is able to provide more information about a field that has been dominated by the reduction of wear. It should be considered in future pre-clinical testing protocols given by international organizations of standardization. PMID:28886102

  6. Peptide chain dynamics in light and heavy water: zooming in on internal friction.

    PubMed

    Schulz, Julius C F; Schmidt, Lennart; Best, Robert B; Dzubiella, Joachim; Netz, Roland R

    2012-04-11

    Frictional effects due to the chain itself, rather than the solvent, may have a significant effect on protein dynamics. Experimentally, such "internal friction" has been investigated by studying folding or binding kinetics at varying solvent viscosity; however, the molecular origin of these effects is hard to pinpoint. We consider the kinetics of disordered glycine-serine and α-helix forming alanine peptides and a coarse-grained protein folding model in explicit-solvent molecular dynamics simulations. By varying the solvent mass over more than two orders of magnitude, we alter only the solvent viscosity and not the folding free energy. Folding dynamics at the near-vanishing solvent viscosities accessible by this approach suggests that solvent and internal friction effects are intrinsically entangled. This finding is rationalized by calculation of the polymer end-to-end distance dynamics from a Rouse model that includes internal friction. An analysis of the friction profile along different reaction coordinates, extracted from the simulation data, demonstrates that internal as well as solvent friction varies substantially along the folding pathways and furthermore suggests a connection between friction and the formation of hydrogen bonds upon folding. © 2012 American Chemical Society

  7. Nonmonotonic Aging and Memory in a Frictional Interface

    NASA Astrophysics Data System (ADS)

    Dillavou, Sam; Rubinstein, Shmuel M.

    2018-06-01

    We measure the static frictional resistance and the real area of contact between two solid blocks subjected to a normal load. We show that following a two-step change in the normal load the system exhibits nonmonotonic aging and memory effects, two hallmarks of glassy dynamics. These dynamics are strongly influenced by the discrete geometry of the frictional interface, characterized by the attachment and detachment of unique microcontacts. The results are in good agreement with a theoretical model we propose that incorporates this geometry into the framework recently used to describe Kovacs-like relaxation in glasses as well as thermal disordered systems. These results indicate that a frictional interface is a glassy system and strengthen the notion that nonmonotonic relaxation behavior is generic in such systems.

  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. Determining friction and effective loading for sled sprinting.

    PubMed

    Cross, Matt R; Tinwala, Farhan; Lenetsky, Seth; Samozino, Pierre; Brughelli, Matt; Morin, Jean-Benoit

    2017-11-01

    Understanding the impact of friction in sled sprinting allows the quantification of kinetic outputs and the effective loading experienced by the athlete. This study assessed changes in the coefficient of friction (µ k ) of a sled sprint-training device with changing mass and speed to provide a means of quantifying effective loading for athletes. A common sled equipped with a load cell was towed across an athletics track using a motorised winch under variable sled mass (33.1-99.6 kg) with constant speeds (0.1 and 0.3 m · s -1 ), and with constant sled mass (55.6 kg) and varying speeds (0.1-6.0 m · s -1 ). Mean force data were analysed, with five trials performed for each condition to assess the reliability of measures. Variables were determined as reliable (ICC > 0.99, CV < 4.3%), with normal-force/friction-force and speed/coefficient of friction relationships well fitted with linear (R 2  = 0.994-0.995) and quadratic regressions (R 2  = 0.999), respectively (P < 0.001). The linearity of composite friction values determined at two speeds, and the range in values from the quadratic fit (µ k  = 0.35-0.47) suggested µ k and effective loading were dependent on instantaneous speed on athletics track surfaces. This research provides a proof-of-concept for the assessment of friction characteristics during sled towing, with a practical example of its application in determining effective loading and sled-sprinting kinetics. The results clarify effects of friction during sled sprinting and improve the accuracy of loading applications in practice and transparency of reporting in research.

  10. 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.

  11. Yield surfaces for frictional sphere assemblages

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Goddard, J.D.; Didwania, A.K.

    1995-12-31

    By means of a recently developed computer algorithm for simulation of the quasi-static I mechanics of sphere assemblages, we have performed extensive computations of the dilatancy and plasticity of such systems for various proportional loading histories. We have investigated the effect of initial packing density or void ratio, size polydispersity, friction coefficient and plastic strain on the evolution of the yield surface. We find that all the yield surfaces tend to an asymptotic form which is well represented by the Lade-Duncan yield surface, developed originally for sand, suggesting that the Lade-Duncan form may reflect some universality in the behavior ofmore » assemblages of rigid frictional particles.« less

  12. 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.

  13. On the turbulent friction layer for rising pressure

    NASA Technical Reports Server (NTRS)

    Wieghardt, K; Tillmann, W

    1951-01-01

    Among the information presented are included displacement, momentum, and kinetic energy thicknesses, shearing stress distributions across boundary layer, and surface friction coefficients. The Gruschwitz method and its modifications are examined and tested. An energy theorem for the turbulent boundary layer is introduced and discussed but does not lead to a method for the prediction of the behavior of the turbulent boundary layer because relations for the shearing stress and the surface friction are lacking.

  14. 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.

  15. Earthquake triggering by transient and static deformations

    USGS Publications Warehouse

    Gomberg, J.; Beeler, N.M.; Blanpied, M.L.; Bodin, P.

    1998-01-01

    Observational evidence for both static and transient near-field and far-field triggered seismicity are explained in terms of a frictional instability model, based on a single degree of freedom spring-slider system and rate- and state-dependent frictional constitutive equations. In this study a triggered earthquake is one whose failure time has been advanced by ??t (clock advance) due to a stress perturbation. Triggering stress perturbations considered include square-wave transients and step functions, analogous to seismic waves and coseismic static stress changes, respectively. Perturbations are superimposed on a constant background stressing rate which represents the tectonic stressing rate. The normal stress is assumed to be constant. Approximate, closed-form solutions of the rate-and-state equations are derived for these triggering and background loads, building on the work of Dieterich [1992, 1994]. These solutions can be used to simulate the effects of static and transient stresses as a function of amplitude, onset time t0, and in the case of square waves, duration. The accuracies of the approximate closed-form solutions are also evaluated with respect to the full numerical solution and t0. The approximate solutions underpredict the full solutions, although the difference decreases as t0, approaches the end of the earthquake cycle. The relationship between ??t and t0 differs for transient and static loads: a static stress step imposed late in the cycle causes less clock advance than an equal step imposed earlier, whereas a later applied transient causes greater clock advance than an equal one imposed earlier. For equal ??t, transient amplitudes must be greater than static loads by factors of several tens to hundreds depending on t0. We show that the rate-and-state model requires that the total slip at failure is a constant, regardless of the loading history. Thus a static load applied early in the cycle, or a transient applied at any time, reduces the stress

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

    PubMed

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

    2016-05-26

    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).

  17. Characterization of friction in the 3.6m Devasthal optical telescope

    NASA Astrophysics Data System (ADS)

    Kumar, T. S.; Bastin, Christian; Kumar, Brijesh

    2016-07-01

    In this paper, we present the work on characterization of friction in the 3.6 m Devasthal optical telescope axes. The telescope azimuth axis is supported on a hydrostatic bearing while the altitude and rotator axes are supported on hydrodynamic bearings. Both altitude and azimuth axes are driven directly by high power BLDC motors and the rotator is driven by BLDC motor via a gearbox. This system is designed by AMOS, Belgium and tuned to achieve a tracking accuracy better than 0.1 arcsec RMS. Friction poses control related problems at such low speeds hence it is important to periodically characterize the behaviour at each axes. Compensation is necessary if the friction behaviour changes over the time and starts dominating the overall system response. For identifying friction each axis of telescope is rotated at different constant speeds and speed versus torque maps are generated. The LuGre model for friction is employed and nonlinear optimization is performed to identify the four static parameters of friction. The behaviour of friction for each axis is presented and the results are discussed.

  18. Dynamics of translational friction in needle-tissue interaction during needle insertion.

    PubMed

    Asadian, Ali; Patel, Rajni V; Kermani, Mehrdad R

    2014-01-01

    In this study, a distributed approach to account for dynamic friction during needle insertion in soft tissue is presented. As is well known, friction is a complex nonlinear phenomenon. It appears that classical or static models are unable to capture some of the observations made in systems subjected to significant frictional effects. In needle insertion, translational friction would be a matter of importance when the needle is very flexible, or a stop-and-rotate motion profile at low insertion velocities is implemented, and thus, the system is repeatedly transitioned from a pre-sliding to a sliding mode and vice versa. In order to characterize friction components, a distributed version of the LuGre model in the state-space representation is adopted. This method also facilitates estimating cutting force in an intra-operative manner. To evaluate the performance of the proposed family of friction models, experiments were conducted on homogeneous artificial phantoms and animal tissue. The results illustrate that our approach enables us to represent the main features of friction which is a major force component in needle-tissue interaction during needle-based interventions.

  19. Stick-slip friction and ageing in Velcro®

    NASA Astrophysics Data System (ADS)

    Mariani, Lisa; Angiolillo, Paul

    2014-03-01

    The mesoscopic hook and loop system of Velcro® provides a model of stick-slip friction that exhibits behavior reminiscent of results seen in nanoscale model systems. The friction is linearly dependent on contact area and independent of driving velocity. Morever, there is a power law dependence of the friction on loading, with exponent between 1/4 and 1/3. Furthermore, the evolution of stick-slip to more smooth sliding, as controlled by contact area, is also noted. These transition predictions follow power law profiles, as well, with respect to increasing contact area. Thus, the hook-and-loop system shows to be a good mesoscale model system of stick-slip friction and provides a link between nanoscale and macroscale friction. Through an investigation into the ageing of the hooks in the system, the data suggests that the hooks age during the shearing regime and take a characteristic time to return to initial attachment strength. Additionally, there does not appear to be a significant affect of ageing on the kinetic friction experienced by the system.

  20. Friction measurements on InAs NWs by AFM manipulation

    NASA Astrophysics Data System (ADS)

    Pettersson, Hakan; Conache, Gabriela; Gray, Struan; Bordag, Michael; Ribayrol, Aline; Froberg, Linus; Samuelson, Lars; Montelius, Lars

    2008-03-01

    We discuss a new approach to measure the friction force between elastically deformed nanowires and a surface. The wires are bent, using an AFM, into an equilibrium shape determined by elastic restoring forces within the wire and friction between the wire and the surface. From measurements of the radius of curvature of the bent wires, elasticity theory allows the friction force per unit length to be calculated. We have studied friction properties of InAs nanowires deposited on SiO2, silanized SiO2 and Si3N4 substrates. The wires were typically from 0.5 to a few microns long, with diameters varying between 20 and 80 nm. Manipulation is done in a `Retrace Lift' mode, where feedback is turned off for the reverse scan and the tip follows a nominal path. The effective manipulation force during the reverse scan can be changed by varying an offset in the height of the tip over the surface. We will report on interesting static- and sliding friction experiments with nanowires on the different substrates, including how the friction force per unit length varies with the diameter of the wires.

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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

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

    2014-04-01

    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. 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. 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. 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.

  6. Mechanism of axial strain effects on friction in carbon nanotube rotating bearings.

    PubMed

    Huang, Jianzhang; Han, Qiang

    2018-08-10

    A systematic study of axial strain effects on friction in carbon nanotube bearings is conducted in this paper. The relationships between friction and axial strains are determined by implementing molecular dynamics simulations. It is found that the dependence of friction on velocity and temperature is altered by axial strains. The mechanism of strain effects is revealed through numerical and theoretical analyses. Based on phonon computations, axial strain effects tune friction by adjusting the distribution of the phonon frequency density, which affects the transfer efficiency of orderly kinetic energy into disorderly thermal energy. The findings in this work advance the understanding of friction in carbon nanotubes and suggest the great potential of axial strain effects on tuning friction in nanodevice applications.

  7. Nonequilibrium fluctuations in a frictional granular motor: Experiments and kinetic theory

    NASA Astrophysics Data System (ADS)

    Gnoli, Andrea; Sarracino, Alessandro; Puglisi, Andrea; Petri, Alberto

    2013-05-01

    We report the study of an experimental granular Brownian motor, inspired by the one published in Eshuis [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.104.248001 104, 248001 (2010)], but different in some ingredients. As in that previous work, the motor is constituted by a rotating blade, the surfaces of which break the rotation-inversion symmetry through alternated patches of different inelasticity, immersed in a gas of granular particles. The main difference of our experimental setup is in the orientation of the main axis, which is parallel to the (vertical) direction of shaking of the granular fluid, guaranteeing an isotropic distribution for the velocities of colliding grains, characterized by a variance v02. We also keep the granular system diluted, in order to compare with Boltzmann-equation-based kinetic theory. In agreement with theory, we observe the crucial role of Coulomb friction which induces two main regimes: (i) rare collisions, with an average angular velocity <ω>˜v03, and (ii) frequent collisions (FC), with <ω>˜v0. We also study the fluctuations of the angle spanned in a large-time interval Δθ, which in the FC regime is proportional to the work done upon the motor. We observe that the fluctuation relation is satisfied with a slope which weakly depends on the relative collision frequency.

  8. 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.

  9. 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

  10. Scalar model for frictional precursors dynamics.

    PubMed

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

    2015-02-02

    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.

  11. Synthesis of silicone softener and its characteristics on cotton fabric.

    PubMed

    Robati, D

    2007-02-15

    This study was undertaken to examine the unresolved questions surrounding the influence of silicon softener on cotton fabrics. Results showed that the synthesized silicon softener was comparable with other tested conventional softener, According to present investigations the emulsions E1 and E2 is not economical and it is not evenly qualified and it become two phased after 24 h. But emulsion E3 was even and more economical. Moreover, it has high stability. In addition, measurement of kinetic and static friction show that the general effect of silicon softener on cotton cloth is the decrease of friction. Also, it was concluded that with increasing the add on percentage of softener, the crease of reflection angle did not change bending length and static and kinetic friction index significantly.

  12. Temperature dependence of internal friction in enzyme reactions.

    PubMed

    Rauscher, Anna Á; Simon, Zoltán; Szöllosi, Gergely J; Gráf, László; Derényi, Imre; Malnasi-Csizmadia, Andras

    2011-08-01

    Our aim was to elucidate the physical background of internal friction of enzyme reactions by investigating the temperature dependence of internal viscosity. By rapid transient kinetic methods, we directly measured the rate constant of trypsin 4 activation, which is an interdomain conformational rearrangement, as a function of temperature and solvent viscosity. We found that the apparent internal viscosity shows an Arrhenius-like temperature dependence, which can be characterized by the activation energy of internal friction. Glycine and alanine mutations were introduced at a single position of the hinge of the interdomain region to evaluate how the flexibility of the hinge affects internal friction. We found that the apparent activation energies of the conformational change and the internal friction are interconvertible parameters depending on the protein flexibility. The more flexible a protein was, the greater proportion of the total activation energy of the reaction was observed as the apparent activation energy of internal friction. Based on the coupling of the internal and external movements of the protein during its conformational change, we constructed a model that quantitatively relates activation energy, internal friction, and protein flexibility.

  13. Quasi-equilibrium melting of quartzite upon extreme friction

    NASA Astrophysics Data System (ADS)

    Lee, Sung Keun; Han, Raehee; Kim, Eun Jeong; Jeong, Gi Young; Khim, Hoon; Hirose, Takehiro

    2017-06-01

    The friction on fault planes that controls how rocks slide during earthquakes decreases significantly as a result of complex fault-lubrication processes involving frictional melting. Fault friction has been characterized in terms of the preferential melting of minerals with low melting points--so-called disequilibrium melting. Quartz, which has a high melting temperature of about 1,726 °C and is a major component of crustal rocks, is not expected to melt often during seismic slip. Here we use high-velocity friction experiments on quartzite to show that quartz can melt at temperatures of 1,350 to 1,500 °C. This implies that quartz within a fault plane undergoing rapid friction sliding could melt at substantially lower temperatures than expected. We suggest that depression of the melting temperature is caused by the preferential melting of ultra-fine particles and metastable melting of β-quartz at about 1,400 °C during extreme frictional slip. The results for quartzite are applicable to complex rocks because of the observed prevalence of dynamic grain fragmentation, the preferential melting of smaller grains and the kinetic preference of β-quartz formation during frictional sliding. We postulate that frictional melting of quartz on a fault plane at temperatures substantially below the melting temperature could facilitate slip-weakening and lead to large earthquakes.

  14. Properties of Interfacial Tribo-Films

    DTIC Science & Technology

    1993-06-01

    cf these rods is such as to have the center of gravity of or the attraction of water into the re-entrant peripheral gap the whole sample as close as...difference between the fluid dynamics, acoustic effects in stringed musical static and the kinetic friction coefficients increases with instruments...interfacial fluid molecules to static minimize oscillations, the center of gravity of the sample friction have been explored and, in this regard, adsorbed

  15. A Study Of High Speed Friction Behavior Under Elastic Loading Conditions

    NASA Astrophysics Data System (ADS)

    Crawford, P. J.; Hammerberg, J. E.

    2005-03-01

    The role of interfacial dynamics under high strain-rate conditions is an important constitutive relationship in modern modeling and simulation studies of dynamic events (<100 μs in length). The frictional behavior occurring at the interface between two metal surfaces under high elastic loading and sliding speed conditions is studied using the Rotating Barrel Gas Gun (RBGG) facility. The RBGG utilizes a low-pressure gas gun to propel a rotating annular projectile towards an annular target rod. Upon striking the target, the projectile imparts both an axial and a torsional impulse into the target. Resulting elastic waves are measured using strain gauges attached to the target rod. The kinetic coefficient of friction is obtained through an analysis of the resulting strain wave data. Experiments performed using Cu/Cu, Cu/Stainless steel and Cu/Al interfaces provide some insight into the kinetic coefficient of friction behavior at varying sliding speeds and impact loads.

  16. Experimental and Theoretical Investigations on the Nanoscale Kinetic Friction in Ambient Environmental Conditions.

    PubMed

    Gueye, Birahima; Zhang, Yan; Wang, Yujuan; Chen, Yunfei

    2015-07-08

    The liquid lubrication, thermolubricity and dynamic lubricity due to mechanical oscillations are investigated with an atomic force microscope in ambient environmental conditions with different relative humidity (RH) levels. Experimental results demonstrate that high humidity at low-temperature regime enhances the liquid lubricity while at high-temperature regime it hinders the effect of the thermolubricity due to the formation of liquid bridges. Friction response to the dynamic lubricity in both high- and low-temperature regimes keeps the same trends, namely the friction force decreases with increasing the amplitude of the applied vibration on the tip regardless of the RH levels. An interesting finding is that for the dynamic lubricity at high temperature, high-humidity condition leads to the friction forces higher than that at low-humidity condition while at low temperature the opposite trend is observed. An extended two-dimensional dynamic model accounting for the RH is proposed to interpret the frictional mechanism in ambient conditions.

  17. 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.

  18. 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.

  19. 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. Copyright © 2011 Elsevier Ltd. All rights reserved.

  20. Static and sliding contact of rough surfaces: Effect of asperity-scale properties and long-range elastic interactions

    NASA Astrophysics Data System (ADS)

    Hulikal, Srivatsan; Lapusta, Nadia; Bhattacharya, Kaushik

    2018-07-01

    Friction in static and sliding contact of rough surfaces is important in numerous physical phenomena. We seek to understand macroscopically observed static and sliding contact behavior as the collective response of a large number of microscopic asperities. To that end, we build on Hulikal et al. (2015) and develop an efficient numerical framework that can be used to investigate how the macroscopic response of multiple frictional contacts depends on long-range elastic interactions, different constitutive assumptions about the deforming contacts and their local shear resistance, and surface roughness. We approximate the contact between two rough surfaces as that between a regular array of discrete deformable elements attached to a elastic block and a rigid rough surface. The deformable elements are viscoelastic or elasto/viscoplastic with a range of relaxation times, and the elastic interaction between contacts is long-range. We find that the model reproduces the main macroscopic features of evolution of contact and friction for a range of constitutive models of the elements, suggesting that macroscopic frictional response is robust with respect to the microscopic behavior. Viscoelasticity/viscoplasticity contributes to the increase of friction with contact time and leads to a subtle history dependence. Interestingly, long-range elastic interactions only change the results quantitatively compared to the meanfield response. The developed numerical framework can be used to study how specific observed macroscopic behavior depends on the microscale assumptions. For example, we find that sustained increase in the static friction coefficient during long hold times suggests viscoelastic response of the underlying material with multiple relaxation time scales. We also find that the experimentally observed proportionality of the direct effect in velocity jump experiments to the logarithm of the velocity jump points to a complex material-dependent shear resistance at the

  1. The MEMS process of a micro friction sensor

    NASA Astrophysics Data System (ADS)

    Yuan, Ming-Quan; Lei, Qiang; Wang, Xiong

    2018-02-01

    The research and testing techniques of friction sensor is an important support for hypersonic aircraft. Compared with the conventional skin friction sensor, the MEMS skin friction sensor has the advantages of small size, high sensitivity, good stability and dynamic response. The MEMS skin friction sensor can be integrated with other flow field sensors whose process is compatible with MEMS skin friction sensor to achieve multi-physical measurement of the flow field; and the micro-friction balance sensor array enable to achieve large area and accurate measurement for the near-wall flow. A MEMS skin friction sensor structure is proposed, which sensing element not directly contacted with the flow field. The MEMS fabrication process of the sensing element is described in detail. The thermal silicon oxide is used as the mask to solve the selection ratio problem of silicon DRIE. The optimized process parameters of silicon DRIE: etching power 1600W/LF power 100 W; SF6 flux 360 sccm; C4F8 flux 300 sccm; O2 flux 300 sccm. With Cr/Au mask, etch depth of glass shallow groove can be controlled in 30°C low concentration HF solution; the spray etch and wafer rotate improve the corrosion surface quality of glass shallow groove. The MEMS skin friction sensor samples were fabricated by the above MEMS process, and results show that the error of the length and width of the elastic cantilever is within 2 μm, the depth error of the shallow groove is less than 0.03 μm, and the static capacitance error is within 0.2 pF, which satisfy the design requirements.

  2. Fragility and hysteretic creep in frictional granular jamming.

    PubMed

    Bandi, M M; Rivera, M K; Krzakala, F; Ecke, R E

    2013-04-01

    The granular jamming transition is experimentally investigated in a two-dimensional system of frictional, bidispersed disks subject to quasistatic, uniaxial compression without vibrational disturbances (zero granular temperature). Three primary results are presented in this experimental study. First, using disks with different static friction coefficients (μ), we experimentally verify numerical results that predict jamming onset at progressively lower packing fractions with increasing friction. Second, we show that the first compression cycle measurably differs from subsequent cycles. The first cycle is fragile-a metastable configuration with simultaneous jammed and unjammed clusters-over a small packing fraction interval (φ(1)<φ<φ(2)) and exhibits simultaneous exponential rise in pressure and exponential decrease in disk displacements over the same packing fraction interval. This fragile behavior is explained through a percolation mechanism of stressed contacts where cluster growth exhibits spatial correlation with disk displacements and contributes to recent results emphasizing fragility in frictional jamming. Control experiments show that the fragile state results from the experimental incompatibility between the requirements for zero friction and zero granular temperature. Measurements with several disk materials of varying elastic moduli E and friction coefficients μ show that friction directly controls the start of the fragile state but indirectly controls the exponential pressure rise. Finally, under repetitive loading (compression) and unloading (decompression), we find the system exhibits pressure hysteresis, and the critical packing fraction φ(c) increases slowly with repetition number. This friction-induced hysteretic creep is interpreted as the granular pack's evolution from a metastable to an eventual structurally stable configuration. It is shown to depend on the quasistatic step size Δφ, which provides the only perturbative mechanism in the

  3. Confinement-Dependent Friction in Peptide Bundles

    PubMed Central

    Erbaş, Aykut; Netz, Roland R.

    2013-01-01

    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

  4. 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.

  5. 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

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

    PubMed

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

    2015-04-01

    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. 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. 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 higher amount of frictional forces

  7. 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).

  8. Effect of roughness on stiction

    NASA Astrophysics Data System (ADS)

    Fuadi, Zahrul; Zahouani, Hassan; Takagi, Toshiyuki; Miki, Hiroyuki

    2018-05-01

    In this paper, the viscoelastic material was used to investigate the effect of roughness on stiction. The material is chosen because it is highly deformable so that contact during friction can be fully elastic. The soft surfaces were prepared by casting the silicon material on metal surfaces having smooth and unidirectional grooved texture. Two tests were conducted, indentation and friction, to find out the effect of roughness on parameters of normal contact stiffness, friction force and the difference between static and kinetic friction coefficient, μs-μk. As the results, it is found that all parameters are related to the surface roughness. Smoother surface tends to have a higher value of normal contact stiffness and higher value of friction force thus resulting in a larger difference between the static and kinetic coefficient of friction. Since the value of μs-μk is commonly related to the stick-slip motion, the smoother surface tends to have a larger propensity of stiction. It is shown by the result that the texture can reduce the stiction because it reduces the value of normal contact stiffness, resulting in a lower value of μs-μk.

  9. Friction law and hysteresis in granular materials

    NASA Astrophysics Data System (ADS)

    DeGiuli, E.; Wyart, M.

    2017-08-01

    The macroscopic friction of particulate materials often weakens as the flow rate is increased, leading to potentially disastrous intermittent phenomena including earthquakes and landslides. We theoretically and numerically study this phenomenon in simple granular materials. We show that velocity weakening, corresponding to a nonmonotonic behavior in the friction law, μ(I), is present even if the dynamic and static microscopic friction coefficients are identical, but disappears for softer particles. We argue that this instability is induced by endogenous acoustic noise, which tends to make contacts slide, leading to faster flow and increased noise. We show that soft spots, or excitable regions in the materials, correspond to rolling contacts that are about to slide, whose density is described by a nontrivial exponent θs. We build a microscopic theory for the nonmonotonicity of μ(I), which also predicts the scaling behavior of acoustic noise, the fraction of sliding contacts χ, and the sliding velocity, in terms of θs. Surprisingly, these quantities have no limit when particles become infinitely hard, as confirmed numerically. Our analysis rationalizes previously unexplained observations and makes experimentally testable predictions.

  10. Low-friction nanojoint prototype

    NASA Astrophysics Data System (ADS)

    Vlassov, Sergei; Oras, Sven; Antsov, Mikk; Butikova, Jelena; Lõhmus, Rünno; Polyakov, Boris

    2018-05-01

    High surface energy of individual nanostructures leads to high adhesion and static friction that can completely hinder the operation of nanoscale systems with movable parts. For instance, silver or gold nanowires cannot be moved on silicon substrate without plastic deformation. In this paper, we experimentally demonstrate an operational prototype of a low-friction nanojoint. The movable part of the prototype is made either from a gold or silver nano-pin produced by laser-induced partial melting of silver and gold nanowires resulting in the formation of rounded bulbs on their ends. The nano-pin is then manipulated into the inverted pyramid (i-pyramids) specially etched in a Si wafer. Due to the small contact area, the nano-pin can be repeatedly tilted inside an i-pyramid as a rigid object without noticeable deformation. At the same time in the absence of external force the nanojoint is stable and preserves its position and tilt angle. Experiments are performed inside a scanning electron microscope and are supported by finite element method simulations.

  11. Nonlinear shear wave interaction at a frictional interface: energy dissipation and generation of harmonics.

    PubMed

    Meziane, A; Norris, A N; Shuvalov, A L

    2011-10-01

    Analytical and numerical modeling of the nonlinear interaction of shear wave with a frictional interface is presented. The system studied is composed of two homogeneous and isotropic elastic solids, brought into frictional contact by remote normal compression. A shear wave, either time harmonic or a narrow band pulse, is incident normal to the interface and propagates through the contact. Two friction laws are considered and the influence on interface behavior is investigated: Coulomb's law with a constant friction coefficient and a slip-weakening friction law which involves static and dynamic friction coefficients. The relationship between the nonlinear harmonics and the dissipated energy, and the dependence on the contact dynamics (friction law, sliding, and tangential stress) and on the normal contact stress are examined in detail. The analytical and numerical results indicate universal type laws for the amplitude of the higher harmonics and for the dissipated energy, properly non-dimensionalized in terms of the pre-stress, the friction coefficient and the incident amplitude. The results suggest that measurements of higher harmonics can be used to quantify friction and dissipation effects of a sliding interface. © 2011 Acoustical Society of America

  12. Non-linear programming in shakedown analysis with plasticity and friction

    NASA Astrophysics Data System (ADS)

    Spagnoli, A.; Terzano, M.; Barber, J. R.; Klarbring, A.

    2017-07-01

    Complete frictional contacts, when subjected to cyclic loading, may sometimes develop a favourable situation where slip ceases after a few cycles, an occurrence commonly known as frictional shakedown. Its resemblance to shakedown in plasticity has prompted scholars to apply direct methods, derived from the classical theorems of limit analysis, in order to assess a safe limit to the external loads applied on the system. In circumstances where zones of plastic deformation develop in the material (e.g., because of the large stress concentrations near the sharp edges of a complete contact), it is reasonable to expect an effect of mutual interaction of frictional slip and plastic strains on the load limit below which the global behaviour is non dissipative, i.e., both slip and plastic strains go to zero after some dissipative load cycles. In this paper, shakedown of general two-dimensional discrete systems, involving both friction and plasticity, is discussed and the shakedown limit load is calculated using a non-linear programming algorithm based on the static theorem of limit analysis. An illustrative example related to an elastic-plastic solid containing a frictional crack is provided.

  13. Concerted dihedral rotations give rise to internal friction in unfolded proteins.

    PubMed

    Echeverria, Ignacia; Makarov, Dmitrii E; Papoian, Garegin A

    2014-06-18

    Protein chains undergo conformational diffusion during folding and dynamics, experiencing both thermal kicks and viscous drag. Recent experiments have shown that the corresponding friction can be separated into wet friction, which is determined by the solvent viscosity, and dry friction, where frictional effects arise due to the interactions within the protein chain. Despite important advances, the molecular origins underlying dry friction in proteins have remained unclear. To address this problem, we studied the dynamics of the unfolded cold-shock protein at different solvent viscosities and denaturant concentrations. Using extensive all-atom molecular dynamics simulations we estimated the internal friction time scales and found them to agree well with the corresponding experimental measurements (Soranno et al. Proc. Natl. Acad. Sci. U.S.A. 2012, 109, 17800-17806). Analysis of the reconfiguration dynamics of the unfolded chain further revealed that hops in the dihedral space provide the dominant mechanism of internal friction. Furthermore, the increased number of concerted dihedral moves at physiological conditions suggest that, in such conditions, the concerted motions result in higher frictional forces. These findings have important implications for understanding the folding kinetics of proteins as well as the dynamics of intrinsically disordered proteins.

  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.

  15. Precisely cyclic sand: self-organization of periodically sheared frictional grains.

    PubMed

    Royer, John R; Chaikin, Paul M

    2015-01-06

    The disordered static structure and chaotic dynamics of frictional granular matter has occupied scientists for centuries, yet there are few organizational principles or guiding rules for this highly hysteretic, dissipative material. We show that cyclic shear of a granular material leads to dynamic self-organization into several phases with different spatial and temporal order. Using numerical simulations, we present a phase diagram in strain-friction space that shows chaotic dispersion, crystal formation, vortex patterns, and most unusually a disordered phase in which each particle precisely retraces its unique path. However, the system is not reversible. Rather, the trajectory of each particle, and the entire frictional, many-degrees-of-freedom system, organizes itself into a limit cycle absorbing state. Of particular note is that fact that the cyclic states are spatially disordered, whereas the ordered states are chaotic.

  16. Precisely cyclic sand: Self-organization of periodically sheared frictional grains

    PubMed Central

    Royer, John R.; Chaikin, Paul M.

    2015-01-01

    The disordered static structure and chaotic dynamics of frictional granular matter has occupied scientists for centuries, yet there are few organizational principles or guiding rules for this highly hysteretic, dissipative material. We show that cyclic shear of a granular material leads to dynamic self-organization into several phases with different spatial and temporal order. Using numerical simulations, we present a phase diagram in strain–friction space that shows chaotic dispersion, crystal formation, vortex patterns, and most unusually a disordered phase in which each particle precisely retraces its unique path. However, the system is not reversible. Rather, the trajectory of each particle, and the entire frictional, many–degrees-of-freedom system, organizes itself into a limit cycle absorbing state. Of particular note is that fact that the cyclic states are spatially disordered, whereas the ordered states are chaotic. PMID:25538298

  17. Improved analysis and visualization of friction loop data: unraveling the energy dissipation of meso-scale stick-slip motion

    NASA Astrophysics Data System (ADS)

    Kokorian, Jaap; Merlijn van Spengen, W.

    2017-11-01

    In this paper we demonstrate a new method for analyzing and visualizing friction force measurements of meso-scale stick-slip motion, and introduce a method for extracting two separate dissipative energy components. Using a microelectromechanical system tribometer, we execute 2 million reciprocating sliding cycles, during which we measure the static friction force with a resolution of \

  18. Slip Morphology of Elastic Strips on Frictional Rigid Substrates.

    PubMed

    Sano, Tomohiko G; Yamaguchi, Tetsuo; Wada, Hirofumi

    2017-04-28

    The morphology of an elastic strip subject to vertical compressive stress on a frictional rigid substrate is investigated by a combination of theory and experiment. We find a rich variety of morphologies, which-when the bending elasticity dominates over the effect of gravity-are classified into three distinct types of states: pinned, partially slipped, and completely slipped, depending on the magnitude of the vertical strain and the coefficient of static friction. We develop a theory of elastica under mixed clamped-hinged boundary conditions combined with the Coulomb-Amontons friction law and find excellent quantitative agreement with simulations and controlled physical experiments. We also discuss the effect of gravity in order to bridge the difference in the qualitative behaviors of stiff strips and flexible strings or ropes. Our study thus complements recent work on elastic rope coiling and takes a significant step towards establishing a unified understanding of how a thin elastic object interacts vertically with a solid surface.

  19. Systematic Breakdown of Amontons' Law of Friction for an Elastic Object Locally Obeying Amontons' Law

    PubMed Central

    Otsuki, Michio; Matsukawa, Hiroshi

    2013-01-01

    In many sliding systems consisting of solid object on a solid substrate under dry condition, the friction force does not depend on the apparent contact area and is proportional to the loading force. This behaviour is called Amontons' law and indicates that the friction coefficient, or the ratio of the friction force to the loading force, is constant. Here, however, using numerical and analytical methods, we show that Amontons' law breaks down systematically under certain conditions for an elastic object experiencing a friction force that locally obeys Amontons' law. The macroscopic static friction coefficient, which corresponds to the onset of bulk sliding of the object, decreases as pressure or system length increases. This decrease results from precursor slips before the onset of bulk sliding, and is consistent with the results of certain previous experiments. The mechanisms for these behaviours are clarified. These results will provide new insight into controlling friction. PMID:23545778

  20. Friction behavior for clay minerals during dehydration process: implication for unstable friction at shallow portion along subducting plate

    NASA Astrophysics Data System (ADS)

    Kubo, T.; Katayama, I.

    2016-12-01

    dehydration reaction kinetics. Dehydration of clay minerals change friction behavior, and play a key role for the occurrence of earthquakes along subducting plate.

  1. 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.

  2. Localizing internal friction along the reaction coordinate of protein folding by combining ensemble and single-molecule fluorescence spectroscopy.

    PubMed

    Borgia, Alessandro; Wensley, Beth G; Soranno, Andrea; Nettels, Daniel; Borgia, Madeleine B; Hoffmann, Armin; Pfeil, Shawn H; Lipman, Everett A; Clarke, Jane; Schuler, Benjamin

    2012-01-01

    Theory, simulations and experimental results have suggested an important role of internal friction in the kinetics of protein folding. Recent experiments on spectrin domains provided the first evidence for a pronounced contribution of internal friction in proteins that fold on the millisecond timescale. However, it has remained unclear how this contribution is distributed along the reaction and what influence it has on the folding dynamics. Here we use a combination of single-molecule Förster resonance energy transfer, nanosecond fluorescence correlation spectroscopy, microfluidic mixing and denaturant- and viscosity-dependent protein-folding kinetics to probe internal friction in the unfolded state and at the early and late transition states of slow- and fast-folding spectrin domains. We find that the internal friction affecting the folding rates of spectrin domains is highly localized to the early transition state, suggesting an important role of rather specific interactions in the rate-limiting conformational changes.

  3. Friction law and hysteresis in granular materials

    PubMed Central

    Wyart, M.

    2017-01-01

    The macroscopic friction of particulate materials often weakens as the flow rate is increased, leading to potentially disastrous intermittent phenomena including earthquakes and landslides. We theoretically and numerically study this phenomenon in simple granular materials. We show that velocity weakening, corresponding to a nonmonotonic behavior in the friction law, μ(I), is present even if the dynamic and static microscopic friction coefficients are identical, but disappears for softer particles. We argue that this instability is induced by endogenous acoustic noise, which tends to make contacts slide, leading to faster flow and increased noise. We show that soft spots, or excitable regions in the materials, correspond to rolling contacts that are about to slide, whose density is described by a nontrivial exponent θs. We build a microscopic theory for the nonmonotonicity of μ(I), which also predicts the scaling behavior of acoustic noise, the fraction of sliding contacts χ, and the sliding velocity, in terms of θs. Surprisingly, these quantities have no limit when particles become infinitely hard, as confirmed numerically. Our analysis rationalizes previously unexplained observations and makes experimentally testable predictions. PMID:28811373

  4. 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.

  5. Downhill Cycling Symmetry Breaking: How the Rider Foils Experiment

    ERIC Educational Resources Information Center

    Abu, Yuval Ben; Wolfson, Ira; Bran, Gil; Yizhaq, Hezi

    2017-01-01

    In high-school teaching of mechanics, we deal, among other things, with the nature of static and kinetic friction, forces that are proportional to the normal force. Under the influence of frictional forces, a body moves down a rough sloped decline at a fixed rate of acceleration that is independent of its mass. This situation does not apply to…

  6. Friction and lubrication of pleural tissues.

    PubMed

    D'Angelo, Edgardo; Loring, Stephen H; Gioia, Magda E; Pecchiari, Matteo; Moscheni, Claudia

    2004-08-20

    The frictional behaviour of rabbit's visceral pleura sliding against parietal pleura was assessed in vitro while oscillating at physiological velocities and amplitudes under physiological normal forces. For sliding velocities up to 3 cm s(-1) and normal compressive loads up to 12 cm H2O, the average value of the coefficient of kinetic friction (mu) was constant at 0.019 +/- 0.002 (S.E.) with pleural liquid as lubricant. With Ringer-bicarbonate solution, mu was still constant, but significantly increased (Deltamu = 0.008 +/- 0.001; P < 0.001). Under these conditions, no damage of the sliding pleural surfaces was found on light and electron microscopy. Additional measurements, performed also on peritoneum, showed that changes in nominal contact area or strain of the mesothelia, temperature in the range 19-39 degrees C, and prolonged sliding did not affect mu. Gentle application of filter paper increased mu approximately 10-fold and irreversibly, suggesting alteration of the mesothelia. With packed the red blood cells (RBC) between the sliding mesothelia, mu increased appreciably but reversibly on removal of RBC suspension, whilst no ruptures of RBC occurred. In conclusion, the results indicate a low value of sliding friction in pleural tissues, partly related to the characteristics of the pleural liquid, and show that friction is independent of velocity, normal load, and nominal contact area, consistent with boundary lubrication.

  7. 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.

  8. The influence of resting periods on friction in the artificial hip.

    PubMed

    Nassutt, Roman; Wimmer, Markus A; Schneider, Erich; Morlock, Michael M

    2003-02-01

    Insufficient tribologic performance of total joint components is a major cause of prostheses failure. Wear has been studied intensively using testing machines that apply continuous motions. Human locomotion, however, is not well represented by continuous motions alone. Singular events and resting periods are a substantial part of daily activities. Resting does influence adhesion in the artificial joint with possible effects on friction, wear, and loosening. The current study evaluated the effects of resting on the frictional properties of hip prosthesis components. The activity measurements of 32 patients with artificial hip replacements were analyzed for resting durations of the hip. A pin-on-ball screening device was used to determine friction after characteristic resting periods and during continuous oscillating motion. All common articulation pairings were investigated. Prolonged and frequent resting periods of the hip were found for the patients. Initial friction increased with increasing resting duration for all tested materials (between 41% and 191%). The metal-on-metal articulations showed the highest friction level (0.098 for sliding) and the highest increase (191%) in friction with resting duration (0.285 after resting periods of 60 seconds). A high static frictional moment after resting periods might present a risk for aseptic implant loosening. Therefore, large head diameters of metal-on-metal joints should be used with caution, especially when additional unfavorable risk factors such as obesity, weak bone-implant interface, or high activity level are present.

  9. Localizing internal friction along the reaction coordinate of protein folding by combining ensemble and single-molecule fluorescence spectroscopy

    PubMed Central

    Borgia, Alessandro; Wensley, Beth G.; Soranno, Andrea; Nettels, Daniel; Borgia, Madeleine B.; Hoffmann, Armin; Pfeil, Shawn H.; Lipman, Everett A.; Clarke, Jane; Schuler, Benjamin

    2012-01-01

    Theory, simulations and experimental results have suggested an important role of internal friction in the kinetics of protein folding. Recent experiments on spectrin domains provided the first evidence for a pronounced contribution of internal friction in proteins that fold on the millisecond timescale. However, it has remained unclear how this contribution is distributed along the reaction and what influence it has on the folding dynamics. Here we use a combination of single-molecule Förster resonance energy transfer, nanosecond fluorescence correlation spectroscopy, microfluidic mixing and denaturant- and viscosity-dependent protein-folding kinetics to probe internal friction in the unfolded state and at the early and late transition states of slow- and fast-folding spectrin domains. We find that the internal friction affecting the folding rates of spectrin domains is highly localized to the early transition state, suggesting an important role of rather specific interactions in the rate-limiting conformational changes. PMID:23149740

  10. 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.

  11. 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.

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

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Silva, J.M.; Lima, J.A.S.; De Souza, R.E.

    2016-05-01

    The motion of a point like object of mass M passing through the background potential of massive collisionless particles ( m || 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. Inmore » 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.« less

  13. 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.

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

    PubMed

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

    2015-07-10

    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.

  15. Static Recrystallization Behavior of Z12CN13 Martensite Stainless Steel

    NASA Astrophysics Data System (ADS)

    Luo, Min; Zhou, Bing; Li, Rong-bin; Xu, Chun; Guo, Yan-hui

    2017-09-01

    In order to increase the hot workability and provide proper hot forming parameters of forging Z12CN13 martensite stainless steel for the simulation and production, the static recrystallization behavior has been studied by double-pass hot compression tests. The effects of deformation temperature, strain rate and inter-pass time on the static recrystallization fraction by the 2% offset method are extensively studied. The results indicate that increasing the inter-pass time and the deformation temperature as well as strain rate appropriately can increase the fraction of static recrystallization. At the temperature of 1050-1150 °C, inter-pass time of 30-100 s and strain rate of 0.1-5 s-1, the static recrystallization behavior is obvious. In addition, the kinetics of static recrystallization behavior of Z12CN13 steel has been established and the activation energy of static recrystallization is 173.030 kJ/mol. The substructure and precipitates have been studied by TEM. The results reveal that the nucleation mode is bulging at grain boundary. Undissolved precipitates such as MoNi3 and Fe3C have a retarding effect on the recrystallization kinetics. The effect is weaker than the accelerating effect of deformation temperature.

  16. Earthquake Nucleation on Faults With Heterogeneous Frictional Properties, Normal Stress

    NASA Astrophysics Data System (ADS)

    Ray, Sohom; Viesca, Robert C.

    2017-10-01

    We examine the development of an instability of fault slip rate. We consider a slip rate and state dependence of fault frictional strength, in which frictional properties and normal stress are functions of position. We pose the problem for a slip rate distribution that diverges quasi-statically within finite time in a self-similar fashion. Scenarios of property variations are considered and the corresponding self-similar solutions found. We focus on variations of coefficients, a and b, respectively, controlling the magnitude of a direct effect on strength due to instantaneous changes in slip rate and of strength evolution due to changes in a state variable. These results readily extend to variations in fault-normal stress, σ, or the characteristic slip distance for state evolution, Dc. We find that heterogeneous properties lead to a finite number of self-similar solutions, located about critical points of the distributions: maxima, minima, and between them. We examine the stability of these solutions and find that only a subset is asymptotically stable, occurring at just one of the critical point types. Such stability implies that during instability development, slip rate and state evolution can be attracted to develop in the manner of the self-similar solution, which is also confirmed by solutions to initial value problems for slip rate and state. A quasi-static slip rate divergence is ultimately limited by inertia, leading to the nucleation of an outward expanding dynamic rupture: asymptotic stability of self-similar solutions then implies preferential sites for earthquake nucleation, which are determined by distribution of frictional properties.

  17. Reciprocal Sliding Friction Model for an Electro-Deposited Coating and Its Parameter Estimation Using Markov Chain Monte Carlo Method

    PubMed Central

    Kim, Kyungmok; Lee, Jaewook

    2016-01-01

    This paper describes a sliding friction model for an electro-deposited coating. Reciprocating sliding tests using ball-on-flat plate test apparatus are performed to determine an evolution of the kinetic friction coefficient. The evolution of the friction coefficient is classified into the initial running-in period, steady-state sliding, and transition to higher friction. The friction coefficient during the initial running-in period and steady-state sliding is expressed as a simple linear function. The friction coefficient in the transition to higher friction is described with a mathematical model derived from Kachanov-type damage law. The model parameters are then estimated using the Markov Chain Monte Carlo (MCMC) approach. It is identified that estimated friction coefficients obtained by MCMC approach are in good agreement with measured ones. PMID:28773359

  18. Friction between a surrogate skin (Lorica Soft) and nonwoven fabrics used in hygiene products

    NASA Astrophysics Data System (ADS)

    Falloon, Sabrina S.; Cottenden, Alan

    2016-09-01

    Incontinence pad wearers often suffer from sore skin, and a better understanding of friction between pads and skin is needed to inform the development of less damaging materials. This work investigated friction between a skin surrogate (Lorica Soft) and 13 nonwoven fabrics representing those currently used against the skin in commercial pads. All fabrics were found to behave consistently with Amontons’ law: coefficients of friction did not differ systematically when measured under two different loads. Although the 13 fabrics varied considerably in composition and structure, their coefficients of friction (static and dynamic) against Lorica Soft were remarkably similar, especially for the ten fabrics comprising just polypropylene (PP) fibres. The coefficients of friction for one PP fabric never differed by more than 15.7% from those of any other, suggesting that the ranges of fibre decitex (2.0-6.5), fabric area density (13-30 g m-2) and bonding area (11%-25%) they exhibited had only limited impact on their friction properties. It is likely that differences were largely attributable to variability in properties between multiple samples of a given fabric. Of the remaining fabrics, the one comprising polyester fibres had significantly higher coefficients of friction than the highest friction PP fabric (p < 0.005), while the one comprising PP fibres with a polyethylene sheath had significantly lower coefficients of friction than the lowest friction PP fabric (p < 10-8). However, fabrics differed in too many other ways to confidently attribute these differences in friction properties just to the choice of base polymer.

  19. Comparison of Octopus Semi-Automated Kinetic Perimetry and Humphrey Peripheral Static Perimetry in Neuro-Ophthalmic Cases

    PubMed Central

    Rowe, Fiona J.; Noonan, Carmel; Manuel, Melanie

    2013-01-01

    Aim. To compare semikinetic perimetry (SKP) on Octopus 900 perimetry to a peripheral static programme with Humphrey automated perimetry. Methods. Prospective cross-section study comparing Humphrey full field (FF) 120 two zone programme to a screening protocol for SKP on Octopus perimetry. Results were independently graded for presence/absence of field defect plus type and location of defect. Results. 64 patients (113 eyes) underwent dual perimetry assessment. Mean duration of assessment for SKP was 4.54 minutes ±0.18 and 6.17 ± 0.12 for FF120 (P = 0.0001). 80% of results were correctly matched for normal or abnormal visual fields using the I4e target versus FF120, and 73.5% were correctly matched using the I2e target versus FF120. When comparing Octopus results with combined I4e and I2e isopters to the FF120 result, a match for normal or abnormal fields was recorded in 87%. Conclusions. Humphrey perimetry test duration was generally longer than Octopus SKP. In the absence of kinetic perimetry, peripheral static suprathreshold programme options such as FF120 may be useful for detection of visual field defects. However, statokinetic dissociation may occur. Octopus SKP utilising both I4e and I2e targets provides detailed information of both the defect depth and size and may provide a more representative view of the actual visual field defect. PMID:24558605

  20. 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.

  1. 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.

  2. Computational methods for frictional contact with applications to the Space Shuttle orbiter nose-gear tire: Comparisons of experimental measurements and analytical predictions

    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.

  3. 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

  4. 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

  5. Frictional processes of bimaterial interfaces at seismic slip rates.

    NASA Astrophysics Data System (ADS)

    Passelegue, F. X.; Fabbri, O.; Leclère, H.; Spagnuolo, E.; Di Toro, G.

    2017-12-01

    Large subduction earthquakes ruptures propagate from crustal rock toward the sea floor along frictional interfaces of different lythologies. Up to now, frictional processes of rocks were mainly investigated along single material experimental faults. Here, we present the results of high velocity friction experiments coupled with high frequency acoustic monitoring system on biomaterial interfaces including gabbro, pyroxenite and serpentinized peridotite (>95%), following a recent field investigation highlighting bimaterial contacts in the Corsica ophiolitic nappe. We first studied the frictional processes of single materials which result in a mechanical behaviour comparable to previous studies. Both gabbro and pyroxenite exhibit two weakening stages. The first one corresponds to flash heating and the second stage occurs concomitantly with complete melting of the interface. In the case of serpentinite, only one weakening stage is observed, after a weakening slip distance of only few centimeters. We then conducted bimaterial experiments. The two couples tested were gabbro/pyroxenite and gabbro/serpentinite, as observed along natural fault zones (Corsica, France). In the case of gabbro/serpentinite, we observe that frictional processes are controlled by serpentinite. Mechanical curves replicate the behaviour of single serpentinite friction experiments. We observe that few melting occurs, and that the product of experiments consists in fine grained cataclasite, as observed in the field. The case of gabbro/pyroxenite is more complicated. The first weakening is controlled by the lithology of the sample installed on the static part of the rotary apparatus. However, the second weakening is controlled by the gabbro and mechanical curves are identical than those obtained in the case of single gabbro experiments. Supported by microstructural analysis and acoustic activity, our results suggest that frictional processes of bimaterial interfaces are controlled by the material

  6. Effect of blocking tactile information from the fingertips on adaptation and execution of grip forces to friction at the grasping surface.

    PubMed

    Bilaloglu, Seda; Lu, Ying; Geller, Daniel; Rizzo, John Ross; Aluru, Viswanath; Gardner, Esther P; Raghavan, Preeti

    2016-03-01

    Adaptation of fingertip forces to friction at the grasping surface is necessary to prevent use of inadequate or excessive grip forces. In the current study we investigated the effect of blocking tactile information from the fingertips noninvasively on the adaptation and efficiency of grip forces to surface friction during precision grasp. Ten neurologically intact subjects grasped and lifted an instrumented grip device with 18 different frictional surfaces under three conditions: with bare hands or with a thin layer of plastic (Tegaderm) or an additional layer of foam affixed to the fingertips. The coefficient of friction at the finger-object interface of each surface was obtained for each subject with bare hands and Tegaderm by measuring the slip ratio (grip force/load force) at the moment of slip. We found that the foam layer reduced sensibility for two-point discrimination and pressure sensitivity at the fingertips, but Tegaderm did not. However, Tegaderm reduced static, but not dynamic, tactile discrimination. Adaptation of fingertip grip forces to surface friction measured by the rate of change of peak grip force, and grip force efficiency measured by the grip-load force ratio at lift, showed a proportional relationship with bare hands but were impaired with Tegaderm and foam. Activation of muscles engaged in precision grip also varied with the frictional surface with bare hands but not with Tegaderm and foam. The results suggest that sensitivity for static tactile discrimination is necessary for feedforward and feedback control of grip forces and for adaptive modulation of muscle activity during precision grasp. Copyright © 2016 the American Physiological Society.

  7. Friction surfacing and linear friction welding

    NASA Astrophysics Data System (ADS)

    Nicholas, E. D.

    The paper describes the development of the friction-surfacing and linear-friction welding technologies, with particular attention given to the equipment evolution and the application of the processes and advanced materials (such as intermetallics, metal-matrix composites (MMCs), ODS alloys, and powder metallurgy alloys) for the aerospace industry. The use of friction surfacing to modify the surface material with MMCs, to repair defects by plugging, and manufacture/reprocess materials is described.

  8. Prehension Synergies in the Grasps With Complex Friction Patterns: Local Versus Synergic Effects and the Template Control

    PubMed Central

    Niu, Xun; Latash, Mark L.; Zatsiorsky, Vladimir M.

    2010-01-01

    We studied adjustments of digit forces to changes in the friction. The subjects held a handle statically in a three-digit grasp. The friction under each digit was either high or low, resulting in eight three-element friction sets (such grasps were coined the grasps with complex friction pattern). The total load was also manipulated. It was found that digit forces were adjusted not only to the supported load and local friction, but also to friction at other digits (synergic effects). When friction under a digit was low, its tangential force decreased and the normal force increased (local effects). The synergic effects were directed to maintain the equilibrium of the handle. The relation between the individual digit forces and loads agreed with the triple-product model: fin=ki(2)ki(1)L, where fin is normal force of digit i, L is the load (newtons), ki(1) is a dimensionless coefficient representing sharing the total tangential force among the digits (Σki(1)=1.0), and ki(2) is a coefficient representing the relation between the tangential and normal forces of digit i (the overall friction equivalent, OFE). At each friction set, the central controller selected the grasping template—a three-element array of ki(2)ki(1) products—and then scaled the template with the load magnitude. PMID:17493928

  9. Kinematic and Kinetic Analysis of Repeated and Static Elevé in Adolescent Female Dance Students.

    PubMed

    Abraham, Amit; Dunsky, Ayelet; Hackney, Madeleine E; Dickstein, Ruth

    2018-03-15

    Elevé is a fundamental dance movement practiced routinely by dance students and serving as an integral component of screening in dance. It consists of ankle plantar flexion (PF) movement and is considered to be a frequent cause of foot and ankle injuries among dancers, with adolescent female dance students being at greatest risk for such injuries. Therefore, gaining additional knowledge regarding elevé functional range of motion (ROM) and inter-leg weightbearing distribution (WBD) properties among adolescent dance students is warranted for pedagogic, screening, injury prevention, and rehabilitation purposes. The aims of this study were three-fold: 1. to report and compare dance-specific, functional kinematic (ankle PF maximum angle and ankle PF ROM), kinetic (inter-leg WBD), and self-reported level of difficulty (balance, muscular force, and concentration) properties of repeated and static elevé among adolescent female dance students; 2. to look for correlations between elevé properties and participants' demographics (age, height, weight, dance experience, and leg dominance); and 3. to describe the relationships between the two kinematic properties in both elevé tasks. Twenty-three adolescent female dance students (mean age 13.57 ± 0.50 years) were measured while performing two elevé tasks: 10 repetitions ("repeated elevé task") and 10 consecutive seconds hold ("static elevé task"). Data regarding ankle motion and WBD were collected and analyzed using three-dimensional motion capture and two force plates. The data gained from this study expand our current understanding of elevé dance movement and may contribute to clinical relevancy and applicability of screening procedures being conducted in pre-professional dance settings. This may help to identify adolescent dance students with the potential to undertake a career in professional dance as well as to investigate the parameters associated with risk of ankle injuries in this population.

  10. Kinetic effect of heating rate on the thermal maturity of carbonaceous material as an indicator of frictional heat during earthquakes

    NASA Astrophysics Data System (ADS)

    Kaneki, Shunya; Hirono, Tetsuro

    2018-06-01

    Because the maximum temperature reached in the slip zone is significant information for understanding slip behaviors during an earthquake, the maturity of carbonaceous material (CM) is widely used as a proxy for detecting frictional heat recorded by fault rocks. The degree of maturation of CM is controlled not only by maximum temperature but also by the heating rate. Nevertheless, maximum slip zone temperature has been estimated previously by comparing the maturity of CM in natural fault rocks with that of synthetic products heated at rates of about 1 °C s-1, even though this rate is much lower than the actual heating rate during an earthquake. In this study, we investigated the kinetic effect of the heating rate on the CM maturation process by performing organochemical analyses of CM heated at slow (1 °C s-1) and fast (100 °C s-1) rates. The results clearly showed that a higher heating rate can inhibit the maturation reactions of CM; for example, extinction of aliphatic hydrocarbon chains occurred at 600 °C at a heating rate of 1 °C s-1 and at 900 °C at a heating rate of 100 °C s-1. However, shear-enhanced mechanochemical effects can also promote CM maturation reactions and may offset the effect of a high heating rate. We should thus consider simultaneously the effects of both heating rate and mechanochemistry on CM maturation to establish CM as a more rigorous proxy for frictional heat recorded by fault rocks and for estimating slip behaviors during earthquake.

  11. Wood variables affecting the friction coefficient of spruce pine on steel

    Treesearch

    Truett J. Lemoine; Charles W. McMillin; Floyd G. Manwiller

    1970-01-01

    Wood of spruce pine, Pinus glabra Walk., was factorially segregated by moisture content (0, 10, and 18 percent), specific gravity (less than 0.45 and more than 0.45), and extractive content (unextracted and extractive-freE), and the kinetic coefficient of friction on steel (having surface roughness of 9 microinches RMS) determined for tangential...

  12. Evaluation and Description of Friction between an Electro-Deposited Coating and a Ceramic Ball under Fretting Condition

    PubMed Central

    Kim, Kyungmok

    2015-01-01

    This article describes fretting behavior of zirconia and silicon nitride balls on an electro-deposited coating. Fretting tests are performed using a ball-on-flat configuration. The evolution of the kinetic friction coefficient is determined, along with slip ratio. Experimental results show that the steady-state friction coefficient between ceramic balls (Si3N4 and ZrO2) and an electro-deposited coating is about 0.06, lower than the value between AISI 52100 ball and the coating. After a steady-state sliding, the transition of the friction coefficient is varied with a ball. The friction coefficient for ZrO2 balls became a critical value after higher fretting cycles than those for Si3N4 and AISI 52100 balls. In addition, it is identified that two parameters can describe the transition of the friction coefficient. Finally, the evolution of the friction coefficient is expressed as an exponential or a power-law form. PMID:28793471

  13. Measuring internal friction of an ultrafast-folding protein.

    PubMed

    Cellmer, Troy; Henry, Eric R; Hofrichter, James; Eaton, William A

    2008-11-25

    Nanosecond laser T-jump was used to measure the viscosity dependence of the folding kinetics of the villin subdomain under conditions where the viscogen has no effect on its equilibrium properties. The dependence of the unfolding/refolding relaxation time on solvent viscosity indicates a major contribution to the dynamics from internal friction. The internal friction increases with increasing temperature, suggesting a shift in the transition state along the reaction coordinate toward the native state with more compact structures, and therefore, a smaller diffusion coefficient due to increased landscape roughness. Fitting the data with an Ising-like model yields a relatively small position dependence for the diffusion coefficient. This finding is consistent with the excellent correlation found between experimental and calculated folding rates based on free energy barrier heights using the same diffusion coefficient for every protein.

  14. In vitro investigation of friction at the interface between bone and a surgical instrument.

    PubMed

    Parekh, Jugal; Shepherd, Duncan E T; Hukins, David W L; Hingley, Carl; Maffulli, Nicola

    2013-06-01

    This study investigated the friction between surgical instruments and bone to aid improvements to instrument design. The bases of orthopaedic surgical instruments are usually made of metal, especially stainless steel. Silicone elastomer was chosen as an alternate biocompatible material, which would be compliant on the bone surface when used as the base of an instrument. The coefficient of static friction was calculated at the bone/material interface in the presence of a synthetic solution that had a comparable viscosity to that of blood, to assess the friction provided by each base material. Three types of silicone elastomers with different hardnesses (Shore A hardness 23, 50 and 77) and three distinct stainless steel surfaces (obtained by spark erosion, sand blasting and surface grinding) were used to assess the friction provided by the materials on slippery bone. The bone specimens were taken from the flattest region of the femoral shaft of a bovine femur; the outer surfaces of the specimens were kept intact. In general, the stainless steel surfaces exhibited higher values of coefficient of static friction, compared to the silicone elastomer samples. The stainless steel surface finished by spark erosion (surface roughness Ra  = 8.9 ± 1.6 µm) had the highest coefficient value of 0.74 ± 0.04. The coefficient values for the silicone elastomer sample with the highest hardness (Dow Corning Silastic Q7-4780, Shore A hardness 77) was not significantly different to values provided by the stainless steel surface finished by sand blasting (surface roughness Ra  = 2.2 ± 0.1 µm) or surface grinding (surface roughness Ra  = 0.1 ± 0.0 µm). Based on the results of this study, it is concluded that silicone could be a potentially useful material for the design of bases of orthopaedic instruments that interface with bone.

  15. Analysis Method of Friction Torque and Weld Interface Temperature during Friction Process of Steel Friction Welding

    NASA Astrophysics Data System (ADS)

    Kimura, Masaaki; Inoue, Haruo; Kusaka, Masahiro; Kaizu, Koichi; Fuji, Akiyoshi

    This paper describes an analysis method of the friction torque and weld interface temperature during the friction process for steel friction welding. The joining mechanism model of the friction welding for the wear and seizure stages was constructed from the actual joining phenomena that were obtained by the experiment. The non-steady two-dimensional heat transfer analysis for the friction process was carried out by calculation with FEM code ANSYS. The contact pressure, heat generation quantity, and friction torque during the wear stage were calculated using the coefficient of friction, which was considered as the constant value. The thermal stress was included in the contact pressure. On the other hand, those values during the seizure stage were calculated by introducing the coefficient of seizure, which depended on the seizure temperature. The relationship between the seizure temperature and the relative speed at the weld interface in the seizure stage was determined using the experimental results. In addition, the contact pressure and heat generation quantity, which depended on the relative speed of the weld interface, were solved by taking the friction pressure, the relative speed and the yield strength of the base material into the computational conditions. The calculated friction torque and weld interface temperatures of a low carbon steel joint were equal to the experimental results when friction pressures were 30 and 90 MPa, friction speed was 27.5 s-1, and weld interface diameter was 12 mm. The calculation results of the initial peak torque and the elapsed time for initial peak torque were also equal to the experimental results under the same conditions. Furthermore, the calculation results of the initial peak torque and the elapsed time for initial peak torque at various friction pressures were equal to the experimental results.

  16. Quantifying internal friction in unfolded and intrinsically disordered proteins with single-molecule spectroscopy

    PubMed Central

    Soranno, Andrea; Buchli, Brigitte; Nettels, Daniel; Cheng, Ryan R.; Müller-Späth, Sonja; Pfeil, Shawn H.; Hoffmann, Armin; Lipman, Everett A.; Makarov, Dmitrii E.; Schuler, Benjamin

    2012-01-01

    Internal friction, which reflects the “roughness” of the energy landscape, plays an important role for proteins by modulating the dynamics of their folding and other conformational changes. However, the experimental quantification of internal friction and its contribution to folding dynamics has remained challenging. Here we use the combination of single-molecule Förster resonance energy transfer, nanosecond fluorescence correlation spectroscopy, and microfluidic mixing to determine the reconfiguration times of unfolded proteins and investigate the mechanisms of internal friction contributing to their dynamics. Using concepts from polymer dynamics, we determine internal friction with three complementary, largely independent, and consistent approaches as an additive contribution to the reconfiguration time of the unfolded state. We find that the magnitude of internal friction correlates with the compactness of the unfolded protein: its contribution dominates the reconfiguration time of approximately 100 ns of the compact unfolded state of a small cold shock protein under native conditions, but decreases for more expanded chains, and approaches zero both at high denaturant concentrations and in intrinsically disordered proteins that are expanded due to intramolecular charge repulsion. Our results suggest that internal friction in the unfolded state will be particularly relevant for the kinetics of proteins that fold in the microsecond range or faster. The low internal friction in expanded intrinsically disordered proteins may have implications for the dynamics of their interactions with cellular binding partners. PMID:22492978

  17. Quantifying internal friction in unfolded and intrinsically disordered proteins with single-molecule spectroscopy.

    PubMed

    Soranno, Andrea; Buchli, Brigitte; Nettels, Daniel; Cheng, Ryan R; Müller-Späth, Sonja; Pfeil, Shawn H; Hoffmann, Armin; Lipman, Everett A; Makarov, Dmitrii E; Schuler, Benjamin

    2012-10-30

    Internal friction, which reflects the "roughness" of the energy landscape, plays an important role for proteins by modulating the dynamics of their folding and other conformational changes. However, the experimental quantification of internal friction and its contribution to folding dynamics has remained challenging. Here we use the combination of single-molecule Förster resonance energy transfer, nanosecond fluorescence correlation spectroscopy, and microfluidic mixing to determine the reconfiguration times of unfolded proteins and investigate the mechanisms of internal friction contributing to their dynamics. Using concepts from polymer dynamics, we determine internal friction with three complementary, largely independent, and consistent approaches as an additive contribution to the reconfiguration time of the unfolded state. We find that the magnitude of internal friction correlates with the compactness of the unfolded protein: its contribution dominates the reconfiguration time of approximately 100 ns of the compact unfolded state of a small cold shock protein under native conditions, but decreases for more expanded chains, and approaches zero both at high denaturant concentrations and in intrinsically disordered proteins that are expanded due to intramolecular charge repulsion. Our results suggest that internal friction in the unfolded state will be particularly relevant for the kinetics of proteins that fold in the microsecond range or faster. The low internal friction in expanded intrinsically disordered proteins may have implications for the dynamics of their interactions with cellular binding partners.

  18. Coefficient of friction of dry slash pine and southern red oak on three tension-grip facings

    Treesearch

    T.J. Lemoine; P. Koch

    1975-01-01

    A urethane material proved to have nine times higher static friction coefficient (0.9) than smooth steel (0.1) on radial and tangential wood surfaces pulled parallel to the grain. It is probably superior to 22O-grit garnet paper or sand coatings for tension-grip facings in lumber testing machines.

  19. Coefficient of friction of dry slash pine and southern red oak on three tension-grip facings

    Treesearch

    Truett J. Lemoine; Peter Koch

    1974-01-01

    A urethane material proved to have nine times higher static friction coefficient (0.9) than smooth steel (0.1) on radial and tangential wood surfaces pulled parallel to the grain. It is probably superior to 220-grit garnet paper or sand coatings for tension-grip facings in lumber testing machines.

  20. 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.

  1. 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

  2. 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.

  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. Aqueous Viscosity Is the Primary Source of Friction in Lipidic Pore Dynamics

    PubMed Central

    Ryham, Rolf; Berezovik, Irina; Cohen, Fredric S.

    2011-01-01

    A new theory, to our knowledge, is developed that describes the dynamics of a lipidic pore in a liposome. The equations of the theory capture the experimentally observed three-stage functional form of pore radius over time—stage 1, rapid pore enlargement; stage 2, slow pore shrinkage; and stage 3, rapid pore closure. They also show that lipid flow is kinetically limited by the values of both membrane and aqueous viscosity; therefore, pore evolution is affected by both viscosities. The theory predicts that for a giant liposome, tens of microns in radius, water viscosity dominates over the effects of membrane viscosity. The edge tension of a lipidic pore is calculated by using the theory to quantitatively account for pore kinetics in stage 3, rapid pore closing. This value of edge tension agrees with the value as standardly calculated from the stage of slow pore closure, stage 2. For small, submicron liposomes, membrane viscosity affects pore kinetics, but only if the viscosity of the aqueous solution is comparable to that of distilled water. A first-principle fluid-mechanics calculation of the friction due to aqueous viscosity is in excellent agreement with the friction obtained by applying the new theory to data of previously published experimental results. PMID:22208191

  5. Evaluation of the friction coefficient, the radial stress, and the damage work during needle insertions into agarose gels.

    PubMed

    Urrea, Fabián A; Casanova, Fernando; Orozco, Gustavo A; García, José J

    2016-03-01

    Agarose hydrogels have been extensively used as a phantom material to mimic the mechanical behavior of soft biological tissues, e.g. in studies aimed to analyze needle insertions into the organs producing tissue damage. To better predict the radial stress and damage during needle insertions, this study was aimed to determine the friction coefficient between the material of commercial catheters and hydrogels. The friction coefficient, the tissue damage and the radial stress were evaluated at 0.2, 1.8, and 10mm/s velocities for 28, 30, and 32 gauge needles of outer diameters equal to 0.36, 0.31, and 0.23mm, respectively. Force measurements during needle insertions and retractions on agarose gel samples were used to analyze damage and radial stress. The static friction coefficient (0.295±0.056) was significantly higher than the dynamic (0.255±0.086). The static and dynamic friction coefficients were significantly smaller for the 0.2mm/s velocity compared to those for the other two velocities, and there was no significant difference between the friction coefficients for 1.8 and 10mm/s. Radial stress averages were 131.2±54.1, 248.3±64.2, and 804.9±164.3Pa for the insertion velocity of 0.2, 1.8, and 10mm/s, respectively. The radial stress presented a tendency to increase at higher insertion velocities and needle size, which is consistent with other studies. However, the damage work did not show to be a good predictor of tissue damage, which appears to be due to simplifications in the analytical model. Differently to other approaches, the method proposed here based on radial stress may be extended in future studies to quantity tissue damage in vivo along the entire needle track. Copyright © 2015 Elsevier Ltd. All rights reserved.

  6. Contact compliance effects in the frictional response of bioinspired fibrillar adhesives

    PubMed Central

    Piccardo, Marco; Chateauminois, Antoine; Fretigny, Christian; Pugno, Nicola M.; Sitti, Metin

    2013-01-01

    The shear failure and friction mechanisms of bioinspired adhesives consisting of elastomer arrays of microfibres terminated by mushroom-shaped tips are investigated in contact with a rigid lens. In order to reveal the interplay between the vertical and lateral loading directions, experiments are carried out using a custom friction set-up in which normal stiffness can be made either high or low when compared with the stiffness of the contact between the fibrillar adhesive and the lens. Using in situ contact imaging, the shear failure of the adhesive is found to involve two successive mechanisms: (i) cavitation and peeling at the contact interface between the mushroom-shaped fibre tip endings and the lens; and (ii) side re-adhesion of the fibre's stem to the lens. The extent of these mechanisms and their implications regarding static friction forces is found to depend on the crosstalk between the normal and lateral loading directions that can result in contact instabilities associated with fibre buckling. In addition, the effects of the viscoelastic behaviour of the polyurethane material on the rate dependence of the shear response of the adhesive are accounted for. PMID:23554349

  7. Velocity dependence of sliding friction on a crystalline surface

    PubMed Central

    Apostoli, Christian; Giusti, Giovanni; Ciccoianni, Jacopo; Riva, Gabriele; Capozza, Rosario; Woulaché, Rosalie Laure; Vanossi, Andrea; Panizon, Emanuele

    2017-01-01

    We introduce and study a minimal 1D model for the simulation of dynamic friction and dissipation at the atomic scale. This model consists of a point mass (slider) that moves over and interacts weakly with a linear chain of particles interconnected by springs, representing a crystalline substrate. This interaction converts a part of the kinetic energy of the slider into phonon waves in the substrate. As a result, the slider experiences a friction force. As a function of the slider speed, we observe dissipation peaks at specific values of the slider speed, whose nature we understand by means of a Fourier analysis of the excited phonon modes. By relating the phonon phase velocities with the slider velocity, we obtain an equation whose solutions predict which phonons are being excited by the slider moving at a given speed. PMID:29114445

  8. 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.

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

    PubMed

    Guo, Ying; Hou, Yubin; Lu, Qingyou

    2014-05-01

    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.

  10. The effect of microscopic friction and size distributions on conditional probability distributions in soft particle packings

    NASA Astrophysics Data System (ADS)

    Saitoh, Kuniyasu; Magnanimo, Vanessa; Luding, Stefan

    2017-10-01

    Employing two-dimensional molecular dynamics (MD) simulations of soft particles, we study their non-affine responses to quasi-static isotropic compression where the effects of microscopic friction between the particles in contact and particle size distributions are examined. To quantify complicated restructuring of force-chain networks under isotropic compression, we introduce the conditional probability distributions (CPDs) of particle overlaps such that a master equation for distribution of overlaps in the soft particle packings can be constructed. From our MD simulations, we observe that the CPDs are well described by q-Gaussian distributions, where we find that the correlation for the evolution of particle overlaps is suppressed by microscopic friction, while it significantly increases with the increase of poly-dispersity.

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

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Guo, Ying; Lu, Qingyou, E-mail: qxl@ustc.edu.cn; Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026

    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 increasemore » 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.« less

  12. Frictional behavior of carbonate-rich sediments in subduction zones

    NASA Astrophysics Data System (ADS)

    Rabinowitz, H. S.; Savage, H. M.; Carpenter, B. M.; Collettini, C.

    2016-12-01

    Deformation in rocks and sediments is controlled by multiple mechanisms, each governed by its own pressure- (P), temperature- (T), and slip velocity- (v) dependent kinetics. Frictional behavior depends on which of these mechanisms are dominant, and, thus, varies with P, T, and v. Carbonates are a useful material with which to interrogate the PTv controls on friction due to the fact that a wide range of mechanisms can be easily accessed in the lab at geologically relevant conditions. In addition, carbonate-rich layers make up a significant component of subducting sediments around the world and may impact the frictional behavior of shallow subduction zones. In order to investigate the effect of carbonate subduction and the evolution of friction at subduction zone conditions, we conducted deformation experiments on input sediments for two subduction zones, the Hikurangi trench, New Zealand (ODP Site 1124) and the Peru trench (DSDP Site 321), which have carbonate/clay contents of 40/60 wt% and 80/20 wt%, respectively. Samples were saturated with distilled water mixed with 35g/l sea salt and deformed at room temperature. Experiments were conducted at σeff = 1-100 MPa and T = 20-100 °C with sliding velocities of 1-300 μm/s and hold times of 1-1000 s. We test the changes in velocity dependence and healing over these PT conditions to elucidate the frictional behavior of carbonates in subduction zone settings. The mechanical results are complemented by microstructural analysis. In lower stress experiments, there is no obvious shear localization; however, by 25 MPa, pervasive boundary-parallel shears become dominant, particularly in the Peru samples. Optical observations of these shear zones under cross-polarized light show evidence of plastic deformation (CPO development) while SEM-EDS observations indicate phase segregation in the boundary shears. Degree of microstructural localization appears to correspond with the trends observed in velocity-dependence. Our

  13. Real-Time Dynamic Observation of Micro-Friction on the Contact Interface of Friction Lining

    PubMed Central

    Zhang, Dekun; Chen, Kai; Guo, Yongbo

    2018-01-01

    This paper aims to investigate the microscopic friction mechanism based on in situ microscopic observation in order to record the deformation and contact situation of friction lining during the frictional process. The results show that friction coefficient increased with the shear deformation and energy loss of the surfacee, respectively. Furthermore, the friction mechanism mainly included adhesive friction in the high-pressure and high-speed conditions, whereas hysteresis friction was in the low-pressure and low-speed conditions. The mixed-friction mechanism was in the period when the working conditions varied from high pressure and speed to low pressure and speed. PMID:29498677

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

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Fang, Yi; Elsworth, Derek; Wang, Chaoyi

    There is wide concern that fluid injection in the subsurface, such as for the stimulation of shale reservoirs or for geological CO 2 sequestration (GCS), has the potential to induce seismicity that may change reservoir permeability due to fault slip. However, the impact of induced seismicity on fracture permeability evolution remains unclear due to the spectrum of modes of fault reactivation (e.g., stable versus unstable). As seismicity is controlled by the frictional response of fractures, we explore friction-stability-permeability relationships through the concurrent measurement of frictional and hydraulic properties of artificial fractures in Green River shale (GRS) and Opalinus shale (OPS).more » We observe that carbonate-rich GRS shows higher frictional strength but weak neutral frictional stability. The GRS fracture permeability declines during shearing while an increased sliding velocity reduces the rate of permeability decline. By comparison, the phyllosilicate-rich OPS has lower friction and strong stability while the fracture permeability is reduced due to the swelling behavior that dominates over the shearing induced permeability reduction. Hence, we conclude that the friction-stability-permeability relationship of a fracture is largely controlled by mineral composition and that shale mineral compositions with strong frictional stability may be particularly subject to permanent permeability reduction during fluid infiltration.« less

  15. Development of a Kinetic Assay for Late Endosome Movement.

    PubMed

    Esner, Milan; Meyenhofer, Felix; Kuhn, Michael; Thomas, Melissa; Kalaidzidis, Yannis; Bickle, Marc

    2014-08-01

    Automated imaging screens are performed mostly on fixed and stained samples to simplify the workflow and increase throughput. Some processes, such as the movement of cells and organelles or measuring membrane integrity and potential, can be measured only in living cells. Developing such assays to screen large compound or RNAi collections is challenging in many respects. Here, we develop a live-cell high-content assay for tracking endocytic organelles in medium throughput. We evaluate the added value of measuring kinetic parameters compared with measuring static parameters solely. We screened 2000 compounds in U-2 OS cells expressing Lamp1-GFP to label late endosomes. All hits have phenotypes in both static and kinetic parameters. However, we show that the kinetic parameters enable better discrimination of the mechanisms of action. Most of the compounds cause a decrease of motility of endosomes, but we identify several compounds that increase endosomal motility. In summary, we show that kinetic data help to better discriminate phenotypes and thereby obtain more subtle phenotypic clustering. © 2014 Society for Laboratory Automation and Screening.

  16. 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.

  17. 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.

  18. Moving Fingers under a Stick: A Laboratory Activity

    ERIC Educational Resources Information Center

    Massalha, Taha; Lanir, Yuval; Gluck, Paul

    2011-01-01

    We consider a demonstration in which pupils alternately slide and stop their fingers under a long horizontal rod which they support. The changeover is described in terms of the relevant kinetic and static friction. We present a model calculation, performed on a spreadsheet, which clarifies the process and describes graphically the stepwise…

  19. 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.

  20. Incorporation of experimentally derived friction laws in numerical simulations of earthquake generated tsunamis

    NASA Astrophysics Data System (ADS)

    Murphy, Shane; Spagnuolo, Elena; Lorito, Stefano; Di Toro, Giulio; Scala, Antonio; Festa, Gaetano; Nielsen, Stefan; Piatanesi, Alessio; Romano, Fabrizio; Aretusini, Stefano

    2016-04-01

    Seismological, tsunami and geodetic observations have shown that subduction zones are complex systems where the properties of earthquake rupture vary with depth. For example nucleation and high frequency radiation generally occur at depth but low frequency radiation and large tsunami-genic slip appear to occur in the shallow crustal depth. Numerical simulations used to describe these features predominantly use standardised theoretical equations or experimental observations often assuming that their validity extends to all slip-rates, lithologies and tectonic environments. However recent rotary-shear experiments performed on a range of diverse materials and experimental conditions highlighted the large variability of the evolution of friction during slipping pointing to a more complex relationship between material type, slip rate and normal stress. Simulating dynamic rupture using a 2D spectral element methodology on a Tohoku like fault, we apply experimentally derived friction laws (i.e. thermal slip distance friction law, Di Toro et al. 2011) Choice of parameters for the friction law are based on expected material type (e.g. cohesive and non-cohesive clay rich material representative of an accretionary wedge), the normal stress which is controlled by the interaction between the regional stress field and the fault geometry. The shear stress distribution on the fault plane is fractal with the yield stress dependent on the static coefficient of friction and the normal stress, parameters that are dependent on the material type and geometry. We use metrics such as the slip distribution, ground motion and fracture energy to explore the effect of frictional behaviour, fault geometry and stress perturbations and its potential role in tsunami generation. Preliminary results will be presented. This research is funded by the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 603839 (Project ASTARTE - Assessment, Strategy and Risk Reduction

  1. Physical and mechanical properties of spinach for whole-surface online imaging inspection

    NASA Astrophysics Data System (ADS)

    Tang, Xiuying; Mo, Chang Y.; Chan, Diane E.; Peng, Yankun; Qin, Jianwei; Yang, Chun-Chieh; Kim, Moon S.; Chao, Kuanglin

    2011-06-01

    The physical and mechanical properties of baby spinach were investigated, including density, Young's modulus, fracture strength, and friction coefficient. The average apparent density of baby spinach leaves was 0.5666 g/mm3. The tensile tests were performed using parallel, perpendicular, and diagonal directions with respect to the midrib of each leaf. The test results showed that the mechanical properties of spinach are anisotropic. For the parallel, diagonal, and perpendicular test directions, the average values for the Young's modulus values were found to be 2.137MPa, 1.0841 MPa, and 0.3914 MPa, respectively, and the average fracture strength values were 0.2429 MPa, 0.1396 MPa, and 0.1113 MPa, respectively. The static and kinetic friction coefficient between the baby spinach and conveyor belt were researched, whose test results showed that the average coefficients of kinetic and maximum static friction between the adaxial (front side) spinach leaf surface and conveyor belt were 1.2737 and 1.3635, respectively, and between the abaxial (back side) spinach leaf surface and conveyor belt were 1.1780 and 1.2451 respectively. These works provide the basis for future development of a whole-surface online imaging inspection system that can be used by the commercial vegetable processing industry to reduce food safety risks.

  2. 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

  3. 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.

  4. 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

  5. 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-

  6. A first step towards a consensus static in vitro model for simulating full-term infant digestion.

    PubMed

    Ménard, O; Bourlieu, C; De Oliveira, S C; Dellarosa, N; Laghi, L; Carrière, F; Capozzi, F; Dupont, D; Deglaire, A

    2018-02-01

    In vitro alternatives to clinical trials are used for studying human food digestion. For simulating infant digestion, only a few models, lacking physiological relevance, are available. Thanks to an extensive literature review of the in vivo infant digestive conditions, a gastrointestinal static in vitro model was developed for infants born at term and aged 28days. The model was applied to the digestion of a commercial infant formula. Kinetics of digestion, as well as the structural evolution, were compared with those obtained while submitting the same formula to the adult international consensus protocol of in vitro static digestion. The kinetics of proteolysis and lipolysis differed according to the physiological stage resulting mainly from the reduced level of enzymes and bile salts, as well as the higher gastric pH in the infant model. This in vitro static model of infant digestion is of interest for scientists, food or pharmaceutical manufacturers. Copyright © 2017 Elsevier Ltd. All rights reserved.

  7. Vitrinite reflectance and Raman spectra of carbonaceous material as indicators of frictional heating on faults: Constraints from friction experiments

    NASA Astrophysics Data System (ADS)

    Furuichi, Hiroyuki; Ujiie, Kohtaro; Kouketsu, Yui; Saito, Tsubasa; Tsutsumi, Akito; Wallis, Simon

    2015-08-01

    Vitrinite reflectance (Ro) and Raman spectra of carbonaceous material (RSCM) are both widely used as indicators of the maximum attained temperatures in sedimentary and metamorphic rocks. However, the potential of these methods to estimate temperature increases associated with fault slip has not been closely studied. To examine this issue, friction experiments were conducted on a mixture of powdered clay-rich fault material and carbonaceous material (CM) at slip rates of 0.15 mm/s and 1.3 m/s in nitrogen (N2) gas with or without distilled water. After the experiments, we measured Ro and RSCM and compared to those in starting material. The results indicate that when fault material suffers rapid heating at >500 °C in ∼9 s at 1.3 m/s, Ro and the intensity ratio of D1 and D2 Raman bands of CM (ID2/ID1) markedly increase. Comminution with very small temperature rise in ∼32 min at 0.15 mm/s is responsible for very limited changes in Ro and ID2/ID1. Our results demonstrate that Ro and RSCM could be useful for the detection of frictional heating on faults when the power density is ≥0.52 MW/m2. However, the conventionally used Ro and RSCM geothermometers are inadequate for the estimation of peak temperature during seismic fault slip. The reaction kinetics incorporating the effects of rapid heating at high slip rates and studies of the original microtexture and composition of CM are required to establish a reliable thermometer for frictional heating on faults.

  8. Frictional response of simulated faults to normal stresses perturbations probed with ultrasonic waves

    NASA Astrophysics Data System (ADS)

    Shreedharan, S.; Riviere, J.; Marone, C.

    2017-12-01

    adequately accounted for the effect of large slip velocity excursions. Here, we attempt to do so by using the measured ultrasonic amplitudes as a proxy for frictional state during transient shear stress evolution. Our work aims to improve understanding of induced and triggered seismicity with focus on simulating static triggering using rate and state friction.

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

    PubMed

    Makarov, Dmitrii E

    2013-01-07

    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.

  10. 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.

  11. Effect of Interface Modified by Graphene on the Mechanical and Frictional Properties of Carbon/Graphene/Carbon Composites

    PubMed Central

    Yang, Wei; Luo, Ruiying; Hou, Zhenhua

    2016-01-01

    In this work, we developed an interface modified by graphene to simultaneously improve the mechanical and frictional properties of carbon/graphene/carbon (C/G/C) composite. Results indicated that the C/G/C composite exhibits remarkably improved interfacial bonding mode, static and dynamic mechanical performance, thermal conductivity, and frictional properties in comparison with those of the C/C composite. The weight contents of carbon fibers, graphene and pyrolytic carbon are 31.6, 0.3 and 68.1 wt %, respectively. The matrix of the C/G/C composite was mainly composed of rough laminar (RL) pyrocarbon. The average hardness by nanoindentation of the C/G/C and C/C composite matrices were 0.473 and 0.751 GPa, respectively. The flexural strength (three point bending), interlaminar shear strength (ILSS), interfacial debonding strength (IDS), internal friction and storage modulus of the C/C composite were 106, 10.3, 7.6, 0.038 and 12.7 GPa, respectively. Those properties of the C/G/C composite increased by 76.4%, 44.6%, 168.4% and 22.8%, respectively, and their internal friction decreased by 42.1% in comparison with those of the C/C composite. Owing to the lower hardness of the matrix, improved fiber/matrix interface bonding strength, and self-lubricating properties of graphene, a complete friction film was easily formed on the friction surface of the modified composite. Compared with the C/C composite, the C/G/C composite exhibited stable friction coefficients and lower wear losses at simulating air-plane normal landing (NL) and rejected take-off (RTO). The method appears to be a competitive approach to improve the mechanical and frictional properties of C/C composites simultaneously. PMID:28773613

  12. Comparative Evaluation of Friction Resistance of Titanium, Stainless Steel, Ceramic and Ceramic with Metal Insert Brackets with Varying Dimensions of Stainless Steel Wire: An In vitro Multi-center Study.

    PubMed

    Kumar, B Sunil; Miryala, Suresh; Kumar, K Kiran; Shameem, K; Regalla, Ravindra Reddy

    2014-09-01

    The orthodontist seeks an archwire-bracket combination that has both good biocompatibility and low friction. Hence, the aim of this multicenter in vitro study was to evaluate and compare the frictional resistance generated between titanium (Ti), stainless steel (SS), ceramic and ceramic with metal insert (CMI) brackets with SS wires of varying dimensions in a specially designed apparatus. The material used in this study were Ti, SS, Ceramic and CMI with 0.018″ slot manufactured with zero degree tip and -7° torque premolar brackets (3M, Unitek) and SS wires of varying dimensions (0.016″ round, 0.016 × 0.016″ square, 0.016 × 0.022″ rectangular and 0.017 × 0.025″ rectangular) used. The frictional resistance was measured using Instron Universal testing machine (Model no. 4301). The specimen population in each center composed each of 160 brackets and wires. Differences among the all bracket/wire combinations were tested using (one-way) ANOVA, followed by the student Newman Keuls multiple comparisons of means ranking (at P < 0.05) for the determination of differences among the groups. Ti bracket in combination with 0.017 × 0.025″ SS rectangular wire produced significant force levels for an optimum orthodontic movement with least frictional resistance. Ti brackets have least resistance and rectangular wires produced significant force. These can be used to avoid hazards of Nickel. SS brackets revealed higher static frictional force values as the wire dimension increased and showed lower static friction than Ti brackets for all wires except the thicker wire. Our study recommends the preclusion of brackets with rough surface texture (Ti brackets) with SS ligature wire for ligating bracket and archwire are better to reduce friction.

  13. Thermophoretic transport of water nanodroplets confined in carbon nanotubes: The role of friction

    NASA Astrophysics Data System (ADS)

    Oyarzua, Elton; Walther, Jens H.; Zambrano, Harvey A.

    2017-11-01

    The development of efficient nanofluidic devices requires driving mechanisms that provide controlled transport of fluids through nanoconduits. Temperature gradients have been proposed as a mechanism to drive particles, fullerenes and nanodroplets inside carbon nanotubes (CNTs). In this work, molecular dynamics (MD) simulations are conducted to study thermophoresis of water nanodroplets inside CNTs. To gain insight into the interplay between the thermophoretic force acting on the droplet and the retarding liquid-solid friction, sets of constrained and unconstrained MD simulations are conducted. The results indicate that the thermophoretic motion of a nanodroplet displays two kinetic regimes: an initial regime characterized by a decreasing acceleration and afterwards a terminal regime with constant velocity. During the initial regime, the magnitude of the friction force increases linearly with the droplet velocity whereas the thermophoretic force has a constant magnitude defined by the magnitude of the thermal gradient and the droplet size. Subsequently, in the terminal regime, the droplet moves at constant velocity due to a dynamic balance between the thermophoretic force and the retarding friction force. We acknowledge partial support from CONICYT (Chile) under scholarship No. 21140427.

  14. Effective potential kinetic theory for strongly coupled plasmas

    NASA Astrophysics Data System (ADS)

    Baalrud, Scott D.; Daligault, Jérôme

    2016-11-01

    The effective potential theory (EPT) is a recently proposed method for extending traditional plasma kinetic and transport theory into the strongly coupled regime. Validation from experiments and molecular dynamics simulations have shown it to be accurate up to the onset of liquid-like correlation parameters (corresponding to Γ ≃ 10-50 for the one-component plasma, depending on the process of interest). Here, this theory is briefly reviewed along with comparisons between the theory and molecular dynamics simulations for self-diffusivity and viscosity of the one-component plasma. A number of new results are also provided, including calculations of friction coefficients, energy exchange rates, stopping power, and mobility. The theory is also cast in the Landau and Fokker-Planck kinetic forms, which may prove useful for enabling efficient kinetic computations.

  15. In vitro evaluation of frictional forces of two ceramic orthodontic brackets versus a stainless steel bracket in combination with two types of archwires.

    PubMed

    Arash, Valiollah; Rabiee, Mahmoud; Rakhshan, Vahid; Khorasani, Sara; Sobouti, Farhad

    2015-01-01

    The aim of this study was to compare frictional forces between monocrystalline alumina (MA), polycrystalline alumina (PA), and stainless steel (SS) brackets with two SS wires: Rectangular and round. In this in vitro study, 60 0.022 brackets [20 PA (0° torque, Forestadent, Germany) and 20 MA (0° torque, Ormco, California, USA)] brackets plus 20 SS brackets (0° torque, Foretadent, Germany) and 60 SS archwires (30 rectangular 0.019 ×0.025 archwires and 30 round 0.018 archwires, Ortho Technology, USA) were used in subgroups of 10 from the combination of all brackets and all archwires. A universal testing machine (Instron, Model STM 250, Germany) was used to investigate the static frictional resistance. The angulation between the bracket and wire was 0°, and the wires were pulled through the slots at a crosshead speed of 10 mm/min. Two-way and one-way analyses of variance (ANOVA) and Tukey tests were used to analyze the data. Mean (SD) static frictional force for each group was as follows: MA + round: 3.47 (0.38); MA + rectangular: 4.05 (0.47); PA + round: 4.14 (0.37); PA + rectangular: 4.45 (0.65); SS + round: 3.28 (0.22); and SS + rectangular: 4.22 (0.61). Significant effects of bracket types (P = 0.001) and archwire types (P = 0.000) on the friction force were detected using ANOVA. Tukey test indicated significant differences between PA brackets with both SS and MA brackets (P < 0.05), but not between SS and MA brackets. The two archwires as well had significantly different effects (Tukey P = 0.000). Based on the present in-vitro study, the PA brackets might create higher frictional forces compared to both SS and MA brackets. The rectangular 0.019 ×0.025 archwire might create greater forces than round 0.018 archwire.

  16. Stiffness and frictional resistance of a superelastic nickel-titanium orthodontic wire with low-stress hysteresis.

    PubMed

    Liaw, Yu-Cheng; Su, Yu-Yu M; Lai, Yu-Lin; Lee, Shyh-Yuan

    2007-05-01

    Stress-induced martensite formation with stress hysteresis that changes the elasticity and stiffness of nickel-titanium (Ni-Ti) wire influences the sliding mechanics of archwire-guided tooth movement. This in-vitro study investigated the frictional behavior of an improved superelastic Ni-Ti wire with low-stress hysteresis. Improved superelastic Ni-Ti alloy wires (L & H Titan, Tomy International, Tokyo, Japan) with low-stress hysteresis were examined by using 3-point bending and frictional resistance tests with a universal test machine at a constant temperature of 35 degrees C, and compared with the former conventional austenitic-active superelastic Ni-Ti wires (Sentalloy, Tomy International). Wire stiffness levels were derived from differentiation of the polynomial regression of the unloading curves, and values for kinetic friction were measured at constant bending deflection distances of 0, 2, 3, and 4 mm, respectively. Compared with conventional Sentalloy wires, the L & H Titan wire had a narrower stress hysteresis including a lower loading plateau and a higher unloading plateau. In addition, L & H Titan wires were less stiff than the Sentalloy wires during most unloading stages. Values of friction measured at deflections of 0, 2, and 3 mm were significantly (P <.05) increased in both types of wire. However, they showed a significant decrease in friction from 3 to 4 mm of deflection. L & H Titan wires had less friction than Sentalloy wires at all bending deflections (P <.05). Stress-induced martensite formation significantly reduced the stiffness and thus could be beneficial to decrease the binding friction of superelastic Ni-Ti wires during sliding with large bending deflections. Austenitic-active alloy wires with low-stress hysteresis and lower stiffness and friction offer significant potential for further investigation.

  17. Low cost friction seismic base-isolation of residential new masonry buildings in developing countries: A small masonry house case study

    NASA Astrophysics Data System (ADS)

    Habieb, A. B.; Milani, G.; Tavio, T.; Milani, F.

    2017-07-01

    A Finite element model was established to examine performance of a low-cost friction base-isolation system in reducing seismic vulnerability of rural buildings. This study adopts an experimental investigation of the isolation system which was conducted in India. Four friction isolation interfaces, namely, marble-marble, marble-high-density polyethylene, marble-rubber sheet, and marble-geosynthetic were involved. Those interfaces differ in static and dynamic friction coefficient obtained through previous research. The FE model was performed based on a macroscopic approach and the masonry wall is assumed as an isotropic element. In order to observe structural response of the masonry house, elastic and plastic parameters of the brick wall were studied. Concrete damage plasticity (CDP) model was adopted to determine non-linear behavior of the brick wall. The results of FE model shows that involving these friction isolation systems could much decrease response acceleration at roof level. It was found that systems with marble-marble and marble-geosynthetic interfaces reduce the roof acceleration up to 50% comparing to the system without isolation. Another interesting result is there was no damage appearing in systems with friction isolation during the test. Meanwhile a severe failure was clearly visible for a system without isolation.

  18. Friction in hip prostheses.

    PubMed

    Hall, R M; Unsworth, A

    1997-08-01

    Although the reduction of frictional torques was the driving force behind the design of the Charnley prosthesis, later concerns about wear and subsequent loosening of this and other hip replacements have dominated debate within the bioengineering community. To stimulate discussion on the role of friction in loosening, a review of the frictional characteristics of different prostheses was undertaken. The use of simple laboratory screening-type machines in the frictional assessment of different material combinations is discussed together with experiments performed on single axis simulators using both conventional and experimental prostheses. In particular, recent developments in the use of soft layer components are highlighted. Further, the possible link between excessively high frictional torques and loosening is discussed in the light of current results obtained from explanted prostheses.

  19. Dynamic effects in friction and adhesion through cooperative rupture and formation of supramolecular bonds.

    PubMed

    Blass, Johanna; Albrecht, Marcel; Bozna, Bianca L; Wenz, Gerhard; Bennewitz, Roland

    2015-05-07

    We introduce a molecular toolkit for studying the dynamics in friction and adhesion from the single molecule level to effects of multivalency. As experimental model system we use supramolecular bonds established by the inclusion of ditopic adamantane connector molecules into two surface-bound cyclodextrin molecules, attached to a tip of an atomic force microscope (AFM) and to a flat silicon surface. The rupture force of a single bond does not depend on the pulling rate, indicating that the fast complexation kinetics of adamantane and cyclodextrin are probed in thermal equilibrium. In contrast, the pull-off force for a group of supramolecular bonds depends on the unloading rate revealing a non-equilibrium situation, an effect discussed as the combined action of multivalency and cantilever inertia effects. Friction forces exhibit a stick-slip characteristic which is explained by the cooperative rupture of groups of host-guest bonds and their rebinding. No dependence of friction on the sliding velocity has been observed in the accessible range of velocities due to fast rebinding and the negligible delay of cantilever response in AFM lateral force measurements.

  20. Assessment of local friction in protein folding dynamics using a helix cross-linker.

    PubMed

    Markiewicz, Beatrice N; Jo, Hyunil; Culik, Robert M; DeGrado, William F; Gai, Feng

    2013-11-27

    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 measurable 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 nonperturbing cross-linker to help quantify the effect of internal friction. In addition, we estimate that a m-xylene cross-linker could lead to an increase in the roughness of the folding energy landscape by as much as 0.4-1.0k(B)T.

  1. 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".…

  2. Rubber friction directional asymmetry

    NASA Astrophysics Data System (ADS)

    Tiwari, A.; Dorogin, L.; Steenwyk, B.; Warhadpande, A.; Motamedi, M.; Fortunato, G.; Ciaravola, V.; Persson, B. N. J.

    2016-12-01

    In rubber friction studies it is usually assumed that the friction force does not depend on the sliding direction, unless the substrate has anisotropic properties, like a steel surface grinded in one direction. Here we will present experimental results for rubber friction, where we observe a strong asymmetry between forward and backward sliding, where forward and backward refer to the run-in direction of the rubber block. The observed effect could be very important in tire applications, where directional properties of the rubber friction could be induced during braking.

  3. The role of large-scale eddies in the climate equilibrium. Part 2: Variable static stability

    NASA Technical Reports Server (NTRS)

    Zhou, Shuntai; Stone, Peter H.

    1993-01-01

    Lorenz's two-level model on a sphere is used to investigate how the results of Part 1 are modified when the interaction of the vertical eddy heat flux and static stability is included. In general, the climate state does not depend very much on whether or not this interaction is included, because the poleward eddy heat transport dominates the eddy forcing of mean temperature and wind fields. However, the climatic sensitivity is significantly affected. Compared to two-level model results with fixed static stability, the poleward eddy heat flux is less sensitive to the meridional temperature gradient and the gradient is more sensitive to the forcing. For example, the logarithmic derivative of the eddy flux with respect to the gradient has a slope that is reduced from approximately 15 on a beta-plane with fixed static stability and approximately 6 on a sphere with fixed static stability, to approximately 3 to 4 in the present model. This last result is more in line with analyses from observations. The present model also has a stronger baroclinic adjustment than that in Part 1, more like that in two-level beta-plane models with fixed static stability, that is, the midlatitude isentropic slope is very insensitive to the forcing, the diabatic heating, and the friction, unless the forcing is very weak.

  4. Making Enzyme Kinetics Dynamic via Simulation Software

    ERIC Educational Resources Information Center

    Potratz, Jeffrey P.

    2017-01-01

    An interactive classroom demonstration that enhances students' knowledge of steady-state and Michaelis-Menten enzyme kinetics is described. The instructor uses a free version of professional-quality KinTek Explorer simulation software and student input to construct dynamic versions of three static hallmark images commonly used to introduce enzyme…

  5. 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.

  6. The role of frictional contact of constituent blocks on the stability of masonry domes.

    PubMed

    Beatini, Valentina; Royer-Carfagni, Gianni; Tasora, Alessandro

    2018-01-01

    The observation of old construction works confirms that masonry domes can withstand tensile hoop stresses, at least up to a certain level. Here, such tensile resistance, rather than a priori assumed as a property of the bulk material, is attributed to the contact forces that are developed at the interfaces between interlocked blocks under normal pressure, specified by Coulomb's friction law. According to this rationale, the aspect ratio of the blocks, as well as the bond pattern, becomes of fundamental importance. To investigate the complex assembly of blocks, supposed rigid, we present a non-smooth contact dynamic analysis, implemented in a custom software based on the Project Chrono C++ framework and complemented with parametric-design interfaces for pre- and post-processing complex geometries. Through this advanced tool, we investigate the role of frictional forces resisting hoop stresses in the stability of domes, either circular or oval, under static and dynamic loading, focusing, in particular, on the structural role played by the underlying drum and the surmounting tiburium .

  7. Friction and wear behaviors and mechanisms of ZnO and graphite in Cu-based friction materials

    NASA Astrophysics Data System (ADS)

    Chen, Tianhua

    2018-03-01

    Based on powder metallurgy method, nanometer graphite reinforced copper matrix friction materials were prepared. The nanometer zinc oxide were obtained by the hydro-thermal synthesis. Nanoparticles on friction performances of copper-based materials was studied. The wear morphology were investigated by metallographic microscopes. Tribological performance were use the inertia friction and wear testing machine. Experimental results show that the friction factor of the friction material added by nanometer zinc oxide and nano graphite are high and stable, which has no obvious recession phenomenon with the increase of number of joint compared with not add nanoparticles of friction materials.

  8. Origins of Rolling Friction

    ERIC Educational Resources Information Center

    Cross, Rod

    2017-01-01

    When a hard object rolls on a soft surface, or vice versa, rolling friction arises from deformation of the soft object or the soft surface. The friction force can be described in terms of an offset in the normal reaction force or in terms of energy loss arising from the deformation. The origin of the friction force itself is not entirely clear. It…

  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. Consistent description of quantum Brownian motors operating at strong friction.

    PubMed

    Machura, L; Kostur, M; Hänggi, P; Talkner, P; Luczka, J

    2004-09-01

    A quantum Smoluchowski equation is put forward that consistently describes thermal quantum states. In particular, it notably does not induce a violation of the second law of thermodynamics. This so modified kinetic equation is applied to study analytically directed quantum transport at strong friction in arbitrarily shaped ratchet potentials that are driven by nonthermal two-state noise. Depending on the mutual interplay of quantum tunneling and quantum reflection these quantum corrections can induce both, a sizable enhancement or a suppression of transport. Moreover, the threshold for current reversals becomes markedly shifted due to such quantum fluctuations.

  11. GEOMETRIC, VOLUMETRIC, COLOUR AND FRICTIONAL PROPERTIES OF SELECTED SALVIA SPECIES OF TURKEY.

    PubMed

    Bayram, Mustafa; Altuntas, Ebubekir; Yilar, Melih

    2017-01-01

    Salvia seeds are promite to dietary and healthy oils because they contain essential fatty acids. Salvia seeds frequently produce mucilage on soaking, and this mucilage is used for the treatment of eye diseases in eastern countries. Salvia species studied for medicine, food and cosmetics, have the potential to be used in the various fields. In the present study, selected engineering (geometrical, volumetrical, colour and frictional) properties of 6 Salvia species seeds were determined and compared. This study was performed on selected engineering properties of seeds of 6 Salvia species ( Salvia viridis L., Salvia aethiopis L., Salvia cryptantha Montbert & Aucher ex Benthan., Salvia tomentosa Mill ., Salvia sclarea L., Salvia virgata Jacq.,) cultivated in Turkey. Plants were collected during the vegetation in 2012-2013 (May-Agust). The seeds were cleaned from foreign matter, dirt and broken seeds manually. The average length, width and thickness were found in the range of 2.61 to 3.53 mm, 1.59 to 2.92 mm and 1.14 to 2.52 mm, respectively. Salvia viridis L. specie had the lowest geometric mean diameter and surface area, whereas Salvia cryptantha L. had the least values among these 6 Salvia species for these properties. The bulk density, true density and the porosity were between 296.83 and 702.80 kg m -3 , 285.69 and 718.08 kg m -3 , 10.27 and 44.05%, respectively. The volume of unit seed and sphericity ranged between 2.56 and 13.64 mm 3 , 62.90 and 90.40%, respectively. The coefficient of friction of salvia species were largely influenced by the friction surfaces studied, and highest values were found for polywood in the Salvia crytantha L.. In the study, the static friction coefficient and the angle of repose of salvia species changed from 0.477 to 0.955, and from 14.09 to 23.57°, respectively. Determination of geometric, volumetric, colour and frictional properties of Salvia spp. seeds may increase their economic value.

  12. GEOMETRIC, VOLUMETRIC, COLOUR AND FRICTIONAL PROPERTIES OF SELECTED SALVIA SPECIES OF TURKEY

    PubMed Central

    Bayram, Mustafa; Altuntas, Ebubekir; Yilar, Melih

    2017-01-01

    Background: Salvia seeds are promite to dietary and healthy oils because they contain essential fatty acids. Salvia seeds frequently produce mucilage on soaking, and this mucilage is used for the treatment of eye diseases in eastern countries. Salvia species studied for medicine, food and cosmetics, have the potential to be used in the various fields. In the present study, selected engineering (geometrical, volumetrical, colour and frictional) properties of 6 Salvia species seeds were determined and compared. Materials and Methods: This study was performed on selected engineering properties of seeds of 6 Salvia species (Salvia viridis L., Salvia aethiopis L., Salvia cryptantha Montbert & Aucher ex Benthan., Salvia tomentosa Mill., Salvia sclarea L., Salvia virgata Jacq.,) cultivated in Turkey. Plants were collected during the vegetation in 2012-2013 (May-Agust). The seeds were cleaned from foreign matter, dirt and broken seeds manually. Results: The average length, width and thickness were found in the range of 2.61 to 3.53 mm, 1.59 to 2.92 mm and 1.14 to 2.52 mm, respectively. Salvia viridis L. specie had the lowest geometric mean diameter and surface area, whereas Salvia cryptantha L. had the least values among these 6 Salvia species for these properties. The bulk density, true density and the porosity were between 296.83 and 702.80 kg m-3, 285.69 and 718.08 kg m-3, 10.27 and 44.05%, respectively. The volume of unit seed and sphericity ranged between 2.56 and 13.64 mm3, 62.90 and 90.40%, respectively. The coefficient of friction of salvia species were largely influenced by the friction surfaces studied, and highest values were found for polywood in the Salvia crytantha L.. In the study, the static friction coefficient and the angle of repose of salvia species changed from 0.477 to 0.955, and from 14.09 to 23.57°, respectively. Conclusion: Determination of geometric, volumetric, colour and frictional properties of Salvia spp. seeds may increase their economic

  13. Tactile friction of topical formulations.

    PubMed

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

    2016-02-01

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

  14. Friction laws at the nanoscale.

    PubMed

    Mo, Yifei; Turner, Kevin T; Szlufarska, Izabela

    2009-02-26

    Macroscopic laws of friction do not generally apply to nanoscale contacts. Although continuum mechanics models have been predicted to break down at the nanoscale, they continue to be applied for lack of a better theory. An understanding of how friction force depends on applied load and contact area at these scales is essential for the design of miniaturized devices with optimal mechanical performance. Here we use large-scale molecular dynamics simulations with realistic force fields to establish friction laws in dry nanoscale contacts. We show that friction force depends linearly on the number of atoms that chemically interact across the contact. By defining the contact area as being proportional to this number of interacting atoms, we show that the macroscopically observed linear relationship between friction force and contact area can be extended to the nanoscale. Our model predicts that as the adhesion between the contacting surfaces is reduced, a transition takes place from nonlinear to linear dependence of friction force on load. This transition is consistent with the results of several nanoscale friction experiments. We demonstrate that the breakdown of continuum mechanics can be understood as a result of the rough (multi-asperity) nature of the contact, and show that roughness theories of friction can be applied at the nanoscale.

  15. Investigation on Static Softening Behaviors of a Low Carbon Steel Under Ferritic Rolling Condition

    NASA Astrophysics Data System (ADS)

    Dong, Haifeng; Cai, Dayong; Zhao, Zhengzheng; Wang, Zhiyong; Wang, Yuhui; Yang, Qingxiang; Liao, Bo

    2010-03-01

    The study aims to postulate a theoretical hypothesis for the finishing period of ferritic rolling technique of the low carbon steel. The static softening behavior during multistage hot deformation of a low carbon steel has been studied by double hot compression tests at 700-800 °C and strain rate of 1 s-1 using a Gleeble-3500 simulator. Interrupted deformation is conducted with interpass times varying from 1 to 100 s after achieving a true strain of 0.5 in the first stage. The results indicate that the flow stress value at the second deformation is lower than that at the first one, and the flow stress drops substantially. The static softening effects increase with the increase of deformation temperature, holding temperature, and interpass time. The value of the ferritic static softening activation energy is obtained, and the static softening kinetics is modeled by the Avrami equation.

  16. Friction of Aviation Engines

    NASA Technical Reports Server (NTRS)

    Sparrow, S W; Thorne, M A

    1928-01-01

    The first portion of this report discusses measurements of friction made in the altitude laboratory of the Bureau of Standards between 1920 and 1926 under research authorization of the National Advisory Committee for Aeronautics. These are discussed with reference to the influence of speed, barometric pressure, jacket-water temperature, and throttle opening upon the friction of aviation engines. The second section of the report deals with measurements of the friction of a group of pistons differing from each other in a single respect, such as length, clearance, area of thrust face, location of thrust face, etc. Results obtained with each type of piston are discussed and attention is directed particularly to the fact that the friction chargeable to piston rings depends upon piston design as well as upon ring design. This is attributed to the effect of the rings upon the thickness and distribution of the oil film which in turn affects the friction of the piston to an extent which depends upon its design.

  17. In vitro evaluation of frictional forces of two ceramic orthodontic brackets versus a stainless steel bracket in combination with two types of archwires

    PubMed Central

    Arash, Valiollah; Rabiee, Mahmoud; Rakhshan, Vahid; Khorasani, Sara; Sobouti, Farhad

    2015-01-01

    Purpose: The aim of this study was to compare frictional forces between monocrystalline alumina (MA), polycrystalline alumina (PA), and stainless steel (SS) brackets with two SS wires: Rectangular and round. Materials and Methods: In this in vitro study, 60 0.022 brackets [20 PA (0° torque, Forestadent, Germany) and 20 MA (0° torque, Ormco, California, USA)] brackets plus 20 SS brackets (0° torque, Foretadent, Germany) and 60 SS archwires (30 rectangular 0.019 ×0.025 archwires and 30 round 0.018 archwires, Ortho Technology, USA) were used in subgroups of 10 from the combination of all brackets and all archwires. A universal testing machine (Instron, Model STM 250, Germany) was used to investigate the static frictional resistance. The angulation between the bracket and wire was 0°, and the wires were pulled through the slots at a crosshead speed of 10 mm/min. Two-way and one-way analyses of variance (ANOVA) and Tukey tests were used to analyze the data. Results: Mean (SD) static frictional force for each group was as follows: MA + round: 3.47 (0.38); MA + rectangular: 4.05 (0.47); PA + round: 4.14 (0.37); PA + rectangular: 4.45 (0.65); SS + round: 3.28 (0.22); and SS + rectangular: 4.22 (0.61). Significant effects of bracket types (P = 0.001) and archwire types (P = 0.000) on the friction force were detected using ANOVA. Tukey test indicated significant differences between PA brackets with both SS and MA brackets (P < 0.05), but not between SS and MA brackets. The two archwires as well had significantly different effects (Tukey P = 0.000). Conclusions: Based on the present in-vitro study, the PA brackets might create higher frictional forces compared to both SS and MA brackets. The rectangular 0.019 ×0.025 archwire might create greater forces than round 0.018 archwire. PMID:26020037

  18. LSENS, The NASA Lewis Kinetics and Sensitivity Analysis Code

    NASA Technical Reports Server (NTRS)

    Radhakrishnan, K.

    2000-01-01

    A general chemical kinetics and sensitivity analysis code for complex, homogeneous, gas-phase reactions is described. The main features of the code, LSENS (the NASA Lewis kinetics and sensitivity analysis code), are its flexibility, efficiency and convenience in treating many different chemical reaction models. The models include: static system; steady, one-dimensional, inviscid flow; incident-shock initiated reaction in a shock tube; and a perfectly stirred reactor. In addition, equilibrium computations can be performed for several assigned states. An implicit numerical integration method (LSODE, the Livermore Solver for Ordinary Differential Equations), which works efficiently for the extremes of very fast and very slow reactions, is used to solve the "stiff" ordinary differential equation systems that arise in chemical kinetics. For static reactions, the code uses the decoupled direct method to calculate sensitivity coefficients of the dependent variables and their temporal derivatives with respect to the initial values of dependent variables and/or the rate coefficient parameters. Solution methods for the equilibrium and post-shock conditions and for perfectly stirred reactor problems are either adapted from or based on the procedures built into the NASA code CEA (Chemical Equilibrium and Applications).

  19. 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.

  20. 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.

  1. 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.

  2. The Role of Compliance and Reaction Rate in Dehydration Weakening and Frictional Stability of Antigorite

    NASA Astrophysics Data System (ADS)

    Burdette, E.; Okazaki, K.; Hirth, G.

    2017-12-01

    The complicated brittle-ductile rheology of antigorite at subduction zone pressures and temperatures, resulting from its anisotropic mechanical properties, low dehydration temperature, and high water content has made interpretation of dehydration weakening problematic. Recent analyses indicate that antigorite is both ductile and brittle at high temperatures, and follows effective pressure frictional laws while dehydrating. In this study we focus on the role of rig compliance and reaction kinetics on frictional weakening and frictional stability. In addition, we correlate the evolution of mechanical behavior with AE activity at conditions within and above the thermal stability limit of antigorite. We conducted experiments at confining pressures from 0.25 GPa to 1GPa in a Griggs apparatus and modified rig compliance by including compliant components within the loading frame. We also modeled in-situ reaction progress using parameters from Sawai et al. (2013) to quantify relationships between weakening and fluid production. Without modifying the compliance, low pressure runs show stable dehydration weakening. With a modified, low compliance, results were nearly identical to stable weakening at standard compliance at 1 GPa. However, at lower pressures, many acoustic emissions were recorded at peak reaction rates during temperature ramping, with a rapid failure event occurring several minutes afterward (with the caveat that we still need to verify that AEs occur within the sample). No AEs are observed during room temperature experiments in samples that fault, nor were any observed in the high temperature experiments at conditions within the antigorite stability field - consistent with prior studies. Our results demonstrate that understanding in-situ dehydration reaction kinetics and their feedback with rheology and system compliance are key to scaling laboratory antigorite rheology to earth.

  3. Static Strain Aging Behavior of a Manganese-Silicon Steel After Single and Multi-stage Straining

    NASA Astrophysics Data System (ADS)

    Seraj, P.; Serajzadeh, S.

    2016-03-01

    In this work, static strain aging behavior of an alloy steel containing high amounts of silicon and manganese was examined while the influences of initial microstructure and pre-strain on the aging kinetics were evaluated as well. The rate of strain aging in a low carbon steel was also determined and compared with that occurred in the alloy steel. The rates of static strain aging in the steels were defined at room temperature and at 95 °C by means of double-hit tensile testing and hardness measurements. In addition, three-stage aging experiments at 80 °C were carried out to estimate aging behavior under multi-pass deformation processing. The results showed that in-solution manganese and silicon atoms could significantly affect the aging behavior of the steel and reduce the kinetics of static strain aging as compared to the low carbon steel. The initial microstructure also played an important role on the aging behavior. The rapidly cooled steel having mean ferrite grain size of 9.7 μm showed the least aging susceptibility index during the aging experiments. Accordingly, the activation energies for static strain aging were calculated as 93.2 and 85.7 kJ/mole for the alloy steel having fine and coarse ferrite-pearlite structures, respectively while it was computed as 79.1 kJ/mole for the low carbon steel with ferrite mean grain size of about 16.2 μm.

  4. Numerical Study of Frictional Properties and the Role of Cohesive End-Zones in Large Strike- Slip Earthquakes

    NASA Astrophysics Data System (ADS)

    Lovely, P. J.; Mutlu, O.; Pollard, D. D.

    2007-12-01

    Cohesive end-zones (CEZs) are regions of increased frictional strength and/or cohesion near the peripheries of faults that cause slip distributions to taper toward the fault-tip. Laboratory results, field observations, and theoretical models suggest an important role for CEZs in small-scale fractures and faults; however, their role in crustal-scale faulting and associated large earthquakes is less thoroughly understood. We present a numerical study of the potential role of CEZs on slip distributions in large, multi-segmented, strike-slip earthquake ruptures including the 1992 Landers Earthquake (Mw 7.2) and 1999 Hector Mine Earthquake (Mw 7.1). Displacement discontinuity is calculated using a quasi-static, 2D plane-strain boundary element (BEM) code for a homogeneous, isotropic, linear-elastic material. Friction is implemented by enforcing principles of complementarity. Model results with and without CEZs are compared with slip distributions measured by combined inversion of geodetic, strong ground motion, and teleseismic data. Stepwise and linear distributions of increasing frictional strength within CEZs are considered. The incorporation of CEZs in our model enables an improved match to slip distributions measured by inversion, suggesting that CEZs play a role in governing slip in large, strike-slip earthquakes. Additionally, we present a parametric study highlighting the very great sensitivity of modeled slip magnitude to small variations of the coefficient of friction. This result suggests that, provided a sufficiently well-constrained stress tensor and elastic moduli for the surrounding rock, relatively simple models could provide precise estimates of the magnitude of frictional strength. These results are verified by comparison with geometrically comparable finite element (FEM) models using the commercial code ABAQUS. In FEM models, friction is implemented by use of both Lagrange multipliers and penalty methods.

  5. Metadynamic and static recrystallization softening behavior of a bainite steel

    NASA Astrophysics Data System (ADS)

    Li, Lixin; Zheng, Liangyu; Ye, Ben; Tong, Zeqiong

    2018-01-01

    The metadynamic recrystallization (MDRX) and static recrystallization (SRX) softening behavior of a bainite steel was investigated by two-pass isothermal compression experiments at temperatures of 1173, 1273, 1373, and 1473 K and strain rates of 0.01, 0.1, 1, and 10 s-1 with inter-pass times of 1, 5, 10, and 30 s on a Gleeble-1500 thermo-mechanical simulator. Kinetic equations were developed to evaluate the softening fractions caused by MDRX and SRX. A comparison between the experimental and predicted softening fractions showed that the proposed kinetic equations can provide a precise estimation of the MDRX and SRX behavior of the studied steel. The results based on the kinetic equations indicated that the MDRX and SRX softening fraction increases with the increase in strain rate, deformation temperature, inter-pass time, and pre-strain; the activation energy of MDRX is much smaller than that of SRX; and the no-recrystallization temperature of the investigated steel is 1179.4 K.

  6. 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.

  7. 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.

  8. Friction surfaced Stellite6 coatings

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Rao, K. Prasad; Damodaram, R.; Rafi, H. Khalid, E-mail: khalidrafi@gmail.com

    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 formore » 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.« less

  9. Solid friction between soft filaments

    DOE PAGES

    Ward, Andrew; Hilitski, Feodor; Schwenger, Walter; ...

    2015-03-02

    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,more » can be induced by coating F-actin with polymeric brushes. Furthermore, we observe similar transitions in filamentous microtubules and bacterial flagella. In conclusion, 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.« less

  10. Development of a penetration friction apparatus (PFA) to measure the frictional performance of surgical suture.

    PubMed

    Zhang, Gangqiang; Ren, Tianhui; Lette, Walter; Zeng, Xiangqiong; van der Heide, Emile

    2017-10-01

    Nowadays there is a wide variety of surgical sutures available in the market. Surgical sutures have different sizes, structures, materials and coatings, whereas they are being used for various surgeries. The frictional performances of surgical sutures have been found to play a vital role in their functionality. The high friction force of surgical sutures in the suturing process may cause inflammation and pain to the person, leading to a longer recovery time, and the second trauma of soft or fragile tissue. Thus, the investigation into the frictional performance of surgical suture is essential. Despite the unquestionable fact, little is actually known on the friction performances of surgical suture-tissue due to the lack of appropriate test equipment. This study presents a new penetration friction apparatus (PFA) that allowed for the evaluation of the friction performances of various surgical needles and sutures during the suturing process, under different contact conditions. It considered the deformation of tissue and can realize the puncture force measurements of surgical needles as well as the friction force of surgical sutures. The developed PFA could accurately evaluate and understand the frictional behaviour of surgical suture-tissue in the simulating clinical conditions. The forces measured by the PFA showed the same trend as that reported in literatures. Copyright © 2017 Elsevier Ltd. All rights reserved.

  11. Exploratory Calibration of Adjustable-Protrusion Surface-Obstacle (APSO) Skin Friction Vector Gage

    NASA Technical Reports Server (NTRS)

    Hakkinen, Raimo J.; Neubauer, Jeremy S.; Hamory, Philip J.; Bui, Trong T.; Noffz, Gregory K.; Young, Ron (Technical Monitor)

    2003-01-01

    The design of an adjustable-protrusion surface-obstacle (APSO) skin friction vector gage is presented. Results from exploratory calibrations conducted in laminar and turbulent boundary layers at the Washington University Low-Speed Wind Tunnel and for turbulent boundary layers at speeds up to Mach 2 on the ceiling of the NASA Glenn Research Center 8- X 6-ft Supersonic Wind Tunnel are also discussed. The adjustable-height gage was designed to yield both the magnitude and direction of the surface shear stress vector and to measure the local static pressure distribution. Results from the NASA test show good correlation for subsonic and low supersonic conditions covering several orders of magnitude in terms of the adopted similarity variables. Recommendations for future work in this area consist of identifying the physical parameters responsible for the disagreement between the university and NASA data sets, developing a compressibility correction specific to the APSO geometry, and examining the effect that static pressure distribution and skewed boundary layers have on the results from the APSO.

  12. Optimization of wheel-rail interface friction using top-of-rail friction modifiers: State of the art

    NASA Astrophysics Data System (ADS)

    Khan, M. Roshan; Dasaka, Satyanarayana Murty

    2018-05-01

    High Speed Railways and Dedicated Freight Corridors are the need of the day for fast and efficient transportation of the ever growing population and freight across long distances of travel. With the increase in speeds and axle loads carried by these trains, wearing out of rails and train wheel sections are a common issue, which is due to the increase in friction at the wheel-rail interfaces. For the cases where the wheel-rail interface friction is less than optimum, as in case of high speed trains with very low axle loads, wheel-slips are imminent and loss of traction occurs when the trains accelerate rapidly or brake all of a sudden. These vast variety of traction problems around the wheel-rail interface friction need to be mitigated carefully, so that the contact interface friction neither ascents too high to cause material wear and need for added locomotive power, nor be on the lower side to cause wheel-slips and loss of traction at high speeds. Top-of-rail friction modifiers are engineered surface coatings applied on top of rails, to maintain an optimum frictional contact between the train wheels and the rails. Extensive research works in the area of wheel-rail tribology have revealed that the optimum frictional coefficients at wheel-rail interfaces lie at a value of around 0.35. Application of top-of-rail (TOR) friction modifiers on rail surfaces add an extra layer of material coating on top of the rails, with a surface frictional coefficient of the desired range. This study reviews the common types of rail friction modifiers, the methods for their application, issues related with the application of friction modifiers, and a guideline on selection of the right class of coating material based on site specific requirements of the railway networks.

  13. Frictional strength of wet- and dry- talc gouge in high-velocity shear experiments

    NASA Astrophysics Data System (ADS)

    Chen, X.; Reches, Z.; Elwood Madden, A. S.

    2015-12-01

    The strength of the creeping segment of the San Andres fault may be controlled by the distinct weakness and stability of talc (Moore & Rymer, 2007). We analyze talc frictional strength at high slip-velocity of 0.002 - 0.66 m/s, long slip-distances of 0.01 m to 33 m, and normal stresses up to 4.1 MPa. This analysis bridges the gap between nucleation stage of low velocity/distance, and the frictional behavior during large earthquakes. We tested wet and dry samples of pure talc gouge in a confined rotary cell, and continuously monitored the slip-velocity, stresses, dilation and temperature. We run 29 experiments of single and stepped velocities to obtain 243 values of quasi-static frictional coefficients. Dry talc gouge showed distinct slip-strengthening: friction coefficient of µ ~0.4 at short slip-distances of D < 0.1 m, and it increased systematically to µ ~0.8 at slip-distances of D = 0.1- 1 m; at D > 1 m, the frictional strength saturated at µ= 0.8 - 1 level. Wet talc gouge (16-20% water) displayed low frictional strength of µ= 0.1-0.3, in agreement with published triaxial tests. The stepped-velocity runs revealed a consistent velocity-strengthening trend. For a velocity jump from V1 to V2, we used VD = (µ2 -µ1)/ln (V2/V1), and found that on average VD = 0.06 and 0.03 for dry and wet talc, respectively, and for slip distances shorter than 1 m. Microstructural analysis of post-shearing wet talc gouge revealed extreme slip localization to a principal-slip-zone of a few microns, and significant shear compaction of 10-30%. In contrast, dry talc gouge exhibited distributed shear in a wide zone and systematic shear dilation (10-50%). We propose slip along weak interlayer talc plates and thermal-pressurization as the possible weakening mechanisms for wet talc. The development of distributed secondary fault network along with substantial grain crushing is responsible for slip-strengthening in dry condition. Fig. 1. Friction maps of talc gouge as function of slip

  14. Studies on centrifugal clutch judder behavior and the design of frictional lining materials

    NASA Astrophysics Data System (ADS)

    Li, Tse-Chang; Huang, Yu-Wen; Lin, Jen-Fin

    2016-01-01

    This study examines the judder behavior of a centrifugal clutch from the start of hot spots in the conformal contact, then the repeated developments of thermoelastic instability, and finally the formation of cyclic undulations in the vibrations, friction coefficient and torque. This behavior is proved to be consistent with the testing results. Using the Taguchi method, 18 kinds of frictional lining specimens were prepared in order to investigate their performance in judder resistance and establish a relationship between judder behavior and the Ts/Td (Ts: static torque; Td: dynamic torque) and dμ/dVx (μ: friction coefficient; Vx: relative sliding velocity of frictional lining and clutch drum) parameters. These specimens are also provided to examine the effects and profitability with regard to the centrifugal clutch, and find the relative importance of the various control factors. Theoretical models for the friction coefficient (μ), the critical sliding velocity (Vc) with clutch judder, and the contact pressure ratio p* /pbar (p*: pressure undulation w.r.t. pbar; pbar: mean contact pressure) and temperature corresponding to judder behavior are developed. The parameters of the contact pressure ratio and temperature are shown to be helpful to explain the occurrence of judder. The frictional torque and the rotational speeds of the driveline, clutch, and clutch drum as functions of engagement time for 100 clutch cycles are obtained experimentally to evaluate dμ/dVx and Ts/Td. A sharp rise in the maximum p* /pbar occurred when the relative sliding velocity reached the critical velocity, Vc. An increase in the maximum p* /pbar generally led to an increase of the (initially negative) dμ/dVx value, and thus the severity of judder. The fluctuation intensity of dμ/dVx becomes a governing factor of the growth of dμ/dVx itself in the engagement process. The mean values of dμ/dVx and Ts/Td for the clutching tests with 100 cycles can be roughly divided into three groups

  15. High-velocity frictional properties of gabbro

    NASA Astrophysics Data System (ADS)

    Tsutsumi, Akito; Shimamoto, Toshihiko

    High-velocity friction experiments have been performed on a pair of hollow-cylindrical specimens of gabbro initially at room temperature, at slip rates from 7.5 mm/s to 1.8 m/s, with total circumferential displacements of 125 to 174 m, and at normal stresses to 5 MPa, using a rotary-shear high-speed friction testing machine. Steady-state friction increases slightly with increasing slip rate at slip rates to about 100 mm/s (velocity strengthening) and it decreases markedly with increasing slip rate at higher velocities (velocity weakening). Steady-state friction in the velocity weakening regime is lower for the non-melting case than the frictional melting case, due perhaps to severe thermal fracturing. A very large peak friction is always recognized upon the initiation of visible frictional melting, presumably owing to the welding of fault surfaces upon the solidification of melt patches. Frictional properties thus change dramatically with increasing displacement at high velocities, and such a non-linear effect must be incorporated into the analysis of earthquake initiation processes.

  16. Atmospheric stability analysis over statically and dynamically rough surfaces

    NASA Astrophysics Data System (ADS)

    Maric, Emina; Metzger, Meredith; Singha, Arindam; Sadr, Reza

    2011-11-01

    The ratio of buoyancy flux to turbulent kinetic energy production in the atmospheric surface layer is investigated experimentally for air flow over two types of surfaces characterized by static and dynamic roughness. In this study, ``static'' refers to the time-invariant nature of naturally-occurring roughness over a mud/salt playa; while, ``dynamic'' refers to the behavior of water waves along an air-water interface. In both cases, time-resolved measurements of the momentum and heat fluxes were acquired from synchronized 3D sonic anemometers mounted on a vertical tower. Field campaigns were conducted at two sites, representing the ``statically'' and ``dynamically'' rough surfaces, respectively: (1) the SLTEST facility in Utah's western desert, and (2) the new Doha airport in Qatar under construction along the coast of the Persian Gulf. Note, at site 2, anemometers were located directly above the water by extension from a tower secured to the end of a 1 km-long pier. Comparisons of the Monin-Obukhov length, flux Richardson number, and gradient Richardson number are presented, and discussed in the context of the observed evolution of the turbulent spectra in response to diurnal variations of atmospheric stability. Supported by the Qatar National Research Fund.

  17. The effect of friction in coulombian damper

    NASA Astrophysics Data System (ADS)

    Wahad, H. S.; Tudor, A.; Vlase, M.; Cerbu, N.; Subhi, K. A.

    2017-02-01

    The study aimed to analyze the damping phenomenon in a system with variable friction, Stribeck type. Shock absorbers with limit and dry friction, is called coulombian shock-absorbers. The physical damping vibration phenomenon, in equipment, is based on friction between the cushioning gasket and the output regulator of the shock-absorber. Friction between them can be dry, limit, mixture or fluid. The friction is depending on the contact pressure and lubricant presence. It is defined dimensionless form for the Striebeck curve (µ friction coefficient - sliding speed v). The friction may damp a vibratory movement or can maintain it (self-vibration), depending on the µ with v (it can increase / decrease or it can be relative constant). The solutions of differential equation of movement are obtained for some work condition of one damper for automatic washing machine. The friction force can transfer partial or total energy or generates excitation energy in damper. The damping efficiency is defined and is determined analytical for the constant friction coefficient and for the parabolic friction coefficient.

  18. Chirality-dependent friction of bulk molecular solids.

    PubMed

    Yang, Dian; Cohen, Adam E

    2014-08-26

    We show that the solid-solid friction between bulk chiral molecular solids can depend on the relative chirality of the two materials. In menthol and 1-phenyl-1-butanol, heterochiral friction is smaller than homochiral friction, while in ibuprofen, heterochiral friction is larger. Chiral asymmetries in the coefficient of sliding friction vary with temperature and can be as large as 30%. In the three compounds tested, the sign of the difference between heterochiral and homochiral friction correlated with the sign of the difference in melting point between racemate (compound or conglomerate) and pure enantiomer. Menthol and ibuprofen each form a stable racemic compound, while 1-phenyl-1-butanol forms a racemic conglomerate. Thus, a difference between heterochiral and homochiral friction does not require the formation of a stable interfacial racemic compound. Measurements of chirality-dependent friction provide a unique means to distinguish the role of short-range intermolecular forces from all other sources of dissipation in the friction of bulk molecular solids.

  19. Estimating Stresses, Fault Friction and Fluid Pressure from Topography and Coseismic Slip Models

    NASA Astrophysics Data System (ADS)

    Styron, R. H.; Hetland, E. A.

    2014-12-01

    Stress is a first-order control on the deformation state of the earth. However, stress is notoriously hard to measure, and researchers typically only estimate the directions and relative magnitudes of principal stresses, with little quantification of the uncertainties or absolute magnitude. To improve upon this, we have developed methods to constrain the full stress tensor field in a region surrounding a fault, including tectonic, topographic, and lithostatic components, as well as static friction and pore fluid pressure on the fault. Our methods are based on elastic halfspace techniques for estimating topographic stresses from a DEM, and we use a Bayesian approach to estimate accumulated tectonic stress, fluid pressure, and friction from fault geometry and slip rake, assuming Mohr-Coulomb fault mechanics. The nature of the tectonic stress inversion is such that either the stress maximum or minimum is better constrained, depending on the topography and fault deformation style. Our results from the 2008 Wenchuan event yield shear stresses from topography up to 20 MPa (normal-sinistral shear sense) and topographic normal stresses up to 80 MPa on the faults; tectonic stress had to be large enough to overcome topography to produce the observed reverse-dextral slip. Maximum tectonic stress is constrained to be >0.3 * lithostatic stress (depth-increasing), with a most likely value around 0.8, trending 90-110°E. Minimum tectonic stress is about half of maximum. Static fault friction is constrained at 0.1-0.4, and fluid pressure at 0-0.6 * total pressure on the fault. Additionally, the patterns of topographic stress and slip suggest that topographic normal stress may limit fault slip once failure has occurred. Preliminary results from the 2013 Balochistan earthquake are similar, but yield stronger constraints on the upper limits of maximum tectonic stress, as well as tight constraints on the magnitude of minimum tectonic stress and stress orientation. Work in progress on

  20. Hip and knee net joint moments that correlate with success in lateral load transfers over a low friction surface.

    PubMed

    Catena, Robert D; Xu, Xu

    2016-12-01

    We previously described two different preferred strategies used to perform a lateral load transfer. The wide stance strategy was not used successfully on a low-friction surface, while the narrow stance strategy was successful. Here, we retrospectively examined lower extremity net joint moments between successful and unsuccessful strategies to determine if there is a kinetic benefit consideration that may go into choosing the preferred strategy. Success vs. failure over a novel slippery surface was used to dichotomise 35 healthy working-age individuals into the two groups (successful and unsuccessful). Participants performed lateral load transfers over three sequential surface conditions: high friction, novel low friction and practised low friction. The unsuccessful strategy required larger start torques, but lower dynamic moments during transfer compared to the successful strategy. These results indicate that the periodically unsuccessful strategy may be preferred because it requires less muscle recruitment and lower stresses on lower extremity soft tissues. Practitioner Summary: The reason for this paper is to retrospectively examine the joint moment in two different load transfer strategies that are used in a lateral load transfer. We found that periodically unsuccessful strategies that we previously reported may be a beneficial toward reduced lower extremity joint stresses.

  1. 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

  2. A study on the kinetic behavior of Listeria monocytogenes in ice cream stored under static and dynamic chilling and freezing conditions.

    PubMed

    Gougouli, M; Angelidis, A S; Koutsoumanis, K

    2008-02-01

    The kinetic behavior of Listeria monocytogenes in 2 commercial ice cream products (A and B) that were inoculated and stored under static chilling (4 to 16 degrees C), static freezing (-5 to -33 degrees C), dynamic chilling, and dynamic chilling-freezing conditions was studied, simulating conditions of the aging process and of normal or abuse conditions during distribution and storage. The ice cream products A and B had different compositions but similar pH (6.50 and 6.67, respectively) and water activity (0.957 and 0.965, respectively) values. For both chilling and freezing conditions, the kinetic behavior of the pathogen was similar in the 2 products, indicating that the pH and water activity, together with temperature, were the main factors controlling growth. Under chilling conditions, L. monocytogenes grew well at all temperatures tested. Under freezing conditions, no significant changes in the population of the pathogen were observed throughout a 90-d storage period for either of the inoculum levels tested (10(3) and 10(6) cfu/g). Growth data from chilled storage conditions were fitted to a mathematical model, and the calculated maximum specific growth rate was modeled as a function of temperature by using a square root model. The model was further validated under dynamic chilling and dynamic chilling-freezing conditions by using 4 different storage temperature scenarios. Under dynamic chilling conditions, the model accurately predicted the growth of the pathogen in both products, with 99.5% of the predictions lying within the +/- 20% relative error zone. The results from the chilling-freezing storage experiments showed that the pathogen was able to initiate growth within a very short time after a temperature upshift from freezing to chilling temperatures. This indicates that the freezing conditions did not cause a severe stress in L. monocytogenes cells capable of leading to a significant "additional" lag phase during the subsequent growth of the pathogen at

  3. Length scale effects of friction in particle compaction using atomistic simulations and a friction scaling model

    NASA Astrophysics Data System (ADS)

    Stone, T. W.; Horstemeyer, M. F.

    2012-09-01

    The objective of this study is to illustrate and quantify the length scale effects related to interparticle friction under compaction. Previous studies have shown as the length scale of a specimen decreases, the strength of a single crystal metal or ceramic increases. The question underlying this research effort continues the thought—If there is a length scale parameter related to the strength of a material, is there a length scale parameter related to friction? To explore the length scale effects of friction, molecular dynamics (MD) simulations using an embedded atom method potential were performed to analyze the compression of two spherical FCC nickel nanoparticles at different contact angles. In the MD model study, we applied a macroscopic plastic contact formulation to determine the normal plastic contact force at the particle interfaces and used the average shear stress from the MD simulations to determine the tangential contact forces. Combining this information with the Coulomb friction law, we quantified the MD interparticle coefficient of friction and showed good agreement with experimental studies and a Discrete Element Method prediction as a function of contact angle. Lastly, we compared our MD simulation friction values to the tribological predictions of Bhushan and Nosonovsky (BN), who developed a friction scaling model based on strain gradient plasticity and dislocation-assisted sliding that included a length scale parameter. The comparison revealed that the BN elastic friction scaling model did a much better job than the BN plastic scaling model of predicting the coefficient of friction values obtained from the MD simulations.

  4. Kinetic nanofriction: a mechanism transition from quasi-continuous to ballistic-like Brownian regime

    PubMed Central

    2012-01-01

    Surface diffusion of mobile adsorbates is not only the key to control the rate of dynamical processes on solid surfaces, e.g. epitaxial growth, but also of fundamental importance for recent technological applications, such as nanoscale electro-mechanical, tribological, and surface probing devices. Though several possible regimes of surface diffusion have been suggested, the nanoscale surface Brownian motion, especially in the technologically important low friction regimes, remains largely unexplored. Using molecular dynamics simulations, we show for the first time, that a C60 admolecule on a graphene substrate exhibits two distinct regimes of nanoscale Brownian motion: a quasi-continuous and a ballistic-like. A crossover between these two regimes is realized by changing the temperature of the system. We reveal that the underlying physical origin for this crossover is a mechanism transition of kinetic nanofriction arising from distinctive ways of interaction between the admolecule and the graphene substrate in these two regimes due to the temperature change. Our findings provide insight into surface mass transport and kinetic friction control at the nanoscale. PMID:22353343

  5. 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

  6. A study of static, kinetic, and dynamic visual acuity in 102 Japanese professional baseball players

    PubMed Central

    Hoshina, Kohji; Tagami, Yuichi; Mimura, Osamu; Edagawa, Hiroshi; Matsubara, Masao; Nakayama, Teiichi

    2013-01-01

    Background It seemed that visual functions might have some effects on the performance of baseball players. We measured static, kinetic, and dynamic visual acuity (SVA, KVA, and DVA, respectively) of Japanese professional baseball players to ascertain whether there would be any difference in SVA, KVA, and DVA among player groups stratified according to their performance level. Methods The subjects were 102 male professional baseball players with a mean age of 26 years who were members of a Japanese professional baseball club from 2000 to 2009. They were stratified into three groups according to their performance level: A (players who were on the roster of the top-level team all the time throughout the study period), B (players who were on the roster of the top-level team sometimes but not all the time), and C (players who were never on the roster of the top-level team). They were interviewed for the use of corrective visual aids, and examined for SVA, KVA, and DVA. The measurements of these parameters were compared among groups A, B, and C. We also investigated and analyzed the association of KVA or DVA with player position (pitchers or fielders) and with hand dominance for batting. KVA was compared between the pitchers and the fielders because they each require different playing skills. DVA was compared between the right-handed and the left-handed batters. Results There was no statistically significant difference among groups A, B, and C. There was a statistically significant difference in KVA between the pitchers and the fielders (t-test; P < 0.05) There was no statistically significant difference in DVA between the right-handed and the left-handed batters. Conclusions There was no significant difference in the examined visual functions among player groups with different performance levels. PMID:23569356

  7. Iliotibial band friction syndrome

    PubMed Central

    2010-01-01

    Published articles on iliotibial band friction syndrome have been reviewed. These articles cover the epidemiology, etiology, anatomy, pathology, prevention, and treatment of the condition. This article describes (1) the various etiological models that have been proposed to explain iliotibial band friction syndrome; (2) some of the imaging methods, research studies, and clinical experiences that support or call into question these various models; (3) commonly proposed treatment methods for iliotibial band friction syndrome; and (4) the rationale behind these methods and the clinical outcome studies that support their efficacy. PMID:21063495

  8. Multiscale physics of rubber-ice friction

    NASA Astrophysics Data System (ADS)

    Tuononen, Ari J.; Kriston, András; Persson, Bo

    2016-09-01

    Ice friction plays an important role in many engineering applications, e.g., tires on icy roads, ice breaker ship motion, or winter sports equipment. Although numerous experiments have already been performed to understand the effect of various conditions on ice friction, to reveal the fundamental frictional mechanisms is still a challenging task. This study uses in situ white light interferometry to analyze ice surface topography during linear friction testing with a rubber slider. The method helps to provide an understanding of the link between changes in the surface topography and the friction coefficient through direct visualization and quantitative measurement of the morphologies of the ice surface at different length scales. Besides surface polishing and scratching, it was found that ice melts locally even after one sweep showing the refrozen droplets. A multi-scale rubber friction theory was also applied to study the contribution of viscoelasticity to the total friction coefficient, which showed a significant level with respect to the smoothness of the ice; furthermore, the theory also confirmed the possibility of local ice melting.

  9. Constraint counting for frictional jamming

    NASA Astrophysics Data System (ADS)

    Quint, D. A.; Henkes, S.; Schwarz, J. M.

    2012-02-01

    While the frictionless jamming transition has been intensely studied in recent years, more realistic frictional packings are less well understood. In frictionless sphere packings, the transition is predicted by a simple mean-field constraint counting argument, the isostaticity argument. For frictional packings, a modified constraint counting argument, which includes slipping contacts at the Coulomb threshold, has had limited success in accounting for the transition. We propose that the frictional jamming transition is not mean field and is triggered by the nucleation of unstable regions, which are themselves dynamical objects due to the Coulomb criterion. We create frictional packings using MD simulations and test for the presence and shape of rigid clusters with the pebble game to identify the partition of the packing into stable and unstable regions. To understand the dynamics of these unstable regions we follow perturbations at contacts crucial to the stability of the ``frictional house of cards.''

  10. Internal friction in enzyme reactions.

    PubMed

    Rauscher, Anna; Derényi, Imre; Gráf, László; Málnási-Csizmadia, András

    2013-01-01

    The empirical concept of internal friction was introduced 20 years ago. This review summarizes the results of experimental and theoretical studies that help to uncover the nature of internal friction. After the history of the concept, we describe the experimental challenges in measuring and interpreting internal friction based on the viscosity dependence of enzyme reactions. We also present speculations about the structural background of this viscosity dependence. Finally, some models about the relationship between the energy landscape and internal friction are outlined. Alternative concepts regarding the viscosity dependence of enzyme reactions are also discussed. Copyright © 2012 International Union of Biochemistry and Molecular Biology, Inc.

  11. On the role of electronic friction for dissociative adsorption and scattering of hydrogen molecules at a Ru(0001) surface.

    PubMed

    Füchsel, Gernot; Schimka, Selina; Saalfrank, Peter

    2013-09-12

    The role of electronic friction and, more generally, of nonadiabatic effects during dynamical processes at the gas/metal surface interface is still a matter of discussion. In particular, it is not clear if electronic nonadiabaticity has an effect under "mild" conditions, when molecules in low rovibrational states interact with a metal surface. In this paper, we investigate the role of electronic friction on the dissociative sticking and (inelastic) scattering of vibrationally and rotationally cold H2 molecules at a Ru(0001) surface theoretically. For this purpose, classical molecular dynamics with electronic friction (MDEF) calculations are performed and compared to MD simulations without friction. The two H atoms move on a six-dimensional potential energy surface generated from gradient-corrected density functional theory (DFT), that is, all molecular degrees of freedom are accounted for. Electronic friction is included via atomic friction coefficients obtained from an embedded atom, free electron gas (FEG) model, with embedding densities taken from gradient-corrected DFT. We find that within this model, dissociative sticking probabilities as a function of impact kinetic energies and impact angles are hardly affected by nonadiabatic effects. If one accounts for a possibly enhanced electronic friction near the dissociation barrier, on the other hand, reduced sticking probabilities are observed, in particular, at high impact energies. Further, there is always an influence on inelastic scattering, in particular, as far as the translational and internal energy distribution of the reflected molecules is concerned. Additionally, our results shed light on the role played by the velocity distribution of the incident molecular beam for adsorption probabilities, where, in particular, at higher impact energies, large effects are found.

  12. Downhill cycling symmetry breaking: how the rider foils experiment

    NASA Astrophysics Data System (ADS)

    Ben Abu, Yuval; Wolfson, Ira; Bran, Gil; Yizhaq, Hezi

    2017-11-01

    In high-school teaching of mechanics, we deal, among other things, with the nature of static and kinetic friction, forces that are proportional to the normal force. Under the influence of frictional forces, a body moves down a rough sloped decline at a fixed rate of acceleration that is independent of its mass. This situation does not apply to cases where the frictional force is dependent upon velocity, such as bodies which are moving through a streaming fluid (such as raindrops falling to the ground). In this case the body moves with a continuously decreasing acceleration, eventually reaching a terminal velocity when the frictional and gravitational forces balance out. This velocity constraint is determined by the dependence of the frictional force on velocity and geometric parameters that determine the strength of the frictional force. We show here that a similar situation takes place when bicycles descend an incline with a fixed slope. We also investigated the dependence of the velocity constraint with mass, using bicycles equipped with sophisticated sensors that metamorphose them into data-processing laboratories.

  13. 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.

  14. Friction Stir Welding Development

    NASA Technical Reports Server (NTRS)

    Romine, Peter L.

    1998-01-01

    The research of this summer was a continuation of work started during the previous summer faculty fellowship period. The Friction Stir Welding process (FSW) patented by The Welding Institute (TWI), in Great Britain, has become a popular topic at the Marshall Space Flight Center over the past year. Last year it was considered a novel approach to welding but few people took it very seriously as a near term solution. However, due to continued problems with cracks in the new aluminum-lithium space shuttle external tank (ET), the friction stir process is being mobilized at full speed in an effort to mature this process for the potential manufacture of flight hardware. It is now the goal of NASA and Lockheed-Martin Corporation (LMC) to demonstrate a full-scale friction stir welding system capable of welding ET size barrel sections. The objectives this summer were: (1) Implementation and validation of the rotating dynamometer on the MSFC FSW system; (2) Collection of data for FSW process modeling efforts; (3) Specification development for FSW implementation on the vertical weld tool; (4) Controls and user interface development for the adjustable pin tool; and (5) Development of an instrumentation system for the planishing process. The projects started this summer will lead to a full scale friction stir welding system that is expected to produce a friction stir welded shuttle external tank type barrel section. The success of this could lead to the implementation of the friction stir process for manufacturing future shuttle external tanks.

  15. 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.

  16. Nonlinear friction model for servo press simulation

    NASA Astrophysics Data System (ADS)

    Ma, Ninshu; Sugitomo, Nobuhiko; Kyuno, Takunori; Tamura, Shintaro; Naka, Tetsuo

    2013-12-01

    The friction coefficient was measured under an idealized condition for a pulse servo motion. The measured friction coefficient and its changing with both sliding distance and a pulse motion showed that the friction resistance can be reduced due to the re-lubrication during unloading process of the pulse servo motion. Based on the measured friction coefficient and its changes with sliding distance and re-lubrication of oil, a nonlinear friction model was developed. Using the newly developed the nonlinear friction model, a deep draw simulation was performed and the formability was evaluated. The results were compared with experimental ones and the effectiveness was verified.

  17. Superradiance-tidal friction correspondence

    NASA Astrophysics Data System (ADS)

    Glampedakis, Kostas; Kapadia, Shasvath J.; Kennefick, Daniel

    2014-01-01

    Since the work of Hartle in the 1970s, and the subsequent development of the membrane paradigm approach to black hole physics it has been widely accepted that superradiant scattering of gravitational waves bears strong similarities with the phenomenon of "tidal friction" (well known from Newtonian gravity) operating in binary systems of viscous material bodies. In this paper we revisit the superradiance-tidal friction analogy within the context of ultracompact relativistic bodies. We advocate that as long as these bodies have nonzero viscosity they should undergo tidal friction that can be construed as a kind of superradiant scattering from the point of view of the dynamics of an orbiting test body. In addition we consider the presence of anisotropic matter, which is required for at least some ultracompact bodies, if they are to sustain a radius very close to the gravitational radius. We find that the tidal friction/superradiance output is enhanced with increasing anisotropy and that strongly anisotropic systems exhibit an unconventional response to tidal and centrifugal forces. Finally, we make contact with the artificial system comprising a black hole with its horizon replaced by a mirror (sometimes used as a proxy for ultracompact material bodies) and discuss superradiance and tidal friction in relation to it.

  18. PREFACE: The International Conference on Science of Friction

    NASA Astrophysics Data System (ADS)

    Miura, Kouji; Matsukawa, Hiroshi

    2007-07-01

    The first international conference on the science of friction in Japan was held at Irago, Aichi on 9-13 September 2007. The conference focused on the elementary process of friction phenomena from the atomic and molecular scale view. Topics covered in the conference are shown below.:

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

  31. Nonmonotonicity of the Frictional Bimaterial Effect

    NASA Astrophysics Data System (ADS)

    Aldam, Michael; Xu, Shiqing; Brener, Efim A.; Ben-Zion, Yehuda; Bouchbinder, Eran

    2017-10-01

    Sliding along frictional interfaces separating dissimilar elastic materials is qualitatively different from sliding along interfaces separating identical materials due to the existence of an elastodynamic coupling between interfacial slip and normal stress perturbations in the former case. This bimaterial coupling has important implications for the dynamics of frictional interfaces, including their stability and rupture propagation along them. We show that while this bimaterial coupling is a monotonically increasing function of the bimaterial contrast, when it is coupled to interfacial shear stress perturbations through a friction law, various physical quantities exhibit a nonmonotonic dependence on the bimaterial contrast. In particular, we show that for a regularized Coulomb friction, the maximal growth rate of unstable interfacial perturbations of homogeneous sliding is a nonmonotonic function of the bimaterial contrast and provides analytic insight into the origin of this nonmonotonicity. We further show that for velocity-strengthening rate-and-state friction, the maximal growth rate of unstable interfacial perturbations of homogeneous sliding is also a nonmonotonic function of the bimaterial contrast. Results from simulations of dynamic rupture along a bimaterial interface with slip-weakening friction provide evidence that the theoretically predicted nonmonotonicity persists in nonsteady, transient frictional dynamics.

  32. Integrated Data Collection and Analysis Project: Friction Correlation Study

    DTIC Science & Technology

    2015-08-01

    methods authorized in AOP-7 include Pendulum Friction, Rotary Friction, Sliding Friction (ABL), BAM Friction and Steel/Fiber Shoe Methods. The...sensitivity can be obtained by Pendulum Friction, Rotary Friction, Sliding Friction (such as the ABL), BAM Friction and Steel/Fiber Shoe Methods.3, 4 Within...Figure 4.16 A variable compressive force is applied downward through the wheel hydraulically (50-1995 psi). The 5 kg pendulum impacts (8 ft/sec is the

  1. Friction Sensitivity of Primary Explosives

    DTIC Science & Technology

    1982-09-01

    diffeomI from. Report) ISI. SUPPLEMENTARY NOTES It. KEY WORDS (Contflnuo on rvotr.. oldo. it nec~oaoty and Identify by block ri,uobr) Friction...friction senisitivity. Primary explosives RD 1333 lead azide, dextrinated lead azide, polyvinyl-alcohol (PVA)-lead a~.ide, colloidal lead azide, nocrnal lead...results for dextrinated lead azide duPont 52-127 13 4 A comparison of friction data at 10% probability of initiation 14 FIGURES 1 Working surfaces of BAM

  2. [Friction: self-ligating brackets].

    PubMed

    Thermac, Guilhem; Morgon, Laurent; Godeneche, Julien

    2008-12-01

    The manufacturers of self-ligating brackets advertise a reduction of the friction engendered between the wire and the bracket, which is an essential parameter for treatment's speed and comfort. We have compared the friction obtained with four types of self-ligating brackets - In-Ovation R, Damon 3, Smart Clip and Quick - with that of a standard bracket Omniarch associated with an elastomeric ligature. All bracket were tested on a bench of traction with three types of wires: steel .019"x.025", TMA .019"x.025" and NEO sentalloy F300 .020"x.020". The results confirm a clear friction reduction for all tested wire.

  3. 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.

  4. 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.

  5. Quasi-Static and Dynamic Response Characteristics of F-4 Bias-Ply and Radial-Belted Main Gear Tires

    NASA Technical Reports Server (NTRS)

    Davis, Pamela A.

    1997-01-01

    An investigation was conducted at Langley Research Center to determine the quasi-static and dynamic response characteristics of F-4 military fighter 30x11.5-14.5/26PR bias-ply and radial-belted main gear tires. Tire properties were measured by the application of vertical, lateral, and fore-and-aft loads. Mass moment-of-inertia data were also obtained. The results of the study include quasi-static load-deflection curves, free-vibration time-history plots, energy loss associated with hysteresis, stiffness and damping characteristics, footprint geometry, and inertia properties of each type of tire. The difference between bias-ply and radial-belted tire construction is given, as well as the advantages and disadvantages of each tire design. Three simple damping models representing viscous, structural, and Coulomb friction are presented and compared with the experimental data. The conclusions discussed contain a summary of test observations.

  6. 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.

  7. Slow rupture of frictional interfaces

    NASA Astrophysics Data System (ADS)

    Bar Sinai, Yohai; Brener, Efim A.; Bouchbinder, Eran

    2012-02-01

    The failure of frictional interfaces and the spatiotemporal structures that accompany it are central to a wide range of geophysical, physical and engineering systems. Recent geophysical and laboratory observations indicated that interfacial failure can be mediated by slow slip rupture phenomena which are distinct from ordinary, earthquake-like, fast rupture. These discoveries have influenced the way we think about frictional motion, yet the nature and properties of slow rupture are not completely understood. We show that slow rupture is an intrinsic and robust property of simple non-monotonic rate-and-state friction laws. It is associated with a new velocity scale cmin, determined by the friction law, below which steady state rupture cannot propagate. We further show that rupture can occur in a continuum of states, spanning a wide range of velocities from cmin to elastic wave-speeds, and predict different properties for slow rupture and ordinary fast rupture. Our results are qualitatively consistent with recent high-resolution laboratory experiments and may provide a theoretical framework for understanding slow rupture phenomena along frictional interfaces.

  8. Landing Biomechanics in Participants With Different Static Lower Extremity Alignment Profiles

    PubMed Central

    Nguyen, Anh-Dung; Shultz, Sandra J.; Schmitz, Randy J.

    2015-01-01

    Context: Whereas static lower extremity alignment (LEA) has been identified as a risk factor for anterior cruciate ligament injury, little is known about its influence on joint motion and moments commonly associated with anterior cruciate ligament injury. Objective: To cluster participants according to combinations of LEA variables and compare these clusters in hip- and knee-joint kinematics and kinetics during the landing phase of a drop-jump task. Design: Descriptive laboratory study. Setting: Research laboratory. Patients or Other Participants: A total of 141 participants (50 men: age = 22.2 ± 2.8 years, height = 177.9 ± 9.3 cm, weight = 80.9 ± 13.3 kg; 91 women: age = 21.2 ± 2.6 years, height = 163.9 ± 6.6 cm, weight = 61.1 ± 8.7 kg). Main Outcome Measure(s): Static LEA included pelvic angle, femoral anteversion, quadriceps angle, tibiofemoral angle, genu recurvatum, tibial torsion, and navicular drop. Cluster analysis grouped participants according to their static LEA profiles, and these groups were compared on their hip- and knee-joint kinematics and external moments during the landing phase of a double-legged drop jump. Results: Three distinct clusters (C1–C3) were identified based on their static LEAs. Participants in clusters characterized with static internally rotated hip and valgus knee posture (C1) and externally rotated knee and valgus knee posture (C3) alignments demonstrated greater knee-valgus motion and smaller hip-flexion moments than the cluster with more neutral static alignment (C2). Participants in C1 also experienced greater hip internal-rotation and knee external-rotation moments than those in C2 and C3. Conclusions: Static LEA clusters that are positioned anatomically with a more rotated and valgus knee posture experienced greater dynamic valgus along with hip and knee moments during landing. Whereas static LEA contributes to differences in hip and knee rotational moments, sex may influence the differences in frontal-plane knee

  9. Results of comparative RBMK neutron computation using VNIIEF codes (cell computation, 3D statics, 3D kinetics). Final report

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Grebennikov, A.N.; Zhitnik, A.K.; Zvenigorodskaya, O.A.

    1995-12-31

    In conformity with the protocol of the Workshop under Contract {open_quotes}Assessment of RBMK reactor safety using modern Western Codes{close_quotes} VNIIEF performed a neutronics computation series to compare western and VNIIEF codes and assess whether VNIIEF codes are suitable for RBMK type reactor safety assessment computation. The work was carried out in close collaboration with M.I. Rozhdestvensky and L.M. Podlazov, NIKIET employees. The effort involved: (1) cell computations with the WIMS, EKRAN codes (improved modification of the LOMA code) and the S-90 code (VNIIEF Monte Carlo). Cell, polycell, burnup computation; (2) 3D computation of static states with the KORAT-3D and NEUmore » codes and comparison with results of computation with the NESTLE code (USA). The computations were performed in the geometry and using the neutron constants presented by the American party; (3) 3D computation of neutron kinetics with the KORAT-3D and NEU codes. These computations were performed in two formulations, both being developed in collaboration with NIKIET. Formulation of the first problem maximally possibly agrees with one of NESTLE problems and imitates gas bubble travel through a core. The second problem is a model of the RBMK as a whole with imitation of control and protection system controls (CPS) movement in a core.« less

  10. Quantum friction in arbitrarily directed motion

    DOE PAGES

    Klatt, J.; Farías, M. Belen; Dalvit, D. A. R.; ...

    2017-05-30

    In quantum friction, the electromagnetic fluctuation-induced frictional force decelerating an atom which moves past a macroscopic dielectric body, has so far eluded experimental evidence despite more than three decades of theoretical studies. Inspired by the recent finding that dynamical corrections to such an atom's internal dynamics are enhanced by one order of magnitude for vertical motion—compared with the paradigmatic setup of parallel motion—here we generalize quantum friction calculations to arbitrary angles between the atom's direction of motion and the surface in front of which it moves. Motivated by the disagreement between quantum friction calculations based on Markovian quantum master equationsmore » and time-dependent perturbation theory, we carry out our derivations of the quantum frictional force for arbitrary angles by employing both methods and compare them.« less

  11. Disturbances to Air-Layer Skin-Friction Drag Reduction at High Reynolds Numbers

    NASA Astrophysics Data System (ADS)

    Dowling, David; Elbing, Brian; Makiharju, Simo; Wiggins, Andrew; Perlin, Marc; Ceccio, Steven

    2009-11-01

    Skin friction drag on a flat surface may be reduced by more than 80% when a layer of air separates the surface from a flowing liquid compared to when such an air layer is absent. Past large-scale experiments utilizing the US Navy's Large Cavitation Channel and a flat-plate test model 3 m wide and 12.9 m long have demonstrated air layer drag reduction (ALDR) on both smooth and rough surfaces at water flow speeds sufficient to reach downstream-distance-based Reynolds numbers exceeding 100 million. For these experiments, the incoming flow conditions, surface orientation, air injection geometry, and buoyancy forces all favored air layer formation. The results presented here extend this prior work to include the effects that vortex generators and free stream flow unsteadiness have on ALDR to assess its robustness for application to ocean-going ships. Measurements include skin friction, static pressure, airflow rate, video of the flow field downstream of the injector, and profiles of the flowing air-water mixture when the injected air forms bubbles, when it is in transition to an air layer, and when the air layer is fully formed. From these, and the prior measurements, ALDR's viability for full-scale applications is assessed.

  12. Preload, Coefficient of Friction, and Thread Friction in an Implant-Abutment-Screw Complex.

    PubMed

    Wentaschek, Stefan; Tomalla, Sven; Schmidtmann, Irene; Lehmann, Karl Martin

    To examine the screw preload, coefficient of friction (COF), and tightening torque needed to overcome the thread friction of an implant-abutment-screw complex. In a customized load frame, 25 new implant-abutment-screw complexes including uncoated titanium alloy screws were torqued and untorqued 10 times each, applying 25 Ncm. Mean preload values decreased significantly from 209.8 N to 129.5 N according to the number of repetitions. The overall COF increased correspondingly. There was no comparable trend for the thread friction component. These results suggest that the application of a used implant-abutment-screw complex may be unfavorable for obtaining optimal screw preload.

  13. 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. © IMechE 2016.

  14. Friction in Forming of UD Composites

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sachs, U.; Haanappel, S. P.; Akkerman, R.

    2011-05-04

    Inter-ply and tool/ply friction play a dominant role in hot stamp forming of UD fiber-reinforced thermoplastic laminates. This research treats friction measurements of a PEEK-AS4 composite system. To this end, an in-house developed friction tester is utilized to pull a laminate through two heat controlled clamping platens. The friction coefficient is determined by relating the clamp force to the pull force. The geometry of the gap between the clamping platens is monitored with micrometer accuracy. A first approach to describe the relation between the geometry and frictional behavior is undertaken by applying a standard thin-film theory for hydrodynamic lubrication. Experimentalmore » measurements showed that the thin-film theory does not entirely cover the underlying physics. Thus a second model is utilized, which employs a Leonov-model to describe the shear deformation of the matrix material, while its viscosity is described with a multi-mode Maxwell model. The combination of both models shows the potential to capture the complete frictional behavior.« less

  15. Friction coefficient of skin in real-time.

    PubMed

    Sivamani, Raja K; Goodman, Jack; Gitis, Norm V; Maibach, Howard I

    2003-08-01

    Friction studies are useful in quantitatively investigating the skin surface. Previous studies utilized different apparatuses and materials for these investigations but there was no real-time test parameter control or monitoring. Our studies incorporated the commercially available UMT Series Micro-Tribometer, a tribology instrument that permits real-time monitoring and calculation of the important parameters in friction studies, increasing the accuracy over previous tribology and friction measurement devices used on skin. Our friction tests were performed on four healthy volunteers and on abdominal skin samples. A stainless steel ball was pressed on to the skin with at a pre-set load and then moved across the skin at a constant velocity of 5 mm/min. The UMT continuously monitored the friction force of the skin and the normal force of the ball to calculate the friction coefficient in real-time. Tests investigated the applicability of Amonton's law, the impact of increased and decreased hydration, and the effect of the application of moisturizers. The friction coefficient depends on the normal load applied, and Amonton's law does not provide an accurate description for the skin surface. Application of water to the skin increased the friction coefficient and application of isopropyl alcohol decreased it. Fast acting moisturizers immediately increased the friction coefficient, but did not have the prolonged effect of the slow, long lasting moisturizers. The UMT is capable of making real-time measurements on the skin and can be used as an effective tool to study friction properties. Results from the UMT measurements agree closely with theory regarding the skin surface.

  16. Coefficient of Friction Patterns Can Identify Damage in Native and Engineered Cartilage Subjected to Frictional-Shear Stress

    PubMed Central

    Whitney, G. A.; Mansour, J. M.; Dennis, J. E.

    2015-01-01

    The mechanical loading environment encountered by articular cartilage in situ makes frictional-shear testing an invaluable technique for assessing engineered cartilage. Despite the important information that is gained from this testing, it remains under-utilized, especially for determining damage behavior. Currently, extensive visual inspection is required to assess damage; this is cumbersome and subjective. Tools to simplify, automate, and remove subjectivity from the analysis may increase the accessibility and usefulness of frictional-shear testing as an evaluation method. The objective of this study was to determine if the friction signal could be used to detect damage that occurred during the testing. This study proceeded in two phases: first, a simplified model of biphasic lubrication that does not require knowledge of interstitial fluid pressure was developed. In the second phase, frictional-shear tests were performed on 74 cartilage samples, and the simplified model was used to extract characteristic features from the friction signals. Using support vector machine classifiers, the extracted features were able to detect damage with a median accuracy of approximately 90%. The accuracy remained high even in samples with minimal damage. In conclusion, the friction signal acquired during frictional-shear testing can be used to detect resultant damage to a high level of accuracy. PMID:25691395

  17. 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

  18. Nano-Sized Grain Refinement Using Friction Stir Processing

    DTIC Science & Technology

    2013-03-01

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

  19. 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. Copyright © 2015 Elsevier Inc. All rights reserved.

  20. 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.

  1. Efficiency of the Inertia Friction Welding Process and Its Dependence on Process Parameters

    NASA Astrophysics Data System (ADS)

    Senkov, O. N.; Mahaffey, D. W.; Tung, D. J.; Zhang, W.; Semiatin, S. L.

    2017-07-01

    It has been widely assumed, but never proven, that the efficiency of the inertia friction welding (IFW) process is independent of process parameters and is relatively high, i.e., 70 to 95 pct. In the present work, the effect of IFW parameters on process efficiency was established. For this purpose, a series of IFW trials was conducted for the solid-state joining of two dissimilar nickel-base superalloys (LSHR and Mar-M247) using various combinations of initial kinetic energy ( i.e., the total weld energy, E o), initial flywheel angular velocity ( ω o), flywheel moment of inertia ( I), and axial compression force ( P). The kinetics of the conversion of the welding energy to heating of the faying sample surfaces ( i.e., the sample energy) vs parasitic losses to the welding machine itself were determined by measuring the friction torque on the sample surfaces ( M S) and in the machine bearings ( M M). It was found that the rotating parts of the welding machine can consume a significant fraction of the total energy. Specifically, the parasitic losses ranged from 28 to 80 pct of the total weld energy. The losses increased (and the corresponding IFW process efficiency decreased) as P increased (at constant I and E o), I decreased (at constant P and E o), and E o (or ω o) increased (at constant P and I). The results of this work thus provide guidelines for selecting process parameters which minimize energy losses and increase process efficiency during IFW.

  2. 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.

  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. Rock Physical Interpretation of the Relationship between Dynamic and Static Young's Moduli of Sedimentary Rocks

    NASA Astrophysics Data System (ADS)

    Takahashi, T.

    2017-12-01

    The static Young's modulus (deformability) of a rock is indispensable for designing and constructing tunnels, dams and underground caverns in civil engineering. Static Young's modulus which is an elastic modulus at large strain level is usually obtained with the laboratory tests of rock cores sampled in boreholes drilled in a rock mass. A deformability model of the entire rock mass is then built by extrapolating the measurements based on a rock mass classification obtained in geological site characterization. However, model-building using data obtained from a limited number of boreholes in the rock mass, especially a complex rock mass, may cause problems in the accuracy and reliability of the model. On the other hand, dynamic Young's modulus which is the modulus at small strain level can be obtained from seismic velocity. If dynamic Young's modulus can be rationally converted to static one, a seismic velocity model by the seismic method can be effectively used to build a deformability model of the rock mass. In this study, we have, therefore, developed a rock physics model (Mavko et al., 2009) to estimate static Young's modulus from dynamic one for sedimentary rocks. The rock physics model has been generally applied to seismic properties at small strain level. In the proposed model, however, the sandy shale model, one of rock physics models, is extended for modeling the static Young's modulus at large strain level by incorporating the mixture of frictional and frictionless grain contacts into the Hertz-Mindlin model. The proposed model is verified through its application to the dynamic Young's moduli derived from well log velocities and static Young's moduli measured in the tri-axial compression tests of rock cores sampled in the same borehole as the logs were acquired. This application proves that the proposed rock physics model can be possibly used to estimate static Young's modulus (deformability) which is required in many types of civil engineering applications

  5. The friction cost method: a comment.

    PubMed

    Johannesson, M; Karlsson, G

    1997-04-01

    The friction cost method has been proposed as an alternative to the human-capital approach of estimating indirect costs. We argue that the friction cost method is based on implausible assumptions not supported by neoclassical economic theory. Furthermore consistently applying the friction cost method would mean that the method should also be applied in the estimation of direct costs, which would mean that the costs of health care programmes are substantially decreased. It is concluded that the friction cost method does not seem to be a useful alternative to the human-capital approach in the estimation of indirect costs.

  6. 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

  7. Static Load Test on Instrumented Pile - Field Data and Numerical Simulations

    NASA Astrophysics Data System (ADS)

    Krasiński, Adam; Wiszniewski, Mateusz

    2017-09-01

    Static load tests on foundation piles are generally carried out in order to determine load - the displacement characteristic of the pile head. For standard (basic) engineering practices this type of test usually provides enough information. However, the knowledge of force distribution along the pile core and its division into the friction along the shaft and the resistance under the base can be very useful. Such information can be obtained by strain gage pile instrumentation [1]. Significant investigations have been completed on this technology, proving its utility and correctness [8], [10], [12]. The results of static tests on instrumented piles are not easy to interpret. There are many factors and processes affecting the final outcome. In order to understand better the whole testing process and soil-structure behavior some investigations and numerical analyses were done. In the paper, real data from a field load test on instrumented piles is discussed and compared with numerical simulation of such a test in similar conditions. Differences and difficulties in the results interpretation with their possible reasons are discussed. Moreover, the authors used their own analytical solution for more reliable determination of force distribution along the pile. The work was presented at the XVII French-Polish Colloquium of Soil and Rock Mechanics, Łódź, 28-30 November 2016.

  8. Characterizing the surface forces between two individual nanowires using optical microscopy based nanomanipulation

    NASA Astrophysics Data System (ADS)

    Xie, Hongtao; Mead, James L.; Wang, Shiliang; Fatikow, Sergej; Huang, Han

    2018-06-01

    The adhesion and friction between two Al2O3 nanowires (NWs) was characterized by the use of optical microscopy based nanomanipulation, with which peeling, shearing and sliding was performed. The elastically deformed shape of the NWs during peeling and shearing was used to calculate the adhesion and frictional forces; force sensing was not required. The obtained adhesion stress between two Al2O3 NWs varied from 0.14 to 0.25 MPa, lower than that observed for carbon nanotube junctions, and was attributed to van der Waals attraction. Stick-slip was observed during the shearing and sliding of two NWs, and was the consequence of discrete contact between surface asperities. The obtained static and kinetic frictional stresses varied from 0.7 to 1.3 MPa and 0.4 to 0.8 MPa, respectively; significantly greater than the obtained adhesion stress.

  9. Characterizing the surface forces between two individual nanowires using optical microscopy based nanomanipulation.

    PubMed

    Xie, Hongtao; Mead, James L; Wang, Shiliang; Fatikow, Sergej; Huang, Han

    2018-06-01

    The adhesion and friction between two Al 2 O 3 nanowires (NWs) was characterized by the use of optical microscopy based nanomanipulation, with which peeling, shearing and sliding was performed. The elastically deformed shape of the NWs during peeling and shearing was used to calculate the adhesion and frictional forces; force sensing was not required. The obtained adhesion stress between two Al 2 O 3 NWs varied from 0.14 to 0.25 MPa, lower than that observed for carbon nanotube junctions, and was attributed to van der Waals attraction. Stick-slip was observed during the shearing and sliding of two NWs, and was the consequence of discrete contact between surface asperities. The obtained static and kinetic frictional stresses varied from 0.7 to 1.3 MPa and 0.4 to 0.8 MPa, respectively; significantly greater than the obtained adhesion stress.

  10. Understanding dynamic friction through spontaneously evolving laboratory earthquakes

    PubMed Central

    Rubino, V.; Rosakis, A. J.; Lapusta, N.

    2017-01-01

    Friction plays a key role in how ruptures unzip faults in the Earth’s crust and release waves that cause destructive shaking. Yet dynamic friction evolution is one of the biggest uncertainties in earthquake science. Here we report on novel measurements of evolving local friction during spontaneously developing mini-earthquakes in the laboratory, enabled by our ultrahigh speed full-field imaging technique. The technique captures the evolution of displacements, velocities and stresses of dynamic ruptures, whose rupture speed range from sub-Rayleigh to supershear. The observed friction has complex evolution, featuring initial velocity strengthening followed by substantial velocity weakening. Our measurements are consistent with rate-and-state friction formulations supplemented with flash heating but not with widely used slip-weakening friction laws. This study develops a new approach for measuring local evolution of dynamic friction and has important implications for understanding earthquake hazard since laws governing frictional resistance of faults are vital ingredients in physically-based predictive models of the earthquake source. PMID:28660876

  11. Comparison of Friction Characteristics on TN and VA Mode Alignment Films with Friction Force Microscopy

    NASA Astrophysics Data System (ADS)

    Kwak, Musun; Chung, Hanrok; Kwon, Hyukmin; Kim, Jehyun; Han, Daekyung; Yi, Yoonseon; Lee, Sangmun; Lee, Chulgu; Cha, Sooyoul

    Using frictional force microscopy (FFM), the friction surface characteristics were compared between twisted nematic (TN) mode and vertical alignment (VA) mode alignment films (AFs). The friction asymmetry was detected depending on temperature conditions on TN mode AF, but not on VA mode AF. The difference between two modes was explained by leaning intermolecular repulsion caused by the pre-tilt angle uniformity and the density of side chain. No level difference according to temperature conditions appeared when the pre-tilt angle were measured after liquid crystal (LC) injection.

  12. Skin Friction Measurements Using Luminescent Oil Films

    NASA Astrophysics Data System (ADS)

    Husen, Nicholas M.

    As aircraft are designed to a greater extent on computers, the need for accurate and fast CFD algorithms has never been greater. The development of CFD algorithms requires experimental data against which CFD output can be validated and from which insight about flow physics can be acquired. Skin friction, in particular, is an important quantity to predict with CFD, and experimental skin friction data sets aid not only with the validation of the CFD predictions, but also in tuning the CFD models to predict specific flow fields. However, a practical experimental technique for collecting spatially and temporally resolved skin friction data on complex models does not yet exist. This dissertation develops and demonstrates a new luminescent oil film skin friction meter which can produce spatially-resolved quantitative steady and unsteady skin friction data on models with complex curvature. The skin friction acting on the surface of a thin film of oil can be approximated by the expression tauw =mu ouh/h, where mu o is the dynamic viscosity of the oil, uh is the velocity of the surface of the oil film, and h is the thickness of the oil film. The new skin friction meter determines skin friction by measuring h and uh. The oil film thickness h is determined by ratioing the intensity of the fluorescent emissions from the oil film with the intensity of the incident light which is scattered from the surface of the model. When properly calibrated, that ratio provides an absolute oil film thickness value. This oil film thickness meter is therefore referred as the Ratioed-Image Film-Thickness (RIFT) Meter. The oil film velocity uh is determined by monitoring the evolution of tagged molecules within the oil film: Photochromic molecules are dissolved into the fluorescent oil and a pattern is written into the oil film using an ultraviolet laser. The evolution of the pattern is recorded, and standard cross-correlation techniques are applied to the resulting sequence of images. This

  13. Aircraft and ground vehicle friction correlation test results obtained under winter runway conditions during joint FAA/NASA Runway Friction Program

    NASA Technical Reports Server (NTRS)

    Yager, Thomas J.; Vogler, William A.; Baldasare, Paul

    1988-01-01

    Aircraft and ground vehicle friction data collected during the Joint FAA/NASA Runway Friction Program under winter runway conditions are discussed and test results are summarized. The relationship between the different ground vehicle friction measurements obtained on compacted snow- and ice-covered conditions is defined together with the correlation to aircraft tire friction performance under similar runway conditions.

  14. 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)

  15. Investigation of the rolling motion of a hollow cylinder using a smartphone

    NASA Astrophysics Data System (ADS)

    Puttharugsa, Chokchai; Khemmani, Supitch; Utayarat, Patipan; Luangtip, Wasutep

    2016-09-01

    This paper describes the use of smartphone’s gyroscope sensor to analyse a hollow cylinder rolling down an inclined plane. The smartphone (iPhone 4s) was attached to the end of hollow cylinder and was equipped with the Sensorlog application (Sensorlog app) to record the angular speed of rolling down an inclined plane. The experimental results agree with the theoretical model that is familiar to students for the rolling motion on an inclined plane. Moreover, the coefficients of static friction and kinetic friction were determined to be 0.205 ± 0.011 and 0.178 ± 0.003 from the measurements, respectively. This experiment demonstrated an alternative way to teach the rolling motion in a physics laboratory.

  16. Tire-to-Surface Friction Especially Under Wet Conditions

    NASA Technical Reports Server (NTRS)

    Sawyer, Richard H.; Batterson, Sidney A.; Harrin, Eziaslav N.

    1959-01-01

    The results of measurements of the maximum friction available in braking on various runway surfaces under various conditions is shown for a C-123B airplane and comparisons of measurements with a tire-friction cart on the same runways are made. The.results of studies of wet-surface friction made with a 12-inch-diameter low-pressure tire on a tire-friction treadmill, with an automobile tire on the tire-friction cart, and with a 44 x 13 extra-high-pressure type VII aircraft tire at the Langley landing-loads track are compared. Preliminary results of tests on the tire-friction treadmill under wet-surface conditions to determine the effect of the wiping action of the front wheel of a tandem-wheel arrangement on the friction available in braking for the rear wheel are given.

  17. Servo Reduces Friction In Flexure Bearing

    NASA Technical Reports Server (NTRS)

    Clingman, W. Dean

    1991-01-01

    Proposed servocontrol device reduces such resistive torques as stiction, friction, ripple, and cogging in flexure bearing described in LAR-14348, "Flexure Bearing Reduces Startup Friction". Reduces frictional "bump" torque encountered when bearing ball runs into buildup of grease on bearing race. Also used as cable follower to reduce torque caused by cable and hoses when they bend because of motion of bearing. New device includes torquer across ball race. Torquer controlled by servo striving to keep flexure at null, removing torque to outer ring. In effect, device is inner control loop reducing friction, but does not control platforms or any outer-control-loop functions.

  18. Updated Chemical Kinetics and Sensitivity Analysis Code

    NASA Technical Reports Server (NTRS)

    Radhakrishnan, Krishnan

    2005-01-01

    An updated version of the General Chemical Kinetics and Sensitivity Analysis (LSENS) computer code has become available. A prior version of LSENS was described in "Program Helps to Determine Chemical-Reaction Mechanisms" (LEW-15758), NASA Tech Briefs, Vol. 19, No. 5 (May 1995), page 66. To recapitulate: LSENS solves complex, homogeneous, gas-phase, chemical-kinetics problems (e.g., combustion of fuels) that are represented by sets of many coupled, nonlinear, first-order ordinary differential equations. LSENS has been designed for flexibility, convenience, and computational efficiency. The present version of LSENS incorporates mathematical models for (1) a static system; (2) steady, one-dimensional inviscid flow; (3) reaction behind an incident shock wave, including boundary layer correction; (4) a perfectly stirred reactor; and (5) a perfectly stirred reactor followed by a plug-flow reactor. In addition, LSENS can compute equilibrium properties for the following assigned states: enthalpy and pressure, temperature and pressure, internal energy and volume, and temperature and volume. For static and one-dimensional-flow problems, including those behind an incident shock wave and following a perfectly stirred reactor calculation, LSENS can compute sensitivity coefficients of dependent variables and their derivatives, with respect to the initial values of dependent variables and/or the rate-coefficient parameters of the chemical reactions.

  19. 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.

  20. Statewide pavement friction testing 2012.

    DOT National Transportation Integrated Search

    2012-11-01

    In 2012, Dynatest conducted friction testing for the Wisconsin Department of Transportation (WisDOT) on a representative subset of its State Trunk Highway Network. Friction testing was performed at 3,394 sites in accordance with ASTM E274 using a Dyn...

  1. Low friction wear resistant graphene films

    DOE Office of Scientific and Technical Information (OSTI.GOV)

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

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

  2. 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. © 2015 The Author(s).

  3. 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

  4. Seismicity around Parkfield correlates with static shear stress changes following the 2003 Mw6.5 San Simeon earthquake

    USGS Publications Warehouse

    Meng, Xiaoteng; Peng, Zhigang; Hardebeck, Jeanne L.

    2013-01-01

    Earthquakes trigger other earthquakes, but the physical mechanism of the triggering is currently debated. Most studies of earthquake triggering rely on earthquakes listed in catalogs, which are known to be incomplete around the origin times of large earthquakes and therefore missing potentially triggered events. Here we apply a waveform matched-filter technique to systematically detect earthquakes along the Parkfield section of the San Andreas Fault from 46 days before to 31 days after the nearby 2003 Mw6.5 San Simeon earthquake. After removing all possible false detections, we identify ~8 times more earthquakes than in the Northern California Seismic Network catalog. The newly identified events along the creeping section of the San Andreas Fault show a statistically significant decrease following the San Simeon main shock, which correlates well with the negative static stress changes (i.e., stress shadow) cast by the main shock. In comparison, the seismicity rate around Parkfield increased moderately where the static stress changes are positive. The seismicity rate changes correlate well with the static shear stress changes induced by the San Simeon main shock, suggesting a low friction in the seismogenic zone along the Parkfield section of the San Andreas Fault.

  5. Assessment of semi-active friction dampers

    NASA Astrophysics Data System (ADS)

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

    2017-09-01

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

  6. Machine Learning of Fault Friction

    NASA Astrophysics Data System (ADS)

    Johnson, P. A.; Rouet-Leduc, B.; Hulbert, C.; Marone, C.; Guyer, R. A.

    2017-12-01

    We are applying machine learning (ML) techniques to continuous acoustic emission (AE) data from laboratory earthquake experiments. Our goal is to apply explicit ML methods to this acoustic datathe AE in order to infer frictional properties of a laboratory fault. The experiment is a double direct shear apparatus comprised of fault blocks surrounding fault gouge comprised of glass beads or quartz powder. Fault characteristics are recorded, including shear stress, applied load (bulk friction = shear stress/normal load) and shear velocity. The raw acoustic signal is continuously recorded. We rely on explicit decision tree approaches (Random Forest and Gradient Boosted Trees) that allow us to identify important features linked to the fault friction. A training procedure that employs both the AE and the recorded shear stress from the experiment is first conducted. Then, testing takes place on data the algorithm has never seen before, using only the continuous AE signal. We find that these methods provide rich information regarding frictional processes during slip (Rouet-Leduc et al., 2017a; Hulbert et al., 2017). In addition, similar machine learning approaches predict failure times, as well as slip magnitudes in some cases. We find that these methods work for both stick slip and slow slip experiments, for periodic slip and for aperiodic slip. We also derive a fundamental relationship between the AE and the friction describing the frictional behavior of any earthquake slip cycle in a given experiment (Rouet-Leduc et al., 2017b). Our goal is to ultimately scale these approaches to Earth geophysical data to probe fault friction. References Rouet-Leduc, B., C. Hulbert, N. Lubbers, K. Barros, C. Humphreys and P. A. Johnson, Machine learning predicts laboratory earthquakes, in review (2017). https://arxiv.org/abs/1702.05774Rouet-LeDuc, B. et al., Friction Laws Derived From the Acoustic Emissions of a Laboratory Fault by Machine Learning (2017), AGU Fall Meeting Session S025

  7. Micromechanics of ice friction

    NASA Astrophysics Data System (ADS)

    Sammonds, P. R.; Bailey, E.; Lishman, B.; Scourfield, S.

    2015-12-01

    Frictional mechanics are controlled by the ice micro-structure - surface asperities and flaws - but also the ice fabric and permeability network structure of the contacting blocks. Ice properties are dependent upon the temperature of the bulk ice, on the normal stress and on the sliding velocity and acceleration. This means the shear stress required for sliding is likewise dependent on sliding velocity, acceleration, and temperature. We aim to describe the micro-physics of the contacting surface. We review micro-mechanical models of friction: the elastic and ductile deformation of asperities under normal loads and their shear failure by ductile flow, brittle fracture, or melting and hydrodynamic lubrication. Combinations of these give a total of six rheological models of friction. We present experimental results in ice mechanics and physics from laboratory experiments to understand the mechanical models. We then examine the scaling relations of the slip of ice, to examine how the micro-mechanics of ice friction can be captured simple reduced-parameter models, describing the mechanical state and slip rate of the floes. We aim to capture key elements that they may be incorporated into mid and ocean-basin scale modelling.

  8. Friction Stir Welding of Magnesium Alloy Type AZ 31

    NASA Astrophysics Data System (ADS)

    Kupec, Tomáš; Behúlová, Mária; Turňa, Milan; Sahul, Miroslav

    The paper deals with welding of Mg alloy of the type AZ 31 by Friction Stir Welding technology (FSW). The FSW technology is at present predominantly used for welding light metals and alloys, as aluminium, magnesium and their alloys. Experimental part consists of performing the simulation and fabrication of welded joints on a new-installed welding equipment available at the Welding Research Institute — Industrial Institute of SR Bratislava. Welding tools made of tool steel type H 13 were used for welding experiments. Geometry of welding tools was designed on the base of literature knowledge. Suitable welding parameters and conditions were determined using numerical simulation. Main emphasis was laid upon the tool revolutions, welding speed and tool bevel angle. The effect of welding parameters on the quality of welded joints was assessed. Assessment of welded joints was carried out by radiography, light microscopy, hardness measurement and EDX microanalysis. Static tensile test was employed for mechanical testing.

  9. Ground Contact Modeling for the Morpheus Test Vehicle Simulation

    NASA Technical Reports Server (NTRS)

    Cordova, Luis

    2014-01-01

    The Morpheus vertical test vehicle is an autonomous robotic lander being developed at Johnson Space Center (JSC) to test hazard detection technology. Because the initial ground contact simulation model was not very realistic, it was decided to improve the model without making it too computationally expensive. The first development cycle added capability to define vehicle attachment points (AP) and to keep track of their states in the lander reference frame (LFRAME). These states are used with a spring damper model to compute an AP contact force. The lateral force is then overwritten, if necessary, by the Coulomb static or kinetic friction force. The second development cycle added capability to use the PolySurface class as the contact surface. The class can load CAD data in STL (Stereo Lithography) format, and use the data to compute line of sight (LOS) intercepts. A polygon frame (PFRAME) is computed from the facet intercept normal and used to convert the AP state to PFRAME. Three flat plane tests validate the transitions from kinetic to static, static to kinetic, and vertical impact. The hazardous terrain test will be used to test for visual reasonableness. The improved model is numerically inexpensive, robust, and produces results that are reasonable.

  10. Ground Contact Modeling for the Morpheus Test Vehicle Simulation

    NASA Technical Reports Server (NTRS)

    Cordova, Luis

    2013-01-01

    The Morpheus vertical test vehicle is an autonomous robotic lander being developed at Johnson Space Center (JSC) to test hazard detection technology. Because the initial ground contact simulation model was not very realistic, it was decided to improve the model without making it too computationally expensive. The first development cycle added capability to define vehicle attachment points (AP) and to keep track of their states in the lander reference frame (LFRAME). These states are used with a spring damper model to compute an AP contact force. The lateral force is then overwritten, if necessary, by the Coulomb static or kinetic friction force. The second development cycle added capability to use the PolySurface class as the contact surface. The class can load CAD data in STL (Stereo Lithography) format, and use the data to compute line of sight (LOS) intercepts. A polygon frame (PFRAME) is computed from the facet intercept normal and used to convert the AP state to PFRAME. Three flat plane tests validate the transitions from kinetic to static, static to kinetic, and vertical impact. The hazardous terrain test will be used to test for visual reasonableness. The improved model is numerically inexpensive, robust, and produces results that are reasonable.

  11. Anisotropic frictional heat dissipation in cyclotrimethylene trinitramine

    NASA Astrophysics Data System (ADS)

    Rajak, Pankaj; Kalia, Rajiv; Nakano, Aiichiro; Vashishta, Priya

    Anisotropic frictional response and corresponding heat dissipation from different crystallographic planes of RDX crystal is studied using molecular dynamics simulations. The effect of frictional force on the nature of damage and system temperature is monitored along different directions on primary slip plane, (010), of RDX and on non-slip planes, (100) and (001). The correlation between the friction coefficient, deformation and the frictional heating in these system is determined. It is observed that friction coefficients on slip planes are smaller than those of non-slip planes. In response to friction on slip plane, RDX crystal deforms via dislocation formation and shows less heating. On non-slip planes due to the inability of the system to deform by dislocation formation, large temperature rise is observed in the system just below the contact area of two surfaces. Frictional sliding on non-slip planes also lead to the formation of damage zone just below the contact area of two surfaces due to the change in RDX ring conformation from chair to boat/half-boat. This research is supported by the AFOSR Grant: FA9550-16- 1-0042.

  12. Dependence of internal friction on folding mechanism.

    PubMed

    Zheng, Wenwei; De Sancho, David; Hoppe, Travis; Best, Robert B

    2015-03-11

    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.

  13. Structure of AA5056 after friction drilling

    NASA Astrophysics Data System (ADS)

    Eliseev, A. A.; Kalashnikova, T. A.; Fortuna, S. V.

    2017-12-01

    Here we present data on the structure of AA5056 alloy after friction drilling to unveil potentials of the process for use in model experiments on friction stir welding. Our analysis of the average size and volume content of precipitates shows that their content decreases immediately beneath the friction surface and that the structure of this zone is the same as the structure of stirring zones formed in friction stir welding. The data suggest that both processes provide similar metal structures.

  14. 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.

  15. 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.

  16. Elastic Properties and Internal Friction of Two Magnesium Alloys at Elevated Temperatures

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Freels, M.; Liaw, P. K.; Garlea, E.

    2011-06-01

    The elastic properties and internal friction of two magnesium alloys were studied from 25 C to 450 C using Resonant Ultrasound Spectroscopy (RUS). The Young's moduli decrease with increasing temperature. At 200 C, a change in the temperature dependence of the elastic constants is observed. The internal friction increases significantly with increasing temperature above 200 C. The observed changes in the temperature dependence of the elastic constants and the internal friction are the result of anelastic relaxation by grain boundary sliding at elevated temperatures. Elastic properties govern the behavior of a materials subjected to stress over a region of strainmore » where the material behaves elastically. The elastic properties, including the Young's modulus (E), shear modulus (G), bulk modulus (B), and Poisson's ratio (?), are of significant interest to many design and engineering applications. The choice of the most appropriate material for a particular application at elevated temperatures therefore requires knowledge of its elastic properties as a function of temperature. In addition, mechanical vibration can cause significant damage in the automotive, aerospace, and architectural industries and thus, the ability of a material to dissipate elastic strain energy in materials, known as damping or internal friction, is also important property. Internal friction can be the result of a wide range of physical mechanisms, and depends on the material, temperature, and frequency of the loading. When utilized effectively in engineering applications, the damping capacity of a material can remove undesirable noise and vibration as heat to the surroundings. The elastic properties of materials can be determined by static or dynamic methods. Resonant Ultrasound Spectroscopy (RUS), used in this study, is a unique and sophisticated non-destructive dynamic technique for determining the complete elastic tensor of a solid by measuring the resonant spectrum of mechanical resonance

  17. Kinetic Equation for an Unstable Plasma

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Balescu, R.

    1963-01-01

    A kinetic equation is derived for the description of the evolution in time of the distribution of velocities in a spatially homogeneous ionized gas that, at the initial time, is able to sustain exponentially growing oscillations. This equation is expressed in terms of a functional of the distribution finction that obeys the same integral equation as in the stable case. Although the method of solution used in the stable case breaks down, the equation can still be solved in closed form under unstable conditions, and hence an explicit form of the kinetic equation is obtained. The latter contains the normalmore » collision term and a new additional term describing the stabilization of the plasma. The latter acts through friction and diffusion and brings the plasma into a state of neutral stability. From there on the system evolves toward thermal equilibrium under the action of the normal collision term as well as of an additional Fokker-Planck- like term with timedependent coefficients, which however becomes less and less efficient as the plasma approaches equilibrium.« less

  18. Stability of Einstein static universe in gravity theory with a non-minimal derivative coupling

    NASA Astrophysics Data System (ADS)

    Huang, Qihong; Wu, Puxun; Yu, Hongwei

    2018-01-01

    The emergent mechanism provides a possible way to resolve the big-bang singularity problem by assuming that our universe originates from the Einstein static (ES) state. Thus, the existence of a stable ES solution becomes a very crucial prerequisite for the emergent scenario. In this paper, we study the stability of an ES universe in gravity theory with a non-minimal coupling between the kinetic term of a scalar field and the Einstein tensor. We find that the ES solution is stable under both scalar and tensor perturbations when the model parameters satisfy certain conditions, which indicates that the big-bang singularity can be avoided successfully by the emergent mechanism in the non-minimally kinetic coupled gravity.

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

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Jo, YuGwon; Cho, Bumhee; Cho, Nam Zin, E-mail: nzcho@kaist.ac.kr

    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 problemmore » are presented.« less

  20. Debris-bed friction of hard-bedded glaciers

    USGS Publications Warehouse

    Cohen, D.; Iverson, N.R.; Hooyer, T.S.; Fischer, U.H.; Jackson, M.; Moore, P.L.

    2005-01-01

    [1] Field measurements of debris-bed friction on a smooth rock tablet at the bed of Engabreen, a hard-bedded, temperate glacier in northern Norway, indicated that basal ice containing 10% debris by volume exerted local shear traction of up to 500 kPa. The corresponding bulk friction coefficient between the dirty basal ice and the tablet was between 0.05 and 0.08. A model of friction in which nonrotating spherical rock particles are held in frictional contact with the bed by bed-normal ice flow can account for these measurements if the power law exponent for ice flowing past large clasts is 1. A small exponent (n < 2) is likely because stresses in ice are small and flow is transient. Numerical calculations of the bed-normal drag force on a sphere in contact with a flat bed using n = 1 show that this force can reach values several hundred times that on a sphere isolated from the bed, thus drastically increasing frictional resistance. Various estimates of basal friction are obtained from this model. For example, the shear traction at the bed of a glacier sliding at 20 m a-1 with a geothermally induced melt rate of 0.006 m a-1 and an effective pressure of 300 kPa can exceed 100 kPa. Debris-bed friction can therefore be a major component of sliding resistance, contradicting the common assumption that debris-bed friction is negligible. Copyright 2005 by the American Geophysical Union.

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. Anomalous electron transport in Hall-effect thrusters: Comparison between quasi-linear kinetic theory and particle-in-cell simulations

    NASA Astrophysics Data System (ADS)

    Lafleur, T.; Martorelli, R.; Chabert, P.; Bourdon, A.

    2018-06-01

    Kinetic drift instabilities have been implicated as a possible mechanism leading to anomalous electron cross-field transport in E × B discharges, such as Hall-effect thrusters. Such instabilities, which are driven by the large disparity in electron and ion drift velocities, present a significant challenge to modelling efforts without resorting to time-consuming particle-in-cell (PIC) simulations. Here, we test aspects of quasi-linear kinetic theory with 2D PIC simulations with the aim of developing a self-consistent treatment of these instabilities. The specific quantities of interest are the instability growth rate (which determines the spatial and temporal evolution of the instability amplitude), and the instability-enhanced electron-ion friction force (which leads to "anomalous" electron transport). By using the self-consistently obtained electron distribution functions from the PIC simulations (which are in general non-Maxwellian), we find that the predictions of the quasi-linear kinetic theory are in good agreement with the simulation results. By contrast, the use of Maxwellian distributions leads to a growth rate and electron-ion friction force that is around 2-4 times higher, and consequently significantly overestimates the electron transport. A possible method for self-consistently modelling the distribution functions without requiring PIC simulations is discussed.

  6. 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)

  7. Tribo-performance evaluation of ecofriendly brake friction composite materials

    NASA Astrophysics Data System (ADS)

    Kumar, Naresh; Singh, Tej; Grewal, G. S.

    2018-05-01

    This paper presents the potential of natural fibre in brake friction materials. Natural fibre filled ecofriendly brake friction materials were developed without Kevlar fibre evaluated for tribo-performance on a chase friction testing machine following SAE J 661a standard. Experimental results indicated that natural fibre enhances the fade performance, but depresses the friction and wear performance, whereas Kevlar fibre improves the friction, wear and recovery performance but depresses the fade performance. Also the results revealed that with the increase in natural fibre content, the friction and fade performances enhanced.

  8. Skin friction fields on delta wings

    NASA Astrophysics Data System (ADS)

    Woodiga, S. A.; Liu, Tianshu

    2009-12-01

    The normalized skin friction fields on a 65° delta wing and a 76°/40° double-delta wing are measured by using a global luminescent oil-film skin friction meter. The detailed topological structures of skin friction fields on the wings are revealed for different angles of attack and the important features are detected such as reattachment lines, secondary separation lines, vortex bursting and vortex interaction. The comparisons with the existing flow visualization results are discussed.

  9. The Required Coefficient of Friction for evaluating gait alterations in people with Multiple Sclerosis during gait.

    PubMed

    Pacifici, Ilaria; Galli, Manuela; Kleiner, Ana Francisca Rozin; Corona, Federica; Coghe, Giancarlo; Marongiu, Elisabetta; Loi, Andrea; Crisafulli, Antonio; Cocco, Eleonora; Marrosu, Maria Giovanna; Pau, Massimiliano

    2016-11-01

    Required Coefficient of Friction (RCOF) is one of the most critical gait parameters associated to the occurrence of slipping in individuals affected by neurological disorders characterized by balance impairments. This study aims to calculate RCOF in people with Multiple Sclerosis (MS) on the basis of three-dimensional Gait Analysis (GA) data. This study enrolls 22 people with MS (pwMS) who were characterized by an Expanded Disability Status Score in the range 1.5-6 and 10 healthy controls (HC). All participants underwent to three-dimensional GA from which we extracted kinematic and kinetic data (i.e. the Ground Reaction Forces, GRF, and joint moments and powers in the sagittal plane). RCOF was calculated as the ratio of the shear to normal GRF components during the stance phase of gait cycle, and normalized by the walking velocity. Thus, the following variables were extracted: first peak (named P1COF), valley (named V1COF), and second peak (named P2COF) in RCOF curve; also computating the maximum ankle dorsi-plantarflexion moment (MOMmax) and the maximum ankle joint power (PWRmax). Our data revealed that P2COF results are significantly lower in pwMS when compared to HC (p=0.043; Z=-2.025). In pwMS, the study found a moderate, positive correlation between V1COF and MOMmax (r=0.558; p<0.001) and a moderate, positive correlation between EDSS score and MOMmax (rho=0.622; p=0.001). While, in HC group, the study detected a moderate positive correlation between P1COF and MOM max (r=0.636; p=0.008). Friction during mid stance and push off phases is critically important to determine whether the frictional capabilities of foot/floor interface are sufficient to prevent slips in pwMS. The impaired ankle moment in MS group causes increased P2COF in comparison to HC, increasing the risk of slipping in the critical phase of transmission of the developed forces to kinematic chain. Also, the correlation analysis among RCOF values and kinetic variables describe the interplay between

  10. Scale-Dependent Friction and Damage Interface law: implications for effective earthquake rupture dynamics and radiation

    NASA Astrophysics Data System (ADS)

    Festa, Gaetano; Vilotte, Jean-Pierre; Raous, Michel; Henninger, Carole

    2010-05-01

    Propagation and radiation of an earthquake rupture is commonly considered as a friction dominated process on fault surfaces. Friction laws, such as the slip weakening and the rate-and-state laws are widely used in the modeling of the earthquake rupture process. These laws prescribe the traction evolution versus slip, slip rate and potentially other internal variables. They introduce a finite cohesive length scale over which the fracture energy is released. However faults are finite-width interfaces with complex internal structures, characterized by highly damaged zones embedding a very thin principal slip interface where most of the dynamic slip localizes. Even though the rupture process is generally investigated at wavelengths larger than the fault zone thickness, which should justify a formulation based upon surface energy, a consistent homogeneization, a very challenging problem, is still missing. Such homogeneization is however be required to derive the consistent form of an effective interface law, as well as the appropriate physical variables and length scales, to correctly describe the coarse-grained dissipation resulting from surface and volumetric contributions at the scale of the fault zone. In this study, we investigate a scale-dependent law, introduced by Raous et al. (1999) in the context of adhesive material interfaces, that takes into account the transition between a damage dominated and a friction dominated state. Such a phase-field formalism describes this transition through an order parameter. We first compare this law to standard slip weakening friction law in terms of the rupture nucleation. The problem is analyzed through the representation of the solution of the quasi-static elastic problem onto the Chebyshev polynomial basis, generalizing the Uenishi-Rice solution. The nucleation solutions, at the onset of instability, are then introduced as initial conditions for the study of the dynamic rupture propagation, in the case of in-plane rupture

  11. 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.

  12. 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.

  13. Tactile texture and friction of soft sponge surfaces.

    PubMed

    Takahashi, Akira; Suzuki, Makoto; Imai, Yumi; Nonomura, Yoshimune

    2015-06-01

    We evaluated the tactile texture and frictional properties of five soft sponges with various cell sizes. The frictional forces were measured by a friction meter containing a contact probe with human-finger-like geometry and mechanical properties. When the subjects touched these sponges with their fingers, hard-textured sponges were deemed unpleasant. This tactile feeling changed with friction factors including friction coefficients, their temporal patterns, as well as mechanical and shape factors. These findings provide useful information on how to control the tactile textures of various sponges. Copyright © 2015 Elsevier B.V. All rights reserved.

  14. 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.

  15. 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.

  16. 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.

  17. Skin friction related behaviour of artificial turf systems.

    PubMed

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

    2017-08-01

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

  18. Ice friction of flared ice hockey skate blades.

    PubMed

    Federolf, Peter A; Mills, Robert; Nigg, Benno

    2008-09-01

    In ice hockey, skating performance depends on the skill and physical conditioning of the players and on the characteristics of their equipment. CT Edge have recently designed a new skate blade that angles outward near the bottom of the blade. The objective of this study was to compare the frictional characteristics of three CT Edge blades (with blade angles of 4 degrees, 60, and 8 degrees, respectively) with the frictional characteristics of a standard skate blade. The friction coefficients of the blades were determined by measuring the deceleration of an aluminium test sled equipped with three test blades. The measurements were conducted with an initial sled speed of 1.8 m s(-1) and with a load of 53 kg on each blade. The friction coefficient of the standard blades was 0.0071 (s = 0.0005). For the CT Edge blades with blade angles of 4 degrees, 6 degrees, and 8 degrees, friction coefficients were lower by about 13%, 21%, and 22%, respectively. Furthermore, the friction coefficients decreased with increasing load. The results of this study show that widely accepted paradigms such as "thinner blades cause less friction" need to be revisited. New blade designs might also be able to reduce friction in speed skating, figure skating, bobsledding, and luge.

  19. Frictional stability-permeability relationships for fractures in shales

    NASA Astrophysics Data System (ADS)

    Fang, Yi; Elsworth, Derek; Wang, Chaoyi; Ishibashi, Takuya; Fitts, Jeffrey P.

    2017-03-01

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

  20. Full-driving soft robotic colonoscope in compliant colon tissue.

    PubMed

    Wang, Kundong; Ma, Jiayi; Wang, Feng; Wang, Zhiwu; Yan, Guozheng; Zhou, Yilu

    2017-11-01

    Robotic colonoscopy is an efficient examination method for finding malignant tumour in its early stage. This research developed a novel robotic endoscope with 13 mm diameter, 105 mm length and 22.3 g weight. A contact biomechanical model is proposed to increase the locomotion safety and efficiency in the soft tissue. The model shows that the friction difference between the robot and the tissue is a key factor to locomotion capability. A soft, full bellow with excellent compatibility was designed to package the robot body. The bellow increased the static friction and decreased the kinetic friction given the change in the contact state. The bellow is divided into three segments. Each segment is composed of a linear locomotor with micromotor, turbine-worm and wire wrapping-sliding mechanism. The robot is tested in in vivo pig colon, which revealed an excellent locomotion capability and safety in soft tissues.

  1. Some aspects of frictional measurements in hip joint simulators.

    PubMed

    Unsworth, Anthony

    2016-05-01

    The measurement of friction in artificial hip joints can lead to the knowledge of the lubrication mechanisms occurring in the joints. However, the measurement of friction, particularly in spherical contacts, is not always straightforward. The important loading and kinematic features must be appropriate and the friction must be measured in the correct plane. Even defining a coefficient of friction is difficult with spherical contacts as friction acts at different moment arms throughout the contact area. Thus, the generated frictional torques depend on the pressure distribution of the contact and the moment arms at which this pressure acts. The pressure distribution depends on the material properties, the surface entraining velocities, the joint diameters, and the clearance between the two surfaces of the ball and socket joint. Equally measuring friction is very taxing for machines which are applying very high loads. Slight misalignments of the application of these loads can produce torques which are very much greater than the frictional torques that we are trying to measure. This article attempts to share the thoughts behind over 40 years of measuring friction in artificial joints using the Durham Friction Simulators. This has led to accrued consistency of measurement and a robust scientific design rationale to understand the nature of friction in these spherical contacts. It also impacts on how to obtain accurate measurements as well as on the understanding of where the difficult issues lie and how to overcome them. © IMechE 2016.

  2. Different singularities in the functions of extended kinetic theory at the origin of the yield stress in granular flows

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Berzi, Diego; Vescovi, Dalila

    2015-01-15

    We use previous results from discrete element simulations of simple shear flows of rigid, identical spheres in the collisional regime to show that the volume fraction-dependence of the stresses is singular at the shear rigidity. Here, we identify the shear rigidity, which is a decreasing function of the interparticle friction, as the maximum volume fraction beyond which a random collisional assembly of grains cannot be sheared without developing force chains that span the entire domain. In the framework of extended kinetic theory, i.e., kinetic theory that accounts for the decreasing in the collisional dissipation due to the breaking of molecularmore » chaos at volume fractions larger than 0.49, we also show that the volume fraction-dependence of the correlation length (measure of the velocity correlation) is singular at random close packing, independent of the interparticle friction. The difference in the singularities ensures that the ratio of the shear stress to the pressure at shear rigidity is different from zero even in the case of frictionless spheres: we identify that with the yield stress ratio of granular materials, and we show that the theoretical predictions, once the different singularities are inserted into the functions of extended kinetic theory, are in excellent agreement with the results of numerical simulations.« less

  3. Physically representative atomistic modeling of atomic-scale friction

    NASA Astrophysics Data System (ADS)

    Dong, Yalin

    Nanotribology is a research field to study friction, adhesion, wear and lubrication occurred between two sliding interfaces at nano scale. This study is motivated by the demanding need of miniaturization mechanical components in Micro Electro Mechanical Systems (MEMS), improvement of durability in magnetic storage system, and other industrial applications. Overcoming tribological failure and finding ways to control friction at small scale have become keys to commercialize MEMS with sliding components as well as to stimulate the technological innovation associated with the development of MEMS. In addition to the industrial applications, such research is also scientifically fascinating because it opens a door to understand macroscopic friction from the most bottom atomic level, and therefore serves as a bridge between science and engineering. This thesis focuses on solid/solid atomic friction and its associated energy dissipation through theoretical analysis, atomistic simulation, transition state theory, and close collaboration with experimentalists. Reduced-order models have many advantages for its simplification and capacity to simulating long-time event. We will apply Prandtl-Tomlinson models and their extensions to interpret dry atomic-scale friction. We begin with the fundamental equations and build on them step-by-step from the simple quasistatic one-spring, one-mass model for predicting transitions between friction regimes to the two-dimensional and multi-atom models for describing the effect of contact area. Theoretical analysis, numerical implementation, and predicted physical phenomena are all discussed. In the process, we demonstrate the significant potential for this approach to yield new fundamental understanding of atomic-scale friction. Atomistic modeling can never be overemphasized in the investigation of atomic friction, in which each single atom could play a significant role, but is hard to be captured experimentally. In atomic friction, the

  4. Environmental influences on the friction behavior of glasses

    NASA Astrophysics Data System (ADS)

    Rolf, Jacqueline C.

    Two aspects of the friction behavior of glasses were the main focus of this investigation. First, the influence of aqueous inorganic salt solutions on friction and damage on soda-lime-silica, vitreous silica, and an aluminosilicate glass high in alumina content were studied. It was found that the pH of a solution has a higher influence on the friction behavior than the concentration of electrolyte and the size of ions in the solution. A minimum at the i.e.p. (iso-electric point) of the network former of the glass was found, i.e., soda-lime-silica and vitreous silica showed a small minimum in friction at a pH of about 1.8, which corresponds to the i.e.p. of silica. Two small minima were observed for the aluminosilicate in the vicinities of the i.e.p.'s of silica and alumina respectively. The damage created by the frictional contact showed variations with environment. Microindentation experiments on the same glasses were performed in the same environments to compare the responses to the findings of the friction test. For soda-lime-silica and vitreous silica, a maximum in hardness was found at the i.e.p. of the glasses, and for the aluminosilicate, two maxima were found in the vicinity of the i.e.p.'s of silica and alumina respectively, confirming the findings of the friction tests. A data-fitting analysis showed that the major contribution to the observed trends originates from the elastic properties of the surface. A model describing the influence of surface charging on the mechanical properties of the glass surface is suggested. The second major aspect of the study was the influence of temperature on the friction coefficients and resulting surface damage of commercial glasses. Four float glasses were selected, and vitreous silica was tested for comparison. As expected, the coefficients of friction were found to increase, with increasing temperature. Very small differences in composition had an effect on the temperature dependence of the coefficients of friction

  5. The frictional response of patterned soft polymer surfaces

    NASA Astrophysics Data System (ADS)

    Rand, Charles J.

    2008-10-01

    Friction plays an intricate role in our everyday lives, it is therefore critical to understand the underlying features of friction to better help control and manipulate the response anywhere two surfaces in contact move past each other by a sliding motion. Here we present results targeting a thorough understanding of soft material friction and how it can be manipulated with patterns. We found that the naturally occurring length scale or periodicity (lambda) of frictionally induced patterns, Schallamach waves, could be described using two materials properties (critical energy release rate Gc and complex modulus (E*), i.e. lambdainfinity Gc /E*). Following this, we evaluated the effect of a single defect at a sliding interface. Sliding over a defect can be used to model the sliding from one feature to another in a patterned surface. Defects decreased the sliding frictional force by as much as 80% sliding and this decrease was attributed to changes in tangential stiffness of the sliding interface. The frictional response of surface wrinkles, where multiple edges or defects are acting in concert, was also evaluated. Wrinkles were shown to decrease friction (F) and changes in contact area (A) could not describe this decrease. A tangential stiffness correction factor (fx) and changes in the critical energy release rate were used to describe this deviation (F infinity Gc *A*fx/ℓ, where ℓ is a materials defined length scale of dissipation). This scaling can be used to describe the friction of any topographically patterned surface including the Gecko's foot, where the feature size is smaller than ℓ and thus replaces ℓ, increasing the friction compared to a flat surface. Also, mechanically-induced surface defects were used to align osmotically driven surface wrinkles by creating stress discontinuities that convert the global biaxial stress state to local uniaxial stresses. Defect spacing was used to control the alignment process at the surface of the wrinkled rigid

  6. 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

  7. Viscous friction of hydrogen-bonded matter

    NASA Astrophysics Data System (ADS)

    Erbas, Aykut; Horinek, Dominik; Netz, Roland R.

    2012-02-01

    Amontons' law successfully describes friction between macroscopic solid bodies for a wide range of velocities and normal forces. For the diffusion and forced sliding of adhering or entangled macromolecules, proteins and biological complexes, temperature effects are invariably important and a similarly successful friction law at biological length and velocity scales is missing. Hydrogen bonds are key to the specific binding of bio-matter. Here we show that friction between hydrogen-bonded matter obeys in the biologically relevant low-velocity viscous regime a simple equations: the friction force is proportional to the number of hydrogen bonds, the sliding velocity, and a friction coefficient γHB. This law is deduced from atomistic molecular dynamics simulations for short peptide chains that are laterally pulled over hydroxylated substrates in the presence of water and holds for widely different peptides, surface polarities and applied normal forces. The value of γHB is extrapolated from simulations at sliding velocities in the range from v=10-2 m/s to 100 m/s by mapping on a simple stochastic model and turns out to be of the order of γHB˜10-8 kg/s. 3 hydrogen bonds act collectively.

  8. 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.

  9. A Hamiltonian Model of Dissipative Wave-particle Interactions and the Negative-mass Effect

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    A. Zhmoginov

    2011-02-07

    The effect of radiation friction is included in the Hamiltonian treatment of wave-particle interactions with autoresonant phase-locking, yielding a generalized canonical approach to the problem of dissipative dynamics near a nonlinear resonance. As an example, the negativemass eff ect exhibited by a charged particle in a pump wave and a static magnetic field is studied in the presence of the friction force due to cyclotron radiation. Particles with negative parallel masses m! are shown to transfer their kinetic energy to the pump wave, thus amplifying it. Counterintuitively, such particles also undergo stable dynamics, decreasing their transverse energy monotonically due tomore » cyclotron cooling, whereas some of those with positive m! undergo cyclotron heating instead, extracting energy from the pump wave.« less

  10. 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.

  11. 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.

  12. Friction Pull Plug and Material Configuration for Anti-Chatter Friction Pull Plug Weld

    NASA Technical Reports Server (NTRS)

    Littell, Justin Anderson (Inventor)

    2016-01-01

    A friction pull plug is provided for use in forming a plug weld in a hole in a material. The friction pull plug includes a shank and a series of three frustoconical sections. The relative sizes of the sections assure that a central one of the sections defines the initial contact point between the hole's sides. The angle defined by the central one of the sections reduces or eliminates chatter as the plug is pulled into the hole.

  13. Inertial frictional ratchets and their load bearing efficiencies

    NASA Astrophysics Data System (ADS)

    Kharkongor, D.; Reenbohn, W. L.; Mahato, Mangal C.

    2018-03-01

    We investigate the performance of an inertial frictional ratchet in a sinusoidal potential driven by a sinusoidal external field. The dependence of the performance on the parameters of the sinusoidally varying friction, such as the mean friction coefficient and its phase difference with the potential, is studied in detail. Interestingly, under certain circumstances, the thermodynamic efficiency of the ratchet against an applied load shows a non-monotonic behaviour as a function of the mean friction coefficient. Also, in the large friction ranges, the efficiency is shown to increase with increasing applied load even though the corresponding ratchet current decreases as the applied load increases. These counterintuitive numerical results are explained in the text.

  14. Understanding and Observing Subglacial Friction Using Seismology

    NASA Astrophysics Data System (ADS)

    Tsai, V. C.

    2017-12-01

    Glaciology began with a focus on understanding basic mechanical processes and producing physical models that could explain the principal observations. Recently, however, more attention has been paid to the wealth of recent observations, with many modeling efforts relying on data assimilation and empirical scalings, rather than being based on first-principles physics. Notably, ice sheet models commonly assume that subglacial friction is characterized by a "slipperiness" coefficient that is determined by inverting surface velocity observations. Predictions are usually then made by assuming these slipperiness coefficients are spatially and temporally fixed. However, this is only valid if slipperiness is an unchanging material property of the bed and, despite decades of work on subglacial friction, it has remained unclear how to best account for such subglacial physics in ice sheet models. Here, we describe how basic seismological concepts and observations can be used to improve our understanding and determination of subglacial friction. First, we discuss how standard models of granular friction can and should be used in basal friction laws for marine ice sheets, where very low effective pressures exist. We show that under realistic West Antarctic Ice Sheet conditions, standard Coulomb friction should apply in a relatively narrow zone near the grounding line and that this should transition abruptly as one moves inland to a different, perhaps Weertman-style, dependence of subglacial stress on velocity. We show that this subglacial friction law predicts significantly different ice sheet behavior even as compared with other friction laws that include effective pressure. Secondly, we explain how seismological observations of water flow noise and basal icequakes constrain subglacial physics in important ways. Seismically observed water flow noise can provide constraints on water pressures and channel sizes and geometry, leading to important data on subglacial friction

  15. 30 CFR 56.19008 - Friction hoist synchronizing mechanisms.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

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

  16. 30 CFR 57.19008 - Friction hoist synchronizing mechanisms.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

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

  17. 30 CFR 56.19008 - Friction hoist synchronizing mechanisms.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Friction hoist synchronizing mechanisms. 56... Personnel Hoisting Hoists § 56.19008 Friction hoist synchronizing mechanisms. Where creep or slip may alter the effective position of safety devices, friction hoists shall be equipped with synchronizing...

  18. 30 CFR 57.19008 - Friction hoist synchronizing mechanisms.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Friction hoist synchronizing mechanisms. 57... MINES Personnel Hoisting Hoists § 57.19008 Friction hoist synchronizing mechanisms. Where creep or slip may alter the effective position of safety devices, friction hoists shall be equipped with...

  19. 30 CFR 57.19008 - Friction hoist synchronizing mechanisms.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Friction hoist synchronizing mechanisms. 57... MINES Personnel Hoisting Hoists § 57.19008 Friction hoist synchronizing mechanisms. Where creep or slip may alter the effective position of safety devices, friction hoists shall be equipped with...

  20. 30 CFR 57.19008 - Friction hoist synchronizing mechanisms.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Friction hoist synchronizing mechanisms. 57... MINES Personnel Hoisting Hoists § 57.19008 Friction hoist synchronizing mechanisms. Where creep or slip may alter the effective position of safety devices, friction hoists shall be equipped with...

  1. 30 CFR 56.19008 - Friction hoist synchronizing mechanisms.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Friction hoist synchronizing mechanisms. 56... Personnel Hoisting Hoists § 56.19008 Friction hoist synchronizing mechanisms. Where creep or slip may alter the effective position of safety devices, friction hoists shall be equipped with synchronizing...

  2. 30 CFR 56.19008 - Friction hoist synchronizing mechanisms.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Friction hoist synchronizing mechanisms. 56... Personnel Hoisting Hoists § 56.19008 Friction hoist synchronizing mechanisms. Where creep or slip may alter the effective position of safety devices, friction hoists shall be equipped with synchronizing...

  3. 30 CFR 57.19008 - Friction hoist synchronizing mechanisms.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Friction hoist synchronizing mechanisms. 57... MINES Personnel Hoisting Hoists § 57.19008 Friction hoist synchronizing mechanisms. Where creep or slip may alter the effective position of safety devices, friction hoists shall be equipped with...

  4. 30 CFR 56.19008 - Friction hoist synchronizing mechanisms.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Friction hoist synchronizing mechanisms. 56... Personnel Hoisting Hoists § 56.19008 Friction hoist synchronizing mechanisms. Where creep or slip may alter the effective position of safety devices, friction hoists shall be equipped with synchronizing...

  5. Damage Tolerance Assessment of Friction Pull Plug Welds

    NASA Technical Reports Server (NTRS)

    McGill, Preston; Burkholder, Jonathan

    2012-01-01

    Friction stir welding is a solid state welding process developed and patented by The Welding Institute in Cambridge, England. Friction stir welding has been implemented in the aerospace industry in the fabrication of longitudinal welds in pressurized cryogenic propellant tanks. As the industry looks to implement friction stir welding in circumferential welds in pressurized cryogenic propellant tanks, techniques to close out the termination hole associated with retracting the pin tool are being evaluated. Friction pull plug welding is under development as a one means of closing out the termination hole. A friction pull plug weld placed in a friction stir weld results in a non-homogenous weld joint where the initial weld, plug weld, their respective heat affected zones and the base metal all interact. The welded joint is a composite, plastically deformed material system with a complex residual stress field. In order to address damage tolerance concerns associated with friction plug welds in safety critical structures, such as propellant tanks, nondestructive inspection and proof testing may be required to screen hardware for mission critical defects. The efficacy of the nondestructive evaluation or the proof test is based on an assessment of the critical flaw size in the test or service environments. Test data relating residual strength capability to flaw size in two aluminum alloy friction plug weld configurations is presented.

  6. The role of fluid pressure on frictional behavior at the base of the seismogenic zone

    USGS Publications Warehouse

    Hirth, Greg; Beeler, Nicholas M.

    2015-01-01

    To characterize stress and deformation style at the base of the seismogenic zone, we investigate how the mechanical properties of fluid-rock systems respond to variations in temperature and strain rate. The role of fluids on the processes responsible for the brittle-ductile transition in quartz-rich rocks has not been explored at experimental conditions where the kinetic competition between microcracking and viscous flow is similar to that expected in the Earth. Our initial analysis of this competition suggests that the effective stress law for sliding friction should not work as efficiently near the brittle-ductile transition as it does at shallow conditions

  7. Prediction of friction coefficients for gases

    NASA Technical Reports Server (NTRS)

    Taylor, M. F.

    1969-01-01

    Empirical relations are used for correlating laminar and turbulent friction coefficients for gases, with large variations in the physical properties, flowing through smooth tubes. These relations have been used to correlate friction coefficients for hydrogen, helium, nitrogen, carbon dioxide and air.

  8. Dynamic recrystallization in friction surfaced austenitic stainless steel coatings

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Puli, Ramesh, E-mail: rameshpuli2000@gmail.com; Janaki Ram, G.D.

    2012-12-15

    Friction surfacing involves complex thermo-mechanical phenomena. In this study, the nature of dynamic recrystallization in friction surfaced austenitic stainless steel AISI 316L coatings was investigated using electron backscattered diffraction and transmission electron microscopy. The results show that the alloy 316L undergoes discontinuous dynamic recrystallization under conditions of moderate Zener-Hollomon parameter during friction surfacing. - Highlights: Black-Right-Pointing-Pointer Dynamic recrystallization in alloy 316L friction surfaced coatings is examined. Black-Right-Pointing-Pointer Friction surfacing leads to discontinuous dynamic recrystallization in alloy 316L. Black-Right-Pointing-Pointer Strain rates in friction surfacing exceed 400 s{sup -1}. Black-Right-Pointing-Pointer Estimated grain size matches well with experimental observations in 316L coatings.

  9. Kinetic Tremor

    PubMed Central

    Louis, Elan D.

    2007-01-01

    Tremor is among the acute effects of nicotine exposure. Published studies have focused on smoking-related postural (static) hand tremor rather than kinetic tremor (tremor during hand use), and gender differences in smoking-related tremor have not been examined. In a group of adults who were sampled from a population (mean ± SD = 65.7 ± 11.5 years, range = 18 - 92 years), the investigator assessed whether the severity of postural and kinetic tremors differed in smokers versus non-smokers, and whether this difference was influenced by gender. Twenty-seven (9.9%) of 273 subjects were current smokers. Greater tremor was observed in smokers than non-smokers during a variety of activities (drawing a spiral, using a spoon, finger-nose-finger maneuver, all p < 0.05) and smokers had a higher total tremor score than non-smokers (5.15 ± 3.06 vs. 3.41 ± 2.88, p < 0.01), even after adjusting for age, caffeine intake and other potential confounding factors. The difference between smokers and non-smokers in terms of hand tremor was more apparent in women than in men. In women, the number of cigarettes smoked on the day of testing was weakly correlated with the total tremor score (r = 0.17, p = 0.03). In summary, smokers had more kinetic hand tremor than non-smokers. This difference between smokers and non-smokers was more apparent in women than in men. These results suggest that smoking habits should be considered carefully in order to avoid over- or underestimating the effects of occupational and non-occupational exposures to other tremor-producing neurotoxins. PMID:17267044

  10. Tool For Friction Stir Tack Welding of Aluminum Alloys

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  11. Micro- and macroscale coefficients of friction of cementitious materials

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lomboy, Gilson; Sundararajan, Sriram, E-mail: srirams@iastate.edu; Wang, Kejin

    2013-12-15

    Millions of metric tons of cementitious materials are produced, transported and used in construction each year. The ease or difficulty of handling cementitious materials is greatly influenced by the material friction properties. In the present study, the coefficients of friction of cementitious materials were measured at the microscale and macroscale. The materials tested were commercially-available Portland cement, Class C fly ash, and ground granulated blast furnace slag. At the microscale, the coefficient of friction was determined from the interaction forces between cementitious particles using an Atomic Force Microscope. At the macroscale, the coefficient of friction was determined from stresses onmore » bulk cementitious materials under direct shear. The study indicated that the microscale coefficient of friction ranged from 0.020 to 0.059, and the macroscale coefficient of friction ranged from 0.56 to 0.75. The fly ash studied had the highest microscale coefficient of friction and the lowest macroscale coefficient of friction. -- Highlights: •Microscale (interparticle) coefficient of friction (COF) was determined with AFM. •Macroscale (bulk) COF was measured under direct shear. •Fly ash had the highest microscale COF and the lowest macroscale COF. •Portland cement against GGBFS had the lowest microscale COF. •Portland cement against Portland cement had the highest macroscale COF.« less

  12. 30 CFR 56.19014 - Friction hoist overtravel protection.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

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

  13. 30 CFR 57.19014 - Friction hoist overtravel protection.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

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

  14. 30 CFR 57.19014 - Friction hoist overtravel protection.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Friction hoist overtravel protection. 57.19014 Section 57.19014 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND... Hoisting Hoists § 57.19014 Friction hoist overtravel protection. In a friction hoist installation, tapered...

  15. 30 CFR 57.19014 - Friction hoist overtravel protection.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Friction hoist overtravel protection. 57.19014 Section 57.19014 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND... Hoisting Hoists § 57.19014 Friction hoist overtravel protection. In a friction hoist installation, tapered...

  16. 30 CFR 57.19014 - Friction hoist overtravel protection.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Friction hoist overtravel protection. 57.19014 Section 57.19014 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND... Hoisting Hoists § 57.19014 Friction hoist overtravel protection. In a friction hoist installation, tapered...

  17. 30 CFR 56.19014 - Friction hoist overtravel protection.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Friction hoist overtravel protection. 56.19014 Section 56.19014 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND... Hoisting Hoists § 56.19014 Friction hoist overtravel protection. In a friction hoist installation, tapered...

  18. 30 CFR 56.19014 - Friction hoist overtravel protection.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Friction hoist overtravel protection. 56.19014 Section 56.19014 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND... Hoisting Hoists § 56.19014 Friction hoist overtravel protection. In a friction hoist installation, tapered...

  19. 30 CFR 57.19014 - Friction hoist overtravel protection.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Friction hoist overtravel protection. 57.19014 Section 57.19014 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND... Hoisting Hoists § 57.19014 Friction hoist overtravel protection. In a friction hoist installation, tapered...

  20. 30 CFR 56.19014 - Friction hoist overtravel protection.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Friction hoist overtravel protection. 56.19014 Section 56.19014 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND... Hoisting Hoists § 56.19014 Friction hoist overtravel protection. In a friction hoist installation, tapered...

  1. 30 CFR 56.19014 - Friction hoist overtravel protection.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Friction hoist overtravel protection. 56.19014 Section 56.19014 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND... Hoisting Hoists § 56.19014 Friction hoist overtravel protection. In a friction hoist installation, tapered...

  2. Effect of friction on the rheology of dense suspensions

    NASA Astrophysics Data System (ADS)

    Gallier, Stany; Lemaire, Elisabeth; Peters, François; Lobry, Laurent

    2014-11-01

    This work reports three-dimensional numerical simulations of sheared non-Brownian concentrated suspensions using a fictitious domain method. Contacts between particles are modeled using a DEM-like approach (Discrete Element Method), which allows for a more physical description, including roughness and friction. This study emphasizes the effect of friction between particles and its role on rheological properties, especially on normal stress differences. Friction is shown to notably increase viscosity and second normal stress difference | N2 | and decrease | N1 | , in better agreement with experiments. The hydrodynamic and contact contributions to the overall particle stress are particularly investigated and this shows that the effect of friction is mostly due to the additional contact stress since the hydrodynamic stress remains unaffected by friction. Simulation results are also compared with experiments and the agreement is improved when friction is accounted for: this suggests that friction is operative in actual suspensions.

  3. Spatial dispersion in atom-surface quantum friction

    DOE PAGES

    Reiche, D.; Dalvit, D. A. R.; Busch, K.; ...

    2017-04-15

    We investigate the influence of spatial dispersion on atom-surface quantum friction. We show that for atom-surface separations shorter than the carrier's mean free path within the material, the frictional force can be several orders of magnitude larger than that predicted by local optics. In addition, when taking into account spatial dispersion effects, we show that the commonly used local thermal equilibrium approximation underestimates by approximately 95% the drag force, obtained by employing the recently reported nonequilibrium fluctuation-dissipation relation for quantum friction. Unlike the treatment based on local optics, spatial dispersion in conjunction with corrections to local thermal equilibrium change notmore » only the magnitude but also the distance scaling of quantum friction.« less

  4. Comparison of frictional resistance among conventional, active and passive selfligating brackets with different combinations of arch wires: a finite elements study.

    PubMed

    Gómez, Sandra L; Montoya, Yesid; Garcia, Nora L; Virgen, Ana L; Botero, Javier E

    2016-09-01

    The aim of this study was to compare frictional resistance among conventional, passive and active selfligating brackets using Finite Elements Analysis (FEA). Seventynine (79) slide tests were performed by combining an upper first bicuspid conventional bracket, 0.018" stainless steel wires and 0.010" ligature by means of an INSTRON 3345 load system to obtain average maximum static frictional resistance (MSFR). This value was compared to the FR (frictional resistance) obtained by simulation of a slide of the same combination by FEA following conventional bracket modeling by means of Computer Aided Design (CAD). Once the FEA was validated, bracket CADs were designed (upper right first bicuspid conventional, active and passive selfligating bracket) and bracket properties calculated. MSFR was compared among conventional, active and passive selfligating brackets with different alloys and archwire cross sections such as 0.018", 0.019" x 0.025"and 0.020" x 0.020". Passive selfligating brackets had the lowest MSFR, followed by conventional brackets and active selfligating brackets. In conventional brackets, a 0.018" archwire produced a linear pattern of stress with maximum concentration at the center. Conversely, stress in 0.020 x 0.020" and 0.019 x 0.025" archwires was distributed across the width of the slot. The highest normal forces were 1.53 N for the 0.018" archwire, 4.85 N for the 0.020 x 0.020" archwire and 8.18 N for the 0.019 x 0.025" archwire. Passive selfligating brackets presented less frictional resistance than conventional and active selfligating brackets. Regardless of bracket type, greater contact area between the slot and the archwire and the spring clip increased frictional resistance. Sociedad Argentina de Pediatría.

  5. Friction and wear of single-crystal manganese-zinc ferrite

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1979-01-01

    Sliding friction experiments were conducted with single crystal manganese-zinc ferrite in contact with itself and with transition metals. Results indicate mating highest atomic density directions (110) on matched crystallographic planes exhibit the lowest coefficient of friction, indicating that direction is important in the friction behavior of ferrite. Matched parallel high atomic density planes and crystallographic directions at the interface exhibit low coefficients of friction. The coefficients of friction for ferrite in contact with various metals are related to the relative chemical activity of these metals. The more active the metal, the higher the coefficient of friction. Cracking and the formation of hexagon- and rectangular-shaped platelet wear debris due to cleavages of (110) planes are observed on the ferrite surfaces as a result of sliding.

  6. 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.

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

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chen, Gaoqiang; Feng, Zhili; Zhu, Yucan

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

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

    DOE PAGES

    Chen, Gaoqiang; Feng, Zhili; Zhu, Yucan; ...

    2016-07-11

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

  9. Ratchet due to broken friction symmetry.

    PubMed

    Nordén, B; Zolotaryuk, Y; Christiansen, P L; Zolotaryuk, A V

    2002-01-01

    A ratchet mechanism that occurs due to asymmetric dependence of the friction of a moving system on its velocity or a driving force is reported. For this kind of ratchet, instead of a particle moving in a periodic potential, the dynamics of which have broken space-time symmetry, the system must be provided with some internal structure realizing such a velocity- or force-friction dependence. For demonstration of a ratchet mechanism of this type, an experimental setup (gadget) that converts longitudinal oscillating or fluctuating motion into a unidirectional rotation has been built and experiments with it have been carried out. In this device, an asymmetry of friction dependence on an applied force appears, resulting in rectification of rotary motion. In experiments, our setup is observed to rotate only in one direction, which is in accordance with given theoretical arguments. Despite the setup being three dimensional, the ratchet rotary motion is proved to be described by one dynamical equation. This kind of motion is a result of the interplay of friction and inertia. We also consider a case with viscous friction, which is irrelevant to this gadget, but it can be a possible mechanism of rotary unidirectional motion of some swimming organisms in a liquid.

  10. The thermodynamic efficiency of heat engines with friction

    NASA Astrophysics Data System (ADS)

    Bizarro, João P. S.

    2012-04-01

    The presence of the work done against friction is incorporated into the analysis of the efficiency of heat engines based on the first and second laws of thermodynamics. We obtain the efficiencies of Stirling and Brayton engines with friction and recover results known from finite-time thermodynamics. We show that ηfric/η ≈ (1 - Wfric/W), where ηfric/η is the ratio of the efficiencies with and without friction and Wfric/W is the fraction of the work W performed by the working fluid which is spent against friction forces.

  11. Friction and wear of plasma-deposited diamond films

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa; Wu, Richard L. C.; Garscadden, Alan; Barnes, Paul N.; Jackson, Howard E.

    1993-01-01

    Reciprocating sliding friction experiments in humid air and in dry nitrogen and unidirectional sliding friction experiments in ultrahigh vacuum were conducted with a natural diamond pin in contact with microwave-plasma-deposited diamond films. Diamond films with a surface roughness (R rms) ranging from 15 to 160 nm were produced by microwave-plasma-assisted chemical vapor deposition. In humid air and in dry nitrogen, abrasion occurred when the diamond pin made grooves in the surfaces of diamond films, and thus the initial coefficients of friction increased with increasing initial surface roughness. The equilibrium coefficients of friction were independent of the initial surface roughness of the diamond films. In vacuum the friction for diamond films contacting a diamond pin arose primarily from adhesion between the sliding surfaces. In these cases, the initial and equilibrium coefficients of friction were independent of the initial surface roughness of the diamond films. The equilibrium coefficients of friction were 0.02 to 0.04 in humid air and in dry nitrogen, but 1.5 to 1.8 in vacuum. The wear factor of the diamond films depended on the initial surface roughness, regardless of environment; it increased with increasing initial surface roughness. The wear factors were considerably higher in vacuum than in humid air and in dry nitrogen.

  12. Frictional constraints on crustal faulting

    USGS Publications Warehouse

    Boatwright, J.; Cocco, M.

    1996-01-01

    We consider how variations in fault frictional properties affect the phenomenology of earthquake faulting. In particular, we propose that lateral variations in fault friction produce the marked heterogeneity of slip observed in large earthquakes. We model these variations using a rate- and state-dependent friction law, where we differentiate velocity-weakening behavior into two fields: the strong seismic field is very velocity weakening and the weak seismic field is slightly velocity weakening. Similarly, we differentiate velocity-strengthening behavior into two fields: the compliant field is slightly velocity strengthening and the viscous field is very velocity strengthening. The strong seismic field comprises the seismic slip concentrations, or asperities. The two "intermediate" fields, weak seismic and compliant, have frictional velocity dependences that are close to velocity neutral: these fields modulate both the tectonic loading and the dynamic rupture process. During the interseismic period, the weak seismic and compliant regions slip aseismically, while the strong seismic regions remain locked, evolving into stress concentrations that fail only in main shocks. The weak seismic areas exhibit most of the interseismic activity and aftershocks but can also creep seismically. This "mixed" frictional behavior can be obtained from a sufficiently heterogenous distribution of the critical slip distance. The model also provides a mechanism for rupture arrest: dynamic rupture fronts decelerate as they penetrate into unloaded complaint or weak seismic areas, producing broad areas of accelerated afterslip. Aftershocks occur on both the weak seismic and compliant areas around a fault, but most of the stress is diffused through aseismic slip. Rapid afterslip on these peripheral areas can also produce aftershocks within the main shock rupture area by reloading weak fault areas that slipped in the main shock and then healed. We test this frictional model by comparing the

  13. Dense, gravity-driven granular-liquid flows down steep channels

    NASA Astrophysics Data System (ADS)

    Armanini, A.; Larcher, M.; Nucci, E.

    2011-12-01

    Debris flows are complex natural phenomena, characterized by a mixture of poorly sorted sediments and water driven by gravity. Depending on the size distribution, on the volume concentration of sediments and on the geometry and topography of the channel, flow conditions may be very different, ranging from very fast flows, dominated by granular collisions and by the turbulence on the liquid phase, to very slow and dense flows, dominated by the frictional contacts among the grains. To investigate the basic physics of debris flows, it is very useful to analyze the flow of a mixture of identical spherical particles saturated by water and driven by gravity down a steep channel in steady flow condition (Armanini et al. 2005). The flow presents three regions: an external one, near to the free surface, dominated by nearly instantaneous contacts among the particles (collisional regime), an internal region dominated by prolonged contacts among the particles (frictional regime) and a static bed in which the particles are immobile. The detailed vertical structure of this kind of flows was obtained by means of experiments carried out by Armanini et al. (2005) and Larcher et al. (2007). Armanini et al. (2009) analysed the stratification of rheological mechanisms inside the flow, focusing on the coexistence of frictional and collisional regimes, on the stress transmission inside the flow and on particles kinematics. In particular, it was observed that debris flows may show locally a typical intermittence of the flow regime, switching alternatively from frictional to collisional. While the rheology of the collisional layers is well described by the dense gas analogy (kinetic theory), a persuasive theoretical description of the frictional regime does not yet exist. A Coulombian scheme is often assumed, but this hypothesis is rather limitative because it requires a constant concentration or a distribution of particles concentration known a priori. An interesting scheme of this kind

  14. The experiment research of the friction sliding isolation structure

    NASA Astrophysics Data System (ADS)

    Zhang, Shirong; Li, Jiangle; Wang, Sheliang

    2018-04-01

    This paper investigated the theory of the friction sliding isolation structure, The M0S2 solid lubricant was adopted as isolation bearing friction materials, and a new sliding isolation bearing was designed and made. The formula of the friction factor and the compression stress was proposed. The feasibility of the material MoS2 used as the coating material in a friction sliding isolation system was tested on the 5 layers concrete frame model. Two application experiment conditions were presented. The results of the experiment research indicated that the friction sliding isolation technology have a good damping effect.

  15. CAM/LIFTER forces and friction

    DOE Office of Scientific and Technical Information (OSTI.GOV)

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

    1992-02-01

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

  16. LSENS, a general chemical kinetics and sensitivity analysis code for gas-phase reactions: User's guide

    NASA Technical Reports Server (NTRS)

    Radhakrishnan, Krishnan; Bittker, David A.

    1993-01-01

    A general chemical kinetics and sensitivity analysis code for complex, homogeneous, gas-phase reactions is described. The main features of the code, LSENS, are its flexibility, efficiency and convenience in treating many different chemical reaction models. The models include static system, steady, one-dimensional, inviscid flow, shock initiated reaction, and a perfectly stirred reactor. In addition, equilibrium computations can be performed for several assigned states. An implicit numerical integration method, which works efficiently for the extremes of very fast and very slow reaction, is used for solving the 'stiff' differential equation systems that arise in chemical kinetics. For static reactions, sensitivity coefficients of all dependent variables and their temporal derivatives with respect to the initial values of dependent variables and/or the rate coefficient parameters can be computed. This paper presents descriptions of the code and its usage, and includes several illustrative example problems.

  17. Ground Simulator Studies of the Effects of Valve Friction, Stick Friction, Flexibility, and Backwash on Power Control System Quality

    NASA Technical Reports Server (NTRS)

    Brown, B Porter

    1958-01-01

    Report presents results of tests made on a power control system by means of a ground simulator to determine the effects of various combinations of valve friction and stick friction on the ability of the pilot to control the system. Various friction conditions were simulated with a rigid control system, a flexible system, and a rigid system having some backlash. For the tests, the period and damping of the simulated airplane were held constant.

  18. Friction and wear of TPS fibers: A study of the adhesion and friction of high modulus fibers

    NASA Technical Reports Server (NTRS)

    Bascom, Willard D.; Lee, Ilzoo

    1990-01-01

    The adhesional and frictional forces between filaments in a woven fabric or felt, strongly influenced the processability of the fiber and the mechanical durability of the final product. Even though the contact loads between fibers are low, the area of contact is extremely small giving rise to very high stresses; principally shear stresses. One consequence of these strong adhesional and frictional forces is the resistance of fibers to slide past each other during weaving or when processed into nonwoven mats or felts. Furthermore, the interfiber frictional forces may cause surface damage and thereby reduce the fiber strength. Once formed into fabrics, flexural handling and manipulation of the material again causes individual filaments to rub against each other resulting in modulus, brittle fibers such as those used in thermal protection systems (TPS). The adhesion and friction of organic fibers, notably polyethylene terephthalate (PET) fibers, have been extensively studied, but there has been very little work reported on high modulus inorganic fibers. An extensive study was made of the adhesion and friction of flame drawn silica fibers in order to develop experimental techniques and a scientific basis for data interpretation. Subsequently, these methods were applied to fibers of interest in TPS materials.

  19. 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.

  20. On the Similarity of Deformation Mechanisms During Friction Stir Welding and Sliding Friction of the AA5056 Alloy

    NASA Astrophysics Data System (ADS)

    Kolubaev, A. V.; Zaikina, A. A.; Sizova, O. V.; Ivanov, K. V.; Filippov, A. V.; Kolubaev, E. A.

    2018-04-01

    A comparative investigation of the structure of an aluminum-manganese alloy is performed after its friction stir welding and sliding friction. Using the methods of optical and electron microscopy, it is shown that during friction identical ultrafine-grained structures are formed in the weld nugget and in the surface layer, in which the grains measure 5 μm irrespective of the initial grain size of the alloy. An assumption is made that the microstructure during both processes under study is formed by the mechanism of rotational plasticity.

  1. Skin friction under pressure. The role of micromechanics

    NASA Astrophysics Data System (ADS)

    Leyva-Mendivil, Maria F.; Lengiewicz, Jakub; Limbert, Georges

    2018-03-01

    The role of contact pressure on skin friction has been documented in multiple experimental studies. Skin friction significantly raises in the low-pressure regime as load increases while, after a critical pressure value is reached, the coefficient of friction of skin against an external surface becomes mostly insensitive to contact pressure. However, up to now, no study has elucidated the qualitative and quantitative nature of the interplay between contact pressure, the material and microstructural properties of the skin, the size of an indenting slider and the resulting measured macroscopic coefficient of friction. A mechanistic understanding of these aspects is essential for guiding the rational design of products intended to interact with the skin through optimally-tuned surface and/or microstructural properties. Here, an anatomically-realistic 2D multi-layer finite element model of the skin was embedded within a computational contact homogenisation procedure. The main objective was to investigate the sensitivity of macroscopic skin friction to the parameters discussed above, in addition to the local (i.e. microscopic) coefficient of friction defined at skin asperity level. This was accomplished via the design of a large-scale computational experiment featuring 312 analyses. Results confirmed the potentially major role of finite deformations of skin asperities on the resulting macroscopic friction. This effect was shown to be modulated by the level of contact pressure and relative size of skin surface asperities compared to those of a rigid slider. The numerical study also corroborated experimental observations concerning the existence of two contact pressure regimes where macroscopic friction steeply and non-linearly increases up to a critical value, and then remains approximately constant as pressure increases further. The proposed computational modelling platform offers attractive features which are beyond the reach of current analytical models of skin

  2. Friction on a single MoS2 nanotube

    PubMed Central

    2012-01-01

    Friction was measured on a single molybdenum disulfide (MoS2) nanotube and on a single MoS2 nano-onion for the first time. We used atomic force microscopy (AFM) operating in ultra-high vacuum at room temperature. The average coefficient of friction between the AFM tip and MoS2 nanotubes was found considerably below the corresponding values obtained from an air-cleaved MoS2 single crystal or graphite. We revealed a nontrivial dependency of friction on interaction strength between the nanotube and the underlying substrate. Friction on detached or weakly supported nanotubes by the substrate was several times smaller (0.023 ± 0.005) than that on well-supported nanotubes (0.08 ± 0.02). We propose an explanation of a quarter of a century old phenomena of higher friction found for intracrystalline (0.06) than for intercrystalline slip (0.025) in MoS2. Friction test on a single MoS2 nano-onion revealed a combined gliding-rolling process. PACS, 62.20, 61.46.Fg, 68.37 Ps PMID:22490562

  3. 2D granular flows with the μ(I) rheology and side walls friction: A well-balanced multilayer discretization

    NASA Astrophysics Data System (ADS)

    Fernández-Nieto, E. D.; Garres-Díaz, J.; Mangeney, A.; Narbona-Reina, G.

    2018-03-01

    We present here numerical modelling of granular flows with the μ (I) rheology in confined channels. The contribution is twofold: (i) a model to approximate the Navier-Stokes equations with the μ (I) rheology through an asymptotic analysis; under the hypothesis of a one-dimensional flow, this model takes into account side walls friction; (ii) a multilayer discretization following Fernández-Nieto et al. (2016) [20]. In this new numerical scheme, we propose an appropriate treatment of the rheological terms through a hydrostatic reconstruction which allows this scheme to be well-balanced and therefore to deal with dry areas. Based on academic tests, we first evaluate the influence of the width of the channel on the normal profiles of the downslope velocity thanks to the multilayer approach that is intrinsically able to describe changes from Bagnold to S-shaped (and vice versa) velocity profiles. We also check the well-balanced property of the proposed numerical scheme. We show that approximating side walls friction using single-layer models may lead to strong errors. Secondly, we compare the numerical results with experimental data on granular collapses. We show that the proposed scheme allows us to qualitatively reproduce the deposit in the case of a rigid bed (i.e. dry area) and that the error made by replacing the dry area by a small layer of material may be large if this layer is not thin enough. The proposed model is also able to reproduce the time evolution of the free surface and of the flow/no-flow interface. In addition, it reproduces the effect of erosion for granular flows over initially static material lying on the bed. This is possible when using a variable friction coefficient μ (I) but not with a constant friction coefficient.

  4. 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.

  5. 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.

  6. The Effect of Humidity and Particle Characteristics on Friction and Stick-slip Instability in Granular Fault Gouge

    NASA Astrophysics Data System (ADS)

    Anthony, J. L.; Marone, C. J.

    2003-12-01

    consists of less than 30% angular grains and begins once the coefficient of friction (shear stress divided by normal stress) reaches a value of 0.35-0.40. Peak friction during stick-slip cycles is 0.40-0.45. Each stick-slip event involves a small amount of quasi-static displacement prior to failure, which we refer to as pre-seismic slip. For unstable sliding regimes, we measure the amount of pre-seismic slip and the magnitude of dynamic stress drop. These parameters vary systematically with sliding velocity, particle characteristics, and bounding roughness. For shear within smooth surfaces, friction is very low (0.15-0.16 for spherical particles) and sliding is stable, without stick-slip instability. As more angular grains are mixed with spherical beads the coefficient of friction increases. This holds true for both the rough and smooth sample experiments. We expand on previous work done by Frye and Marone 2002 (JGR) to study the effect of humidity on 1-D, 2-D, and 3-D gouge layer configurations. Our data show that humidity has a significant effect on frictional strength and stability and that this effect is observed for both smooth surfaces, where grain boundary sliding is the dominant deformation mechanisms, and for shear within rough surfaces where gouge deformation occurs by rolling, dilation, compaction, and grain boundary sliding.

  7. Velocity-strengthening friction significantly affects interfacial dynamics, strength and dissipation

    PubMed Central

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

    2015-01-01

    Frictional interfaces abound in natural and man-made systems, yet their dynamics are not well-understood. Recent extensive experimental data have revealed that velocity-strengthening friction, where the steady-state frictional resistance increases with sliding velocity over some range, is a generic feature of such interfaces. This physical behavior has very recently been linked to slow stick-slip motion. Here we elucidate the importance of velocity-strengthening friction by theoretically studying three variants of a realistic friction model, all featuring identical logarithmic velocity-weakening friction at small sliding velocities, but differ in their higher velocity behaviors. By quantifying energy partition (e.g. radiation and dissipation), the selection of interfacial rupture fronts and rupture arrest, we show that the presence or absence of strengthening significantly affects the global interfacial resistance and the energy release during frictional instabilities. Furthermore, we show that different forms of strengthening may result in events of similar magnitude, yet with dramatically different dissipation and radiation rates. This happens because the events are mediated by rupture fronts with vastly different propagation velocities, where stronger velocity-strengthening friction promotes slower rupture. These theoretical results may have significant implications on our understanding of frictional dynamics. PMID:25598161

  8. Change in Frictional Behavior during Olivine Serpentinization

    NASA Astrophysics Data System (ADS)

    Xing, T.; Zhu, W.; French, M. E.; Belzer, B.

    2017-12-01

    Hydration of mantle peridotites (serpentinization) is pervasive at plate boundaries. It is widely accepted that serpentinization is intrinsically linked to hydromechanical processes within the sub-seafloor, where the interplay between cracking, fluid supply and chemical reactions is responsible for a spectrum of fault slip, from earthquake swarms at the transform faults, to slow slip events at the subduction zone. Previous studies demonstrate that serpentine minerals can either promote slip or creep depend on many factors that include sliding velocity, temperature, pressure, interstitial fluids, etc. One missing link from the experimental investigation of serpentine to observations of tectonic faults is the extent of alteration necessary for changing the frictional behaviors. We quantify changes in frictional behavior due to serpentinization by conducting experiments after in-situ serpentinization of olivine gouge. In the sample configuration a layer of powder is sandwiched between porous sandstone blocks with 35° saw-cut surface. The starting material of fine-grained (63 120 µm) olivine powder is reacted with deionized water for 72 hours at 150°C before loading starts. Under the conventional triaxial configuration, the sample is stressed until sliding occurs within the gouge. A series of velocity-steps is then performed to measure the response of friction coefficient to variations of sliding velocity from which the rate-and-state parameters are deduced. For comparison, we measured the frictional behavior of unaltered olivine and pure serpentine gouges.Our results confirm that serpentinization causes reduced frictional strength and velocity weakening. In unaltered olivine gouge, an increase in frictional resistance with increasing sliding velocity is observed, whereas the serpentinized olivine and serpentine gouges favor velocity weakening behaviors at the same conditions. Furthermore, we observed that high pore pressures cause velocity weakening in olivine but

  9. The damage is done: Low fault friction recorded in the damage zone of the shallow Japan Trench décollement

    NASA Astrophysics Data System (ADS)

    Keren, Tucker T.; Kirkpatrick, James D.

    2016-05-01

    Fault damage zones record the integrated deformation caused by repeated slip on faults and reflect the conditions that control slip behavior. To investigate the Japan Trench décollement, we characterized the damage zone close to the fault from drill core recovered during Integrated Ocean Drilling Program Expedition 343 (Japan Trench Fast Drilling Project (JFAST)). Core-scale and microscale structures include phyllosilicate bands, shear fractures, and joints. They are most abundant near the décollement and decrease in density sharply above and below the fault. Power law fits describing the change in structure density with distance from the fault result in decay exponents (n) of 1.57 in the footwall and 0.73 in the hanging wall. Microstructure decay exponents are 1.09 in the footwall and 0.50 in the hanging wall. Observed damage zone thickness is on the order of a few tens of meters. Core-scale structures dip between ~10° and ~70° and are mutually crosscutting. Compared to similar offset faults, the décollement has large decay exponents and a relatively narrow damage zone. Motivated by independent constraints demonstrating that the plate boundary is weak, we tested if the observed damage zone characteristics could be consistent with low-friction fault. Quasi-static models of off-fault stresses and deformation due to slip on a wavy, frictional fault under conditions similar to the JFAST site predict that low-friction fault produces narrow damage zones with no preferred orientations of structures. These results are consistent with long-term frictional weakness on the décollement at the JFAST site.

  10. 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.

  11. Historical overview of friction testing in Connecticut.

    DOT National Transportation Integrated Search

    2010-03-01

    A historical overview of pavement friction testing in Connecticut is presented. : Photographs of early pavement friction testers are provided, including vintage photos : of a skid trailer from a Federal Highway Administration (formally Bureau of Publ...

  12. Physical Interpretation of Laboratory Friction Laws in the Context of Damage Physics

    NASA Astrophysics Data System (ADS)

    Rundle, J. B.; Tiampo, K. F.; Martins, J. S.; Klein, W.

    2002-12-01

    Frictional on sliding surfaces is ultimately related to processes of surface damage, and can be understood in the context of the physics of dynamical threshold systems. Threshold systems are known to be some of the most important nonlinear, self-organizing systems in nature, including networks of earthquake faults, neural networks, superconductors and semiconductors, and the World Wide Web, as well as political, social, and ecological systems. All of these systems have dynamics that are strongly correlated in space and time, and all typically display a multiplicity of spatial and temporal scales. Here we discuss the physics of self-organization and damage in earthquake threshold systems at the "microscopic" laboratory scale, in which consideration of results from simulations leads to dynamical equations that can be used to derive results obtained from sliding friction experiments, specifically, the empirical "rate-and-state" friction equations of Ruina. Paradoxically, in all of these dissipative systems, long-range interactions induce the existence of locally ergodic dynamics, even though the dissipation of energy is involved. The existence of dissipative effects leads to the appearance of a "leaky threshold" dynamics, equivalent to a new scaling field that controls the size of nucleation events relative to the size of the background fluctuations. The corresponding appearance of a mean field spinodal leads to a general coarse-grained equation, which expresses the balance between rate of stress supplied, and rate of stress dissipated in the processes leading to surface damage. We can use ideas from thermodynamics and kinetics of phase transitions to develop the exact form of the rate-and-state equations, giving clear physical meaning to all terms and variables. Ultimately, the self-organizing dynamics arise from the appearance of an energy landscape in these systems, which in turn arises from the strong correlations and mean field nature of the physics.

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

    PubMed

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

    2015-12-10

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

  14. Quantitative kinetic analysis of lung nodules by temporal subtraction technique in dynamic chest radiography with a flat panel detector

    NASA Astrophysics Data System (ADS)

    Tsuchiya, Yuichiro; Kodera, Yoshie; Tanaka, Rie; Sanada, Shigeru

    2007-03-01

    Early detection and treatment of lung cancer is one of the most effective means to reduce cancer mortality; chest X-ray radiography has been widely used as a screening examination or health checkup. The new examination method and the development of computer analysis system allow obtaining respiratory kinetics by the use of flat panel detector (FPD), which is the expanded method of chest X-ray radiography. Through such changes functional evaluation of respiratory kinetics in chest has become available. Its introduction into clinical practice is expected in the future. In this study, we developed the computer analysis algorithm for the purpose of detecting lung nodules and evaluating quantitative kinetics. Breathing chest radiograph obtained by modified FPD was converted into 4 static images drawing the feature, by sequential temporal subtraction processing, morphologic enhancement processing, kinetic visualization processing, and lung region detection processing, after the breath synchronization process utilizing the diaphragmatic analysis of the vector movement. The artificial neural network used to analyze the density patterns detected the true nodules by analyzing these static images, and drew their kinetic tracks. For the algorithm performance and the evaluation of clinical effectiveness with 7 normal patients and simulated nodules, both showed sufficient detecting capability and kinetic imaging function without statistically significant difference. Our technique can quantitatively evaluate the kinetic range of nodules, and is effective in detecting a nodule on a breathing chest radiograph. Moreover, the application of this technique is expected to extend computer-aided diagnosis systems and facilitate the development of an automatic planning system for radiation therapy.

  15. Estimation of wheel-rail friction for vehicle certification

    NASA Astrophysics Data System (ADS)

    Petrov, Vladislav; Berg, Mats; Persson, Ingemar

    2014-08-01

    In certification of new rail vehicles with respect to running characteristics, a wide variety of operating conditions needs to be considered. However, in associated test runs the wheel-rail friction condition is difficult to handle because the friction coefficient needs to be fairly high and the friction is also generally hard to assess. This is an issue that has been studied in the European project DynoTRAIN and part of the results is presented in this paper. More specifically, an algorithm for estimating the wheel-rail friction coefficient at vehicle certification tests is proposed. Owing to lack of some measurement results, the algorithm here is evaluated in a simulation environment which is also an important step towards practical implementation. A quality measure of the friction estimate is suggested in terms of estimated wheel-rail spin and total creep. It is concluded that, tentatively, the total creep should exceed 0.006 and the spin should be less than 1.0 m-1 for the algorithm to give a good friction estimate. Sensitivity analysis is carried out to imitate measurement errors, but should be expanded in further work.

  16. Psychophysical evaluation of a variable friction tactile interface

    NASA Astrophysics Data System (ADS)

    Samur, Evren; Colgate, J. Edward; Peshkin, Michael A.

    2009-02-01

    This study explores the haptic rendering capabilities of a variable friction tactile interface through psychophysical experiments. In order to obtain a deeper understanding of the sensory resolution associated with the Tactile Pattern Display (TPaD), friction discrimination experiments are conducted. During the experiments, subjects are asked to explore the glass surface of the TPaD using their bare index fingers, to feel the friction on the surface, and to compare the slipperiness of two stimuli, displayed in sequential order. The fingertip position data is collected by an infrared frame and normal and translational forces applied by the finger are measured by force sensors attached to the TPaD. The recorded data is used to calculate the coefficient of friction between the fingertip and the TPaD. The experiments determine the just noticeable difference (JND) of friction coefficient for humans interacting with the TPaD.

  17. Atomic scale friction of molecular adsorbates during diffusion.

    PubMed

    Lechner, B A J; de Wijn, A S; Hedgeland, H; Jardine, A P; Hinch, B J; Allison, W; Ellis, J

    2013-05-21

    Experimental observations suggest that molecular adsorbates exhibit a larger friction coefficient than atomic species of comparable mass, yet the origin of this increased friction is not well understood. We present a study of the microscopic origins of friction experienced by molecular adsorbates during surface diffusion. Helium spin-echo measurements of a range of five-membered aromatic molecules, cyclopentadienyl, pyrrole, and thiophene, on a copper(111) surface are compared with molecular dynamics simulations of the respective systems. The adsorbates have different chemical interactions with the surface and differ in bonding geometry, yet the measurements show that the friction is greater than 2 ps(-1) for all these molecules. We demonstrate that the internal and external degrees of freedom of these adsorbate species are a key factor in the underlying microscopic processes and identify the rotation modes as the ones contributing most to the total measured friction coefficient.

  18. Quantum friction on monoatomic layers and its classical analog

    NASA Astrophysics Data System (ADS)

    Maslovski, Stanislav I.; Silveirinha, Mário G.

    2013-07-01

    We consider the effect of quantum friction at zero absolute temperature resulting from polaritonic interactions in closely positioned two-dimensional arrays of polarizable atoms (e.g., graphene sheets) or thin dielectric sheets modeled as such arrays. The arrays move one with respect to another with a nonrelativistic velocity v≪c. We confirm that quantum friction is inevitably related to material dispersion, and that such friction vanishes in nondispersive media. In addition, we consider a classical analog of the quantum friction which allows us to establish a link between the phenomena of quantum friction and classical parametric generation. In particular, we demonstrate how the quasiparticle generation rate typically obtained from the quantum Fermi golden rule can be calculated classically.

  19. ABL and BAM Friction Analysis Comparison

    DOE PAGES

    Warner, Kirstin F.; Sandstrom, Mary M.; Brown, Geoffrey W.; ...

    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.

  20. Fault Frictional Stability in a Nuclear Waste Repository

    NASA Astrophysics Data System (ADS)

    Orellana, Felipe; Violay, Marie; Scuderi, Marco; Collettini, Cristiano

    2016-04-01

    Exploitation of underground resources induces hydro-mechanical and chemical perturbations in the rock mass. In response to such disturbances, seismic events might occur, affecting the safety of the whole engineering system. The Mont Terri Rock Laboratory is an underground infrastructure devoted to the study of geological disposal of nuclear waste in Switzerland. At the site, it is intersected by large fault zones of about 0.8 - 3 m in thickness and the host rock formation is a shale rock named Opalinus Clay (OPA). The mineralogy of OPA includes a high content of phyllosilicates (50%), quartz (25%), calcite (15%), and smaller proportions of siderite and pyrite. OPA is a stiff, low permeable rock (2×10-18 m2), and its mechanical behaviour is strongly affected by the anisotropy induced by bedding planes. The evaluation of fault stability and associated fault slip behaviour (i.e. seismic vs. aseismic) is a major issue in order to ensure the long-term safety and operation of the repository. Consequently, experiments devoted to understand the frictional behaviour of OPA have been performed in the biaxial apparatus "BRAVA", recently developed at INGV. Simulated fault gouge obtained from intact OPA samples, were deformed at different normal stresses (from 4 to 30 MPa), under dry and fluid-saturated conditions. To estimate the frictional stability, the velocity-dependence of friction was evaluated during velocity steps tests (1-300 μm/s). Slide-hold-slide tests were performed (1-3000 s) to measure the amount of frictional healing. The collected data were subsequently modelled with the Ruina's slip dependent formulation of the rate and state friction constitutive equations. To understand the deformation mechanism, the microstructures of the sheared gouge were analysed. At 7 MPa normal stress and under dry conditions, the friction coefficient decreased from a peak value of μpeak,dry = 0.57 to μss,dry = 0.50. Under fluid-saturated conditions and same normal stress, the