Influence of radiation damage on internal friction background

International Nuclear Information System (INIS)

Burbelo, R.M.; Grinik, Eh.U.; Paliokha, M.I.; Orlinskij, A.B.

1984-01-01

Influence of radiation damage on internal friction background in samples of polycrystalline nickel and iron irradiated by a fast neutron flux approximately 10 14 neutr/(cm 2 xs) at 350 deg C has been studied using the low-frequency unit of the reverse torsion pendulum type. It has been established experimentally that a high-temperature background of internal friction of iron and nickel samples decreases as accumulating radiation defects occurring under neutron irradiation. Assumptions on a possible mechanism of the effect have been proposed. Simple expression for the background magnitude evaluation has been suggested

An internal friction peak caused by hydrogen in maraging steel

International Nuclear Information System (INIS)

Usui, Makoto; Asano, Shigeru

1996-01-01

Internal friction in hydrogen-charged iron and steel has so far been studied by a large number of investigators. For pure iron, a well-defined peak of internal friction has been observed under the cold-worked and hydrogen-charged conditions. This is called the hydrogen cold-work peak, or the Snoek-Koester relaxation, which originates from the hydrogen-dislocation interaction. In the present study, a high-strength maraging steel (Fe-18Ni-9Co-5Mo) was chosen as another high-alloy steel which is known to be very susceptible to hydrogen embrittlement. The purpose of this paper is to show a new internal friction peak caused by hydrogen in the maraging steel and to compare it with those found in stainless steels which have so far been studied as typical engineering high-alloy materials

On the nature of low temperature internal friction peaks in metallic glasses

Energy Technology Data Exchange (ETDEWEB)

Khonik, V.A. [State Pedagogical Univ., Voronezh (Russian Federation); Spivak, L.V. [State Univ., Perm (Russian Federation)

1996-01-01

Low temperature (30 < T < 300 K) internal friction in a metallic glass Ni{sub 60}Nb{sub 40} subjected to preliminary inhomogeneous deformation by cold rolling, homogeneous tensile deformation or electrolytic charging with hydrogen is investigated. Cold rolling or hydrogenation result in appearance of similar internal friction peaks and hysteresis damping. Homogeneous deformation has no influence on low temperature internal friction. The phenomenon of microplastic deformation during hydrogenation of weakly stressed samples is revealed. It is argued that microplastic deformation of metallic glasses during hydrogenation without external stress takes place too. Plastic flow both on cold rolling and hydrogenation occurs via formation and motion of dislocation-like defects which are the reason of the observed anelastic anomalies. It is concluded that low temperature internal friction peaks described in the literature for as-cast, cold deformed and hydrogenated samples have common dislocation-like origin.

Effect of precipitation on internal friction of AZ91 magnesium alloy

Institute of Scientific and Technical Information of China (English)

刘树伟; 姜海昌; 李秀艳; 戎利建

2010-01-01

The effect of precipitation on the internal friction(IF)of AZ91 magnesium alloy was investigated by using X-ray diffraction(XRD)analysis,scanning electron microscope(SEM)observation,and dynamic mechanical analysis(DMA).Six different states of alloy were prepared by applying different heat treatment processes:as-cast,in-complete solid solution,complete solid solution,micro-precipitation,continuous precipitation and continuous-discontinuous precipitation.It was found that the internal friction of in-completely solid-solutionized,completely solid-solutionized and micro-precipitated specimens showed a similar characteristic,and the grain boundary relaxation is completed depressed due to the Al atoms supersaturated in theα-Mg solution.However,a thermal relaxation internal friction peak was observed for continuously precipitated and continuously-discontinuously precipitated specimens at around 438 K and frequency of about 1 Hz,which was attributed to the grain boundaries relaxation.Furthermore,it was found that the relaxation of theβ-Mg17Al12/α-Mg phase interfaces should give its contribution to the background internal friction in the as-cast,continuously precipitated and continuously-discontinuously precipitated specimens.

Internal friction and dislocation collective pinning in disordered quenched solid solutions

Science.gov (United States)

D'Anna, G.; Benoit, W.; Vinokur, V. M.

1997-12-01

We introduce the collective pinning of dislocations in disordered quenched solid solutions and calculate the macroscopic mechanical response to a small dc or ac applied stress. This work is a generalization of the Granato-Lücke string model, able to describe self-consistently short and long range dislocation motion. Under dc applied stress the long distance dislocation creep has at the microscopic level avalanche features, which result in a macroscopic nonlinear "glassy" velocity-stress characteristic. Under ac conditions the model predicts, in addition to the anelastic internal friction relaxation in the high frequency regime, a linear internal friction background which remains amplitude-independent down to a crossover frequency to a strongly nonlinear internal friction regime.

Internal friction and elastic softening in polycrystalline Nb3Sn

International Nuclear Information System (INIS)

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

1981-01-01

The vibrating-reed technique was used to measure internal friction and Young's modulus of polycrystalline Nb 3 Sn in the form of composite Nb/Nb 3 Sn tapes from 6 to 300 K. In tapes with only small residual strain in the A15 layers, a dramatic increase in internal friction with decreasing temperature is observed with an abrupt onset at approx.48 K. The internal friction Q -1 between 6 and 48 K is believed to be associated with stress-induced motion of martensitic-domain walls. In this temperature range, Q -1 is approximately proportional to the square of the tetragonal strain of the martensitic phase; Q -1 α (c/a-1) 2 . With residual compressive strains of approx.0.2%, the internal friction associated with domain-wall motion is considerably reduced. This is attributed to a biasing of domain-wall orientation with residual stress, which reduces wall motion induced by the (much smaller) applied stress. The transformation temperature, however, is unchanged (within +- 1 K) by residual strains of up to 0.2%. Young's modulus exhibits substantial softening on cooling from 300 to 6 K. This softening, is substantially reduced in the presence of small residual compressive strains, indicating a highly nonlinear stress-strain relationship as previously reported for V 3 Si

Young modulus and internal friction of a fiber-reinforced composite

International Nuclear Information System (INIS)

Ledbetter, H.M.; Lei, M.; Austin, M.W.

1986-01-01

By a kilohertz-frequency resonance method we determined the Young modulus and internal friction of a uniaxially fiber-reinforced composite. The composite comprised glass fibers in an epoxy-resin matrix. We studied three fiber contents: 0, 41, and 49 vol %. The Young modulus fit a linear rule of mixture. The internal friction fit a classical free-damped-oscillator model where one assumes a linear rule of mixture for three quantities: mass, force constant, and mechanical-resistance constant

An internal-friction study of reactor-pressure-vessel steel embrittlement

International Nuclear Information System (INIS)

Ouytsel, K. van; Fabry, A.; Batist, R. de; Schaller, R.

1997-01-01

Within an enhanced commercial surveillance strategy, the nuclear-research institute SCK.CEN in Mol, Belgium is investigating, by means of internal friction, the microstructural processes responsible for embrittlement of pressure-vessel steels. The experiments were carried out using a torsion pendulum at the Ecole Polytechnique Federale de Lausanne in Switzerland. Amplitude-independent internal-friction experiments teach us that neutron irradiation induces defects which interact with mobile dislocations. Thermal ageing of JRQ and Doel-IV steel does not cause major embrittlement effects. Amplitude-dependent internal-friction experiments allow us to determine a critical amplitude which corresponds to the yield stress of the material as obtained from static tensile tests. The results also correspond to a three-component model for the yield strength taking into account both hardening and non-hardening embrittlement. Investigations of Doel-I-II weld material in different conditions reveal that embrittlement due to irradiation or thermal ageing can be interpreted in terms of a fine interplay between long- and short-range phenomena. (author)

Internal friction and shear modulus in Al-Ga alloys (80-320 K)

International Nuclear Information System (INIS)

Chountas, K.; Andronikos, P.; Papathanassopoulos, K.

1977-01-01

The internal friction and shear modulus of polycrystalline Al + (0.2, 0.7, 2 and 4) at.% Ga was measured as a function of temperature, using measurements of logarithmic decrement and frequency of free sample vibration. The internal friction curves for the smaller solute concentrations went through a maximum (peak) at 230 K. The height of the peak increased initially with solute concentration, then disappeared at higher concentrations. This peak is probably due to the interaction of solute atoms with dislocations. The continuous increase in internal friction at higher temperatures, reported in pure Al, was not found in these alloys. This absence is probably due to the pinning of dislocations by Ga atoms. (author)

On the nature of low temperature internal friction peaks in metallic glasses

International Nuclear Information System (INIS)

Khonik, V.A.; Spivak, L.V.

1996-01-01

Low temperature (30 60 Nb 40 subjected to preliminary inhomogeneous deformation by cold rolling, homogeneous tensile deformation or electrolytic charging with hydrogen is investigated. Cold rolling or hydrogenation result in appearance of similar internal friction peaks and hysteresis damping. Homogeneous deformation has no influence on low temperature internal friction. The phenomenon of microplastic deformation during hydrogenation of weakly stressed samples is revealed. It is argued that microplastic deformation of metallic glasses during hydrogenation without external stress takes place too. Plastic flow both on cold rolling and hydrogenation occurs via formation and motion of dislocation-like defects which are the reason of the observed anelastic anomalies. It is concluded that low temperature internal friction peaks described in the literature for as-cast, cold deformed and hydrogenated samples have common dislocation-like origin

Mechanical spectroscopy, internal friction and ultrasonic attenuation: Collection of works

International Nuclear Information System (INIS)

Magalas, L.B.

2009-01-01

An extensive collection of recommended books and proceedings from numerous conferences on internal friction, mechanical spectroscopy, and ultrasonic attenuation is provided. Reflecting the complicated history of the 20th century, books published in English and in Russian are presented in two separate sections. International and national conferences organized in various countries are listed. Supplementary lists referring to conferences held in the People's Republic of China, Poland, Russia, the Soviet Union, and Ukraine are also provided. The interesting evolution of mechanical spectroscopy from internal friction and ultrasonic attenuation in solids is clearly demonstrated, and a choice list of retrospective papers illustrates the evolution of the field. A brief review of mechanical spectroscopy, therefore, is included. Numerous research areas investigated by internal friction and mechanical spectroscopy are addressed, including point defect relaxations, electronic and phonon relaxations, dislocation relaxations, grain boundary relaxations, domain induced relaxations (magnetic, ferroelectric), magnetomechanical relaxations, phase transformations, glass transitions, interface effects as well as a wide array of applications specific to physics and materials science. For many years now, there has been a definite need to provide a thorough list of references that might cover major national conferences and books published in English and other languages. This work strives to achieve this goal.

Digitally controlled measurement of sonic elastic moduli and internal friction by phase analysis

International Nuclear Information System (INIS)

O'Brien, M.H.; Hunter, O. Jr.; Rasmussen, M.D.; Skank, H.D.

1983-01-01

An automated system is described for measuring internal friction and elastic moduli using sonic resonance techniques. This mirocomputer-controlled device does phase angle analysis in addition to traditional decay and peak-width internal friction measurement. The apparatus may be programmed to make measurements at any sequence of temperatures between room temperature and 1600 0 C

Internal friction study of microplasticity of aluminum thin films on silicon substrates

Energy Technology Data Exchange (ETDEWEB)

Nishio, Y.; Tanahashi, K.; Asano, S. [Nagoya Institute of Technology, Nagoya (Japan)

1995-12-01

Internal friction in aluminum thin films 0.2 to 2.0 {mu}m thick on silicon substrates has been investigated between 180 and 360 K as a function of strain amplitude by means of a free-decay method of flexural vibration. According to the constitutive equation, the internal friction in the film alone can be evaluated separately from the data on the film/substrate composite. The amplitude-dependent part of internal friction in aluminum films is found in the strain range approximately two orders of magnitude higher than that for bulk aluminum. On the basis of the microplasticity theory, the amplitude-dependent internal friction can be converted into the plastic strain as a function of the effective stress on dislocation motion. The mechanical responses thus obtained for aluminum films show that the plastic strain of the order of 10-9 in creases nonlinearly with increasing stress. These curves tend to shift to a higher stress with decreasing film thickness and also with decreasing temperature, both indicating a suppression of the microplastic deformation. At all temperatures examined, the microflow stress at a constant level of the plastic strain varies inversely with the film thickness, which qualitatively agrees with the variation in macroscopic yield stress. 36 refs., 7 figs.

Influence of electron irradiation on internal friction and structure evolution of polymer composites

International Nuclear Information System (INIS)

Ismailova, G.A.

2007-01-01

Full text: Important qualitative information on structural evolution and radiation alterations in polymer materials under the action of ionizing radiation can be obtained from the analysis of the temperature dependences of internal friction. Changing of internal friction parameters of relax maxima during irradiation is qualitative degree parameter of radiation scission-cross linking of the polymer molecules. In this work, the general phenomenological approach is realized by introduction of the effective 'observed' parameters into the simple kinetic equations. The applicability of such approach is justified by the fact that kinetics of both internal friction and scission-cross linking processes can be characterized by the same effective parameters. Temperature dependences of internal friction are experimentally studied in epoxy irradiated by 2.5 MeV pulse electron beam to different doses (D=3 MGy, 6 MGy and 9 MGy). Time dependences of internal friction characteristics associated with radiation-induced processes of polymer scission and cross-linking are analyzed and discussed. Experimental data on kinetics of structural transformations in epoxy are interpreted on the base of analytical solutions of differential equations for free radical accumulation during and after irradiation subject to the arbitrary effective order of radical recombination. It is shown that in the range of doses and dose rates under study radiation-induced scission predominates during polymer irradiation but in a certain period of time after irradiation scission changes to cross-linking. Characteristics of the kinetic curves obtained essentially depend on the dose

Exploring the role of internal friction in the dynamics of unfolded proteins using simple polymer models

Science.gov (United States)

Cheng, Ryan R.; Hawk, Alexander T.; Makarov, Dmitrii E.

2013-02-01

Recent experiments showed that the reconfiguration dynamics of unfolded proteins are often adequately described by simple polymer models. In particular, the Rouse model with internal friction (RIF) captures internal friction effects as observed in single-molecule fluorescence correlation spectroscopy (FCS) studies of a number of proteins. Here we use RIF, and its non-free draining analog, Zimm model with internal friction, to explore the effect of internal friction on the rate with which intramolecular contacts can be formed within the unfolded chain. Unlike the reconfiguration times inferred from FCS experiments, which depend linearly on the solvent viscosity, the first passage times to form intramolecular contacts are shown to display a more complex viscosity dependence. We further describe scaling relationships obeyed by contact formation times in the limits of high and low internal friction. Our findings provide experimentally testable predictions that can serve as a framework for the analysis of future studies of contact formation in proteins.

Measurement of Internal Friction for Tungsten by the Curve Vibrating Method with Variation of Voltage and Temperature

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Elin Yusibani

2013-12-01

Full Text Available Application of a curved vibrating wire method (CVM to measure gas viscosity has been widely used. A fine Tungsten wire with 50 mm of diameter is bent into a semi-circular shape and arranged symmetrically in a magnetic field of about 0.2 T. The frequency domain is used for calculating the viscosity as a response for forced oscillation of the wire. Internal friction is one of the parameter in the CVM which is has to be measured beforeahead. Internal friction coefficien for the wire material which is the inverse of the quality factor has to be measured in a vacuum condition. The term involving internal friction actually represents the effective resistance of motion due to all non-viscous damping phenomena including internal friction and magnetic damping. The testing of internal friction measurement shows that at different induced voltage and elevated temperature at a vacuum condition, it gives the value of internal friction for Tungsten is around 1 to 4 10-4.

Effect of frequency on amplitude-dependent internal friction in niobium

International Nuclear Information System (INIS)

Ide, Naoki; Atsumi, Tomohiro; Nishino, Yoichi

2006-01-01

Amplitude-dependent internal friction (ADIF) was measured in a polycrystalline niobium using four modes of flexural vibration from the fundamental to the third-order resonance at room temperature. The ADIF was detected in each vibration mode. The internal-friction versus strain-amplitude curve of the ADIF shifted to a larger strain-amplitude range as frequency increased. The stress-strain curves were derived from the ADIF data, and the microplastic flow stress defined as the stress required to produce a plastic strain of 1 x 10 -9 was read from the stress-strain curves. It was found that the microplastic flow stress was proportional to the frequency

Internal friction and lattice anomalies of single-phase Hg-1223

International Nuclear Information System (INIS)

Zhang, Q.M.; Nanjing Univ.; Shao, H.M.; Nanjing Univ.; Huang, Y.N.; Nanjing Univ.; Shen, H.M.; Nanjing Univ.; Wang, Y.N.; Nanjing Univ.

1997-01-01

Internal friction in the kHz range has been performed for single-phase HgBa 2 Ca 2 Cu 3 O 8+δ with the critical temperature T c = 120 K. The results indicate that two peaks of internal friction appear near 150 and 250 K. X-ray diffraction exhibits a lattice parameter stepping at tens of Kelvin above T c . The Grueneisen parameter γ is estimated from the value of thermal expansion coefficients obtained from X-ray diffraction measurements. The discussion suggests that the anomaly at 150 K is caused by lattice instabilities and the other one near 250 K may be associated with a Neel transition. (orig.)

Effect of frequency on amplitude-dependent internal friction in niobium

Energy Technology Data Exchange (ETDEWEB)

Ide, Naoki [Department of Materials Science and Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan)]. E-mail: ide@nitech.ac.jp; Atsumi, Tomohiro [Department of Materials Science and Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Nishino, Yoichi [Department of Materials Science and Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan)

2006-12-20

Amplitude-dependent internal friction (ADIF) was measured in a polycrystalline niobium using four modes of flexural vibration from the fundamental to the third-order resonance at room temperature. The ADIF was detected in each vibration mode. The internal-friction versus strain-amplitude curve of the ADIF shifted to a larger strain-amplitude range as frequency increased. The stress-strain curves were derived from the ADIF data, and the microplastic flow stress defined as the stress required to produce a plastic strain of 1 x 10{sup -9} was read from the stress-strain curves. It was found that the microplastic flow stress was proportional to the frequency.

Internal friction of hydrated soda-lime-silicate glasses.

Science.gov (United States)

Reinsch, S; Müller, R; Deubener, J; Behrens, H

2013-11-07

The internal friction of hydrated soda-lime-silica glasses with total water content (C(W)) up to 1.9 wt. % was studied by dynamic mechanical analysis (DMA) using temperature-frequency sweeps from 723 K to 273 K and from 1 s(-1) to 50 s(-1). Total water content and concentrations of H2O molecules (C(H2O)) and OH groups (C(OH)) in the DMA specimens were determined by infrared spectroscopy. For low water contents (C(W) ≈ C(OH) friction peaks below the glass transition (α relaxation) were assigned to the low-temperature motion of alkali ions (γ relaxation) and cooperative movements of dissimilar mobile species under participation of OH at higher temperature (β(OH) relaxation). For large water contents (C(W) > 1 wt. %), where significant amounts of molecular water are evident (C(H2O) > 0.15 wt. %), however, internal friction spectra change unexpectedly: the β(OH) peak heights saturate and a low temperature shoulder appears on the β-relaxation peak. This emerging relaxation mode (β(H2O) relaxation) was assigned to the motions of H2O molecules. β(H2O) relaxation was found to be faster than β(OH) but slower than γ relaxation. Activation energy of the different relaxation modes increased in the order γ < β(H2O) < β(OH) < α.

Internal friction and linear expansion coefficient in zirconium and cobalt within the range of phase transitions

International Nuclear Information System (INIS)

Boyarskij, S.V.

1986-01-01

Experimental results are presented for internal friction and linear expansion coefficient at zirconium and cobalt in the temperature range from 440 K to the point of the phase transition of the first kind (1138 K for Zr and 706 for Co). Anomalous changes of the internal friction and linear expansion coefficient in the phase transition region are found. Theoretical considerations are given to explain the sharp decrease of the internal friction as temperature approaches the phase transition point

Internal friction of metallic glass Ni74P16B6Al4 near T/sub x/

International Nuclear Information System (INIS)

Li Xiao-Guang; He Yizhen

1986-01-01

The internal friction of metallic glass Ni 74 P 16 B 6 Al 4 near the crystallization temperature T/sub x/ is investigated using a conventional torsion pendulum. Two internal friction peaks, P 1 and P 2 , are observed and the dependence of the peak positions on heating rate is described by the Kissinger equation. Pre-crystallization reduces the height of the peaks (P 1 and P 2 ) and shifts the positions of these peaks but in opposite directions. A formula showing the dependence of apparent internal friction on volume fraction transformed is derived. The variation of internal friction with annealing corresponds to the variation of the fraction transformed. (author)

Low-temperature internal friction in high-purity monocrystalline and impure polycrystalline niobium after plastic deformation

International Nuclear Information System (INIS)

Wasserbaech, W.; Thompson, E.

2001-01-01

The internal friction Q -1 of plastically deformed, high-purity monocrystalline and impure polycrystalline niobium specimens was measured in the temperature range between 65 mK and about 2 K. Plastic deformation has a pronounced effect on the internal friction Q -1 of the high-purity monocrystalline specimens, and the effect has been found to be almost temperature independent. By contrast, surprisingly, the internal friction Q -1 of the impure polycrystalline specimens was found to be almost independent of the extent of plastic deformation. Comparison of the experimental results with different models of a dynamic scattering of acoustic phonons by dislocations leads to the conclusion that the results cannot be explained with the two-level tunneling model. Instead it is suggested that a strong interaction between acoustic phonons and geometrical kinks in non-screw dislocations is responsible for the observed internal friction Q -1 . (orig.)

Measuring internal friction at sonic and ultrasonic frequencies in high temperature superconductors

International Nuclear Information System (INIS)

Anderson, A.R.; Russell, G.J.

1996-01-01

Internal friction measurements provide a sensitive means for probing some structural properties of materials. Defect relaxation processes and phase changes are frequently reflected in internal friction measurements as a function of temperature. Relaxation processes associated with oxygen content have been observed in YBCO and BSCCO (2212). By measuring the internal friction at different frequencies activation energies associated with relaxation processes can be determined. Structural changes are temperature dependent and independent of frequency. The composite bar technique developed employs a piezoelectric quartz bar (with lengths of 2 cm or 3 cm and resonant frequencies of approximately 85 kHz or 120 kHz) with a resonant bar of HTSC attached to one end. The quartz bar is suspended at its nodal points and the system excited electrically using a regenerative feedback system. The composite bar method can also be used at low kilohertz frequencies by attaching the HTSC specimen used in the previous technique to the end of a much longer (e g 30 cm) fused silica rod which has very low damping. The resulting composite bar can be excited electrostatically or electromagnetically at frequencies below 10 kHz. The internal friction can be measured by scanning through the resonant frequency and measuring the bandwidth or by observing the decay of free oscillation in the bar. The advantage of using the two composite bar techniques is that the measurements can be made on the same specimen at different frequencies

Amplitude Dependent Internal Friction in a Mg-Al-Zn Alloy Studied after Thermal and Mechanical Treatment

Directory of Open Access Journals (Sweden)

Zuzanka Trojanová

2017-10-01

Full Text Available The amplitude-dependent internal friction of continuously-cast and rolled AZ31 magnesium alloy was measured in this study. Samples were annealed and quenched step by step; immediately after the treatment, the amplitude dependence of the logarithmic decrement was measured. Changes in the microstructure due to thermomechanical treatment were reflected in changes in the damping. Internal friction is influenced by the dislocation substructure and its modification due to solute atoms migration, microplastic deformation, and twins’ formation. Internal friction in the rolled sheets is affected by the rolling texture.

Low-Frequency Internal Friction Study on the Structural Changes in Polymer Melts

International Nuclear Information System (INIS)

Xue-Bang, Wu; Qiao-Ling, Xu; Shu-Ying, Shang; Jia-Peng, Shui; Chang-Song, Liu; Zhen-Gang, Zhu

2008-01-01

With the help of the low-frequency internal friction method, we investigate the structural properties of polymer melts, such as amorphous polystyrene (PS), poly(methyl methacrylate) (PMMA), and semi-crystalline poly(ethylene oxide) (PEO). An obvious peak of relaxation type is found in each of the internal friction curves. The peak temperature T p follows the relation T p ≈ (1.15 – 1.18) T g for PS and PMMA melts, while it follows T p ≈ 1.22T m for PEO melt, with T g being the glass transition temperature and T m the melting temperature. Based on the analysis of the features of this peak, it is found that this peak is related to the liquid-liquid transition temperature T u of polymer melts. Mechanism of the liquid-liquid transition is suggested to be thermally-activated collective relaxation through cooperation. This finding may be helpful to understand the structural changes in polymer melts. In addition, the internal friction technique proves to be effective in studying dynamics in polymer melts

A study on the determination of diffusion coefficient of carbon in 304 austenitic stainless steels by internal friction method

International Nuclear Information System (INIS)

Kim, K.S.; Kim, T.H.

1982-01-01

Internal friction peaks associated with the presence of carbon in 18-8 type 304 stainless steel have been observed from measurements with a torsion pendulum. The temperature for maximum internal friction lies between 250degC and 300degC with a frequency of vibration. The height of the peak rises and the position of the peak shifts to a lower temperature with an increase of the carbon content. And a comparison of the activation energy and the diffusion coefficient determined by internal friction methods with those measured in conventional macro-diffusion experiments reveals that the diffusion data measured by internal friction method and the diffusion data measured by conventional method exist in the same line. It follows from the above fact that observed internal friction peak is associated with the stress-induced diffusion of carbon in face-centered cubic alloys. (Author)

Internal friction due to domain-wall motion in martensitically transformed A15 compounds

International Nuclear Information System (INIS)

Snead, C.L. Jr.; Welch, D.O.

1985-01-01

A lattice instability in A15 materials in some cases leads to a cubic-to-tetragonal martensitic transformation at low temperatures. The transformed material orients in lamellae with c axes alternately aligned along the directions producing domain walls between the lamellae. An internal-friction (delta) feature below T/sub m/ is attributed to stress-induced domain-wall motion. The magnitude of the friction increases as temperature is lowered below T/sub m/ as (1-c/a) increases, and behaves as (1-c/a) 2 from T/sub m/ down to the superconducting critical temperature where the increasing tetragonality is inhibited. The effect of strain in the lattice is to decrease the domain-wall internal friction, but not affect T/sub m/. Neutron-induced disorder and the addition of some third-elements in alloying decrease both delta and T/sub m/, with some elements reducing only the former. Less than 1 at. % H is seen to completely suppress both delta and T/sub m. Martensitically transformed V 2 Zr demonstrates low-temperature internal-friction and modulus behavior consists with easy β/m wall motion relative to the easy m/m motion of the A15's. For the V 2 Zr, a peak in delta is observed, qualitatively in agreement with expected β/m wall motion

Internal friction behaviours in Zr57Al10Ni12.4Cu15.6Nb5 bulk metallic glass

International Nuclear Information System (INIS)

Zhang Bo; Zu Fangqiu; Zhen Kang; Shui Jiapeng; Wen Ping

2002-01-01

The internal friction patterns of Zr 57 Al 10 Ni 12.4 Cu 15.6 Nb 5 bulk metallic glass (BMG) were investigated with different frequencies and heating rates. An internal friction peak with extremely large magnitude is observed in the internal friction curves as a function of temperature (Q -1 -T curves). The internal friction peak was fitted by an equation Q -1 =AX(T)/η, where A is a constant, X(T) is the fraction of the glass/supercooled liquid and the viscosity η obeys the Vogel-Fulcher-Tammann relation. We confirm that the internal friction peak originates from both of the glass transition and crystallization. The anomalous behaviours of the peak suggest that Zr 57 Al 10 Ni 12.4 Cu 15.6 Nb 5 BMG has a wide supercooled liquid region and the magnitude of the peak can be used to judge the glass forming ability (GFA) of the glass forming alloys. In addition, the internal friction technique proved to be a new powerful tool for studying structural relaxation and phase transition as well as the GFA of BMG. (author)

Internal friction in cold-rolled metallic glasses Cu50Ti50 and Ni78Si8B14

International Nuclear Information System (INIS)

Zolotukhin, I.V.; Khonik, V.A.; Ryabtseva, T.N.; Belyavskii, V.I.

1989-01-01

The influence of cold rolling on the low temperature (30 to 300 K) internal friction of metallic glasses Cu 50 Ti 50 and Ni 78 Si 8 B 14 is investigated. It is shown that cold rolling of both metallic glasses up to 2 to 6% results in the appearance of a high relaxation damping peak around 260 to 280 K. The internal friction background below the peak shows a strong amplitude dependence. In highly predeformed specimens (∼ 16%) the internal friction peak is absent. Electron irradiation (2 MeV, 10 19 cm -2 ) leads to the suppression of the deformation-induced internal friction peak. The results are interpreted in the framework of the dislocation models of plastic flow of metallic glasses. (author)

An automatic measuring system of internal friction at low frequency

International Nuclear Information System (INIS)

Iwasaki, K.

1979-01-01

An inverted torsion pendulum is automatized by means of Tectanel electronic system. Internal friction and the period of vibration are measured fully automatically as a function of temperature and the data obtained are analysed with a computer. (Author) [pt

Microplasticity and dislocation mobility in copper-nickel single crystals evaluated from strain-amplitude-dependent internal friction. [CuNi

Energy Technology Data Exchange (ETDEWEB)

Nishino, Y.; Okada, Y.; Asano, S. (Dept. of Materials Science and Engineering, Nagoya Inst. of Tech. (Japan))

1992-02-16

Internal friction in copper-0.4 to 7.6 at% nickel single crystals is measured as a function of strain amplitude at various temperatures. Analysis of the data on the amplitude-dependent internal friction yields the relation of effective stress and microplastic strain of the order of 10{sup -9}. The stress-strain responses thus obtained exhibit that the microplastic flow stress increases more rapidly on alloying than the macroscopic yield stress. The mean dislocation velocity is also evaluated from the internal-friction data, which corresponds well to the etch-pit data. It is shown that the dislocation motion is impeded by friction due to dispersed solute atoms. (orig.).

Internal friction around Tc connected with superconductivity in high Tc superconductors

International Nuclear Information System (INIS)

Wang Yening

1993-01-01

Internal friction and ultrasonic measurements show that there always exists a phase-like transition (PLT) characterized by the jump of lattice parameters at tens degrees above Tc in superconducting YBaCuO, BiSrCaCuO and TlBaCaCuO. Ferroelastic loops and shape memory effect associated with elastic softening invariably occur at the PLT temperature, showing the characteristics of thermoelastic martensitic transition. Internal frictions in KHz of Bi(Pb)SrCaCuO reveal a static hysteretic plateau (Qp -1 ) above Tc that drops linearly with temperature below Tc. The Qp -1 of YBaCuO decreases with decreasing oxygen content. The origin of the hysteretic Qp -1 is attributed to the lattice distortions around the carriers. (orig.)

Contribution to the study of internal friction in graphites

International Nuclear Information System (INIS)

Merlin, J.

1969-03-01

A study has been made of the internal friction in different graphites between -180 C and +500 C using a torsion pendulum; the graphites had been previously treated thermo-mechanically, by neutron irradiation and subjected to partial annealings. It has been shown that there occurs: a hysteretic type dissipation of energy, connected with interactions between dislocations and other defects in the matrix; a dissipation having a partially hysteretic character which can be interpreted by a Granato-Luke type formalism and which is connected with the presence of an 'ultra-micro porosity'; a dissipation by a relaxation mechanism after a small dose of irradiation; this is attributed to the reorientation of bi-interstitials; a dissipation having the characteristics of a solid state transformation, this during an annealing after irradiation. It is attributed to the reorganization of interstitial defects. Some information has thus been obtained concerning graphites, in particular: their behaviour at low mechanical stresses, the nature of irradiation defects and their behaviour during annealing, the structural changes occurring during graphitization, the relationship between internal friction and macroscopic mechanical properties. (author) [fr

Reflections on Friction in Quantum Mechanics

Directory of Open Access Journals (Sweden)

Yair Rezek

2010-08-01

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

Effect of pulse electron beam characteristics on internal friction and structural alterations in epoxy

International Nuclear Information System (INIS)

Zaikin, Yu.A.; Ismailova, G.A.; Al-Sheikhly, M.

2007-01-01

Temperature dependence of internal friction is experimentally studied in epoxy irradiated by 2.5 MeV pulse electron beam to different doses. Time dependence of internal friction characteristics associated with radiation-induced processes of polymer scission and cross-linking is analyzed and discussed. Experimental data on kinetics of structural transformations in epoxy are interpreted on the base of analytical solutions of differential equations for free radical accumulation during and after irradiation subject to the pulse irradiation mode and an arbitrary effective order of radical recombination

Comparison of internal friction in high Tc superconductors and CuO

International Nuclear Information System (INIS)

Gzowski, O.; Davoli, I.; Stizza, S.; Mancini, G.; Kusz, B.; Barczynski, R.; Gazda, M.; Sadowski, W.; Murawski, L.

1990-01-01

This paper reports on the internal friction and shielding effect in CuO, superconducting yttrium and bismuth ceramics and yttrium monocrystal that have been measured. Several features, some of them common for all specimens, have been found

Study on frictional pressure drop of steam-water two phase flow in optimized four-head internal-ribbed tube

International Nuclear Information System (INIS)

Wang Weishu; Zhu Xiaojing; Bi Qincheng; Wu Gang; Yu Shuiqing

2012-01-01

The optimized internal-ribbed tube is different from the normal internal-ribbed tube on the frictional pressure drop characteristics. The frictional pressure drop characteristics of steam-water two phase flow in horizontal four-head optimized internal-ribbed were studied under adiabatic condition. According to the experimental and calculation results, the two-phase multiplier is greatly affected by the steam quality and pressure. The two-phase multiplier increases with increasing quality, and decreases with increasing pressure. In the near-critical pressure region, the two-phase multiplier is close to 1. The frictional pressure drop of two phase flow in optimized tube is less than that in the normal tube under the same work condition. The good hydrodynamic condition could be achieved when the optimized internal-ribbed tube is used in the heat transfer equipment because the self-compensating characteristics exist due to the reduction of frictional pressure drop. (authors)

Effect of plastic deformation and impurities on internal friction in solid He4

International Nuclear Information System (INIS)

Tsymbalenko, V.L.; AN SSSR, Chernogolovka. Inst. Fiziki Tverdogo Tela)

1979-01-01

The internal friction in solid He 4 samples of 20.55 cm 3 molar volume is measured at frequencies of 15 and 78 kHz. The samples are grown under constant pressure and also by the blocked capillary technique. The construction of the container was such that the damping on plastic deformation of solid helium could be measured. Internal friction is also investigated in solid helium samples containing admixtures of He 3 (from 0.01 to 0.1 at.%). A number of dislocation parameters could be determined on basis of the temperature and amplitude dependences of the damping predicted by the Granato-Lucke theory

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

Science.gov (United States)

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

A molecular dynamics analysis of internal friction effects on the plasticity of Zr65Cu35 metallic glass

International Nuclear Information System (INIS)

Feng, Shidong; Qi, Li; Zhao, Fengli; Pan, Shaopeng; Li, Gong; Ma, Mingzhen; Liu, Riping

2015-01-01

Highlights: • Effects of internal friction on plasticity is investigated at the atomic level. • The simulations allow reproduction of images of internal friction evolution. • The simulation results are in good agreement with experiments and theories. • This simulation can predict the deformation mode with different internal friction. - Abstract: The effects of internal friction (IF) on Zr 65 Cu 35 metallic glass plasticity are investigated through molecular dynamics simulations. Results show that the Voronoi polyhedron 〈0, 3, 6, 3〉 increases as IF increases, thereby effectively inhibiting localized deformation and improving metallic glass plasticity. The simulations allow reproduction of images of IF evolution in metallic glasses subjected to isothermal annealing at 730 K and 850 K respectively, which can help explain the experimental observations. IF could be adjusted by selecting suitable annealing temperatures and cooling rates. The results of this work provide a strong foundation for future metallic glass designs

Internal friction of molybdenum during microplastic deformation in the temperature range of ductile-brittle transition

International Nuclear Information System (INIS)

Beloshenko, V.A.; Datsko, O.I.; Shakhova, A.D.

1986-01-01

Internal friction of Q -1 samples prepared of technically pure molybdenum wire 1.2 mm in diameter in the initial state and after annealing in the inert atmosphere at 800, 1050, 1200 deg C respectively during 2.5 ad 13 hours is investigated. The initial material had fibrous structure. It is shown that the method of low-frequency internal friction can be applied to study ductile-brittle transition (DBT) in metals at amplitude of oscillations bringing about irreversible microplastic strain

Nonlinear internal friction, chaos, fractal and musical instruments

International Nuclear Information System (INIS)

Sun, Z.Q.; Lung, C.W.

1995-08-01

Nonlinear and structure sensitive internal friction phenomena in materials are used for characterizing musical instruments. It may be one of the most important factors influencing timbre of instruments. As a nonlinear dissipated system, chaos and fractals are fundamental peculiarities of sound spectra. It is shown that the concept of multi range fractals can be used to decompose the frequency spectra of melody. New approaches are suggested to improve the fabrication, property characterization and physical understanding of instruments. (author). 18 refs, 4 figs

Frictional coefficient depending on active friction radius with BPV ...

African Journals Online (AJOL)

Frictional coefficient depending on active friction radius with BPV and BTV in automobile disc braking system. ... International Journal of Engineering, Science and Technology. Journal Home · ABOUT ... AJOL African Journals Online. HOW TO ...

Internal friction study of neutron-irradiation effects on an amorphous Cu40Ti60 alloy

International Nuclear Information System (INIS)

Dong, Y.; Wu, G.; Xiao, K.; Li, X.; He, Y.

1988-01-01

Effects of neutron irradiation on the structure of an amorphous Cu 40 Ti 60 alloy have been studied by internal friction measurements. After irradiation, the position of the first internal friction peak remains almost unchanged and the shoulder position shifts towards a higher temperature by about 5 K, which indicates that the Cu 40 Ti 60 glass becomes more stable. These results are finally discussed based on the concept of changes of chemical short-range ordering and geometrical short-range ordering due to radiation damage

Internal Friction of Li7La3Zr2O12 Based Lithium Ionic Conductors

Directory of Open Access Journals (Sweden)

Wang X.P.

2016-03-01

Full Text Available The diffusion mechanisms of lithium ions in tetragonal phase as well as in Al and Nb stabilized cubic Li7La3Zr2O12 compounds were investigated by low-frequency internal friction technique. In the cubic Li7La3Zr2O12 phase, a remarkable relaxation-type internal friction peak PC with a peak height up to 0.12 was observed in the temperature range from 15°C to 60°C. In the tetragonal phase however, the height of the PT peak dropped to 0.01. The obvious difference of the relaxation strength between the cubic and tetragonal phases is due to the different distribution of lithium ions in lattice, ordered in the tetragonal phase and disordered in the cubic phase. Based on the crystalline structure of the cubic garnet-type Li7La3Zr2O12 compound, it is suggested that the high internal friction peak in the cubic phase may be attributed to two diffusion processes of lithium ions: 96h↔96h and 96h↔24d.

Study by internal friction of curing low temperature irradiation defects in graphite

International Nuclear Information System (INIS)

Rouby, Dominique.

1974-01-01

Micromechanical properties and anelastic effects of neutrons irradiated graphites at 300 and 77 0 K are investigated by internal friction analysis and elasticity modulus variations. Defects created by irradiation are studied and evolution versus dose and annealing is followed [fr

Determination of crystal oscillatory spectra by internal friction data spectroscopic analysis

International Nuclear Information System (INIS)

Zaykin, Yu.A.

1998-01-01

Technique for relaxation spectra determination on the basis of internal friction averaging over relaxation frequencies is developed. It is shown that mathematically the problem is reduced to solution of the first type Fredholm integral equation. Impurity oscillatory spectra in alpha-iron, molybdenum and Fe-Cr-Ni alloy are obtained. (author)

Glass and crystallization like transitions at low temperature in Zr-Cu based glasses by internal friction measurements

Directory of Open Access Journals (Sweden)

Aboki A.T.

2011-05-01

Full Text Available Low temperature β internal friction peak evolution upon thermal cycles shows two peculiar peaks similar to high temperature internal friction peak. The modulus softening associated to these peaks suggest a phase transformation phenomenon and the relaxation time τo in order of 10-23–10-35s, close to that observed in grains boundary sliding are due to interface motions in the amorphous structure under combined thermal and mechanical energies.

On the nature of low temperature internal friction peaks in metallic glasses

NARCIS (Netherlands)

Khonik, VA; Spivak, LV

Low temperature (30 internal friction in a metallic glass Ni60Nb40 subjected to preliminary inhomogeneous deformation by cold rolling, homogeneous tensile deformation or electrolytic charging with hydrogen is investigated. Cold rolling or hydrogenation result in appearance of similar

Instrumentation, computer software and experimental techniques used in low-frequency internal friction studies at WNRE

International Nuclear Information System (INIS)

Sprugmann, K.W.; Ritchie, I.G.

1980-04-01

A detailed and comprehensive account of the equipment, computer programs and experimental methods developed at the Whiteshell Nuclear Research Estalbishment for the study of low-frequency internal friction is presented. Part 1 describes the mechanical apparatus, electronic instrumentation and computer software, while Part II describes in detail the laboratory techniques and various types of experiments performed together with data reduction and analysis. Experimental procedures for the study of internal friction as a function of temperature, strain amplitude or time are described. Computer control of these experiments using the free-decay technique is outlined. In addition, a pendulum constant-amplitude drive system is described. (auth)

Effect of the superconducting transition on amplitude-dependent dislocation internal friction in metals

International Nuclear Information System (INIS)

Lomakin, V.V.; Pankrat'eva, G.L.; Roshchupkin, A.M.

1983-01-01

In terms of the Granato-Lucke model, an explanation of the amplitude-dependent internal friction change at the superconducting transition is proposed which takes into account the influence of the electronic viscosity on the fluctuation unpinning of dislocations from local obstacles

Internal friction in irradiated silicon

International Nuclear Information System (INIS)

Kalanov, M.U.; Pajzullakhanov, M.S.; Khajdarov, T.; Ummatov, Kh.

1999-01-01

The submicroscopic heterogeneities in mono- and polycrystal silicon and the influence of X-ray radiation on them were investigated using the ultrasound resonance method. Disk-shaped samples of 27.5 mm in diameter and 4 mm in thickness, with the flat surface parallel to crystallographic plane (111), were irradiated by X-ray beam of 1 Wt/cm 2 (50 KeV, Mo K α ) during 10 hours. Relations of internal frictions (Q -1 ) of samples and their relative attitude (ψ) - Q -1 (ψ) show that there is a presence of double-humped configuration for monocrystal silicon with the peaks at ψ=900 and 270 degrees. The relations Q -1 (ψ) remain the same after the irradiation. However, the peak width becomes larger. This data show that the configuration and attitude of the heterogeneities remain the same after the irradiation. The double-humped configuration was not discovered for the relations Q -1 (ψ) of polycrystal silicon. It is explained by the fact that there is an isotropic distribution in the content of many blocks and granules

Internal friction peaks observed in explosively deformed polycrystalline Mo, Nb, and Cu

Science.gov (United States)

Rieu, G. E.; Grimes, H. H.; Romain, J. P.; Defouquet, J.

1974-01-01

Explosive deformation (50 kbar range) induced, in Cu, Mo and Nb, internal friction peaks identical to those observed after large normal deformation. The variation of the peaks with pressure for Mo and Nb lead to an explanation of these processes in terms of double kink generation in screw and edge dislocations.

Study on phase transformations in superconducting Ti-50%Nb alloy using temperature-dependent internal friction method

International Nuclear Information System (INIS)

Shapoval, B.I.; Tikhinskij, G.F.; Somov, A.I.; Chernyj, O.V.; Rudycheva, T.Yu.; Andrievskaya, N.F.

1980-01-01

The internal friction method is used to study phase transformations in the Ti-50%Nb alloy parallel with other methods. The effect of annealing temperature and time, as well as the content of interstitial impurities in the alloy and its thermomechanical treatment (TMT) is studied. In the 250-300 deg C temperature range the complex maximum of internal friction caused by extraction of secondary phases is observed. The latter is confirmed by the measurement data of mechanical properties and electron microscopic analysis. The maximum consists of three overlapping peaks that reflects stepped form of the decomposition process of the metastable solid solution. The preliminary thermo-mechanical alloy treatment consisting of equidirectional plastic deformation with the following recrystallization annealing leads to peak increase. This fact testifies to the stimulating effect of thermo-mechanical treatment on the degree of solid solution decomposition and reveals in the increase of the critical current density of a wire made of the ingot. The increase of the interstitial impurity content in the alloy has the analogous effect. The reduction of the internal friction level during isothermal stand-up at temperatures higher than the third peak temperature proceeds in two stages [ru

Frictional pressure drop of high pressure steam-water two-phase flow in internally helical ribbed tubes

International Nuclear Information System (INIS)

Tingkuan, C.; Xuanzheng, C.

1987-01-01

It is well known that the internally helical ribbed tubes are effective in suppressing the dry-out in boiling tubes at high pressures, so they are widely used as furnace water wall tubes in modern large steam power boilers. Design of the boilers requires the data on frictional pressure drop characteristics of the ribbed tubes, but they are not sufficient now. This paper describes the experimental results on the adiabatic frictional pressure drop in both horizontal ribbed tubes with measured mean inside diameter of 11.69 mm and 35.42 mm at high pressure from 10 to 21 MPa, mass flow rate from 350 to 3800 kg/m/sup 2/s and steam quality from 0 to 1 in our high pressure electrically heated water loop. Simultaneously, both smooth tubes under the same conditions for comparison. Based on the tests the correlation for determining the frictional pressure drop of internally ribbed tubes are proposed

Internal frictions and their application in the supervision and inspection of a manufacture

International Nuclear Information System (INIS)

Bourgain, L.; Samson, G.; Blay, D.

1975-01-01

The internal frictions of materials subjected to flexion or compression waves were studied. In the first part of the report, devoted to the theoretical aspect of the problem, an attempt is made to estimate how much of the total friction measured is exterior to the structure and how much is intrinsic. The mathematical models generally used to account for these phenomena, those of Maxwell and Voigt, were applied for this purpose. Part two deals with measurement methods and precautions necessary if good precision and reproducible experimental results are required. The last part gives several examples of application. It is shown how internal damping measurements are used to detect variations in a given manufacture. In the application specific to sintered materials a physical explanation is tentatively put forward to account for the peaks recorded at middle frequency (between 1000 and 10000 hertz) in the damping spectrum; these are connected with interface phenomena between the grains, sometimes known as surface/volume effect [fr

Search for stress dependence in the internal friction of fused silica

International Nuclear Information System (INIS)

Willems, Phil; Lamb, Corinne; Heptonstall, Alastair; Hough, Jim

2003-01-01

The quality factor (Q) of the vertical bounce mode of a fused silica fiber pendulum is measured at high and low stresses. The internal friction of fused silica fibers is found to be independent of stress from 12.8 to 213 MPa at a level of 1.6x10 -8 . Comparison with Q's of fiber bending modes is consistent with losses concentrated in the surface of the fiber

Phenomenological description of internal friction spectra in glass-forming and glassy systems

International Nuclear Information System (INIS)

Lomovskij, V.A.

1999-01-01

Dissipative events in different by chemical nature glass-forming systems, including B 2 O 3 , are studied. It is established from the spectra of internal friction of these systems that the maxima of the energy dissipation of the external power impact are positioned both in the area of viscous flow metastable structural liquid state and in the area of solid elastic state

Comparative analysis of internal friction and natural frequency measured by free decay and forced vibration

International Nuclear Information System (INIS)

Wang, Y. Z.; Ding, X. D.; Xiong, X. M.; Zhang, J. X.

2007-01-01

Relations between various values of the internal friction (tgδ, Q -1 , Q -1* , and Λ/π) measured by free decay and forced vibration are analyzed systemically based on a fundamental mechanical model in this paper. Additionally, relations between various natural frequencies, such as vibration frequency of free decay ω FD , displacement-resonant frequency of forced vibration ω d , and velocity-resonant frequency of forced vibration ω 0 are calculated. Moreover, measurement of natural frequencies of a copper specimen of 99.9% purity has been made to demonstrate the relation between the measured natural frequencies of the system by forced vibration and free decay. These results are of importance for not only more accurate measurement of the elastic modulus of materials but also the data conversion between different internal friction measurements

Internal friction and microplasticity of carbon-fiber-reinforced SiC ceramics; Tanso sen`i kyoka SiC ceramics no hakai zenku katei ni okeru naibu masatsu

Energy Technology Data Exchange (ETDEWEB)

Ogawa, H.; Nishino, Y.; Asano, S. [Nagoya Institute of Technology, Nagoya (Japan)

1995-08-20

Mechanical responses of carbon-fiber-reinforced SiC ceramics before fracture were measured in the strain range below 2 {times} 10{sup {minus}3} by two experimental methods: mechanical hysteresis and internal friction. Load-deflection curves were obtained by the three-point bending deformation in loading-unloading cycles. A little permanent strain was found after the first cycle even in the range where fracture never occurred. A closed hysteresis loop was observed after several cycles and stabilized with a symmetrical shape after more than twenty cycles. Such a stabilized hysteresis loop is attributed to the steady-state microplastic deformation and may cause the amplitude-dependent internal friction. Internal friction was measured in the fundamental mode of free-free resonant vibration as a function of strain amplitude. With increasing the amount of prestrain in the bending deformation, internal friction increased and became sensitive to the strain amplitude. The amplitude-dependent internal friction in the composites is considered to originate from fiber pull-out or microcrack propagation. The internal friction data were analyzed on the basis of the microplasticity theory and converted into the plastic strain expressed as a function of stress. Therefore, it becomes possible to non-destructively study the forerunning process of fracture of the fiber-reinforced ceramics. 23 refs., 6 figs.

Studying on tempering transformation and internal friction for low carbon bainitic steel

International Nuclear Information System (INIS)

Li, Weijuan; Cai, Mingyu; Wang, Dong; Zhang, Junwei; Zhao, Shengshi; Shao, Peiying

2017-01-01

The changes of microstructure during the process of tempering transformation were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction and internal friction (IF) for low carbon bainite steel. The yield strength of the steel was tested after tempering transformation. The results showed that the microstructures of the experimental steel in rolled state were composed of lath bainite and granular bainite with a little Mo 2 C and NbC precipitates. The lath width of bainite increased continuously with the tempering time. More cell structures with different orientations were formed in bainite laths. Furthermore, poly-gonization gradually began in some laths. The microstructure of granular bainite increased and was coarsened when it devoured the lath bainite continuously. The dislocation density of the bainitic ferrite decreased continuously as Mo 2 C and NbC precipitations were further increasing. The peak value of Snoek decreased continuously in internal friction-temperature spectrum. The peak value of SKK at the surface decreased at first and then increased. The peak value of SKK at the center decreased firstly and then had little change. Besides, the yield strength of the steel increased firstly and then decreased.

Studying on tempering transformation and internal friction for low carbon bainitic steel

Energy Technology Data Exchange (ETDEWEB)

Li, Weijuan, E-mail: liweijuan826@163.com; Cai, Mingyu; Wang, Dong; Zhang, Junwei; Zhao, Shengshi; Shao, Peiying

2017-01-02

The changes of microstructure during the process of tempering transformation were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction and internal friction (IF) for low carbon bainite steel. The yield strength of the steel was tested after tempering transformation. The results showed that the microstructures of the experimental steel in rolled state were composed of lath bainite and granular bainite with a little Mo{sub 2}C and NbC precipitates. The lath width of bainite increased continuously with the tempering time. More cell structures with different orientations were formed in bainite laths. Furthermore, poly-gonization gradually began in some laths. The microstructure of granular bainite increased and was coarsened when it devoured the lath bainite continuously. The dislocation density of the bainitic ferrite decreased continuously as Mo{sub 2}C and NbC precipitations were further increasing. The peak value of Snoek decreased continuously in internal friction-temperature spectrum. The peak value of SKK at the surface decreased at first and then increased. The peak value of SKK at the center decreased firstly and then had little change. Besides, the yield strength of the steel increased firstly and then decreased.

Labour market frictions and migration

NARCIS (Netherlands)

Cremers, Jan

2016-01-01

The 4th contribution to the series INT-AR papers is dedicated to the methods of assessing labour market frictions. The paper provides a (brief) international comparison of the role of labour migration in solving these frictions.

Design and assembly of a torsion pendulum for the measurement of internal friction at low temperatures

International Nuclear Information System (INIS)

San Juan, J. M.; Gallego, I.; No, M. L.

2001-01-01

In this work we describe the assembly, operation and specifications of an inverted torsion pendulum designed to measure internal friction at low temperatures (from 4.2 K to 500 K). The high precision mechanics allow us to obtain internal friction spectra with low levels of noise from amplitudes as small as 2x10''7. The inertia components of the pendulum have been built with specific materials, so that the resonance frequency of the pendulum can be changed within two orders of magnitude (0.1-10Hz). In addition, the sample can be in situ deformed at any temperature and can be inserted into the pendulum at liquid nitrogen temperature. The operation of the pendulum, all the control p recesses and data acquisition are completely automated. (Author) 4 refs

A review of literature from the First International Conference on Friction Stir Welding

International Nuclear Information System (INIS)

Bowyer, W.H.

2000-06-01

The papers from the first international conference on Friction Stir Welding (FSW) have been reviewed. Taken together the papers provide a very optimistic picture for the development and application of friction stir welding in general and to the case of the copper canister in particular. Whilst a considerable development effort is in progress the process has been industrialised for joining of aluminium sheet and it is accepted by Lloyds register for this purpose. Development of procedures and equipment to weld thicker materials and a wider range of materials is progressing ahead of the research activity to aid the understanding of the process at this stage. Nevertheless, well-established weld assessment procedures are being applied to experimental welds with very encouraging results. Summaries of the key papers are presented in an appendix

Corrosion behaviour of stainless steels by internal friction method

International Nuclear Information System (INIS)

Postnikov, V.S.; Kovalevskij, V.I.

1987-01-01

Corrosion of austenite chromium-nickel stainless steels 12 Kh18N9, 12Kh18N9T, 12Kh18N10 and 12Kh18N10T is investigated. Wire samples 0.7...0.8 mm in diameter before tests were subjected to quenching in water from the temperature of 1050...1100 deg C and part of them - to tempering at 650 deg C for 2 h. Pitting corrosion was brought about by different concentration of iron chloride solutions (C FeCl 3 ). Total corrosion has a slight effect on the character of IF (internal friction) variation that increases without the whole test period up to the moment when mechanical strength of the sample

Friction

Science.gov (United States)

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 In recent years, increased fuel efficiency of passenger car is required due to the CO2 emission issue. One of the solutions to improve fuel efficiency is to

Internal friction in hydrited Zircaloy 4

International Nuclear Information System (INIS)

Piquin, R.; Ghilarducci, Ada A.; Salva, Horacio R.

2007-01-01

The aim of this work is to investigate the microscopic basis of inelastic effects on standard Zry4 alloy, after plastic deformation and hydriding. Polycrystalline samples with cylindrical geometry were taken with dimension 1.62mm in diameter and 40 mm in length. In order to obtain the internal friction and elastic modulus spectra at low frequencies (0.01 to 10Hz), a sub resonant forced pendulum was used, with resonance at about 130Hz. The results are peaks between 150 and 350K. They are analysed on the basis of their response at frequency changes, amplitude of measurement, grade of plastic deformation 'in situ' and cathodical hydriding (650 H wt ppm). The peaks are interpreted as follows: the 250K peak corresponds to the interaction between dislocations and Cottrel cloud of solute atoms surrounding the dislocation cores. After hydruration, the spectrum is dominated by the 220K peak, which is attributed to the hydrogen atoms in solid solution trapped by the dislocation cores. The anelastic parameters allow to evaluate the H concentration segregated on dislocations, in this case it is 300 wt ppm H. (author) [es

Deconvolution analysis to determine relaxation time spectra of internal friction peaks

International Nuclear Information System (INIS)

Cost, J.R.

1985-01-01

A new method for analysis of an internal friction vs temperature peak to obtain an approximation of the spectrum of relaxation time responsible for the peak is described. This method, referred to as direct spectrum analysis (DSA), is shown to provide an accurate estimate of the distribution of relaxation times. The method is validated for various spectra, and it is shown that: (1) It provides approximations to known input spectra which replicate the position, amplitude, width and shape with good accuracy (typically 10%). (2) It does not yield approximations which have false spectral peaks

Internal friction in a new kind of metal matrix composites

International Nuclear Information System (INIS)

San Juan, J.; No, M.L.

2006-01-01

We have developed a new kind of metal matrix composites, based on powders of Cu-Al-Ni shape memory alloys (SMAs) surrounded by an indium matrix, specifically designed to exhibit high mechanical damping. The damping properties have been characterized by mechanical spectroscopy as a function of temperature between 150 and 400 K, frequency between 3 x 10 -3 and 3 Hz, and strain amplitude between 5 x 10 -6 and 10 -4 . The material exhibits, in some range of temperature, internal friction as high as 0.54. The extremely high damping is discussed in the light of the microstructure of the material, which has been characterized in parallel

Studies on internal friction in electron-irradiated iron crystals after plastic deformation

International Nuclear Information System (INIS)

Wolf, J.

1986-01-01

For the analysis of atomic point defects in high-purity the generation of atomic point defects was, above all, carried out by electron radiation, but in addition, also by plastic deformation. The exposure to radiation was realized at different temperatures in the Dynamitron of the University of Stuttgart (80 K, 160 K) and also in the low-temperature radiation facility of the nuclear research plant (KfA) Juelich (50 K). The radiation doses ranged between 2.7.10 21 e - /m 2 and 1.0.10 23 e - /m 2 . In situ plastic deformation was achieved at about 80 K (torsion, 4%). Internal friction which was determined in an inverse torsion pendulum in the temperature range of 80 K - 700 K and at frequencies of about 1 Hz served as defect indicator. In this study simulation programs were developed which were to give information prior to the realization of measurements on the temperatures and the intensity of the damping peaks to be expected. The internal friction peaks measured in the framework of this study could be assigned to the recovery stages I-IV. The measured values were discussed for three temperature ranges with main emphasis on the investigation of the recovering, radiation-induced or deformation-induced, atomic point defect in the temperature range of the recovery stage III (200 K - 270 K). (orig./MM) [de

Internal Friction in L.A.S. Type Glass and Glass-Ceramics

OpenAIRE

Arnault , L.; RiviÈre , A.

1996-01-01

Internal friction measurements have been performed on glass and glass-ceramics of the Li2O-Al2O3-SiO2 type by isothermal mechanical spectroscopy. Experiments were carried out over a large frequency range (10-4Hz - 31.6 Hz) for various temperatures between 260K and 850K. For the glass, a relaxation peak is observed at low temperature (276K for 1Hz). This peak does not appear in the glass-ceramics ; however, for each of them, two other peaks were observed : the first one at about 343K (1Hz) and...

Account of internal friction when estimating recoverable creep strain

International Nuclear Information System (INIS)

Demidov, A.S.

1986-01-01

It is supposed that a difference of empirical and calculated data on the creep strain recovery for Kh18N10T steel under conditions of cyclic variations in stress is specified by the effect of internal friction. In the accepted model of creep β-flow is considered to be reversible and γ-flow- irreversible. Absorptivity is determined as a ratio of the difference between the expended work and work of strain recovery forces to the work expended in cycle. A notion of the equivalent stress acting in the period of the creep strain recovery is introduced. Results of the calculation according to the empirical formula where absorptivity was introduced into are compared with empirical data obtained for Kh18N10T steel at 750 deg C

Normal-state anomalous behaviours studied by the internal friction of YBa sub 2 Cu sub 3 O sub 7 sub - subdelta

CERN Document Server

Ying, X N; Zhang, Q M; Huang, Y N; Wang, Y N

2002-01-01

The internal friction of Ca partially substituted Y sub 1 sub - sub x Ca sub x Ba sub 2 Cu sub 3 O sub 7 sub - subdelta ceramics was measured using the vibrating reed method from liquid-nitrogen temperature to room temperature at kilohertz frequency. There are two thermally activated relaxation peaks (called P1 and P2 at 95 K and 120 K, respectively). The intensity of P1 almost remains unchanged with Ca substitution, while that of P2 decreases. Another internal friction peak appears around 220 K (called P3). With the increase of Ca content, the intensity of P3 decreases and the peak position shifts toward low temperature. We also have observed that Zn substitution affects P3 much less and Fe substitution seems to result in another contribution to the internal friction around 250 K. We expect that the P3 peak originates from a charge-carrier crossover and possibly has some relationship with the occurrence of the dynamic stripe at low temperature.

Mechanism of high-temperature background of internal friction in metals

International Nuclear Information System (INIS)

Shapoval, B.I.; Arzhavitin, V.M.

1988-01-01

Data of theoretical and experimental studies on energy dissipation in vibrating metal at small amplitudes and elevated temperatures (high temperature background of internal friction) are generalized and systematized. Evolution of knowledge of the background as a phenomenon influenced mainly by crystal structure defects - their form, quantity, mobility and interaction is followed. Considered is a wide range of investigated metal states and measurement conditions, and interrelations with other characteristics, for instance, strength ones. On the basis of the data obtained by authors and other investigations a concept of an additional third stage of the background increase with the temperature - the stage of deviation from exponential dependence at premelting point, is introduced. 107 refs.; 32 figs.; 3 tabs

Regularized friction and continuation: Comparison with Coulomb's law

OpenAIRE

Vigué, Pierre; Vergez, Christophe; Karkar, Sami; Cochelin, Bruno

2016-01-01

International audience; Periodic solutions of systems with friction are difficult to investigate because of the irregular nature of friction laws. This paper examines periodic solutions and most notably stick-slip, on a simple one-degre-of-freedom system (mass, spring, damper, belt), with Coulomb's friction law, and with a regularized friction law (i.e. the friction coefficient becomes a function of relative speed, with a stiffness parameter). With Coulomb's law, the stick-slip solution is co...

Friction coefficient and limiter load test analysis by flexibility coefficient model of Hold-Down Spring of nuclear reactor vessel internals

Energy Technology Data Exchange (ETDEWEB)

Xie, Linjun [Zhejiang Univ. of Technology, Hangzhou (China). College of Mechanical Engineering; Xue, Guohong; Zhang, Ming [Shanghai Nuclear Engineering Research and Design Institute, Shanghai (China)

2017-11-15

The friction force between the contact surfaces of a reactor internal hold-down spring (HDS) and core barrel flanges can directly influence the axial stiffness of an HDS. However, friction coefficient cannot be obtained through theoretical analysis. This study performs a mathematical deduction of the physical model of an HDS. Moreover, a mathematical model of axial load P, displacement δ, and flexibility coefficient is established, and a set of test apparatuses is designed to simulate the preloading process of the HDS. According to the experimental research and theoretical analysis, P-δ curves and the flexibility coefficient λ are obtained in the loading processes of the HDS. The friction coefficient f of the M1000 HDS is further calculated as 0.224. The displacement limit load value (4,638 kN) can be obtained through a displacement limit experiment. With the friction coefficient considered, the theoretical load is 4,271 kN, which is relatively close to the experimental result. Thus, the friction coefficient exerts an influence on the displacement limit load P. The friction coefficient should be considered in the design analysis for HDS.

Friction coefficient and limiter load test analysis by flexibility coefficient model of Hold-Down Spring of nuclear reactor vessel internals

International Nuclear Information System (INIS)

Xie, Linjun

2017-01-01

The friction force between the contact surfaces of a reactor internal hold-down spring (HDS) and core barrel flanges can directly influence the axial stiffness of an HDS. However, friction coefficient cannot be obtained through theoretical analysis. This study performs a mathematical deduction of the physical model of an HDS. Moreover, a mathematical model of axial load P, displacement δ, and flexibility coefficient is established, and a set of test apparatuses is designed to simulate the preloading process of the HDS. According to the experimental research and theoretical analysis, P-δ curves and the flexibility coefficient λ are obtained in the loading processes of the HDS. The friction coefficient f of the M1000 HDS is further calculated as 0.224. The displacement limit load value (4,638 kN) can be obtained through a displacement limit experiment. With the friction coefficient considered, the theoretical load is 4,271 kN, which is relatively close to the experimental result. Thus, the friction coefficient exerts an influence on the displacement limit load P. The friction coefficient should be considered in the design analysis for HDS.

Internal friction in iron-aluminium alloys having a high aluminium content

International Nuclear Information System (INIS)

Hillairet, J.; Delaplace, J.; Silvent, A.

1966-01-01

By using a torsion pendulum to measure the internal friction of iron-aluminium alloys containing between 25 and 50 atom per cent of aluminium, it has been possible to show the existence of three damping peaks due to interstitial carbon. Their evolution is followed as a function of the carbon content, of the thermal treatment and of the aluminium content. A model based on the preferential occupation of tetrahedral sites is proposed as an interpretation of the results. A study of the Zener peak in these substitution alloys shows also that a part of the short distance disorder existing at high temperatures can be preserved by quenching. (author) [fr

Discovery of an internal-friction peak in the metallic glass Nb3Ge

International Nuclear Information System (INIS)

Berry, B.S.; Pritchet, W.C.; Tsuei, C.C.

1978-01-01

A well-defined internal-friction peak has been observed near 260 K in amorphous rf-sputtered films of Nb 3 Ge, studied at audio frequencies by a vibrating-reed technique. The characteristics of the peak are consistent with a stress-induced ordering mechanism involving a presently unidentified center which undergoes reorientation by an atomic jump with a sharply defined activation energy of 0.52 eV. The peak appears to be the first example of its type found in a metallic glass

Internal Friction of (SiO2)1-x (GeO2)x Glasses

OpenAIRE

Kosugi , T.; Kobayashi , H.; Kogure , Y.

1996-01-01

Internal friction of (SiO2)1-x (GeO2)x glasses (x = 0, 5, 10, 24 and 100 mole%) is measured at temperatures between 1.6 and 280 K. The data are filted with the equations for thermally activated relaxation with distributing activation energies in symmetrical double-well potentials. From the determined relaxation strength spectra for each sample, the contributions from each type of microscopic structural units are calculated assuming that transverse motion of the bridging O atom in Si-O-Si, Si-...

Relaxation features of the Young's modulus and internal friction of lanthanum

International Nuclear Information System (INIS)

Bodryakov, V.Yu.

1993-01-01

E Young module and Q -1 inner friction of polycrystalline lanthanum specimens are studied comprehensively within 4.2-420 K temperature range using bend autovibrations of a specimen represented by a thin rod within ∼ 1-2 kHz frequency range. Three maximums of relaxation nature innner friction are detected under ∼ 380-410, 250-270 and 90-120 K temperatures with 0.29, 0.21 and 0.02 eV activation energies, respectively, on Q -1 (T) curves. Maximums of inner friction are accompanied by peculiarities of E(T) Young module behaviour. 21 refs., 3 figs., 2 tabs

Internal friction and ultrasonic attenuation in solids, including high Tc superconductors

International Nuclear Information System (INIS)

Magalas, L.B.; Gorczyca, S.

1993-01-01

This volume contains seven invited papers and about eighty refereed contributions from the main sessions of the Sixth European Conference on Internal Friction and Ultrasonic Attenuation in Solids (ECIFUAS-6) held at the Academy of Mining and Metallurgy (Akademia Gorniczo-Hutnicza, AGH) in Krakow, Poland, 5-7 September, 1991. In addition, this volume contains six invited lectures and eight contributed papers presented at the Workshop on High Tc Superconductors on 5 September, 1991. Together these documents constitute the Proceedings of the ECIFUAS-6 Conference. A total of 140 scientists from 20 countries participated in the Conference. The programme of the Conference and the Workshop consisted of 16 invidet papers and 119 contributed papers. 107 papers were presented during 8 poster sessions. (orig.)

Temperature dependence of Young's modulus and internal friction of G-10CR and G-11CR epoxy resins

International Nuclear Information System (INIS)

Ledbetter, H.M.; Maerz, G.

1980-01-01

The Young's moduli of the epoxy-resin matrix material used in NEMA-designation G-10CR and G-11CR fiberglass-cloth-reinforced composites were measured dynamically and semicontinuously between ambient and liquid-nitrogen temperatures. Both materials exhibit regular temperature behavior, showing large Young's-modulus changes, about 125 and 50%, respectively. Internal friction decreased about 80% during cooling to liquid-nitrogen temperature (76 0 K). The different thermoelastic coefficients of the two materials indicate a different internal structure

Internal friction and mechanical properties of Zr - 2.5% Nb alloy after programme loading

International Nuclear Information System (INIS)

Gindin, I.A.; Chirkina, L.A.; Okovit, V.S.; Netesov, V.M.

1984-01-01

Temperature dependence of internal friction in the range 20-600 deg C of the alloy Zr-2.5% Nb in the initial state after programmed loading up to 0.1% of residual elongation and static deformation to the same deformation degree has been studied. It is shown, that the programmed loading promotes the decrease in relaxation rate at 20 and 200 deg C and the increase of strength characteristics of the alloy without the decrease in plasticity margin to fracture in the range 20-400 deg C

Origin of the low-frequency internal friction background of gold

Science.gov (United States)

Baur, J.; Benoit, W.

1986-11-01

The internal friction (IF) background of gold is studied in the kHz frequency range. Systematic measurements of IF as a function of frequency, strain amplitude, and temperature show that the IF is due to the superposition of two contributions: the thermoelastic effect and a dislocation effect. The thermoelastic effect is responsible for the IF background observed when the strain amplitude tends to zero. It is the only contribution to the IF background which is strain amplitude independent. On the contrary, the dislocation effect contributes only to the strain amplitude-dependent IF background. This effect is proportional to the strain amplitude. In particular, it is zero when the strain amplitude tends to zero. Furthermore, the dislocation contribution is frequency independent. The experimental results show that the dislocation effect cannot be explained by a viscous damping of dislocation motion, but must be related to an hysteretic and athermal motion of dislocations.

Two new methods to determine the adhesion by means of internal friction in materials covered with films

International Nuclear Information System (INIS)

Colorado, H. A.; Ghilarducci, A. A.; Salva, H. R.

2006-01-01

Two new models are proposed to determine the adhesion energy be means of the internal friction technique (IF) in thin films layered materials. for the first method is necessary to determine enthalpy by means of the IF technique, for which the adhesion work has been determined with experimental data. In the second method are necessary to perform IF tests at constant temperature. (Author)

Internal friction and absence of dilatancy of packings of frictionless polygons.

Science.gov (United States)

Azéma, Émilien; Radjaï, Farhang; Roux, Jean-Noël

2015-01-01

By means of numerical simulations, we show that assemblies of frictionless rigid pentagons in slow shear flow possess an internal friction coefficient (equal to 0.183±0.008 with our choice of moderately polydisperse grains) but no macroscopic dilatancy. In other words, despite side-side contacts tending to hinder relative particle rotations, the solid fraction under quasistatic shear coincides with that of isotropic random close packings of pentagonal particles. Properties of polygonal grains are thus similar to those of disks in that respect. We argue that continuous reshuffling of the force-bearing network leads to frequent collapsing events at the microscale, thereby causing the macroscopic dilatancy to vanish. Despite such rearrangements, the shear flow favors an anisotropic structure that is at the origin of the ability of the system to sustain shear stress.

Correlation between microstructure and internal friction in a Zr41.2-Ti13.8-Cu12.5-Ni8- Be22.5-Fe2 bulk metallic glass

International Nuclear Information System (INIS)

Wang, Q.; Pelletier, J.M.; Da Dong, Y.; Ji, Y.F.; Xiu, H.

2004-01-01

The microstructural evolution in a Zr-Ti-Cu-Ni-Be-Fe bulk metallic glass (BMG) has been investigated by measurements of dynamical shear modulus and internal friction combined with other analytical methods such as differential scanning calorimetry (DSC), X-ray diffraction (XRD) and high resolution transmission electron microscopy (TEM). When heated from room temperature up to 873 K, the as-received BMG exhibits an exponential increase in internal friction accompanying the strong decrease of storage modulus and the presence of the first loss modulus peak during the dynamic glass transition, which can be well described using quasi-point defect model. The correlative changes of the mechanical response at higher temperature are associated with the crystallisation process of the supercooled liquid phase, which occurs in four different stages. It is shown that the main crystallisation process is completed in the first two stages. With further increasing temperature, the remaining amorphous phases crystallise and/or the metastable crystalline phases are transformed into the stable ones. Isothermal annealing were also performed at temperatures in the supercooled liquid region far below the onset temperature of the crystallisation process (T x ). Their influence on microstucture and internal friction behaviour of the BMG is also presented in this paper. The most striking result is that the internal friction is very sensitive to the local atomic short range ordering induced by the preheating treatment

Experimental research on friction coefficient between grain bulk and bamboo clappers

Science.gov (United States)

Tang, Gan; Sun, Ping; Zhao, Yanqi; Yin, Lingfeng; Zhuang, Hong

2017-12-01

A silo is an important piece of storage equipment, especially in the grain industry. The internal friction angle and the friction coefficient between the grain and the silo wall are the main parameters needed for calculating the lateral pressure of the silo wall. Bamboo is used in silo walls, but there are no provisions about the friction coefficient between bulk grain and bamboo clappers in existing codes. In this paper, the material of the silo wall is bamboo. The internal friction of five types of grain and the friction coefficient between the grain and the bamboo clappers were measured with an equal-strain direct shear apparatus. By comparing the experimental result values with the code values, the friction coefficient between the grain bulk and bamboo clappers is lower than that between grain and steel wall and that between grain and concrete wall. The differences in value are 0.21 and 0.09, respectively.

Low temperature internal friction on γ-irradiated polyvinylidene fluoride (PVDF)

International Nuclear Information System (INIS)

Callens, A.; Eersels, L.; De Batist, R.

1978-01-01

A least-squares fitting of the below room temperature part of the internal friction spectra, obtained by the torsion pendulum technique on as-received and γ-irradiated (up to 1 Grad) strips and fibres of polyvinylidene fluoride by a superposition of single Debye functions, reveals that the spectral component features are determined not only by purely amorphous chain characteristics but also by the dose-dependence of crystallinity. A careful analysis of the relaxation spectra confirms that at least one relaxation effect (approximately 236 K) is created upon irradiation. The analysis of the dose dependence of the characteristics of the β (glass transition; approximately 220 K) and βsub(u) (apparent upper glass transition; approximately 270 K) relaxations, suggests the probable influence of crystallinity on the molecular motion in the amorphous phase. The increase of the intensity of the γ relaxation (approximately 190 K) is related to the irradiation-induced crystallite degradation. (author)

Internal friction of flux motion in Hg-system high-Tc superconductors

International Nuclear Information System (INIS)

Tian, W.; Zhu, J.S.; Shao, H.M.; Li, J.; Wang, Y.N.

1996-01-01

The internal friction(IF) and modulus as functions of temperature were measured for several Hg-system high-Tc superconductors(Hg1201, Hg1223, Hg1223 doped with Fe and Pb), under the applied magnetic field, with vibrating reed technique. An IF peak associated with flux motion can be found below Tc for all samples. The temperature of the IF peak increases with reducing vibrating amplitude. This amplitude dependence of IF indicates that the flux motion is characterized by nonlinear behavior. No apparent shift of IF peak position can be detected by varying the frequency in the range from 10 2 Hz to 10 3 Hz. Furthermore, the IF peak height satisfies a scaling law Q -1 ∝ω -n . This may be originated from phase transition of flux line lattice(FLL) rather than a thermally activated diffusion process. (orig.)

Weld defect identification in friction stir welding using power spectral density

Science.gov (United States)

Das, Bipul; Pal, Sukhomay; Bag, Swarup

2018-04-01

Power spectral density estimates are powerful in extraction of useful information retained in signal. In the current research work classical periodogram and Welch periodogram algorithms are used for the estimation of power spectral density for vertical force signal and transverse force signal acquired during friction stir welding process. The estimated spectral densities reveal notable insight in identification of defects in friction stir welded samples. It was observed that higher spectral density against each process signals is a key indication in identifying the presence of possible internal defects in the welded samples. The developed methodology can offer preliminary information regarding presence of internal defects in friction stir welded samples can be best accepted as first level of safeguard in monitoring the friction stir welding process.

Friction dampers, the positive side of friction

NARCIS (Netherlands)

Lopez Arteaga, I.; Nijmeijer, H.; Busturia, J.M.; Sas, P.; Munck, de M.

2004-01-01

Friction is frequently seen as an unwanted phenomenon whose influence has to be either minimised or controlled. In this work one of the positive sides of friction is investigated: friction damping. Friction dampers can be a cheap and efficient way to reduce the vibration levels of a wide range of

Effect of grain size on amplitude-dependent internal friction in polycrystalline copper. Do takessho no naibu masatsu no shinpuku izon sei ni oyobosu kessho ryukei no eikyo

Energy Technology Data Exchange (ETDEWEB)

Goto, H.; Nishino, Y.; Asano, S. (Nagoya Inst. of Technology, Nagoya (Japan))

1991-08-20

In this research, amplitude-dependency of internal friction was measured on various polycrystalline copper of varying grain size. Furthermore, the measurement data of amplitude-dependency of internal friction were analyzed from the phenomenological standpoint and microplastic strain was calculated as a function of stress. The obtained correlation between microplastic strain and stress corresponded to the stress-strain curve obtainable from normal tensile tests. Hence, comparing with the Hall-Petch relation, the relationship between flow stress and grain size in the microplastiic zone was discussed. The obtained results are summarized as follows: When grains were refined, amplitude dependency of internal friction was inhibited. As a result of the analysis of the data obtained, it was found that the flow stress in the microplastic zone increased following refining of grains. This agreed qualitatively with the macro deformation obtained from normal tensile tests. The grain size dependency of flow stress in the microplastic zone did not follow the normal Hall-Pitch relation, but the plastic strain increased, the dependency moved towards it. 16 refs., 4 figs.

Three-dimensional friction measurement during hip simulation.

Directory of Open Access Journals (Sweden)

Robert Sonntag

Full Text Available 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.

Internal friction study of hydrides in zirconium at low hydrogen contents

International Nuclear Information System (INIS)

Peretti, H.A.; Corso, H.L.; Gonzalez, O.A.; Fernandez, L.; Ghilarducci, A.A.; Salva, H.R.

1999-01-01

Full text: Internal friction and shear modulus measurements were carried out on crystal bar zirconium in the as received and hydride conditions using an inverted forced pendulum. Hydriding was achieved in two ways: inside and out of the pendulum. The final hydrogen content determined by fusion analysis in the 'in situ' hydride sample was of 36 ppm. Another sample was hydride by the cathodic charge method with 25 ppm. The thermal solid solubility (TSS) phase boundary presents hysteresis between the precipitation (TSSP) and the dissolution (TSSD) temperatures for the zirconium hydrides. During the first thermal cycling the anelastic effects could be attributed to the δ, ε and metastable γ zirconium hydrides. After 'in situ' annealing at 490 K, these peaks completely disappear in the electrolytically charged sample, while in the 'in situ' hydride, the peaks remain with decreasing intensity. This effect can be understood in terms of the different surface conditions of the samples. (author)

Analysis of Apex Seal Friction Power Loss in Rotary Engines

Science.gov (United States)

Handschuh, Robert F.; Owen, A. Karl

2010-01-01

An analysis of the frictional losses from the apex seals in a rotary engine was developed. The modeling was initiated with a kinematic analysis of the rotary engine. Next a modern internal combustion engine analysis code was altered for use in a rotary engine to allow the calculation of the internal combustion pressure as a function of rotor rotation. Finally the forces from the spring, inertial, and combustion pressure on the seal were combined to provide the frictional horsepower assessment.

Modeling Friction in Modelica with the Lund-Grenoble Friction Model

OpenAIRE

Aberger, Martin; Otter, Martin

2002-01-01

The properties of the Lund-Grenoble friction model are summarized and different types of friction elements - bearing friction, clutch, one-way clutch, are implemented in Modelica using this friction formulation. The dynamic properties of these components are determined in simulations and compared with the friction models available in the Modelica standard library. This includes also an automatic gearbox model where 6 friction elements are coupled dynamically.

Ratchet due to broken friction symmetry

DEFF Research Database (Denmark)

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

2002-01-01

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

Acoustics of friction

Science.gov (United States)

Akay, Adnan

2002-04-01

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

Low temperature internal friction in La75Al20Si5 metallic glass

International Nuclear Information System (INIS)

Zolotukhin, I.V.; Kalinin, Yu.E.

1991-01-01

Results of investigation of temperature dependence of internal friction (IF) in amorphous alloy La 75 Al 20 Si 5 are presented. The amorphous state was atteined by quenching from liquid melt at a rate of 10 5 -10 6 K/s. Two IF maxima at Q -1 (T) dependence are observed at the temperatures of 185 and 230 K. Increase in the frequency of mechanical vibrations results in the shift of IF maxima to the side of high temperatures, which indicates their relaxation origin. The first peak of IF in the studied alloy La 75 Al 20 Si 5 is in all probability related to reorientation of chemical bonds La-La and La-Al. The maximum at T∼230 K is related to the switching of La-Si chemical bonds

Statistical analysis of the low-temperature dislocation peak of internal friction (Bordoni peak) in nanostructured copper

International Nuclear Information System (INIS)

Vatazhuk, E.N.; Natsik, V.D.

2011-01-01

The temperature-frequency dependence of internal friction in the nanostructured samples of Cu and fibred composite C-32 vol.%Nb with the sizes of structure fragments approx 200 nm is analyzed. Experiments are used as initial information for such analysis. The characteristic for the heavily deformed copper Bordoni peak, located nearby a temperature 90 K, was recorded on temperature dependence of vibration decrement (frequencies 73-350 kHz) in previous experiments. The peak is due to the resonance interaction of sound with the system of thermal activated relaxators, and its width considerably greater in comparison with the width of standard internal friction peak with the single relaxation time. Statistical analysis of the peak is made in terms of assumption that the reason of broadening is random activation energy dispersion of relaxators as a result of intense distortion of copper crystal structure. Good agreement of experimental data and Seeger theory considers thermal activated paired kinks at linear segments of dislocation lines, placed in potential Peierls relief valley, as relaxators of Bordoni peak, was established. It is shown that the registered peak height in experiment correspond to presence at the average one dislocation segment in the interior of crystalline grain with size of 200 nm. Empirical estimates for the critical Peierls stress σp ∼ 2x10 7 Pa and integrated density of the interior grain dislocations ρ d ∼ 10 13 m -2 are made. Nb fibers in the composite Cu-Nb facilitate to formation of nanostructured copper, but do not influence evidently on the Bordoni peak.

A Physics-Based Rock Friction Constitutive Law: Steady State Friction

Science.gov (United States)

Aharonov, Einat; Scholz, Christopher H.

2018-02-01

Experiments measuring friction over a wide range of sliding velocities find that the value of the friction coefficient varies widely: friction is high and behaves according to the rate and state constitutive law during slow sliding, yet markedly weakens as the sliding velocity approaches seismic slip speeds. We introduce a physics-based theory to explain this behavior. Using conventional microphysics of creep, we calculate the velocity and temperature dependence of contact stresses during sliding, including the thermal effects of shear heating. Contacts are assumed to reach a coupled thermal and mechanical steady state, and friction is calculated for steady sliding. Results from theory provide good quantitative agreement with reported experimental results for quartz and granite friction over 11 orders of magnitude in velocity. The new model elucidates the physics of friction and predicts the connection between friction laws to independently determined material parameters. It predicts four frictional regimes as function of slip rate: at slow velocity friction is either velocity strengthening or weakening, depending on material parameters, and follows the rate and state friction law. Differences between surface and volume activation energies are the main control on velocity dependence. At intermediate velocity, for some material parameters, a distinct velocity strengthening regime emerges. At fast sliding, shear heating produces thermal softening of friction. At the fastest sliding, melting causes further weakening. This theory, with its four frictional regimes, fits well previously published experimental results under low temperature and normal stress.

Water weakening of chalk explaied from a fluid-solid friction factor

DEFF Research Database (Denmark)

Andreassen, Katrine Alling; Fabricius, Ida Lykke

2010-01-01

to where it is dominated by inertial forces, i.e. when the pore fluid motion lags behind the applied frequency. It is therefore a measure of the internal surface friction between solid and fluid which can be interpreted as a friction factor on the pore scale and we propose it can be extrapolated...... using the Biot critical frequency as a single reference. Other viscoplastic parameters were investigated in the same manner to verify the range of the functioning of the friction factor. The findings show that the Biot critical frequency can be used as a common friction factor and is useful in combining...... laboratory results. It is also inferred that the observed water weakening phenomenon may be attributed to the friction between solid and fluid....

Proposed apparatus for measuring internal friction in rocks at high temperatures and pressures: a design analysis

Energy Technology Data Exchange (ETDEWEB)

Bonner, B.P.

1977-10-03

An apparatus is described that measures internal friction in rocks at high temperatures (approximately 800/sup 0/C) and pressures (approximately 1.0 GPa). Steady oscillations (approximately 1.0 Hz) are induced in a jacketed sample while coaxial capacitive transducers monitor the resulting radial strain. Sample strains are continuously compared to the deformation of a low-loss standard, which acts as a stress transducer. The stress state produced is uniaxial stress. We use the theory of viscoelasticity to partition the loss into components depending on pure shear and dilatation. The theoretical results emphasize the importance of ultimately measuring each loss independently.

Internal friction of Fe-B alloys neutron irradiated at low temperature

International Nuclear Information System (INIS)

Kitajima, Kazunori; Futagami, Koji; Abe, Hironobu; Yoshida, Hiroyuki.

1975-01-01

Measurements were made on the internal friction of Fe-B alloys irradiated by neutron at 16 0 K to the dose of 3x10 16 nvt (>1 MeV) and 6x10 17 nvt (thermal). Boron was used to enhance the production of defects by the nuclear transformation B 10 (n,α)Li 7 . Relaxation peaks were found in specimens containing dispersed fine precipitates of NbB 2 in range of B 500--7200 wt ppm and Nb 2000--30000 wt ppm. The most prominent peak is the one with the peak temperature of 169 0 K at the frequency of 264 c/sec. Activation energy determined from the peak shift is 0.28+-0.01 eV, which is nearly equal to that of migration of self-interstitial reported on pure iron. However activation energy of the decay of peaks by annealing is about 0.7 eV. Interpretation was presented that the peak may be attributed to re-orientation of self-interstitials loosely bound to a boron atom. (auth.)

Internal friction studies on dynamic strain aging in P91 ferritic steel

International Nuclear Information System (INIS)

Zhou, Hongwei; Fang, Junfei; Chen, Yan; Yang, Lei; Zhang, Hui; Lu, Yun; He, Yizhu

2016-01-01

The temperature of dynamic strain aging (DSA) regime in P91 steel is between 523 K and 773 K. The activation energy (Q) for onset of DSA is 73 kJ/mol, while that for finale of DSA is 202 kJ/mol. Two main Internal friction (IF) speaks were observed, Snoek and SKK with the activation energy of 67.9 kJ/mol and 121 kJ/mol, respectively. IF shows that activation energy of 73 kJ/mol is equal to that of C atom body diffusion in α-Fe, and 202 kJ/mol is equal to binding energy between C atoms and moving dislocations. These results confirm that the mechanism of DSA can be explained by the diffusion of C atoms and pinning between C and moving dislocation. These investigations indicate that DSA in P91 steel is resulted from C atom diffusion, instead of Cr or Mo atoms.

PEBBLES Simulation of Static Friction and New Static Friction Benchmark

International Nuclear Information System (INIS)

Cogliati, Joshua J.; Ougouag, Abderrafi M.

2010-01-01

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

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

CERN Document Server

Abe, T; Kanari, M; Tanzawa, S

2002-01-01

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

Empirical analysis of skin friction under variations of temperature

International Nuclear Information System (INIS)

Parra Alvarez, A. R. de la; Groot Viana, M. de

2014-01-01

In soil geotechnical characterization, strength parameters, cohesion (c) and internal friction angle (Φ) has been traditional measured without taking into account temperature, been a very important issue in energy geostructures. The present document analyzes the variation of these parameters in soil-concrete interface at different temperatures. A traditional shear strength case with a forced plane of failure was used. Several tests were carried out to determine the variation of skin friction in granular and cohesive oils with temperature. (Author)

Rheology of confined granular flows: scale invariance, glass transition, and friction weakening.

Science.gov (United States)

Richard, P; Valance, A; Métayer, J-F; Sanchez, P; Crassous, J; Louge, M; Delannay, R

2008-12-12

We study fully developed, steady granular flows confined between parallel flat frictional sidewalls using numerical simulations and experiments. Above a critical rate, sidewall friction stabilizes the underlying heap at an inclination larger than the angle of repose. The shear rate is constant and independent of inclination over much of the flowing layer. In the direction normal to the free surface, the solid volume fraction increases on a scale equal to half the flowing layer depth. Beneath a critical depth at which internal friction is invariant, grains exhibit creeping and intermittent cage motion similar to that in glasses, causing gradual weakening of friction at the walls.

Financial frictions and substitution between internal and external funds in publicly traded Brazilian companies

Directory of Open Access Journals (Sweden)

Márcio Telles Portal

2012-04-01

Full Text Available The present study aimed to document the effects of financial constraints on the negative relationship between cash flow and external funds, a phenomenon associated with the Pecking Order Theory. This theory suggests that companies subject to more expensive external funds (financially constrained firms should demonstrate a stronger negative relationship with cash flow than companies subject to minor financial frictions (financially unconstrained firms. The results indicate that the external funds of constrained firms consistently present less negative sensitivity to cash flow compared with those of unconstrained companies. Additionally, the internal funds of constrained companies demonstrate a positive sensitivity to cash flow, whereas those of unconstrained companies do not show any such significant behavior. These results are in accordance with the findings of Almeida and Campello (2010, who suggest the following: first, because of the endogenous nature of investment decisions in constrained companies, the complementary relationship between internal and external funds prevails over the substitutive effects suggested by the Pecking Order Theory; and second, the negative relationship between cash flow and external funds cannot be interpreted as evidence of costly external funds and therefore does not corroborate the Pecking Order Theory.

Identification of GMS friction model without friction force measurement

International Nuclear Information System (INIS)

Grami, Said; Aissaoui, Hicham

2011-01-01

This paper deals with an online identification of the Generalized Maxwell Slip (GMS) friction model for both presliding and sliding regime at the same time. This identification is based on robust adaptive observer without friction force measurement. To apply the observer, a new approach of calculating the filtered friction force from the measurable signals is introduced. Moreover, two approximations are proposed to get the friction model linear over the unknown parameters and an approach of suitable filtering is introduced to guarantee the continuity of the model. Simulation results are presented to prove the efficiency of the approach of identification.

Recovery of amplitude dependent internal friction in plastically deformed LiF single crystals

International Nuclear Information System (INIS)

Koshimizu, S.

1977-01-01

The internal friction due to is studied interactions between point defects and dislocations produced in pure LiF single crystais by plastic deformation. The recovery of amplitude dependent damping is investigated in these crystais in the low frequency range. The logarithmic decrement is measured as a function of strain amplitude at several different temperatures in the range 8C - 35C in order to observe thermal breakaway. The results were interpred according to the theory developed by Granato and Lucke. Systematic measurements are also been carried out to determine the logarithmic decrement as a function of time at different temperatures, after driving the specimens at high strains amplitudes, yelding the following results: I) there is a recovery of the amplitude dependent damping upon removal of the high strain excitations, and II) the Kinetic of the recovery follows initially a t sup(2/3) ageing law, changing to tsup(1/3) afterwards [pt

Bioinspired orientation-dependent friction.

Science.gov (United States)

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.

Damage Tolerance Behavior of Friction Stir Welds in Aluminum Alloys

Science.gov (United States)

McGill, Preston; Burkholder, Jonathan

2012-01-01

Friction stir welding is a solid state welding process used in the fabrication of various aerospace structures. Self-reacting and conventional friction stir welding are variations of the friction stir weld process employed in the fabrication of cryogenic propellant tanks which are classified as pressurized structure in many spaceflight vehicle architectures. In order to address damage tolerance behavior associated with friction stir welds in these safety critical structures, nondestructive inspection and proof testing may be required to screen hardware for mission critical defects. The efficacy of the nondestructive evaluation or the proof test is based on an assessment of the critical flaw size. Test data describing fracture behavior, residual strength capability, and cyclic mission life capability of friction stir welds at ambient and cryogenic temperatures have been generated and will be presented in this paper. Fracture behavior will include fracture toughness and tearing (R-curve) response of the friction stir welds. Residual strength behavior will include an evaluation of the effects of lack of penetration on conventional friction stir welds, the effects of internal defects (wormholes) on self-reacting friction stir welds, and an evaluation of the effects of fatigue cycled surface cracks on both conventional and selfreacting welds. Cyclic mission life capability will demonstrate the effects of surface crack defects on service load cycle capability. The fracture data will be used to evaluate nondestructive inspection and proof test requirements for the welds.

Internal Friction of Austenitic Fe-Mn-C-Al Alloys

Science.gov (United States)

Lee, Young-Kook; Jeong, Sohee; Kang, Jee-Hyun; Lee, Sang-Min

2017-12-01

The internal friction (IF) spectra of Fe-Mn-C-Al alloys with a face-centered-cubic (fcc) austenitic phase were measured at a wide range of temperature and frequency ( f) to understand the mechanisms of anelastic relaxations occurring particularly in Fe-Mn-C twinning-induced plasticity steels. Four IF peaks were observed at 346 K (73 °C) (P1), 389 K (116 °C) (P2), 511 K (238 °C) (P3), and 634 K (361 °C) (P4) when f was 0.1 Hz. However, when f increased to 100 Hz, whereas P1, P2, and P4 disappeared, only P3 remained without the change in peak height, but with the increased peak temperature. P3 matches well with the IF peak of Fe-high Mn-C alloys reported in the literature. The effects of chemical composition and vacancy (v) on the four IF peaks were also investigated using various alloys with different concentrations of C, Mn, Al, and vacancy. As a result, the defect pair responsible for each IF peak was found as follows: a v-v pair for P1, a C-v pair for P2, a C-C pair for P3, and a C-C-v complex (major effect) + a Mn-C pair (minor effect) for P4. These results showed that the IF peaks of Fe-Mn-C-Al alloys reported previously were caused by the reorientation of C in C-C pairs, not by the reorientation of C in Mn-C pairs.

First and Second-Law Efficiency Analysis and ANN Prediction of a Diesel Cycle with Internal Irreversibility, Variable Specific Heats, Heat Loss, and Friction Considerations

Directory of Open Access Journals (Sweden)

M. M. Rashidi

2014-04-01

Full Text Available The variability of specific heats, internal irreversibility, heat and frictional losses are neglected in air-standard analysis for different internal combustion engine cycles. In this paper, the performance of an air-standard Diesel cycle with considerations of internal irreversibility described by using the compression and expansion efficiencies, variable specific heats, and losses due to heat transfer and friction is investigated by using finite-time thermodynamics. Artificial neural network (ANN is proposed for predicting the thermal efficiency and power output values versus the minimum and the maximum temperatures of the cycle and also the compression ratio. Results show that the first-law efficiency and the output power reach their maximum at a critical compression ratio for specific fixed parameters. The first-law efficiency increases as the heat leakage decreases; however the heat leakage has no direct effect on the output power. The results also show that irreversibilities have depressing effects on the performance of the cycle. Finally, a comparison between the results of the thermodynamic analysis and the ANN prediction shows a maximum difference of 0.181% and 0.194% in estimating the thermal efficiency and the output power. The obtained results in this paper can be useful for evaluating and improving the performance of practical Diesel engines.

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

Science.gov (United States)

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

Friction of elastomer-on-glass system and direct observation of its frictional interface

International Nuclear Information System (INIS)

Okamoto, Yoshihiro; Nishio, Kazuyuki; Sugiura, Jun-ichi; Hirano, Motohisa; Nitta, Takahiro

2007-01-01

We performed a study on the static friction of PDMS elastomers with well-defined surface topography sliding over glass. An experimental setup for simultaneous measurements of friction force and direct observations of frictional interface has been developed. The static friction force was nearly proportional to normal load. The static friction force was independent of stick time. The simultaneous measurements revealed that the static friction force was proportional to the total area of contact. The coefficient was nearly independent of the surface topography of PDMS elastomers

Effects of Si3+ and H+ Irradiation on Tungsten Evaluated by Internal Friction Method

International Nuclear Information System (INIS)

Hu Jing; Wang Xianping; Fang Qianfeng; Liu Changsong; Zhang Yanwen; Zhao Ziqiang

2013-01-01

Effects of Si 3+ and H + irradiation on tungsten were investigated by internal friction (IF) technique. Scanning electron microscope (SEM) analysis revealed that sequential dual Si+H irradiation resulted in more serious damage than single Si irradiation. After irradiation, the IF background was significantly enhanced. Besides, two obvious IF peaks were initially found in temperature range of 70∼330 K in the sequential Si+H irradiated tungsten sample. The mechanism of increased IF background for the irradiated samples was suggested to originate from the high density dislocations induced by ion irradiation. On the other hand, the relaxation peak P L and non-relaxation peak P H in the Si+H irradiated sample were ascribed to the interaction process of hydrogen atoms with mobile dislocations and transient processes of hydrogen redistribution, respectively. The obtained experimental results verified the high sensitivity of IF method on the irradiation damage behaviors in nuclear materials

Research on friction coefficient of nuclear Reactor Vessel Internals Hold Down Spring: Stress coefficient test analysis method

International Nuclear Information System (INIS)

Linjun, Xie; Guohong, Xue; Ming, Zhang

2016-01-01

Graphical abstract: HDS stress coefficient test apparatus. - Highlights: • This paper performs mathematic deduction to the physical model of Hold Down Spring (HDS), establishes a mathematic model of axial load P and stress, stress coefficient and friction coefficient and designs a set of test apparatuses for simulating the pretightening process of the HDS for the first time according to a model similarity criterion. • The mathematical relation between the load and the strain is obtained about the HDS, and the mathematical model of the stress coefficient and the friction coefficient is established. So, a set of test apparatuses for obtaining the stress coefficient is designed according to the model scaling criterion and the friction coefficient of the K1000 HDS is calculated to be 0.336 through the obtained stress coefficient. • The relation curve between the theoretical load and the friction coefficient is obtained through analysis and indicates that the change of the friction coefficient f would influence the pretightening load under the condition of designed stress. The necessary pretightening load in the design process is calculated to be 5469 kN according to the obtained friction coefficient. Therefore, the friction coefficient and the pretightening load under the design conditions can provide accurate pretightening data for the analysis and design of the reactor HDS according to the operations. - Abstract: This paper performs mathematic deduction to the physical model of Hold Down Spring (HDS), establishes a mathematic model of axial load P and stress, stress coefficient and friction coefficient and designs a set of test apparatuses for simulating the pretightening process of the HDS for the first time according to a model similarity criterion. By carrying out tests and researches through a stress testing technique, P–σ curves in loading and unloading processes of the HDS are obtained and the stress coefficient k f of the HDS is obtained. So, the

Research on friction coefficient of nuclear Reactor Vessel Internals Hold Down Spring: Stress coefficient test analysis method

Energy Technology Data Exchange (ETDEWEB)

Linjun, Xie, E-mail: linjunx@zjut.edu.cn [College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310014 (China); Guohong, Xue; Ming, Zhang [Shanghai Nuclear Engineering Research & Design Institute, Shanghai 200233 (China)

2016-08-01

Graphical abstract: HDS stress coefficient test apparatus. - Highlights: • This paper performs mathematic deduction to the physical model of Hold Down Spring (HDS), establishes a mathematic model of axial load P and stress, stress coefficient and friction coefficient and designs a set of test apparatuses for simulating the pretightening process of the HDS for the first time according to a model similarity criterion. • The mathematical relation between the load and the strain is obtained about the HDS, and the mathematical model of the stress coefficient and the friction coefficient is established. So, a set of test apparatuses for obtaining the stress coefficient is designed according to the model scaling criterion and the friction coefficient of the K1000 HDS is calculated to be 0.336 through the obtained stress coefficient. • The relation curve between the theoretical load and the friction coefficient is obtained through analysis and indicates that the change of the friction coefficient f would influence the pretightening load under the condition of designed stress. The necessary pretightening load in the design process is calculated to be 5469 kN according to the obtained friction coefficient. Therefore, the friction coefficient and the pretightening load under the design conditions can provide accurate pretightening data for the analysis and design of the reactor HDS according to the operations. - Abstract: This paper performs mathematic deduction to the physical model of Hold Down Spring (HDS), establishes a mathematic model of axial load P and stress, stress coefficient and friction coefficient and designs a set of test apparatuses for simulating the pretightening process of the HDS for the first time according to a model similarity criterion. By carrying out tests and researches through a stress testing technique, P–σ curves in loading and unloading processes of the HDS are obtained and the stress coefficient k{sub f} of the HDS is obtained. So, the

Modeling Friction Performance of Drill String Torsional Oscillation Using Dynamic Friction Model

Directory of Open Access Journals (Sweden)

Xingming Wang

2017-01-01

Full Text Available Drill string torsional and longitudinal oscillation can significantly reduce axial drag in horizontal drilling. An improved theoretical model for the analysis of the frictional force was proposed based on microscopic contact deformation theory and a bristle model. The established model, an improved dynamic friction model established for drill strings in a wellbore, was used to determine the relationship of friction force changes and the drill string torsional vibration. The model results were in good agreement with the experimental data, verifying the accuracy of the established model. The analysis of the influence of drilling mud properties indicated that there is an approximately linear relationship between the axial friction force and dynamic shear and viscosity. The influence of drill string torsional oscillation on the axial friction force is discussed. The results indicated that the drill string transverse velocity is a prerequisite for reducing axial friction. In addition, low amplitude of torsional vibration speed can significantly reduce axial friction. Then, increasing the amplitude of transverse vibration speed, the effect of axial reduction is not significant. In addition, by involving general field drilling parameters, this model can accurately describe the friction behavior and quantitatively predict the frictional resistance in horizontal drilling.

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

Science.gov (United States)

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.

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

Science.gov (United States)

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.

Internal friction evidence of intrinsic inhomogeneity in the paramagnetic region of La0.67Ca0.33MnO3

International Nuclear Information System (INIS)

Ma, Y.Q.; Song, W.H.; Zhao, B.C.; Zhang, R.L.; Yang, J.; Lu, W.J.; Du, J.J.; Sun, Y.P.

2005-01-01

We have investigated the optimally doped manganite La 0.67 Ca 0.33 MnO 3 by measurements of the resistivity ρ, magnetization M, Young's modulus E and internal friction Q - 1 . A remarkable peak in the Q - 1 curve is observed in the paramagnetic (PM) region, and it is attributed to the formation of magnetic clusters. Furthermore, this peak is characteristic of thermally activated relaxation. Our observation is discussed combined with the analysis of the electrical transport and magnetic properties in PM region

Friction analysis of kinetic schemes : the friction coefficient

NARCIS (Netherlands)

Lolkema, Juke S.

1995-01-01

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

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

DEFF Research Database (Denmark)

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

2003-01-01

of capillary bridges. However, there is no single value of the static friction coefficient, since it depends upon the initial dwell time and on rate of starting.We argue that the correct basis for the Coulomb friction law, which states that the friction force is proportional to the normal load...

Versatile Friction Stir Welding/Friction Plug Welding System

Science.gov (United States)

Carter, Robert

2006-01-01

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

Proximity friction reexamined

International Nuclear Information System (INIS)

Krappe, H.J.

1989-01-01

The contribution of inelastic excitations to radial and tangential friction form-factors in heavy-ion collisions is investigated in the frame-work of perturbation theory. The dependence of the form factors on the essential geometrical and level-density parameters of the scattering system is exhibited in a rather closed form. The conditions for the existence of time-local friction coefficients are discussed. Results are compared to form factors from other models, in particular the transfer-related proximity friction. For the radial friction coefficient the inelastic excitation mechanism seems to be the dominant contribution in peripheral collisions. (orig.)

Friction Pull Plug Welding in Aluminum Alloys

Science.gov (United States)

Brooke, Shane A.; Bradford, Vann

2012-01-01

NASA's Marshall Space Flight Center (MSFC) has recently invested much time and effort into the process development of Friction Pull Plug Welding (FPPW). FPPW, is a welding process similar to Friction Push Plug Welding in that, there is a small rotating part (plug) being spun and simultaneously pulled (forged) into a larger part. These two processes differ, in that push plug welding requires an internal reaction support, while pull plug welding reacts to the load externally. FPPW was originally conceived as a post proof repair technique for the Space Shuttle fs External Tank. FPPW was easily selected as the primary weld process used to close out the termination hole on the Constellation Program's ARES I Upper Stage circumferential Self-Reacting Friction Stir Welds (SR-FSW). The versatility of FPPW allows it to also be used as a repair technique for both SR-FSW and Conventional Friction Stir Welds. To date, all MSFC led development has been concentrated on aluminum alloys (2195, 2219, and 2014). Much work has been done to fully understand and characterize the process's limitations. A heavy emphasis has been spent on plug design, to match the various weldland thicknesses and alloy combinations. This presentation will summarize these development efforts including weld parameter development, process control, parameter sensitivity studies, plug repair techniques, material properties including tensile, fracture and failure analysis.

Evolution of the internal friction in SIC particle reinforced 8090 Al-Li metal matrix composite; Evolucion de la friccion interna del material compuesto de matriz Al-Li 8090 reforzado con particulas de SiC

Energy Technology Data Exchange (ETDEWEB)

Gutierrez-Urrutia, I.; Gallego, I.; No, M. L.; San Juan, J. M.

2001-07-01

The present study has been undertaken to investigate the mechanisms of thermal stress relief at the range of temperatures below room temperature for the metal matrix composite Al-Li 8090/SiC. For this aim the experimental technique of internal friction has been used which has been showed up very effective. Several thermal cycles from 453 K to 100 K were used in order to measures the internal friction as well as the elastic modules of the material concluding that thermal stresses are relaxed by microplastic deformation around the reinforcements. It has been also related the variation in the elastic modules with the different levels of precipitation. (Author) 18 refs.

Solvent friction effects propagate over the entire protein molecule through low-frequency collective modes.

Science.gov (United States)

Moritsugu, Kei; Kidera, Akinori; Smith, Jeremy C

2014-07-24

Protein solvation dynamics has been investigated using atom-dependent Langevin friction coefficients derived directly from molecular dynamics (MD) simulations. To determine the effect of solvation on the atomic friction coefficients, solution and vacuum MD simulations were performed for lysozyme and staphylococcal nuclease and analyzed by Langevin mode analysis. The coefficients thus derived are roughly correlated with the atomic solvent-accessible surface area (ASA), as expected from the fact that friction occurs as the result of collisions with solvent molecules. However, a considerable number of atoms with higher friction coefficients are found inside the core region. Hence, the influence of solvent friction propagates into the protein core. The internal coefficients have large contributions from the low-frequency modes, yielding a simple picture of the surface-to-core long-range damping via solvation governed by collective low-frequency modes. To make use of these findings in implicit-solvent modeling, we compare the all-atom friction results with those obtained using Langevin dynamics (LD) with two empirical representations: the constant-friction and the ASA-dependent (Pastor-Karplus) friction models. The constant-friction model overestimates the core and underestimates the surface damping whereas the ASA-dependent friction model, which damps protein atoms only on the solvent-accessible surface, reproduces well the friction coefficients for both the surface and core regions observed in the explicit-solvent MD simulations. Therefore, in LD simulation, the solvent friction coefficients should be imposed only on the protein surface.

Chemical origins of frictional aging.

Science.gov (United States)

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.

Friction in levitated superconductors

International Nuclear Information System (INIS)

Brandt, E.H.

1988-01-01

A type I superconductor levitated above a magnet of low symmetry has a unique equilibrium position about which it may oscillate freely. In contrast, a type II superconductor has a continuous range of stable equilibrium positions and orientations where it floats rigidly without swinging or orbiting as if it were stuck in sand. A strong internal friction conspicuously indicates the existence and unpinning of flux lines in oxide superconductors levitated above liquid nitrogen. It is shown how these effects follow from the hysteretic magnetization curves and how the energy is dissipated

Friction induced hunting limit cycles : a comparison between the LuGre and switch friction model

NARCIS (Netherlands)

Hensen, R.H.A.; Molengraft, van de M.J.G.; Steinbuch, M.

2003-01-01

In this paper, friction induced limit cycles are predicted for a simple motion system consisting of a motor-driven inertia subjected to friction and a PID-controlled regulator task. The two friction models used, i.e., (i) the dynamic LuGre friction model and (ii) the static switch friction model,

Novel friction law for the static friction force based on local precursor slipping.

Science.gov (United States)

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

2014-09-10

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

Static frictional resistance with the slide low-friction elastomeric ligature system.

Science.gov (United States)

Jones, Steven P; Ben Bihi, Saida

2009-11-01

This ex-vivo study compared the static frictional resistance of a low-friction ligation system against a conventional elastomeric module, and studied the effect of storage in a simulated oral environment on the static frictional resistance of both ligation systems. Eighty stainless steel brackets were tested by sliding along straight lengths of 0.018 inch round and 0.019 x 0.025 inch rectangular stainless steel wires ligated with either conventional elastomerics or the Slide system (Leone, Florence, Italy). During the tests the brackets and wires were lubricated with artificial saliva. A specially constructed jig assembly was used to hold the bracket and archwire securely. The jig was clamped in an Instron universal load testing machine. Crosshead speed was controlled via a microcomputer connected to the Instron machine. The static frictional forces at 0 degree bracket/wire angulation were measured for both systems, fresh from the pack and after storage in artificial saliva at 37 degrees C for 24 hours. The results of this investigation demonstrated that the Slide ligatures produced significantly lower static frictional resistance than conventional elastomeric modules in the fresh condition and after 24 hours of storage in a simulated oral environment (p static frictional resistance of conventional elastomeric modules and the Slide system (p = 0.525). The claim by the manufacturer that the Slide system produces lower frictional resistance than conventional elastomeric modules is upheld.

Nano-friction behavior of phosphorene.

Science.gov (United States)

Bai, Lichun; Liu, Bo; Srikanth, Narasimalu; Tian, Yu; Zhou, Kun

2017-09-01

Nano-friction of phosphorene plays a significant role in affecting the controllability and efficiency of applying strain engineering to tune its properties. So far, the friction behavior of phosphorene has not been studied. This work studies the friction of single-layer and bilayer phosphorene on an amorphous silicon substrate by sliding a rigid tip. For the single-layer phosphorene, it is found that its friction is highly anisotropic, i.e. the friction is larger along the armchair direction than that along the zigzag direction. Moreover, pre-strain of the phosphorene also exhibits anisotropic effects. The friction increases with the pre-strain along the zigzag direction, but decreases with that along the armchair direction. Furthermore, the strong adhesion between the phosphorene and its substrate increases the friction between the phosphorene and the tip. For bilayer phosphorene, its friction highly depends on its stacking mode, which determines the contact interface with a commensurate or incommensurate pattern. This friction behavior is quite unique and greatly differs from that of graphene and molybdenum disulfide. Detailed analysis reveals that this behavior results from the combination effect of the friction contact area, the potential-energy profile of phosphorene, and its unique elongation.

Frictional Heating with Time-Dependent Specific Power of Friction

Directory of Open Access Journals (Sweden)

Topczewska Katarzyna

2017-06-01

Full Text Available In this paper analytical solutions of the thermal problems of friction were received. The appropriate boundary-value problems of heat conduction were formulated and solved for a homogeneous semi–space (a brake disc heated on its free surface by frictional heat fluxes with different and time-dependent intensities. Solutions were obtained in dimensionless form using Duhamel's theorem. Based on received solutions, evolution and spatial distribution of the dimensionless temperature were analyzed using numerical methods. The numerical results allowed to determine influence of the time distribution of friction power on the spatio-temporal temperature distribution in brake disc.

High speed friction microscopy and nanoscale friction coefficient mapping

International Nuclear Information System (INIS)

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

2014-01-01

As mechanical devices in the nano/micro length scale are increasingly employed, it is crucial to understand nanoscale friction and wear especially at technically relevant sliding velocities. Accordingly, a novel technique has been developed for friction coefficient mapping (FCM), leveraging recent advances in high speed AFM. The technique efficiently acquires friction versus force curves based on a sequence of images at a single location, each with incrementally lower loads. As a result, true maps of the coefficient of friction can be uniquely calculated for heterogeneous surfaces. These parameters are determined at a scan velocity as fast as 2 mm s −1 for microfabricated SiO 2 mesas and Au coated pits, yielding results that are identical to traditional speed measurements despite being ∼1000 times faster. To demonstrate the upper limit of sliding velocity for the custom setup, the friction properties of mica are reported from 200 µm s −1 up to 2 cm s −1 . While FCM is applicable to any AFM and scanning speed, quantitative nanotribology investigations of heterogeneous sliding or rolling components are therefore uniquely possible, even at realistic velocities for devices such as MEMS, biological implants, or data storage systems. (paper)

Internal friction measurements of Mo after low-temperature proton irradiation

International Nuclear Information System (INIS)

Tanimoto, H.; Mizubayashi, H.; Masuda, R.; Okuda, S.; Tagishi, Y.

1992-01-01

Internal friction measurements are performed in Mo after 20 MeV proton irradiation in order to clarify the behavior of self-interstitial atoms (SIA's) in Mo. In the low dose range, strong dislocation pinning suggesting the free migration of defects is observed at about 40 K and weak pinning at about 25 K. The features are very similar to those reported after neutron irradiation except that the 25 K pinning is much smaller after proton irradiation. The result suggests that the migration of free SIA's is responsible for the 40 K pinning and that of SIA-defect clusters, probably di-SIA's, formed during irradiation for the 25 K pinning. In the high dose range, the relaxation peaks are observed at about 13 and 41 K, where the close similarities are found between the present peaks and the corresponding peaks reported after neutron irradiation except that the peak height of the 41 K peak per unit concentration of Frenkel pairs (FP) tends to increase strongly with decreasing dose here. The latter fact suggests the strong interaction between SIA's. Then the smallness of the 41 K peak reported after electron irradiation with very high dose could be explained by an increased interaction between SIA's, but not by the two-dimensional migration of SIA's as proposed by Jacques and Robrock. Deformation given prior to irradiation causes a drastic decrease in the modulus defects associated with FP's (so-called bulk effect) and in the 13 K peak height. After neutron irradiation, no such effect of deformation was reported. A possible origin for this difference is discussed. (orig.)

Frictional behaviour of high performance fibrous tows: Friction experiments

NARCIS (Netherlands)

Cornelissen, Bo; Rietman, Bert; Akkerman, Remko

2013-01-01

Tow friction is an important mechanism in the production and processing of high performance fibrous tows. The frictional behaviour of these tows is anisotropic due to the texture of the filaments as well as the tows. This work describes capstan experiments that were performed to measure the

Flow Function of Pharmaceutical Powders Is Predominantly Governed by Cohesion, Not by Friction Coefficients.

Science.gov (United States)

Leung, Lap Yin; Mao, Chen; Srivastava, Ishan; Du, Ping; Yang, Chia-Yi

2017-07-01

The purpose of this study was to demonstrate that the flow function (FFc) of pharmaceutical powders, as measured by rotational shear cell, is predominantly governed by cohesion but not friction coefficients. Driven by an earlier report showing an inverse correlation between FFc and the cohesion divided by the corresponding pre-consolidation stress (Wang et al. 2016. Powder Tech. 294:105-112), we performed analysis on a large data set containing 1130 measurements from a ring shear tester and identified a near-perfect inverse correlation between the FFc and cohesion. Conversely, no correlation was found between FFc and friction angles. We also conducted theoretical analysis and estimated such correlations based on Mohr-Coulomb failure model. We discovered that the correlation between FFc and cohesion can sustain as long as the angle of internal friction at incipient flow is not significantly larger than the angle of internal friction at steady-state flow, a condition covering almost all pharmaceutical powders. The outcome of this study bears significance in pharmaceutical development. Because the cohesion value is strongly influenced by the interparticle cohesive forces, this study effectively shows that it is more efficient to improve the pharmaceutical powder flow by lowering the interparticle cohesive forces than by lowering the interparticle frictions. Copyright © 2017 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Internal friction behaviors of Ni-Mn-In magnetic shape memory alloy with two-step structural transformation

Directory of Open Access Journals (Sweden)

Zhen-ni Zhou

2017-06-01

Full Text Available The internal friction (IF behaviors of dual-phase Ni52Mn32In16 alloy with two-step structural transformation were investigated by dynamic mechanical analyzer. The IF peak for the martensite transformation (MT is an asymmetric shoulder rather than those sharp peaks for other shape memory alloys. The intermartensitic transformation (IMT peak has the maximum IF value. As the heating rate increases, the height of the IMT peak increases and its position is shifted to higher temperatures. In comparison with the IMT peak, the MT peak is independent on the heating rate. The starting temperatures of the IMT peak are strongly dependent on frequency, while the MT peak is weakly dependent. Meanwhile, the heights of both the MT and IMT peak rapidly decrease with increasing the frequency. This work also throws new light on their structural transformation mechanisms.

Effect of Process Parameters on Friction Model in Computer Simulation of Linear Friction Welding

Directory of Open Access Journals (Sweden)

A. Yamileva

2014-07-01

Full Text Available The friction model is important part of a numerical model of linear friction welding. Its selection determines the accuracy of the results. Existing models employ the classical law of Amonton-Coulomb where the friction coefficient is either constant or linearly dependent on a single parameter. Determination of the coefficient of friction is a time consuming process that requires a lot of experiments. So the feasibility of determinating the complex dependence should be assessing by analysis of effect of approximating law for friction model on simulation results.

METHODS TO MEASURE, PREDICT AND RELATE FRICTION, WEAR AND FUEL ECONOMY

Energy Technology Data Exchange (ETDEWEB)

Gravante, Steve [Ricardo, Inc.; Fenske, George [Argonne National Lab. (ANL), Argonne, IL (United States); Demas, Nicholas [Argonne National Lab. (ANL), Argonne, IL (United States); Erck, Robert [Argonne National Lab. (ANL), Argonne, IL (United States)

2018-03-19

High-fidelity measurements of the coefficient of friction and the parasitic friction power of the power cylinder components have been made for the Isuzu 5.2L 4H on-highway engine. In particular, measurements of the asperity friction coefficient were made with test coupons using Argonne National Lab’s (ANL) reciprocating test rig for the ring-on-liner and skirt-on-liner component pairs. These measurements correlated well with independent measurements made by Electro-Mechanical Associates (EMA). In addition, surface roughness measurements of the Isuzu components were made using white light interferometer (WLI). The asperity friction and surface characterization are key inputs to advanced CAE simulation tools such as RINGPAK and PISDYN which are used to predict the friction power and wear rates of power cylinder components. Finally, motored friction tests were successfully performed to quantify the friction mean effective pressure (FMEP) of the power cylinder components for various oils (High viscosity 15W40, low viscosity 5W20 with friction modifier (FM) and specially blended oil containing consisting of PAO/ZDDP/MoDTC) at 25, 50, and 110 °C. Ricardo's objective is to use this data along with advanced CAE methods to develop empirical characterizations of friction and wear mechanisms in internal combustion engines such that the impact of such mechanisms of engine fuel consumption and/or vehicle fuel economy can be estimated. The value of such predictive schemes is that if one knows how a particular friction reduction technology changes oil viscosity and/or the friction coefficient then the fuel consumption or fuel economy impacts can be estimated without the excessive cost of motored or fired engine tests by utilizing cost effective lab scale tests and in combination with advanced analytical methods. One accomplishment made during this work was the development and validation of a novel technique for quantifying wear using data from WLI through the use of

Friction-induced Vibrations in an Experimental Drill-string System for Various Friction Situations

NARCIS (Netherlands)

Mihajlovic, N.; Wouw, van de N.; Hendriks, M.P.M.; Nijmeijer, H.

2005-01-01

Friction-induced limit cycling deteriorates system performance in a wide variety of mechanical systems. In this paper, we study the way in which essential friction characteristics affect the occurrence and nature of friction-induced limit cycling in flexible rotor systems. This study is performed on

A Generic Friction Model for Radial Slider Bearing Simulation Considering Elastic and Plastic Deformation

Directory of Open Access Journals (Sweden)

Günter Offner

2015-06-01

Full Text Available The investigation of component dynamics is one of the main tasks of internal combustion engine (ICE simulation. This prediction is important in order to understand complex loading conditions, which happen in a running ICE. Due to the need for fuel saving, mechanical friction, in particular in radial slider bearings, is one important investigation target. A generic friction modeling approach for radial slider bearings, which can be applied to lubricated contact regimes, will be presented in this paper. Besides viscous friction, the approach considers in particular boundary friction. The parameterization of the friction model is done using surface material and surface roughness measurement data. Furthermore, fluid properties depending on the applied oil additives are being considered. The application of the model will be demonstrated for a typical engineering task of a connecting rod big end study to outline the effects of contact surface texture. AlSn-based and polymer coated bearing shells will be analyzed and compared with respect to friction reduction effects, running-in behavior and thermal load capabilities.

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

NARCIS (Netherlands)

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

2004-01-01

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

Internal friction and elastic modulus of NdxY1-xBa2Cu3Oy (x 0.0-1.0) at 200 kHz near the orthorhombic-to-tetragonal phase transition

International Nuclear Information System (INIS)

Inagaki, M.

2000-01-01

The internal friction and Young's modulus of a series of superconductors Nd x Y 1-x Ba 2 Cu 3 O y (x = 0.0-1.0) were measured over the temperature range from 300 to 1050 K using a 200 kHz LiNbO3 piezoelectric composite oscillator. Anelastic relaxation peaks due to oxygen migration were observed at about 850 K. The minimum Young's modulus, which is related to the orthorhombic-to-tetragonal phase transition, was also observed near this temperature. The temperature at the minimum Young's modulus decreased with an increase in the neodymium composition. In contrast, the internal friction peak temperature showed an unsystematic shift with an increase in x, while changes of the average cell structure exhibited a linear relationship when plotted versus the average ionic radius for trivalent rare-earth ions with the coordination number eight. (author)

Science 101: What Causes Friction?

Science.gov (United States)

Robertson, Bill

2014-01-01

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

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

OpenAIRE

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

2014-01-01

The sliding of a solid object on a solid substrate requires a shear force that is larger than the maximum static friction force. It is commonly believed that the maximum static friction force is proportional to the loading force and does not depend on the apparent contact area. The ratio of the maximum static friction force to the loading force is called the static friction coefficient µ M, which is considered to be a constant. Here, we conduct experiments demonstrating that the static fricti...

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

Science.gov (United States)

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.

Corrosion effects on friction factors

International Nuclear Information System (INIS)

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

1996-01-01

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

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

Science.gov (United States)

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 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.

Origins of Rolling Friction

Science.gov (United States)

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…

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

Science.gov (United States)

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.

Characterization of friction and wear behavior of friction modifiers used in wheel-rail contacts

NARCIS (Netherlands)

Oomen, M. A.; Bosman, R.; Lugt, P. M.

2017-01-01

Reliable traction between wheel and rail is an important issue in the railway industry. To reduce variations in the coefficient of friction, so-called “friction modifiers” (carrier with particles) are used. Twin-disk tests were done with three commercial friction modifiers, based on different

Tactile friction of topical formulations.

Science.gov (United States)

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

2016-02-01

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

Friction laws at the nanoscale.

Science.gov (United States)

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.

Modelling of the temperature field that accompanies friction stir welding

Directory of Open Access Journals (Sweden)

Nosal Przemysław

2017-01-01

Full Text Available The thermal modelling of the Friction Stir Welding process allows for better recognition and understanding of phenomena occurring during the joining process of different materials. It is of particular importance considering the possibilities of process technology parameters, optimization and the mechanical properties of the joint. This work demonstrates the numerical modelling of temperature distribution accompanying the process of friction stir welding. The axisymmetric problem described by Fourier’s type equation with internal heat source is considered. In order to solve the diffusive initial value problem a fully implicit scheme of the finite difference method is applied. The example under consideration deals with the friction stir welding of a plate (0.7 cm thick made of Al 6082-T6 by use of a tool made of tungsten alloy, whereas the material subjected to welding was TiC powder. Obtained results confirm both quantitatively and qualitatively experimental observations that the superior temperature corresponds to the zone where the pin joints the shoulder.

Friction surfaced Stellite6 coatings

International Nuclear Information System (INIS)

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

2012-01-01

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: ► Stellite6 used as coating material for friction surfacing. ► Friction surfaced (FS) coatings compared with casting, GTA and PTA processes. ► Finer and uniformly distributed carbides in friction surfaced coatings. ► Absence of melting results compositional homogeneity in FS Stellite6 coatings.

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

Science.gov (United States)

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

Argo packing friction research update

International Nuclear Information System (INIS)

VanTassell, D.M.

1994-01-01

This paper focuses on the issue of valve packing friction and its affect on the operability of motor- and air-operated valves (MOVs and AOVs). At this time, most nuclear power plants are required to perform postmaintenance testing following a packing adjustment or replacement. In many cases, the friction generated by the packing does not impact the operability window of a valve. However, to date there has not been a concerted effort to substantiate this claim. To quantify the effects of packing friction, it has become necessary to develop a formula to predict the friction effects accurately. This formula provides a much more accurate method of predicting packing friction than previously used factors based strictly on stem diameter. Over the past 5 years, Argo Packing Company has been developing and testing improved graphite packing systems at research facilities, such as AECL Chalk River and Wyle Laboratories. Much of this testing has centered around reducing and predicting friction that is related to packing. In addition, diagnostic testing for Generic Letter 89-10 MOVs and AOVs has created a significant data base. In July 1992 Argo asked several utilities to provide running load data that could be used to quantify packing friction repeatability and predictability. This technical paper provides the basis to predict packing friction, which will improve calculations for thrust requirements for Generic Leter 89-10 and future AOV programs. In addition, having an accurate packing friction formula will improve packing performance when low running loads are identified that would indicate insufficient sealing force

Study about internal friction in deformed - and irradiated pure titanium

International Nuclear Information System (INIS)

Miyada, L.T.

1979-01-01

Internal friction and modulus are measured in pure Ti at low temperature using an inverted torsion-pendulum at about 1 Hz. The presence of four relaxation peaks P' sub(d)(-140 0 C), P sub(d)(-101 0 C), P' sub(α)(-75 0 C) and P sub(α)(-50 0 C) has been found, and effects of plastic deformation, heat treatment and neutron irradiation on these peaks are investigated in detail. Activation energies and frequency factors of P sub(d) and Pα peaks are consistent with the data in higher frequency range reproted by other workers. The P sub(d) and P' sub(d) peaks grow after deformation and tend to decay after annealing at high temperatures or after neutron irradiation. Both peaks are resonably interpreted in terms of dislocation relaxation mechanisms (Bordoni type) arising from thermally activated motion of dislocations in different slip planes of h.c.f. structure. Peierls stress of dislocations giving rise to each peak have calculated based on Seeger's theory, and found to be consistent with that of f.c.c. metals. On the other hand, P sub(α) and P' sub(α) peaks grow significantly at the expense of P sub(d) and P' sub(d) peaks after neutron irradiation in deformed samples. The behaviour of these peaks as a function of irradiation dose and annealing temperatures strongly indicated that they are due to relaxations resulting from dislocations-point defects interactions (Hasiguti type). It is tentatively suggested that P sub(α) and P' sub(α) peaks are related with interactions of dislocations with divacancies and single vacancies, respectively. Application of Schiller's model showed a consistent result with regard to the P' sub(α) peak experimentally observed. (Author) [pt

Effect of grafted oligopeptides on friction.

Science.gov (United States)

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.

Frictional performance of ball screw

International Nuclear Information System (INIS)

Nakashima, Katuhiro; Takafuji, Kazuki

1985-01-01

As feed screws, ball screws have become to be adopted in place of trapezoidal threads. The structure of ball screws is complex, but those are the indispensable component of NC machine tools and machining centers, and are frequently used for industrial robots. As the problems in the operation of ball screws, there are damage, life and the performance related to friction. As to the damage and life, though there is the problem of the load distribution on balls, the results of the research on rolling bearings are applied. The friction of ball screws consists of the friction of balls and a spiral groove, the friction of a ball and a ball, the friction in a ball-circulating mechanism and the viscous friction of lubricating oil. It was decided to synthetically examine the frictional performance of ball screws, such as driving torque, the variation of driving torque, efficiency, the formation of oil film and so on, under the working condition of wide range, using the screws with different accuracy and the nuts of various circuit number. The experimental setup and the processing of the experimental data, the driving performance of ball screws and so on are reported. (Kako, I.)

Effects of antimony trisulfide (Sb2S3) on sliding friction of automotive brake friction materials

Science.gov (United States)

Lee, Wan Kyu; Rhee, Tae Hee; Kim, Hyun Seong; Jang, Ho

2013-09-01

The effect of antimony trisulfide (Sb2S3) on the tribological properties of automotive brake friction materials was investigated using a Krauss type tribometer and a 1/5 scale dynamometer with a rigid caliper. Results showed that Sb2S3 improved fade resistance by developing transfer films on the disc surface at elevated temperatures. On the other hand, the rubbing surfaces of the friction material exhibited contact plateaus with a broader height distribution when it contained Sb2S3, indicating fewer contact junctions compared to the friction material with graphite. The friction material with Sb2S3 also exhibited a lower stick-slip propensity than the friction material with graphite. The improved fade resistance with Sb2S3 is attributed to its lubricating capability sustained at high temperatures, while the lower stick-slip propensity of the friction material with Sb2S3 is associated with the slight difference between its static and kinetic coefficients of friction and high normal stiffness.

Computational Analysis of Material Flow During Friction Stir Welding of AA5059 Aluminum Alloys

Science.gov (United States)

2011-01-01

structures in Finland; (b) manufacture of Al-Mg-Si-based alloy 181 FSW-joined bullet- train cabins in Japan; (c) fabrication of 182 Al-Cu-based alloy...Simonsen, Visualisation of Material 857Flow in an Autogenous Friction Stir Weld, Proc. 1st International 858Symp. FSW, Thousand Oaks, CA, 1999 85928...A.P. Reynolds, Visualization of Material Flow in an Autogenous 860Friction Stir Weld, Sci. Technol. Weld. Join., 2000, 5, p 120–124 86129. T.U. Seidel

Friction Welding For Cladding Applications: Processing, Microstructure and Mechanical Properties of Inertia Friction Welds of Stainless Steel to Low Carbon Steel and Evaluation of Wrought and Welded Austenitic Stainless Steels for Cladding Applications in Acidchloride Service

Science.gov (United States)

Switzner, Nathan

Friction welding, a solid-state joining method, is presented as a novel alternative process step for lining mild steel pipe and forged components internally with a corrosion resistant (CR) metal alloy for petrochemical applications. Currently, fusion welding is commonly used for stainless steel overlay cladding, but this method is costly, time-consuming, and can lead to disbonding in service due to a hard martensite layer that forms at the interface due to partial mixing at the interface between the stainless steel CR metal and the mild steel base. Firstly, the process parameter space was explored for inertia friction butt welding using AISI type 304L stainless steel and AISI 1018 steel to determine the microstructure and mechanical properties effects. A conceptual model for heat flux density versus radial location at the faying surface was developed with consideration for non-uniform pressure distribution due to frictional forces. An existing 1 D analytical model for longitudinal transient temperature distribution was modified for the dissimilar metals case and to account for material lost to the flash. Microstructural results from the experimental dissimilar friction welds of 304L stainless steel to 1018 steel were used to discuss model validity. Secondly, the microstructure and mechanical property implications were considered for replacing the current fusion weld cladding processes with friction welding. The nominal friction weld exhibited a smaller heat softened zone in the 1018 steel than the fusion cladding. As determined by longitudinal tensile tests across the bond line, the nominal friction weld had higher strength, but lower apparent ductility, than the fusion welds due to the geometric requirements for neck formation adjacent to a rigid interface. Martensite was identified at the dissimilar friction weld interface, but the thickness was smaller than that of the fusion welds, and the morphology was discontinuous due to formation by a mechanism of solid

Effect of friction time on the microstructure and mechanic properties of friction welded AISI 1040/Duplex stainless steel

Directory of Open Access Journals (Sweden)

İhsan Kırık

2000-06-01

Full Text Available In this study, the effect on the characteristic microstructure and mechanic properties of friction time on the couple steels AISI 1040/AISI 2205 stainless steel joining with friction welding method was experimentally investigated. Friction welding experiment were carried out in privately prepared PLC controlled continuous friction welding machine by us. Joints were carried out under 1700 rpm rotation speed, with 30MPa process friction pressure, 60MPa forging pressure, 4 second forging pressure and under 3, 5, 7, 9 and 11 second friction time, respectively. After friction welding, the bonding interface microstructures of the specimens were examined by SEM microscopy and EDS analysis. After weld microhardness and tensile strength of specimens were carried out. The result of applied tests and observations pointed out that the properties of microstructure were changed with friction time increased. The excellent tensile strength of joint observed on 1700 rpm rotation speed and 3 second friction time sample.

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

Science.gov (United States)

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.

Friction in sheet metal forming

DEFF Research Database (Denmark)

Wiklund, D.; Liljebgren, M.; Berglund, J.

2010-01-01

and calls for functional tool surfaces that are durable in these severe tribological conditions. In this study the influence of tool surface topography on friction has been investigated. The frictional response was studied in a Bending Under Tension test. The results did show that a low frictional response...

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

Science.gov (United States)

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.

Analysis of tablet compaction. I. Characterization of mechanical behavior of powder and powder/tooling friction.

Science.gov (United States)

Cunningham, J C; Sinka, I C; Zavaliangos, A

2004-08-01

In this first of two articles on the modeling of tablet compaction, the experimental inputs related to the constitutive model of the powder and the powder/tooling friction are determined. The continuum-based analysis of tableting makes use of an elasto-plastic model, which incorporates the elements of yield, plastic flow potential, and hardening, to describe the mechanical behavior of microcrystalline cellulose over the range of densities experienced during tableting. Specifically, a modified Drucker-Prager/cap plasticity model, which includes material parameters such as cohesion, internal friction, and hydrostatic yield pressure that evolve with the internal state variable relative density, was applied. Linear elasticity is assumed with the elastic parameters, Young's modulus, and Poisson's ratio dependent on the relative density. The calibration techniques were developed based on a series of simple mechanical tests including diametrical compression, simple compression, and die compaction using an instrumented die. The friction behavior is measured using an instrumented die and the experimental data are analyzed using the method of differential slices. The constitutive model and frictional properties are essential experimental inputs to the finite element-based model described in the companion article. Copyright 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:2022-2039, 2004

High-velocity frictional properties of gabbro

Science.gov (United States)

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.

Friction and wear calculation methods

CERN Document Server

Kragelsky, I V; Kombalov, V S

1981-01-01

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

Friction and anchorage loading revisited.

Science.gov (United States)

Dholakia, Kartik D

2012-01-01

Contemporary concepts of sliding mechanics explain that friction is inevitable. To overcome this frictional resistance, excess force is required to retract the tooth along the archwire (ie, individual retraction of canines, en masse retraction of anterior teeth), in addition to the amount of force required for tooth movement. The anterior tooth retraction force, in addition to excess force (to overcome friction), produces reciprocal protraction force on molars, thereby leading to increased anchorage loading. However, this traditional concept was challenged in recent literature, which was based on the finite element model, but did not bear correlation to the clinical scenario. This article will reinforce the fact that clinically, friction increases anchorage loading in all three planes of space, considering the fact that tooth movement is a quasistatic process rather than a purely continuous or static one, and that conventional ways of determining the effects of static or dynamic friction on anchorage load cannot be applied to clinical situations (which consist of anatomical resistance units and a complex muscular force system). The article does not aim to quantify friction and its effect on the amount of anchorage load. Rather, a new perspective regarding the role of various additional factors (which is not explained by contemporary concept) that may influence friction and anchorage loading is provided..

Study of the dislocation contribution to the internal friction background of gold

Science.gov (United States)

Baur, J.; Benoit, W.

1987-04-01

The dislocation contribution to the internal friction (IF) background is studied in annealed gold samples containing various dilute concentrations of platinum impurities. The measurements are performed in the kHz frequency range in order to determine the loss mechanism responsible for the high IF background observed at these low frequencies. To this end, the IF background was systematically measured as a function of frequency, vibration amplitude, temperature, and impurity concentration. The experimental results show that the high dislocation contribution observed in annealed samples is strain-amplitude independent for amplitudes in the range 10-7 to 2×10-6, but rapidly decreases for amplitudes smaller than 10-7. In particular, the dislocation contribution tends to zero when the strain amplitude tends to zero. Furthermore, this contribution is frequency independent. These observations demonstrate that the dislocation contribution cannot be explained by relaxations. In particular, this contribution cannot be attributed to a viscous damping of the dislocation motion. On the contrary, the experiments show that the IF background due to dislocations must be explained by hysteretic and athermal motions of dislocations interacting with point defects. However, these hysteretic motions are not due to breakaway of dislocations from pinning points distributed along their length. The experimental results can be explained by the presence of point defects close to the dislocations, but not on them. The mechanical energy loss is attributed to hysteretic motions of dislocations between potential minima created by point defects.

The effect of friction in coulombian damper

Science.gov (United States)

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.

Effect of hexagonal boron nitride and calcined petroleum coke on friction and wear behavior of phenolic resin-based friction composites

International Nuclear Information System (INIS)

Yi Gewen; Yan Fengyuan

2006-01-01

Calcined petroleum coke (CPC) and hexagonal boron nitride (h-BN) were used as the friction modifiers to improve the friction and wear properties of phenolic resin-based friction composites. Thus, the composites with different relative amounts of CPC and h-BN as the friction modifiers were prepared by compression molding. The hardness and bending strength of the friction composites were measured. The friction and wear behaviors of the composites sliding against cast iron at various temperatures were evaluated using a pin-on-disc test rig. The worn surfaces and wear debris of the friction composites were analyzed by means of scanning electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. It was found that the hybrid of the two friction modifiers was effective to significantly decrease the wear rate and stabilize the friction coefficient of the friction composites at various temperatures by forming a uniform lubricating and/or transferred film on the rubbing surfaces. The uniform and durable transfer films were also able to effectively diminish the direct contact between the friction composite and the cast iron counterpart and hence prevent severe wear of the latter as well. The effectiveness of the hybrid of CPC and h-BN in improving the friction and wear behavior of the phenolic resin-based friction modifiers could be attributed to the complementary action of the 'low temperature' lubricity of CPC and the 'high temperature' lubricity of h-BN. The optimum ratio of the two friction modifiers CPC and h-BN in the friction composites was suggested to be 1:1, and the corresponding friction composite showed the best friction-reducing and antiwear abilities

Advances on LuGre friction model

OpenAIRE

Fuad, Mohammad; Ikhouane, Fayçal

2013-01-01

LuGre friction model is an ordinary differential equation that is widely used in describing the friction phenomenon for mechanical systems. The importance of this model comes from the fact that it captures most of the friction behavior that has been observed including hysteresis. In this paper, we study some aspects related to the hysteresis behavior induced by the LuGre friction model.

A Pedagogical Model of Static Friction

OpenAIRE

Pickett, Galen T.

2015-01-01

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

Friction in volcanic environments

Science.gov (United States)

Kendrick, Jackie E.; Lavallée, Yan

2016-04-01

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

Friction coefficient dependence on electrostatic tribocharging.

Science.gov (United States)

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.

Progressive friction mobilization and enhanced Janssen's screening in confined granular rafts

Science.gov (United States)

Saavedra V., Oscar; Elettro, Hervé; Melo, Francisco

2018-04-01

Confined two-dimensional assemblies of floating particles, known as granular rafts, are prone to develop a highly nonlinear response under compression. Here we investigate the transition to the friction-dominated jammed state and map the gradual development of the internal stress profile with flexible pressure sensors distributed along the raft surface. Surprisingly, we observe that the surface stress screening builds up much more slowly than previously thought and that the typical screening distance later dramatically decreases. We explain this behavior in terms of progressive friction mobilization, where the full amplitude of the frictional forces is only reached after a macroscopic local displacement. At further stages of compression, rafts of large length-to-width aspect ratio experience much stronger screenings than the full mobilization limit described by the Janssen's model. We solve this paradox using a simple mathematical analysis and show that such enhanced screening can be attributed to a localized compaction front, essentially shielding the far field from compressive stresses.

The impact of microgeometry pistons with a stepped bearing surface for the friction loss of the internal combustion engine

Directory of Open Access Journals (Sweden)

Wroblewski Emil

2017-01-01

Full Text Available This paper present the results of experimental piston friction losses on stepped bearing surface microgeometry obtained on the test rig. This test rig is equipped with special temperature control system, which provides better stability to temperature than in standard systems. The results of station tests was discussed. Tests was analyzed depending the moment caused by the friction on the oil temperature in the oil sump. Specified conclusions allow to assess the impact of the stepped profile of the pistons bearing surface microgeometry for different values of engine speed and the oil temperature at the friction losses in the main kinematic engine node which is piston-cylinder.

Chirality-dependent friction of bulk molecular solids.

Science.gov (United States)

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.

A Simple Device For Measuring Skin Friction

Directory of Open Access Journals (Sweden)

Gupta A.B

1995-01-01

Full Text Available A simple device for measuring skin friction in vivo is described. The frictional coefficient of normal Indian skin and the effect of hydration and application of talc and glycerol on the frictional coefficient and also the friction of ichthyotic skin have been determined with its help. The average value of friction of friction of normal India skin at forearm is found to be 0.41 +- 0.08, the hydration raises the value to 0.71 +- 0.11 and the effect of glycerol is also to school it up to 0.70+- 0.05, almost equal to that of water. The effect of talc however is opposite and its application lowers the friction to 0.21+-0.07. The mean coeff of friction for ichthyotic skin is found to be 0.21+- 0.0.5, which closely agrees with talc-treated normal skin. A good positive correlation (p<0.01 between friction and sebum level at skin site, with r = 0.64, has been observed.

The role of financing frictions in agricultural investment decisions: an analysis pre and post financial crisis

OpenAIRE

O'Toole, Conor M.; Newman, Carol F.; Hennessy, Thia C.

2011-01-01

This paper uses a fundamental Q model of investment to consider the role played by financing frictions in agricultural investment decisions, controlling econometrically for censoring, heterogeneity and errors-in-variables. Our findings suggest that farmer's investment decisions are not driven by market fundamentals. We find some evidence that debt overhang restricts investment but investment is not dependent on liquidity or internal funds. The role of financing frictions in determining invest...

Frictional and elastic energy in gecko adhesive detachment.

Science.gov (United States)

Gravish, Nick; Wilkinson, Matt; Autumn, Kellar

2008-03-06

Geckos use millions of adhesive setae on their toes to climb vertical surfaces at speeds of over 1 m s(-1). Climbing presents a significant challenge for an adhesive since it requires both strong attachment and easy, rapid removal. Conventional pressure-sensitive adhesives are either strong and difficult to remove (e.g. duct tape) or weak and easy to remove (e.g. sticky notes). We discovered that the energy required to detach adhering tokay gecko setae (W(d)) is modulated by the angle (theta) of a linear path of detachment. Gecko setae resist detachment when dragged towards the animal during detachment (theta = 30 degrees ) requiring W(d) = 5.0+/-0.86(s.e.) J m(-2) to detach, largely due to frictional losses. This external frictional loss is analogous to viscous internal frictional losses during detachment of pressure-sensitive adhesives. We found that, remarkably, setae possess a built-in release mechanism. Setae acted as springs when loaded in tension during attachment and returned elastic energy when detached along the optimal path (theta=130 degrees ), resulting in W(d) = -0.8+/-0.12 J m(-2). The release of elastic energy from the setal shaft probably causes spontaneous release, suggesting that curved shafts may enable easy detachment in natural, and synthetic, gecko adhesives.

Non-uniform Pressure Distribution in Draw-Bend Friction Test and its Influence on Friction Measurement

International Nuclear Information System (INIS)

Kim, Young Suk; Jain, Mukesh K.; Metzger, Don R.

2005-01-01

From various draw-bend friction tests with sheet metals at lubricated conditions, it has been unanimously reported that the friction coefficient increases as the pin diameter decreases. However, a proper explanation for this phenomenon has not been given yet. In those experiments, tests were performed for different pin diameters while keeping the same average contact pressure by adjusting applied tension forces. In this paper, pressure profiles at pin/strip contacts and the changes in the pressure profiles depending on pin diameters are investigated using finite element simulations. To study the effect of the pressure profile changes on friction measurements, a non-constant friction model (Stribeck friction model), which is more realistic for the lubricated sheet metal contacts, is implemented into the finite element code and applied to the simulations. The study shows that the non-uniformity of the pressure profile increases and the pin/strip contact angle decreases as the pin diameter decreases, and these phenomena increase the friction coefficient, which is calculated from the strip tension forces using a conventional rope-pulley equation

Modeling and data analysis of the NASA-WSTF frictional heating apparatus - Effects of test parameters on friction coefficient

Science.gov (United States)

Zhu, Sheng-Hu; Stoltzfus, Joel M.; Benz, Frank J.; Yuen, Walter W.

1988-01-01

A theoretical model is being developed jointly by the NASA White Sands Test Facility (WSTF) and the University of California at Santa Barbara (UCSB) to analyze data generated from the WSTF frictional heating test facility. Analyses of the data generated in the first seconds of the frictional heating test are shown to be effective in determining the friction coefficient between the rubbing interfaces. Different friction coefficients for carobn steel and Monel K-500 are observed. The initial condition of the surface is shown to affect only the initial value of the friction coefficient but to have no significant influence on the average steady-state friction coefficient. Rotational speed and the formation of oxide film on the rotating surfaces are shown to have a significant effect on the friction coefficient.

Kinetic Friction of Sport Fabrics on Snow

Directory of Open Access Journals (Sweden)

Werner Nachbauer

2016-03-01

Full Text Available After falls, skiers or snowboarders often slide on the slope and may collide with obstacles. Thus, the skier’s friction on snow is an important factor to reduce incidence and severity of impact injuries. The purpose of this study was to measure snow friction of different fabrics of ski garments with respect to roughness, speed, and contact pressure. Three types of fabrics were investigated: a commercially available ski overall, a smooth downhill racing suit, and a dimpled downhill racing suit. Friction was measured for fabrics taped on a short ski using a linear tribometer. The fabrics’ roughness was determined by focus variation microscopy. Friction coefficients were between 0.19 and 0.48. Roughness, friction coefficient, and friction force were highest for the dimpled race suit. The friction force of the fabrics was higher for the higher contact pressure than for the lower one at all speeds. It was concluded that the main friction mechanism for the fabrics was dry friction. Only the fabric with the roughest surface showed friction coefficients, which were high enough to sufficiently decelerate a sliding skier on beginner and intermediate slopes.

Friction coefficient dependence on electrostatic tribocharging

Science.gov (United States)

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

Polymer friction Molecular Dynamics

DEFF Research Database (Denmark)

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

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

Enhanced nanoscale friction on fluorinated graphene.

Science.gov (United States)

Kwon, Sangku; Ko, Jae-Hyeon; Jeon, Ki-Joon; Kim, Yong-Hyun; Park, Jeong Young

2012-12-12

Atomically thin graphene is an ideal model system for studying nanoscale friction due to its intrinsic two-dimensional (2D) anisotropy. Furthermore, modulating its tribological properties could be an important milestone for graphene-based micro- and nanomechanical devices. Here, we report unexpectedly enhanced nanoscale friction on chemically modified graphene and a relevant theoretical analysis associated with flexural phonons. Ultrahigh vacuum friction force microscopy measurements show that nanoscale friction on the graphene surface increases by a factor of 6 after fluorination of the surface, while the adhesion force is slightly reduced. Density functional theory calculations show that the out-of-plane bending stiffness of graphene increases up to 4-fold after fluorination. Thus, the less compliant F-graphene exhibits more friction. This indicates that the mechanics of tip-to-graphene nanoscale friction would be characteristically different from that of conventional solid-on-solid contact and would be dominated by the out-of-plane bending stiffness of the chemically modified graphene. We propose that damping via flexural phonons could be a main source for frictional energy dissipation in 2D systems such as graphene.

Amontonian frictional behaviour of nanostructured surfaces.

Science.gov (United States)

Pilkington, Georgia A; Thormann, Esben; Claesson, Per M; Fuge, Gareth M; Fox, Oliver J L; Ashfold, Michael N R; Leese, Hannah; Mattia, Davide; Briscoe, Wuge H

2011-05-28

With nanotextured surfaces and interfaces increasingly being encountered in technological and biomedical applications, there is a need for a better understanding of frictional properties involving such surfaces. Here we report friction measurements of several nanostructured surfaces using an Atomic Force Microscope (AFM). These nanostructured surfaces provide well defined model systems on which we have tested the applicability of Amontons' laws of friction. Our results show that Amontonian behaviour is observed with each of the surfaces studied. However, no correlation has been found between measured friction and various surface roughness parameters such as average surface roughness (R(a)) and root mean squared (rms) roughness. Instead, we propose that the friction coefficient may be decomposed into two contributions, i.e., μ = μ(0) + μ(g), with the intrinsic friction coefficient μ(0) accounting for the chemical nature of the surfaces and the geometric friction coefficient μ(g) for the presence of nanotextures. We have found a possible correlation between μ(g) and the average local slope of the surface nanotextures. This journal is © the Owner Societies 2011

Static friction between rigid fractal surfaces.

Science.gov (United States)

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

2015-09-01

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

Friction welding method

International Nuclear Information System (INIS)

Ishida, Ryuichi; Hatanaka, Tatsuo.

1969-01-01

A friction welding method for forming a lattice-shaped base and tie plate supporter for fuel elements is disclosed in which a plate formed with a concavity along its edge is pressure welded to a rotating member such as a boss by longitudinally contacting the projecting surfaces remaining on either side of the concavity with the rotating member during the high speed rotation thereof in the presence of an inert gas. Since only the two projecting surfaces of the plate are fused by friction to the rotary member, heat expansion is absorbed by the concavity to prevent distortion; moreover, a two point contact surface assures a stable fitting and promotes the construction of a rigid lattice in which a number of the abovementioned plates are friction welded between rotating members to form any desired complex arrangement. The inert has serves to protect the material quality of the contacting surfaces from air during the welding step. The present invention thus provides a method in which even Zircaloy may be friction welded in place of casting stainless steel in the construction of supporting lattices to thereby enhance neutron economy. (K. J. Owens)

Comparisons of friction models in bulk metal forming

DEFF Research Database (Denmark)

Tan, Xincai

2002-01-01

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

Anticipating the friction coefficient of friction materials used in automobiles by means of machine learning without using a test instrument

OpenAIRE

TİMUR, Mustafa; AYDIN, Fatih

2013-01-01

The most important factor for designs in which friction materials are used is the coefficient of friction. The coefficient of friction has been determined taking such variants as velocity, temperature, and pressure into account, which arise from various factors in friction materials, and by analyzing the effects of these variants on friction materials. Many test instruments have been produced in order to determine the coefficient of friction. In this article, a study about the use ...

Structural Damping with Friction Beams

Directory of Open Access Journals (Sweden)

L. Gaul

2008-01-01

Full Text Available In the last several years, there has been increasing interest in the use of friction joints for enhancing damping in structures. The joints themselves are responsible for the major part of the energy dissipation in assembled structures. The dissipated work in a joint depends on both the applied normal force and the excitation force. For the case of a constant amplitude excitation force, there is an optimal normal force which maximizes the damping. A ‘passive’ approach would be employed in this instance. In most cases however, the excitation force, as well as the interface parameters such as the friction coefficient, normal pressure distribution, etc., are not constant. In these cases, a ‘semi-active’ approach, which implements an active varying normal force, is necessary. For the ‘passive’ and ‘semi-active’ approaches, the normal force has to be measured. Interestingly, since the normal force in a friction joint influences the local stiffness, the natural frequencies of the assembled structure can be tuned by adjusting the normal force. Experiments and simulations are performed for a simple laboratory structure consisting of two superposed beams with friction in the interface. Numerical simulation of the friction interface requires non-linear models. The response of the double beam system is simulated using a numerical algorithm programmed in MATLAB which models point-to-point friction with the Masing friction model. Numerical predictions and measurements of the double beam free vibration response are compared. A practical application is then described, in which a friction beam is used to damp the vibrations of the work piece table on a milling machine. The increased damping of the table reduces vibration amplitudes, which in turn results in enhanced surface quality of the machined parts, reduction in machine tool wear, and potentially higher feed rates. Optimal positioning of the friction beams is based on knowledge of the mode

Elastic modulus and internal friction of SOFC electrolytes at high temperatures under controlled atmospheres

Science.gov (United States)

Kushi, Takuto; Sato, Kazuhisa; Unemoto, Atsushi; Hashimoto, Shinichi; Amezawa, Koji; Kawada, Tatsuya

2011-10-01

Mechanical properties such as Young's modulus, shear modulus, Poisson's ratio and internal friction of conventional electrolyte materials for solid oxide fuel cells, Zr0.85Y0.15 O1.93 (YSZ), Zr0.82Sc0.18O1.91 (ScSZ), Zr0.81Sc0.18Ce0.01O2-δ (ScCeSZ), Ce0.9Gd0.1O2-δ (GDC), La0.8Sr0.2Ga0.8Mg0.15Co0.05O3-δ (LSGMC), La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM), were evaluated by a resonance method at temperatures from room temperature to 1273 K in various oxygen partial pressures. The Young's modulus of GDC gradually decreased with increasing temperature in oxidizing conditions. The Young's moduli of the series of zirconia and lanthanum gallate based materials drastically decreased in an intermediate temperature range and increased slightly with increasing temperature at higher temperatures. The Young's modulus of GDC considerably decreased above 823 K in reducing atmospheres in response to the change of oxygen nonstoichiometry. However, temperature dependences of the Young's moduli of ScCeSZ and LSGMC in reducing atmospheres did not show any significant differences with those in oxidizing atmospheres.

Thermally-activated internal friction peaks in amorphous films of Nb3Ge and Nb3Si

International Nuclear Information System (INIS)

Berry, B.S.; Pritchet, W.C.

1978-01-01

A large number of the thermally-activated internal friction peaks observed in crystalline solids are associated with the general mechanism of stress-induced directional short-range ordering. These peaks are an indirect but nevertheless valuable structural probe, and provide an important means of obtaining quantitative information on the kinetics of local atomic movements. This paper deals with what are thought to be the first-known examples of such peaks in the field of metallic glasses. The peaks have been observed in amorphous films of Nb 3 Ge and Nb 3 Si which are both superconductors with transition temperatures Tsub(c) near 3.6K. Although Tsub(c) is thus well below the record values of approximately equal to 23K reported for crystalline films of Nb 3 Ge, Tsuei has found the amorphous films to be much superior mechanically to their crystalline counterparts. Consequently, the amorphous films have technological interest as an easily-handled source from which the brittle high-Tsub(c) phase may be obtained by a final in-situ anneal. (author)

FRICTION-BOON OR BANE IN ORTHODONTICS

Directory of Open Access Journals (Sweden)

Sameer

2015-11-01

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

Contribution to the study of internal friction in graphites; Contribution a l'etude du frottement interieur des graphites

Energy Technology Data Exchange (ETDEWEB)

Merlin, J [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

1969-03-01

A study has been made of the internal friction in different graphites between -180 C and +500 C using a torsion pendulum; the graphites had been previously treated thermo-mechanically, by neutron irradiation and subjected to partial annealings. It has been shown that there occurs: a hysteretic type dissipation of energy, connected with interactions between dislocations and other defects in the matrix; a dissipation having a partially hysteretic character which can be interpreted by a Granato-Luke type formalism and which is connected with the presence of an 'ultra-micro porosity'; a dissipation by a relaxation mechanism after a small dose of irradiation; this is attributed to the reorientation of bi-interstitials; a dissipation having the characteristics of a solid state transformation, this during an annealing after irradiation. It is attributed to the reorganization of interstitial defects. Some information has thus been obtained concerning graphites, in particular: their behaviour at low mechanical stresses, the nature of irradiation defects and their behaviour during annealing, the structural changes occurring during graphitization, the relationship between internal friction and macroscopic mechanical properties. (author) [French] L'etude du coefficient de frottement interieur au moyen d'un pendule de torsion entre -180 C et +500 C a ete realisee pour differents graphites apres des traitements thermo-mecaniques, des irradiations neutroniques et des guerisons partielles. Il a ete mis en evidence: une dissipation d'energie a caractere hysteretique, reliee aux interactions des dislocations avec les autres defauts de la matrice; une dissipation a caractere partiellement hysteretique, interpretable par un formalisme type Granato-Lucke et reliee a la presence d'une ''ultra-microporosite''; une dissipation par un mecanisme de relaxation, apres irradiation a faible dose, attribuee a la reorientation de di-interstitiels; une dissipation presentant les caracteristiques d

Nonlinear friction model for servo press simulation

Science.gov (United States)

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.

Friction between silicon and diamond at the nanoscale

International Nuclear Information System (INIS)

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

2015-01-01

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

Nonmonotonicity of the Frictional Bimaterial Effect

Science.gov (United States)

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.

Surface Friction of Polyacrylamide Hydrogel Particles

Science.gov (United States)

Cuccia, Nicholas; Burton, Justin

Polyacrylamide hydrogel particles have recently become a popular system for modeling low-friction, granular materials near the jamming transition. Because a gel consists of a polymer network filled with solvent, its frictional behavior is often explained using a combination of hydrodynamic lubrication and polymer-surface interactions. As a result, the frictional coefficient can vary between 0.001 and 0.03 depending on several factors such as contact area, sliding velocity, normal force, and the gel surface chemistry. Most tribological measurements of hydrogels utilize two flat surfaces, where the contact area is not well-defined. We have built a custom, low-force tribometer to measure the single-contact frictional properties of spherical hydrogel particles on flat hydrogel surfaces under a variety of measurement conditions. At high velocities (> 1 cm/s), the friction coefficient depends linearly on velocity, but does not tend to zero at zero velocity. We also compare our measurements to solid particles (steel, glass, etc.) on hydrogel surfaces, which exhibit larger frictional forces, and show less dependence on velocity. A physical model for the friction which includes the lubrication layer between the deformed surfaces will be discussed. National Science Foundation Grant No. 1506446.

Paediatric treadmill friction injuries.

Science.gov (United States)

Jeremijenko, Luke; Mott, Jonathan; Wallis, Belinda; Kimble, Roy

2009-05-01

The aim of this study was to report on the severity and incidence of children injured by treadmills and to promote the implementation of safety standards. This retrospective review of children with treadmill friction injuries was conducted in a single tertiary-level burns centre in Australia between January 1997 and June 2007. The study revealed 37 children who sustained paediatric treadmill friction injuries. This was a presentation of 1% of all burns. Thirty-three (90%) of the injuries occurred in the last 3.5 years (January 2004 to June 2007). The modal age was 3.2 years. Thirty-three (90%) injuries were either full thickness or deep partial friction burns. Eleven (30%) required split thickness skin grafts. Of those who became entrapped, 100% required skin grafting. This study found that paediatric treadmill friction injuries are severe and increasing in incidence. Australian standards should be developed, implemented and mandated to reduce this preventable and severe injury.

Gas desorption during friction of amorphous carbon films

International Nuclear Information System (INIS)

Rusanov, A; Fontaine, J; Martin, J-M; Mogne, T L; Nevshupa, R

2008-01-01

Gas desorption induced by friction of solids, i.e. tribodesorption, is one of the numerous physical and chemical phenomena, which arise during friction as result of thermal and structural activation of material in a friction zone. Tribodesorption of carbon oxides, hydrocarbons, and water vapours may lead to significant deterioration of ultra high vacuum conditions in modern technological equipment in electronic, optoelectronic industries. Therefore, knowledge of tribodesorption is crucial for the performance and lifetime of vacuum tribosystems. Diamond-like carbon (DLC) coatings are interesting materials for vacuum tribological systems due to their high wear resistance and low friction. Highly hydrogenated amorphous carbon (a-C:H) films are known to exhibit extremely low friction coefficient under high vacuum or inert environment, known as 'superlubricity' or 'superlow friction'. However, the superlow friction period is not always stable and then tends to spontaneous transition to high friction. It is supposed that hydrogen supply from the bulk to the surface is crucial for establishing and maintaining superlow friction. Thus, tribodesorption can serve also as a new technique to determine the role of gases in superlow friction mechanisms. Desorption of various a-C:H films, deposited by PECVD, ion-beam deposition and deposition using diode system, has been studied by means of ultra-high vacuum tribometer equipped with a mass spectrometer. It was found that in superlow friction period desorption rate was below the detection limit in the 0-85 mass range. However, transition from superlow friction to high friction was accompanied by desorption of various gases, mainly of H 2 and CH 4 . During friction transition, surfaces were heavily damaged. In experiments with DLC films with low hydrogen content tribodesorption was significant during the whole experiment, while low friction was not observed. From estimation of maximum surface temperature during sliding contact it

Meniscus formation in a capillary and the role of contact line friction.

Science.gov (United States)

Andrukh, Taras; Monaenkova, Daria; Rubin, Binyamin; Lee, Wah-Keat; Kornev, Konstantin G

2014-01-28

We studied spontaneous formation of an internal meniscus by dipping glass capillaries of 25 μm to 350 μm radii into low volatile hexadecane and tributyl phosphate. X-ray phase contrast and high speed optical microscopy imaging were employed. We showed that the meniscus completes its formation when the liquid column is still shorter than the capillary radius. After that, the meniscus travels about ten capillary radii at a constant velocity. We demonstrated that the experimental observations can be explained by introducing a friction force linearly proportional to the meniscus velocity with a friction coefficient depending on the air/liquid/solid triplet. It was demonstrated that the friction coefficient does not depend on the capillary radius. Numerical solution of the force balance equation revealed four different uptake regimes that can be specified in a phase portrait. This phase portrait was found to be in good agreement with the experimental results and can be used as a guide for the design of thin porous absorbers.

Showing Area Matters: A Work of Friction

Science.gov (United States)

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…

Friction Stir Welding and Processing

Energy Technology Data Exchange (ETDEWEB)

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

2015-05-01

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

[Friction: self-ligating brackets].

Science.gov (United States)

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.

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

Directory of Open Access Journals (Sweden)

F. Beyer

2015-12-01

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

A thermodynamic model of sliding friction

Directory of Open Access Journals (Sweden)

Lasse Makkonen

2012-03-01

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

Slow rupture of frictional interfaces

Science.gov (United States)

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.

Analysis of the Journal Bearing Friction Losses in a Heavy-Duty Diesel Engine

Directory of Open Access Journals (Sweden)

Christoph Knauder

2015-04-01

Full Text Available Internal combustion engines (ICE for the use in heavy-duty trucks and buses have to fulfil demanding requirements for both vehicle efficiency as well as for emission of greenhouse gases. Beside the piston assembly the journal bearings are among the largest contributors to friction in the ICE. Through a combination of measurements and validated simulation methods the journal bearing friction losses of a state-of-the-art heavy-duty Diesel engine are investigated for a large range of real world operating conditions. To this task recently developed and extensively validated simulation methods are used together with realistic lubricant models that consider the Non-Newtonian behaviour as well as the piezoviscous effect. In addition, the potential for further friction reduction with the use of ultra-low viscosity lubricants is explored. The results reveal a potential of about 8% friction reduction in the journal bearings using a 0W20 ultra-low viscosity oil with an HTHS-viscosity (The HTHS-viscosity is defined as the dynamic viscosity of the lubricant measured at 150 °C and at a shear rate of 106 s

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

Science.gov (United States)

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.

Friction anisotropy in boronated graphite

International Nuclear Information System (INIS)

Kumar, N.; Radhika, R.; Kozakov, A.T.; Pandian, R.; Chakravarty, S.; Ravindran, T.R.; Dash, S.; Tyagi, A.K.

2015-01-01

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

Friction anisotropy in boronated graphite

Energy Technology Data Exchange (ETDEWEB)

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

2015-01-01

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

Friction measurement in a hip wear simulator.

Science.gov (United States)

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.

Friction coefficient of skin in real-time.

Science.gov (United States)

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.

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

Science.gov (United States)

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

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

Science.gov (United States)

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

2015-09-01

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.

Pressure and Friction Injuries in Primary Care.

Science.gov (United States)

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.

Rubber friction and tire dynamics

International Nuclear Information System (INIS)

Persson, B N J

2011-01-01

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

Rubber friction and tire dynamics.

Science.gov (United States)

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.

Effect of friction time on the properties of friction welded YSZ‐alumina composite and 6061 aluminium alloy

Directory of Open Access Journals (Sweden)

Uday M. Basheer

2012-03-01

Full Text Available The aim of this work was to study the effect of friction time on the microstructure and mechanical properties of alumina 0, 25, 50 wt% yttria stabilized zirconia (YSZ composite and 6061 aluminium alloy joints formed by friction welding. The alumina-YSZ composites were prepared through slip casting in plaster of Paris molds (POP and subsequently sintered at 1600°C, while the aluminium rods were machined down using a lathe machine to the dimension required. The welding process was carried out under different rotational speeds and friction times, while friction force (0.5 ton-force was kept constant. Scanning electron microscopy was used to characterize the interface of the joints structure. The experimental results showed that the friction time has a significant effect on joint structure and mechanical properties.

Systematic investigation of the fatigue performance of a friction stir welded low alloy steel

International Nuclear Information System (INIS)

Toumpis, Athanasios; Galloway, Alexander; Molter, Lars; Polezhayeva, Helena

2015-01-01

Highlights: • The fatigue behaviour of a friction stir welded low alloy steel has been assessed. • The welds’ fatigue lives outperform the International Institute of Welding’s recommendations for fusion welds. • The slow weld exhibits the best fatigue performance of the investigated welds. • Fracture surface analysis shows that minor embedded flaws do not offer crack initiation sites. • Process-related surface breaking flaws have a significant effect on the fatigue life. - Abstract: A comprehensive fatigue performance assessment of friction stir welded DH36 steel has been undertaken to address the relevant knowledge gap for this process on low alloy steel. A detailed set of experimental procedures specific to friction stir welding has been put forward, and the consequent study extensively examined the weld microstructure and hardness in support of the tensile and fatigue testing. The effect of varying welding parameters was also investigated. Microstructural observations have been correlated to the weldments’ fatigue behaviour. The typical fatigue performance of friction stir welded steel plates has been established, exhibiting fatigue lives well above the weld detail class of the International Institute of Welding even for tests at 90% of yield strength, irrespective of minor instances of surface breaking flaws which have been identified. An understanding of the manner in which these flaws impact on the fatigue performance has been established, concluding that surface breaking irregularities such as these produced by the tool shoulder’s features on the weld top surface can be the dominant factor for crack initiation under fatigue loading

Friction and wear performance of low-friction carbon coatings under oil lubrication

International Nuclear Information System (INIS)

Kovalchenko, A.; Ajayi, O. O.; Erdemir, A.; Fenske, G. R.

2001-01-01

Amorphous carbon coatings with very low friction properties were recently developed at Argonne National Laboratory. These coatings have shown good promise in mitigating excessive wear and scuffing problems associated with low-lubricity diesel fuels. To reduce the negative effect of sulfur and other lubricant additives in poisoning the after-treatment catalyst, a lubricant formulation with a low level of sulfur may be needed. Exclusion of proven sulfur-containing extreme pressure (EP) and antiwear additives from oils will require other measures to ensure durability of critical lubricated components. The low-friction carbon coating has the potential for such applications. In the present study, we evaluated the friction and wear attributes of three variations of the coating under a boundary lubrication regime. Tests were conducted with both synthetic and mineral oil lubricants using a ball-on-flat contact configuration in reciprocating sliding. Although the three variations of the coating provided modest reductions in friction coefficient, they all reduced wear substantially compared to an uncoated surface. The degradation mode of oxidative wear on the uncoated surface was replaced by a polishing wear mode on the coated surfaces

Intelligent Flow Friction Estimation.

Science.gov (United States)

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.

Intelligent Flow Friction Estimation

Directory of Open Access Journals (Sweden)

Dejan Brkić

2016-01-01

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

Micromechanical simulation of frictional behaviour in metal forming

International Nuclear Information System (INIS)

Zhang, S.; Hodgson, P.D.; Cardew-Hall, M.J.; Kalyanasundaram, S.

2000-01-01

Friction is a critical factor for Sheet Metal Forming (SMF). The Coulomb friction model is usually used in most Finite Element (FE) simulation for SMF. However, friction is a function of the local contact deformation conditions, such as local pressure, roughness and relative velocity. This paper will present a micromechanical model that accounts for the local frictional behaviour through finite element simulations performed at the micromechanical level. Frictional behaviour between contact surfaces can be based on three cases: boundary, hydrodynamic and mixed lubrication. In our microscopic friction model based on FEM, the case of boundary lubrication contact between sheet and tool has been considered. In the view of microscopic geometry, roughness depends upon amplitude and wavelength of surface asperities of sheet and tool. The mean pressure applied on the surface differs from the pressure over the actual contact area. The effect of roughness (microscopic geometric condition) and relative speed of contact surfaces on friction coefficient was examined in the FE model for the microscopic friction behaviour. The analysis was performed using an explicit finite element formulation. In this study, it was found that the roughness of deformable sheet decreases during sliding and the coefficient of friction increases with increasing roughness of contact surfaces. The coefficient of friction increases with the increase of relative velocity and adhesive friction coefficient between contact surfaces. (author)

The friction cost method: a comment.

Science.gov (United States)

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.

Apparatus for measurement of coefficient of friction

Science.gov (United States)

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

1990-01-01

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

FRICTION TORQUE IN THE SLIDE BEARINGS

Directory of Open Access Journals (Sweden)

BONDARENKO L. N.

2016-09-01

Full Text Available Summary. Problem statement. Until now slide bearings are used widely in engineering. But the calculation is made on obsolete method that is based on undetermined parameters such as wear of the bearing shell. It is accepted in the literature that if the shaft and liner material are homogeneous, the workpiece surface are cylindrical as they wear and contact between them occurs at all points contact arc. Research objective. The purpose of this study is determine a friction torque in the slide bearings of power-basis parameters. Conclusions. Since the friction is primarily responsible for wear of cinematic pairs “pin – liner” and “pivot – liner” slide bearings. It is shown that the friction torquesof angles wrap, that are obtained by the formulas and given in literature, are not only qualitatively but also quantitatively, namely, the calculation by literature to the formulas the friction torques are proportional to the angle wrap and the calculation by improved formulas the friction torques are inversely proportional to the angle wrap due to the reduction the normal pressure. Underreporting friction torque at large angle wrap is between 40 and 15 %. The difference in the magnitude of friction torque in the run-in and run-out cinematic pairs with real method of machining is 2...3 %, which it is possible to declare of reducing the finish of contacting surface of slide bearings.

Blades Couple Dry Friction Connection

Czech Academy of Sciences Publication Activity Database

Půst, Ladislav; Pešek, Luděk; Radolfová, Alena

2015-01-01

Roč. 9, č. 1 (2015), s. 31-40 ISSN 1802-680X Institutional support: RVO:61388998 Keywords : stick-slip dry friction * 3D friction characteristic * tangential contact stiffness * hysterezis loop * response curves Subject RIV: BI - Acoustics

Empirical analysis of skin friction under variations of temperature; Variacion de la resistencia al corte con temperatura

Energy Technology Data Exchange (ETDEWEB)

Parra Alvarez, A. R. de la; Groot Viana, M. de

2014-07-01

In soil geotechnical characterization, strength parameters, cohesion (c) and internal friction angle (Φ) has been traditional measured without taking into account temperature, been a very important issue in energy geostructures. The present document analyzes the variation of these parameters in soil-concrete interface at different temperatures. A traditional shear strength case with a forced plane of failure was used. Several tests were carried out to determine the variation of skin friction in granular and cohesive oils with temperature. (Author)

A Novel Time-Varying Friction Compensation Method for Servomechanism

Directory of Open Access Journals (Sweden)

Bin Feng

2015-01-01

Full Text Available Friction is an inevitable nonlinear phenomenon existing in servomechanisms. Friction errors often affect their motion and contour accuracies during the reverse motion. To reduce friction errors, a novel time-varying friction compensation method is proposed to solve the problem that the traditional friction compensation methods hardly deal with. This problem leads to an unsatisfactory friction compensation performance and the motion and contour accuracies cannot be maintained effectively. In this method, a trapezoidal compensation pulse is adopted to compensate for the friction errors. A generalized regression neural network algorithm is used to generate the optimal pulse amplitude function. The optimal pulse duration function and the pulse amplitude function can be established by the pulse characteristic parameter learning and then the optimal friction compensation pulse can be generated. The feasibility of friction compensation method was verified on a high-precision X-Y worktable. The experimental results indicated that the motion and contour accuracies were improved greatly with reduction of the friction errors, in different working conditions. Moreover, the overall friction compensation performance indicators were decreased by more than 54% and this friction compensation method can be implemented easily on most of servomechanisms in industry.

Friction, Free Axes of Rotation and Entropy

Directory of Open Access Journals (Sweden)

Alexander Kazachkov

2017-03-01

Full Text Available Friction forces acting on rotators may promote their alignment and therefore eliminate degrees of freedom in their movement. The alignment of rotators by friction force was shown by experiments performed with different spinners, demonstrating how friction generates negentropy in a system of rotators. A gas of rigid rotators influenced by friction force is considered. The orientational negentropy generated by a friction force was estimated with the Sackur-Tetrode equation. The minimal change in total entropy of a system of rotators, corresponding to their eventual alignment, decreases with temperature. The reported effect may be of primary importance for the phase equilibrium and motion of ubiquitous colloidal and granular systems.

Friction Material Composites Materials Perspective

CERN Document Server

Sundarkrishnaa, K L

2012-01-01

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

Understanding dynamic friction through spontaneously evolving laboratory earthquakes.

Science.gov (United States)

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

2017-06-29

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.

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

Science.gov (United States)

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.

[Determination of a Friction Coefficient for THA Bearing Couples].

Science.gov (United States)

Vrbka, M; Nečas, D; Bartošík, J; Hartl, M; Křupka, I; Galandáková, A; Gallo, J

2015-01-01

The wear of articular surfaces is considered one of the most important factors limiting the life of total hip arthroplasty (THA). It is assumed that the particles released from the surface of a softer material induce a complex inflammatory response, which will eventually result in osteolysis and aseptic loosening. Implant wear is related to a friction coefficient which depends on combination of the materials used, roughness of the articulating surfaces, internal clearance, and dimensions of the prosthesis. The selected parameters of the bearing couples tested were studied using an experimental device based on the principle of a pendulum. Bovine serum was used as a lubricant and the load corresponded to a human body mass of 75 kg. The friction coefficient was derived from a curve of slowdown of pendulum oscillations. Roughness was measured with a device working on the principle of interferometry. Clearance was assessed by measuring diameters of the acetabular and femoral heads with a 3D optical scanner. The specimens tested included unused metal-on-highly cross-linked polyethylene, ceramic-on-highly cross-linked polyethylene and ceramic-on-ceramic bearing couples with the diameters of 28 mm and 36 mm. For each measured parameter, an arithmetic mean was calculated from 10 measurements. 1) The roughness of polyethylene surfaces was higher by about one order of magnitude than the roughness of metal and ceramic components. The Protasul metal head had the least rough surface (0.003 μm). 2) The ceramic-on-ceramic couples had the lowest clearance. Bearing couples with polyethylene acetabular liners had markedly higher clearances ranging from 150 μm to 545 μm. A clearance increased with large femoral heads (up to 4-fold in one of the couple tested). 3) The friction coefficient was related to the combination of materials; it was lowest in ceramic-on-ceramic surfaces (0.11 to 0.12) and then in ceramic-on-polyethylene implants (0.13 to 0.14). The friction coefficient is

Asbestos free friction composition for brake linings

Indian Academy of Sciences (India)

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

Effect of electrostatic field on dynamic friction coefficient of pistachio

Directory of Open Access Journals (Sweden)

M. H Aghkhani

2016-04-01

Full Text Available Introduction: Separation and grading of agricultural products from the production to supply, has notable importance. The separation can be done based on physical, electrical, magnetic, optical properties and etc. It is necessary for any development of new systems to study enough on the properties and behavior of agricultural products. Some characteristics for separation are size (length, width and thickness, hardness, shape, density, surface roughness, color, speed limit, aerodynamic properties, electrical conductivity, elasticity and coefficient of static friction point. So far, the friction properties of agricultural products used in the separating process, but the effect of electrostatic charging on static and dynamic coefficients of friction for separation had little attention. The aim of this study was to find out the interactions between electrostatic and friction properties to find a way to separate products that separation is not possible with conventional methods or not sufficiently accurate. In this paper, the separation of close and smiley pistachios by electrostatic charging was investigated. Materials and Methods: Kallehghoochi pistachio cultivar has the top rank in production in Iran. Therefore, it was used as a sample. The experimental design that used in this study, had moisture content at three levels (24.2, 14.5 and 8.1 percent, electric field intensity at three levels (zero, 4000 and 7000 V, speed of movement on the surface at three levels (1300, 2500 and 3300 mm per minute, friction surface (galvanized sheet iron, aluminum and flat rubber and pistachio type at two levels (filled splits and closed that was measured and analyzed in completely randomized factorial design. A friction measuring device (built in Ferdowsi University of Mashhad used to measure the friction force. It has a removable table that can move in two directions with adjustable speed. The test sample put into the vessel with internal dimensions of 300 × 150 �

Internal friction and Young's modulus measurements in Zr-2.5Nb alloy doped with hydrogen

International Nuclear Information System (INIS)

Ritchie, I.G.; Pan, Z.-L.

1992-01-01

The presence of hydrides is an important factor in assessing the potential for delayed hydride cracking in Zr-2.5Nb alloys, and consequently, the terminal solid solubility (TSS) of hydrogen in the material is an important parameter. In pure zirconium doped with hydrogen, the TSS is marked by a dissolution peak of internal friction on heating and a truncated precipitation peak associated with hydride nucleation on cooling. These phenomena occur only at low frequencies and are accompanied in torsion pendulum studies by autotwisting of the sample (or zero-point drift) that stops abruptly at the TSS. Neither the dissolution/precipitation peaks nor the autotwisting phenomena are observed in Zr-2.5Nb. However, the TSS is also marked by an abrupt change in the slope of Young's modulus as a function of temperature. This phenomenon is observed regardless of the frequency (in the range 1 Hz to 120 kHz) and in both pure zirconium and Zr-2.5Nb alloys. The reasons for the absence of the dissolution/precipitation peak in Zr-2.5Nb alloys are discussed and the use of Young's modulus changes to investigate the TSS of hydrogen and the hysteresis between heat-up and cool-down TSS curves is demonstrated. (author)

Frictional properties of jointed welded tuff

International Nuclear Information System (INIS)

Teufel, L.W.

1981-07-01

The results of the experiments on simulated joints in welded tuff from the Grouse Canyon Member of the Belted Range Tuff warrant the following conclusions: (1) The coefficient of friction of the joints is independent of normal stress at a given sliding velocity. (2) The coefficient of friction increases with both increasing time of stationary contact and decreasing sliding velocity. (3) Time and velocity dependence of friction is due to an increase in the real area of contact on the sliding surface, caused by asperity creep. (4) Joints in water-saturated tuff show a greater time and velocity dependence of friction than those in dehydrated tuff. (5) The enhanced time and velocity dependence of friction with water saturation is a result of increased creep at asperity contacts, which is in turn due to a reduction in the surface indentation hardness by hydrolytic weakening and/or stress corrosion cracking

Noise and vibration in friction systems

CERN Document Server

Sergienko, Vladimir P

2015-01-01

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

Servo Reduces Friction In Flexure Bearing

Science.gov (United States)

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.

Velocity Dependence in the Cyclic Friction Arising with Gears

OpenAIRE

García Armada, Elena; González de Santos, Pablo; Canudas de Wit, Carlos

2002-01-01

Recent research on friction in robot joints and transmission systems has considered meshing friction a position-dependent friction component. However, in this paper we show experimental evidence that meshing friction depends highly on joint speed.We identify the meshing friction in the gearboxes of a robotic leg, and we propose a new mathematical model that considers the rate dependency of meshing friction. The resulting model is validated through experimentation. Results...

Are there reliable constitutive laws for dynamic friction?

Science.gov (United States)

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).

Quantum field theory of van der Waals friction

International Nuclear Information System (INIS)

Volokitin, A. I.; Persson, B. N. J.

2006-01-01

van der Waals friction between two semi-infinite solids, and between a small neutral particle and semi-infinite solid is studied using thermal quantum field theory in the Matsubara formulation. We show that the friction to linear order in the sliding velocity can be obtained from the equilibrium Green functions and that our treatment can be extended for bodies with complex geometry. The calculated friction agrees with the friction obtained using a dynamical modification of the Lifshitz theory, which is based on the fluctuation-dissipation theorem. We show that it should be possible to measure the van der Waals friction in noncontact friction experiment using state-of-the-art equipment

Methods and Devices used to Measure Friction

DEFF Research Database (Denmark)

Jeswiet, Jack; Arentoft, Mogens; Henningsen, Poul

2004-01-01

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

Friction Anisotropy with Respect to Topographic Orientation

Science.gov (United States)

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

Assessment of semi-active friction dampers

Science.gov (United States)

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

2017-09-01

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

Machine Learning of Fault Friction

Science.gov (United States)

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

On the geometric phenomenology of static friction.

Science.gov (United States)

Ghosh, Shankar; Merin, A P; Nitsure, Nitin

2017-09-06

In this note we introduce a hierarchy of phase spaces for static friction, which give a graphical way to systematically quantify the directional dependence in static friction via subregions of the phase spaces. We experimentally plot these subregions to obtain phenomenological descriptions for static friction in various examples where the macroscopic shape of the object affects the frictional response. The phase spaces have the universal property that for any experiment in which a given object is put on a substrate fashioned from a chosen material with a specified nature of contact, the frictional behaviour can be read off from a uniquely determined classifying map on the control space of the experiment which takes values in the appropriate phase space.

Friction and dissipative phenomena in quantum mechanics

International Nuclear Information System (INIS)

Kostin, M.D.

1975-01-01

Frictional and dissipative terms of the Schroedinger equation are studied. A proof is given showing that the frictional term of the Schroedinger--Langevin equation causes the quantum system to lose energy. General expressions are derived for the frictional term of the Schroedinger equation. (U.S.)

Friction characteristics of hardfacing materials in high temperature sodium

International Nuclear Information System (INIS)

Mizobuchi, Syotaro; Kano, Shigeki; Nakayama, Kohichi; Atsumo, Hideo

1980-01-01

Friction and self-welding test were conducted on several materials used for the contacting and sliding components of a sodium cooled fast breeder reactor. In the present study, the friction and self-welding characteristics of each material were evaluated through measuring the kinetic and breakaway friction coefficients. The influence of oscillating rotation and vertical reciprocating motion on the friction mode was also investigated. The results obtained are as follows: (1) Colmonoy No.6, the nickel base hardfacing alloy, indicated the lowest kinetic friction coefficient of all the materials in the present study. Also, Cr 3 C 2 /Ni-Cr material prepared by a detonation gun showed the most stable friction behavior. (2) The breakaway friction coefficient of each material was dependent upon dwelling time in a sodium environment. (3) The friction behavior of Cr 3 C 2 /Ni-Cr material was obviously related with the finishing roughness of the friction surface. It was anticipated that nichrome material as the binder of the chrome carbide diffused and exuded to the friction surface by sliding in sodium. (4) The friction coefficient in sliding mode of vertical reciprocating was lower than that of oscillating rotation. (author)

Learning from Local Wisdom: Friction Damper in Traditional Building

Directory of Open Access Journals (Sweden)

Pudjisuryadi P.

2012-01-01

Full Text Available Indonesia is situated in the so called “Ring of Fire” where earthquake are very frequent. Despite of all the engineering effort, due to the March 28, 2005 strong earthquake (8.7 on Richter scale a lot of modern buildings in Nias collapsed, while the traditional Northern Nias house (omohada survived without any damage. Undoubtedly many other traditional buildings in other area in Indonesia have survived similar earthquake. Something in common of the traditional building are the columns which usually are not fixed on the ground, but rest on top of flat stones. In this paper some traditional building are subjected to non linear time history analysis to artificial earthquake equivalent to 500 years return period earthquake. This study shows that apparently the columns which rest on top of flat stone acts as friction damper or base isolation. The presence of sliding at the friction type support significantly reduces the internal forces in the structure.

Friction and Lubrication of Large Tilting-Pad Thrust Bearings

Directory of Open Access Journals (Sweden)

Michał Wasilczuk

2015-04-01

Full Text Available Fluid film bearings have been extensively used in the industry because of their unbeatable durability and extremely low friction coefficient, despite a very low coefficient of friction dissipation of energy being noticeable, especially in large bearings. Lubricating systems of large tilting pad thrust bearings utilized in large, vertical shaft hydrogenerators are presented in this paper. A large amount of heat is generated due to viscous shearing of the lubricant large tilting pad thrust bearings, and this requires systems for forced cooling of the lubricant. In the dominant bath lubrication systems, cooling is realized by internal coolers or external cooling systems, with the latter showing some important advantages at the cost of complexity and also, potentially, lower reliability. Substantial losses in the bearings, reaching 1 MW in extreme cases, are a good motivation for the research and development aimed at reducing them. Some possible methods and their potential efficiency, along with some effects already documented, are also described in the paper.

Friction Properties of Carbon Fiber Brush

OpenAIRE

大塚, 由佳; 月山, 陽介; 野老山, 貴行; 梅原, 徳次; OHTSUKA, Yuka; TSUKIYAMA, Yosuke; TOKOROYAMA, Takayuki; UMEHARA, Noritsugu

2011-01-01

直径数μmのカーボンファイバーを束ねたカーボンファイバーブラシ材料と金属材料のすべり摩擦におけるすべり出しの摩擦及び平均摩擦特性と,金属同士のそれらの摩擦特性の相違を調べ,カーボンファイバーブラシ材料の摩擦の特異性を明らかにした. Friction properties as initial and average friction coefficient were investigated for carbon brush materials. Experimental results shows that static friction coefficient of carbon fiber brush is smaller than kinetic friction after a macro slip. This phenomena is different from the usual friction properties between metals. I...

Friction forces on phase transition fronts

International Nuclear Information System (INIS)

Mégevand, Ariel

2013-01-01

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

A field theoretic model for static friction

OpenAIRE

Mahyaeh, I.; Rouhani, S.

2013-01-01

We present a field theoretic model for friction, where the friction coefficient between two surfaces may be calculated based on elastic properties of the surfaces. We assume that the geometry of contact surface is not unusual. We verify Amonton's laws to hold that friction force is proportional to the normal load.This model gives the opportunity to calculate the static coefficient of friction for a few cases, and show that it is in agreement with observed values. Furthermore we show that the ...

Two new methods to determine the adhesion by means of internal friction in materials covered with films; Dos nuevos metodos para determinar la adhesion mediante friccion interna en materiales recubiertos con peliculas

Energy Technology Data Exchange (ETDEWEB)

Colorado, H. A.; Ghilarducci, A. A.; Salva, H. R.

2006-07-01

Two new models are proposed to determine the adhesion energy be means of the internal friction technique (IF) in thin films layered materials. for the first method is necessary to determine enthalpy by means of the IF technique, for which the adhesion work has been determined with experimental data. In the second method are necessary to perform IF tests at constant temperature. (Author)

Adaptive friction compensation: a globally stable approach

NARCIS (Netherlands)

Verbert, K.A.; Tóth, R.; Babuska, R.

2016-01-01

In this paper, an adaptive friction compensation scheme is proposed. The friction force is computed as a timevarying friction coefficient multiplied by the sign of the velocity and an on-line update law is designed to estimate this coefficient based on the actual position and velocity errors.

Skin friction measurements using He-Ne laser

Energy Technology Data Exchange (ETDEWEB)

Choi, S.H. [Hankuk Aviation University Graduate School, Kyonggi-do (Korea, Republic of); Lee, Y. [Hankuk Aviation University, Kyonggi-do (Korea, Republic of)

1997-07-01

An experimental study of the skin friction measurement in a turbulent boundary-layer has been carried out. The skin friction measurements are made using the laser interferometer skin friction (LISF) meter, which optically detects the rate of thinning of an oil applied to the test surface. This technique produces reliable skin friction data over a wide range of flow situations up to 3-dimensional complicated flows with separation, where traditional skin friction measurement techniques are not applicable. The present measured data in a turbulent boundary-layer on a flat plate using the LISF technique shows a good comparison with the result from the previous velocity profile techniques, which proves the validity of the present technique. An extensive error analysis is carried out for the present technique yielding an uncertainty of about {+-}8%, which makes them suitable for CFD code validation purposes. Finally the measurements of the skin friction in a separated region after a surface-mounted obstacle are also presented. (author). 19 refs., 12 figs., 3 tabs.

NASA tire/runway friction projects

Science.gov (United States)

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.

Multiscale friction modeling for sheet metal forming

NARCIS (Netherlands)

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

2010-01-01

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

Large Friction Anisotropy of a Polydiacetylene Monolayer

International Nuclear Information System (INIS)

Burns, A.R.; Carpick, R.W.; Sasaki, D.Y.

1999-01-01

Friction force microscopy measurements of a polydiacetylene monolayer film reveal a 300% friction anisotropy that is correlated with the film structure. The film consists of a monolayer of the red form of N-(2-ethanol)- 10,12 pentacosadiynamide, prepared on a Langmuir trough and deposited on a mica substrate. As confirmed by atomic force microscopy and fluorescence microscopy, the monolayer consists of domains of linearly oriented conjugated backbones with pendant hydrocarbon side chains above and below the backbones. Maximum friction occurs when the sliding direction is perpendicular to the backbone. We propose that the backbones impose anisotropic packing of the hydrocarbon side chains which leads to the observed friction anisotropy. Friction anisotropy is therefore a sensitive, optically-independent indicator of polymer backbone direction and monolayer structural properties

Nonlinear friction dynamics on polymer surface under accelerated movement

Directory of Open Access Journals (Sweden)

Yuuki Aita

2017-04-01

Full Text Available 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.

Size scaling of static friction.

Science.gov (United States)

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

2013-02-22

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

Energy based optimization of viscous–friction dampers on cables

International Nuclear Information System (INIS)

Weber, F; Boston, C

2010-01-01

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

Tribo-performance evaluation of ecofriendly brake friction composite materials

Science.gov (United States)

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.

Position Control of Servo Systems Using Feed-Forward Friction Compensation

International Nuclear Information System (INIS)

Park, Min Gyu; Kim, Han Me; Shin, Jong Min; Kim, Jong Shik

2009-01-01

Friction is an important factor for precise position tracking control of servo systems. Servo systems with highly nonlinear friction are sensitive to the variation of operating condition. To overcome this problem, we use the LuGre friction model which can consider dynamic characteristics of friction. The LuGre friction model is used as a feed-forward compensator to improve tracking performance of servo systems. The parameters of the LuGre friction model are identified through experiments. The experimental result shows that the tracking performance of servo systems with higherly nonlinear friction can be improved by using feed-forward friction compensation

The role of investment, fundamental Q and financing frictions in agricultural investment decisions: an analysis pre and post financial crisis

OpenAIRE

Conor M. O'Toole; Carol Newman; Thia Hennessy

2011-01-01

This paper uses a fundamental Q model of investment to consider the role played by financing frictions in agricultural investment decisions, controlling econometrically for censoring, heterogeneity and errors-in-variables. Our findings suggest that farmer's in- vestment decisions are not driven by market fundamentals. We find some evidence that debt overhang restricts investment but investment is not dependent on liquidity or internal funds. The role of nancing frictions in determining invest...

Flow Friction or Spontaneous Ignition?

Science.gov (United States)

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.

Friction mediated by redox-active supramolecular connector molecules.

Science.gov (United States)

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

2015-10-06

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

Anomalous friction of graphene nanoribbons on waved graphenes

Directory of Open Access Journals (Sweden)

Jun Fang

2015-11-01

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

[Study of friction and loosening in hip endoprostheses].

Science.gov (United States)

Dovzak Bajs, Ivana; Cvjetko, Ivan; Car, Dolores; Kokić, Visnja

2002-01-01

Like any other operative procedure, the implantation of hip prosthesis is associated with certain complications, which diminishes the value and purpose of such a procedure. One of the complications in artificial hip implantation is loosening of the alloplastic material. Therefore, the aim of this study was to examine the effect of lubrication on the torsional moment and its role in the loosening of the femoral component, using an experimental mechanical model. The following hypothesis was tested: the magnitude of torsional loading in the "bone-endoprosthesis-bone cement system" is similar to any other known loading. The testing device was constructed with the possibility of simulation of positions similar to original performances in the implanted hip prosthesis. It refers primarily to the possibilities of achieving definite forces and velocities. The intention was to point quantitatively to the role of friction moment between the acetabular and femoral endoprosthesis part. Trials were conducted by combining 7 types of loading and 4 kinds of lubrication: dry, water, plasma, and light oil. The testing joint (Ring's prosthesis) was connected through tensometric measuring shaft upon the working forepart oscillating mechanism. Graded by the changeable static loading by means of the pendulum and via lever mechanism the testing joint was loaded by force from 610 to 7137 N. As the cause of friction resistance in the moving joint, torque deformaties of the measuring shaft occurred. The testing joint enabled oscillating movement using a four-part mechanism. In this way, it was possible to define not only the maximum values of the frictional moment (or the coefficient of friction) during one movement cycle but also to examine its relation to the kind of lubrication. Change in the measuring torsional moment were computer recorded. Before each trial, the gauging of the complete outfit was performed. Thereafter, cleaning of the frictional surfaces of the whole outfit was done

International business cycles and the relative price of investment goods

OpenAIRE

Parantap Basu; Christoph Thoenissen

2009-01-01

Is the relative price of investment goods a good proxy for investment frictions? We model this relative price in a flexible price international economy with two fundamental shocks, namely the total factor productivity (TFP) shock and the investment specific technology (IST) shock. The paper argues that the one-to-one correspondence between investment friction and the relative price of investment goods breaks down in an international economy because of the short run correlation between the ter...

Status of Stellite 6 friction testing

International Nuclear Information System (INIS)

Watkins, J.C.; DeWall, K.G.

1998-01-01

For the past several years, researchers at the Idaho National Engineering and Environmental Laboratory, under the sponsorship of the US Nuclear Regulatory Commission, Office of Nuclear Regulatory Research, have been investigating the performance of motor-operated valves subjected to design basis flow and pressure loads. Part of this research addresses the friction that occurs at the interface between the valve disc and the valve body seats during operation of a gate valve. In most gate valves, these surfaces are hardfaced with Stellite 6, a cobalt-based alloy. Analytical methods exist for predicting the thrust needed to operate these valves at specific pressure conditions. To produce accurate valve thrust predictions, the analyst must have a reasonably accurate, though conservative, estimate of the coefficient of friction at the disc-to-seat interface. One of the questions that remains to be answered is whether, and to what extent, aging of the disc and seat surfaces effects the disc-to-seat coefficient of friction. Specifically, does the environment in a nuclear plants piping system cause the accumulation of an oxide film on these surfaces that increases the coefficient of friction; and if so, how great is the increase? This paper presents results of specimen tests addressing this issue, with emphasis on the following: (1) the characteristics and thickness of the oxide film that develops on Stellite 6 as it ages; (2) the change in the friction coefficient of Stellite 6 as it ages, including the question of whether the friction coefficient eventually reaches a plateau; and (3) the effect in-service cycling has on the characteristics and thickness of the oxide film and on the friction coefficient

Thermal effects in static friction: thermolubricity.

Science.gov (United States)

Franchini, A; Bortolani, V; Santoro, G; Brigazzi, M

2008-10-01

We present a molecular dynamics analysis of the static friction between two thick slabs. The upper block is formed by N2 molecules and the lower block by Pb atoms. We study the effects of the temperature as well as the effects produced by the structure of the surface of the lower block on the static friction. To put in evidence the temperature effects we will compare the results obtained with the lower block formed by still atoms with those obtained when the atoms are allowed to vibrate (e.g., with phonons). To investigate the importance of the geometry of the surface of the lower block we apply the external force in different directions, with respect to a chosen crystallographic direction of the substrate. We show that the interaction between the lattice dynamics of the two blocks is responsible for the strong dependence of the static friction on the temperature. The lattice dynamics interaction between the two blocks strongly reduces the static friction, with respect to the case of the rigid substrate. This is due to the large momentum transfer between atoms and the N2 molecules which disorders the molecules of the interface layer. A further disorder is introduced by the temperature. We perform calculations at T = 20K which is a temperature below the melting, which for our slab is at 50K . We found that because of the disorder the static friction becomes independent of the direction of the external applied force. The very low value of the static friction seems to indicate that we are in a regime of thermolubricity similar to that observed in dynamical friction.

Friction Compensation in the Upsetting of Cylindrical Test Specimens

DEFF Research Database (Denmark)

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

2016-01-01

This manuscript presents a combined numerical andexperimental methodology for determining the stress-straincurve of metallic materials from the measurements of forceand displacement obtained in the axial compression of cylindrical test specimens with friction between the specimens and the platens....... The methodology is based on minimizing the errorbetween the average surface pressure obtained from the experimental measurements of the force and displacement and thatobtained from the slab method of analysis of metal plasticity.Three different friction models based on Coulomb friction, the constant friction...... model or combined friction models are utilized .Experimental results obtained from cylindrical and Rastegaev test specimens with different lubricants combined with the experimental determination of friction by means of ring compression tests allows compensating the effect of friction...

Mechanisms of shock-induced dynamic friction

International Nuclear Information System (INIS)

Winter, R E; Ball, G J; Keightley, P T

2006-01-01

The mechanism of shock-induced dynamic friction has been explored through an integrated programme of experiments and numerical simulations. A novel experimental technique has been developed for observing the sub-surface deformation in aluminium when sliding against a steel anvil at high velocity and pressure. The experimental observations suggest that slight differences in conditions at the interface between the metals affect frictional behaviour even at the very high-velocity, high-pressure regime studied here. However, a clear finding from the experimental work is the presence of two distinct modes of deformation termed deep and shallow. The deep deformation is observed in a region of the aluminium specimen where the interfacial velocity is relatively low and the shallow deformation is observed in a region where the interfacial velocity is higher. A 1D numerical treatment is presented which predicts the existence of two mechanisms for dynamic friction termed 'asymptotic melting' and 'slide-then-lock'. In both modes there is a warm-up phase in which the interface temperature is increased by frictional heating. For high initial sliding velocity, this is followed by the onset of the asymptotic melting state, in which the temperature is almost constant and melting is approached asymptotically. This mechanism produces low late-time frictional stress and shallow deformation. For lower initial sliding velocity, the warm-up terminates in a violent work hardening event that locks the interface and launches a strong plastic shear wave into the weaker material. This slide-then-lock mechanism is characterized by sustained high frictional stress and deep plastic deformation. These predicted mechanisms offer a plausible and consistent explanation for the abrupt transitions in the depth of sub-surface deformation observed in the experiments. A key conclusion arising from the current work is that the frictional stress does not vary smoothly with pressure or sliding velocity

Experimental investigation and correlation of two-phase frictional pressure drop of R410A-oil mixture flow boiling in a 5 mm microfin tube

Energy Technology Data Exchange (ETDEWEB)

Ding, Guoliang; Hu, Haitao; Huang, Xiangchao [Institute of Refrigeration and Cryogenics, Shanghai Jiaotong University, Shanghai 200240 (China); Deng, Bin [Institute of Heat Transfer Technology, Golden Dragon Precise Copper Tube Group Inc., Shanghai 200135 (China); Gao, Yifeng [International Copper Association, Shanghai Office, Shanghai 200020 (China)

2009-01-15

This study presents experimental two-phase frictional data for R410A-oil mixture flow boiling in an internal spiral grooved microfin tube with outside diameter of 5 mm. Experimental parameters include the evaporation temperature of 5 C, the mass flux from 200 to 400 kg m{sup -2} s{sup -1}, the heat flux from 7.46 to 14.92 kW m{sup -2}, the inlet vapor quality from 0.1 to 0.8, and nominal oil concentration from 0 to 5%. The test results show that the frictional pressure drop of R410A initially increases with vapor quality and then decreases, presenting a local maximum in the vapor quality range between 0.7 and 0.8; the frictional pressure drop of R410A-oil mixture increases with the mass flux, the presence of oil enhances two-phase frictional pressure drop, and the effect of oil on frictional pressure drop is more evident at higher vapor qualities where the local oil concentrations are higher. The enhanced factor is always larger than unity and increases with nominal oil concentration at a given vapor quality. The range of the enhanced factor is about 1.0-2.2 at present test conditions. A new correlation to predict the local frictional pressure drop of R410A-oil mixture flow boiling inside the internal spiral grooved microfin tube is developed based on local properties of refrigerant-oil mixture, and the measured local frictional pressure drop is well correlated with the empirical equation proposed by the authors. (author)

Skin friction related behaviour of artificial turf systems.

Science.gov (United States)

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

2017-08-01

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

Frictional stability-permeability relationships for fractures in shales

Science.gov (United States)

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.

Friction of ice measured using lateral force microscopy

International Nuclear Information System (INIS)

Bluhm, Hendrik; Inoue, Takahito; Salmeron, Miquel

2000-01-01

The friction of nanometer thin ice films grown on mica substrates is investigated using atomic force microscopy (AFM). Friction was found to be of similar magnitude as the static friction of ice reported in macroscopic experiments. The possible existence of a lubricating film of water due to pressure melting, frictional heating, and surface premelting is discussed based on the experimental results using noncontact, contact, and lateral force microscopy. We conclude that AFM measures the dry friction of ice due to the low scan speed and the squeezing out of the water layer between the sharp AFM tip and the ice surface. (c) 2000 The American Physical Society

Friction characteristics for density of micro dimples using photolithography

International Nuclear Information System (INIS)

Chae, Young Jun; Kim, Seock Sam

2005-01-01

Surface texturing of tribological application is another attractive technology of friction reducing. Also, reduction of friction is therefore considered to be a necessary requirement for improved efficiency of machine. In this paper attempts to investigate the effect of density for micro-scale dimple pattern using photolithography on bearing steel flat mated with pin-on-disk. We demonstrated the lubrication mechanism for a Stribeck curve, which has a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. It is found that friction coefficient is depended on the density of surface pattern. It was thus verified that micro-scale dimple could affect the friction reduction considerably under mixed and hydrodynamic lubrication conditions from based on friction map. Lubrication condition regime has an influence on the friction coefficient induced the density of micro dimple

Friction tensor concept for textured surfaces

Indian Academy of Sciences (India)

Directionality of grinding marks influences the coefficient of friction ... Menezes et al (2006a,b) studied the effect of roughness parameters and grinding angle on ... as coefficient of friction, sliding velocity, normal load, hardness and thermal.

Physically representative atomistic modeling of atomic-scale friction

Science.gov (United States)

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

Friction anisotropy-driven domain imaging on exfoliated monolayer graphene.

Science.gov (United States)

Choi, Jin Sik; Kim, Jin-Soo; Byun, Ik-Su; Lee, Duk Hyun; Lee, Mi Jung; Park, Bae Ho; Lee, Changgu; Yoon, Duhee; Cheong, Hyeonsik; Lee, Ki Ho; Son, Young-Woo; Park, Jeong Young; Salmeron, Miquel

2011-07-29

Graphene produced by exfoliation has not been able to provide an ideal graphene with performance comparable to that predicted by theory, and structural and/or electronic defects have been proposed as one cause of reduced performance. We report the observation of domains on exfoliated monolayer graphene that differ by their friction characteristics, as measured by friction force microscopy. Angle-dependent scanning revealed friction anisotropy with a periodicity of 180° on each friction domain. The friction anisotropy decreased as the applied load increased. We propose that the domains arise from ripple distortions that give rise to anisotropic friction in each domain as a result of the anisotropic puckering of the graphene.

A molecular dynamics (MD simulation on tire-aggregate friction

Directory of Open Access Journals (Sweden)

Fengyan Sun

2017-07-01

Full Text Available The friction between tire and road surface is fundamentally depending on the molecular forces. In this paper, the nanoscale 3D contact model is employed to investigate the tire-aggregate friction mechanism. The tire and aggregate micro-structure are both constructed to evaluate the microscopic performance of tire-aggregate friction influence. Simulation results show for a high velocity, the energy dissipation of sliding on crystal structure is small, which results in a small friction coefficient; temperature will have influences on the friction coefficient, and with the increasing of velocity, the effect will gradually reduce. Keywords: Tire, Aggregate, Friction coefficient, Microscopic mechanism, MD simulation

Sliding friction: From microscopic contacts to Amontons’ law

OpenAIRE

Weber, B.A.

2017-01-01

Most engineers describe sliding friction using the friction coefficient, the ratio of frictional force to normal force. While this proportionality is very simple, its origin is not trivial at all and has been subject of investigation for more than a century. The current consensus is that both frictional and normal force are proportional to the 'real contact area'. Surface roughness prevents surfaces from coming into full contact; the real contact area is simply the fraction of the apparent co...

An empirical model for friction in cold forging

DEFF Research Database (Denmark)

Bay, Niels; Eriksen, Morten; Tan, Xincai

2002-01-01

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

Cationic agent contrast-enhanced computed tomography imaging of cartilage correlates with the compressive modulus and coefficient of friction.

Science.gov (United States)

Lakin, B A; Grasso, D J; Shah, S S; Stewart, R C; Bansal, P N; Freedman, J D; Grinstaff, M W; Snyder, B D

2013-01-01

The aim of this study is to evaluate whether contrast-enhanced computed tomography (CECT) attenuation, using a cationic contrast agent (CA4+), correlates with the equilibrium compressive modulus (E) and coefficient of friction (μ) of ex vivo bovine articular cartilage. Correlations between CECT attenuation and E (Group 1, n = 12) and μ (Group 2, n = 10) were determined using 7 mm diameter bovine osteochondral plugs from the stifle joints of six freshly slaughtered, skeletally mature cows. The equilibrium compressive modulus was measured using a four-step, unconfined, compressive stress-relaxation test, and the coefficients of friction were determined from a torsional friction test. Following mechanical testing, samples were immersed in CA4+, imaged using μCT, rinsed, and analyzed for glycosaminoglycan (GAG) content using the 1,9-dimethylmethylene blue (DMMB) assay. The CECT attenuation was positively correlated with the GAG content of bovine cartilage (R(2) = 0.87, P coefficients of friction: CECT vs μ(static) (R(2) = 0.71, P = 0.002), CECT vs μ(static_equilibrium) (R(2) = 0.79, P coefficient of friction. Copyright © 2012 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.

Experimental studies of the magnetized friction force

International Nuclear Information System (INIS)

Fedotov, A. V.; Litvinenko, V. N.; Gaalnander, B.; Lofnes, T.; Ziemann, V.; Sidorin, A.; Smirnov, A.

2006-01-01

High-energy electron cooling, presently considered as an essential tool for several applications in high-energy and nuclear physics, requires an accurate description of the friction force which ions experience by passing through an electron beam. Present low-energy electron coolers can be used for a detailed study of the friction force. In addition, parameters of a low-energy cooler can be chosen in a manner to reproduce regimes expected in future high-energy operation. Here, we report a set of dedicated experiments in CELSIUS aimed at a detailed study of the magnetized friction force. Some results of the accurate comparison of experimental data with the friction force formulas are presented

Anisotropy in cohesive, frictional granular media

International Nuclear Information System (INIS)

Luding, Stefan

2005-01-01

The modelling of cohesive, frictional granular materials with a discrete particle molecular dynamics is reviewed. From the structure of the quasi-static granular solid, the fabric, stress, and stiffness tensors are determined, including both normal and tangential forces. The influence of the material properties on the flow behaviour is also reported, including relations between the microscopic attractive force and the macroscopic cohesion as well as the dependence of the macroscopic friction on the microscopic contact friction coefficient. Related to the dynamics, the anisotropy of both structure and stress are exponentially approaching the maximum

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

Science.gov (United States)

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.

A study of kinetic friction: The Timoshenko oscillator

Science.gov (United States)

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).

Understanding and Observing Subglacial Friction Using Seismology

Science.gov (United States)

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

30 CFR 57.19008 - Friction hoist synchronizing mechanisms.

Science.gov (United States)

2010-07-01

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

30 CFR 56.19008 - Friction hoist synchronizing mechanisms.

Science.gov (United States)

2010-07-01

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

Friction reduction using discrete surface textures: principle and design

International Nuclear Information System (INIS)

Hsu, Stephen M; Jing, Yang; Hua, Diann; Zhang, Huan

2014-01-01

There have been many reports on the use of dimples, grooves, and other surface textures to control friction in sliding interfaces. The effectiveness of surface textures in friction reduction has been demonstrated in conformal contacts under high speed low load applications such as mechanical seals and automotive water pump seals, etc., resulting in reduced friction and longer durability. For sliding components with higher contact pressures or lower speeds, conflicting results were reported. Reasons for the inconsistency may be due to the differences in texture fabrication techniques, lack of dimple size and shape uniformity, and different tester used. This paper examines the basic principles on which surface textural patterns influence friction under the three principle lubrication regimes: hydrodynamic, elastohydrodynamic, and boundary lubrication regimes. Our findings suggest that each regime requires specific dimple size, shape, depth, and areal density to achieve friction reduction. Control experiments were also conducted to explore mechanisms of friction reduction. The dimple geometric shape and the dimple's orientation with respect to the sliding direction influence friction significantly. The underlying mechanisms for friction control via textures are discussed. (paper)

Current status of Joint FAA/NASA Runway Friction Program

Science.gov (United States)

Yager, Thomas J.; Vogler, William A.

1989-01-01

Tests with specially instrumented NASA B-737 and FAA B-727 aircraft together with several different ground friction measuring devices have been conducted for a variety of runway surface types and wetness conditions. This effort is part of the Joint FAA/NASA Aircraft Ground Vehicle Runway Friction Program aimed at obaining a better understanding of aircraft ground handling performance under adverse weather conditions and defining relationships between aircraft and ground vehicle tire friction measurements. Aircraft braking performance on dry, wet, snow-, and ice-covered runway conditions is discussed together with ground vehicle friction data obtained under similar runway conditions. For the wet, compacted snow- and ice-covered runway conditions, the relationship between ground vehicles and aircraft friction data is identified. The influence of major test parameters on friction measurements such as speed, test tire characteristics, and surface contaminant type are discussed. The test results indicate that use of properly maintained and calibrated ground vehicles for monitoring runway friction conditions should be encouraged particularly under adverse weather conditions. The current status of the runway friction program is summarized and future test plans are identified.

Literature survey on microscopic friction modeling

NARCIS (Netherlands)

Hol, J.

2010-01-01

To better understand contact and friction conditions, experimental and theoretical studies have been performed in order to take microscopic dependencies into account. Friction is developed on microscopic level by adhesion between contacting asperities, the ploughing effect between asperities and the

Prediction of friction coefficients for gases

Science.gov (United States)

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.

Frictional processes in smectite-rich gouges sheared at slow to high slip rates

Science.gov (United States)

Aretusini, Stefano; Mittempergher, Silvia; Gualtieri, Alessandro; Di Toro, Giulio

2015-04-01

The slipping zones of shallow sections of megathrusts and of large landslides are often smectite-rich (e.g., montmorillonite type). Consequently, similar "frictional" processes operating at high slip rates (> 1 m/s) might be responsible of the large slips estimated in megathrust (50 m for the 2011 Tohoku Mw 9.1 earthquake) and measured in large landslides (500 m for the 1963 Vajont slide, Italy). At present, only rotary shear apparatuses can reproduce simultaneously the large slips and slip rates of these events. Noteworthy, the frictional processes proposed so far (thermal and thermochemical pressurization, etc.) remain rather obscure. Here we present preliminary results obtained with the ROtary Shear Apparatus (ROSA) installed at Padua University. Thirty-one experiments were performed at ambient conditions on pure end-members of (1) smectite-rich standard powders (STx-1b: ~68 wt% Ca-montmorillonite, ~30 wt% opal-CT and ~2 wt% quartz), (2) quartz powders (qtz) and (3) on 80:20 = Stx-1b:qtz mixtures. The gouges were sandwiched between two (1) hollow (25/15 mm external/internal diameter) or (2) solid (25 mm in diameter) stainless-steel made cylinders and confined by inner and outer Teflon rings (only outer for solid cylinders). Gouges were sheared at a normal stress of 5 MPa, slip rates V from 300 μm/s to 1.5 m/s and total slip of 3 m. The deformed gouges were investigated with quantitative (Rietveld method with internal standard) X-ray powder diffraction (XRPD) and Scanning Electron Microscopy (SEM). In the smectite-rich standard endmember, (1) for 300 μm/s ≤ V ≤ 0.1 m/s, initial friction coefficient (μi) was 0.6±0.05 whereas the steady-state friction coefficient (μss) was velocity and slip strengthening (μss 0.85±0.05), (2) for 0.1 m/s 0.8 m/s, velocity and slip weakening (μi = 0.7±0.1 and μss = 0.25±0.05). In the 80:20 Stx-1b:qtz mixtures, (1) for 300 μm/s ≤ V ≤ 0.1 m/s, μi ranged was 0.7±0.05 and increased with slip to μss = 0.77±0

Tuning the Friction of Silicon Surfaces Using Nanopatterns at the Nanoscale

Directory of Open Access Journals (Sweden)

Jing Han

2017-12-01

Full Text Available Friction and wear become significant at small scale lengths, particularly in MEMS/NEMS. Nanopatterns are regarded as a potential approach to solve these problems. In this paper, we investigated the friction behavior of nanopatterned silicon surfaces with a periodical rectangular groove array in dry and wear-less single-asperity contact at the nanoscale using molecular dynamics simulations. The synchronous and periodic oscillations of the normal load and friction force with the sliding distance were determined at frequencies defined by the nanopattern period. The linear load dependence of the friction force is always observed for the nanopatterned surface and is independent of the nanopattern geometry. We show that the linear friction law is a formal Amontons’ friction law, while the significant linear dependence of the friction force-versus-real contact area and real contact area-versus-normal load captures the general features of the nanoscale friction for the nanopatterned surface. Interestingly, the nanopattern increases the friction force at the nanoscale, and the desired friction reduction is also observed. The enlargement and reduction of the friction critically depended on the nanopattern period rather than the area ratio. Our simulation results reveal that the nanopattern can modulate the friction behavior at the nanoscale from the friction signal to the friction law and to the value of the friction force. Thus, elaborate nanopatterning is an effective strategy for tuning the friction behavior at the nanoscale.

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

Science.gov (United States)

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

2016-04-01

Friction in orthodontic treatment does exist and is thought to reduce the efficiency of orthodontic appliances during sliding mechanics. During sliding mechanics, a friction force is produced at the bracket archwire-ligature unit which tends to counteract the applied force and in turn resists the desired movement. The aim of this invitro study was to determine the friction between archwire of different sizes, cross section, alloy and brackets ligated with different brands of low friction elastic ligatures. An 0.022-in slot, 10 stainless steel brackets and various orthodontic archwires which were ligated with low-friction ligatures and subjected to evaluate frictional resistance i.e. static friction and dynamic friction. The archwires of 0.014″ and 0.016″ nickel titanium (NiTi), 0.016 × 0.022″ stainless steel (SS), 0.017 × 0.025″ NiTi, 0.017 × 0.025″ SS, 0.017 × 0.025″ titanium molybdenum alloy (TMA), 0.019 × 0.025″ SS were used. Each bracket/archwire combination was evaluated 10 times at room temperature of 27 ± 2°C. The study groups included Group I of conventional round shape module with reduced friction coating i.e. super slick and synergy and Group II contained figure of "8" shape module i.e. Octavia ties and Slide ligature. The mean static friction force and dynamic friction force for all 7 types of wires was lower in Group II (C, D) combined compared to Group I (A, B) and the difference was statistically very highly significant (pfriction mechanics.

Possible stibnite transformation at the friction surface of the semi-metallic friction composites designed for car brake linings

Science.gov (United States)

Matějka, V.; Lu, Y.; Matějková, P.; Smetana, B.; Kukutschová, J.; Vaculík, M.; Tomášek, V.; Zlá, S.; Fan, Y.

2011-12-01

After a friction process several changes in phase composition of friction composites are often registered. High temperature, accompanied by high pressure induced during braking can cause initiation of chemical reactions which do not run at room or elevated temperatures under the atmospheric pressure. Most of the studies in the field of tribochemistry at friction surfaces of automotive semi-metallic brake linings deal with phenolic resin degradation and corrosion of metallic components. The paper addresses the formation of elemental antimony as well as the alloying process of iron with antimony observed on the surface of laboratory prepared semi-metallic friction composites containing stibnite. The role of alumina abrasives in the process of stibnite transformation is also discussed and mechanism of stibnite transformation was outlined.

Micro- and macroscale coefficients of friction of cementitious materials

International Nuclear Information System (INIS)

Lomboy, Gilson; Sundararajan, Sriram; Wang, Kejin

2013-01-01

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 on 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

Atomic-scale friction : thermal effects and capillary condensation

NARCIS (Netherlands)

Jinesh, Kochupurackal Balakrishna Pillai

2006-01-01

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

30 CFR 56.19014 - Friction hoist overtravel protection.

Science.gov (United States)

2010-07-01

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

30 CFR 57.19014 - Friction hoist overtravel protection.

Science.gov (United States)

2010-07-01

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

Sliding friction : From microscopic contacts to Amontons’ law

NARCIS (Netherlands)

Weber, B.A.

2017-01-01

Most engineers describe sliding friction using the friction coefficient, the ratio of frictional force to normal force. While this proportionality is very simple, its origin is not trivial at all and has been subject of investigation for more than a century. The current consensus is that both

Shape optimization in 2D contact problems with given friction and a solution-dependent coefficient of friction

Czech Academy of Sciences Publication Activity Database

Haslinger, J.; Outrata, Jiří; Pathó, R.

2012-01-01

Roč. 20, č. 1 (2012), s. 31-59 ISSN 1877-0533 R&D Projects: GA AV ČR IAA100750802 Institutional research plan: CEZ:AV0Z10750506 Institutional support: RVO:67985556 Keywords : shape optimization * Signorini problem * model with given frinction * solution-dependent coefficient of friction * mathematical probrams with equilibrium constraints Subject RIV: BA - General Mathematics Impact factor: 1.036, year: 2012 http://library.utia.cas.cz/separaty/2012/MTR/outrata-shape optimization in 2d contact problems with given friction and a solution-dependent coefficient of friction .pdf

Friction material composites copper-metal-free material design perspective

CERN Document Server

Sundarkrishnaa, K L

2015-01-01

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

Two dimensional modeling of elastic wave propagation in solids containing cracks with rough surfaces and friction - Part II: Numerical implementation.

Science.gov (United States)

Delrue, Steven; Aleshin, Vladislav; Truyaert, Kevin; Bou Matar, Olivier; Van Den Abeele, Koen

2018-01-01

Our study aims at the creation of a numerical toolbox that describes wave propagation in samples containing internal contacts (e.g. cracks, delaminations, debondings, imperfect intergranular joints) of known geometry with postulated contact interaction laws including friction. The code consists of two entities: the contact model and the solid mechanics module. Part I of the paper concerns an in-depth description of a constitutive model for realistic contacts or cracks that takes into account the roughness of the contact faces and the associated effects of friction and hysteresis. In the crack model, three different contact states can be recognized: contact loss, total sliding and partial slip. Normal (clapping) interactions between the crack faces are implemented using a quadratic stress-displacement relation, whereas tangential (friction) interactions were introduced using the Coulomb friction law for the total sliding case, and the Method of Memory Diagrams (MMD) in case of partial slip. In the present part of the paper, we integrate the developed crack model into finite element software in order to simulate elastic wave propagation in a solid material containing internal contacts or cracks. We therefore implemented the comprehensive crack model in MATLAB® and introduced it in the Structural Mechanics Module of COMSOL Multiphysics®. The potential of the approach for ultrasound based inspection of solids with cracks showing acoustic nonlinearity is demonstrated by means of an example of shear wave propagation in an aluminum sample containing a single crack with rough surfaces and friction. Copyright © 2017 Elsevier B.V. All rights reserved.

Performance evaluation for darcy friction factor formulae using ...

African Journals Online (AJOL)

It is concluded that Newton Raphson ; Prandtl and Nikurdse; Zingrang and Sylvester ; Serghide ; Barr; Swamee and Jain; Eck ; Haaland ; Brkic ; Wood and Moody are first choice friction formulae based on the values of model of selection criterion. Keywords: Darcy Friction Factor, Pipe Flow, Statistical Methods, Darcy Friction ...

Spatial dispersion in atom-surface quantum friction

International Nuclear Information System (INIS)

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

2017-01-01

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 not only the magnitude but also the distance scaling of quantum friction.

Fragility and hysteretic creep in frictional granular jamming.

Science.gov (United States)

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)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 experimental protocol, and the friction coefficient μ, which acts to stabilize the pack.

Cohesive delamination and frictional contact on joining surface via XFEM

Directory of Open Access Journals (Sweden)

Francesco Parrinello

2018-02-01

Full Text Available In the present paper, the complex mechanical behaviour of the surfaces joining two differentbodies is analysed by a cohesive-frictional interface constitutive model. The kinematical behaviouris characterized by the presence of discontinuous displacement fields, that take place at the internalconnecting surfaces, both in the fully cohesive phase and in the delamination one. Generally, in order tocatch discontinuous displacement fields, internal connecting surfaces (adhesive layers are modelled bymeans of interface elements, which connect, node by node, the meshes of the joined bodies, requiringthe mesh to be conforming to the geometry of the single bodies and to the relevant connecting surface.In the present paper, the Extended Finite Element Method (XFEM is employed to model, both fromthe geometrical and from the kinematical point of view, the whole domain, including the connectedbodies and the joining surface. The joining surface is not discretized by specific finite elements, butit is defined as an internal discontinuity surface, whose spatial position inside the mesh is analyticallydefined. The proposed approach is developed for two-dimensional composite domains, formed by twoor more material portions joined together by means of a zero thickness adhesive layer. The numericalresults obtained with the proposed approach are compared with the results of the classical interfacefinite element approach. Some examples of delamination and frictional contact are proposed withlinear, circular and curvilinear adhesive layer.

Deformation During Friction Stir Welding

Science.gov (United States)

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.

Friction in textile thermoplastic composites forming

NARCIS (Netherlands)

Akkerman, Remko; ten Thije, R.H.W.; Sachs, Ulrich; de Rooij, Matthias B.; Binetruy, C.; Boussu, F.

2010-01-01

A previously developed mesoscopic friction model for glass/PP textile composite laminates during forming is evaluated for glass and carbon/PPS laminates, at higher temperatures and lower viscosities than before. Experiments were performed for tool/ply and ply/ply configurations in a new friction

Friction interface mechanics and self-induced vibrations

OpenAIRE

Wernitz, Boris Alexander

2013-01-01

Vibrations in braking systems have been studied since the beginning of the last century and despite several insights, still many phenomena, particularly in the area of friction induced vibrations, are not fully understood. The objective of the actual study was the identification of the complex dynamics in the friction interface of a dry friction brake system. In this context, particular consideration was given to the generation of instabilities and brake squeal. In work presently being ...

Friction Joint Between Basalt-Reinforced Composite and Aluminum

DEFF Research Database (Denmark)

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

2015-01-01

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

Symmetric-Galerkin BEM simulation of fracture with frictional contact

CSIR Research Space (South Africa)

Phan, AV

2003-06-14

Full Text Available FOR NUMERICAL METHODS IN ENGINEERING Int. J. Numer. Meth. Engng 2003; 57:835?851 (DOI: 10.1002/nme.707) Symmetric-Galerkin BEM simulation of fracture with frictional contact A.-V. Phan1;asteriskmath;?, J. A. L. Napier2, L. J. Gray3 and T. Kaplan3 1Department... Methods in Engineering 1975; 9:495?507. 35. Barsoum RS. On the use of isoparametric FFnite elements in linear fracture mechanics. International Journal for Numerical Methods in Engineering 1976; 10:25?37. 36. Gray LJ, Phan A-V, Paulino GH, Kaplan T...

Mechanism of ultra low friction of multilayer graphene studied by coarse-grained molecular simulation.

Science.gov (United States)

Washizu, Hitoshi; Kajita, Seiji; Tohyama, Mamoru; Ohmori, Toshihide; Nishino, Noriaki; Teranishi, Hiroshi; Suzuki, Atsushi

2012-01-01

Coarse-grained Metropolis Monte Carlo Brownian Dynamics simulations are used to clarify the ultralow friction mechanism of a transfer film of multilayered graphene sheets. Each circular graphene sheet consists of 400 to 1,000,000 atoms confined between the upper and lower sliders and are allowed to move in 3 translational and 1 rotational directions due to thermal motion at 300 K. The sheet-sheet interaction energy is calculated by the sum of the pair potential of the sp2 carbons. The sliding simulations are done by moving the upper slider at a constant velocity. In the monolayer case, the friction force shows a stick-slip like curve and the average of the force is high. In the multilayer case, the friction force does not show any oscillation and the average of the force is very low. This is because the entire transfer film has an internal degree of freedom in the multilayer case and the lowest sheet of the layer is able to follow the equipotential surface of the lower slider.

Position-dependent friction in quantum mechanics

International Nuclear Information System (INIS)

Srokowski, T.

1985-01-01

The quantum description of motion of a particle subjected to position-dependent frictional forces is presented. The two cases are taken into account: a motion without external forces and in the harmonic oscillator field. As an example, a frictional barrier penetration is considered. 16 refs. (author)

Adaptive robust motion trajectory tracking control of pneumatic cylinders with LuGre model-based friction compensation

Science.gov (United States)

Meng, Deyuan; Tao, Guoliang; Liu, Hao; Zhu, Xiaocong

2014-07-01

Friction compensation is particularly important for motion trajectory tracking control of pneumatic cylinders at low speed movement. However, most of the existing model-based friction compensation schemes use simple classical models, which are not enough to address applications with high-accuracy position requirements. Furthermore, the friction force in the cylinder is time-varying, and there exist rather severe unmodelled dynamics and unknown disturbances in the pneumatic system. To deal with these problems effectively, an adaptive robust controller with LuGre model-based dynamic friction compensation is constructed. The proposed controller employs on-line recursive least squares estimation (RLSE) to reduce the extent of parametric uncertainties, and utilizes the sliding mode control method to attenuate the effects of parameter estimation errors, unmodelled dynamics and disturbances. In addition, in order to realize LuGre model-based friction compensation, the modified dual-observer structure for estimating immeasurable friction internal state is developed. Therefore, a prescribed motion tracking transient performance and final tracking accuracy can be guaranteed. Since the system model uncertainties are unmatched, the recursive backstepping design technology is applied. In order to solve the conflicts between the sliding mode control design and the adaptive control design, the projection mapping is used to condition the RLSE algorithm so that the parameter estimates are kept within a known bounded convex set. Finally, the proposed controller is tested for tracking sinusoidal trajectories and smooth square trajectory under different loads and sudden disturbance. The testing results demonstrate that the achievable performance of the proposed controller is excellent and is much better than most other studies in literature. Especially when a 0.5 Hz sinusoidal trajectory is tracked, the maximum tracking error is 0.96 mm and the average tracking error is 0.45 mm. This

Effect of friction on the motion of plasma filaments

DEFF Research Database (Denmark)

Garcia, Odd Erik; Madsen, Jens; Naulin, Volker

is influenced by the collisional friction with the neutral gas fluid. In magnetically confined plasmas, the motion of filamentary structures in the edge region can be influenced by parallel dynamics in a manner that resembles an effective friction. In the presence of strong ballooning, such a frictional...... an effective friction, is investigated. In the inertial regime the radial filament velocity scales as the square root of its size. In the limit of strong friction regime the velocity scales as the inverse of the structure size. A discussion of these results will be given in the context of irregularities...

The experiment research of the friction sliding isolation structure

Science.gov (United States)

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.

Methods and devices used to measure friction in rolling

DEFF Research Database (Denmark)

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

2006-01-01

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

Coefficient of friction and wear of sputtered a-C thin coatings containing Mo

Czech Academy of Sciences Publication Activity Database

Novák, P.; Musil, Jindřich; Čerstvý, R.; Jäger, Aleš

2010-01-01

Roč. 205, č. 5 (2010), s. 1486-1490 ISSN 0257-8972. [International Conference on Metallurgical Coatings and Thin Films /37./. San Diego, CA, 26.04.2010-30.04.2010] Institutional research plan: CEZ:AV0Z10100520 Keywords : Mo-C coating * mechanical properties * friction * wear * magnetron sputtering Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.135, year: 2010

Gimballed Shoulders for Friction Stir Welding

Science.gov (United States)

Carter, Robert; Lawless, Kirby

2008-01-01

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

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

Science.gov (United States)

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.

Skin friction under pressure. The role of micromechanics

Science.gov (United States)

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

Ultra Low Friction of DLC Coating with Lubricant

International Nuclear Information System (INIS)

Kano, M; Yoshida, K

2010-01-01

The objective of this study was to find a trigger to make clear a mechanism of the ultra low friction by evaluating the friction property of DLC-DLC combination under lubrication with the simple fluid. The Pin-on-disc reciprocating and rotating sliding tests were conducted to evaluate the friction property. The super low friction property of pure sliding with the ta-C(T) pair coated by the filtered arc deposition process under oleic acid lubrication was found at the mixed lubrication condition. It was thought that the low share strength tribofilm composed of water and acid seemed to be formed on ta-C sliding interface. Additionally, the smooth sliding surface formed on ta-C(T) was seemed to be required to keep this tribofilm. Then, the super low friction was thought to be obtained by this superlubrication condition. Although the accurate and direct experimental data must be required to make clear this super low friction mechanism, the advanced effect obtained by the simple material combination is expected to be applied on the large industrial fields in near future.

In-Vivo Human Skin to Textiles Friction Measurements

Science.gov (United States)

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.

Implementing unsteady friction in pressure-time measurements

OpenAIRE

Jonsson, Pontus; Ramdal, Jorgen; Cervantes, Michel; Nielsen, Torbjørn Kristian

2012-01-01

Laboratory measurements using the pressure‐time method showed a velocity or Reynolds number dependent error of the flow estimate. It was suspected that the quasi steady friction formulation of the method was the cause. This was investigated, and it was proved that implementing a model for unsteady friction into the calculations improved the result. This paper presents the process of this investigation, and proposes a new method for treatment of the friction term in the pressure‐time method.

Gimbaled-shoulder friction stir welding tool

Science.gov (United States)

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

2010-01-01

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

Simulations of the Static Friction Due to Adsorbed Molecules

OpenAIRE

He, Gang; Robbins, Mark O.

2001-01-01

The static friction between crystalline surfaces separated by a molecularly thin layer of adsorbed molecules is calculated using molecular dynamics simulations. These molecules naturally lead to a finite static friction that is consistent with macroscopic friction laws. Crystalline alignment, sliding direction, and the number of adsorbed molecules are not controlled in most experiments and are shown to have little effect on the friction. Temperature, molecular geometry and interaction potenti...

A set-valued force law for spatial Coulomb-Contensou friction

NARCIS (Netherlands)

Leine, R.I.; Glocker, C.

2003-01-01

The aim of this paper is to develop a set-valued contact law for combined spatial Coulomb-Contensou friction, taking into account a normal friction torque (drilling friction) and spin. The set-valued Coulomb-Contensou friction law is derived from a non-smooth velocity pseudo potential. A

Transport properties under the influence of finite friction

Institute of Scientific and Technical Information of China (English)

展永; 赵同军; 于慧; 宋艳丽

2002-01-01

Using the Langevin Monte Carlo method, the influence of friction on the directed motion of a Brownian particle driven by an external noise source is investigated. The results show that the existence and change of the environment friction influence the establishment and development of the steady motion of a Brownian particle derived by non- equilibrium fluctuation. The most probable correlation time, which corresponds to the maximum current, is inversely proportional to the friction coefficient. The abnormal transition of the current with different friction appears because of the coupling between the effective ratchet potential and coloured noise intensity.

Time-dependent friction and solvation time correlation function

International Nuclear Information System (INIS)

Samanta, Alok; Ali, Sk Musharaf; Ghosh, Swapan K

2005-01-01

We have derived a new relation between the time-dependent friction and solvation time correlation function (STCF) for non-polar fluids. The friction values calculated using this relation and simulation results on STCF for a Lennard-Jones fluid are shown to have excellent agreement with the same obtained through mode-coupling theory. Also derived is a relation between the time-dependent dielectric friction and STCF for polar fluids. Routes are thus provided to obtain the time-dependent friction (non-polar as well as dielectric) from an experimentally measured quantity like STCF, even if the interparticle interaction potential is not known

Friction stir welding (FSW) of AA 6061 T6

International Nuclear Information System (INIS)

Cabot, Pedro; Monglioni, Alberto; Carella, Eduardo

2002-01-01

The friction-stir process (FSW) developed by England's TWI in the last decade is a new concept in solid phase friction welding that is particularly appropriate for soldering aluminum and its alloys. It offers interesting aspects and can advantageously replace the usual arch processes. It is an automatic process that solders together long pieces by butt or lap welding and, therefore, overcomes the greater limitation of the conventional friction process that can be applied only to pieces with revolution symmetry. FSW is based essentially on the use of a cylindrical tool with a special profile, which is inserted between the surfaces where the materials meet to join them together at a certain rotation speed and under a specific force. The pieces must be rigidly butt bonded or overlapped to prevent movement when the tool moves forward along the joint producing the dispersion of oxides, local plastisizing of the material and the weld. Since its creation FSW has been the subject of many international publications, but until the present work there was no technologically relevant data about tools and procedures. For this reason, when its promising and novel nature was noticed, the CNEA began its own development project in 1997. The main characteristics of the tool are reviewed here and the results of tests carried out to evaluate the influence of the feed velocity on the mechanical properties of the butt joining of a 6.25 mm thick AA6061 T6 plate. Different accumulated aspects of the experience are discussed as well (cw)

Evaluation of deep drawing force under different friction conditions

Directory of Open Access Journals (Sweden)

Lăzărescu Lucian

2017-01-01

Full Text Available The purpose of this study is to investigate the variation of the required punch load during the deep drawing process under different friction conditions. In this regards, several deep-drawing tests of cylindrical cups were conducted under four friction conditions at the tool–blank interface. The first case was the dry deep-drawing, considered as a reference friction condition, while in the other three cases hydraulic oil, lithium-based grease and animal fat were used as lubricants. For each friction case, three levels of blank holding force were adopted, namely 10, 20 and 25 kN. The finite element simulation of the deep-drawing process was used to generate a set of calibration curves. By overlapping the experimental load-stroke curves on the calibration curves, the friction coefficient was estimated for each friction case.

Microstructures of friction surfaced coatings. A TEM study

International Nuclear Information System (INIS)

Akram, Javed; Kalvala, Prasad Rao; Misra, Mano

2016-01-01

The microstructures of dissimilar metal welds between 9Cr-1Mo (Modified) (P91) and austenitic stainless steel (AISI 304) with Ni-based alloy interlayers (Inconel 625, Inconel 600 and Inconel 800H) are reported. These interlayers were deposited by the friction surfacing method one over the other on P91 alloy, which was finally friction welded to AISI 304. In this paper, the results of microstructural evolution in the friction surfaced coated interlayers (Inconel 625, 600, 800H) are reported. For comparative purposes, the microstructures of consumable rods (Inconel 625, 600, 800H) and dissimilar metal base metals (P91 and AISI 304) were also reported. Friction surfaced coatings exhibited dynamic recrystallization. In friction surfaced coatings, the carbide particles were found to be finer and distributed uniformly throughout the matrix, compared to their rod counterparts.

Change in Frictional Behavior during Olivine Serpentinization

Science.gov (United States)

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

FRICTION - WELDING MACHINE AUTOMATIC CONTROL CIRCUIT DESIGN AND APPLICATION

OpenAIRE

Hakan ATEŞ; Ramazan BAYINDIR

2003-01-01

In this work, automatic controllability of a laboratory-sized friction-welding machine has been investigated. The laboratory-sized friction-welding machine was composed of motor, brake, rotary and constant samples late pliers, and hydraulic unit. In automatic method, welding parameters such as friction time, friction pressure, forge time and forge pressure can be applied sensitively using time relays and contactors. At the end of the experimental study it's observed that automatic control sys...

Confinement-Dependent Friction in Peptide Bundles

Science.gov (United States)

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

ANALYSIS OF THE MAGNETIZED FRICTION FORCE.

Energy Technology Data Exchange (ETDEWEB)

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

2006-05-29

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

Tribology - friction, lubrication and wear: fifty years on. 2 v

International Nuclear Information System (INIS)

1987-01-01

The paper presents the proceedings of the International Tribology Conference held in London (United Kingdom), 1987, and organised by the Institution of Mechanical Engineers. The aim of the conference was to address the current status and future developments in all aspects of tribology. The conference proceedings contained 121 papers, and the sessions were structured under six headings: hydrodynamic, elastohydrodynamic and mixed lubrication; friction and wear; contact mechanics; materials; design and applications; and lubricants. Four papers were chosen for INIS and indexed separately. (U.K.)

Slow rupture of frictional interfaces

OpenAIRE

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

2011-01-01

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 comple...

Scale dependence of rock friction at high work rate.

Science.gov (United States)

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

2015-12-10

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

Asbestos free friction composition for brake linings

Indian Academy of Sciences (India)

WINTEC

Abstract. An asbestos free friction material composite for brake linings is synthesized containing fibrous re- inforcing ... every manufacturer of automotive friction materials uses phenolics as ... The resin binder is a critical compo- nent. The limits ...

Modeling of Instabilities and Self-organization at the Frictional Interface

Science.gov (United States)

Mortazavi, Vahid

The field of friction-induced self-organization and its practical importance remains unknown territory to many tribologists. Friction is usually thought of as irreversible dissipation of energy and deterioration; however, under certain conditions, friction can lead to the formation of new structures at the interface, including in-situ tribofilms and various patterns at the interface. This thesis studies self-organization and instabilities at the frictional interface, including the instability due to the temperature-dependency of the coefficient of friction, the transient process of frictional running-in, frictional Turing systems, the stick-and-slip phenomenon, and, finally, contact angle (CA) hysteresis as an example of solid-liquid friction and dissipation. All these problems are chosen to bridge the gap between fundamental interest in understanding the conditions leading to self-organization and practical motivation. We study the relationship between friction-induced instabilities and friction-induced self-organization. Friction is usually thought of as a stabilizing factor; however, sometimes it leads to the instability of sliding, in particular when friction is coupled with another process. Instabilities constitute the main mechanism for pattern formation. At first, a stationary structure loses its stability; after that, vibrations with increasing amplitude occur, leading to a limit cycle corresponding to a periodic pattern. The self-organization is usually beneficial for friction and wear reduction because the tribological systems tend to enter a state with the lowest energy dissipation. The introductory chapter starts with basic definitions related to self-organization, instabilities and friction, literature review, and objectives. We discuss fundamental concepts that provide a methodological tool to investigate, understand and enhance beneficial processes in tribosystems which might lead to self-organization. These processes could result in the ability of a

Psychophysical evaluation of a variable friction tactile interface

Science.gov (United States)

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.

The friction influence on stress in micro extrusion

Directory of Open Access Journals (Sweden)

J. Piwnik

2010-01-01

Full Text Available Manufacturing of metallic parts by forming methods is industrially widespread due to high production rate, high accuracy, dimension’s and shape’s repeatability and good surface quality. The application of metal extrusion methods for the production of micro parts is possible, but there are some technological problems caused by small dimensions. Size effect is appearing. One of size effect symptom in micro extrusion, is a significant influence of rough contact between workpiece and tool while processing. In the case of rough contact without friction, material flows in the vicinity of the die surface. In order to explain more accurately a friction distribution in this area, the plastic wave friction model is proposed. This paper analyses specifications of a metal extrusion in micro scale. Using the friction model, a substitute friction shear factor mz and its influence on extrusion loading curves is determined in relationship to size of asperities.

Study of nano-scale friction using vortices in superconductors

International Nuclear Information System (INIS)

Maeda, A.; Nakamura, D.; Kitano, H.; Matsumura, H.

2007-01-01

Toward the microscopic understanding of physics of friction at the solid interface, we use the dynamics of driven vortices of superconductor as a new model system. We measured the static friction as a function of the aging time, and compared with the kinetic friction as a function of velocity for the driven vortex lattice of La 1.85 Sr 0.15 CuO 4 . No definite relationship, such as the one proposed for the friction of thick papers, was observed. This supports our previous proposal of the critical phenomena view that the non-Amontons-Coulomb-like behavior of the kinetic friction is a broadened dynamic transition between the static and kinetic regimes

Benchmarking of direct and indirect friction tests in micro forming

DEFF Research Database (Denmark)

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

2012-01-01

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

Static and kinetic friction characteristics of nanowire on different substrates

Energy Technology Data Exchange (ETDEWEB)

Kim, Hyun-Joon [Department of Precision Mechanical Engineering, Kyungpook National University, Sangju 37224 (Korea, Republic of); Nguyen, Gia Hau; Ky, Dinh Le Cao; Tran, Da Khoa [School of Mechanical Engineering, University of Ulsan, Ulsan 44610 (Korea, Republic of); Jeon, Ki-Joon [Department of Environmental Engineering, Inha University, Incheon 22212 (Korea, Republic of); Chung, Koo-Hyun, E-mail: khchung@ulsan.ac.kr [School of Mechanical Engineering, University of Ulsan, Ulsan 44610 (Korea, Republic of)

2016-08-30

Highlights: • Direct measurement of kinetic friction of oxidized Si NW using AFM. • Determination of static friction of oxidized Si NW from most bent state. • Friction characteristics of oxidized Si NW on SiO{sub 2} and graphene. • Estimation of shear stress between cylindrical NW and flat substrate. • No significant dependence of shear stress on NW radius. - Abstract: Friction characteristics of nanowires (NWs), which may be used as building blocks for nano-devices, are crucial, especially for cases where contact sliding occurs during the device operation. In this work, the static and kinetic friction characteristics of oxidized Si NWs deposited on thermally grown SiO{sub 2} and chemical vapor-deposited single layer graphene were investigated using an atomic force microscope (AFM). Kinetic friction between the oxidized Si NWs and the substrates was directly measured by the AFM. Static friction was also obtained from the most bent state of the NWs using the individually determined elastic moduli of the NWs from kinetic friction experiments based on elastic beam theory. Furthermore, the shear stress between the oxidized Si NWs and the substrates was estimated based on adhesive contact theory. It was found that both static and kinetic friction increased as the radius of the NWs increased. The friction of the oxidized Si NWs on the graphene substrate was found to be smaller than that on the SiO{sub 2} substrate, which suggests that chemical vapor-deposited graphene can be used as a lubricant or as a protective layer in nano-devices to reduce friction. The shear stress estimated from the kinetic friction data between the oxidized Si NWs and the SiO{sub 2} substrate ranged from 7.5 to 12.3 MPa while that between the oxidized Si NWs and the graphene substrate ranged from 4.7 to 7.0 MPa. The result also indicated that the dependence of shear stress on the radius of the NWs was not significant. These findings may provide insight into the friction characteristics

Static and kinetic friction characteristics of nanowire on different substrates

International Nuclear Information System (INIS)

Kim, Hyun-Joon; Nguyen, Gia Hau; Ky, Dinh Le Cao; Tran, Da Khoa; Jeon, Ki-Joon; Chung, Koo-Hyun

2016-01-01

Highlights: • Direct measurement of kinetic friction of oxidized Si NW using AFM. • Determination of static friction of oxidized Si NW from most bent state. • Friction characteristics of oxidized Si NW on SiO 2 and graphene. • Estimation of shear stress between cylindrical NW and flat substrate. • No significant dependence of shear stress on NW radius. - Abstract: Friction characteristics of nanowires (NWs), which may be used as building blocks for nano-devices, are crucial, especially for cases where contact sliding occurs during the device operation. In this work, the static and kinetic friction characteristics of oxidized Si NWs deposited on thermally grown SiO 2 and chemical vapor-deposited single layer graphene were investigated using an atomic force microscope (AFM). Kinetic friction between the oxidized Si NWs and the substrates was directly measured by the AFM. Static friction was also obtained from the most bent state of the NWs using the individually determined elastic moduli of the NWs from kinetic friction experiments based on elastic beam theory. Furthermore, the shear stress between the oxidized Si NWs and the substrates was estimated based on adhesive contact theory. It was found that both static and kinetic friction increased as the radius of the NWs increased. The friction of the oxidized Si NWs on the graphene substrate was found to be smaller than that on the SiO 2 substrate, which suggests that chemical vapor-deposited graphene can be used as a lubricant or as a protective layer in nano-devices to reduce friction. The shear stress estimated from the kinetic friction data between the oxidized Si NWs and the SiO 2 substrate ranged from 7.5 to 12.3 MPa while that between the oxidized Si NWs and the graphene substrate ranged from 4.7 to 7.0 MPa. The result also indicated that the dependence of shear stress on the radius of the NWs was not significant. These findings may provide insight into the friction characteristics of NWs.

Fault Frictional Stability in a Nuclear Waste Repository

Science.gov (United States)

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

Static friction of stainless steel wire rope–rubber contacts.

NARCIS (Netherlands)

Loeve, A.J.; Krijger, T.; Mugge, W.; Breedveld, P.; Dodou, D.; Dankelman, J.

2014-01-01

Little is known about static friction of stainless-steel wire ropes ('cables') in contact with soft rubbers, an interface of potential importance for rigidifiable medical instruments. Although friction theories imply that the size and profile of the cables affect static friction, there are no

Fingerprints are unlikely to increase the friction of primate fingerpads.

Science.gov (United States)

Warman, Peter H; Ennos, A Roland

2009-07-01

It is generally assumed that fingerprints improve the grip of primates, but the efficiency of their ridging will depend on the type of frictional behaviour the skin exhibits. Ridges would be effective at increasing friction for hard materials, but in a rubbery material they would reduce friction because they would reduce contact area. In this study we investigated the frictional performance of human fingertips on dry acrylic glass using a modified universal mechanical testing machine, measuring friction at a range of normal loads while also measuring the contact area. Tests were carried out on different fingers, fingers at different angles and against different widths of acrylic sheet to separate the effects of normal force and contact area. The results showed that fingertips behaved more like rubbers than hard solids; their coefficients of friction fell at higher normal forces and friction was higher when fingers were held flatter against wider sheets and hence when contact area was greater. The shear stress was greater at higher pressures, suggesting the presence of a biofilm between the skin and the surface. Fingerprints reduced contact area by a factor of one-third compared with flat skin, however, which would have reduced the friction; this casts severe doubt on their supposed frictional function.

Velocity Dependence of Friction of Confined Hydrocarbons

DEFF Research Database (Denmark)

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

2010-01-01

We present molecular dynamics friction calculations for confined hydrocarbon “polymer” solids with molecular lengths from 20 to 1400 carbon atoms. Two cases are considered: (a) polymer sliding against a hard substrate and (b) polymer sliding on polymer. We discuss the velocity dependence of the f......We present molecular dynamics friction calculations for confined hydrocarbon “polymer” solids with molecular lengths from 20 to 1400 carbon atoms. Two cases are considered: (a) polymer sliding against a hard substrate and (b) polymer sliding on polymer. We discuss the velocity dependence...... of the frictional shear stress for both cases. In our simulations, the polymer films are very thin (∼3 nm), and the solid walls are connected to a thermostat at a short distance from the polymer slab. Under these circumstances we find that frictional heating effects are not important, and the effective temperature...... in the polymer film is always close to the thermostat temperature. In the first setup (a), for hydrocarbons with molecular lengths from 60 to 1400 carbon atoms, the shear stresses are nearly independent of molecular length, but for the shortest hydrocarbon C20H42 the frictional shear stress is lower. In all...

Mechanism for Self-Reacted Friction Stir Welding

Science.gov (United States)

Venable, Richard; Bucher, Joseph

2004-01-01

A mechanism has been designed to apply the loads (the stirring and the resection forces and torques) in self-reacted friction stir welding. This mechanism differs somewhat from mechanisms used in conventional friction stir welding, as described below. The tooling needed to apply the large reaction loads in conventional friction stir welding can be complex. Self-reacted friction stir welding has become popular in the solid-state welding community as a means of reducing the complexity of tooling and to reduce costs. The main problems inherent in self-reacted friction stir welding originate in the high stresses encountered by the pin-and-shoulder assembly that produces the weld. The design of the present mechanism solves the problems. The mechanism includes a redesigned pin-and-shoulder assembly. The welding torque is transmitted into the welding pin by a square pin that fits into a square bushing with set-screws. The opposite or back shoulder is held in place by a Woodruff key and high-strength nut on a threaded shaft. The Woodruff key reacts the torque, while the nut reacts the tensile load on the shaft.

LOW-ENGINE-FRICTION TECHNOLOGY FOR ADVANCED NATURAL-GAS RECIPROCATING ENGINES

Energy Technology Data Exchange (ETDEWEB)

Victor Wong; Tian Tian; Luke Moughon; Rosalind Takata; Jeffrey Jocsak

2006-03-31

This program aims at improving the efficiency of advanced natural-gas reciprocating engines (ANGRE) by reducing piston and piston ring assembly friction without major adverse effects on engine performance, such as increased oil consumption and wear. An iterative process of simulation, experimentation and analysis is being followed towards achieving the goal of demonstrating a complete optimized low-friction engine system. To date, a detailed set of piston and piston-ring dynamic and friction models have been developed and applied that illustrate the fundamental relationships among mechanical, surface/material and lubricant design parameters and friction losses. Demonstration of low-friction ring-pack designs in the Waukesha VGF 18GL engine confirmed total engine FEMP (friction mean effective pressure) reduction of 7-10% from the baseline configuration without significantly increasing oil consumption or blow-by flow. This represents a substantial (30-40%) reduction of the ringpack friction alone. The measured FMEP reductions were in good agreement with the model predictions. Further improvements via piston, lubricant, and surface designs offer additional opportunities. Tests of low-friction lubricants are in progress and preliminary results are very promising. The combined analysis of lubricant and surface design indicates that low-viscosity lubricants can be very effective in reducing friction, subject to component wear for extremely thin oils, which can be mitigated with further lubricant formulation and/or engineered surfaces. Hence a combined approach of lubricant design and appropriate wear reduction offers improved potential for minimum engine friction loss. Piston friction studies indicate that a flatter piston with a more flexible skirt, together with optimizing the waviness and film thickness on the piston skirt offer significant friction reduction. Combined with low-friction ring-pack, material and lubricant parameters, a total power cylinder friction

Controlling friction in a manganite surface by resistive switching

OpenAIRE

Schmidt, Hendrik; Krisponeit, Jon-Olaf; Samwer, Konrad; Volkert, Cynthia A.

2016-01-01

We report a significant change in friction of a $\\rm La_{0.55}Ca_{0.45}MnO_3$ thin film measured as a function of the materials resistive state under ultrahigh vacuum conditions at room temperature by friction force microscopy. While friction is high in the insulating state, it clearly changes to lower values if the probed local region is switched to the conducting state via nanoscale resistance switching. Thus we demonstrate active control of friction without having to change the temperature...

FRICTION - WELDING MACHINE AUTOMATIC CONTROL CIRCUIT DESIGN AND APPLICATION

Directory of Open Access Journals (Sweden)

Hakan ATEŞ

2003-02-01

Full Text Available In this work, automatic controllability of a laboratory-sized friction-welding machine has been investigated. The laboratory-sized friction-welding machine was composed of motor, brake, rotary and constant samples late pliers, and hydraulic unit. In automatic method, welding parameters such as friction time, friction pressure, forge time and forge pressure can be applied sensitively using time relays and contactors. At the end of the experimental study it's observed that automatic control system has been worked successfully.

Friction Properties of Surface-Fluorinated Carbon Nanotubes

Science.gov (United States)

Wal, R. L. Vander; Miyoshi, K.; Street, K. W.; Tomasek, A. J.; Peng, H.; Liu, Y.; Margrave, J. L.; Khabashesku, V. N.

2005-01-01

Surface modification of the tubular or sphere-shaped carbon nanoparticles through chemical treatment, e.g., fluorination, is expected to significantly affect their friction properties. In this study, a direct fluorination of the graphene-built tubular (single-walled carbon nanotubes) structures has been carried out to obtain a series of fluorinated nanotubes (fluoronanotubes) with variable C(n)F (n =2-20) stoichiometries. The friction coefficients for fluoronanotubes, as well as pristine and chemically cut nanotubes, were found to reach values as low as 0.002-0.07, according to evaluation tests run in contact with sapphire in air of about 40% relative humidity on a ball-on-disk tribometer which provided an unidirectional sliding friction motion. These preliminary results demonstrate ultra-low friction properties and show a promise in applications of surface modified nanocarbons as a solid lubricant.

A rare case of severe third degree friction burns and large Morel-Lavallee lesion of the abdominal wall.

Science.gov (United States)

Brown, Darnell J; Lu, Kuo Jung G; Chang, Kristina; Levin, Jennifer; Schulz, John T; Goverman, Jeremy

2018-01-01

Morel-Lavallee lesions (MLLs) are rare internal degloving injuries typically caused by blunt traumatic injuries and most commonly occur around the hips and in association with pelvic or acetabular fractures. MLL is often overlooked in the setting of poly-trauma; therefore, clinicians must maintain a high degree of suspicion and be familiar with the management of such injuries, especially in obese poly-trauma patients. We present a 30-year-old female pedestrian struck by a motor vehicle who sustained multiple long bone fractures, a mesenteric hematoma, and full-thickness abdominal skin friction burn which masked a significant underlying abdominal MLL. The internal degloving caused significant devascularization of the overlying soft tissue and skin which required surgical drainage of hematoma, abdominal wall reconstruction with tangential excision, allografting, negative pressure wound therapy, and ultimately autografting. MLL is a rare, often overlooked, internal degloving injury. Surgeons must maintain a high index of suspicion when dealing with third degree friction burns as they may mask underlying injuries such as MLL, and a delay in diagnosis can lead to increased morbidity.

Magnetic Viscous Drag for Friction Labs

Science.gov (United States)

Gaffney, Chris; Catching, Adam

2016-01-01

The typical friction lab performed in introductory mechanics courses is usually not the favorite of either the student or the instructor. The measurements are not all that easy to make, and reproducibility is usually a troublesome issue. This paper describes the augmentation of such a friction lab with a study of the viscous drag on a magnet…

Estimating Fault Friction From Seismic Signals in the Laboratory

Science.gov (United States)

Rouet-Leduc, Bertrand; Hulbert, Claudia; Bolton, David C.; Ren, Christopher X.; Riviere, Jacques; Marone, Chris; Guyer, Robert A.; Johnson, Paul A.

2018-02-01

Nearly all aspects of earthquake rupture are controlled by the friction along the fault that progressively increases with tectonic forcing but in general cannot be directly measured. We show that fault friction can be determined at any time, from the continuous seismic signal. In a classic laboratory experiment of repeating earthquakes, we find that the seismic signal follows a specific pattern with respect to fault friction, allowing us to determine the fault's position within its failure cycle. Using machine learning, we show that instantaneous statistical characteristics of the seismic signal are a fingerprint of the fault zone shear stress and frictional state. Further analysis of this fingerprint leads to a simple equation of state quantitatively relating the seismic signal power and the friction on the fault. These results show that fault zone frictional characteristics and the state of stress in the surroundings of the fault can be inferred from seismic waves, at least in the laboratory.

Nuclear friction and chaotic motion

International Nuclear Information System (INIS)

Srokowski, T.; Szczurek, A.; Drozdz, S.

1990-01-01

The concept of nuclear friction is considered from the point of view of regular versus chaotic motion in an atomic nucleus. Using a realistic nuclear Hamiltonian it is explicitly shown that the frictional description of the gross features of nuclear collisions is adequate if the system behaves chaotically. Because of the core in the Hamiltonian, the three-body nuclear system already reveals a structure of the phase space rich enough for this concept to be applicable

Slipforming - Materials effect on friction

OpenAIRE

Busterud, Jørgen Thomasgaard

2016-01-01

Master's thesis in Structural engineering Slipforming is a construction method for concrete and it is especially suited for tall constructions with simple geometry. This method have occasionally caused lifting cracks and other surface damages, due to the friction between the slipform panel and the concrete has become to high. The thesis will look at how the choice of material composition in concrete mixes in the combination of a given slipform rate would affect the friction between the ...

Labor Supply and Optimization Frictions

DEFF Research Database (Denmark)

Søgaard, Jakob Egholt

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

Dynamic contact with Signorini's condition and slip rate dependent friction

Directory of Open Access Journals (Sweden)

Kenneth Kuttler

2004-06-01

Full Text Available Existence of a weak solution for the problem of dynamic frictional contact between a viscoelastic body and a rigid foundation is established. Contact is modelled with the Signorini condition. Friction is described by a slip rate dependent friction coefficient and a nonlocal and regularized contact stress. The existence in the case of a friction coefficient that is a graph, which describes the jump from static to dynamic friction, is established, too. The proofs employ the theory of set-valued pseudomonotone operators applied to approximate problems and a priori estimates.

Comparative evaluation of frictional characteristics of coated low friction ligatures - Super Slick Ties™ with conventional uncoated ligatures

Directory of Open Access Journals (Sweden)

Deepu Leander

2011-01-01

Conclusions: SST produced lower levels of friction (11% for all archwire materials when compared to conventional uncoated ligatures (Dispense-A-Stix and both conventional uncoated ligatures and coated ligatures gave a rank order of coefficient of kinetic friction (μkf among archwires, with stainless steel archwires exhibiting the least and TMA TM showing the highest.

Effect of friction time on mechanical and metallurgical properties of continuous drive friction welded Ti6Al4V/SUS321 joints

International Nuclear Information System (INIS)

Li, Peng; Li, Jinglong; Salman, Muhammad; Liang, Li; Xiong, Jiangtao; Zhang, Fusheng

2014-01-01

Highlights: • The effect of friction time on the microstructure and joint strength was studied. • The fit of burn-off lengths at different times yields a simple equation. • The longer friction time leads to oversized flash in Ti6Al4V side and overgrown IMCs. • An IMZ with width less than 3 μm is beneficial to make a strong metallurgical bond. • The average strength of 560 MPa is obtained and higher than ever reported results. - Abstract: Dissimilar joint of Ti6Al4V titanium alloy and SUS321 stainless steel was fabricated by continuous drive friction welding. The effect of friction time on the mechanical properties was evaluated by hardness measurement and tensile test, while the interfacial microstructure and fracture morphologies were analyzed by scanning electron microscope, energy dispersive spectroscope and X-ray Diffraction. The results show that the tensile strength increases with friction time under the experimental conditions. And the maximum average strength 560 MPa, which is 90.3% of the SUS321 base metal, is achieved at a friction time of 4 s. For all samples, studied fracture occurred along the joint interface, where intermetallic compounds like FeTi, Fe 2 Ti, Ni 3 (Al, Ti) and Fe 3 Ti 3 O and many other phases were formed among elements from the two base metals. The width of intermetallic compounds zone increases with friction time up to 3 μm, below which it is beneficial to make a strong metallurgical bond. However, the longer friction time leads to oversized flash on the Ti6Al4V side and overgrown intermetallic compounds. Finally the optimized friction time was discussed to be in the range of 2–4 s, under which the sound joint with good reproducibility can be expected

High Friction Surface Treatments, Transportation Research Synthesis

Science.gov (United States)

2018-03-01

MnDOT and local transportation agencies in Minnesota are considering the use of a high friction surface treatment (HFST) as a safety strategy. HFST is used as a spot pavement surfacing treatment in locations with high friction demand (for example, cr...

The role of friction in tow mechanics

NARCIS (Netherlands)

Cornelissen, Bo

2013-01-01

Friction plays and important role in the processing of fibrous materials: during production of tow materials, during textile manufacturing and during preforming operations for composite moulding processes. One of the poorly understood phenomena in these processes is the dynamic frictional behaviour

Friction brake cushions acceleration and vibration loads

Science.gov (United States)

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

1966-01-01

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

Existence for viscoplastic contact with Coulomb friction problems

Directory of Open Access Journals (Sweden)

Amina Amassad

2002-01-01

frictional contact between an elastic-viscoplastic body and a rigid obstacle. We model the frictional contact both by a Tresca's friction law and a regularized Coulomb's law. We assume, in a first part, that the contact is bilateral and that no separation takes place. In a second part, we consider the Signorini unilateral contact conditions. Proofs are based on a time-discretization method, Banach and Schauder fixed point theorems.

Anisotropic Friction of Wrinkled Graphene Grown by Chemical Vapor Deposition.

Science.gov (United States)

Long, Fei; Yasaei, Poya; Yao, Wentao; Salehi-Khojin, Amin; Shahbazian-Yassar, Reza

2017-06-21

Wrinkle structures are commonly seen on graphene grown by the chemical vapor deposition (CVD) method due to the different thermal expansion coefficient between graphene and its substrate. Despite the intensive investigations focusing on the electrical properties, the nanotribological properties of wrinkles and the influence of wrinkle structures on the wrinkle-free graphene remain less understood. Here, we report the observation of anisotropic nanoscale frictional characteristics depending on the orientation of wrinkles in CVD-grown graphene. Using friction force microscopy, we found that the coefficient of friction perpendicular to the wrinkle direction was ∼194% compare to that of the parallel direction. Our systematic investigation shows that the ripples and "puckering" mechanism, which dominates the friction of exfoliated graphene, plays even a more significant role in the friction of wrinkled graphene grown by CVD. The anisotropic friction of wrinkled graphene suggests a new way to tune the graphene friction property by nano/microstructure engineering such as introducing wrinkles.

Wedge geometry, frictional properties and interseismic coupling of the Java megathrust

Science.gov (United States)

Koulali, Achraf; McClusky, Simon; Cummins, Phil; Tregoning, Paul

2018-06-01

The mechanical interaction between rocks at fault zones is a key element for understanding how earthquakes nucleate and propagate. Therefore, estimating frictional properties along fault planes allows us to infer the degree of elastic strain accumulation throughout the seismic cycle. The Java subduction zone is an active plate boundary where high seismic activity has long been documented. However, very little is known about the seismogenic processes of the megathrust, especially its shallowest portion where onshore geodetic networks are insensitive to recover the pattern of elastic strain. Here, we use the geometry of the offshore accretionary prism to infer frictional properties along the Java subduction zone, using Coulomb critical taper theory. We show that large portions of the inner wedge in the eastern part of the Java subduction megathrust are in a critical state, where the wedge is on the verge of failure everywhere. We identify four clusters with an internal coefficient of friction μint of ∼ 0.8 and hydrostatic pore pressure within the wedge. The average effective coefficient of friction ranges between 0.3 and 0.4, reflecting a strong décollement. Our results also show that the aftershock sequence of the 1994 Mw 7.9 earthquake halted adjacent to a critical segment of the wedge, suggesting that critical taper wedge areas in the eastern Java subduction interface may behave as a permanent barrier to large earthquake rupture. In contrast, in western Java topographic slope and slab dip profiles suggest that the wedge is mechanically stable, i.e deformation is restricted to sliding along the décollement, and likely to coincide with a seismogenic portion of the megathrust. We discuss the seismic hazard implications and highlight the importance of considering the segmentation of the Java subduction zone when assessing the seismic hazard of this region.

Frictional properties of single crystals HMX, RDX and PETN explosives

International Nuclear Information System (INIS)

Wu, Y.Q.; Huang, F.L.

2010-01-01

The frictional properties of single crystals of cyclotetramethylene tetranitramine (HMX), cyclotrimethylene trinitramine (RDX) and pentaerythritol tetranitrate (PETN) secondary explosives are examined using a sensitive friction machine. The explosive crystals used for the measurements are at least 3.5 mm wide. The friction coefficients between crystals of the same explosive (i.e., HMX on HMX, etc.), crystals of different explosives (i.e., HMX on RDX, etc.), and each explosive and a well-polished gauge steel surface are determined. The frictional surfaces are also studied under an environmental scanning electron microscope (ESEM) to analyze surface microstructural changes under increasing loading forces. The friction coefficients vary considerably with increasing normal loading forces and are particularly sensitive to slider shapes, crystal roughness and the mechanical properties of both the slider and the sample. With increasing loading forces, most friction experiments show surface damage, consisting of grooves, debris, and nano-particles, on both the slider and sample. In some cases, a strong evidence of a localized molten state is found in the central region of the friction track. Possible mechanisms that affect the friction coefficient are discussed based on microscopic observations.

Friction behavior of a microstructured polymer surface inspired by snake skin.

Science.gov (United States)

Baum, Martina J; Heepe, Lars; Gorb, Stanislav N

2014-01-01

The aim of this study was to understand the influence of microstructures found on ventral scales of the biological model, Lampropeltis getula californiae, the California King Snake, on the friction behavior. For this purpose, we compared snake-inspired anisotropic microstructured surfaces to other microstructured surfaces with isotropic and anisotropic geometry. To exclude that the friction measurements were influenced by physico-chemical variations, all friction measurements were performed on the same epoxy polymer. For frictional measurements a microtribometer was used. Original data were processed by fast Fourier transformation (FFT) with a zero frequency related to the average friction and other peaks resulting from periodic stick-slip behavior. The data showed that the specific ventral surface ornamentation of snakes does not only reduce the frictional coefficient and generate anisotropic frictional properties, but also reduces stick-slip vibrations during sliding, which might be an adaptation to reduce wear. Based on this extensive comparative study of different microstructured polymer samples, it was experimentally demonstrated that the friction-induced stick-slip behavior does not solely depend on the frictional coefficient of the contact pair.

Friction behavior of a microstructured polymer surface inspired by snake skin

Directory of Open Access Journals (Sweden)

Martina J. Baum

2014-01-01

Full Text Available The aim of this study was to understand the influence of microstructures found on ventral scales of the biological model, Lampropeltis getula californiae, the California King Snake, on the friction behavior. For this purpose, we compared snake-inspired anisotropic microstructured surfaces to other microstructured surfaces with isotropic and anisotropic geometry. To exclude that the friction measurements were influenced by physico-chemical variations, all friction measurements were performed on the same epoxy polymer. For frictional measurements a microtribometer was used. Original data were processed by fast Fourier transformation (FFT with a zero frequency related to the average friction and other peaks resulting from periodic stick-slip behavior. The data showed that the specific ventral surface ornamentation of snakes does not only reduce the frictional coefficient and generate anisotropic frictional properties, but also reduces stick-slip vibrations during sliding, which might be an adaptation to reduce wear. Based on this extensive comparative study of different microstructured polymer samples, it was experimentally demonstrated that the friction-induced stick-slip behavior does not solely depend on the frictional coefficient of the contact pair.

Multi-scale friction modeling for sheet metal forming: the boundary lubrication regime

NARCIS (Netherlands)

Hol, J.D.; Meinders, Vincent T.; de Rooij, Matthias B.; van den Boogaard, Antonius H.

2015-01-01

A physical based friction model is presented to describe friction in full-scale forming simulations. The advanced friction model accounts for the change in surface topography and the evolution of friction in the boundary lubrication regime. The implementation of the friction model in FE software

A method for evaluating dynamical friction in linear ball bearings.

Science.gov (United States)

Fujii, Yusaku; Maru, Koichi; Jin, Tao; Yupapin, Preecha P; Mitatha, Somsak

2010-01-01

A method is proposed for evaluating the dynamical friction of linear bearings, whose motion is not perfectly linear due to some play in its internal mechanism. In this method, the moving part of a linear bearing is made to move freely, and the force acting on the moving part is measured as the inertial force given by the product of its mass and the acceleration of its centre of gravity. To evaluate the acceleration of its centre of gravity, the acceleration of two different points on it is measured using a dual-axis optical interferometer.

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

Science.gov (United States)

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

2016-07-08

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

Optimum design of brake friction material using hybrid entropy-GRA approach

Directory of Open Access Journals (Sweden)

Kumar Naresh

2016-01-01

Full Text Available The effect of Kevlar and natural fibres on the performance of brake friction materials was evaluated. Four friction material specimens were developed by varying the proportion of Kevlar and natural fibres. Two developed composite contained 5-10 wt.% of Kevlar fibre while in the other two the Kevlar fibre was replaced with same amount of natural fibre. SAE J661 protocol was used for the assessment of the tribological properties on a Chase testing machine. Result shows that the specimens containing Kevlar fibres shows higher friction and wear performance, whereas Kevlar replacement with natural fibre resulted in improved fade, recovery and friction fluctuations. Further hybrid entropy-GRA (grey relation analysis approach was applied to select the optimal friction materials using various performance defining attributes (PDA including friction, wear, fade, recovery, friction fluctuations and cost. The friction materials with 10 wt% of natural fibre exhibited the best overall quality.

Experimental research on friction factor of end faces of contacting mechanical seals

Science.gov (United States)

Wei, Long; Gu, Bo-qin; Feng, Xiu; Sun, Jian-jun

2008-11-01

The friction of the seal faces is the most important phenomenon in working process of contacting mechanical seals. The friction factor f is a key parameter for expressing the friction regime of the seal faces, the frictional power, the wearing capacity, the friction heat productivity, the temperature distortion of the end face and the temperature of the end face. The relationship between the friction factor f and the friction regime of the end faces of contacting mechanical seals was discussed from a microscopic point of view. The friction factor is usually worked out by the friction torque which is measured in the test. In the computer aided testing device of the mechanical seal system, the experimental investigations on the basic performance of the B104a-70 contacting mechanical seal was carried out. The test results indicate that the bigger the spring pressure of B104a-70 contacting mechanical seal, the bigger the friction factor. When the spring pressure is less, the bigger the rotational speed, the bigger the friction factor. But when the spring pressure is equal to 0.0866 MPa, the friction factor is not almost influenced by the rotational speed. When the rotational speed and spring pressure are less, the medium pressure has a less influence on the friction factor. When the rotational speed or spring pressure is bigger, the bigger the medium pressure, the less the friction factor.

Velocity dependence of friction of confined polymers

DEFF Research Database (Denmark)

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

2009-01-01

We present molecular dynamics friction calculations for confined hydrocarbon solids with molecular lengths from 20 to 1400 carbon atoms. Two cases are considered: (a) polymer sliding against a hard substrate, and (b) polymer sliding on polymer. We discuss the velocity dependence of the frictional...... shear stress for both cases. In our simulations, the polymer films are very thin (approx. 3 nm), and the solid walls are connected to a thermostat at a short distance from the polymer slab. Under these circumstances we find that frictional heating effects are not important, and the effective temperature...... in the polymer film is always close to the thermostat temperature. In the first setup (a), for hydrocarbons with molecular lengths from 60 to 1400 carbon atoms, the shear stresses are nearly independent of molecular length, but for the shortest hydrocarbon C20H42 the frictional shear stress is lower. In all...

The coefficient of friction, particularly of ice

International Nuclear Information System (INIS)

Mills, Allan

2008-01-01

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

Shape Optimization in Contact Problems with Coulomb Friction and a Solution-Dependent Friction Coefficient

Czech Academy of Sciences Publication Activity Database

Beremlijski, P.; Outrata, Jiří; Haslinger, Jaroslav; Pathó, R.

2014-01-01

Roč. 52, č. 5 (2014), s. 3371-3400 ISSN 0363-0129 R&D Projects: GA ČR(CZ) GAP201/12/0671 Grant - others:GA MŠK(CZ) CZ.1.05/1.1.00/02.0070; GA MŠK(CZ) CZ.1.07/2.3.00/20.0070 Institutional support: RVO:67985556 ; RVO:68145535 Keywords : shape optimization * contact problems * Coulomb friction * solution-dependent coefficient of friction * mathematical programs with equilibrium constraints Subject RIV: BA - General Mathematics Impact factor: 1.463, year: 2014 http://library.utia.cas.cz/separaty/2014/MTR/outrata-0434234.pdf

A technique for measuring dynamic friction coefficient under impact loading.

Science.gov (United States)

Lin, Y L; Qin, J G; Chen, R; Zhao, P D; Lu, F Y

2014-09-01

We develop a novel setup based on the split Hopkinson pressure bar technique to test the dynamic friction coefficient under impact loading. In the setup, the major improvement is that the end of the incident bar near the specimen is wedge-shaped, which results in a combined compressive and shear loading applied to the specimen. In fact, the shear loading is caused by the interfacial friction between specimen and bars. Therefore, when the two loading force histories are measured, the friction coefficient histories can be calculated without any assumptions and theoretical derivations. The geometry of the friction pairs is simple, and can be either cuboid or cylindrical. Regarding the measurements, two quartz transducers are used to directly record the force histories, and an optical apparatus is designed to test the interfacial slip movement. By using the setup, the dynamic friction coefficient of PTFE/aluminum 7075 friction pairs was tested. The time resolved dynamic friction coefficient and slip movement histories were achieved. The results show that the friction coefficient changes during the loading process, the average data of the relatively stable flat plateau section of the friction coefficient curves is 0.137, the maximum normal pressure is 52 MPa, the maximum relative slip velocity is 1.5 m/s, and the acceleration is 8400 m(2)/s. Furthermore, the friction test was simulated using an explicit FEM code LS-DYNA. The simulation results showed that the constant pressure and slip velocity can both be obtained with a wide flat plateau incident pulse. For some special friction pairs, normal pressure up to a few hundred MPa, interfacial slip velocities up to 10 m/s, and slip movement up to centimeter-level can be expected.

Existence of Stick-Slip Periodic Solutions in a Dry Friction Oscillator

International Nuclear Information System (INIS)

Li Qun-Hong; Chen Yu-Ming; Qin Zhi-Ying

2011-01-01

The stick-slip behavior in friction oscillators is very complicated due to the non-smoothness of the dry friction, which is the basic form of motion of dynamical systems with friction. In this paper, the stick-slip periodic solution in a single-degree-of-freedom oscillator with dry friction is investigated in detail. Under the assumption of kinetic friction being the Coulomb friction, the existence of the stick-slip periodic solution is considered to give out an analytic criterion in a class of friction systems. A two-parameter unfolding diagram is also described. Moreover, the time and states of motion on the boundary of the stick and slip motions are semi-analytically obtained in a single stick-slip period. (general)

Internal Friction and Young's Modulus Measurements on SiO2 and Ta2O5 Films Done with an Ultra-High Q Silicon-Wafer Suspension

Directory of Open Access Journals (Sweden)

Granata M.

2015-04-01

Full Text Available In order to study the internal friction of thin films a nodal suspension system called GeNS (Gentle Nodal Suspension has been developed. The key features of this system are: i the possibility to use substrates easily available like silicon wafers; ii extremely low excess losses coming from the suspension system which allows to measure Q factors in excess of 2×108 on 3” diameter wafers; iii reproducibility of measurements within few percent on mechanical losses and 0.01% on resonant frequencies; iv absence of clamping; v the capability to operate at cryogenic temperatures. Measurements at cryogenic temperatures on SiO2 and at room temperature only on Ta2O5 films deposited on silicon are presented.

Language friction and partner selection in cross-border R&D alliance formation

OpenAIRE

Amol M Joshi; Nandini Lahiri

2015-01-01

How does language friction affect alliance formation? Language friction is a form of cultural friction arising from structural differences in the respective languages used by potential partners to reason and solve problems together. A little language friction may prompt partners to rethink solutions, thereby enhancing collaboration, but excessive friction may impede collaboration. We develop a Language Friction Index (LFI) to quantify relative differences in linguistic structure for any langu...

Friction and drag forces on spheres propagating down inclined planes

Science.gov (United States)

Tee, Yi Hui; Longmire, Ellen

2017-11-01

When a submerged sphere propagates along an inclined wall at terminal velocity, it experiences gravity, drag, lift, and friction forces. In the related equations of motion, the drag, lift and friction coefficients are unknown. Experiments are conducted to determine the friction and drag coefficients of the sphere over a range of Reynolds numbers. Through high speed imaging, translational and rotational velocities of spheres propagating along a glass plate are determined in liquids with several viscosities. The onset of sliding motion is identified by computing the dimensionless rotation rate of the sphere. Using drag and lift coefficients for Re friction coefficients are calculated for several materials. The friction coefficients are then employed to estimate the drag coefficient for 350 frictional force over this Re range. Supported by NSF (CBET-1510154).

Mechanism of sliding friction on a film-terminated fibrillar interface.

Science.gov (United States)

Shen, Lulin; Jagota, Anand; Hui, Chung-Yuen

2009-03-03

We study the mechanism of sliding friction on a film-terminated fibrillar interface. It has been shown that static friction increases significantly with increasing spacing between fibrils, and with increasing rate of loading. However, surprisingly, the sliding friction remains substantially unaffected both by geometry and by the rate of loading. The presence of the thin terminal film is a controlling factor in determining the sliding friction. Experimentally, and by a simple model in which the indenter is held up by the tension in the thin film, we show how the indenter maintains a nearly constant contact area that is independent of the fibril spacing, resulting in constant sliding friction. By this mechanism, using the film-terminated structure, one can enhance the static friction without affecting the sliding behavior.

Frictional forces between hydrophilic and hydrophobic particle coated nanostructured surfaces

DEFF Research Database (Denmark)

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

2013-01-01

Friction forces have long been associated with the famous Amontons' rule that states that the friction force is linearly dependent on the applied normal load, with the proportionality constant being known as the friction coefficient. Amontons' rule is however purely phenomenological and does...... not in itself provide any information on why the friction coefficient is different for different material combinations. In this study, friction forces between a colloidal probe and nanostructured particle coated surfaces in an aqueous environment exhibiting different roughness length scales were measured...... by utilizing the atomic force microscope (AFM). The chemistry of the surfaces and the probe was varied between hydrophilic silica and hydrophobized silica. For hydrophilic silica surfaces, the friction coefficient was significantly higher for the particle coated surfaces than on the flat reference surface. All...

Low-Engine-Friction Technology for Advanced Natural-Gas Reciprocating Engines

Energy Technology Data Exchange (ETDEWEB)

Victor Wong; Tian Tian; G. Smedley; L. Moughon; Rosalind Takata; J. Jocsak

2006-11-30

This program aims at improving the efficiency of advanced natural-gas reciprocating engines (ANGRE) by reducing piston and piston ring assembly friction without major adverse effects on engine performance, such as increased oil consumption and wear. An iterative process of simulation, experimentation and analysis has been followed towards achieving the goal of demonstrating a complete optimized low-friction engine system. In this program, a detailed set of piston and piston-ring dynamic and friction models have been adapted and applied that illustrate the fundamental relationships among mechanical, surface/material and lubricant design parameters and friction losses. Demonstration of low-friction ring-pack designs in the Waukesha VGF 18GL engine confirmed ring-pack friction reduction of 30-40%, which translates to total engine FEMP (friction mean effective pressure) reduction of 7-10% from the baseline configuration without significantly increasing oil consumption or blow-by flow. The study on surface textures, including roughness characteristics, cross hatch patterns, dimples and grooves have shown that even relatively small-scale changes can have a large effect on ring/liner friction, in some cases reducing FMEP by as much as 30% from a smooth surface case. The measured FMEP reductions were in good agreement with the model predictions. The combined analysis of lubricant and surface design indicates that low-viscosity lubricants can be very effective in reducing friction, subject to component wear for extremely thin oils, which can be mitigated with further lubricant formulation and/or engineered surfaces. Hence a combined approach of lubricant design and appropriate wear reduction offers improved potential for minimum engine friction loss. Testing of low-friction lubricants showed that total engine FMEP reduced by up to {approx}16.5% from the commercial reference oil without significantly increasing oil consumption or blow-by flow. Piston friction studies

Effects of heat transfer, friction and variable specific heats of working fluid on performance of an irreversible dual cycle

International Nuclear Information System (INIS)

Chen Lingen; Ge Yanlin; Sun Fengrui; Wu Chih

2006-01-01

The thermodynamic performance of an air standard dual cycle with heat transfer loss, friction like term loss and variable specific heats of working fluid is analyzed. The relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between power output and the efficiency of the cycle, are derived by detailed numerical examples. Moreover, the effects of variable specific heats of the working fluid and the friction like term loss on the irreversible cycle performance are analyzed. The results show that the effects of variable specific heats of working fluid and friction like term loss on the cycle performance are obvious, and they should be considered in practical cycle analysis. The results obtained in this paper may provide guidance for the design of practical internal combustion engines

Friction in total hip joint prosthesis measured in vivo during walking.

Science.gov (United States)

Damm, Philipp; Dymke, Joern; Ackermann, Robert; Bender, Alwina; Graichen, Friedmar; Halder, Andreas; Beier, Alexander; Bergmann, Georg

2013-01-01

Friction-induced moments and subsequent cup loosening can be the reason for total hip joint replacement failure. The aim of this study was to measure the in vivo contact forces and friction moments during walking. Instrumented hip implants with Al2O3 ceramic head and an XPE inlay were used. In vivo measurements were taken 3 months post operatively in 8 subjects. The coefficient of friction was calculated in 3D throughout the whole gait cycle, and average values of the friction-induced power dissipation in the joint were determined. On average, peak contact forces of 248% of the bodyweight and peak friction moments of 0.26% bodyweight times meter were determined. However, contact forces and friction moments varied greatly between individuals. The friction moment increased during the extension phase of the joint. The average coefficient of friction also increased during this period, from 0.04 (0.03 to 0.06) at contralateral toe off to 0.06 (0.04 to 0.08) at contralateral heel strike. During the flexion phase, the coefficient of friction increased further to 0.14 (0.09 to 0.23) at toe off. The average friction-induced power throughout the whole gait cycle was 2.3 W (1.4 W to 3.8 W). Although more parameters than only the synovia determine the friction, the wide ranges of friction coefficients and power dissipation indicate that the lubricating properties of synovia are individually very different. However, such differences may also exist in natural joints and may influence the progression of arthrosis. Furthermore, subjects with very high power dissipation may be at risk of thermally induced implant loosening. The large increase of the friction coefficient during each step could be caused by the synovia being squeezed out under load.

Friction in total hip joint prosthesis measured in vivo during walking.

Directory of Open Access Journals (Sweden)

Philipp Damm

Full Text Available Friction-induced moments and subsequent cup loosening can be the reason for total hip joint replacement failure. The aim of this study was to measure the in vivo contact forces and friction moments during walking. Instrumented hip implants with Al2O3 ceramic head and an XPE inlay were used. In vivo measurements were taken 3 months post operatively in 8 subjects. The coefficient of friction was calculated in 3D throughout the whole gait cycle, and average values of the friction-induced power dissipation in the joint were determined. On average, peak contact forces of 248% of the bodyweight and peak friction moments of 0.26% bodyweight times meter were determined. However, contact forces and friction moments varied greatly between individuals. The friction moment increased during the extension phase of the joint. The average coefficient of friction also increased during this period, from 0.04 (0.03 to 0.06 at contralateral toe off to 0.06 (0.04 to 0.08 at contralateral heel strike. During the flexion phase, the coefficient of friction increased further to 0.14 (0.09 to 0.23 at toe off. The average friction-induced power throughout the whole gait cycle was 2.3 W (1.4 W to 3.8 W. Although more parameters than only the synovia determine the friction, the wide ranges of friction coefficients and power dissipation indicate that the lubricating properties of synovia are individually very different. However, such differences may also exist in natural joints and may influence the progression of arthrosis. Furthermore, subjects with very high power dissipation may be at risk of thermally induced implant loosening. The large increase of the friction coefficient during each step could be caused by the synovia being squeezed out under load.

Dynamic frictional contact for elastic viscoplastic material

Directory of Open Access Journals (Sweden)

Kenneth L. Kuttler

2007-05-01

Full Text Available Using a general theory for evolution inclusions, existence and uniqueness theorems are obtained for weak solutions to a frictional dynamic contact problem for elastic visco-plastic material. An existence theorem in the case where the friction coefficient is discontinuous is also presented.

Advanced friction modeling for sheet metal forming

NARCIS (Netherlands)

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

2012-01-01

The Coulomb friction model is frequently used for sheet metal forming simulations. This model incorporates a constant coefficient of friction and does not take the influence of important parameters such as contact pressure or deformation of the sheet material into account. This article presents a

Advanced friction modeling in sheet metal forming

NARCIS (Netherlands)

Hol, J.; Cid Alfaro, M.V.; Meinders, Vincent T.; Huetink, Han

2011-01-01

The Coulomb friction model is frequently used for sheet metal forming simulations. This model incorporates a constant coefficient of friction and does not take the influence of important parameters such as contact pressure or deformation of the sheet material into account. This article presents a

Study on friction behaviour of brake shoe materials for mining hoist

Science.gov (United States)

Ungureanu, M.; Ungureanu, N. S.; Crăciun, I.

2017-02-01

The friction coefficient in the brake linkages has an important influence on the braking efficiency and safety of machines. The paper presents a method for the study of the friction coefficient of the friction couple brake shoe-drum for mining hoist. In this context, it is interesting to define the friction coefficient, not just according to the materials in contact, but according to the entire ensemble of tribological factors of the friction couple.

An Extension of the Burridge-Knopoff Model for Friction

Directory of Open Access Journals (Sweden)

Veturia Chiroiu

2015-09-01

Full Text Available The paper presents an extension of the Burridge-Knopoff (BK model with an additional kinetic equation for the friction force in order to reproduce the both the velocity weakening friction between the tire and the road and the increase of static friction with time when the car is not moving. The BK was initially proposed to investigate statistical properties of earthquakes. In this model the sliding force decreases monotonously from a reference value, and the static friction can have negative values to prevent back sliding. The stability of the system is affected and the sliding regime at small sliding velocities and large stiffness cannot be reproduced. The extended model BK assures the stability of the diagram sliding-stationary sliding, and correctly reproduces the stability diagram for sliding friction under various loading conditions.

Frictions in Project-Based Supply of Permits

International Nuclear Information System (INIS)

Liski, M.; Virrankoski, J.

2004-01-01

Emissions trading in climate change can entail large overall cost savings and transfers between developed and developing countries. However, the search for acceptable JI or CDM projects implies a deviation from the perfect market framework used in previous estimations. Our model combines the search market for projects with a frictionless permit market to quantify the supply-side frictions in the CO2 market. We also decompose the effects of frictions into the effects of search friction, bargaining, and bilateralism. A calibration using previous cost estimates of CO2 reductions illustrate changes in cost savings and allocative implications

Rubber friction: role of the flash temperature