Integrated view of internal friction in unfolded proteins from single-molecule FRET, contact quenching, theory, and simulations

PubMed Central

Soranno, Andrea; Holla, Andrea; Dingfelder, Fabian; Nettels, Daniel; Makarov, Dmitrii E.; Schuler, Benjamin

2017-01-01

Internal friction is an important contribution to protein dynamics at all stages along the folding reaction. Even in unfolded and intrinsically disordered proteins, internal friction has a large influence, as demonstrated with several experimental techniques and in simulations. However, these methods probe different facets of internal friction and have been applied to disparate molecular systems, raising questions regarding the compatibility of the results. To obtain an integrated view, we apply here the combination of two complementary experimental techniques, simulations, and theory to the same system: unfolded protein L. We use single-molecule Förster resonance energy transfer (FRET) to measure the global reconfiguration dynamics of the chain, and photoinduced electron transfer (PET), a contact-based method, to quantify the rate of loop formation between two residues. This combination enables us to probe unfolded-state dynamics on different length scales, corresponding to different parts of the intramolecular distance distribution. Both FRET and PET measurements show that internal friction dominates unfolded-state dynamics at low denaturant concentration, and the results are in remarkable agreement with recent large-scale molecular dynamics simulations using a new water model. The simulations indicate that intrachain interactions and dihedral angle rotation correlate with the presence of internal friction, and theoretical models of polymer dynamics provide a framework for interrelating the contribution of internal friction observed in the two types of experiments and in the simulations. The combined results thus provide a coherent and quantitative picture of internal friction in unfolded proteins that could not be attained from the individual techniques. PMID:28223518

Integrated view of internal friction in unfolded proteins from single-molecule FRET, contact quenching, theory, and simulations.

PubMed

Soranno, Andrea; Holla, Andrea; Dingfelder, Fabian; Nettels, Daniel; Makarov, Dmitrii E; Schuler, Benjamin

2017-03-07

Internal friction is an important contribution to protein dynamics at all stages along the folding reaction. Even in unfolded and intrinsically disordered proteins, internal friction has a large influence, as demonstrated with several experimental techniques and in simulations. However, these methods probe different facets of internal friction and have been applied to disparate molecular systems, raising questions regarding the compatibility of the results. To obtain an integrated view, we apply here the combination of two complementary experimental techniques, simulations, and theory to the same system: unfolded protein L. We use single-molecule Förster resonance energy transfer (FRET) to measure the global reconfiguration dynamics of the chain, and photoinduced electron transfer (PET), a contact-based method, to quantify the rate of loop formation between two residues. This combination enables us to probe unfolded-state dynamics on different length scales, corresponding to different parts of the intramolecular distance distribution. Both FRET and PET measurements show that internal friction dominates unfolded-state dynamics at low denaturant concentration, and the results are in remarkable agreement with recent large-scale molecular dynamics simulations using a new water model. The simulations indicate that intrachain interactions and dihedral angle rotation correlate with the presence of internal friction, and theoretical models of polymer dynamics provide a framework for interrelating the contribution of internal friction observed in the two types of experiments and in the simulations. The combined results thus provide a coherent and quantitative picture of internal friction in unfolded proteins that could not be attained from the individual techniques.

Internal friction of single polypeptide chains at high stretch.

PubMed

Khatri, Bhavin S; Byrne, Katherine; Kawakami, Masaru; Brockwell, David J; Smith, D Alastair; Radford, Sheena E; McLeish, Tom C B

2008-01-01

Experiments that measure the viscoelasticity of single molecules from the Brownian fluctuations of an atomic force microscope (AFM) have provided a new window onto their internal dynamics in an underlying conformational landscape. Here we develop and apply these methods to examine the internal friction of unfolded polypeptide chains at high stretch. The results reveal a power law dependence of internal friction with tension (exponent 1.3 +/- 0.5) and a relaxation time approximately independent of force. To explain these results we develop a frictional worm-like chain (FWLC) model based on the Rayleigh dissipation function of a stiff chain with dynamical resistance to local bending. We analyse the dissipation rate integrated over the chain length by its Fourier components to calculate an effective tension-dependent friction constant for the end-to-end vector of the chain. The result is an internal friction that increases as a power law with tension with an exponent 3/2, consistent with experiment. Extracting the intrinsic bending friction constant of the chain it is found to be approximately 7 orders of magnitude greater than expected from solvent friction alone; a possible explanation we offer is that the underlying energy landscape for bending amino acids and/or peptide bond is rough, consistent with recent results on both proteins and polysaccharides.

Driving- stress waveform and the determination of rock internal friction by the stress-strain curve method.

USGS Publications Warehouse

Hsi-Ping, Liu

1980-01-01

Harmonic distortion in the stress-time function applied to rock specimens affects the measurement of rock internal friction in the seismic wave periods by the stress-strain hysteresis loop method. If neglected, the harmonic distortion can cause measurements of rock internal friction to be in error by 3O% in the linear range. The stress-time function therefore must be recorded and Fourier analysed for correct interpretation of the experimental data. Such a procedure would also yield a value for internal friction at the higher harmonic frequencies.-Author

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

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

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

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 viamore » 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.« less

Is internal friction friction?

USGS Publications Warehouse

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

1996-01-01

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

Internal friction measurement in high purity tungsten single crystal

NASA Technical Reports Server (NTRS)

Rieu, G. E.

1974-01-01

Internal friction peaks observed after small deformation in high purity tungsten single crystals between liquid helium temperature and 800 K in the frequency range 30-50 KHz, are studied as a function of orientation. An orientation effect is observed in the internal friction spectra due to the creation of internal stresses. The elementary processes related to these peaks are discussed in terms of kink generation and geometric kink motion on screw and edge dislocations in an internal stress field.

Internal friction and nonequilibrium unfolding of polymeric globules.

PubMed

Alexander-Katz, Alfredo; Wada, Hirofumi; Netz, Roland R

2009-07-10

The stretching response of a single collapsed homopolymer is studied using Brownian dynamic simulations. The irreversibly dissipated work is found to be dominated by internal friction effects below the collapse temperature, and the internal viscosity grows exponentially with the effective cohesive strength between monomers. These results explain friction effects of globular DNA and are relevant for dissipation at intermediate stages of protein folding.

Internal friction in an intrinsically disordered protein—Comparing Rouse-like models with experiments

NASA Astrophysics Data System (ADS)

Soranno, Andrea; Zosel, Franziska; Hofmann, Hagen

2018-03-01

Internal friction is frequently found in protein dynamics. Its molecular origin however is difficult to conceptualize. Even unfolded and intrinsically disordered polypeptide chains exhibit signs of internal friction despite their enormous solvent accessibility. Here, we compare four polymer theories of internal friction with experimental results on the intrinsically disordered protein ACTR (activator of thyroid hormone receptor). Using nanosecond fluorescence correlation spectroscopy combined with single-molecule Förster resonance energy transfer (smFRET), we determine the time scales of the diffusive chain dynamics of ACTR at different solvent viscosities and varying degrees of compaction. Despite pronounced differences between the theories, we find that all models can capture the experimental viscosity-dependence of the chain relaxation time. In contrast, the observed slowdown upon chain collapse of ACTR is not captured by any of the theories and a mechanistic link between chain dimension and internal friction is still missing, implying that the current theories are incomplete. In addition, a discrepancy between early results on homopolymer solutions and recent single-molecule experiments on unfolded and disordered proteins suggests that internal friction is likely to be a composite phenomenon caused by a variety of processes.

Internal friction in an intrinsically disordered protein-Comparing Rouse-like models with experiments.

PubMed

Soranno, Andrea; Zosel, Franziska; Hofmann, Hagen

2018-03-28

Internal friction is frequently found in protein dynamics. Its molecular origin however is difficult to conceptualize. Even unfolded and intrinsically disordered polypeptide chains exhibit signs of internal friction despite their enormous solvent accessibility. Here, we compare four polymer theories of internal friction with experimental results on the intrinsically disordered protein ACTR (activator of thyroid hormone receptor). Using nanosecond fluorescence correlation spectroscopy combined with single-molecule Förster resonance energy transfer (smFRET), we determine the time scales of the diffusive chain dynamics of ACTR at different solvent viscosities and varying degrees of compaction. Despite pronounced differences between the theories, we find that all models can capture the experimental viscosity-dependence of the chain relaxation time. In contrast, the observed slowdown upon chain collapse of ACTR is not captured by any of the theories and a mechanistic link between chain dimension and internal friction is still missing, implying that the current theories are incomplete. In addition, a discrepancy between early results on homopolymer solutions and recent single-molecule experiments on unfolded and disordered proteins suggests that internal friction is likely to be a composite phenomenon caused by a variety of processes.

Internal Friction And Instabilities Of Rotors

NASA Technical Reports Server (NTRS)

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

1992-01-01

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

PREFACE: The International Conference on Science of Friction

NASA Astrophysics Data System (ADS)

Miura, Kouji; Matsukawa, Hiroshi

2007-07-01

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

Internal friction and dislocation collective pinning in disordered quenched solid solutions

NASA Astrophysics Data System (ADS)

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.

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

PubMed

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

2014-06-18

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

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

PubMed Central

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

2012-01-01

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

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

PubMed

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

2012-01-01

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

Dispersion Forces and the Molecular Origin of Internal Friction in Protein.

PubMed

Sashi, Pulikallu; Ramakrishna, Dasari; Bhuyan, Abani K

2016-08-23

Internal friction in macromolecules is one of the curious phenomena that control conformational changes and reaction rates. It is held here that dispersion interactions and London-van der Waals forces between nonbonded atoms are major contributors to internal friction. To demonstrate this, the flipping motion of aromatic rings of F10 and Y97 amino acid residues of cytochrome c has been studied in glycerol/water mixtures by cross relaxation-suppressed exchange nuclear magnetic resonance spectroscopy. The ring-flip rate is highly overdamped by glycerol, but this is not due to the effect of protein-solvent interactions on the Brownian dynamics of the protein, because glycerol cannot penetrate into the protein to slow the internal collective motions. Sound velocity in the protein under matching solvent conditions shows that glycerol exerts its effect by rather smothering the protein interior to produce reduced molecular compressibility and root-mean-square volume fluctuation (δVRMS), implying an increased number of dispersion interactions of nonbonded atoms. Hence, δVRMS can be used as a proxy for internal friction. By using the ansatz that internal friction is related to nonbonded interactions by the equation f(n) = f0 + f1n + f2n(2) + ..., where the variable n is the extent of nonbonded interactions with fi coefficients, the barrier to aromatic ring rotation is found to be flat. Also interesting is the appearance of a turnover region in the δVRMS dependence of the ring-flip rate, suggesting anomalous internal diffusion. We conclude that cohesive forces among nonbonded atoms are major contributors to the molecular origin of internal friction.

Linear viscoelasticity of a single semiflexible polymer with internal friction.

PubMed

Hiraiwa, Tetsuya; Ohta, Takao

2010-07-28

The linear viscoelastic behaviors of single semiflexible chains with internal friction are studied based on the wormlike-chain model. It is shown that the frequency dependence of the complex compliance in the high frequency limit is the same as that of the Voigt model. This asymptotic behavior appears also for the Rouse model with internal friction. We derive the characteristic times for both the high frequency limit and the low frequency limit and compare the results with those obtained by Khatri et al.

Temperature-Dependent Friction and Wear Behavior of PTFE and MoS 2

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

Babuska, T. F.; Pitenis, A. A.; Jones, M. R.

2016-06-16

We present an investigation of the temperature-dependent friction behavior of PTFE, MoS 2, and PTFE-on- MoS 2. Friction behavior was measured while continuously varying contact temperature in the range -150 to 175°C while sliding in dry nitrogen, as well as for self-mated PTFE immersed in liquid nitrogen. These results contrast with previous reports of monotonic inverse temperature dependent friction behavior, as well as reported high-friction transitions and plateaus at temperatures below about -20°C that were not observed, providing new insights about the molecular mechanisms of macro-scale friction. The temperature-dependent friction behavior characteristic of self-mated PTFE was found also on themore » PTFE-on-MoS 2 sliding contact, suggesting that PTFE friction was defined by sub-surface deformation mechanisms and internal friction even when sliding against a lamellar lubricant with extremely low friction coefficient (μ ~ 0.02). The various relaxation temperatures of PTFE were found in the temperature-dependent friction behavior, showing excellent agreement with reported values acquired using torsional techniques measuring internal friction. Additionally, hysteresis in friction behavior suggests an increase in near-surface crystallinity at upon exceeding the high temperature relaxation, T α~ 116°C.« less

A summary of Viking sample-trench analyses for angles of internal friction and cohesions

NASA Technical Reports Server (NTRS)

Moore, H. J.; Clow, G. D.; Hutton, R. E.

1982-01-01

Analyses of sample trenches excavated on Mars, using a theory for plowing by narrow blades, provide estimates of the angles of internal friction and the cohesions of the Martian surface materials. Angles of internal friction appear to be the same as those of many terrestrial soils because they are generally between 27 degrees and 39 degrees. Drift material, at the Lander 1 site, has a low angle of internal friction (near 18 degrees). All the materials excavated have low cohesions, generally between 0.2 and 10 kPa. The occurrence of cross bedding, layers of crusts, and blocky slabs shows that these materials are heterogeneous and that they contain planes of weakness. The results reported here have significant implications for future landed missions, Martian eolian processes, and interpretation of infrared temperatures.

Experimental research on friction coefficient between grain bulk and bamboo clappers

NASA Astrophysics Data System (ADS)

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.

Dynamics of hydrated mucopolysaccharides in cartilaginous tissues treated by laser radiation

NASA Astrophysics Data System (ADS)

Omelchenko, Alexander I.; Sobol, Emil N.; Ignatieva, Natalia Y.; Lunin, Valerii V.; Jumel, Kornelia; Harding, Stephen E.; Jones, Nicholas

2001-05-01

Dynamic mechanical properties of hydrated mucopolysaccharides have been studied in heated solutions by means of molecular hydrodynamic and acoustic techniques. These experiments model the thermal condition used for laser reshaping of cartilage. It has been shown that elastic modulus and internal friction depends on concentration of chondroitine sulphate in the solution and temperature. Maximum of internal friction was revealed at about 40 degree(s)C that corresponds to temperature of breakdown of hydrophobic bonds. Temperature dependence of internal friction manifests structural changes in polysaccharides molecules under laser heating.

The attenuation of Love waves and toroidal oscillations of the earth.

NASA Technical Reports Server (NTRS)

Jackson, D. D.

1971-01-01

An attempt has been made to invert a large set of attenuation data for Love waves and toroidal oscillations in the earth, using a recent method by Backus and Gilbert. The difficulty in finding an acceptable model of internal friction which explains the data, under the assumption that the internal friction is independent of frequency, casts doubt on the validity of this assumption. A frequency-dependent model of internal friction is presented which is in good agreement with the seismic data and with recent experimental measurements of attenuation in rocks.

Expansion and internal friction in unfolded protein chain.

PubMed

Yasin, U Mahammad; Sashi, Pulikallu; Bhuyan, Abani K

2013-10-10

Similarities in global properties of homopolymers and unfolded proteins provide approaches to mechanistic description of protein folding. Here, hydrodynamic properties and relaxation rates of the unfolded state of carbonmonoxide-liganded cytochrome c (cyt-CO) have been measured using nuclear magnetic resonance and laser photolysis methods. Hydrodynamic radius of the unfolded chain gradually increases as the solvent turns increasingly better, consistent with theory. Curiously, however, the rate of intrachain contact formation also increases with an increasing denaturant concentration, which, by Szabo, Schulten, and Schulten theory for the rate of intramolecular contact formation in a Gaussian polymer, indicates growing intramolecular diffusion. It is argued that diminishing nonbonded atom interactions with increasing denaturant reduces internal friction and, thus, increases the rate of polypeptide relaxation. Qualitative scaling of the extent of unfolding with nonbonded repulsions allows for description of internal friction by a phenomenological model. The degree of nonbonded atom interactions largely determines the extent of internal friction.

Weld defect identification in friction stir welding using power spectral density

NASA Astrophysics Data System (ADS)

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.

Biomechanical analysis of the influence of friction in jaw joint disorders.

PubMed

Koolstra, J H

2012-01-01

Increased friction due to impaired lubrication in the jaw joint has been considered as one of the possible causes for internal joint disorders. A very common internal disorder in the jaw joint is an anteriorly dislocated articular disc. This is generally considered to contribute to the onset of arthritic injuries. Increase of friction as caused by impairment of lubrication is suspected to be a possible cause for such a disorder. The influence of friction was addressed by analysis of its effects on tensions and deformations of the cartilaginous structures in the jaw joint using computational biomechanical analysis. Jaw open-close movements were simulated while in one or two compartments of the right joint friction was applied in the articular contact. The left joint was treated as the healthy control. The simulations predicted that friction primarily causes increased shear stress in the articular cartilage layers, but hardly in the articular disc. This suggests that impaired lubrication may facilitate deterioration of the cartilage-subchondral bone unit of the articular surfaces. The results further suggest that increased friction is not a plausible cause for turning a normally functioning articular disc into an anteriorly dislocated one. Copyright © 2011 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.

Mechanical properties of thin-film materials evaluated from amplitude-dependent internal friction

NASA Astrophysics Data System (ADS)

Nishino, Yoichi

1999-09-01

A method is presented to evaluate the mechanical properties of thin-film materials from measurements of the amplitude-dependent internal friction. According to the constitutive equation, the internal friction in the film can be determined separately from measured damping of the film/substrate composite. The internal friction in aluminum films is dependent on the strain amplitude that is approximately two orders of magnitude higher than that for bulk aluminum. On the basis of the microplasticity theory, the amplitude-dependent internal friction in the film can be converted into the plastic strain as a function of effective stress on dislocation motion. The mechanical responses thus obtained for aluminum films show that the plastic strain of the order of 10-9 increases 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 microplastic flow. The microflow stress at a constant level of the plastic strain varies inversely with the film thickness, provided the grain size is larger than the film thickness. The film thickness effect in the microplastic range can be well explained by the bowing of a dislocation segment whose ends are pinned at the film surface and at the film/substrate interface.

Internally architectured materials with directionally asymmetric friction

PubMed Central

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

2015-01-01

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

Molecular Origins of Internal Friction Effects on Protein Folding Rates

PubMed Central

Sirur, Anshul

2014-01-01

Recent experiments on protein folding dynamics have revealed strong evidence for internal friction effects. That is, observed relaxation times are not simply proportional to the solvent viscosity as might be expected if the solvent were the only source of friction. However, a molecular interpretation of this remarkable phenomenon is currently lacking. Here, we use all-atom simulations of peptide and protein folding in explicit solvent, to probe the origin of the unusual viscosity dependence. We find that an important contribution to this effect, explaining the viscosity dependence of helix formation and the folding of a helix-containing protein, is the insensitivity of torsion angle isomerization to solvent friction. The influence of this landscape roughness can, in turn, be quantitatively explained by a rate theory including memory friction. This insensitivity of local barrier crossing to solvent friction is expected to contribute to the viscosity dependence of folding rates in larger proteins. PMID:24986114

Molecular origins of internal friction effects on protein-folding rates.

PubMed

de Sancho, David; Sirur, Anshul; Best, Robert B

2014-07-02

Recent experiments on protein-folding dynamics have revealed strong evidence for internal friction effects. That is, observed relaxation times are not simply proportional to the solvent viscosity as might be expected if the solvent were the only source of friction. However, a molecular interpretation of this remarkable phenomenon is currently lacking. Here, we use all-atom simulations of peptide and protein folding in explicit solvent, to probe the origin of the unusual viscosity dependence. We find that an important contribution to this effect, explaining the viscosity dependence of helix formation and the folding of a helix-containing protein, is the insensitivity of torsion angle isomerization to solvent friction. The influence of this landscape roughness can, in turn, be quantitatively explained by a rate theory including memory friction. This insensitivity of local barrier crossing to solvent friction is expected to contribute to the viscosity dependence of folding rates in larger proteins.

Surface effects on friction-induced fluid heating in nanochannel flows.

PubMed

Li, Zhigang

2009-02-01

We investigate the mechanism of friction-induced fluid heating under the influence of surfaces. The temperature distributions of liquid argon and helium in nanoscale Poiseuille flows are studied through molecular dynamics simulations. It is found that the fluid heating is mainly caused by the viscous friction in the fluid when the external force is small and there is no slip at the fluid-solid interface. When the external force is larger than the fluid-surface binding force, the friction at the fluid-solid interface dominates over the internal friction of the fluid and is the major contribution to fluid heating. An asymmetric temperature gradient in the fluid is developed in the case of nonidentical walls and the general temperature gradient may change sign as the dominant heating factor changes from internal to interfacial friction with increasing external force. The effect of temperature on the fluid heating is also discussed.

Analysis of Apex Seal Friction Power Loss in Rotary Engines

NASA Technical Reports Server (NTRS)

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.

Friction Stir Welding of Thick Section Aluminum for Military Vehicle Applications

DTIC Science & Technology

2012-12-01

Friction Stir Welding of Thick Section Aluminum for Military Vehicle Applications by Brian Thompson, Kevin Doherty, Craig Niese, Mike Eff...International Symposium on Friction Stir Welding (9ISFSW), Huntsville, AL, 15–17 May 2012. Approved for public release...Aberdeen Proving Ground, MD 21005-5069 ARL-RP-417 December 2012 Friction Stir Welding of Thick Section Aluminum for Military

Food waste impact on municipal solid waste angle of internal friction.

PubMed

Cho, Young Min; Ko, Jae Hac; Chi, Liqun; Townsend, Timothy G

2011-01-01

The impact of food waste content on the municipal solid waste (MSW) friction angle was studied. Using reconstituted fresh MSW specimens with different food waste content (0%, 40%, 58%, and 80%), 48 small-scale (100-mm-diameter) direct shear tests and 12 large-scale (430 mm × 430 mm) direct shear tests were performed. A stress-controlled large-scale direct shear test device allowing approximately 170-mm sample horizontal displacement was designed and used. At both testing scales, the mobilized internal friction angle of MSW decreased considerably as food waste content increased. As food waste content increased from 0% to 40% and from 40% to 80%, the mobilized internal friction angles (estimated using the mobilized peak (ultimate) shear strengths of the small-scale direct shear tests) decreased from 39° to 31° and from 31° to 7°, respectively, while those of large-scale tests decreased from 36° to 26° and from 26° to 15°, respectively. Most friction angle measurements produced in this study fell within the range of those previously reported for MSW. Copyright © 2010 Elsevier Ltd. All rights reserved.

The measurement and theory of tire friction on contaminated surfaces

DOT National Transportation Integrated Search

1998-01-01

In the past five years there has been an International Experiment to Harmonize Friction Measurement by the World Road Association (PIARC) and within the past three years there have been at least four separate studies on winter friction, a five year j...

Role of Friction in Materials Selection for Automotive Applications

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

Blau, Peter Julian

This is an invited article for a special issue of the ASM International monthly magazine that concerns "Automotive Materials and Applications." The article itself overviews frictional considerations in material selection for automobiles. It discusses implications for energy efficiency (engine friction) and safety (brakes) among other topics.

Internal friction, Young's modulus, and electrical resistivity of submicrocrystalline titanium

NASA Astrophysics Data System (ADS)

Kardashev, B. K.; Sapozhnikov, K. V.; Betekhtin, V. I.; Kadomtsev, A. G.; Narykova, M. V.

2017-12-01

The variation of the internal friction, Young's modulus, and electrical resistivity of two grades of polycrystalline titanium (VT1-0 and Grade 4) in the area of low temperatures (100-300 K) as depending on the initial structure and subsequent severe plastic deformation converting the material into the submicrocrystalline structural state in relation to the grain size is studied. The maximum of the internal friction is detected in submicrocrystalline titanium, which is interpreted as a Bordoni peak. All the studied characteristics are sensitive indicators for a nonequilibrium state of the grain boundaries after the deformation. The effect of the initial structure of the metal on its properties after the severe deformation is revealed.

Relevance of Internal Friction and Structural Constraints for the Dynamics of Denatured Bovine Serum Albumin.

PubMed

Ameseder, Felix; Radulescu, Aurel; Holderer, Olaf; Falus, Peter; Richter, Dieter; Stadler, Andreas M

2018-05-17

A general property of disordered proteins is their structural expansion that results in a high molecular flexibility. The structure and dynamics of bovine serum albumin (BSA) denatured by guanidinium hydrochloride (GndCl) were investigated using small-angle neutron scattering (SANS) and neutron spin-echo spectroscopy (NSE). SANS experiments demonstrated the relevance of intrachain interactions for structural expansion. Using NSE experiments, we observed a high internal flexibility of denatured BSA in addition to center-of-mass diffusion detected by dynamic light scattering. Internal motions measured by NSE were described using concepts based on polymer theory. The contribution of residue-solvent friction was accounted for using the Zimm model including internal friction (ZIF). Disulfide bonds forming loops of amino acids of the peptide backbone have a major impact on internal dynamics that can be interpreted with a reduced set of Zimm modes.

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

NASA Technical Reports Server (NTRS)

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.

Low-temperature internal friction in quenched amorphous selenium films

NASA Astrophysics Data System (ADS)

Metcalf, Thomas; Liu, Xiao; Abernathy, Matthew; Stephens, Richard

Using ultra-high-quality-factor silicon mechanical resonators, we have measured the internal friction and shear modulus of amorphous selenium (a-Se) films at liquid helium temperatures. The glass transition temperature of selenium lies at a conveniently accessible 40 -50° C, facilitating a series of in- and ex-situ annealing and quench cycles. The a-Se films exhibit the low-temperature internal friction plateau (10-4 <=Q-1 <=10-3) found in almost all amorphous solids, which is a result of (and direct measure of) a broad distribution of two-level tunneling systems (TLS), whose origin is still unknown. We find a clear correlation between the post-anneal quench rate and the value of this plateau. The implications of these observations for understanding the microscopic origin of TLS will be discussed. Principally, the observed changes in the internal friction plateau could show the way in which the density of TLS could be manipulated or suppressed in other amorphous systems. Work supported by the Office of Naval Research and the University of Pennsylvania Materials Research Science and Engineering Center.

Effect of Mn and Cr additions on kinetics of recrystallization and parameters of grain-boundary relaxation of Al-4.9Mg alloy

NASA Astrophysics Data System (ADS)

Mikhailovskaya, A. V.; Golovin, I. S.; Zaitseva, A. A.; Portnoi, V. K.; Dröttboom, P.; Cifre, J.

2013-03-01

Methods of microstructural analysis, measurements of hardness, and temperature and time dependences of internal friction (TDIF and TDIF(iso), respectively) have been used to study recrystallization in cold-rolled alloys and grain-boundary relaxation in annealed alloys. A complex analysis of the effect of additions of transition metals (Mn, Cr) on the magnitude of the activation energy of the background of the internal friction in deformed and annealed states and on the activation parameters of grain-boundary relaxation has been performed. Methods of amplitude dependences of internal friction (ADIF) have been used to determine the critical amplitude that corresponds to the beginning of microplastic deformation in the alloys at different temperatures.

Internal friction and vulnerability of mixed alkali glasses.

PubMed

Peibst, Robby; Schott, Stephan; Maass, Philipp

2005-09-09

Based on a hopping model we show how the mixed alkali effect in glasses can be understood if only a small fraction c(V) of the available sites for the mobile ions is vacant. In particular, we reproduce the peculiar behavior of the internal friction and the steep fall ("vulnerability") of the mobility of the majority ion upon small replacements by the minority ion. The single and mixed alkali internal friction peaks are caused by ion-vacancy and ion-ion exchange processes. If c(V) is small, they can become comparable in height even at small mixing ratios. The large vulnerability is explained by a trapping of vacancies induced by the minority ions. Reasonable choices of model parameters yield typical behaviors found in experiments.

Unfolding and folding internal friction of β-hairpins is smaller than that of α-helices.

PubMed

Schulz, Julius C F; Miettinen, Markus S; Netz, R R

2015-04-02

By the forced unfolding of polyglutamine and polyalanine homopeptides in competing α-helix and β-hairpin secondary structures, we disentangle equilibrium free energetics from nonequilibrium dissipative effects. We find that α-helices are characterized by larger friction or dissipation upon unfolding, regardless of whether they are free energetically preferred over β-hairpins or not. Our analysis, based on MD simulations for atomistic peptide models with explicit water, suggests that this difference is related to the internal friction and mostly caused by the different number of intrapeptide hydrogen bonds in the α-helix and β-hairpin states.

Conformational dynamics and internal friction in homopolymer globules: equilibrium vs. non-equilibrium simulations.

PubMed

Einert, T R; Sing, C E; Alexander-Katz, A; Netz, R R

2011-12-01

We study the conformational dynamics within homopolymer globules by solvent-implicit Brownian dynamics simulations. A strong dependence of the internal chain dynamics on the Lennard-Jones cohesion strength ε and the globule size N (G) is observed. We find two distinct dynamical regimes: a liquid-like regime (for ε < ε(s) with fast internal dynamics and a solid-like regime (for ε > ε(s) with slow internal dynamics. The cohesion strength ε(s) of this freezing transition depends on N (G) . Equilibrium simulations, where we investigate the diffusional chain dynamics within the globule, are compared with non-equilibrium simulations, where we unfold the globule by pulling the chain ends with prescribed velocity (encompassing low enough velocities so that the linear-response, viscous regime is reached). From both simulation protocols we derive the internal viscosity within the globule. In the liquid-like regime the internal friction increases continuously with ε and scales extensive in N (G) . This suggests an internal friction scenario where the entire chain (or an extensive fraction thereof) takes part in conformational reorganization of the globular structure.

Locomotive and reptation motion induced by internal force and friction.

PubMed

Sakaguchi, Hidetsugu; Ishihara, Taisuke

2011-06-01

We propose a simple mechanical model of locomotion induced by internal force and friction. We first construct a system of two elements as an analog of the bipedal motion. The internal force does not induce a directional motion by itself because of the action-reaction law, but a directional motion becomes possible by the control of the frictional force. The efficiency of these model systems is studied using an analogy to the heat engine. As a modified version of the two-element model, we construct a model that exhibits a bipedal motion similar to kinesin's motion of molecular motor. Next, we propose a linear chain model and a ladder model as an extension of the original two-element model. We find a transition from a straight to a snake-like motion in a ladder model by changing the strength of the internal force.

Strain amplitude-dependent anelasticity in Cu-Ni solid solution due to thermally activated and athermal dislocation-point obstacle interactions

NASA Astrophysics Data System (ADS)

Kustov, S.; Gremaud, G.; Benoit, W.; Golyandin, S.; Sapozhnikov, K.; Nishino, Y.; Asano, S.

1999-02-01

Experimental investigations of the internal friction and the Young's modulus defect in single crystals of Cu-(1.3-7.6) at. % Ni have been performed for 7-300 K over a wide range of oscillatory strain amplitudes. Extensive data have been obtained at a frequency of vibrations around 100 kHz and compared with the results obtained for the same crystals at a frequency of ˜1 kHz. The strain amplitude dependence of the anelastic strain amplitude and the average friction stress acting on a dislocation due to solute atoms are also analyzed. Several stages in the strain amplitude dependence of the internal friction and the Young's modulus defect are revealed for all of the alloy compositions, at different temperatures and in different frequency ranges. For the 100 kHz frequency, low temperatures and low strain amplitudes (˜10-7-10-5), the amplitude-dependent internal friction and the Young's modulus defect are essentially temperature independent, and are ascribed to a purely hysteretic internal friction component. At higher strain amplitudes, a transition stage and a steep strain amplitude dependence of the internal friction and the Young's modulus defect are observed, followed by saturation at the highest strain amplitudes employed. These stages are temperature and frequency dependent and are assumed to be due to thermally activated motion of dislocations. We suggest that the observed regularities in the entire strain amplitude, temperature and frequency ranges correspond to a motion of dislocations in a two-component system of obstacles: weak but long-range ones, due to the elastic interaction of dislocations with solute atoms distributed in the bulk of the crystal; and strong short-range ones, due to the interaction of dislocations with solute atoms distributed close to dislocation glide planes. Based on these assumptions, a qualitative explanation is given for the variety of experimental observations.

General theory of frictional heating with application to rubber friction

NASA Astrophysics Data System (ADS)

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

2015-05-01

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

General theory of frictional heating with application to rubber friction.

PubMed

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

2015-05-08

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

Control of rotordynamic instability in a typical gas turbine's power system

NASA Technical Reports Server (NTRS)

Veikos, N. M.; Page, R. H.; Tornillo, E. J.

1984-01-01

The effect of rotor internal friction on the system's stability was studied when operated above the first critical speed. This internal friction is commonly caused by sliding press fits or sliding splines. Under conditions of high speed and low bearing damping, these systems will occassionally whirl at a frequency less than the shaft's rotational speed. This subsynchronous precession is a self excited phenomenon and stress reversals are created. This phenomenon was observed during engine testing. The reduction of spline friction and/or the inclusion of squeeze film damping have controlled the instability. Case history and the detail design of the squeeze film dampers is discussed.

Analytical skin friction and heat transfer formula for compressible internal flows

NASA Technical Reports Server (NTRS)

Dechant, Lawrence J.; Tattar, Marc J.

1994-01-01

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

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

PubMed

Makarov, Dmitrii E

2013-01-07

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

Granular self-organization by autotuning of friction.

PubMed

Kumar, Deepak; Nitsure, Nitin; Bhattacharya, S; Ghosh, Shankar

2015-09-15

A monolayer of granular spheres in a cylindrical vial, driven continuously by an orbital shaker and subjected to a symmetric confining centrifugal potential, self-organizes to form a distinctively asymmetric structure which occupies only the rear half-space. It is marked by a sharp leading edge at the potential minimum and a curved rear. The area of the structure obeys a power-law scaling with the number of spheres. Imaging shows that the regulation of motion of individual spheres occurs via toggling between two types of motion, namely, rolling and sliding. A low density of weakly frictional rollers congregates near the sharp leading edge whereas a denser rear comprises highly frictional sliders. Experiments further suggest that because the rolling and sliding friction coefficients differ substantially, the spheres acquire a local time-averaged coefficient of friction within a large range of intermediate values in the system. The various sets of spatial and temporal configurations of the rollers and sliders constitute the internal states of the system. Experiments demonstrate and simulations confirm that the global features of the structure are maintained robustly by autotuning of friction through these internal states, providing a previously unidentified route to self-organization of a many-body system.

Measuring internal friction of an ultrafast-folding protein.

PubMed

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

2008-11-25

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

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

PubMed

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

2007-10-01

Relations between various values of the internal friction (tgdelta, Q(-1), Q(-1*), and Lambda/pi) 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 omega(FD), displacement-resonant frequency of forced vibration omega(d), and velocity-resonant frequency of forced vibration omega(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.

[Integrate the surgical hand disinfection as a quality indicator in an operating room of urology].

PubMed

Francois, M; Girard, R; Mauranne, C C; Ruffion, A; Terrier, J E

2017-12-01

The surgical hand disinfection by friction (SDF) helps to reduce the risk of surgical site infections. For this purpose and in order to promote good compliance to quality care, the urology service of Centre Hospitalier Lyon Sud achieved a continuous internal audit to improve the quality of the SDF. An internal audit executed by the medical students of urology was established in 2013. The study population was all operators, instrumentalists and operating aids of urology operating room (OR). Each student realized 5-10 random observations, of all types of professionals. The criteria measured by the audit were criteria for friction. The evolution of indicators was positive. Particularly, the increasing duration of the first and second friction was statistically significant during follow-up (P=0.001). The total duration of friction shows a similar trend for all professionals. The surgical hand disinfection by friction in the urology OR of the Centre Hospitalier Lyon Sud has gradually improved over the iterative audits. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

A km-scale "triaxial experiment" reveals the extreme mechanical weakness and anisotropy of mica-schists (Grandes Rousses Massif, France)

NASA Astrophysics Data System (ADS)

Bolognesi, Francesca; Bistacchi, Andrea

2018-02-01

The development of Andersonian faults is predicted, according to theory and experiments, for brittle/frictional deformation occurring in a homogeneous medium. In contrast, in an anisotropic medium it is possible to observe fault nucleation and propagation that is non-Andersonian in geometry and kinematics. Here, we consider post-metamorphic brittle/frictional deformation in the mechanically anisotropic mylonitic mica-schists of the Grandes Rousse Massif (France). The role of the mylonitic foliation (and of any other source of mechanical anisotropy) in brittle/frictional deformation is a function of orientation and friction angle. According to the relative orientation of principal stress axes and foliation, a foliation characterized by a certain coefficient of friction will be utilized or not for the nucleation and propagation of brittle/frictional fractures and faults. If the foliation is not utilized, the rock behaves as if it was isotropic, and Andersonian geometry and kinematics can be observed. If the foliation is utilized, the deviatoric stress magnitude is buffered and Andersonian faults/fractures cannot develop. In a narrow transition regime, both Andersonian and non-Andersonian structures can be observed. We apply stress inversion and slip tendency analysis to determine the critical angle for failure of the metamorphic foliation of the Grandes Rousses schists, defined as the limit angle between the foliation and principal stress axes for which the foliation was brittlely reactivated. This approach allows defining the ratio of the coefficient of internal friction for failure along the mylonitic foliation to the isotropic coefficient of friction. Thus, the study area can be seen as a km-scale triaxial experiment that allows measuring the degree of mechanical anisotropy of the mylonitic mica-schists. In this way, we infer a coefficient of friction μweak = 0.14 for brittle-frictional failure of the foliation, or 20 % of the isotropic coefficient of internal friction.

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

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

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

2011-06-01

The elastic properties and internal friction of two magnesium alloys were studied from 25 C to 450 C using Resonant Ultrasound Spectroscopy (RUS). The Young's moduli decrease with increasing temperature. At 200 C, a change in the temperature dependence of the elastic constants is observed. The internal friction increases significantly with increasing temperature above 200 C. The observed changes in the temperature dependence of the elastic constants and the internal friction are the result of anelastic relaxation by grain boundary sliding at elevated temperatures. Elastic properties govern the behavior of a materials subjected to stress over a region of strainmore » where the material behaves elastically. The elastic properties, including the Young's modulus (E), shear modulus (G), bulk modulus (B), and Poisson's ratio (?), are of significant interest to many design and engineering applications. The choice of the most appropriate material for a particular application at elevated temperatures therefore requires knowledge of its elastic properties as a function of temperature. In addition, mechanical vibration can cause significant damage in the automotive, aerospace, and architectural industries and thus, the ability of a material to dissipate elastic strain energy in materials, known as damping or internal friction, is also important property. Internal friction can be the result of a wide range of physical mechanisms, and depends on the material, temperature, and frequency of the loading. When utilized effectively in engineering applications, the damping capacity of a material can remove undesirable noise and vibration as heat to the surroundings. The elastic properties of materials can be determined by static or dynamic methods. Resonant Ultrasound Spectroscopy (RUS), used in this study, is a unique and sophisticated non-destructive dynamic technique for determining the complete elastic tensor of a solid by measuring the resonant spectrum of mechanical resonance for a sample of known geometry, dimensions, and mass. In addition, RUS allows determination of internal friction, or damping, at different frequencies and temperatures. Polycrystalline pure magnesium (Mg) exhibits excellent high damping properties. However, the poor mechanical properties limit the applications of pure Mg. Although alloying can improve the mechanical properties of Mg, the damping properties are reduced with additions of alloying elements. Therefore, it becomes necessary to study and develop Mg-alloys with simultaneous high damping capacity and improved mechanical properties. Moreover, studies involving the high temperature dynamic elastic properties of Mg alloys are limited. In this study, the elastic properties and internal friction of two magnesium alloys were studied at elevated temperatures using RUS. The effect of alloy composition and grain size was investigated. The wrought magnesium alloys AZ31 and ZK60 were employed. Table 1 gives the nominal chemical compositions of these two alloys. The ZK60 alloy is a commercial extruded plate with a T5 temper, i.e. solution-treated at 535 C for two hours, quenched in hot water, and aged at 185 C for 24 hours. The AZ31 alloy is a commercial rolled plate with a H24 temper, i.e. strain hardened and partially annealed.« less

Laboratory evaluation of friction loss and compactability of asphalt mixtures.

DOT National Transportation Integrated Search

2012-04-01

This study aimed to develop prediction models for friction loss and laboratory compaction of asphalt : mixtures. In addition, the study evaluated the effect of compaction level and compaction method of skid : resistance and the internal structure of ...

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

PubMed

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

2007-05-01

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

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

PubMed Central

Yang, Wei; Luo, Ruiying; Hou, Zhenhua

2016-01-01

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

Tribochemical Competition within a MoS2/Ti Dry Lubricated Macroscale Contact in Ultrahigh Vacuum: A Time-of-Flight Secondary Ion Mass Spectrometry Investigation.

PubMed

Colas, Guillaume; Saulot, Aurélien; Philippon, David; Berthier, Yves; Léonard, Didier

2018-06-13

Controlling and predicting the tribological behavior of dry lubricants is a necessity to ensure low friction, long life, and low particle generation. Understanding the tribochemistry of the materials as a function of the environment is of primary interest as synergistic effects exist between the mechanics, the physicochemistry, and the thermodynamics within a contact. However, in most studies the role of the coating internal contaminants in the process is often discarded to the benefit of a more common approach in which the performances of the materials are compared as a function of different atmospheric pressure environments. The study focuses on the understanding of the tribochemical processes occurring between the materials and their internal contaminants inside an AISI440C contact lubricated by a MoS 2 /Ti coating. Time-of-flight secondary ion mass spectrometry is used to study at the molecular level, the material before and after friction. Friction tests with different durations are performed in ultrahigh vacuum at the macroscale to stay relevant to the real application (space). The adsorption/desorption of gaseous species during friction is monitored by mass spectrometry to ensure reliable study of the tribochemical processes inside the contact. The study shows that a competition exists between the Ti- and MoS 2 -based materials to create the appropriate lubricating materials via (i) recrystallization of MoS 2 materials with creation of a MoS x O y material via reactions with internal contaminants (presumably H 2 O), (ii) reaction of Ti-based materials with internal contaminants (mostly H 2 O and N 2 ). The biphasic material created is highly similar to the one created in both humid air and dry N 2 environments and providing low friction and low particle generation. However, the process is incomplete. The study thus brings insight into the possibility of controlling friction via a rational inclusion of reactants in a form of contaminants to control the tribochemical processes governing the low friction and long life.

Internal friction in particulate composites of (x)Mn0.4Zn0.6Fe2O4 –(1-x)PbZr0.53Ti0.47O3 in the vicinity of the structural phase transition temperatures

NASA Astrophysics Data System (ADS)

Kalgin, A. V.; Gridnev, S. A.

2018-03-01

The internal friction in particulate ceramic composites of (x)Mn0.4Zn0.6Fe2O4 –(1-x)PbZr0.53Ti0.47O3 (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.6) in the vicinity of the phase transition temperatures was studied. We observed the influence of the composite composition on the exponent that characterizes a temperature dependence of the internal friction near the ferroelectric Curie point. The reason for this influence is shown to be the doping of the PbZr0.53Ti0.47O3 ferroelectric phase with atoms of the Mn04Zn0.6Fe2O4 ferrite phase that occurs during high- temperature sintering of composite samples.

Quantum friction in arbitrarily directed motion

DOE PAGES

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

2017-05-30

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

The influence of nitrogen ion implantation on the tribological properties of piston rings made of Hardox and Raex steels

NASA Astrophysics Data System (ADS)

Budzyński, P.; Kamiński, M.; Pyszniak, K.

2016-09-01

The implantation of nitrogen, carbon, and oxygen can be used for enhancing the tribological properties of critical components for internal combustion engines. Hardox and Raex steels have very similar strength parameters as for steel used for piston rings in internal combustion engines. An essential criterion when selecting material for the production of piston rings is a low friction factor and a low wear index. The aim of this study was to determine the extent to which these parameters can be enhanced by nitrogen ion implantation. Samples were implanted with nitrogen ions with 65 keV energy and the fluence of implanted ions set to 1.1017 N + /cm2. Friction and wear measurements were performed on a pin-on disc stand. The results demonstrate that implantation with nitrogen ions significantly reduces the friction factor and wear of Hardox 450 and Raex 400 steels. Implantation can and should be used for enhancing the tribological properties of steel used for friction elements in internal combustion engines, particularly when heat treatment is excluded. Final elements can be subjected to implantation, as the process does not change their dimensions.

Internal friction of hydrated soda-lime-silicate glasses.

PubMed

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) < 0.25 wt. %) two discrete internal 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.

a Study on the Effect of Annealing Process on Sound Velocity and Internal Friction Using the Vibrating Reed Technique

NASA Astrophysics Data System (ADS)

Mukhopadhyay, P. K.; Kumar, Uday; Badawi, Emad

Al has unique intrinsic characteristics, which are of interest to scientists as well as engineers. Al and its alloys are slightly paramagnetic materials. Al has very low cross section for thermal neutrons of 0.23 barn, hence Al can be used in nuclear fields as a structural material which is virtually transparent to neutrons. We report VRT as a new technique to study material problems. We also discuss, the results of sound velocity and internal friction, and resonance frequency as a function of temperature range for a pure aluminum sample under investigation. By using VRT, we found that the annealing temperature (450°C) is sufficient to remove the type of defects introduced in the materials under study. The activation energy to remove point defect for Al samples was calculated and found to be about 0.0624 eV. Also, we could easily observe that Q-1 is a function of annealing time. From these measurements of sound velocity and internal friction we can conclude that VRT is a powerful tool for detecting and probing the physical properties of the material under study. Internal friction is a microscopic property for the indication of the purity of the sample. Sound velocity depends on the state of the materials (which depends on the process of treatment).

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

PubMed

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.

Observations on the deformation-induced beta internal friction peak in bcc metals

NASA Technical Reports Server (NTRS)

Dicarlo, J. A.

1974-01-01

During a study of the effects of electron irradiation on the tungsten alpha mechanism, internal friction data were obtained. The data indicate that the mechanism underlying the beta peak does not possess the relaxation parameters generally associated with a simple dislocation process. The significance of the experimental results in the light of beta observations in other metals is discussed. It is suggested that the beta peaks in deformed bcc metals are the anelastic result of the thermally-activated relaxation of deformation-induced imperfections.

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

PubMed

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

2016-05-26

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

Atomic scale friction of molecular adsorbates during diffusion.

PubMed

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

2013-05-21

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

Drag force scaling for penetration into granular media.

PubMed

Katsuragi, Hiroaki; Durian, Douglas J

2013-05-01

Impact dynamics is measured for spherical and cylindrical projectiles of many different densities dropped onto a variety non-cohesive granular media. The results are analyzed in terms of the material-dependent scaling of the inertial and frictional drag contributions to the total stopping force. The inertial drag force scales similar to that in fluids, except that it depends on the internal friction coefficient. The frictional drag force scales as the square-root of the density of granular medium and projectile, and hence cannot be explained by the combination of granular hydrostatic pressure and Coulomb friction law. The combined results provide an explanation for the previously observed penetration depth scaling.

Effects of Cu and Ag as ternary and quaternary additions on some physical properties of SnSb7 bearing alloy

NASA Astrophysics Data System (ADS)

El-Bediwi, A. B.

2004-02-01

The structure, electrical resistivity, and elastic modulus of SnSb7 and SnSb7X (X = Cu , Ag, or Cu and Ag) rapidly solidified alloys have been investigated using X-ray diffractometer, double bridge, and dynamic resonance techniques. Copper and silver additions to SnSb result in the formation of a eutectic matrix containing embedded crystals (intermetallic phases) of SnCu, SnAg, and SnSb. The hard crystals SnCu, SnAg, and SnSb increase the overall hardness and wear resistance of SnSb bearing alloys. Addition of copper and silver improves internal friction, electrical conductivity, and elastic modulus values of SnSb rapidly solidified bearing alloys. The internal friction, elastic modulus, and electrical resistivity values are relatively sensitive to the composition of the intermediate phases in the matrix. The SbSb(7)Cu(2)g(2) has better properties (lowest internal friction, cost, adequate elastic modulus, and electrical resistivity) for bearing alloys as compared to cast iron and bronzes.

Effects of the internal friction and the solvent quality on the dynamics of a polymer chain closure.

PubMed

Yu, Wancheng; Luo, Kaifu

2015-03-28

Using 3D Langevin dynamics simulations, we investigate the effects of the internal friction and the solvent quality on the dynamics of a polymer chain closure. We show that the chain closure in good solvents is a purely diffusive process. By extrapolation to zero solvent viscosity, we find that the internal friction of a chain plays a non-ignorable role in the dynamics of the chain closure. When the solvent quality changes from good to poor, the mean closure time τc decreases by about 1 order of magnitude for the chain length 20 ≤ N ≤ 100. Furthermore, τc has a minimum as a function of the solvent quality. With increasing the chain length N, the minimum of τc occurs at a better solvent. Finally, the single exponential distributions of the closure time in poor solvents suggest that the negative excluded volume of segments does not alter the nearly Poisson statistical characteristics of the process of the chain closure.

49 CFR 173.36 - Hazardous materials in Large Packagings.

Code of Federal Regulations, 2012 CFR

2012-10-01

... Packagings (e.g., 51H) are only authorized for use with flexible inner packagings. (3) Friction. The nature and thickness of the outer packaging must be such that friction during transportation is not likely to... transportation in inner packagings appropriately resistant to an increase of internal pressure likely to develop...

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

PubMed

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.

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

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

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

2014-06-25

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 propagatesmore » 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. Furthermore, in LD simulation, the solvent friction coefficients should be imposed only on the protein surface.« less

International Congress NONLINEAR DYNAMICAL ANALYSIS 2007 dedicated to the 150th Anniversary of Academician A. M. Lyapunov

DTIC Science & Technology

2010-05-14

and Coulomb friction. We consider a simple mass spring system submitted to an external force and constrained to remain in a half -space. The contact of... the mass with the boundary of the half -space is assumed to hold with Coulomb friction. The unilateral contact and Coulomb friction laws are strict...Lyapunov frequently discussed this problem with Henry Poincare (1854-1912) and George Darwin (1845 - 1912). They both considered the "pear-form" figure as

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

NASA Astrophysics Data System (ADS)

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-state mixing. Thirdly, the corrosion resistance of multiple austenitic stainless steels (types 304, 316, and 309) processed in varying ways was compared for acid chloride environments using advanced electrochemical techniques. Physical simulation of fusion claddings and friction weld claddings (wrought stainless steels) was used for sample preparation to determine compositional and microstructural effects. Pitting resistance correlated firstly with Cr content, with N and Mo additions providing additional benefits. The high ferrite fraction of as-welded samples reduced their corrosion resistance. Wrought type 309L outperformed as-welded type 309L in dissolved mass loss and reverse corrosion rate from the potentiodynamic scan in 1.0 N HCl/3.5% NaCl solution. Electrochemical impedance results indicated that wrought 309L and 316L developed a corrosion resistant passive film more rapidly than other alloys in 0.1 N HCl/3.5% NaCl, and also performed well in long term (160-day) corrosion testing in the same environment. Fourthly, to prove the concept of internal CR lining by friction welding, a conical work piece of 304L stainless steel was friction welded internally to 1018 steel.

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

PubMed

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

Transduction channels' gating can control friction on vibrating hair-cell bundles in the ear.

PubMed

Bormuth, Volker; Barral, Jérémie; Joanny, Jean-François; Jülicher, Frank; Martin, Pascal

2014-05-20

Hearing starts when sound-evoked mechanical vibrations of the hair-cell bundle activate mechanosensitive ion channels, giving birth to an electrical signal. As for any mechanical system, friction impedes movements of the hair bundle and thus constrains the sensitivity and frequency selectivity of auditory transduction. Friction is generally thought to result mainly from viscous drag by the surrounding fluid. We demonstrate here that the opening and closing of the transduction channels produce internal frictional forces that can dominate viscous drag on the micrometer-sized hair bundle. We characterized friction by analyzing hysteresis in the force-displacement relation of single hair-cell bundles in response to periodic triangular stimuli. For bundle velocities high enough to outrun adaptation, we found that frictional forces were maximal within the narrow region of deflections that elicited significant channel gating, plummeted upon application of a channel blocker, and displayed a sublinear growth for increasing bundle velocity. At low velocity, the slope of the relation between the frictional force and velocity was nearly fivefold larger than the hydrodynamic friction coefficient that was measured when the transduction machinery was decoupled from bundle motion by severing tip links. A theoretical analysis reveals that channel friction arises from coupling the dynamics of the conformational change associated with channel gating to tip-link tension. Varying channel properties affects friction, with faster channels producing smaller friction. We propose that this intrinsic source of friction may contribute to the process that sets the hair cell's characteristic frequency of responsiveness.

Transduction channels’ gating can control friction on vibrating hair-cell bundles in the ear

PubMed Central

Bormuth, Volker; Barral, Jérémie; Joanny, Jean-François; Jülicher, Frank; Martin, Pascal

2014-01-01

Hearing starts when sound-evoked mechanical vibrations of the hair-cell bundle activate mechanosensitive ion channels, giving birth to an electrical signal. As for any mechanical system, friction impedes movements of the hair bundle and thus constrains the sensitivity and frequency selectivity of auditory transduction. Friction is generally thought to result mainly from viscous drag by the surrounding fluid. We demonstrate here that the opening and closing of the transduction channels produce internal frictional forces that can dominate viscous drag on the micrometer-sized hair bundle. We characterized friction by analyzing hysteresis in the force–displacement relation of single hair-cell bundles in response to periodic triangular stimuli. For bundle velocities high enough to outrun adaptation, we found that frictional forces were maximal within the narrow region of deflections that elicited significant channel gating, plummeted upon application of a channel blocker, and displayed a sublinear growth for increasing bundle velocity. At low velocity, the slope of the relation between the frictional force and velocity was nearly fivefold larger than the hydrodynamic friction coefficient that was measured when the transduction machinery was decoupled from bundle motion by severing tip links. A theoretical analysis reveals that channel friction arises from coupling the dynamics of the conformational change associated with channel gating to tip-link tension. Varying channel properties affects friction, with faster channels producing smaller friction. We propose that this intrinsic source of friction may contribute to the process that sets the hair cell’s characteristic frequency of responsiveness. PMID:24799674

Internal rotor friction instability

NASA Technical Reports Server (NTRS)

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

1990-01-01

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

Analysis of Full-Test tools and their limitations as applied to terminal junction blocks

NASA Technical Reports Server (NTRS)

Smith, J. L.

1983-01-01

Discovery of unlocked contacts in Deutsch Block terminal junctions in Solid Rocket Booster flight hardware prompted an investigation into pull test techniques to help insure against possible failures. Internal frictional forces between socket and pin and between wire and grommet were examined. Pull test force must be greater than internal friction yet less than the crimp strength of the pin or socket. For this reason, a 100 percent accurate test is impossible. Test tools were evaluated. Available tools are adequate for pull testing.

Influence of moisture content on physical properties of minor millets.

PubMed

Balasubramanian, S; Viswanathan, R

2010-06-01

Physical properties including 1000 kernel weight, bulk density, true density, porosity, angle of repose, coefficient of static friction, coefficient of internal friction and grain hardness were determined for foxtail millet, little millet, kodo millet, common millet, barnyard millet and finger millet in the moisture content range of 11.1 to 25% db. Thousand kernel weight increased from 2.3 to 6.1 g and angle of repose increased from 25.0 to 38.2°. Bulk density decreased from 868.1 to 477.1 kg/m(3) and true density from 1988.7 to 884.4 kg/m(3) for all minor millets when observed in the moisture range of 11.1 to 25%. Porosity decreased from 63.7 to 32.5%. Coefficient of static friction of minor millets against mild steel surface increased from 0.253 to 0.728 and coefficient of internal friction was in the range of 1.217 and 1.964 in the moisture range studied. Grain hardness decreased from 30.7 to 12.4 for all minor millets when moisture content was increased from 11.1 to 25% db.

Fault detection in mechanical systems with friction phenomena: an online neural approximation approach.

PubMed

Papadimitropoulos, Adam; Rovithakis, George A; Parisini, Thomas

2007-07-01

In this paper, the problem of fault detection in mechanical systems performing linear motion, under the action of friction phenomena is addressed. The friction effects are modeled through the dynamic LuGre model. The proposed architecture is built upon an online neural network (NN) approximator, which requires only system's position and velocity. The friction internal state is not assumed to be available for measurement. The neural fault detection methodology is analyzed with respect to its robustness and sensitivity properties. Rigorous fault detectability conditions and upper bounds for the detection time are also derived. Extensive simulation results showing the effectiveness of the proposed methodology are provided, including a real case study on an industrial actuator.

Normal and frictional interactions of purified human statherin adsorbed on molecularly-smooth solid substrata.

PubMed

Harvey, Neale M; Carpenter, Guy H; Proctor, Gordon B; Klein, Jacob

2011-09-01

Human salivary statherin was purified from parotid saliva and adsorbed to bare hydrophilic (HP) mica and STAI-coated hydrophobic (HB) mica in a series of Surface Force Balance experiments that measured the normal (F(n)) and friction forces (F(s)*) between statherin-coated mica substrata. Readings were taken both in the presence of statherin solution (HP and HB mica) and after rinsing (HP mica). F(n) measurements showed, for both substrata, monotonic steric repulsion that set on at a surface separation D ~20 nm, indicating an adsorbed layer whose unperturbed thickness was ca 10 nm. An additional longer-ranged repulsion, probably of electrostatic double-layer origin, was observed for rinsed surfaces under pure water. Under applied pressures of ~1 MPa, each surface layer was compressed to a thickness of ca 2 nm on both types of substratum, comparable with earlier estimates of the size of the statherin molecule. Friction measurements, in contrast with F(n) observations, were markedly different on the two different substrata: friction coefficients, μ ≡ ∂F(s)*/∂F(n), on the HB substratum (μ ≈ 0.88) were almost an order of magnitude higher than on the HP substratum (μ ≈ 0.09 and 0.12 for unrinsed and rinsed, respectively), and on the HB mica there was a lower dependence of friction on sliding speed than on the HP mica. The observations were attributed to statherin adsorbing to the mica in multimer aggregates, with internal re-arrangement of the protein molecules within the aggregate dependent on the substratum to which the aggregate adsorbed. This internal re-arrangement permitted aggregates to be of similar size on HP and HB mica but to have different internal molecular orientations, thus exposing different moieties to the solution in each case and accounting for the very different friction behaviour.

Solvent friction changes the folding pathway of the tryptophan zipper TZ2.

PubMed

Narayanan, Ranjani; Pelakh, Leslie; Hagen, Stephen J

2009-07-17

Because the rate of a diffusional process such as protein folding is controlled by friction encountered along the reaction pathway, the speed of folding is readily tunable through adjustment of solvent viscosity. The precise relationship between solvent viscosity and the rate of diffusion is complex and even conformation-dependent, however, because both solvent friction and protein internal friction contribute to the total reaction friction. The heterogeneity of the reaction friction along the folding pathway may have subtle consequences. For proteins that fold on a multidimensional free-energy surface, an increase in solvent friction may drive a qualitative change in folding trajectory. Our time-resolved experiments on the rapidly and heterogeneously folding beta-hairpin TZ2 show a shift in the folding pathway as viscosity increases, even though the energetics of folding is unaltered. We also observe a nonlinear or saturating behavior of the folding relaxation time with rising solvent viscosity, potentially an experimental signature of the shifting pathway for unfolding. Our results show that manipulations of solvent viscosity in folding experiments and simulations may have subtle and unexpected consequences on the folding dynamics being studied.

Characterization of Martian near-subsurface materials by determination of cohesion and angle of internal friction

NASA Technical Reports Server (NTRS)

Sullivan, R. J.

1992-01-01

Back-analysis (reconstruction) of the stability of thirty avalanche chutes was performed in the very limited areas where high resolution imaging overlapped with available 1:500 K topographic map coverage. A new technique was developed to incorporate the third dimension (width) of an avalanche chute in stability back-analysis in order to yield unambiguous values of cohesion and angle of internal friction. The procedure is based upon extending the ordinary method of slices to three dimensions, in order to construct avalanche chute cross-sections whose widths and depths vary as a function of gradient, gravity, density of material, and phi and c. Applying the technique to the well documented slide at Lodalen, Norway as a test produces excellent correspondence with reality. Generally, the technique reveals that the width:depth ratio of any avalanche chute decreases with increasing contrast between the average slope angle and the angle of internal friction. Applying this technique to the martian avalanche chute yields results consistent with indications from earlier work, but with greater certainty. Values of cohesion and angle of internal friction identify the materials at the time of failure as moderately cohesive debris. If Sharp's identification of these features as avalanche chutes is correct, then the results here imply that weathering processes have had a significant effect to depths of tens of meters (where failure has occured) below the martian surface. It is also implied that on relatively steep slopes within Valles Marineris, sizable, unaltered, unmantled bedrock exposures for high resolution spectral and spatial scanning by Mars Observer may be scarce.

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

PubMed

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.

Friction Effects of Lead-Based and Lead-Free Primers in 5.56mm NATO

DTIC Science & Technology

2014-01-30

Temperatures – A Review,” Tribology International 15(5), pp. 303-315. Martin, J.M., Le Mogne, T., Chassagnette, C., and Gardos, M.N., 1992. “Friction of...Hexagonal Boron Nitride in Various Environments,” Tribology Transactions 35(3), pp. 462-472. White, L. and Siewert, J., 2007. “Final Report of the

Three-dimensional friction measurement during hip simulation

PubMed Central

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

2017-01-01

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

Three-dimensional friction measurement during hip simulation.

PubMed

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

2017-01-01

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

Flowability parameters for chopped switchgrass, wheat straw and corn stover

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

Chevanan, Nehru; Womac, A.R.; Bitra, V.S.P.

2009-02-01

A direct shear cell to measure the shear strength and flow properties of chopped switchgrass, wheat straw, and corn stover was designed, fabricated, and tested. Yield loci (r2=0.99) determined at pre-consolidation pressures of 3.80 kPa and 5.02 kPa indicated that chopped biomass followed Mohr-Coulomb failure. Normal stress significantly affected the displacement required for shear failure, as well as the friction coefficient values for all three chopped biomass types. Displacement at shear failure ranged from 30 to 80 mm, and depended on pre-consolidation pressure, normal stress, and particle size. Friction coefficient was inversely related to normal stress, and was highest formore » chopped corn stover. Also, chopped corn stover exhibited the highest angle of internal friction, unconfined yield strength, major consolidation strength, and cohesive strength, all of which indicated increased challenges in handling chopped corn stover. The measured angle of internal friction and cohesive strength indicated that chopped biomass cannot be handled by gravity alone. The measured angle of internal friction and cohesive strength were 43 and 0.75 kPa for chopped switchgrass; 44 and 0.49 kPa for chopped wheat straw; and 48 and 0.82 kPa for chopped corn stover. Unconfined yield strength and major consolidation strength used for characterization of bulk flow materials and design of hopper dimensions were 3.4 and 10.4 kPa for chopped switchgrass; 2.3 and 9.6 kPa for chopped wheat straw and 4.2 and 11.8 kPa for chopped corn stover. These results are useful for development of efficient handling, storage, and transportation systems for biomass in biorefineries.« less

Mechanical response of the flux lines in ceramic YBa2Cu3O7-δ

NASA Astrophysics Data System (ADS)

Luzuriaga, J.; André, M.-O.; Benoit, W.

1992-06-01

We have studied the mechanical response of the flux-line lattice (FLL) in ceramic samples of YBa2Cu3O7 by means of a low-frequency forced pendulum. The internal friction and elastic modulus variation of the FLL have been measured as a function of temperature for different values of the applied stress. A somewhat different behavior was observed whether a zero-field-cooling or field-cooling procedure was followed. Measurements of the internal friction and elastic modulus as a function of the applied stress at constant temperature show amplitude-dependent dissipation, with a maximum dissipation at intermediate values of the stress. This dependence is well fitted by a rheological model of extended dry friction, if we restrict ourselves to the dissipation and modulus at fixed temperature. The agreement is not so good when attempting to extend the model to fit the temperature dependence.

Method and device for frictional welding

DOEpatents

Peacock, H.B.

1991-01-01

A method for friction welding that produces a seal having essentially no gas porosity, comprises two rotationally symmetric, generally cylindrical members, spaced apart and coaxially aligned, that are rotated with respect to each other and brought together under high pressure. One member is preferably a generally cylindrical cannister that stores uranium within its hollow walls. The other member is preferably a generally cylindrical, hollow weld ring. An annular channel formed in the weld ring functions as an internal flash trap and is uniquely designed so that substantially all of the welding flash generated from the friction welding is directed into the channel`s recessed bottom. Also, the channel design limits distortion of the two members during the friction welding, process, further contributing to the complete seal that is obtained.

Method and device for frictional welding

DOEpatents

Peacock, Harold B.

1992-01-01

A method for friction welding that produces a seal having essentially no gas porosity, comprises two rotationally symmetric, generally cylindrical members, spaced apart and coaxially aligned, that are rotated with respect to each other and brought together under high pressure. One member is preferably a generally cylindrical cannister that stores uranium within its hollow walls. The other member is preferably a generally cylindrical, hollow weld ring. An annular channel formed in the weld ring functions as an internal flash trap and is uniquely designed so that substantially all of the welding flash generated from the friction welding is directed into the channel's recessed bottom. Also, the channel design limits distortion of the two members during the friction welding process, further contributing to the complete seal that is obtained.

Friction Syndromes of the Knee: The Iliotibial Band and Anterior Fat Pads.

PubMed

Wissman, Robert D; Pomeranz, Stephen J

2018-01-01

As participation in sporting activities increases among the general population, the incidence of overuse injuries continues to rise. Friction syndromes of the knee are common and are often clinically diagnosed without the need for imaging. However, clinical symptoms may overlap with other joint abnormalities, and physical examination may be limited in individuals with excessive pain. Magnetic resonance imaging has remained the modality of choice for the evaluation of internal derangements of the joints and is a useful aid in the diagnosis of friction syndrome of the knee. This case report provides clinicians with an understanding of the most common friction syndromes of the knee joint as well as their imaging findings. (Journal of Surgical Orthopaedic Advances 27(1):77-80, 2018).

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

PubMed

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.

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

PubMed

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

2013-11-27

Internal friction arising from local steric hindrance and/or the excluded volume effect plays an important role in controlling not only the dynamics of protein folding but also conformational transitions occurring within the native state potential well. However, experimental assessment of such local friction is difficult because it does not manifest itself as an independent experimental observable. Herein, we demonstrate, using the miniprotein trp-cage as a testbed, that it is possible to selectively increase the local mass density in a protein and hence the magnitude of local friction, thus making its effect directly measurable via folding kinetic studies. Specifically, we show that when a helix cross-linker, m-xylene, is placed near the most congested region of the trp-cage it leads to a significant decrease in both the folding rate (by a factor of 3.8) and unfolding rate (by a factor of 2.5 at 35 °C) but has little effect on protein stability. Thus, these results, in conjunction with those obtained with another cross-linked trp-cage and two uncross-linked variants, demonstrate the feasibility of using a nonperturbing cross-linker to help quantify the effect of internal friction. In addition, we estimate that a m-xylene cross-linker could lead to an increase in the roughness of the folding energy landscape by as much as 0.4-1.0k(B)T.

Study of Plastic Deformation in Binary Aluminum Alloys by Internal-Friction Methods

NASA Technical Reports Server (NTRS)

Olson, E. C.; Maringer, R. E.; Marsh, L. L.; Manning, G. K.

1959-01-01

The damping capacity of several aluminum-copper alloys has been investigated during tensile elongation. This damping is shown to depend on strain rate, strain, temperature, alloy content, and heat treatment. A tentative hypothesis, based on the acceleration of solute atom diffusion by deformation-produced vacancies, is proposed to account for the observed behavior. Internal-friction maxima are observed in deformed aluminum and aluminum-copper alloys at -70 deg and -50 deg C. The peaks appear to be relatively insensitive to frequency and alloy content, but they disappear after annealing at temperatures nearing the recrystallization temperature.

Damage Tolerance Behavior of Friction Stir Welds in Aluminum Alloys

NASA Technical Reports Server (NTRS)

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.

Probing Interfacial Friction and Dissipation in Granular Gold­ Nickel Alloys with a Quartz Crystal Oscillator in an External Magnetic Field

NASA Astrophysics Data System (ADS)

Stevens, K. M.; Krim, J.

2015-03-01

We present here a quartz crystal microbalance study of two-phase gold nickel alloys whose internal granular properties are probed by exposure to a fluctuating external magnetic field. The work is motivated by prior studies demonstrating that granular two-phase materials exhibited lower friction and wear than solid solution alloys with identical compositions. In particular, we report a ``flexing'' effect which appears when an external magnetic field is applied, and is manifested as a decrease in the magnitude of oscillation amplitude that is synchronized with the applied field; the effect is not seen on the complimentary solid solution samples. The effect is consistent with internal interfacial friction between nickel and gold grains, indicating a degree of freedom which may decrease friction even in the absence of an external magnetic field. This is supported through analysis of energy dissipation in the system, using the Butterworth­-Van Dyke equivalent circuit model. Data and interpretation are also presented that rule out alternate explanations such as giant magnetoresistance and/or other resistive phenomenon within the film. Funding provided by NSF DMR0805204. Thanks to L. Pan for sample preparation.

Internal (Annular) and Compressible External (Flat Plate) Turbulent Flow Heat Transfer Correlations.

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

Dechant, Lawrence; Smith, Justin

Here we provide a discussion regarding the applicability of a family of traditional heat transfer correlation based models for several (unit level) heat transfer problems associated with flight heat transfer estimates and internal flow heat transfer associated with an experimental simulation design (Dobranich 2014). Variability between semi-empirical free-flight models suggests relative differences for heat transfer coefficients on the order of 10%, while the internal annular flow behavior is larger with differences on the order of 20%. We emphasize that these expressions are strictly valid only for the geometries they have been derived for e.g. the fully developed annular flow ormore » simple external flow problems. Though, the application of flat plate skin friction estimate to cylindrical bodies is a traditional procedure to estimate skin friction and heat transfer, an over-prediction bias is often observed using these approximations for missile type bodies. As a correction for this over-estimate trend, we discuss a simple scaling reduction factor for flat plate turbulent skin friction and heat transfer solutions (correlations) applied to blunt bodies of revolution at zero angle of attack. The method estimates the ratio between axisymmetric and 2-d stagnation point heat transfer skin friction and Stanton number solution expressions for sub-turbulent Reynolds numbers %3C1x10 4 . This factor is assumed to also directly influence the flat plate results applied to the cylindrical portion of the flow and the flat plate correlations are modified by« less

Solvent viscosity and friction in protein folding dynamics.

PubMed

Hagen, Stephen J

2010-08-01

The famous Kramers rate theory for diffusion-controlled reactions has been extended in numerous ways and successfully applied to many types of reactions. Its application to protein folding reactions has been of particular interest in recent years, as many researchers have performed experiments and simulations to test whether folding reactions are diffusion-controlled, whether the solvent is the source of the reaction friction, and whether the friction-dependence of folding rates generally can provide insight into folding dynamics. These experiments involve many practical difficulties, however. They have also produced some unexpected results. Here we briefly review the Kramers theory for reactions in the presence of strong friction and summarize some of the subtle problems that arise in the application of the theory to protein folding. We discuss how the results of these experiments ultimately point to a significant role for internal friction in protein folding dynamics. Studies of friction in protein folding, far from revealing any weakness in Kramers theory, may actually lead to new approaches for probing diffusional dynamics and energy landscapes in protein folding.

Biofilms inducing ultra-low friction on titanium.

PubMed

Souza, J C M; Henriques, M; Oliveira, R; Teughels, W; Celis, J-P; Rocha, L A

2010-12-01

Biofilm formation is widely reported in the literature as a problem in the healthcare, environmental, and industrial sectors. However, the role of biofilms in sliding contacts remains unclear. Friction during sliding was analyzed for titanium covered with mixed biofilms consisting of Streptococcus mutans and Candida albicans. The morphology of biofilms on titanium surfaces was evaluated before, during, and after sliding tests. Very low friction was recorded on titanium immersed in artificial saliva and sliding against alumina in the presence of biofilms. The complex structure of biofilms, which consist of microbial cells and their hydrated exopolymeric matrix, acts like a lubricant. A low friction in sliding contacts may have major significance in the medical field. The composition and structure of biofilms are shown to be key factors for an understanding of friction behavior of dental implant connections and prosthetic joints. For instance, a loss of mechanical integrity of dental implant internal connections may occur as a consequence of the decrease in friction caused by biofilm formation. Consequently, the study of the exopolymeric matrix can be important for the development of high-performance novel joint-based systems for medical and other engineering applications.

Method and device for frictional welding

DOEpatents

Peacock, H.B.

1992-10-13

A method is described for friction welding that produces a seal having essentially no gas porosity, comprises two rotationally symmetric, generally cylindrical members, spaced apart and coaxially aligned, that are rotated with respect to each other and brought together under high pressure. One member is preferably a generally cylindrical canister that stores uranium within its hollow walls. The other member is preferably a generally cylindrical, hollow weld ring. An annular channel formed in the weld ring functions as an internal flash trap and is uniquely designed so that substantially all of the welding flash generated from the friction welding is directed into the channel's recessed bottom. Also, the channel design limits distortion of the two members during the friction welding process, further contributing to the complete seal that is obtained. 5 figs.

Development of devices for self-injection: using tribological analysis to optimize injection force

PubMed Central

Lange, Jakob; Urbanek, Leos; Burren, Stefan

2016-01-01

This article describes the use of analytical models and physical measurements to characterize and optimize the tribological behavior of pen injectors for self-administration of biopharmaceuticals. One of the main performance attributes of this kind of device is its efficiency in transmitting the external force applied by the user on to the cartridge inside the pen in order to effectuate an injection. This injection force characteristic is heavily influenced by the frictional properties of the polymeric materials employed in the mechanism. Standard friction tests are available for characterizing candidate materials, but they use geometries and conditions far removed from the actual situation inside a pen injector and thus do not always generate relevant data. A new test procedure, allowing the direct measurement of the coefficient of friction between two key parts of a pen injector mechanism using real parts under simulated use conditions, is presented. In addition to the absolute level of friction, the test method provides information on expected evolution of friction over lifetime as well as on expected consistency between individual devices. Paired with an analytical model of the pen mechanism, the frictional data allow the expected overall injection system force efficiency to be estimated. The test method and analytical model are applied to a range of polymer combinations with different kinds of lubrication. It is found that material combinations used without lubrication generally have unsatisfactory performance, that the use of silicone-based internal lubricating additives improves performance, and that the best results can be achieved with external silicone-based lubricants. Polytetrafluoroethylene-based internal lubrication and external lubrication are also evaluated but found to provide only limited benefits unless used in combination with silicone. PMID:27274319

Work and power outputs determined from pedalling and flywheel friction forces during brief maximal exertion on a cycle ergometer.

PubMed

Hibi, N; Fujinaga, H; Ishii, K

1996-01-01

Work and power outputs during short-term, maximal exertion on a friction loaded cycle ergometer are usually calculated from the friction force applied to the flywheel. The inertia of the flywheel is sometimes taken into consideration, but the effects of internal resistances and other factors have been ignored. The purpose of this study was to estimate their effects by comparing work or power output determined from the force exerted on the pedals (pedalling force) with work or power output determined from the friction force and the moment of inertia of the rotational parts. A group of 22 male college students accelerated a cycle ergometer as rapidly as possible for 3 s. The total work output determined from the pedalling force (TWp) was significantly greater than that calculated from the friction force and the moment of inertia (TWf). Power output determined from the pedalling force during each pedal stroke (SPp) was also significantly greater than that calculated from the friction force and the moment of inertia. Percentage difference (% diff), defined by % diff = ¿(TWp - TWf)/TWf¿ x 100, ranged from 16.8% to 49.3% with a mean value of 30.8 (SD 9.1)%. It was observed that % diff values were higher in subjects with greater TWp or greater maximal SPp. These results would indicate that internal resistances and other factors, such as the deformation of the chain and the vibrations of the entire system, may have significant effects on the measurements of work and power outputs. The effects appear to depend on the magnitudes of pedalling force and pedal velocity.

A reduced Iwan model that includes pinning for bolted joint mechanics

DOE PAGES

Brake, M. R. W.

2016-10-28

Bolted joints are prevalent in most assembled structures; however, predictive models for their behavior do not exist. Calibrated models, such as the Iwan model, are able to predict the response of a jointed structure over a range of excitations once calibrated at a nominal load. The Iwan model, though, is not widely adopted due to the high computational expense of implementation. To address this, an analytical solution of the Iwan model is derived under the hypothesis that for an arbitrary load reversal, there is a new distribution of dry friction elements, which are now stuck, that approximately resemble a scaledmore » version of the original distribution of dry friction elements. The dry friction elements internal to the Iwan model do not have a uniform set of parameters and are described by a distribution of parameters, i.e., which internal dry friction elements are stuck or slipping at a given load, that ultimately governs the behavior of the joint as it transitions from microslip to macroslip. This hypothesis allows the model to require no information from previous loading cycles. Additionally, the model is extended to include the pinning behavior inherent in a bolted joint. Modifications of the resulting framework are discussed to highlight how the constitutive model for friction can be changed (in the case of an Iwan–Stribeck formulation) or how the distribution of dry friction elements can be changed (as is the case for the Iwan plasticity model). Finally, the reduced Iwan plus pinning model is then applied to the Brake–Reuß beam in order to discuss methods to deduce model parameters from experimental data.« less

On the motion of a rigid body with an internal moving point mass on a horizontal plane

NASA Astrophysics Data System (ADS)

Bardin, B. S.; Panev, A. S.

2018-05-01

We consider motions of a body carrying movable internal mass. The internal mass is a particle moving in a circle inside the body, which performs a rectilinear motion on a horizontal plane. We suppose that viscous and dry friction acts between the plane and the body. We also assume that the body moves without jumps on the plane. Our study has shown that depending on values of parameters the body moves either periodically stoping and resting for certain time intervals or it approaches a periodic mode of motion without quiescence intervals. The above conclusions are in good correspondence with results obtained in our previous papers, where the above problem has been studied under assumption that the viscous friction is absent.

Relaxation peak near 200 K in NiTi alloy

NASA Astrophysics Data System (ADS)

Zhu, J. S.; Schaller, R.; Benoit, W.

1989-10-01

Internal friction (IF), frequency ( f), electrical resistance ( R) and zero point movement of the torsion pendulum (ɛ) have been measured in near equi-atomic NiTi alloy in order to clarify the mechanism for the relaxation peak near 200 K. The height of the relaxation peak decreases successively with thermal cycling and settles down to a lower stable value in running 15 cycles. However, the electrical resistance of the sample shows a variation in contrast with the internal friction. Both of them will return to the initial state after a single annealing at 773 K for 1 h. The probable mechanism of this relaxation peak was discussed.

Probing the molecular design of hyper-branched aryl polyesters towards lubricant applications

NASA Astrophysics Data System (ADS)

Robinson, Joshua W.; Zhou, Yan; Bhattacharya, Priyanka; Erck, Robert; Qu, Jun; Bays, J. Timothy; Cosimbescu, Lelia

2016-01-01

We report novel polymeric materials that may be used as viscosity index improvers (VII) for lubricant applications. Our efforts included probing the comb-burst hyper-branched aryl polyester architecture for beneficial viscosity and friction behavior when utilized as an additive in a group I oil. The monomer was designed as to undergo polymerization via polycondensation within the architectural construct (AB2), typical of hyperbranched polymers. The monomer design was comprised of aliphatic arms (12 or 16 methylenes) to provide the necessary lipophilicity to achieve solubility in a non-polar medium. Once polymerized, via catalyst and heat, the surface alcohols were functionalized with fatty acids (lauric and palmitic). Controlling the aliphatic nature of the internal arms and peripheral end-groups provided four unique flexible polymer designs. Changing the reaction time and concentration provided opportunities to investigate the influence of molecular weight and branching density on oil-solubility, viscosity, and friction. Oil-solubility was found to decrease with fewer internal carbons, but the number of internal carbons appears to have little influence on the bulk solution viscosity. At concentrations of 2 wt % in a group I base oil, these polymer additives demonstrated an improved viscosity index and reduced friction coefficient, validating the basic approach.

The impact of particle shape on the angle of internal friction and the implications for sediment dynamics at a steep, mixed sand-gravel beach

NASA Astrophysics Data System (ADS)

Stark, N.; Hay, A. E.; Cheel, R.; Lake, C. B.

2014-08-01

The impact of particle shape on the angle of internal friction, and the resulting impact on beach sediment dynamics, is still poorly understood. In areas characterized by sediments of specific shape, particularly non-rounded particles, this can lead to large departures from the expected sediment dynamics. The steep slope (1 : 10) of the mixed sand-gravel beach at Advocate Harbour is stable in large-scale morphology over decades, despite a high tidal range of 10 m or more, and intense shore-break action during storms. The Advocate sand (d < 2 mm) was found to have an elliptic, plate-like shape (Corey Shape Index, CSI ≈ 0.2-0.6). High angles of internal friction of this material were determined using direct shear, ranging from φ ≈ 41 to 49°, while the round to angular gravel was characterized as φ = 33°. The addition of 25% of the elliptic plate-like sand-sized material to the gravel led to an immediate increase in friction angle to φ = 38°. Furthermore, re-organization of the particles occurred during shearing, characterized by a short phase of settling and compaction, followed by a pronounced strong dilatory behavior and an accompanying strong increase of resistance to shear and, thus, shear stress. Long-term shearing (24 h) using a ring shear apparatus led to destruction of the particles without re-compaction. Finally, submerged particle mobilization was simulated using a tilted tray submerged in a water-filled tank. Despite a smooth tray surface, particle motion was not initiated until reaching tray tilt angles of 31° and more, being ≥7° steeper than for motion initiation of the gravel mixtures. In conclusion, geotechnical laboratory experiments quantified the important impact of the elliptic, plate-like shape of Advocate Beach sand on the angles of internal friction of both pure sand and sand-gravel mixtures. The resulting effect on initiation of particle motion was confirmed in tilting tray experiments. This makes it a vivid example of how particle shape can contribute to the stabilization of the beach face.

Load-bearing Characters Analysis of Large Diameter Rock-Socketed Filling Piles Based on Self-Balanced Method

NASA Astrophysics Data System (ADS)

tongqing, Wu; liang, Li; xinjian, Liu; Xu, nianchun; Tian, Mao

2018-03-01

Self-balanced method is carried out on the large diameter rock-socketed filling piles of high-pile wharf at Inland River, to explore the distribution laws of load-displacement curve, pile internal force, pile tip friction resistance and pile side friction resistance under load force. The results showed that: the tip resistance of S1 and S2 test piles accounted for 53.4% and 53.6% of the pile bearing capacity, respectively, while the total side friction resistance accounted for 46.6% and 46.4% of the pile bearing capacity, respectively; both the pile tip friction resistance and pile side friction resistance can be fully played, and reach to the design requirements. The reasonability of large diameter rock-socketed filling design is verified through test analysis, which can provide basis for the optimization of high-pile wharf structural type, thus reducing the wharf project cost, and also providing reference for the similar large diameter rock-socketed filling piles of high-pile wharf at Inland River.

Influence of friction forces on the motion of VTOL aircraft during landing operations on ships at sea

NASA Technical Reports Server (NTRS)

Howard, J. C.; Chin, D. O.

1981-01-01

Equations describing the friction forces generated during landing operations on ships at sea were formulated. These forces depend on the platform reaction and the coefficient of friction. The platform reaction depends on the relative sink rate and the shock absorbing capability of the landing gear. The friction coefficient varies with the surface condition of the landing platform and the angle of yaw of the aircraft relative to the landing platform. Landings by VTOL aircraft, equipped with conventional oleopneumatic landing gears are discussed. Simplifications are introduced to reduce the complexity of the mathematical description of the tire and shock strut characteristics. Approximating the actual complicated force deflection characteristic of the tire by linear relationship is adequate. The internal friction forces in the shock strut are included in the landing gear model. A set of relatively simple equations was obtained by including only those tire and shock strut characteristics that contribute significantly to the generation of landing gear forces.

A cohesive-frictional force field (CFFF) for colloidal calcium-silicate-hydrates

NASA Astrophysics Data System (ADS)

Palkovic, Steven D.; Yip, Sidney; Büyüköztürk, Oral

2017-12-01

Calcium-silicate-hydrate (C-S-H) gel is a cohesive-frictional material that exhibits strength asymmetry in compression and tension and normal-stress dependency of the maximum shear strength. Experiments suggest the basic structural component of C-S-H is a colloidal particle with an internal layered structure. These colloids form heterogeneous assemblies with a complex pore network at the mesoscale. We propose a cohesive-frictional force field (CFFF) to describe the interactions in colloidal C-S-H materials that incorporates the strength anisotropy fundamental to the C-S-H molecular structure that has been omitted from recent mesoscale models. We parameterize the CFFF from reactive force field simulations of an internal interface that controls mechanical performance, describing the behavior of thousands of atoms through a single effective pair interaction. We apply the CFFF to study the mesoscale elastic and Mohr-Coulomb strength properties of C-S-H with varying polydispersity and packing density. Our results show that the consideration of cohesive-frictional interactions lead to an increase in stiffness, shear strength, and normal-stress dependency, while also changing the nature of local deformation processes. The CFFF and our coarse-graining approach provide an essential connection between nanoscale molecular interactions and macroscale continuum behavior for hydrated cementitious materials.

Facts or friction: the evolving role of science in phytosanitary issues

Treesearch

Eric Allen

2008-01-01

With the expansion of global trade, problems with invasive alien pests have also grown. In order to reduce the international movement of plant pests and protect valuable plant resources, national plant protection regulations and international standards continue to be developed. Science is critical to the development of effective national and international plant...

Ratchet due to broken friction symmetry.

PubMed

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

2002-01-01

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

Lunar sample analysis

NASA Technical Reports Server (NTRS)

Tittmann, B. R.

1975-01-01

Previous studies have shown that very small amounts of absorbed volatiles only removed by outgassing in high vacuum and elevated temperatures-drastically increase the internal friction in terrestrial analogs of lunar basalt. Recently room temperature Q values as high as 2000 were achieved by thorough outgassing procedures in 10 to the 8th power torr. Results are presented on Q measurements for lunar rock 70215.85, along with some data on the effect on Q of a variety of gases. Data show that substantially greater increases in Q are obtainable in a lunar rock sample than in the terrestrial analog samples studied, and that in addition to H2O other gases also can make non-negligible contributions to the internal friction.

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

NASA Technical Reports Server (NTRS)

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

1976-01-01

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

Characterization of Al-ALLOYS (50xx) by Using Positron Annihilation, X-Ray Diffraction and Vibrating Reed Techniques

NASA Astrophysics Data System (ADS)

Kumar, Uday; Badawi, Emad; Mukhopadhyay, P. K.

A series of Al-Mgx alloys, with x = 0.82, 2.09, 2.28, 2.49 and 4.47 wt.%, respectively were characterized by using positron annihilation lifetime studies (PAL), X-ray diffraction (XRD), and sound velocity and internal friction using a vibrating reed technique (VRT). PAL lifetime values increase linearly as the composition is varied, but texturing or preferential orientation is maximum at an intermediate value of composition (x = 2.49%). The internal friction shows a minimum at the same composition, and the sound velocity changes show the maximum value here too. This means that at this composition the sample is the most ordered and defect free.

Aircraft and Ground Vehicle Winter Runway Friction Assessment

NASA Technical Reports Server (NTRS)

Yager, Thomas J.

1999-01-01

Some background information is given together with the scope and objectives of a 5-year, Joint Winter Runway Friction Measurement Program between the National Aeronautics & Space Administration (NASA), Transport Canada (TC), and the Federal Aviation Administration (FAA). The primary objective of this effort is to perform instrumented aircraft and ground vehicle tests aimed at identifying a common number that all the different ground vehicle devices would report. This number, denoted the International Runway Friction Index (IRFI), will be related to all types of aircraft stopping performance. The range of test equipment, the test sites, test results and accomplishments, the extent of the substantial friction database compiled, and future test plans will be described. Several related studies have also been implemented including the effects of contaminant type on aircraft impingement drag, and the effectiveness of various runway and aircraft de-icing chemical types, and application rates.

Probing the molecular design of hyper-branched aryl polyesters towards lubricant applications

PubMed Central

Robinson, Joshua W.; Zhou, Yan; Bhattacharya, Priyanka; Erck, Robert; Qu, Jun; Bays, J. Timothy; Cosimbescu, Lelia

2016-01-01

We report novel polymeric materials that may be used as viscosity index improvers (VII) for lubricant applications. Our efforts included probing the comb-burst hyper-branched aryl polyester architecture for beneficial viscosity and friction behavior when utilized as an additive in a group I oil. The monomer was designed as to undergo polymerization via polycondensation within the architectural construct (AB2), typical of hyperbranched polymers. The monomer design was comprised of aliphatic arms (12 or 16 methylenes) to provide the necessary lipophilicity to achieve solubility in a non-polar medium. Once polymerized, via catalyst and heat, the surface alcohols were functionalized with fatty acids (lauric and palmitic). Controlling the aliphatic nature of the internal arms and peripheral end-groups provided four unique flexible polymer designs. Changing the reaction time and concentration provided opportunities to investigate the influence of molecular weight and branching density on oil-solubility, viscosity, and friction. Oil-solubility was found to decrease with fewer internal carbons, but the number of internal carbons appears to have little influence on the bulk solution viscosity. At concentrations of 2 wt % in a group I base oil, these polymer additives demonstrated an improved viscosity index and reduced friction coefficient, validating the basic approach. PMID:26727881

Probing the molecular design of hyper-branched aryl polyesters towards lubricant applications

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

Robinson, Joshua W.; Zhou, Yan; Bhattacharya, Priyanka

We report novel polymeric materials that may be used as viscosity index improvers (VII) for lubricant applications. Our efforts included probing the comb-burst hyper-branched aryl polyester architecture for beneficial viscosity and friction behavior when utilized as an additive in a group I oil. The monomer was designed as to undergo polymerization via polycondensation within the architectural construct (AB2), typical of hyperbranched polymers. The monomer design was comprised of aliphatic arms (12 or 16 methylenes) to provide the necessary lipophilicity to achieve solubility in a non-polar medium. Once polymerized, via catalyst and heat, the surface alcohols were functionalized with fatty acidsmore » (lauric and palmitic). Controlling the aliphatic nature of the internal arms and peripheral end-groups provided four unique flexible polymer designs. Changing the reaction time and concentration provided opportunities to investigate the influence of molecular weight and branching density on oil-solubility, viscosity, and friction. Oil-solubility was found to decrease with fewer internal carbons, but the number of internal carbons appears to have little influence on the bulk solution viscosity. At concentrations of 2 wt % in a group I base oil, these polymer additives demonstrated an improved viscosity index and reduced friction coefficient, validating the basic approach.« less

Internal friction controls the speed of protein folding from a compact configuration.

PubMed

Pabit, Suzette A; Roder, Heinrich; Hagen, Stephen J

2004-10-05

Several studies have found millisecond protein folding reactions to be controlled by the viscosity of the solvent: Reducing the viscosity allows folding to accelerate. In the limit of very low solvent viscosity, however, one expects a different behavior. Internal interactions, occurring within the solvent-excluded interior of a compact molecule, should impose a solvent-independent upper limit to folding speed once the bulk diffusional motions become sufficiently rapid. Why has this not been observed? We have studied the effect of solvent viscosity on the folding of cytochrome c from a highly compact, late-stage intermediate configuration. Although the folding rate accelerates as the viscosity declines, it tends toward a finite limiting value approximately 10(5) s(-1) as the viscosity tends toward zero. This limiting rate is independent of the cosolutes used to adjust solvent friction. Therefore, interactions within the interior of a compact denatured polypeptide can limit the folding rate, but the limiting time scale is very fast. It is only observable when the solvent-controlled stages of folding are exceedingly rapid or else absent. Interestingly, we find a very strong temperature dependence in these "internal friction"-controlled dynamics, indicating a large energy scale for the interactions that govern reconfiguration within compact, near-native states of a protein.

The temperature dependences of electromechanical properties of PLZT ceramics

NASA Astrophysics Data System (ADS)

Czerwiec, M.; Zachariasz, R.; Ilczuk, J.

2008-02-01

The mechanical and electrical properties in lanthanum modified lead zirconate-titanate ceramics of 5/50/50 and 10/50/50 were studied by mechanical loss Q - 1, Young's modulus E, electric permittivity ɛ and tangent of dielectric loss of angle tgδ measurements. The internal friction Q - 1 and Young modulus E measured from 290 K to 600 K shows that Curie temperature TC is located at 574 K and 435 K (1st cycle of heating) respectively for ceramic samples 5/50/50 and 10/50/50. The movement of TC in second cycle of heating to lower temperature (561 K for 5/50/50 and 420 K for 10/50/50) has been observed. Together with Q - 1 and E measurements, temperature dependences of ɛ=f(T) and tgδ=f(T) were determinated in temperature range from 300 K to 730 K. The values of TC obtained during ɛ and tgδ measurements were respectively: 560 K for 5/50/50 and 419 K for 10/50/50. These temperatures are almost as high as the temperatures obtained by internal friction Q - 1 measurements in second cycle of heating. In ceramic sample 10/50/50 the additional maximum on internal friction Q - 1 curve at the temperature 316 K was observed.

Folding of the four-helix bundle FF domain from a compact on-pathway intermediate state is governed predominantly by water motion.

PubMed

Sekhar, Ashok; Vallurupalli, Pramodh; Kay, Lewis E

2012-11-20

Friction plays a critical role in protein folding. Frictional forces originating from random solvent and protein fluctuations both retard motion along the folding pathway and activate protein molecules to cross free energy barriers. Studies of friction thus may provide insights into the driving forces underlying protein conformational dynamics. However, the molecular origin of friction in protein folding remains poorly understood because, with the exception of the native conformer, there generally is little detailed structural information on the other states participating in the folding process. Here, we study the folding of the four-helix bundle FF domain that proceeds via a transiently formed, sparsely populated compact on-pathway folding intermediate whose structure was elucidated previously. Because the intermediate is stabilized by both native and nonnative interactions, friction in the folding transition between intermediate and folded states is expected to arise from intrachain reorganization in the protein. However, the viscosity dependencies of rates of folding from or unfolding to the intermediate, as established by relaxation dispersion NMR spectroscopy, clearly indicate that contributions from internal friction are small relative to those from solvent, so solvent frictional forces drive the folding process. Our results emphasize the importance of solvent dynamics in mediating the interconversion between protein configurations, even those that are highly compact, and in equilibrium folding/unfolding fluctuations in general.

Comparing internal migration across the countries of Latin America: A multidimensional approach

PubMed Central

Bernard, Aude; Rowe, Francisco; Bell, Martin; Ueffing, Philipp; Charles-Edwards, Elin

2017-01-01

While considerable progress has been made in understanding the way particular aspects of internal migration, such as its intensity, age profile and spatial impact, vary between countries around the world, little attention to date has been given to establishing how these dimensions of migration interact in different national settings. We use recently developed measures of internal migration that are scale-independent to compare the overall intensity, age composition, spatial impact, and distance profile of internal migration in 19 Latin American countries. Comparisons reveal substantial cross-national variation but cluster analysis suggests the different dimensions of migration evolve systematically to form a broad sequence characterised by low intensities, young ages at migration, unbalanced flows and high friction of distance at lower levels of development, trending to high intensities, an older age profile of migration, more closely balanced flows and lower friction of distance at later stages of development. However, the transition is not linear and local contingencies, such as international migration and political control, often distort the migration-development nexus, leading to unique migration patterns in individual national contexts. PMID:28328932

Reflection-Type Oil-Film Skin-Friction Meter

NASA Technical Reports Server (NTRS)

Bandyopadhyay, Promode R.; Weinstein, Leonard M.

1993-01-01

Oil-film skin-friction meter for both flight and wind-tunnel applications uses internal reflection and is self-contained, compact unit. Contained in palm-sized housing, in which source of light, mirrors, and sensor mounted rigidly in alignment. Entire unit mounted rigidly under skin of aircraft or wind tunnel, eliminating any relative vibration between optical elements and skin of aircraft or wind tunnel. Meter primarily applicable to flight and wind-tunnel tests, also used in chemical-processing plants.

Frictionless bead packs have macroscopic friction, but no dilatancy.

PubMed

Peyneau, Pierre-Emmanuel; Roux, Jean-Noël

2008-07-01

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

Single-Molecule Tribology: Force Microscopy Manipulation of a Porphyrin Derivative on a Copper Surface.

PubMed

Pawlak, Rémy; Ouyang, Wengen; Filippov, Alexander E; Kalikhman-Razvozov, Lena; Kawai, Shigeki; Glatzel, Thilo; Gnecco, Enrico; Baratoff, Alexis; Zheng, Quanshui; Hod, Oded; Urbakh, Michael; Meyer, Ernst

2016-01-26

The low-temperature mechanical response of a single porphyrin molecule attached to the apex of an atomic force microscope (AFM) tip during vertical and lateral manipulations is studied. We find that approach-retraction cycles as well as surface scanning with the terminated tip result in atomic-scale friction patterns induced by the internal reorientations of the molecule. With a joint experimental and computational effort, we identify the dicyanophenyl side groups of the molecule interacting with the surface as the dominant factor determining the observed frictional behavior. To this end, we developed a generalized Prandtl-Tomlinson model parametrized using density functional theory calculations that includes the internal degrees of freedom of the side group with respect to the core and its interactions with the underlying surface. We demonstrate that the friction pattern results from the variations of the bond length and bond angles between the dicyanophenyl side group and the porphyrin backbone as well as those of the CN group facing the surface during the lateral and vertical motion of the AFM tip.

Optical tweezers reveal force plateau and internal friction in PEG-induced DNA condensation.

PubMed

Ojala, Heikki; Ziedaite, Gabija; Wallin, Anders E; Bamford, Dennis H; Hæggström, Edward

2014-03-01

The simplified artificial environments in which highly complex biological systems are studied do not represent the crowded, dense, salty, and dynamic environment inside the living cell. Consequently, it is important to investigate the effect of crowding agents on DNA. We used a dual-trap optical tweezers instrument to perform force spectroscopy experiments at pull speeds ranging from 0.3 to 270 μm/s on single dsDNA molecules in the presence of poly(ethylene glycol) (PEG) and monovalent salt. PEG of sizes 1,500 and 4,000 Da condensed DNA, and force-extension data contained a force plateau at approximately 1 pN. The level of the force plateau increased with increasing pull speed. During slow pulling the dissipated work increased linearly with pull speed. The calculated friction coefficient did not depend on amount of DNA incorporated in the condensate, indicating internal friction is independent of the condensate size. PEG300 had no effect on the dsDNA force-extension curve. The force plateau implies that condensation induced by crowding agents resembles condensation induced by multivalent cations.

Experimental investigation into biomechanical and biotribological properties of a real intestine and their significance for design of a spiral-type robotic capsule.

PubMed

Zhou, Hao; Alici, Gursel; Than, Trung D; Li, Weihua

2014-03-01

This article reports on the results and implications of our experimental investigation into the biomechanical and biotribological properties of a real intestine for the optimal design of a spiral-type robotic capsule. Dynamic shear experiments were conducted to evaluate how the storage and loss moduli and damping factor of the small intestine change with the speed or the angular frequency. The sliding friction between differently shaped test pieces, with a topology similar to that of the spirals, and the intestine sample was experimentally determined. Our findings demonstrate that the intestine's biomechanical and biotribological properties are coupled, suggesting that the sliding friction is strongly related to the internal friction of the intestinal tissue. The significant implication of this finding is that one can predict the reaction force between the capsule with a spiral-type traction topology and the intestine directly from the intestine's biomechanical measurements rather than employing complicated three-dimensional finite element analysis or an inaccurate analytical model. Sliding friction experiments were also conducted with bar-shaped solid samples to determine the sliding friction between the samples and the small intestine. This sliding friction data will be useful in determining spiral material for an optimally designed robotic capsule.

Effects of annealing and additions on dynamic mechanical properties of SnSb quenched alloy

NASA Astrophysics Data System (ADS)

El-Bediwi, A. B.

2004-08-01

The elastic modulus, internal friction and stiffness values of quenched SnSb bearing alloy have been evaluated using the dynamic resonance technique. Annealing for 2 and 4 h at 120, 140 and 160degreesC caused variations in the elastic modulus. internal friction and stiffness values. This is due to structural changes in the SnSb matrix during isothermal annealing such as coarsening in the phases (Sn, Sb or intermetallic compounds), recrystallization and stress relief. In addition, adding a small amount (1 wt.%) of Cu or Ag improved the bearing mechanical properties of the SnSb bearing alloy. The SnSbCu1 alloy has the best bearing mechanical properties with thermo-mechanical stability for long time at high temperature.

Young's modulus and internal friction of the SiC/Si biomorphic composite based on the sapele wood precursor

NASA Astrophysics Data System (ADS)

Kardashev, B. K.; Orlova, T. S.; Smirnov, B. I.; de Arellano-Lopez, A. R.; Martinez-Fernandez, J.

2009-04-01

The effect of the vibrational strain amplitude on the Young’s modulus and ultrasound absorption (internal friction) of a SiC/Si biomorphic composite prepared by pyrolysis of sapele wood followed by infiltration of silicon were investigated. The studies were conducted in air and in vacuum by the acoustic resonance method with the use of a composite vibrator in longitudinal vibrations at frequencies of about 100 kHz. Measurements performed on sapele wood-based bio-SiC/Si samples revealed a substantial effect of adsorption-desorption of molecules contained in air on the effective elasticity modulus and elastic vibration decrement. Microplastic characteristics of the SiC/Si composites prepared from wood of different tree species were compared.

Investigation of internal friction in fused quartz, steel, Plexiglass, and Westerly granite from 0.01 to 1.00 Hertz at 10- 8 to 10-7 strain amplitude.

USGS Publications Warehouse

Hsi-Ping, Liu; Peselnick, L.

1983-01-01

A detailed evaluation on the method of internal friction measurement by the stress-strain hysteresis loop method from 0.01 to 1 Hz at 10-8-10-7 strain amplitude and 23.9oC is presented. Significant systematic errors in relative phase measurement can result from convex end surfaces of the sample and stress sensor and from end surface irregularities such as nicks and asperities. Preparation of concave end surfaces polished to optical smoothness having a radius of curvature >3.6X104 cm reduces the systematic error in relative phase measurements to <(5.5+ or -2.2)X10-4 radians. -from Authors

Internal friction of rocks and volatiles on the moon

NASA Technical Reports Server (NTRS)

Tittmann, B. R.; Housley, R. M.; Cirlin, E. H.

1973-01-01

Internal friction quality factors Q up to 2200 have been observed in a strongly outgassed terrestrial analog of lunar basalt. This was accomplished by successively cycling a bar shaped sample vibrating in its fundamental longitudinal mode at 15 kHz to higher and higher temperatures in a vacuum between 100 and 10 nanotorr. After each cycle, Q measured at room temperature in the vacuum was observed to decrease with time suggesting that gas reabsorption was taking place even at these low pressures. A study of the effect of exposing a sample to a variety of gases and vapors showed that of the volatiles most likely to be present in the lunar environment H2O was by far the most effective in lowering Q.

A Study of Three Intrinsic Problems of the Classic Discrete Element Method Using Flat-Joint Model

NASA Astrophysics Data System (ADS)

Wu, Shunchuan; Xu, Xueliang

2016-05-01

Discrete element methods have been proven to offer a new avenue for obtaining the mechanics of geo-materials. The standard bonded-particle model (BPM), a classic discrete element method, has been applied to a wide range of problems related to rock and soil. However, three intrinsic problems are associated with using the standard BPM: (1) an unrealistically low unconfined compressive strength to tensile strength (UCS/TS) ratio, (2) an excessively low internal friction angle, and (3) a linear strength envelope, i.e., a low Hoek-Brown (HB) strength parameter m i . After summarizing the underlying reasons of these problems through analyzing previous researchers' work, flat-joint model (FJM) is used to calibrate Jinping marble and is found to closely match its macro-properties. A parametric study is carried out to systematically evaluate the micro-parameters' effect on these three macro-properties. The results indicate that (1) the UCS/TS ratio increases with the increasing average coordination number (CN) and bond cohesion to tensile strength ratio, but it first decreases and then increases with the increasing crack density (CD); (2) the HB strength parameter m i has positive relationships to the crack density (CD), bond cohesion to tensile strength ratio, and local friction angle, but a negative relationship to the average coordination number (CN); (3) the internal friction angle increases as the crack density (CD), bond cohesion to tensile strength ratio, and local friction angle increase; (4) the residual friction angle has little effect on these three macro-properties and mainly influences post-peak behavior. Finally, a new calibration procedure is developed, which not only addresses these three problems, but also considers the post-peak behavior.

Articulated Multimedia Physics, Lesson 13, Internal Energy, Heat, and Temperature.

ERIC Educational Resources Information Center

New York Inst. of Tech., Old Westbury.

As the thirteenth lesson of the Articulated Multimedia Physics Course, instructional materials are presented in this study guide with relation to internal energy, heat, and temperature. The topics are concerned with collisions, thermometers, friction forces, degrees Centigrade and Fahrenheit, calories, Brownian motion, and state changes. The…

Seminar on Education for International Understanding.

ERIC Educational Resources Information Center

Australian National Advisory Committee for Unesco, Canberra.

This report presents three seminar papers and associated discussion session reports from the Adelaide seminar which focused on education as it relates to the advancement of international understanding. In the first paper, A. M. Thomas stressed the necessity for continuing cooperation among nations to solve problems of friction and poverty.…

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

PubMed

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

2010-10-01

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

Probing the molecular design of hyper-branched aryl polyesters towards lubricant applications

DOE PAGES

Robinson, Joshua W.; Zhou, Yan; Bhattacharya, Priyanka; ...

2016-01-05

We report novel polymeric materials that may be used as viscosity index improvers (VII) for lubricant applications. Our efforts included probing the comb-burst hyper-branched aryl polyester architecture for beneficial viscosity and friction behavior when utilized as an additive in a group I oil. The monomer was designed as to undergo polymerization via polycondensation within the architectural construct (AB2), typical of hyperbranched polymers. The monomer design was comprised of aliphatic arms (12 or 16 methylenes) to provide the necessary lipophilicity to achieve solubility in a non-polar medium. Once polymerized, via catalyst and heat, the surface alcohols were functionalized with fatty acidsmore » (lauric and palmitic). Controlling the aliphatic nature of the internal arms and peripheral end-groups provided four unique flexible polymer designs. Changing the reaction time and concentration provided opportunities to investigate the influence of molecular weight and branching density on oil-solubility, viscosity, and friction. Oil-solubility was found to decrease with fewer internal carbons, but the number of internal carbons appears to have little influence on the bulk solution viscosity. Increased branching and degree of polymerization, and thus molecular weight, were found to reduce the solubility of these systems in the base oil. At concentrations of 2 wt % in a group I base oil, these polymer additives demonstrated improved viscosity index and reduced friction coefficient, validating the basic approach.« less

Numerical Modeling of Mechanical Behavior for Buried Steel Pipelines Crossing Subsidence Strata

PubMed Central

Han, C. J.

2015-01-01

This paper addresses the mechanical behavior of buried steel pipeline crossing subsidence strata. The investigation is based on numerical simulation of the nonlinear response of the pipeline-soil system through finite element method, considering large strain and displacement, inelastic material behavior of buried pipeline and the surrounding soil, as well as contact and friction on the pipeline-soil interface. Effects of key parameters on the mechanical behavior of buried pipeline were investigated, such as strata subsidence, diameter-thickness ratio, buried depth, internal pressure, friction coefficient and soil properties. The results show that the maximum strain appears on the outer transition subsidence section of the pipeline, and its cross section is concave shaped. With the increasing of strata subsidence and diameter-thickness ratio, the out of roundness, longitudinal strain and equivalent plastic strain increase gradually. With the buried depth increasing, the deflection, out of roundness and strain of the pipeline decrease. Internal pressure and friction coefficient have little effect on the deflection of buried pipeline. Out of roundness is reduced and the strain is increased gradually with the increasing of internal pressure. The physical properties of soil have a great influence on the mechanical properties of buried pipeline. The results from the present study can be used for the development of optimization design and preventive maintenance for buried steel pipelines. PMID:26103460

Probing the molecular design of hyper-branched aryl polyesters towards lubricant applications

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

Robinson, Joshua W.; Zhou, Yan; Bhattacharya, Priyanka

We report novel polymeric materials that may be used as viscosity index improvers (VII) for lubricant applications. Our efforts included probing the comb-burst hyper-branched aryl polyester architecture for beneficial viscosity and friction behavior when utilized as an additive in a group I oil. The monomer was designed as to undergo polymerization via polycondensation within the architectural construct (AB2), typical of hyperbranched polymers. The monomer design was comprised of aliphatic arms (12 or 16 methylenes) to provide the necessary lipophilicity to achieve solubility in a non-polar medium. Once polymerized, via catalyst and heat, the surface alcohols were functionalized with fatty acidsmore » (lauric and palmitic). Controlling the aliphatic nature of the internal arms and peripheral end-groups provided four unique flexible polymer designs. Changing the reaction time and concentration provided opportunities to investigate the influence of molecular weight and branching density on oil-solubility, viscosity, and friction. Oil-solubility was found to decrease with fewer internal carbons, but the number of internal carbons appears to have little influence on the bulk solution viscosity. Increased branching and degree of polymerization, and thus molecular weight, were found to reduce the solubility of these systems in the base oil. At concentrations of 2 wt % in a group I base oil, these polymer additives demonstrated improved viscosity index and reduced friction coefficient, validating the basic approach.« less

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

NASA Astrophysics Data System (ADS)

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.

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

PubMed

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.

Self-Lubricating, Wear-Resistant Diamond Films Developed for Use in Vacuum Environment

NASA Technical Reports Server (NTRS)

1996-01-01

Diamond's outstanding properties--extreme hardness, chemical and thermal inertness, and high strength and rigidity--make it an ideal material for many tribological applications, such as the bearings, valves, and engine parts in the harsh environment found in internal-combustion engines, jet engines, and space propulsion systems. It has been demonstrated that chemical-vapor-deposited diamond films have low coefficients of friction (on the order of 0.01) and low wear rates (less than 10(sup -7) mm (sup 3/N-m)) both in humid air and dry nitrogen but that they have both high coefficients of friction (greater than 0.4) and high wear rates (on the order of 1(sup -4) mm sup 3/N-m)) in vacuum. It is clear that surface modifications that provide acceptable levels of friction and wear properties will be necessary before diamond films can be used for tribological applications in a space-like, vacuum environment. Previously, it was found that coatings of amorphous, non-diamond carbon can provide low friction in vacuum. Therefore, to reduce the friction and wear of diamond film in vacuum, carbon ions were implanted in an attempt to form a surface layer of amorphous carbon phases on the diamond films.

Scalar model for frictional precursors dynamics

PubMed Central

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

2015-01-01

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

Scalar model for frictional precursors dynamics.

PubMed

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

2015-02-02

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

Demonstration of a Large-Scale Tank Assembly via Circumferential Friction Stir Welds

NASA Technical Reports Server (NTRS)

Jones, Clyde S.; Adams, Glynn; Colligan, Kevin

2000-01-01

A collaborative effort between NASA/Marshall Space Flight Center and the Michoud Unit of Lockheed Martin Space Systems Company was undertaken to demonstrate assembly of a large-scale aluminum tank using circumferential friction stir welds. The hardware used to complete this demonstration was fabricated as a study of near-net- shape technologies. The tooling used to complete this demonstration was originally designed for assembly of a tank using fusion weld processes. This presentation describes the modifications and additions that were made to the existing fusion welding tools required to accommodate circumferential friction stir welding, as well as the process used to assemble the tank. The tooling modifications include design, fabrication and installation of several components. The most significant components include a friction stir weld unit with adjustable pin length capabilities, a continuous internal anvil for 'open' circumferential welds, a continuous closeout anvil, clamping systems, an external reaction system and the control system required to conduct the friction stir welds and integrate the operation of the tool. The demonstration was intended as a development task. The experience gained during each circumferential weld was applied to improve subsequent welds. Both constant and tapered thickness 14-foot diameter circumferential welds were successfully demonstrated.

An exact closed form solution for constant area compressible flow with friction and heat transfer

NASA Technical Reports Server (NTRS)

Sturas, J. I.

1971-01-01

The well-known differential equation for the one-dimensional flow of a compressible fluid with heat transfer and wall friction has no known solution in closed form for the general case. This report presents a closed form solution for the special case of constant heat flux per unit length and constant specific heat. The solution was obtained by choosing the square of a dimensionless flow parameter as one of the independent variables to describe the flow. From this exact solution, an approximate simplified form is derived that is applicable for predicting subsonic flow performance characteristics for many types of constant area passages in internal flow. The data included in this report are considered sufficiently accurate for use as a guide in analyzing and designing internal gas flow systems.

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

PubMed

Füchsel, Gernot; Schimka, Selina; Saalfrank, Peter

2013-09-12

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

Cross-Cultural "Distance", "Friction" and "Flow": Exploring the Experiences of Pre-Service Teachers on International Practicum

ERIC Educational Resources Information Center

Uusimaki, Liisa; Swirski, Teresa

2016-01-01

The focus of this paper is to illustrate Australian regional pre-service teachers' perceptions of an international practicum: their cross-cultural understanding, notions of privilege and teacher/professional identity development. Findings indicate that there were three overlapping dimensions of cross-cultural understanding for pre-service…

49 CFR 173.308 - Lighters.

Code of Federal Regulations, 2013 CFR

2013-10-01

..., must be capable of withstanding, without leakage or rupture, an internal pressure of at least two times... plastic tray, a plastic, fiberboard or paperboard partition must be used to prevent friction between the...

49 CFR 173.308 - Lighters.

Code of Federal Regulations, 2012 CFR

2012-10-01

..., must be capable of withstanding, without leakage or rupture, an internal pressure of at least two times... plastic tray, a plastic, fiberboard or paperboard partition must be used to prevent friction between the...

On the relationship between forearc deformation, frictional properties and megathrust earthquakes

NASA Astrophysics Data System (ADS)

Cubas, Nadaya; Singh, Satish

2014-05-01

A better understanding of the relation between the structural geology and the morphology of forearc wedges with frictional properties could provide insights on earthquake mechanics. Therefore, we study, with simple mechanical analysis allowing for inverse studies, the three subduction zones that produced the major earthquakes of the 21st century : Central Chile (Maule 2010 Mw 8.8), NE Japan (Tohoku-Oki 2011 Mw 9.0) and Sumatra (Sumatra-Andaman 2004 Mw 9.1, Nias 2005 Mw 8.7). We first apply the critical taper theory that yields the effective friction of the subduction interface, the wedge internal friction and pore fluid pressure. We then apply the limit analysis approach to constrain variations of frictional properties along the megathrust from the location and style of forearc faulting. We show that seismic ruptures most often coincide with the mechanically stable part of the wedge whereas regions undergoing aseismic slip are at critical state, consistent with evidence for active deformation. In the rupture area, we found a low effective dynamic friction, probably reflecting strong dynamic weakening. Where no frontal rupture was observed, we obtain intermediate values of long-term effective friction along the frontal aseismic zone, implying hydrostatic pore pressure. On the contrary, where the rupture reached the seafloor (Tohoku-Oki earthquake, parts of the Sumatra-Andaman 2004 earthquake), a very low long-term effective friction and a high pore pressure are observed. The difference of properties of the frontal wedge might reflect differences in permeability. A lower permeability would enhance dynamic weakening and allow for frontal propagation of ruptures. We also show that spatial variations of frictional properties between aseismic and seismogenic zones can lead to the activation of splay faults. We also show that a high pore pressure along accretionary wedges can change the vergence of frontal thrusts. As a consequence, wedge morphology and deformation can be used to improve seismic and tsunamigenic risk assessment.

Internal friction and modulus in rocks at depth

NASA Technical Reports Server (NTRS)

Tittmann, B. R.; Clark, V. A.; Anlberg, L.

1980-01-01

Experimental results relevant to the seismic wave attenuation observed for the lunar crust are presented along with some results bearing on the mechanism by which the presence of volatiles increases the attenuation.

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

PubMed

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.

Temperature dependences of internal friction and shear modulus in glass-textolites irradiated with electrons

NASA Astrophysics Data System (ADS)

Zaikin, Yu. A.; Kozhamkulov, B. A.; Koztaeva, U. P.

1997-07-01

A study is made of mechanical relaxation mechanisms and the correlation between parameters characterizing the temperature dependence of internal friction and shear modulus when the mechanical and electrical properties of glass-textolites of grades ST-11 and ST-ETF are altered by exposure to different doses of high-energy electrons. High-temperature α- and α'- transformation are observed, these transformations being due to the unfreezing of segmental mobility in the polymer matrix and the boundary layers at the surfaces of the glass fibers under the influence of the radiation. A discussion is presented of features of radiation-induced degradation processes in the polymer binder and at points where it contacts the filler. The data that is obtained shows that glass-texolites ST-ETF and ST-11 are highly resistant to radiation.

Flowability of JSC-1a

NASA Technical Reports Server (NTRS)

Rame, Enrique; Wilkinson, Allen; Elliot, Alan; Young, Carolyn

2009-01-01

We have done a complete flowability characterization of the lunar soil simulant, JSC-1a, following closely the ASTM-6773 standard for the Schulze ring shear test. The measurements, which involve pre-shearing the material before each yield point, show JSC-1a to be cohesionless, with an angle of internal friction near 40 deg. We also measured yield loci after consolidating the material in a vibration table which show it to have significant cohesion (approximately equal to 1 kPa) and an angle of internal friction of about 60 deg. Hopper designs based on each type of flowability test differ significantly. These differences highlight the need to discern the condition of the lunar soil in the specific process where flowability is an issue. We close with a list not necessarily comprehensive of engineering rules of thumb that apply to powder flow in hoppers.

Thermal characterization of phacoemulsification probes operated in axial and torsional modes.

PubMed

Zacharias, Jaime

2015-01-01

To analyze temperature increases and identify potential sources of heat generated when sleeved and sleeveless phacoemulsification probes were operated in axial and torsional modes using the Infiniti Vision System with the Ozil torsional handpiece. Phacodynamics Laboratory, Pasteur Ophthalmic Clinic, Santiago, Chile. Experimental study. Two computer-controlled thermal transfer systems were developed to evaluate the contribution of internal metal stress and tip-to-sleeve friction on heat generation during phacoemulsification using axial and torsional ultrasound modalities. Both systems incorporated infrared thermal imaging and used a black-body film to accurately capture temperature measurements. Axial mode was consistently associated with greater temperature increases than torsional mode whether tips were operated with or without sleeves. In tests involving bare tips, axial mode and torsional mode peaked at 51.7°C and 34.2°C, respectively. In an example using sleeved tips in which a 30.0 g load was applied for 1 second, temperatures for axial mode reached 45°C and for torsional mode, 38°C. Friction between the sleeved probe and the incisional wall contributed more significantly to the temperature increase than internal metal stress regardless of the mode used. In all experiments, the temperature increase observed with axial mode was greater than that observed with torsional mode, even when conditions such as power or amplitude and flow rate were varied. Tip-to-sleeve friction was a more dominant source of phaco probe heating than internal metal stress. The temperature increase due to internal metal stress was greater with axial mode than with torsional mode. Dr. Zacharias received research funding from Alcon Laboratories, Inc., to conduct this study. He has no financial or proprietary interest in any material or method mentioned. Copyright © 2015 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

Internal structure of inertial granular flows.

PubMed

Azéma, Emilien; Radjaï, Farhang

2014-02-21

We analyze inertial granular flows and show that, for all values of the inertial number I, the effective friction coefficient μ arises from three different parameters pertaining to the contact network and force transmission: (1) contact anisotropy, (2) force chain anisotropy, and (3) friction mobilization. Our extensive 3D numerical simulations reveal that μ increases with I mainly due to an increasing contact anisotropy and partially by friction mobilization whereas the anisotropy of force chains declines as a result of the destabilizing effect of particle inertia. The contact network undergoes topological transitions, and beyond I≃0.1 the force chains break into clusters immersed in a background "soup" of floating particles. We show that this transition coincides with the divergence of the size of fluidized zones characterized from the local environments of floating particles and a slower increase of μ with I.

Internal Structure of Inertial Granular Flows

NASA Astrophysics Data System (ADS)

Azéma, Emilien; Radjaï, Farhang

2014-02-01

We analyze inertial granular flows and show that, for all values of the inertial number I, the effective friction coefficient μ arises from three different parameters pertaining to the contact network and force transmission: (1) contact anisotropy, (2) force chain anisotropy, and (3) friction mobilization. Our extensive 3D numerical simulations reveal that μ increases with I mainly due to an increasing contact anisotropy and partially by friction mobilization whereas the anisotropy of force chains declines as a result of the destabilizing effect of particle inertia. The contact network undergoes topological transitions, and beyond I≃0.1 the force chains break into clusters immersed in a background "soup" of floating particles. We show that this transition coincides with the divergence of the size of fluidized zones characterized from the local environments of floating particles and a slower increase of μ with I.

Rock mechanics. Superplastic nanofibrous slip zones control seismogenic fault friction.

PubMed

Verberne, Berend A; Plümper, Oliver; de Winter, D A Matthijs; Spiers, Christopher J

2014-12-12

Understanding the internal mechanisms controlling fault friction is crucial for understanding seismogenic slip on active faults. Displacement in such fault zones is frequently localized on highly reflective (mirrorlike) slip surfaces, coated with thin films of nanogranular fault rock. We show that mirror-slip surfaces developed in experimentally simulated calcite faults consist of aligned nanogranular chains or fibers that are ductile at room conditions. These microstructures and associated frictional data suggest a fault-slip mechanism resembling classical Ashby-Verrall superplasticity, capable of producing unstable fault slip. Diffusive mass transfer in nanocrystalline calcite gouge is shown to be fast enough for this mechanism to control seismogenesis in limestone terrains. With nanogranular fault surfaces becoming increasingly recognized in crustal faults, the proposed mechanism may be generally relevant to crustal seismogenesis. Copyright © 2014, American Association for the Advancement of Science.

Joule-Thomson effect and internal convection heat transfer in turbulent He II flow

NASA Technical Reports Server (NTRS)

Walstrom, P. L.

1988-01-01

The temperature rise in highly turbulent He II flowing in tubing was measured in the temperature range 1.6-2.1 K. The effect of internal convection heat transport on the predicted temperature profiles is calculated from the two-fluid model with mutual friction. The model predictions are in good agreement with the measurements, provided that the pressure gradient term is retained in the expression for internal convection heat flow.

Friction Pull Plug Welding in Aluminum Alloys

NASA Technical Reports Server (NTRS)

Brooke, Shane A.; Bradford, Vann; Burkholder, Jonathon

2011-01-01

NASA fs 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 External Tank. FPPW was easily selected as the primary process used to close out the termination hole on the Constellation Program fs 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 fs 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.

Friction Pull Plug Welding in Aluminum Alloys

NASA Technical Reports Server (NTRS)

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.

Geometrical and Friction Properties of Perennial Grasses and Their Weeds in View of an Electro-Separation Method

NASA Astrophysics Data System (ADS)

Kovalyshyn, Stepan J.; Dadak, Viktor O.; Sokolyk, Vitalij V.; Grundas, Stanisław; Stasiak, Mateusz; Tys, Jerzy

2015-04-01

Many seed mixtures of herbs are difficult to separate. This is confirmed by studies determining the basic geometrical and friction properties of the seeds of perennial grasses and seeds of their weeds. The results show that in most cases the value of their geometrical parameters (length, thickness, and width) and friction properties (friction coefficients for different external surfaces of internal friction coefficients) are substantially similar and differ slightly among each other. This is the evidence that these properties are impractical to use in the process of separation as signs of divisibility. In the paper, a method for electro-separation of seed mixtures of herbs based on the use of complex physical, mechanical properties and electrical components in the separation are presented. The electric field that acts as an additional working body allows considering the surface conditions and biological status of seed mixtures of particles and significantly expands the functionality of the separators. Confirmation of the effectiveness of the proposed method for separation can be seen in the example of purification of red clover and sorrel seeds. By imposition of an electric field on an inclined moving separating plane, we can completely separate weed seeds from the main crop. The results confirm the effectiveness of the electro-separating method.

How geometrical constraints contribute to the weakness of mature faults

USGS Publications Warehouse

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

1993-01-01

Increasing evidence that the San Andreas fault has low shear strength1 has fuelled considerable discussion regarding the role of fluid pressure in controlling fault strength. Byerlee2,3 and Rice4 have shown how fluid pressure gradients within a fault zone can produce a fault with low strength while avoiding hydraulic fracture of the surrounding rock due to excessive fluid pressure. It may not be widely realised, however, that the same analysis2-4 shows that even in the absence of fluids, the presence of a relatively soft 'gouge' layer surrounded by harder country rock can also reduce the effective shear strength of the fault. As shown most recently by Byerlee and Savage5, as the shear stress across a fault increases, the stress state within the fault zone evolves to a limiting condition in which the maximum shear stress within the fault zone is parallel to the fault, which then slips with a lower apparent coefficient of friction than the same material unconstrained by the fault. Here we confirm the importance of fault geometry in determining the apparent weakness of fault zones, by showing that the apparent friction on a sawcut granite surface can be predicted from the friction measured in intact rock, given only the geometrical constraints introduced by the fault surfaces. This link between the sliding friction of faults and the internal friction of intact rock suggests a new approach to understanding the microphysical processes that underlie friction in brittle materials.

Frictional properties of saponite-rich gouge from a serpentinite-bearing fault zone along the Gokasho-Arashima Tectonic Line, central Japan

USGS Publications Warehouse

Sone, Hiroki; Shimamoto, Toshihiko; Moore, Diane E.

2012-01-01

We studied a serpentinite-bearing fault zone in Gokasho-Arashima Tectonic Line, Mie Prefecture, central Japan, characterizing its internal structures, mineral assemblage, permeability, and frictional properties. The fault core situated between the serpentinite breccia and the adjacent sedimentary rocks is characterized by a zone locally altered to saponite. The clayey gouge layer separates fault rocks of serpentinite origin containing talc and tremolite from fault rocks of sedimentary origin containing chlorite but no quartz. The minerals that formed within the fault are the products of metasomatic reaction between the serpentinite and the siliceous rocks. Permeability measurements show that serpentinite breccia and fault gouge have permeability of 10−14–10−17 m2 and 10−15–10−18 m2, respectively, at 5–120 MPa confining pressure. Frictional coefficient of the saponite-rich clayey fault gouge ranged between 0.20 and 0.35 under room-dry condition, but was reduced to 0.06–0.12 when saturated with water. The velocity dependence of friction was strongly positive, mostly ranging between 0.005 and 0.006 in terms of a–b values. The governing friction law is not constrained yet, but we find that the saponite-rich gouge possesses an evolutional behavior in the opposite direction to that suggested by the rate and state friction law, in addition to its direct velocity dependence.

Stochastic estimation of human arm impedance under nonlinear friction in robot joints: a model study.

PubMed

Chang, Pyung Hun; Kang, Sang Hoon

2010-05-30

The basic assumption of stochastic human arm impedance estimation methods is that the human arm and robot behave linearly for small perturbations. In the present work, we have identified the degree of influence of nonlinear friction in robot joints to the stochastic human arm impedance estimation. Internal model based impedance control (IMBIC) is then proposed as a means to make the estimation accurate by compensating for the nonlinear friction. From simulations with a nonlinear Lugre friction model, it is observed that the reliability and accuracy of the estimation are severely degraded with nonlinear friction: below 2 Hz, multiple and partial coherence functions are far less than unity; estimated magnitudes and phases are severely deviated from that of a real human arm throughout the frequency range of interest; and the accuracy is not enhanced with an increase of magnitude of the force perturbations. In contrast, the combined use of stochastic estimation and IMBIC provides with accurate estimation results even with large friction: the multiple coherence functions are larger than 0.9 throughout the frequency range of interest and the estimated magnitudes and phases are well matched with that of a real human arm. Furthermore, the performance of suggested method is independent of human arm and robot posture, and human arm impedance. Therefore, the IMBIC will be useful in measuring human arm impedance with conventional robot, as well as in designing a spatial impedance measuring robot, which requires gearing. (c) 2010 Elsevier B.V. All rights reserved.

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

PubMed

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.

Partial squeeze film levitation modulates fingertip friction.

PubMed

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

2016-08-16

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

Partial squeeze film levitation modulates fingertip friction

PubMed Central

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

2016-01-01

When touched, a glass plate excited with ultrasonic transverse waves feels notably more slippery than it does at rest. To study this phenomenon, we use frustrated total internal reflection to image the asperities of the skin that are in intimate contact with a glass plate. We observed that the load at the interface is shared between the elastic compression of the asperities of the skin and a squeeze film of air. Stroboscopic investigation reveals that the time evolution of the interfacial gap is partially out of phase with the plate vibration. Taken together, these results suggest that the skin bounces against the vibrating plate but that the bounces are cushioned by a squeeze film of air that does not have time to escape the interfacial separation. This behavior results in dynamic levitation, in which the average number of asperities in intimate contact is reduced, thereby reducing friction. This improved understanding of the physics of friction reduction provides key guidelines for designing interfaces that can dynamically modulate friction with soft materials and biological tissues, such as human fingertips. PMID:27482117

Friction

NASA Astrophysics Data System (ADS)

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

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

49 CFR 173.167 - Consumer commodities.

Code of Federal Regulations, 2013 CFR

2013-10-01

... exceed 30 kg (66 pounds) gross weight as prepared for shipment. (2) Closures. Friction-type closures must...) prescribed in § 173.27(c) of this part. The capability of a packaging to withstand an internal pressure...

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

NASA Astrophysics Data System (ADS)

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 paper constructs an adaptive robust controller which can compensate the friction force in the cylinder.

Simultaneous measurement of friction and wear in hip simulators.

PubMed

Haider, Hani; Weisenburger, Joel N; Garvin, Kevin L

2016-05-01

We propose and have evaluated a method to measure hip friction during wear testing on a popular multi-station hip simulator. A 6-degree-of-freedom load cell underneath the specimen sensed forces and torques during implant wear testing of simulated walking. This included internal-external and adduction-abduction rotations which are often neglected during friction testing on pendulum-type machines. Robust mathematical analysis and data processing provided friction estimates in three simultaneous orthogonal rotations, over extended multi-million cycle wear tests. We tested various bearing couples including metal-on-plastic, ceramic-on-plastic, and metal-on-metal material couples. In one test series, new and intentionally scratched CoCrMo 40-mm-diameter femoral heads were tested against conventional ultrahigh-molecular-weight polyethylene, highly cross-linked, and highly cross-linked with vitamin E versions. The scratching significantly increased friction and doubled the wear of all groups. Before scratching, friction levels for the aforementioned plastic groups were 0.056 ± 0.0060, 0.062 ± 0.0080, and 0.070 ± 0.0045, respectively, but after scratching increased to 0.088 ± 0.018, 0.076 ± 0.0066, and 0.082 ± 0.0049, respectively, all statistically significant increases (p = 0.00059, 0.00005, 0.0115, respectively). In another test series of 44-mm femoral head diameter hips, metal-on-plastic hips with conventional ultrahigh-molecular-weight polyethylene showed the lowest friction at 0.045 ± 0.0085, followed by highly cross-linked with 0.046 ± 0.0035 (not significantly different). In a ceramic-on-plastic design with conventional ultrahigh-molecular-weight polyethylene, higher friction 0.079 ± 0.0070 was measured likely due to that ceramic surface being rougher than usual. Metal-on-metal hips were compared without and with a TiN coating, resulting in 0.049 ± 0.014 and 0.097 ± 0.020 friction factors, respectively (statistically significant, p < 0.001), and the coating wore away on all coated hips eventually. Higher friction mostly correlated with higher wear or damage to femoral heads or implant coatings, except for the highly cross-linked wear resistant ultrahigh-molecular-weight polyethylene which had slightly higher friction, confirming the same finding in other independent studies. This type of friction measurements can help screen for clamping and elevated wear of metal-on-metal and resurfacing total hip replacements, surgical malpositioning, and abraded and otherwise damaged surfaces. © IMechE 2016.

A method for evaluating dynamical friction in linear ball bearings.

PubMed

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.

Effect of thermal cycling on the R-phase and martensitic transformations in a Ti-rich NiTi alloy

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

Pelosin, V.; Riviere, A.

1998-04-01

The effect of thermal cycling on transformation temperature was studied on a Ti-rich NiTi alloy. The study was carried out by determining the electrical resistance, the internal friction, and the elastic modulus vs temperature. This study shows that the martensite microstructure is modified by the successive cycling transformation. In addition, the authors established that both the martensite internal friction and the transition peak are sensitive to the transient effect (the vibration frequency lies around 300 Hz). But the major results concern the behavior associated with the R phase occurrence and its evolution. They have stated that the premartensitic phase becomesmore » stable following the diminishment of the beginning of the martensite formation (M{sub s}). Interrupted cooling has also shown that, contrary to the martensite, the R phase exhibits no hysteretic behavior.« less

Origin of the low-frequency internal friction background of gold

NASA Astrophysics Data System (ADS)

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.

Cost-effective use of liquid nitrogen in cryogenic wind tunnels, phase 2

NASA Technical Reports Server (NTRS)

Mcintosh, Glen E.; Lombard, David S.; Leonard, Kenneth R.; Morhorst, Gerald D.

1990-01-01

Cryogenic seal tests were performed and Rulon A was selected for the subject nutating positive displacement expander. A four-chamber expander was designed and fabricated. A nitrogen reliquefier flow system was also designed and constructed for testing the cold expander. Initial tests were unsatisfactory because of high internal friction attributed to nutating Rulon inlet and outlet valve plates. Replacement of the nutating valves with cam-actuated poppet valves improved performance. However, no net nitrogen reliquefaction was achieved due to high internal friction. Computer software was developed for accurate calculation of nitrogen reliquefaction from a system such as that proposed. These calculations indicated that practical reliquefaction rates of 15 to 19 percent could be obtained. Due to mechanical problems, the nutating expander did not demonstrate its feasibility nor that of the system. It was concluded that redesign and testing of a smaller nutating expander was required to prove concept feasibility.

Revisiting the factors which control the angle of shear bands in geodynamic numerical models of brittle deformation

NASA Astrophysics Data System (ADS)

Thieulot, Cedric

2017-04-01

In this work I present Finite Element numerical simulations of brittle deformation in two-dimensional Cartesian systems subjected to compressional or extensional kinematical boundary conditions with a basal velocity discontinuity. The rheology is visco-plastic and is characterised by a cohesion and an angle of internal friction (Drucker-Prager type). I will explore the influence of the following factors on the recovered shear band angles when the angle of internal friction is varied: a) element type (quadrilateral vs triangle), b) element order, c) continuous vs discontinous pressure, d) visco-plasticity model implementation, e) the nonlinear tolerance value, f) the use of markers, g) Picard vs Newton-Raphson, h) velocity discontinuity nature. I will present these results in the light of already published literature (e.g. Lemiale et al, PEPI 171, 2008; Kaus, Tectonophysics 484, 2010).

A parametric investigation on a solar dish-Stirling system

NASA Astrophysics Data System (ADS)

Gholamalizadeh, Ehsan; Chung, Jae Dong

2018-06-01

The aim of this study is to analyze the performance of a solar dish-Stirling system. A mathematical model for the overall thermal efficiency of the solar-powered high-temperature-differential dish-Stirling engine is described. This model takes into account pressure losses due to fluid friction which is internal to the engine, mechanical friction between the moving parts, actual heat transfer includes the effects of both internal and external irreversibilities of the cycle and finite regeneration processes time. Validation was done through comparison with the actual power output of the "EuroDish" system. Moreover, the effects of dish diameter and working fluid on the performance of the system were studied. An increase of about 7.2% was observed for the power output using hydrogen as the working fluid rather than helium. Also, the focal distance for any diameter of dish was calculated.

Internal friction and mode relaxation in a simple chain model.

PubMed

Fugmann, S; Sokolov, I M

2009-12-21

We consider the equilibrium relaxation properties of the end-to-end distance and of the principal components in a one-dimensional polymer chain model with nonlinear interaction between the beads. While for the single-well potentials these properties are similar to the ones of a Rouse chain, for the double-well interaction potentials, modeling internal friction, they differ vastly from the ones of the harmonic chain at intermediate times and intermediate temperatures. This minimal description within a one-dimensional model mimics the relaxation properties found in much more complex polymer systems. Thus, the relaxation time of the end-to-end distance may grow by orders of magnitude at intermediate temperatures. The principal components (whose directions are shown to coincide with the normal modes of the harmonic chain, whatever interaction potential is assumed) not only display larger relaxation times but also subdiffusive scaling.

Rapid internal contraction boosts DNA friction.

PubMed

Otto, Oliver; Sturm, Sebastian; Laohakunakorn, Nadanai; Keyser, Ulrich F; Kroy, Klaus

2013-01-01

Macroscopic objects are usually manipulated by force and observed with light. On the nanoscale, however, this is often done oppositely: individual macromolecules are manipulated by light and monitored with force. This procedure, which is the basis of single-molecule force spectroscopy, has led to much of our quantitative understanding of how DNA works, and is now routinely applied to explore molecular structure and interactions, DNA-protein reactions and protein folding. Here we develop the technique further by introducing a dynamic force spectroscopy set-up for a non-invasive inspection of the tension dynamics in a taut strand of DNA. The internal contraction after a sudden release of the molecule is shown to give rise to a drastically enhanced viscous friction, as revealed by the slow relaxation of an attached colloidal tracer. Our systematic theory explains the data quantitatively and provides a powerful tool for the rational design of new dynamic force spectroscopy assays.

Internal friction and velocity measurements. [vacuum effects on lunar basalt resonance

NASA Technical Reports Server (NTRS)

Tittmann, B. R.; Ahlberg, L.; Curnow, J.

1976-01-01

The Q of a lunar basalt sample was measured under varying vacuum conditions, and it was found that even at pressures as low as 10 to the -7th to 10 to the -10th torr, substantial increases in Q with decreasing pressure are observed, while the resonant frequency increases only slightly. This suggests that only small amounts of volatiles are sufficient to increase the internal friction (lower the Q) dramatically. The technique of vibrating encapsulated samples in the torsional mode was used to measure Q of terrestrial rocks as a function of hydrostatic pressure under lunar vacuum conditions. Young's modulus measurements in the temperature range 25-600 C under a variety of conditions including high vacuum show no evidence of any irreversibility upon temperature cycling and no indication that the high Q-values obtained are associated with any permanent structure changes such as the formation of lossless 'welded' contacts.

Some exact velocity profiles for granular flow in converging hoppers

NASA Astrophysics Data System (ADS)

Cox, Grant M.; Hill, James M.

2005-01-01

Gravity flow of granular materials through hoppers occurs in many industrial processes. For an ideal cohesionless granular material, which satisfies the Coulomb-Mohr yield condition, the number of known analytical solutions is limited. However, for the special case of the angle of internal friction δ equal to ninety degrees, there exist exact parametric solutions for the governing coupled ordinary differential equations for both two-dimensional wedges and three-dimensional cones, both of which involve two arbitrary constants of integration. These solutions are the only known analytical solutions of this generality. Here, we utilize the double-shearing theory of granular materials to determine the velocity field corresponding to these exact parametric solutions for the two problems of gravity flow through converging wedge and conical hoppers. An independent numerical solution for other angles of internal friction is shown to coincide with the analytical solution.

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

NASA Astrophysics Data System (ADS)

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

2010-05-01

Propagation and radiation of an earthquake rupture is commonly considered as a friction dominated process on fault surfaces. Friction laws, such as the slip weakening and the rate-and-state laws are widely used in the modeling of the earthquake rupture process. These laws prescribe the traction evolution versus slip, slip rate and potentially other internal variables. They introduce a finite cohesive length scale over which the fracture energy is released. However faults are finite-width interfaces with complex internal structures, characterized by highly damaged zones embedding a very thin principal slip interface where most of the dynamic slip localizes. Even though the rupture process is generally investigated at wavelengths larger than the fault zone thickness, which should justify a formulation based upon surface energy, a consistent homogeneization, a very challenging problem, is still missing. Such homogeneization is however be required to derive the consistent form of an effective interface law, as well as the appropriate physical variables and length scales, to correctly describe the coarse-grained dissipation resulting from surface and volumetric contributions at the scale of the fault zone. In this study, we investigate a scale-dependent law, introduced by Raous et al. (1999) in the context of adhesive material interfaces, that takes into account the transition between a damage dominated and a friction dominated state. Such a phase-field formalism describes this transition through an order parameter. We first compare this law to standard slip weakening friction law in terms of the rupture nucleation. The problem is analyzed through the representation of the solution of the quasi-static elastic problem onto the Chebyshev polynomial basis, generalizing the Uenishi-Rice solution. The nucleation solutions, at the onset of instability, are then introduced as initial conditions for the study of the dynamic rupture propagation, in the case of in-plane rupture, using high-order Spectral Element Methods and non-smooth contact mechanics. In particular, we investigate the implications of this new interface law in terms of the rupture propagation and arrest. Special attention is focused on radiation and supershear transition. Comparison with the classical slip weakening friction law is provided. Finally, first results toward a dynamic consistent homogeneization of damaged fault zones will be discussed. Raous, M., Cangémi, L. and Cocou, M. (1999). A consistent model coupling adhesion, friction and unilateral contact', Computer Methods in Applied Mechanics and Engineering, Vol. 177, pp.383-399.

Fast antibody fragment motion: flexible linkers act as entropic spring

PubMed Central

Stingaciu, Laura R.; Ivanova, Oxana; Ohl, Michael; Biehl, Ralf; Richter, Dieter

2016-01-01

A flexible linker region between three fragments allows antibodies to adjust their binding sites to an antigen or receptor. Using Neutron Spin Echo Spectroscopy we observed fragment motion on a timescale of 7 ns with motional amplitudes of about 1 nm relative to each other. The mechanistic complexity of the linker region can be described by a spring model with Brownian motion of the fragments in a harmonic potential. Displacements, timescale, friction and force constant of the underlying dynamics are accessed. The force constant exhibits a similar strength to an entropic spring, with friction of the fragment matching the unbound state. The observed fast motions are fluctuations in pre-existing equilibrium configurations. The Brownian motion of domains in a harmonic potential is the appropriate model to examine functional hinge motions dependent on the structural topology and highlights the role of internal forces and friction to function. PMID:27020739

Analyzing Axial Stress and Deformation of Tubular for Steam Injection Process in Deviated Wells Based on the Varied (T, P) Fields

PubMed Central

Liu, Yunqiang; Xu, Jiuping; Wang, Shize; Qi, Bin

2013-01-01

The axial stress and deformation of high temperature high pressure deviated gas wells are studied. A new model is multiple nonlinear equation systems by comprehensive consideration of axial load of tubular string, internal and external fluid pressure, normal pressure between the tubular and well wall, and friction and viscous friction of fluid flowing. The varied temperature and pressure fields were researched by the coupled differential equations concerning mass, momentum, and energy equations instead of traditional methods. The axial load, the normal pressure, the friction, and four deformation lengths of tubular string are got ten by means of the dimensionless iterative interpolation algorithm. The basic data of the X Well, 1300 meters deep, are used for case history calculations. The results and some useful conclusions can provide technical reliability in the process of designing well testing in oil or gas wells. PMID:24163623

Fast antibody fragment motion: flexible linkers act as entropic spring

DOE PAGES

Stingaciu, Laura R.; Ivanova, Oxana; Ohl, Michael; ...

2016-03-29

A flexible linker region between three fragments allows antibodies to adjust their binding sites to an antigen or receptor. Using Neutron Spin Echo Spectroscopy we observed fragment motion on a timescale of 7 ns with motional amplitudes of about 1 nm relative to each other. The mechanistic complexity of the linker region can be described by a spring model with Brownian motion of the fragments in a harmonic potential. Displacements, timescale, friction and force constant of the underlying dynamics are accessed. The force constant exhibits a similar strength to an entropic spring, with friction of the fragment matching the unboundmore » state. The observed fast motions are fluctuations in pre-existing equilibrium configurations. In conclusion, the Brownian motion of domains in a harmonic potential is the appropriate model to examine functional hinge motions dependent on the structural topology and highlights the role of internal forces and friction to function.« less

Fast antibody fragment motion: flexible linkers act as entropic spring.

PubMed

Stingaciu, Laura R; Ivanova, Oxana; Ohl, Michael; Biehl, Ralf; Richter, Dieter

2016-03-29

A flexible linker region between three fragments allows antibodies to adjust their binding sites to an antigen or receptor. Using Neutron Spin Echo Spectroscopy we observed fragment motion on a timescale of 7 ns with motional amplitudes of about 1 nm relative to each other. The mechanistic complexity of the linker region can be described by a spring model with Brownian motion of the fragments in a harmonic potential. Displacements, timescale, friction and force constant of the underlying dynamics are accessed. The force constant exhibits a similar strength to an entropic spring, with friction of the fragment matching the unbound state. The observed fast motions are fluctuations in pre-existing equilibrium configurations. The Brownian motion of domains in a harmonic potential is the appropriate model to examine functional hinge motions dependent on the structural topology and highlights the role of internal forces and friction to function.

Mechanical and Structural Behavior of Granular Material Packed Beds for Space Life Support System Applications

NASA Technical Reports Server (NTRS)

Malla, Ramesh B.; Anandakumar, Ganesh

2005-01-01

Long-term human mission to space, such as living in International Space Station (ISS), Lunar, and Martian bases, and travel to Mars, must m ake use of Advanced Life Support Systems (ALSS) to generate and recycle critical life supporting elements like oxygen and water. Oxygen Gen eration Assembly (OGA) and Water Processor Assembly (WPA), critical c omponents of ALSS, make use of series of granular material packed beds for generation and recycling of oxygen and water. Several granular m aterials can be used for generation, recycling, processing and recovery of oxygen and water. For example, they may include soft bed media, e.g. ion exchange resins for oxygen generation assembly and hard bed media such as, activated alumina, magchem (Magnesium oxide) and activa ted carbon to remove organic species like ethanol, methanol, and urea from wastewater in Water recovery/processing assembly. These beds are generally packed using a plate-spring mechanism to provide sufficien t compaction to the bed media throughout the course of operation. This paper presents results from an experimental study of a full-scale, 3 8.1 cm (15 inches) long and 3.7 cm (1.44 inches) diameter. activated alumina bed enclosed in a cylinder determining its force-displacement behavior, friction mobilizing force, and axial normal stress distribu tion under various axially applied loads and at different levels of packing. It is observed that force-displacement behavior is non-linear for low compaction level and becomes linear with increase in compaction of the bed media. Axial normal stress distribution along the length of the bed media decreased non-linearly with increase in depth from the loading end of the granular media. This paper also presents experimental results on the amount of particulates generated corresponding to various compaction levels. Particulates generated from each of the tests were measured using standard US sieves. It was found that the p articulates and the overall displacement of the bed media increased with decrease in initial compaction of the bed media. This effect could be attributed to the greater tendency for inter-particle sliding/rub bing due to smaller internal friction angles, as seen from the shear tests, at lesser initial compacted levels. Upon unloading, it was obse rved that there was no change in displacement (especially rebounding) in the bed media. This effect could be attributed to the fact that th e porous activated alumina particles fracture/break upon increase in applied load (during loading phase) and occupy void spaces in between the material grains; thereby leading to settling of the media. The lo ad-displacement curve becomes more linear with increase in initial compaction of the bed media. It is concluded that compaction considerabl y affects the load-displacement behavior of the bed media. A series of tests were also conducted on the packed bed media to determine the f orce required to mobilize the friction between the bed media and the housing cylinder. The results from these tests showed the existence of significant friction between the bed media and the encasing stainles s steel cylinder. Further, it was found that friction effects were more pronounced for media with higher initial compaction. Internal frict ion of the granular media was measured using direct shear apparatus. It was observed that the internal friction increased with increase in initial compaction of the bed media. In this study, a computational m odel (CM) is also developed using finite element software ANSYS to verify experimental results obtained for the distribution of the axial n ormal stress and axial displacement along the length of the full-scal e activated alumina bed media. In the computational model, the granular material is considered to have appropriate failure and frictional c ontact exists between the wall and the granular media. It is observed that the model predicts results closely with the experimental method. The compational results show that the axial normal stress distribution along the length of the activated alumina media decreases non-linea rly from the loading end and is negligible beyond a certain depth. Th is can be attributed to the existence of friction between the walls and the media and that the friction takes up most of the applied load.

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

Rossi, Mariana; Manolopoulos, David E.; Ceriotti, Michele

Two of the most successful methods that are presently available for simulating the quantum dynamics of condensed phase systems are centroid molecular dynamics (CMD) and ring polymer molecular dynamics (RPMD). Despite their conceptual differences, practical implementations of these methods differ in just two respects: the choice of the Parrinello-Rahman mass matrix and whether or not a thermostat is applied to the internal modes of the ring polymer during the dynamics. Here, we explore a method which is halfway between the two approximations: we keep the path integral bead masses equal to the physical particle masses but attach a Langevin thermostatmore » to the internal modes of the ring polymer during the dynamics. We justify this by showing analytically that the inclusion of an internal mode thermostat does not affect any of the established features of RPMD: thermostatted RPMD is equally valid with respect to everything that has actually been proven about the method as RPMD itself. In particular, because of the choice of bead masses, the resulting method is still optimum in the short-time limit, and the transition state approximation to its reaction rate theory remains closely related to the semiclassical instanton approximation in the deep quantum tunneling regime. In effect, there is a continuous family of methods with these properties, parameterised by the strength of the Langevin friction. Here, we explore numerically how the approximation to quantum dynamics depends on this friction, with a particular emphasis on vibrational spectroscopy. We find that a broad range of frictions approaching optimal damping give similar results, and that these results are immune to both the resonance problem of RPMD and the curvature problem of CMD.« less

Computational upscaling of Drucker-Prager plasticity from micro-CT images of synthetic porous rock

NASA Astrophysics Data System (ADS)

Liu, Jie; Sarout, Joel; Zhang, Minchao; Dautriat, Jeremie; Veveakis, Emmanouil; Regenauer-Lieb, Klaus

2018-01-01

Quantifying rock physical properties is essential for the mining and petroleum industry. Microtomography provides a new way to quantify the relationship between the microstructure and the mechanical and transport properties of a rock. Studies reporting the use microtomographic images to derive permeability and elastic moduli of rocks are common; only rare studies were devoted to yield and failure parameters using this technique. In this study, we simulate the macroscale plastic properties of a synthetic sandstone sample made of calcite-cemented quartz grains using the microscale information obtained from microtomography. The computations rely on the concept of representative volume elements (RVEs). The mechanical RVE is determined using the upper and lower bounds of finite-element computations for elasticity. We present computational upscaling methods from microphysical processes to extract the plasticity parameters of the RVE and compare results to experimental data. The yield stress, cohesion and internal friction angle of the matrix (solid part) of the rock were obtained with reasonable accuracy. Computations of plasticity of a series of models of different volume-sizes showed almost overlapping stress-strain curves, suggesting that the mechanical RVE determined by elastic computations is also valid for plastic yielding. Furthermore, a series of models were created by self-similarly inflating/deflating the porous models, that is keeping a similar structure while achieving different porosity values. The analysis of these models showed that yield stress, cohesion and internal friction angle linearly decrease with increasing porosity in the porosity range between 8 and 28 per cent. The internal friction angle decreases the most significantly, while cohesion remains stable.

How Well Does a Funneled Energy Landscape Capture the Folding Mechanism of Spectrin Domains?

PubMed Central

2013-01-01

Three structurally similar domains from α-spectrin have been shown to fold very differently. Firstly, there is a contrast in the folding mechanism, as probed by Φ-value analysis, between the R15 domain and the R16 and R17 domains. Secondly, there are very different contributions from internal friction to folding: the folding rate of the R15 domain was found to be inversely proportional to solvent viscosity, showing no apparent frictional contribution from the protein, but in the other two domains a large internal friction component was evident. Non-native misdocking of helices has been suggested to be responsible for this phenomenon. Here, I study the folding of these three proteins with minimalist coarse-grained models based on a funneled energy landscape. Remarkably, I find that, despite the absence of non-native interactions, the differences in folding mechanism of the domains are well captured by the model, and the agreement of the Φ-values with experiment is fairly good. On the other hand, within the context of this model, there are no significant differences in diffusion coefficient along the chosen folding coordinate, and the model cannot explain the large differences in folding rates between the proteins found experimentally. These results are nonetheless consistent with the expectations from the energy landscape perspective of protein folding: namely, that the folding mechanism is primarily determined by the native-like interactions present in the Gō-like model, with missing non-native interactions being required to explain the differences in “internal friction” seen in experiment. PMID:23947368

Elasto-plastic properties of Cu-Nb nanolaminate

NASA Astrophysics Data System (ADS)

Betekhtin, V. I.; Kolobov, Yu. R.; Kardashev, B. K.; Golosov, E. V.; Narykova, M. V.; Kadomtsev, A. G.; Klimenko, D. N.; Karpov, M. I.

2012-02-01

The Young's modulus, internal friction, and microplastic flow stress in Cu-Nb nanolaminate has been determined by an acoustic technique. The influence of high hydrostatic compression (1 GPa) on these elasto-plastic properties of the nanolaminate has been studied.

Predicting boundary shear stress and sediment transport over bed forms

USGS Publications Warehouse

McLean, S.R.; Wolfe, S.R.; Nelson, J.M.

1999-01-01

To estimate bed-load sediment transport rates in flows over bed forms such as ripples and dunes, spatially averaged velocity profiles are frequently used to predict mean boundary shear stress. However, such averaging obscures the complex, nonlinear interaction of wake decay, boundary-layer development, and topographically induced acceleration downstream of flow separation and often leads to inaccurate estimates of boundary stress, particularly skin friction, which is critically important in predicting bed-load transport rates. This paper presents an alternative methodology for predicting skin friction over 2D bed forms. The approach is based on combining the equations describing the mechanics of the internal boundary layer with semiempirical structure functions to predict the velocity at the crest of a bedform, where the flow is most similar to a uniform boundary layer. Significantly, the methodology is directed toward making specific predictions only at the bed-form crest, and as a result it avoids the difficulty and questionable validity of spatial averaging. The model provides an accurate estimate of the skin friction at the crest where transport rates are highest. Simple geometric constraints can be used to derive the mean transport rates as long as bed load is dominant.To estimate bed-load sediment transport rates in flows over bed forms such as ripples and dunes, spatially averaged velocity profiles are frequently used to predict mean boundary shear stress. However, such averaging obscures the complex, nonlinear interaction of wake decay, boundary-layer development, and topographically induced acceleration downstream of flow separation and often leads to inaccurate estimates of boundary stress, particularly skin friction, which is critically important in predicting bed-load transport rates. This paper presents an alternative methodology for predicting skin friction over 2D bed forms. The approach is based on combining the equations describing the mechanics of the internal boundary layer with semiempirical structure functions to predict the velocity at the crest of a bedform, where the flow is most similar to a uniform boundary layer. Significantly, the methodology is directed toward making specific predictions only at the bed-form crest, and as a result it avoids the difficulty and questionable validity of spatial averaging. The model provides an accurate estimate of the skin friction at the crest where transport rates are highest. Simple geometric constraints can be used to derive the mean transport rates as long as bed load is dominant.

Estimation of a Stopping Criterion for Geophysical Granular Flows Based on Numerical Experimentation

NASA Astrophysics Data System (ADS)

Yu, B.; Dalbey, K.; Bursik, M.; Patra, A.; Pitman, E. B.

2004-12-01

Inundation area may be the most important factor for mitigation of natural hazards related to avalanches, debris flows, landslides and pyroclastic flows. Run-out distance is the key parameter for inundation because the front deposits define the leading edge of inundation. To define the run-out distance, it is necessary to know when a flow stops. Numerical experiments are presented for determining a stopping criterion and exploring the suitability of a Savage-Hutter granular model for computing inundation areas of granular flows. The TITAN2D model was employed to run numerical experiments based on the Savage-Hutter theory. A potentially reasonable stopping criterion was found as a function of dimensionless average velocity, aspect ratio of pile, internal friction angle, bed friction angle and bed slope in the flow direction. Slumping piles on a horizontal surface and geophysical flows over complex topography were simulated. Several mountainous areas, including Colima volcano (MX), Casita (Nic.), Little Tahoma Peak (WA, USA) and the San Bernardino Mountains (CA, USA) were used to simulate geophysical flows. Volcanic block and ash flows, debris avalanches and debris flows occurred in these areas and caused varying degrees of damage. The areas have complex topography, including locally steep open slopes, sinuous channels, and combinations of these. With different topography and physical scaling, slumping piles and geophysical flows have a somewhat different dependence of dimensionless stopping velocity on power-law constants associated with aspect ratio of pile, internal friction angle, bed friction angle and bed slope in the flow direction. Visual comparison of the details of the inundation area obtained from the TITAN2D model with models that contain some form of viscous dissipation point out weaknesses in the model that are not evident by investigation of the stopping criterion alone.

Skin friction measurement in complex flows using thin oil film techniques

NASA Technical Reports Server (NTRS)

1994-01-01

The NASA Grant NAG2-261 was initiated to support a program of research to study complex flows that occur in flight and laboratory experiments by building, testing and optimizing an on-board technique for direct measurement of surface shear stress using thin oil film techniques. The program of research has proceeded under the supervision of the NASA Ames Research Center and with further cooperation from the NASA Ames-Dryden and NASA Langley Research Centers. In accordance with the original statement of work, the following research milestones were accomplished: (1) design and testing of an internally mounted one-directional skin friction meter to demonstrate the feasibility of the concept; (2) design and construction of a compact instrument capable of measuring skin friction in two directions; (3) study of transitional and fully turbulent boundary layers over a flat plate with and without longitudinal pressure gradients utilizing the compact two-directional skin friction meter; (4) study of the interaction between a turbulent boundary layer and a shock wave generated by a compression corner using the two-directional meter; and (5) flight qualification of the compact meter and accompanying electronic and pneumatic systems, preliminary installation into flight test fixture.

Glass Microbeads in Analog Models of Thrust Wedges.

PubMed

D'Angelo, Taynara; Gomes, Caroline J S

2017-01-01

Glass microbeads are frequently used in analog physical modeling to simulate weak detachment zones but have been neglected in models of thrust wedges. Microbeads differ from quartz sand in grain shape and in low angle of internal friction. In this study, we compared the structural characteristics of microbeads and sand wedges. To obtain a better picture of their mechanical behavior, we determined the physical and frictional properties of microbeads using polarizing and scanning electron microscopy and ring-shear tests, respectively. We built shortening experiments with different basal frictions and measured the thickness, slope and length of the wedges and also the fault spacings. All the microbeads experiments revealed wedge geometries that were consistent with previous studies that have been performed with sand. However, the deformation features in the microbeads shortened over low to intermediate basal frictions were slightly different. Microbeads produced different fault geometries than sand as well as a different grain flow. In addition, they produced slip on minor faults, which was associated with distributed deformation and gave the microbeads wedges the appearance of disharmonic folds. We concluded that the glass microbeads may be used to simulate relatively competent rocks, like carbonates, which may be characterized by small-scale deformation features.

Graphene Coating via Chemical Vapor Deposition for Improving Friction and Wear of Gray Cast Iron at Interfaces.

PubMed

Tripathi, Khagendra; Gyawali, Gobinda; Lee, Soo Wohn

2017-09-20

This study reports the influence of CVD-graphene on the tribological performance of gray cast iron (GCI) from the internal combustion engine (ICE) cylinder liners by performing a ball-on-disk friction tests. The graphene-coated specimen exhibited a significant reduction (∼53%) of friction as compared to that of the uncoated specimen, whereas wear resistance increased by 2- and 5-fold regarding the wear of specimen and ball, respectively. Extremely low shear strength and highly lubricating nature of graphene contribute to the formation of a lubricative film between the sliding surfaces and decreases the interaction between surfaces in the dry environment. Under the applied load, a uniform film of iron oxides such as Fe 2 O 3 , Fe 3 O 4 , and FeOOH is found to be formed between the surfaces. It is proposed that the graphene encapsulation with the metal debris and oxides formed between the specimens increases the lubricity and decreases the shear force. The transformation of graphene/graphite into nanocrystalline graphites across the contact interfaces following the amorphization trajectory further increases the lubricity of the film that ultimately reduces friction and wear of the material.

46 CFR 160.077-15 - Construction and Performance-Recreational Hybrid PFD.

Code of Federal Regulations, 2012 CFR

2012-10-01

... internal, that are sufficiently sharp to damage the PFD or cause injury to anyone using or maintaining the... of locking in the open or closed position except that, a friction-fit dust cap that only locks in the...

Elasticity and inelasticity of silicon nitride/boron nitride fibrous monoliths.

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

Smirnov, B. I.; Burenkov, Yu. A.; Kardashev, B. K.

A study is reported on the effect of temperature and elastic vibration amplitude on Young's modulus E and internal friction in Si{sub 3}N{sub 4} and BN ceramic samples and Si{sub 3}N{sub 4}/BN monoliths obtained by hot pressing of BN-coated Si{sub 3}N{sub 4} fibers. The fibers were arranged along, across, or both along and across the specimen axis. The E measurements were carried out under thermal cycling within the 20-600 C range. It was found that high-modulus silicon-nitride specimens possess a high thermal stability; the E(T) dependences obtained under heating and cooling coincide well with one another. The low-modulus BN ceramicmore » exhibits a considerable hysteresis, thus indicating evolution of the defect structure under the action of thermoelastic (internal) stresses. Monoliths demonstrate a qualitatively similar behavior (with hysteresis). This behavior of the elastic modulus is possible under microplastic deformation initiated by internal stresses. The presence of microplastic shear in all the materials studied is supported by the character of the amplitude dependences of internal friction and the Young's modulus. The experimental data obtained are discussed in terms of a model in which the temperature dependences of the elastic modulus and their features are accounted for by both microplastic deformation and nonlinear lattice-atom vibrations, which depend on internal stresses.« less

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

Sánchez-Salcedo, F. J.; Chametla, Raul O., E-mail: jsanchez@astro.unam.mx

Using time-dependent linear theory, we investigate the morphology of the gravitational wake induced by a binary, whose center of mass moves at velocity V{sub cm} against a uniform background of gas. For simplicity, we assume that the components of the binary are on circular orbits about their common center of mass. The consequences of dynamical friction is twofold. First, gas dynamical friction may drag the center of mass of the binary and cause the binary to migrate. Second, drag forces also induce a braking torque, which causes the orbits of the components of the binary to shrink. We compute themore » drag forces acting on one component of the binary due to the gravitational interaction with its own wake. We show that the dynamical friction force responsible for decelerating the center of mass of the binary is smaller than it is in the point-mass case because of the loss of gravitational focusing. We show that the braking internal torque depends on the Mach numbers of each binary component about their center of mass, and also on the Mach number of the center of mass of the binary. In general, the internal torque decreases with increasing the velocity of the binary relative to the ambient gas cloud. However, this is not always the case. We also mention the relevance of our results to the period distribution of binaries.« less

Change and anisotropy of elastic modulus in sheet metals due to plastic deformation

NASA Astrophysics Data System (ADS)

Ishitsuka, Yuki; Arikawa, Shuichi; Yoneyama, Satoru

2015-03-01

In this study, the effect of the plastic deformation on the microscopic structure and the anisotropy of the elastic modulus in the cold-rolled steel sheet (SPCC) is investigated. Various uniaxial plastic strains (0%, 2.5%, 5%, 7.5%, and 10%) are applied to the annealed SPCC plates, then, the specimens for the tensile tests are cut out from them. The elastic moduli in the longitudinal direction and the transverse direction to the direction that are pre-strained are measured by the tensile tests. Cyclic tests are performed to investigate the effects of the internal friction caused by the movable dislocations in the elastic deformation. Also, the movable dislocations are quantified by the boundary tracking for TEM micrographs. In addition, the behaviors of the change of the elastic modulus in the solutionized and thermal aged aluminum alloy (A5052) are measured to investigate the effect on the movable dislocations with the amount of the depositions. As a result in SPCC, the elastic moduli of the 0° and 90° directions decrease more than 10% as 10% prestrain applied. On the other hand, the elastic modulus shows the recovery behavior after the strain aging and the annealing. The movable dislocation and the internal friction show a tendency to increase as the plastic strain increases. The marked anisotropy is not observed in the elastic modulus and the internal friction. The elastic modulus in A5052 with many and few depositions decreases similarly by the plastic deformation. From the above, the movable dislocations affect the elastic modulus strongly without depending on the deposition amount. Moreover, the elastic modulus recovers after the plastic deformation by reducing the effects of them with the strain aging and the heat treatment.

The evolving energy budget of accretionary wedges

NASA Astrophysics Data System (ADS)

McBeck, Jessica; Cooke, Michele; Maillot, Bertrand; Souloumiac, Pauline

2017-04-01

The energy budget of evolving accretionary systems reveals how deformational processes partition energy as faults slip, topography uplifts, and layer-parallel shortening produces distributed off-fault deformation. The energy budget provides a quantitative framework for evaluating the energetic contribution or consumption of diverse deformation mechanisms. We investigate energy partitioning in evolving accretionary prisms by synthesizing data from physical sand accretion experiments and numerical accretion simulations. We incorporate incremental strain fields and cumulative force measurements from two suites of experiments to design numerical simulations that represent accretionary wedges with stronger and weaker detachment faults. One suite of the physical experiments includes a basal glass bead layer and the other does not. Two physical experiments within each suite implement different boundary conditions (stable base versus moving base configuration). Synthesizing observations from the differing base configurations reduces the influence of sidewall friction because the force vector produced by sidewall friction points in opposite directions depending on whether the base is fixed or moving. With the numerical simulations, we calculate the energy budget at two stages of accretion: at the maximum force preceding the development of the first thrust pair, and at the minimum force following the development of the pair. To identify the appropriate combination of material and fault properties to apply in the simulations, we systematically vary the Young's modulus and the fault static and dynamic friction coefficients in numerical accretion simulations, and identify the set of parameters that minimizes the misfit between the normal force measured on the physical backwall and the numerically simulated force. Following this derivation of the appropriate material and fault properties, we calculate the components of the work budget in the numerical simulations and in the simulated increments of the physical experiments. The work budget components of the physical experiments are determined from backwall force measurements and incremental velocity fields calculated via digital image correlation. Comparison of the energy budget preceding and following the development of the first thrust pair quantifies the tradeoff of work done in distributed deformation and work expended in frictional slip due to the development of the first backthrust and forethrust. In both the numerical and physical experiments, after the pair develops internal work decreases at the expense of frictional work, which increases. Despite the increase in frictional work, the total external work of the system decreases, revealing that accretion faulting leads to gains in efficiency. Comparison of the energy budget of the accretion experiments and simulations with the strong and weak detachments indicate that when the detachment is strong, the total energy consumed in frictional sliding and internal deformation is larger than when the detachment is relatively weak.

Temperature-Dependent Effect of Boric Acid Additive on Surface Roughness and Wear Rate

NASA Astrophysics Data System (ADS)

Ekinci, Şerafettin

Wear and friction hold an important place in engineering. Currently, scientific societies are struggling to control wear by means of studies on lubricants. Boric acid constitutes an important alternative with its good tribological properties similar to MO2S and graphite alongside with low environmental impacts. Boric acid can be used as a solid lubricant itself whereas it can be added or blended into mineral oils in order to yield better mechanical and tribological properties such as low shear stress due to the lamellar structure and low friction, wear and surface roughness rates. In this study, distinguishing from the literature, boric acid addition effect considering the temperature was investigated for the conventional ranges of internal combustion engines. Surface roughness, wear and friction coefficient values were used in order to determine tribological properties of boric acid as an environmentally friendly additive and mineral oil mixture in the present study. Wear experiments were conducted with a ball on disc experimental setup immersed in an oil reservoir at room temperature, 50∘C and 80∘C. The evolution of both the friction coefficient and wear behavior was determined under 10N load, at 2m/s sliding velocity and a total sliding distance of 9000m. Surface roughness was determined using atomic-force microscopy (AFM). Wear rate was calculated utilizing scanning electron microscope (SEM) visuals and data. The test results showed that wear resistance increased as the temperature increased, and friction coefficient decreased due to the presence of boric acid additive.

Landward vergence in accretionary prism, evidence for frontal propagation of earthquakes?

NASA Astrophysics Data System (ADS)

cubas, Nadaya; Souloumiac, Pauline

2016-04-01

Landward vergence in accretionary wedges is rare and have been described at very few places: along the Cascadia subduction zone and more recently along Sumatra where the 2004 Mw 9.1 Sumatra-Andaman event and the 2011 tsunami earthquake occurred. Recent studies have suggested a relation between landward thrust faults and frontal propagation of earthquakes for the Sumatra subduction zone. The Cascadia subduction zone is also known to have produced in 1700 a Mw9 earthquake with a large tsunami across the Pacific. Based on mechanical analysis, we propose to investigate if specific frictional properties could lead to a landward sequence of thrusting. We show that landward thrust requires very low effective friction along the megathrust with a rather high internal effective friction. We also show that landward thrust appears close to the extensional critical limit. Along Cascadia and Sumatra, we show that to get landward vergence, the effective basal friction has to be lower than 0.08. This very low effective friction is most likely due to high pore pressure. This high pore pressure could either be a long-term property or due to dynamic effects such as thermal pressurization. The fact that landward vergence appears far from the compressional critical limit favors a dynamic effect. Landward vergence would then highlight thermal pressurization due to occasional or systematic propagation of earthquakes to the trench. As a consequence, the vergence of thrusts in accretionary prism could be used to improve seismic and tsunamigenic risk assessment.

Study on turbulent flow and heat transfer performance of tubes with internal fins in EGR cooler

NASA Astrophysics Data System (ADS)

Liu, Lin; Ling, Xiang; Peng, Hao

2015-07-01

In this paper, flow and heat transfer performances of the tubes with internal longitudinal fins in Exhaust Gas Recirculation (EGR ) cooler were investigated by three-dimension computation and experiment . Each test tube was a single-pipe structure, without inner tube. Three-dimension computation was performed to determine the thermal characteristics difference between the two kinds of tubes, that is, the tube with an inner solid staff as a blocked structure and the tube without the blocked structure. The effects of fin width and fin height on heat transfer and flow are examined. For proving the validity of numerical method, the calculated results were compared with corresponding experimental data. The tube-side friction factor and heat transfer coefficient were examined. As a result, the maximum deviations between the numerical results and the experimental data are approximately 5.4 % for friction factor and 8.6 % for heat transfer coefficient, respectively. It is found that two types of internally finned tubes enhance significantly heat transfer. The heat transfer of the tube with blocked structure is better, while the pressure drop of the tube without blocked structure is lower. The comprehensive performance of the unblocked tube is better to applied in EGR cooler.

HEAT INPUT AND POST WELD HEAT TREATMENT EFFECTS ON REDUCED-ACTIVATION FERRITIC/MARTENSITIC STEEL FRICTION STIR WELDS

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

Tang, Wei; Chen, Gaoqiang; Chen, Jian

Reduced-activation ferritic/martensitic (RAFM) steels are an important class of structural materials for fusion reactor internals developed in recent years because of their improved irradiation resistance. However, they can suffer from welding induced property degradations. In this paper, a solid phase joining technology friction stir welding (FSW) was adopted to join a RAFM steel Eurofer 97 and different FSW parameters/heat input were chosen to produce welds. FSW response parameters, joint microstructures and microhardness were investigated to reveal relationships among welding heat input, weld structure characterization and mechanical properties. In general, FSW heat input results in high hardness inside the stir zonemore » mostly due to a martensitic transformation. It is possible to produce friction stir welds similar to but not with exactly the same base metal hardness when using low power input because of other hardening mechanisms. Further, post weld heat treatment (PWHT) is a very effective way to reduce FSW stir zone hardness values.« less

The Use of Empirical Methods for Testing Granular Materials in Analogue Modelling

PubMed Central

Montanari, Domenico; Agostini, Andrea; Bonini, Marco; Corti, Giacomo; Del Ventisette, Chiara

2017-01-01

The behaviour of a granular material is mainly dependent on its frictional properties, angle of internal friction, and cohesion, which, together with material density, are the key factors to be considered during the scaling procedure of analogue models. The frictional properties of a granular material are usually investigated by means of technical instruments such as a Hubbert-type apparatus and ring shear testers, which allow for investigating the response of the tested material to a wide range of applied stresses. Here we explore the possibility to determine material properties by means of different empirical methods applied to mixtures of quartz and K-feldspar sand. Empirical methods exhibit the great advantage of measuring the properties of a certain analogue material under the experimental conditions, which are strongly sensitive to the handling techniques. Finally, the results obtained from the empirical methods have been compared with ring shear tests carried out on the same materials, which show a satisfactory agreement with those determined empirically. PMID:28772993

Development of a new instrument for direct skin friction measurements

NASA Technical Reports Server (NTRS)

Vakili, A. D.; Wu, J. M.

1986-01-01

A device developed for the direct measurement of wall shear stress generated by flows is described. Simple and symmetric in design with optional small moving mass and no internal friction, the features employed in the design eliminate most of the difficulties associated with the traditional floating element balances. The device is basically small and can be made in various sizes. Vibration problems associated with the floating element skin friction balances were found to be minimized due to the design symmetry and optional damping provided. The design eliminates or reduces the errors associated with conventional floating element devices: such as errors due to gaps, pressure gradient, acceleration, heat transfer, and temperature change. The instrument is equipped with various sensing systems and the output signal is a linear function of the wall shear stress. Dynamic measurements could be made in a limited range and measurements in liquids could be performed readily. Measurement made in the three different tunnels show excellent agreement with data obtained by the floating element devices and other techniques.

A new skin friction balance and selected measurements

NASA Technical Reports Server (NTRS)

Vakili, A. D.

1992-01-01

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

Lubricant Formulations to Enhance Engine Efficiency in Modern Internal Combustion Engines

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

Cheng, Wai; Wong, Victor; Plumley, Michael

2017-04-19

The research program presented aimed to investigate, develop, and demonstrate low-friction, environmentally-friendly and commercially-feasible lubricant formulations that would significantly improve the mechanical efficiency of modern engines without incurring increased wear, emissions or deterioration of the emission-aftertreatment system.

The Perls Perversion

ERIC Educational Resources Information Center

Morris, Kenneth T.

1975-01-01

Author describes the Perls perversion, the ego-centered attitude that people should live up to one's expectations and satisfy one's whims, which causes interpersonal friction. RET helps people counteract this perversion by sensitizing them to their internalized irrational belief system, disputing it, and trying to behave rationally. Commentary by…

The Microstructural Basis of Damping in High Damping Alloys

DTIC Science & Technology

1989-09-01

This transformation is diffusionless and is characterized by the cooperative movement of atoms in a given section of crystal. Removal of the stress...martensites. The cooperative movement of atoms causes large internal friction and high damping. The temperature range in which this transformation can

Friction Stir Welding and Processing

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

Hovanski, Yuri; Carsley, John; Clarke, Kester D.

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, whichmore » 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.« less

Performance of discrete heat engines and heat pumps in finite time

PubMed

Feldmann; Kosloff

2000-05-01

The performance in finite time of a discrete heat engine with internal friction is analyzed. The working fluid of the engine is composed of an ensemble of noninteracting two level systems. External work is applied by changing the external field and thus the internal energy levels. The friction induces a minimal cycle time. The power output of the engine is optimized with respect to time allocation between the contact time with the hot and cold baths as well as the adiabats. The engine's performance is also optimized with respect to the external fields. By reversing the cycle of operation a heat pump is constructed. The performance of the engine as a heat pump is also optimized. By varying the time allocation between the adiabats and the contact time with the reservoir a universal behavior can be identified. The optimal performance of the engine when the cold bath is approaching absolute zero is studied. It is found that the optimal cooling rate converges linearly to zero when the temperature approaches absolute zero.

Study of Mechanical Properties and Characterization of Pipe Steel welded by Hybrid (Friction Stir Weld + Root Arc Weld) Approach

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

Lim, Yong Chae; Sanderson, Samuel; Mahoney, Murray

Friction stir welding (FSW) has recently attracted attention as an alternative construction process for gas/oil transportation applications due to advantages compared to fusion welding techniques. A significant advantage is the ability of FSW to weld the entire or nearly the entire wall thickness in a single pass, while fusion welding requires multiple passes. However, when FSW is applied to a pipe or tube geometry, an internal back support anvil is required to resist the plunging forces exerted during FSW. Unfortunately, it may not be convenient or economical to use internal backing support due to limited access for some applications. Tomore » overcome this issue, ExxonMobil recently developed a new concept, combining root arc welding and FSW. That is, a root arc weld is made prior to FSW that supports the normal loads associated with FSW. In the present work, mechanical properties of a FSW + root arc welded pipe steel are reported including microstructure and microhardness.« less

Impulse Excitation Internal Friction Study of Dislocation and Point Defect Interactions in Ultra-Low Carbon Bake-Hardenable Steel

NASA Astrophysics Data System (ADS)

Jung, Il-Chan; Kang, Deok-Gu; De Cooman, Bruno C.

2014-04-01

The simultaneous presence of interstitial solutes and dislocations in an ultra-low carbon bake-hardenable steel gives rise to two characteristic peaks in the internal friction (IF) spectrum: the dislocation-enhanced Snoek peak and the Snoek-Kê-Köster peak. These IF peaks were used to study the dislocation structure developed by the pre-straining and the static strain aging effect of C during the bake-hardening process. A Ti-stabilized interstitial-free steel was used to ascertain the absence of a γ-peak in the IF spectrum of the deformed ultra-low carbon steel. The analysis of the IF data shows clearly that the bake-hardening effect in ultra-low carbon steel is entirely due to atmosphere formation, with the dislocation segment length being the main parameter affecting the IF peak amplitude. Recovery annealing experiments showed that the rearrangement of the dislocation structure lead to the elimination of the C atmosphere.

Fluctuation-induced transport of two coupled particles: effect of the interparticle interaction.

PubMed

Makhnovskii, Yurii A; Rozenbaum, Viktor M; Sheu, Sheh-Yi; Yang, Dah-Yen; Trakhtenberg, Leonid I; Lin, Sheng Hsien

2014-06-07

We consider a system of two coupled particles fluctuating between two states, with different interparticle interaction potentials and particle friction coefficients. An external action drives the interstate transitions that induces reciprocating motion along the internal coordinate x (the interparticle distance). The system moves unidirectionally due to rectification of the internal motion by asymmetric friction fluctuations and thus operates as a dimeric motor that converts input energy into net movement. We focus on how the law of interaction between the particles affects the dimer transport and, in particular, the role of thermal noise in the motion inducing mechanism. It is argued that if the interaction potential behaves at large distances as x(α), depending on the value of the exponent α, the thermal noise plays a constructive (α > 2), neutral (α = 2), or destructive (α < 2) role. In the case of α = 1, corresponding piecewise linear potential profiles, an exact solution is obtained and discussed in detail.

Perturbation solutions for flow through symmetrical hoppers with inserts and asymmetrical wedge hoppers

NASA Astrophysics Data System (ADS)

Cox, G. M.; Mccue, S. W.; Thamwattana, N.; Hill, J. M.

Under certain circumstances, an industrial hopper which operates under the "funnel-flow" regime can be converted to the "mass-flow" regime with the addition of a flow-corrective insert. This paper is concerned with calculating granular flow patterns near the outlet of hoppers that incorporate a particular type of insert, the cone-in-cone insert. The flow is considered to be quasi-static, and governed by the Coulomb-Mohr yield condition together with the non-dilatant double-shearing theory. In two-dimensions, the hoppers are wedge-shaped, and as such the formulation for the wedge-in-wedge hopper also includes the case of asymmetrical hoppers. A perturbation approach, valid for high angles of internal friction, is used for both two-dimensional and axially symmetric flows, with analytic results possible for both leading order and correction terms. This perturbation scheme is compared with numerical solutions to the governing equations, and is shown to work very well for angles of internal friction in excess of 45°.

An analytical model of capped turbulent oscillatory bottom boundary layers

NASA Astrophysics Data System (ADS)

Shimizu, Kenji

2010-03-01

An analytical model of capped turbulent oscillatory bottom boundary layers (BBLs) is proposed using eddy viscosity of a quadratic form. The common definition of friction velocity based on maximum bottom shear stress is found unsatisfactory for BBLs under rotating flows, and a possible extension based on turbulent kinetic energy balance is proposed. The model solutions show that the flow may slip at the top of the boundary layer due to capping by the water surface or stratification, reducing the bottom shear stress, and that the Earth's rotation induces current and bottom shear stress components perpendicular to the interior flow with a phase lag (or lead). Comparisons with field and numerical experiments indicate that the model predicts the essential characteristics of the velocity profiles, although the agreement is rather qualitative due to assumptions of quadratic eddy viscosity with time-independent friction velocity and a well-mixed boundary layer. On the other hand, the predicted linear friction coefficients, phase lead, and veering angle at the bottom agreed with available data with an error of 3%-10%, 5°-10°, and 5°-10°, respectively. As an application of the model, the friction coefficients are used to calculate e-folding decay distances of progressive internal waves with a semidiurnal frequency.

Field evaluation of two commonly used slipmeters.

PubMed

Chang, Wen-Ruey; Cotnam, John P; Matz, Simon

2003-01-01

A variety of slipmeters have been used to assess the slipperiness of floor surfaces. International standards for the operation of slipmeters describe the protocol for a single measurement. These standards usually do not cover some of the critical elements in safety assessment such as methods for the selection of measurement locations and the necessary number of repeated measurements at each location. Furthermore, most of the slipmeters were evaluated in laboratory settings with new floor surfaces and artificial contaminants. Two commonly used slipmeters, the Brungraber Mark II and the English XL, were evaluated at actual worksites in this experiment. Four floor tiles in each of four different work areas in the kitchens of 18 fast food restaurants were selected for repeated measurements with these two slipmeters. The results indicated that sanding of footwear materials has a significant effect on the outcomes of friction measurements, and the tile-to-tile variations in friction in the same areas of restaurants were also mostly statistically significant. Significant local variation in friction among tiles in the same area could potentially increase the chances of slip and fall incidents. Both slipmeters used in this experiment could potentially have problems in the areas with grease, such as grill and fryer areas, since the build-up of grease during repeated strikes could alter the outcome of friction measured.

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

NASA Technical Reports Server (NTRS)

Kibbey, Timothy P.

2014-01-01

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

Quantum turbulence in superfluids with wall-clamped normal component.

PubMed

Eltsov, Vladimir; Hänninen, Risto; Krusius, Matti

2014-03-25

In Fermi superfluids, such as superfluid (3)He, the viscous normal component can be considered to be stationary with respect to the container. The normal component interacts with the superfluid component via mutual friction, which damps the motion of quantized vortex lines and eventually couples the superfluid component to the container. With decreasing temperature and mutual friction, the internal dynamics of the superfluid component becomes more important compared with the damping and coupling effects from the normal component. As a result profound changes in superfluid dynamics are observed: the temperature-dependent transition from laminar to turbulent vortex motion and the decoupling from the reference frame of the container at even lower temperatures.

Quantum turbulence in superfluids with wall-clamped normal component

PubMed Central

Eltsov, Vladimir; Hänninen, Risto; Krusius, Matti

2014-01-01

In Fermi superfluids, such as superfluid 3He, the viscous normal component can be considered to be stationary with respect to the container. The normal component interacts with the superfluid component via mutual friction, which damps the motion of quantized vortex lines and eventually couples the superfluid component to the container. With decreasing temperature and mutual friction, the internal dynamics of the superfluid component becomes more important compared with the damping and coupling effects from the normal component. As a result profound changes in superfluid dynamics are observed: the temperature-dependent transition from laminar to turbulent vortex motion and the decoupling from the reference frame of the container at even lower temperatures. PMID:24704879

Methods for determining the internal thrust of scramjet engine modules from experimental data

NASA Technical Reports Server (NTRS)

Voland, Randall T.

1990-01-01

Methods for calculating zero-fuel internal drag of scramjet engine modules from experimental measurements are presented. These methods include two control-volume approaches, and a pressure and skin-friction integration. The three calculation techniques are applied to experimental data taken during tests of a version of the NASA parametric scramjet. The methods agree to within seven percent of the mean value of zero-fuel internal drag even though several simplifying assumptions are made in the analysis. The mean zero-fuel internal drag coefficient for this particular engine is calculated to be 0.150. The zero-fuel internal drag coefficient when combined with the change in engine axial force with and without fuel defines the internal thrust of an engine.

Effects of internal tidal dissipation and self-attraction and loading on semidiurnal tides in the Bohai Sea, Yellow Sea and East China Sea: a numerical study

NASA Astrophysics Data System (ADS)

Teng, Fei; Fang, Guohong; Xu, Xiaoqing

2017-09-01

A parameterized internal tide dissipation term and self-attraction and loading (SAL) tide term are introduced in a barotropic numerical model to investigate the dynamics of semidiurnal tidal constituents M 2 and S 2 in the Bohai Sea, Yellow Sea and East China Sea (BYECS). The optimal parameters for bottom friction and internal dissipation are obtained through a series of numerical computations. Numerical simulation shows that the tide-generating force contributes 1.2% of M 2 power for the entire BYECS and up to 2.8% for the East China Sea deep basin. SAL tide contributes 4.4% of M 2 power for the BYECS and up to 9.3% for the East China Sea deep basin. Bottom friction plays a major role in dissipating tidal energy in the shelf regions, and the internal tide effect is important in the deep water regions. Numerical experiments show that artificial removal of tide-generating force in the BYECS can cause a significant difference (as much as 30 cm) in model output. Artificial removal of SAL tide in the BYECS can cause even greater difference, up to 40 cm. This indicates that SAL tide should be taken into account in numerical simulations, especially if the tide-generating force is considered.

Effects of thermal annealing on the structural, mechanical, and tribological properties of hard fluorinated carbon films deposited by plasma enhanced chemical vapor deposition

NASA Astrophysics Data System (ADS)

Maia da Costa, M. E. H.; Baumvol, I. J. R.; Radke, C.; Jacobsohn, L. G.; Zamora, R. R. M.; Freire, F. L.

2004-11-01

Hard amorphous fluorinated carbon films (a-C:F) deposited by plasma enhanced chemical vapor deposition were annealed in vacuum for 30 min in the temperature range of 200-600 °C. The structural and compositional modifications were followed by several analytical techniques: Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA), x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Nanoidentation measurements and lateral force microscopy experiments were carried out in order to provide the film hardness and the friction coefficient, respectively. The internal stress and contact angle were also measured. RBS, ERDA, and XPS results indicate that both fluorine and hydrogen losses occur for annealing temperatures higher than 300 °C. Raman spectroscopy shows a progressive graphitization upon annealing, while the surface became slightly more hydrophobic as revealed by the increase of the contact angle. Following the surface wettability reduction, a decrease of the friction coefficient was observed. These results highlight the influence of the capillary condensation on the nanoscale friction. The film hardness and the internal stress are constant up to 300 °C and decrease for higher annealing temperatures, showing a direct correlation with the atomic density of the films. Since the thickness variation is negligible, the mass loss upon thermal treatment results in amorphous structures with a lower degree of cross-linking, explaining the deterioration of the mechanical properties of the a-C:F films.

Measurement of earth pressure in the iron-ore mines of eastern France

USGS Publications Warehouse

Tincelin, M.E.

1953-01-01

The values of the tangential stresses along the periphery being known, they will be compared with the values that would be given by the computations based on various hypotheseses, that of elasticity, perfect plasticity, masses with internal friction, irreversibility of stresses, stratified masses, etc. 

The influence of landing mat composition on ankle injury risk during a gymnastic landing: a biomechanical quantification.

PubMed

Xiao, Xiaofei; Hao, Weiya; Li, Xuhong; Wan, Bingjun; Shan, Gongbing

2017-01-01

About 70% injury of gymnasts happened during landing - an interaction between gymnast and landing mat. The most injured joint is the ankle. The current study examined the effect of mechanical properties of landing mat on ankle loading with aims to identify means of decreasing the risk of ankle injury. Gymnastic skill - salto backward stretched with 3/2 twist was captured by two high-speed camcorders and digitized by using SIMI-Motion software. A subject-specific, 14-segment rigid-body model and a mechanical landing-mat model were built using BRG.LifeMODTM. The landings were simulated with varied landing-mat mechanical properties (i.e., stiffness, dampness and friction coefficients). Real landing performance could be accurately reproduced by the model. The simulations revealed that the ankle angle was relatively sensitive to stiffness and dampness of the landing mat, the ankle loading rate increased 26% when the stiffness was increased by 30%, and the changing of dampness had notable effect on horizontal ground reaction force and foot velocity. Further, the peak joint-reaction force and joint torque were more sensitive to friction than to stiffness and dampness of landing mat. Finally, ankle muscles would dissipate about twice energy (189%) when the friction was increased by 30%. Loads to ankles during landing would increase as the stiffness and dampness of the landing mat increase. Yet, increasing friction would cause a substantial rise of the ankle internal loads. As such, the friction should be a key factor influencing the risk of injury. Unfortunately, this key factor has rarely attracted attention in practice.

Sliding friction between polymer surfaces: A molecular interpretation

NASA Astrophysics Data System (ADS)

Allegra, Giuseppe; Raos, Guido

2006-04-01

For two contacting rigid bodies, the friction force F is proportional to the normal load and independent of the macroscopic contact area and relative velocity V (Amonton's law). With two mutually sliding polymer samples, the surface irregularities transmit deformation to the underlying material. Energy loss along the deformation cycles is responsible for the friction force, which now appears to depend strongly on V [see, e.g., N. Maeda et al., Science 297, 379 (2002)]. We base our theoretical interpretation on the assumption that polymer chains are mainly subjected to oscillatory "reptation" along their "tubes." At high deformation frequencies—i.e., with a large sliding velocity V—the internal viscosity due to the rotational energy barriers around chain bonds hinders intramolecular mobility. As a result, energy dissipation and the correlated friction force strongly diminish at large V. Derived from a linear differential equation for chain dynamics, our results are basically consistent with the experimental data by Maeda et al. [Science 297, 379 (2002)] on modified polystyrene. Although the bulk polymer is below Tg, we regard the first few chain layers below the surface to be in the liquid state. In particular, the observed maximum of F vs V is consistent with physically reasonable values of the molecular parameters. As a general result, the ratio F /V is a steadily decreasing function of V, tending to V-2 for large velocities. We evaluate a much smaller friction for a cross-linked polymer under the assumption that the junctions are effectively immobile, also in agreement with the experimental results of Maeda et al. [Science 297, 379 (2002)].

Numerical simulation of the debris flow dynamics with an upwind scheme and specific friction treatment

NASA Astrophysics Data System (ADS)

Sánchez Burillo, Guillermo; Beguería, Santiago; Latorre, Borja; Burguete, Javier

2014-05-01

Debris flows, snow and rock avalanches, mud and earth flows are often modeled by means of a particular realization of the so called shallow water equations (SWE). Indeed, a number of simulation models have been already developed [1], [2], [3], [4], [5], [6], [7]. Debris flow equations differ from shallow water equations in two main aspects. These are (a) strong bed gradient and (b) rheology friction terms that differ from the traditional SWE. A systematic analysis of the numerical solution of the hyperbolic system of equations rising from the shallow water equations with different rheological laws has not been done. Despite great efforts have been done to deal with friction expressions common in hydraulics (such as Manning friction), landslide rheologies are characterized by more complicated expressions that may deal to unphysical solutions if not treated carefully. In this work, a software that solves the time evolution of sliding masses over complex bed configurations is presented. The set of non- linear equations is treated by means of a first order upwind explicit scheme, and the friction contribution to the dynamics is treated with a suited numerical scheme [8]. In addition, the software incorporates various rheological models to accommodate for different flow types, such as the Voellmy frictional model [9] for rock and debris avalanches, or the Herschley-Bulkley model for debris and mud flows. The aim of this contribution is to release this code as a free, open source tool for the simulation of mass movements, and to encourage the scientific community to make use of it. The code uses as input data the friction coefficients and two input files: the topography of the bed and the initial (pre-failure) position of the sliding mass. In addition, another file with the final (post-event) position of the sliding mass, if desired, can be introduced to be compared with the simulation obtained result. If the deposited mass is given, an error estimation is computed by means of the Nash-Shutcliffe statistic [10]. This error estimation can be used to calibrate the input friction coefficients, providing an efficient tool for risk analysis in many regions of the world and specially in areas with steep topographic gradients such as mountain ranges, heavily incised river networks, coastal cliffs, etc. References: [1] H. J. Koerner, "Reichweite und geschwindigkeit von bergstürzen und fleisschneelawinen". Rock Mechanics, 8, 225-256 (1976) [2] P. J. McLellan and P. K. Kaiser, "Application of a two-parameter model to rock avalanches in the mackenzine mountains". 4th International Symposium on Landslides, 135-140 (1984). [3] A. Kent and O. Hungr, "Runout characteristics of debris from dump failures in mountainous terrain: stage 2: analysis, modelling and prediction". British Columbia Mine Waste Rock Pile Research Committee and CANMET (1995). [4] O. Hungr and S. G. Evans, "Rock avalanche runout prediction using a dynamic model". 7th International Symposium on Landslides, 233-238 (1996). [5] D. Rickenmann and T. Koch, "Comparison of debris flow modelling approaches". First International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction, and Assessment. ASCE, ed. New York. C.L. Chen (1997). [6] P. Bertolo and G. F. Wieczorek, "Calibration of numerical models for small debris flows in Yosemite Valley, California, USA". Natural Hazards in Earth System Sciences (5) 993-1001 (2005). [7] S. Beguería and Th. J. van Asch and J. P. Malet and S. Gröndahl, "A GIS-based numerical model for simulating the kinematics of mud and debris flows over complex terrain". Natural Hazards in Earth System Sciences (9) 1897-1909 (2009). [8] G. Sánchez Burillo, S. Beguería, B. Latorre and J. Burguete, "Numerical treatment of the friction term in upwind schemes in debris flow runout modelling". ASCE Journal of Hydraulic Engineering (sent for publication). [9] A. Voellmy, Über die Zerstörungskraft von Lawinen. Schweizer. Bauzeitung (1955). [10] J. E. Nash and J. V. Shutcliffe, "River flow forecasting through conceptual models part I - A discussion of principles". Journal of Hydrology, 10 (3) 282-290 (1970).

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

NASA Astrophysics Data System (ADS)

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 < V < 0.3 m/s, velocity and slip neutral (μi = μss = 0.62±0.08) and (3) for V > 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±0.02 (slip-strengthening behavior), (2) for V = 0.1 m/s velocity and slip neutral (μi = μss = 0.77±0.02) and (3) for V ≥ 0.3 m/s the friction coefficient was velocity and slip weakening with μss = 0.32±0.02 for V = 1.5 m/s. The Rietveld analysis of the smectite-rich standard endmember showed (1) the insensitivity of the amount of the amorphous fraction with frictional work and (2) the shift and broadening of both the (001) and (110) peaks of Ca-montmorillonite with increasing frictional work (i.e., product of shear stress with slip, here from 5.2 Jm-2 to 11.8 Jm-2). Instead, mineralogical and lattice changes were unrelated to the frictional work rate (i.e., product of shear stress with slip rate). Strain localization in the gouge layer was observed for V ≥ 0.3 m/s (SEM investigations); for V < 0.3 m/s, strain was distributed and the gouge layer pervasively foliated. We conclude that the degree of amorphization of the sheared gouges was not responsible of the measured frictional weakening; instead, weakening was concomitant to strain localization.

Two dimensional modeling of elastic wave propagation in solids containing cracks with rough surfaces and friction - Part I: Theoretical background.

PubMed

Aleshin, Vladislav; Delrue, Steven; Trifonov, Andrey; 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 the modeling of internal contacts (called cracks for brevity), while part II is related to the integration of the developed contact model into a solid mechanics module that allows the description of wave propagation processes. The contact model is used to produce normal and tangential load-displacement relationships, which in turn are used by the solid mechanics module as boundary conditions at the internal contacts. Due to friction, the tangential reaction curve is hysteretic and memory-dependent. In addition, it depends on the normal reaction curve. An essential feature of the proposed contact model is that it takes into account the roughness of the contact faces. On one hand, accounting for roughness makes the contact model more complicated since it gives rise to a partial slip regime when some parts on the contact area experience slip and some do not. On the other hand, as we will show, the concept of contact surfaces covered by asperities receding under load makes it possible to formulate a consistent contact model that provides nonlinear load-displacement relationships for any value of the drive displacements and their histories. This is a strong advantage, since this way, the displacement-driven model allows for a simple explicit procedure of data exchange with the solid mechanics module, while more traditional flat-surface contacts driven by loads generate a complex iterative procedure. More specifically, the proposed contact model is based on the previously developed method of memory diagrams that allows one to automatically obtain memory-dependent solutions to frictional contact problems in the particular case of partial slip. Here we extend the solution onto cases of total sliding and contact loss which is possible while using the displacement-driven formulation. The method requires the knowledge of the normal contact response obtained in our case as a result of statistical consideration of roughness of contact faces. Copyright © 2017 Elsevier B.V. All rights reserved.

International Conference on Internal Friction and Ultrasonic Attenuation in Solids (ICIFUAS) (10th) held in Roma, Italy on September 6 - 9, 1993

DTIC Science & Technology

1993-09-09

decomposition in Fe-Cr system on non-elastic properties were investigated. Taking mechanism of appearing of microplastic deformation as the base, the...found out the general principles of LPT- induced microplasticity and examined several particular cases. The basic idea is the great change of the line...Physics, Russian Acad. of Sci., 142432 Chernogolovka, Moscow distr., Russia on heefect o sea stes V103 If S The investigations were c rried o4 on

Vibrations of an Euler-Bernoulli beam with hysteretic damping arising from dispersed frictional microcracks

NASA Astrophysics Data System (ADS)

Maiti, Soumyabrata; Bandyopadhyay, Ritwik; Chatterjee, Anindya

2018-01-01

We study free and harmonically forced vibrations of an Euler-Bernoulli beam with rate-independent hysteretic dissipation. The dissipation follows a model proposed elsewhere for materials with randomly dispersed frictional microcracks. The virtual work of distributed dissipative moments is approximated using Gaussian quadrature, yielding a few discrete internal hysteretic states. Lagrange's equations are obtained for the modal coordinates. Differential equations for the modal coordinates and internal states are integrated together. Free vibrations decay exponentially when a single mode dominates. With multiple modes active, higher modes initially decay rapidly while lower modes decay relatively slowly. Subsequently, lower modes show their own characteristic modal damping, while small amplitude higher modes show more erratic decay. Large dissipation, for the adopted model, leads mathematically to fast and damped oscillations in the limit, unlike viscously overdamped systems. Next, harmonically forced, lightly damped responses of the beam are studied using both a slow frequency sweep and a shooting-method based search for periodic solutions along with numerical continuation. Shooting method and frequency sweep results match for large ranges of frequency. The shooting method struggles near resonances, where internal states collapse into lower dimensional behavior and Newton-Raphson iterations fail. Near the primary resonances, simple numerically-aided harmonic balance gives excellent results. Insights are also obtained into the harmonic content of secondary resonances.

Exact solution of a linear molecular motor model driven by two-step fluctuations and subject to protein friction.

PubMed

Fogedby, Hans C; Metzler, Ralf; Svane, Axel

2004-08-01

We investigate by analytical means the stochastic equations of motion of a linear molecular motor model based on the concept of protein friction. Solving the coupled Langevin equations originally proposed by Mogilner et al. [Phys. Lett. A 237, 297 (1998)], and averaging over both the two-step internal conformational fluctuations and the thermal noise, we present explicit, analytical expressions for the average motion and the velocity-force relationship. Our results allow for a direct interpretation of details of this motor model which are not readily accessible from numerical solutions. In particular, we find that the model is able to predict physiologically reasonable values for the load-free motor velocity and the motor mobility.

Splay fault slip in a subduction margin, a new model of evolution

NASA Astrophysics Data System (ADS)

Conin, Marianne; Henry, Pierre; Godard, Vincent; Bourlange, Sylvain

2012-08-01

In subduction zones, major thrusts called splay faults are thought to slip coseismically during large earthquakes affecting the main plate interface. We propose an analytical condition for the activation of a splay fault based on force balance calculations and suggest thrusting along the splay fault is generally conditioned by the growth of the accretionary wedge, or by the erosion of the hanging wall. In theory, normal slip on the splay fault may occur when the décollement has a very low friction coefficient seaward. Such a low friction also implies an unstable extensional state within the outer wedge. Finite element elasto-plastic calculations with a geometry based on the Nankai Kumano section were performed and confirm that this analytical condition is a valid approximation. Furthermore, localized extension at a shallow level in the splay hanging wall is observed in models for a wide range of friction coefficients (from ∼0 to the value of internal friction coefficient of the rock, here equals to 0.4). The timing of slip established for the splay fault branch drilled on Nankai Kumano transect suggests a phase of concurrent splay and accretionary wedge growth ≈2 Ma to ≈1.5 Ma, followed by a locking of the splay ≈1.3 Ma. Active extension is observed in the hanging wall. This evolution can be explained by the activation of a deeper and weaker décollement, followed by an interruption of accretion. Activation of a splay as a normal fault, as hypothesized in the case of the Tohoku 2011 earthquake, can be achieved only if the friction coefficient on the décollement drops to near zero. We conclude that the tectonic stress state largely determines long-term variations of tightly related splay fault and outer décollement activity and thus influences where and how coseismic rupture ends, but that occurrence of normal slip on a splay fault requires coseismic friction reduction.

Comparison of the effects of friction varnish and electroforming on the retention of telescopic crowns.

PubMed

Özyemişci-Cebeci, Nuran; Yavuzyilmaz, Hüsnü

2013-06-01

Methods to improve the retention of telescopic crowns, including the application of friction varnish and electroforming, are available. However, information about their efficiency is limited. The purpose of this study was to compare the influence of 2 different friction varnishes and an electroforming method on the retention of telescopic crowns. Thirty inner and outer crowns were fabricated from cobalt-chromium-molybdenum alloy having lengths and cervical diameters of 6 mm, 2-degree tapers, and shoulder margins of 1 mm. Fifty-μm thick layers were removed from the internal surfaces of the outer crowns with a vertical machining center to simulate wear. The retentive forces of these specimens were measured with a testing machine. FGP friction varnish (FGP Friction-Fit-System), SD friction varnish (Servo-dental), and an electroforming method (GES\\Gold Electroforming System) were applied to the specimens. After the application of the 3 methods, retention values were measured, and the results analyzed with 1-way ANOVA, paired sample t test (α=.05). The increase in the retentive forces of all specimens was statistically significant (P<.01). The mean retentive forces increased from 3.6 N to 9.8 N for group FGP, 3.6 N to 4.6 N for group SD, and 3.7 N to 6.0 N for group EF. Group FGP was significantly different from group SD and group EF (P<.05), and no significant difference was observed between group SD and group EF. Mean standard deviation values of retentive forces for group FGP before, FGP after, SD before, SD after, EF before and EF after is 0.5, 2.7, 0.6, 1.3, 0.8, 2.3, respectively. Group FGP showed the maximum retention values. Group EF showed higher retention values than group SD. Copyright © 2013 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Mosby, Inc. All rights reserved.

Detection and assessment of flaws in friction stir welded metallic plates

NASA Astrophysics Data System (ADS)

Fakih, Mohammad Ali; Mustapha, Samir; Tarraf, Jaafar; Ayoub, Georges; Hamade, Ramsey

2017-04-01

Investigated is the ability of ultrasonic guided waves to detect flaws and assess the quality of friction stir welds (FSW). AZ31B magnesium plates were friction stir welded. While process parameters of spindle speed and tool feed were fixed, shoulder penetration depth was varied resulting in welds of varying quality. Ultrasonic waves were excited at different frequencies using piezoelectric wafers and the fundamental symmetric (S0) mode was selected to detect the flaws resulting from the welding process. The front of the first transmitted wave signal was used to capture the S0 mode. A damage index (DI) measure was defined based on the amplitude attenuation after wave interaction with the welded zone. Computed Tomography (CT) scanning was employed as a nondestructive testing (NDT) technique to assess the actual weld quality. Derived DI values were plotted against CT-derived flaw volume resulting in a perfectly linear fit. The proposed approach showed high sensitivity of the S0 mode to internal flaws within the weld. As such, this methodology bears great potential as a future predictive method for the evaluation of FSW weld quality.

Investigation of Friction Stir Welding of Al Metal Matrix Composite Materials

NASA Technical Reports Server (NTRS)

Diwan, Ravinder M.

2003-01-01

The innovative process of Friction Stir Welding (FSW) has generated tremendous interest since its inception about a decade or so ago since the first patent in 1991 by TWI of Cambridge, England. This interest has been seen in many recent international conferences and publications on the subject and relevant published literature. Still the process needs both intensive basic study of deformation mechanisms during this FSW process and analysis and feasibility study to evaluate production methods that will yield high quality strong welds from the stirring action of the appropriate pin tool into the weld plate materials. Development of production processes is a complex task that involves effects of material thickness, materials weldability, pin tool design, pin height, and pin shoulder diameter and related control conditions. The frictional heating with rotational speeds of the pin tool as it plunges into the material and the ensuing plastic flow arising during the traverse of the welding faying surfaces provide the known special advantages of the FSW process in the area of this new advanced joining technology.

The effects of physical and chemical preprocessing on the flowability of corn stover

DOE PAGES

Crawford, Nathan C.; Nagle, Nick; Sievers, David A.; ...

2015-12-20

Continuous and reliable feeding of biomass is essential for successful biofuel production. However, the challenges associated with biomass solids handling are commonly overlooked. In this study, we examine the effects of preprocessing (particle size reduction, moisture content, chemical additives, etc.) on the flow properties of corn stover. Compressibility, flow properties (interparticle friction, cohesion, unconfined yield stress, etc.), and wall friction were examined for five corn stover samples: ground, milled (dry and wet), acid impregnated, and deacetylated. The ground corn stover was found to be the least compressible and most flowable material. The water and acid impregnated stovers had similar compressibilities.more » Yet, the wet corn stover was less flowable than the acid impregnated sample, which displayed a flow index equivalent to the dry, milled corn stover. The deacetylated stover, on the other hand, was the most compressible and least flowable examined material. However, all of the tested stover samples had internal friction angles >30°, which could present additional feeding and handling challenges. All of the ''wetted'' materials (water, acid, and deacetylated) displayed reduced flowabilities (excluding the acid impregnated sample), and enhanced compressibilities and wall friction angles, indicating the potential for added handling issues; which was corroborated via theoretical hopper design calculations. All of the ''wetted'' corn stovers require larger theoretical hopper outlet diameters and steeper hopper walls than the examined ''dry'' stovers.« less

Repeatability of gradient ultrahigh pressure liquid chromatography-tandem mass spectrometry methods in instrument-controlled thermal environments.

PubMed

Grinias, James P; Wong, Jenny-Marie T; Kennedy, Robert T

2016-08-26

The impact of viscous friction on eluent temperature and column efficiency in liquid chromatography is of renewed interest as the need for pressures exceeding 1000bar to use with columns packed with sub-2μm particles has grown. One way the development of axial and radial temperature gradients that arise due to viscous friction can be affected is by the thermal environment the column is placed in. In this study, a new column oven integrated into an ultrahigh pressure liquid chromatograph that enables both still-air and forced-air operating modes is investigated to find the magnitude of the effect of the axial thermal gradient that forms in 2.1×100mm columns packed with sub-2μm particles in these modes. Temperature increases of nearly 30K were observed when the generated power of the column exceeded 25W/m. The impact of the heating due to viscous friction on the repeatability of peak capacity, elution time, and peak area ratio to an internal standard for a gradient UHPLC-MS/MS method to analyze neurotransmitters was found to be limited. This result indicates that high speed UHPLC-MS/MS gradient methods under conditions of high viscous friction may be possible without the negative effects typically observed with isocratic separations under similar conditions. Copyright © 2016 Elsevier B.V. All rights reserved.

The effects of physical and chemical preprocessing on the flowability of corn stover

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

Crawford, Nathan C.; Nagle, Nick; Sievers, David A.

Continuous and reliable feeding of biomass is essential for successful biofuel production. However, the challenges associated with biomass solids handling are commonly overlooked. In this study, we examine the effects of preprocessing (particle size reduction, moisture content, chemical additives, etc.) on the flow properties of corn stover. Compressibility, flow properties (interparticle friction, cohesion, unconfined yield stress, etc.), and wall friction were examined for five corn stover samples: ground, milled (dry and wet), acid impregnated, and deacetylated. The ground corn stover was found to be the least compressible and most flowable material. The water and acid impregnated stovers had similar compressibilities.more » Yet, the wet corn stover was less flowable than the acid impregnated sample, which displayed a flow index equivalent to the dry, milled corn stover. The deacetylated stover, on the other hand, was the most compressible and least flowable examined material. However, all of the tested stover samples had internal friction angles >30°, which could present additional feeding and handling challenges. All of the ''wetted'' materials (water, acid, and deacetylated) displayed reduced flowabilities (excluding the acid impregnated sample), and enhanced compressibilities and wall friction angles, indicating the potential for added handling issues; which was corroborated via theoretical hopper design calculations. All of the ''wetted'' corn stovers require larger theoretical hopper outlet diameters and steeper hopper walls than the examined ''dry'' stovers.« less

Roughness-dependent friction force of the tarsal claw system in the beetle Pachnoda marginata (Coleoptera, Scarabaeidae).

PubMed

Dai, Zhendong; Gorb, Stanislav N; Schwarz, Uli

2002-08-01

This paper studies slide-resisting forces generated by claws in the free-walking beetle Pachnoda marginata (Coleoptera, Scarabaeoidea) with emphasis on the relationship between the dimension of the claw tip and the substrate texture. To evaluate the force range by which the claw can interact with a substrate, forces generated by the freely moving legs were measured using a load cell force transducer. To obtain information about material properties of the claw, its mechanical strength was tested in a fracture experiment, and the internal structure of the fractured claw material was studied by scanning electron microscopy. The bending stress of the claw was evaluated as 143.4-684.2 MPa, depending on the cross-section model selected. Data from these different approaches led us to propose a model explaining the saturation of friction force with increased texture roughness. The forces are determined by the relative size of the surface roughness R(a) (or an average particle diameter) and the diameter of the claw tip. When surface roughness is much bigger than the claw tip diameter, the beetle can grasp surface irregularities and generate a high degree of attachment due to mechanical interlocking with substrate texture. When R(a) is lower than or comparable to the claw tip diameter, the frictional properties of the contact between claw and substrate particles play a key role in the generation of the friction force.

An unusual landslide feature on Mars

NASA Technical Reports Server (NTRS)

Veverka, J.; Liang, T.

1975-01-01

A flow feature on a crater wall, characteristic of a landslide, has been identified in a Mariner 9 high resolution photograph. Although other evidence of mass wasting is common in Mariner 9 photography, the case presented appears unique. A tentative conclusion is that, at least in some cases, Martian soil exhibits significant internal friction in mass movements.

Integrated Business Process Adaptation towards Friction-Free Business-to-Business Collaboration

ERIC Educational Resources Information Center

Shan, Zhe

2011-01-01

One key issue in process-aware E-commerce collaboration is the orchestration of business processes of multiple business partners throughout a supply chain network in an automated and seamless way. Since each partner has its own internal processes with different control flow structures and message interfaces, the real challenge lies in verifying…

The effect of dissipation on the resistive admittance of an elastic medium.

PubMed

Photiadis, Douglas M

2012-03-01

The effect of dissipation on the real part of the admittance of an elastic half-space is typically thought to be unimportant if the loss factor ζ of the elastic medium is small. However, dissipation induces losses in the near field of the source and, provided the size of the source is small enough, this phenomenon can be more important than elastic wave radiation. Such losses give rise to a fundamental limit in the quality factor of an oscillator attached to a substrate. Near field losses associated with strains in the elastic substrate can actually be larger than intrinsic losses in the oscillator itself if the internal friction of the substrate is larger than the internal friction of the oscillator. For a uniform stress applied to a disk of radius a, a monopole source, such phenomena become significant for k(L)a<ζ, while for higher order multipole sources of order l, near field losses are important for (k(L)a)(l+1)<ζ, a far less restrictive constraint. © 2012 Acoustical Society of America

Metallic materials for mechanical damping capacity applications

NASA Astrophysics Data System (ADS)

Crăciun, R. C.; Stanciu, S.; Cimpoeșu, R.; (Dragoș Ursanu, A. I.; Manole, V.; Paraschiv, P.; Chicet, D. L.

2016-08-01

Some metallic materials exhibit good damping capacity of mechanical energy into thermal energy. This property along with the others metallic characteristics make this materials interesting for a big number of applications. These materials can be used as bumpers in different applications including automotive field. Beside grey cast iron and shape memory alloys few new metallic materials are presented for the supposition of high damping capacity. We analyze the causes that increase the internal friction of some metallic materials and possibilities to enhance this property through different mechanical, physical or chemical methods. Shape memory alloys, especially those based on copper, present a different damping capacity on martensite, austenite or transition state. In the transformation range M ↔A, which in case of copper base shape memory alloys is quite large, the metallic intelligent materials present a high internal friction, almost comparable with natural rubber behavior that can transform mechanical energy into thermal energy till a certain value of the external solicitation. These materials can be used as noise or small vibrations bumpers or even as shock absorbers in automotive industry.

Acoustic-pseudoelastic effect and internal friction during stress-induced martensitic transformation in Cu-Al-Ni single crystals

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

Sapozhnikov, K.V.; Vetrov, V.V.; Pulnev, S.A.

1996-05-15

Internal friction (IF) during temperature-induced thermoelastic martensitic transformation (TMT) has been studied extensively, whereas IF behavior during stress-induced TMT has not attracted much attention so far. It is known that quasistatic flow stress may decrease under superimposition of an oscillatory stress in the case of dislocation plasticity (acoustoplastic or Blaha effect). Strain originating from the reversible TMT (so-called transformation pseudoelasticity), in contrast to the dislocation plastic strain, may be completely reversible, however, accompanied by macroscopic hysteresis. The existence of the pseudoelastic hysteresis is usually attributed to the presence of obstacles impeding the mobility of interfaces during stress-induced transformation. A numbermore » of theories also consider the mobility of interfaces as the main source of IF during TMT. As a consequence, one should expect certain interconnection between the ADIF during stress-induced TMT and the macroscopically observed hysteresis. Thus the purpose of present paper is to study in a wide oscillatory strain amplitude range the ADIF during stress-induced TMT and the effect of ultrasound on this mode of deformation.« less

Measurement of sample temperatures under magic-angle spinning from the chemical shift and spin-lattice relaxation rate of 79Br in KBr powder

PubMed Central

Thurber, Kent R.; Tycko, Robert

2009-01-01

Accurate determination of sample temperatures in solid state nuclear magnetic resonance (NMR) with magic-angle spinning (MAS) can be problematic, particularly because frictional heating and heating by radio-frequency irradiation can make the internal sample temperature significantly different from the temperature outside the MAS rotor. This paper demonstrates the use of 79Br chemical shifts and spin-lattice relaxation rates in KBr powder as temperature-dependent parameters for the determination of internal sample temperatures. Advantages of this method include high signal-to-noise, proximity of the 79Br NMR frequency to that of 13C, applicability from 20 K to 320 K or higher, and simultaneity with adjustment of the MAS axis direction. We show that spin-lattice relaxation in KBr is driven by a quadrupolar mechanism. We demonstrate a simple approach to including KBr powder in hydrated samples, such as biological membrane samples, hydrated amyloid fibrils, and hydrated microcrystalline proteins, that allows direct assessment of the effects of frictional and radio-frequency heating under experimentally relevant conditions. PMID:18930418

Measurement of sample temperatures under magic-angle spinning from the chemical shift and spin-lattice relaxation rate of 79Br in KBr powder.

PubMed

Thurber, Kent R; Tycko, Robert

2009-01-01

Accurate determination of sample temperatures in solid state nuclear magnetic resonance (NMR) with magic-angle spinning (MAS) can be problematic, particularly because frictional heating and heating by radio-frequency irradiation can make the internal sample temperature significantly different from the temperature outside the MAS rotor. This paper demonstrates the use of (79)Br chemical shifts and spin-lattice relaxation rates in KBr powder as temperature-dependent parameters for the determination of internal sample temperatures. Advantages of this method include high signal-to-noise, proximity of the (79)Br NMR frequency to that of (13)C, applicability from 20 K to 320 K or higher, and simultaneity with adjustment of the MAS axis direction. We show that spin-lattice relaxation in KBr is driven by a quadrupolar mechanism. We demonstrate a simple approach to including KBr powder in hydrated samples, such as biological membrane samples, hydrated amyloid fibrils, and hydrated microcrystalline proteins, that allows direct assessment of the effects of frictional and radio-frequency heating under experimentally relevant conditions.

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

NASA Astrophysics Data System (ADS)

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.

Predicting orogenic wedge styles as a function of analogue erosion law and material softening

NASA Astrophysics Data System (ADS)

Mary, Baptiste C. L.; Maillot, Bertrand; Leroy, Yves M.

2013-10-01

The evolution of a compressive frictional wedge on a weak, frictional and planar décollement, subjected to frontal accretion, is predicted with a two step method called sequential limit analysis. The first step consists in finding, with the kinematic approach of limit analysis, the length of the active décollement and the dips of the emerging ramp and of the conjugate shear plane composing the emerging thrust fold. The second step leads to a modification of the geometry, first, because of the thrust fold development due to compression and, second, because of erosion. Erosion consists in removing periodically any material above a fictitious line at a selected slope, as done in analogue experiments. This application of sequential limit analysis generalizes the critical Coulomb wedge theory since it follows the internal deformation development. With constant frictional properties, the deformation is mostly diffuse, a succession of thrust folds being activated so that the topographic slope reaches exactly the theoretical, critical value. Frictional weakening on the ramps results in a deformation style composed of thrust sheets and horses. Applying an erosion slope at the critical topographic value leads to exhumation in the frontal, central, or rear region of the wedge depending on the erosion period and the weakening. Erosion at slopes slightly above or below the critical value results in exhumation toward the foreland or the hinterland, respectively, regardless of the erosion period. Exhumation is associated with duplexes, imbricate fans, antiformal stacks, and major backthrusting. Comparisons with sandbox experiments confirm that the thickness, dips, vergence, and exhumation of thrust sheets can be reproduced with friction and erosion parameters within realistic ranges of values.

Evaluation of the head-helmet sliding properties in an impact test.

PubMed

Trotta, Antonia; Ní Annaidh, Aisling; Burek, Roy Owen; Pelgrims, Bart; Ivens, Jan

2018-05-18

The scalp plays a crucial role in head impact biomechanics, being the first tissue involved in the impact and providing a sliding interface between the impactor and/or helmet and the skull. It is important to understand both the scalp-skull and the scalp-helmet sliding in order to determine the head response due to an impact. However, experimental data on the sliding properties of the scalp is lacking. The aim of this work was to identify the sliding properties of the scalp using cadaver heads, in terms of scalp-skull and scalp-liner (internal liner of the helmet) friction and to compare these values with that of widely used artificial headforms (HIII and magnesium EN960). The effect of the hair, the direction of sliding, the speed of the test and the normal load were considered. The experiments revealed that the sliding behaviour of the scalp under impact loading is characterised by three main phases: (1) the low friction sliding of the scalp over the skull (scalp-skull friction), (2) the tensioning effect of the scalp and (3) the sliding of the liner fabric over the scalp (scalp-liner friction). Results showed that the scalp-skull coefficient of friction (COF) is very low (0.06 ± 0.048), whereas the scalp-liner COF is 0.29 ± 0.07. The scalp-liner COF is statistically different from the value of the HIII-liner (0.75 ± 0.06) and the magnesium EN960-liner (0.16 ± 0.026). These data will lead to the improvement of current headforms for head impact standard tests, ultimately leading to more realistic head impact simulations and the optimization of helmet designs. Copyright © 2018 Elsevier Ltd. All rights reserved.

Impact of petroleum products on soil composition and physical-chemical properties

NASA Astrophysics Data System (ADS)

Brakorenko, N. N.; Korotchenko, T. V.

2016-03-01

The article describes the grain-size distribution, physical and mechanical properties, swelling and specific electrical resistivity of soils before and after the contact with petroleum products. The changes in mechanical properties of soils contaminated with petroleum products have been stated. It leads to the increase in compressibility values, decline in internal friction angle and cohesion.

Logistical and Analytical Approach to a Failure Aboard the International Space Station

NASA Technical Reports Server (NTRS)

McDanels, Seve; Wright, M. Clara; Salazar, Victoria; Lubas, David; Tucker, Bryan

2009-01-01

The starboard Solar Alpha Rotary Joint (SARJ) from the International Space Station (ISS) began exhibiting off-nominal electrical demands and vibration. Examination by spacewalking astronauts revealed metallic debris contaminating the system and damage to the outboard race of the SARJ. Samples of the contamination were returned to Earth and analyzed. Excessive friction caused the nitride region of the 15-5 PH stainless steel race to spall, generating the debris and damaging the race surface. Excessive vibration and excess power was required to operate the system as a result.

Seismicity in a model governed by competing frictional weakening and healing mechanisms

NASA Astrophysics Data System (ADS)

Hillers, G.; Carlson, J. M.; Archuleta, R. J.

2009-09-01

Observations from laboratory, field and numerical work spanning a wide range of space and time scales suggest a strain dependent progressive evolution of material properties that control the stability of earthquake faults. The associated weakening mechanisms are counterbalanced by a variety of restrengthening mechanisms. The efficiency of the healing processes depends on local material properties and on rheologic, temperature, and hydraulic conditions. We investigate the relative effects of these competing non-linear feedbacks on seismogenesis in the context of evolving frictional properties, using a mechanical earthquake model that is governed by slip weakening friction. Weakening and strengthening mechanisms are parametrized by the evolution of the frictional control variable-the slip weakening rate R-using empirical relationships obtained from laboratory experiments. In our model, weakening depends on the slip of an earthquake and tends to increase R, following the behaviour of real and simulated frictional interfaces. Healing causes R to decrease and depends on the time passed since the last slip. Results from models with these competing feedbacks are compared with simulations using non-evolving friction. Compared to fixed R conditions, evolving properties result in a significantly increased variability in the system dynamics. We find that for a given set of weakening parameters the resulting seismicity patterns are sensitive to details of the restrengthening process, such as the healing rate b and a lower cutoff time, tc, up to which no significant change in the friction parameter is observed. For relatively large and small cutoff times, the statistics are typical of fixed large and small R values, respectively. However, a wide range of intermediate values leads to significant fluctuations in the internal energy levels. The frequency-size statistics of earthquake occurrence show corresponding non-stationary characteristics on time scales over which negligible fluctuations are observed in the fixed-R case. The progressive evolution implies that-except for extreme weakening and healing rates-faults and fault networks possibly are not well characterized by steady states on typical catalogue time scales, thus highlighting the essential role of memory and history dependence in seismogenesis. The results suggest that an extrapolation to future seismicity occurrence based on temporally limited data may be misleading due to variability in seismicity patterns associated with competing mechanisms that affect fault stability.

Shear flow of angular grains: acoustic effects and nonmonotonic rate dependence of volume.

PubMed

Lieou, Charles K C; Elbanna, Ahmed E; Langer, J S; Carlson, J M

2014-09-01

Naturally occurring granular materials often consist of angular particles whose shape and frictional characteristics may have important implications on macroscopic flow rheology. In this paper, we provide a theoretical account for the peculiar phenomenon of autoacoustic compaction-nonmonotonic variation of shear band volume with shear rate in angular particles-recently observed in experiments. Our approach is based on the notion that the volume of a granular material is determined by an effective-disorder temperature known as the compactivity. Noise sources in a driven granular material couple its various degrees of freedom and the environment, causing the flow of entropy between them. The grain-scale dynamics is described by the shear-transformation-zone theory of granular flow, which accounts for irreversible plastic deformation in terms of localized flow defects whose density is governed by the state of configurational disorder. To model the effects of grain shape and frictional characteristics, we propose an Ising-like internal variable to account for nearest-neighbor grain interlocking and geometric frustration and interpret the effect of friction as an acoustic noise strength. We show quantitative agreement between experimental measurements and theoretical predictions and propose additional experiments that provide stringent tests on the new theoretical elements.

Design and Performance of Property Gradient Ternary Nitride Coating Based on Process Control.

PubMed

Yan, Pei; Chen, Kaijie; Wang, Yubin; Zhou, Han; Peng, Zeyu; Jiao, Li; Wang, Xibin

2018-05-09

Surface coating is an effective approach to improve cutting tool performance, and multiple or gradient coating structures have become a common development strategy. However, composition mutations at the interfaces decrease the performance of multi-layered coatings. The key mitigation technique has been to reduce the interface effect at the boundaries. This study proposes a structure design method for property-component gradient coatings based on process control. The method produces coatings with high internal cohesion and high external hardness, which could reduce the composition and performance mutations at the interface. A ZrTiN property gradient ternary nitride coating was deposited on cemented carbide by multi-arc ion plating with separated Ti and Zr targets. The mechanical properties, friction behaviors, and cutting performances were systematically investigated, compared with a single-layer coating. The results indicated that the gradient coating had better friction and wear performance with lower wear rate and higher resistance to peeling off during sliding friction. The gradient coating had better wear and damage resistance in cutting processes, with lower machined surface roughness Ra. Gradient-structured coatings could effectively inhibit micro crack initiation and growth under alternating force and temperature load. This method could be extended to similar ternary nitride coatings.

The influence of micro-scale dimples and nano-sized grains on the fretting characteristics generated by laser pulses.

PubMed

Amanov, Auezhan; Watabe, Tsukasa; Sasaki, Shinya

2013-12-01

The tribological characteristics of micro-scale dimpled Cu-based alloy specimen generated using a laser surface texturing (LST) were assessed and compared with that of the untextured specimen. The objective of this study is to improve the tribological characteristics of internal combustion engine (ICE) bearings and bushings made of Cu-based alloy by generating micro-scale dimples using an LST. Fretting wear tests were performed by sliding a hardened SAE52100 steel ball against the untextured and LSTed specimens at a normal load of 5 N under oil-lubricated conditions. The friction force and relative movement between the specimens were measured simultaneously during the fretting tests. The test results showed that the LSTed specimens showed a reduction in friction coefficient and an enhancement in fretting wear resistance compared to that of the untextured specimen. The friction coefficient and fretting wear volume increased with increasing frequency for both untextured and LSTed specimens. The improved tribological properties of the LSTed specimen may be attributed to the micro-scale dimples, refined grain size and high lattice strain. In addition, a model for the nanocrystallization mechanism of the LSTed specimen was proposed.

How to predict deformation for geometrically and mechanically non-uniform accretionary wedges

NASA Astrophysics Data System (ADS)

Souloumiac, Pauline; Cubas, Nadaya; Caër, Typhaine

2017-04-01

The mechanical understanding of fold-and-thrust belts and accretionary prisms strongly relies on the critical taper theory (CTT). The latter considers their mechanics as analogous to sand pushed by a moving bulldozer along a frictional décollement. The wedge evolves into a critical geometry, corresponding to a point of internal state of stress for which the whole wedge including the basal décollement is on the verge of Coulomb failure. If the décollement is planar and material properties are homogeneous and cohesionless, the critical wedge is triangular. The force of the CCT relies on the fact that conditions for stress equilibrium, Coulomb yielding of the wedge and basal frictional sliding have an analytical solution. However, this theory suffers from several limits. As stated above, the analytical solution applies for perfectly triangular wedges. However, the critical taper is shaped by internal thrusts that lead to a non-uniform topographic slope. What is then the scale of topographic variability for which the CCT will stand? The second limit is that CCT applies for homogeneous frictional properties in the wedge and as well as along the décollement. We can also wonder if there is a scaling parameter for which variations of properties along the decollement would impact the topography. We here show how the limit analysis, an efficient semi-analytical approach, can help us to overcome these limits. We aim to provide simple analytical solutions to structural geologists to evaluate the critical state of their field study cases. We first show that the effect of topographic slope variability relies on a competition between the surface of potential hanging-walls and the surface of theoretical critical hanging-walls. Dips of thrust and backthrust are controlled by the frictional parameters. Along a wedge with a non-regular topography, an out-of-sequence system will appear if there is a position along the wedge for which the hanging-wall will have a lower surface than the critical one. The impact of basal friction variations on the topography can be resolve in the same manner but by comparing force balances and not only surfaces. To validate our findings, analytical solutions are compared to sandbox experiments. We will also compare our results to natural cases such as the Jura (France) fold-and-thrust belt. Finally, we will discuss how the same approach can be applied to variations of the décollement geometry.

Implications of loading/unloading a subduction zone with a heterogeneously coupled interface

NASA Astrophysics Data System (ADS)

Herman, M. W.; Furlong, K. P.; Govers, R. M. A.

2017-12-01

Numerical models of subduction zones with appropriate physical properties may help understand deformation throughout great earthquake cycles, as well as associated observations such as the distribution of smaller magnitude megathrust earthquakes and surface displacements. Of particular interest are displacements near the trench, where tsunamis are generated. The patterns of co-seismic strain release in great megathrust earthquakes depend on the frictional coupling of the plate interface prior to the event. Geodetic observations during the inter-seismic stage suggest that the plates are fully locked at asperities surrounded by zones of apparent partial coupling. We simulate the accumulation (and release) of elastic strain in the subduction system using a finite element model with a relatively simple geometry and material properties. We demonstrate that inter-seismic apparent partial coupling can be dominantly explained by a distribution of completely locked asperities and zero friction elsewhere. In these models, the interface up-dip of the locked zone (< 15 km depth) accumulates large slip deficit even if its coefficient of friction is zero, as might be inferred from the scarcity of megathrust earthquakes shallower than 15 km in global earthquake catalogs. In addition, the upper plate above a low-friction shallow megathrust accumulates large displacements with little internal strain, potentially leading to large co-seismic block displacements (low displacement gradients) of the near-trench seafloor like those observed following the 2011 Mw 9.0 Tohoku earthquake. This is also consistent with anomalously low co-seismic frictional heating of the shallow megathrust indicated by borehole heat flow measurements after the Tohoku event. Our models also yield insights into slip partitioning throughout multiple earthquake cycles. In smaller ruptures, fault slip is inhibited by nearby locked zones; in subsequent multi-segment ruptures, the rest of this slip deficit may be released, producing significantly larger slip than might be expected based on historical earthquake magnitudes. Finally, because low-friction areas around asperities accumulate some slip deficit but may not rupture co-seismically, these regions may be the primary locations of afterslip following the rupture of the locked patch.

Cyclically modulated dissipation and friction in ice and ice mixtures: how tidal forcing influences the mechanical properties in an icy shell

NASA Astrophysics Data System (ADS)

McCarthy, C.; Savage, H. M.; Cooper, R. F.; Kaczynski, T.; Nielson, M.; Domingos, A.

2017-12-01

Measuring the response of ice to dynamic, time-varying stress at appropriate planetary conditions is important to improving estimates of long-term heat flux and satellite evolution. The viscoelastic and frictional responses of ice may play important roles in tidal heating and convection, but at different time and lengthscales. We will share results from two different types of laboratory experiments on polycrystalline ice samples that reproduce tidally modulated behavior: (1) forced oscillation compression experiments that measure attenuation; and (2) periodic velocity biaxial experiments that measure friction. The former inform us about the influences of frequency, temperature, grain size, and strain history on mechanical dissipation of tidal energy in the deep interiors of icy crusts. In particular, we examine the combination of low amplitude tidal forcing with a relentless (steady-state) background stress, such as that from convection. The beauty of attenuation is that it can potentially be used as mechanical spectroscopy to identify structure and mechanisms that are otherwise shrouded by steady-state behavior. Friction experiments were conducted in a biaxial apparatus in which a central ice piece is forced between two stationary pieces at constant velocity with a sinusoidal oscillation super-imposed. The rig is fitted with a new, low-temperature cryostat ( 100 - 200 K) that also employs a vacuum. These experiments explore the dependence of frictional stability on the amplitude and frequency of the oscillating load. Additionally, small quantities of impurities that are thought to be important in icy satellites: sulfuric acid and ammonia (systems with deep eutectics with ice) are added to polycrystalline ice samples and tested at subsolidus conditions to discern when/if frictional heating can cause melting at icy satellite surface temperatures. The combination of the two types of experiments will provide valuable parameters for modeling of tidal response of planetary objects. Tidal response can potentially be measured during future missions, in which case characterization of its amplitude and phase could provide direct constraints on the internal and thermal structures of these bodies.

Analysis of the characteristics of slot design affecting resistance to sliding during active archwire configurations

PubMed Central

2013-01-01

Background During orthodontic treatment, a low resistance to slide (RS) is desirable when sliding mechanics are used. Many studies showed that several variables affect the RS at the bracket-wire interface; among these, the design of the bracket slot has not been deeply investigated yet. This study aimed to clarify the effect of different slot designs on the RS expressed by five types of low-friction brackets in vertical and horizontal active configurations of the wire. Methods Five low-friction brackets (Damon SL II, Ormco, Orange, CA, USA; In-Ovation, GAC International, Bohemia, NY, USA; Quick, Forestadent, Pforzheim, Germany; Time 2, AO, Sheboygan, WI, USA; Synergy, RMO, Denver, CO, USA) coupled with an 0.014-in NiTi thermal wire (Therma-Lite, AO) were tested in two three-bracket experimental models simulating vertical and horizontal bracket displacements. A custom-made machine was used to measure frictional resistance with tests repeated on ten occasions for each bracket-wire combination. Design characteristics such as the mesio-distal slot width, slot depth, and presence of chamfered edges at the extremities of the slot were evaluated on SEM images (SUPRA, Carl Zeiss, Oberkochen, Germany) and analyzed in relation to the data of RS recorded. Results Time 2 was found to show the higher frictional forces (1.50 and 1.35 N) in both experimental models (p < 0.05), while Quick and Synergy brackets showed the lower frictional values in the vertical (0.66 N) and in the horizontal (0.68 N) bracket displacements, respectively. With vertically displaced brackets, the increased mesio-distal slot width and the presence of clear angle at mesial and distal slot edges increase the values of RS. With brackets horizontally displaced, the RS expressed by the wire is influenced simultaneously by the depth of the slot, the mesio-distal slot width, and the presence of clear angle at the extremities of the slot base, the clip, or the slide. Conclusion In order to select the proper low-friction bracket system, clinicians should consider specific characteristics of slot design apart from the wire engaging method. PMID:24325837

Anelastic properties of (TaSe 4) 2I at low frequencies

NASA Astrophysics Data System (ADS)

Salva, H.; Ghilarducci, A.; Monceau, P.; Levy, F.; D'Anna, G.; Benoit, W.

1995-05-01

We have performed torsion measurements in (TaSe 4) 2I in the temperature range 110-290 K and 5.10 -3-10 Hz measuring frequency. We have always found a dip in modulus at the Peierls transition and that deformation of measurement gives additional response in modulus and internal friction spectra. These results are compared with existing models.

Frictions between Formal Education Policy and Actual School Choice: Case Studies in an International Comparative Perspective

ERIC Educational Resources Information Center

Teelken, Christine; Driessen, Geert; Smit, Frederik

2005-01-01

This contribution is based on comparative case studies of secondary schools in England, the Netherlands and Scotland. The authors conclude that although opportunities for school choice are offered in a formal sense in each of the locations studied, in certain cases choice is not particularly encouraged. In order to explain this disparity between…

Seven Experiment Designs Addressing Problems of Safety and Capacity on Two-Lane Rural Highways : Volume 7. Experimental Design to Develop and Evaluate Measures for Reducing the Effects of Roadside Friction on Traffic Flow

DOT National Transportation Integrated Search

1994-04-01

This operational test case study is one of six performed in response to a Volpe National Transportation Systems Center technical task directive (TTD) to Science Applications International Corporation (SAIC) entitled, "IVHS Institutional Issues and Ca...

Tribology and Friction of Soft Materials: Mississippi State Case Study

DTIC Science & Technology

2010-03-18

elastomers , foams, and fabrics. B. Develop internal state variable (ISV) material model. Model will be calibrated using database and verified...Rubbers Natural rubber Santoprene (Vulcanized Elastomer ) Styrene Butadiene Rubber (SBR) Foams Polypropylene Foam Polyurethane Foam Fabrics Kevlar...Axially symmetric model PC Disk PC Numerical Implementation in FEM Codes Experiment SEM Optical methods ISV Model Void Nucleation FEM Analysis

One-Dimensional Modelling of Internal Ballistics

NASA Astrophysics Data System (ADS)

Monreal-González, G.; Otón-Martínez, R. A.; Velasco, F. J. S.; García-Cascáles, J. R.; Ramírez-Fernández, F. J.

2017-10-01

A one-dimensional model is introduced in this paper for problems of internal ballistics involving solid propellant combustion. First, the work presents the physical approach and equations adopted. Closure relationships accounting for the physical phenomena taking place during combustion (interfacial friction, interfacial heat transfer, combustion) are deeply discussed. Secondly, the numerical method proposed is presented. Finally, numerical results provided by this code (UXGun) are compared with results of experimental tests and with the outcome from a well-known zero-dimensional code. The model provides successful results in firing tests of artillery guns, predicting with good accuracy the maximum pressure in the chamber and muzzle velocity what highlights its capabilities as prediction/design tool for internal ballistics.

Modeling of hybrid vehicle fuel economy and fuel engine efficiency

NASA Astrophysics Data System (ADS)

Wu, Wei

"Near-CV" (i.e., near-conventional vehicle) hybrid vehicles, with an internal combustion engine, and a supplementary storage with low-weight, low-energy but high-power capacity, are analyzed. This design avoids the shortcoming of the "near-EV" and the "dual-mode" hybrid vehicles that need a large energy storage system (in terms of energy capacity and weight). The small storage is used to optimize engine energy management and can provide power when needed. The energy advantage of the "near-CV" design is to reduce reliance on the engine at low power, to enable regenerative braking, and to provide good performance with a small engine. The fuel consumption of internal combustion engines, which might be applied to hybrid vehicles, is analyzed by building simple analytical models that reflect the engines' energy loss characteristics. Both diesel and gasoline engines are modeled. The simple analytical models describe engine fuel consumption at any speed and load point by describing the engine's indicated efficiency and friction. The engine's indicated efficiency and heat loss are described in terms of several easy-to-obtain engine parameters, e.g., compression ratio, displacement, bore and stroke. Engine friction is described in terms of parameters obtained by fitting available fuel measurements on several diesel and spark-ignition engines. The engine models developed are shown to conform closely to experimental fuel consumption and motored friction data. A model of the energy use of "near-CV" hybrid vehicles with different storage mechanism is created, based on simple algebraic description of the components. With powertrain downsizing and hybridization, a "near-CV" hybrid vehicle can obtain a factor of approximately two in overall fuel efficiency (mpg) improvement, without considering reductions in the vehicle load.

Effects of surface pressure and internal friction on the dynamics of shear-driven supported lipid bilayers.

PubMed

Jönsson, Peter; Höök, Fredrik

2011-02-15

Supported lipid bilayers (SLBs) are one of the most common model systems for cell membrane studies. We have previously found that when applying a bulk flow of liquid above an SLB the lipid bilayer and its constituents move in the direction of the bulk flow in a rolling type of motion, with the lower monolayer being essentially stationary. In this study, a theoretical platform is developed to model the dynamic behavior of a shear-driven SLB. In most regions of the moving SLB, the dynamics of the lipid bilayer is well explained by a balance between the hydrodynamic shear force arising from the bulk flow above the lipid bilayer and the friction between the upper and lower monolayers of the SLB. These two forces result in a drift velocity profile for the lipids in the upper monolayer of the SLB that is highest at the center of the channel and decreases to almost zero at the corners of the channel. However, near the front of an advancing SLB a very different flow behavior is observed, showing an almost constant drift velocity of the lipids over the entire bilayer front. In this region, the motion of the SLB is significantly influenced by gradients in the surface pressure as well as internal friction due to molecules that have accumulated at the front of the SLB. It is shown that even a modest surface fraction of accumulated molecules (∼1%) can drastically affect the behavior of the SLB near the bilayer front, forcing the advancing lipids in the SLB away from the center of the channel out toward the sides.

Characterization of physico-mechanical properties of Z-phase strengthened ferritic steels using internal friction measurements in the range 25 ÷ 750°C

NASA Astrophysics Data System (ADS)

Kutelia, E. R.; Dzigrashvili, T. A.; Kukava, T. G.; Darsavelidze, G. Sh.; Kurashvili, I. R.; Riedel, H.; Donth, B.

2017-02-01

The present research is dealing with the comparative study of inelastic/elastic behavior of reference ˜12%Cr steel ZL3 and three new trial steels ZU1, ZU2, ZU3, with different ratio of alloying elements and equal content of Cr, using internal friction measurements. The samples were examined in "as-received" condition and after additional electric current tempering at 700˚C under different fixed external mechanical tensions. The values of deformation critical amplitudes for dislocation breakaway (ɛ1) and for microplastic deformation beginning (ɛ2) were determined in addition to the activation energies of relaxation processes in the investigated steels. It is shown that all the three trial steel samples in "as-received" condition exhibit considerably higher values of ɛ2 in comparison to those of reference ZL3 steel. Among them the ZU3 steel has the highest values of ɛ1 and ɛ2, and demonstrates the visible (˜40%) increase in strength characteristics at elevated temperatures (600÷750˚C), achieved by the additional electric current tempering under mechanical tension.

Which ureteral access sheath is compatible with your flexible ureteroscope?

PubMed

Al-Qahtani, Saeed M; Letendre, Julien; Thomas, Alexandre; Natalin, Ricardo; Saussez, Thibaud; Traxer, Olivier

2014-03-01

Our aim is to evaluate different ureteral access sheaths (UASs), which are available in the international market and their compatibility with different available flexible ureteroscopes (F-URSs) to help the urologist choose the proper ureteral access sheath for his or her endoscope before commencing the procedure. A total of 21 UASs and 12 F-URSs were evaluated. Measurements were obtained in French (F) units considering different characteristics for each UAS and each F-URS. Insertion test without friction between F-URS and UAS was considered as a successful test and was referred as (YES). All UASs and F-URSs were successfully submitted to the insertion test. All F-URSs that were inserted into UASs without friction had an internal diameter of at least 12F. Different lengths of UAS did not influence the test outcome. This study was able to establish a correlation table between different UASs and different flexible ureteroscopes. As of now, the 12/14F UAS is considered the universal UAS that accepts all F-URSs that are available in the endourology field. Nevertheless, we are expecting a significant change with the new standard size 10/12F UAS as well as huge advances in minimizing the size of different endoscopes.

The Influence of SAND’s Gradation and Clay Content of Direct Sheart Test on Clayey Sand

NASA Astrophysics Data System (ADS)

Wibisono, Gunawan; Agus Nugroho, Soewignjo; Umam, Khairul

2018-03-01

The shear strength of clayey-sand can be affected by several factors, e.g. gradation, density, moisture content, and the percentage of clay and sand fraction. The same percentage of clay and sand fraction in clayey-sand mixtures may have different shear strengths due to those factors. This research aims to study the effect of clay content on sand that cause the change of its shear strength. Samples consisted of different clay and sand fractions were reconstituted at a certain moisture content. Sand fractions varied from well-graded to poorly-graded sand. Shear strength was measured in terms of the direct shear test. Prior to the test, surcharge loads were applied to represent overburden pressures. Shear strength results and their components (i.e. Cohesion and internal angle of friction) were correlated with physical properties of samples (i.e. grading coefficient of curvature, coefficient of uniformity, and density). Results showed that samples classified as well-graded and dense sand had higher shear strength. In the other hand, the shear strengths decreased when the mixtures became poorly-graded and less dense. The inclusion of the clay fraction increased cohesion component and decreased internal angle of friction.

Integrated Data Collection and Analysis Project: Friction Correlation Study

DTIC Science & Technology

2015-08-01

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

Enhancing pressure ulcer prevention using wound dressings: what are the modes of action?

PubMed

Call, Evan; Pedersen, Justin; Bill, Brian; Black, Joyce; Alves, Paulo; Brindle, C Tod; Dealey, Carol; Santamaria, Nick; Clark, Michael

2015-08-01

Recent clinical research has generated interest in the use of sacral wound dressings as preventive devices for patients at risk of ulceration. This study was conducted to identify the modes of action through which dressings can add to pressure ulcer prevention, for example, shear and friction force redistribution and pressure distribution. Bench testing was performed using nine commercially available dressings. The use of dressings can reduce the amplitude of shear stress and friction reaching the skin of patients at risk. They can also effectively redirect these forces to wider areas which minimises the mechanical loads upon skeletal prominences. Dressings can redistribute pressure based upon their effective Poisson ratio and larger deflection areas, providing greater load redistribution. © 2013 The Authors. International Wound Journal © 2013 Medicalhelplines.com Inc and John Wiley & Sons Ltd.

Test Validation of the Repair to the Space Station Solar Alpha Rotary Joint (SARJ)

NASA Technical Reports Server (NTRS)

Allmon, Curtis; Wilkinson, Will; Loewenthal, Stu

2010-01-01

The SARJ LITE (Lubrication Interval Test) test rig was built as a method to evaluate the performance of the grease repair on the Starboard SARJ of the International Space Station(ISS). The on-orbit SARJ was temporarily parked after receiving significant degradation on one of its race ring nitrided surfaces as a result of inadequate lubrication ( high dry contact friction) and unaccounted for roller traction kinematics. In a scaled down rig, flight like roller bearings were preloaded and cycled on a nitrided 15-5 race surface. Grease was added to the track and with instrumentation monitoring performance, trending data will be extracted and used to determine lubrication intervals for both Port and Starboard ISS SARJ's. The grease lubrication was found to be effective in eliminating the high friction that contributed to the on-orbit race degradation.

Fracture resistance of the implant-abutment connection in implants with internal hex and internal conical connections under oblique compressive loading: an in vitro study.

PubMed

Coppedê, Abílio Ricciardi; Bersani, Edmilson; de Mattos, Maria da Gloria Chiarello; Rodrigues, Renata Cristina Silveira; Sartori, Ivete Aparecida de Mattias; Ribeiro, Ricardo Faria

2009-01-01

The objective of this study was to verify if differences in the design of internal hex (IH) and internal conical (IC) connection implant systems influence fracture resistance under oblique compressive forces. Twenty implant-abutment assemblies were utilized: 10 with IH connections and 10 with IC connections. Maximum deformation force for IC implants (90.58 +/- 6.72 kgf) was statistically higher than that for IH implants (83.73 +/- 4.94 kgf) (P = .0182). Fracture force for the IH implants was 79.86 +/- 4.77 kgf. None of the IC implants fractured. The friction-locking mechanics and the solid design of the IC abutments provided greater resistance to deformation and fracture under oblique compressive loading when compared to the IH abutments.

Microphysically derived expressions for rate-and-state friction and fault stability parameters

NASA Astrophysics Data System (ADS)

Chen, Jianye; Niemeijer, Andre; Spiers, Christopher

2017-04-01

Rate-and-state friction (RSF) laws and associated parameters are extensively applied to fault mechanics, mainly on an empirical basis with a limited understanding of the underlying physical mechanisms. We recently established a general microphysical model [Chen and Spiers, 2016], for describing both steady-state and transient frictional behavior of any granular fault gouge material undergoing deformation by granular flow plus an arbitrary creep mechanism at grain contacts, such as pressure solution. We further showed that the model is able to reproduce typical experimental frictional results, namely "velocity stepping" and "slide-hold-slide" sequences, in satisfactory agreement with the main features and trends observed. Here, we extend our model, which we explored only numerically thus far, to obtain analytical solutions for the classical rate and state friction parameters from a purely microphysical modelling basis. By analytically solving the constitutive equations of the model under various boundary conditions, physically meaningful, theoretical expressions for the RSF parameters, i.e. a, b and Dc, are obtained. We also apply linear stability analysis to a spring-slider system, describing interface friction using our model, to yield analytical expressions of the critical stiffness (Kc) and critical recurrence wavelength (Wc) of the system. The values of a , b and Dc, as well as Kc and Wc, predicted by these expressions agree well with the numerical modeling results and acceptably with values obtained from experiments, on calcite for instance. Inserting the parameters obtained into classical RSF laws (slowness and slip laws) and conducting forward modelling gives simulated friction behavior that is fully consistent with the direct predictions of our numerically implemented model. Numerical tests with friction obeying our model show that the slip stability of fault motion exhibits a transition from stable sliding, via self-sustained oscillations, to stick slips with decreasing elastic stiffness, decreasing loading rate, and increasing normal stress, which is fully consistent with our linear stability analysis and also with previous RSF models that employed constant values of the RSF parameters. Importantly, our analytical expressions for. a, b, Dc, Kc and Wc, are functions of the internal microstructure of the fault (porosity, grain size and shear zone thickness), the material properties of the fault gouge (e.g. creep law parameters like activation energy, stress sensitivity, grain size sensitivity), and the ambient conditions the fault is subjected to (temperature and normal stress). The expressions obtained thus have clear physical meaning allowing a more meaningful extrapolation to natural conditions. On the basis of these physics-based expressions, seismological implications for slip on natural faults (e.g. subduction zone interfaces, faults in carbonate terrains) are discussed. Reference Chen, J., and C. J. Spiers (2016), Rate and state frictional and healing behavior of carbonate fault gouge explained using microphysical model, J. Geophys. Res., 121, doi:10.1002/2016JB013470.

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

PubMed

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 supposed to increase with a decreasing femoral head diameter. However, in the bearing couples with polyethylene liners manufactured by one company, paradoxically, the friction coefficient slightly increased with an increase in femoral head size from 28 mm to 36 mm. 4) The lowest friction moment (< 3.5 Nm) was found for ceramic-on-ceramic implants 28 mm in diameter; the highest values were recorded in metal-on-polyethylene bearing couples 36 mm in diameter (> 7 Nm). Although our study confirmed that the bearing couples produced by different manufacturers varied to some extent in the parameters studied, in our opinion, this variability was not significant because it was not within an order of magnitude in any of the tests. The study showed that both the friction coefficient and the friction moment are affected more by the combination of materials than by the diameter of a femoral head. The best results were achieved in ceramic-on-ceramic implants.

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

PubMed Central

Zhang, Dekun; Chen, Kai; Guo, Yongbo

2018-01-01

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

Evaluating Titan2D mass-flow model using the 1963 Little Tahoma Peak avalanches, Mount Rainier, Washington

NASA Astrophysics Data System (ADS)

Sheridan, M. F.; Stinton, A. J.; Patra, A.; Pitman, E. B.; Bauer, A.; Nichita, C. C.

2005-01-01

The Titan2D geophysical mass-flow model is evaluated by comparing its simulation results and those obtained from another flow model, FLOW3D, with published data on the 1963 Little Tahoma Peak avalanches on Mount Rainier, Washington. The avalanches, totaling approximately 10×10 6 m 3 of broken lava blocks and other debris, traveled 6.8 km horizontally and fell 1.8 km vertically ( H/ L=0.246). Velocities calculated from runup range from 24 to 42 m/s and may have been as high as 130 m/s while the avalanches passed over Emmons Glacier. Titan2D is a code for an incompressible Coulomb continuum; it is a depth-averaged, 'shallow-water', granular-flow model. The conservation equations for mass and momentum are solved with a Coulomb-type friction term at the basal interface. The governing equations are solved on multiple processors using a parallel, adaptive mesh, Godunov scheme. Adaptive gridding dynamically concentrates computing power in regions of special interest; mesh refinement and coarsening key on the perimeter of the moving avalanche. The model flow initiates as a pile defined as an ellipsoid by a height ( z) and an elliptical base defined by radii in the x and y planes. Flow parameters are the internal friction angle and bed friction angle. Results from the model are similar in terms of velocity history, lateral spreading, location of runup areas, and final distribution of the Little Tahoma Peak deposit. The avalanches passed over the Emmons Glacier along their upper flow paths, but lower in the valley they traversed stream gravels and glacial outwash deposits. This presents difficulty in assigning an appropriate bed friction angle for the entire deposit. Incorporation of variable bed friction angles into the model using GIS will help to resolve this issue.

Minimum work analysis on the critical taper accretionary wedges- insights from analogue modeling

NASA Astrophysics Data System (ADS)

Santimano, Tasca; Rosenau, Matthias; Oncken, Onno

2014-05-01

The Critical taper theory (CTT) is a fundamental concept for the understanding of mountain building processes. Based on force balance it predicts the preferred steady state geometry of an accretionary wedge system and its tectonic regime (extensive, compressive, stable). However, it does not specify which structures are formed and reactivated to reach the preferred state. The latter can be predicted by the minimum work concept. Here we test both concepts and their interplay by analysing two simple sand wedge models which differ only in the thickness of the basal detachment (a layer of glass beads). While the steady state critical taper is controlled by internal and basal friction coefficients and therefore the same in all experiments, different processes can minimise work by 1. reducing gravitational work e.g. by lowering the amount of uplift or volume uplifted, or 2. reducing frictional work e.g. by lowering the load or due to low friction coefficient along thrusts. Since a thick detachment allows entrainment of low friction material and therefore lowering of the friction along active thrusts, we speculate that the style of wedge growth will differ between the two models. We observe that the wedge with a thin basal detachment localizes strain at the toe of the wedge periodically and reactivate older faults to reach the critical topography. On the contrary, in the wedge with the thicker detachment layer, friction along thrusts is lowered due to the entrainment of low friction material from the detachment zone, subsequently increasing the lifetime of a thrust. Long thrust episodes are always followed by a fault of shorter lifetime, with the aim of reaching the critical taper. From the two experiments, we analyze the time-series evolution of the wedge to infer the work done by the two styles of deformation and predict the trend over time to differ but the maximum work to be similar Our observations show that the critical taper theory determines the geometry of the wedge in particular the taper angle. However the path and style of deformation that the wedge adopts i.e. strain partitioning or deformation along one fault, is determined by the energetically lowest pathway. The observation is especially evident in wedges with added complexities or random changes as the wedge matures. This study combines two theories to explain variability in the results of analogue models and perhaps may aid in understanding the complexity in natural wedges. It also delineates that two different mechanics of deformation can lead to the same geometrical wedge or final topography.

Study of Effect of Impacting Direction on Abrasive Nanometric Cutting Process with Molecular Dynamics

NASA Astrophysics Data System (ADS)

Li, Junye; Meng, Wenqing; Dong, Kun; Zhang, Xinming; Zhao, Weihong

2018-01-01

Abrasive flow polishing plays an important part in modern ultra-precision machining. Ultrafine particles suspended in the medium of abrasive flow removes the material in nanoscale. In this paper, three-dimensional molecular dynamics (MD) simulations are performed to investigate the effect of impacting direction on abrasive cutting process during abrasive flow polishing. The molecular dynamics simulation software Lammps was used to simulate the cutting of single crystal copper with SiC abrasive grains at different cutting angles (0o-45o). At a constant friction coefficient, we found a direct relation between cutting angle and cutting force, which ultimately increases the number of dislocation during abrasive flow machining. Our theoretical study reveal that a small cutting angle is beneficial for improving surface quality and reducing internal defects in the workpiece. However, there is no obvious relationship between cutting angle and friction coefficient.

Granular dynamics during impact.

PubMed

Nordstrom, K N; Lim, E; Harrington, M; Losert, W

2014-06-06

We study the impact of a projectile onto a bed of 3 mm grains immersed in an index-matched fluid. We vary the amount of prestrain on the sample, strengthening the force chains within the system. We find this affects only the prefactor of the linear depth-dependent term in the stopping force. We propose a simple model to account for the strain dependence of this term, owing to increased pressure in the pile. Interestingly, we find that the presence of the fluid does not affect the impact dynamics, suggesting that dynamic friction is not a factor. Using a laser sheet scanning technique to visualize internal grain motion, we measure the trajectory of each grain throughout an impact. Microscopically, our results indicate that weaker initial force chains result in more irreversible, plastic rearrangements, suggesting static friction between grains does play a substantial role in the energy dissipation.

Study of Effect of Impacting Direction on Abrasive Nanometric Cutting Process with Molecular Dynamics.

PubMed

Li, Junye; Meng, Wenqing; Dong, Kun; Zhang, Xinming; Zhao, Weihong

2018-01-11

Abrasive flow polishing plays an important part in modern ultra-precision machining. Ultrafine particles suspended in the medium of abrasive flow removes the material in nanoscale. In this paper, three-dimensional molecular dynamics (MD) simulations are performed to investigate the effect of impacting direction on abrasive cutting process during abrasive flow polishing. The molecular dynamics simulation software Lammps was used to simulate the cutting of single crystal copper with SiC abrasive grains at different cutting angles (0 o -45 o ). At a constant friction coefficient, we found a direct relation between cutting angle and cutting force, which ultimately increases the number of dislocation during abrasive flow machining. Our theoretical study reveal that a small cutting angle is beneficial for improving surface quality and reducing internal defects in the workpiece. However, there is no obvious relationship between cutting angle and friction coefficient.

Test Validation of the Repair to the Space Station Solar Alpha Rotary Joint

NASA Technical Reports Server (NTRS)

Allmon, Curtis; Wilkinson, Will; Loewenthal, Stu

2010-01-01

The Solar Array Alpha Joint Lubrication Interval Test (SARJ LITE) test rig was built as a method to evaluate the performance of the grease repair on the Starboard SARJ of the International Space Station (ISS) . The on-orbit SARJ was temporarily parked after receiving significant damage on one of its race ring surfaces as a result of inadequate lu brication (high dry contact friction) and unaccounted for roller traction kinematics. In a scaled down rig, flight-like roller bearings wer e preloaded and cycled on a nitrided 15-5 race surface. Grease was ad ded to the track and with instrumentation monitoring performance, trending data will be extracted and used to determine lubrication interva ls for both Port and Starboard ISS SARJ?s. The grease lubrication was found to be effective in eliminating the high friction that contributed to the onorbit race damage.

Wall shear stress measurements using a new transducer

NASA Technical Reports Server (NTRS)

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

1986-01-01

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

Rheology of three-dimensional packings of aggregates: microstructure and effects of nonconvexity.

PubMed

Azéma, Emilien; Radjaï, Farhang; Saint-Cyr, Baptiste; Delenne, Jean-Yves; Sornay, Philippe

2013-05-01

We use three-dimensional contact dynamics simulations to analyze the rheological properties of granular materials composed of rigid aggregates. The aggregates are made from four overlapping spheres and described by a nonconvexity parameter depending on the relative positions of the spheres. The macroscopic and microstructural properties of several sheared packings are analyzed as a function of the degree of nonconvexity of the aggregates. We find that the internal angle of friction increases with the nonconvexity. In contrast, the packing fraction first increases to a maximum value but declines as the nonconvexity increases further. At a high level of nonconvexity, the packings are looser but show a higher shear strength. At the microscopic scale, the fabric and force anisotropy, as well as the friction mobilization, are enhanced by multiple contacts between aggregates and interlocking, thus revealings the mechanical and geometrical origins of shear strength.

Reflection type skin friction meter

NASA Technical Reports Server (NTRS)

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

1993-01-01

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

Development of Novel Fe-Based Coating Systems for Internal Combustion Engines

NASA Astrophysics Data System (ADS)

Bobzin, K.; Öte, M.; Königstein, T.; Dröder, K.; Hoffmeister, H.-W.; Mahlfeld, G.; Schläfer, T.

2018-04-01

Nowadays, combustion engines are the most common way to power vehicles. Thereby, losses occur due to cooling, exhaust gas and friction. With regard to frictional losses, highest potentials for optimization can be found in the tribological system of the inner surface of combustion chamber and piston ring. Besides friction, corrosive stress increases, e.g., due to utilization of exhaust gas recovery. In order to save energy, reduce emissions and enhance the life span of combustion engines, the demand for innovative coating material systems, especially for the inner surface of combustion chamber, increases. This study focuses on the development of innovative iron-based coating materials for the combustion chamber. As a first step, the plasma transferred wire arc and rotating single wire arc (RSW) technologies were compared using 0.8% C-steel as a reference. Subsequently, RSW was used for coating deposition using an innovative iron-based feedstock material. In order to improve wear and corrosion resistance, boron and chromium were added to the feedstock material. After deposition, different honing topographies were manufactured and compared under tribological load. Furthermore, electrochemical corrosion tests were conducted using an electrolyte simulating the exhaust gas concentrate. Especially with regard to corrosion, the novel coating system FeCrBMn showed promising results.

Skin friction measurements of systematically-varied roughness: Probing the role of roughness amplitude and skewness

NASA Astrophysics Data System (ADS)

Barros, Julio; Flack, Karen; Schultz, Michael

2017-11-01

Real-world engineering systems which feature either external or internal wall-bounded turbulent flow are routinely affected by surface roughness. This gives rise to performance degradation in the form of increased drag or head loss. However, at present there is no reliable means to predict these performance losses based upon the roughness topography alone. This work takes a systematic approach by generating random surface roughness in which the surface statistics are closely controlled. Skin friction and roughness function results will be presented for two groups of these rough surfaces. The first group is Gaussian (i.e. zero skewness) in which the root-mean-square roughness height (krms) is varied. The second group has a fixed krms, and the skewness is varied from approximately -1 to +1. The effect of the roughness amplitude and skewness on the skin friction will be discussed. Particular attention will be paid to the effect of these parameters on the roughness function in the transitionally-rough flow regime. For example, the role these parameters play in the monotonic or inflectional nature of the roughness function will be addressed. Future research into the details of the turbulence structure over these rough surfaces will also be outlined. Research funded by U.S. Office of Naval Research (ONR).

Internal and external atomic steps in graphite exhibit dramatically different physical and chemical properties.

PubMed

Lee, Hyunsoo; Lee, Han-Bo-Ram; Kwon, Sangku; Salmeron, Miquel; Park, Jeong Young

2015-04-28

We report on the physical and chemical properties of atomic steps on the surface of highly oriented pyrolytic graphite (HOPG) investigated using atomic force microscopy. Two types of step edges are identified: internal (formed during crystal growth) and external (formed by mechanical cleavage of bulk HOPG). The external steps exhibit higher friction than the internal steps due to the broken bonds of the exposed edge C atoms, while carbon atoms in the internal steps are not exposed. The reactivity of the atomic steps is manifested in a variety of ways, including the preferential attachment of Pt nanoparticles deposited on HOPG when using atomic layer deposition and KOH clusters formed during drop casting from aqueous solutions. These phenomena imply that only external atomic steps can be used for selective electrodeposition for nanoscale electronic devices.

Probable Rotation States of Rocket Bodies in Low Earth Orbit

NASA Astrophysics Data System (ADS)

Ojakangas, G.; Anz-Meador, P.; Cowardin, H.

2012-09-01

In order for Active Debris Removal to be accomplished, it is critically important to understand the probable rotation states of orbiting, spent rocket bodies (RBs). However, rotational dynamics is non-intuitive and misconceptions are common. Determinations of rotation and precession rates from light curves have been published that are inconsistent with the theory presented here. In a state of free precession, the total angular momentum of the object is constant, while kinetic energy decreases due to internal friction, approaching rotation about the axis of maximum inertia. For solid internal friction the timescale is hundreds to thousands of years for quality factors of ~100 and assuming metallic rigidities, but for friction in partially-filled liquid fuel tanks we predict that the preferred rotational state is approached rapidly, within days to months. However, history has shown that theoretical predictions of the timescale have been notoriously inaccurate. In free precession, the 3-1-3 Euler angle rates dphi/dt (precession rate of long axis about fixed angular momentum with cone angle theta) and dpsi/dt (roll rate around long axis) have comparable magnitudes until very close to theta=pi/2, so that otherwise the true rotation period is not simply twice the primary light curve period. Furthermore dtheta/dt, nonzero due to friction, becomes asymptotically smaller as theta=pi/2 is approached, so that theta can linger within several degrees of flat spin for a relatively long time. Such a condition is likely common, and cannot be distinguished from the wobble of a cylinder with a skewed inertia tensor unless the RB has non-axisymmetric reflectivity characteristics. For an RB of known dimensions, a given value of theta fixes the relative values of dpsi/dt and dphi/dt. In forced precession, the angular momentum precesses about a symmetry axis defined by the relevant torque. However, in LEO, only gravity gradient and magnetic eddy current torques are dominant, and these cannot cause precession periods shorter than a week, or more likely, months. Thus forced precession is probably not observable over observation campaigns spanning a few days or less. Spin-orbit resonances are likely for low rotation rates approaching the mean motion, possibly causing large deviations between the symmetry axis and the geocentric direction. An expression for the eddy current torque on an arbitrarily rotating cylinder, hitherto not available in the literature, is presented here. Numerical integrations of the equations of motion for a cylindrical RB in LEO with arbitrary initial conditions and subject to eddy current and gravity gradient torques as well as prescribed internal dissipation are in progress. Acknowledgements: This work was produced under NASA contract NNJ05HI05.

Acquisition and Retaining Granular Samples via a Rotating Coring Bit

NASA Technical Reports Server (NTRS)

Bar-Cohen, Yoseph; Badescu, Mircea; Sherrit, Stewart

2013-01-01

This device takes advantage of the centrifugal forces that are generated when a coring bit is rotated, and a granular sample is entered into the bit while it is spinning, making it adhere to the internal wall of the bit, where it compacts itself into the wall of the bit. The bit can be specially designed to increase the effectiveness of regolith capturing while turning and penetrating the subsurface. The bit teeth can be oriented such that they direct the regolith toward the bit axis during the rotation of the bit. The bit can be designed with an internal flute that directs the regolith upward inside the bit. The use of both the teeth and flute can be implemented in the same bit. The bit can also be designed with an internal spiral into which the various particles wedge. In another implementation, the bit can be designed to collect regolith primarily from a specific depth. For that implementation, the bit can be designed such that when turning one way, the teeth guide the regolith outward of the bit and when turning in the opposite direction, the teeth will guide the regolith inward into the bit internal section. This mechanism can be implemented with or without an internal flute. The device is based on the use of a spinning coring bit (hollow interior) as a means of retaining granular sample, and the acquisition is done by inserting the bit into the subsurface of a regolith, soil, or powder. To demonstrate the concept, a commercial drill and a coring bit were used. The bit was turned and inserted into the soil that was contained in a bucket. While spinning the bit (at speeds of 600 to 700 RPM), the drill was lifted and the soil was retained inside the bit. To prove this point, the drill was turned horizontally, and the acquired soil was still inside the bit. The basic theory behind the process of retaining unconsolidated mass that can be acquired by the centrifugal forces of the bit is determined by noting that in order to stay inside the interior of the bit, the frictional force must be greater than the weight of the sample. The bit can be designed with an internal sleeve to serve as a container for granular samples. This tube-shaped component can be extracted upon completion of the sampling, and the bottom can be capped by placing the bit onto a corklike component. Then, upon removal of the internal tube, the top section can be sealed. The novel features of this device are: center dot A mechanism of acquiring and retaining granular samples using a coring bit without a closed door. center dot An acquisition bit that has internal structure such as a waffle pattern for compartmentalizing or helical internal flute to propel the sample inside the bit and help in acquiring and retaining granular samples. center dot A bit with an internal spiral into which the various particles wedge. center dot A design that provides a method of testing frictional properties of the granular samples and potentially segregating particles based on size and density. A controlled acceleration or deceleration may be used to drop the least-frictional particles or to eventually shear the unconsolidated material near the bit center.

Constitutive equation of friction based on the subloading-surface concept

PubMed Central

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

2016-01-01

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

The "soil" of Mars (viking 1).

PubMed

Shorthill, R W; Moore, H J; Scott, R F; Hutton, R E; Liebes, S; Spitzer, C R

1976-10-01

The location of the Viking 1 lander is most ideal for the study of soil properties because it has one footpad in soft material and one on hard material. As each soil sample was acquired, information on soil properties was obtained. Although analysis is still under way, early results on bulk density, particle size, angle of internal friction, cohesion, adhesion, and penetration resistance of the soil of Mars are presented.

Duke of Wellington’s Command of the Spanish Army in the Peninsular War

DTIC Science & Technology

2017-06-09

SUBJECT TERMS Peninsular War, Spanish Army, Command Structure , International Friction 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT...Horse Guards and the Secretary for War and the Colonies, poorly trained and equipped partner armies, the difficulty in creating a unity of command...armies of three nations in the Peninsula. Wellington accepted the daunting challenge of unifying disparate command structures of Spain and Britain

The "Soil" of mars (viking 1)

USGS Publications Warehouse

Shorthill, R.W.; Moore, H.J.; Scott, R.F.; Hutton, R.E.; Liebes, S.; Spitzer, G.R.

1976-01-01

The location of the Viking 1 lander is most ideal for the study of soil properties because it has one footpad in soft material and one on hard material. As each soil sample was acquired, information on soil properties was obtained. Although analysis is still under way, early results on bulk density, particle size, angle of internal friction, cohesion, adhesion, and penetration resistance of the soil of Mars are presented.

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

NASA Astrophysics Data System (ADS)

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.

Escaping the Ashby limit for mechanical damping/stiffness trade-off using a constrained high internal friction interfacial layer.

PubMed

Unwin, A P; Hine, P J; Ward, I M; Fujita, M; Tanaka, E; Gusev, A A

2018-02-06

The development of new materials with reduced noise and vibration levels is an active area of research due to concerns in various aspects of environmental noise pollution and its effects on health. Excessive vibrations also reduce the service live of the structures and limit the fields of their utilization. In oscillations, the viscoelastic moduli of a material are complex and it is their loss part - the product of the stiffness part and loss tangent - that is commonly viewed as a figure of merit in noise and vibration damping applications. The stiffness modulus and loss tangent are usually mutually exclusive properties so it is a technological challenge to develop materials that simultaneously combine high stiffness and high loss. Here we achieve this rare balance of properties by filling a solid polymer matrix with rigid inorganic spheres coated by a sub-micron layer of a viscoelastic material with a high level of internal friction. We demonstrate that this combination can be experimentally realised and that the analytically predicted behaviour is closely reproduced, thereby escaping the often termed 'Ashby' limit for mechanical stiffness/damping trade-off and offering a new route for manufacturing advanced composite structures with markedly reduced noise and vibration levels.

Behaviour of Cohesionless Soil Reinforced with Three Dimensional Inclusions Under Plane Strain Conditions

NASA Astrophysics Data System (ADS)

Harikumar, M.; Sankar, N.; Chandrakaran, S.

2015-09-01

Since 1969, when the concept of earth reinforcing was brought about by Henry Vidal, a large variety of materials such as steel bars, tire shreds, polypropylene, polyester, glass fibres, coir and jute fibres etc. have been widely added to soil mass randomly or in a regular, oriented manner. The conventional reinforcements in use were two dimensional or planar, in the form of strips with negligible widths or in the form of sheets. In this investigation, a novel concept of multi oriented plastic reinforcement (hexa-pods) is discussed. Direct shear tests were conducted on unreinforced and reinforced dry fine, medium and coarse sands. Detailed parametric studies with respect to the effective grain size of soil (d10), normal stress (σ) and the volume ratio of hexa-pods (Vr) were performed. It was noticed that addition of hexa-pods resulted in increase in the shear strength parameters viz. peak deviatoric stresses and increased angle of internal friction. The hexa-pods also changed the brittle behaviour of unreinforced sand samples to ductile ones. Although the peak shear stress did not show a considerable improvement, the angle of internal friction improved noticeably. Addition of a single layer of reinforcement along the shear plane also reduced the post peak loss of strength and changed the soil behavior from brittle to a ductile one.

Internal friction quality-factor Q under confining pressure. [of lunar rocks

NASA Technical Reports Server (NTRS)

Tittmann, B. R.; Ahlberg, L.; Nadler, H.; Curnow, J.; Smith, T.; Cohen, E. R.

1977-01-01

It has been found in previous studies that small amounts of adsorbed volatiles can have a profound effect on the internal friction quality-factor Q of rocks and other porous media. Pandit and Tozer (1970) have suggested that the laboratory-measured Q of volatile-free rocks should be similar to the in situ seismic Q values of near-surface lunar rocks which according to Latham et al. (1970) are in the range of 3000-5000. Observations of dramatic increases in Q with outgassing up to values approaching 2000 in the seismic frequency range confirm this supposition. Measurements under confining pressures with the sample encapsulated under hard vacuum are reported to aid in the interpretation of seismic data obtained below the lunar surface. It has been possible to achieve in the experiments Q values just under 2000 at about 1 kbar for a terrestrial analog of lunar basalt. It was found that a well-outgassed sample maintains a high Q whereas one exposed to moisture maintains a low Q as the confining pressure is raised to 2.5 kbar. This result suggests that volatiles can indeed affect Q when cracks are partially closed and the high lunar seismic Q values reported are concomitant with very dry rock down to depths of at least 50 km.

Geotechnical properties of ash deposits near Hilo, Hawaii

USGS Publications Warehouse

Wieczorek, G.F.; Jibson, R.W.; Wilson, R.C.; Buchanan-Banks, J. M.

1982-01-01

Two holes were hand augered and sampled in ash deposits near Hilo, Hawaii. Color, water content and sensitivity of the ash were measured in the field. The ash alternated between reddish brown and dark reddish brown in color and had water contents as high as 392%. A downhole vane shear device measured sensitivities as high as 6.9. A series of laboratory tests including grain size distribution, Atterberg limits, X-ray diffraction analysis, total carbon determination, vane shear, direct shear and triaxial tests were performed to determine the composition and geotechnical properties of the ash. The ash is very fine grained, highly plastic and composed mostly of gibbsite and amorphous material presumably allophane. The ash has a high angle of internal friction ranging from 40-43? and is classified as medium to very sensitive. A series of different ash layers was distinguished on the basis of plasticity and other geotechnical properties. Sensitivity may be due to a metastable fabric, cementation, leaching, high organic content, and thixotropy. The sensitivity of the volcanic ash deposits near Hilo is consistent with documented slope instability during earthquakes in Hawaii. The high angles of internal friction and cementation permit very steep slopes under static conditions. However, because of high sensitivity of the ash, these slopes are particularly susceptible to seismically-induced landsliding.

On Critical States, Rupture States and Interlocking Strength of Granular Materials.

PubMed

Szalwinski, Chris M

2017-07-27

The Mohr-Coulomb theory of strength identifies cohesion and internal friction as the two principal contributions to the shear strength of a granular material. The contribution of cohesion in over-compacted granular materials has been challenged and replacing cohesion with interlocking has been proposed. A theory of rupture strength that includes interlocking is derived herein. The physics-chemistry concept of critical state is elaborated to accommodate granular materials, based on empirical definitions established in the fields of soil mechanics and bulk solids' flow. A surface in state space, called the critical compaction surface, separates over-compacted states from lightly compacted states. The intersection of this surface with the Mohr-Coulomb envelope forms the critical state surface for a granular material. The rupture strength of an over-compacted granular material is expressed as the sum of cohesion, internal friction and interlocking strength. Interlocking strength is the shear strength contribution due to over-compaction and vanishes at critical state. The theory allows migrations from one critical state to another. Changes in specific volume during such migrations are related to changes in mean-normal effective stress and uncoupled from changes in shearing strain. The theory is reviewed with respect to two established research programs and underlying assumptions are identified.

Frequency-dependent solvent friction and torsional damping in liquid 1,2-difluoroethane

NASA Astrophysics Data System (ADS)

MacPhail, Richard A.; Monroe, Frances C.

1991-04-01

We have used Raman spectroscopy to study the torsional dynamics, rotational dynamics, and conformational solvation energy of liquid 1,2-difluoroethane. From the Raman intensities, we obtain Δ H(g-t) = -2.4±0.1 kcal/mol, indicating strong dipolar solvation of the gauche conformer. We analyze the Raman linewidths of the CCF bending bands to obtain the zero-frequency torsional damping coefficient or well friction for the gauche conformer, and from the linewidth of the torsion band we obtain the friction evaluated at the torsional frequency. The zero-frequency well friction shows deviations from hydrodynamic behavior reminiscent of those observed for barrier friction, whereas the high-frequency friction is considerably smaller in magnitude and independent of temperature and viscosity. The zero-frequency torsional friction correlates linearly with the rotational friction. It is argued that the small amplitude of the torsional fluctuations emphasizes the short distance, or high wavevector components of the solvent friction. Dielectric friction apparently does not contribute to the torsional friction at the observed frequencies.

The effect of friction in coulombian damper

NASA Astrophysics Data System (ADS)

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

2017-02-01

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

Bioinspired orientation-dependent friction.

PubMed

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

2014-09-23

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

Mapping of power consumption and friction reduction in piezoelectrically-assisted ultrasonic lubrication

NASA Astrophysics Data System (ADS)

Dong, Sheng; Dapino, Marcelo J.

2015-04-01

Ultrasonic lubrication has been proven effective in reducing dynamic friction. This paper investigates the relationship between friction reduction, power consumption, linear velocity, and normal stress. A modified pin-on-disc tribometer was adopted as the experimental set-up, and a Labview system was utilized for signal generation and data acquisition. Friction reduction was quantified for 0.21 to 5.31 W of electric power, 50 to 200 mm/s of linear velocity, and 23 to 70 MPa of normal stress. Friction reduction near 100% can be achieved under certain conditions. Lower linear velocity and higher electric power result in greater friction reduction, while normal stress has little effect on friction reduction. Contour plots of friction reduction, power consumption, linear velocity, and normal stress were created. An efficiency coefficient was proposed to calculate power requirements for a certain friction reduction or reduced friction for a given electric power.

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

NASA Astrophysics Data System (ADS)

Liu, Xiaogang; Meehan, Paul A.

2016-06-01

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

Chemical origins of frictional aging.

PubMed

Liu, Yun; Szlufarska, Izabela

2012-11-02

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

Fifty Years of Boundary-Layer Theory and Experiment

NASA Technical Reports Server (NTRS)

Dryden, Hugh L.

1955-01-01

The year 1954 marked the 50th anniversary of the Prandtl boundary-layer theory from which we may date the beginning of man's understanding of the dynamics of real fluids. A backward look at this aspect of the history of the last 50 years may be instructive. This paper (1) attempts to compress the events of those 50 years into a few thousand words, to tell in this brief space the interesting story of the development of a new concept, its slow acceptance and growth, its spread from group to group within its country of origin, and its diffusion to other countries of the world. The original brief paper of Prandtl (2) was presented at the Third International Mathematical Congress at Heidelberg in 1904 and published in the following year. It was an attempt to explain the d'Alembert paradox, namely, that the neglect of the small friction of air in the theory resulted in the prediction of zero resistance to motion. Prandtl set himself the task of computing the motion of a fluid of small friction, so small that its effect could be neglected everywhere except where large velocity differences were present or a cumulative effect of friction occurred This led to the concept of boundary layer, or transition layer, near the wall of a body immersed in a fluid stream in which the velocity rises from zero to the free-stream value. It is interesting that Prandtl used the term Grenzsehicht (boundary layer) only once and the term Ubergangsschicht (transition layer) seven times in the brief article. Later writers also used Reibungsschicht (friction layer), but most writers today use Grenzschicht (boundary layer).

Installation and testing of a cummins Qsk19 lean burn natural gas engine

NASA Astrophysics Data System (ADS)

Sutley, Franklin H.

The goal for a more efficient engine will never disappear. Over the years many different techniques have been explored within the common goal of higher efficiency. Lean combustion has proven to be effective at increasing efficiencies as well as reducing emissions. The purpose of this thesis is to install a modern Cummins QSK19G and perform certain test that will explore the lean combustion limits and other methods that could possibly increase efficiency even more. The entire installation and instrumentation process is documented within this thesis. The engine was installed in the Engines and Energy Conversion Laboratory at Colorado State University. The engine was installed with the hopes of instilling the desire for endless future tests from Cummins as well as other companies seeking this type of research engine. The lean limit was explored in the most detail. Cummins supplied a test plan that satisfied their desired stopping at a lean limit when the coefficient of variance of indicated mean effective pressure reached 5%. For the curiosity of others involved and this thesis, the lean limit was explored further until the engine could no longer ignite the ultra-lean combustion mixture. Friction accounts for a significant loss in a modern internal combustion engine. One role of the engine oil is to reduce these frictional losses as much as possible without causing increased wear. A test was conducted on the QSK19G to explore the effects of varying the engine oil viscosity. Frictional losses of two different viscosity oils were compared to the stock engine oil losses. The fact that reducing oil viscosity reduces frictional losses was proven in the test.

Detection and assessment of flaws in friction stir welded joints using ultrasonic guided waves: experimental and finite element analysis

NASA Astrophysics Data System (ADS)

Fakih, Mohammad Ali; Mustapha, Samir; Tarraf, Jaafar; Ayoub, Georges; Hamade, Ramsey

2018-02-01

Ultrasonic guided waves (GWs), e.g. Lamb waves, have been proven effective in the detection of defects such as corrosion, cracking, delamination, and debonding in both composite and metallic structures. They are a significant tool employed in structural health monitoring. In this study, the ability of ultrasonic GWs to assess the quality of friction stir welding (FSW) was investigated. Four friction stir welded AZ31B magnesium plates processed with different welding parameters and a non-welded plate were used. The fundamental symmetric (S0) Lamb wave mode was excited using piezoelectric wafers (PZTs). Further, the S0 mode was separated using the "Improved complete ensemble empirical mode decomposition with adaptive noise (Improved CEEMDAN)" technique. A damage index (DI) was defined based on the variation in the amplitude of the captured wave signals in order to detect the presence and asses the severity of damage resulting from the welding process. As well, computed tomography (CT) scanning was used as a non-destructive testing (NDT) technique to assess the actual weld quality and validate predictions based on the GW approach. The findings were further confirmed using finite element analysis (FEA). To model the actual damage profile in the welds, "Mimics" software was used for the 3D reconstruction of the CT scans. The built 3D models were later used for evaluation of damage volume and for FEA. The damage volumes were correlated to the damage indices computed from both experimental and numerical data. The proposed approach showed high sensitivity of the S0 mode to internal flaws within the friction stir welded joints. This methodology has great potential as a future classification method of FSW quality.

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

NASA Astrophysics Data System (ADS)

Chen, Tianhua

2018-03-01

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

The use of surface layer with boron in friction pairs lubricated by engine oils

NASA Astrophysics Data System (ADS)

Szczypiński-Sala, W.; Lubas, J.

2016-09-01

The aim of the present work is to determine the influence of surface layers with boron and engine oil on the processes of friction and wear in friction pairs. The ring samples with borided surface layer cooperated under test conditions with counterparts made with CuPb30 and AlSn20 bearing alloys. During the tests, the friction pairs were lubricated with 15W/40 Lotos mineral oil and 5W/40 Lotos synthetic oil. The lubrication of friction area with Lotos mineral oil causes the reduction of the friction force, the temperature in the friction area and the wear of the bearing alloys under study, whereas the lubrication with Lotos synthetic oil reduces the changes in the geometrical structure of the cooperating friction pair elements. Lubrication of the friction area in the start-up phase of the friction pair by mineral oil causes faster stabilization of the friction conditions in the contact area than in the cause of lubrication of the friction pair by synthetic oil. The intensity of wear of the AlSn20 bearing alloy cooperating with the borided surface layer is three times smaller than the intensity of use of the CuPb30 alloy bearing.

Prediction and validation of the energy dissipation of a friction damper

NASA Astrophysics Data System (ADS)

Lopez, I.; Nijmeijer, H.

2009-12-01

Friction dampers can be a cheap and efficient way to reduce the vibration levels of a wide range of mechanical systems. In the present work it is shown that the maximum energy dissipation and corresponding optimum friction force of friction dampers with stiff localized contacts and large relative displacements within the contact, can be determined with sufficient accuracy using a dry (Coulomb) friction model. Both the numerical calculations with more complex friction models and the experimental results in a laboratory test set-up show that these two quantities are relatively robust properties of a system with friction. The numerical calculations are performed with several friction models currently used in the literature. For the stick phase smooth approximations like viscous damping or the arctan function are considered but also the non-smooth switch friction model is used. For the slip phase several models of the Stribeck effect are used. The test set-up for the laboratory experiments consists of a mass sliding on parallel ball-bearings, where additional friction is created by a sledge attached to the mass, which is pre-stressed against a friction plate. The measured energy dissipation is in good agreement with the theoretical results for Coulomb friction.

Influence of the pressure dependent coefficient of friction on deep drawing springback predictions

NASA Astrophysics Data System (ADS)

Gil, Imanol; Galdos, Lander; Mendiguren, Joseba; Mugarra, Endika; Sáenz de Argandoña, Eneko

2016-10-01

This research studies the effect of considering an advanced variable friction coefficient on the springback prediction of stamping processes. Traditional constant coefficient of friction considerations are being replaced by more advanced friction coefficient definitions. The aim of this work is to show the influence of defining a pressure dependent friction coefficient on numerical springback predictions of a DX54D mild steel, a HSLA380 and a DP780 high strength steel. The pressure dependent friction model of each material was fitted to the experimental data obtained by Strip Drawing tests. Then, these friction models were implemented in a numerical simulation of a drawing process of an industrial automotive part. The results showed important differences between defining a pressure dependent friction coefficient or a constant friction coefficient.

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

NASA Astrophysics Data System (ADS)

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

2011-12-01

Debris flows are complex natural phenomena, characterized by a mixture of poorly sorted sediments and water driven by gravity. Depending on the size distribution, on the volume concentration of sediments and on the geometry and topography of the channel, flow conditions may be very different, ranging from very fast flows, dominated by granular collisions and by the turbulence on the liquid phase, to very slow and dense flows, dominated by the frictional contacts among the grains. To investigate the basic physics of debris flows, it is very useful to analyze the flow of a mixture of identical spherical particles saturated by water and driven by gravity down a steep channel in steady flow condition (Armanini et al. 2005). The flow presents three regions: an external one, near to the free surface, dominated by nearly instantaneous contacts among the particles (collisional regime), an internal region dominated by prolonged contacts among the particles (frictional regime) and a static bed in which the particles are immobile. The detailed vertical structure of this kind of flows was obtained by means of experiments carried out by Armanini et al. (2005) and Larcher et al. (2007). Armanini et al. (2009) analysed the stratification of rheological mechanisms inside the flow, focusing on the coexistence of frictional and collisional regimes, on the stress transmission inside the flow and on particles kinematics. In particular, it was observed that debris flows may show locally a typical intermittence of the flow regime, switching alternatively from frictional to collisional. While the rheology of the collisional layers is well described by the dense gas analogy (kinetic theory), a persuasive theoretical description of the frictional regime does not yet exist. A Coulombian scheme is often assumed, but this hypothesis is rather limitative because it requires a constant concentration or a distribution of particles concentration known a priori. An interesting scheme of this kind was recently proposed by GDR-Midi (2004), but this model does not contain a suitable formulation for the granular pressure (equation of state of the mixture). Following Armanini (2010), we propose a reinterpretation of the model, as weighted average of a pure Coulombian stress (dependent on the static friction angle at the static bed level) and of a dynamic stress, represented by a dynamic friction angle. Besides, a state relation is introduced for the granular pressure and the dynamic friction angle is derived from the kinetic theory. The proposed relations are finally successfully compared with the experimental data introduced above. REFERENCES A. Armanini, H. Capart, L. Fraccarollo, M. Larcher, 2005, J.F.M., 532, 269-319. A. Armanini, M. Larcher, L. Fraccarollo, Ph. Rev. E, 2009, 79, 051306. A. Armanini, 2010, Palermo, Proc. XXXII Conv. Naz. di Idr. e C.I. (in Italian) GDR MiDi, 2004. Eur. Phys. J. E, 14, 341-365 M. Larcher, L. Fraccarollo, A. Armanini, H. Capart, 2007, Journal Hydr. Res., 45, 59-71.

Toward Realistic Dynamics of Rotating Orbital Debris, and Implications for Lightcurve Interpretation

NASA Technical Reports Server (NTRS)

Ojakangas, Gregory W.; Cowardin, H.; Hill, N.

2011-01-01

Optical observations of rotating space debris near GEO contain important information on size, shape, composition, and rotational states, but these aspects are difficult to extract due to data limitations and the high number of degrees of freedom in the modeling process. For tri-axial rigid debris objects created by satellite fragmentations, the most likely initial rotation state has a large component of initial angular velocity directed along the intermediate axis of inertia, leading to large angular reorientations of the body on the timescale of the rotation period. This lends some support to the simplest possible interpretation of light curves -- that they represent sets of random orientations of the objects of study. However, effects of internal friction and solar radiation are likely to cause significant modification of rotation states within a time as short as a few orbital periods. In order to examine the rotational dynamics of debris objects under the influences of these effects, a set of seven first-order coupled equations of motion were assembled in state form: three are Euler equations describing the rates of change of the components of angular velocity in the body frame, and four describe the rates of change of the components of the unit quaternion. Quaternions are a four-dimensional extension of complex numbers that form a seamless, singularity-free representation of body orientation on S3. The Euler equations contain explicit terms describing torque from solar radiation in terms of spherical harmonics, and terms representing effects of a prescribed rate of internal friction. Numerical integrations of these equations of motion are being performed, and results will be presented. Initial tests show that internal friction without solar radiation torque leads to rotation about the maximum principal axis of inertia, as required, and solar radiation torque is expected to lead to spin-up of objects. Because the axis of maximum rotational inertia tends to be roughly coincident with the normal to the largest projected cross-sectional area, internal friction is expected to lead to reduced variation of light curve amplitudes at a given phase angle, but a large dependence of the same on phase angle. At a given phase angle, databases are generated which contain reflected intensities for comprehensive sets of equally-likely orientations, represented as unit quaternions. When projected onto three dimensions (S2) and color-coded by intensity, the set is depicted as points within a solid, semi-transparent unit sphere, within which all possible reflected intensities for an object at a given phase angle may be inspected simultaneously. Rotational sequences are represented by trajectories through the sphere. Databases are generated for each of a set of phase angles separately, forming a comprehensive dataset of reflected intensities spanning all object orientations and solar phase angles. Symmetries in the problem suggest that preferred rotation states are likely, defined relative to the object-sun direction in inertial space and relative to the maximum principal axis of inertia in the body coordinate system. Such rotation states may greatly simplify the problem of light curve interpretation by reducing the number of degrees of freedom in the problem.

40 CFR 63.9565 - What definitions apply to this subpart?

Code of Federal Regulations, 2010 CFR

2010-07-01

.... Friction materials manufacturing facility means a facility that manufactures friction materials using a... (CONTINUED) National Emission Standards for Hazardous Air Pollutants for Friction Materials Manufacturing... components used in the manufacture of friction materials, excluding the HAP solvent. Friction ingredients...

Micromachine friction test apparatus

DOEpatents

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

2002-01-01

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

Nano-Sized Grain Refinement Using Friction Stir Processing

DTIC Science & Technology

2013-03-01

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

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

PubMed

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

2011-11-30

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

Tribo-performance evaluation of ecofriendly brake friction composite materials

NASA Astrophysics Data System (ADS)

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

2018-05-01

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

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

NASA Astrophysics Data System (ADS)

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

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

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

PubMed Central

Kim, Kyungmok; Lee, Jaewook

2016-01-01

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

Chirality-dependent friction of bulk molecular solids.

PubMed

Yang, Dian; Cohen, Adam E

2014-08-26

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

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

NASA Technical Reports Server (NTRS)

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

1988-01-01

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

Nonlinear friction dynamics on polymer surface under accelerated movement

NASA Astrophysics Data System (ADS)

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

2017-04-01

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

Autovibration and chaotic motion of an unbalanced rotor in massive non-linear compliant supports

NASA Astrophysics Data System (ADS)

Pasynkova, I. A.; Stepanova, P. P.

2018-05-01

Stability loss scenarios of an unbalanced rotor with a flexible massless shaft mounted in massive non-linear compliant supports are studied on the example of cylindrical precession. Dyffing type of non-linearity in compliant supports is considered. The system "rotor - supports" has eight degrees of freedom. Internal and external friction are taken into account. Autovibrations and chaotic vibrations are obtained. The results are confirmed by numerical check.

Experimental and Computational Studies of Heat Transfer in Complex Internal Flows.

DTIC Science & Technology

1981-01-01

project, extending from September 15, 1979 to December 15, 1980 . The details of five distinct pieces of research are set forth. These research problems... Hislop , C. I., and Morris, R., "Effect on the Local Heat Transfer Coefficient in a Pipe of an Abrupt Disturbance of the Fluid Flow: Abrupt...Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota, 1980 . 10. Petukhov, B. S., "Heat Transfer and Friction in Turbulent

Proceedings of Fuel Safety Workshop Held at Alexandria, Virginia on 29 October-1 November 1985.

DTIC Science & Technology

1985-12-31

DC-10 at JFK International Airport on November 12, 1975. While it had many of the CID elements, it did not have the critical high yaw angle that...Important heat transfer, friction, and viscoelastic rheological properties of the fuel have been explained and quantified. Higher airport fuel handling...commodities, people and time, and perhaps the concepts of deregulation were applied with a disproportionate concern for marketplace economics without

On the Hamilton approach of the dissipative systems

NASA Astrophysics Data System (ADS)

Zimin, B. A.; Zorin, I. S.; Sventitskaya, V. E.

2018-05-01

In this paper we consider the problem of constructing equations describing the states of dissipative dynamical systems (media with absorption or damping). The approaches of Lagrange and Hamilton are discussed. A non-symplectic extension of the Poisson brackets is formulated. The application of the Hamiltonian formalism here makes it possible to obtain explicit equations for the dynamics of a nonlinear elastic system with damping and a one-dimensional continuous medium with internal friction.

Memory effects on stochastic resonance

NASA Astrophysics Data System (ADS)

Neiman, Alexander; Sung, Wokyung

1996-02-01

We study the phenomenon of stochastic resonance (SR) in a bistable system with internal colored noise. In this situation the system possesses time-dependent memory friction connected with noise via the fluctuation-dissipation theorem, so that in the absence of periodic driving the system approaches the thermodynamic equilibrium state. For this non-Markovian case we find that memory usually suppresses stochastic resonance. However, for a large memory time SR can be enhanced by the memory.

Second International Symposium on Structural Intermetallics

DTIC Science & Technology

1997-09-01

former case, twin Price [18], as schematically illustrated in Fig. 3 (c). formation can be further described by two mechanisms. One is the pole... source (Figure 5(c)). on how the heights of the jogs are distributed. These Dipoles become unstable when numbers may be compared with the measured friction... source the variation within growth of gamma grains, but the HIP temperature could only be reduced castings is not known, so far and still close

Heinrich-type glacial surges in a low-order dynamical climate model

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

Verbitsky, M.; Saltzman, B.

1994-07-01

Recent studies suggest the occurrence of sporadic episodes during which the ice streams that discharge ice sheets become enormously active, producing large numbers of icebergs (reflected in North Atlantic sea cores as {open_quotes}Heinrich events{close_quotes}) and possibly causing the partial collapse of the ice sheets. To simulate the mechanism of implied internal thermo-hydrodynamical instability in the context of a more general paleoclimate dynamics model (PDM), a new sliding-catastrophe function that can account for ice-sheet surges in terms of the thickness, density, viscosity, heat-capacity. and heat-conductivity of ice is introduced. Analysis suggests these events might be of three possible kinds: the firstmore » occurs in periods of glacial maximum when temperature conditions on the ice surface are extremely cold, but internal friction within bottom boundary layer is also at its maximum and is strong enough to melt ice and cause its surge. The second may happen during an interglacial, when the ice thickness is small but relatively warm climate conditions on the upper surface of ice can be easily advected with the flow of ice to the bottom where even a small additional heating due to friction may cause melting. The third and, perhaps, most interesting type is one that may occur during ice sheet growth: in this period particles of ice reaching the bottom {open_quotes}remember{close_quotes} the warm temperature conditions of the previous interglacial and additional heating due to increasing friction associated with the growing ice sheet may again cause melting. This third introduces the interesting possibility that earlier CO{sub 2} concentrations may be as important for the present-day climate as its current value. According to our model the climate system seems more vulnerable to surges during the penultimate interglacial period than in present one contributing to an explanation of the recent results of the Greenland Ice Core Project. 18 refs., 3 figs., 1 tab.« less

Discrete Element Simulations of Density-Driven Volcanic Deformation: Applications to Martian and Terrestrial Volcanoes

NASA Astrophysics Data System (ADS)

Farrell, L. L.; McGovern, P. J.; Morgan, J. K.

2008-12-01

We have carried out 2-D numerical simulations using the discrete element method (DEM) to investigate density-driven deformation in volcanic edifices on Earth (e.g., Hawaii) and Mars (e.g., Olympus Mons and Arsia Mons). Located within volcanoes are series of magma chambers, reservoirs, and conduits where magma travels and collects. As magma differentiates, dense minerals settle out, building thick accumulations referred to as cumulates that can flow ductilely due to stresses imparted by gravity. To simulate this process, we construct granular piles subject to Coulomb frictional rheology, incrementally capture internal rectangular regions to which higher densities and lower interparticle friction values are assigned (analogs for denser, weaker cumulates), and then bond the granular edifice. Thus, following each growth increment, the edifice is allowed to relax gravitationally with a reconfigured weak cumulate core. The presence and outward spreading of the cumulate causes the development of distinctive structural and stratigraphic patterns. We obtained a range of volcanic shapes that vary from broad, shallowly dipping flanks reminiscent of those of Olympus Mons, to short, steep surface slopes more similar to Arsia Mons. Edifices lacking internal cumulate exhibit relatively horizontal strata compared to the high-angle, inward dipping strata that develops within the cumulate-bearing edifices. Our simulated volcanoes also illustrate a variety of gravity driven deformation features, including regions of thrust faulting within the flanks and large-scale flank collapses, as observed in Hawaii and inferred on Olympus Mons. We also see significant summit subsidence, and of particular interest, distinct summit calderas. The broad, flat caldera and convex upward profile of Arsia Mons appears to be well-simulated by cumulate-driven volcanic spreading. In contrast, the concave upward slopes of Olympus Mons are more challenging to reproduce, and instead are attributed to volcanic spreading along a pore-fluid- pressurized decollement with low basal friction.

Perception and Haptic Rendering of Friction Moments.

PubMed

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

2011-01-01

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

Nonlinear friction model for servo press simulation

NASA Astrophysics Data System (ADS)

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

2013-12-01

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

Study on the friction of κ-carrageenan hydrogels in air and aqueous environments.

PubMed

Kozbial, Andrew; Li, Lei

2014-03-01

Understanding the friction mechanism of polysaccharide hydrogels, which is the key component of human cartilage that has very low friction coefficient, is critical to develop next generation artificial joint replacement materials. In this study, the friction of the polysaccharide κ-carrageenan hydrogel was investigated to elucidate the effect of external load, cross-linking density, velocity, and environment on friction. Our experimental results show that (1) coefficient of friction (COF) decreases with normal load in air and remains constant in water, (2) increasing cross-linking density concurrently increases friction and is proportional to Young's modulus, (3) COF increases with testing velocity in both air and water, and (4) friction is reduced in aqueous environment due to the lubricating effect of water. The underlying frictional mechanism is discussed on the basis of water transport from bulk to surface and a previously proposed "repulsion-adsorption" model. Copyright © 2013 Elsevier B.V. All rights reserved.

Time-dependent friction and the mechanics of stick-slip

USGS Publications Warehouse

Dieterich, J.H.

1978-01-01

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

The Indeterminate Case of Classical Static Friction When Coupled with Tension

NASA Astrophysics Data System (ADS)

Hahn, Kenneth D.; Russell, Jacob M.

2018-02-01

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

Analysis of Fault Spacing in Thrust-Belt Wedges Using Numerical Modeling

NASA Astrophysics Data System (ADS)

Regensburger, P. V.; Ito, G.

2017-12-01

Numerical modeling is invaluable in studying the mechanical processes governing the evolution of geologic features such as thrust-belt wedges. The mechanisms controlling thrust fault spacing in wedges is not well understood. Our numerical model treats the thrust belt as a visco-elastic-plastic continuum and uses a finite-difference, marker-in-cell method to solve for conservation of mass and momentum. From these conservation laws, stress is calculated and Byerlee's law is used to determine the shear stress required for a fault to form. Each model consists of a layer of crust, initially 3-km-thick, carried on top of a basal décollement, which moves at a constant speed towards a rigid backstop. A series of models were run with varied material properties, focusing on the angle of basal friction at the décollement, the angle of friction within the crust, and the cohesion of the crust. We investigate how these properties affected the spacing between thrusts that have the most time-integrated history of slip and therefore have the greatest effect on the large-scale undulations in surface topography. The surface position of these faults, which extend through most of the crustal layer, are identifiable as local maxima in positive curvature of surface topography. Tracking the temporal evolution of faults, we find that thrust blocks are widest when they first form at the front of the wedge and then they tend to contract over time as more crustal material is carried to the wedge. Within each model, thrust blocks form with similar initial widths, but individual thrust blocks develop differently and may approach an asymptotic width over time. The median of thrust block widths across the whole wedge tends to decrease with time. Median fault spacing shows a positive correlation with both wedge cohesion and internal friction. In contrast, median fault spacing exhibits a negative correlation at small angles of basal friction (<17˚) and a positive correlation with larger angles of basal friction. From these correlations, we will derive scaling laws that can be used to predict fault spacing in thrust-belt wedges.

Basal erosion: barrier to earthquake propagation? Insight from the northern chilean forearc

NASA Astrophysics Data System (ADS)

Cubas, N.

2017-12-01

Subducted topographic features have often been suspected as barriers to large earthquake propagation. These features would induce basal erosion, leading to a large network of fractures impeding large nucleation or shear localization. Looking for correlation between basal erosion and megathrust ruptures is thus critical nowadays to understand earthquake mechanics and infer rupture scenarios. In this study, we propose to seek possible location of basal erosion from the forearc morphology by applying the critical taper theory. We focus on the North Chile subduction zone that has experienced four major earthquakes during the last two decades and where basal erosion and seamount subduction have already been suspected. Basal erosion should occur when the basal friction approaches the internal friction. We thus seek what part of the forearc is at critical state and select areas for which the two frictions are almost equal. We find a large band, located at 25km depth, from the Mejillones peninsula to the Iquique region at critical state with very high basal friction. The critical areas seem to surround the Tocopilla 2007 Mw 7.7 and the Iquique 2014 Mw 8.1 ruptures. When compared with the interseismic coupling, except for the Tocopilla segment, the critical areas are located in low-coupled zones. More interestingly, the reported normal faults of the forearc do not appear above the erosional areas but rather between them. These normal faults are systematically located above locked patches and seismic asperities. These areas are actually at extensional critical state and characterized by a very low effective friction. We thus suspect the extensional features to be related to earthquakes rather than basal erosion. We then look for similar relationships along the Sumatra subduction zone to see if basal erosion is a common process. The Tocopilla and Iquique earthquakes ruptured only part of the northern Chile seismic gap although the full segment was ready for a new large rupture. Areas of basal erosion might have impeded the propagation of these ruptures and could as well delineate the future mega-earthquake.

The Architecture and Frictional Properties of Faults in Shale

NASA Astrophysics Data System (ADS)

De Paola, N.; Imber, J.; Murray, R.; Holdsworth, R.

2015-12-01

The geometry of brittle fault zones in shale rocks, as well as their frictional properties at reservoir conditions, are still poorly understood. Nevertheless, these factors may control the very low recovery factors (25% for gas and 5% for oil) obtained during fracking operations. Extensional brittle fault zones (maximum displacement < 3 m) cut exhumed oil mature black shales in the Cleveland Basin (UK). Fault cores up to 50 cm wide accommodated most of the displacement, and are defined by a stair-step geometry. Their internal architecture is characterised by four distinct fault rock domains: foliated gouges; breccias; hydraulic breccias; and a slip zone up to 20 mm thick, composed of a fine-grained black gouge. Hydraulic breccias are located within dilational jogs with aperture of up to 20 cm. Brittle fracturing and cataclastic flow are the dominant deformation mechanisms in the fault core of shale faults. Velocity-step and slide-hold-slide experiments at sub-seismic slip rates (microns/s) were performed in a rotary shear apparatus under dry, water and brine-saturated conditions, for displacements of up to 46 cm. Both the protolith shale and the slip zone black gouge display shear localization, velocity strengthening behaviour and negative healing rates, suggesting that slow, stable sliding faulting should occur within the protolith rocks and slip zone gouges. Experiments at seismic speed (1.3 m/s), performed on the same materials under dry conditions, show that after initial friction values of 0.5-0.55, friction decreases to steady-state values of 0.1-0.15 within the first 10 mm of slip. Contrastingly, water/brine saturated gouge mixtures, exhibit almost instantaneous attainment of very low steady-state sliding friction (0.1), suggesting that seismic ruptures may efficiently propagate in the slip zone of fluid-saturated shale faults. Stable sliding in faults in shale can cause slow fault/fracture propagation, affecting the rate at which new fracture areas are created and, hence, limiting oil and gas production during reservoir stimulation. However, fluid saturated conditions can favour seismic slip propagation, with fast and efficient creation of new fracture areas. These processes are very effective at dilational jogs, where fluid circulation may be enhanced, facilitating oil and gas production.

Prediction of Sliding Friction Coefficient Based on a Novel Hybrid Molecular-Mechanical Model.

PubMed

Zhang, Xiaogang; Zhang, Yali; Wang, Jianmei; Sheng, Chenxing; Li, Zhixiong

2018-08-01

Sliding friction is a complex phenomenon which arises from the mechanical and molecular interactions of asperities when examined in a microscale. To reveal and further understand the effects of micro scaled mechanical and molecular components of friction coefficient on overall frictional behavior, a hybrid molecular-mechanical model is developed to investigate the effects of main factors, including different loads and surface roughness values, on the sliding friction coefficient in a boundary lubrication condition. Numerical modelling was conducted using a deterministic contact model and based on the molecular-mechanical theory of friction. In the contact model, with given external loads and surface topographies, the pressure distribution, real contact area, and elastic/plastic deformation of each single asperity contact were calculated. Then asperity friction coefficient was predicted by the sum of mechanical and molecular components of friction coefficient. The mechanical component was mainly determined by the contact width and elastic/plastic deformation, and the molecular component was estimated as a function of the contact area and interfacial shear stress. Numerical results were compared with experimental results and a good agreement was obtained. The model was then used to predict friction coefficients in different operating and surface conditions. Numerical results explain why applied load has a minimum effect on the friction coefficients. They also provide insight into the effect of surface roughness on the mechanical and molecular components of friction coefficients. It is revealed that the mechanical component dominates the friction coefficient when the surface roughness is large (Rq > 0.2 μm), while the friction coefficient is mainly determined by the molecular component when the surface is relatively smooth (Rq < 0.2 μm). Furthermore, optimal roughness values for minimizing the friction coefficient are recommended.

Friction in Total Hip Joint Prosthesis Measured In Vivo during Walking

PubMed Central

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. PMID:24260114

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

PubMed

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.

Tribology of monolayer films: comparison between n-alkanethiols on gold and n-alkyl trichlorosilanes on silicon.

PubMed

Booth, Brandon D; Vilt, Steven G; McCabe, Clare; Jennings, G Kane

2009-09-01

This Article presents a quantitative comparison of the frictional performance for monolayers derived from n-alkanethiolates on gold and n-alkyl trichlorosilanes on silicon. Monolayers were characterized by pin-on-disk tribometry, contact angle analysis, ellipsometry, and electrochemical impedance spectroscopy (EIS). Pin-on-disk microtribometry provided frictional analysis at applied normal loads from 10 to 1000 mN at a speed of 0.1 mm/s. At low loads (10 mN), methyl-terminated n-alkanethiolate self-assembled monolayers (SAMs) exhibited a 3-fold improvement in coefficient of friction over SAMs with hydroxyl- or carboxylic-acid-terminated surfaces. For monolayers prepared from both n-alkanethiols on gold and n-alkyl trichlorosilanes on silicon, a critical chain length of at least eight carbons is required for beneficial tribological performance at an applied load of 9.8 mN. Evidence for disruption of chemisorbed alkanethiolate SAMs with chain lengths n

Stress rotation across the Cascadia megathrust requires a weak subduction plate boundary at seismogenic depths

NASA Astrophysics Data System (ADS)

Li, Duo; McGuire, Jeffrey J.; Liu, Yajing; Hardebeck, Jeanne L.

2018-03-01

The Mendocino Triple Junction region is the most seismically active part of the Cascadia Subduction Zone. The northward moving Pacific plate collides with the subducting Gorda plate causing intense internal deformation within it. Here we show that the stress field rotates rapidly with depth across the thrust interface from a strike-slip regime within the subducting plate, reflecting the Pacific plate collision, to a thrust regime in the overriding plate. We utilize a dense focal mechanism dataset, including observations from the Cascadia Initiative ocean bottom seismograph experiment, to constrain the stress orientations. To quantify the implications of this rotation for the strength of the plate boundary, we designed an inversion that solves for the absolute stress tensors in a three-layer model subject to assumptions about the strength of the subducting mantle. Our results indicate that the shear stress on the plate boundary fault is likely no more than about ∼50 MPa at ∼20 km depth. Regardless of the assumed mantle strength, we infer a relatively weak megathrust fault with an effective friction coefficient of ∼0 to 0.2 at seismogenic depths. Such a low value for the effective friction coefficient requires a combination of high fluid pressures and/or fault-zone minerals with low inherent friction in the region where a great earthquake is expected in Cascadia.

Operational limit conditions of the spur gears in lubricated modes

NASA Astrophysics Data System (ADS)

Benilha, S.; Belarifi, F.

2018-01-01

The calculation of the gear teeth resistance, shows the using of a certain number of coefficients determined experimentally and which are accepted by the various international standards. However, this kind of calculation determines the gears by excess material and does not support the tribological parameters of operation. We propose in this work the support of these parameters, to determine the limit operation conditions of the spur gears, using the equivalent geometry. This is represented by two cylinders, which geometrically models of the contact between two teeth of a gear and whose lubrication is generally in mixed lubrication mode. The concept of Mc cool is used to determine the distribution of the load and the friction force, which are distributed in liquid (elastohydrodynamic) and solid domains and interact with each other. The phenomenon of interaction between the two domains is used, to predict the tribological limit conditions of operation. The proposed model is based on the resolution of elastohydrodynamic equations for the determination of load and friction as well as the deduction of mixed friction by tracing the Stribeck curve. This is calculated by the model of the decomposition of the patterns profile of rough surfaces in contacts. The results of non-dimensional calculations allow us to deduce the boundary conditions and can be adapted for any type of gear pair defined according to pre-established operating conditions.

Strength anisotropy of shales deformed under uppermost crustal conditions

NASA Astrophysics Data System (ADS)

Bonnelye, Audrey; Schubnel, Alexandre; David, Christian; Henry, Pierre; Guglielmi, Yves; Gout, Claude; Fauchille, Anne-Laure; Dick, Pierre

2017-01-01

Conventional triaxial tests were performed on three sets of samples of Tournemire shale along different orientations relative to bedding (0°, 45°, and 90°). Experiments were carried out up to failure at increasing confining pressures ranging from 2.5 to 160 MPa, at strain rates ranging between 3 × 10-7s-1 and 3 × 10-5s-1. This allowed us to determine the entire anisotropic elastic compliance matrix as a function of confining pressure. Results show that the orientation of principal stress relative to bedding plays an important role on the brittle strength, with 45° orientation being the weakest. We fit our results with a wing crack micromechanical model and an anisotropic fracture toughness. We found low values of internal friction coefficient and apparent friction coefficient in agreement with friction coefficient of clay minerals (between 0.2 and 0.3) and values of KIc comparable to that already published in the literature. We also showed that strain rate has a strong impact on peak stress and that dilatancy appears right before failure and hence highlighting the importance of plasticity mechanisms. Although brittle failure was systematically observed, stress drops and associated slips were slow and deformation always remained aseismic (no acoustic emission were detected). This confirms that shales are good lithological candidates for shallow crust aseismic creep and slow slip events.

Interface architecture for superthick carbon-based films toward low internal stress and ultrahigh load-bearing capacity.

PubMed

Wang, Junjun; Pu, Jibin; Zhang, Guangan; Wang, Liping

2013-06-12

Superthick diamond-like carbon (DLC) films [(Six-DLC/Siy-DLC)n/DLC] were deposited on 304 stainless steel substrates by using a plane hollow cathode plasma-enhanced chemical vapor deposition method. The structure was investigated by scanning electron microscopy and transmission electron microscopy. Chemical bonding was examined by Raman, Auger electron, and X-ray photoelectron spectroscopy techniques. Mechanical and tribological properties were evaluated using nanoindentation, scratch, interferometry, and reciprocating-sliding friction testing. The results showed that implantation of a silicon ion into the substrate and the architecture of the tensile stress/compressive stress structure decreased the residual stress to almost 0, resulting in deposition of (Six-DLC/Siy-DLC)n/DLC films with a thickness of more than 50 μm. The hardness of the film ranged from 9 to 23 GPa, and the adhesion strength ranged from 4.6 to 57 N depending on the thickness of the film. Friction coefficients were determined in three tested environments, namely, air, water, and oil. Friction coefficients were typically below 0.24 and as low as 0.02 in a water environment. The as-prepared superthick films also showed an ultrahigh load-bearing capacity, and no failure was detected in the reciprocating wear test with contact pressure higher than 3.2 GPa. Reasons for the ultrahigh load-bearing capacity are proposed in combination with the finite-element method.

Rate-Dependent Behavior of the Amorphous Phase of Spider Dragline Silk

PubMed Central

Patil, Sandeep P.; Markert, Bernd; Gräter, Frauke

2014-01-01

The time-dependent stress-strain behavior of spider dragline silk was already observed decades ago, and has been attributed to the disordered sequences in silk proteins, which compose the soft amorphous matrix. However, the actual molecular origin and magnitude of internal friction within the amorphous matrix has remained inaccessible, because experimentally decomposing the mechanical response of the amorphous matrix from the embedded crystalline units is challenging. Here, we used atomistic molecular dynamics simulations to obtain friction forces for the relative sliding of peptide chains of Araneus diadematus spider silk within bundles of these chains as a representative unit of the amorphous matrix in silk fibers. We computed the friction coefficient and coefficient of viscosity of the amorphous phase to be in the order of 10−6 Ns/m and 104 Ns/m2, respectively, by extrapolating our simulation data to the viscous limit. Finally, we used a finite element method for the amorphous phase, solely based on parameters derived from molecular dynamics simulations including the newly determined coefficient of viscosity. With this model the time scales of stress relaxation, creep, and hysteresis were assessed, and found to be in line with the macroscopic time-dependent response of silk fibers. Our results suggest the amorphous phase to be the primary source of viscosity in silk and open up the avenue for finite element method studies of silk fiber mechanics including viscous effects. PMID:24896131

Bio-derived Fuel Blend Dilution of Marine Engine Oil and Imapct on Friction and Wear Behavior

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

Ajayi, Oyelayo O.; Lorenzo-Martin, Cinta; Fenske, George R.

To reduce the amount of petroleum-derived fuel used in vehicles and vessels powered by internal combustion engines, the addition of bio-derived fuel extenders is a common practice. Ethanol is perhaps the most common bio-derived fuel used for blending, and butanol is being evaluated as a promising alternative. The present study determined the fuel dilution rate of three lubricating oils (E0, E10, and i-B16) in a marine engine operating in on-water conditions with a start-and-stop cycle protocol. The level of fuel dilution increased with the number of cycles for all three fuels. The most dilution was observed with i-B16 fuel, andmore » the least with E10 fuel. In all cases, fuel dilution substantially reduced the oil viscosity. The impacts of fuel dilution and the consequent viscosity reduction on the lubricating capability of the engine oil in terms of friction, wear, and scuffing prevention were evaluated by four different tests protocols. Although the fuel dilution of the engine oil had minimal effect on friction, because the test conditions were under the boundary lubrication regime, significant effects were observed on wear in many cases. Fuel dilution also was observed to reduce the load-carrying capacity of the engine oils in terms of scuffing load reduction.« less

Stress rotation across the Cascadia megathrust requires a weak subduction plate boundary at seismogenic depths

USGS Publications Warehouse

Li, Duo; McGuire, Jeffrey J.; Liu, Yajing; Hardebeck, Jeanne L.

2018-01-01

The Mendocino Triple Junction region is the most seismically active part of the Cascadia Subduction Zone. The northward moving Pacific plate collides with the subducting Gorda plate causing intense internal deformation within it. Here we show that the stress field rotates rapidly with depth across the thrust interface from a strike-slip regime within the subducting plate, reflecting the Pacific plate collision, to a thrust regime in the overriding plate. We utilize a dense focal mechanism dataset, including observations from the Cascadia Initiative ocean bottom seismograph experiment, to constrain the stress orientations. To quantify the implications of this rotation for the strength of the plate boundary, we designed an inversion that solves for the absolute stress tensors in a three-layer model subject to assumptions about the strength of the subducting mantle. Our results indicate that the shear stress on the plate boundary fault is likely no more than about ∼50 MPa at ∼20 km depth. Regardless of the assumed mantle strength, we infer a relatively weak megathrust fault with an effective friction coefficient of ∼0 to 0.2 at seismogenic depths. Such a low value for the effective friction coefficient requires a combination of high fluid pressures and/or fault-zone minerals with low inherent friction in the region where a great earthquake is expected in Cascadia.

Science 101: What Causes Friction?

ERIC Educational Resources Information Center

Robertson, Bill

2014-01-01

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

Showing Area Matters: A Work of Friction

ERIC Educational Resources Information Center

Van Domelen, David

2010-01-01

Typically, we teach the simplified friction equation of the form F[subscript s] = [mu][subscript s]N for static friction, where F[subscript s] is the maximum static friction, [mu][subscript s] is the coefficient of static friction, and "N" is the normal force pressing the surfaces together. However, this is a bit too simplified, and…

Synergy and Self-organization in Tribosystem’s evolution. Energy Model of Friction

NASA Astrophysics Data System (ADS)

Fedorov, S. V.; Assenova, E.

2018-01-01

Different approaches are known to treat self-organization in tribosystems, related to the structural adaptation in the formation of dissipative surface structures and of frictional or tribo-films, using of synergistic modifying of layers and coatings, e.g. of the selective material transfer during friction, etc. Regarding tribological processes in contact systems, self-organization is observed as spontaneous creation of higher ordered structures during the contact interaction. The proposed paper considers friction as process of transformation and dissipation of energy and process of elasto-plastic deformation localized in thin surface layers of the interacting bodies. Еnergetic interpretation of friction is proposed. Based on the energy balance equations of friction, the evolution of tribosystems is followed in its adaptive-dissipative character. It reflects the variable friction surfaces compatibility and the nonlinear dynamics of friction evolution. Structural-energy relationships in the contacting surfaces evolution are obtained. Maximum of tribosystem’s efficiency during the evolution is the stage of self-organzation of the friction surface layers, which is a state of abnormal low friction and wear.

Research on the Mechanism of In-Plane Vibration on Friction Reduction

PubMed Central

Wang, Peng; Ni, Hongjian; Wang, Ruihe; Liu, Weili; Lu, Shuangfang

2017-01-01

A modified model for predicting the friction force between drill-string and borehole wall under in-plane vibrations was developed. It was found that the frictional coefficient in sliding direction decreased significantly after applying in-plane vibration on the bottom specimen. The friction reduction is due to the direction change of friction force, elastic deformation of surface asperities and the change of frictional coefficient. Normal load, surface topography, vibration direction, velocity ratio and interfacial shear factor are the main influence factors of friction force in sliding direction. Lower driving force can be realized for a pair of determinate rubbing surfaces under constant normal load by setting the driving direction along the minimum arithmetic average attack angle direction, and applying intense longitudinal vibration on the rubbing pair. The modified model can significantly improve the accuracy in predicting frictional coefficient under vibrating conditions, especially under the condition of lower velocity ratio. The results provide a theoretical gist for friction reduction technology by vibrating drill-string, and provide a reference for determination of frictional coefficient during petroleum drilling process, which has great significance for realizing digitized and intelligent drilling. PMID:28862679

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

PubMed

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.

Damage Tolerance Assessment of Friction Pull Plug Welds in an Aluminum Alloy

NASA Technical Reports Server (NTRS)

McGill, Preston; Burkholder, Jonathan

2012-01-01

Friction stir welding is a solid state welding process used in the fabrication of cryogenic propellant tanks. Self-reacting friction stir welding is one variation of the friction stir weld process being developed for manufacturing tanks. Friction pull plug welding is used to seal the exit hole that remains in a circumferential self-reacting friction stir weld. A friction plug weld placed in a self-reacting friction stir weld results in a non-homogenous weld joint where the initial weld, plug weld, their respective heat affected zones and the base metal all interact. The welded joint is a composite plastically deformed material system with a complex residual stress field. In order to address damage tolerance concerns associated with friction plug welds in safety critical structures, such as propellant tanks, nondestructive inspection and proof testing may be required to screen hardware for mission critical defects. The efficacy of the nondestructive evaluation or the proof test is based on an assessment of the critical flaw size. Test data relating residual strength capability to flaw size in an aluminum alloy friction plug weld will be presented.

Effect of grafted oligopeptides on friction.

PubMed

Iarikov, Dmitri D; Ducker, William A

2013-05-14

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

Tire-to-Surface Friction Especially Under Wet Conditions

NASA Technical Reports Server (NTRS)

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

1959-01-01

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

Impact of great subduction earthquakes on the long-term forearc morphology, insight from mechanical modelling

NASA Astrophysics Data System (ADS)

Cubas, Nadaya

2017-04-01

The surge of great subduction earthquakes during the last fifteen years provided numerous observations requiring revisiting our understanding of large seismic events mechanics. For instance, we now have clear evidence that a significant part of the upper plate deformation is permanently acquired. The link between great earthquakes and long-term deformation offers a new perspective for the relief construction understanding. In addition, a better understanding of these relations could provide us with new constraints on earthquake mechanics. It is also of fundamental importance for seismic risk assessment. In this presentation, I will compile recent results obtained from mechanical modelling linking megathrust ruptures with upper-plate permanent deformation and discuss their impact. We will first show that, in good accordance with lab experiments, aseismic zones are characterized by frictions larger or equal to 0.1 whereas seismic asperities have dynamic frictions lower than 0.05. This difference will control the long-term upper-plate morphology. The larger values along aseismic zones allow the wedge to reach the critical state, and will lead to active thrust systems forming a relief. On the contrary, low dynamic friction along seismic asperities will place the taper in the sub-critical domain impeding any internal deformation. This will lead to the formation of forearc basins inducing negative gravity anomalies. Since aseismic zones have higher friction and larger taper, fully creeping segments will tend to develop peninsulas. On the contrary, fully locked segments with low dynamic friction and very low taper will favor subsiding coasts. The taper variation due to megathrust friction is also expressed through a correlation between coast-to-trench distance and forearc coupling (e.g., Mexican and South-American subduction zones). We will then discuss how variations of frictional properties along the megathrust can induce splay fault activation. For instance, we can reactivate normal faults at the down-dip limit of the seismogenic zone or at an increasing slip transition (e.g., Chile and Japan). Finally, we will show that the fault vergence is controlled by the frictional properties. Sudden and successive decreases of the megathrust effective friction during frontal propagation of earthquakes will lead to the formation of landward-vergent frontal thrusts in the accretionary prism. Therefore, a particular attention needs to be paid to accretionary prisms with normal faults implying large up-dip ruptures (e.g., Alaska and Japan) or with frontal landward-vergent thrust faults, markers of past seafloor coseismic ruptures leading to very large tsunamis (e.g., Cascadia and Sumatra). If the forearc long-term deformation seems in good accordance with our understanding of earthquake mechanics, recent studies have pointed to a major discrepancy between short- and long-term deformation at the coast (i.e., the Central Andes subduction zone). An analogue discrepancy has been pointed out for the Himalaya after the 2015 Mw 7.8 Gorkha earthquake. Melnick (2016) proposed that the coastal long-term deformation could be related to deep and less frequent earthquakes instead of standard subduction events. It is now of fundamental importance to understand the link between the coastal long-term record and the short-term deformation for seismic risk assessment and relief building processes understanding. It will probably constitute the next challenge for mechanical modelling.

Are there reliable constitutive laws for dynamic friction?

PubMed

Woodhouse, Jim; Putelat, Thibaut; McKay, Andrew

2015-09-28

Structural vibration controlled by interfacial friction is widespread, ranging from friction dampers in gas turbines to the motion of violin strings. To predict, control or prevent such vibration, a constitutive description of frictional interactions is inevitably required. A variety of friction models are discussed to assess their scope and validity, in the light of constraints provided by different experimental observations. Three contrasting case studies are used to illustrate how predicted behaviour can be extremely sensitive to the choice of frictional constitutive model, and to explore possible experimental paths to discriminate between and calibrate dynamic friction models over the full parameter range needed for real applications. © 2015 The Author(s).

Friction Durability of Extremely Thin Diamond-Like Carbon Films at High Temperature

PubMed Central

Miyake, Shojiro; Suzuki, Shota; Miyake, Masatoshi

2017-01-01

To clarify the friction durability, both during and after the high-temperature heating of nanometer-thick diamond-like carbon (DLC) films, deposited using filtered cathodic vacuum arc (FCVA) and plasma chemical vapor deposition (P-CVD) methods, the dependence of the friction coefficient on the load and sliding cycles of the DLC films, were evaluated. Cluster-I consisted of a low friction area in which the DLC film was effective, while cluster-II consisted of a high friction area in which the lubricating effect of the DLC film was lost. The friction durability of the films was evaluated by statistical cluster analysis. Extremely thin FCVA-DLC films exhibited an excellent wear resistance at room temperature, but their friction durability was decreased at high temperatures. In contrast, the durability of the P-CVD-DLC films was increased at high temperatures when compared with that observed at room temperature. This inverse dependence on temperature corresponded to the nano-friction results obtained by atomic force microscopy. The decrease in the friction durability of the FCVA-DLC films at high temperatures, was caused by a complex effect of temperature and friction. The tribochemical reaction produced by the P-CVD-DLC films reduced their friction coefficient, increasing their durability at high temperatures. PMID:28772520

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

PubMed

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

2015-03-11

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

Friction Durability of Extremely Thin Diamond-Like Carbon Films at High Temperature.

PubMed

Miyake, Shojiro; Suzuki, Shota; Miyake, Masatoshi

2017-02-10

To clarify the friction durability, both during and after the high-temperature heating of nanometer-thick diamond-like carbon (DLC) films, deposited using filtered cathodic vacuum arc (FCVA) and plasma chemical vapor deposition (P-CVD) methods, the dependence of the friction coefficient on the load and sliding cycles of the DLC films, were evaluated. Cluster-I consisted of a low friction area in which the DLC film was effective, while cluster-II consisted of a high friction area in which the lubricating effect of the DLC film was lost. The friction durability of the films was evaluated by statistical cluster analysis. Extremely thin FCVA-DLC films exhibited an excellent wear resistance at room temperature, but their friction durability was decreased at high temperatures. In contrast, the durability of the P-CVD-DLC films was increased at high temperatures when compared with that observed at room temperature. This inverse dependence on temperature corresponded to the nano-friction results obtained by atomic force microscopy. The decrease in the friction durability of the FCVA-DLC films at high temperatures, was caused by a complex effect of temperature and friction. The tribochemical reaction produced by the P-CVD-DLC films reduced their friction coefficient, increasing their durability at high temperatures.

Analysis of dry friction damping characteristics for short cylindrical shell structures

NASA Astrophysics Data System (ADS)

Wang, Nengmao; Wang, Yanrong

2018-05-01

An efficient mathematical model to describe the friction of short cylindrical shell structures with a dry friction damping sleeve is proposed. The frictional force in the circumference and axial direction is caused by the opposing bending strains at the interface. Slipping will occur at part region of the interface and the mathematic model of the slipping region is established. Ignoring the effect of contact stiffness on the vibration analysis, the friction energy dissipation capability of damping sleeve would be calculated. Structural vibration mode, positive pressure at the interface and vibration stress of the short cylindrical shell structures is analyzed as influence factors to the critical damping ratio. The results show that the circumferential friction energy dissipation is more sensitive to the number of nodal diameter, and the circumferential friction damping ratio increases rapidly with the number of nodal diameter. The slipping frictional force would increase along with the positive pressure, but the slipping region would decrease with it. The peak damping ratio keeps nearly constant. But the vibration stress corresponding to peak damping ratio would increases with the positive pressure. The dry friction damping ratio of damping sleeve contains the effect of frictional force in the circumference and axial direction, and the axial friction plays a major role.

Experimental study on ignition mechanisms of wet granulation sulfur caused by friction.

PubMed

Dai, Haoyuan; Fan, Jianchun; Wu, Shengnan; Yu, Yanqiu; Liu, Di; Hu, Zhibin

2018-02-15

It is common to see fire accidents caused by friction during the storage and transportation of wet granulation sulfur. To study the sulfur ignition mechanism under friction conditions, a new rotating test apparatus is developed to reproduce friction scenes at lab scale. A series of experiments are performed under different normal loads. The SEM-EDS and the XRD were utilized to examine the morphologies and compositions of the tested specimens and the friction products. Experimental results show that these two methods are mostly in agreement with each other. The iron-sulfide compounds are produced and the proportion of iron-sulfide compounds is reduced with normal loads increasing, compared to the total number of the friction products. The facts implied by the integration analysis of friction products with the temperature changes of the near friction surface unveil an underlying mechanism that may explain sulfur ignition by friction in real scenarios. The sulfur ignition may be mainly caused by the spontaneous combustion of iron sulfide compounds produced by friction under low normal load with 200N. With the increase of normal loads, the resulting iron-sulfide compounds are decreasing and the high temperature from friction heat begins to play a major role in causing fire. Copyright © 2017 Elsevier B.V. All rights reserved.

Triaxial testing of Lopez Fault gouge at 150 MPa mean effective stress

USGS Publications Warehouse

Scott, D.R.; Lockner, D.A.; Byerlee, J.D.; Sammis, C.G.

1994-01-01

Triaxial compression experiments were performed on samples of natural granular fault gouge from the Lopez Fault in Southern California. This material consists primarily of quartz and has a self-similar grain size distribution thought to result from natural cataclasis. The experiments were performed at a constant mean effective stress of 150 MPa, to expose the volumetric strains associated with shear failure. The failure strength is parameterized by the coefficient of internal friction ??, based on the Mohr-Coulomb failure criterion. Samples of remoulded Lopez gouge have internal friction ??=0.6??0.02. In experiments where the ends of the sample are constrained to remain axially aligned, suppressing strain localisation, the sample compacts before failure and dilates persistently after failure. In experiments where one end of the sample is free to move laterally, the strain localises to a single oblique fault at around the point of failure; some dilation occurs but does not persist. A comparison of these experiments suggests that dilation is confined to the region of shear localisation in a sample. Overconsolidated samples have slightly larger failure strengths than normally consolidated samples, and smaller axial strains are required to cause failure. A large amount of dilation occurs after failure in heavily overconsolidated samples, suggesting that dilation is occurring throughout the sample. Undisturbed samples of Lopez gouge, cored from the outcrop, have internal friction in the range ??=0.4-0.6; the upper end of this range corresponds to the value established for remoulded Lopez gouge. Some kind of natural heterogeneity within the undisturbed samples is probably responsible for their low, variable strength. In samples of simulated gouge, with a more uniform grain size, active cataclasis during axial loading leads to large amounts of compaction. Larger axial strains are required to cause failure in simulated gouge, but the failure strength is similar to that of natural Lopez gouge. Use of the Mohr-Coulomb failure criterion to interpret the results from this study, and other recent studies on intact rock and granular gouge, leads to values of ?? that depend on the loading configuration and the intact or granular state of the sample. Conceptual models are advanced to account for these descrepancies. The consequences for strain-weakening of natural faults are also discussed. ?? 1994 Birkha??user Verlag.

Development of a New Method to Investigate the Dynamic Friction Behavior of Interfaces Using a Kolsky Tension Bar

DOE PAGES

Sanborn, B.; Song, B.; Nishida, E.

2017-11-02

In order to understand interfacial interaction of a bi-material during an impact loading event, the dynamic friction coefficient is one of the key parameters that must be characterized and quantified. In this study, a new experimental method to determine the dynamic friction coefficient between two metals was developed by using a Kolsky tension bar and a custom-designed friction fixture. Polyvinylidene fluoride (PVDF) force sensors were used to measure the normal force applied to the friction tribo pairs and the friction force was measured with conventional Kolsky tension bar method. To evaluate the technique, the dynamic friction coefficient between 4340 steelmore » and 7075-T6 aluminum was investigated at an impact speed of approximately 8 m/s. Additionally, the dynamic friction coefficient of the tribo pairs with varied surface roughness was also investigated. The data suggest that higher surface roughness leads to higher friction coefficients at the same speed of 8 m/s.« less

Understanding dynamic friction through spontaneously evolving laboratory earthquakes

PubMed Central

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

2017-01-01

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

High-velocity frictional properties of gabbro

NASA Astrophysics Data System (ADS)

Tsutsumi, Akito; Shimamoto, Toshihiko

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

Comparative Research on Characteristics of the Isolation Systems with Dry Friction Damping and with Vicious Damping under Base Excitation

NASA Astrophysics Data System (ADS)

Hou, Junfang; jing, Min; Zhang, Weihua; Lu, Yahui; He, Haiwen

2017-12-01

As for the isolation problem of electronic equipments on vehicle, the vibration response characteristics of dry friction damping isolation system under base displacement excitation was analyzed in theory by harmonic balance method, and the displacement response was compared between the isolation systems with dry friction damping and vicious damping separately. The results show that the isolation system with small dry friction damping can’t meet the demands of displacement reduction close to the natural frequency, and it can realize full-frequency vibration isolation by improving dry friction damping when the lock frequency passes beyond the resonance frequency band. The results imply that the damping mechanism of dry friction isolator can’t be described only by dry friction damping, and the composite damping with dry friction and vicious damping is more appropriate.

Some aspects of frictional measurements in hip joint simulators.

PubMed

Unsworth, Anthony

2016-05-01

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

Effects of Friction and Plastic Deformation in Shock-Comminuted Damaged Rocks on Impact Heating

NASA Astrophysics Data System (ADS)

Kurosawa, Kosuke; Genda, Hidenori

2018-01-01

Hypervelocity impacts cause significant heating of planetary bodies. Such events are recorded by a reset of 40Ar-36Ar ages and/or impact melts. Here we investigate the influence of friction and plastic deformation in shock-generated comminuted rocks on the degree of impact heating using the iSALE shock-physics code. We demonstrate that conversion from kinetic to internal energy in the targets with strength occurs during pressure release, and additional heating becomes significant for low-velocity impacts (<10 km s-1). This additional heat reduces the impact-velocity thresholds required to heat the targets with the 0.1 projectile mass to temperatures for the onset of Ar loss and melting from 8 and 10 km s-1, respectively, for strengthless rocks to 2 and 6 km s-1 for typical rocks. Our results suggest that the impact conditions required to produce the unique features caused by impact heating span a much wider range than previously thought.

A Method to Capture Macroslip at Bolted Interfaces

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

Hopkins, Ronald Neil; Heitman, Lili Anne Akin

2015-10-01

Relative motion at bolted connections can occur for large shock loads as the internal shear force in the bolted connection overcomes the frictional resistive force. This macroslip in a structure dissipates energy and reduces the response of the components above the bolted connection. There is a need to be able to capture macroslip behavior in a structural dynamics model. A linear model and many nonlinear models are not able to predict marcoslip effectively. The proposed method to capture macroslip is to use the multi-body dynamics code ADAMS to model joints with 3-D contact at the bolted interfaces. This model includesmore » both static and dynamic friction. The joints are preloaded and the pinning effect when a bolt shank impacts a through hole inside diameter is captured. Substructure representations of the components are included to account for component flexibility and dynamics. This method was applied to a simplified model of an aerospace structure and validation experiments were performed to test the adequacy of the method.« less

A Method to Capture Macroslip at Bolted Interfaces [PowerPoint

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

Hopkins, Ronald Neil; Heitman, Lili Anne Akin

2016-01-01

Relative motion at bolted connections can occur for large shock loads as the internal shear force in the bolted connection overcomes the frictional resistive force. This macroslip in a structure dissipates energy and reduces the response of the components above the bolted connection. There is a need to be able to capture macroslip behavior in a structural dynamics model. A linear model and many nonlinear models are not able to predict marcoslip effectively. The proposed method to capture macroslip is to use the multi-body dynamics code ADAMS to model joints with 3-D contact at the bolted interfaces. This model includesmore » both static and dynamic friction. The joints are preloaded and the pinning effect when a bolt shank impacts a through hole inside diameter is captured. Substructure representations of the components are included to account for component flexibility and dynamics. This method was applied to a simplified model of an aerospace structure and validation experiments were performed to test the adequacy of the method.« less

Antifriction coating of Cu-Fe-Al-Pb system for plain bearings

NASA Astrophysics Data System (ADS)

Kotenkov, Pavel; Kontsevoi, Yurii; Mejlakh, Anna; Pastukhov, Eduard; Shubin, Alexey; Goyda, Eduard; Sipatov, Ivan

2017-09-01

Aluminium, copper and their compounds are used in common as basis for antifriction coatings of plain bearings. Antifriction testing of plain bearings (based on Al and Cu) made by leading automotive manufacturers from Germany, Japan, USA, United Kingdom and Russia were carried out to make judicious selection of basis for development of new antifriction material. Testing was carried out using friction machine. It was defined that materials based on Cu provide better durability and robustness of plain bearings in comparison with Al based ones. The new antifriction composite coatings based on copper were developed taking into account the requirements specified for plain bearings of internal-combustion engine. Pilot samples of plain bearings with antifriction coatings of Cu-Fe-Al-Pb system were produced. The antifriction composite having Cu-5Fe-5Al5Fe2-10Pb (mass %) composition has demonstrated low friction factor and high wear-resistance. Metallographic analysis of pilot samples was carried out by means of optical and scanning electron microscopy.

Capturing the Elite in Marine Conservation in Northeast Kalimantan.

PubMed

Kusumawati, Rini; Visser, Leontine

This article takes the existence of power networks of local elites as a social fact of fundamental importance and the starting point for the study of patronage in the governance of the coastal waters of East Kalimantan. We address the question of how to capture the elites for project implementation, rather than assuming the inevitability of elite capture of project funds. We analyze the multiple-scale networks of local power holders ( punggawa ) and the collaboration and friction between the political-economic interests and historical values of local actors and the scientific motivations of international environmental organizations. We describe how collaboration and friction between members of the elite challenge models that categorically exclude or co-opt local elites in foreign projects. In-depth ethnographic study of these networks shows their resilience through flows of knowledge and power in a highly volatile coastal environment. Results indicate the need for inclusion in decision making of local entrepreneurs, and - indirectly - their dependents in decentralized coastal governance.

Co-seismic thermal dissociation of carbonate fault rocks: Naukluft Thrust, central Namibia

NASA Astrophysics Data System (ADS)

Rowe, C. D.; Miller, J. A.; Sylvester, F.; Backeberg, N.; Faber, C.; Mapani, B.

2009-12-01

Frictional heating has been shown to dissociate carbonate minerals in fault rocks and rock slides at high velocities, producing in-situ fluid pressure spikes and resulting in very low effective friction. We describe the textural and geochemical effects of repeated events of frictional-thermal dissociation and fluidization along a low-angle continental thrust fault. The Naukluft Thrust in central Namibia is a regional décollement along which the Naukluft Nappe Complex was emplaced over the Nama Basin in the southern foreland of the ~ 550Ma Damara Orogen. Fault rocks in the thrust show a coupled geochemical and structural evolution driven by dolomitization reactions during fault activity and facilitated by fluid flow along the fault surface. The earliest developed fault rocks are calcite-rich calcmylonites which were progressively dolomitized along foliation. Above a critical dolomite/calcite ratio, the rocks show only brittle deformation fabrics dominated by breccias, cataclasites, and locally, a thin (1-3cm) microcrystalline, smooth white ultracataclasite. The fault is characterized by the prevalence of an unusual “gritty dolomite” yellow cataclasite containing very well rounded clasts in massive to flow-banded fine dolomitic matrix. This cataclasite, locally known as the “gritty dolomite”, may reach thicknesses of up to ~ 10m without evidence of internal cross-cutting relations with randomly distributed clasts (an “unsorted” texture). The gritty dolomite also forms clastic injections into the hanging wall of the fault, frequently where the fault surface changes orientation. Color-cathodoluminescence images show that individual carbonate grains within the “gritty dolomite” have multiple layers of thin (~10-100 micron) dolomite coatings and that the grains were smoothed and rounded between each episode of coating precipitation. Coated grains are in contact with one another but grain cores are never seen in contact. CL-bright red dolomite which forms the coatings is never observed as pore-fill between grains or other geometries typical of cement precipitates. Smoothness and radial symmetry of the coatings suggest that the grains were coated in suspension by very fine material, potentially analogous to the frictionally-generated CaO developed on the base of some landslides in carbonate rocks (Hewitt, 1988). The very thick layers of cataclasite without internal crosscutting suggest free particle paths associated with fluidization at high fluid pressure and low effective normal stress. We suggest that co-seismic frictional heating along the Naukluft Thrust caused dissociation of dolomite fault rock, producing in-situ spikes in fluid pressure (CO2) and very fine caustic CaO which chemically attacked the carbonate grains in suspension causing the smoothing and rounding. These residues then coated individual grains prior to loss of fluid pressure and settling in the fault zone. Such an event would have been associated with near total strength drop along the Naukluft Thrust. Hewitt, K., 1988 Science, v. 242, no. 4875, p. 64-67.

Research on friction torque analysis of planetary roller screw mechanism considering load distribution

NASA Astrophysics Data System (ADS)

Gan, Fajin; Mao, Pengcheng; Zheng, Shicheng; Li, Guangliang; Xin, Shupeng

2018-04-01

Based on the Hertzian contact theory, frictional moment of planetary roller screw mechanism (RSM) caused by elastic hysteresis, roller's spinning sliding, and differential sliding was analyzed, which were considering load distribution of rollers threads. The relationship between friction torque of screw pairs and its input axial load were obtained. Finally, the frictional moment of the screw pairs under the situation overstress will created at some localized contact surfaces were discussed. Results shows that the frictional moment caused by elastic hysteresis gives the greatest rise to the total frictional moment and that due to differential sliding can be ignored. The stress uniformity has great influence on the frictional moment.

Dynamic recrystallization in friction surfaced austenitic stainless steel coatings

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

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

2012-12-15

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

Mars Secular Obliquity Change Due to Water Ice Caps

NASA Technical Reports Server (NTRS)

Rubincam, David P.

1998-01-01

Mars may have substantially changed its average axial tilt over geologic time due to the waxing and waning of water ice caps. Depending upon Mars' climate and internal structure, the average obliquity could have increased or decreased through climate friction by tens of degrees. A decrease could account for the apparent youthfulness of the polar layered terrain. Alternatively, Mars' average obliquity may have changed until it became "stuck" at its present value of 24.4 deg.

Evolutions of elastic-plastic shock compression waves in different materials

NASA Astrophysics Data System (ADS)

Kanel, G. I.; Zaretsky, E. B.; Razorenov, S. V.; Savinykh, A. S.; Garkushin, G. V.

2017-01-01

In the paper, we discuss such unexpected features in the wave evolution in solids as a departure from self-similar development of the wave process which is accompanied with apparent sub-sonic wave propagation, changes of shape of elastic precursor wave as a result of variations in the material structure and the temperature, unexpected peculiarities of reflection of elastic-plastic waves from free surface, effects of internal friction at shock compression of glasses and some other effects.

Effect of Ta Additions on the Microstructure, Damping, and Shape Memory Behaviour of Prealloyed Cu-Al-Ni Shape Memory Alloys.

PubMed

Saud, Safaa N; Hamzah, E; Bakhsheshi-Rad, H R; Abubakar, T

2017-01-01

The influence of Ta additions on the microstructure and properties of Cu-Al-Ni shape memory alloys was investigated in this paper. The addition of Ta significantly affects the green and porosity densities; the minimum percentage of porosity was observed with the modified prealloyed Cu-Al-Ni-2.0 wt.% Ta. The phase transformation temperatures were shifted towards the highest values after Ta was added. Based on the damping capacity results, the alloy of Cu-Al-Ni-3.0 wt.% Ta has very high internal friction with the maximum equivalent internal friction value twice as high as that of the prealloyed Cu-Al-Ni SMA. Moreover, the prealloyed Cu-Al-Ni SMAs with the addition of 2.0 wt.% Ta exhibited the highest shape recovery ratio in the first cycle (i.e., 100% recovery), and when the number of cycles is increased, this ratio tends to decrease. On the other hand, the modified alloys with 1.0 and 3.0 wt.% Ta implied a linear increment in the shape recovery ratio with increasing number of cycles. Polarization tests in NaCl solution showed that the corrosion resistance of Cu-Al-Ni-Ta SMA improved with escalating Ta concentration as shown by lower corrosion current densities, higher corrosion potential, and formation of stable passive film.

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

PubMed Central

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

2015-01-01

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

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

PubMed

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

2011-10-01

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

Frequency dependence of fatigue life and internal heating of a fiber-reinforced/ceramic-matrix composite

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

Holmes, J.W.; Wu, X.; Sorensen, B.F.

The influence of loading frequency on the fatigue life and internal (frictional) heating of unidirectional SiC-fiber/calcium aluminosilicate-matrix composites was investigated at room temperature. Specimens were subjected to tension-tension fatigue at sinusoidal loading frequencies from 25 to 350 Hz and maximum fatigue stresses of 180 to 240 MPa. The key findings of the study were that (1) fatigue life decreased sharply as the loading frequency was increased, (2) for all loading frequencies, fatigue failures occurred at stress levels that were significantly below the monotonic proportional limit stress if [approximately]285 MPa, and (3) pronounced internal heating occurred during fatigue, with the surfacemore » temperature of the fatigue specimens increasing by 160 K during 350-Hz fatigue at a peak stress of 240 MPa.« less

Computational Methods for Nonlinear Dynamic Problems in Solid and Structural Mechanics: Progress in the Theory and Modeling of Friction and in the Control of Dynamical Systems with Frictional Forces

DTIC Science & Technology

1989-03-31

present several numerical studies designed to reveal the effect that some of the governing parameters have on the behavior of the system and, whenever...Friction and in the Control of Dynamical Systems with Frictional Forces FINAL TECHNICAL REPORT March 31, 1989 _ -- I -.7: .-.- - : AFOSR Contract F49620...SOLID AND STRUCTURAL MECHANICS: Progress in the Theory and Modeling of Friction and in the Control of Dynamical Systems with Frictional Forces I I * FINAL

Determination of the Frictional Behavior at Compaction of Powder Materials Consisting of Spray-Dried Granules

NASA Astrophysics Data System (ADS)

Staf, Hjalmar; Olsson, Erik; Lindskog, Per; Larsson, Per-Lennart

2018-03-01

The frictional behavior during powder compaction and ejection is studied using an instrumented die with eight radial sensors. The average friction over the total powder pillar is used to determine a local friction coefficient at each sensor. By comparing forces at compaction with forces at ejection, it can be shown that the Coulomb's friction coefficient can be described as a function of normal pressure. Also stick phenomena has been investigated in order to assess its influence on the determination of the local friction coefficient.

Auto-Adjustable Tool for Self-Reacting and Conventional Friction Stir Welding

NASA Technical Reports Server (NTRS)

Carter, Robert W. (Inventor)

2002-01-01

A friction stir welding dcvice that is configured to perform convention friction stir welding as well as self-reacting friction stir welding is described. A pin passes hrough an upper shoulder and can selectively attach 10 and detach from a lower shoulder in a preferred embodiment. A controller maintains thc discrete position of, and/or force applied by, the upper and lower shoulders during self-reacting friction stir welding, or maintains the pin at a desired depth and/or applied force during conventional friction stir welding.

Effects of simulated clay gouges on the sliding behavior of Tennessee sandston

NASA Astrophysics Data System (ADS)

Shimamoto, Toshihiko; Logan, John M.

1981-06-01

The effects of simulated fault gouge on the sliding behavior of Tennessee sandstone are studied experimentally with special reference to the stabilizing effect of clay minerals mixed into the gouge. About 30 specimens with gouge composed of pure clays, of homogeneously mixed clay and anhydrite, or of layered clay and anhydrite, along a 35° precut are deformed dry in a triaxial apparatus at a confining pressure of 100 MPa, with a shortening rate of about 5 · 10 -4/sec, and at room temperature. Pure clay gouges exhibit only stable sliding, and the ultimate frictional strength is very low for bentonite (mont-morillonite), intermediate for chlorite and illite, and considerably higher for kaolinite. Anhydrite gouge shows violent stick-slip at 100 MPa confining pressure. When this mineral is mixed homogeneously with clays, the frictional coefficient of the mixed gouge, determined at its ultimate frictional strength, decreases monotonically with an increase in the clay content. The sliding mode changes from stick-slip to stable sliding when the frictional coefficient of the mixed clay-anhydrite gouge is lowered down below 90-95% of the coefficient of anhydrite gouge. The stabilizing effect of clay in mixed gouge is closely related to the ultimate frictional strength of pure clays; that is, the effect is conspicuous only for a mineral with low frictional strength. Only 15-20% of bentonite suppresses the violent stick-slip of anhydrite gouge. In contrast, violent stick-slip occurs even if the gouge contains as much as 75% of kaolinite. The behavior of illite and chlorite is intermediate between that of kaolinite and bentonite. Bentonite—anhydrite two-layer gouge exhibits stable sliding even when the bentonite content is only 5%. Thus, the presence of a thin, clay-rich layer in a fault zone stabilizes the behavior much more effectively than do the clay minerals mixed homogeneously with the gouge. This result brings out the mechanical significance of internal structures of a fault zone in understanding the effects of intrafault materials on the fault motion. Based on the present experimental results incorporated with some other experimental data, it is argued that although the stabilizing effect of montmorillonite and vermiculite is indeed remarkable at room temperature, the effect should be much less pronounced at elevated temperatures, due perhaps to the dewatering of the clays. In most geological environments where shallow earthquakes occur, the stabilizing effect of clays is probably not so conspicuous as to completely suppress the unstable motion of a fault.

Lateral Variations of Interplate Coupling along the Mexican Subduction Interface: Relationships with Long-Term Morphology and Fault Zone Mechanical Properties

NASA Astrophysics Data System (ADS)

Rousset, Baptiste; Lasserre, Cécile; Cubas, Nadaya; Graham, Shannon; Radiguet, Mathilde; DeMets, Charles; Socquet, Anne; Campillo, Michel; Kostoglodov, Vladimir; Cabral-Cano, Enrique; Cotte, Nathalie; Walpersdorf, Andrea

2016-10-01

Although patterns of interseismic strain accumulation above subduction zones are now routinely characterised using geodetic measurements, their physical origin, persistency through time, and relationships to seismic hazard and long-term deformation are still debated. Here, we use GPS and morphological observations from southern Mexico to explore potential mechanical links between variations in inter-SSE (in between slow slip events) coupling along the Mexico subduction zone and the long-term topography of the coastal regions from Guerrero to Oaxaca. Inter-SSE coupling solutions for two different geometries of the subduction interface are derived from an inversion of continuous GPS time series corrected from slow slip events. They reveal strong along-strike variations in the shallow coupling (i.e. at depths down to 25 km), with high-coupling zones (coupling >0.7) alternating with low-coupling zones (coupling <0.3). Coupling below the continent is typically strong (>0.7) and transitions to uncoupled, steady slip at a relatively uniform ˜ 175-km inland from the trench. Along-strike variations in the coast-to-trench distances are strongly correlated with the GPS-derived forearc coupling variations. To explore a mechanical explanation for this correlation, we apply Coulomb wedge theory, constrained by local topographic, bathymetric, and subducting-slab slopes. Critical state areas, i.e. areas where the inner subduction wedge deforms, are spatially correlated with transitions at shallow depth between uncoupled and coupled areas of the subduction interface. Two end-member models are considered to explain the correlation between coast-to-trench distances and along-strike variations in the inter-SSE coupling. The first postulates that the inter-SSE elastic strain is partitioned between slip along the subduction interface and homogeneous plastic permanent deformation of the upper plate. In the second, permanent plastic deformation is postulated to depend on frictional transitions along the subduction plate interface. Based on the location and friction values of the critical state areas identified by our Coulomb wedge analysis, we parameterise frictional transitions in plastic-static models of deformation over several seismic cycles. This predicts strong shear dissipation above frictional transitions on the subduction interface. The comparison of modelled surface displacements over a critical zone at a frictional transition and over a stable area with no internal wedge deformation shows differences of long-term uplift consistent with the observed along-strike variations in the coast-to-trench distances. Our work favours a model in which frictional asperities partly control short-term inter-SSE coupling as measured by geodesy and in which those asperities persist through time.

Effect of Coulomb friction on orientational correlation and velocity distribution functions in a sheared dilute granular gas.

PubMed

Gayen, Bishakhdatta; Alam, Meheboob

2011-08-01

From particle simulations of a sheared frictional granular gas, we show that the Coulomb friction can have dramatic effects on orientational correlation as well as on both the translational and angular velocity distribution functions even in the Boltzmann (dilute) limit. The dependence of orientational correlation on friction coefficient (μ) is found to be nonmonotonic, and the Coulomb friction plays a dual role of enhancing or diminishing the orientational correlation, depending on the value of the tangential restitution coefficient (which characterizes the roughness of particles). From the sticking limit (i.e., with no sliding contact) of rough particles, decreasing the Coulomb friction is found to reduce the density and spatial velocity correlations which, together with diminished orientational correlation for small enough μ, are responsible for the transition from non-gaussian to gaussian distribution functions in the double limit of small friction (μ→0) and nearly elastic particles (e→1). This double limit in fact corresponds to perfectly smooth particles, and hence the maxwellian (gaussian) is indeed a solution of the Boltzmann equation for a frictional granular gas in the limit of elastic collisions and zero Coulomb friction at any roughness. The high-velocity tails of both distribution functions seem to follow stretched exponentials even in the presence of Coulomb friction, and the related velocity exponents deviate strongly from a gaussian with increasing friction.

Effect of friction on the rheology of dense suspensions

NASA Astrophysics Data System (ADS)

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

2014-11-01

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

Water-vapor effects on friction of magnetic tape in contact with nickel-zinc ferrite

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1984-01-01

The effects of humidity of moist nitrogen on the friction and deformation behavior of magnetic tape in contact with a nickel-zinc ferrite spherical pin were studied. The results indicate that the coefficient of friction is markedly dependent on the ambient relative humidity. Although the coefficient of friction remains low below 40-percent relative humidity, it increases rapidly with increasing relative humidity above 40 percent. The general ambient environment of the tape does not have any effect on the friction behavior if the area where the tape is in sliding contact with the ferrite pin is flooded with controlled nitrogen. The response time for the friction of the tape to humidity changes is about 10 sec. The effect of friction as a function of relative humidity on dehumidifying is very similar to that on humidifying. A surface softening of the tape due to water vapor increases the friction of the tape.

Reduction of friction stress of ethylene glycol by attached hydrogen ions

PubMed Central

Li, Jinjin; Zhang, Chenhui; Deng, Mingming; Luo, Jianbin

2014-01-01

In the present work, it is shown that the friction stress of ethylene glycol can decrease by an order of magnitude to achieve superlubricity if there are hydrogen ions attached on the friction surfaces. An ultra-low friction coefficient (μ = 0.004) of ethylene glycol between Si3N4 and SiO2 can be obtained with the effect of hydrogen ions. Experimental result indicates that the hydrogen ions adsorbed on the friction surfaces forming a hydration layer and the ethylene glycol in the contact region forming an elastohydrodynamic film are the two indispensable factors for the reduction of friction stress. The mechanism of superlubricity is attributed to the extremely low shear strength of formation of elastohydrodynamic film on the hydration layer. This finding may introduce a new approach to reduce friction coefficient of liquid by attaching hydrogen ions on friction surfaces. PMID:25428584

Recent Progress Towards Predicting Aircraft Ground Handling Performance

NASA Technical Reports Server (NTRS)

Yager, T. J.; White, E. J.

1981-01-01

The significant progress which has been achieved in development of aircraft ground handling simulation capability is reviewed and additional improvements in software modeling identified. The problem associated with providing necessary simulator input data for adequate modeling of aircraft tire/runway friction behavior is discussed and efforts to improve this complex model, and hence simulator fidelity, are described. Aircraft braking performance data obtained on several wet runway surfaces is compared to ground vehicle friction measurements and, by use of empirically derived methods, good agreement between actual and estimated aircraft braking friction from ground vehilce data is shown. The performance of a relatively new friction measuring device, the friction tester, showed great promise in providing data applicable to aircraft friction performance. Additional research efforts to improve methods of predicting tire friction performance are discussed including use of an instrumented tire test vehicle to expand the tire friction data bank and a study of surface texture measurement techniques.

Effects of friction layer characteristics on the tribological properties of Ni3Al solid-lubricating composites at different load conditions

NASA Astrophysics Data System (ADS)

Lu, Guanchen; Shi, Xiaoliang; Huang, Yuchun; Liu, Xiyao; Yang, Meijun

2018-05-01

This paper investigates the effects of friction layer characteristics of Ni3Al matrix self-lubricating composites (NMCs) on the tribological properties sliding against ceramic ball Si3N4 at dry friction process at the different load conditions. The characteristics of friction layer are performed in terms of hardness of wear scars, thickness and elemental distributions of friction layer. The results show that the microhardness of wear scars of NMCs increases with the increase of the sliding time and applied load, which results in friction coefficient reduced and wear rate decreased, indicating that the tribological performance of NMCs is obviously affected by microhardness of wear scar. However, under excessive applied load, the performance of friction layer of NMCs is deteriorated for the spalling of wear debris and deformation of contact surface. Therefore, selecting appropriate load conditions during the sliding contact, at the transition to the optimal properties of friction layer maybe occur. NMCs exhibits excellent tribological properties at 15N, which leads to the lowest friction coefficient (0.386) and wear rate (2.48 × 10‑5 mm3 N‑1 m‑1), as well as the smoothest surface of wear track compared with the other load conditions. Meanwhile, the elemental distributions analysis of cross-section of friction layer of NMCs shows that the frictional structures can be divided into three main layers. The thickness of the friction-affected layer varies with the changing of applied load. These results could provide a reference for preparing the solid-lubrication materials with better tribological properties.

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

NASA Astrophysics Data System (ADS)

Falloon, Sabrina S.; Cottenden, Alan

2016-09-01

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

SRM propellant, friction/ESD testing

NASA Technical Reports Server (NTRS)

Campbell, L. A.

1989-01-01

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

Friction behavior of 304 stainless steel of varying hardness lubricated with benzene and some benzyl structures

NASA Technical Reports Server (NTRS)

Buckley, D. H.

1974-01-01

The lubricating properties of some benzyl and benzene structures were determined by using 304 stainless steel surfaces strained to various hardness. Friction coefficients and wear track widths were measured with a Bowden-Leben type friction apparatus by using a pin-on-disk specimen configuration. Results obtained indicate that benzyl monosulfide, dibenzyl disulfide, and benzyl alcohol resulted in the lowest friction coefficients for 304 stainless steel, while benzyl ether provided the least surface protection and gave the highest friction. Strainhardening of the 304 stainless steel prior to sliding resulted in reduced friction in dry sliding. With benzyl monosulfide, dibenzyl disulfide, and benzyl alcohol changes in 304 stainless steel hardness had no effect upon friction behavior.

Friction and wear of single-crystal manganese-zinc ferrite

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1979-01-01

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

Friction coefficient dependence on electrostatic tribocharging

PubMed Central

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

2013-01-01

Friction between dielectric surfaces produces patterns of fixed, stable electric charges that in turn contribute electrostatic components to surface interactions between the contacting solids. The literature presents a wealth of information on the electronic contributions to friction in metals and semiconductors but the effect of triboelectricity on friction coefficients of dielectrics is as yet poorly defined and understood. In this work, friction coefficients were measured on tribocharged polytetrafluoroethylene (PTFE), using three different techniques. As a result, friction coefficients at the macro- and nanoscales increase many-fold when PTFE surfaces are tribocharged, but this effect is eliminated by silanization of glass spheres rolling on PTFE. In conclusion, tribocharging may supersede all other contributions to macro- and nanoscale friction coefficients in PTFE and probably in other insulating polymers. PMID:23934227

Evaluation of Wear Resistance of Friction Materials Prepared by Granulation.

PubMed

Ma, Yunhai; Liu, Yucheng; Menon, Carlo; Tong, Jin

2015-10-21

The tribological properties of friction materials prepared by hot-pressing pellets of different sizes were experimentally investigated. Friction and wear tests of the specimens were performed and morphological analysis was carried out by investigating images acquired with both scanning electron and confocal laser microscopes. The highest friction coefficient of friction materials was obtained with pellets having 1-5 mm size. The lowest wear rate was obtained with pellets having 8-10 mm size. Specimens processed by mixing pellets of different sizes had the highest density and the lowest roughness and were the least expensive to fabricate. The results show that granulation generally enabled increasing the friction coefficient, decreasing the wear rate, and reducing the number of defects on the surface of friction materials.

A Correction to the Stress-Strain Curve During Multistage Hot Deformation of 7150 Aluminum Alloy Using Instantaneous Friction Factors

NASA Astrophysics Data System (ADS)

Jiang, Fulin; Tang, Jie; Fu, Dinfa; Huang, Jianping; Zhang, Hui

2018-04-01

Multistage stress-strain curve correction based on an instantaneous friction factor was studied for axisymmetric uniaxial hot compression of 7150 aluminum alloy. Experimental friction factors were calculated based on continuous isothermal axisymmetric uniaxial compression tests at various deformation parameters. Then, an instantaneous friction factor equation was fitted by mathematic analysis. After verification by comparing single-pass flow stress correction with traditional average friction factor correction, the instantaneous friction factor equation was applied to correct multistage stress-strain curves. The corrected results were reasonable and validated by multistage relative softening calculations. This research provides a broad potential for implementing axisymmetric uniaxial compression in multistage physical simulations and friction optimization in finite element analysis.

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

PubMed

Huang, Jianzhang; Han, Qiang

2018-08-10

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

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

PubMed

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

2013-08-01

The frictional characteristics of skin-object interactions are important when handling objects, in the assessment of perception and comfort of products and materials and in the origins and prevention of skin injuries. In this study, based on statistical methods, a quantitative model is developed that describes the friction behaviour of human skin as a function of the subject characteristics, contact conditions, the properties of the counter material as well as environmental conditions. Although the frictional behaviour of human skin is a multivariable problem, in literature the variables that are associated with skin friction have been studied using univariable methods. In this work, multivariable models for the static and dynamic coefficients of friction as well as for the hydration of the skin are presented. A total of 634 skin-friction measurements were performed using a recently developed tribometer. Using a statistical analysis, previously defined potential influential variables were linked to the static and dynamic coefficient of friction and to the hydration of the skin, resulting in three predictive quantitative models that descibe the friction behaviour and the hydration of human skin respectively. Increased dynamic coefficients of friction were obtained from older subjects, on the index finger, with materials with a higher surface energy at higher room temperatures, whereas lower dynamic coefficients of friction were obtained at lower skin temperatures, on the temple with rougher contact materials. The static coefficient of friction increased with higher skin hydration, increasing age, on the index finger, with materials with a higher surface energy and at higher ambient temperatures. The hydration of the skin was associated with the skin temperature, anatomical location, presence of hair on the skin and the relative air humidity. Predictive models have been derived for the static and dynamic coefficient of friction using a multivariable approach. These two coefficients of friction show a strong correlation. Consequently the two multivariable models resemble, with the static coefficient of friction being on average 18% lower than the dynamic coefficient of friction. The multivariable models in this study can be used to describe the data set that was the basis for this study. Care should be taken when generalising these results. © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Atomic-scale friction modulated by potential corrugation in multi-layered graphene materials

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

Zhuang, Chunqiang, E-mail: chunqiang.zhuang@bjut.edu.cn; Liu, Lei

2015-03-21

Friction is an important issue that has to be carefully treated for the fabrication of graphene-based nano-scale devices. So far, the friction mechanism of graphene materials on the atomic scale has not yet been clearly presented. Here, first-principles calculations were employed to unveil the friction behaviors and their atomic-scale mechanism. We found that potential corrugations on sliding surfaces dominate the friction force and the friction anisotropy of graphene materials. Higher friction forces correspond to larger corrugations of potential energy, which are tuned by the number of graphene layers. The friction anisotropy is determined by the regular distributions of potential energy.more » The sliding along a fold-line path (hollow-atop-hollow) has a relatively small potential energy barrier. Thus, the linear sliding observed in macroscopic friction experiments may probably be attributed to the fold-line sliding mode on the atomic scale. These findings can also be extended to other layer-structure materials, such as molybdenum disulfide (MoS{sub 2}) and graphene-like BN sheets.« less

Evaluation of two transport aircraft and several ground test vehicle friction measurements obtained for various runway surface types and conditions. A summary of test results from joint FAA/NASA Runway Friction Program

NASA Technical Reports Server (NTRS)

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

1990-01-01

Tests with specially instrumented NASA Boeing 737 and 727 aircraft together with several different ground friction measuring devices were conducted for a variety of runway surface types and conditions. These tests are part of joint FAA/NASA Aircraft/Ground Vehicle Runway Friction Program aimed at obtaining 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 as well as ground vehicle friction data obtained under similar runway conditions. For a given contaminated runway surface condition, the correlation between ground vehicles and aircraft friction data is identified. The influence of major test parameters on friction measurements such as speed, test tire characteristics, type and amount of surface contaminant, and ambient temperature are discussed. The effect of surface type on wet friction levels is also evaluated from comparative data collected on grooved and ungrooved concrete and asphalt surfaces.

Assembling of carbon nanotubes film responding to significant reduction wear and friction on steel surface

NASA Astrophysics Data System (ADS)

Zhang, Bin; Xue, Yong; Qiang, Li; Gao, Kaixong; Liu, Qiao; Yang, Baoping; Liang, Aiming; Zhang, Junyan

2017-11-01

Friction properties of carbon nanotubes have been widely studied and reported, however, the friction properties of carbon nanotubes related on state of itself. It is showing superlubricity under nanoscale, but indicates high shear adhesion as aligned carbon nanotube film. However, friction properties under high load (which is commonly in industry) of carbon nanotube films are seldom reported. In this paper, carbon nanotube films, via mechanical rubbing method, were obtained and its tribology properties were investigated at high load of 5 to 15 N. Though different couple pairs were employed, the friction coefficients of carbon nanotube films are nearly the same. Compared with bare stainless steel, friction coefficients and wear rates under carbon nanotube films lubrication reduced to, at least, 1/5 and 1/(4.3-14.5), respectively. Friction test as well as structure study were carried out to reveal the mechanism of the significant reduction wear and friction on steel surface. One can conclude that sliding and densifying of carbon nanotubes at sliding interface contribute to the sufficient decrease of friction coefficients and wear rates.

Methods to Measure, Predict and Relate Friction, Wear and Fuel Economy

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

Gravante, Steve; Fenske, George; Demas, Nicholas

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 RINGPAKmore » 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.« less

Friction Surface Treatment Selection: Aggregate Properties, Surface Characteristics, Alternative Treatments, and Safety Effects

DOT National Transportation Integrated Search

2017-07-01

This study aimed to evaluate the long term performance of the selected surface friction treatments, including high friction surface treatment (HFST) using calcined bauxite and steel slag, and conventional friction surfacing, in particular pavement pr...

Friction surfacing and linear friction welding

NASA Astrophysics Data System (ADS)

Nicholas, E. D.

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

Friction angle measurements on a naturally formed gravel streambed: Implications for critical boundary shear stress

Treesearch

John M. Buffington; William E. Dietrich; James W. Kirchner

1992-01-01

We report the first measurements of friction angles for a naturally formed gravel streambed. For a given test grain size placed on a bed surface, friction angles varied from 10º to over 100º; friction angle distributions can be expressed as a function of test grain size, median bed grain size, and bed sorting parameter. Friction angles decrease with increasing grain...

Stress-dependent grain size evolution of nanocrystalline Ni-W and its impact on friction behavior

DOE PAGES

Argibay, N.; Furnish, T. A.; Boyce, B. L.; ...

2016-06-07

The friction behavior of ultra-nanocrystalline Ni-W coatings was investigated. A critical stress threshold was identified below which friction remained low, and above which a time-dependent evolution toward higher friction behavior occurred. Founded on established plasticity models we propose a correlation between surface grain size and applied stress that can be used to predict the critical stress separating the two friction regimes. Lastly, this interpretation of plasticity models suggests that macro-scale low and high friction regimes are respectively associated with the nano-scale mechanisms of grain boundary and dislocation-mediated plasticity.

Friction-induced surface activity of some hydrocarbons with clean and oxide-covered iron

NASA Technical Reports Server (NTRS)

Buckley, D. H.

1973-01-01

Sliding friction studies were conducted on a clean and oxide-covered iron surface with exposure of that surface to various hydrocarbons. The hydrocarbons included ethane, ethylene ethyl chloride, methyl chloride, and vinyl chloride. Auger cylindrical mirror analysis was used to follow interactions of the hydrocarbon with the iron surface. Results with vinyl chloride indicate friction induced surface reactivity, adsorption to surface oxides, friction sensitivity to concentration and polymerization. Variation in the loads employed influence adsorption and accordingly friction. In contrast with ethyl and vinyl chloride, friction induced surface reactivity was not observed with ethane and ethylene.

Influence of the cage on friction torque in low loaded thrust ball bearing operating in dry conditions

NASA Astrophysics Data System (ADS)

Olaru, D.; Balan, M. R.; Tufescu, A.

2016-08-01

The authors investigated analytically and experimentally the friction torque in a modified thrust ball bearing operating at very low axial load in dry conditions by using only three balls and a cage. The experiments were conducted by using spin-down methodology. The results evidenced the influence of the sliding friction between the cage and the balls on the total friction torque. It was concluded that at very low loads the friction between cage and balls in a thrust ball bearing has an important contribution on total friction torque.

Frictional Characteristics of graphene

NASA Astrophysics Data System (ADS)

Lee, Changgu; Carpick, Robert; Hone, James

2009-03-01

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

Tactile texture and friction of soft sponge surfaces.

PubMed

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

2015-06-01

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

Pressure and Friction Injuries in Primary Care.

PubMed

Phillips, Shawn; Seiverling, Elizabeth; Silvis, Matthew

2015-12-01

Pressure and friction injuries are common throughout the lifespan. A detailed history of the onset and progression of friction and pressure injuries is key to aiding clinicians in determining the underlying mechanism behind the development of the injury. Modifying or removing the forces that are creating pressure or friction is the key to both prevention and healing of these injuries. Proper care of pressure and friction injuries to the skin is important to prevent the development of infection. Patient education on positioning and ergonomics can help to prevent recurrence of pressure and friction injuries. Copyright © 2015 Elsevier Inc. All rights reserved.

The experiment research of the friction sliding isolation structure

NASA Astrophysics Data System (ADS)

Zhang, Shirong; Li, Jiangle; Wang, Sheliang

2018-04-01

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

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

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

Victor W. Wong; Tian Tian; Grant Smedley

2003-08-28

This program aims at improving the efficiency of advanced natural-gas reciprocating engines (ANGRE) by reducing piston/ring assembly friction without major adverse effects on engine performance, such as increased oil consumption and emissions. A detailed set of piston/ring dynamic and friction models have been developed and applied that illustrated the fundamental relationships between design parameters and friction losses. Various low-friction strategies and concepts have been explored, and engine experiments will validate these concepts. An iterative process of experimentation, simulation and analysis, will be followed with the goal of demonstrating a complete optimized low-friction engine system. As planned, MIT has developed guidelinesmore » for an initial set of low-friction piston-ring-pack designs. Current recommendations focus on subtle top-piston-ring and oil-control-ring characteristics. A full-scale Waukesha F18 engine has been installed at Colorado State University and testing of the baseline configuration is in progress. Components for the first design iteration are being procured. Subsequent work includes examining the friction and engine performance data and extending the analyses to other areas to evaluate opportunities for further friction improvement and the impact on oil consumption/emission and wear, towards demonstrating an optimized reduced-friction engine system.« less

Three Three-Axis IEPE Accelerometers on the Inner Liner of a Tire for Finding the Tire-Road Friction Potential Indicators.

PubMed

Niskanen, Arto; Tuononen, Ari J

2015-08-05

Direct tire-road contact friction estimation is essential for future autonomous cars and active safety systems. Friction estimation methods have been proposed earlier for driving conditions in the presence of a slip angle or slip ratio. However, the estimation of the friction from a freely-rolling tire is still an unsolved topic. Knowing the existing friction potential would be beneficial since vehicle control systems could be adjusted before any remarkable tire force has been produced. Since accelerometers are well-known and robust, and thus a promising sensor type for intelligent tires, this study uses three three-axis IEPE accelerometers on the inner liner of a tire to detect friction potential indicators on two equally smooth surfaces with different friction levels. The equal roughness was chosen for both surfaces in order to study the friction phenomena by neglecting the effect of surface texture on vibrations. The acceleration data before the contact is used to differentiate the two friction levels between the tire and the road. In addition, the contact lengths from the three accelerometers are used to validate the acceleration data. A method to differentiate the friction levels on the basis of the acceleration signal is also introduced.

Tool For Friction Stir Tack Welding of Aluminum Alloys

NASA Technical Reports Server (NTRS)

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

2003-01-01

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

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

NASA Astrophysics Data System (ADS)

Piotrowski, J.

2010-07-01

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

Micro- and macroscale coefficients of friction of cementitious materials

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

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

2013-12-15

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

Friction measurement in a hip wear simulator.

PubMed

Saikko, Vesa

2016-05-01

A torque measurement system was added to a widely used hip wear simulator, the biaxial rocking motion device. With the rotary transducer, the frictional torque about the drive axis of the biaxial rocking motion mechanism was measured. The principle of measuring the torque about the vertical axis above the prosthetic joint, used earlier in commercial biaxial rocking motion simulators, was shown to sense only a minor part of the total frictional torque. With the present method, the total frictional torque of the prosthetic hip was measured. This was shown to consist of the torques about the vertical axis above the joint and about the leaning axis. Femoral heads made from different materials were run against conventional and crosslinked polyethylene acetabular cups in serum lubrication. Regarding the femoral head material and the type of polyethylene, there were no categorical differences in frictional torque with the exception of zirconia heads, with which the lowest values were obtained. Diamond-like carbon coating of the CoCr femoral head did not reduce friction. The friction factor was found to always decrease with increasing load. High wear could increase the frictional torque by 75%. With the present system, friction can be continuously recorded during long wear tests, so the effect of wear on friction with different prosthetic hips can be evaluated. © IMechE 2016.

Electrochemistry with double electrical layers in frictional interaction metal-polymer tribolink

NASA Astrophysics Data System (ADS)

Volchenko, N. A.; Krasin, P. S.; Volchenko, D. A.; Voznyi, A. V.

2018-03-01

The materials of the article illustrate the estimation of the energy loading of a metal friction element in a “metal-electrolyte-polymer” friction pair while forming various types of double electrical layers with the release of its thermal stabilization state. The rapidity of the processes of oxidation and reduction of the working surfaces of friction pairs during their electrothermomechanical frictional interaction leaves an imprint on all other additional processes that subsequently lead to the thermostabilizing and steady state of the metal friction element. Depending on the type of a brake device, the metal friction element has a different metal consumption and the temperature range varies. In addition, it is shown that the materials of the friction pair play an important role in the formation of electric tribosystems, namely: chemical elements that make up the materials, their valence, and the predominant type of intrinsic conductivity, as well as the sign of the electric charge of the friction pair elements that determines the laws of triboelectricity. Thus, an in-depth approach to the evaluation of the thermal stabilization state of a metal element in a “metal-electrolyte” friction pair is shown due to double electric layers that promote the emergence of current densities of different directions.

Three Three-Axis IEPE Accelerometers on the Inner Liner of a Tire for Finding the Tire-Road Friction Potential Indicators †

PubMed Central

Niskanen, Arto; Tuononen, Ari J.

2015-01-01

Direct tire-road contact friction estimation is essential for future autonomous cars and active safety systems. Friction estimation methods have been proposed earlier for driving conditions in the presence of a slip angle or slip ratio. However, the estimation of the friction from a freely-rolling tire is still an unsolved topic. Knowing the existing friction potential would be beneficial since vehicle control systems could be adjusted before any remarkable tire force has been produced. Since accelerometers are well-known and robust, and thus a promising sensor type for intelligent tires, this study uses three three-axis IEPE accelerometers on the inner liner of a tire to detect friction potential indicators on two equally smooth surfaces with different friction levels. The equal roughness was chosen for both surfaces in order to study the friction phenomena by neglecting the effect of surface texture on vibrations. The acceleration data before the contact is used to differentiate the two friction levels between the tire and the road. In addition, the contact lengths from the three accelerometers are used to validate the acceleration data. A method to differentiate the friction levels on the basis of the acceleration signal is also introduced. PMID:26251914

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

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

Fang, Yi; Elsworth, Derek; Wang, Chaoyi

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

Dynamic weakening is limited by granular dynamics

NASA Astrophysics Data System (ADS)

Kuwano, O.; Hatano, T.

2011-12-01

Earthquakes are the result of the frictional instability of faults containing fine rock powders called gouge derived from attrition in past fault motions. Understanding the frictional instability of granular matter in terms of constitutive laws is thus important. Because of the importance of granular matter for industries and engineering, the friction of granular matter has been studied in the field of solid earth science and other fields, such as statistical physics. In solid earth science, the rate- and state-dependent friction law was established by laboratory experiments at a very low sliding velocity (μm/s to mm/s). Recent experiments conducted at sub-seismic to seismic sliding velocities (mm/s to m/s), however, show that frictional properties are much richer than those predicted by the rate- and state-dependent friction law. One of the most important findings in such experiments is the remarkable weakening due to mechano-chemical effects by frictional heating [Tullis, 2007]. In statistical physics, another empirical law holds for much faster deformation than the former, showing positive shear-rate dependence. Until Recently, friction of granular matter has been investigated independently in the fields of solid earth science and statistical physics, and thus the relation between these distinct constitutive laws is not clear. Recently, some experimental studies have been reported to connect the achievements in these two fields. For example, a laboratory experiment on dry glass beads under very low normal stress (0.02 to 0.05 MPa) in which the frictional heat is negligible reveals the transition from velocity-weakening friction at low sliding velocities to velocity-strengthening friction at high sliding velocities [Kuwano et al., 2011]. Importantly, the velocity-strengthening nature at high sliding velocities is quantitatively the same as those observed in simulations. The inelastic deformation of the grains therefore plays a vital role at high sliding velocities. In this study, we report a friction experiment under higher pressure (0.1 to 0.9 MPa), in which the frictional heat is significant. To clarify the effect of frictional heat in high-speed friction systematically, we investigated both the pressure and the velocity dependence of the friction coefficient over a wide range of sliding velocities ranging from aseismic to seismic slip velocities. We observed considerable weakening, described well by a flash-heating theory, above the sliding velocity of 1 cm/s regardless of pressure. At higher velocities, the velocity strengthening behavior replaced the velocity weakening behavior. This strengthening at higher velocities agrees with data from numerical simulations on sheared granular matter and is therefore described in terms of energy dissipation due to the inelastic deformation of grains. We propose a unified steady-state friction law that well describes the velocity and pressure dependence of the steady-state friction coefficient.

Poroelasticity-driven lubrication in hydrogel interfaces.

PubMed

Reale, Erik R; Dunn, Alison C

2017-01-04

It is widely accepted that hydrogel surfaces are slippery, and have low friction, but dynamic applied stresses alter the hydrogel composition at the interface as water is displaced. The induced osmotic imbalance of compressed hydrogel which cannot swell to equilibrium should drive the resistance to slip against it. This paper demonstrates the driving role of poroelasticity in the friction of hydrogel-glass interfaces, specifically how poroelastic relaxation of hydrogels increases adhesion. We translate the work of adhesion into an effective surface energy density that increases with the duration of applied pressure from 10 to 50 mJ m -2 , as measured by micro-indentation. A model of static friction coefficient is derived from an area-based rules of mixture for the surface energies, and predicts the friction coefficient changes upon initiation of slip. For kinetic friction, the competition between duration of contact and relaxation time is quantified by a contacting Péclet number, Pe C . A single length parameter on the scale of micrometers fits these two models to experimental micro-friction data. These models predict how short durations of applied pressure and faster sliding speeds, do not disrupt interfacial hydration; this prevailing water maintains low friction. At low speeds where interface drainage dominates, the osmotic suction works against slip for higher friction. The prediction of friction coefficients after adhesion characterization by micro-indentation makes use of the interplay between poroelasticity, adhesion, and friction. This approach provides a starting point for prediction of, and design for, hydrogel interfacial friction.

78 FR 69927 - Notice to Manufacturers of Continuous Friction Measurement Equipment (CFME)

Federal Register 2010, 2011, 2012, 2013, 2014

2013-11-21

... Friction Measurement Equipment (CFME) AGENCY: Federal Aviation Administration (FAA), US DOT. ACTION: Notice... (FAA) is considering issuing waivers to foreign manufacturers of Continuous Friction Measurement... entitled, Continuous Friction Measurement Equipment Request for Qualifications. The FAA wants to determine...

Investigating the feasibility of integrating pavement friction and texture depth data in modeling for INDOT PMS.

DOT National Transportation Integrated Search

2012-11-01

Under INDOTs current friction testing program, the friction is measured annually on interstates but only once every three years on noninterstate : roadways. The states Pavement Management System, however, would require current data if friction ...

Friction-induced skin injuries-are they pressure ulcers? An updated NPUAP white paper.

PubMed

Brienza, David; Antokal, Steven; Herbe, Laura; Logan, Susan; Maguire, Jeanine; Van Ranst, Jennifer; Siddiqui, Aamir

2015-01-01

Friction injuries are often misdiagnosed as pressure ulcers. The reason for the misdiagnosis may be a misinterpretation of classic pressure ulcer literature that reported friction increased the susceptibility of the skin to pressure damage. This analysis assesses the classic literature that led to the inclusion of friction as a causative factor in the development of pressure ulcers in light of more recent research on the effects of shear. The analysis in this article suggests that friction can contribute to pressure ulcers by creating shear strain in deeper tissues, but friction does not appear to contribute to pressure ulcers in the superficial layers of the skin. Injuries to the superficial layers of the skin caused by friction are not pressure ulcers and should not be classified or treated as such.

Frictional behavior of large displacement experimental faults

USGS Publications Warehouse

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

1996-01-01

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

A technique for measuring dynamic friction coefficient under impact loading

NASA Astrophysics Data System (ADS)

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 m2/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.

A technique for measuring dynamic friction coefficient under impact loading.

PubMed

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.

University Engineering Design Challenge

DTIC Science & Technology

2015-01-29

solution was to design a sort of friction winch which would use friction to grip the rope sufficiently to wind itself up the rope without slipping ...provide enough friction to wind itself up the rope. It was determined through analysis that the friction pulley method would be the better solution...squeezed the rope becomes in the groove. This provides the friction which allows the rope not to slip in the pulley as it climbs the rope. The Metric

Joint Winter Runway Friction Program Accomplishments

NASA Technical Reports Server (NTRS)

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

2002-01-01

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

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

NASA Astrophysics Data System (ADS)

Khan, M. Roshan; Dasaka, Satyanarayana Murty

2018-05-01

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

Internal Forced Convection to Low Prandtl Number Gas Mixtures.

DTIC Science & Technology

1984-07-15

heating; v iV 0" ..- . --- NCX~ENCLATURE (continued) Greek Symbols -/K Force constant in Lennard - Jones potential ; y Ratio of specific heats, c p/cV...Absolute viscosity; V Kinematic viscosity; P Density; C Force constant in Lennard - Jones potential ; Nondimensional Parameters 2 f Friction factor, g P DAp...Reynolds and Perkins, 1968] id= c = (T - Tref)and (9) C VyRT= v(5/3)RT The Lennard - Jones (6-12) potential can be employed in the Chapman- Enskog kinetic

An Energy Absorber for the International Space Station

NASA Technical Reports Server (NTRS)

Wilkes, Bob; Laurence, Lora

2000-01-01

The energy absorber described herein is similar in size and shape to an automotive shock absorber, requiring a constant, high load to compress over the stroke, and self-resetting with a small load. The differences in these loads over the stroke represent the energy absorbed by the device, which is dissipated as friction. This paper describes the evolution of the energy absorber, presents the results of testing performed, and shows the sensitivity of this device to several key design variables.

Development of a Nondestructive Non-Contact Acousto-Thermal Evaluation Technique for Damage Detection in Materials (Preprint)

DTIC Science & Technology

2011-11-01

horn and the sample to obtain a repeatable excitation for detection of the damage of interest. Varieties of materials, including card stock, leather ...per cycle is, (2). where Tan , is the internal friction in the material, E is the Young’s modulus and σmax is the maximum amplitude of the...of acoustic energy to thermal energy depends on both the elastic properties (E and tan ) and the thermal properties (k, Cp) of the material. It

Indirect evidence for substantial damping of low-mode internal tides in the open ocean

DTIC Science & Technology

2015-09-12

see also Arbic et al., 2012; M€uller et al., 2012; Waterhouse et al., 2014] (C. B. Rocha, Mesoscale to submesoscale wavenumber spectra in Drake Passage...nominal horizontal resolution, at the equator , of 1/ 12.58. The simulations are forced by the M2 tide, the largest tidal constit- uent in the ocean, and by...2005] is given below. Thorough discussions on topographic wave drag and quadratic bottom friction and their appearance in the momentum equations can

Quasi-one-dimensional compressible flow across face seals and narrow slots. 2: Computer program

NASA Technical Reports Server (NTRS)

Zuk, J.; Smith, P. J.

1972-01-01

A computer program is presented for compressible fluid flow with friction across face seals and through narrow slots. The computer program carries out a quasi-one-dimensional flow analysis which is valid for laminar and turbulent flows under both subsonic and choked flow conditions for parallel surfaces. The program is written in FORTRAN IV. The input and output variables are in either the International System of Units (SI) or the U.S. customary system.

Soviet Research in Production and Physical Metallurgy of Pure Metals

DTIC Science & Technology

1964-01-10

theeby the level of internal friction. Conclusions 1. A methodology was developed for growing nP27bdemn slag crystals from the gaseous phae using the...case of zinc and cadmium the base may be situated perpendicularly to the axis of the specimen, i.e., parallel to the crystallization front. The same...separately, the latter being soldered to the ring with copper- zinc solder. With the modulator in a position as shown in Figure 2, the geometrical center

Scraping and stapling of end-grafted DNA chains by a bioadhesive spreading vesicle to reveal chain internal friction and topological complexity.

PubMed

Nam, Gimoon; Hisette, Marie Laure; Sun, Yuting Liang; Gisler, Thomas; Johner, Albert; Thalmann, Fabrice; Schröder, André Pierre; Marques, Carlos Manuel; Lee, Nam-Kyung

2010-08-20

Stained end-grafted DNA molecules about 20 μm long are scraped away and stretched out by the spreading front of a bioadhesive vesicle. Tethered biotin ligands bind the vesicle bilayer to a streptavidin substrate, stapling the DNAs into frozen confinement paths. Image analysis of the stapled DNA gives access, within optical resolution, to the local stretching values of individual DNA molecules swept by the spreading front, and provides evidence of self-entanglements.

Heat Transfer and Cooling in Gas Turbines

DTIC Science & Technology

1985-09-01

The friction factor results of the present study are in agreement with Ref. 9, but the heat transfer data for oblong pin fins are not. This is...AG ARD Conference P ioecd igs 353, 62nd Meceting, October ! 98,3 DTW- I" c LrU a : ol-.• ,’ 󈧏• ![ Hazard Studies for Solid Propeliant Rocket Motors...Internal Flows 71 AGARI) Advisory Report 181 (in English and French). Results of WG 14 (June/August 1983) I’rodueibility and Cost Studies of Aviation

30 CFR 56.19008 - Friction hoist synchronizing mechanisms.

Code of Federal Regulations, 2012 CFR

2012-07-01

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

30 CFR 57.19008 - Friction hoist synchronizing mechanisms.

Code of Federal Regulations, 2012 CFR

2012-07-01

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

30 CFR 57.19008 - Friction hoist synchronizing mechanisms.

Code of Federal Regulations, 2011 CFR

2011-07-01

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

30 CFR 57.19008 - Friction hoist synchronizing mechanisms.

Code of Federal Regulations, 2014 CFR

2014-07-01

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

30 CFR 56.19008 - Friction hoist synchronizing mechanisms.

Code of Federal Regulations, 2013 CFR

2013-07-01

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

30 CFR 56.19008 - Friction hoist synchronizing mechanisms.

Code of Federal Regulations, 2011 CFR

2011-07-01

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

30 CFR 57.19008 - Friction hoist synchronizing mechanisms.

Code of Federal Regulations, 2013 CFR

2013-07-01

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

30 CFR 56.19008 - Friction hoist synchronizing mechanisms.

Code of Federal Regulations, 2014 CFR

2014-07-01

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

30 CFR 56.19008 - Friction hoist synchronizing mechanisms.

Code of Federal Regulations, 2010 CFR

2010-07-01

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

30 CFR 57.19008 - Friction hoist synchronizing mechanisms.

Code of Federal Regulations, 2010 CFR

2010-07-01

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

Nanoscale lubrication of ionic surfaces controlled via a strong electric field

DOE PAGES

Strelcov, Evgheni; Bocharova, Vera; Sumpter, Bobby G.; ...

2015-01-27

Frictional forces arise whenever objects around us are set in motion. Controlling them in a rational manner means gaining leverage over mechanical energy losses and wear. This paper presents a way of manipulating nanoscale friction by means of in situ lubrication and interfacial electrochemistry. Water lubricant is directionally condensed from the vapor phase at a moving metal-ionic crystal interface by a strong confined electric field, thereby allowing friction to be tuned up or down via an applied bias. The electric potential polarity and ionic solid solubility are shown to strongly influence friction between the atomic force microscope (AFM) tip andmore » salt surface. An increase in friction is associated with the AFM tip digging into the surface, whereas reducing friction does not influence its topography. No current flows during friction variation, which excludes Joule heating and associated electrical energy losses. Lastly, the demonstrated novel effect can be of significant technological importance for controlling friction in nano- and micro-electromechanical systems.« less

Aircraft and ground vehicle friction measurements obtained under winter runway conditions

NASA Technical Reports Server (NTRS)

Yager, Thomas J.

1989-01-01

Tests with specially instrumented NASA B-737 and 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 obtaining 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.

Frictional properties of lubrication greases with the addition of nickel nanoparticles in pneumatic cylinder

NASA Astrophysics Data System (ADS)

Chang, Ho; Lan, Chou-Wei; Guo, Jia-Bin

2011-12-01

This paper studies the influence of addition of 100 nm diameter nickel nano-particles on the friction properties of synthetic grease (Li base, VG100) in pneumatic cylinder. The friction force test of pneumatic cylinder equipment measures the frictional force between seal and cylinder bore in pneumatic cylinders. The lubricants with addition of nickel nano-particles were used for lubricating the contact interface between seal and cylinder bore. The friction force test equipment employ a load cell force sensor to measure the friction force between seals and cylinder bores. Results obtained from experimental tests are compared to determine the friction force between seals and cylinder bore in pneumatic cylinders. The study leads to the conclusion that the addition of nickel nano-particles to synthetic grease results in a decrease in friction force between seals and cylinder bores in pneumatic cylinder. This tribological behavior is closely related to the deposition of nano-particles on the rubbing surfaces

Effect of friction on vibrotactile sensation of normal and dehydrated skin.

PubMed

Chen, S; Ge, S; Tang, W; Zhang, J

2016-02-01

Vibrotactile sensation mediated is highly dependent on surface mechanical and frictional properties. Dehydration of skin could change these properties. To investigate the relationship between friction and vibrotactile sensation of normal and dehydrated skin. Vibrations were firstly measured during surface exploration using a biomimetic sensor. Piglet skin was used as human skin model to study frictional properties for both normal and dehydrated skin using an atomic force microscope on nanoscale and a pin-on-disk tribometer on macroscale. Effect of vibrational frequency on friction and vibrotactile perception was also observed on nano and macro scale for normal and dehydrated skin. The result indicated that dehydrated skin was less sensitive than normal skin. The coefficient of friction of dehydrated skin is smaller than that of normal skin on both nano and macro scale. The coefficient of friction increases as increasing scanning frequencies. There is a positive correlation between coefficient of friction and vibrotactile sensation on nanoscale and macroscale. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Influence of Laser Shock Texturing on W9 Steel Surface Friction Property

NASA Astrophysics Data System (ADS)

Fan, Yujie; Cui, Pengfei; Zhou, Jianzhong; Dai, Yibin; Guo, Erbin; Tang, Deye

2017-09-01

To improve surface friction property of high speed steel, micro-dent arrays on W9Mo3Cr4V surface were produced by laser shock processing. Friction test was conducted on smooth surface and texturing surface and effect of surface texturing density on friction property was studied. The results show that, under the same condition, friction coefficient of textured surface is lower than smooth surface with dent area density less than 6%, wear mass loss, width and depth of wear scar are smaller; Wear resistance of the surface is the best and the friction coefficient is the smallest when dent area density is 2.2%; Friction coefficient, wear mass loss, width and depth of wear scar increase correspondingly as density of dent area increases when dent area density is more than 2.2%. Abrasive wear and adhesive wear, oxidative wear appear in the wear process. Reasonable control of geometric parameters of surface texturing induced by laser shock processing is helpful to improve friction performance.

Friction of hard surfaces and its application in earthquakes and rock slope stability

NASA Astrophysics Data System (ADS)

Sinha, Nitish; Singh, Arun K.; Singh, Trilok N.

2018-05-01

In this article, we discuss the friction models for hard surfaces and their applications in earth sciences. The rate and state friction (RSF) model, which is basically modified form of the classical Amontons-Coulomb friction laws, is widely used for explaining the crustal earthquakes and the rock slope failures. Yet the RSF model has further been modified by considering the role of temperature at the sliding interface known as the rate, state and temperature friction (RSTF) model. Further, if the pore pressure is also taken into account then it is stated as the rate, state, temperature and pore pressure friction (RSTPF) model. All the RSF models predict a critical stiffness as well as a critical velocity at which sliding behavior becomes stable/unstable. The friction models are also used for predicting time of failure of the rock mass on an inclined plane. Finally, the limitation and possibilities of the proposed friction models are also highlighted.

Multiscale physics of rubber-ice friction

NASA Astrophysics Data System (ADS)

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

2016-09-01

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

Simulation on friction taper plug welding of AA6063-20Gr metal matrix composite

NASA Astrophysics Data System (ADS)

Hynes, N. Rajesh Jesudoss; Nithin, Abeyram M.

2016-05-01

Friction taper plug welding a variant of friction welding is useful in welding of similar and dissimilar materials. It could be used for joining of composites to metals in sophisticated aerospace applications. In the present work numerical simulation of friction taper plug welding process is carried out using finite element based software. Graphite reinforced AA6063 is modelled using the software ANSYS 15.0 and temperature distribution is predicted. Effect of friction time on temperature distribution is numerically investigated. When the friction time is increased to 30 seconds, the tapered part of plug gets detached and fills the hole in the AA6063 plate perfectly.

Adaptive back-stepping control of the harmonic drive system with LuGre model-based friction compensation

NASA Astrophysics Data System (ADS)

Liu, Sen; Gang, Tieqiang

2018-03-01

Harmonic drives are widely used in aerospace and industrial robots. Flexibility, friction and parameter uncertainty will result in transmission performance degradation. In this paper, an adaptive back-stepping method with friction compensation is proposed to improve the tracking performance of the harmonic drive system. The nonlinear friction is described by LuGre model and compensated with a friction observer, and the uncertainty of model parameters is resolved by adaptive parameter estimation method. By using Lyapunov stability theory, it is proved that all the errors of the closed-loop system are uniformly ultimately bounded. Simulations illustrate the effectiveness of our friction compensation method.

Temporal variation in fault friction and its effects on the slip evolution of a thrust fault over several earthquake cycles

NASA Astrophysics Data System (ADS)

Hampel, Andrea; Hetzel, Ralf

2013-04-01

The friction coefficient is a key parameter for the slip evolution of faults, but how temporal changes in friction affect fault slip is still poorly known. By using three-dimensional numerical models with a thrust fault that is alternately locked and released, we show that variations in the friction coefficient affect both coseismic and long-term fault slip (Hampel and Hetzel, 2012). Decreasing the friction coefficient by 5% while keeping the duration of the interseismic phase constant leads to a four-fold increase in coseismic slip, whereas a 5% increase nearly suppresses slip. A gradual decrease or increase of friction over several earthquake cycles (1-5% per earthquake) considerably alters the cumulative fault slip. In nature, the slip deficit (surplus) resulting from variations in the friction coefficient would presumably be compensated by a longer (shorter) interseismic phase, but the magnitude of the changes required for compensation render variations of the friction coefficient of >5% unlikely. Reference Hampel, A., R. Hetzel (2012) Temporal variation in fault friction and its effects on the slip evolution of a thrust fault over several earthquake cycles. Terra Nova, 24, 357-362, doi: 10.1111/j.1365-3121.2012.01073.x.

Physical and Constructive (Limiting) Criterions of Gear Wheels Wear

NASA Astrophysics Data System (ADS)

Fedorov, S. V.

2018-01-01

We suggest using a generalized model of friction - the model of elastic-plastic deformation of the body element, which is located on the surface of the friction pairs. This model is based on our new engineering approach to the problem of friction-triboergodynamics. Friction is examined as transformative and dissipative process. Structural-energetic interpretation of friction as a process of elasto-plastic deformation and fracture contact volumes is proposed. The model of Hertzian (heavy-loaded) friction contact evolution is considered. The least wear particle principle is formulated. It is mechanical (nano) quantum. Mechanical quantum represents the least structural form of solid material body in conditions of friction. It is dynamic oscillator of dissipative friction structure and it can be examined as the elementary nanostructure of metal’s solid body. At friction in state of most complete evolution of elementary tribosystem (tribocontact) all mechanical quanta (subtribosystems) with the exception of one, elasticity and reversibly transform energy of outer impact (mechanic movement). In these terms only one mechanical quantum is the lost - standard of wear. From this position we can consider the physical criterion of wear and the constructive (limiting) criterion of gear teeth and other practical examples of tribosystems efficiency with new tribology notion - mechanical (nano) quantum.