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Sample records for friction torque studies

  1. The effect of frictional torque and bending moment on corrosion at the taper interface : an in vitro study.

    PubMed

    Panagiotidou, A; Meswania, J; Osman, K; Bolland, B; Latham, J; Skinner, J; Haddad, F S; Hart, A; Blunn, G

    2015-04-01

    The aim of this study was to assess the effect of frictional torque and bending moment on fretting corrosion at the taper interface of a modular femoral component and to investigate whether different combinations of material also had an effect. The combinations we examined were 1) cobalt-chromium (CoCr) heads on CoCr stems 2) CoCr heads on titanium alloy (Ti) stems and 3) ceramic heads on CoCr stems. In test 1 increasing torque was imposed by offsetting the stem in the anteroposterior plane in increments of 0 mm, 4 mm, 6 mm and 8 mm when the torque generated was equivalent to 0 Nm, 9 Nm, 14 Nm and 18 Nm. In test 2 we investigated the effect of increasing the bending moment by offsetting the application of axial load from the midline in the mediolateral plane. Increments of offset equivalent to head + 0 mm, head + 7 mm and head + 14 mm were used. Significantly higher currents and amplitudes were seen with increasing torque for all combinations of material. However, Ti stems showed the highest corrosion currents. Increased bending moments associated with using larger offset heads produced more corrosion: Ti stems generally performed worse than CoCr stems. Using ceramic heads did not prevent corrosion, but reduced it significantly in all loading configurations. PMID:25820883

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

    SciTech Connect

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

    1992-05-01

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

  3. Spatial and temporal variations of global frictional torque during the period 1948-2011

    NASA Astrophysics Data System (ADS)

    Gong, He; Huang, Mei; Zhu, Lin; Guo, Shengli; Shao, Yaping

    2016-02-01

    Frictional torque is an important mean for momentum exchange between the atmosphere and earth, and significantly influences the variation in atmospheric angular momentum. Using NCEP-NCAR reanalysis data for the period 1948-2011, we examined the spatial and temporal patterns of frictional torque. It was found that the globally integrated frictional torque turned from positive to negative in 1972, suggesting that angular momentum was transferred from the earth to the atmosphere before 1972, but from the atmosphere to the earth thereafter. The global frictional torque steadily declined from 1948 to 1994, but has been increasing since 1995. It was also found that the global frictional torque is mainly determined by the wind systems in the mid and low latitudes of the Southern Hemisphere (SH), where large changes in frictional torque occurred during the study period. Westerly wind increased continuously in the midlatitudes after 1948, while easterly wind decreased in the tropics of the SH after the 1980s.

  4. Heat Control via Torque Control in Friction Stir Welding

    NASA Technical Reports Server (NTRS)

    Venable, Richard; Colligan, Kevin; Knapp, Alan

    2004-01-01

    In a proposed advance in friction stir welding, the torque exerted on the workpiece by the friction stir pin would be measured and controlled in an effort to measure and control the total heat input to the workpiece. The total heat input to the workpiece is an important parameter of any welding process (fusion or friction stir welding). In fusion welding, measurement and control of heat input is a difficult problem. However, in friction stir welding, the basic principle of operation affords the potential of a straightforward solution: Neglecting thermal losses through the pin and the spindle that supports it, the rate of heat input to the workpiece is the product of the torque and the speed of rotation of the friction stir weld pin and, hence, of the spindle. Therefore, if one acquires and suitably processes data on torque and rotation and controls the torque, the rotation, or both, one should be able to control the heat input into the workpiece. In conventional practice in friction stir welding, one uses feedback control of the spindle motor to maintain a constant speed of rotation. According to the proposal, one would not maintain a constant speed of rotation: Instead, one would use feedback control to maintain a constant torque and would measure the speed of rotation while allowing it to vary. The torque exerted on the workpiece would be estimated as the product of (1) the torque-multiplication ratio of the spindle belt and/or gear drive, (2) the force measured by a load cell mechanically coupled to the spindle motor, and (3) the moment arm of the load cell. Hence, the output of the load cell would be used as a feedback signal for controlling the torque (see figure).

  5. Frictional Torque on a Rotating Disc

    ERIC Educational Resources Information Center

    Mungan, Carl E.

    2012-01-01

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

  6. A torque motor for a low friction single axis turntable

    NASA Astrophysics Data System (ADS)

    Joosten, L. J. M.

    1982-08-01

    A single axis turntable motor for a virtually frictionless turntable used for testing satellite attitude control systems is described. The torque motor simulates pulse jets for attitude control, low torques acting on the satellite, and compensates disturbance torques acting on the table. The torques are applied by forcing a current in the ironless rotor fixed to the ground, while the permanent magnet stator transfers the torques to the turntable, to which the stator is attached. The rotor is mounted on a servocontrolled subtable so that the angular position of the stator and rotor is maintained, in order to keep the torque transfer independent of the turntable position. The torquer can accept pulses as short as 3 msec and has a gain accuracy better than 0.5% within its range of 50 times 10 to the power -3 nanometers. The torquer is used to compensate the position dependent disturbance torques on the turntable, so that the friction of the table is lowered towards 3 times 10 to the power -6 nanometers.

  7. Measuring Micro-Friction Torque in MEMS Gas Bearings

    PubMed Central

    Fang, Xudong; Liu, Huan

    2016-01-01

    An in situ measurement of micro-friction torque in MEMS gas bearings, which has been a challenging research topic for years, is realized by a system designed in this paper. In the system, a high accuracy micro-force sensor and an electronically-driven table are designed, fabricated and utilized. With appropriate installation of the sensor and bearings on the table, the engine rotor can be driven to rotate with the sensor using a silicon lever beam. One end of the beam is fixed to the shaft of the gas bearing, while the other end is free and in contact with the sensor probe tip. When the sensor begins to rotate with the table, the beam is pushed by the sensor probe to rotate in the same direction. For the beam, the friction torque from the gas bearing is balanced by the torque induced by pushing force from the sensor probe. Thus, the friction torque can be calculated as a product of the pushing force measured by the sensor and the lever arm, which is defined as the distance from the sensor probe tip to the centerline of the bearing. Experimental results demonstrate the feasibility of this system, with a sensitivity of 1.285 mV/μN·m in a range of 0 to 11.76 μN·m when the lever arm is 20 mm long. The measuring range can be modified by varying the length of the lever arm. Thus, this system has wide potential applications in measuring the micro-friction torque of gas bearings in rotating MEMS machines. PMID:27213377

  8. Measuring Micro-Friction Torque in MEMS Gas Bearings.

    PubMed

    Fang, Xudong; Liu, Huan

    2016-01-01

    An in situ measurement of micro-friction torque in MEMS gas bearings, which has been a challenging research topic for years, is realized by a system designed in this paper. In the system, a high accuracy micro-force sensor and an electronically-driven table are designed, fabricated and utilized. With appropriate installation of the sensor and bearings on the table, the engine rotor can be driven to rotate with the sensor using a silicon lever beam. One end of the beam is fixed to the shaft of the gas bearing, while the other end is free and in contact with the sensor probe tip. When the sensor begins to rotate with the table, the beam is pushed by the sensor probe to rotate in the same direction. For the beam, the friction torque from the gas bearing is balanced by the torque induced by pushing force from the sensor probe. Thus, the friction torque can be calculated as a product of the pushing force measured by the sensor and the lever arm, which is defined as the distance from the sensor probe tip to the centerline of the bearing. Experimental results demonstrate the feasibility of this system, with a sensitivity of 1.285 mV/μN·m in a range of 0 to 11.76 μN·m when the lever arm is 20 mm long. The measuring range can be modified by varying the length of the lever arm. Thus, this system has wide potential applications in measuring the micro-friction torque of gas bearings in rotating MEMS machines. PMID:27213377

  9. Instantaneous engine frictional torque, its components and piston assembly friction. Final report

    SciTech Connect

    Nichols, F.A.; Henein, N.A.

    1992-05-01

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

  10. Effects of Structural Deformations of the Crank-Slider Mechanism on the Estimation of the Instantaneous Engine Friction Torque

    NASA Astrophysics Data System (ADS)

    CHALHOUB, N. G.; NEHME, H.; HENEIN, N. A.; BRYZIK, W.

    1999-07-01

    The focus on the current study is to assess the effects of structural deformations of the crankshaft/connecting-rod/piston mechanism on the computation of the instantaneous engine friction torque. This study is performed in a fully controlled environment in order to isolate the effects of structural deformations from those of measurement errors or noise interference. Therefore, a detailed model, accounting for the rigid and flexible motions of the crank-slider mechanism and including engine component friction formulations, is considered in this study. The model is used as a test bed to generate the engine friction torque,Tfa, and to predict the rigid and flexible motions of the system in response to the cylinder gas pressure. The torsional vibrations and the rigid body angular velocity of the crankshaft, as predicted by the detailed model of the crank-slider mechanism, are used along with the engine load torque and the cylinder gas pressure in the (P-ω) method to estimate the engine friction torque,Tfe. This method is well suited for the purpose of this study because its formulation is based on the rigid body model of the crank-slider mechanism. The digital simulation results demonstrate that the exclusion of the structural deformations of the crank-slider mechanism from the formulation of the (P-ω) method leads to an overestimation of the engine friction torque near the top-dead-center (TDC) position of the piston under firing conditions. Moreover, for the remainder of the engine cycle, the estimated friction torque exhibits large oscillations and takes on positive numerical values as if it is inducing energy into the system. Thus, the adverse effects of structural deformations of the crank-slider mechanism on the estimation of the engine friction torque greatly differ in their nature from one phase of the engine cycle to another.

  11. A novel analytical approach for determining the frictional moments and torques acting on modular femoral components in total hip replacements.

    PubMed

    Farhoudi, H; Oskouei, R H; Jones, C F; Taylor, M

    2015-04-13

    A three dimensional analytical approach was developed to determine the frictional moment vector generated by the relative sliding of the head-cup bearing couple of a total hip replacement. The frictional moment projection onto the femoral neck was also determined over the loading cycle. Predicted frictional moments for nine combinations of bearing materials and diameters were in close agreement with existing in vitro data. The analytical method was then applied to simplified gait (lubrication conditions of dry and serum), ISO standard gait and physiological level gait loading cycles. ISO standard gait had a total contact force of about two fold of physiological level gait and there was a corresponding increase in the maximum frictional torque on neck from 0.66×BW%m to 0.88×BW%m. For the ISO standard gait, the maximum frictional torque occurred at the same instance of maximum frictional moment and the maximum contact force. In contrast, for the physiological level gait, the frictional torque did not occur at the same instance as the peak load. This suggests that the neck frictional torque is a function of other parameters, such as angle between neck axis and frictional moment vector, as well as the magnitude of the contact force and frictional moment. The developed methodology was able to predict the maximum magnitude and change of directions of moments and the variation of torque at the head neck interface. The data will be useful for experimental studies assessing the fretting behaviour of the head neck junction, by providing appropriate loading data. PMID:25721768

  12. High-velocity frictional strength across the Tohoku-Oki megathrust determined from surface drilling torque

    NASA Astrophysics Data System (ADS)

    Ujiie, K.; Inoue, T.; Ishiwata, J.

    2015-12-01

    Frictional strength at seismic slip rates is a key to evaluate fault weakening and rupture propagation during earthquakes. The Japan Trench First Drilling Project (JFAST) drilled through the shallow plate-boundary thrust, where huge displacements of ~50 m occurred during the 2011 Tohoku-Oki earthquake. To determine the downhole frictional strength at drilled site (Site C0019), we analyzed surface drilling data. The equivalent slip rate estimated from the rotation rate and inner and outer radiuses of the drill bit ranges from 0.8 to 1.3 m/s. The measured torque includes the frictional torque between the drilling string and borehole wall, the viscous torque between the drilling string and seawater/drilling fluid, and the drilling torque between the drill bit and sediments. We subtracted the former two from the measured torque using the torque data during bottom-up rotating operations at several depths. Then, the shear stress was calculated from the drilling torque taking the configuration of the drill bit into consideration. The normal stress was estimated from the weight on bit data and the projected area of the drill bit. Assuming negligible cohesion, the frictional strength was obtained by dividing shear stress by normal stress. The results show a clear contrast in high-velocity frictional strength across the plate-boundary thrust: the friction coefficient of frontal prism sediments (hemipelagic mudstones) in hanging wall is 0.1-0.2, while that in subducting sediments (hemipelagic to pelagic mudstones and chert) in footwall increases to 0.2-0.4. The friction coefficient of smectite-rich pelagic clay in the plate-boundary thrust is ~0.1, which is consistent with that obtained from high-velocity (1.3 m/s) friction experiments and temperature measurements. We conclude that surface drilling torque provides useful data to obtain a continuous downhole frictional strength.

  13. TIDAL FRICTION AND TIDAL LAGGING. APPLICABILITY LIMITATIONS OF A POPULAR FORMULA FOR THE TIDAL TORQUE

    SciTech Connect

    Efroimsky, Michael; Makarov, Valeri V. E-mail: vvm@usno.navy.mil

    2013-02-10

    Tidal torques play a key role in rotational dynamics of celestial bodies. They govern these bodies' tidal despinning and also participate in the subtle process of entrapment of these bodies into spin-orbit resonances. This makes tidal torques directly relevant to the studies of habitability of planets and their moons. Our work begins with an explanation of how friction and lagging should be built into the theory of bodily tides. Although much of this material can be found in various publications, a short but self-consistent summary on the topic has been lacking in the hitherto literature, and we are filling the gap. After these preparations, we address a popular concise formula for the tidal torque, which is often used in the literature, for planets or stars. We explain why the derivation of this expression, offered in the paper by Goldreich and in the books by Kaula (Equation (4.5.29)) and Murray and Dermott (Equation (4.159)), implicitly sets the time lag to be frequency independent. Accordingly, the ensuing expression for the torque can be applied only to bodies having a very special (and very hypothetical) rheology which makes the time lag frequency independent, i.e., the same for all Fourier modes in the spectrum of tide. This expression for the torque should not be used for bodies of other rheologies. Specifically, the expression cannot be combined with an extra assertion of the geometric lag being constant, because at finite eccentricities the said assumption is incompatible with the constant-time-lag condition.

  14. Effects of Filtering the Angular Motion of the Crankshaft on the Estimation of the Instantaneous Engine Friction Torque

    NASA Astrophysics Data System (ADS)

    NEHME, H. K.; CHALHOUB, N. G.; HENEIN, N. A.

    2000-10-01

    The focus of this study is to investigate the effects of filtering the actual angular displacement, velocity and acceleration of the crankshaft on the computation of the instantaneous engine friction torque. These effects are isolated from those of measurement errors and/or noise by relying on a detailed model of the crank-slider mechanism to generate the rigid and flexible motions of the piston/connecting-rod/crankshaft mechanism along with the engine friction torque. The (P-ω) method is used herein to estimate the instantaneous engine friction torque based on the actual and the filtered angular displacement, velocity and acceleration of the crankshaft. The digital simulation results have demonstrated that the (P-ω) method cannot produce an acceptable estimation of the instantaneous engine friction torque in spite of filtering the actual angular motion of the crankshaft. It should be mentioned that the low-pass filter is commonly implemented to attenuate the measurement noise and the effects of structural deformations on the measured angular velocity of the crankshaft. However, the ineffectiveness of the low-pass filter stems from the non-linearities of the crank-slider mechanism that induced superharmonic and combination resonance frequencies in the angular displacement, velocity and acceleration of the crankshaft. The filter has severely attenuated some of the superharmonic resonance frequencies, which constitute an important part of the rigid-body behavior of the crankshaft that is needed by the (P-ω) method to accurately predict the engine friction torque. Moreover, the filtered signals would still be contaminated by the combination resonance frequencies that may appear in the low-frequency range commonly assumed to be dominated by the frequency components of the rigid-body motion of the crankshaft.

  15. High-velocity frictional strength across the Tohoku-Oki megathrust determined from surface drilling torque

    NASA Astrophysics Data System (ADS)

    Ujiie, Kohtaro; Inoue, Tomoya; Ishiwata, Junya

    2016-03-01

    High-velocity frictional strength is one of the primary factors controlling earthquake faulting. The Japan Trench Fast Drilling Project drilled through the shallow plate boundary fault, where displacement was ~50 m during the 2011 Tohoku-Oki earthquake. To determine downhole frictional strength, we analyzed the surface drilling torque data acquired at rotation rates equivalent to seismic slip rates (0.8-1.3 m/s). The results show a clear contrast in high-velocity frictional strength across the plate boundary fault: the apparent friction coefficient of frontal prism sediments (hemipelagic mudstones) in the hanging wall is 0.1-0.3, while that of the underthrust sediments (mudstone, laminar pelagic claystone, and chert) in the footwall increases to 0.2-0.4. The apparent friction coefficient of the smectite-rich pelagic clay in the plate boundary fault is 0.08-0.19, which is consistent with that determined from high-velocity (1.1-1.3 m/s) friction experiments. This suggests that surface drilling torque is useful in obtaining downhole frictional strength.

  16. The effect of sterilization and number of use on the accuracy of friction-style mechanical torque limiting devices for dental implants

    PubMed Central

    Fayaz, Ali; Mahshid, Minoo; Saboury, Aboulfazl; Sadr, Seyed Jalil; Ansari, Ghassem

    2014-01-01

    Background: Mechanical torque limiting devices (MTLDs) are necessary tools to control a peak torque and achieving target values of screw component of dental implants. Due to probable effect of autoclaving and number of use on the accuracy of these devices, this study aimed to evaluate the effect of sterilization and number of use on the accuracy of friction-style mechanical torque limiting devices (F-S MTLDs) in achieving their target torque values. Materials and Methods: Peak torque measurements of 15 new F-S MTLDs from three different manufacturers (Astra Tech, BioHorizons, Dr. Idhe) were measured ten times before and after 100 steam sterilization using a digital torque gauge. To simulate the clinical situation of aging (number of use) target torque application process was repeated 10 times after each sterilization cycle and the peak torque values were registered. Comparison of the mean differences with target torque in each cycle was performed using one sample t test. Considering the type of MTLDs as inter subject comparison, One-way repeated measure ANOVA was used to evaluate the absolute values of differences between devices of each manufacturer in each group (α = 0.05). Results: The results of this study in Dr. Idhe group showed that, mean of difference values significantly differed from the target torque (P = 0.002) until 75 cycles. In Astra Tech group, also mean of difference values with under estimation trend, showed a significant difference with the target torque (P < 0.001). Mean of difference values significantly differed from the target torque with under estimation trend during all the 100 cycles in BioHorizons group (P < 0.05). Conclusion: The torque output of each individual device stayed in 10% difference from target torque values before 100 sterilization cycles, but more than 10% difference from the target torque was seen in varying degrees during these consequent cycles. PMID:24688564

  17. Carbon phenolic roll torque measurements using a two component skin friction balance

    NASA Astrophysics Data System (ADS)

    Martellucci, A.; Somers, J.; Driftmyer, R.

    The objective of the current effort was to evaluate the reentry roll torque performance potential of the heatshield of a ballistic vehicle which has undergone exospheric nuclear damage. This damage causes the vehicle's heatshield to be rough on one side (i.e., with a velvet-like finish caused by phenolic removal and raised carbon fibers) and smooth on the other side. Roll torque performance of the heatshield specimens was established through a series of ground tests in ablation test and supersonic wind tunnel facilities. The roll torque performance was measured with a two component skin friction balance developed as part of this program. The balance was required to simultaneously resolve a side (torque) force of a fraction of a gram and which is more than an order of magnitude smaller than the axial force. This paper will describe details of the balance design and highlights of the results of these tests.

  18. A molecular dynamics study of dielectric friction

    SciTech Connect

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

    1996-07-01

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

  19. Effects of friction and high torque on fatigue crack propagation in Mode III

    NASA Astrophysics Data System (ADS)

    Nayeb-Hashemi, H.; McClintock, F. A.; Ritchie, R. O.

    1982-12-01

    Turbo-generator and automotive shafts are often subjected to complex histories of high torques. To provide a basis for fatigue life estimation in such components, a study of fatigue crack propagation in Mode III (anti-plane shear) for a mill-annealed AISI 4140 steel (RB88, 590 MN/m2 tensile strength) has been undertaken, using torsionally-loaded, circumferentially-notched cylindrical specimens. As demonstrated previously for higher strength AISI 4340 steel, Mode III cyclic crack growth rates (dc/dN) IIIcan be related to the alternating stress intensity factor ΔKIII for conditions of small-scale yielding. However, to describe crack propagation behavior over an extended range of crack growth rates (˜10-6 to 10-2 mm per cycle), where crack growth proceeds under elastic-plastic and full plastic conditions, no correlation between (dc/dN) III and ΔKIII is possible. Accordingly, a new parameter for torsional crack growth, termed the plastic strain intensity Γ III, is introduced and is shown to provide a unique description of Mode III crack growth behavior for a wide range of testing conditions, provided a mean load reduces friction, abrasion, and interlocking between mating fracture surfaces. The latter effect is found to be dependent upon the mode of applied loading (i.e., the presence of superimposed axial loads) and the crack length and torque level. Mechanistically, high-torque surfaces were transverse, macroscopically flat, and smeared. Lower torques showed additional axial cracks (longitudinal shear cracking) perpendicular to the main transverse surface. A micro-mechanical model for the main radi l Mode III growth, based on the premise that crack advance results from Mode II coalescence of microcracks initiated at inclusions ahead of the main crack front, is extended to high nominal stress levels, and predicts that Mode III fatigue crack propagation rates should be proportional to the range of plastic strain intensity (ΔΓIII if local Mode II growth rates are

  20. Feasibility study for convertible engine torque converter

    NASA Technical Reports Server (NTRS)

    1985-01-01

    The feasibility study has shown that a dump/fill type torque converter has excellent potential for the convertible fan/shaft engine. The torque converter space requirement permits internal housing within the normal flow path of a turbofan engine at acceptable engine weight. The unit permits operating the engine in the turboshaft mode by decoupling the fan. To convert to turbofan mode, the torque converter overdrive capability bring the fan speed up to the power turbine speed to permit engagement of a mechanical lockup device when the shaft speed are synchronized. The conversion to turbofan mode can be made without drop of power turbine speed in less than 10 sec. Total thrust delivered to the aircraft by the proprotor, fan, and engine during tansient can be controlled to prevent loss of air speed or altitude. Heat rejection to the oil is low, and additional oil cooling capacity is not required. The turbofan engine aerodynamic design is basically uncompromised by convertibility and allows proper fan design for quiet and efficient cruise operation. Although the results of the feasibility study are exceedingly encouraging, it must be noted that they are based on extrapolation of limited existing data on torque converters. A component test program with three trial torque converter designs and concurrent computer modeling for fluid flow, stress, and dynamics, updated with test results from each unit, is recommended.

  1. Experiment study on friction drive

    NASA Astrophysics Data System (ADS)

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

    2004-09-01

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

  2. Accurate torque control of a bi-directional magneto-rheological actuator considering hysteresis and friction effects

    NASA Astrophysics Data System (ADS)

    Nguyen, Phuong-Bac; Choi, Seung-Bok

    2013-05-01

    This paper presents a novel type of magneto-rheological (MR) actuator called a bi-directional magneto-rheological (BMR) actuator and accurate torque control results considering both hysteresis and friction compensation. The induced torque of this actuator varies from negative to positive values. As a result, it can work as either a brake or a clutch depending on the scheme of current input. In our work, the configuration of the actuator as well as its driving system is presented first. Subsequently, a congruency hysteresis based (CBH) model to take account of the effect of the hysteresis is proposed. After that, a compensator based on this model is developed. In addition, the effect of dry friction, which exists inherently with MR actuators in general, is also considered. In order to assess the effectiveness of the hysteresis compensator, several experiments on modeling and control of the actuator with different waveforms are carried out.

  3. Turbine blade friction damping study

    NASA Technical Reports Server (NTRS)

    Dominic, R. J.

    1985-01-01

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

  4. Valgus torque in youth baseball pitchers: A biomechanical study.

    PubMed

    Sabick, Michelle B; Torry, Michael R; Lawton, Richard L; Hawkins, Richard J

    2004-01-01

    The purpose of this study was to determine the biomechanical and anthropometric factors contributing to elbow valgus torque during pitching. Video data of 14 youth pitchers throwing fastballs were used to calculate shoulder and elbow kinematics and kinetics. Peak elbow valgus torque averaged 18 Nm and occurred just before maximal shoulder external rotation. The magnitude of valgus torque was most closely correlated with the thrower's weight. When subject weight and height were controlled for, maximum shoulder abduction torque and maximum shoulder internal rotation torque were most strongly associated with elbow valgus torque, accounting for 85% of its variance (P <.001). When only kinematic variables were considered, maximum shoulder external rotation accounted for 33% of the variance in valgus torque. Given that the biomechanical variables correlated with peak valgus torque are not easily modifiable, limiting the number of innings pitched is likely the best way to reduce elbow injury in youth pitchers. PMID:15111908

  5. Missile rolling tail brake torque system. [simulating bearing friction on canard controlled missiles

    NASA Technical Reports Server (NTRS)

    Davis, W. T. (Inventor)

    1984-01-01

    Apparatus for simulating varying levels of friction in the bearings of a free rolling tail afterbody on a canard-controlled missile to determine friction effects on aerodynamic control characteristics is described. A ring located between the missile body and the afterbody is utilized in a servo system to create varying levels of friction between the missile body and the afterbody to simulate bearing friction.

  6. Study of ball bearing torque under elastohydrodynamic lubrication

    NASA Technical Reports Server (NTRS)

    Townsend, D. P.; Zaretsky, E. V.; Allen, C. W.

    1973-01-01

    Spinning and rolling torques were measured in an angular-contact ball bearing with and without a cage under several lubrication regimes in a modified NASA spinning torque apparatus. Two lubricants were used - a di-2 ethylhexyl sebacate and a synthetic paraffinic oil, at shaft speeds of 1000, 2000, and 3000 rpm and bearing loads from 45 newtons (10 lb) to 403 newtons (90 lb). An analytical model was developed from previous spinning friction models to include rolling with spinning under lubrication regimes from thin film to flooded conditions. The bearing torque values have a wide variation, under any condition of speed and load, depending on the amount of lubricant present in the bearing. The analytical model compared favorably with experimental results under several lubrication regimes.

  7. Torque meter aids study of hysteresis motor rings

    NASA Technical Reports Server (NTRS)

    Cole, M.

    1967-01-01

    Torque meter, simulating hysteresis motor operation, allows rotor ring performance characteristics to be analyzed. The meter determines hysteresis motor torque and actual stresses of the ring due to its mechanical situation and rotation, aids in the study of asymmetries or defects in motor rings, and measures rotational hysteresis.

  8. Modeling and Compensation of the Internal Friction Torque of a Travelling Wave Ultrasonic Motor.

    PubMed

    Giraud, F; Sandulescu, P; Amberg, M; Lemaire-Semail, B; Ionescu, F

    2011-01-01

    This paper deals with the control and experimentation of a one-degree-of-freedom haptic stick, actuated by a travelling wave ultrasonic motor. This type of actuator has many interesting properties such as low-speed operation capabilities and a high torque-to-weight ratio, making it appropriate for haptic applications. However, the motor used in this application displays nonlinear behavior due to the necessary contact between its rotor and stator. Moreover, due to its energy conversion process, the torque applied to the end-effector is not a straightforward function of the supply current or voltage. This is why a force-feedback control strategy is presented, which includes an online parameter estimator. Experimental runs are then presented to examine the fidelity of the interface. PMID:26963660

  9. Study of torque matching of revolving vane compressor and expander

    NASA Astrophysics Data System (ADS)

    Subiantoro, A.; Ooi, K. T.

    2015-08-01

    An investigation was carried out to find the most optimum configuration, particularly the torque matching characteristics, of an integrated Revolving Vane compressor- expander. To carry out the study, a mathematical model of the integrated compressor-expander was developed. An open cycle air refrigeration system was adopted. The controlled parameter was the angle shift between the compressor and the expander. The observed parameters were the peak torque requirement and the bearing load. The results show that when properly matched, the peak torque can be reduced by more than 65% while the bearing loads can be reduced by up to 25%, depending on operating conditions. Unfortunately, the optimum angle shifts for peak torque do not always coincide with those for bearing load. When the pressure and inertial components of the torques are comparable or when the inertial component is dominant, the optimum angle shifts for peak torque and bearing load are around 180° and 330°, respectively. When the pressure component is dominant, the optimum angle shift for peak torque is equal to the angle difference between the pressure peak torques of the compressor and the expander while for bearing load is around 150°.

  10. [Brackets and friction in orthodontics: experimental study].

    PubMed

    Ben Rejeb Jdir, Saloua; Tobji, Samir; Turki, Wiem; Dallel, Ines; Khedher, Nedra; Ben Amor, Adel

    2015-09-01

    Many authors have been involved in developing brackets in order to improve the quality, stability, speed and efficiency of orthodontic treatment. In order to reduce friction between bracket and archwire, new therapeutic approaches have been devised based on novel technologies. Among these innovative techniques, self-ligating brackets are increasingly popular. SLBs can be classified into several categories according to their mode of action and their materials. We performed an experimental study to compare the friction forces generated during the sliding of orthodontic archwires made from various alloys through conventional and self-ligating brackets. Results show the favorable influence of SLBs, compared to conventional systems using elastomeric or metal ligatures, on the level of friction, particularly when shape-memory Ni-Ti archwires are used. PMID:26370596

  11. 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 A Study on Tactile Friction and Wear

    NASA Astrophysics Data System (ADS)

    Sugishita, Junji; Usami, Hatsuhiko; Hattori, Tomokazu

    The tactile wear (“tezure” in Japanese) is an abrasion phenomenon of material surfaces caused by the contact of human hand over a long period of time. Though this phenomenon has been the focus of various articles, an extensive study with regard to the wear characteristics is of a profound importance. To date, we have several remarkable examples such as the statue of Pindola Bharadvaja (Buddhist) and the St. Peter statue (Christian). Followers of the respective religions who are deeply attached and rooted have been touching the statues as part of their rituals for many generations over centuries. In this study, an attempt is done to verify the friction and wear characteristics of various soft metals with contact of human finger. The results of our experiments show that the friction coefficient upon the contact of the human finger and pure copper are very high and thus proving tactile wear of soft metals can be generated easily.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  13. Study of a Satellite Attitude Control System Using Integrating Gyros as Torque Sources

    NASA Technical Reports Server (NTRS)

    White, John S.; Hansen, Q. Marion

    1961-01-01

    This report considers the use of single-degree-of-freedom integrating gyros as torque sources for precise control of satellite attitude. Some general design criteria are derived and applied to the specific example of the Orbiting Astronomical Observatory. The results of the analytical design are compared with the results of an analog computer study and also with experimental results from a low-friction platform. The steady-state and transient behavior of the system, as determined by the analysis, by the analog study, and by the experimental platform agreed quite well. The results of this study show that systems using integrating gyros for precise satellite attitude control can be designed to have a reasonably rapid and well-damped transient response, as well as very small steady-state errors. Furthermore, it is shown that the gyros act as rate sensors, as well as torque sources, so that no rate stabilization networks are required, and when no error sensor is available, the vehicle is still rate stabilized. Hence, it is shown that a major advantage of a gyro control system is that when the target is occulted, an alternate reference is not required.

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

    PubMed Central

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

    2016-01-01

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

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

    PubMed

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

    2016-01-01

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

  16. Initial Study of Friction Pull Plug Welding

    NASA Technical Reports Server (NTRS)

    Rich, Brian S.

    1999-01-01

    Pull plug friction welding is a new process being developed to conveniently eliminate defects from welded plate tank structures. The general idea is to drill a hole of precise, optimized dimensions and weld a plug into it, filling the hole perfectly. A conically-shaped plug is rotated at high angular velocity as it is brought into contact with the plate material in the hole. As the plug is pulled into the hole, friction rapidly raises the temperature to the point at which the plate material flows plastically. After a brief heating phase, the plug rotation is terminated. The plug is then pulled upon with a forging force, solidly welding the plug into the hole in the plate. Three aspects of this process were addressed in this study. The transient temperature distribution was analyzed based on slightly idealized boundary conditions for different plug geometries. Variations in hole geometry and ram speed were considered, and a program was created to calculate volumes of displaced material and empty space, as well as many other relevant dimensions. The relation between the axially applied forging force and the actual forging pressure between the plate and plug surfaces was determined for various configurations.

  17. Studying the Frictional Force Directions via Bristles

    ERIC Educational Resources Information Center

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

    2010-01-01

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

  18. DETAILED STUDIES OF ELECTRON COOLING FRICTION FORCE.

    SciTech Connect

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

    2005-09-18

    High-energy electron cooling for RHIC presents many unique features and challenges. An accurate estimate of the cooling times requires detailed simulation of the electron cooling process. The first step towards such calculations is to have an accurate description of the cooling force. Numerical simulations are being used to explore various features of the friction force which appear due to several effects, including the anisotropy of the electron distribution in velocity space and the effect of a strong solenoidal magnetic field. These aspects are being studied in detail using the VORFAL code, which explicitly resolves close binary collisions. Results are compared with available asymptotic and empirical formulas and also, using the BETACOOL code, with direct numerical integration of less approximate expressions over the specified electron distribution function.

  19. Detailed Studies of Electron Cooling Friction Force

    SciTech Connect

    Fedotov, A. V.; Bruhwiler, D. L.; Abell, D. T.; Sidorin, A. O.

    2006-03-20

    High-energy electron cooling for RHIC presents many unique features and challenges. An accurate estimate of the cooling times requires detailed simulation of the electron cooling process. The first step towards such calculations is to have an accurate description of the cooling force. Numerical simulations are being used to explore various features of the friction force which appear due to several effects, including the anisotropy of the electron distribution in velocity space and the effect of a strong solenoidal magnetic field. These aspects are being studied in detail using the VORPAL code, which explicitly resolves close binary collisions. Results are compared with available asymptotic and empirical formulas and also, using the BETACOOL code, with direct numerical integration of less approximate expressions over the specified electron distribution function.

  1. Fundamental Study of Material Flow in Friction Stir Welds

    NASA Technical Reports Server (NTRS)

    Reynolds, Anthony P.

    1999-01-01

    The presented research project consists of two major parts. First, the material flow in solid-state, friction stir, butt-welds as been investigated using a marker insert technique. Changes in material flow due to welding parameter as well as tool geometry variations have been examined for different materials. The method provides a semi-quantitative, three-dimensional view of the material transport in the welded zone. Second, a FSW process model has been developed. The fully coupled model is based on fluid mechanics; the solid-state material transport during welding is treated as a laminar, viscous flow of a non-Newtonian fluid past a rotating circular cylinder. The heat necessary for the material softening is generated by deformation of the material. As a first step, a two-dimensional model, which contains only the pin of the FSW tool, has been created to test the suitability of the modeling approach and to perform parametric studies of the boundary conditions. The material flow visualization experiments agree very well with the predicted flow field. Accordingly, material within the pin diameter is transported only in the rotation direction around the pin. Due to the simplifying assumptions inherent in the 2-D model, other experimental data such as forces on the pin, torque, and weld energy cannot be directly used for validation. However, the 2-D model predicts the same trends as shown in the experiments. The model also predicts a deviation from the "normal" material flow at certain combinations of welding parameters, suggesting a possible mechanism for the occurrence of some typical FSW defects. The next step has been the development of a three-dimensional process model. The simplified FSW tool has been designed as a flat shoulder rotating on the top of the workpiece and a rotating, cylindrical pin, which extends throughout the total height of the flow domain. The thermal boundary conditions at the tool and at the contact area to the backing plate have been varied

  2. Aligning, leveling, and torque control--a pilot study.

    PubMed

    Andreasen, G F; Amborn, R M

    1989-01-01

    Aligning, leveling, and anterior torque control of teeth from the onset of treatment is suggested with thermal ni-ti rectangular low stiffness wires. Before and after superimpositions show the degree that torque control was achieved on four clinical patients. PMID:2923323

  3. Seasonal Distributions of Mountain Torques during FGGE.

    NASA Astrophysics Data System (ADS)

    Wei, Ming-Ying; Schaack, Todd K.

    1984-10-01

    Based on surface pressure and terrain height analyses from the National Meteorological Center, mountain torques are calculated for January, April, July and October 1979 during the First GARP Global Experiment. The zonally integrated mountain torques are generally in good agreement with previous studies. For all four months, positive torque exists in the tropical latitudes as well as in the polar and subtropical latitudes of the Northern Hemisphere; negative torque exists in northern middle latitudes and most of the Southern Hemisphere. An exception occurs in July when the mountain torque is negative between 5 and 25°N and positive in the Southern Hemisphere subtropics. Over latitudes where large terrain variation exists such as near 20°S due to the Andes, the estimate obtained in this study is larger in magnitude than that from previous work. The difference is due to the differences in both grid resolution and the particular atmospheric data and topography selected.The meridional profiles of individual continental mountain torques are examined to illustrate geographical contributions to the net zonal torque. The positive mountain torque in northern high latitudes is due mainly to North America and Greenland. Both North America and Eurasia contribute to the sink of angular momentum in northern middle latitudes and the source in the subtropical latitudes. The negative torque between 5 and 25°N in July is due to the influence of the Indian monsoon trough on Arabia and Africa. The negative mountain torque over South America dominates the positive torque over Africa and Australia in the Southern Hemisphere in January and October.Although the monthly averaged zonally integrated mountain torque assumes lesser importance when compared to the frictional torque, regional mountain torque at the synoptic time scale is quite large and can have considerable influence on the large scale circulation. Hemispheric torques are in qualitative agreement with previous work. Due to

  4. 11th Grade Students' Conceptual Understanding about Torque Concept: A Longitudinal Study

    ERIC Educational Resources Information Center

    Bostan Sarioglan, Ayberk; Küçüközer, Hüseyin

    2014-01-01

    In this study, it is aimed to reveal the effect of instruction on students' ideas about torque before instruction, after instruction and fifteen weeks after instruction. The working group consists of twenty five high school eleventh grade students. To reveal these students' ideas about the concept of torque a concept test consisting of seven…

  5. Torque Loss After Miniscrew Placement: An In-Vitro Study Followed by a Clinical Trial

    PubMed Central

    Migliorati, Marco; Drago, Sara; Barberis, Fabrizio; Schiavetti, Irene; Dalessandri, Domenico; Benedicenti, Stefano; Biavati, Armando Silvestrini

    2016-01-01

    To evaluate torque loss a week after insertion, both in an in vivo and an in vitro experimental setup were designed. In the in vivo setup a total of 29 miniscrews were placed in 20 patients who underwent orthodontic treatment. Maximum insertion torque (MIT) was evaluated at insertion time (T1). A week later, insertion torque was measured again by applying a quarter turn (T2); no load was applied on the screw during the first week. In the in vitro setup a total of 20 miniscrews were placed in pig rib bone samples. MIT was evaluated at insertion time (T1). Bone samples were kept in saline solution and controlled environment for a week during which the solution was refreshed every day. Afterwards, torque was measured again by applying a quarter turn (T2). The comparison of MIT over time was done calculating the percentage difference of the torque values between pre- and post-treatment and using the parametric two independent samples t-test or the non-parametric Mann–Whitney test. After a week unloaded miniscrews showed a mean loss of rotational torque of 36.3% and 40.9% in in vitro and in in vivo conditions, respectively. No statistical differences were found between the two different setups. Torque loss was observed after the first week in both study models; in vitro experimental setup provided a reliable study model for studying torque variation during the first week after insertion. PMID:27386011

  6. Scale effects in sliding friction: An experimental study

    SciTech Connect

    Blau, P.J.

    1991-07-24

    Solid friction is considered by some to be a fundamental property of two contacting materials, while others consider it to be a property of the larger tribosystem in which the materials are contained. A set of sliding friction experiments were designed to investigate the hypothesis that the unlubricated sliding friction between two materials is indeed a tribosystems-related property and that the relative influence of the materials properties or those of the machine on friction varies from one situation to another. Three tribometers were used: a friction microprobe (FMP), a typical laboratory-scale reciprocating pin-on-flat device, and a heavy-duty commercial wear tester. The slider material was stainless steel (AISI 440C) and the flat specimen material was an ordered alloy of Ni{sub 3}Al (IC-50). Sphere-on-flat geometry was used at ambient conditions and at normal forces ranging from 0.01 N to 100 N and average sliding velocities of 0.01 to 100.0 mm/s. The nominal, steady-state sliding friction coefficient tended to decrease with increases in normal force for each of the three tribometers, and the steady state value of sliding friction tended to increase as the mass of the machine increased. The variation of the friction force during sliding was also a characteristic of the test system. These studies provide further support to the idea that the friction of both laboratory-scale and engineering tribosystems should be treated as a parameter which may take on a range of characteristic values and not conceived as having a single, unique value for each material pair.

  7. Split torque transmission load sharing

    NASA Technical Reports Server (NTRS)

    Krantz, T. L.; Rashidi, M.; Kish, J. G.

    1992-01-01

    Split torque transmissions are attractive alternatives to conventional planetary designs for helicopter transmissions. The split torque designs can offer lighter weight and fewer parts but have not been used extensively for lack of experience, especially with obtaining proper load sharing. Two split torque designs that use different load sharing methods have been studied. Precise indexing and alignment of the geartrain to produce acceptable load sharing has been demonstrated. An elastomeric torque splitter that has large torsional compliance and damping produces even better load sharing while reducing dynamic transmission error and noise. However, the elastomeric torque splitter as now configured is not capable over the full range of operating conditions of a fielded system. A thrust balancing load sharing device was evaluated. Friction forces that oppose the motion of the balance mechanism are significant. A static analysis suggests increasing the helix angle of the input pinion of the thrust balancing design. Also, dynamic analysis of this design predicts good load sharing and significant torsional response to accumulative pitch errors of the gears.

  8. Does sensorimotor cortex activity change with quadriceps femoris torque output? A human electroencephalography study.

    PubMed

    Fry, A; Vogt, T; Folland, J P

    2014-09-01

    Encoding muscular force output during voluntary contractions is widely perceived to result, at least in part, from modulations in neuronal activity within the sensorimotor cortex. However the underlying electrophysiological phenomena associated with increased force output remains unclear. This study directly assessed sensorimotor cortex activity using electroencephalography (EEG) in humans performing isometric knee-extensions at a range of discrete torque levels. Fifteen healthy males (age 24 (s=5) years) completed one familiarization and one experimental trial. Participants performed a cyclic series of 60 isometric knee-extension contractions with the right leg, including 15 contractions of a 5-s duration at each of four discrete torque levels: 15%, 30%, 45% and 60% of maximal voluntary torque (MVT). Isometric knee-extension torque, quadriceps electromyography and EEG were recorded at rest and throughout all the contractions. EEG (0.5-50 Hz) was collected using a 32-channel active-electrode cap. A voxel-based low-resolution brain electromagnetic tomography (LORETA) analysis calculated cortical activation within the sensorimotor cortex (one of 27 MNI coordinates) for the entire 0.5-50-Hz range (cortical current density (CCD)), as well as for each constituent frequency band in this range (delta, theta, alpha, beta and gamma). Gamma band (30-50 Hz) cortical activity increased with contraction torque (analysis of variance [ANOVA], P=0.03). Conversely, activity within the other frequency bands was not modulated by torque (P≥0.09), nor was overall CCD (P=0.11). Peripheral neuromuscular activation (quadriceps electromyography (EMG) amplitude) demonstrated distinct increases between each torque level (P<0.01). In conclusion, sensorimotor cortical activity within the gamma band demonstrated an overall increase with contraction torque, whereas both CCD and each of the other constituent frequency bands were not modulated by increments in torque magnitude during isometric

  9. Steady-state wear and friction in boundary lubrication studies

    NASA Technical Reports Server (NTRS)

    Loomis, W. R.; Jones, W. R., Jr.

    1980-01-01

    A friction and wear study was made at 20 C to obtain improved reproducibility and reliability in boundary lubrication testing. Ester-base and C-ether-base fluids were used to lubricate a pure iron rider in sliding contact with a rotating M-50 steel disk in a friction and wear apparatus. Conditions included loads of 1/2 and 1 kg and sliding velocities of 3.6 to 18.2 m/min in a dry air atmosphere and stepwise time intervals from 1 to 250 min for wear measurements. The wear rate results were compared with those from previous studies where a single 25 min test period was used. Satisfactory test conditions for studying friction and wear in boundary lubrication for this apparatus were found to be 1 kg load; sliding velocities of 7.1 to 9.1 m/min (50 rpm disk speed); and use of a time stepwise test procedure. Highly reproducible steady-state wear rates and steady-state friction coefficients were determined under boundary conditions. Wear rates and coefficients of friction were constant following initially high values during run-in periods.

  10. Experimental Study of Sliding Friction for PET Track Membranes

    NASA Astrophysics Data System (ADS)

    Filippova, E. O.; Filippov, A. V.; Shulepov, I. A.

    2016-04-01

    The article is presented results of a study of the process for a dry friction metal-polymer couple on scheme disc-finger. Track membrane from polyethylene terephthalate was a research material. Membrane had pores with 0.4 and 0.8 μm diameters. The effect of the sliding velocity for membranes with pores of 0.8 microns was determined. Research was shown that increasing pore’s diameter caused a reduction of the friction coefficient and downturn its magnitude vibrations. The study showed that track membrane have adequate resistance to wear and can be successfully used in surgical procedures in the layers of the cornea.

  11. Comparative study of torque expression among active and passive self-ligating and conventional brackets

    PubMed Central

    Franco, Érika Mendonça Fernandes; Valarelli, Fabrício Pinelli; Fernandes, João Batista; Cançado, Rodrigo Hermont; de Freitas, Karina Maria Salvatore

    2015-01-01

    Abstract Objective: The aim of this study was to compare torque expression in active and passive self-ligating and conventional brackets. Methods: A total of 300 segments of stainless steel wire 0.019 x 0.025-in and six different brands of brackets (Damon 3MX, Portia, In-Ovation R, Bioquick, Roth SLI and Roth Max) were used. Torque moments were measured at 12°, 24°, 36° and 48°, using a wire torsion device associated with a universal testing machine. The data obtained were compared by analysis of variance followed by Tukey test for multiple comparisons. Regression analysis was performed by the least-squares method to generate the mathematical equation of the optimal curve for each brand of bracket. Results: Statistically significant differences were observed in the expression of torque among all evaluated bracket brands in all evaluated torsions (p < 0.05). It was found that Bioquick presented the lowest torque expression in all tested torsions; in contrast, Damon 3MX bracket presented the highest torque expression up to 36° torsion. Conclusions: The connection system between wire/bracket (active, passive self-ligating or conventional with elastic ligature) seems not to interfere in the final torque expression, the latter being probably dependent on the interaction between the wire and the bracket chosen for orthodontic mechanics. PMID:26691972

  12. Study on Transmission Torque Characteristics of a Surface-Permanent-Magnet-Type Magnetic Gear

    NASA Astrophysics Data System (ADS)

    Niguchi, Noboru; Hirata, Katsuhiro; Hayakawa, Yuichi

    Magnetic gears have some advantages such as low mechanical loss and maintenance-free operation that are not observed in conventional mechanical gears. In addition, magnetic gears have inherent overload protection. Therefore, magnetic gears are expected to be used in special applications; for example, they can be used in a joint of a humanoid robot. Recently, various types of new magnetic gears have been proposed. Among these new gears, a surface-permanent-magnet-type (SPM-type) magnetic gear employing harmonic magnetic flux has gained attention because of its high transmission torque density, though it has a complex structure with multipole magnets. Some studies on an SPM-type magnetic gear have been carried out, but there are few papers on cogging torque. This paper describes the transmission torque characteristics of an SPM-type magnetic gear. The operating principle and the transmission torque under synchronous operation are formulated in accordance with the gear ratio. High orders of the cogging torque are computed by employing the 3-D finite element method, and the validity of the analysis is verified by carrying out measurements on a prototype. Furthermore, a method for reducing the cogging torque is discussed.

  13. A frictional study of total hip joint replacements

    NASA Astrophysics Data System (ADS)

    Scholes, S. C.; Unsworth, A.; Goldsmith, A. A. J.

    2000-12-01

    Polymeric wear debris produced by articulation of the femoral head against the ultra-high-molecular-weight polyethylene socket of a total hip replacement has been implicated as the main cause of osteolysis and subsequent failure of these implants. Potential solutions to this problem are to employ hard bearing surface combinations such as metal-on-metal or ceramic-on-ceramic prostheses. The aim of this study was to investigate the difference in lubrication modes and friction of a range of material combinations using synthetic and biological fluids as the lubricants. The experimental results were compared with theoretical predictions of film thicknesses and lubrication modes. A strong correlation was observed between experiment and theory when employing carboxy methyl cellulose (CMC) fluids as the lubricant. Under these conditions the ceramic-on-ceramic joints showed full fluid film lubrication while the metal-on-metal, metal-on-plastic, diamond-like carbon-coated stainless steel (DLC)-on-plastic and ceramic-on-plastic prostheses operated under a mixed lubrication regime. With bovine serum as the lubricant in the all ceramic joints, however, the full fluid film lubrication was inhibited due to adsorbed proteins. In the metal-on-metal joints this adsorbed protein layer acted to reduce the friction while in the ceramic coupling the friction was increased. The use of bovine serum as the lubricant also significantly increased the friction in both the metal-on-plastic and ceramic-on-plastic joints. The friction produced by the DLC-on-plastic joints depended on the quality of the coating. Those joints with a less consistent coating and therefore a higher surface roughness gave significantly higher friction than the smoother, more consistently coated heads.

  14. Computational study of radiation torque on arbitrary shaped particles with MLFMA.

    PubMed

    Yang, Minglin; Ren, Kuan Fang; Petkov, Theodor; Pouligny, Bernard; Loudet, Jean-Christophe; Sheng, Xinqing

    2015-09-01

    The surface integral equation (SIE) method is used for the computational study of radiation torque on arbitrarily shaped homogeneous particles. The Multilevel Fast Multipole Algorithm (MLFMA) is employed to reduce memory requirements and improve the capability of SIE. The resultant matrix equations are solved iteratively to obtain equivalent electric and magnetic currents. Then, radiation torque is computed using the vector flux of the pseudotensor over a spherical surface tightly enclosing the particle. We use, therefore, the analytical electromagnetic field expression for incident waves in the near region, instead of the far-field approximation. This avoids the error which may be caused when describing the incident beam. The numerical results of three kinds of non-spherical particles are presented to illustrate the validity and capability of the developed method. It is shown that our method can be applied to predict, in the rigorous sense, the torque from a beam of any shape on a particle of complex configuration with a size parameter as large as 650. The radiation torques on large ellipsoids are exemplified to show the performance of the method and to study the influence that different aspect ratios have on the results. Then, the code is used for the calculation of radiation torque on objects of complex shape including a biconcave cell-like particle and a motor with a non-smooth surface. PMID:26368438

  15. Characterizing the effects of friction liner materials on the performance of piezoelectric motors using finite element analysis

    SciTech Connect

    Gute, G.D.; Halter, S.L.

    1995-10-01

    A finite element model of a Panasonic USM-40D piezoelectric motor`s rotor was coupled with a finite element model of the motor`s friction liner/rotor so that the frictional interface could be further studied. Results from the model were used to study the affects of various friction liner material properties on motor stall torque. Statistical methods were used to determine the significant friction liner material properties and their interactions. An equation for predicting the stall torque as a function of the significant variables and their interactions was established.

  16. Preliminary Study of a Pull Plug Friction Weld

    NASA Technical Reports Server (NTRS)

    Buchanan, George R.

    1999-01-01

    A pull plug friction weld, simply defined, comprises inserting a rotating cone-shaped cylinder into a somewhat cone-shaped hole in a plate. The rotating plug makes contact with the edge of the plate and the resulting friction generates heat. The temperature of the plate material eventually reaches a magnitude that will cause the plate material at the edge of the hole to flow. This can be termed a temperature dependent plastic flow. The rotation of the plug is terminated, additional pressure is applied and the metal at the interface of the two materials cools and welding occurs. This preliminary study addresses only three aspects of a complete analysis that is multi-faceted. The transient temperature distribution for different pull plug configurations has been studied in some detail even though the initial conditions and boundary conditions may still be deemed tentative. The stress distribution within the pull plug caused by the heating pressure was studied along with a preliminary analysis of the thermoelastic stress distribution caused by friction heating. There are no definitive results for the stress analysis. Additional study will be required.

  17. Design and MHD modeling of ATLAS experiments to study friction

    SciTech Connect

    Faehl, R. J.; Hammerberg, J. E.

    2002-01-01

    Transverse shear at the interface of two solids occurs when these solids move at different velocities. This frictional phenomenon is being studied in a series of experiments on the ATLAS capacitor bank at Los Alamos. Cylindrical targets to test friction force models are composed of alternating regions of high- and low-shock speed materials. When the target is impacted by a cylindrical, magnetically-accelerated aluminum liner, the differential shock velocity in the two materials establishes the desired shear at the interface. One- and two-dimensional MHD calculations have been performed to design liners with suitable properties to drive these 'friction-like' ATLAS experiments. A thick impactor allows the shock to be maintained for several microseconds. The ATLAS experiments use a liner that is approximately 10 mm thick at impact, with an inner surface velocity of {approx} 1.4-1.5 km/s. Interaction of this thick liner with the electrodes, or glide planes, results in significant deformation of the hardened stainless steel electrodes. Data from the ATLAS experiments and comparisons with the calculations will be presented, along with plans for future experiments.

  18. A numerical study of the rolling friction between a microsphere and a substrate considering the adhesive effect

    NASA Astrophysics Data System (ADS)

    Zhang, Yuyan; Wang, Xiaoli; Li, Hanqing; Yang, Weixu

    2016-01-01

    A numerical model of the rolling friction between a microsphere and a substrate is established by introducing the adhesion hysteresis between the front and rear sides of the contact region into Zhang’s adhesive contact model. Effects of the size ratio which is defined as the sphere radius divided by the equilibrium separation, relative amount of adhesion hysteresis and Tabor parameter on the dimensionless maximum rolling friction torque in the case of zero normal force are inspected, and the quantitative relationship between the maximum rolling friction torque and the normal force is achieved. Results indicate that due to adhesion hysteresis at microscale, the dimensionless maximum rolling friction torque at zero normal force is not zero, which not only increases with decreasing size ratio, showing clear size effects, but also increases with increasing relative amount of adhesion hysteresis and Tabor parameter. In addition, the maximum rolling friction torque at microscale presents a sublinear relationship with the normal force, and the exponent of the normal force is influenced by the size ratio, relative amount of adhesion hysteresis and Tabor parameter, which are remarkably different from the superlinear relationship at macroscale.

  19. Molecular simulation studies of nanoscale friction between phosphorylcholine self-assembled monolayer surfaces: Correlation between surface hydration and friction

    NASA Astrophysics Data System (ADS)

    He, Yi; Chen, Shengfu; Hower, Jason C.; Bernards, Matthew T.; Jiang, Shaoyi

    2007-08-01

    We performed all-atom molecular dynamics simulations to study the friction between surfaces covered with two phosphorylcholine self-assembled monolayers (PC-SAM) under shear. PC-SAM surfaces with a √7×√7R19° lattice structure and a parallel arrangement of the head groups were used as model zwitterionic surfaces. They provide a full representation of the zwitterionic nature of phospholipid surfaces, which are believed to play an important role in the lubrication of biological joints such as knees and hips. The surfaces were immersed in aqueous solutions and kept in contact with two regions of bulk water. Sodium chloride and potassium chloride solutions at various concentrations were employed to study the effects of the presence of ions on friction. The results show a strong relationship between surface hydration and friction. Higher ionic concentrations or ions with shorter Debye lengths cause a larger disruption to the hydration around the zwitterionic surfaces, leading to larger friction forces. In addition, the results show that under nanoscale confinement, the friction coefficients of PC-SAM surfaces in pure water are directly proportional to both shear velocity and surface separation distance. These results are comparable to previously published experimental studies.

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

    NASA Technical Reports Server (NTRS)

    Bascom, Willard D.; Lee, Ilzoo

    1990-01-01

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

  1. An Electromyographic-driven Musculoskeletal Torque Model using Neuro-Fuzzy System Identification: A Case Study.

    PubMed

    Jafari, Zohreh; Edrisi, Mehdi; Marateb, Hamid Reza

    2014-10-01

    The purpose of this study was to estimate the torque from high-density surface electromyography signals of biceps brachii, brachioradialis, and the medial and lateral heads of triceps brachii muscles during moderate-to-high isometric elbow flexion-extension. The elbow torque was estimated in two following steps: First, surface electromyography (EMG) amplitudes were estimated using principal component analysis, and then a fuzzy model was proposed to illustrate the relationship between the EMG amplitudes and the measured torque signal. A neuro-fuzzy method, with which the optimum number of rules could be estimated, was used to identify the model with suitable complexity. Utilizing the proposed neuro-fuzzy model, the clinical interpretability was introduced; contrary to the previous linear and nonlinear black-box system identification models. It also reduced the estimation error compared with that of the most recent and accurate nonlinear dynamic model introduced in the literature. The optimum number of the rules for all trials was 4 ± 1, that might be related to motor control strategies and the % variance accounted for criterion was 96.40 ± 3.38 which in fact showed considerable improvement compared with the previous methods. The proposed method is thus a promising new tool for EMG-Torque modeling in clinical applications. PMID:25426427

  2. Torque magnetometry study of Fe and Ni doped SmB6

    NASA Astrophysics Data System (ADS)

    Tinsman, Colin; Li, Gang; Lawson, Benjamin; Yu, Fan; Asaba, Tomoya; Wang, Xiangfeng; Paglione, Johnpierre; Li, Lu

    2015-03-01

    There has been renewed interest in the past few years regarding Samarium Hexaboride, a promising candidate to be a topological Kondo insulator. Work on this material represents an extension of the categorization of materials by the topology of their electronic band structure into systems with strong correlation effects. It is known that by introducing magnetic impurities, such as Iron, Nickel, and Europium, the magnetic ground state of SmB6 could be greatly altered. In this study we will present our torque magnetometry data of Fe and Ni doped SmB6, down to 20 mK, and up to 45 Tesla. It is found that the overall symmetry of the angular dependence of torque with respect to magnetic field changed for both Fe-doped SmB6 and Ni-doped SmB6. For pure SmB6, the angular dependence is proportional to sin (2 θ) , as expected for a paramagnetic material. By contrast, for Fe-doped SmB6 and Ni-doped SmB6, the torque vs. tilt angle profile becomes sin (4 θ) . Furthermore, for FexSmB6 the field dependence of torque shows a sharp bend feature around 9 Tesla, which softens with elevating temperature, and could be related to magnetic moment re-alignment.

  3. An Electromyographic-driven Musculoskeletal Torque Model using Neuro-Fuzzy System Identification: A Case Study

    PubMed Central

    Jafari, Zohreh; Edrisi, Mehdi; Marateb, Hamid Reza

    2014-01-01

    The purpose of this study was to estimate the torque from high-density surface electromyography signals of biceps brachii, brachioradialis, and the medial and lateral heads of triceps brachii muscles during moderate-to-high isometric elbow flexion-extension. The elbow torque was estimated in two following steps: First, surface electromyography (EMG) amplitudes were estimated using principal component analysis, and then a fuzzy model was proposed to illustrate the relationship between the EMG amplitudes and the measured torque signal. A neuro-fuzzy method, with which the optimum number of rules could be estimated, was used to identify the model with suitable complexity. Utilizing the proposed neuro-fuzzy model, the clinical interpretability was introduced; contrary to the previous linear and nonlinear black-box system identification models. It also reduced the estimation error compared with that of the most recent and accurate nonlinear dynamic model introduced in the literature. The optimum number of the rules for all trials was 4 ± 1, that might be related to motor control strategies and the % variance accounted for criterion was 96.40 ± 3.38 which in fact showed considerable improvement compared with the previous methods. The proposed method is thus a promising new tool for EMG-Torque modeling in clinical applications. PMID:25426427

  4. Hysteretic effects of dry friction: modelling and experimental studies.

    PubMed

    Wojewoda, Jerzy; Stefański, Andrzej; Wiercigroch, Marian; Kapitaniak, Tomasz

    2008-03-13

    In this paper, the phenomena of hysteretic behaviour of friction force observed during experiments are discussed. On the basis of experimental and theoretical analyses, we argue that such behaviour can be considered as a representation of the system dynamics. According to this approach, a classification of friction models, with respect to their sensitivity on the system motion characteristic, is introduced. General friction modelling of the phenomena accompanying dry friction and a simple yet effective approach to capture the hysteretic effect are proposed. Finally, the experimental results are compared with the numerical simulations for the proposed friction model. PMID:17947206

  5. Friction measurement in a hip wear simulator.

    PubMed

    Saikko, Vesa

    2016-05-01

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

  6. Penetration into dry porous rock: A numerical study on sliding friction simulation

    SciTech Connect

    Chen, E.P.

    1988-10-01

    Penetration of Antelope tuff targets by steel penetrators is the subject of discussion in the present investigation. Specifically, the effect of sliding friction between projectile and target on penetration is examined. The finite element code PRONTO 2D is used to perform a parametric study of the coefficient of friction. Both constant and velocity dependent coefficient of friction representation have been included in the current investigation. Results indicate that increases in the coefficient of friction increase the penetration resistance although the relationship is nonlinear in nature. In terms of peak deceleration and depth of penetration, both the constant and velocity dependent coefficient of friction representation provide almost identical results. However, only the velocity dependent cases show the characteristic of increasing deceleration prior to the conclusion of the penetration event. For this reason, the velocity dependent representation of the coefficient of friction is preferred over the constant friction coefficient representation. 8 refs., 13 figs., 1 tab.

  7. High torque bellows seal rotary drive

    NASA Technical Reports Server (NTRS)

    Diaguila, A. J.; Macomber, J. W.; Adams, D. W.

    1972-01-01

    Bellows seal rotary drive device was developed which allows high torque transmission through sealed compartments. Bearing friction which would normally be carried by sealing bellows in comparable devices is absorbed by universal-gimbal joint. It can be used to transmit high torque, low speed, rotary motion through sealed barriers to prevent contamination or escape of fluids.

  8. A computational study of brush seal contact loads with friction

    NASA Astrophysics Data System (ADS)

    Aksit, Mahmut Faruk

    The brush seal is emerging as a new technology to effectively control cooling and leakage flows in gas turbine engines. With their superior leakage performance, they show the potential to replace current labyrinth seals in gas turbine engines. Because the bristles slide against the rotor surface, wear at the contact becomes a major concern as it determines the life and efficiency of the seal. To optimize seal life and efficiency, an in-depth study of the factors causing the seal stiffness is needed, and a good choice of materials must be made. Although considerable research has been done on material selection and tribopairs, a brief survey reveals the lack of reliable analyses to evaluate contact loads, and to address heat transfer issues. As material pairs have been optimized for most cases, understanding and management of contact loads hold the key for further improvements in seal life. The complicated nature of bristle behavior under various combinations of pressure load and rotor interference requires computer analysis to study details that may not be available through analytical formulations. In an attempt to meet this need, this study presents a 3-D finite element model of a brush seal. The model consists of a representative bristle bundle with a backing plate and a rotor surface. Every bristle is defined by a number of 3-D quadratic beam elements. Bristles are fixed at the top nodes, while they are free to move in any direction at the tip touching the rotor surface. The model consists of 10 to 13 circumferential rows of bristles. The number of rows are based on the actual packing thickness of the seal modeled. Unlike previous analytical studies on brush seal contact loads, this work includes nonlinear frictional effects between the bristles. Frictional effects are known to drastically change the seal behavior, and are crucial in determining the contact forces. The model applies the available published experimental data to define the boundary conditions and

  9. Parametric study of turbine blade platform friction damping using the lumped parameter analysis

    NASA Technical Reports Server (NTRS)

    Dominic, R. J.

    1984-01-01

    The hardware configuration used in the present study of turbine blade planform friction damping, by means of the lumped parameter analysis, is the first turbine stage of the Space Shuttle Main Engine's High Pressure Fuel Turbopump. The analysis procedure solves the nonlinear equations of motion for a turbine blade that is acted on by a platform friction damper, using an iterative matrix method. Attention is given to the effects on blade deflection response of variations in friction coefficient, the normal force on the friction surface interface, blade hysteretic damping, the blade-to-blade phase angle of the harmonic forcing function, and the amplitude of the forcing function.

  10. Analytic and simulation studies on the use of torque-wheel actuators for the control of flexible robotic arms

    NASA Technical Reports Server (NTRS)

    Montgomery, Raymond C.; Ghosh, Dave; Kenny, Sean

    1991-01-01

    This paper presents results of analytic and simulation studies to determine the effectiveness of torque-wheel actuators in suppressing the vibrations of two-link telerobotic arms with attached payloads. The simulations use a planar generic model of a two-link arm with a torque wheel at the free end. Parameters of the arm model are selected to be representative of a large space-based robotic arm of the same class as the Space Shuttle Remote Manipulator, whereas parameters of the torque wheel are selected to be similar to those of the Mini-Mast facility at the Langley Research Center. Results show that this class of torque-wheel can produce an oscillation of 2.5 cm peak-to-peak in the end point of the arm and that the wheel produces significantly less overshoot when the arm is issued an abrupt stop command from the telerobotic input station.

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

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

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

  12. van der Waals torque

    NASA Astrophysics Data System (ADS)

    Esquivel-Sirvent, Raul; Schatz, George

    2014-03-01

    The theory of generalized van der Waals forces by Lifshtz when applied to optically anisotropic media predicts the existence of a torque. In this work we present a theoretical calculation of the van der Waals torque for two systems. First we consider two isotropic parallel plates where the anisotropy is induced using an external magnetic field. The anisotropy will in turn induce a torque. As a case study we consider III-IV semiconductors such as InSb that can support magneto plasmons. The calculations of the torque are done in the Voigt configuration, that occurs when the magnetic field is parallel to the surface of the slabs. The change in the dielectric function as the magnetic field increases has the effect of decreasing the van der Waals force and increasing the torque. Thus, the external magnetic field is used to tune both the force and torque. The second example we present is the use of the torque in the non retarded regime to align arrays of nano particle slabs. The torque is calculated within Barash and Ginzburg formalism in the nonretarded limit, and is quantified by the introduction of a Hamaker torque constant. Calculations are conducted between anisotropic slabs of materials including BaTiO3 and arrays of Ag nano particles. Depending on the shape and arrangement of the Ag nano particles the effective dielectric function of the array can be tuned as to make it more or less anisotropic. We show how this torque can be used in self assembly of arrays of nano particles. ref. R. Esquivel-Sirvent, G. C. Schatz, Phys. Chem C, 117, 5492 (2013). partial support from DGAPA-UNAM.

  13. Experimental and Numerical Analysis of the Friction Drilling Process

    SciTech Connect

    Miller, Scott F; Li, Rui; Wang, Hsin; McSpadden Jr, Samuel Boyce; Shih, Albert J.

    2006-01-01

    Friction drilling is a nontraditional hole-making process. A rotating conical tool is applied to penetrate a hole and create a bushing in a single step without generating chips. Friction drilling relies on the heat generated from the frictional force between the tool and sheet metal workpiece to soften, penetrate, and deform the work-material into a bushing shape. The mechanical and thermal aspects of friction drilling are studied in this research. Under the constant tool feed rate, the experimentally measured thrust force and torque were analyzed. An infrared camera is applied to measure the temperature of the tool and workpiece. Two models are developed for friction drilling. One is the thermal finite element model to predict the distance of tool travel before the workpiece reaches the 250 C threshold temperature that is detectable by an infrared camera. Another is a force model to predict the thrust force and torque in friction drilling based on the measured temperature, material properties, and estimated area of contact. The results of this study are used to identify research needs and build the foundation for future friction drilling process optimization.

  14. Flexure Bearing Reduces Startup Friction

    NASA Technical Reports Server (NTRS)

    Clingman, W. Dean

    1991-01-01

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

  15. Laboratory Study of the Frictional Properties of Simulated Basal ice

    NASA Astrophysics Data System (ADS)

    Emerson, L.; Rempel, A.

    2006-12-01

    Sediment entrained in ice modifies the shear traction beneath warm-based glaciers. In an attempt to understand how entrained sediment affects the frictional behavior of melting ice against hard, impermeable substrates, we conducted a series of constant-velocity sliding experiments. We simulate basal ice by freezing sediment particles with controlled size distributions and concentrations into ice disks. Our sliding apparatus is driven by a motor coupled to a lead ball screw which displaces a carriage secured by two additional bearing rods. This design increases apparatus stiffness. The normal force was applied with a series of dead weights and the shear force was recorded with a gauge linked to the sliding carriage. The ratio of the measured shear force to the applied normal force produces an effective friction coefficient. Two regimes of frictional behavior are observed. The first, we call slippery, exhibits effective friction coefficients approaching zero and is indistinguishable from the debris free ice used as a control. The second, we call sandy, is indistinguishable from a sand block used as a control, has friction coefficients near 0.3, and high variability. Our results demonstrate that at higher particle loadings, the transition between these regimes occurs when the particle diameter approaches the thickness of the water layer between the ice and sliding surface. The thickness of the water layer is inferred from lubrication theory as a function of the melt rate and normal force, both measured experimental parameters. A similar transition from sandy to slippery with larger particle sizes is observed at low particle concentrations. This effect is likely related to the inability of the fluid above the particle to maintain a pressure gradient sufficient to transmit the imposed normal load to the particles and thus produce high effective friction coefficients.

  16. Tool Wear in Friction Drilling

    SciTech Connect

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

    2007-01-01

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

  17. Friction welding.

    NASA Technical Reports Server (NTRS)

    Moore, T. J.

    1972-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Ansari, N.; Ashurst, W. R.

    2012-02-01

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

  19. Experimental Study of Reciprocating Friction between Rape Stalk and Bionic Nonsmooth Surface Units.

    PubMed

    Ma, Zheng; Li, Yaoming; Xu, Lizhang

    2015-01-01

    Background. China is the largest producer of rape oilseed in the world; however, the mechanization level of rape harvest is relatively low, because rape materials easily adhere to the cleaning screens of combine harvesters, resulting in significant cleaning losses. Previous studies have shown that bionic nonsmooth surface cleaning screens restrain the adhesion of rape materials, but the underlying mechanisms remain unclear. Objective. The reciprocating friction between rape stalk and bionic nonsmooth metal surface was examined. Methods. The short-time Fourier transform method was used to discriminate the stable phase of friction signals and the stick-lag distance was defined to analyze the stable reciprocating friction in a phase diagram. Results. The reciprocating friction between rape stalk and metal surface is a typical stick-slip friction, and the bionic nonsmooth metal surfaces with concave or convex units reduced friction force with increasing reciprocating frequency. The results also showed that the stick-lag distance of convex surface increased with reciprocating frequency, which indicated that convex surface reduces friction force more efficiently. Conclusions. We suggest that bionic nonsmooth surface cleaning screens, especially with convex units, restrain the adhesion of rape materials more efficiently compared to the smooth surface cleaning screens. PMID:27034611

  20. Study Friction Distribution during the Cold Rolling of Material by Matroll Software

    SciTech Connect

    Abdollahi, H.; Dehghani, K.

    2007-04-07

    Rolling process is one of the most important ways of metal forming. Since the results of this process are almost finished product, therefore controlling the parameters affecting this process is very important in order to have cold rolling products with high quality. Among the parameters knowing the coefficient of friction within the roll gap is known as the most significant one. That is because other rolling parameters such as rolling force, pressure in the roll gap, forward slip, surface quality of sheet, and the life of work rolls are directly influenced by friction. On the other hand, in rolling calculation due to lake of a true amount for coefficient of friction a supposed value is considered for it. In this study, a new software (Matroll), is introduced which can determine the coefficient of friction (COF) and plot the friction hills for an industrial mill. Besides, based on rolling equations, it offers about 30 rolling parameters as outputs. Having the rolling characteristics as inputs, the software is able to calculate the coefficient of friction. Many rolling passes were performed on real industrial aluminum mill. The coefficient of friction was obtained for all passes. The results are in good agreement with the findings of the other researchers.

  1. Experimental Study of Reciprocating Friction between Rape Stalk and Bionic Nonsmooth Surface Units

    PubMed Central

    Ma, Zheng; Li, Yaoming; Xu, Lizhang

    2015-01-01

    Background. China is the largest producer of rape oilseed in the world; however, the mechanization level of rape harvest is relatively low, because rape materials easily adhere to the cleaning screens of combine harvesters, resulting in significant cleaning losses. Previous studies have shown that bionic nonsmooth surface cleaning screens restrain the adhesion of rape materials, but the underlying mechanisms remain unclear. Objective. The reciprocating friction between rape stalk and bionic nonsmooth metal surface was examined. Methods. The short-time Fourier transform method was used to discriminate the stable phase of friction signals and the stick-lag distance was defined to analyze the stable reciprocating friction in a phase diagram. Results. The reciprocating friction between rape stalk and metal surface is a typical stick-slip friction, and the bionic nonsmooth metal surfaces with concave or convex units reduced friction force with increasing reciprocating frequency. The results also showed that the stick-lag distance of convex surface increased with reciprocating frequency, which indicated that convex surface reduces friction force more efficiently. Conclusions. We suggest that bionic nonsmooth surface cleaning screens, especially with convex units, restrain the adhesion of rape materials more efficiently compared to the smooth surface cleaning screens. PMID:27034611

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

    NASA Technical Reports Server (NTRS)

    Brown, B Porter

    1958-01-01

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

  3. Torsional Tribological Behavior and Torsional Friction Model of Polytetrafluoroethylene against 1045 Steel

    PubMed Central

    Wang, Shibo; Niu, Chengchao

    2016-01-01

    In this work, the plane-on-plane torsional fretting tribological behavior of polytetrafluoroethylene (PTFE) was studied. A model of a rigid, flat-ended punch acting on an elastic half-space was built according to the experimental conditions. The results indicate that the shape of T–θ curves was influenced by both the torsional angle and the normal load. The torsion friction torque and wear rate of PTFE exponentially decreased when the torsion angle rose. The torsional torque increased from 0.025 N·m under a normal load of 43 N to 0.082 N·m under a normal load of 123 N. With sequentially increasing normal load, the value of torque was maintained. With rising normal load, the wear mass loss of PTFE disks was increased and the wear rate was decreased. Good agreement was found with the calculated torque according to the model and the experimental torque except for that under a normal load of 163 N. The difference under a normal load of 163 N was caused by the coefficient of friction. Usually the coefficient of friction of a polymer decreases with increasing normal load, whereas a constant coefficient of friction was applied in the model. PMID:26799324

  4. Torsional Tribological Behavior and Torsional Friction Model of Polytetrafluoroethylene against 1045 Steel.

    PubMed

    Wang, Shibo; Niu, Chengchao

    2016-01-01

    In this work, the plane-on-plane torsional fretting tribological behavior of polytetrafluoroethylene (PTFE) was studied. A model of a rigid, flat-ended punch acting on an elastic half-space was built according to the experimental conditions. The results indicate that the shape of T-θ curves was influenced by both the torsional angle and the normal load. The torsion friction torque and wear rate of PTFE exponentially decreased when the torsion angle rose. The torsional torque increased from 0.025 N·m under a normal load of 43 N to 0.082 N·m under a normal load of 123 N. With sequentially increasing normal load, the value of torque was maintained. With rising normal load, the wear mass loss of PTFE disks was increased and the wear rate was decreased. Good agreement was found with the calculated torque according to the model and the experimental torque except for that under a normal load of 163 N. The difference under a normal load of 163 N was caused by the coefficient of friction. Usually the coefficient of friction of a polymer decreases with increasing normal load, whereas a constant coefficient of friction was applied in the model. PMID:26799324

  5. Further experimental studies in wet-brake friction

    SciTech Connect

    Staph, H.E.; Marbach, H.W. Jr.

    1986-01-01

    This paper describes further experimental efforts to determine friction characteristics that define the chatter potential in wet-brake systems as used in tractors and other off-road applications. Changes and improvements to a bench facility described at the 1985 Off-Highway Conference are described. Of particular interest is the decision to examine the very low sliding velocity regime, particularly below 0.34 m/s sliding velocity. Interesting and informative data have been obtained by feeding the input of an accelerometer attached in effect to the caliper brake pads to a frequency analyzer. A spectrum of the energy developed by the vibrating pads over the frequency range of 0 to 250 Hz while the sliding velocity is increased from 0 to 0.85 m/s is obtained. Specifically, the area under the composite frequency curve from 70 to 125 Hz shows good correlation to the chatter propensity of the oil. The results of tests on several oils are described. The ultimate purpose of the research is to provide a relatively rapid screening test for evaluating brake oils for the John Deere-type qualification tests. The overall results emphasize the importance of a low ratio between the breakaway friction and the friction at moderate sliding velocities for low or no chatter.

  6. Acceleration and torque feedback for robotic control - Experimental results

    NASA Technical Reports Server (NTRS)

    Mclnroy, John E.; Saridis, George N.

    1990-01-01

    Gross motion control of robotic manipulators typically requires significant on-line computations to compensate for nonlinear dynamics due to gravity, Coriolis, centripetal, and friction nonlinearities. One controller proposed by Luo and Saridis avoids these computations by feeding back joint acceleration and torque. This study implements the controller on a Puma 600 robotic manipulator. Joint acceleration measurement is obtained by measuring linear accelerations of each joint, and deriving a computationally efficient transformation from the linear measurements to the angular accelerations. Torque feedback is obtained by using the previous torque sent to the joints. The implementation has stability problems on the Puma 600 due to the extremely high gains inherent in the feedback structure. Since these high gains excite frequency modes in the Puma 600, the algorithm is modified to decrease the gain inherent in the feedback structure. The resulting compensator is stable and insensitive to high frequency unmodeled dynamics. Moreover, a second compensator is proposed which uses acceleration and torque feedback, but still allows nonlinear terms to be fed forward. Thus, by feeding the increment in the easily calculated gravity terms forward, improved responses are obtained. Both proposed compensators are implemented, and the real time results are compared to those obtained with the computed torque algorithm.

  7. Computational study of the electromagnetic forces and torques on different ITER first wall designs.

    SciTech Connect

    Kotulski, Joseph Daniel; Garde, Joseph Maurico; Coats, Rebecca Sue; Pasik, Michael Francis; Ulrickson, Michael Andrew

    2009-06-01

    An electromagnetic analysis is performed on different first wall designs for the ITER device. The electromagnetic forces and torques present due to a plasma disruption event are calculated and compared for the different designs.

  8. Evaluation of Friction in Orthodontics Using Various Brackets and Archwire Combinations-An in Vitro Study

    PubMed Central

    Kumar, Sujeet; Hamsa P.R, Rani; Ahmed, Sameer; Prasanthma; Bhatnagar, Apoorva; Sidhu, Manreet; Shetty, Pramod

    2014-01-01

    AIM: The aim of this study was to compare frictional resistance which was produced between conventional brackets (0.022 slot Otho-Organiser) and self ligating brackets (active Forestadent and passive Damon III) by using various arch wire combinations (0.016 Niti, 0.018 Niti, 0.017 x 0.025 SS and 0.019 x 0.025 SS). Methods: An experimental model which consisted of 5 aligned stainless steel 0.022-in brackets was used to assess frictional forces which were produced by SLBs (self ligating brackets) and CELs (conventional elastomeric ligatures) with use of 0.016 nickel titanium, 0.018 nickel titanium, 0.017 X 0.025”stainless steel and 0.019 X 0.025”stainless steel wires. Statistical analysis: One way ANOVA test was used to study the effect of the bracket type, wire alloy and section on frictional resistance test . Results: Conventional brackets produced highest levels of friction for all bracket/archwire combinations. Both Damon III and Forestadent brackets were found to produce significantly lower levels of friction when they were compared with elastomerically tied conventional brackets. Conclusion: SLBs are valid alternatives for low friction during sliding mechanics. PMID:24995241

  9. A study of the frictional characteristics of four commercially available self-ligating bracket systems.

    PubMed

    Budd, Steven; Daskalogiannakis, John; Tompson, Bryan D

    2008-12-01

    The objective of this investigation was to assess and compare the in vitro tribological behaviour of four commercially available self-ligating bracket systems. The frictional characteristics of the Damon3, Speed, In-Ovation R, and Time2 bracket systems were studied using a jig that mimics the three-dimensional movements that occur during sliding mechanics. Each bracket system was tested on the following stainless steel archwires: 0.016 x 0.022, 0.019 x 0.025, 0.020 round, and 0.021 x 0.021 inch Speed D-wire. An Instron testing machine with a 50 N load cell was used to measure the frictional resistance for each bracket/tooth assembly. The crosshead speed was set at a constant rate of 1 mm/minute, and each typodont tooth was moved along a fixed wire segment for a distance of 8 mm. Descriptive statistical analysis for each bracket/archwire combination with regard to frictional resistance was performed with a two-way, balanced analysis of variance for bracket type and wire size. The Damon3 bracket consistently demonstrated the lowest frictional resistance to sliding, while the Speed bracket produced significantly (P < 0.001) more frictional resistance than the other brackets tested for any given archwire. The self-ligation design (passive versus active) appears to be the primary variable responsible for the frictional resistance generated by self-ligating brackets during translation. Passively ligated brackets produce less frictional resistance; however, this decreased friction may result in decreased control compared with actively ligated systems. PMID:18974067

  10. A study of Kramers' turnover theory in the presence of exponential memory friction

    NASA Astrophysics Data System (ADS)

    Ianconescu, Reuven; Pollak, Eli

    2015-09-01

    Originally, the challenge of solving Kramers' turnover theory was limited to Ohmic friction, or equivalently, motion of the escaping particle governed by a Langevin equation. Mel'nikov and Meshkov [J. Chem. Phys. 85, 1018 (1986)] (MM) presented a solution valid for Ohmic friction. The turnover theory was derived more generally and for memory friction by Pollak, Grabert, and Hänggi [J. Chem. Phys. 91, 4073 (1989)] (PGH). Mel'nikov proceeded to also provide finite barrier corrections to his theory [Phys. Rev. E 48, 3271 (1993)]. Finite barrier corrections were derived only recently within the framework of PGH theory [E. Pollak and R. Ianconescu, J. Chem. Phys. 140, 154108 (2014)]. A comprehensive comparison between MM and PGH theories including finite barrier corrections and using Ohmic friction showed that the two methods gave quantitatively similar results and were in quantitative agreement with numerical simulation data. In the present paper, we extend the study of the turnover theories to exponential memory friction. By comparing with numerical simulation, we find that PGH theory is rather accurate, even in the strong friction long memory time limit, while MM theory fails. However, inclusion of finite barrier corrections to PGH theory leads to failure in this limit. The long memory time invalidates the fundamental assumption that consecutive traversals of the well are independent of each other. Why PGH theory without finite barrier corrections remains accurate is a puzzle.

  11. Mechanistic Studies in Friction and Wear of Bulk Materials

    NASA Astrophysics Data System (ADS)

    Sawyer, W. Gregory; Argibay, Nicolas; Burris, David L.; Krick, Brandon A.

    2014-07-01

    From the context of a contemporary understanding of the phenomenological origins of friction and wear of materials, we review insightful contributions from recent experimental investigations of three classes of materials that exhibit uniquely contrasting tribological behaviors: metals, polymers, and ionic solids. We focus on the past decade of research by the community to better understand the correlations between environment parameters, materials properties, and tribological behavior in systems of increasingly greater complexity utilizing novel synthesis and in situ experimental techniques. In addition to such review, and a half-century after seminal publications on the subject, we present recently acquired evidence linking anisotropy in friction response with anisotropy in wear behavior of crystalline ionic solids as a function of crystallographic orientation. Although the tribological behaviors of metals, polymers, and ionic solids differ widely, it is increasingly more evident that the mechanistic origins (such as fatigue, corrosion, abrasion, and adhesion) are essentially the same. However, we hope to present a clear and compelling argument favoring the prominent and irreplaceable role of in situ experimental techniques as a bridge between fundamental atomistic and molecular processes and emergent behaviors governing tribological contacts.

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

    PubMed Central

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

    2014-01-01

    Background: The orthodontist seeks an archwire–bracket combination that has both good biocompatibility and low friction. Hence, the aim of this multicenter in vitro study was to evaluate and compare the frictional resistance generated between titanium (Ti), stainless steel (SS), ceramic and ceramic with metal insert (CMI) brackets with SS wires of varying dimensions in a specially designed apparatus. Materials and Methods: The material used in this study were Ti, SS, Ceramic and CMI with 0.018″ slot manufactured with zero degree tip and −7° torque premolar brackets (3M, Unitek) and SS wires of varying dimensions (0.016″ round, 0.016 × 0.016″ square, 0.016 × 0.022″ rectangular and 0.017 × 0.025″ rectangular) used. The frictional resistance was measured using Instron Universal testing machine (Model no. 4301). The specimen population in each center composed each of 160 brackets and wires. Differences among the all bracket/wire combinations were tested using (one-way) ANOVA, followed by the student Newman Keuls multiple comparisons of means ranking (at P < 0.05) for the determination of differences among the groups. Results: Ti bracket in combination with 0.017 × 0.025″ SS rectangular wire produced significant force levels for an optimum orthodontic movement with least frictional resistance. Conclusion: Ti brackets have least resistance and rectangular wires produced significant force. These can be used to avoid hazards of Nickel. SS brackets revealed higher static frictional force values as the wire dimension increased and showed lower static friction than Ti brackets for all wires except the thicker wire. Our study recommends the preclusion of brackets with rough surface texture (Ti brackets) with SS ligature wire for ligating bracket and archwire are better to reduce friction. PMID:25395796

  13. Comparative study of vehicle tyre-road friction coefficient estimation with a novel cost-effective method

    NASA Astrophysics Data System (ADS)

    Li, Boyuan; Du, Haiping; Li, Weihua

    2014-08-01

    This paper qualitatively and quantitatively reviews and compares three typical tyre-road friction coefficient estimation methods, which are the slip slope method, individual tyre force estimation method and extended Kalman filter method, and then presents a new cost-effective tyre-road friction coefficient estimation method. Based on the qualitative analysis and the numerical comparisons, it is found that all of the three typical methods can successfully estimate the tyre force and friction coefficient in most of the test conditions, but the estimation performance is compromised for some of the methods during different simulation scenarios. In addition, all of these three methods need global positioning system (GPS) to measure the absolute velocity of a vehicle. To overcome the above-mentioned problem, a novel cost-effective estimation method is proposed in this paper. This method requires only the inputs of wheel angular velocity, traction/brake torque and longitudinal acceleration, which are all easy to be measured using available sensors installed in passenger vehicles. By using this method, the vehicle absolute velocity and slip ratio can be estimated by an improved nonlinear observer without using GPS, and the friction force and tyre-road friction coefficient can be obtained from the estimated vehicle velocity and slip ratio. Simulations are used to validate the effectiveness of the proposed estimation method.

  14. Dynamics of Braking Vehicles: From Coulomb Friction to Anti-Lock Braking Systems

    ERIC Educational Resources Information Center

    Tavares, J. M.

    2009-01-01

    The dynamics of braking of wheeled vehicles is studied using the Coulomb approximation for the friction between road and wheels. The dependence of the stopping distance on the mass of the vehicle, on the number of its wheels and on the intensity of the braking torque is established. It is shown that there are two regimes of braking, with and…

  15. Prolegomena to the Study of Friction Stir Welding

    NASA Technical Reports Server (NTRS)

    Nunes, Arthur C., Jr.

    2010-01-01

    The literature contains many approaches toward modeling of the friction stir welding (FSW) process with varying treatments of the weld metal properties. It is worthwhile to consider certain fundamental features of the process before attempting to interpret FSW phenomena: Because of the unique character of metal deformation (as opposed to, say, viscous deformation) a velocity "discontinuity" or shear surface occurs in FSW and determines much of the character of the welding mechanism. A shear surface may not always produce a sound bond. Balancing mechanical power input against conduction and convection heat losses yields a relation, a "temperature index", between spindle speed and travel speed to maintain constant weld temperature. But many process features are only weakly dependent upon temperature. Thus, unlike modeling of metal forming processes, it may be that modeling the FSW process independently of the material conditions has some merit.

  16. 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.

  17. Experimental, numerical and analytical studies of abrasive wear: correlation between wear mechanisms and friction coefficient

    NASA Astrophysics Data System (ADS)

    Mezlini, Salah; Zidi, M.; Arfa, H.; Ben Tkaya, Mohamed; Kapsa, Philippe

    2005-11-01

    The transport of granular material often generates severe damage. Understanding the correlation between the friction coefficient, particle geometry and wear mechanisms is of primary importance for materials undergoing abrasive wear. The aim of this study is to investigate the effect of particle geometry on wear mechanisms and the friction coefficient. Numerical and analytical simulations and experimental results have been compared. The process to be studied is the scratch made by a rigid cone with different attack angles on a 5xxx aluminium alloy (Al-Mg) flat surface. A scratch test was used and the wear mechanisms were observed for different attack angles. A numerical study with a finite element code was made in order to understand the effect of attack angle on the friction coefficient. The contact surface and the friction coefficient were also studied, and the results compared to the Bowden and Tabor model. The superposition of the numerical, analytical and experimental results showed a better correlation between the wear mechanisms and the friction coefficient. It also showed the importance of the model hypothesis used to simulate the scratch phenomenon. To cite this article: S. Mezlini et al., C. R. Mecanique 333 (2005).

  18. Perpendicular Magnetic Anisotropy of Tb/Fe and Gd/Fe Multilayers Studied with Torque Magnetometer

    NASA Astrophysics Data System (ADS)

    Chowdhury, Ataur

    Perpendicular magnetic anisotropy (PMA) of multilayers critically depend on the magnetic and structural ordering of the interface. To study the effect of interface on PMA, Tb/Fe and Gd/Fe multilayers with varying Fe (0.8-9.0 nm) and Gd (0.5-2.8 nm) or Tb (0.3-6.3 nm) layer thicknesses were fabricated by planar magnetron sputtering. The magnetometer results of spin orientation clearly reveals that samples with Gd or Tb layer thickness of more than 1.2 nm display no PMA, regardless of the Fe layer thickness. Tb/Fe and Gd/Fe multilayers with thin (<1.2 nm) Tb or Gd layers display large PMA, but no PMA is observed when the Fe layer thickness is increased to 4.0 nm and higher. The bulk magnetization and anisotropy energy constant of the samples are found to increase with increasing Fe layer thickness. Torque measurement also reveals that there are two distinctly different axes of spin alignment at different energy. Tb/Fe and Gd/Fe multilayers with similar composition reveal similar magnetic and structural characteristics, and it may imply that single-ion-anisotropy of rare-earth element, which is quite large for Tb ions and very small for Gd ions, may not be the dominating cause of PMA in Td/Fe and Gd/Fe multilayers. A detailed explanation of the results will be provided based on exchange interaction at the interface.

  19. Comparison of the frictional resistance between archwire and different bracket system: An in vitro study

    PubMed Central

    Pillai, Ajith R.; Gangadharan, Anil; Kumar, Satheesh; Shah, Anwar

    2014-01-01

    Background and Objectives: The purpose of this study is to evaluate the frictional resistance generated by conventional stainless steel, radiance ceramic bracket, self-ligating and composite brackets using a 0.019 × 0.025 stainless steel straight length wires in a 022 slot and to select brackets based on their frictional characteristic. Methodology: In order to conduct this study, four different types of bracket system were selected of the mclaughlin-bennet-trevesi (MBT) discipline. They are Group 1 - stainless steel, Group 2 - composite bracket Group 3 - (American Orthodontics) radiance ceramic bracket Group 4 - self-ligating bracket (SLB) (Empower). In this study, five maxillary brackets of an arch of each type were used. All brackets are 0.022 × 0.028 in preadjusted edgewise appliance which simulates the dental arch. Five brackets were bonded to a stainless steel bar of dimension 150 mm × 25 mm × 3 mm. The bracket-arch wire units were submitted to mechanical test with an Instron universal testing machine 3365. A testing apparatus or holding jig was designed to hold the bracket during the mechanical test. Each sample was pulled at a speed of 6 mm for 1 min. Descriptive statistical information including mean and standard deviation of maximum friction force was calculated for each bracket wire combination. Interpretation and Conclusion: The SLB has the least friction among the four groups. The ceramic bracket showed the highest friction followed by stainless steel bracket, composite bracket, and SLB. PMID:25210359

  20. FMR and torque studies of highly stressed magnetostrictive polycrystalline CoPd alloy films

    SciTech Connect

    Dubowik, J.; Szymanski, B.

    1994-03-01

    Ferromagnetic resonance (FMR) and torque curves have been measured in electrodeposited CoPd alloy films with composition ranged from Co{sub 13}Pd{sub 83} to Co{sub 45}Pd{sub 55}. The authors show that the origin of the multimode structure of FMR spectra in these strongly magnetostrictive polycrystalline films can be satisfactory explained on the basis of the independent-grain-approach for a textured microstructure. The fourfold periodicity of the torque curves for the compositional range of 30--35 at% is assumed to be oriented by inhomogeneous distribution of the magnetization direction.

  1. Rolling-Friction Robotic Gripper

    NASA Technical Reports Server (NTRS)

    Vranish, John M.

    1992-01-01

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

  2. A comparison of the forces required to produce tooth movement ex vivo through three types of pre-adjusted brackets when subjected to determined tip or torque values.

    PubMed

    Sims, A P; Waters, N E; Birnie, D J

    1994-11-01

    Friction in fixed appliance systems has received considerable attention in recent literature, although that attributable to varying second order (tip) and third order (torque) adjustments in either the bracket or the archwire has not been fully investigated. The ex vivo study of 0.022 x 0.028-inch slot Minitwin, Activa, and Standard Straight Wire brackets investigates friction when known values of tip or torque were applied to 0.018 x 0.025-inch stainless steel wires. The resistance to sliding of the wire through the ligated brackets was measured on a vertically-mounted Instron testing machine. The results showed that the self-ligating Activa brackets consistently produced less friction than the other conventionally tied brackets. Minitwin brackets were slightly more resistant to movement than the Standard brackets during torquing, but the converse was found when tip was applied. Increasing tip and torque (ranges tested 0-6 degrees and 0-25 degrees, respectively) produced almost linear increases in friction for all brackets, although increasing tip had the more profound effect on friction, particularly in Activa brackets. PMID:7857896

  3. Studies of friction drag and pressure drag of airfoils using the Eppler program

    NASA Technical Reports Server (NTRS)

    Phillips, William H.

    1988-01-01

    Most previous studies of the drag and two-dimensional airfoils consider only the total drag. The present report gives results of a study of three airfoils, using the Eppler program, to determine the distribution of friction drag along the chord and to obtain relative values of friction drag and pressure drag over a wide range of angle of attack and Reynolds number. The effects of boundary-layer suction in the turbulent region of the boundary layer of two of the airfoils are also investigated. The pressure drag is found to be an important component of the total drag, reaching values of 60 to 80 percent of the total drag near the stall. The use of suction producing a uniform inflow in the turbulent region of the boundary layer results in large increases in maximum lift, and increases the skin-friction drag but reduces or even changes the sign of the pressure drag.

  4. A Feasiblity Study on Spot Friction Welding of Magnesium Alloy AZ31

    SciTech Connect

    Santella, Michael L; Pan, Dr. Tsung-Yu; Frederick, David Alan; Schwartz, William

    2007-01-01

    Spot friction welding (SFW) is a novel variant of the linear friction stir welding process with the potential to create strong joints between similar, as well as dissimilar sheet metals. It is particularly suitable for soft, low melting point metals such as aluminum, magnesium, and their alloys where resistance spot welding can cause defects such as voids, trapped gas and micro-cracks due to the intense heat requirement for joint formation. Up to now, spot friction welding has focused primarily on aluminum alloys. This paper presents a feasibility study on spot friction welding of AZ31, a wrought magnesium alloy available in sheet form. Lap joints of 1.58-mm-thick magnesium alloy AZ31B-O sheet were produced by spot friction welding. The spot welds were made in 2 sec with 15-mm-diameter pin tool rotating at 500-2,000 rpm. The tool was inserted into 2-sheet stack-ups to depths of either 2.4 or 2.8 mm relative to the top sheet surface. Tensile-shear testing showed that joint strengths up to 4.75 kN were obtained. The removal of surface oxides from the sheets prior to welding increased lap shear strengths about 50% at the 2.4-mm insertion depth and it promoted failure by nugget pull-out rather than by interface separation.

  5. Studies of friction and wear characteristics of various wires for wire-brush skids

    NASA Technical Reports Server (NTRS)

    Dreher, R. C.

    1977-01-01

    The friction and wear characteristics of 22 types and sizes of wires for potential use in wire-brush skids were studied. These characteristics were determined by placing brushes made from candidate wires on a belt sander whose moving belt simulated landing roll-out distance. At the same time, the drag force and wear behavior were monitored. Data were obtained over distances up to 3048 m (10,000 ft) at preselected bearing pressures of 172 to 1034 kPa (25 to 150 psi). In general, the friction coefficient developed by the candidate wires was found to be independent of bearing pressure and ranged between 0.4 and 0.6 under the test conditions of this investigation. The friction coefficient was not degraded when the surface was wetted and appears to be independent of wire diameter except perhaps when wire size is relatively large compared with the surface asperities. Generally, the high friction demonstrated by the soft materials was accompanied by high wear rates; conversely, the hard materials provided greater wear resistance but offered lower friction. For all test wires, the wear was shown to increase with increasing bearing pressure, in general, for the same bearing pressure, wear increased with increasing wire diameter and decreased when the surface was wetted.

  6. Numerical and experimental study of the nonlinear interaction between a shear wave and a frictional interface.

    PubMed

    Blanloeuil, Philippe; Croxford, Anthony J; Meziane, Anissa

    2014-04-01

    The nonlinear interaction of shear waves with a frictional interface are presented and modeled using simple Coulomb friction. Analytical and finite difference implementations are proposed with both in agreement and showing a unique trend in terms of the generated nonlinearity. A dimensionless parameter ξ is proposed to uniquely quantify the nonlinearity produced. The trends produced in the numerical study are then validated with good agreement experimentally. This is carried out loading an interface between two steel blocks and exciting this interface with different amplitude normal incidence shear waves. The experimental results are in good agreement with the numerical results, suggesting the simple friction model does a reasonable job of capturing the fundamental physics. The resulting approach offers a potential way to characterize a contacting interface; however, the difficulty in activating that interface may ultimately limit its applicability. PMID:25234971

  7. Study on Friction and Wear Properties of Silver Matrix Brush Material with Different Additives

    NASA Astrophysics Data System (ADS)

    Chen, Xiaoli; Wang, Wenfang; Hong, Yu; Wu, Yucheng

    2013-07-01

    Friction and wear processes of AgCuX (G, CF and AlN) composites-CuAgV alloy friction pair and effects of different additive content in silver based composite on friction and wear behavior are studied in this paper. The microstructure of the brush wear surface is observed by SEM. The results show that when graphite content is up to 9 wt.%, Ag-Cu-CF-G composite exhibits the best wear properties; when the content of aluminum nitride is up to 0.5 wt.%, Ag-Cu-AlN-G composites has the most comprehensive performance. The wear loss of both composites arises with the increase of both pressure and speed, but when speed reaches a critical value, the increased amplitude of wear loss tends to be steady.

  8. Rolling Friction on a Wheeled Laboratory Cart

    ERIC Educational Resources Information Center

    Mungan, Carl E.

    2012-01-01

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

  9. Momentum Confinement at Low Torque

    SciTech Connect

    Solomon, W M; Burrell, K H; deGrassie, J S; Budny, R; Groebner, R J; Heidbrink, W W; Kinsey, J E; Kramer, G J; Makowski, M A; Mikkelsen, D; Nazikian, R; Petty, C C; Politzer, P A; Scott, S D; Van Zeeland, M A; Zarnstorff, M C

    2007-06-26

    Momentum confinement was investigated on DIII-D as a function of applied neutral beam torque at constant normalized {beta}{sub N}, by varying the mix of co (parallel to the plasma current) and counter neutral beams. Under balanced neutral beam injection (i.e. zero total torque to the plasma), the plasma maintains a significant rotation in the co-direction. This 'intrinsic' rotation can be modeled as being due to an offset in the applied torque (i.e. an 'anomalous torque'). This anomalous torque appears to have a magnitude comparable to one co-neutral beam source. The presence of such an anomalous torque source must be taken into account to obtain meaningful quantities describing momentum transport, such as the global momentum confinement time and local diffusivities. Studies of the mechanical angular momentum in ELMing H-mode plasmas with elevated q{sub min} show that the momentum confinement time improves as the torque is reduced. In hybrid plasmas, the opposite effect is observed, namely that momentum confinement improves at high torque/rotation. The relative importance of E x B shearing between the two is modeled using GLF23 and may suggest a possible explanation.

  10. Study of stirred layers on 316L steel created by friction stir processing

    NASA Astrophysics Data System (ADS)

    Langlade, C.; Roman, A.; Schlegel, D.; Gete, E.; Folea, M.

    2014-08-01

    Nanostructured materials are known to exhibit attractive properties, especially in the mechanical field where high hardness is of great interest. The friction stir process (FSP) is a recent surface engineering technique derived from the friction stir welding method (FSW). In this study, the FSP of an 316L austenitic stainless steel has been evaluated. The treated layers have been characterized in terms of hardness and microstructure and these results have been related to the FSP operational parameters. The process has been analysed using a Response Surface Method (RSM) to enable the stirred layer thickness prediction.

  11. Lubrication and friction prediction in metal-on-metal hip implants

    NASA Astrophysics Data System (ADS)

    Wang, F. C.; Brockett, C.; Williams, S.; Udofia, I.; Fisher, J.; Jin, Z. M.

    2008-03-01

    A general methodology of mixed lubrication analysis and friction prediction for a conforming spherical bearing in hip implants was developed, with particular reference to a typical metal-on-metal hip replacement. Experimental measurement of frictional torque for a similar implant was carried out to validate the theoretical prediction. A ball-in-socket configuration was adopted to represent the articulation between the femoral head and the acetabular cup under cyclic operating conditions of representative load and motion. The mixed lubrication model presented in this study was first applied to identify the contact characteristics on the bearing surfaces, consisting of both fluid-film and boundary lubricated regions. The boundary lubricated contact was assumed to occur when the predicted fluid film thickness was less than a typical boundary protein layer absorbed on the bearing surfaces. Subsequently, the friction was predicted from the fluid-film lubricated region with viscous shearing due to both Couette and Poiseuille flows and the boundary protein layer contact region with a constant coefficient of friction. The predicted frictional torque of the typical metal-on-metal hip joint implant was compared with the experimental measurement conducted in a functional hip simulator and a reasonably good agreement was found. The mixed lubrication regime was found to be dominant for the conditions considered. Although the percentage of the boundary lubricated region was quite small, the corresponding contribution to friction was quite large and the resultant friction factor was quite high.

  12. A study of friction mechanisms between a surrogate skin (Lorica soft) and nonwoven fabrics.

    PubMed

    Cottenden, David J; Cottenden, Alan M

    2013-12-01

    Hygiene products such as incontinence pads bring nonwoven fabrics into contact with users' skin, which can cause damage in various ways, including the nonwoven abrading the skin by friction. The aim of the work described here was to develop and use methods for understanding the origin of friction between nonwoven fabrics and skin by relating measured normal and friction forces to the nature and area of the contact (fibre footprint) between them. The method development work reported here used a skin surrogate (Lorica Soft) in place of skin for reproducibility. The work was primarily experimental in nature, and involved two separate approaches. In the first, a microscope with a shallow depth of field was used to determine the length of nonwoven fibre in contact with a facing surface as a function of pressure, from which the contact area could be inferred; and, in the second, friction between chosen nonwoven fabrics and Lorica Soft was measured at a variety of anatomically relevant pressures (0.25-32.1kPa) and speeds (0.05-5mms(-1)). Both techniques were extensively validated, and showed reproducibility of about 5% in length and force, respectively. Straightforward inspection of the data for Lorica Soft against the nonwovens showed that Amontons' law (with respect to load) was obeyed to high precision (R(2)>0.999 in all cases), though there was the suggestion of sub-linearity at low loads. More detailed consideration of the friction traces suggested that two different friction mechanisms are important, and comparison with the contact data suggests tentatively that they may correspond to adhesion between two different populations of contacts, one "rough" and one "smooth". This additional insight is a good illustration of how these techniques may prove valuable in studying other, similar interfaces. In particular, they could be used to investigate interfaces between nonwovens and skin, which was the primary motivation for developing them. PMID:23768960

  13. Experimental study of an electromagnetic flow meter for liquid metals based on torque measurement during pumping process

    NASA Astrophysics Data System (ADS)

    Dubovikova, N.; Kolesnikov, Y.; Karcher, Ch

    2015-11-01

    This paper presents a detailed experimental study on an electromagnetic flow measurement technique to measure the flow rate of liquid metals. The experimental setup consists of a contactless electromagnetic pump with a torque sensor mounted on the pump shaft. The electromagnetic pump is composed of two rotating steel discs having embedded permanent magnets with alternating poles. The rotation of the discs creates a travelling sinusoidal magnetic field and eddy currents within the liquid metal. The metal is contained inside the duct located between the discs of the pump. The interaction of the magnetic field and the induced eddy currents generates an electromagnetic Lorentz force providing the pumping effect. The flow rate is proportional to this force. The torque sensor measures the moment of the discs due to the Lorentz force, which is converted to a flow rate value. We name the method Lorentz torque velocimetry (LTV). The full calibration procedure and experimental investigation of the LTV are described. The method can be used as a non-contact flow rate control technique for liquid metals.

  14. Electro-orientation of a metal nanowire counterbalanced by thermal torques.

    PubMed

    Arcenegui, Juan J; García-Sánchez, Pablo; Morgan, Hywel; Ramos, Antonio

    2014-06-01

    The rotational diffusion of electrically polarized metal nanowires suspended in an electrolyte is studied. The alignment of a Brownian nanowire in an ac field with a given direction is not complete due to thermal (fluctuating) torques. The orientation distribution allows us to examine the electrokinetic torques acting on the nanowire for smaller voltages than in previous deterministic experiments. In addition, the torques are obtained without recurring to the rotational friction coefficient as in dynamic deterministic experiments. The present results are in accordance with previous deterministic results of electro-orientation of metal nanowires. Nanowire rotation is originated by both the electrical torque on the induced dipole and by induced-charge electro-osmotic flow around the particle. At low frequencies of the applied ac field, induced-charge electro-osmotic orientation dominates while induced dipole torque orientation dominates at high frequencies. The angular standard deviation and the rotational rate are calculated from the measured fluctuating angle as a function of time, and good agreement with theoretical predictions is found. The experiments at high frequency indicate that the electrical torque on a nanowire near an insulating wall is reduced with respect to the bulk. PMID:25019775

  15. Nanotribology and Nanoscale Friction

    SciTech Connect

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

    2008-01-01

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

  16. Propagating spin waves excited by spin-transfer torque: A combined electrical and optical study

    NASA Astrophysics Data System (ADS)

    Madami, M.; Iacocca, E.; Sani, S.; Gubbiotti, G.; Tacchi, S.; Dumas, R. K.; Åkerman, J.; Carlotti, G.

    2015-07-01

    Nanocontact spin-torque oscillators are devices in which the generation of propagating spin waves can be sustained by spin transfer torque. In the present paper, we perform combined electrical and optical measurements in a single experimental setup to systematically investigate the excitation of spin waves by a nanocontact spin-torque oscillator and their propagation in a N i80F e20 extended layer. By using microfocused Brillouin light scattering we observe an anisotropic emission of spin waves, due to the broken symmetry imposed by the inhomogeneous Oersted field generated by the injected current. In particular, spin waves propagate on the side of the nanocontact where the Oersted field and the in-plane component of the applied magnetic field are antiparallel, while propagation is inhibited on the opposite side. Moreover, propagating spin waves are efficiently excited only in a limited frequency range corresponding to wavevectors inversely proportional to the size of the nanocontact. This frequency range obeys the dispersion relation for exchange-dominated spin waves in the far field, as confirmed by micromagnetic simulations of similar devices. The present results have direct consequences for spin wave based applications, such as synchronization, computation, and magnonics.

  17. Design of a telerobotic controller with joint torque sensors

    SciTech Connect

    Jansen, J.F.; Herndon, J.N.

    1990-01-01

    The purpose of this paper is to analytically show how to design a joint controller for a telerobotic system when joint torque sensors are available. Other sensors such as actuator position, actuator velocity, joint position, and joint velocity are assumed to be accessible; however, the results of this paper will also be useful when only partial measurements are available. The controller presented in this paper can be applied to either mode of operation of a manipulator (i.e., teleoperation or robotic). Mechanical manipulators with high levels of friction are assumed in this study. Finally, the results are applied to a telerobotic system built for NASA. Very high levels of friction have been reduced using high-grain feedback while avoiding limit cycles. 14 refs., 5 figs.

  18. Development of Nanofluids as Lubricant to Study Friction and Wear Behavior of Stainless Steels

    NASA Astrophysics Data System (ADS)

    Sahoo, Rashmi Ranjan; Bhattacharjee, Santu; Das, Tuhin

    A number of nanofluids have been prepared to study the effect of lubrication properties of nanofluids on stainless steels taking Kaolin and Boron Nitride (BN) as the lubricant particles and Sodium Dodecyl Sulfate (SDS), Cetyl Trimethyl Ammonium Bromide (CTAB), Sodium Hexa Meta Phosphate (SHMP) as dispersants in the same liquid medium i.e. water. A pin on disc tribometer is being used to access the tribological behaviour of the prepared nanofluids. The particle size of these particle dispersions are examined with a nanoparticle size analyzer. It has been found that the use of dispersants significantly control the particle size and tribological behavior of the nanofluids as for Boron Nitride particle with Sodium Dodecyl Sulfate (SDS) as dispersant has got a very low value of coefficient of friction being equal to 0.142 while without dispersant the value is 0.498. Similarly, in case of Kaolin water with SDS as dispersant the value of coefficient of friction obtained is 0.161 and without dispersant it is 0.333. Sodium Dodecyl Sulfate (SDS) as dispersant has resulted a very low coefficient of friction compared to other dispersants tested even though it doesn’t always assure a least particle size. The role of SDS in yielding the lowest friction has pursued significant attention for further investigation.

  19. Experimental studies of skyrmion textures and spin torque effects in chiral magnets

    NASA Astrophysics Data System (ADS)

    Ritz, Robert

    2012-02-01

    Small angle neutron scattering and measurements of a topological Hall signal identify the formation of skyrmion lattices in the non-centrosymmetric B20 compounds MnSi [1], Mn1-xFexSi, Mn1-xCoxSi and the strongly doped semiconductor Fe1-xCoxSi [2]. This observation has been confirmed by Lorentz force microscopy in thin samples of Fe1-xCoxSi, FeGe and, most recently, MnSi, where even individual skyrmions have been spotted [3]. Because the skyrmion lattices are exceptionally weakly pinned to the crystal lattice, extreme care has to be exercised when studying the precise intrinsic morphology of related spin textures in bulk samples. As a particularly striking property each skyrmion supports precisely one quantum of emergent magnetic flux. This permits a highly efficient coupling between skyrmions and conduction electrons which results in spin torque effects at ultra-low current densities as seen in small angle neutron scattering [4] and the emergent electric field when the skyrmions move [5].[4pt] Work in collaboration with: T. Adams, A. Bauer, B. Binz, P. B"oni, G. Brandl, R. A. Duine, K. Everschor, C. Franz, M. Garst, R. Georgii, S. Gottlieb-Sch"onmeyer, W. Heusler, M. Janoschek, F. Jonietz, T. Keller, K. Mitterm"uller, S. M"uhlbauer, W. M"unzer, A. Neubauer, P.G. Niklowitz, C. Pfleiderer, A. Rosch, T. Schulz, A. Tischendorf, M. Wagner.[4pt] [1] S. M"uhlbauer et al., Science 323, 915 (2009); A. Neubauer et al., Phys. Rev. Lett. 102, 186602 (2010); C. Pfleiderer et al., J. Phys. Cond. Matter 22, 164207 (2010); T. Adams et al., Phys. Rev. Lett., in press, arXiv/1107.0993. [0pt] [2] W. M"unzer et al., Phys. Rev. B 81, 041203(R) (2010). [0pt] [3] X. Z. Yu et al., Nature 465, 901 (2010); X. Z. Yu et al., Nature Materials 10, 106 (2010). [0pt] [4] F. Jonietz et al., Science, 330, 1648 (2010). [0pt] [5] Emergent electrodynamics of skyrmions in a chiral magnet, T. Schulz, R. Ritz, A. Bauer, M. Halder, M. Wagner, C. Franz, and C. Pfleiderer, K. Everschor, M. Garst, and A

  20. The role of interaction torque and muscle torque in the control of downward squatting.

    PubMed

    Fujisawa, Hiroyuki; Suzuki, Hiroto; Murakami, Kenichi; Kawakami, Shingo; Suzuki, Makoto

    2016-01-01

    [Purpose] The purposes of this study were first to analyze the multijoint dynamics of downward squatting, and to examine the contribution of interaction torque and muscle torque to net torque, and second, to examine mechanisms of movement control. [Subjects] The subjects were 31 healthy men with a mean age of 21.0 ± 1.2 years (range, 19-24 years). [Methods] Squatting tasks with the trunk in two positions, an erect and anterior tilt position, were performed by the subjects. Net, interaction, muscle, and gravity torque were calculated according to the Lagrange equation using 3D tracking data. [Results] The contribution ratio of interaction torque to net torque was approximately 90%, irrespective of the joint and task. In contrast, muscle torque showed complicated behavior to compensate for gravity torque. A combined muscle and gravity torque profile showed flexion or dorsiflexion immediately after the initiation of the movement, and it later changed to extension or plantar flexion. [Conclusion] The torque that contributes almost exclusively to the net torque was interaction torque. The combination of muscle and gravity torque at the knee joint and the hip joint is important for movement control, independent of the starting position. PMID:27065552

  1. The role of interaction torque and muscle torque in the control of downward squatting

    PubMed Central

    Fujisawa, Hiroyuki; Suzuki, Hiroto; Murakami, Kenichi; Kawakami, Shingo; Suzuki, Makoto

    2016-01-01

    [Purpose] The purposes of this study were first to analyze the multijoint dynamics of downward squatting, and to examine the contribution of interaction torque and muscle torque to net torque, and second, to examine mechanisms of movement control. [Subjects] The subjects were 31 healthy men with a mean age of 21.0 ± 1.2 years (range, 19–24 years). [Methods] Squatting tasks with the trunk in two positions, an erect and anterior tilt position, were performed by the subjects. Net, interaction, muscle, and gravity torque were calculated according to the Lagrange equation using 3D tracking data. [Results] The contribution ratio of interaction torque to net torque was approximately 90%, irrespective of the joint and task. In contrast, muscle torque showed complicated behavior to compensate for gravity torque. A combined muscle and gravity torque profile showed flexion or dorsiflexion immediately after the initiation of the movement, and it later changed to extension or plantar flexion. [Conclusion] The torque that contributes almost exclusively to the net torque was interaction torque. The combination of muscle and gravity torque at the knee joint and the hip joint is important for movement control, independent of the starting position. PMID:27065552

  2. 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.

  3. Studying Kittel-like modes in a 3D YIG disk using Torque-mixing Magnetic Resonance Spectroscopy

    NASA Astrophysics Data System (ADS)

    Fani Sani, Fatemeh; Losby, Joseph; Grandmont, Dylan; Diao, Zhu; Belov, Miro; Burgess, Jacob; Compton, Shawn; Hiebert, Wayne; Vick, Doug; Mohammad, Kaveh; Salimi, Elham; Bridges, Gregory; Thomson, Douglas; Freeman, Mark

    We report a study of ferrimagnetic resonance in a mesoscopic, single-crystalline YIG disk using torque-mixing magnetic resonance spectroscopy (TMRS). The Kittel model for magnetic resonance is a touchstone in measuring fundamental magnetic properties for magnetic films, which does not significantly depend on the film size. In 3D structures, ladders of confined resonance modes are observed, and these can exhibit the non-monotonic evolution of frequency with field familiar from Kittel modes. TMRS is a tool uniquely suited for observing this physics in individual 3D structures, on account of its combination of high sensitivity and broadband capability coupled with fine frequency resolution.

  4. A study of the frictional and stick-slip behavior of magnetic recording tapes

    NASA Technical Reports Server (NTRS)

    Kalfayan, S. H.; Silver, R. H.; Hoffman, J. K.

    1972-01-01

    Methods were developed to determine the coefficient of friction and the extent of stick-slip of magnetic recording tapes. After a preliminary phase during which experimental procedures were established and screening of candidate tapes was carried out, the frictional and stick-slip behavior of four selected tapes, using four different kinds of magnetic heads, was studied at various temperatures, under dry and humid conditions, and in various gaseous atmospheres, such as argon, helium, nitrogen and air. The effects of tape speed and outgassing on the drag properties of the tapes were also studied. A rank was assigned to each tape and magnetic head as a result of these tests. This study helped in the selection of a magnetic tape in a flight project, and will be useful in the consideration of tapes and magnetic heads for future spacecraft applications.

  5. Uses of Auger and x ray photoelectron spectroscopy in the study of adhesion and friction

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa

    1990-01-01

    Three studies are described characterizing the possible contributions of surface science to tribology. These include surface contamination formed by the interaction of a surface with the environment, contaminants obtained with diffusion of compounds, and surface chemical changes resulting from selective thermal evaporation. Surface analytical tools such as Auger electron spectroscopy (AES) and x ray photoelectron spectroscopy (XPS) incorporated directly into adhesion and friction systems are primarily used to define the nature of tribological surfaces before and after tribological experimentation and to characterize the mechanism of solid-to-solid interaction. Emphasis is on fundamental studies involving the role of surfaces in controlling the adhesion and friction properties of materials emerging as a result of the surface analyses. The materials which were studied include metals and ceramics such as elemental metals, amorphous alloys (metallic glasses), and silicon-based ceramics.

  6. Language and International Studies: The Rhetoric of Friction.

    ERIC Educational Resources Information Center

    Hayden, Rose L.

    This paper outlines the ways in which natural, functional areas in international studies overlap with foreign language proficiencies. An overview of international studies and language developments is given along with contrasts between needs and realities, showing that educational practice in this area is out-of-phase. Today, the situation is…

  7. Torque Magnetometry and Thermomagnetic Capacity Studies on a 2-d Cr^4+ Antiferromagnet

    NASA Astrophysics Data System (ADS)

    Kaur, Narpinder; Nellutla, Saritha; Jo, Youn-Jung; Balicas, Luis; van Tol, Johan; Dalal, Naresh

    2007-03-01

    We report torque magnetometry and magnetic heat capacity measurements on a rare complex, Cr^IV-Diethylenetriamine diperoxo. The motivation here was to search for a simple spin-gap system that could exhibit a Bose-Einstein type condensation (BEC) of magnons. Our earlier reported magnetization and specific heat (Cp) measurements had indicated that this compound is a 2-d antiferromagnet, with a TN of 2.55 K in zero-field [1]. These magnetization and Cp data have now been augmented by use of additional magnetic fields, and the newly found B-T phase diagram is seen to be clearly parabolic. Torque magnetometry confirmed the Cp data and has enabled measurements close to the T -> 0 K, B ˜ 12.5 T region. Measurements in the dilution fridge are planned to extract the critical exponent (α) from the relation kbTc˜ (Bc-B)^α . We surmise that this system will constitute a simple new model for examining the BEC of magnons in detail. [1] C.M. Ramsey, B. Cage, P. Nguyen, K.A. Abboud, N.S. Dalal, Chem. Mater. 15, 92 (2003).

  8. A Study of Friction Stir Welded 2195 Al-Li Alloy by the Scanning Reference Electrode Technique

    NASA Technical Reports Server (NTRS)

    Donford, M. D.; Ding, R. J.

    1998-01-01

    A study of the corrosion of friction stir welded 2195 Al-Li alloy has been carried out using the scanning reference electrode technique (SRET). The results are compared to those obtained from a study of heterogeneously welded samples.

  9. A fundamental study on the structural integrity of magnesium alloys joined by friction stir welding

    NASA Astrophysics Data System (ADS)

    Rao, Harish Mangebettu

    The goal of this research is to study the factors that influence the physical and mechanical properties of lap-shear joints produced using friction stir welding. This study focuses on understanding the effect of tool geometry and weld process parameters including the tool rotation rate, tool plunge depth and dwell time on the mechanical performance of similar magnesium alloy and dissimilar magnesium to aluminum alloy weld joints. A variety of experimental activities were conducted including tensile and fatigue testing, fracture surface and failure analysis, microstructure characterization, hardness measurements and chemical composition analysis. An investigation on the effect of weld process conditions in friction stir spot welding of magnesium to magnesium produced in a manner that had a large effective sheet thickness and smaller interfacial hook height exhibited superior weld strength. Furthermore, in fatigue testing of friction stir spot welded of magnesium to magnesium alloy, lap-shear welds produced using a triangular tool pin profile exhibited better fatigue life properties compared to lap-shear welds produced using a cylindrical tool pin profile. In friction stir spot welding of dissimilar magnesium to aluminum, formation of intermetallic compounds in the stir zone of the weld had a dominant effect on the weld strength. Lap-shear dissimilar welds with good material mixture and discontinues intermetallic compounds in the stir zone exhibited superior weld strength compared to lap-shear dissimilar welds with continuous formation of intermetallic compounds in the stir zone. The weld structural geometry like the interfacial hook, hook orientation and bond width also played a major role in influencing the weld strength of the dissimilar lap-shear friction stir spot welds. A wide scatter in fatigue test results was observed in friction stir linear welds of aluminum to magnesium alloys. Different modes of failure were observed under fatigue loading including crack

  10. A theoretical study of the influence of technological friction stir welding parameters on weld structures

    NASA Astrophysics Data System (ADS)

    Astafurov, Sergey; Shilko, Evgeny; Kolubaev, Evgeny; Psakhie, Sergey

    2015-10-01

    Computer simulation by the movable cellular automaton method was performed to study the dynamics of friction stir welding of duralumin plates. It was shown that the ratio of the rotation rate to the translational velocity of the rotating tool has a great influence on the quality of the welded joint. A suitably chosen ratio of these parameters combined with an additional ultrasonic impact reduces considerably the porosity and the amount of microcracks in the weld.

  11. Experimental study of heat transfer and flow friction characteristics of automotive evaporators

    SciTech Connect

    Chiou, C.B.; Lu, D.C.; Wang, C.C.; Chang, Y.J.

    1994-12-31

    An experimental study on two brazed aluminum serpentine evaporators was carried out in a forced-circulation wind tunnel These two heat exchangers were made of flat tubes with internal membranes and with louver fins on the air side. Although these serpentine evaporators have been widely used in the automotive industry, few performance data are available in the open literature. In the present investigation, the performance characteristics of the coils in the dimensionless Colburn j factor and the friction factor (f) are presented.

  12. Quick torque coupling

    DOEpatents

    Luft, Peter A.

    2009-05-12

    A coupling for mechanically connecting modular tubular struts of a positioning apparatus or space frame, comprising a pair of toothed rings (10, 12) attached to separate strut members (16), the teeth (18, 20) of the primary rings (10, 12) mechanically interlocking in both an axial and circumferential manner, and a third part comprising a sliding, toothed collar (14) the teeth (22) of which interlock the teeth (18, 20) of the primary rings (10, 12), preventing them from disengaging, and completely locking the assembly together. A secondary mechanism provides a nesting force for the collar, and/or retains it. The coupling is self-contained and requires no external tools for installation, and can be assembled with gloved hands in demanding environments. No gauging or measured torque is required for assembly. The assembly can easily be visually inspected to determine a "go" or "no-go" status. The coupling is compact and relatively light-weight. Because of it's triply interlocking teeth, the connection is rigid. The connection does not primarily rely on clamps, springs or friction based fasteners, and is therefore reliable in fail-safe applications.

  13. A study on friction stir welding of 12mm thick aluminum alloy plates

    NASA Astrophysics Data System (ADS)

    Kumar, Deepati Anil; Biswas, Pankaj; Tikader, Sujoy; Mahapatra, M. M.; Mandal, N. R.

    2013-12-01

    Most of the investigations regarding friction stir welding (FSW) of aluminum alloy plates have been limited to about 5 to 6 mm thick plates. In prior work conducted the various aspects concerning the process parameters and the FSW tool geometry were studied utilizing friction stir welding of 12 mm thick commercial grade aluminum alloy. Two different simple-to-manufacture tool geometries were used. The effect of varying welding parameters and dwell time of FSW tool on mechanical properties and weld quality was examined. It was observed that in order to achieve a defect free welding on such thick aluminum alloy plates, tool having trapezoidal pin geometry was suitable. Adequate tensile strength and ductility can be achieved utilizing a combination of high tool rotational speed of about 2000 r/min and low speed of welding around 28 mm/min. At very low and high dwell time the ductility of welded joints are reduced significantly.

  14. A Micro-Electrochemical Study of Friction Stir Welded Aluminum 6061-T6

    NASA Technical Reports Server (NTRS)

    Hintze, Paul E.; Calle, Luz M.

    2005-01-01

    The corrosion behavior of friction stir welded Aluminum alloy 606 1-T6 was studied using a micro-electrochemical cell. The micro-electrochemical cell has a measurement area of about 0.25 square mm which allows for measurement of corrosion properties at a very small scale. The corrosion and breakdown potentials were measured at many points inside and outside the weld along lines perpendicular to the weld. The breakdown potential is approximately equal inside and outside the weld; however, it is lower in the narrow border between the weld and base material. The results of electrochemical measurements were correlated to micro-structural analysis. The corrosion behavior of the friction stir welded samples was compared to tungsten inert gas (TIG) welded samples of the same material.

  15. Dynamic SEM wear studies of tungsten carbide cermets. [friction and wear experiments

    NASA Technical Reports Server (NTRS)

    Brainard, W. A.; Buckley, D. H.

    1975-01-01

    Dynamic friction and wear experiments were conducted in a scanning electron microscope. The wear behavior of pure tungsten carbide and composite with 6 and 15 weight percent cobalt binder was examined, and etching of the binder was done to selectively determine the role of the binder in the wear process. Dynamic experiments were conducted as the tungsten carbide (WC) and bonded WC cermet surfaces were transversed by a 50 micron radiused diamond stylus. These studies show that the predominant wear process in WC is fracture initiated by plastic deformation, and the wear of the etched cermets is similar to pure WC. The presence of the cobalt binder reduces both friction and wear. The cementing action of the cobalt reduces granular separation, and promotes a dense polished layer because of its low shear strength film-forming properties. The wear debris generated from unetched surface is approximately the same composition as the bulk.

  16. Magnetic torque study of Weyl semimetal compounds TaP and NbP up to 45 Tesla

    NASA Astrophysics Data System (ADS)

    Li, Gang; Asaba, Tomoya; Tinsman, Colin; Yu, Fan; Lawson, Benjamin; Chen, Yulin; Li, Lu

    Weyl semimetal is a recently proposed new state in condensed matter physics, in which the bulk bands could have three dimensional linear dispersion but the degeneracy at the cross point is lifted into a pair of Weyl points with opposite chirality. Among the predicted candidates, Tantalum monophorspide (TaP) and Niobium monophorspide (NbP) have the simplest composition and do not require extrinsic tuning. Photoemission data is accumulating and the unique Fermi-arc surface state is observed. Magnetotransport experiments has shown highly anisotropic magnetoresistance and quantum oscillations has been observed. Because both linear dispersive bands and conventional bands exist in these materials, a detailed study of the electronic strucuture of the bulk is highly desirable. We use torque magnetometry to study quantum oscillations of TaP and NbP down to 300 mK, and up to 45 Tesla, with focus on the angular dependence of oscillation frequencies. Our comparison shows clear difference in geometry of different bulk bands in these materials. Besides, a discussion will be made on high field torque data since 45 Tesla is high enough to push several of the bands into quantum limit.

  17. Study on linear and nonlinear bottom friction parameterizations for regional tidal models using data assimilation

    NASA Astrophysics Data System (ADS)

    Zhang, Jicai; Lu, Xianqing; Wang, Ping; Wang, Ya Ping

    2011-04-01

    Data assimilation technique (adjoint method) is applied to study the similarities and the differences between the Ekman (linear) and the Quadratic (nonlinear) bottom friction parameterizations for a two-dimensional tidal model. Two methods are used to treat the bottom friction coefficient (BFC). The first method assumes that the BFC is a constant in the entire computation domain, while the second applies the spatially varying BFCs. The adjoint expressions for the linear and the nonlinear parameterizations and the optimization formulae for the two BFC methods are derived based on the typical Largrangian multiplier method. By assimilating the model-generated 'observations', identical twin experiments are performed to test and validate the inversion ability of the presented methodology. Four experiments, which employ the linear parameterization, the nonlinear parameterizations, the constant BFC and the spatially varying BFC, are carried out to simulate the M 2 tide in the Bohai Sea and the Yellow Sea by assimilating the TOPEX/Poseidon altimetry and tidal gauge data. After the assimilation, the misfit between model-produced and observed data is significantly decreased in the four experiments. The simulation results indicate that the nonlinear Quadratic parameterization is more accurate than the linear Ekman parameterization if the traditional constant BFC is used. However, when the spatially varying BFCs are used, the differences between the Ekman and the Quadratic approaches diminished, the reason of which is analyzed from the viewpoint of dissipation rate caused by bottom friction. Generally speaking, linear bottom friction parameterizations are often used in global tidal models. This study indicates that they are also applicable in regional ocean tidal models with the combination of spatially varying parameters and the adjoint method.

  18. A Fluctuating Torque

    NASA Astrophysics Data System (ADS)

    Zamorano, Nelson; Gómez, Alfredo

    2013-04-01

    The existence of a fluctuating torque generates a wide variety of possible orbits. This situation contrasts with those examples where the torque vanishes and the angular momentum remains constant. Here we study a two dimensional example with a logarithmic effective potential V(x,y)= 12,,^2o,[ x^2 + (y/b)^2], with a small deviation from the axis symmetry given by the constant b with b < 1. Briefly, the effective potential models the gravitational force exerted by the N point particles on a test object. This potential is used to learn about the dynamics of galaxies and among other features, generates a fluctuating torque which is our main interest here. There is not an analytical solution for these two equations of motion. A simple numerical approach (provided) is required. Also, a change on the initial conditions may generate a different shape for the orbit. This apparently simple potential, represents a challenge for the students. We propose it as a good pedagogical tool for reviewing the main concepts of newtonian dynamics.

  19. On the torque and wear behavior of selected thin film MOS2 lubricated gimbal bearings

    NASA Technical Reports Server (NTRS)

    Bohner, John J.; Conley, Peter L.

    1988-01-01

    During the thermal vacuum test phase of the GOES 7 spacecraft, the primary scan mirror system exhibited unacceptably high drive friction. The observed friction was found to correlate with small misalignments in the mirror structure and unavoidable loads induced by the vehicle spin. An intensive effort to understand and document the performance of the scan mirror bearing system under these loads is described. This effort involved calculation of the bearing loads and expected friction torque, comparison of the computed values to test data, and verification of the lubrication system performance and limitations under external loads. The study culminated in a successful system launch in February of 1987. The system has operated as predicted since that time.

  20. Stability study of the Large Space Telescope /LST/ system with nonlinear CMG gimbal friction. [Control Moment Gyroscopes

    NASA Technical Reports Server (NTRS)

    Kuo, B. C.; Singh, G.; Seltzer, S. M.

    1974-01-01

    The purpose of the investigation reported upon is to study the existence and characteristics of self-sustained oscillations in the dynamic behavior of the Large Space Telescope (LST) system due to the presence of nonlinear gimbal friction in the control moment gyroscopes (CMGs). A continuous-data single-axis model of the LST is considered. A solid friction model is used to represent CMG gimbal friction. A rigorous mathematical model is derived for use in a continuous describing function analysis. Conditions for self-sustained oscillations are then determined.

  1. Rubber friction and tire dynamics.

    PubMed

    Persson, B N J

    2011-01-12

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

  2. Rubber friction and tire dynamics

    NASA Astrophysics Data System (ADS)

    Persson, B. N. J.

    2011-01-01

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

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

    PubMed

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

    2014-05-01

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

  4. Clinical outcome and bone healing of implants placed with high insertion torque: 12-month results from a multicenter controlled cohort study.

    PubMed

    Grandi, T; Guazzi, P; Samarani, R; Grandi, G

    2013-04-01

    This study evaluated the clinical outcome and the crestal bone resorption of implants placed with high insertion torque (up to 80 N cm). 102 patients were treated with 156 tapered implants. 42 implants (control group) presented insertion torque between 30 and 45 N cm (mean=37.4 SD 8.2). 114 implants (experimental group) were placed with insertion torque between 50 and 80 N cm (mean=74.8 SD 7.9). All implants were early loaded after 2 months. Peri-implant marginal bone levels were assessed immediately after surgery, and at 6- and 12-month follow up examinations. At the 12-month follow up all implants were clinically stable. After 12 months, patients in the experimental group lost an average of 0.41 mm (CI 95% 0.522; 0.263) of crestal bone compared with 0.45 mm (CI 95% 0.561; 0.286) for those in the control group. There were no significant differences between the two groups. No direct or inverse relationship was observed between the insertion torque values and crestal bone resorption. The results show that the use of high insertion torque (up to 80 N cm) did not prevent osseointegration and did not increase bone resorption around tapered implants early loaded up to 1 year after implant placement. PMID:23159169

  5. Ultralow Friction in a Superconducting Magnetic Bearing

    NASA Technical Reports Server (NTRS)

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

    1996-01-01

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

  6. Optimization of conical hydrostatic bearing for minimum friction.

    NASA Technical Reports Server (NTRS)

    Nypan, L. J.; Hamrock, B. J.; Scibbe, H. W.; Anderson, W. J.

    1971-01-01

    Equations for the flow rate, load capacity, and friction torque for a conical hydrostatic bearing were developed. These equations were solved by a digital computer program to determine bearing configurations for minimum friction torque. Design curves are presented that show optimal bearing dimensions for minimum friction torque as a function of dimensionless flow rate for a range of dimensionless load capacity. Results are shown for both laminar and turbulent flow conditions. The results indicate that hydrostatic pocket friction is a significant portion of the total friction torque. However, the bearing dimensions for a minimum friction design are affected very little by inclusion of pocket friction in the analysis. For laminar flow the values of the outer-land radius ratio X3 and outer bearing radius ratio X4 did not change significantly with increasing friction factor. For turbulent flow, the outer bearing radius ratio X4 did not change with increasing friction factor; therefore the value determined for X4 in the laminar flow case is valid for all turbulent flows.

  7. Study of spin orbit torque switching in ferrimagnetic Gdx (Fe90Co10)100-x alloy

    NASA Astrophysics Data System (ADS)

    Roschewsky, Niklas; Matsumura, Tomoya; Kato, Takeshi; Iwata, Satoshi; Cheema, Suraj; Clarkson, James; Salahuddin, Sayeef

    Magnetization switching in ferromagnetic metals (FM) with spin-orbit torques (SOT) is a well established technique. The SOT originates from spin accumulation at the interface of the FM generated by the spin Hall effect in an adjacent heavy metal. Here we report measurements of SOT in the alloy Gdx (Fe90Co10)100-x , where the transition metal sub-lattice and the rare earth sub-lattice couple antiferromagnetically. By varying the composition x of the alloy we can tune the total magnetization. Anormalous Hall effect measurements are conducted to study the effect of SOT on the Gdx (Fe90Co10)100-x magnetization. This work was supported by Department of Energy Basic Energy Sciences Award No DE -SC0012371.

  8. Friction Stir Welding

    NASA Technical Reports Server (NTRS)

    Nunes, Arthur C., Jr.

    2008-01-01

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

  9. Bevel gear driver and method having torque limit selection

    NASA Technical Reports Server (NTRS)

    Cook, Joseph S., Jr. (Inventor)

    1994-01-01

    This invention comprises a torque drive mechanism utilizing axially translatable, mutually engageable transmission members having mating crown gears, driven and driving members with a three-element drive train being biased together by resilient means or by a fluid actuator system, the apparatus being operable to transmit a precisely controlled degree of torque to a driven member. The apparatus is applicable for use in hand tools and as a replacement for impact torque drivers, torque wrenches, motorized screw drivers, or the like, wherein the applied torque must be precisely controlled or limited. The bevel torque drive includes a drive gear which is axially displaceable and rotatable within cylindrical driver housing, a rotatable intermediate gear, and an output gear. Key rotationally secures displaceable gear with respect to input shaft but permits axial movement therebetween. A thrust bearing is preferably connected to the lower end of shaft for support to reduce play and friction between shaft and a transmission joint disc during rotation of the gear train. Coaxially mounted coiled spring is footed against displaceable gear for biasing the displaceable gear toward and into engagement with the intermediate gear for driving intermediate gear and output gear. Torque control is achieved by the use of straight or spiral beveled gears which are of configurations adapted to withdraw from mutual engagement upon the torque exceeding a predetermined limit. The novel, advantageous features of the invention include the configuration of the mating, crown gear sets and the axially translatable, slidable drive gear. The mechanism is capable of transmitting a high degree of torque within a narrow, compact transmission housing. The compact size and narrow, elongated configuration of the housing is particularly applicable for use in hand tools and in multiple torque driver mechanisms in which it is necessary to drive multiple fasteners which are located in close proximity. Prior

  10. Analysis of cementless implants using interface nonlinear friction--experimental and finite element studies.

    PubMed

    Dammak, M; Shirazi-Adl, A; Zukor, D J

    1997-02-01

    Measured interface nonlinear friction properties are used to develop models to study the short-term fixation response of smooth- and porous-surfaced posts, bone screws, and plates fixed with and without posts/screws. Experimental studies are carried out to validate the model predictions and identify the relative role of posts and screws in fixation of a plate on a polyurethane block under symmetric/eccentric axial compression loads. The idealized Coulomb's friction is also used for the sake of comparison. The incorporation of measured nonlinear, rather than the idealized Coulomb, friction is essential to compute realistic results. For plate fixation, the experimental and finite element results show that the screw fixation yields the stiffest response followed by the smooth- and then porous-coated post fixation. For example, under 1000 N eccentric axial compression, the edge of the plate opposite the loaded edge is measured to lift by 1147 +/- 72, 244 +/- 38, or 112 +/- 28 microns, respectively, for the cases with no fixation, with smooth-surfaced posts, or with screws. The corresponding models predict, respectively, values of 1538, 347, or 259 microns and also 556 microns for the plate fixed with porous coated posts. The satisfactory agreement between numerical and experimental results confirms the importance of proper interface modelling for the analysis of posts, screws, and complex fixation systems. This becomes further evident when considering cementless implants in which the bone-implant interface exhibits relatively large displacements as the maximum resistance force is reached. The developed models can be used to investigate the post-operative short-term stability of various cementless implant designs. PMID:9001932

  11. Torque characteristics of a 122-centimeter butterfly valve with a hydro/pneumatic actuator

    NASA Technical Reports Server (NTRS)

    Lin, F. N.; Moore, W. I.; Lundy, F. E.

    1981-01-01

    Actuating torque data from field testing of a 122-centimeter (48 in.) butterfly valve with a hydro/pneumatic actuator is presented. The hydraulic cylinder functions as either a forward or a reverse brake. Its resistance torque increases when the valve speeds up and decreases when the valve slows down. A reduction of flow resistance in the hydraulic flow path from one end of the hydraulic cylinder to the other will effectively reduce the hydraulic resistance torque and hence increase the actuating torque. The sum of hydrodynamic and friction torques (combined resistance torque) of a butterfly valve is a function of valve opening time. An increase in the pneumatic actuating pressure will result in a decrease in both the combined resistance torque and the actuator opening torque; however, it does shorten the valve opening time. As the pneumatic pressure increases, the valve opening time for a given configuration approaches an asymptotical value.

  12. Experimental Study of Characteristics of Micro-Hole Porous Skins for Turbulent Skin Friction Reduction

    NASA Technical Reports Server (NTRS)

    Hwang, Danny P.

    2002-01-01

    Characteristics of micro-hole porous skins for the turbulent skin friction reduction technology called the micro-blowing technique (MBT) were assessed experimentally at Mach 0.4 and blowing fractions from zero to 0.005. The objective of this study was to provide guidelines for the selection of porous plates for MBT. The hole angle, pattern, diameter, aspect ratio, and porosity were the parameters considered for this study. The additional effort to angle and stagger the holes was experimentally determined to be unwarranted in terms of skin friction benefit; therefore, these parameters were systematically eliminated from the parametric study. The impact of the remaining three parameters was evaluated by fixing two parameters at the reference values while varying the third parameter. The best hole-diameter Reynolds number was found to be around 400, with an optimum aspect ratio of about 6. The optimum porosity was not conclusively discerned because the range of porosities in the test plates considered was not great enough. However, the porosity was estimated to be about 15 percent or less.

  13. Frictional interactions in forming processes: New studies with transparent sapphire strip-drawing dies

    NASA Astrophysics Data System (ADS)

    Rao, R. S.; Lu, C. Y.; Wright, P. K.; Devenpeck, M. L.; Richmond, O.; Appleby, E. J.

    1982-05-01

    This research is concerned with the frictional interactions at the toolwork interfaces in the machining and strip-drawing processes. A novel feature is that transparent sapphire (single crystal Al2O3) is being used as the tool and die material. This allows the tribological features of the interface to be directly observed and recorded on movie-film. These qualitative studies provide information on the role of lubricants. In addition, techniques are being developed to quantify the velocity gradient along the interface. For example, in the drawing work it has been found that tracer markings (e.g. dye-spots), applied to the undrawn strip, remain intact during drawing and can be tracked along the sapphire/strip interface. Such data will be used as input to a finite-element, elasto-plastic-workhardening model of the deformation process. The latter can compute strip deformation characteristics, drawing forces and local coefficients of friction at the interface. Introductory results will be presented in this paper, obtained from drawing tin-plated mild steel with sapphire and cemented carbide dies. Drawing loads and die-separating forces will be presented and movie-films of the action of tracer markings at the interface shown. In order to demonstrate how this data can be used in an analysis of a large strain deformation process with friction, initial results from running the FIPDEF elasto-plastic code will be discussed. From a commercial viewpoint research on strip-drawing is of special interest to the can-making industry. From a physical viewpoint stripdrawing is of particular interest because it is a symmetrical, plane strain deformation and, in comparison with other metal processing operations, it is more readily modeled. However, until now the elasto-plastic codes that have been developed to predictively model drawing have had limitations: the most notable being that of quantifying the friction conditions at the die-work interface. Hence the specification of the

  14. Friction in orthodontics

    PubMed Central

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

    2015-01-01

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

  15. Atmospheric Gravitational Torque Variations Based on Various Gravity Fields

    NASA Technical Reports Server (NTRS)

    Sanchez, Braulio V.; Rowlands, David; Smith, David E. (Technical Monitor)

    2001-01-01

    Advancements in the study of the Earth's variable rate of rotation and the motion of its rotation axis have given impetus to the analysis of the torques between the atmosphere, oceans and solid Earth. The output from global general circulation models of the atmosphere (pressure, surface stress) is being used as input to the torque computations. Gravitational torque between the atmosphere, oceans and solid Earth is an important component of the torque budget. Computation of the gravitational torque involves the adoption of a gravitational model from a wide variety available. The purpose of this investigation is to ascertain to what extent this choice might influence the results of gravitational torque computations.

  16. Effects of Different Ligature Materials on Friction in Sliding Mechanics

    PubMed Central

    Khamatkar, Aparna; Sonawane, Sushma; Narkhade, Sameer; Gadhiya, Nitin; Bagade, Abhijit; Soni, Vivek; Betigiri, Asha

    2015-01-01

    Background: During orthodontic tooth movement friction occurs at the bracket wire interface. Out of the total force applied to the tooth movement, some of it is dissipated as friction, and the remainder is transferred to the supporting structures of the tooth to mediate tooth movement. However many factors affect friction, and method of arch wire ligation being an important contributing factor. Hence, this study was carried out to evaluate the effects of different ligature materials on friction in sliding mechanics and to compare the effect of environment (dry and wet) on friction produced in sliding mechanics. Materials and Methods: The evaluation of friction between the bracket and the archwire consisted of a simulated half arch fixed appliance with archwire ligated in a vertical position. Four 0.022” maxillary stainless steel premolar brackets having a - 0° torque and 0° angulation were aligned with a 0.019” × 0.025” stainless steel arch wire onto a rigid Plexiglass sheet. The movable test bracket was fitted with a 10 mm long, 0.045” thick stainless steel power arm on the bonding surface. Testing was performed on a Hounsfield material testing machine. A total of 100 g weight was suspended from the power arm and the load needed to move the bracket over the distance of not <4 mm across the central span was recorded separately. Fifteen representative readings were taken with one reading per test sample. Results: The results showed that the mean frictional force of different groups in dry and wet state was statistically significantly different. The mean frictional force in a dry state was statistically significantly higher than wet state in elastomeric group. Conclusion: The type of ligation material and environment significantly affected the degree of friction generated during sliding mechanics. Teflon coated stainless steel ligatures produced the least friction among the materials tested in both dry and wet conditions and there was no significant effect

  17. Exploratory study of friction welds in Udimet 700 and TD-Nickel bar

    NASA Technical Reports Server (NTRS)

    Moore, T. J.

    1971-01-01

    Friction welded butt joints were made in both Udimet 700 and TD-Nickel bar. Also, dissimilar metal friction welds were made between these materials. Friction welding of Udimet 700 shows great promise because the welds were found to be as strong as the parent metal in stress rupture and tensile tests at 760 and 980 C. The weld line was not detectable metallographically in the heat treated condition. Friction welding for TD-Nickel, however, holds little if any promise. TD-Nickel friction weldments could support only 9 percent as much stress as the base metal for a 10-hour stress-rupture life at 1090 C. Dissimilar Udimet 700/TD-Nickel friction welds could sustain only 15 percent as much stress as the TD-Nickel parent metal for a 10-hour rupture life at 930 C.

  18. Study of the interactions between friction, wear and system rigidity. Progress report, July 1, 1979-June 30, 1980

    SciTech Connect

    Aronov, V.; D'Souza, A.F.; Kalpakjian, S.; Shareef, I.

    1980-03-01

    Progress in friction and wear studies is reported. After an extensive study of various possible systems for friction, wear and vibration measurements, a pin and disk sliding system has been designed to be used on a rigid lathe bed. This versatile design has the capability of controlling the applied load, rigidity and damping of the total frictional system. The design and construction of the pin holding assembly has been completed with certain features to render it suitable for acquisition of appropriate data such as forces and displacements. Special instrumentation has been obtained the major components of which are a tri-axial quartz piezoelectric force transducer, a tri-axial ceramic piezoelectric accelerometer for measurements of vibrations of the slider, charge preamplifiers with dc power supply, and monitoring equipment such as a spectral analyzer and an oscillograph. Preliminary experiments indicate that the system, as designed and constructed, is appropriate for the type of study undertaken in this project. Some preliminary experimental results are included here. The method of describing functions and harmonic balance is being employed for the study of friction induced self-excited vibrations. Some new developments of this method have been obtained to take into account the coupling between the degrees of freedom in the normal and frictional directions.

  19. A Study of a Handrim-Activated Power-Assist Wheelchair Based on a Non-Contact Torque Sensor.

    PubMed

    Nam, Ki-Tae; Jang, Dae-Jin; Kim, Yong Chol; Heo, Yoon; Hong, Eung-Pyo

    2016-01-01

    Demand for wheelchairs is increasing with growing numbers of aged and disabled persons. Manual wheelchairs are the most commonly used assistive device for mobility because they are convenient to transport. Manual wheelchairs have several advantages but are not easy to use for the elderly or those who lack muscular strength. Therefore, handrim-activated power-assist wheelchairs (HAPAW) that can aid driving power with a motor by detecting user driving intentions through the handrim are being researched. This research will be on HAPAW that judge user driving intentions by using non-contact torque sensors. To deliver the desired motion, which is sensed from handrim rotation relative to a fixed controller, a new driving wheel mechanism is designed by applying a non-contact torque sensor, and corresponding torques are simulated. Torques are measured by a driving wheel prototype and compared with simulation results. The HAPAW prototype was developed using the wheels and a driving control algorithm that uses left and right input torques and time differences are used to check if the non-contact torque sensor can distinguish users' driving intentions. Through this procedure, it was confirmed that the proposed sensor can be used effectively in HAPAW. PMID:27509508

  20. Transformation and Deformation Texture Study in Friction Stir Processed API X80 Pipeline Steel

    NASA Astrophysics Data System (ADS)

    Abbasi, Majid; Nelson, Tracy W.; Sorensen, Carl D.

    2012-12-01

    The nature of deformation in friction stir welding/processing (FSW/P) is complex which is further complicated when allotropic phase transformations are present. Electron backscattered diffraction (EBSD) is used as a means to reconstruct prior austenite texture and grain structure to study deformation and recrystallization in austenite and ferrite in FSW/P of high strength low alloy (HSLA) steels. Analyses show evidence of shear deformation textures such as A1* (111)[-1-12], B (1-12)[110], and -B (-11-2)[-1-10], as well as rotated-cube recrystallization texture in the reconstructed prior austenite. Existence of rotated-cube texture as well as polygonal grain structure of the prior austenite implies that recrystallization is partially occurring in elevated temperatures. Room temperature ferrite exhibits well-defined shear deformation texture components. The observed shear deformation texture in the room temperature microstructure implies that FSW/P imposes deformation during the phase transformation. The evolution of both elevated and room temperature textures in friction stir processed API X80 steel are presented.

  1. Experimental Study on Frictional Vibration in Bearing Case of Centrifugal Fan

    NASA Astrophysics Data System (ADS)

    Fujii, Takeo; Nakagawa, Noritoshi

    In the operation of a centrifugal fan installed on a steel plate floor reinforced with steel frames, applied to the heated air recirculation for the paint drier plant, abnormal vibration of the fan was observed in the transient condition of the plant operation. In view of the complexity of the vibration on the fan at the site, an experimental study on the vibration characteristics was conducted by using an identical fan and a simulated steel plate floor. As a result, there were three characteristic vibration phenomena during heating-up or cooling-down operation. The instantaneous increase of vibration occurred when the bearing case was new and there was insufficient lubrication even on the concrete slab. The temporary increase of vibration in vertical direction was caused by raising or sinking of the floor and the fan base due to thermal expansion. And, the fluctuation of vibration in axial direction was caused by friction, which yielded when the bearing moved inside the bearing case due to thermal expansion or contraction of the shaft. It seems that this fluctuation was due to self-excited vibration by friction.

  2. Dynamics of a split torque helicopter transmission. M.S. Thesis - Cleveland State Univ.

    NASA Technical Reports Server (NTRS)

    Krantz, Timothy L.

    1994-01-01

    Split torque designs, proposed as alternatives to traditional planetary designs for helicopter main rotor transmissions, can save weight and be more reliable than traditional designs. This report presents the results of an analytical study of the system dynamics and performance of a split torque gearbox that uses a balance beam mechanism for load sharing. The Lagrange method was applied to develop a system of equations of motion. The mathematical model includes time-varying gear mesh stiffness, friction, and manufacturing errors. Cornell's method for calculating the stiffness of spur gear teeth was extended and applied to helical gears. The phenomenon of sidebands spaced at shaft frequencies about gear mesh fundamental frequencies was simulated by modeling total composite gear errors as sinusoid functions. Although the gearbox has symmetric geometry, the loads and motions of the two power paths differ. Friction must be considered to properly evaluate the balance beam mechanism. For the design studied, the balance beam is not an effective device for load sharing unless the coefficient of friction is less than 0.003. The complete system stiffness as represented by the stiffness matrix used in this analysis must be considered to precisely determine the optimal tooth indexing position.

  3. Comparative Evaluation of Frictional Properties, Load Deflection Rate and Surface Characteristics of Different Coloured TMA Archwires - An Invitro Study

    PubMed Central

    Aloysius, Arul Pradeep; Deepika; Soundararajan, Nagachandran Kandasamy; Manohar, Vijaykumar Neelam; Khan, Nayeemullah

    2015-01-01

    Introduction During tooth movement the success of sliding mechanics is dependent upon various factors which include frictional resistance at bracket-archwire interface, surface roughness of archwire materials and elastic properties of archwires. Ion implantation techniques reduce the frictional force and allow better tooth movement clinically. Aim The main objective of this study was to evaluate and compare the frictional properties, load deflection rate and surface characteristics of Honey dew and Purple coloured (Ion implanted) TMA wires with uncoated TMA wires. Materials and Methods Fifteen archwire samples were divided into three groups comprising of five samples in each group namely, Group I – Uncoated TMA wires (Control), Group II – Purple coloured TMA wires and Group III- Honey dew TMA wires. Friction and load deflection rate testing were performed with the Instron Universal testing machine and the surface characteristics of the wires were evaluated before and after sliding using Scanning Electron Microscope. Results The mean frictional characteristics and surface roughness for Honey dew TMA wires was lesser than Purple coloured TMA wires which was statistically significant. Both the coloured TMA wires showed low frictional characteristics and less surface roughness than uncoated TMA wires (the control). The mean load deflection rate was low for both coloured ion implanted TMA wires when compared to uncoated TMA wires which was statistically significant. Conclusion Coloured ion implanted TMA wires, especially Honey dew TMA wires have low friction, low load deflection rate and improved surface finish. Hence they can be used in frictionless as well as sliding mechanics, where uncoated TMA wires are inefficient. PMID:26816988

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

    SciTech Connect

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

    1999-01-08

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

  5. Kinetics of a Frictional Granular Motor

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

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

  6. Flexible pivot mount eliminates friction and hysteresis

    NASA Technical Reports Server (NTRS)

    Highman, C. O.

    1970-01-01

    Flexible steel pivot mount, suspended by flat vertical beryllium copper springs, is capable of rotation, free of hysteresis and starting friction. Mount requires no lubrication, is made in varying sizes, and is driven with either dc torque motor or mechanical linkage.

  7. Smart friction driven systems

    NASA Astrophysics Data System (ADS)

    Nitsche, Rainer; Gaul, Lothar

    2005-02-01

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

  8. Determining Spacecraft Reaction Wheel Friction Parameters

    NASA Technical Reports Server (NTRS)

    Sarani, Siamak

    2009-01-01

    Software was developed to characterize the drag in each of the Cassini spacecraft's Reaction Wheel Assemblies (RWAs) to determine the RWA friction parameters. This tool measures the drag torque of RWAs for not only the high spin rates (greater than 250 RPM), but also the low spin rates (less than 250 RPM) where there is a lack of an elastohydrodynamic boundary layer in the bearings. RWA rate and drag torque profiles as functions of time are collected via telemetry once every 4 seconds and once every 8 seconds, respectively. Intermediate processing steps single-out the coast-down regions. A nonlinear model for the drag torque as a function of RWA spin rate is incorporated in order to characterize the low spin rate regime. The tool then uses a nonlinear parameter optimization algorithm based on the Nelder-Mead simplex method to determine the viscous coefficient, the Dahl friction, and the two parameters that account for the low spin-rate behavior.

  9. Frictional force released during sliding mechanics in nonconventional elastomerics and self-ligation: An in vitro comparative study

    PubMed Central

    Kumar, Davender; Dua, Vinay; Mangla, Rajat; Solanki, Ravinder; Solanki, Monika; Sharma, Rekha

    2016-01-01

    Aim and Objectives: The aim of this study is to evaluate the frictional forces generated by five different orthodontic brackets when used in combination with stainless steel (SS), titanium molybdenum alloy (TMA), and nickel-titanium (NiTi) archwires in dry conditions at physiological temperature. Materials and Methods: Five different types of maxillary upper right side self-ligating brackets (SLBs) (Damon 3MX, Smart Clip and Carriere LX) and conventional SS brackets (Mini 2000, Optimum Series and Victory Series) with a slot size 0.022 inch were coupled with 0.016” NiTi and 0.019 × 0.025” SS/titanium molybdenum alloy (TMA) archwires. Tests were carried out for each group of the bracket-wire combination at physiological temperature and in the dry state. Frictional forces were measured by Instron universal testing machine. Results: SLB showed lower fictional values in comparison with elastic ligatures. Frictional force increased proportionally to the wire size; TMA and NiTi archwires presented higher frictional resistance than SS archwires. Conclusion: SS brackets tied with conventional ligatures produced high and low friction when ligated with SLBs with passive clip. PMID:27433047

  10. Study of friction properties of lunar surface material and its analogs

    NASA Technical Reports Server (NTRS)

    Dukhovskoy, Y. A.; Motovilov, E. A.; Silin, A. A.; Smorodinov, M. I.; Shvarev, V. V.

    1974-01-01

    A description is given of instruments for determining the friction properties of the surficial layer of lunar surface material returned by the Luna 16 automatic lunar station, as well as the friction properties of its analogs: andesite-basaltic sand and basalts. The experimental method and results are presented.

  11. Exploratory Study of the Reduction in Friction Drag Due to Streamwise Injection of Helium

    NASA Technical Reports Server (NTRS)

    Swenson, Byron L.

    1961-01-01

    The effects on average skin-friction drag and pressure drag of the streamwise injection of helium into the boundary layer near the nose of a 6 deg. half-angle cone at Mach numbers of 3 to 5 are presented. Large reductions in skin friction are shown to be possible with relatively small amounts of helium injection.

  12. Torque Loss in En-Masse Retraction of Maxillary Anterior Teeth Using Miniimplants with Force Vectors at Different Levels: 3D FEM Study

    PubMed Central

    Aileni, Kaladhar Reddy; Rachala, Madhukar Reddy; Shashidhar, Nagam Reddy; Mallikarjun, Vankre; Parik, Nupur

    2014-01-01

    Objective: This FEM study was conducted to quantify the amount of torque loss in maxillary anterior teeth by applying force vectors from different levels to the anterior retraction hook at various heights and comparing with that of molar anchorage system. Materials and Methods: Five 3D FEM models were constructed with force vectors at different levels: HOT-High Orthodontic Traction (13.5mm from archwire) to ARH1– Anterior Retraction Hook (5mm), HOT to ARH2 (8mm), LOT- Low Orthodontic Traction (8 mm) to ARH1, LOT to ARH2 and from conventional molar hook to ARH1. Mini-implants were placed buccally between the roots of second premolar and first molar. Torque loss was calculated by measuring the displacement of the teeth at crown tip and root apex in two planes i.e. sagittal and vertical using Y and Z axis respectively in all the five models. The results were statistically analyzed by using Kruskal Wallis ANOVA and Mann-Whitney U-test. Results: HOT to ARH1 showed that the anterior teeth moved bodily (p =0.5127), followed by molar hook - ARH1(p=0.0495*) which showed mild uncontrolled tipping. Whereas the HOT- ARH2, LOT - ARH1,and LOT - ARH2 models exhibited uncontrolled tipping with maximum torque loss in LOT - ARH1 (p=0.0001*). Conclusion: It can be concluded that bodily movement with very minimal torque loss was observed in HOT-ARH1 model whereas the maximum torque loss was recorded in LOT-ARH2 model. Conventional molar anchorage group showed uncontrolled tipping with some amount of extrusion and anchor loss of posteriors. PMID:25654038

  13. Angular Acceleration Without Torque?

    NASA Astrophysics Data System (ADS)

    Kaufman, Richard D.

    2012-01-01

    Hardly. Just as Robert Johns qualitatively describes angular acceleration by an internal force in his article "Acceleration Without Force?" here we will extend the discussion to consider angular acceleration by an internal torque. As we will see, this internal torque is due to an internal force acting at a distance from an instantaneous center.2

  14. Angular Acceleration without Torque?

    ERIC Educational Resources Information Center

    Kaufman, Richard D.

    2012-01-01

    Hardly. Just as Robert Johns qualitatively describes angular acceleration by an internal force in his article "Acceleration Without Force?" here we will extend the discussion to consider angular acceleration by an internal torque. As we will see, this internal torque is due to an internal force acting at a distance from an instantaneous center.

  15. Study of confinement and sliding friction of fluids using sum frequency generation spectroscopy

    NASA Astrophysics Data System (ADS)

    Nanjundiah, Kumar

    2007-12-01

    Friction and wear are important technologically. Tires on wet roads, windshield wipers and human joints are examples where nanometer-thick liquids are confined between flexible-rigid contact interfaces. Fundamental understanding of the structure of these liquids can assist in the design of products such as artificial joints and lubricants for Micro-electromechanical systems [MEMS]. Prior force measurements have suggested an increase in apparent viscosity of confined liquid and sometimes solid-like responses. But, these have not given the state of molecules under confinement. In the present study, we have used a surface sensitive, non-linear optical technique (infrared-visible sum frequency generation spectroscopy [SFG]) to investigate molecular structure at hidden interfaces. SFG can identify chemical groups, concentration and orientation of molecules at an interface. A friction cell was developed to study sliding of a smooth elastomeric lens against a sapphire surface. Experiments were done with dry sliding as well as lubricated sliding in the presence of linear alkane liquids. SFG spectra at the alkane/sapphire interface revealed ordering of the confined alkane molecules. These were more ordered than alkane liquid, but less ordered than alkane crystal. Cooling of the confined alkane below its melting temperature [TM] led to molecular orientation that was different from that of bulk crystal next to a sapphire surface. Molecules were oriented with their symmetry axis parallel to the surface normal. In addition, the melting temperature [Tconf] under confinement for a series of linear alkanes (n =15--27) showed a surprising trend. Intermediate molecular weights showed melting point depression. The T conf values suggested that melting started at the alkane/sapphire interface. In another investigation, confinement of water between an elastomeric PDMS lens and sapphire was studied. SFG spectra at the sapphire/water/PDMS interface revealed a heterogeneous morphology. The

  16. Study on the Friction and Wear Behavior of a TA15 Alloy and Its Ni-SiC Composite Coating

    NASA Astrophysics Data System (ADS)

    Guo, Bao-hui; Wang, Zhen-ya; Li, Hai-long

    2016-05-01

    Ni-SiC composite coatings were prepared on TA15 alloy by composite electroplating technology. The friction and wear behavior of TA15 alloy, and the coating were comparatively studied at both room temperature and 600 °C using GCr15 as the counterparts. The results show that the obtained coating is relatively dense and compact, and possesses higher micro-hardness than TA15 alloy. The coating has significant friction reduction effect sliding at 600 °C, but has no obvious friction reduction effect sliding at room temperature. The coating possesses superior wear resistance than TA15 alloy, evidenced by its much lower mass losses than those of TA15 alloy sliding at both room temperature and 600 °C. The TA15 alloy and the coating showed different wear mechanisms under the given sliding conditions.

  17. Fuzzy logic inference-based Pavement Friction Management and real-time slippery warning systems: A proof of concept study.

    PubMed

    Najafi, Shahriar; Flintsch, Gerardo W; Khaleghian, Seyedmeysam

    2016-05-01

    Minimizing roadway crashes and fatalities is one of the primary objectives of highway engineers, and can be achieved in part through appropriate maintenance practices. Maintaining an appropriate level of friction is a crucial maintenance practice, due to the effect it has on roadway safety. This paper presents a fuzzy logic inference system that predicts the rate of vehicle crashes based on traffic level, speed limit, and surface friction. Mamdani and Sugeno fuzzy controllers were used to develop the model. The application of the proposed fuzzy control system in a real-time slippery road warning system is demonstrated as a proof of concept. The results of this study provide a decision support model for highway agencies to monitor their network's friction and make appropriate judgments to correct deficiencies based on crash risk. Furthermore, this model can be implemented in the connected vehicle environment to warn drivers of potentially slippery locations. PMID:26914521

  18. Friction in metal-on-metal total disc arthroplasty: effect of ball radius.

    PubMed

    Moghadas, Parshia; Mahomed, Aziza; Hukins, David W L; Shepherd, Duncan E T

    2012-02-01

    Total disc arthroplasty (TDA) can be used to replace a degenerated intervertebral disc in the spine. There are different designs of prosthetic discs, but one of the most common is a ball-and-socket combination. Contact between the bearing surfaces can result in high frictional torque, which can then result in wear and implant loosening. This study was designed to determine the effects of ball radius on friction. Generic models of metal-on-metal TDA were manufactured with ball radii of 10, 12, 14 and 16 mm, with a radial clearance of 0.015 mm. A simulator was used to test each sample in flexion-extension, lateral bending and axial rotation at frequencies of 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75 and 2 Hz under loads of 50, 600, 1200 and 2000 N, in new born calf serum. Frictional torque was measured and Stribeck curves were plotted to illustrate the lubrication regime in each case. It was observed that implants with a smaller ball radius showed lower friction and showed boundary and mixed lubrication regimes, whereas implants with larger ball radius showed boundary lubrication only. This study suggests designing metal-on-metal TDAs with ball radius of 10 or 12 mm, in order to reduce wear and implant loosening. PMID:22177670

  19. Magnetic Torque Studies of π-d System κ-(BDH-TTP)2FeX4 (X = Br, Cl)

    NASA Astrophysics Data System (ADS)

    Sugii, Kaori; Takai, Kazuyuki; Tsuchiya, Satoshi; Uji, Shinya; Terashima, Taichi; Akutsu, Hiroki; Wada, Atsushi; Ichikawa, Shun; Yamada, Jun-ichi; Enoki, Toshiaki

    2014-02-01

    Systematic measurements of the magnetic torque of organic π-d conductors κ-(BDH-TTP)2FeX4 (X = Br, Cl) have been performed to investigate the magnetic properties. The Fe 3d spins of both salts show antiferromagnetic (AF) orders at low temperatures. A simple two-sublattice model is found to well reproduce the essential features of the torque data in the AF states. The exchange interaction and anisotropic parameter of the ligand field obtained by the simulations are consistent with previous experimental results.

  20. Comparative study of friction between metallic and conventional interactive self-ligating brackets in different alignment conditions

    PubMed Central

    Jakob, Sérgio Ricardo; Matheus, Davison; Jimenez-Pellegrin, Maria Cristina; Turssi, Cecília Pedroso; do Amaral, Flávia Lucisano Botelho

    2014-01-01

    Objective The aim of this study was to compare the friction between three bracket models: conventional stainless steel (Ovation, Dentsply GAC), self-ligating ceramic (In-Ovation, Denstply GAC) and self-ligating stainless steel brackets (In-Ovation R, Dentsply GAC). Methods Five brackets were used for each model. They were bonded to an aluminum prototype that allowed the simulation of four misalignment situations (n = 10). Three of these situations occurred at the initial phase (in which a 0.016-in nickel-titanium wire was used): 1. horizontal; 2. vertical; and 3. simultaneous horizontal/vertical. One of the situations occurred at the final treatment phase: 4. no misalignment (in which a 0.019 x 0.025-inch stainless steel rectangular wire was used). The wires slipped through the brackets and friction was measured by a Universal Testing Machine. Results Analysis of variance followed by Tukey's Test for multiple comparisons (α = 0.05) were applied to assess the results. Significant interaction (p < 0.01) among groups was found. For the tests that simulated initial alignment, Ovation® bracket produced the highest friction. The two self-ligating models resulted in lower and similar values, except for the horizontal situation, in which In-Ovation C® showed lower friction, which was similar to the In-Ovation R® metallic model. For the no misalignment situation, the same results were observed. Conclusion The self-ligating system was superior to the conventional one due to producing less friction. With regard to the material used for manufacturing the brackets, the In-Ovation C® ceramic model showed less friction than the metallic ones. PMID:25162570

  1. Observation of a Dislocation-Related Interfacial Friction Mechanism in Mobile Solid 4He

    NASA Astrophysics Data System (ADS)

    Eyal, Anna; Livne, Ethan; Polturak, Emil

    2016-04-01

    We report a study of the temperature and stress dependence of the friction associated with a relative motion of crystallites of solid 4He in contact with each other. A situation where such motion exists emerges spontaneously during a disordering of a single crystal contained inside an annular sample space of a torsional oscillator (TO). Under the torque applied by the oscillating walls of the TO these crystallites move relative to each other, generating measurable dissipation at their interface. We studied this friction between 0.5 and 1.8 K in solid samples grown from commercially pure 4He and from a 100 ppm 3He-4He mixture. The data were analyzed by modeling the TO as a driven harmonic oscillator. In this model, an analysis of the resonant frequency and amplitude of the TO yields the temperature dependence of the friction coefficient. By fitting the data to specific forms, we found that over our temperature range, the dominant friction mechanism associated with the interfacial motion of the crystallites results from climb of individual dislocations. The characteristic energy scale associated with this friction can be 3 or 6 K, depending on the sample. The motion of the solid in the presence of such friction can perhaps be described as the low limit of "slip-stick" motion.

  2. Friction compensation strategies in large telescopes

    NASA Astrophysics Data System (ADS)

    Smith, David R.; Souccar, Kamal

    2010-07-01

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

  3. Modeling Attitude Dynamics in Simulink: A Study of the Rotational and Translational Motion of a Spacecraft Given Torques and Impulses Generated by RMS Hand Controllers

    NASA Technical Reports Server (NTRS)

    Mauldin, Rebecca H.

    2010-01-01

    In order to study and control the attitude of a spacecraft, it is necessary to understand the natural motion of a body in orbit. Assuming a spacecraft to be a rigid body, dynamics describes the complete motion of the vehicle by the translational and rotational motion of the body. The Simulink Attitude Analysis Model applies the equations of rigid body motion to the study of a spacecraft?s attitude in orbit. Using a TCP/IP connection, Matlab reads the values of the Remote Manipulator System (RMS) hand controllers and passes them to Simulink as specified torque and impulse profiles. Simulink then uses the governing kinematic and dynamic equations of a rigid body in low earth orbit (LE0) to plot the attitude response of a spacecraft for five seconds given known applied torques and impulses, and constant principal moments of inertia.

  4. Establishing a relationship between maximum torque production of isolated joints to simulate EVA ratchet push-pull maneuver: A case study

    NASA Technical Reports Server (NTRS)

    Pandya, Abhilash; Maida, James; Hasson, Scott; Greenisen, Michael; Woolford, Barbara

    1993-01-01

    As manned exploration of space continues, analytical evaluation of human strength characteristics is critical. These extraterrestrial environments will spawn issues of human performance which will impact the designs of tools, work spaces, and space vehicles. Computer modeling is an effective method of correlating human biomechanical and anthropometric data with models of space structures and human work spaces. The aim of this study is to provide biomechanical data from isolated joints to be utilized in a computer modeling system for calculating torque resulting from any upper extremity motions: in this study, the ratchet wrench push-pull operation (a typical extravehicular activity task). Established here are mathematical relationships used to calculate maximum torque production of isolated upper extremity joints. These relationships are a function of joint angle and joint velocity.

  5. Thermal Spin Transfer Torques

    NASA Astrophysics Data System (ADS)

    Bauer, Gerrit

    2009-03-01

    The coupling between spin and charge in electronic transport is studied in the field of spintronics. Heat currents are coupled to both charge and spin currents as well [1]. This extension of spintronics to what may be called ``spin caloritronics'' recently enjoys renewed attention [2]. The spin-transfer torque associated with electric currents can excite magnetizations in nanostructures, switching magnetic configuration in spin valves and move domain walls in magnetic wires when exceeding critical values of the order of 10^7Acm-2 [3]. Also heat currents transfer spin angular momentum [4], either intrinsically or via the thermoelectric generation of particle spin currents. We predict that temperature differences of the order of 100 K over typical metallic nanostructures cause effects equivalent to the critical charge current densities. In this talk I will give a brief review of various aspects of spin caloritronics with emphasis on thermal spin transfer torques. This work has been carried out in collaboration with Moosa Hatami, Qinfang Zhang, Paul Kelly, Hans Joakim Skadsem, Arne Brataas and Sadamichi Maekawa. [4pt] [1] M. Johnson and R.H. Silsbee, Phys. Rev. B 35, 4959 (1987).[0pt] [2] International Workshop on Spin Caloritronics, Lorentz Center of Leiden University, 9-13 February 2009, http://www.lorentzcenter.nl/lc/web/2009/323/info.php3?wsid=323[0pt] [3] D. C. Ralph and M. D. Stiles, J. Magn. Magn. Mater. 320, 1190 (2008).[0pt] [4] M. Hatami, G.E.W. Bauer, Q. Zhang, and P.J. Kelly, Phys. Rev. Lett. 99, 066603 (2007).

  6. An Experimental Study of Turbulent Skin Friction Reduction in Supersonic Flow Using a Microblowing Technique

    NASA Technical Reports Server (NTRS)

    Hwang, Danny P.

    1999-01-01

    A new turbulent skin friction reduction technology, called the microblowing technique has been tested in supersonic flow (Mach number of 1.9) on specially designed porous plates with microholes. The skin friction was measured directly by a force balance and the boundary layer development was measured by a total pressure rake at the tailing edge of a test plate. The free stream Reynolds number was 1.0(10 exp 6) per meter. The turbulent skin friction coefficient ratios (C(sub f)/C(sub f0)) of seven porous plates are given in this report. Test results showed that the microblowing technique could reduce the turbulent skin friction in supersonic flow (up to 90 percent below a solid flat plate value, which was even greater than in subsonic flow).

  7. Numerical Studies of Friction Between Metallic Surfaces and of its Dependence on Electric Currents

    NASA Astrophysics Data System (ADS)

    Meintanis, Evangelos; Marder, Michael

    2009-03-01

    We will present molecular dynamics simulations that explore the frictional mechanisms between clean metallic surfaces. We employ the HOLA molecular dynamics code to run slider-on-block experiments. Both objects are allowed to evolve freely. We recover realistic coefficients of friction and verify the importance of cold-welding and plastic deformations in dry sliding friction. We also find that plastic deformations can significantly affect both objects, despite a difference in hardness. Metallic contacts have significant technological applications in the transmission of electric currents. To explore the effects of the latter to sliding, we had to integrate an electrodynamics solver into the molecular dynamics code. The disparate time scales involved posed a challenge, but we have developed an efficient scheme for such an integration. A limited electrodynamic solver has been implemented and we are currently exploring the effects of currents in the friction and wear of metallic contacts.

  8. Friction, wear, and thermal stability studies of some organotin and organosilicon compounds

    NASA Technical Reports Server (NTRS)

    Jones, W. R., Jr.

    1973-01-01

    Thermal decomposition temperatures were determined for a number of organotin and organosilicon compounds. A ball-on-disk sliding friction apparatus was used to determine the friction and wear characteristics of two representative compounds, (1) 3-tri-n-butylstannyl (diphenyl) and (2) 3-tri-n-butylsilyl (diphenyl). Friction and wear test conditions included a 1-kg load, 25 to 225 C disk temperatures, and a dry air atmosphere. The tin and silicon compounds yielded friction and wear results either lower than or similar to those obtained with a polyphenyl ether and a C-ether. The maximum thermal decomposition temperatures obtained in the silicon and tin series were 358 and 297 C, respectively. Increasing the steric hindrance around the silicon or tin atoms increased the thermal stability. Future work with these compounds will emphasize their use as antiwear additives rather than base fluids.

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

    PubMed Central

    Lee, Souk Min

    2015-01-01

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

  10. A Computational Study of the Mechanics of Gravity-induced Torque on Cells

    NASA Astrophysics Data System (ADS)

    Haranas, Ioannis; Gkigkitis, Ioannis; Zouganelis, George D.

    2013-10-01

    In this paper, we study the effects of the acceleration gravity on the sedimentation deposition probability, as well as the aerosol deposition rate on the surface of the Earth and Mars, but also aboard a spacecraft in orbit around Earth and Mars as well. For particles with density ?p = 1300 kg/m3, diameters dp = 1, 10, 30 μm and residence times t = 0.0272, 0.2 s respectively, we find that, on the surface of Earth and Mars the deposition probabilities are higher at the poles when compared to the ones at the equator. Similarly, when in orbit around Earth we find that the deposition probabilities exhibit 0.0001 % higher percentage difference in equatorial circular and elliptical orbits when compared to polar ones. For both residence times particles with the diameters considered above in circular and elliptical orbits around Mars, the deposition probabilities appear to be the same for all orbital inclinations. Sedimentation probability increases drastically with particle diameter and orbital eccentricity of the orbiting spacecraft. Finally, as an alternative framework for the study of interaction and the effect of gravity in biology, and in particular gravity and the respiratory system we introduce is the term information in a way Shannon has introduced it, considering the sedimentation probability as a random variable. This can be thought as a way in which gravity enters the cognitive processes of the system (processing of information) in the cybernetic sense.

  11. Algorithm for calculating torque base in vehicle traction control system

    NASA Astrophysics Data System (ADS)

    Li, Hongzhi; Li, Liang; Song, Jian; Wu, Kaihui; Qiao, Yanjuan; Liu, Xingchun; Xia, Yongguang

    2012-11-01

    Existing research on the traction control system(TCS) mainly focuses on control methods, such as the PID control, fuzzy logic control, etc, aiming at achieving an ideal slip rate of the drive wheel over long control periods. The initial output of the TCS (referred to as the torque base in this paper), which has a great impact on the driving performance of the vehicle in early cycles, remains to be investigated. In order to improve the control performance of the TCS in the first several cycles, an algorithm is proposed to determine the torque base. First, torque bases are calculated by two different methods, one based on states judgment and the other based on the vehicle dynamics. The confidence level of the torque base calculated based on the vehicle dynamics is also obtained. The final torque base is then determined based on the two torque bases and the confidence level. Hardware-in-the-loop(HIL) simulation and vehicle tests emulating sudden start on low friction roads have been conducted to verify the proposed algorithm. The control performance of a PID-controlled TCS with and without the proposed torque base algorithm is compared, showing that the proposed algorithm improves the performance of the TCS over the first several cycles and enhances about 5% vehicle speed by contrast. The proposed research provides a more proper initial value for TCS control, and improves the performance of the first several control cycles of the TCS.

  12. Fabricated torque shaft

    DOEpatents

    Mashey, Thomas Charles

    2002-01-01

    A fabricated torque shaft is provided that features a bolt-together design to allow vane schedule revisions with minimal hardware cost. The bolt-together design further facilitates on-site vane schedule revisions with parts that are comparatively small. The fabricated torque shaft also accommodates stage schedules that are different one from another in non-linear inter-relationships as well as non-linear schedules for a particular stage of vanes.

  13. Study the friction behaviour of poly[2-(dimethylamino)ethyl methacrylate] brush with AFM probes in contact mechanics

    NASA Astrophysics Data System (ADS)

    Raftari, Maryam; Zhang, Zhenyu; Leggett, Graham J.; Geoghegan, Mark

    2011-10-01

    We have studied the frictional behaviour of grafted poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) films using friction force microscopy (FFM). The films were prepared on native oxide-terminated silicon substrates using the technique of atom transfer radical polymerization (ATRP). We show that single asperity contact mechanics (Johnson-Kendall-Roberts(JKR) and Derjaguin-Muller-Toporov(DMT)) as well as a linear (Amontons) relation between applied load and frictional load depending on the pH of the FFM probe. Measurements were made using functionalized and unfunctionalized silicon nitride triangular probes. Functionalized probes included gold-coated probes, and ones coated with a self-assembled monolayer of dodecanethiol (DDT). The frictional behaviour between PDMAEMA and all tips immersed in pH from 3 to 11 are corresponded to the DMT or JKR model and are linear in pH=1, 2, and 12. These results show that contact mechanics of polyelectrolytes in water is complex and strongly dependent on the environmental pH.

  14. Research on new dynamic torque calibration system

    NASA Astrophysics Data System (ADS)

    Zhang, Li; Wang, Zhong Yu; Yin, Xiao

    2016-06-01

    Dynamic torque calibration method based on rotating table and interferometric system is studied in this paper. A load mass with certain moment of inertia are screwed on the top of torque transducer, the dynamic torque is realized by load object are traceable to angular acceleration and moment of inertia of the object by M (t)=I θ ¨(t) , where I is the total moment of inertia acting on the sensing element of the torque transducer and θ ¨ is the time and spatial-dependent angular acceleration of the load object which is directly measured by a laser interferometer. This paper will introduce a dynamic torque calibration system developed at Changcheng Institute of Metrology and Measurement (CIMM). It uses servomotor to generate dynamic torque in the range from 0.1Nm to 200Nm, and heterodyne laser interferometers cooperated with column grating are used for angular acceleration measurement. An airbearing system is developed to increase the performance of the dynamic turque calibration system. This paper introduce the setup of the dynamic torque calibration system.

  15. A Comparative Study of Material Flow Behavior in Friction Stir Welding Using Laminar and Turbulent Models

    NASA Astrophysics Data System (ADS)

    Kadian, Arun Kumar; Biswas, Pankaj

    2015-10-01

    Friction stir welding has been quite successful in joining aluminum alloy which has gained importance in almost all industrial sectors over the past two decades. It is a newer technique and therefore needs more attention in many sectors, flow of material being one among them. The material flow pattern actually helps in deciding the parameters required for particular tool geometry. The knowledge of material flow is very significant in removing defects from the weldment. In the work presented in this paper, the flow behavior of AA6061 under a threaded tool has been studied. The convective heat loss has been considered from all the surfaces, and a comparative study has been made with and without the use of temperature-dependent properties and their significance in the finite volume method model. The two types of models that have been implemented are turbulent and laminar models. Their thermal histories have been studied for all the cases. The material flow velocity has been analyzed to predict the flow of material. A swirl inside the weld material has been observed in all the simulations.

  16. Displaceable Gear Torque Controlled Driver

    NASA Technical Reports Server (NTRS)

    Cook, Joseph S., Jr. (Inventor)

    1997-01-01

    Methods and apparatus are provided for a torque driver including a displaceable gear to limit torque transfer to a fastener at a precisely controlled torque limit. A biasing assembly biases a first gear into engagement with a second gear for torque transfer between the first and second gear. The biasing assembly includes a pressurized cylinder controlled at a constant pressure that corresponds to a torque limit. A calibrated gage and valve is used to set the desired torque limit. One or more coiled output linkages connect the first gear with the fastener adaptor which may be a socket for a nut. A gear tooth profile provides a separation force that overcomes the bias to limit torque at the desired torque limit. Multiple fasteners may be rotated simultaneously to a desired torque limit if additional output spur gears are provided. The torque limit is adjustable and may be different for fasteners within the same fastener configuration.

  17. Efficacy of 15% Trichloroacetic Acid and 50% Glycolic Acid Peel in the Treatment of Frictional Melanosis: A Comparative Study

    PubMed Central

    Sacchidanand, S; Shetty, Ashvith B; Leelavathy, B

    2015-01-01

    Background: Frictional dermal melanosis is aesthetically displeasing. Various modalities ranging from depigmenting agents to lasers have been tried but it continues to be a difficult problem to treat. Objective: To study and compare the efficacy of 15% trichloroacetic acid (TCA) and 50% glycolic acid in the treatment of frictional melanosis of the forearm. Materials and Methods: 40 patients of frictional melanosis of the forearm were included in the study. Patients were randomly divided into two equal groups A and B. Pre-peel priming was carried out with 12% glycolic acid and sunscreen for 2 weeks. Group A was treated with trichloroacetic acid (TCA-15%) peel and Group B with glycolic acid (GA-50%) peel. Four peels were done one every 15 days. Clinical photographs were taken to assess the response. Response to therapy was evaluated by both objective and subjective methods. The patients were followed up for 3 months after the last peel to note any relapse. Results: Both TCA and glycolic acid peels were effective in frictional melanosis. TCA showed better response compared to glycolic acid at the end of the treatment, both by subjective and objective methods. However, this difference was not statistically significant (P > 0.05). No permanent side effects were seen in any of the treated patients and the improvement was sustained without any relapse at 3 months. Conclusion: Chemical peeling with both tricholoroacetic acid (15%) and glycolic acid (50%) is safe and effective for the treatment of frictional dermal melanosis. Tricholoroacetic acid was found to be marginally superior to glycolic acid. PMID:25949021

  18. Analytical and Computational Study of Flame Acceleration due to Wall Friction in Combustion Tubes and Channels

    NASA Astrophysics Data System (ADS)

    Demirgok, Berk; Akkerman, V'yacheslav

    2013-11-01

    Deflagration-to-detonation transition constitutes one of the fundamental problems within the studies of reacting flows. It occurs when a subsonic flamefront accelerates, with velocity jump by several orders of magnitude. According to the Shelkin model, the key element of the process is wall friction at non-slip walls, driving a flow of the fresh pre-mixture to be non-uniform, leading to a positive flame-flow feedback and thereby flame acceleration. We perform analytical and computational study of the phenomenon, with very good agreement between them in the domain of intrinsic accuracy of the theory. Theory assumes large Reynolds number (Re) and thermal expansion as well as plane-parallel flow ahead of flamefront. Simulations are performed for complete set of combustion and hydrodynamic equations. Analytical and computational results are also validated by recent experiments on ethylene-oxygen combustion. It is proven realistic flames with a large density drop at the front accelerate in a self-sustained manner and may initiate detonation in a sufficiently long tube. Before this event, the flame shape and the velocity profile remain self-similar. Acceleration rate grows with thermal expansion in the burning process but decreases with Re related to flame propagation.

  19. Self-oscillation in spin torque oscillator stabilized by field-like torque

    SciTech Connect

    Taniguchi, Tomohiro; Tsunegi, Sumito; Kubota, Hitoshi; Imamura, Hiroshi

    2014-04-14

    The effect of the field-like torque on the self-oscillation of the magnetization in spin torque oscillator with a perpendicularly magnetized free layer was studied theoretically. A stable self-oscillation at zero field is excited for negative β while the magnetization dynamics stops for β = 0 or β > 0, where β is the ratio between the spin torque and the field-like torque. The reason why only the negative β induces the self-oscillation was explained from the view point of the energy balance between the spin torque and the damping. The oscillation power and frequency for various β were also studied by numerical simulation.

  20. Anisotropy of Multilayered (cu, C)BA2CA3CU4OY Superconductors Studied by Torque Magnetometry

    NASA Astrophysics Data System (ADS)

    Tokiwa, K.; Koganezawa, T.; Mikusu, S.; Watanabe, T.; Iyo, A.; Tanaka, Y.

    The magnetic torque of (Cu,C)Ba2Ca3Cu4Oy ( (Cu,C)-1234) aligned samples with various carrier concentrations has been measured under a magnetic field of 9 T at 80 K and 90 K. The carrier concentration was determined by Hall effect measurements. From angular dependent torque measurements, the anisotropy ratio γ was estimated using the 3D anisotropic London model. The γvalues decreased from 23 to 10 with an increase in the average Hall number per CuO2 plane (nH); however, these samples showed a nearly constant Tc of about 117 K. These results indicate that the anisotropy of (Cu,C)-1234 strongly reflects the doping levels of the outer planes.

  1. Spin-orbit torque-driven magnetization switching and thermal effects studied in TaCoFeBMgO nanowires

    NASA Astrophysics Data System (ADS)

    Lo Conte, R.; Hrabec, A.; Mihai, A. P.; Schulz, T.; Noh, S.-J.; Marrows, C. H.; Moore, T. A.; Kläui, M.

    2014-09-01

    We demonstrate magnetization switching in out-of-plane magnetized TaCoFeBMgO nanowires by current pulse injection along the nanowires, both with and without a constant and uniform magnetic field collinear to the current direction. We deduce that an effective torque arising from spin-orbit effects in the multilayer drives the switching mechanism. While the generation of a component of the magnetization along the current direction is crucial for the switching to occur, we observe that even without a longitudinal field thermally generated magnetization fluctuations can lead to switching. Analysis using a generalized Néel-Brown model enables key parameters of the thermally induced spin-orbit torques-driven switching process to be estimated, such as the attempt frequency and the effective energy barrier.

  2. Spin Torque Study of the Spin Hall Conductivity and Spin Diffusion Length in Platinum Thin Films with Varying Resistivity

    NASA Astrophysics Data System (ADS)

    Nguyen, Minh-Hai; Ralph, D. C.; Buhrman, R. A.

    2016-03-01

    We report measurements of the spin torque efficiencies in perpendicularly magnetized Pt /Co bilayers where the Pt resistivity ρPt is strongly dependent on thickness tPt . The dampinglike spin Hall torque efficiency per unit current density ξDLj varies significantly with tPt , exhibiting a peak value ξDLj=0.12 at tPt=2.8 - 3.9 nm . In contrast, ξDLj/ρPt increases monotonically with tPt and saturates for tPt>5 nm , consistent with an intrinsic spin Hall effect mechanism, in which ξDLj is enhanced by an increase in ρPt . Assuming the Elliott-Yafet spin scattering mechanism dominates, we estimate that the spin diffusion length λs=(0.77 ±0.08 )×10-15 Ω .m2/ρPt .

  3. Torque, chemistry and efficiency in molecular motors: a study of the rotary-chemical coupling in F1-ATPase.

    PubMed

    Mukherjee, Shayantani; Bora, Ram Prasad; Warshel, Arieh

    2015-11-01

    Detailed understanding of the action of biological molecular machines must overcome the challenge of gaining a clear knowledge of the corresponding free-energy landscape. An example for this is the elucidation of the nature of converting chemical energy to torque and work in the rotary molecular motor of F1-ATPase. A major part of the challenge involves understanding the rotary-chemical coupling from a non-phenomenological structure/energy description. Here we focused on using a coarse-grained model of F1-ATPase to generate a structure-based free-energy landscape of the rotary-chemical process of the whole system. In particular, we concentrated on exploring the possible impact of the position of the catalytic dwell on the efficiency and torque generation of the molecular machine. It was found that the experimentally observed torque can be reproduced with landscapes that have different positions for the catalytic dwell on the rotary-chemical surface. Thus, although the catalysis is undeniably required for torque generation, the experimentally observed position of the catalytic dwell at 80° might not have a clear advantage for the force generation by F1-ATPase. This further implies that the rotary-chemical couplings in these biological motors are quite robust and their efficiencies do not depend explicitly on the position of the catalytic dwells. Rather, the specific positioning of the dwells with respect to the rotational angle is a characteristic arising due to the structural construct of the molecular machine and might not bear any clear connection to the thermodynamic efficiency for the system. PMID:26537397

  4. A Preliminary Study of Deformation Behavior of Friction Stir Welded Ti-6Al-4V

    NASA Astrophysics Data System (ADS)

    Wang, Jiye; Su, Jianqing; Mishra, Rajiv S.; Xu, Ray; Baumann, John A.

    2014-08-01

    A preliminary study of deformation behavior of friction stir welded (FSW) Ti-6Al-4V was performed using two different tools with cylindrical and stepped spiral pin design for the welding process. The nugget regions experienced temperature above β transus and the matrix transformed to fine acicular α during cooling of the nugget. By using stepped spiral pin design, a local region with much refined grain structure and significant tool debris particles were observed. Room temperature tensile test showed increased strength and decreased ductility in the material from this region. Fractographic analysis revealed that tool debris particles served as void nucleation sites. Tensile tests of FSW material were carried out at 625 °C in the strain rates of 3 × 10-4 and 1 × 10-3 s-1. The strength was higher as compared to the as-received material. Microstructural evolution during tensile test was also investigated. Results showed that dynamic globularization occurred during the high temperature tensile test.

  5. Temperature distribution study during the friction stir welding process of Al2024-T3 aluminum alloy

    NASA Astrophysics Data System (ADS)

    Yau, Y. H.; Hussain, A.; Lalwani, R. K.; Chan, H. K.; Hakimi, N.

    2013-08-01

    Heat flux characteristics are critical to good quality welding obtained in the important engineering alloy Al2024-T3 by the friction stir welding (FSW) process. In the present study, thermocouples in three different configurations were affixed on the welding samples to measure the temperatures: in the first configuration, four thermocouples were placed at equivalent positions along one side of the welding direction; the second configuration involved two equivalent thermocouple locations on either side of the welding path; while the third configuration had all the thermocouples on one side of the layout but with unequal gaps from the welding line. A three-dimensional, non-linear ANSYS computational model, based on an approach applied to Al2024-T3 for the first time, was used to simulate the welding temperature profiles obtained experimentally. The experimental thermal profiles on the whole were found to be in agreement with those calculated by the ANSYS model. The broad agreement between the two kinds of profiles validates the basis for derivation of the simulation model and provides an approach for the FSW simulation in Al2024-T3 and is potentially more useful than models derived previously.

  6. Electromagnetic Torque in Tokamaks with Toroidal Asymmetries

    NASA Astrophysics Data System (ADS)

    Logan, Nikolas Christopher

    Toroidal rotation and rotation shear strongly influences stability and confinement in tokamaks. Breaking of the toroidal symmetry by fields orders of magnitude smaller than the axisymmetric field can, however, produce electromagnetic torques that significantly affect the plasma rotation, stability and confinement. These electromagnetic torques are the study of this thesis. There are two typical types of electromagnetic torques in tokamaks: 1) "resonant torques" for which a plasma current defined by a single toroidal and single poloidal harmonic interact with external currents and 2) "nonresonant torques" for which the global plasma response to nonaxisymmetric fields is phase shifted by kinetic effects that drive the rotation towards a neoclassical offset. This work describes the diagnostics and analysis necessary to evaluate the torque by measuring the rate of momentum transfer per unit area in the vacuum region between the plasma and external currents using localized magnetic sensors to measure the Maxwell stress. These measurements provide model independent quantification of both the resonant and nonresonant electromagnetic torques, enabling direct verification of theoretical models. Measured values of the nonresonant torque are shown to agree well with the perturbed equilibrium nonambipolar transport (PENT) code calculation of torque from cross field transport in nonaxisymmetric equilibria. A combined neoclassical toroidal viscosity (NTV) theory, valid across a wide range of kinetic regimes, is fully implemented for the first time in general aspect ratio and shaped plasmas. The code captures pitch angle resonances, reproducing previously inaccessible collisionality limits in the model. The complete treatment of the model enables benchmarking to the hybrid kinetic MHD stability codes MARS-K and MISK, confirming the energy-torque equivalency principle in perturbed equilibria. Experimental validations of PENT results confirm the torque applied by nonaxisymmetric

  7. NUMERICAL STUDIES OF THE FRICTION FORCE FOR THE RHIC ELECTRON COOLER.

    SciTech Connect

    FEDOTOV,A.V.; BEN-ZVI,I.; LITVINENKO, V.

    2005-05-16

    Accurate calculation of electron cooling times requires an accurate description of the dynamical friction force. The proposed RHIC cooler will require {approx}55 MeV electrons, which must be obtained from an RF linac, leading to very high transverse electron temperatures. A strong solenoid will be used to magnetize the electrons and suppress the transverse temperature, but the achievable magnetized cooling logarithm will not be large. In this paper, we explore the magnetized friction force for parameters of the RHIC cooler, using the VORPAL code [l]. VORPAL can simulate dynamical friction and diffusion coefficients directly from first principles [2]. Various aspects of the fiction force are addressed for the problem of high-energy electron cooling in the RHIC regime.

  8. Special cases of friction and applications

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

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

  9. Tangential torque effects on the control of grip forces when holding objects with a precision grip.

    PubMed

    Kinoshita, H; Bäckström, L; Flanagan, J R; Johansson, R S

    1997-09-01

    When we manipulate small objects, our fingertips are generally subjected to tangential torques about the axis normal to the grasp surface in addition to linear forces tangential to the grasp surface. Tangential torques can arise because the normal force is distributed across the contact area rather than focused at a point. We investigated the effects of tangential torques and tangential forces on the minimum normal forces required to prevent slips (slip force) and on the normal forces actually employed by subjects to hold an object in a stationary position with the use of the tips of the index finger and thumb. By changing the location of the object's center of gravity in relation to the grasp surface, various levels of tangential torque (0-50 N x mm) were created while the subject counteracted object rotation. Tangential force (0-3.4 N) was varied by changing the weight of the object. The flat grasp surfaces were covered with rayon, suede, or sandpaper, providing differences in friction in relation to the skin. Under zero tangential force, both the employed normal force and the slip force increased in proportion to tangential torque with a slope that reflected the current frictional condition. Likewise, with pure tangential force, these forces increased in proportion to tangential force. The effects of combined tangential torques and tangential forces on the slip force were primarily additive, but there was a significant interaction of these variables. Specifically, the increase in slip force for a given increment in torque decreases as a function of tangential force. A mathematical model was developed that successfully predicted slip force from tangential torque, tangential force, and an estimate of coefficient of static friction in the digit-surface interface. The effects of combined tangential torques and forces on the employed normal force showed the same pattern as the effects on the slip force. The safety margin against frictional slips, measured as the

  10. Negative Optical Torque

    NASA Astrophysics Data System (ADS)

    Chen, Jun; Ng, Jack; Ding, Kun; Fung, Kin Hung; Lin, Zhifang; Chan, C. T.

    2014-09-01

    Light carries angular momentum, and as such it can exert torques on material objects. Applications of these opto-mechanical effects were limited initially due to their smallness in magnitude, but later becomes powerful and versatile after the invention of laser. Novel and practical approaches for harvesting light for particle rotation have since been demonstrated, where the structure is always subjected to a positive optical torque along a certain axis if the incident angular momentum has a positive projection on the same axis. We report here an interesting phenomenon of ``negative optical torque'', meaning that incoming photons carrying angular momentum rotate an object in the opposite sense. Surprisingly this can be realized quite straightforwardly in simple planar structures. Field retardation is a necessary condition and discrete rotational symmetry of material object plays an important role. The optimal conditions are explored and explained.

  11. Ironless armature torque motor

    NASA Technical Reports Server (NTRS)

    Fisher, R. L.

    1972-01-01

    Four iron-less armature torque motors, four Hall device position sensor assemblies, and two test fixtures were fabricated. The design approach utilized samarium cobalt permanent magnets, a large airgap, and a three-phase winding in a stationary ironless armature. Hall devices were employed to sense rotor position. An ironless armature torque motor having an outer diameter of 4.25 inches was developed to produce a torque constant of 65 ounce-inches per ampere with a resistance of 20.5 ohms. The total weight, including structural elements, was 1.58 pounds. Test results indicated that all specifications were met except for generated voltage waveform. It is recommended that investigations be made concerning the generated voltage waveform to determine if it may be improved.

  12. Spin Transfer Torque in Graphene

    NASA Astrophysics Data System (ADS)

    Lin, Chia-Ching; Chen, Zhihong

    2014-03-01

    Graphene is an idea channel material for spin transport due to its long spin diffusion length. To develop graphene based spin logic, it is important to demonstrate spin transfer torque in graphene. Here, we report the experimental measurement of spin transfer torque in graphene nonlocal spin valve devices. Assisted by a small external in-plane magnetic field, the magnetization reversal of the receiving magnet is induced by pure spin diffusion currents from the injector magnet. The magnetization switching is reversible between parallel and antiparallel configurations by controlling the polarity of the applied charged currents. Current induced heating and Oersted field from the nonlocal charge flow have also been excluded in this study. Next, we further enhance the spin angular momentum absorption at the interface of the receiving magnet and graphene channel by removing the tunneling barrier in the receiving magnet. The device with a tunneling barrier only at the injector magnet shows a comparable nonlocal spin valve signal but lower electrical noise. Moreover, in the same preset condition, the critical charge current density for spin torque in the single tunneling barrier device shows a substantial reduction if compared to the double tunneling barrier device.

  13. Experimental study on seismic responses of piping systems with friction. Part 1: Large-scale shaking table vibration test

    SciTech Connect

    Suzuki, K.; Watanabe, T.; Mitsumori, T.; Shimizu, N.; Kobayashi, H.; Ogawa, N.

    1995-08-01

    This report deals with the experimental study of seismic response behavior of piping systems in industrial facilities such as petrochemical, oil refinery, and nuclear plants. Special attention is focused on the nonlinear dynamic response of piping systems due to frictional vibration appearing in piping and supporting devices. A three-dimensional mock-up piping and supporting structure model wherein piping is of 30-m length and 200-mm diameter is excited by a large-scale (15 m x 15 m) shaking table belong to the National Research Institute for Earth Science and Disaster Prevention in Tsukuba, Ibaraki. Power spectra of the response vibration and the loading-response relationship in the form of a hysteresis loop under several loading conditions are obtained. The response reduction effect caused by frictional vibration is evaluated and demonstrated in terms of response reduction factor.

  14. Features of the microstructure development under conditions, reproducing the process of friction stir welding. Molecular-dynamics study

    SciTech Connect

    Nikonov, Anton Yu. E-mail: dmitr@ispms.tsc.ru; Dmitriev, Andrey I. E-mail: dmitr@ispms.tsc.ru; Kolubaev, Evgeniy A. E-mail: rvy@ispms.tsc.ru; Rubtsov, Valeriy E. E-mail: rvy@ispms.tsc.ru

    2014-11-14

    Friction stir welding is a recently developed technology which is used in various branches of modern engineering. The basis of this technology is the friction of the rotating cylindrical or specially shaped tool between two metal plates brought together either to meet their ends of one above another with the overlap. When applying the FSW process in various economical sectors, the important task is to study the mechanisms and identify the physical laws and factors leading to formation of structural inhomogeneities and discontinuities in the weld seam. This paper analyzes the basic mechanisms behind the structural state generation in the material subjected to severe plastic deformation and heating. To investigate the atomic mechanisms of structural changes in FSW, the modeling at atomic scale has been carried out. Results of work can be a basis for new knowledge about the microstructure evolution in FSW.

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

    NASA Astrophysics Data System (ADS)

    Maeda, Yoshihiro; Iwasaki, Makoto

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

  16. Studies of the frictional heating of polycrystalline diamond compact drag tools during rock cutting

    SciTech Connect

    Ortega, A.; Glowka, D.A.

    1982-06-01

    A numerical-analytical model is developed to analyze temperatures in polycrystalline diamond compact (PDC) drag tools subject to localized frictional heating at a worn flat area and convective cooling at exposed lateral surfaces. Experimental measurements of convective heat transfer coefficients of PDC cutters in a uniform crossflow are presented and used in the model to predict temperatures under typical drilling conditions with fluid flow. The analysis compares favorably with measurements of frictional temperatures in controlled cutting tests on Tennessee marble. It is found that average temperatures at the wearflat contact zone vary directly with frictional force per unit area and are proportional to the one-half power of the cutting speed at the velocities investigated. Temperatures are found to be much more sensitive to decreases in the dynamic friction by lubrication than to increases in convective cooling rates beyond currently achievable levels with water or drilling fluids. It is shown that use of weighted drilling fluids may actually decrease cooling rates compared to those achieved with pure water. It is doubtful that tool temperatures can be kept below critical levels (750/sup 0/C) if air is employed as the drilling fluid. The degree of tool wear is found to have a major influence on the thermal response of the friction contact zone, so that for equal heating per contact area, a worn tool will run much hotter than a sharp tool. It is concluded that tool temperatures may be kept below critical levels with conventional water or mud cooling as long as the fluid provides good cutter-rock lubrication.

  17. Design of a telerobotic controller with joint torque sensors

    NASA Technical Reports Server (NTRS)

    Jansen, J. F.; Herndon, J. N.

    1990-01-01

    The purpose was to analytically show how to design a joint controller for a telerobotic system when joint torque sensors are available. Other sensors such as actuator position, actuator velocity, joint position, and joint velocity are assumed to be accessible; however, the results will also be useful when only partial measurements are available. The controller presented can be applied to either mode of operation of a manipulator (i.e., teleoperation or robotic). Mechanical manipulators with high levels of friction are assumed. The results are applied to a telerobotic system built for NASA. Very high levels of friction have been reduced using high-gain feedback while avoiding limit cycles.

  18. The comparison of frictional resistance in titanium, self-ligating stainless steel, and stainless steel brackets using stainless steel and TMA archwires: An in vitro study

    PubMed Central

    Khalid, Syed Altaf; Kumar, Vadivel; Jayaram, Prithviraj

    2012-01-01

    Aim: The aim of the study was to compare the frictional resistance of titanium, self-ligating stainless steel, and conventional stainless steel brackets, using stainless steel and titanium molybdenum alloy (TMA) archwires. Materials and Methods: We compared the frictional resistance in 0.018 slot and 0.022 slot of the three brackets – titanium, self-ligating stainless steel, and conventional stainless steel – using stainless steel archwires and TMA archwires. An in vitro study of simulated canine retraction was undertaken to evaluate the difference in frictional resistance between titanium, self-ligating stainless steel, and stainless steel brackets, using stainless steel and TMA archwires. Results and Conclusion: We compared the frictional resistance of titanium, self-ligating stainless steel, and conventional stainless steel brackets, using stainless steel and TMA archwires, with the help of Instron Universal Testing Machine. One-way analysis of variance (ANOVA), Student's “t” test, and post hoc multiple range test at level of <0.05 showed statistically significant difference in the mean values of all groups. Results demonstrated that the titanium, self-ligating stainless steel, and stainless steel brackets of 0.018-inch and 0.022-inch slot had no significant variations in frictional résistance. The self-ligating bracket with TMA archwires showed relatively less frictional resistance compared with the other groups. The titanium bracket with TMA archwires showed relatively less frictional resistance compared with the stainless steel brackets. PMID:23066253

  19. Knudsen torque on heated micro beams

    SciTech Connect

    Li, Qi; Liang, Tengfei; Ye, Wenjing

    2014-12-09

    Thermally induced mechanical loading has been shown to have significant effects on micro/nano objects immersed in a gas with a non-uniform temperature field. While the majority of existing studies and related applications focus on forces, we investigate the torque, and thus the rotational motion, produced by such a mechanism. Using the asymptotic analysis in the near continuum regime, the Knudsen torque acting on an asymmetrically located uniformly heated microbeam in a cold enclosure is investigated. The existence of a non-zero net torque is demonstrated. In addition, it has been found that by manipulating the system configuration, the rotational direction of the torque can be changed. Two types of rotational motion of the microbeam have been identified: the pendulum motion of a rectangular beam, and the unidirectional rotation of a cylindrical beam. A rotational frequency of 4 rpm can be achieved for the cylindrical beam with a diameter of 3μm at Kn = 0.005. Illustrated by the simulations using the direct simulation of Monte Carlo, the Knudsen torque can be much increased in the transition regime, demonstrating the potential of Knudsen torque serving as a rotation engine for micro/nano objects.

  20. Overflow: Facts on Friction

    NASA Technical Reports Server (NTRS)

    Lawrence, Scott

    1999-01-01

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

  1. EBSD Study on Grain Boundary and Microtexture Evolutions During Friction Stir Processing of A413 Cast Aluminum Alloy

    NASA Astrophysics Data System (ADS)

    Shamanian, Morteza; Mostaan, Hossein; Safari, Mehdi; Szpunar, Jerzy A.

    2016-07-01

    The as-cast Al alloys contain heterogeneous distributions of non-deforming particles due to non-equilibrium solidification effects. Therefore, these alloys have poor tribological and mechanical behaviors. It is well known that using friction stir processing (FSP), very fine microstructure is created in the as-cast Al alloys, while their wear resistance can be improved. In this research work, FSP is used to locally refine a surface layer of the coarse as-cast microstructure of cast A413 Al alloy. The main objective of this study is to investigate the effect of FSP on microstructure and microtexture evolutions in A413 cast Al alloy. The grain boundary character distribution, grain structure, and microtexture evolutions in as-cast and friction stir processed A413 Al alloy are analyzed by electron back scatter diffraction technique. It is found that with the FSP, the fraction of low ∑boundary such as ∑3, 7, and 9 are increased. The obtained results show that there are no deformation texture components in the structure of friction stir processed samples. However, some of the main recrystallization texture components such as BR and cubeND are formed during FSP which indicate the occurrence of dynamic recrystallization phenomenon due to the severe plastic deformation induced by the rotation of tool.

  2. EBSD Study on Grain Boundary and Microtexture Evolutions During Friction Stir Processing of A413 Cast Aluminum Alloy

    NASA Astrophysics Data System (ADS)

    Shamanian, Morteza; Mostaan, Hossein; Safari, Mehdi; Szpunar, Jerzy A.

    2016-05-01

    The as-cast Al alloys contain heterogeneous distributions of non-deforming particles due to non-equilibrium solidification effects. Therefore, these alloys have poor tribological and mechanical behaviors. It is well known that using friction stir processing (FSP), very fine microstructure is created in the as-cast Al alloys, while their wear resistance can be improved. In this research work, FSP is used to locally refine a surface layer of the coarse as-cast microstructure of cast A413 Al alloy. The main objective of this study is to investigate the effect of FSP on microstructure and microtexture evolutions in A413 cast Al alloy. The grain boundary character distribution, grain structure, and microtexture evolutions in as-cast and friction stir processed A413 Al alloy are analyzed by electron back scatter diffraction technique. It is found that with the FSP, the fraction of low ∑boundary such as ∑3, 7, and 9 are increased. The obtained results show that there are no deformation texture components in the structure of friction stir processed samples. However, some of the main recrystallization texture components such as BR and cubeND are formed during FSP which indicate the occurrence of dynamic recrystallization phenomenon due to the severe plastic deformation induced by the rotation of tool.

  3. A Study on Tooling and Its Effect on Heat Generation and Mechanical Properties of Welded Joints in Friction Stir Welding

    NASA Astrophysics Data System (ADS)

    Tikader, Sujoy; Biswas, Pankaj; Puri, Asit Baran

    2016-06-01

    Friction stir welding (FSW) has been the most attracting solid state welding process as it serves numerous advantages like good mechanical, metallurgical properties etc. Non weldable aluminium alloys like 5XXX, 7XXX series can be simply joined by this process. In this present study a mathematical model has been developed and experiments were successfully performed to evaluate mechanical properties of FSW on similar aluminium alloys i.e. AA1100 for different process parameters and mainly two kind of tool geometry (straight cylindrical and conical or cylindrical tapered shaped pin with flat shoulder). Tensile strength and micro hardness for different process parameters are reported of the welded plate sample. It was noticed that in FSW of similar alloy with tool made of SS-310 tool steel, friction is the major contributor for the heat generation. It was seen that tool geometry, tool rotational speed, plunging force by the tool and traverse speed have significant effect on tensile strength and hardness of friction stir welded joints.

  4. Torque magnetometry in unconventional superconductors

    NASA Astrophysics Data System (ADS)

    Li, Lu

    This thesis describes torque magnetometry studies on unconventional superconductors. Torque magnetometry measures the anisotropic magnetization of samples by recording their torque signals in a tilted magnetic field. Applied to superconductors, this method provides a reliable way to measure the field dependence of magnetization with high resolution under extreme conditions: DC magnetic fields from zero to 45.2 T, and temperature from 300 mK to 300K. The results can be used to determine many important parameters, such as the upper critical field H c2, the superconducting condensation energy, the onset temperature of diamagnetic signals, and so on. We carried out the torque magnetometry measurements on unconventional superconductors---high Tc superconductors and the p-wave superconductor Sr2RuO4---and uncovered new features that do not exist in conventional BCS superconductors. In high Tc superconductors, our torque magnetometry studies focus on the properties of the vortex liquid state. First, by comparing the observed magnetization curves with the Nernst effect results in Bi 2Sr2CaCu2O8+delta, we confirm that the unusually large Nernst effect signals originate from the surviving vortex liquid state above Tc. Second, the M-H curves near the critical temperature Tc suggest that the nature of the transition is the Kosterlitz-Thouless transition. Near Tc, the magnetization response at low field is strongly nonlinear, and the T dependence of the magnetic susceptibility in the low-field limit approaches the predicted curve from the Kosterlitz-Thouless transition. Third, the measurements in intense magnetic field up to 45 T reveal the unusual, weak T-dependence of Hc2. These observations strongly support the existence of the vortex liquid state above Tc. The superconducting state is destroyed by the phase fluctuation of the pair condensate, while the pair condensate keeps its amplitude above T c. Further studies in single-layered high Tc superconductors reveal more

  5. Development of infant leg coordination: Exploiting passive torques.

    PubMed

    Sargent, Barbara; Scholz, John; Reimann, Hendrik; Kubo, Masayoshi; Fetters, Linda

    2015-08-01

    Leg joint coordination systematically changes over the first months of life, yet there is minimal data on the underlying change in muscle torques that might account for this change in coordination. The purpose of this study is to investigate the contribution of torque changes to early changes in leg joint coordination. Kicking actions were analyzed of 10 full-term infants between 6 and 15-weeks of age using three-dimensional kinematics and kinetics. We found 11 of 15 joint angle pairs demonstrated a change from more in-phase intralimb coordination at 6-weeks to less in-phase coordination at 15-weeks. Although the magnitude of joint torques normalized to the mass of the leg remained relatively consistent, we noted more complex patterns of torque component contribution across ages. By focusing on the change in torques associated with hip-knee joint coordination, we found that less in-phase hip-knee joint coordination at 15-weeks was associated with decreased influence of knee muscle torque and increased influence of knee gravitational and motion-dependent torques, supporting that infants coordinate hip muscle torque with passive knee gravitational and motion-dependent torques to generate kicks with reduced active knee muscle torque. We propose that between 6 and 15-weeks of age less in-phase hip-knee coordination emerges as infants exploit passive dynamics in the coordination of hip and knee motions. PMID:26117493

  6. Centaur engine gimbal friction characteristics under simulated thrust load

    NASA Technical Reports Server (NTRS)

    Askew, J. W.

    1986-01-01

    An investigation was performed to determine the friction characteristics of the engine gimbal system of the Centaur upper stage rocket. Because the Centaur requires low-gain autopilots in order to meet all stability requirements for some configurations, control performance (response to transients and limit-cycle amplitudes) depends highly on these friction characteristics. Forces required to rotate the Centaur engine gimbal system were measured under a simulated thrust load of 66,723 N (15,000 lb) and in an altitude/thermal environment. A series of tests was performed at three test conditions; ambient temperature and pressure, ambient temperature and vacuum, and cryogenic temperature and vacuum. Gimbal rotation was controlled, and tests were performed in which rotation amplitude and frequency were varied by using triangular and sinusoidal waveforms. Test data revealed an elastic characteristic of the gimbal, independent of the input signal, which was evident prior to true gimbal sliding. The torque required to initiate gimbal sliding was found to decrease when both pressure and temperature decreased. Results from the low amplitude and low frequency data are currently being used in mathematically modeling the gimbal friction characteristics for Centaur autopilot performance studies.

  7. Multiple-Cantilever Torque Sensor

    NASA Technical Reports Server (NTRS)

    Lurie, Boris J.; Schier, J. Alan; Socha, Michael

    1989-01-01

    Sensitivity to spurious loads small. High stiffness, high resolution, and ease of fabrication among features of specially designed torque sensor. Device flexible and sensitive to torque about its cylindrical axis and stiff enough to be insensitive to bending about any perpendicular axis. Measures and transmits torque between driving and driven plates.

  8. Torque, Cognitive Ability, and Schooling.

    ERIC Educational Resources Information Center

    Csapo, Marg

    1985-01-01

    West African Hausan Children (N=110) aged 5-6 were administered a torque test and relationshps between the torque task and visual spatial tasks were analyzed. Findings supported the assumption that educational experience related to circling accounts for decrease in torque, or that the educational experiences have potential influence on cortical…

  9. Acid-Base Interactions at the Molecular Level: Adhesion and Friction Studies with Interfacial Force Microscopy

    SciTech Connect

    Burns, A.R.; Carpick, R.W.; Houston, J.E.; Michalske, T.A.

    1998-12-09

    To examine the forces of acid-base adhesive interactions at the molecular level, we utilize the scanning probe Interracial Force Microscope (IFM). Unlike cantilever-based atomic force microscopes, the EM is a non-compliant, mechanically stable probe that provides a complete adhesive profile without jump-to-contact. In this way, we are able to quantitatively measure the work of adhesion and bond energies at well-defined, nanometer-scale single asperity contacts. In particular, we will discuss the displacement-controlled adhesive forces between self-assembled monolayer of functionalized alkanethiols strongly bound to a gold substrate and a similarly functionalized tip. We also discuss a method utilizing decoupled lateral and normal force sensors to simultaneously observe the onset of both friction and chemical bond formation. Measurements show that friction can be directly attributed to bond formation and rupture well before repulsive contact.

  10. Friction surfacing for enhanced surface protection of marine engineering components: erosion-corrosion study

    NASA Astrophysics Data System (ADS)

    Rajakumar, S.; Balasubramanian, V.; Balakrishnan, M.

    2016-08-01

    Good mechanical properties combined with outstanding corrosion-resistance properties of cast nickel-aluminum bronze (NAB) alloy lead to be a specific material for many marine applications, including ship propellers. However, the erosion-corrosion resistance of cast-NAB alloy is not as good as wrought NAB alloy. Hence, in this investigation, an attempt has been made to improve the erosion-corrosion resistance of cast NAB alloy by depositing wrought (extruded) NAB alloy applying the friction surfacing (FS) technique. Erosion-corrosion tests were carried out in slurries composed of sand particles of 3.5% NaCl solution. Silica sand having a nominal size range of 250-355 μm is used as an erodent. Specimens were tested at 30° and 90° impingement angles. It is observed that the erosion and erosion-corrosion resistance of friction surfaced NAB alloy exhibited an improvement as compared to cast NAB alloy. Scanning electron microscope (SEM) analysis showed that the erosion tracks developed on the cast NAB alloy were wider and deeper than those formed on the friction surfaced extruded NAB alloy.

  11. Friction of drill bits under Martian pressure

    NASA Astrophysics Data System (ADS)

    Zacny, K. A.; Cooper, G. A.

    2007-03-01

    Frictional behavior was investigated for two materials that are good candidates for Mars drill bits: Diamond Impregnated Segments and Polycrystalline Diamond Compacts (PDC). The bits were sliding against dry sandstone and basalt rocks under both Earth and Mars atmospheric pressures and also at temperatures ranging from subzero to over 400 °C. It was found that the friction coefficient dropped from approximately 0.16 to 0.1 as the pressure was lowered from the Earth's pressure to Mars' pressure, at room temperature. This is thought to be a result of the loss of weakly bound water on the sliding surfaces. Holding the pressure at 5 torr and increasing the temperature to approximately 200°C caused a sudden increase in the friction coefficient by approximately 50%. This is attributed to the loss of surface oxides. If no indication of the bit temperature is available, an increase in drilling torque could be misinterpreted as being caused by an increase in auger torque (due to accumulation of cuttings) rather than being the result of a loss of oxide layers due to elevated bit temperatures. An increase in rotational speed (to allow for clearing of cuttings) would then cause greater frictional heating and would increase the drilling torque further. Therefore it would be advisable to monitor the bit temperature or, if that is not possible, to include pauses in drilling to allow the heat to dissipate. Higher friction would also accelerate the wear of the drill bit and in turn reduce the depth of the hole.

  12. A rotary-shear low to high-velocity friction apparatus in Beijing to study rock friction at plate to seismic slip rates

    NASA Astrophysics Data System (ADS)

    Ma, Shengli; Shimamoto, Toshihiko; Yao, Lu; Togo, Tetsuhiro; Kitajima, Hiroko

    2014-10-01

    This paper reviews 19 apparatuses having high-velocity capabilities, describes a rotary-shear low to high-velocity friction apparatus installed at Institute of Geology, China Earthquake Administration, and reports results from velocity-jump tests on Pingxi fault gouge to illustrate technical problems in conducting velocity-stepping tests at high velocities. The apparatus is capable of producing plate to seismic velocities (44 mm/a to 2.1 m/s for specimens of 40 mm in diameter), using a 22 kW servomotor with a gear/belt system having three velocity ranges. A speed range can be changed by 103 or 106 by using five electromagnetic clutches without stopping the motor. Two cam clutches allow fivefold velocity steps, and the motor speed can be increased from zero to 1,500 rpm in 0.1-0.2 s by changing the controlling voltage. A unique feature of the apparatus is a large specimen chamber where different specimen assemblies can be installed easily. In addition to a standard specimen assembly for friction experiments, two pressure vessels were made for pore pressures to 70 MPa; one at room temperature and the other at temperatures to 500 °C. Velocity step tests are needed to see if the framework of rate-and-state friction is applicable or not at high velocities. We report results from velocity jump tests from 1.4 mm/s to 1.4 m/s on yellowish gouge from a Pingxi fault zone, located at the northeastern part of the Longmenshan fault system that caused the 2008 Wenchuan earthquake. An instantaneous increase in friction followed by dramatic slip weakening was observed for the yellowish gouge with smooth sliding surfaces of host rock, but no instantaneous response was recognized for the same gouge with roughened sliding surfaces. Instantaneous and transient frictional properties upon velocity steps cannot be separated easily at high velocities, and technical improvements for velocity step tests are suggested.

  13. A rotary-shear low to high-velocity friction apparatus in Beijing to study rock friction at plate to seismic slip rates

    NASA Astrophysics Data System (ADS)

    Ma, Shengli; Shimamoto, Toshihiko; Yao, Lu; Togo, Tetsuhiro; Kitajima, Hiroko

    2014-09-01

    This paper reviews 19 apparatuses having high-velocity capabilities, describes a rotary-shear low to high-velocity friction apparatus installed at Institute of Geology, China Earthquake Administration, and reports results from velocity-jump tests on Pingxi fault gouge to illustrate technical problems in conducting velocity-stepping tests at high velocities. The apparatus is capable of producing plate to seismic velocities (44 mm/a to 2.1 m/s for specimens of 40 mm in diameter), using a 22 kW servomotor with a gear/belt system having three velocity ranges. A speed range can be changed by 103 or 106 by using five electromagnetic clutches without stopping the motor. Two cam clutches allow fivefold velocity steps, and the motor speed can be increased from zero to 1,500 rpm in 0.1-0.2 s by changing the controlling voltage. A unique feature of the apparatus is a large specimen chamber where different specimen assemblies can be installed easily. In addition to a standard specimen assembly for friction experiments, two pressure vessels were made for pore pressures to 70 MPa; one at room temperature and the other at temperatures to 500 °C. Velocity step tests are needed to see if the framework of rate-and-state friction is applicable or not at high velocities. We report results from velocity jump tests from 1.4 mm/s to 1.4 m/s on yellowish gouge from a Pingxi fault zone, located at the northeastern part of the Longmenshan fault system that caused the 2008 Wenchuan earthquake. An instantaneous increase in friction followed by dramatic slip weakening was observed for the yellowish gouge with smooth sliding surfaces of host rock, but no instantaneous response was recognized for the same gouge with roughened sliding surfaces. Instantaneous and transient frictional properties upon velocity steps cannot be separated easily at high velocities, and technical improvements for velocity step tests are suggested.

  14. Preparation Torque Limit for Composites Joined with Mechanical Fasteners

    NASA Technical Reports Server (NTRS)

    Thomas, Frank P.; Yi, Zhao

    2005-01-01

    Current design guidelines for determining torque ranges for composites are based on tests and analysis from isotropic materials. Properties of composites are not taken into account. No design criteria based upon a systematic analytical and test analyses is available. This paper is to study the maximum torque load a composite component could carry prior to any failure. Specifically, the torque-tension tests are conducted. NDT techniques including acoustic emission, thermography and photomicroscopy are also utilized to characterize the damage modes.

  15. Factor Analysis on Cogging Torques in Segment Core Motors

    NASA Astrophysics Data System (ADS)

    Enomoto, Yuji; Kitamura, Masashi; Sakai, Toshihiko; Ohara, Kouichiro

    The segment core method is a popular method employed in motor core manufacturing; however, this method does not allow the stator core precision to be enhanced because the stator is assembled from many cores. The axial eccentricity of rotor and stator and the internal roundness of the stator core are regarded as the main factors which affect cogging torque. In the present study, the way in which a motor with a split-type stator generates a cogging torque is investigated to determine whether high- precision assembly of stator cores can reduce cogging torque. Here, DC brushless motors were used to verify the influence of stator-rotor eccentricity and roundness of the stator bore on cogging torque. The evaluation results prove the feasibility of reducing cogging torque by improving the stator core precision. Therefore, improving the eccentricity and roundness will enable stable production of well controlled motors with few torque ripples.

  16. Type-1 and Type-2 Fuzzy Logic and Sliding-Mode Based Speed Control of Direct Torque and Flux Control Induction Motor Drives - A Comparative Study

    NASA Astrophysics Data System (ADS)

    Ramesh, Tejavathu; Panda, A. K.; Kumar, S. Shiva

    2013-08-01

    In this research study, the performance of direct torque and flux control induction motor drive (IMD) is presented using five different speed control techniques. The performance of IMD mainly depends on the design of speed controller. The PI speed controller requires precise mathematical model, continuous and appropriate gain values. Therefore, adaptive control based speed controller is desirable to achieve high-performance drive. The sliding-mode speed controller (SMSC) is developed to achieve continuous control of motor speed and torque. Furthermore, the type-1 fuzzy logic speed controller (T1FLSC), type-1 fuzzy SMSC and a new type-2 fuzzy logic speed controller are designed to obtain high performance, dynamic tracking behaviour, speed accuracy and also robustness to parameter variations. The performance of each control technique has been tested for its robustness to parameter uncertainties and load disturbances. The detailed comparison of different control schemes are carried out in a MATALB/Simulink environment at different speed operating conditions, such as, forward and reversal motoring under no-load, load and sudden change in speed.

  17. Laboratory studies of frictional sliding and the implications of precursory seismicity

    NASA Astrophysics Data System (ADS)

    Selvadurai, Paul A.

    The dynamic transition from slow to rapid sliding along a frictional interface is of interest to geophysicists, engineers and scientists alike. In our direct shear experiment, we simulated a pre-existing frictional fault similar to those occurring naturally in the Earth. The laboratory study reported here has incorporated appropriate sensors that can detect foreshock events on the fringe of a nucleation zone prior to a gross fault rupture (main shock). During loading we observed foreshocks sequences as slip transitioned from slow to rapid sliding. These laboratory-induced foreshocks showed similar acoustic characteristics and spatio-temporal evolution as those detected in nature. Through direct observation (video camera), foreshocks were found to be the rapid, localized (millimeter length scale) failure of highly stresses asperities formed along the interface. The interface was created by the meshing of two rough polymethyl methacrylate (PMMA) bodies in a direct shear configuration. A carefully calibrated pressure sensitive film was used to map the contact junctions (asperities) throughout the interface at a range of applied normal loads Fn. Foreshocks were found to coalesce in a region of the fault that exhibited a more dense distribution of asperities (referred to as the seismogenic region). Microscopy of the interface in the seismogenic region displayed a variety of surface roughness at various length scales. This may have been introduced from the surface preparation techniques use to create a mature interface. The mature interface consisted of 'flat-topped' asperity regions with separating sharp valleys. The 'flat-topped' sections spanned millimetric length scales and were considerably flatter (nanometric roughness) that the roughness exhibited at longer length scales (tens of millimeters). We believe that the smoother, 'flat-topped' sections were responsible for the individual asperity formation (determining their size and strength), whereas the longer length

  18. Hex ball torque test

    NASA Technical Reports Server (NTRS)

    Robinson, B. A.; Foster, C. L.

    1986-01-01

    A series of torque tests were performed on four flight-type hex ball universal joints in order to characterize and determine the actual load-carrying capability of this device. The universal joint is a part of manual actuation rods for scientific instruments within the Hubble Space Telescope. It was found that the hex ball will bind slightly during the initial load application. This binding did not affect the function of the universal joint, and the units would wear-in after a few additional loading cycles. The torsional yield load was approximately 50 ft-lb, and was consistent among the four test specimens. Also, the torque required to cause complete failure exceeded 80 ft-lb. It is concluded that the hex ball universal joint is suitable for its intended applications.

  19. Negative Optical Torque

    PubMed Central

    Chen, Jun; Ng, Jack; Ding, Kun; Fung, Kin Hung; Lin, Zhifang; Chan, C. T.

    2014-01-01

    Light carries angular momentum, and as such it can exert torques on material objects. Applications of these opto-mechanical effects were limited initially due to their smallness in magnitude, but later becomes powerful and versatile after the invention of laser. Novel and practical approaches for harvesting light for particle rotation have since been demonstrated, where the structure is always subjected to a positive optical torque along a certain axis if the incident angular momentum has a positive projection on the same axis. We report here an interesting phenomenon of “negative optical torque”, meaning that incoming photons carrying angular momentum rotate an object in the opposite sense. Surprisingly this can be realized quite straightforwardly in simple planar structures. Field retardation is a necessary condition and discrete rotational symmetry of material object plays an important role. The optimal conditions are explored and explained. PMID:25226863

  20. Friction losses in a lubricated thrust-loaded cageless angular-contract bearing

    NASA Technical Reports Server (NTRS)

    Townsend, D. P.; Allen, C. W.; Zaretsky, E. V.

    1973-01-01

    The NASA spinning torque apparatus was modified to measure the spinning torque on a cageless ball thrust bearing. Friction torque was measured for thrust loads varying from 44.5 to 403 newtons (10 to 90 lb) at speeds of 1000, 2000, and 3000 rpm. Tests were conducted with di-2-ethylhexyl sebacate and a synthetic paraffinic oil. These tests were run with either oil jet lubrication or with a thin surface film of lubricant only. An analytical model which included rolling resistance was developed and extended from previous models for spinning torque and lubricant rheology. The model was extended by the inclusion of rolling resistance. The computed values were in fair agreement with the experimental results and confirmed previous hypotheses that a thin lubricant film gives minimum bearing torque and an oil jet flow of a viscous lubricant will result in considerable rolling torque in addition to the torque due to ball spin.

  1. Comparison of Contamination of Low-Frictional Elastomeric Rings with That of Conventional Elastomeric Rings by Streptococcus mutans - An In-vivo Study

    PubMed Central

    Mogra, Subraya; Shetty, V. Surendra; Shetty, Siddarth; Jose, Nidhin Philip

    2015-01-01

    Introduction: The presence of brackets and ligatures has been shown to be related to an increase in gingival inflammation and increased risk of decalcification. The various measures were taken to reduce the plaque accumulation and also lot of efforts were made by manufacturers that reduced the binding friction between the ligature rings and arch wire that facilitated easy sliding of the tooth through the wire. The low frictional ligatures rings manufactured by different manufacturers presumed to attract fewer bacteria due to greater reduction in surface roughness. Our study aimed to evaluate whether the low frictional elastomeric rings accumulate fewer bacteria than conventional ligature rings. Materials and Methods: Thirty patients (15 males and 15 females) who underwent fixed appliance therapy were selected. The study was done using split-mouth design. In each volunteer, synergy low frictional elastomeric rings were tied to brackets bonded to the maxillary premolar on the right side and mandibular premolar on the left side. Conventional elastomeric rings that served as control group were tied to the contralateral teeth, with the same design. Samples were collected after four weeks (28 days) and cultured for bacteria Streptococcus mutans. Results: There was no statistical difference between Streptococcus mutans count in low frictional elastomeric rings with that of conventional rings. Conclusion: We concluded that adherence of Streptococcus mutans is similar in both synergy low frictional elastomeric rings and conventional clear elastomeric rings and thus the manufacturer’s claim of minimal bacterial adherence was discarded. PMID:26023638

  2. Remote control canard missile with a free-rolling tail brake torque system

    NASA Technical Reports Server (NTRS)

    Blair, A. B., Jr.

    1981-01-01

    An experimental wind-tunnel investigation has been conducted at supersonic Mach numbers to determine the static aerodynamic characteristics of a cruciform canard-controlled missile with fixed and free-rolling tail-fin afterbodies. Mechanical coupling effects of the free-rolling tail afterbody were investigated using an electronic/electromagnetic brake system that provides arbitrary tail-fin brake torques with continuous measurements of tail-to-mainframe torque and tail-roll rate. Results are summarized to show the effects of fixed and free-rolling tail-fin afterbodies that include simulated measured bearing friction torques on the longitudinal and lateral-directional aerodynamic characteristics.

  3. Advances in the analysis and design of constant-torque springs

    NASA Technical Reports Server (NTRS)

    McGuire, John R.; Yura, Joseph A.

    1996-01-01

    In order to improve the design procedure of constant-torque springs used in aerospace applications, several new analysis techniques have been developed. These techniques make it possible to accurately construct a torque-rotation curve for any general constant-torque spring configuration. These new techniques allow for friction in the system to be included in the analysis, an area of analysis that has heretofore been unexplored. The new analysis techniques also include solutions for the deflected shape of the spring as well as solutions for drum and roller support reaction forces. A design procedure incorporating these new capabilities is presented.

  4. 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.

  5. A study of elastic behaviour and internal friction of aluminium substituted magnesium-copper ferrites

    NASA Astrophysics Data System (ADS)

    Reddy, P. Venugopal; Mulay, V. N.; Reddy, K. Bhupal; Ramana, Y. V.

    1988-07-01

    The compressional ( Vl) and shear velocities ( Vs) of polycrystalline Al-substituted MgCu mixed ferrites having seven different compositions have been measured at room temperature by ultrasonic pulse transmission technique. The Young's modulus ( E0), rigidity modulus ( n0) and bulk modulus ( k0), corrected to zero porosity are found to decrease continuously with increasing Al-content. The variation of elastic moduli with composition has been explained in terms of binding forces between the ions. Internal friction (Q -1) for all the specimens has also been determined at room temperature by the pulse-echo technique.

  6. Investigation and Improvement of Torque Response of Control System Based on Direct Torque Control in Interior Permanent Magnet Synchronous Motors

    NASA Astrophysics Data System (ADS)

    Inoue, Yukinori; Morimoto, Shigeo; Sanada, Masayuki

    In this study, we investigate the torque response of a control system that is based on the direct torque control (DTC) principle for an interior permanent magnet synchronous motor (IPMSM). We also propose a gain-scheduling method for improving the torque response. Reference flux vector calculation (RFVC) DTC is used in this study. In RFVC DTC, a PI controller is used for torque control; this is in contrast to the use of the hysteresis comparator and switching table in basic DTC. In this paper, we present the relationship between the torque response and the gain of the PI controller. This relationship is derived by using the transfer function of the torque control loop. In this study, we also examine the difference between the torque responses of two motors that have different machine parameters. The proposed method can be used to realize a torque response that is independent of the operating torque. The simulation results and experimental results presented in this paper show the validity of the derived relationship as well as the effectiveness of the proposed method.

  7. CAM/LIFTER forces and friction

    SciTech Connect

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

    1992-02-01

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

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

    PubMed

    Karim, M Yasinul; Corwin, Eric I

    2014-05-01

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

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

    NASA Astrophysics Data System (ADS)

    Karim, M. Yasinul; Corwin, Eric I.

    2014-05-01

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

  10. Adaptive controller for regenerative and friction braking system

    DOEpatents

    Davis, R.I.

    1990-10-16

    A regenerative and friction braking system for a vehicle having one or more road wheels driven by an electric traction motor includes a driver responsive device for producing a brake demand signal having a magnitude corresponding to the level of braking force selected by the driver and friction and regenerative brakes operatively connected with the road wheels of the vehicle. A system according to this invention further includes control means for operating the friction and regenerative braking subsystems so that maximum brake torques sustainable by the road wheels of the vehicle without skidding or slipping will not be exceeded. 8 figs.