Slip Speeds Research Articles

Pulsed High Power Brush Research

The successful utilization of homopolar machines for pulsed power applications requires the development of solid brushes capable of operating at very high current densities and slip ring speeds. Relevant data on the major current collection parameters are reviewed and, where possible, functional variations are suggested. Measured data on voltage drops, friction coefficients and wear rates at current densities up to 27.9 MA/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (18 kA/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) and slip ring speeds up to 360 m/s in air, hydrogen and carbon dioxide are discussed.

Traction Characteristics of Lugs for Tires

ABSTRACT THE lug design factors affecting the traction force of tires were tested in a sandy loam soil. The lug length, angle, width and lug cross-sectional area were varied along with different normal loads and variable slip speeds in order to identify lug design for the best traction force. The soil reaction on rectangular tire lugs is analyzed by a mechanical model of three dimensional soil failure.

PLANE WAVE PROPAGATION IN ANISOTROPIC JOINTED MEDIA

The propagation of plane waves through a rock mass containing a major set of regularly spaced parallel joints is analyzed for wavelengths large compared with joint spacing, using a continuum description. The intact rock is isotropic elastic and the joint motion is restricted to tangential slip governed by a Coulomb failure criterion and subsequent ideal slip. Plane strain is assumed in a plane containing the joint normal and the propagation direction, with the joint normal inclined to the propagation direction. During slip the response is analogous to that of an anisotropic elastic-plastic model with a non-associated flow rule. The three physical parameters governing the response are the ratio of the bulk and shear elastic moduli, the joint friction coefficient, and the joint inclination. A detailed analysis is made of the motion initiated by a purely longitudinal pulse. Conditions for real characteristics in both elastic and slip regions are discussed, and also conditions for the interleaving of the elastic and slip wave speeds (two of each) necessary for proper matching conditions across an elastic-slip interface. Finally, the possible wave motions initiated by a monotonic normal pressure over a plane boundary are discussed.

Traction Characteristics of a MIL-L-7808 Oil

Traction versus slip curves for a full matrix of loads, speeds, and temperatures are given for one MIL-L-7808. Hertzian contact pressures from 80,000 psi (551.6 MN/m2) to 150,000 psi (1034.2 MN/m2), speeds from 900 ips (22.9 m/s) to 1,820 ips (46.2 m/s), and temperatures from 75°F (23.9°C) to 160°F (71.1°C) are the test matrix limits of variation. Slip speeds up to 10 percent of the rolling speeds are shown for the full matrix test range.

The Frictional Traction Characteristics of Greases in Heavily Loaded Contacts

Experimental results using a disc machine are given which clearly demonstrate the increase in frictional traction with time until a steady-state value less than that of the carrier oil is achieved. This increasing traction is associated with the mechanical degradation of the grease structure, which also results in a reduced film thickness. It is also shown that greases can lead to starvation, and hence failure, at higher slip speeds, and this effect is probably associated with the viscoelastic properties of the grease. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference held in Atlanta, Georgia, October 16–18, 1973

A theory of viscous hydroplaning

The traction developed in the contact area of a pneumatic tyre rolling and accelerating on a wet road surface is simulated by a block of rubber slipping on a two-dimensional sinusoidal surface covered with a thin water film. The resulting pressure-wedge formation on individual asperities of the surface provides a net uplift which tends to force tyre-tread and surface apart, thus promoting the onset of skidding or viscous hydroplaning. The important factor in minimizing skidding hazards is the provision of an adequate micro-roughness at asperity tips which contributes an adhesional mechanism to the overall friction coefficient. It is shown that in comparison with the adhesional contribution to friction, the contribution of hysteresis and viscous shear of the film are insignificant at low slip speeds.

NERVOUS CONTROL OF OPTOKINETIC RESPONSES IN THE CRAB CARCINUS.

The eyes of the crab Carcinus follow the movement of a horizontally rotating striped drum with a constantly increasing lag. The relative movement or slip speed is the stimulus for the eye, which with increasing stimulus increases its speed of response over a range of slip speeds from 0.001°/s to 10.0°/s. The gain in the forward control system, i. e. the ratio of eye speed to slip speed, can be as great as 15. The slowest effective slip speed is very low, about a sixth of the speed of the sun across the sky. Whether a seeing eye is allowed to move or not, it will drive the other eye if the latter sees no contrasting objects. An eye can also be driven in this way after section of its optic tract or after painting the cornea. When an eye which is free to move is exposed to a stationary striped field it suppresses the optokinetic response of the other eye, but if the eye exposed to the stationary contrasting field is clamped to the carapace, it no longer suppresses the optokinetic response of the contralateral eye; i. e. clamping the eye has here the same effect as blinding it. The control of the eye movement appears to be unaffected statically or dynamically by proprioceptors of the eye region. The initiation of the rapid flick back in the optokinetic response also takes no account of proprioceptors, but seems to occur when the efferent impulses to eye muscles reach a threshold frequency, which is only slightly modified by blinding one eye. The flick back is synchronized on the two sides. A different reflex, protective retraction, is a fast movement of the eye back into its socket, for which the minimum stimulus can be a touch to one sensory hair alone. During the rapid return phase of the optokinetic response, and during the retraction reflex, the efferent optokinetic impulses are suppressed, and, in addition, peripheral neuromuscular inhibition of tonic motor activity occurs when protective retraction over-rides the optokinetic response. On extending again after retraction, the blinded eye of a unilaterally blinded crab returns to the point in the optokinetic response where it left off. There are spontaneous eye movements which, although of less than one degree, are adequate to excite visual receptors in a stationary visual field. This is demonstrated by the decrease of the tremor when the visual field is changed from a blank one to a contrasting one. In addition, a small scanning movement of a few degrees is initiated when a contrasting object is introduced into the visual field. Therefore there is every reason to suppose that stationary contrasting objects can be perceived by spontaneous and by scanning movements. Similarities of the control system with that in mammals are the lack of a positional proprioceptive effect, coupled with the importance of the motor outflow as a controlling factor. Although there is eye tremor, as in mammals, the main control of eye movements in the crab is by the movement and not by position of a striped field relative to the eye.

On the Abrasion Test of High Manganese Point : (Under the Influenc of Lubrication)

Following the Abrasion test of High Manganese Steel under the dry condition which has been reported by the author, an Amsler-type abrasion testing machine, and the condition that is at various slip speeds of 0∼15cm/s, and contact pressures of 50∼90kg/mm2 is used. The test piece of tyre is standard structure steel, containing about 0.7% C, and the other material of High Manganese Steel is water quenched at a temperature of 1050°C. The ideal combination of High Manganese Steel and tyre was researched under the influence of lubrication in which same number of drops of #40 Motor-oil were supplied every day. The result of this research is as follows : 1) "Pitting" of the high manganese steel is less than that of the carbon steel, therefore the wearing amount of the specimen is very little and the effect of lubrication is very remarkable. 2) The fact that the effect of wear prevention on the high manganese steel is satisfactory under the influence of lubrication is supposed to be due to work-hardening.

A new method of determining rotor leakage reactance and resistance of a three-phase induction motor

The paper develops a new method of determining the rotor leakage reactance and resistance of a 3-phase induction motor. Stationary flux distribution of constant magnitude is produced in the air-gap of the machine by supplying direct current to the stator windings. The rotor is driven at various slip speeds simulating the conditions of a 3-phase induction motor. The power input to the rotor is measured. The flux distribution in the stator teeth per pole pitch is measured by use of search coils and a ballistic galvanometer when d.c. excitation to all three phases of the stator is suddenly removed. The voltage induced per phase in the stator due to this change of flux linkage is calculated. An expression is developed for rotor leakage reactance and resistance.The theory is proved by experimental work. The performance is calculated using the rotor constants measured by this method and is compared with that obtained by no-load and locked-rotor tests and by an actual load test. A comparison of results justifies the determination of rotor constants by this new method.

Measuring friction at high speeds

The present paper describes results of plate-impact pressure-shear friction experiments conducted to study time-resolved growth of molten metal films during dry metal-on-metal slip under extreme interfacial conditions. By employing tribo-pairs comprising hard tool-steel against relatively low melt-point metals such as 7075-T6 aluminum alloys, interfacial friction stress ranging from 100 to 400MPa and slip speeds of approximately 100m/s have been generated. These relatively high levels of friction stress combined with high slip-speeds generate conditions conducive for interfacial temperatures to approach the melting point of the lower melt point metal (Al alloy) comprising the tribo-pair.A Lagrangian finite element code is developed to understand the evolution of the thermo-mechanical fields and their relationship to the observed slip response. The code accounts for dynamic effects, heat conduction, contact with friction, and full thermo-mechanical coupling. At temperatures below the melting point the material is described as an isotropic thermally softening elastic-viscoplastic solid. For material elements with temperatures in excess of the melt point a purely Newtonian fluid constitutive model is employed.The results of the hybrid experimental-computational study provides new insights into the thermoelastic–plastic interactions during high speed metal-on-metal slip under extreme interfacial conditions. During the early part of frictional slip the coefficient of kinetic friction is observed to decrease with increasing slip velocity. During the later part transition in interfacial slip occurs from dry metal-on-metal sliding to the formation of molten Al films at the tribo-pair interface. Under these conditions the interfacial resistance approaches the shear strength of the molten aluminum alloy under normal pressures of approximately 1–3GPa and shear strain rates of ∼107s−1. The results of the study indicate that under these extreme conditions molten aluminum films maintain a shearing resistance as high as 100MPa.Scanning electron microscopy of the slip surfaces reveal molten aluminum to be smeared on the tribo-pair interface. Knoop hardness measurements in 7075-T6 Al alloy at various depths from the slip interface indicate that the hardness increases approximately linearly with depth and reaches a plateau at approximately 40μm from the surface.

A Constant-Torque Friction Clutch for Film Take-Up&lt;!--&lt;xref ref-type="other" rid="fn1-10.5594_J09918"&gt;*&lt;/xref&gt;--&gt;

An analysis of fractional take-up devices in general use discloses the reasons for their failure or improper operation. An improved friction clutch is described and analyzed, which embodies means for canceling the effect of a varying coefficient of friction encountered at variable slip speeds, thus maintaining a constant torque at the take-up spindle. Automatic declutching occurs when the load exceeds the amount of torque transmitted, thus protecting the film from excessive tension, and eliminating declutching levers and ratchets when rewinding. The novel construction enables bidirectional operation, both in direction of rotation and in direction of transmission of torque.