Showing papers on "Contact area published in 1973"

The shear strength of thin lubricant films

Abstract: This paper describes a study of the effects of pressure and temperature on the shear strength of very thin layers of a number of lubricants. The shear strength is deduced from measurements of the tangential (frictional) force required to slide glass spheres over glass plates coated with the lubricant. It is assumed that no glass-glass contact occurs through the lubricant film and that the area of lubricant sheared is the geometrical contact area determined by the elastic constants of the sliding surfaces. Consequently by varying the radius of the sphere and the normal load the contact pressure can be varied from 10$^{7}$ to $5\times 10^{9}$ Pa (1 Pa = 1 Nm$^{-2}$). The results show that the shear strength of Langmuir-Blodgett films of calcium stearate is constant at low pressures, but at pressures greater than 5 $\times $ 10$^{7}$ Pa it increases approximately in proportion to the pressure. At higher temperatures the behaviour is similar but the shear strength is reduced at all pressures. Similar experiments have been carried out on retracted stearic acid films, on vapour deposited sebacic acid films and on smeared films of copper stearate and anthracene. Thin films of high density polythene and PTFE have also been studied. For these materials both the absolute value of the shear strength and its variation with pressure resemble the behaviour of calcium stearate. Experiments on the effect of temperature on the shear strength show that calcium stearate, stearic acid and high density polythene exhibit similar 'activation energies' for the shear process. This suggests that these materials all shear by a similar process involving the sliding of linearly orientated methylene groups over one another. PTFE behaves in a similar way although its 'activation energy' is a little higher. By contrast anthracene and sebacic acid have much lower activation energies suggesting that a different shear process is involved.

An eigenvalue problem for elastic contact with finite friction

Abstract: The two-dimensional indentation of an elastic half space by a rigid punch under a slowly applied normal load is considered, for the case in which there is a finite coefficient of friction μ between the surfaces. The contact area is then divided into an inner adhesive region −c 0, gives the adhesive boundary c in terms of μ and Poisson's ratio ν. A similarity transformation shows that c has the same value for both flat-faced and power law punches.

Electrical connecting members requiring lower insertion and retraction forces and providing for low contact wear

Abstract: The improved pair of mating electrical connecting members are incorporated into a variety of matable contacts, connectors and other electrical devices. In one specific application, an improved edge board connector receives an improved printed circuit board and includes therein a plurality of contact members which are normally biased to a disengaged position and to provide a predetermined contact force against the mating conductor paths of the board when it is fully engaged with the connector. The improvements include surfaces on a free end of the contact member and on a cam bar on the board which surfaces cooperate during engagement and disengagement to perform a camming action to deflect the contact member against biasing to cause it to pivot about a fixed end to maintain a contact area on the member between the fixed and free ends away from the board unless they are fully engaged. The camming action is applied to the free end of the member so that the member is less resistant to deflection than it would be if applied at the contact area. As a result, the insertion force during engagement and the retraction force during disengagement are lessened by the fact that the frictional forces between the contact members and the board are being produced by normal forces at the free end of the member rather than by the contact force at the contact area.

Apparatus for testing and sorting cups

Abstract: A device for sorting relatively fragile cups manufactured from coated paper, thin plastic, foamed plastic material and the like. A nonporous, resilient, thin membrane is provided which has an annular contact area for receiving the rim area of the cup and establishing continuous contact with a cup surface extending around the cup adjacent the rim area in a closed loop. The membrane is fixedly supported only outside of and around at least one edge of the annular contact area, leaving the membrane movable throughout the contact area. Air impervious means spans the area defined by an inner edge of the annular contact area of the membrane. The air pressure on the cup-adjacent side of the air impervious element is reduced below the ambient air pressure to cause relative sealing movement of the annular contact area of the membrane and the closed loop surface of the cup received on the membrane. The pressure on the cup-adjacent side of the air impervious element is monitored to detect the presence or absence of a sealing contact between the membrane and the closed loop surface of the cup to sort good cups from defective cups.

The steady state forces and moments on a railway wheelset including flange contact conditions.

Abstract: Railway vehicles are fitted with coned wheels to provide a measure of stability, but it can be shown that since the forces between wheel and track are non-conservative, dynamic instability occurs at a certain critical speed. Under these conditions the wheelsets sway from side-to-side of the, track with the flanges of the wheels contacting the rails. This can lead to derailment when the wheel climbs up the rail and eventually jumps off. The forces which exist between wheel and rail are due to the phenomenon known as "creepage", and various theories exist which predict these forces in the plane of the contact area. An investigation has been carried out into these theories with the railway wheelset problem in view, particularly the flange contact case. It is possible, by assuming small displacements which avoid flange contact, to carry out a linearised study of the lateral dynamics of a wheelset, but the presence of the wheel flanges introduces a nonlinearity into the problem. A mathematical model of a wheelset and track has been defined based on real wheels with a "worn" tyre profile and real track. Computer programs have been written which calculate the contact points when the wheelset is displaced laterally and yawed by various amounts, including flange ,contact conditions. Up to three contact points can exist between the wheelset, and track. Forces in the contact areas have been calculated using the various theories assuming the wheelset to be rolling along the track a ta constant velocity in a displaced position. These forces have been manipulated to give the total forces and, moments on the wheelset and are presented for various vertical load distributions and for various angular and lateral displacements of the wheelset from its central position. Although theories exist which predict the forces for flange type contact, i. e. very elongated contact ellipse with a large amount of spin present, it became apparent during the course of the investigation that very little experimental evidence was available for such conditions. As a result a roller rig was built to provide this data, and measurements were made of· the lateral force due to various amounts of lateral creep and spin on elongated contact ellipses. Results from these tests have been compared with the available theories and show reasonable agreement.

Mechanical Behavior of O-Rings

Abstract: O-ring deformation is approximated as a plane strain contact problem. An integral equation is written for the contact stress which is solved for small deflections. The contact area agrees with the results of the conventional Hertz theory. The displacements of the deformed o-ring are found by requiring zero displacement at the center of the circular cross section. Experimental results on silicone rubber cylinders and o-rings agree with the theory up to approximately 15 per cent strain. A linear viscoelastic solution is constructed from the elastic solution for an o-ring held at fixed deflection for t > 0. For this case the contact area remains constant and the average load is proportional to the relaxation modulus.

Alloy for through-the-partition intercell connectors formed by an extrusion-fusion technique

Abstract: Improved extrusion-fusion-type intercell connectors and process involving: casting the plate strap lugs to be welded from a leadantimony alloy comprising between about 2 percent by weight to about 45 percent by weight antimony, at least 003 but less than about 03 percent by weight tin and less than 0001 percent sulfur; initially extruding the lugs into contact through an aperture in a battery intercell partition, the contact area being between 15 and 75 percent of the area of the aperture; and gradually heating the lug extrusions through a softening stage, an antimony-rich-phase melting stage, and an antimony-lean-phase melting stage Force applied by rapid-response, declining force welding electrodes causes (1) the softened extrusions to reshape somewhat prior to melting, and (2) the antimony-rich-phase of the alloy to exude out of the welding zone filling voids in the aperture before any substantial melting of the antimony-leanphase occurs The resulting weld is dense (void-free), has an antimony-rich ring adjacent the aperture wall, and after rupturing, displays an indicator core useful for evaluating the welds made and monitoring the stability of the manufacturing process/equipment for making them

Gear rolling method and apparatus

Abstract: In the cold rolling of fully-rolled finished gear teeth, the smooth periphery of a rotatable metal gear blank is forcefully engaged by the circumference of an appropriately arranged and profiled rotatable forming roll The desired tooth-forming forceful engagement of the roll with the blank is established progressively over the several rotations of the blank The initial engagement force is sufficient in view of the initial contact area to produce inelastic deformation of the blank material However, the initial engagement force is of a magnitude substantially less than the ultimately desired engagement force

Effect of Operational Conditions on the Formation of Ultra Fine Powders by a Reciprocating Friction Mill

Abstract: An experimental study on the effects of operational conditions on the formation of ultra fine powders was carried out by a reciprocating friction mill with marble as the specimen. The effects of the working speed, the working pressure and the contact area on the production rate of powder were investigated and the following results were obtained.(1) The effects of the working speed and the working pressure were not significant for the particle size of the powders produced by this mutual friction and abrasion method. The mean particle size was almost constant around the size of 0.2∼0.3μ.(2) The production rate of powder was greater when the contact area of specimens was smaller.(3) It seems that the mechanism of abrasion of marble has analogy with the wearing mechanism of metals in consideration of the relation between the mass of produced powder and the working speed. The details have to be experimentally studied from the mechano-chemical point of view.(4) The mass of the produced powder varied with the working speed and the working pressure when the contact area was constant, and the maximum mass was obtained at the speed of about 6cm/sec and the pressure of 1.5Kg/cm2 in this experiment.(5) Between the production rate of powder Q and the working pressure P, the relation of Q=cPn was obtained. From the correlation of the index n and the working speed, it seems possible to conjecture the dependence of abrasion mechanisms on the working speed.

Study on Determination of the Optimum Welding Condition in Resistance Spot Weldng

Abstract: Up to the present not a few sutdies on calculation of temperature distribution in resistance spot weld have been reported. In these studies, however, electrical contact area between two sheets being welded was not taken into consideration. Hence, their results of numerical calculation did not coincide with their experimental data.In this study the authors derived the following formula for calculating the electric contact area under pressure by means of theory of elasticity, i.e., dc=de+ktwherein dc is diameter of contact area; de, electrode diameter; t, plate thickness; k, constant. It is to be noted that the above formula does not contain the term of electrode force. However, the constant k is dependent on electrode force, hence, the formula might be said to involve electrode force term implicitly. The validity of the formula was confirmed by the results of photoeleastic experiment.On the basis of the above finding and the experimental result that the contact area initially formed is kept practically unchanged during the entire process of welding, they derived the following formula for determining the optimum welding condititon for mild steel sheets of equal thickness, namely, s=7.63×107 (de+0.8t)4/I2wherein s is welding time (see); de, electrode diameter (cm); t, plate thickness (cm); I, welding current (A). The formula elucidates a useful relation between temperature rise in the contact zone and welding current.This formula is proved to be correct by the welding experiments with the newly designed weld specimens.

Dry Friction between Soft Rough and Hard Smooth Surfaces

Abstract: The frictional behavior under unlubricated condition was investigated, which is affected by the surface conditions such as surface films, adhesion and wear When the surface films on the contact asperities were ruptured during sliding, the real area of metallic contact generally grew as sliding proceeded There was a simultaneous growth in the friction force resisting sliding Two frictional experiments have been carried out to examine the mechanism of the friction One consisted of measuring the friction force at a single point of contact for sliding of a soft slider on a hard flat surface This assured understanding of the behaviors of the breakdown of films and the junction growth The other comprised the measurements of friction force at the multiple points of contact between a soft rough and a hard smooth surface The friction force was also deduced theoretically in both cases of the single and multiple points of contact

Electrical contact apparatus

Abstract: Electrical contact apparatus for continuous, efficient and uniform application of high current to a moving wire or similar elongate element in a continuous electroplating process, and for mechanical guidance of such wire into a plating bath. A plurality of large area electrical contact members are biased toward and into intimate engagement with the wire and are flexibly mounted to enable positive uniform electrical contact to be maintained notwithstanding spurious motion and irregularities of the moving wire. The contact areas of the electrical contact members which confront the moving wire are configured to complement the confronting cross-sectional curvature of the wire, thereby providing a relatively large contact area for application of high current at low current density.

Friction properties of highly elastic materials at high contact pressures

Abstract: A newly designed high-pressure tribometer has been employed to investigate the pressure dependence of the friction force of SKN-40 crosslinked butadiene-nitrile rubber in contact with a steel surface on the pressure range to 1200 kgf/cm2 (20°C). Over the entire range of contact pressures the friction process is molecular-kinetic in nature and characterized by a linear dependence of the friction force on the logarithm of the sliding velocity. In the region of normal pressures up to 200 kgf/cm2, where the effect of pressure on the friction force reduces to the formation of the actual contact area, the friction constant (proportionality factor relating the friction force and the actual contact area) is practically independent of the pressure. At pressures above 200–300 kgf/cm2 the increase in the friction force at fixed actual contact area is attributable to the effect of pressure on the friction constant. The nature of this effect is related not with an increase in the chain-surface interaction energy (the activation energy does not increase), but with an increase in the forces of adhesion owing to the greater number of polymer chain-steel surface contacts on the actual contact area (increase in contact density).

Investigation of the contact area of a rigid spherical indenter and a polymeric surface at various pressures, temperatures, and contact times

Abstract: The effect of temperature and normal load on the variation with time of the indentation depth of a rigid spherical indenter in polymeric materials has been investigated with the object of obtaining the dependence of the contact area on the principal parameters of the process. Plexiglas, PVC and polyformaldehyde were selected for study. It is shown that at a given temperature the ratio σm/(a/R)n−2=A is a function of time only and almost independent of the applied load. It is established that the time-temperature superposition principle can be used for investigating metal-thermoplastic contact phenomena. An expression is obtained for calculating the contact area at various temperatures and loading times.