Showing papers on "Contact area published in 1969"

Thermoelastic Instabilities in the Sliding of Comforming Solids

Abstract: If two sliding solids are nominally in contact over a large area, the inevitable irregularities in the surfaces will cause the pressure distribution to be non-uniform. The generation of heat due to friction at the interface will also be non-uniform and the solids will be distorted by thermal expansion. The highest parts of the surface will carry the greatest pressure, reach the highest temperature and consequently expand more than the surroundings. Thus the thermal distortion tends to exaggerate the initial irregularity of the surface. The wear at the interface has the opposite effect, but under suitable conditions the process can be unstable. Experiments are described in which the effects of this instability are observed: the load is concentrated into a few small parts of the surface causing high local temperatures. After a few seconds, the load is transferred to a new part of the surface and, when the original contact area has returned to the temperature of the surroundings, it contracts leaving an observable depression in the surface. The scale of this process is large in comparison with the size of the surface asperities. An experimental model has been produced which demonstrates the characteristics of the instability in a simplified form. The thermal expansion drives the surfaces apart at the beginning of the cycle and this movement has been observed experimentally. An analysis of the instability is produced and a good correlation is obtained with experiment.

On the Mechanism of Contact between Solid Surfaces : 1st Report, The Initial Separation and the Distributions of Slopes of Facets on Surface and on Profile Curve

Abstract: Assuming that the distribution curve obtained from the profile curve of the surface has a normal distribution, the relation between the surface roughness, the apparent contact area and the initial separation which is the distance between two median planes of surface in the beginning of contact is obtained theoretically. If the asperities are cones of the slopes which depend on the surface roughness, the relation between the distributions of slopes of cones and of slopes of small facets measured manually with a protractor on the profile curve is also deduced theoretically. The results of the theoretical analyses are compared with the experimental results for the initial separation and the distribution of slopes of facets on the profile curve. Results seem to support the plausibility of the proposed theory. Moreover this plausibility shows the possibility estimating the effects of the surface roughness and the apparent contact area of end faces of an object by length measurement.

Indium antimonide infrared detector contact

Abstract: The invention here disclosed is an indium antimonide infrared detector having a novel contact region. The detector comprises a substrate, constituted of an N-material with a P-region fused thereon. An anodized surface oxide film is superimposed over the diffused P-region and over the adjacent surface of the substrate. A silicon oxide layer is disposed over most of the anodized surface oxide film but exposes a portion of the P-region which portion comprises superimposed layers of chromium and gold which form the contact region, said layers masking the contact area and rendering it insensitive to infrared radiation and simultaneously providing a pad to which an electrical connection may conveniently be made.

Influence of Asperity Deformation Mode on Gas Leakage between Contacting Surfaces

Abstract: The gas flow between two surfaces in contact is affected by the way in which the surface asperities are deformed by the contact load. The plastic deformation of wedge-shaped model asperities, supported on rigid bases, is examined. Full account is taken of the effect of displaced material on the deformation pressure and on the rate of fluid leakage between the contacting surfaces. Characteristics of deformation pressure versus compression are plotted for a range of wedge asperity angles, assuming two-dimensional deformation and non-hardening material, and from these are derived expressions for fluid leakage between the contacting surfaces. It is shown that a critical contact pressure exists for a given seal contact load at which the leakage rate has a maximum value. This contact pressure may be avoided by either increasing or decreasing the seal length.

On the Mechanism of Contact between Solid Surfaces : 2nd Report, The Real Area of Contact, the Separation and the Penetrating Depth

Abstract: Assuming that the asperities on normally distributed surface are cones of the same slope that depends on the surface roughness, it is deduced theoretically by the slip-line theory that the real area of contact in the case of contact between a soft conical asperity and a hard flat surface or between a hard conical asperity and a soft flat surface depends on the slopes of the conical asperities, the coefficient of friction at the interface of contact asperities, and the flow pressure. If the real area of contact is corresponding to the geometrical area obtained immediately from the bearing-area curve, the relation between the real area of contact and the separation or the penetrating depth is also obtained theoretically. A comparison of calculated values based on this theory with experimental data shows good agreement.

On the Mechanism of Contact between Solid Surfaces : 3rd Report, The Number and the Distribution of Radii of Contact Points

Abstract: Assuming that the asperities on normally distributed surface are cones or pyramids the slopes of which depend on the surface roughness, the three dimensional number and the distribution of the radii of contact points are deduced theoretically. The results of the theoretical analyses are compared with the experimental results for the numbers and the distribution of the radii of contact points in the case of contact between two nominally flat metal surfaces prepared by sandpaper-finishing, sandblasting and grinding. Results seem to support the plausibility of the proposed theory. Moreover they show that over a wide load range the average radii of contact points are almost constant ; consequently the total contact area is increased mainly owing to the increase in the number of the contact points.

Secondary terminal and shorting device

Abstract: The secondary terminals of a current transformer are provided with a cutout section which provides a flat contact surface on each terminal. A short circuit member has a pair of depending angular legs having faces which are parallel to the flat contact surfaces of the secondary terminals. This provides a large contact area with good electrical contact between the secondary terminals and the shorting device.

Adhesion of Metallic Bodies Initiated by Physical Contact

Abstract: Metallic adhesion produced by surfaces compression, discussing asperities plastic deformation and macrodeformation caused by contact area growth

Thickness dependence of the indentation hardness of glass plates

Abstract: The load required to produce fracture in glass plates by pressing steel balls onto both upper and lower surfaces of the plate has been recorded experimentally as a function of the thickness of the plate and the diameter of the indenter. It is observed that for a sufficiently large indenter the fracture load decreases rapidly as the thickness of the plate decreases. The variation of the fracture load with plate thickness is shown to be a consequence of the fact that the value of the maximum tensile stress at the boundary of the contact area is larger in a thin plate than in a thick plate, for the same indentation pressure. A method of calculation is described for determining the maximum tensile stress in an elastic plate subjected to arbitrary symmetrical spherical indentations.

Speed sensitive dual tread tire

Abstract: A TREADED TIRE OF THE PNEUMATIC TYPE WHICH HAS A LOCALIZED CIRCUMFERENTIAL INCREASED WEIGHT AREA ADAPTED TO INCREASES THE DIAMETER OF A LOCALIZED PORTION OF THE TIRE TREAD DUE TO CENTRIFUGAL FORCE AT HIGH SPEEDS. THE INCREASED DIAMETER PORTION OF THE TREAD REDUCES THE CONTACT AREA BETWEEN THE TIRE AND THE ROAD AT HIGH SPEEDS, THEREBY REDUCING THE DRAG WHILE AT THE SAME TIME REDUCING HEAT AND FRICTION AND PREVENTING HYDROPLANING OF THE TIRE. THE INCREASED DIAMETER PORTION MAY BE CONSTRUCTED OF A LONGER-WEARING MATERIAL THAN THE REMAINDER OF THE TREAD. THE INVENTION DOES NOT INTERFERE WITH FULL TREAD CONTACT AT SLOW SPEEDS OR WHILE BRAKING THE VEHICLE.

The Relationship between Lubrication and Surface Condition of Metals Deformed under Compression

Abstract: It is well known that the surface condition of deformed metal is affected by lubrication. In this paper, experimental and theoretical analyses are presented for surface condition of the specimens which are initially polished to flat surfaces and compressed by flat tools with liquid lubricants. Simple models are suggested for roughening of surface under free deformation and flattening of the surface by tool. With these models and some assumptions, the relationship between compressive strain and the fraction of the true contact area is derived as a function of roughening rate of the free surface and the thickness of the initially trapped lubricant film. The experimental result agrees well with the theoretical result. A relationship among contact area, C.L.A. roughness and lubricant film thickness is also derived from the surface model.

The Relationship between Lubrication and Surface Condition of Metals Deformed under Compression : 2nd Report, Experimental Study

Abstract: In the first report, it was found through analysis that the surface condition of a compressed specimen depends on the film thickness of liquid lubricant and the roughening rate of free surface during deformation when the initial surface is flat. In this report, an experimental study on film thickness and roughening rate of free surface is presented. The film thickness on a round aluminium specimen compressed at low speed is proportional to D2/3V1/3p1/3 where D is diameter of the specimen, ν is viscosity of the lubricant and p is the loading rate. The roughening rate of free surface increases with an increasing grain size of the specimen material. From an additional experiment, it is found that the true contact area with tool increases with grain size, and experimental result agrees qualitatively well with the analysis.

A hardness tester for polymer films and their applications

Abstract: A micro-hardness tester based on the static indentation method was designed to study the hardness of polymer films. The contact area of a film with an indenter under loading was measurable in the terter. This tester has the following characteristics:1) The error caused by elastic recovery characteristic of visco-elastic materials can be decreased.2) The testing load changes continuously from 1g to 300g.3) The testing temperature can be changes widely.The results obtained by application of the tester are as follows;i) The Vickers and Brinell hardness of thin polymer films was measured with an indenter under a proper small load. The hardness was independent upon the thickness of samples used in this experiment. A difference between the hardness under loaded and unloaded states for thin polymer films was observed. The hardness under unloaded state agreed with the value obtained by a commercial tester.ii) In the case of uniaxially drawn PET, the shape of the contact area of the film with a ball indenter was ellipse, whose minor axis coincids with the drawing direction. The ratio of the major axis to the minor was proportional to the birefringence of the samples.

Formation of the true contact area between high-elastic materials and a hard smooth surface

Abstract: The change in the true contact area between rubber and glass on passing from static to dynamic friction has been studied experimentally. The extent of this change depends on the applied normal load and the contact time. The change of friction force is determined by the conditions of formation of the true contact area under the action of normal and tangential forces.

Calculations of the coefficient of friction under elastic contact conditions

Abstract: Expressions for the friction coefficient were derived for the case of elastic contact between rough materials The computation was based on the assumption that the friction force in the case under consideration is due to hysteresis losses during the deformation of a thin surface layer of one friction pair component by protuberances on the counterpart surface and due to molecular interaction at the solid/solid interface in the contact zones The minimum value of the friction coefficient was calculated, and it was shown that it depends on the degree of surface roughness, physicomechanical properties of friction pair materials and the magnitude of tangential stresses τ0 at the solid/solid interface

Silicon contact for area reduction of integrated circuits

Abstract: In the design of integrated circuits, the contacts are made smaller than the diffused semiconductor area. The reason for the smaller contact area is to avoid the contact of the metal to areas of opposite conductivity type to that of diffused area when misalignment occurs. Because aluminum is universally used as the interconnecting metal and the aluminum work function is comparable to that of silicon, an alloyed aluminum contact makes good ohmic connection with p-type silicon, but a leaky reverse junction with the n-type silicon. For n-channel MOS transistors, the situation is even worse because the alloyed aluminum in contact with p-type substrate would cause a short circuit.