Showing papers on "Contact area published in 1974"

Determining the contact area in elastic-indentation problems

Abstract: unit distance into the elastic solid. If the punch has a continuous profile, it is not generally possible to determine the extent of the contact area from purely geometrical considerations, though it may be poss- ible to determine its shape from considerations of sym- metry as with the axi-symmetric punch. For this latter case, Sneddon

Method for welding between metallic body and precision tube body

Abstract: A hollow precision-machined body, such as a circular waveguide for transmission of millimeter wavelengths, is welded to a metallic body with minimum distortion of the precision body, by directing a concentrated beam of heat-producing energy such as an electron beam or a laser beam or a plasma across and peripherally about the interface between the precision and metallic bodies to produce a bead whose width at the contact area is related to the clearance between the bead and the inner surface of the precision tube and the maximum allowable strain at the inner face of the precision tube. Alternately, the energy beam is directed along the interface and around the periphery thereof to produce a bead whose depth of penetration is related to the thickness of the precision body and the maximum permissible strain at the inner surface of the precision body.

Contact Problem for an Elastic Reinforcement Bonded to an Elastic Plate

Abstract: The contact problem for a thin elastic reinforcement bonded to an elastic plate is considered. The stiffening layer is treated as an elastic membrane and the base plate is assumed to be an elastic continuum. The bonding between the two materials is assumed to be either one of direct adhesion or through a thin adhesive layer which is treated as a shear spring. The solution for the simple case in which both the stiffener and the base plate are treated as membranes is also given. The contact stress is obtained for a series of numerical examples. In the direct adhesion case the contact stress becomes infinite at the stiffener ends with a typical square root singularity for the continuum model and behaving as a delta function for the membrane model. In the case of bonding through an adhesive layer the contact stress becomes finite and continuous along the entire contact area.

Electrochemical capacitance characterization of n-type gallium arsenide

Abstract: The depletion layer capacitance of n-type gallium arsenide was measured as a function of its anodic potential in an electrochemical cell. It was shown that these measurements can lead to accurate values of carrier concentration, and are compatible with stripping by electrochemical dissolution, provided that surface area is preserved. The experimental conditions required to maintain the electrolyte-semiconductor contact area constant, are described. Also, it is shown that excursions into regions outside those specified lead to significant enhancement of capacity (via real area increase). Under these conditions the carrier concentration can no longer be obtained but much can be learnt about the internal structure of the material.

Liquid crystal display device with improved contact means

Abstract: In a liquid crystal display device having opposing plates, the plates are so disposed that at least one edge of one of the plates extends beyond an edge of the other. The exposed edge has contact areas thereon connected to conductive areas in the display portion of the device. A frame holds the plates in position with respect to each other and the frame has mounted thereon resilient conductive fingers so positioned that each one makes contact with a separate contact area on the extended edge, the contact being restricted in area to increase the contact pressure. These conductive fingers are resilient and provide a convenient means for removably connecting each of the contact areas to an outside voltage source. Wiping contact between the fingers and the contact area may be provided.

Contact area dependence of minority‐carrier injection in Schottky barrier diodes

Abstract: A general theory of the Schottky barrier diode capable of incorporating geometrical effects is shown to predict the widely different minority‐carrier injection properties of planar and point contact metal‐semiconductor structures.

Current confining light emitting diode

Abstract: The resistivity of particular layers of a gallium arsenide-gallium aluminum arsenide light emitting diode is altered to provide current confinement in the central regions around the well hole. This is accomplished by proton bombardment to increase resistivity of layers around the lower metal contact area while leaving a low resistivity path over the contact, by diffusion of a low resistivity region into an added high resistivity layer adjacent the light emitting well hole, or by diffusion into a reverse conductivity barrier layer over the lower metal contact area.

The mechanics of elastic contact with film‐covered surfaces

Abstract: Solutions to the Hertz problem, which predict the contact area between cylindrical or spherical bodies elastically loaded against one another, have frequently been applied to situations in which one of the bodies is coated with a thin film of different material, notably in the analysis of bearings lubricated with thin solid films. In reality the film may often exert a profound influence on the contact area and the Hertzian assumption will be inappropriate. The present work offers approximate analytical solutions for film‐coated cylindrical and spherical contacts, that are valid provided the contact dimensions are large compared to the film thickness and provided also that the Young's modulus of the film material is less than that of the surfaces with which it interacts. It is hoped that the expressions derived here will prove to be particularly useful in the study of lubricant films deposited by such processes as sputtering and ion plating, where a knowledge of the true area of contact is a crucial factor...

Frictional Heating of a Uniform Finite Thickness Material Rubbing Against an Elastomer

Abstract: In this paper a general mathematical analysis is presented to study the rise in temperature due to frictional heating of two surfaces rubbing against one another. The problem has been formulated in terms of a plane of finite thickness rubbing against rectangular and pyramidal shaped elastomeric sliders. The plane has been treated as a rigid solid, but the analysis is also expected to hold for an elastomeric plane. Formulas for the average and maximum temperatures in the contact area and the distribution of the temperature in the bodies of the slider and the plane are presented. The parameters investigated include the coefficient of friction, velocity of slide, normal load, thickness of the plane, geometric dimensions of the slider, and the elastic and thermal constants of the plane and the slider. The results are presented in closed form analytical expressions which can be easily evaluated on an electronic computer. The analytical predictions are correlated with measurements on a lightly loaded pyramidal shaped rubber slider moving over a smooth plane.

Elementary Effects in the Contact Area of Sliding Rubber

Abstract: Visual observation of the contact area of sliding rubber reveals that the motion between the frictional members is often not sliding in the accepted sense. Often motion is by “waves of detachment” passing along the contact in the same direction as the relative displacement of the rubber. These waves are folds in the rubber surface that are almost certainly produced by buckling. Adhesion appears to be complete between the waves. Buckling is attributed to compressive tangential stresses in the contact area which are theoretically predicted and qualitatively confirmed by experiment. The motive force driving the waves is a tangential stress gradient. The mechanism of wave initiation for hard sliders on rubber tracks is different from that for rubber sliders on hard tracks. The measured frictional force reflects predominantly the energy dissipation accompanying the propagation of the waves.

An Analysis of the Elastic and Plastic Deformation of Machined Surfaces in Contact : 4th Report, Deformation of Contacting Rough Surfaces when Directional Asperities and Nondirectional Ones are in Contact

Abstract: When machined surfaces are divided into directional asperities and nondirectional ones, the analysis of normal deformations at metal joints are classified as follows. (i) Contact between directional asperities and a flat surface. (ii) Contact between two surfaces with directional asperities whose directions are crossed each other. (iii) Contact between two surfaces with nondirectional asperities. (iv) Contact between directional asperities and nondirectional ones. In this report, the elastic deformation and the plastic one for the 4th case were analyzed. Projections of directional asperities and nondirectional ones were assumed as wedge shape and conic one respectively. The elastic deformation and the plastic one at metal joints were synthesized by statistic of surface asperities in contact. Results were as follows. (1) Relation between the deformations and the normal pressure is linear on a double logarithmic paper. (2) The deformations are classified by the contact surface coefficient.

A thermal, thermoelastic, and wear analysis of high-energy disk brakes

Abstract: A thermomechanical investigation of the sliding contact problem encountered in high-energy disk brakes is described. The analysis includes a modelling, using the finite element method of the thermoelastic instabilities that cause transient changes in contact area to occur on the friction surface. In order to include the effect of wear at the contact surface, a wear criterion is proposed that results in the prediction of wear rates for disk brakes that are quite close to experimentally determined wear rates. The thermal analysis shows that the transient temperature distribution in a disk brake assembly can be determined more accurately by use of this thermomechanical analysis than by a more conventional analysis that assumes constant contact conditions. It also shows that lower, more desirable, temperatures in disk brakes can be attained by increasing the volume, the thermal conductivity, and, especially, the heat capacity of the brake components.

Effect of friction on the performance of texture test cells

Abstract: The relationship was measured between the normal contact force and the force required to overcome friction between food samples and a surface simulating a typical texture test cell. Peas produced frictional behavior that combined the characteristics of dry friction and fluid flow. Friction coefficients for selected foods ranged from 0.04 to 0.52. Friction force was linearly related to the normal contact force and non-linearly to the area of contact between the sample and the surface, and the speed of the sample relative to the surface. This verifies the fact that, with empirical texture test devices, these test variables must be held constant. The estimated friction forces represented a significant amount of the total force required to operate a wire extrusion cell and a back extrusion cell. It was concluded that standardization of the test cell would be easier to achieve if the contact area between the sample and the cell surfaces was minimized and if low friction materials were used to construct the cells.

Spot welding of fastener to trowel blade - using unequal contact surface electrodes, the larger contacting the trowel blade surface

Abstract: The fasteners for handles are attached to bricklayers blades by spot welding without impairment of the trowel blade surface by employing a relatively larger contact area electrode against the working surface of the blade and a smaller contact area electrode against the fastener rear surface. The method is used for fixing a corrugated strip which is forced mechanically into grooves in the handler, to the rear of a smoothening trowel.

An Analysis of the Elastic and Plastic Deformations of Machined Surfaces in Contact : 5th Report, Formulae of Deformations of Plane Joints Machined by Various Methods for Practical Use

Abstract: The elastic and plastic deformations of plane joints were analyzed in previous reports and it was revealed that the theoretical results agreed with the experimental data. The calculations of these deformations, however, were very burdensome. Therefore, in this report, the formulae for practical use of these deformations were considered. The formulae for practical use are δE=Ae{(p+p0)0.09-p00.09} δS=As{(p+p0)0.18-p00.18} where δE, δS: elastic and plastic deformation, p: mean interface pressure, Ae, As, p0: constants. In this report, the methods to determine these constants from contact area, hardness of materials in contact and asperity heights were developed. Furthermore, a FORTRAN program to determine these constants from the above-mentioned factors and the machining methods of surfaces was presented and the notices to apply these formulae to various contact conditions were proposed.

Spreading Resistance Measurements on Silicon with Non-blocking Aluminum-Silicon Contacts

Abstract: The paper concerns the measurement of resistivity fluctuations in n-type silicon starting material in the resistivity range from 1 to 1000 Ω cm. The microscopic resistivity fluctuations that are associated with the well-known striations require a measurement technique of high accuracy and high local resolution. We chose the spreading resistance method. However, in contrast to the conventional method, in which the metal probe is pressed directly onto the silicon surface, we supply the silicon slice with non-blocking aluminum-silicon contacts. The radius of the contact area is exactly defined. Any contact radius can be realized according to the resolution desired in lateral direction and in depth. When the metal probe is applied to the aluminum-silicon contact, the contact is not destroyed. Thus it is possible to perform spreading resistance measurements and four-point probe measurements along one and the same measuring track and in this manner at the same time to vary the local resolution. A comparison of both measurement results will in particular yield information on the conditions of the resistivity in axial direction of the slice. Essential prerequisites for an absolute measurement are fulfilled with the aluminum-silicon contact. However, the investigations made up to now show that the resistivity calculated from the spreading resistance is smaller than the one obtained with the four-point probe measurement by approximately a factor of 0.8.

Friction of polymeric materials: 2. Dependence of contact area on time and calculation of the coefficient of friction

Abstract: The case of contact of polymer and metallic surface has been examined. A formula is proposed for calculating the contact area as a function of time of holding the compression surface under load and for calculating the coefficient of friction, the dependence of Young's modulus and shear strength on temperature, deformation rate, and average force on the contact surface being taken into account. The nature of deformation of irregularities on the surfaces of polymeric materials under the action of normal and tangential loading has been examined.

The Effects of High Contact Pressures and Temperatures on the Adhesion of Amorphous Polystyrene to Borosilicate (Pyrex) Glass

Abstract: The effects on adhesive joint strength of four pressure-temperature histories, each over the range of pressures from 1 to 1500 bars and temperatures from 25 to 200°C, has been investigated with polystyrene-Pyrex glass butt joint specimens. The various pressure-temperature histories were designed to show the separate effects of permanent stresses, transient stresses and interfacial contact on joint strength. This strength increased as the number of stress concentration loci were reduced through application of high contact pressures on the melt. However, isobaric solidification of the polymer led to a maximum in fracture stress as a function of applied molding pressure because of the existence of a critical pressure at which permanent thermal stresses were minimized. A series of isothermal compression-decompression molding operations showed fracture stress to increase with interfacial contact area until maximum contact was achieved. A 100 per cent gain in bond strength was realized when interfacial...

Application of the Point-matching Method to the Three-Dimensional Elastic Contact Problems

Abstract: Hertz's theory for an elastic contact problem has been very useful up to now, but many practical problems can not be analysed by it because this theory is established on the many assumptions. In this paper, a method of three-dimensional stress analysis for the contact problem between two arbitrary elastic bodies is described in detail. Particularly, concerning a contact problem, to decide the contact area, the displacement formulars at a contact surface and the contact conditions is very important and a specific technique is here presented using the point-matching method. Moreover, by applying this method, the indentation problem of a reactangular rigid punch on a semi-infinite elastic body is analysed.

A study of the characteristics of a Mg-Si diode

Abstract: Diodes of Mg contact to both n and p-typo Si respectively have been fabricated. I-V characteristics and Specific contact resistance Re. were studied. Specific contact resistance can be reduced by increasing temperature, and decreasing contact area. Diodes of Mg to p-type non-degenerate Si contact possess better rectifying properties than those of mg to n-type non-degenerate Si. Studios of specific contact resistances for different contact arena reveal the current. crowding effect.

Investigation of the relation between the depth of penetration and indentation diameter in polymer hardness measurements

Abstract: It has been experimentally demonstrated that for polymeric materials the area of the indentation should not be calculated from the depth of penetration of the spherical indenter, since this gives hardness values that are too low. It is shown that when the surface of a polymeric specimen is indented by a rigid ball, the effect of the spherical stress tensor on the yield point is important; the average stress on the contact area at the beginning for forced high-elastic deformation is close to the compressive yield stress of the polymeric material and considerably higher than its tensile yield stress.