Showing papers on "Contact area published in 1981"

The mechanics of adhesion of viscoelastic solids

Abstract: The experimental study of adhesion between common solids is bedevilled by the fad that, with exception of cleaved mica, inevitable roughness of the surfaces is greater than the range of surface forces. A new situation arose with the technique of casting low-modulus rubber with an optically smooth surface. When placed in contact with each other, or with a smooth hard surface like plate glass, such specimens are sufficiently compliant to make intimate contact throughout the whole of their apparent contact area. High adhesion is then observed; in fact the measured force required to separate the surfaces is generally greatly in excess of that which would be expected from the action of surface forces alone. The measured force of adhesion is found to depend on the rate of separation and to correlate with the viscoelastic properties of the rubber. The present state of knowledge of this phenomenon is reviewed and the mechanics of the process whereby the viscoelastic properties of the solids amplify their...

Alloyed ohmic contacts to GaAs

Abstract: The alloyed AuGe‐based contact is widely used to make ohmic connections to GaAs. It has been presumed that the regrown alloyed region is heavily doped so that carrier transport is by tunneling. The electrical and metallurgical properties of this heterogeneous system have been extensively studied and have been shown to be spatially nonuniform. Details of fabrication technique, analysis, and theoretical interpretation of its behavior will be discussed. It is suggested that the observed (doping)−1 dependence of the contact resistance is due to spreading resistance domination of current paths through submicron regions of the contact area where heavy doping occurs.

The effect of carbon fiber reinforcement on contact area, contact pressure, and time-dependent deformation in polyethylene tibial components.

Abstract: To study the mechanical behavior of a commercially available UHMWPE reinforced with carbon fibers, measurements of contact area, contact pressure and time-dependent deformation were made on tibial components from a contemporary total knee replacement loaded to physiological levels. For comparison, similar measurements were performed on identical components manufactured from plain UHMWPE. Contact area and pressure results reflected the increased stiffness of the carbon-UHMWPE material, with smaller contact areas and generally higher contact pressures versus the plain UHMWPE at the same load. Stresses in both materials under the contact area approached or exceeded the yield stresses for the materials when the physiological load was high or the radius of the femoral component indenter decreased (similar to flexion of the knee). Time-dependent deformation over a 24 h period was reduced significantly in the carbon-UHMWPE components for a high physiological load.

The Boundary Element Method applied to Two-Dimensional Contact Problems with Friction

Abstract: Contact problems and the study of load transfer in mechanical assemblages are of great importance in mechanical engineering. For nearly one century, since H Hertz (1881) published his famous work on normal contact between elastic bodies, much research has been performed in this area, both theoretical and experimental work. An interesting survey of the mechanics of contact between solid bodies is given by Kalker (1977). He gives an account for the classical formulation of the contact problem as well as for the variational one. The latter has been used especially for numerical calculations, for instance with the finite element method, (FEM). In most contact problems the contact area is a function of the external forces. When friction has to be taken into account, the whole load history has to be followed. Thus when using numerical methods, contact problems have to be solved by iteration and in the frictional case also with incremental technique. A lot of computer time has to be spent which makes it important for the system matrix to be small. When sliding occurs in the contact zone, the normal and tangential forces have to be coupled with a friction parameter. The possibility of coupling the normal- and tangential tractions in the matrix system is an advantage for the Boundary Element Method (BEM) over the displacement FEM. This makes it fruitful to use BEM for solving contact problems with friction.

Shallow and parallel silicide contacts.

Abstract: Ways of making silicide contacts to Si which have a contact depth of about 10 nm are reviewed. Both Si alloys and refractory metal alloys have been explored for shallow silicide formation, and both high (0.85 to 0.75 eV) and low (0.50 to 0.40 eV) Schottky contacts have been demonstrated. Shallow contacts may not be uniform over the entire contact area due to nonuniform interfacial reaction, so nonuniform contacts consisting of a high barrier silicide and a low barrier silicide in parallel have been analyzed.

The area of contact between a small sphere and a flat surface

Abstract: Measurements have been made of the area of contact between a small sphere and a flat surface under load. The spheres were of steel or tungsten carbide, 1 mm in diameter. The fiat specimens were of fused silica, soda-lime glass and sapphire. The loads ranged from 5 to 900 g. With a steel ball on soda lime glass, good agreement was obtained between measured values and those calculated by Hertzian theory. However, for fused silica and sapphire the measured radii were significantly larger than the calulated radii. The contact radius was also measured on fused silica at much higher loads, corresponding to the first appearance of a ring crack. In many eases the crack appeared at the edge of the contact area, which was again larger than the calculated area. Discrepancies between these results and some previous work are discussed.

The Gas-Tightness of Separable Base Metal Electric Contacts

Abstract: The interface between two contacting metals, neither of which is noble, can be established under conditions such that the electrical resistance is essentially the same as for clean metals. In addition, this behavior has been observed over extended periods of time in chemically hostile environments. Some basic physical properties of contacts are applied for a qualitative understanding of these results. Surface topographical studies have shown that the real load bearing area in a local indentation is never less than 50 percent of · the nominal area of contact. The nature of the bulk deformation during the loading of the interface and the behavior of multiple electrical contact spots ensure that, even in the presence of insulating films, the fraction of true area in electrical contact is sufficient for good conduction. The application of percolation theory to the problem of sealing a contact against ingress of corrosive atmospheres predicts that roughly 44 percent of randomly placed real contact area is a threshold value, beyond which open pathways for diffusion of the external atmosphere become blocked. Since the true contact area exceeds this threshold, such interfaces will be gas-tight.

Container for the storage of radioactive material

Abstract: In a container for the storage of radioactive material comprising an inner casing for receiving the material and an outer casing made of a ceramic material which surrounds the inner casing, it is of prime importance that mechanical and thermal stresses which occur during storage and transport do not lead to destruction of the outer casing. In order to achieve this, the inner casing is held within the outer casing by contact distributed over a large surface area of the inner wall of the outer casing, the contact being achieved solely by frictional engagement, or by frictional engagement assisted by an adhesive. Preferably a contact element forming a frictional engagement element consists of a slotted sleeve and an abutment which is connected to the inner casing. Instead of a single contact element exhibiting a large contact area, a plurality of smaller contact elements can be used with an essentially uniform distribution of their individual contact areas over a large surface of the inner wall of the outer casing.

Modelling electrical behaviour of nonuniform AlSi Schottky diodes

Abstract: The heat-treated AlSi contacts show large nonuniformities and cannot be described by a one-dimensional theory. The authors partially succeed in describing circular Al/nSi contacts by a crude model: two diodes in parallel (the first central and circular, the second peripheral and annular). It was shown that only a part of the contact area is effective for samples treated at lower temperatures, due to the interfacial oxide layer. However, the contacts treated at 550°C seem to have more or less uniform electrical properties, despite large nonuniformities in the contact geometry. Moreover, the effective energy barrier of these contacts is little influenced by the preparation conditions, including the amount of Al available for AlSi interaction and the rate of cooling. These results may modify the present conception of the formation of the Al-doped layer at the AlSi interface.

Stress distribution in diametral compression tests.

Abstract: In an attempt to find an explanation for an experimentally found strong connection between the extension of the loaded area and the load required for fracture, an analysis of the diametral compression test was carried out by means of the finite element method. The distribution of the stresses in a quadrant of a circular specimen section was studied for varying contact surface but at a given load distribution within this surface. Below a limit value for the width of the contact surface tensile stresses appeared peripherically outside the contact area, which had a magnitude exceeding those stresses which are centrally located and should normally initiate fracture. For that reason, peripherical fracture initiation must be regarded as a possibility. Only marginal importance could be attached to changes in the extension and magnitude of the central tensile stresses, as compared with the potential impact of the peripherical tensile stresses.

Pressure-Wear Theory for Sliding Electrical Contacts

Abstract: The concept of wear-dependent contact phenomena is developed for sliding electrical contacts, where geometric constraints on wear directly influence contact pressure distribution under the face of a brush. In terms of general contact theory, this pressure distribution is related to the number of contacting asperities, the true area of each contact, or the frequency of asperity encounters. The concept is proposed as a potential new tool to be used in the formulation of a descriptive analytical model of the brush interface. Analytical relationships are developed for friction, wear, and electrical contact resistance for composite and other multicomponent brush configurations.

Secondary sealing element with U-shaped sealing ring for mechanical seals

Abstract: A secondary sealing element for axial seal rings, is resistant to stresses due to temperature, pressure, vibration, corrosion, swelling and shrinking. This sealing element is produced of non-rubber-type elastic and non brittle material and its shape, in cross-section, consists of a ring, with a pair of arms to give it an elastic reaction. The double-arm ring forms three radial-type sealing surfaces and is completely locked into a chamber. Special material with low static friction and higher thermal conductivity than rubber material is used. Furthermore the dissipation of heat, produced by the axial sliding rings, will be increased through the double contact area to the shaft by the arms in comparison to an O-ring, and through a wear-resistant and non-corrosive layer on the shaft having at least the thermal conductivity of the basic material.

The Numerical Calculation of the Contact Problem in the Theory of Elasticity

Abstract: In the present paper, distinction is made between frictional and frictionless contact problems. After their formulation, the epitome of frictional problems, viz. the problem of frictional rolling contact is considered, and the two most recent and successful methods for dealing with it are presented. Then the frictionless problems is considered. Two pairs of methods are presented, each pair consisting of a non-variational method, with its variational counterpart authored by us. The first pair, viz. Paul & Hashemi / Kalker & Allaert, deal with the general half-space frictionless contact problem. The second pair, viz. Reusner / Kalker & De Mul, deal with the contact of bodies of revolution, which may be approximated by half-spaces. The codes implementing the frictionless problems suffer from long operating times. Research is still in progress to speed up the codes.

Holding apparatus for hydrogen storing metal

Abstract: PURPOSE:To enhance the heat recovering efficiency and the hydrogen absorbing and separating efficiency by enclosing the wall faces of a hydrogen storing metal holding chamber except the heat exchange face with a special heat insulating material and supporting the surface of the material facing to a hydrogen gas pass with a laminated wire net. CONSTITUTION:Reaction tube 1 of the titled apparatus is composed of inner tube 2 made of laminated wire net forming hydrogen gas pass 5, partition tube (heat exchange face) 3 and outer tube 4. Space 10 holding hydrogen storing metal 11 is formed between tubes 2, 3, and the wall faces of space 10 except heat exchange face 3 is enclosed with heat insulating material 8, 9 having suitable heat retaining property, gas permeability and volume elasticity. Stored H2 is released by a heat medium passing through pass 6, and when H2 is allowed to be absorbed in metal 11, H2 is fed into pass 5. Since the wire net and material 8, 9 are of fine mesh, metal 11 is finely granulated to increase the contact area, resulting in enhanced H2 absorbing and separating reaction efficiency.

Electromagnetic dual break contactor

Abstract: An electromagnetically operated, straight-line motion dual-break electrical contactor has current conductors entering a contact area from opposite directions. In the contact area the conductors are closely spaced and have finite parallel substantially flat portions with an insulative divider to prevent conductor to conductor arcing. A pivotable contact carrying bridge spans the conductors. The pivotable bridge compensates for contact wear or displacement. Screens are arranged in arc blow paths to aid in extinguishing arcs. The contactor arrangement and spacing controls the direction and enhances the magnitude of arc blow.

Vacuum interrupter with a spacially modulated axial magnetic field contact

Abstract: A vacuum circuit interrupter including axial magnetic field generating means, and arc contact structure comprising means for spacially modulating the axial magnetic field over the area of the contact. This contact structure produces adjacent regions of different magnetic field strength over the contact area, whereby a plurality of spaced apart low arc voltage, stable parallel arc current paths are established over the contact area.

Method of growing single crystal of semiconductor

Abstract: PURPOSE:As a lump of quartz is continuously inserted into the melted semiconductor, the crystal of the semiconductor is lifted and grown, thus permitting the growth of the semiconductor single crystal with a constant concentration of oxygen included in the crystal from the top of the bottom. CONSTITUTION:The melted material for semiconductor single crystal 2 is held in a cone or truncated cone of quartz crucible 6. As the grown crystal is lifted up, the surface level of the melted material goes down and the vaporizing surface continuously diminishes. At this time, the contact area also decreases continuously. In order to keep the contact area substantially constant and compensate and moderate the reduction in oxygen concentration expressed by the segregation constant with the ratio of the contact area to the vaporization area, a quartz lump 8 that has such a symmetric shape that it does not disturb the thermal convection and temperature distribution, when necessary, is made to revolve around the same shaft as that of the seed crystal is inserted into the melted material at a constant speed continuously. For example, the lump of quartz has a cage shape.

Physical significance of contact angles

Abstract: The physical significance of contact angles has been interpreted on the basis of a model derived from known surface energy relationships. The degrees of non-spreading and spreading have been expressed in terms of the magnitude of contact angles. On the basis of the physical picture, hysteresis of contact angle has been calculated from the experimental values of equilibrium contact angle and surface tension of the liquid. It has been suggested that it is not necessary to assume that hysteresis of contact angles is due to surface roughness of solids. The picture also explains why apparent contact angle on a non-flat solid surface is more than that on a flat solid.

The Mechanics and Physics of Adhesion of Elastic Solids

Abstract: The paper discusses a number of important questions raised in the theory of adhesion between elastic bodies under the action of normal forces. the relation between the microscopic quantities such as the interaction energies of attractive and repulsive forces, the equilibrium separations of atoms and the macroscopic quantities used in the continuum mechanics like the area of contact, the work of adhesion is examined, at first, by taking the interaction between rigid bodies as an example. This leads us to the concept of a thermodynamical, effective contact area between the interacting solids. the effective contact area of deformable bodies is calculated for the case of a Hertzian contact. It is shown that the inclusion of the term “work of adhesion” in the analysis based upon continuum theory of contacts is justifiable within the limits of the theory. The rest of the paper deals with the theory of adhesion in the framework of continuum mechanics and briefly reviews the recent work inspired by the various new developments in the fields of fracture mechanics. the relatively straight-forward extension of Johnson's theory of adhesion to more general axisymmetric shapes is indicated. the most important limitation of the previous work is that the choice of materials is severely restricted. the present work extends the theory to include the practically interesting case of contact between dissimilar elastic materials. in this case, the constraint imposed by adhesion on the tangential displacements within the contact area gives rise to shear stresses. the role of the shear stresses in the mechanics of adhesion is found to be significant.

Method and device for high-temperature abrasion test

Abstract: PURPOSE:To reproduce the same condition for a sample as that in which the sample is practically applied to obtain a highly reliable data, by securing a contact between the inner surface of a ring heated up to a high temperature and the outer surface of sample material, then repeating heating and cooling alternately at the contact area. CONSTITUTION:The test ring sample 15 is fitted to the outer circumference of a fixed disk 28 and then press-contacted with a proper contact pressure onto the inner surface of the heating ring 14 to be rotated. A supporting disk 21 for supporting the heating ring 14 rotates around a shaft 22. The outer surface of the contact position of the ring 14 is supported by the bearing roll 20. The ring 14 is heated by a heating device 16 such as the burner or the like. The sample 15 is also heated by the device 19, if necessary. At the same time, the sample 15 is cooled by a cooling device 17 such as a water-cooled nozzle or the like. Thus the heating and cooling are repeated alternately. In such way, the nearly the same conditions is reproduced as that in which the sample is practically applied to obtain a highly reliable data.

Semiconductor integrated circuit device having a Schottky barrier diode

Abstract: An integrated Schottky barrier diode having a low forward voltage is disclosed. It has been discovered that, contrary to previous theory, the mathematical relationships between the contact area of a Schottky barrier diode and the series resistance thereof and between the contact area and the forward current at zero forward voltage are non-linear for sufficiently small contact areas. According to the present invention, a Schottky barrier diode comprises several smaller Schottky barrier diodes connected in parallel and sharing a common cathode, the Schottky barrier contact area of each of the component diodes being sufficiently small to fall within the range in which barrier contact area is non-linearly related to at least one of series resistance and forward current at zero forward voltage. A Schottky barrier diode formed of several smaller diodes in this manner has a lower forward voltage than an SBD that has the same total barrier contact area but that is not split up into several component diodes.

Method of manufacturing a semiconductor device

Abstract: A method of manufacturing devices in a semiconductor body 20 of a first conductivity type. An oxygen impervious masking medium 22 is placed on the body 20. Portions of the medium 22 are removed to define field areas 31 and field oxide is formed in the field areas. The surface of the silicon wafer 23 is thereafter masked to define gate areas 26 and electrical contact areas 30. The exposed medium is removed and the exposed body areas doped to form interconnect runs 28 and a source/drain region 29 of a second conductivity type. An oxide 48, 50 is formed over the doped interconnect runs and source/drain regions of the wafer. The masking medium covering the contact area 30 is removed and the contact area is doped to a second conductivity type. Finally conductors 60, 61 are positioned to provide the desired electrical connections. In a first alternate embodiment the masking medium is a sandwich of different material layers 70, 72 and in a second alternate embodiment the masking medium is a sandwich of three different layers 80, 82 and 84.

Effect of load, area of contact, and contact stress on the tribological properties of polyimide bonded graphite fluoride films

Abstract: A pin-on-disk type of friction and wear apparatus was used to study the effect of load, contact stress and rider area of contact on the friction and wear properties of polyimide-bonded graphite fluoride films. Different rider area contacts were obtained by initially generating flats (with areas of 0.0035, 0.0071, 0.0145, and 0.0240 cm) on 0.476-cm radius hemispherically-tipped riders. Different projected contact stresses were obtained by applying loads of 2.5-to 58.8-N to the flats. Two film wear mechanisms were observed. The first was found to be a linear function of contact stress and was independent of rider area of contact. The second was found to increase exponentially as the stress increased. The second also appeared to be a function of rider contact area. Wear equations for each mechanism were empirically derived from the experimental data. In general, friction coefficients increased with increasing rider contact area and with sliding duration. This was related to the build-up of thick rider transfer films.