Showing papers on "Contact area published in 1991"

The joint-contact area of the ankle. The contribution of the posterior malleolus.

Abstract: Eight ankles from fresh cadavera were tested under simulated clinical conditions to determine the effect of increasing the size of the posterior malleolar fracture on the contact area of the ankle joint and on the distribution of joint pressure. The surface area of contact decreased with increased size of the posterior malleolar fragment. However, the documented changes were smaller than expected on the basis of the findings of Ramsey and Hamilton; they reported a 42 per cent reduction in contact area with only a one-millimeter lateral shift of the talus, which clinically would be associated with a similar one-millimeter shift of the distal tibial fragment. In addition, clinical experience has shown a high rate of post-traumatic degenerative arthritis associated with an inadequately reduced one-half-size posterior fragment. There were considerable changes in the load-distribution patterns, with increased confluence and concentration of loads as the size of the fragment was increased. In plantar flexion, many specimens had three separate areas of contact between the tibia and the talus. With increased size of the posterior fragment, the three areas of contact always joined to become one. Similarly, for all positions of the ankle, increased size of the posterior fragment caused decreases in the contact area. The maximum loss of contact area was 35 per cent for specimens with one-half-size fractures that were tested in the neutral position.

Design Considerations for Cushion Form Bearings in Artificial Hip Joints

Abstract: Lubrication mechanisms and contact mechanics have been analysed in a new generation of ‘cushion form’ bearings for artificial hip joints, which comprise low elastic modulus layers on the articulating surfaces. Comparisons have been made with ‘ hard’ bearings used in existing prostheses and also with the natural hip joint. Lubricating film thicknesses are enhanced by larger contact areas and lower contact pressures. For a fixed contact area, simultaneous changes in layer thickness and radial clearance have been shown to have a small effect on elastohydrodynamic film thickness. Hard bearings designed with the same contact area as the cushion bearings produced a similar film thickness, but lubricant film thickness is not optimized in current designs. The main advantage of using a cushion bearing with low elastic modulus layers was found to be associated with microelastohydrodynamic lubrication. Careful selection of the elastic modulus is important in order to ensure that this lubrication regime was effective...

Nanomechanics and dynamics of tip–substrate interactions

Abstract: The consequences of tip–substrate interactions are investigated using large‐scale molecular dynamics simulations for a large (001) gold tip and a Ni(001) surface. The simulations reveal processes of adhesive contact formation upon approach of the tip to the substrate, tip elongation, and formation of an extended ordered neck upon retraction of the tip from contact, (111) reconstruction of the interfacial gold layers and the atomistic mechanisms of tip flattening and increase in contact area upon compression past the adhesive contact point. The hysteresis in the force versus tip to sample distance relationship, found upon approach and subsequent separation of the tip from the sample, is related to processes induced by adhesion and intermetallic bonding. The atomic‐scale mechanisms underlying the jump‐to‐contact phenomenon at small tip to surface separation (∼4.2 A) and of the inelastic processes and structural transformations involved in tip elongation, neck formation, and tip compression are discussed, and the results are compared to our earlier studies of a nickel tip interacting with a goldsurface.

Fractal Crushing of Ice and Brittle Solids

Abstract: A significant `scale effect' is observed when sea ice forces on structures are measured at field scale: the force per unit contact area is not independent of area, but decreases with increasing area Fragments of broken materials are found to have a fractal size distribution, with a fractal dimension close to 25 over a remarkably wide range of fragment size The research described in this paper brings these two observations together, and shows that they can be explained by a simple model of crushing, which incorporates the relation between fragment size and splitting force predicted by linear elastic fracture mechanics The model indicates a special role for the fractal dimension of 25, and predicts a relation between force and area, consistent with field observations

Normal Vibrations and Friction Under Harmonic Loads: Part II—Rough Planar Contacts

Abstract: Nonlinear normal contact vibrations, excited by the application of a dynamic normal load to the contact region formed between rough surfaces, are studied using the method of multiple scales. The planar rough surface is described by the Greenwood and Williamson model. The contact region behaves as a nonlinear spring in parallel with a viscous damper, and supports a rigid mass. It is shown that the average contact separation in the presence of dynamic loading is greater than the static separation under the same average load. In contrast to some previous results, this increase in average separation does not result in a significant change in the average friction force.

Numerical simulation of friction between contacting rough surfaces

Abstract: A model for predicting the friction of contacting rough surfaces is presented. Numerical simulation techniques are used to generate randomly rough surfaces with Gaussian statistics, An elastic Hertzian analysis is then used to calculate the contact of each generated surface with a rigid, perfectly smooth, half plane of specified applied load. The number, location and size of the contact points are determined. Contact is also calculated according to simple plasticity theory, and the authors show how the results from the elastic analysis tend to the plasticity results, as surface roughness increases. For each calculated contact profile, the friction coefficient for that contact is calculated, using two method, one 'microscopic' and one 'macroscopic'. For the microscopic method he calculates the adhesive force required to break each junction, and sum these to produce the total frictional force. This assumes that each contact point must be broken simultaneously, and is likely to overestimate the frictional force for a large number of contact points. In the macroscopic approach the total frictional force is related to the total true contact area, but does not take account of the details of each individual contacting junction. He presents results from the models, showing the effects of applied load, and of surface and material properties, on quantities such as the total contact area, mean contact pressure and mean surface separation, and hence on frictional force. The numerical approach allows one to study the typical variations in friction that might reasonably be expected to arise from the statistical nature of the surface contact. He finds that these variations are generally smaller than those measured in a typical friction experiment. Model predictions are compared with experimental measurements of the friction of MoS2 coated substrates. The macroscopic model is shown to predict the variation of friction with roughness, whereas the microscopic model performs better when studying the effect of applied load on friction. In both cases, agreement is better for the metallic substrates than for the ceramic substrate. Reasons for these results, and possible extensions of the model, are discussed.

Corrugated storage contact capacitor and method for forming a corrugated storage contact capacitor

Abstract: A dynamic random access memory (DRAM) cell having a corrugated storage contact capacitor for enhancing capacitance. A noncritical alignment is effected between the substrate contact area and the lower capacitor plate by using an etch stop layer to protect wordlines, field-effect transistors (FETs), and field oxide regions during the patterning and etching of storage capacitor regions. The corrugated storage contact capacitor is fabricated by depositing alternating layers of dielectric materials having either substantially different etch rates or wet etch selectivity one toward the other. The layers are isotropically etched and a cavity having corrugated sidewalls is provided. A doped poly layer is deposited to function as the storage-node capacitor plate. The deposition of a dielectric layer is followed by an insitu-doped poly layer deposited to form the upper capacitor plate. The capacitor thus formed is typified as having the storage-node capacitor plate self-aligned to the contact area of the substrate.

Friction-Heating Maps and Their Applications

Abstract: Friction is often a nuisance, but it can be useful too. Brakes, clutches, and tires rely on it, of course, though the inevitable fractional heat remains a problem. Other applications use frictional heat: friction cutting and welding, skiing, skating, and curling. The damage to magnetic disks caused by head-disk contact and the striking of matches are also examples.This article illustrates a framework where the thermal aspects of friction can be analyzed in an informative way. It uses a unified approach to the calculation of flash and bulk heating, and a helpful diagram—the frictional temperature map—to display the results. The method is approximate, but the approximations have been carefully chosen and calibrated to give precision adequate to most tasks, and the gain in simplicity is great.The symbols used in this article are defined in Table I.When two contacting solids 1 and 2, pressed together by a normal force F, slide at a relative velocity ν and with coefficient of friction u, heat is generated at the surface where they meet. The heat generated, q, per unit of nominal contact area, An, per second isThe heat flows into the two solids, partitioned between them in a way that depends on their geometry and thermal properties. Figure 1 shows one geometry commonly used for laboratory tests: the pin-on-disk configuration. The pin is identified by the subscript 1, the disk by subscript 2. Solid 1 can have properties which differ from those of solid 2.

An investigation of the Pd‐In‐Ge nonspiking Ohmic contact to n‐GaAs using transmission line measurement, Kelvin, and Cox and Strack structures

Abstract: The Pd‐In‐Ge nonspiking Ohmic contact to n‐GaAs has been investigated using the transmission line, the Kelvin, and the Cox and Strack structures. It has been found that a layered structure of Pd/In/Pd/n‐GaAs with 10–20 A of Ge imbedded in the Pd layer adjacent to the GaAs can lead to a hybrid contact. When the Ohmic formation temperature is above 550 °C, a layer of InxGa1−xAs doped with Ge is formed between the GaAs structure and the metallization. When the Ohmic formation temperature is below 550 °C, a regrown layer of GaAs also doped with Ge is formed at the metallization/GaAs interface. The contact resistivity of 2–3×10−7 Ω cm2 for this contact structure is nearly independent of the contact area from 900 to 0.2 μm2. Low‐temperature Ohmic characteristics and thermal stability are also examined.

Friction of diamond on diamond and chemical vapour deposition diamond coatings

Abstract: In this work the friction of diamond on diamond in air was studied in an attempt to understand the friction mechanisms. The friction of diamond on chemical vapour deposition (CVD) diamond coatings was also investigated. A reciprocating friction apparatus with a sliding configuration of a stylus on a plate, which enabled the contact area and pressure to be estimated from Hertz theory, was used. The effects of temperature, the number of sliding traversals and the environmental conditions were investigated. It was found that adhesion is important in the friction process of diamond sliding on diamond in air, and that water plays an important role in reducing the adhesion. In the case of the friction of diamond on CVD diamond coatings, relatively low loads were used because of the poor adhesion between the diamond coatings and the substrates (silicon). The friction coefficient of diamond sliding on CVD diamond coating was higher than that of diamond on diamond for the same experimental conditions. It is suggested that this is due to the rougher surface compared with that of a polished diamond. However, the friction coefficient could be substantially reduced by applying water, indicating that adhesion was also present in the friction process.

A Simple, Versatile Miniaturized Disk-Bend Test Apparatus for Quantitative Yield-Stress Measurements

Abstract: A miniaturized disk-bend test (MDBT) apparatus for testing specimens 3 mm in diameter and a range of thicknesses is described. It incorporates several features not generally found in previous designs, including direct measurement of specimen displacement, noncritical alignment, and the flexibility to conduct tests on clamped or undamped samples. The test is similar to a microbulge test in that the load is applied through a ball bearing 1 mm in diameter. Displacement of the center of the specimen is measured using a linear variable differential transformer (LVDT), the core of which is attached to a rod maintained in contact with the specimen through the use of a weak spring. Results on four materials are presented, with sample thicknesses ranging from 25 to 250 μm: annealed OFHC copper, fine-grained Ni3Al, irradiated and unirradiated Zr3Al, and an amorphous Fe78Si9B13 alloy ribbon. A simple procedure for measuring the contact area at yielding between the ball bearing and the specimen is described. It enables accurate values of the yield stress to be calculated from equations for the elastic deformation of clamped specimens; previously, measurements of the yield stress from the MDBT relied on a finite element model. The accuracy was confirmed by tests on fine-grained specimens of Ni3Al which were cut from the grip sections of previously tested tensile samples. The effects of varying the clamping force on the load-displacement curves are described, and the sensitivity of the apparatus to near-surface microstructural effects is demonstrated by comparison of the results on two of the materials tested: Zr3Al, the irradiated samples of which are affected microstructurally only within 2 μm from the surface, and Fe78Si9B13, in which the loads at fracture depend on which surface of the ribbon experiences tensile loading during the test.

Conductive fine-grain, electrode connection structural body and manufacture thereof

Abstract: PURPOSE:To provide conductive fine-grains having improved reliability in the connection with electrodes and reducing the contact resistance CONSTITUTION:A conductive fine-grain 9 consists of a base fine-grain 3, an inside metal layer 2, of which melting point is not less than 900 degC, provided on the surface of the fine-grain 3, and an outside metal layer, of which melting point is not more than 350 degC, provided on the outside of the inside metal layer 2 When each conductive fine-grain 9 is arranged and heated between each pair of electrodes 4, 5 opposite to each other, the outside metal layer of each conductive fine-grain 9 is fused and stuck to the electrodes 4, 5 By this sticking, a contact area between the electrodes 4, 5 and each conductive fine-grain 9 is increased On the other hand, since the inside metal layer 2 is on the surface of the base fine-grain 3, connection reliability between each conductive fine-grain 9 and the electrodes 4, 5 is improved and a contact resistance is also reduced

Method and apparatus for video imaging of tire ground contact patch

Abstract: A method and apparatus for video imaging of a tire ground contact patch or tire footprint is presented. A digitized image of the footprint is generated as an array of pixels. Each pixel is attributed a binary value of one or zero, to present a two-valued image. Contact areas within the image are attributed a first value, while void or noncontact areas are attributed a second value. The image is then dilated and eroded in an appropriate sequence to eliminate all white pixels from the image and to eliminate surface anomalies or the like which are not of interest in the tire analysis. An image of the footprint, accurate in size and dimensions, is thereby generated and, from such footprint, total area, contact area, and void area can be determined, as well as measurements of width, center line length, and other desired lengths at various lateral width locations. This data may be used to analyze the tire construction, operation, noise generation, and performance.

Measurements of friction in cold flat rolling

Abstract: The effect of reduction, rolling speed and material properties on the variation of interfacial frictional and normal stresses in the roll gap during cold flat rolling is studied. The results confirm the conclusions of earlier research, emphasizing the dependence of the coefficient of friction, and hence the interfacial shear stress, on the process parameters. Preliminary experiments, using mineral oil with 1% oleic acid as lubricant, show the possible existence of hydrodynamic lubrication, at least over part of the contact area. The validity of the data is substantiated by comparing the roll separating forces, measured by transducers located under the bottom workroll, to those obtained by integrating the measured roll pressure distribution over the arc of contact. The comparison is found to be favorable, indicating that in spite of its shortcomings, the embedded pin technique gives reliable measurements. An empirical relationship, giving the average coefficient of friction in terms of density, real contact area, rolling speed, and normal load, is developed.

Dynamic shear rheometer and method

Abstract: An improvement in a rheometer and the method for measuring rheological properties of a viscoelastic test specimen at different temperatures, at which different temperatures the viscoelastic properties exhibit a relatively wide difference, wherein the test specimen is placed between and is coupled with opposed plates, one of the opposed plates is oscillated angularly relative the other of the opposed plates, and the angular displacement of one of the plates relative to the other of the plates and the torque associated with the relative angular displacement are measured within a predetermined optimum range of torque and angular displacement for determining the rheological properties, couples a first contact surface on one of the opposed plates with the test specimen to establish a first contact area between the one of the opposed plates and the test specimen when the test specimen is at one of the different temperatures, and couples a second contact surface on the one of the opposed plates with the test specimen to establish a second contact area between the one of the opposed plates and the test specimen when the test specimen is at another of the different temperatures, the first contact area being different in area from the second contact area such that, by virtue of the difference in area between the first and second contact areas, the torque and the relative angular displacement measured at each of the one and the another of the different temperatures fall within the predetermined optimum range.

A new technique for measuring contact areas in human joints--the '3S technique'.

Abstract: The need for estimating average stresses acting in human joints has prompted the measurement of contact areas. Various existing methods predict contact areas much larger than the actual ones occurring in vivo. This discrepancy is due to the inevitable flow of the interstitial water of articular cartilage in the form of creep deformation. Some of the tests are also too complicated and time consuming for them to be suitable for tests where a large body of data are to be collected. In this report, the authors present a new technique of indicating contact areas occurring in human synovial joints. The new technique employs silicone oil-carbon black powder suspension which is applied to one of the contact surfaces. The suspension is squeezed out of the contact area on applying the load leaving the contact area clearly indicated and possible to record photographically. This Silicone oil-carbon black powder Suspension Squeeze technique (the ‘3S technique’ in short) has been validated and compared with another tec...

Patterning of epitaxial YBa2Cu3Ox insulator multilayers with a high‐temperature‐resistant lift‐off mask

Abstract: A new process for patterning of YBa2Cu3Ox‐insulator multilayers is described, using a high‐temperature‐resistant CaO process mask, which can be evaporated directly onto previously patterned YBa2Cu3Ox layers and removed after film deposition A crossover contact of two 3 μm wide and 30 μm long YBa2Cu3Ox striplines has been fabricated by laser deposition, using this patterning technique The upper and the lower stripline of the crossover contact show Tc values of ≊89 K and a critical current density jc (77 K) of 2 and 4×106 A/cm2, respectively The contact between the upper and the lower stripline is superconducting below 87 K At 100 K, the normal conducting contact resistivity is 5×10−8 Ω cm2, based on a contact area of 3×3 μm

Self-retaining contact assembly

Abstract: An electrical contact assembly (10) comprises a housing having a bottom portion (26) and a top portion (24), the top portion having a first inverted wall section (29) and a second inverted wall section (28), the housing having at least one aperture (31 and 32), the aperture extending from the bottom of the first inverted wall section to the bottom of the second inverted wall section. The assembly further comprises a substrate (20) within the housing having at least one contact area (22), and a contact finger (11) for placement in the housing aperture, the contact finger having at least a first portion (12), a second portion (14) and a third portion (16). The first portion protrudes below the aperture and contacts the contact area (22) on the substrate. The second portion (14) clips on to opposing walls of the second inverted wall (28) and the third portion (16) protrudes from the aperture (31) forming an external contact area.