Showing papers on "Contact area published in 1994"

Direct observation of frictional contacts: New insights for state-dependent properties

Abstract: Rocks and many other materials display a rather complicated, but characteristic, dependence of friction on sliding history. These effects are well-described by empirical rate- and state-dependent constitutive formulations which have been utilized for analysis of fault slip and earthquake processes. We present a procedure for direct quantitative microscopic observation of frictional contacts during slip. The observations reveal that frictional state dependence represents an increase of contact area with contact age. Transient changes of sliding resistance correlate with changes in contact area and arise from shifts of contact population age. Displacement-dependent replacement of contact populations is shown to cause the diagnostic evolution of friction over a characteristic sliding distance that occurs whenever slip begins or sliding conditions change.

Deformation and fracture of mica-containing glass-ceramics in Hertzian contacts

Abstract: The Hertzian indentation response of a machinable mica-containing glass-ceramic is studied. Relative to the highly brittle base glass from which it is formed, the glass-ceramic shows evidence of considerable “ductility” in its indentation stress-strain response. Section views through the indentation sites reveal a transition from classical cone fracture outside the contact area in the base glass to accumulated subsurface deformation-microfracture in the glass-ceramic. The deformation is attributed to shear-driven sliding at the weak interfaces between the mica flakes and glass matrix. Extensile microcracks initiate at the shear-fault interfaces and propagate into the matrix, ultimately coalescing with neighbors at adjacent mica flakes to effect easy material removal. The faults are subject to strong compressive stresses in the Hertzian field, suggesting that frictional tractions are an important element in the micromechanics. Bend-test measurements on indented specimens show that the glass-ceramic, although weaker than its base glass counterpart, has superior resistance to strength degradation at high contact loads. Implications of the results in relation to microstructural design of glass-ceramics for optimal toughness, strength, and wear and fatigue properties are discussed.

A Comprehensive Study of Pressure Distribution in the Ankle Joint with Inversion and Eversion

Abstract: The understanding of load transfer characteristics is the baseline for biomechanics of the ankle joint. Changes in contact patterns of the articular cartilage from the norm may indicate pathologic conditions. Measurement of the contact in human cadaver ankles provides a direct measurement for this understanding. The force transfer characteristics of the three facets of the ankle joint were investigated. Five fresh-frozen cadaver lower extremities were tested in 12 positions under three axial loads of 490, 686, and 980 N. Fuji film served as the pressure transducer and the prints were analyzed by a computerized video digitizer. The results demonstrated that as the foot was moved into inversion or eversion with the ankle in neutral flexion or dorsiflexion, there was a decrease in total contact area and an increase in the average high pressure. In plantarflexion, the contact area was lower and the average high pressure was higher, indicating a greater force per unit area as compared with dorsiflexion and neutral flexion. In plantarflexion, however, little change was noted with inversion or eversion. In dorsiflexion, the total contact area was higher and the average high pressure slightly lower as compared with neutral flexion. With inversion, the contact area of the medial facet of the ankle increased and with eversion it increased on the lateral facet, especially in dorsiflexion. With an increase in loading, the pressure did not significantly increase but the contact area did increase. The centroid of the contact moved anteriorly to posteriorly on the talus as the joint moved from dorsiflexion to plantar-flexion.(ABSTRACT TRUNCATED AT 250 WORDS)

Study of the self-adhesion hysteresis of a siloxane elastomer using the JKR method

Abstract: The JKR method measures the adhesion between two spheres or a sphere and a plane surface, all materials being elastomers. We have used this technique to study the self-adhesion of a siloxane elastomer. Our results demonstrate that there is a large difference of behavior (hysteresis) between the loading and unloading regimes when the soluble fraction of the networks has been extracted. The unloading regime is then not described by the classical application of the JKR model. We believe that the work of adhesion measured during the unloading regime is not constant along the contact area but rather decreases from its center toward its edges. This behavior may be the signature of the JKR pressure profile (compressive in the center of the contact area and tensile near its edges) the sign and magnitude of which influence the formation of hydrogen bonds across the interface. A generalization of the JKR model that includes this feature is proposed and gives a good description of the experimental data.

A comparison of contact pressures in tibial and patellar total knee components before and after service in vivo

Abstract: Laboratory testing of total knee components indicates that many designs produce contact stresses that exceed the yield strength of ultra-high molecular weight polyethylenes (UHMWPEs). It is often assumed that the polyethylene component will creep and wear to become more conforming over time, thus reducing these stresses. To test this theory, retrieved polyethylene tibial and patellar components, which showed signs of increased contact area through in vivo deformation, were tested for contact stress against matching components using Fuji Prescale pressure-sensitive film. The results showed an inverse relationship between initial conformity and in vivo changes in contact stress

Method for forming a temporary attachment between a semiconductor die and a substrate using a metal paste comprising spherical modules

Abstract: A nodular metal paste (42) is used to temporarily attach the bumps (34) on a semiconductor die (32) to a substrate (38). The spherical nodules (44) composing the metal paste are dispensed onto contact pads (40) on the substrate, and then heated until they partially melt. The partial liquid region permits bonding of the individual metal nodules to the contact pads and to adjacent nodules. Subsequently, a bumped die is placed over the nodules and heated to a minimum temperature required to partially remelt to form a local tack joint. Because the metallurgical contact area between the paste nodules and the bumps is minimized, electrical contact can be sustained with a small cross-sectional area of connected material to create an electrically sound but physically weak link between die and the substrate. Once connected to the substrate, the die may be tested and burned-in, and removed afterwards with little damage to the bumps.

A review of the friction of snow skis.

Abstract: Snow friction results from a mixture of processes. With little meltwater present, the surfaces are partially separated and, when too much water is present, the contact area increases and there may be capillary attachments. Slider thermal conductivity and even colour are very important. Heat is generated by friction and solar radiation absorbtion and is conducted away by both slider and ice particles. The remaining heat is available to generate meltwater which acts as a lubricant. While sliders must be designed for use over a narrow range of snow and weather conditions, polyethylene bases can be structured and waxed to broaden that range. The important processes operate not at the air temperature, but at the ski base temperature, which is highly dependent on such things as snow‐surface temperature, load and speed. The roughness elements and contact areas must be characterized before the basic processes can be understood further.

Method of forming contact areas between vertical conductors

Abstract: A method of forming a contact area between two vertical structures. A first layer of material conforming to an extending between vertical sidewalls is covered with a mask layer. The mask layer is patterned and etched to remove the horizontal region of the mask layer between the vertical sidewalls, thereby exposing the first layer of material at the desired location of the contact area, while retaining at least a portion of the vertical regions of the mask layer. Using the remaining vertical regions of the mask layer as etch mask, the exposed portions of the first layer are then etched away to form the contact area. Another aspect of the invention provides a method of making a DRAM that utilizes a capacitor insulating layer over the capacitor second conductor (or cell poly) to self-align the bit line contact to the capacitor second conductor. In accordance with this aspect of the invention, a capacitor is formed over a semiconductor wafer. The capacitor includes a first conductor, a dielectric layer on the first conductor and a second conductor on the dielectric layer. A capacitor insulating layer is formed on the second conductor. The capacitor insulating layer is patterned and etched to expose portions of the second conductor at the desired location of the bit line contact. Then, using the capacitor insulating layer as a hard mask, the exposed portions of the second conductor are etched away in the area in which the bit line contact will subsequently be formed.

An Analytical Approach to Elastic-Plastic Stress Analysis of Rolling Contact

Abstract: Based on a stress invariant hypothesis and a stress/strain relaxation procedure, an analytical approach is forwarded for approximate determination of residual stresses and strain accumulation in elastic-plastic stress analysis of rolling contact. For line rolling contact problems, the proposed method produces residual stress distributions in favorable agreement with the existing finite element findings. It constitutes a significant improvement over the Merwin-Johnson and the McDowell-Moyar methods established earlier. The proposed approach is employed to study combined rolling and sliding for selected materials, with special attention devoted to 1070 steel behavior. Normal load determines the subsurface residual stresses and the size of the subsurface plastic zone. On the other hand, the influence of tangential force penetrates to a depth of 0.3a, where a is the half width of the contact area, and has diminishing influence on the residual stresses beyond this thin layer. A two-surface plasticity model, commensurate with nonlinear kinematic hardening, is utilized in solution of incremental surface displacements with repeated rolling. It is demonstrated that a driven wheel undergoes greater plastic deformation than the driving wheel, suggesting that the driven wheel experiences enhanced fatigue damage. Furthermore, the calculated residual stresses are compared with the existing experimental data from the literature with exceptional agreements.

Scaling of Rock Friction Constitutive Parameters: The Effects of Surface Roughness and Cumulative Offset on Friction of Gabbro

Abstract: We describe experiments in which large (14×40 cm nominal contact area) blocks of gabbro were sheared in a direct shear apparatus at room temperature, 5 MPa normal stress, and slip velocities from 0.1 to 10 μm/s. The apparatus was servocontrolled using a displacement feedback measurement made directly between the gabbro blocks. Two surface roughnesses were studied (rough, produced by sandblasting, and smooth, produced by lapping with #60 grit) and accumulated displacements reached 60 mm. Measurements of surface topography were used to characterize roughness and asperity dimensions. Step changes in loading velocity were used to interrogate friction constitutive properties. Both rough and smooth surfaces showed appreciable displacement hardening. The coefficient of friction μ for rough surfaces was about 0.45 for initial slip and 0.7 after sliding 50 mm. Smooth surfaces exhibited higher μ and a greater tendency for unstable slip. The velocity dependence of frictiona−b and the characteristic friction distanceD c show systematic variations with accumulated displacement. For rough surfacesa−b started out positive and became negative after about 50 mm displacement andD c increased from 1 to 4 μm over the same interval. For smooth surfaces,a−b began negative and decreased slightly with displacement andD c was about 2 μm, independent of displacement. For displacements <30 mm, rough surfaces exhibit a second state variable with characteristic distance about 20 μm. The decrease ina−b with displacement is associated with disappearance of the second state variable. Our data indicate thatD c is controlled by surface roughness in a complex way, including but not limited to the effect of roughness on contact junction dimensions for bare rock surfaces. The data show that simple descriptions of roughness, such as rms and peak-to-trough, are not sufficient to inferD c . Our observations are consistent with a model in whichD c scales with gouge thickness.

The adhesion-induced deformation and the removal of submicrometer particles

Abstract: Adhesion-induced deformations of submicrometer polystyrene particles on silicon substrates were observed as a function of time using scanning electron microscopy. The contact area between the particle and the substrate was found to increase with time for a period of approximately 72 hours before reaching a constant value. The ratio of the final contact radius to the particle radius was ~ 0.4. The time dependence of this deformation appears similar to the creep phenomenon in bulk polymers. These results are related to the studies of particle removal conducted for different time periods, using hydrodynamic and centrifugal removal forces. The removal efficiency was found to decrease with time. This correlates well with the increase in the adhesion force on the particles with time as observed from the SEM measurements. The effect of the particle diameter on the removal efficiency and the correlation between the time dependent adhesion-induced deformation and particle removal efficiency is discussed.

Contact Mechanics Using Boundary Elements

Abstract: Theoretical development in contact analysis numerical development in contact analysis contact and fracture mechanics analysis - contact mechanics fracture mechanics the boundary element method in elastostatics - governing equations of elasticity the boundary integral formulation of elasticity fundamental solutions the boundary integral equation numerical implementation of the boundary element method internal points application of BEM to contact problems - BEM solutions to contact problems load modelling strategy - methods of load application development of fully incremental leading technique further modelling considerations - choice of element type for the potential contact area the phenomenon of partial slip numerical examples - contact problems without cracks numerical examples - contact problems with cracks. (Part contents).

Micromechanics of the velocity and normal stress dependence of rock friction

Abstract: Among the second-order effects on friction the most important are those of variable normal stress and of slip velocity. Velocity weakening, which is usually considered the source of the stick-slip instability in rock friction, has been observed in velocity stepping experiments with Westerly granite. The friction change, Δμ, was −0.01 to −0.008 for a tenfold velocity increase. Using normal closure measurements, we observed dilation upon each increase in sliding rate. We also observed, for the first time, time-dependent closure between surfaces during static loading. The dilation that occurred during the velocity stepping experiment was found to be that expected from the static time-dependent closure phenomenon. This change in closure was used to predict friction change with an elastic contact model. The calculated friction change which results from a change in contact area and asperity interlocking, is in good agreement with the observed velocity dependence of steady-state friction. Variable normal stress during sliding has two effects, first in creating new partial slip contacts and locking some existing fully sliding contacts and second in increasing interlocking, for instance when normal load is suddenly increased. As a result, a transient change in friction occurs upon a sudden change in normal load.

Process of making a polysilicon barrier layer in a self-aligned contact module

Abstract: A method for forming a metal contact in a self aligned contact region over a impurity region in a substrate which comprises forming a doped polysilicon layer over the device surface except in a contact area A thin polysilicon barrier layer and a metal layer, preferably tungsten, are then formed over the polysilicon layer and the contact area The resulting metal contact has superior step coverage, lower resistivity, and maintains the shallow junction depth of buried impurity regions

Contact characteristics of the ankle joint. Part 1. The normal joint.

Abstract: The contact characteristics of ankle joints in 18 fresh cadaver specimens were studied by using pressure-sensitive film to provide baseline information for subsequent studies of various pathologic ankle conditions. Specimens, consisting of the distal half of the tibia and fibula and the intact ankle and foot, were mounted in a materials testing system on a loading frame that allowed positioning in neutral, and 20 degrees of plantarflexion and dorsiflexion. An 800 N load (1 body weight) was axially applied to the specimens through the tibia with 10% of the total load distributed through the fibula. Transducers made of pressure-sensitive film were used to make a contact print and were scanned along with calibration strips to form a digital image. The image was analyzed quantitatively to determine total contact area, mean contact pressure, ratio of contact to plafond areas, and high pressure zone centroid location as a function of sagittal plane foot position in the normal ankle joint. The results demonstrated significant changes in ankle joint contact characteristics with different foot positions.

Method of forming a transistor

Abstract: A method is provided for forming a transistor for a bipolar, CMOS, or bipolar CMOS integrated circuit. The method is applicable to forming a double polysilicon self-aligned bipolar transistor using a single masking step for defining the emitter structure with a narrow emitter-base contact area and a large emitter contact area. The method comprises selectively providing a tapered body of dielectric to mask a region of the substrate on which an emitter is to be formed. A conductive layer is provided around the tapered body to form base contact electrodes. The tapered body is selectively removed from the substrate without damaging the underlying silicon substrate, to leave a tapered opening; localized dielectric isolation is provided in the form of sidewall spacers on the first conductive layer. The tapered opening is filled with a layer of a second conductive material to form a second electrode i.e. an emitter structure. The resulting structure is fully planarized, preferably by chemical mechanical polishing, to form coplanar contact areas to the base and emitter.

A comparison of vibrotactile thresholds on the finger obtained with different equipment

Abstract: Vibrotactile thresholds on the finger have been compared using two alternative systems. One system prescribed the push force, the contact force, and the surround, while this was not defined for the other system. The experiment was performed with nine male subjects attending on three different days. It was found that the two systems yielded vibrotactile thresholds which were significantly different. The dependence of vibrotactile thresholds on the frequency of vibration, the area of contact with vibration, the conditions surrounding the contact area, the contact force, the push force, the finger temperature, and the distortion of waveform must be considered when quantifying vibrotactile thresholds.

Method for fabricating dynamic random access memory capacitor

Abstract: A method for fabricating a DRAM capacitor, including the steps of forming a double contact hole structure by utilizing an insulating spacer two times, filling only the lower portion of the contact hole, forming a pattern having an undercut portion from two insulating films exhibiting a superior wet etch rate difference, coating a conduction layer over the pattern to form an insulating spacer from a portion of the conduction layer disposed on the stepped pattern portion, and etching the resulting structure at its full surface using the insulating spacer as a mask to isolate a capacitor to be finally formed, whereby a capacitor electrode having a double rectangular frame shape is formed. With such a structure, the inner area of the contact hole can be used as a part of the capacitor, thereby enabling the surface area of capacitor to be increased. Since no separate mask is used for the etching step, it is possible to simplify the fabrication of DRAM capacitor. Furthermore, the fabricated DRAM capacitor has a reduced contact area and an increased surface area. This achieves an increase in capacitance and improvement in integration degree while reducing the topology.

Elastic behavior of contacting surfaces under normal loads: A computer simulation using three-dimensional surface topographies

Abstract: It is very important to understand the potential and limitation of the contact theories in order to apply them to geophysical problems. Using three-dimensional topographies, a computer simulation concerning the behavior of contacting surfaces under normal loads was performed to examine the contact models previously proposed. Two models, the Brown and Scholz (B&S model) and the Yamada et al. (Y model), were compared in detail. It is found that the Y model neglects the contacts between asperities and valleys or shoulders, which results in a smaller area of contact and smaller stiffness than with the B&S model. The contact area formed between asperities and shoulders or valleys is estimated at about 20% of the total contact area, a value that does not depend on either normal stress or surface roughness. The real area of contact is proportional to normal load even under purely elastic conditions, as originally proposed by Archard, and it is much smaller than 1% of the total area of contact up to the normal stress of 30 MPa. Average area of contact, contact density, mean contact pressure, and maximum contact pressure were also calculated as a function of normal stress, which revealed the detailed process of contact mechanics under normal loads.

Soap-Thickener Induced Local Pressure Fluctuations in a Grease-Lubricated Elastohydrodynamic Point Contact

Abstract: In several experimental investigations of grease-lubricated elastohydrodynamic (EHD) contacts indications of soap-thickener formations that enter the contact area have been reported, for example by...

Contact Area Effects on Discomfort

Abstract: Most “ergonomic” products attempt to adopt a uniform force distribution strategy to improve comfort. The rationale being that force distribution over a large area reduces pressure and thereby enhances user comfort. However, sensory literature alludes to the concept of spatial summation, i.e. greater sensation by stimulating a larger surface area. Hence spatial summation would tend to suggest a greater discomfort when forces are applied over large surface areas. This study reports the effect of surface area on maximum discomfort causing pressure or maximum pressure tolerance (MPT). Two circular probes of different cross sectional area were used to stimulate the skin surface. The mean MPT with a probe of 5mm diameter was 3.3 times higher than the MPT with a probe of 13mm diameter. These findings suggest the following:•Perceived discomfort and contact area seem to have a “U-relationship” above a critical force value. Traditional thinking of distributing forces is successful only in the first half of the U-cu...

Method of fabricating junction termination extension structure for high-voltage diode devices

Abstract: A method of fabricating high-voltage diode device on a silicon substrate which includes a first region and a second region is provided. The first and second regions having a first contact and a second contact area respectively. First, a first protective layer is formed on the first and second contact areas. A second protective layer is formed on the first protective layer and a portion of the first region adjacent to the first contact area. Next. Halogen ions are implanted into the first and second regions by using the second protective layer as a mask. The second protective layer is removed to expose unimplanted portion of the first region. Then, the first and second regions are oxidized to form a field oxide layer by using the first protective layer as a mask, wherein the unimplanted portion of the first region has a relatively lower oxidation rate and thereby a stepped part of the field oxide layer is formed over the first region. After removing the first protective layer, a first electrode plate is formed on the first contact area and the stepped part of the field oxide layer. A dielectric layer is formed overlying the first electrode plate and the field oxide layer. Finally, a second electrode plate is formed on the second contact area and the dielectric layer, completing the fabrication of high-voltage diode device.

Low insertion force mating electrical contact structure

Abstract: An electrical connector assembly (30) having a low insertion force, high normal force mating contact structure (10) comprising a male terminal (34) and a female terminal (20). The male terminal is an elongate conductor including a final contact area (36) joining a forwardly extending lead-in portion (38, 40). The female terminal includes dual-cantilever spring arms (24, 26) with mutually opposing contact portions (24b, 26b) which define a lead-in mouth therebetween. The contact portions of the female terminal are adapted to electrically engage the lead-in portion of the male terminal as the male terminal is inserted into the mouth between the contact portions of the female terminal. The lead-in portion of the male terminal is split and defines a pair of diverging beams (38, 40) extending forwardly and angled outwardly form the final contact area (36). The beams have inwardly facing, laterally offset, opposing camming portions (38b, 40b) adapted to engage and increasingly deflect the contact portions of the spring arms of the female terminal as the male terminal is moved from an initial position to a final position wherein the female contact portions are in engagement with the final contact area of the male terminal. The normal force between the contact portion of the spring arm and the corresponding camming portion gradually increases until the final mated position is achieved. The split male configuration allows for increased terminal mating length and adjustment of the wiping action of the contacts as desired.

Contacting system or reader for chip cards

Abstract: A flexible circuit board is used to provide the contact elements of a chip card reader. The contact area of the contact elements is obtained by deforming the flexible circuit board into cusps, with a contacting force being applied to the cusps by a single spring element. The flexible circuit board can be folded along a line which is either transverse or parallel to the card insertion direction in order to enable engagement of contact elements with both sides of the card.

Contact Angle Hysteresis on a Heterogeneous Surface: Solution in the Limit of a Weakly Distorted Contact Line

Abstract: In the case of a weakly distorted contact line, we construct a one-variable equation giving the metastable configurations of a fluid interface in contact with a heterogeneous solid surface. In this limit it is possible to study the contact angle hysteresis created by semi-concentrated assemblies of individual defects. The results exhibit many collective effects, some of which can be described by a convenient renormalization of the hysteresis threshold and of the defect density. They are consistent with available experimental data.

Ceramic coating system or water oxidation environments

Abstract: A process for water oxidation of combustible materials in which during at least a part of the oxidation corrosive material is present and makes contact with at least a portion of the apparatus over a contact area on the apparatus. At least a portion of the contact surface area comprises titanium dioxide coated onto a titanium metal substrate. Such ceramic composites have been found to be highly resistant to environments encountered in the process of supercritical water oxidation. Such environments typically contain greater than 50 mole percent water, together with oxygen, carbon dioxide, and a wide range of acids, bases, and salts. Pressures are typically about 27.5 to about 1000 bar while temperatures range as high as 700° C. The ceramic composites are also resistant to degradation mechanisms caused by thermal stresses.