Showing papers on "Contact area published in 1986"

The effect of conformity, thickness, and material on stresses in ultra-high molecular weight components for total joint replacement.

Abstract: Debris resulting from damage to the surface of polyethylene components of total joint replacements has previously been shown to contribute to long-term problems such as loosening and infection. Surface damage has been associated with fatigue processes due to stresses arising from contact between the metal and polyethylene components in these prostheses. In the present study, we used elasticity and finite-element solutions to determine these stresses for total hip replacements with head diameters of twenty-two and twenty-eight millimeters and for a condylar total knee replacement. We also examined the effect on these stresses of using carbon-fiber-reinforced polyethylene instead of plain polyethylene. Stresses associated with surface damage in the tibial component of the total knee replacement were much larger than those in the hip replacements. The analysis of contact stress as a function of thickness of the polyethylene insert for tibial components showed that a thickness of more than eight to ten millimeters should be maintained when possible. The contact stress in the tibial components was reduced most when the articulating surfaces were more conforming in the medial-lateral direction. Contact stresses were much less sensitive to changes in geometry in the anterior-posterior direction. For the hip components, the stresses were lower in the acetabular component of the twenty-eight-millimeter hip replacement than in the twenty-two-millimeter replacement. The use of carbon-fiber-reinforced polyethylene resulted in stresses that were higher by as much as 40 per cent. Because the contact area between articulating surfaces moves during flexion, portions of the surface will be subjected to cyclic stresses. The contact area for the knee replacements in flexion was smaller than for the hip replacements, and the range of the maximum principal stress was larger. Consequently, the combination of the higher stress and the moving contact area is more likely to cause surface damage due to fatigue in tibial components than in acetabular components, which is consistent with clinical observations.

Friction, stability and the design of robotic finger

Abstract: For practical reasons, compliant materials are often used on the gripping surfaces of robotic hands. Such materials are not well described by the Coulomb friction law or by simple point-contact or line-contact kinematics. In this paper, a shearing model is used to describe the contact friction. Models ofpointed, curved, flat, soft, and soft-curved fingertips are then developed and compared in terms of their contribu tion to the stiffness and stability of a simple grasp. There is a spectrum of contact conditions defined by the fingertip radius and contact area relative to the object size. This spectrum provides insights for designing and controlling robotic fingers.

Rubber friction variation with rate and temperature: some new observations

Abstract: Friction measurements are reported for the sliding of rubber over individual glass lenses, wavy-surface glass and abrasive paper. Two different apparatuses were employed to obtain friction data. All the experiments were made with the same vulcanised rubber compound moulded with smooth test surfaces to facilitate contact area observations. The measurements covered large ranges of sliding speed (0.001 to 10 mm s-1), ambient temperature (-60 to +90 degrees C), normal load (0.01-57 N) and contact geometry (R=1-18 mm). Some results are given as a function of the sliding velocity by use of the WLF transform. It was found that, particularly for smooth surfaces, the friction varied only slightly with rate (WLF parameter). For the test arrangements employed the viscoelastic response of the rubber compound appeared to be of less importance than the geometry of contact, except when operating conditions were near to the glassy region of the rubber. A simple plot of friction coefficient as a function of the Hertz contact area brought together all the diverse measurements. In the course of experimentation the influence of the method of surface cleaning upon friction was investigated. New insight was also obtained concerning the nature and magnitude of the static friction of rubber.

Computer simulation for the conductance of a contact interface. II

Abstract: With the remarkable increase in the performance of computers, techniques of computer simulation are widely applied. A computer simulation based on the finite element method and Monte Carlo method is applied to the problem of contact, and the conductance of a global model for contact is studied. The model consists of two unit cubes and a random interface between the cubes. More specifically, the two identical uniform conducting cubes are in contact across a pair of adjacent faces through a layer of thickness 2d subdivided into N x N small subsquares of which a randomly selected area fraction f has the same conductivity as the cubes (a clean-contact state), while the remaining area.fraction (1 - f) represents zero conductivity. The conductance of this global model for contact is computed and compared with previously published results. Particularly, when N, d, and f are changed, the behavior of the global conductance is investigated and discussed. It is clearly shown that because of extreme current concentration through the contact area the conductance does not decrease until f becomes close to zero.

Electrical conductivity of brine-saturated fractured rock

Abstract: A theoretical analysis shows that electrical conductivity along fractures in a saturated porous rock is a function of many factors: fluid and rock conductivities, initial fracture aperture and contact area, fracture surface geometry (asperity height distribution and tip curvature), elastic moduli of the rock, and confining pressure or normal stress acting across the fracture. The conductivity in the fracture plane decreases approximately in proportion to log pressure, but the conductivity is influenced by the increased contact area, and hence flow‐path tortuosity, along the fracture surface at elevated pressures. Electrical conductivity in fractures is more affected by flow‐path tortuosity than is permeability. The dependence on pressure was tested using laboratory measurements of conductivity through split cores containing ground, saw‐cut surfaces in a variety of rocks under confining pressures to 200 MPa. The conductivity decreased approximately in proportion to log pressure (there was little effect of ...

Magnetic behaviors of elongated single‐domain particles by chain‐of‐spheres model

Abstract: We consider the chain of N spheres contacting each other with an area and study the change of the magnetic behaviors of this chain by the contact area. Critical field Hcri for the discontinuous jump of the magnetization and coercive force Hc by both the parallel rotation and fanning mechanisms, and uniaxial magnetic anisotropy constant Ku due to the shape of the chain are found to increase, reach the maximum value, and decrease with an increase in the contact area. The ratios of the maximum value to the value at the point contact for Hcri, Hc, and Ku are also found to increase with an increase in the number of the spheres.

Comparison between use of TiN-coated and uncoated high-speed steel and fine-grained cemented carbide tools in cutting of resulphurized 0·08 wt-%C free-cutting steel

Abstract: A free-cutting 0·08%C steel has been turned dry using uncoated fine–grained cemented carbide tools and both uncoated and TiN-coated (by chemical vapour deposition)T 42 high-speed steel tools. Temperature estimates from the high–speed steel tools show that coating reduces the maximum rake-face temperature by about 125 K over a range of cutting speeds, permitting higher cutting speeds to be used before the onset of cratering. The wear mechanisms and built-up-edge behaviour have been investigated in terms of the tool/chip interface temperature and the relative plasticity of MnS inclusions. Manganese sulphide seems to have a higher affinity for the TiN coating than for the uncoated tools, permitting easier interfacial shear, and reducing contact area and built-up-edge size. With coated tools a built-up cap of workpiece material forms over the cutting edge, protecting it from wear; as a result there is only a small initial improvement in surface finish, but since nose wear is reduced, surface finish is...

A finite element formulation of three-dimensional contact problems with slip and friction

Abstract: The paper describes a special finite element for three-dimensional, large displacement analysis of contact problems with slip and friction. This element may be used to model contact between several finite element bodies or contact between a finite element body and a flexible or rigid geometrical surface fixed in space or moving with time. The contact formulation is based on the concept of a spring-supported, moving disk that transfers normal contact forces and Coulomb friction forces. The contact surface has a finite, prescribed boundary. The contact element has been incorporated into the general-purpose, nonlinear, finite element program FENRIS. Three examples of its application are described in the paper.

Determination of contact parameters of interconnecting layers in VLSI circuits

Abstract: This paper presents a generalized electrical model of the interlayer contacts in integrated circuits and discusses various test structures capable of providing experimental data on the contacts. The techniques used for obtaining the specific contact resistance for the contacts and, where appropriate, the modification to conducting layer resistivities due to interactions Within the contact area are outlined. Using one of the techniques, experimental data on a polysilicon to single-crystal silicon contact is used as an example to obtain contact information. These results are discussed along with the experimental limitations applicable to the various techniques.

Semiconductor device in which electrodes are formed in a self-aligned manner

Abstract: A bipolar transistor capable of operating at high speeds In a bipolar transistor designed for operation at high speeds, a polycrystalline silicon layer used as a base electrode effects is a contact area with respect to the base region which lacks precision or tends to increase Further, when the transistor is formed in a small size, the ratio of the contact area with respect to the polycrystalline area increases, making it difficult to increase the operation speed In order to reduce the contact area of the polycrystalline silicon layer, this invention deals with the structure in which the polycrystalline silicon layer is brought into contact with a portion near the edge of the convex semiconductor layer maintaining a small size and a high precision

An Analytical and Experimental Study of Post-Arc Phenomena in Vacuum

Abstract: The post-arc behavior of rapidly commutated (1.2 kA/?s) diffuse vacuum arcs has been studied both experimentally and analytically. Three interrupters were tested in a synthetic test circuit which allowed independent variation of current prior to commutation and dI/dt at, and dV/dt following, current zero. The interrupters differed in contact material, effective contact area, and contact spacing. An analytical model for sheath growth has been developed which takes into account current variations during the ion flight time. The model predictions agree well with experimental results.

A Virtual Work Principle Using Penalty Function Method for Impact Contact Problems of Two Bodies

Abstract: This paper presents that an impact contact force can be expressed as a product series of penalty functions and subsidiary contact conditions on a contact area between two bodies. Using the expression of the impact force, all the subsidiary conditions are included in a virtual work principle for two bodies, and penalty function method can be transformed from the method of a least square into that of a virtual work. This paper also describes a virtual work principle using penalty functions for various impact contact states of two bodies. A two-dimensional response for longitudinal elastic impact of two uniform rods is calculated using a finite element method (FEM) based on this principle, in order to examine the validity of the impact force. The mean value of the impact force by the FEM agrees with the value from the one-dimensional theory of propagation of elastic stress wave.

TRIBOS: A Performance Evaluation Tool for Traction-Transmitting Partial EHD Contacts

Abstract: The details are given of a computer model for performing a state-of-the-art tribological assessment of the performance of a lubricated concentrated rolling/sliding/spinning/contact comprising general anisotropic rough surfaces. The name chosen for this program is TRIBOS. It computes: 1. The contact ellipse dimensions and area 2. The elastohydrodynamic (EHD) film thickness both at the plateau and at the constriction that forms at the rear of a lubricated concentrated contact under fully flooded (un-starved) and isothermal lubricant inlet conditions 3. The apportionment of the applied load between the asperities and the lubricant film 4. The magnitude and direction of the tractive force transmitted between the contacting bodies by the combined effects of (a) shearing of the fluid film and (b) coulomb friction between contacting asperities 5. The mean number of asperity contacts and the real contact area, i.e. the total contact area of the elastically deformed asperities 6. A film thickness correction factor...

Film-mounted circuit and method for fabricating the same

Abstract: A film-mounted circuit includes a support film, metallic conductor runs formed of solderable material disposed on the support film, the conductor runs each having two ends, a contact area containing solder material electroplated on one of the ends and external terminal contacts containing solder material electroplated on the other of the ends for receiving a solder connection to external wiring, and a metallic semiconductor chip having hump-like terminal contacts each having a side with a surface area soldered to a respective one of the contact areas, the terminal contacts being formed of solderable material at least at the surface area thereof, the solderable material of the surface area of the terminal contacts forming an alloy together with the solder material of the contact areas deposited by electroplating during soldering, the alloy having an alloy ratio defined by a eutectic point, the melting point temperature of which is at least 20° C. above the melting point temperature of the solder material of the external terminal contacts but below a temperature at which the semiconductor chip is thermally damaged by the soldering, and a method of fabricating the same.

Dynamic photoelastic investigation of wave propagation and energy transfer across contacts

Abstract: This paper deals with the dynamic contact of an explosively excited disc with another disc or a half-plane. Dynamic photoelastic recordings show the development of the time-dependent contact area and the formation of the highly complex diffraction pattern.

On contact problems of elasticity theory

Abstract: Certain contact problems are reviewed in the two-dimensional theory of elasticity when round bodies touch without friction along most of the boundary and, therefore, Herz' hypothesis on the smallness of the contact area cannot be used. Fundamental equations were derived coinciding externally with the equation in the theory of a finite-span wing with unkown parameter. These equations are solved using Multhopp's well-known technique, and numerical calculations are performed in specific examples.

Axisymmetric contact problem for a frictionless elastic layer indented by an elastic cylinder

Abstract: This paper is concerned with the elastostatic contact problem of a semi-infinite cylinder compressed against a layer lying on a rigid foundation. It is assumed that all the contacting surfaces are frictionless and that only compressive normal tractions can be transmitted through the interfaces. Upon loading the contact along the layer-foundation interface shrinks to a circular area whose radius is unknown. The analysis leads to a system of singular integral equations of the second kind. The integral equations are solved numerically and the contact pressures, extent of the contact area between the layer and the foundation, and the stress intensity factor round the edge of the cylinder are calculated for various material pairs.

Drilling machine comprising a pressure foot with a contact pad

Abstract: In a drilling machine, a pressure foot is provided with a central bore (62) fractionally larger in diameter than the diameter of a drill bit which passes through the pressure foot to reach a workpiece during a drilling operation The pressure foot includes a contact pad (54) coaxial with the bore and includes a rim (58) surrounding an exit of the bore to form a contacting surface which abuts the surface of a workpiece being drilled Thereby, the contacting area is minimized and the outermost dimension of the contacting area is minimized so as to permit the contact pad to establish a reference plane for gauging the depth of a drilled hole substantially without influence of irregularities in the surface of the workpiece, particularly irregularities at a distance from the drilling site An elongated chamber (64) is formed in a sidewall of the bore to serve as a duct for guiding vacuum drawing air past the contact area to remove debris for further precision in the drilling operation

Study of Adherence of Elastomers by Cyclic Unloading Experiments

Abstract: We have studied the time evolution of the contact area between a spherical punch and a half-space elastomer sample by means of a cyclic push-on/pull-off test. The contact area edge is assumed to be a crack tip which propagates in the interface, moving backward and forward. It is shown that the equation of the kinetics of adherence, proposed in 1978 by Maugis and Barquins3 G - w = wo(aT v), linking the strain energy release rate G, the Dupre energy of adhesion w and the function o characteristic of the viscoelastic material tested, is valid if w takes two particular values. The first, w 1 depends on the initial contact time, the second, w 2 w 1, depends on the compression time. These values are calculated theoretically according to Johnson et al. 2 by measuring the contact area radius. Thanks to this kinetic law, we can predict the number of cycles needed for separating the materials in contact. Moreover, it stresses the fact that the rupture does not occur if the application time of the tensile f...

Computation and analysis of texture-induced contact information in tire-pavement interaction

Abstract: In tire-pavement interaction, road surface texture is an important parameter that influences many factors such as tire noise, skid resistance, vehicle performance, and rolling resistance. Efforts to understand and quantify the texture effects in tire-pavement interaction have been limited because of the difficulties in experimentally and theoretically determining the many individual contact areas and contact pressures produced by irregularly shaped asperities indenting the tire tread. A numerical method is developed and incorporated into a computational algorithm to approximate contact pressure resulting directly from road surface texture in tire-pavement interaction. Only 2-D road surface profile geometry and tire inflation pressure are required as input parameters. The purpose of this paper is to demonstrate application of the method. Several types of surface textures are analyzed using the contact approximation method. The road surfaces are characterized by analyzing the individual pressure distributions, contact lengths, and tire deformations that make up the pressure profiles. The contact length information is combined with the surface profile geometry to approximate the geometry of the deformed tire surface. Analysis of the deformed tire geometry provides information concerning factors such as void area and depth of penetration. Two-dimensional pressure profiles associated with the 2-D surface texture profiles are computed and transformed into force time-histories of tire input excitation.