Showing papers on "Contact area published in 2002"
TL;DR: In this paper, the effects of the substrate on the determination of mechanical properties of thin films by nanoindentation were examined, and the properties of aluminum and tungsten films on the following substrates: aluminum, glass, silicon and sapphire.
1,410 citations
TL;DR: In this article, the sliding behavior of water droplets over pillarlike and groove structures was investigated and a proper design of the surface with respect to shape and extent of the three-phase line is more effective than the increase of contact angles merely by decreasing the solid−water contact area.
Abstract: Hydrophobicity and sliding behavior of water droplets were investigated on various hydrophobic pillarlike and groove structures prepared on a silicon wafer by dicing and subsequently coating with fluoroalkylsilane. The dominant hydrophobicity mode was changed from Wenzel's mode to Cassie's mode at a smaller roughness than that expected from the calculation based on the sinusoidal surface by Johnson and Dettre. The effect of water intrusion on the microstructure due to droplet weight was revealed to be an important factor governing the water sliding angle on the surface. In a comparison of the sliding behavior of water droplets over pillarlike and groove structures, it was demonstrated that a proper design of the surface with respect to shape and extent of the three-phase line is more effective than the increase of contact angles merely by decreasing the solid−water contact area.
1,083 citations
TL;DR: An elastic-plastic finite element model for the frictionless contact of a deformable sphere pressed by a rigid flat is presented in this paper, which provides dimensionless expressions for the contact load, contact area and mean contact pressure, covering a large range of interference values from yielding inception to fully plastic regime of the spherical contact zone.
Abstract: An elastic-plastic finite element model for the frictionless contact of a deformable sphere pressed by a rigid flat is presented. The evolution of the elastic-plastic contact with increasing interference is analyzed revealing three distinct stages that range from fully elastic through elastic-plastic to fully plastic contact interface. The model provides dimensionless expressions for the contact load, contact area, and mean contact pressure, covering a large range of interference values from yielding inception to fully plastic regime of the spherical contact zone. Comparison with previous elastic-plastic models that were based on some arbitrary assumptions is made showing large differences. ©2002 ASME
867 citations
TL;DR: In this article, a criterion based on contact line density is proposed for predicting the conditions that produce ultrahydrophobic surfaces, where, above a critical value, drops are suspended by asperities.
Abstract: Very rough surfaces can suspend small water drops, prevent wetting, and cause contact angles to approach 180°. A criterion based on contact line density is proposed for predicting the conditions that produce these ultrahydrophobic surfaces, where, above a critical value, drops are suspended by asperities. Critical values of the contact line density can be calculated from contact angles, asperity shape, and information about the contact liquid, such as density and surface tension. The criterion was found to correctly predict suspension for several model surfaces prepared by lithography techniques. Apparent contact angles from suspended and collapsed drops also were modeled by accounting for rough edges and employing a linear average of contact angle along the perimeter of the drop, rather than an area average of cosine. This linear model suggests that, for suspended drops, both advancing and receding angles should increase. Alternatively, for drops that have collapsed over surface asperities, advancing con...
568 citations
TL;DR: Among the principal conclusions of the study are that accurate finite element solutions of tibio-femoral contact behavior can be obtained by treating the bones as rigid, however, unrealistic constraints on rotations other than flexion/extension can result in relatively large errors in contact variables.
Abstract: As a step towards developing a finite element model of the knee that can be used to study how the variables associated with a meniscal replacement affect tibio-femoral contact, the goals of this study were 1) to develop a geometrically accurate three-dimensional solid model of the knee joint with special attention given to the menisci and articular cartilage, 2) to determine to what extent bony deformations affect contact behavior, and 3) to determine whether constraining rotations other than flexion/extension affects the contact behavior of the joint during compressive loading. The model included both the cortical and trabecular bone of the femur and tibia, articular cartilage of the femoral condyles and tibial plateau, both the medial and lateral menisci with their horn attachments, the transverse ligament, the anterior cruciate ligament, and the medial collateral ligament. The solid models for the menisci and articular cartilage were created from surface scans provided by a noncontacting, laser-based, three-dimensional coordinate digitizing system with an root mean squared error (RMSE) of less than 8 microns. Solid models of both the tibia and femur were created from CT images, except for the most proximal surface of the tibia and most distal surface of the femur which were created with the three-dimensional coordinate digitizing system. The constitutive relation of the menisci treated the tissue as transversely isotropic and linearly elastic. Under the application of an 800 N compressive load at 0 degrees of flexion, six contact variables in each compartment (ie., medial and lateral) were computed including maximum pressure, mean pressure, contact area, total contact force, and coordinates of the center of pressure. Convergence of the finite element solution was studied using three mesh sizes ranging from an average element size of 5 mm by 5 mm to 1 mm by 1 mm. The solution was considered converged for an average element size of 2 mm by 2 mm. Using this mesh size, finite element solutions for rigid versus deformable bones indicated that none of the contact variables changed by more than 2% when the femur and tibia were treated as rigid. However, differences in contact variables as large as 19% occurred when rotations other than flexion/extension were constrained. The largest difference was in the maximum pressure. Among the principal conclusions of the study are that accurate finite element solutions of tibio-femoral contact behavior can be obtained by treating the bones as rigid. However, unrealistic constraints on rotations other than flexion/extension can result in relatively large errors in contact variables.
476 citations
TL;DR: In this paper, the impact of stamp deformation on the dimensional stability of the microcontact printing process is investigated. But the authors consider limitations imposed due to reversible deformation of a single stamp.
Abstract: Stamp deformation can affect the dimensional stability of the microcontact printing process. We consider limitations imposed due to reversible deformation of a single stamp. Detailed analyses of several modes of stamp deformation have been carried out. Stability criteria have been obtained for both vertical and lateral collapse of surface relief features, including buckling. The shape change of surface features imposed by surface tension has been analyzed, and the corresponding internal stresses are given in closed form. The residual stresses induced by chemical and thermal shrinkage when the elastomeric stamp is bonded to a stiff substrate are analyzed. In addition, the relation between applied load and displacement of a stamp supported by a stiff substrate is given in closed form. Contact stresses between the stamp and substrate have been analyzed both analytically and numerically by a finite element method. The role of adhesion in determining the contact area is clarified. The effect of surface roughne...
433 citations
TL;DR: There are two pure modes of evaporation of liquid drops on surfaces: (1) constant contact area and (2) at constant contact angle as discussed by the authors, which is the dominating mode for liquid drops.
Abstract: There are two pure modes of evaporation of liquid drops on surfaces: one at constant contact area and one at constant contact angle. Constant contact area mode is the dominating evaporation mode f...
336 citations
TL;DR: In this paper, the amplitude and phase of the cantilever vibration as well as the shift of the resonance frequencies contain information about local tip-sample contact stiffness and can be used as imaging quantities.
Abstract: In atomic force acoustic microscopy (AFAM) the cantilever of an atomic force microscope is vibrated at ultrasonic frequencies while a sample surface is scanned with the sensor tip contacting the sample. As a consequence, the amplitude and phase of the cantilever vibration as well as the shift of the cantilever resonance frequencies contain information about local tip-sample contact stiffness and can be used as imaging quantities. An appropriate theoretical description of the transfer of ultrasound in an atomic force microscope enables the measurement of the local mechanical material parameters of the sample surface by evaluating experimental cantilever vibration spectra. In the experiments presented here, we examine the sensitivity of the technique using silicon single crystals. Furthermore, we show that the ferroelectric domains of lead zirconate-titanate ceramics can be imaged by AFAM and that local elastic constants of the sample surface can be determined quantitatively. The lateral resolution of the technique is given by the contact area formed by the sensor tip and the sample surface, which can have a diameter of <10 nm.
227 citations
TL;DR: An important result is that even when the surface roughness is so high that no adhesion can be detected in a pull-off experiment, the area of real contact may still be several times larger than when the adhesion is neglected.
Abstract: I have developed a theory of adhesion between an elastic solid and a hard randomly rough substrate. The theory takes into account that partial contact may occur between the solids on all length scales. I present numerical results for the case where the substrate surface is self-affine fractal. When the fractal dimension is close to 2, complete contact typically occurs in the macro-asperity contact areas, while when the fractal dimension is larger than 2.5, the area of (apparent) contact decreases continuously when the magnification is increased. An important result is that even when the surface roughness is so high that no adhesion can be detected in a pull-off experiment, the area of real contact (when adhesion is included) may still be several times larger than when the adhesion is neglected. Since it is the area of real contact which determines the sliding friction force, the adhesion interaction may strongly affect the friction force even when no adhesion can be detected in a pull-off experiment.
211 citations
TL;DR: It was found that the model recently proposed by Rabinovich et al. closely predicts the pull-off forces for glass and lactose particles and the adhesion of the peptide material and polystyrene particle to polypropylene is underestimated by about an order of magnitude with the theoretical model, in which the interacting substrates are treated as rigid materials.
188 citations
Patent•
01 Apr 2002TL;DR: In this article, a hot spot is used as the hot spot of the computer, which is normally offset above the contact area, except when the touch area is close to the bottom of the screen.
Abstract: In one embodiment of the invention, a hot spot is normally centered in an area of contact between a user's finger and a touch screen to position the hot spot on an icon or other feature thereby selecting a program or function corresponding to the icon or feature. When the contact area is near an edge, the hot spot is offset toward the edge so that it coincides more closely to the center of the users finger, thus allowing an icon or other feature adjacent the edge of the screen to be more easily selected. In another embodiment, a cursor is displayed on a touch screen at a location that is offset from the contact area between a finger and the screen. The cursor, which is used as the hot spot of the computer, is normally offset above the contact area except when the contact area is close to the bottom of the screen. The cursor is then offset to the left or right of the contact area depending on whether the contact are is to the left or right of the screen, respectively, so that icons or features adjacent the left or right edges of the screen can be selected. Similarly, when the contact area is very close to the bottom of the screen, the cursor is offset downwardly and to the right or left so that icons or features adjacent the bottom edge of the screen can be selected. Alternatively, a touch sensitive area incapable of displaying an image may be provided beneath a display area of the touch screen to allow icons or features adjacent the bottom edge of the display area to be selected.
TL;DR: In this paper, a pin-on-disc configuration was employed for studying the formation and wear mechanism of tribo-oxides on sliding contact surfaces of some steels and three wear mechanisms were found from the micrographic results.
TL;DR: In this article, a study concerning the hardness and the Young's modulus results determined by Vickers indentation on different materials was performed, and two methods were proposed for performing the indentation geometrical calibration of the contact area; these are compared with a former method proposed by Oliver and Pharr (OP).
Abstract: Depth-sensing indentation equipment is widely used for evaluation of the hardness and Young's modulus of materials. The depth resolution of this technique allows the use of ultra-low loads. However, aspects related to the determination of the contact area under indentation should be cautiously considered when using this equipment. These are related to the geometrical imperfections of the tip, the diamond pyramidal punch and the formation of pileup or the presence of sink-in, which alter the shape and size of the indent. These and other aspects, such as the thermal drift of the equipment and the scattering at the zero indentation depth position related to surface finishing, are discussed in this work. A study concerning the hardness and the Young's modulus results determined by Vickers indentation on different materials was performed. Samples of fused silica, BK7 glass, aluminium, copper and mild steel (for which the values of Young's modulus were previously known) were tested using indentation loads in the range 10–1000 mN. Moreover, two methods are proposed for performing the indentation geometrical calibration of the contact area; these are compared with a former method proposed by Oliver and Pharr (OP). The present methods are based on: (i) analysis of the punch profile using atomic force microscopy (AFM); and (ii) a linear penetration-depth function correction (LM), based on knowledge of the values of the Young's modulus of several materials. By applying these methods to the indentation load/indentation depth results, it was possible to draw some conclusions about the benefit of the AFM and LM methods now under proposal.
TL;DR: In this article, a finite element simulation is performed to analyze the contact deformation regimes induced by a sharp indenter in elastic-power-law plastic solids, where piling-up of material at the contact area is correlated with uniaxial mechanical properties.
Abstract: Finite element simulations are performed to analyze the contact deformation regimes induced by a sharp indenter in elastic – power-law plastic solids. As the yield strength (σys) and strain hardening coefficient (n) decrease or, alternatively, as Young’s modulus (E) increases, the contact regime evolves from (i) an elastic–plastic transition, to (ii) a fully plastic contact response, and to (iii) a fully plastic regime where piling-up of material at the contact area prevails. In accordance with preliminary analyses by Johnson, it is found that Tabor’s equation, where hardness (H) = 2.7σr, applies within the fully plastic regime of elastic – power-law plastic materials. The results confirm the concept of the uniqueness of the characteristic strain, ∈r = 0.1, that is associated with the uniaxial stress, σr. A contact deformation map is constructed to provide bounds for the elastic–plastic transition and the fully plastic contact regimes for a wide range of values of σ ys, n, and E. Finally, the development of piling-up and sinking-in at the contact area is correlated with uniaxial mechanical properties. The present correlation holds exclusively within the fully plastic contact regime and provides a tool to estimate σ ys and n from indentation experiments.
TL;DR: In this article, a number of TiAlN(Si, C,…) hard thin films were deposited onto the cemented carbide substrates using cathodic arc PVD and various failure modes were activated either by a cycle of indentation or by microscratching of the samples to provide an estimation of the fracture toughness and interfacial fracture energies.
TL;DR: In this article, an artificial elastic finger skin for robot fingers was developed for controlling the grasp force when the weight and friction coefficient of the grasped object are unknown, which is useful for control the grasping force.
Abstract: An artificial elastic finger skin for robot fingers was developed for controlling the grasp force when the weight and friction coefficient of the grasped object are unknown. The elastic finger skin has ridges at the surface to divide the stick/slip area. It also has a pair of tactile sensors embedded per one ridge similar to human fingertips. The surface of the whole finger is curved so that the reaction force can be distributed. A finite element (FE) model of the elastic finger skin was developed to perform a dynamic contact analysis using the FE method in order to design the elastic finger skin. The elastic finger skin was then constructed. It was confirmed by calculation and experiment that the incipient slippage of the ridge that occurs near the edge of contact area can be detected. This result is useful for controlling the grasping force when the weight and friction coefficient between the elastic finger skin and grasping object are unknown.
Patent•
12 Dec 2002
TL;DR: In this article, a prosthetic component is configured to have intentional interruptions in an articulating face of the prosthesis, which are configured to yield an optimum contact area or bearing surface, particularly with regard to low wear and greater lubricity through the application of lubrication and contact mechanics theory.
Abstract: A prosthetic component is configured to have intentional interruptions in an articulating face thereof. The intentional interruptions are configured to yield an optimum contact area or bearing surface, particularly with regard to low wear and greater lubricity through the application of lubrication and contact mechanics theory for the particular prosthetic component. Such optimization is applied to a wide range of prosthetic component sizes of the particular prosthetic component. The optimum range of percentage area of relief or interruptions, defined as a percentage of a baseline uninterrupted bearing surface area to be removed by the features of the interrupted bearing surface configuration is from 0.3% to 73.7% for hard-on-hard bearing components and from 5.7% to 83.2% for polyethylene-on-hard bearing components. The range for both hard-on-hard and polyethylene-on-hard implants translates to a relieved area ranging from 0.3% to 31.9% of the area of the entire articulating surface, depending on the size of the implant. For both hard-on-hard and polyethylene-on-hard bearing combinations, optimally decreasing the contact area or bearing surface by interruptions in the articulating surfaces will allow for the benefits of larger diameter prosthetic components with an increased range of motion and decreased potential for dislocation, and the low frictional torques and lower wear of smaller diameter components.
Patent•
23 Jul 2002TL;DR: In this article, a fuse is formed by a first contact member and a second contact member over a patterned, electrically-conductive silicide layer, where the first contact members and the second contact members electrically contact the silicide layers, thereby defining a first interface and second interface, respectively.
Abstract: The present invention relates to a fuse and a method for forming a fuse over a semiconductor substrate. The fuse comprises forming a first contact member and a second contact member over a respective first region and a second region of a patterned, electrically-conductive silicide layer, wherein the first contact member and the second contact member electrically contact the silicide layer, thereby defining a first interface and a second interface, respectively. A first contact area and a second contact area are associated with the respective first contact member and second contact member, wherein the first contact area is larger than the second contact area, thereby defining a fusible link at the second interface. According to one example, the silicide resides over a patterned polysilicon layer, wherein the patterned polysilicon layer generally tapered, and wherein the first region is wider than the second region.
Patent•
17 May 2002
TL;DR: In this paper, a head and disk system for use in a disk drive that includes a slider having a surface that contacts the disk is described, which is textured with pads, bumps, an etched surface or an otherwise roughened surface.
Abstract: A head and disk system for use in a disk drive that includes a slider having a surface that contacts the disk. This disk contacting surface of the slider is textured with pads, bumps, an etched surface or an otherwise roughened surface. The contact area of the disk has a greater roughness than a data zone. The head disk system exhibits acceptable stiction. Additionally, low glide avalanche over the CSS zone, thus enabling low fly height, is achieved.
TL;DR: In this article, the authors used amine-terminated polyamidoamine (PAMAM) dendrimer generation 4 as ink for contact printing, and used the conformal contact area and the mechanical properties of elastomeric stamp to determine the printed pattern.
Abstract: We have used amine-terminated polyamidoamine (PAMAM) dendrimer generation 4 as ink for contact printing. Periodic dendrimer lines with widths of 140 nm and interline widths of 70 nm were printed directly on a silicon substrate. Without obvious molecular diffusion during printing, the printed pattern is only determined by the conformal contact area, which is in turn determined by the mechanical properties of elastomeric stamp.
TL;DR: In this paper, a three-dimensional elastic-plastic rolling contact stress analysis was conducted incorporating elastic and plastic shakedown concepts, where tangential forces in both the rolling and lateral directions were considered and were assumed to be proportional to the Hertzian pressure.
Abstract: Three-dimensional elastic-plastic rolling contact stress analysis was conducted incorporating elastic and plastic shakedown concepts. The Hertzian distribution was assumed for the normal surface contact load over a circular contact area. The tangential forces in both the rolling and lateral directions were considered and were assumed to be proportional to the Hertzian pressure. The elastic and plastic shakedown limits obtained for the three-dimensional contact problem revealed the role of both longitudinal and lateral shear traction on the shakedown results. An advanced cyclic plasticity model was implemented into a finite element code via the material subroutine. Finite element simulations were conducted to study the influences of the tangential surface forces in the two shear directions on residual stresses and residual strains. For all the cases simulated, the p 0 /k ratio (p 0 is the maximum Hertzian pressure and k is the yield stress in shear) was 6.0. The Q x /P ratio, where Q x is the total tangential force on the contact surface in the rolling direction and P is the total normal surface pressure, ranged from 0 to 0.6. The Q y /P ratio (Q y is the total tangential force in the lateral direction) was either zero or 0.25. Residual stresses increase with increasing rolling passes but tend to stabilize. Residual strains also increase but the increase in residual strain per rolling pass (ratchetting rate) decays with rolling cycles. Residual stress levels can be as high as 2k when the Q x /P ratio is 0.6. Local accumulated shear strains can exceed 20 times the yield strain in shear after six rolling passes under extreme conditions. Comparisons of the two-dimensional and three-dimensional rolling contact results were provided to elucidate the differences in residual stresses and ratchetting strain predictions.
TL;DR: In this article, the ultrasonic method has been used to estimate the distribution of contact pressure in a real wheel-rail system, and a finite element model has also been developed to calculate pressure distribution over the whole contact area.
01 Jun 2002
TL;DR: The contact mechanics in ceramic-on-ceramic hip implants are investigated in this study under the microseparation condition where the edge contact occurs between the superolateral rim of the acetabular cup and the femoral head and the predicted contact pressure is significantly increased.
Abstract: The contact mechanics in ceramic-on-ceramic hip implants are investigated in this study under the microseparation condition where the edge contact occurs between the superolateral rim of the acetabular cup and the femoral head. A three-dimensional finite element model is developed to examine the effect of the microseparation distance between the femoral head and the acetabular cup on the contact area and contact stresses between the bearing surfaces. It is shown that microseparation leads to edge contact and elevated contact stresses, and these are mainly dependent on the magnitude of separation, the radial clearance between the femoral head and the acetabular cup, and the cup inclination angle. For a small microseparation distance (less than the diametrical clearance), the contact occurs within the acetabular cup, and consequently an excellent agreement of the predicted contact pressure distribution is obtained between the present three-dimensional anatomical model and a simple two-dimensional ax...
TL;DR: The data suggest that the ability of the inlay to translate on the tibial baseplate permits theInlay to align itself on the femoral component so that the contact surface area is maximized and contact stresses are reduced.
Abstract: We measured tibiofemoral contact stresses and the load-bearing contact area of fixed and mobile-bearing inlay knee prostheses under dynamic loading conditions. An electronic resistive pressure-measuring sensor was used to detect contact stresses and contact area in five cadaver knees. Stresses were measured with the tibial component aligned normally, as well as in internally- and externally-rotated positions. The average peak contact stresses measured on the fixed inlay were greater (medial 21 MPa and lateral 21 MPa) than those on the mobile inlay (medial/lateral 7.7/5.3 MPa, p = 0.04). Although the average peak contact stresses of the fixed standard inlay greatly exceeded the contact stresses of the other two inlay designs in each malrotated position tested, no statistically significant differences were seen. The data suggest that the ability of the inlay to translate on the tibial baseplate permits the inlay to align itself on the femoral component so that the contact surface area is maximized and contact stresses are reduced.
TL;DR: In this paper, the effect of temperature on the material removal mechanism in chemical mechanical polishing (CMP) was investigated and it was concluded that material removal in CMP under the influence of increasing temperature, is dominated by the increase in chemical reactions rather than mechanical ones.
Patent•
12 Feb 2002TL;DR: In this article, a precleaning process suitable for fabricating metal plugs in a low-κ, carbon-containing dielectric was proposed, which can repair damage caused by preceding process steps, such as oxygen plasma ashing processes for removing photoresist.
Abstract: The invention is a precleaning process suitable for fabricating metal plugs in a low-κ, carbon-containing dielectric. More specifically, the invention is a process for cleaning a contact area of a metal conductor on a semiconductor workpiece so as to minimize damage to a low-κ, carbon-containing dielectric overlying the metal. After forming contact openings in the low-κ dielectric so as to expose contact areas on the underlying metal conductor, the contact areas are cleaned by exposing the workpiece to an atmosphere formed by plasma decomposition of a mixture of hydrogen-containing and helium gases. Surprisingly, our preclean process can repair damage to the dielectric caused by preceding process steps, such as oxygen plasma ashing processes for removing photoresist.
TL;DR: A vesicle bilayer loaded with molecules that can bind (upon contact) with a solid surface is considered, following the classical model of Bell, Dembo, and Bongrand, and detailed predictions for the growth laws are given.
Abstract: We consider a vesicle bilayer loaded with molecules that can bind (upon contact) with a solid surface, following the classical model of Bell, Dembo, and Bongrand. We are interested in situations where the contact area varies with time: we assume that binders can then migrate via diffusion. The resulting dissipation and lag create a retarded force on the contact line, which could be significant in squeezing or rolling experiments. However, there are two cases where we expect the lag force to be ineffective: (i) separation by shrinking of an adhesive patch (where the Evans "tear out" process turns out to be less costly) and (ii) spontaneous growth of a patch from a point contact. In this last case, the lag force is weak, and we give detailed predictions for the growth laws.
TL;DR: Fretting fatigue tests were conducted, using cylindrical pad and flat pad with rounded edges, at various applied pad displacements and at two normal forces on the pad under a constant bulk stress amplitude condition as discussed by the authors.
TL;DR: In this paper, Sneddon's solution for indentation of an elastic half-space by rigid axisymmetric indenters is used to determine elastic modulus and hardness.
Abstract: The fundamental relations used in the analysis of nanoindentation load–displacement data to determine elastic modulus and hardness are based on Sneddon’s solution for indentation of an elastic half-space by rigid axisymmetric indenters It has been recently emphasized that several features that have important implications for nanoindentation measurements are generally ignored The first one concerns the measurement of the contact depth, which is actually determined by using a constant value e = 075 for the geometry of a Berkovich indenter and for any kind of material, whereas the reality is that e is a function of the power law exponent deduced from the analysis of the unloading curve The second feature concerns the relation between contact stiffness, elastic modulus, and contact area, in which a correction factor γ larger than unity is usually ignored leading to a systematic overestimation of the area function and thus to errors in the measured hardness and modulus Experimental measurements on fused quartz are presented that show the variation of e with the geometry of the tip–sample contact; that is to say with the contact depth, as well as the existence of the correction factor γ, as predicted in some recent articles Effects of both e and γ on harness and modulus measurements are also shown
TL;DR: The results showed that separation work is a good measure of specific interactions between FN and the cell surface, and the system developed here is a promising quantitative method to evaluate cell adhesion force.