Smooth Contact Surface Research Articles

A Three-Dimensional Model of Line-Contact Elastohydrodynamic Lubrication for Heterogeneous Materials with Inclusions

This paper develops a three-dimensional (3D) model for a heterogeneous half-space with inclusions distributed periodically beneath its surface subject to elastohydrodynamic lubrication (EHL) line-contact applied by a cylindrical loading body. The model takes into account the interactions between the loading body, the fluid lubricant and the heterogeneous half-space. In the absence of subsurface inclusions, the surface contact pressure distribution, the half-space surface deformation and the lubricant film thickness profile are obtained through solving a unified Reynolds equation system. The inclusions are homogenized according to Eshelby’s equivalent inclusion method (EIM) with unknown eigenstrains to be determined. The disturbed half-space surface deformations induced by the subsurface inclusions or eigenstrains are iteratively introduced into the lubricant film thickness until the surface deformation finally converges. Both time-independent smooth surface contact and time-dependent rough surface contact are considered for the lubricated contact problem.

Dry rolling/sliding wear of nanostructured pearlite

The dry rolling–sliding wear behaviour of pearlite that has an interlamellar spacing of just 85 nm has been characterised. Its wear resistance is found to be comparable to that of much harder bainitic steels. Microstructural observations indicate that there is substantial plastic deformation of both ferrite and cementite components of pearlite in the vicinity of the wear surface. Plasticity is not expected from Hertzian analysis that assumes a smooth contact surface. Instead, it is likely to be a consequence of exaggerated stresses due to surface roughness. The material remains ductile to shear strains in the order of 4. Diffraction data indicate that the coherent domain size is reduced to about half the interlamellar spacing and that some of the cementite may dissolve and contribute to the expansion of the lattice parameter of ferrite.

Adhesive Gripping Elements in a Construction of Gripping Heads

The paper describes possibilities to use industrially adhesive gripping elements in automatized handling processes especially for flat objects but also for objects slightly dissected according to height (e.g. sheets of glass, plastics, metals, plastic products etc.) which have dry, relatively clean, and smooth contact surfaces. It begins by analyzing results obtained in the field of designing combined vacuum-adhesive gripping elements, and the exclusively adhesive (passive) ones being suitable for technologically difficult handling conditions, e.g. in vacuum, as well. Furthermore, problems of the maximum carrying capacity of individual gripping elements being arranged parallel on a frame of a multi-element gripping head. A new concept of a compensation module of the gripping element position is presented as well, namely in relation to the head frame and to the handling object contact surface dissected according to height.

Advanced silicate-based lubricant additive induced diamond-like carbon structured restoration layer

An advanced silicate based lubricant additive has been employed in long-term pin-on-disk tribological experiments. The worn steel/steel surfaces were characterized using nano-indentation, SEM, XPS, and Raman spectroscopy for their physical, mechanical, and chemical properties. The average nano-hardness of the repaired layers on the disk and the pin is 10.2GPa and 16.7GPa respectively, which is substantially higher than that of the disk (HV 221, or 0.71GPa) and the pin (HRC55, or 1.8GPa) before tribological tests, forming super hard surfaces on the contact pair surfaces. Combined Raman spectroscopy and XPS studies suggest the formation of diamond-like carbon based restoration layers. A new formation mechanism of the restoration DLC layer contributing to hard and smooth contact surfaces is proposed.

2A22 Influence of Surface Roughness and Temperature on the Adhesion of Wheel and Rail in Wet Conditions(Boundary)

A series of experiments on the traction between wheel and rail were carried out for the purpose of obtaining the fundamental knowledge of how to prevent the occurrence of wheel slips in driving and wheel slides in braking. A twin disc rolling contact machine was used for the experiments by varying the surface roughness and the temperatures of wheel and rail discs, as well as the sprayed water. Adhesion coefficient acquired from the relationship between slip parameters and traction coefficients which can be obtained by experiments and film parameter which is the minimum EHL film thickness with smooth contact surfaces divided by the combined roughness were estimated. Relationship between the adhesion coefficients and combined roughness shows that the adhesion coefficients have a local maximum or almost constant values at 1〜3μm combined roughness and become large with an increase of the temperature of the wheel disc in the range where adhesion coefficients have a local maximum or almost constant values, however, the influence of temperature becomes smaller with the decrease of the combined roughness in the region of less than 1μm. Re-adhesion which is a phenomenon characterized by the dramatic increase of the traction coefficient occurs in some experimented conditions.

New Generation of Mobile Platform of Service Robot for Motion along Vertical Walls

The paper sums up results achieved during in the last few years of the development and research of service robots aiming their use for service applications on vertically oriented walls with predominantly smooth contact surfaces having minimal altitude unevenesses within the range ± 5 mm. Two robot generations are described step by step, and both of them use the same mechanical principle of the patented system of motion. The system uses the intermittent motion when positions of the robot legs and body alternate cyclically, and the appropriate gripping force of a holding-down system is realized by vacuum. As compared with the first version, the current one allows legs to move independent in part. In that way it is possible to compensate better variations of parallelism between a contact plane of the robot holding-down system and a vertical wall. Moreover, the robot is provided with a rotary unit making possible a rotation on the axis going through the robot center and being perpendicular to the contact plane, which guarantees a change in the robot orientation in the plane. As for drives, very compact rotary actuating mechanisms (servo drives) are used, having a high ratio of power parameters in relation to weight and dimensions, combined with a control based on an industrial PC.

A general 3D contact smoothing method based on radial point interpolation

This paper presents a general 3D contact smoothing method based on the meshfree radial point interpolation method to improve the numerical simulation of contact problems. In particular, a locally smooth contact surface is constructed from the scattered surface nodes by point interpolation using the combination of polynomial and radial bases. With such bases, this method reproduces smooth surfaces even for coarse meshes and the constructed surface passes exactly through the surface nodes. Results for contact problems involving deformable bodies are included to demonstrate its advantages.

Applying Nagata Patches in the Description of Smooth Tool Surfaces Used in Sheet Metal Forming Simulations

This study deals with the new strategy currently implemented in DD3IMP in-house code to describe the forming tools using Nagata patches. The strategy is based on the use of the Nagata patch interpolation to generate smooth contact surfaces over coarse faceted finite element meshes. The description of the adopted algorithm is briefly presented, highlighting the contact search algorithm employed. The reverse deep drawing of cylindrical cups, proposed as benchmark at the Numisheet’99 conference, is selected to examine the accuracy and robustness of the proposed approach. The effect of the gap between the blank-holder and the die is studied, adopting two distinct strategies: fixed gap and variable gap. The numerical results are compared with the experimental ones, previously presented and discussed in [1]. It is shown that the agreement is very good both in terms of punch force evolution and thickness distribution.

Development of an asymptotic modeling methodology for tibio-femoral contact in multibody dynamic simulations of the human knee joint

A new methodology for modeling articular tibio-femoral contact based on the recently developed asymptotic model of frictionless elliptical contact interaction between thin biphasic cartilage layers is presented. The developed mathematical model of articular contact is extended to the case of contact between arbitrary viscoelastic incompressible coating layers. The approach requires use of the smooth contact surface geometry and efficient contact points detection methods. A generalization of the influence surface theory based method for representing articular surfaces from the unstructured noisy surface data is proposed. The normal contact forces are determined analytically based on the exact solution for elliptical contact between thin cartilage layers modeled as viscoelastic incompressible layers. The effective geometrical characteristics of articular surfaces are introduced for use in the developed asymptotic models of elliptical contact between articular surfaces.

In Vitro Biomechanical Comparison of Dynamic Compression Plates with a Rough Contact Surface and a Polished Contact Surface for Fixation of Osteotomized Equine Third Metacarpal Bones

To compare the number of cycles to failure of 4.5 mm broad dynamic compression plates (DCP), 4.5 mm broad limited-contact dynamic compression plates (4.5-LC-DCP), and 5.5 mm broad limited-contact dynamic compression plates (5.5-LC-DCP) having a rough (denoted by a prefix R-) versus a standard smooth contact surface for the fixation of osteotomized equine 3rd metacarpal (MC3) bones. Experimental. Fifteen pairs of adult equine cadaveric MC3 bones. Fifteen pairs of equine MC3 were divided into 3 test groups (5 pairs each) for comparison of (1) R-DCP fixation with DCP fixation, (2) R-4.5-LC-DCP fixation with 4.5-LC-DCP fixation, and (3) R-5.5-LC-DCP fixation with 5.5-LC-DCP fixation to repair osteotomized equine MC3 bones under palmarodorsal 4-point bending cyclic fatigue testing. For each group an 8-hole plate with rough contact surface was applied to the dorsal surface of one randomly selected bone from each pair and a corresponding 8-hole plate with smooth contact surface was applied dorsally to the contralateral bone from each pair. All plates and screws were applied using standard ASIF techniques. All MC3 bones had mid-diaphyseal osteotomies. Mean number of cycles to failure for each method were compared using a paired t-test within each group. Significance was set at P < .05. Mean cycles to failure ± standard deviation was significantly greater for the R-DCP fixation (230,025 ± 23,129) compared with the DCP fixation (103,451 ± 14,556), for the R-4.5-LC-DCP fixation (99,237 ± 14,390) compared with the 4.5-LC-DCP fixation (46,464 ± 6325) and for the R-5.5-LC-DCP fixation (65,113 ± 7796) compared with the 5.5-LC-DCP fixation (34,224 ± 3835). For the fixation of osteotomized MC3 bones, the constructs with plates having rough contact surface were superior to the corresponding constructs with plates having standard smooth contact surfaces in resisting cyclic fatigue under palmarodorsal 4-point bending.

Physics-based modeling for partial slip behavior of spherical contacts

A physics-based modeling approach for partial slip behavior of a spherical contact is proposed. In this approach, elastic and elastic–plastic normal preload and preload-dependent friction coefficient models are integrated into the Cattaneo–Mindlin partial slip solution. Partial slip responses to cyclic tangential loading (fretting loops) obtained by this approach are favorably compared with experiments and finite element results from the literature. In addition to load-deformation curves, tangential stiffness of the contact and energy dissipation per fretting cycle predictions of the models are also provided. Finally, the critical assumptions of elastically similar bodies, smooth contact surface and negligible adhesion, and limitations of this physics-based modeling approach are discussed.

CMP For Direct Wafer Bonding of Hermetically Sealed Cavity Structures

Direct wafer bonding (DWB) is being increasingly utilized for advanced device and packaging applications, but both surfaces must be extremely smooth to achieve a uniform bond. Chemical mechanical polishing (CMP) is the ideal process for pre-bond surface preparation. This work focused on developing a process sequence for DWB of both patterned and unpatterned substrates as part of a project to develop hermetically sealed cavities. Deep cavities were etched into various substrates and a CMP process was developed to achieve a target surface roughness, Ra, below 1 nm on borofloat 33 glass substrates. During the optimization phase, it was found that DWB of a patterned substrate requires not only a smooth contact surface, but also that edge rounding of the patterned cavities be minimized. Finally, a series of samples were prepared and tested for suitability of the final process sequence. Data for bond toughness (J/m2) and hermeticity (MIL-STD-883) clearly show that the technique can produce sealed cavities.

楕円振動を利用した分別搬送 : 垂直振動が跳躍限界を超える場合(機械力学,計測,自動制御)

Simultaneously separating and transporting works by using elliptical vibration with vertical vibration over the jump limit is described. In the condition of vertical vibration from 1.2 to 2.0G, works with a smooth contact surface and those without a smooth contact surface can be separated and transported by adequately controlling the phase difference of elliptical vibration. Experimental results show that electronic parts with electric terminals can be separated at high speed in accordance with the difference between the shapes of the face and reverse sides. A change in the transportation characteristics of electronic parts without a smooth surface increases the speed of the separation and transportation. The difference between the transportation characteristics of parts without a smooth surface and those of parts with a smooth surface has increased. We clarified that the change in the transportation characteristics was derived from the jumps of parts by observing the behavior of electronic parts during separation and transportation with a high speed camera.

High-pressure on-chip mechanical valves for thermoplastic microfluidic devices

A facile method enabling the integration of elastomeric valves into rigid thermoplastic microfluidic chips is described. The valves employ discrete plugs of elastomeric polydimethylsiloxane (PDMS) integrated into the thermoplastic substrate and actuated using a threaded stainless steel needle. The fabrication process takes advantage of poly(ethylene glycol) (PEG) as a sacrificial molding material to isolate the PDMS regions from the thermoplastic flow channels, while yielding smooth contact surfaces with the PDMS valve seats. The valves introduce minimal dead volumes, and provide a simple mechanical means to achieve reproducible proportional valving within thermoplastic microfluidic systems. Burst pressure tests reveal that the valves can withstand pressures above 12 MPa over repeated open/close cycles without leakage, and above 24 MPa during a single use, making the technology well suited for applications such as high performance liquid chromatography. Proportional valve operation is demonstrated using a multi-valve chemical gradient generator fabricated in cyclic olefin polymer.

The effect of friction on indentation test results

A smooth contact analysis is commonly adopted in simulated indentation. Limited studies have been performed to investigate the possibility of deviation due to this simplification. This study involves the finite element simulation of indentation by conical indenters and the Berkovich family of indenters with three different apex angles of indenter tips of 50°, 60° and 70.3°. Loading curvatures and the ratio of the remaining work done to the total work done of the load-indentation curves resulting from the simulated indentation tests considering friction and smooth contact surfaces were compared and discussed. A wide range of elasto-plastic materials obeying the power law strain hardening model were considered in this study. The results as presented herein demonstrate that the effect of friction on the two essential basic parameters from the load–indentation curves, namely, the loading curvatures and the ratio of the work done, varies depending on both mechanical properties of the target materials and the geometries of the indenter tips adopted in the investigation.

Continuous velocity fields for the T‐bar problem

AbstractThis paper deals with the problem of T‐bar penetration. New kinematically admissible velocity fields are derived from elastic solutions of incompressible material using Airy stress function. These velocity fields are used to obtain upper bounds to collapse loads. Two particular solutions are presented, one for a rough contact surface between the T‐bar and soil and the other for a smooth contact surface. The merit of the solutions is that within the boundaries of the velocity field, the soil is required to shear compatibly and continuously. Therefore, these solutions can easily be combined with the strain path method to estimate rate and softening effects. Analysis including consideration of strain rate effect showed that the new mechanisms predict, under certain conditions, lower values than previously published upper bound solutions. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Rail corrugation formation studied with a full-scale test facility and numerical analysis

The current paper reviews and discusses the results of some important papers on rail corrugation in detail, and introduces the experimental study on mechanism of rail corrugation formation on curved track carried out using a full-scale test facility. The corrugation with different wavelengths on the test wheel tread is reproduced in the experiment. It is found that the passing frequency of the reproduced corrugation is the same as the excited natural frequency of the test rig. The natural frequencies of the test rig are identified through the modal experiment of the test rig using impulse method. The corrugation in the experiment is numerically analysed in the paper. In the analysis the contact geometry and steady creepage of the wheels/rollers in rolling contact are calculated. Kalker's rolling contact theory with non-Hertzian form is modified and used to calculate the frictional work density in the contact area of the wheel/roller. A model concerning the material loss per unit area proportional to the frictional work density is used to determine the wear on the contact surface of the wheel. The numerical results are in good agreement with the experimental results. They show that the test rig vibrating at high frequency can initiate a corrugation passing the same frequency on the smooth contact surface of the wheel under specific test conditions. The specific conditions include the non-zero steady creepage of the wheelset/rollers, the circumference of the wheel rolling circle approximately equal to multiple of the corrugation wavelength. The corrugation wavelength depends on the excited natural frequency of the test rig and the rolling speed of the wheelset. The depth and growth speed of corrugation depend on the fluctuation amplitude of the contact normal load of the wheelset/rollers.

Joining of Aluminium Metal Matrix Composites

ABSTRACT Aluminium metal matrix composites (AlMMCs) offer several advantages relative to monolithic aluminium alloys such as high stiffness, strength, wear resistance, low thermal expansion coefficient, etc. However, despite considerable improvements in developing AlMMCs, the lack of reliable joining methods restrict their greater application. Fusion welding of AlMMCs has not proved successful because high temperature nature of the process normally causes unfavorable reactions between the reinforcement and the matrix, leading to the formation of a variety of defects. On the other hand, solid-state welding and diffusion bonding may not be suitable due to the presence of chemically stable surface layer of aluminium oxide, which, being insoluble in aluminium, inhibits metal-to-metal contact during diffusion bonding. Furthermore, diffusion bonding requires a very smooth and clean contact surface, which is difficult to obtain in industrial applications. As an alternative, transient liquid phase (TLP) diffusion bonding, which operates at a lower temperature, can be used to circumvent the problems associated with the oxide layer. The formation of liquid phase (eutectic) can assist the disruption of the oxide layer and promote metallic contact. The composite material used in the present study consisted of 6061 alloy containing 15 volume % of SiC particulates of 23 μm diameter. TLP bonding was carried out at 560 ˚C in argon atmosphere using copper as an interlayer with different pressures and holding times. TLP-bonded AlMMCs were characterized by optical and scanning electron microscopy, microhardness survey, and shear tests. The results indicated that adequate bond strength could be achieved with suitable bonding parameters such as holding time and initial pressure.

Numerical simulation of rail corrugation on a curved track

The effects of track vibration with its natural frequency in the vertical and lateral directions on the formation and development of rail corrugation are analysed in detail in the present study. Kalker’s rolling contact theory with non-Hertzian form is modified and then used to calculate the frictional work density on the contact area of the wheel and rail in rolling when a wheelset is steadily curving. A model presenting the material loss of unit area proportional to the frictional work density is used to determine the wear of contact surface material of the rail. Due to the continuous and repeated rolling/slip contact of the wheel and rail the accumulation of the wear obtained by calculation reveals a periodical change in the rolling direction of the wheel. The numerical results also show that the track vibration with its natural frequencies can cause the formation of initial corrugation on the smooth contact surface of rail during the first passage of wheelset. The occurring wavelength of the corrugation depends on the frequencies and the rolling speed of the wheelset, and the depth and growth speed of corrugation depend on the vibration amplitude of the contact normal load and the lateral vibration of track.

Changes in the Mechanical Environment of Stenotic Arteries During Interaction With Stents: Computational Assessment of Parametric Stent Designs

Clinical studies have identified factors such as the stent design and the deployment technique that are one cause for the success or failure of angioplasty treatments. In addition, the success rate may also depend on the stenosis type. Hence, for a particular stenotic artery, the optimal intervention can only be identified by studying the influence of factors such as stent type, strut thickness, geometry of the stent cell, and stent-artery radial mismatch with the wall. We propose a methodology that allows a set of stent parameters to be varied, with the aim of evaluating the difference in the mechanical environment within the wall before and after angioplasty with stenting. Novel scalar quantities attempt to characterize the wall changes inform of the contact pressure caused by the stent struts, and the stresses within the individual components of the wall caused by the stent. These quantities are derived numerically and serve as indicators, which allow the determination of the correct size and type of the stent for each individual stenosis. In addition, the luminal change due to angioplasty may be computed as well. The methodology is demonstrated by using a full three-dimensional geometrical model of a postmortem specimen of a human iliac artery with a stenosis using imaging data. To describe the material behavior of the artery, we considered mechanical data of eight different vascular tissues, which formed the stenosis. The constitutive models for the tissue components capture the typical anisotropic, nonlinear and dissipative characteristics under supra-physiological loading conditions. Three-dimensional stent models were parametrized in such a way as to enable new designs to be generated simply with regard to variations in their geometric structure. For the three-dimensional stent-artery interaction we use a contact algorithm based on smooth contact surfaces of at least C-continuity, which prevents numerical problems known from standard facet-based contact algorithm. The proposed methodology has the potential to provide a scientific basis for optimizing treatment procedures and stent geometries and materials, to help stent designers examine new stent designs "virtually," and to assist clinicians in choosing the most suitable stent for a particular stenosis.