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The behaviours of point contact elastohydrodynamic lubrication (EHL) films under impact loads are investigated by direct observations using the optical interferometry technique. It has been found that when the initial impact gap is large, a central dimple is formed and the maximum film thickness occurs at the centre of the contact region. When the initial impact gap becomes small, a periphery dimple is generated and the maximum film thickness occurs at the contact periphery. When impact is applied to an oily Hertzian contact, the maximum film thickness of the periphery dimple is determined by the increasing rate of the Hertzian contact radius. The impact load under rolling/sliding conditions results in a crescent-shaped oil entrapment originally at the inlet of the EHL conjunction, which passes through the EHL conjunction approximately at the entrainment velocity. Some numerical results are also presented to show that the experimental observation in the periphery region is induced by the local squeeze effect.

Friction and antifriction composite materials of multilayer structure [1] have recently become very popular in the engineering industry. Antifriction materials are widely used in sliding bearings, and friction materials are widely used in brakes. In the first case, the friction forces between the contacting surfaces are negligible, but in the second case, they are rather large.

The squeal generation mechanism in disk brakes is clarified by measuring the stiffness between the disk and pad in the contact region (contact stiffness) and performing an analysis using the surface contact analysis model. The results of a squeal test using a squeal testing machine with a simple structure show that the squeal frequency becomes higher as the thrust pressure for braking becomes larger. Since we thought that the contact stiffness depends on the thrust pressure and influences the squeal frequency because the vibration characteristics of the disk do not change with thrust pressure, we measured the contact stiffness under squeal generating conditions. The pad was given constant pressure and excitation force generated by random noise with the squeal bandwidth. Measurement results show that the contact stiffness depends on the thrust pressure and is different for each pad. To clarify the influence of contact stiffness on squeal, the disk-pad-caliper system was analyzed by using the surface contact analysis model, which connects the disk with the pad via distributed springs (contact stiffness). The analytical results show that squeal is easily generated and its frequency easily changes when the dependence of contact stiffness on thrust pressure is large.

Some problems of multipurpose analysis and optimization of deformed structures and thin-walled structural elements are studied in this paper under some constraints including incomplete data. The first problem is the multipurpose optimization of layered plate made from given set of materials in context of optimization of ballistic limit velocity. Incomplete data concerning the thickness of layers of optimized multilayered shield structure are taken into account. The Pareto-approach and numerical evolutionary method (genetic algorithm) are used for solving of the considered multipurpose problem. The second problem studied in the paper is the shape optimization problem for rigid punch moving on the surface of elastic half-space, which is solved analytically in multipurpose formulation taking into account friction of contacted surfaces, wear of materials and arising pressure distributions. The relative movement is considered in frame of quasi-static formulation. Formulated optimization problem is studied analytically using the developed decomposition approach and exact solutions are obtained for the punch which has a rectangular contact region and moves translationally with a constant velocity.

The existing tire models are basically of three kinds: essentially empirical (“magic formulas”), or mixed empirical/analytical, or extremely complex theoretical models almost useless in practical situations. The model here proposed does not require any empirical data, and presents a simple theoretical approach very suitable to use in project and analysis of real suspension systems. This paper suggests a physical and mathematical model for the mechanical behavior of pneumatic car tires, based on the relationship between the relative displacement of the wheel to the tire-ground contact region. This formulation, assuming small displacements, is the first step to a more comprehensive model of the tire dynamic behavior, which will be published later.

Previous adhesion maps, such as the JG (Johnson-Greenwood) and YCG (Yao-Ciavarella-Gao) maps, are used to guide the selection of Bradley, DMT, M-D, JKR and Hertz models. However, when the size of the contact sphere decreases to the small scale, the applicability of JG and YCG maps is limited because the assumptions regarding the contact region profile, interaction between contact bodies and sphere shape in the classical models constituting these two maps are no longer valid. To avoid this limitation, in this paper, a new numerical model considering size effects of the sphere is established first and then introduced into the new adhesion maps together with the YGG (Yao-Guduru-Gao) model and Hertz model. Regimes of these models in the new map under a certain sphere radius are demarcated by the criteria related to the relative force differences and the ratio of contact radius to sphere radius. In addition, the approaches at pull-off, jump-in and jump-out for different Tabor parameters and sphere radii are provided in the new maps. Finally, to make the new maps more feasible, the numerical results of approaches, force and contact radius involved in the maps are formularized by using the piecewise fitting.

The performance of electronic and optoelectronic devices based on two-dimensional layered crystals, including graphene, semiconductors of the transition metal dichalcogenide family such as molybdenum disulphide (MoS2) and tungsten diselenide (WSe2), as well as other emerging two-dimensional semiconductors such as atomically thin black phosphorus, is significantly affected by the electrical contacts that connect these materials with external circuitry. Here, we present a comprehensive treatment of the physics of such interfaces at the contact region and discuss recent progress towards realizing optimal contacts for two-dimensional materials. We also discuss the requirements that must be fulfilled to realize efficient spin injection in transition metal dichalcogenides. © 2015 Macmillan Publishers Limited. All rights reserved.

The analytical solution for the plane contact between nonconforming C1 profiles with a curvature discontinuity is obtained and discussed. The initial gap between the undeformed profiles was represented by a double parabolic function having the curvature discontinuity within the contact region. On the basis of the analytical solution, the complete analysis of pressure distribution was obtained. A raw technique to find an approximate solution is presented and comparison to the analytic one provided. For the limit case of strong curvature ratio the asymptotic treatment is discussed in terms of consistency with hypotheses claimed.

The most expedient method of applying metallic coatings is friction plating with the use of rotating wire brushes (RWB). The coating metal is pressed against the bristles of the RWB and heated to high temperatures in the contact region. Particles of the coating metal are then captured by the ends of the bristles and transferred to the surface of the product being coated. The surface layer is simultaneously subjected to plastic deformation. The article presents the main parameters of the process and describes its ranges of application.

This study investigated the complete history of residual stress evolution in a stress-free titanium alloy, Ti–6Al–4 V under fretting fatigue loading condition. Compressive residual stress developed in the contact region due to the local plastic deformation between contacting bodies. The compressive residual stress then increased initially with increasing number of fretting fatigue cycles reaching to a maximum value, and then it decreased (or relaxed) with further cycling. This relaxation of compressive residual stress was due to the delamination and detachment of flake-like (wear sheet) material in the fretted region.

Solidification and caking of bulk solids often occurs during storage or while being transported to the customer. To investigate the formation and growth of solid bridges between two discrete particles, the modification of the contact region between these two particles stored in a climatic chamber is examined. The effect of load, temperature, relative humidity, and storage time on the formation of a bridge is analyzed. The objective is to describe the behavior of crystalline or salt-like granules under real storage conditions.

To investigate the formation and growth of solid bridges between urea particles, the changes in the contact region between two discrete particles are measured. The work is carried out using a Double-Particle-System (DPS). The DPS was stored in a climatic chamber. The effect of load, temperature, relative humidity, and storage time on the formation of a bridge between these particles was analyzed. The objective was to describe the geometrical changes in the contact region and to measure the strength of the resulting interparticle bridge.

Contact problems in the classical formulation are posed for topographically smooth surfaces; this ensures that the contact region will be continuous.

An axisymmetric contact problem of thermoelasticity for rotating bodies is analyzed with regard for heat generation in the contact region and convective heat exchange between the bodies and the ambient medium. The distribution of stresses in the bodies is determined. Special attention is given to the maximum tangential stresses and the possibility of appearance of tensile stresses.

This article presents a method to calculate the fracture parameters at interfacial cracks in laminated composites. Depending on the applied loading and crack length, a contact region may develop that changes the nature of the resulting stress intensity factors and energy release rates with respect to the open crack. A combined analytical and numerical model based on frictionless contact is used to eliminate the overlapping of the crack faces where applicable to obtain the correct results. In cases where the contact region is very small, an approximate method to obtain the fracture parameters is derived by consideration of the J-integral. The laminates studied include cross-ply and angle-ply laminates in three-point bending containing a central delamination. The present results are compared with results in the literature obtained by the virtual crack closure integral technique for the special case of cross-ply laminates and a close agreement is found. In addition, results are given for the extent of the contact zone as well as Mode I and II stress intensity factors and energy release rates as a function of the lamination angle. Overall, the method used provides an effective way to analyze interfacial cracks and delaminations in composite plates in cylindrical bending subjected to transverse loads or low velocity impacts.

The present work was undertaken to investigate the effect of sliding condition and wear surface state on the dry sliding wear behaviour of SiCp/Cu composite. Three kinds of sliding conditions, namely continuous sliding, interrupted sliding, and interrupted and cleaning sliding were employed. It was observed that a compact mechanically mixed layer (MML) was present on the worn surface of the composite, which effectively decreased the wear loss of the sliding pair. The new running in period of the interrupted tests led to breakage of the MML. Sufficient sliding and entrapment of wear debris in the contact region were two important preconditions for the formation of an MML. Therefore, continuous sliding or long period sliding is favoured to extend the life of this dry tribosystem.

When one explores a solid object with a fingertip, a contact region is usually defined. When the trajectory of this region on the fingerpad is artificially controlled so as to resemble the trajectory that is normally present while exploring a real object, the experience of shape is created. In order to generate appropriate local deformation trajectories, we built a servo-controlled mechanism that rolled a flat plate on the fingerpad during the manual exploration of virtual surfaces so that the plate was kept tangent to a virtual shape at the point of virtual contact. An experiment was then designed to test which mode of exploration maximized the shape information gain: active versus semi-active exploration, where semi-active exploration is when one hand touches passively and the other moves the target object, and the use of single versus multiple points of contact. We found that subjects were able to perform curvature discrimination at levels comparable to those achieved when using direct manual contact with real objects, and that the highly simplified stimulus provided by the device was a sufficient cue to give the illusion of touching three-dimensional surfaces.

A size effect has been observed in cylinder-on-flat partial slip contact fatigue experiments (Hills et al., 1988 and 1990). The size effect in this case is defined as a discontinuous drop in the fatigue life beyond some critical value of the width of the contact region. New analysis that directly accounts for the finite substrate thickness used in the original experiments shows that both the maximum local bulk stress and maximum local bulk cyclic stress range increased systematically with contact width in the original cylinder-on-flat experiments, rather than remaining approximately constant as intended in the original experimental design.

When two liquid drops come into contact, they coalesce rapidly, owing to the large curvature and unbalanced surface-tension forces in the neck region. We use an ultra-high-speed video camera to study the coalescence of a pendent and a sessile drop, over a range of drop sizes and liquid viscosities. For low viscosity, the outward motion of the liquid contact region is successfully described by a dynamic capillary-inertial model based on the local vertical spacing between the two drop surfaces. This model applies even when the drops are of different sizes. Increasing viscosity slows down the coalescence when the Reynolds number m. For the largest viscosities, the neck region initially grows in size at a constant velocity. The neck curvature also becomes progressively sharper with increasing viscosity. The results are compared to previously predicted power laws, finding slight, but significant deviations from the predicted exponents. These deviations are most probably caused by the finite initial contact radius.

Slipline field solutions for orthogonal metal machining are presented by considering elastic effects on chip formation and assuming adhesion friction at the chip-tool interface. The slipline fields are constructed following the matrix operational procedure developed by Dewhurst and Collins and by Dewhurst and assuming a linear relation between the angular range of α and β lines within the secondary shear zone. The limits of validity of the proposed solutions are examined using Hill's overstressing criteria. Elastic, plastic, total cutting, and total thrust forces and contact lengths are computed assuming an exponential pressure distribution in the elastic contact region. Results indicate that for any given rake angle and coefficient of friction the machining parameters are not uniquely determined but may have a range of allowable values and this is due to the non-unique nature of the machining process. Rake angle and rake friction are found to be the most important variables that influence cutting forces, cutting ratio, and contact length. The predicted results show excellent agreement with experimental observations, especially at small rake angles.

In this letter, we proposed a new layout structure for RF laterally diffused metal-oxide-semiconductor (LDMOS) transistors. In a multifinger layout, the drain contact region was designed to be wider than the channel region. The wider drain increases the equivalent drift region width to reduce the drift resistance and suppress the quasi-saturation effect. We found that the wide-drain multifinger LDMOS devices have lower on-resistance, higher cutoff frequency, higher maximum oscillation frequency, and better power performances than the standard multifinger ones.

Frictional force behavior during fretting fatigue and its interdependence on other fretting variables are investigated. Both coefficient of static friction and the normalized frictional force (i.e., the ratio of frictional force and normal contact load) increase during the earlier part of a fretting fatigue test and then both reach to a stabilized value. The variation of temperature in the contact region and normalized frictional force with increasing cycle numbers and bulk stress show similar trend implying that normalized frictional force represents the average friction in the contact region during a fretting fatigue. An increase in bulk stress, relative slip, and hardness of pad material results in an increase of the normalized frictional force, while an increase in contact load, frequency and temperature decreases the normalized frictional force. The normalized frictional force is also affected by the contact geometry. On the other hand, coefficient of static friction increases with an increase in the hardness of mating material, temperature and roughness from shot-peening treatment, but is not affected by contact geometry and displacement rate. Further, the normalized frictional force is not affected by the contact geometry, roughness and applied bulk stress level when fretting fatigue test is conducted under slip controlled mode, however it increases with increasing applied relative slip and decreasing contact load in this case.

The problem of a thermoelastic interaction of two cylinders with separation of their contact surfaces due to local loading of lateral surfaces is formulated and solved. The effect of the multiply connected contact region is shown to exist under a certain relation between the linear thermal expansion coefficients of the bodies.

The influence of load on the wear and abrasiveness of hard boron carbide (nominally B4C) thin films is studied. We analyze the wear and abrasiveness data obtained from pin-on-disk tests in which the disks are coated and the counterparts (sliders) are steel balls. It is assumed that the dominant mechanism for slider wear by these nominally smooth coatings is mechanical abrasion of the slider by nano-scale asperities having relatively large attack angles, i.e. by sharp asperities. We propose a model in which we assume that (1) the abrasiveness of a contact is proportional to the number of asperities in the contact; (2) the areal contact density is uniform; and (3) the effect of increasing the load is to enlarge the initial apparent contact region between the ball and the disk. Using this model, the observed dependence of the wear rate on load follows relationships that are similar to Hertzian relationships.

We study stresses formed in two rigidly connected elastic half spaces made of different materials in the case where their interface contains a circular crack. The contact of the crack surfaces along the crack contour is taken into account and the solution of the integral equation of the problem is obtained by the Wiener–Hopf method in the closed form. The size of the zone of contact of the crack surfaces and the distributions of stresses in the contact region and on the interface of the half spaces outside the crack are found explicitly.

Silicon carbide (SiC) based devices perform very well in severe environments and show excellent device characteristics at very high temperatures and in high radiation environments. An analytical model for a lateral MOSFET that includes the effects of temperature variation in 6H–SiC poly-type has been developed. The effects of elevated ambient and substrate temperatures (300–600 K) on the electrical characteristics as well as the variation of large and small signal parameters of the lateral MOSFET have been studied. The model includes the effects of temperature on the threshold voltage, carrier mobility, the body leakage current, and the drain and source contact region resistances. The MOSFET output characteristics and parameter values have been compared with previously measured experimental data. A good agreement between the analytical model and the experimental data has been observed.

We report the results of the analysis of the extended soft emission discovered in the Chandra ACIS pointing at the merging system NGC 4038/4039 ("the Antennae"). We present a multicolor X-ray image that suggests both extensive absorption by the dust in this system, peaking in the contact region, as well as variations in the temperature of different emitting regions of the hot interstellar medium (ISM). Spectral fits to multicomponent thermal emission models confirm this picture and give a first evaluation of the parameters of the hot plasma. We compare the diffuse X-ray emission with radio continuum (6 cm), H I, CO, and Hα images to take a first look at the multiphase ISM of "the Antennae" galaxies. We find that the hot (X-ray) and cold (CO) gas have comparable thermal pressures in the two nuclear regions. We also conclude that the displacement between the peak of the diffuse X-ray emission in the north of the galaxy system, toward the inner regions of the northern spiral arm (as defined by Hα, radio continuum, and H I), could result from ram pressure of infalling H I clouds.

The application of an ultrasonic technique to estimate the Real Contact Area (RCA) in a wheel-rail system is proposed. The method is based on the analysis of the reflection of ultrasonic waves which are sent over the contact region and reflected by it according to the state of contact. The interaction of the experimental data with a theoretical model formulated in the early 1990s by Krolikowski allows us to calculate the RCA for the area illuminated by the ultrasonic beam. By varying the external load and the surface conditions of the contacting elements, it is possible to obtain the trend of the RCA with increasing load (for a certain roughness) as well to explore changes in RCA for different roughness while the load is kept fixed. Results showed that RCA grows almost linearly with the applied load and that an increase of one order of magnitude in combined roughness of the wheel-rail system leads to a roughly sevenfold reduction in RCA under a given load.

The plasma formations that appear in the contact region between two negative glow discharges have been studied by means of electrical and spectral methods. The experimental and theoretical research of the plasma formations show that the double layer is the final stage of a more complex plasma structure which is formed first.

Background : Epithelial cells have apicobasal polarity and an asymmetric junctional complex that provides the bases for development and tissue maintenance. In both vertebrates and invertebrates, the evolutionarily conserved protein complex, PAR-6/aPKC/PAR-3, localizes to the subapical region and plays critical roles in the establishment of a junctional complex and cell polarity. In Drosophila , another set of proteins called tumor suppressors, such as Lgl, which localize separately to the basolateral membrane domain but genetically interact with the subapical proteins, also contribute to the establishment of cell polarity. However, how physically separated proteins interact remains to be clarified. Results : We show that mammalian Lgl competes for PAR-3 in forming an independent complex with PAR-6/aPKC. During cell polarization, mLgl initially colocalizes with PAR-6/aPKC at the cell-cell contact region and is phosphorylated by aPKC, followed by segregation from apical PAR-6/aPKC to the basolateral membrane after cells are polarized. Overexpression studies establish that increased amounts of the mLgl/PAR-6/aPKC complex suppress the formation of epithelial junctions; this contrasts with the previous observation that the complex containing PAR-3 promotes it. Conclusions : These results indicate that PAR-6/aPKC selectively interacts with either mLgl or PAR-3 under the control of aPKC activity to regulate epithelial cell polarity.

An h-adaptive algorithm was developed to enhance modeling of 3D impact problems. The algorithm utilizes a recovery-based error indicator involving the root mean square error of the Green–Lagrange strain. This indicator proved effective for identifying refinements in the contact region, which lead to improved solution accuracy. The effectiveness of the algorithm is demonstrated for both a reverse Taylor impact test and a ballistic penetration problem. Both the algorithm and implementation issues are discussed herein.

The results of the research by A. Yu. Ishlinskii and others on the theory of rolling contact of deformable bodies, taking into account their imperfect elasticity and partial slip in the area contact region, are presented.

This paper investigates the reliability behavior of IGZO TFT with different widths under AC gate and drain stress. Device of larger width suffers from worse current degradation. By comparing the contact resistance after stress such behavior can be attributed to the damaged contact region by large current during stress.

Negative impact of activities on nature, natural resources and human environment occur because of natural resources misuse. Studies of vulnerability plan to modify natural resources because of influence of different activities. Geographical aspects in those studies are not presented well enough because of narrow sector interests, that diminish the importance of environment. Use of natural potential is presented on ground of biotope with the case study of contact region Dravinjske gorice, between Pannonian and alpine region. Zaradi neustrezne rabe naravnih potencialov se kažejo negativni vplivi v naravi, v naravnih virih in v človekovem bivalnem okolju. Spreminjanje naravnih potencialov zaradi vpliva različnih dejavnosti načrtujejo študije ranljivosti okolja. Geografski vidiki so v teh študijah premalo zastopani, saj se uveljavljajo ozki sektorski interesi, ki zapostavljajo pomembnost okolja kot geografskega kompleksa. Na primeru Dravinjskih goric, ki je kontaktna regija med panonsko in alpsko Slovenijo, je prikazana raba naravnih potencialov na osnovi biotopov.

The ring rolling process involves three-dimensional non-steady material flow and continuous change of radius and thickness of the ring workpiece. In this study, the deformation analysis and geometric updating algorithm of the ring rolling process were verified by using the three-dimensional rigid-plastic finite element method. Manufacturing processes for plain ring and T-shaped ring were investigated by comparing experiments with simulation results, especially in side spread, load-stroke and pressure distribution, showing a good agreement. It was concluded that the simulation method would be a useful tool for the design of a ring rolling process.

In this article the coupled problem of crack/contact mechanics in a nonhomogeneous medium is considered. The underlying physical problem to which the results might be applicable is the initiation and the subcritical growth of surface cracks in a graded medium loaded by a sliding rigid stamp in the presence of friction. The dimensions of the graded medium are assumed to be very large in comparison with the local length parameters of the crack/contact region. Thus in formulating the problem the graded medium is assumed to be semi-infinite. The objective of the study is to determine, in addition to contact stresses, the in-plane component of the surface stress and the stress intensity factors at the crack tip. These are the primary load factors controlling the initiation and the subsequent growth of surface cracks in the graded medium. The coupled mixed boundary value problem is solved and the results are presented for various combinations of friction coefficient, material nonhomogeneity constant and crack/contact length parameters.

Researches on wear and fatigue in rolling contact from a tribological viewpoint are introduced. Transmission of traction and accompanying microslip in the contact region play critical roles in these phenomena. First, a quantitative analysis of wear in rolling contact with microslip is introduced, and it is shown that a simplified microslip theory can explain its behavior. Second, a marked change in contact fatigue life with traction is demonstrated, and a theory is introduced which relates the fatigue life with cumulative shear strain in the subsurface.

The formation, oxidation, and agglomeration of wear debris of coatings were investigated in this study. The rheology of the third body and its influence on the fretting wear behavior were studied in depth and systemically. The results showed that the shape and nature of the debris were the essential factors determining the mobility of the third body. All factors that could make the debris layer or third body remain on the contact surfaces would decrease the friction coefficient and fretting wear. The soft and large plate-like debris particles were apt to remain in the contact region. Conversely, the hard and sphereshaped debris particles tended to be squeezed from the contact surfaces and to increase the fretting wear.

The contribution of adsorption in a contact zone to adhesion between two nonporous bodies is discussed in the framework of the theory of adsorption in micropores. A contact region is presented as a...

This article is devoted to the experimental study of the ohmic contacts based on Ti/Al/Ni/Au metallization to the n+-doped region of the AlGaN / GaN heterostructure. Formed phases are studied at different temperatures. Based on the thermodynamic analysis of possible intermetallic reactions in the contact region, the optimum temperature range was found for the formation of ohmic contacts with a low contact resistance. The optimality of the modeled range is experimentally confirmed.

Recent work in the literature has identified a new heating mechanism during induction processing of carbon thermoplastic prepreg stacks: contact resistance between fibers of adjacent plies. An experimental methodology has been developed to estimate the contact resistance through heating tests based on the properties of the composite and geometry of the specimen. Measured values indicate comparable resistance values at the contact region, compared to resistance in the fiber direction, for AS-4/PEI prepreg stacks under vacuum pressure. The measured values can serve as inputs for induction heating models and process models of carbon thermoplastic prepreg stacks.

The paper presents an analysis of tangential interaction between flexural properties of tyres and frictional properties of the tyre-road interface. Using simple models to represent tyre structure and friction, the traction-slip characteristics are derived for various situations of practical interest: a standing tyre subjected to monotonic and oscillatory loading, a stationary rolling tyre and especially that of the transition from standing to steady rolling. To gain deeper insight into the requirements for modelling flexural and the complex friction properties, the study examines the influence of the normal pressure profile, tyre structural properties and friction in the contact region on the overall and detailed characteristics of tyre traction. The analysis presented serves as a basic framework for modelling the complex tyre-road interactions such as that encountered in the snap-start problem of road vehicles.