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This paper aims to determine the effect of contact geometry on temperature distribution and thermal buckling in an in-wheel brake system. Numerical analysis is conducted to investigate the variatio...

Solving the wheel-turnout contact geometry is complex because the rail section is varying along its longitudinal position. Besides, a large yaw angle will occur, especially when the vehicle passes ...

The ride quality of the railway vehicle is not only affected by the wheel-rail contact geometry but also by the yaw damper. In order to explore this variation law, an equivalent parameter model of the yaw damper was established based on the internal characteristics of the yaw damper, which is both accurate and efficient. Then, considering the influence of wheel wear and wheel-rail contact geometry, ride quality of the railway vehicle under different parameters of yaw damper and wheel-rail contact parameters was analysed. The results show that the wheel-rail contact points are scattered on the wheel profile after the wheel wears out, and the equivalent conicity also tends to increase with the increasing operating mileage. The distribution of ride quality space is sensitive to the change of equivalent conicity. In the low equivalent conicity area, the expansion rate of excellent ride quality space is faster. In the high equivalent conicity area, the expansion rate of qualified ride quality space is faster. Appropriate additional stiffness which is oil stiffness in parallel with structural damping in the equivalent parameter model of the yaw damper can improve the vehicle ride quality. The lateral ride quality is influenced obviously with the condition of the damping of the yaw damper being less than 440 kN·s·m−1. Properly reducing the joint stiffness of the yaw damper could reduce the influence of characteristic parameters of the yaw damper and equivalent conicity of the wheel-rail contact on vehicle lateral ride quality. The optimized characteristic parameters of the yaw damper are used in the actual vehicle test, and the ride quality is effectively improved.

A general model is developed, and on its basis, there are special models formulated of the grinding process with crossed axes of the tool and workpiece with a profile in the form of a circle arc. A new method of control of the grinding process is proposed, which will provide processing by equidistant curves, and the amount of cutting of a circle equal to the allowance. This will increase the productivity and quality of grinding. The presented method of grinding implements the processing with the spatial contact line of the tool and workpiece. When the axes are crossed, the contact line is stretched, which leads to an increase of the contact area and, accordingly, to a decrease of the temperature in the processing area. This allows processing of workpieces with more productive cutting conditions.

The contact geometry of rough surfaces markedly affects the functional properties such as sealing and lubrication. The effect of surface roughness on the percolation characteristic of elastic contact was studied. The elastic contact of randomly rough surfaces with a glass plate was performed using four different surface roughnesses of silicone rubber blocks as specimens. The results illustrate that the percolation threshold was significantly affected by the valley morphology of a surface. The increase in depth and void volume of valleys improved the connectivity between valleys, but impeded the coalescence of contact clusters, resulting in the extinction of the spanning void cluster allowing fluid flow when the relative contact area was large. Furthermore, the critical pressure and connectivity at the percolation threshold were related to the maximum peak height and autocorrelation length of a surface, respectively.

The use of detailed wheel/rail contact models has long been frustrated by the complicated preparations needed, to analyse the profiles for the local geometry and creep situation for the planar cont...

Traditional physics-based contact models have been widely used for describing various contact phenomena such as robotic grasping and assembly. However, difficulties in carrying out contact parameter identification as well as the relatively low measurement accuracy due to complex contact geometry and surface uncertainties are the limiting factors of the physics-based contact modeling methods. In this paper, we present a novel hybrid contact modeling (HCM) method as an endeavor to discover models that can more accurately simulate practical contact scenarios than traditional physics-based contact models. The proposed method is implemented by combining a physics-based contact model and a data-driven error model. This approach is validated by using simulations of a bouncing ball, a flat-shot, and a three-dimensional (3D) peg-in-hole. The results demonstrate the feasibility and consistent performance of the HCM method.

A model is proposed for calculating the actual radial feed in internal grinding on a CNC machine. The model establishes the relation between the actual and programmed feed, as a function of the cutting forces, the elastic deformation of the machining system, the cutting conditions, the wheel–workpiece contact geometry, the wheel characteristics, and other parameters. The model is used to predict the change in radius of the machined hole surface in the workpiece, from the initial to the final value for a specified automatic cycle, in various internal-grinding conditions. The model provides the basis for multiparametric optimization of the grinding cycles in multidimensional control-parameter space.

The orientation of, and contacts between, grains of sand reflect the processes that deposit the sands. Grain orientation and contact geometry also influence mechanical properties. Quantifying and understanding sand microstructure thus provide an opportunity to understand depositional processes better and connect microstructure and macroscopic properties. Using x-ray computed microtomography, we compare the microstructure of naturally-deposited beach sands and laboratory sands created by air pluviation in which samples are formed by raining sand grains into a container. We find that naturally-deposited sands have a narrower distribution of coordination number (i.e., the number of grains in contact) and a broader distribution of grain orientations than pluviated sands. The naturally-deposited sand grains orient inclined to the horizontal, and the pluviated sand grains orient horizontally. We explain the microstructural differences between the two different depositional methods by flowing water at beaches that re-positions and reorients grains initially deposited in unstable grain configurations.

Polyacrylamide (PAAm) hydrogels with brush-covered or crosslinked surfaces were produced and their tribological behavior was studied over a wide range of sliding speeds for two different contact geometries: sphere-on-flat and flat-pin-on-flat. Irrespective of the contact geometry, the brushy hydrogel surfaces displayed up to an order of magnitude lower coefficients of friction mu (COF) compared to the crosslinked surfaces, even achieving superlubricity (mu < 0.01). In general, a hydrogel sphere showed a lower coefficient of friction than a flat hydrogel pin at a similar contact pressure over the entire range of sliding speeds. However, after normalizing the friction force by the contact area, the shear stress of hydrogels with either crosslinked or brushy surfaces was found to be similar for both contact geometries at low speeds, indicating that hydrogel friction is unaffected by the contact geometry at these speeds. At high sliding speeds, the shear stress was found to be lower for a sphere-on-flat configuration compared to a flat-pin-on-flat configuration. This can be attributed to the larger equivalent hydrodynamic thickness due to the convergent inlet zone ahead of the sphere-on-flat contact, which presumably enhances the water supply in the contact, promotes rehydration, and thus reduces the friction at high sliding speeds compared to that measured for the flat-pin-on-flat contact., Friction, 10 (3), ISSN:2223-7704, ISSN:2223-7690

Fictional contacts occur in many mechanical systems, and often affect their dynamic response, since the collisions cause a significant change the systems’ characteristics, namely in terms of velocities. This work describes and compared different formulations to handle frictional contacts in multi-rigid-body dynamics. For that, regularized and non-smooth techniques are revisited. In a simple manner, the regularized methods describe the contact forces as a continuous function of the indentation, while the non-smooth formulations use unilateral constraints to model the contact problems, which prevent the indentation from occurring. The main motivation for the performing this study came from the permanent interest in developing computational models for the dynamic modeling of contactimpact events under the framework of multibody systems methodologies. The problem of modeling and simulating contacts with friction in multibody systems includes several steps, the definition of the contact geometry; the determination of the contact points; the resolution of the contact itself; and the evaluation of the transitions between different contact regimens. The last two aspects are investigated in this work within the context of contact dynamics. In the sequel of this process, an application example is utilized to show the effectiveness of the modelling process of contact problems in multibody systems. Finally, future developments and new perspectives for further developments related to contact-impact problems are presented and discussed in this study., This work has been supported by FCT, under the national support to R&D units grant, with the reference project UIDB/04436/2020 and UIDP/04436/2020.

This paper studies the instantaneous second-order total freedom of two smooth objects initially in contact at a single point. The analytical determination of the set of physically allowed second-order motions is formulated in the Euclidean space using the screw theoretic concepts of twist and twist-derivative. Mathematical expression that characterizes the nature of second-order motion for an arbitrary contact geometry is derived in terms of twist coordinates, twist-derivative coordinates and the principle normal curvatures of the two surfaces at the point of contact. It is shown that the characteristic of this expression is equivalent to that of the derivative of reciprocal product of the instantaneous twist and contact normal line. The efficacy of the theory developed is demonstrated through two illustrative examples.

A two-parametric geometry optimization problem for a symmetrical punch with compound curvature in frictionless contact with and an elastic half-plane is considered. An almost constant pressure distribution is sought for by means of least-square method. Another sub-optimal solution, which equalizes the three local maximum peaks (one at the center, and two at either side of the contact interval), is constructed using an asymptotic modeling approach and compared with the exact solution known in the literature.

Secondary air systems of civil aircraft engines require labyrinth seals with a minimum gap clearance for optimal functioning. In the case of high speed contact during the engine running-in period, an abradable material is deposited on the stationary part of the seal to limit the damage of the rotating shaft, which is made of a titanium alloy. Such situations are potentially critical for the seal; hence, the present study aims to observe the material behaviour during these contact conditions and to establish the tribological circuit of a third body through the interface. A high-speed contact test rig was developed to recreate contact conditions occurring in an aircraft engine. Two contact configurations occurring in different locations of the engine, with different materials and surface areas were explored. Thermal and mechanical instrumentation were used in each test. The influence of the contact geometry and the test conditions show that material flows through the contact determine the life cycle of the contact (by establishing a balance between the source, internal and material flow) and allows for the control of the thermomechanical constraints in a high-speed contact.

This paper focuses on the systematic type synthesis of parallel robot manipulators by using new structural formulas based on the screw theory. New structural formulas as a total number of screw in kinematic pairs , number of screws with variable pitch , total number of screws that represent the contact geometry of lower and higher joint elements (t), mobility equation for robot manipulators (M), dimension of the closed loop , motion of end effector of parallel manipulator , number degree of freedom of kinematic pairs , refers to find the kinematic structure of robot manipulators realizing a specified motion requirement. Twenty kinematic pairs with structural parameters are introduced. History of six structural formulas using for structural synthesis of parallel robot manipulators from space and different subspaces are presented as a table with equations, authors, years and some commentaries. The structural synthesis approach is based on the elementary notions of screw theory. Using the proposed of structural formulas approach, families of platform manipulators are constructed from a set of structural units. This paper is appropriate for engineers with interest in robotics, rovers, space docking parallel manipulators and screw theory.

Harmonic wear is one of the common wear phenomena of high-speed train wheels. The change of wheel/rail rolling contact geometry leads to unstable characteristics of wheel/rail contact, which directly affects the quality and safety of high-speed train operation. Because wheelset lateral displacement directly affected the wheel/rail contact geometry, in this paper, the UM software was used to establish a high-speed train vehicle-track coupled dynamics simulation model of the CRH2 (China Railway High-speed 2) head car. Lateral displacement of harmonic wear wheel was calculated under different wear condition to analyze the influence of harmonic wear wheels on wheelset lateral displacement. Then according to macroscopic dimension change of the wheel profile from lateral and radial directions of high-speed train induced by harmonic wear wheels, wheel profiles under different wear condition were selected. And wheel/rail contact geometry under different harmonic wear stages was calculated to discuss the influence of harmonic wear wheel on wheel/rail contact geometry. The results show that harmonic order and wave depth of harmonic wear wheel have small influence on the lateral displacement of wheelset, but the influence of wave depth is greater than harmonic order. The average difference of lateral displacement between harmonic wear wheel and no harmonic wear wheel increases with the increase of wave depth and order. In a harmonic wave length, the maximum value of both equivalent conicity and contact angle appear in deepest wave depth. The greater the wave depth, the more obvious the fluctuations, and equivalent conicity changes are less obvious.

Liu et al. recently published a study on friction in heavily loaded lubricated contacts. They compare measurements obtained from tests carried out on two tribometers, at constant entrainment speed, temperature and contact pressure. They observe deviations they attribute to the influence of scale and contact geometry effects. We show, by means of experiments conducted under the same conditions and with the same lubricant, that three alternative effects, somehow dependent on each other, can explain their results: very different elastohydrodynamic conditions, the pervasive presence of significant thermal effects and the occurrence of a mixed lubrication regime in some tests. This discussion provides an opportunity to reconsider how to conduct friction tests with in mind to focus on the lubricant response only. Proposals are presented in terms of operating conditions and lubricant selection, with the subsequent objective to better understand the mechanisms behind friction in highly loaded EHD contacts.

Energy efficiency and functional reliability are the two key requirements in the design of high-performance transmissions. Therefore, a representative analysis replicating real operating conditions is essential. This paper presents the thermoelastohydrodynamic lubrication (TEHL) of meshing spur gear teeth of high-performance racing transmission systems, where high generated contact pressures and lubricant shear lead to non-Newtonian traction. The determination of the input contact geometry of meshing pairs as well as contact kinematics are essential steps for representative TEHL. These are incorporated in the current analysis through the use of Lubricated Loaded Tooth Contact Analysis (LLTCA), which is far more realistic than the traditional Tooth Contact Analysis (TCA). In addition, the effects of lubricant and flash surface temperature rise of contacting pairs, leading to the thermal thinning of lubricant, are taken into account using a thermal network model. Furthermore, high-speed contact kinematics lead to shear thinning of the lubricant and reduce the film thickness under non-Newtonian traction. This comprehensive approach based on established TEHL analysis, particularly including the effect of LLTCA on the TEHL of spur gears, has not hitherto been reported in literature.

To investigate the effects of the contact geometry, interfacial friction, and substrate recovery on the behavior of polymer scratching using a conical tip, an analytical model is proposed. The normal stress acting on the contact surface between the tip and the substrate is described as a function of the included angle θ, representing the angle between two planes across the axis of the conical tip, and the attack angle β, representing the angle between the conical surface and the substrate material surface. The effects of the rear contact geometry on the scratch friction between the tip and substrate, represented by recovery angle φ, owing to the instantaneous elastic recovery of the polymer substrate, are also introduced. Validated by the experimental and numerical results from the literature, the proposed analytical model can describe well the scratch coefficient of friction (SCOF), which is defined as the ratio of the tangential force to the normal force. Meaningful guidance is provided to understand the scratch friction behavior.

This study investigates the thermal response of titanium alloy fretting sliding through a numerical approach with the consideration of the friction dissipation, plastic dissipation, surface roughness and wear. The fretting sliding of a cylindrical pad on a specimen with surface roughness is modeled to predict the temperature distribution, the evolution of the wear profile, and the fields of surface and subsurface stresses. Specifically, a thermo-elasto-plastic constitutive model considering the thermal-induced softening of material properties is developed to evaluate the contact pressure and the tangential stress on the surfaces as well as the subsurface stresses in the contacting components. The friction and plastic energy dissipations function together as the heat source to cause the temperature rise in the contact zone. A modified Archard model is used to predict the wear profile of the contact surface and change the contact geometry. The models are then incorporated in the finite element analysis of the fretting sliding to evaluate the thermal response. The influences of the plastic dissipation and the surface roughness on the temperature rise in the fretting sliding are discussed.

In the last two decades, significant progress has been made on developing new nanoscale mechanical property measurement techniques including instrumented indentation and atomic force microscopy based techniques. The changes in the tip-sample contact mechanics during measurements uniquely modify the displacement and force sensed by a measurement sensor and much effort is dedicated to correctly retrieve the sample mechanical properties from the measured signal. It turns out that in many cases, for the sake of simplicity, a simple contact mechanics model is adopted by overlooking the complexity of the actual contact geometry. In this work, a newly developed matrix formulation is used to solve the stress and strain equations for samples with edge geometries. Such sample geometries are often encountered in today’s nanoscale integrated electronics in the form of high-aspect-ratio fins with widths in the range of tens of nanometers. In the matrix formulation, the fin geometries can be easily modeled as adjacent overlapped half-spaces and the contact problem can be solved by a numerical implementation of the conjugate gradient method. This method is very versatile in terms of contact geometry and contact interaction, either non-adhesive or adhesive. The discussion will incorporate a few model examples that are relevant for the nanoscale mechanics investigated by intermittent contact resonance AFM (ICR-AFM) on low-k dielectric fins of high-aspect-ratio. In such ICR-AFM measurements, distinct dependence of the contact stiffness was observed as a function of the applied force and distance from the edges of the fins. These dependences were correctly predicted by the model and used to retrieve the mechanical changes undergone by fins during fabrication and processing.

Wheel flat is one kind of railway train wheelset defects. It has great influence on wheel/rail dynamics and damages. In most of the presented studies, wheel/rail impact velocity or rolling radius v...

A procedure for the design of contact systems with consideration of the electrical and tribological properties is presented. Wear and electrical tests under variation of the parameters coating system, contact geometry, and contact force are performed with the aim to find optimum contact parameters and to use the results for calculations. Example calculations are carried out, and the results are summarized in selection diagrams, which can be used in the product development as the basis for the design of plug-in connectors.

An appropriate clearance is required between mating gears for effective power transmission. In the present work, the effect of radial misalignment on mild wear of spur gear is modeled and simulated. The changes in the gear tooth contact geometry due to progressive wear have also been accounted in the model. The simulation results show that in the pinion dedendum region, pressure angle increases, while the contact pressure and wear depth decrease with increase in number of wear cycles. As far as the effect of radial misalignment is concerned, contact pressure decreases and wear depth increases with the increase in misalignment. In the pinion addendum region, pressure angle and wear depth increase with the increase in wear cycles, while the contact pressure and wear depth decrease with the increase in misalignment. The pressure angle and pitch point change from initial 20° (23rd pitch point) to 20.95° (26th pitch point) and 21.86° (28th pitch point) due to 0.5- and 1-mm radial misalignment, respectively. The wear depths after 50,000 wear cycles are − 1.32 × 10−2 μm, − 3.33 × 10−3 μm and − 4.39 × 10−4 μm at 23rd, 26th and 28th pitch points, respectively. The effect of radial misalignment on backlash, pressure angle, pitch point, contact ratio, double tooth contact region and speed ratio is also discussed.

The ‘simple double-elliptical contact’ (SDEC) approach by Piotrowski et al. [The Kalker book of tables for non-Hertzian contact of wheel and rail. Vehicle Syst Dyn. 2017;55:875–901] generates a-symmetrical contact patches in an elegant way. This allows to extend the table-based approach for the wheel–rail creep force calculation towards non-Hertzian contact geometry. This is an important line of research, because FASTSIM is intricate for non-Hertzian contacts, whereas CONTACT requires long calculation times.Here, we comment on the further motivation that's provided for the approach. According to the authors, ‘the spin creepage generates longitudinal creep force in non-symmetric, non-elliptical contacts’, which is ‘completely lost’ when using elliptical regularisation. We demonstrate that this mainly depends on the choice of contact origin, and that the interaction is much reduced if different choices are made. This suggests that elliptical regularisation may be viable still, if the details are pro...

This paper presents an experimental investigation into the effects of contact conformity, contact pressure and displacement amplitude on the gross-slip fretting behaviour grease-lubricated cylinder-on-flat contacts in the context of flexible marine riser pressure armour wire, and compares behaviour with that observed in unlubricated conditions. Characterisation of friction and wear is critical to fretting fatigue life prediction in flexible risers since friction directly controls trailing-edge fretting stresses and hence fatigue crack initiation, on the one hand, and on the other hand, directly affects wear via relative tangential slip (displacement). Wear can have a beneficial or detrimental effect on fatigue crack initiation and propagation, depending on relative slip and slip regime. It is shown that friction and wear are higher for dry conditions than for grease-lubricated conditions. For grease-lubricated conditions, behaviour is determined by whether grease can be retained in the contact (as opposed to being extruded out). Retention (or replenishment) of grease in the contact results in low rates of wear and low coefficients of friction; these conditions are favoured by fretting displacements above a critical value, by low contact conformity, and by low applied loads. The authors would like to thank the Irish Research Council and Wood Group Kenny for funding of this project through the Enterprise Partnership Scheme (EPSPG/2013/638), the National University of Ireland for funding through a NUI Travelling Scholarship. We also wish to acknowledge the help and support we have received from Dr. Adrian Connaire and Mr. Kieran Kavanagh (Wood Group). The authors also wish to acknowledge the support of the Faculty of Engineering at the University of Nottingham where this research was conducted. peer-reviewed

Foot–ground contact models are an important part of forward dynamic biomechanic models, particularly those used to model gait, and have many challenges associated with them. Contact models can dramatically increase the complexity of the multibody system equations, especially if the contact surface is relatively large or conforming. Since foot–ground contact has a large potential contact area, creating a computationally efficient model is challenging. This is particularly problematic in predictive simulations, which may determine optimal performance by running a model simulation thousands of times. An ideal contact model must find a balance between accuracy for large, conforming surfaces, and computational efficiency. Volumetric contact modelling is explored as a computationally efficient model for foot–ground contact. Previous foot models have used volumetric contact before, but were limited to 2D motion and approximated the surfaces as spheres or 2D shapes. The model presented here improves on current work by using ellipsoid contact geometry and considering 3D motion and geometry. A gait experiment was used to parametrise and validate the model. The model ran over 100 times faster than real-time (in an inverse simulation at 128 fps) and matched experimental normal force and centre of pressure location with less than 7% root-mean-square error. In most gait studies, only the net reaction forces, centre of pressure, and body motions are recorded and used to identify parameters. In this study, contact pressure was also recorded and used as a part of the identification, which was found to increase parameter optimisation time from 10 to 164 s (due to the additional time needed to calculate the pressure distribution) but helped the results converge to a more realistic model. The model matched experimental pressures with 33–45% root-mean-square error, though some of this was due to measurement errors. The same parametrisation was done with friction included in the foot model. It was determined that the velocity-based friction model that was used was inappropriate for use in an inverse-dynamics simulation. Attempting to optimise the model to match experimental friction resulted in a poor match to the experimental friction forces, inaccurate values for the coefficient of friction, and a poorer match to the experimental normal force.

Vertical dynamic vehicle-track interaction in the through route of a railway crossing is simulated in the time domain based on a Green's function approach for the track in combination with an implementation of Kalker's variational method to solve the non-Hertzian, and potentially multiple, wheel-rail contact. The track is described by a linear, three-dimensional and non-periodic finite element model of a railway turnout accounting for the variations in rail cross-sections and sleeper lengths, and including baseplates and resilient elements. To reduce calculation time due to the complexity of the track model, involving a large number of elements and degrees-of-freedom, a complex-valued modal superposition with a truncated mode set is applied before the impulse response functions are calculated at various positions along the crossing panel. The variation in three-dimensional contact geometry of the crossing and wheel is described by linear surface elements. In each time step of the contact detection algorithm, the lateral position of the wheelset centre is prescribed but the contact positions on wheel and rail are not, allowing for an accurate prediction of the wheel transition between wing rail and crossing rail. The method is demonstrated by calculating the wheel-rail impact load and contact stress distribution for a nominal S1002 wheel profile passing over a nominal crossing geometry. A parameter study is performed to determine the influence of vehicle speed, rail pad stiffness, lateral wheelset position and wheel profile on the impact load generated at the crossing. It is shown that the magnitude of the impact load is more influenced the wheel-rail contact geometry than by the selection of rail pad stiffness.

The strength of an adhesive contact between two bodies can strongly depend on the macroscopic and microscopic shape of the surfaces. In the past, the influence of roughness has been investigated thoroughly. However, even in the presence of perfectly smooth surfaces, geometry can come into play in form of the macroscopic shape of the contacting region. Here we present numerical and experimental results for contacts of rigid punches with flat but oddly shaped face contacting a soft, adhesive counterpart. When it is carefully pulled off, we find that in contrast to circular shapes, detachment occurs not instantaneously but detachment fronts start at pointed corners and travel inwards, until the final configuration is reached which for macroscopically isotropic shapes is almost circular. For elongated indenters, the final shape resembles the original one with rounded corners. We describe the influence of the shape of the stamp both experimentally and numerically. Numerical simulations are performed using a new formulation of the boundary element method for simulation of adhesive contacts suggested by Pohrt and Popov. It is based on a local, mesh dependent detachment criterion which is derived from the Griffith principle of balance of released elastic energy and the work of adhesion. The validation of the suggested method is made both by comparison with known analytical solutions and with experiments. The method is applied for simulating the detachment of flat-ended indenters with square, triangle or rectangular shape of cross-section as well as shapes with various kinds of faults and to “brushes”. The method is extended for describing power-law gradient media.

This contribution reports on an ongoing research project aimed in developing a unified theoretical framework for the description of interconnected thermo-mechanical systems with a particular emphasis on thermodynamic engines. We analyse from the geometrical viewpoint the structure of thermodynamic and mechanical interconnection and propose an approach to the unified description of thermo-mechanical systems. The theoretical results are illustrated by a physical example.

Fretting can lead to surface wear and/or crack nucleation depending on the sliding condition and contact geometry. To formalize this aspect, Ti-6Al-4V cylinder/plane and punch/plane contacts were investigated. The experimental crack nucleation domains in partial and gross slip conditions were established and simulated combining SWT cumulative damage analysis with FEM surface wear simulations. Good correlations were achieved if the experimental boundary conditions including system tangential accommodation and micro-rotations measured using DIC analysis, were considered. Fretting maps were simulated by predicting partial slip and gross slip displacement amplitudes above which cracks were respectively nucleated and removed by surface wear. Finally, it was shown that whatever the contact geometry, the gross slip cracking domain was inversely proportional to the surface wear rate.

The application of polymers in power-transmitting machine elements, e.g., gears, is limited by moderate thermo-mechanical properties and the detrimental accumulation of contact heat, even with external lubrication. Hence, polymer rolling–sliding elements are often prone to thermo-mechanical overload or abrasive wear. Diamond-like carbon (DLC) coatings are well known from steel applications for enhancing wear resistance and reducing friction. Since preliminary results indicate promising results for such coatings for polymers as well, their influence on the behavior of lubricated polymer contacts is investigated by numerical simulation. For polymer–steel contacts, the mechanical and thermophysical properties of coating and polymer are varied. The contact geometry is dominated by a local conformity, in which most of the deformation is related to the polymer. The DLC coatings affect film thickness and hydrodynamic pressure only little even for untypical high coating thicknesses. In contrast, the contact temperature decreases already for very thin coatings due to enhanced heat removal. Hence, DLC coatings can act as a thermal barrier protecting the polymer from detrimental heat and protecting the polymer from abrasive wear.

In this chapter, fundamental aspects of molecular dynamics simulation and several considerations are accounted for to attain accurate results that are comparable with experimental works. The multitude of potential functions is discussed with emphasis on those frequently used in modelling of brittle material. Several example theoretical models for nanometric machining of silicon and silicon carbide are presented, in view of these materials being regularly used across widespread application of industries. Different interatomic potentials used for these materials, along with the possible output data, are reviewed. Finally, the stress distribution is discussed by considering the interactive atomic forces and an empirical relationship of the tool-workpiece contact geometry.

For an SF 6 circuit breaker in capacitor bank making operation, the inrush current may cause serious erosion to its arcing contacts. In order to observe the contact erosion property and electrical life under making process, an arc extinguish chamber of SF 6 circuit breaker with Cu-W arcing contacts was designed, and experiments of capacitor bank making were carried out under different experimental conditions. In the experiment under various conditions, the arc duration and inrush current have been recorded, the mass loss has been measured after 100 times of operation, and the mass loss rate and friction coefficient have been calculated. Based on the failure mode of reversed order contacting between arcing and main contacts, an estimation method has been proposed to calculate the electrical life of arcing contact in making operation. This method can be used to support the design of the arcing contacts. Changing the arcing contact geometry and reducing arc energy in making operation will improve electrical life of arcing contact.

In machinery structures with joints, the contact pressures at contact interfaces are usually high enough to ensure that the contacting components stay joined and the gross slip does not occur. Nevertheless, the small relative slip over parts of the contact interface, i.e. the microslip, contributes significantly to the vibration damping. In the high-fidelity analysis of practical bladed discs, the macroslip model cannot provide sufficient accuracy for the predictive analysis of the properties of the friction damping in the contact interfaces. In this article, numerical studies of microslip damping effects is performed using 2D and 3D models of blade root joints. Analysis of hysteresis loops is performed to assess the influence of modeling parameters: choice of reference points, mesh configurations, and other physical parameters. The impact of the physical parameters, such as the contact geometry, friction coefficient, contact stiffness and tangential and normal loading, on the friction damping is numerically examined. The numerical results demonstrate the possibilities of microslip prediction using finite element modeling and show the microslip friction damping effects using simplified and realistic blade root models.

The blade-disc dovetail interface in an aero-engine compressor is characterized by a non-uniform pressure distribution which can be obtained by an equivalent flat with round edge-on-plate configuration. The contact tractions for a mating pair are affected by many parameters which include, contact geometry, loading conditions, and material properties; with contact geometry being one of the prominent factors. In the present work, a 2-D elastic and elasto-plastic finite element analysis has been carried out for a rounded contact geometry to study the influence of the radius of the corners ‘R’ and length of the flat region ‘2a’. It is observed that the peak tensile stress in the fretting direction was found to decrease with increasing ‘a’ (for constant ‘R’) which is likely to delay the crack initiation. Also, as compared to elasto-plastic analysis, elastic analysis overestimates peak tensile stress and possibly give a conservative estimate for the fretting fatigue life. Further, the effect of modelling elastic-plastic behaviour is significant for low a/R ratio (for constant ‘R’). However, opposite trend was observed when ‘R’ was varied keeping ‘a’ constant. Also, it is found that the effect of contact geometry cannot be characterized using a single parameter like a/R ratio or contact area.

The down-scaling of electrical components requires a proper understanding of the physical mechanisms governing charge transport. Here, we have investigated atomic-scale contacts and their transport characteristics on WS2 using conductive atomic force microscopy (c-AFM). We demonstrate that c-AFM can provide true atomic resolution, revealing atom vacancies, adatoms, and periodic modulations arising from electronic effects. Moreover, we find a lateral variation of the surface conductivity that arises from the lattice periodicity of WS2. Three distinct sites are identified, i.e., atop, bridge, and hollow. The current transport across these atomic metal-semiconductor interfaces is understood by considering thermionic emission and Fowler-Nordheim tunnelling. Current modulations arising from point defects and the contact geometry promise a novel route for the direct control of atomic point contacts in diodes and devices.

In this paper, we present the theoretical formula for calculating a friction-induced energy loss in a mechanical contact system consisting of two convex axisymmetric bodies subject to arbitrarily varying oblique loading. Non-flat contact geometry engenders a particular regime, partial slip, in which weakly compressed areas of the contact zone slip, while strongly compressed ones stick. Mechanical energy is transformed into heat only in the slip area in which two field characteristics should be calculated: the local infinitesimal slip distance distribution and shear stress. Their product equals the spatial distribution of the energy loss or heat source density, while the integration over the slip zone produces the global energy loss. The energetic characteristics are obtained in a general situation. In the proposed method, energy losses can be calculated at any time during a loading protocol, in the general case of an arbitrary load expressed in terms of normal and tangential displacements. This is a step forward in comparison to more traditional approaches in contact mechanics allowing to calculate the energy loss per period in the case where the contact is excited by a single periodic input. All required contact characteristics, including displacement and stress distributions, are provided by the semianalytical Method of Memory Diagrams (MMD) that has initially been developed to obtain memory-dependent solutions to the problem of frictional contact between axisymmetric profiles and has later been generalized for rough surfaces. In this work, the loading is limited to two dimensions: one normal and one tangential, as MMD is two-dimensional. The tangential loading is therefore colinear with the tangential displacement. Correspondingly, the proposed solution is exact for axisymmetric bodies and is approximately valid in the case of rough surfaces for which the energy loss per unit nominal area is calculated. The obtained theoretical results for energy dissipation are compared to analytical and numerical calculations for periodic and non-periodic loading situations, illustrating the potential of this method in realistic contact settings. ispartof: International Journal Of Solids And Structures vol:158 pages:268-276 status: published

In a dynamic radial shaft sealing (RSS) system good wear resistance is crucial for proper functionality. This contribution is dedicated to the analysis of wear in radial shaft seal applications in a sealing system itself and on a tribologically equivalent system. To make elastomers more wear resistant, new and innovative material concepts and compounds have to be evaluated. To do so a simple tribologically equivalent system, the ring-cone-tribometer (RFT), consisting of an elastomer ring and a coned shaft, was used. Two different radial shaft seal types were compared under identical test conditions on a multi-shaft test bench, to the results generated on the RFT. This was done to evaluate and compare the tribological properties of the RFT towards RSS. To avoid ageing or batch-to-batch influences the slabs for the production of the ring samples were molded from the same elastomer material batch as the radial shaft seals. Initial differences in terms of wear, friction, contact width and hardness between RSS and RFT were reduced step by step using an optimized, stiffer test setup on the RFT and a FE-simulation model to optimize the contact geometry. Data scattering on the RFT was reduced to a minimum so that the higher scatter within the results of the RSS test population was in a similar dimension as the deviation in both systems. To determine the wear during a test run, an online-wear measurement system, based on eddy current sensors, was developed that allows for the online estimation of seal wear progress on the RFT at any time. This process is based on a geometrical approach using the initial contact width and the axial displacement during the operation. The online-wear measurement correlates very well with the post-mortem wear measurement. All results form a set of tools which constitutes a solid foundation for online evaluation of rubber and seals in the future.

For the thermal modeling of cup wheel grinding process, most previous studies ignored the effect of wheel-work contact geometry on the amplitude and distribution of heat flux and grinding temperature, which oversimplifies the heat transfer condition when compared with that in the real grinding process, as a cup wheel typically has a rounded edge, due to the rapid wear during the initial grinding passes. In this paper, the relationships among the wheel-work contact geometry, the local material removal pattern at the grinding zone and the grinding temperature distribution have been investigated. A comprehensive 3D analytical thermal model considering the wheel-work contact geometry and its effect on the grinding heat flux distribution has been established and experimentally validated. The heat flux distribution in cup wheel grinding varies with the contact geometry and also the grinding parameters, which has never been mentioned in previous works. It has been found that the variation of the contact geometry significantly changes the local material removal pattern, and thus affects the grinding temperature distribution. Validation experiment results have demonstrated that the developed model could, to a great extent, describe the realistic grinding temperature. The relative errors of the maximum temperature are less than 6.6%, and the relative errors of the position of the maximum temperature are less than 8.5%. This research not only provides a new method to predict grinding temperature, but also enhances the understanding of cup wheel grinding processes.

Plint (IMechE 182 (1):300–306,1967) reported a reduced coefficient of friction with increasing roller sizes in EHL traction measurements. In this study, a similar scale effect has been observed when comparing measured traction curves at the same operating conditions between a ball-on-disc rig and a twin-disc machine of different geometrical sizes. This scale effect has been studied numerically for point contacts of different radii of curvature Rx based on thermal EHL simulations. Results show that the reduced friction for large Rx is caused by an increase in film thickness and the enhanced thermal effects. The mechanisms are: (1) heat is hard to conduct across a thicker EHL film due to bad thermal conductivity; (2) shear is mainly localized in the middle film.

An analytical method is developed for determining the contact parameters of cylinders when the contact geometry and structure are taken into account. If there is a gap in the roller bearing, this method permits determination of the maximum load on the roller, the roller displacement and rigidity, and the number of loaded rollers as a function of the gap width and external load.

Here we compare the wear performance of silica and polyurethane in a vacuum gripper. The problem is modeled numerically by evaluating the energy dissipated at the interface, and experimentally by examining surface damage in contact subjected to cyclic normal loading. In the numerical model, the energy dissipated during unloading is found to be negligible with respect to that of loading. Changing the contact geometry has a good effect in terms of frictional work reduction, but this is not as significant as the effect obtained by changing the material. Replacing silica with polyurethane reduces the frictional work by a factor of at least 20. The latter finding is qualitatively validated in experiments.

The initial stage of contact formation during field-activated/assisted sintering of powders is investigated experimentally and numerically for spherical particles of nickel, steel, and copper. The results of experimental studies of the contact resistance and the neck formation process due to melting/sintering in two- to three-particle systems under a single high-current pulse from a capacitor discharge are compared with results of fully coupled thermo-electrical finite-element simulations. The impact of particle size, contact geometry, and electrical load on the temperature and temperature gradient distribution during the pulse discharge is analyzed numerically for nickel spheres. The influence of the material itself is compared for nickel, steel, and copper systems.

Ball screws are robust and economic linear positioning systems that are widely employed in high speed and high precision machines. Due to precision and stability requirements, the preload force has been considered one of the main parameters in order to define the axial rigidity and the maximum axial load capacity of ball screw feed drives. In high speed motions, thermal effects are also considerably relevant regarding positioning precision and dynamic stability of the machine. The temperature increase and the thermal gradient between the screw, the balls and the nuts led to a variation in the contact geometry and consequently in the preload force. This paper presents an experimental analysis of the preload variation due to the temperature increase. The study has been performed for several initial preload forces and linear speeds in a preloaded double nut ball screw. The heating of the system results in a decrease of the preload force, where a maximum decrease of 60 % has been observed for a temperature increase of 28 K in the test bed of the study. Regarding the consequences of the loss of rigidity, the first eigenvalue decreased by only 5 % for a preload drop of 33 %.

A comprehensive thermal model is developed to analyse the heat transfer mechanism in form grinding of involute gears. The model analyses the thermal effects of a transient non-uniform heat source, moving with a three-dimensional curved shape, on the involute tooth profile. The variation of the contact geometry along the tooth profile is considered and analysed in detail, including the local grinding depth, equivalent wheel diameter and local contact arc length as well as the variation of the three-dimensional heat flux distribution and the heat partitioning to different thermal parts on the curved tooth profile. Based on the model established, the grinding temperature distribution patterns along the involute contact profile under different Peclet numbers, numbers of teeth and gear modules have been investigated. Along the tooth profile, the temperature increases significantly with the rolling angle. Grinding temperatures along the tooth profile of a straight spur gear, made of 20CrMnTi low-carbon steel, are measured using a special test rig designed with thermocouples imbedded into workpiece at different measurement positions. The results demonstrate that the calculated temperature distribution along the tooth profile has a rather good agreement with the measured result. This research provides a new method to predict grinding temperature in form grinding mode of precision gears.

This work presents a complete and systematic method for the analysis and simulation of geometric characteristics of mating surfaces of globoidal cam mechanisms. Based on the fundamental forms of globoidal cam surface, the asymptotic curves, the principal directions and curvatures, and the Dupin's indicatrix are obtained and simulated. The curvatures of asymptotic curves are calculated to verify whether the cam surface is a ruled surface or not, which is an important issue to determine the machining process of the globoidal cam. In addition, the relationship between the local shapes of the cam surface and the motion periods is presented. The characteristic curves of relative normal curvature at different contact points are depicted and compared as well. Based on the Dupin's indicatrix, the indicatrix of conformity (Dr. Radzevich, 1980s) is first applied to analyze the contact geometry of mating surfaces of globoidal cam mechanism. The indicatrix of conformity in the case of contact of saddle-like surface with convex parabolic-like surface is first discussed here. A globoidal cam mechanism used in automatic tool changer of CNC machines is presented to clarify the outlined methods. The proposed methodology is important for design, manufacture, and contact analysis of globoidal cam mechanisms.

A transient three-dimensional thermal elastohydrodynamic calculation model is introduced to simulate the contact of tooth flanks of helical gear pairs with involute gearing. At any time, contact geometry is derived from the real involute curves of gears. In addition to the consideration of mass conserving cavitation and the non-Newtonian fluid behavior, models to capture conditions of mixed friction and microhydrodynamic effects are included. To consider the non-Newtonian fluid behavior, a shear thinning fluid model with limiting shear stress is applied. A selected helical gear pair is used as example to examine the influence DLC coated tooth flanks have on tribological behavior. It shows that friction and temperature behavior of the gearing can be significantly influenced with DLC coating.

In this study the influence of tool inclination angle on deformation of thin wall cantilever shape part has been analyzed using finite element numerical simulations. Polycrystalline diamond, PCD tool has been chosen as a tool material in this study because PCD tool has given better results in terms of surface roughness, tool life and productivity in end milling of titanium alloy Ti-6Al-4V. Firstly, in this study, the effect of tool inclination angle on tool contact geometry, cutting speed and cutting forces has been discussed. Then, finite element numerical simulations (FEM) have been carried out in AdvantEdge® for the prediction of cutting forces with PCD tool at four different tilt angles viz. 70°, 75°, 80° and 85° and the results have been compared to the coated carbide tool. Then the maximum magnitude of the forces which occurred in tangential direction (FY) were input in the Abaqus® software as a load acting on the thin long cantilever part and deformation results were analyzed. Results show that PCD tool due to its high hardness, strength and better wear resistance produce lower cutting forces at all angles studied and at an angle near the perpendicular to the surface being machined both tools have lower values of the deformation. The FEM simulation results match well with the theoretical study as theoretical analysis also shows that at angles nearer to perpendicular to the surface being machined, the tool will have lower effective cutting speed & forces and hence proved as the key to achieving better accuracies for long thin wall parts.

Thermal damage control in high efficiency form grinding of precision gears is critical for obtaining the required gear surface integrity and ensuring the contact strength in service life. Complex thermal models have been developed to determine the variation of burn thresholds of power under different grinding parameters in form grinding mode of gears. The thermal models analyse in detail the variation of local contact geometry between the grinding wheel and gear surface, and the variation of heat partitioning to different thermal parts including the workpiece, wheel, grinding fluid and grinding chips. The burn thresholds of power in the form grinding of carbonised steel gears have been determined by relating the grinding temperature with the Barkhausen Noise and micro-hardness measurements for the ground surfaces. The models and the determined burn thresholds can be used for presetting the parameters and conditions of grinding process and monitoring the grinding process to avoid the occurrence of thermal damages to the gear surfaces.