Multipoint Contact Research Articles

Numerical simulation of rail surface-initiated rolling contact fatigue in the switch panel of railway turnouts

Considering the complex characteristics of the track structure in railway turnouts, it is difficult and also expensive to experimentally study rail damages; therefore, numerical methods are an effective alternative. This study presents a numerical method to simulate rail surface-initiated rolling contact fatigue in the switch panel of railway turnouts. This method includes simulation of the vehicle–turnout wheel–rail dynamic interaction, analysis of the wheel–rail multipoint non-Hertzian rolling contact that considers the relative motion between the switch and stock rails, and calculation of the accumulated rail surface-initiated rolling contact fatigue. The accumulated rail surface-initiated rolling contact fatigue after the vehicles passed a turnout switch panel 80 times (the average number of vehicles running on the Chinese high-speed railway lines per day) in the through route with facing move was simulated based on this procedure. The result showed that the maximum surface-initiated rolling contact fatigue damage of the switch rail and the stock rail was 1.57 × 10−2 and 0.62 × 10−2, respectively. Surface-initiated rolling contact fatigue in the switch rail mainly occurred at the gauge angle, and in the stock rail it mainly occurred at the center of the rail. In addition, the influence of track parameters (rail inclination, track gauge, and friction coefficient) is analyzed. The friction coefficient influenced the rail surface-initiated rolling contact fatigue. When the coefficient exceeded 0.3 in particular, the rail rolling contact fatigue damage increased sharply. Hence, suitable friction control measures should be taken during rail maintenance in order to mitigate the rail surface-initiated rolling contact fatigue damage, e.g. by keeping the wheel–rail friction coefficient below 0.3.

Multipoint Contact Dynamics and the Detumbling Strategy for a Fast-Tumbling Target

To ensure the safety of operations with a fast-tumbling target, a detumbling strategy implemented by a dual-arm space robot with finger-type end effectors is proposed to attenuate the target rotation. A detumbling system that consists of the robot and the target is established. Through the contact effects between the two parts, the energy of the target is gradually dissipated. Evaluated by the detumbling duration, energy consumed, and the target movement, the contact strategy is developed. Through numerical simulations, the multipoint contact detumbling is verified feasible to detumble a fast-tumbling target. With suitable parameters, the kinematic response of the detumbling system could be bounded and steady, which makes further operation for the target easier.

Tailoring the interfaces of silicon/carbon nanotube for high rate lithium-ion battery anodes

Micrometer-sized silicon powders, due to its high specific capacity, easy accessibility, and low cost, have been regarded as an attractive anode material for lithium-ion batteries. The severer mechanical instability and high inter-particle resistance during cycling, however, hinder its further application. In this work, a novel potholed micrometer-sized silicon powders (PMSi)/carbon nanotubes (CNT)/C electrode is proposed. The resulting three-dimensional (3D) conductive framework and multi-point contact network exhibit ideal structural stability and high-rate cycling property. Hence, the volume resistivity of PMSi/CNT/C (157 Ω m) is reduced significantly relative to traditional PMSi/commercial carbon nanotubes (CCT)/C composite (400 Ω m). By testing the fabricated half-cell LIB with the PMSi/CNT/C composite anode, high reversible specific capacity of 2533 mAh g−1 with a remarkable high initial coulombic efficiency of 89.07% and over 840 mA h g−1 for 1000 cycles at 2 A g−1 is measured. Even at the rate of 20 A g−1, the PMSi/CNT/C electrode shows a capacity of 463 mAh g−1. A full cell contained the PMSi/CNT/C anode and a LiFePO4/LiMn2O4 cathode successfully ignites an LED array (~1.5 W), further demonstrating its outstanding electrical driving property.

Investigation on Wheel-Rail Contact and Damage Behavior in a Flange Bearing Frog with Explicit Finite Element Method

Flange bearing frogs are designed to provide continuous rolling surfaces for trains traveling on the through line, but the interaction between wheel and rail in a diverging line is more complex than that for a common crossing, especially including flange bearing mode and multipoint contact during the transition. The wheel load will be transited from tread to flange and back to tread, which will intensify the wheel-rail interaction. In this paper, a numerical procedure is presented for the analysis of wheel-rail rolling contact behavior and damage prediction for the flange bearing frog. The three-dimensional explicit finite element (FE) model of a wheel passing the flange bearing frog is established to obtain the dynamic wheel-rail interaction in both the facing and the trailing move. The evolution of contact forces, the distribution of adhesion-slip regions, and shear surface stress and microslip at the contact patch are revealed. Then, the competition relationship between RCF (rolling contact fatigue) and wear of a flange bearing frog is analyzed. The results of numerical simulations can contribute to an understanding of the mechanism of the transient rolling contact behavior and provide guidance in design optimization for flange bearing frogs.

An efficient multibody dynamic model of three-dimensional meshing contacts in helical gear-shaft system and its solution

The dynamics of helical gear-shaft systems are characterized by three-dimensional (3D) meshing contacts that have significant variations in the location and size of the contact area, resulting in noise that is unavoidably transmitted to the gearbox through the shaft. Accurate and efficient predictions of the dynamic behaviors of helical gear and shaft are indispensable in reliable and cost-effective gearbox design. Available analytical methods, though computationally feasible, cannot consider multi-point contacts and uneven tooth-load distribution. In contrast, the finite element (FE) method provides a high-fidelity approach to compute the dynamic behaviors of a general gear-shaft system at high expenses of computation. This paper aims to establish a high-efficiency multibody dynamic model for 3D contacts in helical gear-shaft systems, in which the helical gear is pertinently represented under the framework of Arbitrary Lagrangian Eulerian formulation and the shaft is discretized by 3D Timoshenko beam elements. The computational efficiency is greatly improved through the following four steps. First, the low-frequency approximation technique is adopted to reduce the degrees of freedom (DOFs) resulting from the fixed boundary normal modes. Second, under the framework of ALE formulation, only the FE nodes of three meshing tooth-faces are defined as boundary nodes. Then, the dynamic equations and Jacobian matrix are simplified by ignoring the inertial forces associated with deformation. Finally, a two-step algorithm is adopted to accelerate the contact detection process. The accuracy and efficiency of the proposed method are demonstrated through five numerical tests with correlation to commercial nonlinear finite element software.

Analysis on limiting value of rail corrugation of floating-slab track based on wheel/rail multi-point contact

Analysis on limiting value of rail corrugation of floating-slab track based on wheel/rail multi-point contact

'Delayed Forbearance': Multipoint Contact and Mutual Forbearance in Inaugural and Subsequent Actions

One strand of theoretical development in the multimarket competition literature asks the important question of whether or not mutual forbearance applies uniformly to all types of competitive actions. For example, scholars have shown that mutual forbearance takes effect for exploitation, but not exploration-based actions. Extending this line of research, we study how the onset of mutual forbearance also differs across inaugural and subsequent competitive actions. The key difference between the two lies in the identity of the initiator -- inaugural actions are by firms new to the market domain, and subsequent ones are by existing incumbents. The crux of our argument is that mutual forbearance has a delayed onset for subsequent competitive actions (relative to inaugural ones). We test our predictions in the context of product segment entry decisions of automobile firms in the US market between 1980 and 2015. We find an inverted-U shaped effect of multisegment overlap on a firm's likelihood of making inaugural and subsequent entries into a product segment. Crucially, however, we also find that the inflection point of the inverted U-shaped curve is substantially higher for subsequent entries than for inaugural entries. This corroborates our key argument that mutual forbearance sets in later for subsequent competitive actions than for inaugural ones.

Effects of central symmetry and elongation on the dense disordered packings of entangled particles

Geometric shape is an important factor that affects the packing and mechanical properties of granular material. In this paper, we use four families of assembled rods to model an entangled material in simulations. The particles are all non-convex and have the ability to interpenetrate. Together with elongation, central symmetry, which is attributed to the intersection location of the elementary rods, is also a main factor that produces varieties of particle shapes. With a certain total elongation, the dense disordered packing density is verified to be independent of the elongation distribution of the elementary rods. The specific shape hardly affects the packing densities. Therefore, the empirical formula to predict the packing density is extended to apply to all assembled rods with any elongation distribution. Different from the packing density, the shape disparity caused by central symmetry is found to significantly influence the contacts between neighboring particles. Due to more multipoint contacts contributing more constraints around the central particle, the centrally symmetric 3DX-shaped particles can more easily interpenetrate in the granular system. Moreover, the higher number of constraints contributed by neighboring contacts reflects the hyperstaticity of packings, which suggests mechanical stability for disordered packings of non-convex assembled rods.

Modeling three-dimensional surface-to-surface rigid contact and impact

This work presents a rigid body framework for analyzing three-dimensional surface contacts and impacts as a simultaneous multi-point impact problem with friction. A method is developed to address the indeterminacy issue typically associated with multi-point contact and impact analysis. This is accomplished using the constraints on impulses and contact forces defined by the Coulomb friction law and rigid body constraints. The proposed approach relies on a global interpretation of Stronge’s energetic coefficient of restitution (ECOR) to maintain energetic consistency. A key aspect of this work involves addressing the three-dimensionality of this problem, which requires a numerical integration in the impulse domain to address the slip/no-slip behavior in the tangential plane of the impact. This work also models the transition to contact after a series of impacts, and proposes a method for enforcing frictional contact constraints. Several examples of simulation results using the proposed method are presented here.

Study on Multi-Point Random Contact Characteristics of Metal Rubber Spiral Mesh Structure

Metal rubber (MR) is a porous damping material, which achieves the damping energy consumption by the contact friction between the internal wires. Complex wire structure makes explanation of energy dissipation mechanism by the traditional theoretical models limited to comparison with equivalent models or microcell models, which cannot truly reflect the spatial multi-point contact characteristics of each wire. This work demonstrates numerical modeling based on actual preparation process parameters of annular MR. Using the penalty function to solve the complex contact that is difficult to predict between the internal spiral wires, the variation laws for equivalent stress and strain recorded during the loading-unloading process of MR, were obtained. The small-ball algorithm and the Tabu search algorithm were used to realize the accurate assessment of contact points between the wires and the hyper dimension matrix was used to track the friction state of the contact points in real time, thereby obtaining a proportional relationship between various friction forms during the loading-unloading process. It is found that sliding friction accounts for the majority of the total number of contact points, which is about 81.38%, consistent with the equivalent plastic strain law of stepwise change. It becomes further clarified from the microscopic point that MR accomplishes macroscopic energy dissipation mechanism through the fretting slip friction between the internal wires. In order to verify the authenticity of the simulation, a quasi-static loading-unloading experiment of MR was carried out under identical parameters, and the experimental macroscopic results were in excellent agreement with the simulation results. The research indicates that the MR finite element model established in this paper can precisely describe the dynamic contact of the internal structural features of MR materials, for providing a theoretical basis for guiding the preparation and application of MR.

High‐Speed Train‐Track‐Bridge Dynamic Interaction considering Wheel‐Rail Contact Nonlinearity due to Wheel Hollow Wear

Wheel hollow wear is a common form of wheel‐surface damage in high‐speed trains, which is of great concern and a potential threat to the service performance and safety of the high‐speed railway system. At the same time, rail corridors in high‐speed railways are extensively straightened through the addition of bridges. However, only few studies paid attention to the influence of wheel‐profile wear on the train‐track‐bridge dynamic interaction. This paper reports a study of the high‐speed train‐track‐bridge dynamic interactions under new and hollow worn wheel profiles. A nonlinear rigid‐flexible coupled model of a Chinese high‐speed train travelling on nonballasted tracks supported by a long‐span continuous girder bridge is formulated. This modelling is based on the train‐track‐bridge interaction theory, the wheel‐rail nonelliptical multipoint contact theory, and the modified Craig–Bampton modal synthesis method. The effects of wheel‐rail nonlinearity caused by the wheel hollow wear are fully considered. The proposed model is applied to predict the vertical and lateral dynamic responses of the high‐speed train‐track‐bridge system under new and worn wheel profiles, in which a high‐speed train passing through a long‐span continuous girder bridge at a speed of 350 km/h is considered. The numerical results show that the wheel hollow wear changes the geometric parameters of the wheel‐rail contact and then deteriorates the train‐track‐bridge interactions. The worn wheels can increase the vibration response of the high‐speed railway bridges.

Contact and Noncontact Measurement of Electronic Transport in Individual 2D SnS Colloidal Semiconductor Nanocrystals.

Colloidal-based solution syntheses offer a scalable and cost-efficient means of producing 2D nanomaterials in high yield. While much progress has been made toward the controlled and tailorable synthesis of semiconductor nanocrystals in solution, it remains a substantial challenge to fully characterize the products' inherent electronic transport properties. This is often due to their irregular morphology or small dimensions, which demand the formation of colloidal assemblies or films as a prerequisite to performing electrical measurements. Here, we report the synthesis of nearly monodisperse 2D colloidal nanocrystals of semiconductor SnS and a thorough investigation of the intrinsic electronic transport properties of single crystals. We utilize a combination of multipoint contact probe measurements and ultrafast terahertz spectroscopy to determine the carrier concentration, carrier mobility, conductivity/resistivity, and majority carrier type of individual colloidal semiconductor nanocrystals. Employing this metrological approach, we compare the electronic properties extracted for distinct morphologies of 2D SnS and relate them to literature values. Our results indicate that the electronic transport of colloidal semiconductors may be tuned through prudent selection of the synthetic conditions. We find that these properties compare favorably to SnS grown using vapor deposition techniques, illustrating that colloidal solution synthesis is a promising route to scalable production of nanoscale 2D materials.

Predictive modeling of chatter stability considering force-induced deformation effect in milling thin-walled parts

Abstract Force-induced deformation is an inevitable phenomenon in thin-wall milling operations, which makes the actual radial depth of cut deviate from its nominal value and changes tool-part engagement angle boundaries. This paper presents an accurate modeling of dynamic milling system with the force-induced deformation effect. Both the thin-walled part and the cutter are discretized into differential elements, such that the influences of the force-induced deformation and multi-point contact structure dynamics can be simultaneously considered at the contact zones. A detail flexible iteration strategy is first presented to calculate the force-induced deformation and the resulting tool-part engagement angle boundaries. After that, time-varying multi-modal dynamic parameters with actual material removal effect are obtained by simultaneously modifying structural static and dynamic stiffness at each tool feed position. The system involving regenerative dynamic displacements is formulated as a matrix of time-periodic delay differential equation. Chatter stability of the system is predicted by an extended second order semi-discretization method. Milling experiments are conducted to validate the proposed approach, and two types of parts with different wall thickness are designed. The results show that chatter can be well predicted by using the proposed approach.

Aspects regarding the contact between wheels and turnouts

Wheel and turnouts life safe operation and life span prediction may be improved through a more thorough research. Currently, numerical methods for the study of the before mentioned problem bring significant overhead in computing systems. The present work describes a multi-point contact study between wheel and switch using Kalker’s three-dimensional theory, using CONTACT software. This method has the advantage to suit well the frictional aspects of the phenomena. More than that, comparisons between results obtained with FE software and with CONTACT software reveal a remarkable similarity. The latter method however, is significantly more efficient from the numerical method point of view and it also allows computing the contact points position either on the fly or using look up tables.

Triboelectrification-enabled thin-film tactile matrix for self-powered high-resolution imaging

Tactile sensors have broad applications in human-machine interfacing technologies. In this work, we report a type of a thin-film-based flexible integrated triboelectric sensing matrix (ITESM) that is of high resolution and large area. It has a total of 3600 sensing units and a resolution of 50 dots per inch (dpi), which are 14 times and 25 times of the state-of-the-art works on the triboelectric sensor array, respectively. When touched by an external object, the ITESM generates a voltage signal in its bit electrode lines and word electrode lines due to the combination of triboelectrification and electrostatic induction. With the assistance of a signal processing circuit that filters and amplifies the electric signal, an average voltage signal of 0.4 V can be acquired. Due to the design of a shielding layer, the electrostatic induction among adjacent electrode lines are effectively eliminated, resulting in a near end crosstalk (NEXT) of merely 0.05. As a result, single-point as well as multi-point contacts can be explicitly revealed. Therefore, the ITESM in this work presents a major step in the direction of high-resolution and large-area triboelectric sensing.

Adhesion failure propagation analyses of Spar Wingskin Joints made with curved laminated FRP composite and FGM panels

Spar Wingskin Joint (SWJ) comprises of a thin spar which overlaps and is co-cured to a thick wingskin by suitable adhesive materials. These joints are mostly used in integral modular fabrication of aircraft and fuselage wing structures usually made with curved laminated Fibre Reinforced Polymeric (FRP) composite panels. This paper deals with the analyses of initiation of adhesion failure and its propagation in SWJs subjected to transverse loadings using Finite Element Analyses (FEA) and fracture mechanics approach. Normal and shear stress distributions at different interfacial locations between the adherends and the adhesive have been evaluated. Tsai-Wu coupled stress failure criteria have been used to identify the location of onset of adhesion failure. The critical location for onset of adhesion failure has been found to be at the toe-end of the spar wingskin overlap region. Pre-embedded adhesion failure has been simulated at this location and Strain Energy Release Rate (SERR) components corresponding to Mode I, Mode II and Mode III of adhesion failure have been determined using the principle of Virtual Crack Closure Technique (VCCT). Rate of propagation of adhesion failure has been evaluated by sequential release of Multi-Point Constraint (MPC) and contact finite elements provided at the pre-embedded failure front. It has been observed that Mode I component of SERR primarily governs the process of adhesion failure propagation. The appropriate spar overlap length on the wingskin has been determined in order to prevent adhesion failure. Further, an attempt has been made to improve the structural integrity of the SWJ by reducing the stress concentration at the ends of spar and wingskin overlap. This has been achieved by obtaining a favourable stress distribution over the entire joint structure by using Functionally Graded Materials (FGM) in the spar and wingskin adherend instead of FRP composite panels. Exponential gradation indices have been used for material grading of the spar and wingskin adherends. It has been seen that peel and shear stresses and values of SERR components as well as total SERR reduce significantly by use of FGMs with suitable exponential material grading index.

A New Resistive Belt Sensor for Multipoint Contact Detection of Robotic Wheels

In this paper, a new, simple and cheap sensor is proposed to detect the multipoint contact of a typical robotic wheel. The new sensor empowers a wheeled robot to scan the surface and to find stability margins during real-time locomotion without camera or laser sensors. Furthermore, it enhances the ability of the real-time solution of the dynamic equations. The new sensor is based on the total resistance of a circuit and can be classified into two types. In the first type, the resistive circuit includes a conductive path, a direct voltage source and some resistors by various values. The main advantage of this type of the new sensor is to determine the exact locations of multipoint contact only by means of an input data detecting the voltage of a resistor. The implementation of the new idea is easy to use and to be experimented. It can be used to improve the control process, especially on the rough surfaces and to enhance the locomotion stability. The second type of the new sensor contains a continuous resistive belt with higher accuracy than the first type. The algorithm of the multipoint contact detection is explained and the kinematics relations of the robot are obtained. The surface is scanned during the robot locomotion, and the error of the estimated surface profile is calculated. Finally, the static stability margins are extracted using the new sensor data.

Numerical simulation of high-temperature thermal contact resistance and its reduction mechanism

High-temperature thermal contact resistance (TCR) plays an important role in heat-pipe-cooled thermal protection structures due to the existence of contact interface between the embedded heat pipe and the heat resistive structure, and the reduction mechanism of thermal contact resistance is of special interests in the design of such structures. The present paper proposed a finite element model of the high-temperature thermal contact resistance based on the multi-point contact model with the consideration of temperature-dependent material properties, heat radiation through the cavities at the interface and the effect of thermal interface material (TIM), and the geometry parameters of the finite element model are determined by simple surface roughness test and experimental data fitting. The experimental results of high-temperature thermal contact resistance between superalloy GH600 and C/C composite material are employed to validate the present finite element model. The effect of the crucial parameters on the thermal contact resistance with and without TIM are also investigated with the proposed finite element model.

Mathematical simulation of thermocouple characteristics

Within this article, the investigation of the electrical characteristics of two thermocouples in parallel connection was mathematically simulated for further research of the effect of multi-point contact between the sensing thermocouple electrodes and the inspected sample in thermoelectric inspection devices.

Influence of Heterogeneous Contact Stiffness and Heterogeneous Friction Coefficient on Frictional Squeal

Contact stiffness and friction coefficient are excitation sources and key influencing factors to frictional squeal with obvious inhomogeneous characteristic that is always neglected. In this paper, a multipoint contact flexible pin‐on‐disc system is established considering tangential stiffness. Then influence of contact stiffness and friction coefficient with heterogeneous distribution on frictional squeal is studied using the complex modal analysis. The research shows that contact stiffness and friction coefficient heterogeneities influence the likelihood of occurrence of the squeal, the frequency of the squeal, and the real part of the complex eigenvalue of the system. And when the contact stiffness and friction coefficient are close to the boundary of the region of mode‐coupling instability, flexible pin‐on‐disc system with homogeneous contact stiffness and friction coefficient cannot predict whether frictional squeal occurs or not. Besides, uncertain distribution of contact stiffness and friction coefficient can induce the uncertainty of brake squeal.