Dynamic Contact Behavior Research Articles

Analysis of the dynamic contact behaviour of high-speed train transmission gear excited by wheel defects

Studies on wheel flatness and polygonal wear have demonstrated that wheel defects cause severe impact forces at the wheel–rail interfaces. This study investigated the dynamic contact mechanical behaviour of high–speed train transmission gears when subjected to wheel defects. First, a train-track coupling dynamics model was established, considering the localized contact characteristics of transmission gears. This model was developed using the slice method and the Hertz contact model, exploring the spatial coupling effects between the gear contact interface and the train–track interface. Subsequently, the dynamic model was employed to extract essential contact mechanical parameters of the transmission gear under the influence of wheel defects, including gear meshing load, gear contact stress, and sliding velocity. Furthermore, an analysis was conducted to uncover and elucidate the mechanism by which wheel flatness and polygonal wear impact the dynamic contact behaviour of the transmission gear. This study underscores the importance of considering wheel defects when assessing the contact fatigue and wear performance of high-speed train transmission gears.

Aluminum oxide droplet collisions: Molecular dynamics study

In this work, the induced coalescence mechanism and dynamic contact behavior of alumina (Al2O3) droplets at different impact velocities were investigated for the first time from a microscopic point of view by molecular dynamics (MD) methods through the analysis of axial speed, shrinkage, neck radius ratio, contact force, temperature, kinetic energy, surface energy, and the amount of change in the internal energy of the droplets. The results show that the minimum speed at which collisional coalescence of Al2O3 droplets occurs is 30 m/s. When the speed is lower than 30 m/s, the droplets undergo bounce phenomena due to the Coulomb force. Under the high-speed impact, the inertia force of Al2O3 droplets acts less than the surface tension and viscous resistance. The droplets don’t get squashed in the whole collision process. For the different initial velocities, the magnitude of the contact force on a unilateral droplet during the collision process does not always increase with speed. When the collision speed is not higher than 400[Formula: see text]m/s, the contact force on the droplets eventually stabilizes at about 0.28[Formula: see text]Kcal/(mol⋅Å), whereas this value is about 0.36[Formula: see text]Kcal/(mol⋅Å) and about 0.5[Formula: see text]Kcal/(mol⋅Å) for the intervals from 500[Formula: see text]m/s to 700[Formula: see text]m/s and from 800[Formula: see text]m/s to 1000[Formula: see text]m/s, respectively. The increase of the droplet’s initial speed has a limited contribution to the temperature of the system after the collision, and the amount of loss of the total energy (the sum of kinetic energy, surface energy, and internal energy changes) becomes more pronounced, even up to about 20% when the speed reaches 900[Formula: see text]m/s. At the same time, we predicted the Al2O3 melting point and compared it with the standard melting point with an error of 2%, proving the accuracy of the model. This work can strengthen our understanding of the industrial processes with applications in high-energy nanomaterials, rocket propellants, rocket structure design and performance optimization.

Dynamic behavior of rack vehicle-track(rack) coupled system on super-large-slope bridges

Rack railways are mainly used in mountainous areas, where inevitably, super-large-slope bridge structures appear. The dynamic behavior of the rack vehicle-track(rack) coupled system on super-large-slope bridge is rarely studied. To address this issue, a dynamic interaction model for rack vehicle-track(rack)-bridge system is established by considering the detailed dynamic meshing behavior of gear-rack and the dynamic contact behavior of the wheel-rail. On this basis, the gear-rack meshing force and the wheel-rail contact force of rack vehicles are studied under lines with varying slopes, and the dynamic behavior of the rack vehicle and the track-bridge system with a slope of 250‰ is further analyzed. Research results show that as the slope line increases, the gear and rack meshing force increases, but the wheel-rail vertical force decreases. Concurrently, the stability index of the vehicle changed considerably, and the stability of the vehicle decreases substantially. The maximum values of the vibration acceleration of the vehicle body and bridge are 0.4 m/s2 and 0.5 m/s2, respectively, meeting the requirements of the relevant standards for the vibration acceleration of the vehicle body and bridge. Further analysis reveals that the vibration of rack is mainly affected by the meshing force, and the vibration of the bridge is mainly affected by the wheel-rail force. These research results can offer a theoretical basis for the pre-design, post-operation, and maintenance of rack railways.

Soil conditioning of clay based on interface adhesion mechanism: Microscopic simulation and laboratory experiment

Clogging frequently occurs in the cutter head, excavation chamber or screw conveyor when an earth pressure balance (EPB) shield machine is tunneling in soft or silty clay ground with high clay mineral content. In this paper, montmorillonite, kaolinite, and illite were selected as research objects, and molecular dynamics simulation and laboratory experiment were adopted. At the microscopic scale, dynamic contact behavior and interfacial mechanical behavior of the interface between clay minerals and water/surfactant solution was simulated and the interfacial adhesion and conditioning mechanism between clay minerals and water/surfactant solution was revealed. Thus, sodium dodecyl benzene sulfonate surfactant was selected as the main composition of the soil conditioner. Then, the adhesion stress before and after soil conditioning and the contact angles between clay minerals and water/surfactant solution were tested and analyzed at the macroscopic scale. The result shows that the contact angle between droplet and clay mineral surface is an important parameter to characterize soil adhesion. The simulation rules of the microscopic contact angle are consistent with the experiment results. Furthermore, the adsorption energy between microscopic substances is dominated by electrostatic force, which can reflect the adhesion stress between macroscopic substances. Soil adhesion stress can be effectively decreased by adding the surfactant to the soil conditioner.

Reliability of super-slope bridge-rack system on rack railway

ABSTRACT During the operation of rack railway on super-slope bridges (especially under temperature load), structural deformation of bridge-end is much larger than that of rack due to the difference of structural continuity between bridge and rack, which greatly increases local stress in rack, damages rack and fastener, and seriously threatens the operation reliability. To investigate the reliability of rack caused by temperature load and nonlinear dynamic interaction between super-slope bridge and rack, a detailed vehicle-rack(rail)-bridge coupled dynamic model is established with consideration of nonlinear dynamic meshing behaviour of gear-rack system and nonlinear dynamic contact behaviour of wheel-rail system. Then a field test is performed to obtain the basis dynamic behaviour of rack railway and validate the established numerical model. On this basis, the effects of temperature load, gear-rack meshing behaviour and wheel-rail contact behaviour on deformation and internal stress of rack-bridge system are investigated. Finally, the method to guarantee the structural reliability of rack railway on super-slope bridge is proposed. Results show that rack deformation nearby bridge gap is highly inconsistent with bridge deformation subject to different loads, and the internal stresses in rack and bolt exceed limit values written in relevant code, which seriously threatens the reliability of the rack structure. The maximum rack stress is 898 MPa, which exceeds the tensile strength of rack. The maximum shear stresses of bolts between fastener and rack and between fastener and sleeper are 1510 MPa and 656 MPa respectively, which exceed the shear strength of bolts. According to the calculation results in this paper, elastic fastener is suggested to be used to connect rack and sleeper, which can effectively reduce stress in rack and bolt, and improve the reliability of the rack structure.

Study on Dynamic Contact Behavior of Multi-Component Droplet and Dust Surface

The dynamic contact behavior between multi-component droplets and the surface of iron ore dust was taken as the research object, analysis of the maximum spreading coefficient, maximum acting diameter, maximum acting area, and maximum bouncing height of solid-liquid contact, from a microscopic perspective, using high-speed photography and image analysis and processing technology. The experimental results indicate that (1) with the particle size of dust particles decreases, the solid-liquid contact behavior sequentially manifests as spread immediately after broken, retraction, negative bounce, primary bounce, and secondary bounce. (2) When the surface tension of the droplets decreases from 55.5 to 34.8 mN/m, the maximum spreading diameter of the droplet has increased by 30% to 40%, the maximum bounce heights (coefficients) decreased by 100%, 57.14%, and 53.57%, respectively, the maximum spreading coefficient of the droplet exhibits no obvious pattern. (3) With decreasing droplet surface tension, the unidirectional acting diameter and the maximum acting area increase when the dust surface size is over 100 μm. When the surface particle size is less than 100 μm, there is no significant change in the unidirectional acting diameter and maximum acting area despite decreasing surface tension. Thus, droplet diffusion is mainly influenced by particle size. These findings contribute to enhancing the theory of water mist dust removal and improving dust removal efficiency.

Investigation of transient wheel-rail interaction and interface contact behaviour in movable-point crossing panel

The high-speed turnout is a key part of railway track infrastructure. A process of wheel-load transition and single-wheel/multi-track contact take place in the turnout area, causing significant wheel-rail interaction. Most high-speed turnouts include movable-point crossings. To investigate the wheel-rail transient rolling contact behaviour in movable-point crossings, a 3D finite element (FE) model of a wheelset rolling over a crossing was introduced. The actual geometrical profile of the wheel and the rails in turnouts, the nonlinear materials, the actual relative motion between the point/wing rail, and the moving postures of the wheelset were considered. The simulated mode shape was compared with the experimental mode shape to verify the wheel-rail coupling model. Precise frictional rolling contact solutions and dynamic response, including wheel-rail force, contact stress, equivalent stress, equivalent plastic strain, and stick-slip distribution of the contact patches, were all studied. After this, the parametric analysis of dynamic wheel-rail contact behaviour was carried out. The simulated results indicate that the proposed explicit finite element method can characterise wheel-rail coupled dynamic interaction and mesoscopic rolling contact behaviour well, and improve the understanding of wheel-rail contact behaviour in the movable-point crossing panel of the high-speed turnouts.

Zoom disrupts eye contact behaviour: problems and solutions.

Natural, dynamic eye contact behaviour is critical to social interaction but is dysfunctional in video conferencing. In analysing the problem, I introduce the concept of directionality and emphasize the critical role of motion parallax. I then sketch approaches towards re-establishing directionality and enabling natural, dynamic eye contact in video conferences.

Transient study of droplet oscillation characteristics driven by an electric field

Electrowetting technology, a microfluidic technology, has attracted more and more attention in recent years and has broad prospects in terms of microdroplet drive. In this paper, the dynamic contact angle theory is used to develop a numerical model to predict the droplet dynamic contact behavior and internal flow field under electrowetting. In particular, based on the established computational model of droplet force balance, the dynamic process of a droplet under electrowetting is analyzed, including the perspective of pressure variation and force balance inside the droplet. The results show that when the alternating current frequency increases from 50 Hz to 500 Hz, the amplitude of the oscillation waveform after droplet stabilization is 0.036 mm, 0.016 mm, 0.013 mm and 0.002 mm, while the relevant droplet oscillation period T is 11 ms, 4 ms, 2 ms and 1 ms, respectively. It is also found that the initial phase angle does not affect the droplet oscillation amplitude. In addition, the pressure on the droplet surface under alternating current electrowetting increases rapidly to the maximum value with resonant waveform oscillation, and the droplet will present different resonance modes under voltage stimulation. The higher the resonance mode is, the smaller the droplet oscillation amplitude is and the streamline at the interface will present an eddy current, in which the number of vortices matches the resonance mode. A high resonance mode corresponds to a small droplet amplitude, while there are more vortices with a smaller size.

Numerical studies on contact behavior in polymer composite sprocket - Roller chain drive under dynamic conditions

The unique properties along with ease of manufacturing make short fiber reinforced polyamide 66 composites ideal for sprockets used in low positive power transmission. An explicit dynamic finite element simulation of short fiber reinforced polyamide 66 composite sprocket—roller chain drive was carried out. The sprocket was approximated as a plane stress body and roller was considered as a rigid circle. The contact force extracted from the numerical simulation was validated with the analytical results for a standard chain. The deviations in the pitch of the chain produced a varied dynamic contact behavior in terms of a distinct contact width and pressure distribution pattern. The position of maximum contact shear stress altered from subsurface to surface due to low contact normal stress and associated slip. The variation in the chain pitch (up to 3%) affected the peak force of driver sprocket significantly (up to 41%). The increase of pretension of roller chain from 100 to 300 N induced the rise in contact force of driver sprocket up to 169% without changing the pattern.

Dynamic contact behavior of graphite-like carbon films on ductile substrate under nano/micro-scale impact

Coated components are often subjected to high strain rate and repetitive contact damage in practical service, so how to quickly evaluate the dynamic contact behavior of the thin protective coating is particularly important. Highly resolved single nano-impact and novel multiple micro-scale impact tests were used to investigate the dynamic hardness and fatigue failure of 0.55–1.52 μm thick graphite-like carbon (GLC) films on 316L stainless steel with varied thickness, respectively. By analyzing the impact depth and velocity before and after the indenter first contact with the sample, the dynamic hardness of GLC film/substrate system was obtained reasonably based on the energy approach in single nano-impact tests. Possible reasons for the higher dynamic hardness than quasi-static hardness include overestimation of the plastic absorbed energy W p and the strain rate sensitivity of materials. The thickest film/substrate system studied had a higher dynamic hardness than the thinner films due to its higher load carrying capability. Results with the multiple micro-impact technique showed that a GLC film with intermediate thickness (1.1 μm) was more resistant to the impact fatigue, while the thinnest film, 0.55 μm, exhibited more pronounced radial cracks under the indent and the thickest film , 1.52 μm, showed more significant edge ring cracks, these differences resulting from the combined action of stress distribution, film microstructure and mechanical properties . • Provide an energy-based method to evaluate the dynamic mechanical properties of thin films or film/substrate system. • Improve the understanding of impact failure of hard coatings deposited on ductile substrates by the novel micro-impact. • Investigate the influence of acceleration force on the dynamic contact behavior of hard coatings on ductile substrates. • Discuss the influence of film thickness on their dynamic contact behavior.

Identification of the Effect of Ultrasonic Friction Reduction in Metal-Elastomer Contacts Using a Two-Control-Loop Tribometer

Pneumatic cylinders are widely used in highly dynamic processes, such as handling and conveying tasks. They must work both reliably and accurately. The positioning accuracy suffers from the stick-slip effect due to strong adhesive forces during the seal contact and the associated high breakaway forces. To achieve smooth motion of the piston rod and increased position accuracy despite highly variable position dynamics, sliding friction and breakaway force must be reduced. This contribution presents a specially designed linear tribometer that has two types of control. Velocity control allows the investigation of sliding friction mechanisms. Friction force control allows investigation of the breakaway force. Due to its bearing type, the nearly disturbance-free detection of stick-slip transients and the dynamic contact behavior of the sliding friction force was possible. The reduction of the friction force was achieved by a superposition of the piston rod’s movement by longitudinal ultrasonic vibrations. This led to significant reductions in friction forces at the rubber/metal interface. In addition, the effects of ultrasonic frequency and vibration amplitude on the friction reduction were investigated. With regard to the breakaway force, significant success was achieved by the excitation. The force control made it possible to identify the characteristic movement of the sealing ring during a breakaway process.

Dynamic contact between CRTS II slab track and bridge due to time-dependent effect of bridge and its influence on train-track-bridge interaction

Concrete creep and concrete shrinkage are unavoidable in the operation of concrete bridges in high-speed railways, which lead to bridge deformation and then cause gaps between CRTS (China Railway Track System) II slab track and bridge. Aiming at the dynamic contact between CRTS II slab track and bridge due to time-dependent effect of bridge and its influence on train-track-bridge interaction, this work proposes a method for investigating this dynamic contact behavior after exploring its generation mechanism. Adopting the established model, the nonlinear contacts between CRTS II slab track and bridge are deeply analyzed from static and dynamic perspectives. Finally, the influence of the dynamic contact on the train-track-bridge interaction is also investigated. Results show that the proposed methodology is effective in studying the contact behaviors between CRTS II slab track and bridges subject to time-dependent effect of bridge. Gaps appear at beam-end locations, and sharp contact behaviors are aroused at the locations of gap-edges. The length of gap is greatly decreased by running train. Creep and shrinkage have great influence on the train vibrations, while have almost no effect on track-bridge vibrations. Interlayer forces of track are obviously affect by bridge deformation and running train.

Dynamic contact behavior of asymmetric spur gear

Abstract There is a growing demand for superior performing gear drives which can bear huge loads and has better endurance at high speed. Also, these gear pair should cost less and have a longer life of operation. There are some applications like automobile drive train, Aero-Engine, wind turbines where the loading on the gear drive is uni-directional. This gives the designers to freely look into non-standard gear design, where the drive side of the the gear needs not be symmetric when compared with the coast side. This led to developing of Asymmetric gear teeth. This work assesses in depth the dynamic contact behaviors of an involute asymmetric gear pair. The effect of the pressure angle change on the drive side is analyzed. Matlab was used to generate the gear teeth. This research gave an insight for evaluating the dynamic gear contact and predicting the dynamic loads occurring on gear tooth, which helps to optimize gear parameter design and to understand the complex gear meshing effect phenomenon. Dynamic analysis of spur gear pairs was solved numerically using LS-DYNA. The spur gear pair's dynamic fillet stress was correlated with an experimental result. The simulation results indicate that the stress distribution of the gear surface is governed by alteration of the tooth pressure angle. The current solution by the finite element application is intended to be implemented in gear dynamics for better understanding of the transient behavior and its harmonics.

A Lagrangian meshfree mesoscale simulation of powder bed fusion additive manufacturing of metals

AbstractWe present a powder‐scale computational framework to predict the microstructure evolution of metals in powder bed fusion additive manufacturing (PBF AM) processes based on the hot optimal transportation meshfree (HOTM) method. The powder bed is modeled as discrete and deformable three‐dimensional bodies by integrating statistic information from experiments, including particle size and shape, and powder packing density. Tractions in Lagrangian framework are developed to model the recoil pressure and surface tension. The laser beam is applied to surfaces of particles and substrate dynamically as a heat flux with user‐specified beam size, power, scanning speed, and path. The linear momentum and energy conservation equations are formulated in the Lagrangian configuration and solved simultaneously in a monolithic way by the HOTM method to predict the deformation, temperature, contact mechanisms, and fluid‐structure interactions in the powder bed. The numerical results are validated against single track experiments. Various powder bed configurations, laser powers, and speed are investigated to understand the influence of dynamic contact and inelastic material behavior on the deformation, heat transfer, and phase transition of the powder bed. The formation of defects in the microstructure of 3D printed metals, including pores, partially, and unmelted particles, is predicted by the proposed computational scheme.

Contact Behavior of Worn Bearings with Elastoplastic Functionally Graded Coating Based on Mixed Elastohydrodynamic Lubrication

The dynamic contact behavior of worn bearings with elastoplastic functionally graded coating is studied, and the interacting effect between worn band and functionally graded surface is analyzed. The surface deformation and roughness are included in the film thickness. The mixed elastohydrodynamic lubrication combined with point contact model is introduced to analyze the oil pressure in the contact zone. By using the Fourier transform method and Papkovich–Neuber potential function, the displacements and stress fields in the elastoplastic functionally graded coating are obtained. The second-order central difference method is used to solve the Reynolds equation. It is found that the repeated surface interaction can result in the sharp increase in pressure in bearings, and the oil pressure increases with increasing graded index. The entrainment of oil in the inlet and outlet zones becomes more evident if a large graded index is selected.

Transient response and rub-impact phenomenon of liquid lubricated non-contacting mechanical seals during external pressure fluctuation

The purpose of this paper is to investigate the dynamic contact behavior and transient response of liquid lubricated non-contacting mechanical seals during external pressure fluctuation. The presented model of spiral groove mechanical seals includes the Reynolds equation considering surface roughness and mass-conserving cavitation boundary, elastoplastic asperity contact model expressing rub-impact phenomenon, as well as the dynamic equation describing the vibrations of stator which were solved simultaneously with a numerical method. Results indicate that the vibration amplitude and frequency of sealing performances are affected significantly by the external pressure. The increment of rotational speed avoids face rub-contact and reduces the instantaneous variation of leakage. The results presented in the study are expected to provide a theoretical guidance to improve stability and safety of sealing system.

Evolution of interfacial contact during low pressure rotary friction welding: A finite element analysis

Development of rotary friction welding (RFW) is of critical importance for extending the RFW technology to join large-scale structures, such as rods/pipes for generator rotors and nuclear power plants. In this paper, finite element (FE) analysis is employed to analyze the thermal-mechanical process during low-pressure rotary friction welding (RFW), and the dynamic evolution process of interface contact is illustrated. Low-pressure RFW process of D50Re steel rod with a diameter of 100 mm is investigated by using the fully coupled thermal-mechanical FE analysis. In the analysis process, the two work pieces are regarded as two contacting entities, and a new method based on equivalent thermal expansion (TE) coefficient is proposed in order to study the dynamic contact behavior during low-pressure RFW. Three simulation cases, which consider no TE, real TE coefficient and equivalent TE coefficient respectively, are performed. It is shown from the comparison between the simulation results and the experimental data that, the equivalent TE coefficient is viable approach in the FE analysis to improve the prediction on the axial shortening and the welding torque. It was demonstrated that significant incomplete interfacial contact occurs during the friction stage in low-pressure RFW. The formation and expansion of the contact zone is in a thermo-mechanical fully coupled manner. Since the temperature is not uniform across the friction interface, the contact area is first formed in the high temperature area, and the expansion of the contact area occurs subsequently. When the temperature at the interface is uniform, almost full contact would be achieved over the friction interface. The modeling and simulation method proposed in this paper is helpful for understanding the underlying physical phenomenon during RFW process. If experimental tests can be extended to determine the equivalent TE coefficient, the accuracy and the reliability of the proposed simulation method in this paper will be further improved.

Developing a laboratory facility to assess friction coefficients of standing samples

The numerical representation of the dynamic response of art works is the most reliable instrument to predict their seismic safety. Their adoption, however, require the knowledge of the effective mechanical properties of the artifacts and their restraint conditions. Namely, the amount of friction arising between standing art works and their supports largely affects the quality of their collapse and, therefore, the choice of the model to adopt in the analysis. In this work a facility for assessing the dynamic contact behaviour of marble sample standing on different supports has been investigated. The facility consists of a dynamic test to perform through the bidirectional shaking table at the Disaster Resilience Simulation Laboratory at the Politecnico di Torino. The friction coefficient has been found from the dynamic test by comparing the acceleration registered at the load cell, which is related to the reaction of the sample, and one measured at the shaking table surface. The obtained values of friction coefficient have been related to the velocity of the adopted input. A preliminary test on a single concrete sample has been performed to check the proposed procedure, by considering three different loading conditions: one of them is the acceleration history of a real ground motion, while the other two have a constant amplitude and a constant frequency, respectively.

Coupled finite element and multibody systems dynamics modelling for the investigation of the bridge approach problem

Railways are the most common mode of transportation for both people and cargo due to its advantages in economy, safety, and comfort. The finite element method has been broadly used for more than three decades to model the different components of the railroad system such as rails, sleepers (cross ties), and substructure and has been used to investigate a variety of problems associated with rail mechanics. Different multibody systems dynamics software programs have also been developed to investigate the dynamic performance and contact behaviour between the rails and the wheels and to determine the contact forces. In this work, a full three-dimensional model that couples both the finite element method and the multibody systems dynamics has been used to study the railroad system. The main focus of this study is to model the bridge approach problem under dynamic load. The bridge approach problem arises from the sudden change in the foundation's stiffness under the rails at the bridge entry and exit, leading to high levels of stress and settlement that can also cause further problems over time. The effect of using a concrete slab at the bridge entry is also investigated in this study, using two slab designs: rectangular and inclined. The results show the effectiveness of the three-dimensional model and slab implementation on the forces and the vertical deformation, especially the inclined slab that applies a gradual change in the stiffness rather than a sudden change.