Stick-slip Motion Research Articles

Drops on Polymer Brushes: Advances in Thin-Film Modeling of Adaptive Substrates.

We briefly review recent advances in the hydrodynamic modeling of the dynamics of droplets on adaptive substrates, in particular, solids that are covered by polymer brushes. Thereby, the focus is on long-wave and full-curvature variants of mesoscopic hydrodynamic models in gradient dynamics form. After introducing the approach for films/drops of nonvolatile simple liquids on a rigid smooth solid substrate, it is first expanded to an arbitrary number of coupled degrees of freedom before considering the specific case of drops of volatile liquids on brush-covered solids. After presenting the model, its usage is illustrated by briefly considering the natural and forced spreading of drops of nonvolatile liquids on a horizontal brush-covered substrate, stick-slip motion of advancing contact lines as well as drops sliding down a brush-covered incline. Finally, volatile liquids are also considered.

Mechanical resistance behind fiber-reinforced polymer pile: Role of clay minerals

Due to the geotechnical design requirements of the fiber-reinforced polymer (FRP) pile embedded in clay, interface friction evolution between the FRP pile and clay plays a crucial role in determining the pile shaft resistance. It is observed from the experimental evaluation that the earth pressure and shear rate affect the pile-soil interface behavior. In this study, a cross-linked epoxy resin is created to contact a siloxane surface of kaolinite in the molecular dynamic simulation. The interfacial accommodation between kaolinite and epoxy resin is studied. In order to investigate the effect of normal stress and sliding velocity on nanoscale friction characteristics, the steered molecular dynamics is utilized to simulate the sliding of the kaolinite model on the surface of the epoxy resin. Simulation results show that the calculated peak interface shear coefficient decreases nonlinearly as the normal stress increases, which follows a logarithmic relationship consistent with the FRP-soil interface shear test. On the other hand, it is observed that two distinct velocity regions, slow pulling mode (5–200 m/s) and fast pulling modes (300–800 m/s), are well fitted by extended Bell theory. The stick–slip motion is only found in slow sliding velocity mode. This increasing tendency of the energy barrier with the normal stresses indicates that higher pulling forces are required for the FRP to slide along the soil at higher normal stress. The present work provides a fundamental understanding of the friction mechanisms between kaolinite and epoxy resin.

Mechanosensitive bonds induced complex cell motility patterns

The one-dimensional crawling movement of a cell is considered in this theoretical study. Our active gel model shows that a moving cell with weakly mechanosensitive adhesion complexes tends to move at constant velocity. As the mechanosensitivity of the adhesion complexes increases, a cell with sufficiently strong myosin contractile or high actin polymerization rate can exhibit stick-slip motion. Finally, a cell with highly mechanosensitive adhesion complexes exhibits periodic back-and-forth migration. A simplified model that assumes that the cell crawling dynamics are controlled by the evolution of the myosin density dipole and the asymmetry of adhesion complex distribution captures the motility behaviors of crawling cells qualitatively. It suggests that complex cell crawling behaviors could result from the interplay between the distribution of contractile force and mechanosensitive bonds. Published by the American Physical Society 2024

Design and Analysis of a Micro Displacement Actuator Based on Stick-slip Principle Using Piezoelectric Ceramic

This work introduces a triangular shape piezoelectric actuator using the principle of piezoelectric ceramic bending vibration and stick-slip motion. The lateral displacement of the driving foot is used to press the slider, while the vertical displacement is used to drive the slider. The structural dimensions are determined by simulation considering the required parameters. Finite element software is used to analyze the static performance. The dynamic performance of the actuator are simulated and analyzed, including its response to different input voltages and frequencies. Dynamic model provides a comprehensive understanding of the behaviour of the actuator during operation and further reveals the principle. The actuator combines piezoelectric bending vibration and stick-slip motion with the merits of compactness, high accuracy and fast response.

Wheel-Rail Stick-Slip Characteristics under Coupling Damages of Rail Corrugation and Wheel Flat in Metro

To investigate wheel-rail contact stick-slip characteristics (SSCs) under coupling damages of rail corrugation and wheel flat and explain the co-action mechanism of the two damages, a vehicle-track system model was built, and the SSCs were analyzed by employing the index of the overall dispersion rate of adhesion coefficient (ODRAC). The results show that both inner and outer wheel-rail systems (WRSs) on the curve have a propensity for stick-slip motion. Since the values of SSCs of the inner WRS are 1.204 to 2.963 times higher than those of the outer one, the inner WRS is easier to stick-slip vibration (SSV). When the rail corrugation is fixed, the overall dispersion rates of adhesion coefficients (ODRACs) progressively decrease with the increase of flat depth and length, and the decrease range is 2.766–41.775%. When the wheel flat is fixed, the ODRACs also progressively decrease as the corrugation wavelength increases, and the decrease ranges from 7.129% to 42.474%; the ODRACs incrementally increase together with the increase of the corrugation wave depth, and the increase ranges from 10.030% to 30.380%. The presence of flat will attenuate the level of SSV of the original system with rail corrugation, whilst the presence of corrugation will intensify the level of SSV of the original system with wheel flat.

Fractal contact resistance model of wind pitch slip ring considering wear and self-excited vibration

Purpose The purpose of this paper is to reveal the dynamic contact characteristics of the slip ring. Dynamic contact resistance models considering wear and self-excited were established based on fractal theory. Design/methodology/approach The effects of tangential velocity, stiffness and damping coefficient on dynamic contact resistance are studied. The relationships between fractal parameters, wear time and contact parameters are revealed. Findings The results show that the total contact area decreases with the friction coefficient and fractal roughness under the same load. Self-excited vibration occurs at a low speed (less than 0.6 m/s). It transforms from stick-slip motion at 0.4 m/s to pure sliding at 0.5 m/s. A high stiffness makes contact resistance fluctuate violently, while increasing the damping coefficient can suppress the self-excited vibration and reduce the dynamic contact resistance. The fractal contact resistance model considering wear is established based on the fractal parameters models. The validity of the model is verified by the wear tests. Originality/value The results have a great significance to study the electrical contact behavior of conductive slip ring. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2023-0300/

Molecular dynamics simulations of the interface friction behavior between fiber-reinforced polymer pile and sand

The interfacial friction performance of the fiber-reinforced polymer (FRP) pile-sand interface plays an essential role in determining the load capacity of the foundation. It is necessary to identify its friction behavior in the marine environment due to the unique pile-soil interaction characteristics, which have not been well established at the nanoscale. The cross-linked epoxy resin and crystalline silica substrate are utilized to investigate the nanoscale friction characteristics at different normal stresses and sliding velocities in the dry, pure water, and salt water systems using the molecular dynamics (MD) simulation. The obtained coefficients of friction in three systems are ranked as dry > salt water > pure water systems. There is a tendency for the coefficient of friction to decrease with increasing normal stress, which is consistent with the experimental results. The interface roughness is validated by an analytical equation based on Archard’s elastic deformation friction theory. The increase in normal stress shortens the distance between the silica and the epoxy and increases the van der Waals force between the two layers, resulting in the increase of maximum friction force in three systems. The higher normal stress induces the more pronounced stick-slip motion of the silica substrate in the dry system, which can be reduced in the pure water system due to the lubrication effect of water, while the NaCl ions weaken the lubrication effect. On the other hand, the lubrication effect of the water molecules has more beneficial at lower sliding velocity because the diffusion of water molecules is more intense, which leads to the reduction of the amplitude of friction force in the stick-slip motion. By considering the effects of sliding velocity, normal stress, water, and NaCl ions, this study provides the fundamental insight for the friction process of FRP pile embedded in sand.

Self-assembled concentric stripes of diamond particles by a pinning-depinning mechanism

We describe the novel mechanism of spontaneous formation of the concentric stripe patterns of microdiamonds via gradual solvent evaporation from a suspension confined in a teardrop well. The self-organized patterns exhibit a series of arcs with regular spacings varying between hundreds of micrometers and millimeters. They result from an interplay between the directional forced circulation of the solvent and a stick-slip movement of its contact line during the gradual drying of the suspension. We reveal the mechanism of the phenomenon and discuss the effects of various parameters on the obtained structures.

The surface diffusivity of nanoparticles physically adsorbed at a solid-liquid interface.

This work proposes an analytical model considering the effects of hydrodynamic drag and kinetic barriers induced by liquid solvation forces to predict the translational diffusivity of a nanoparticle on an adsorbing surface. Small nanoparticles physically adsorbed to a well-wetted surface can retain significant in-plane mobility through thermally activated stick-slip motion, which can result in surface diffusivities comparable to the bulk diffusivity due to free-space Brownian motion. Theoretical analysis and molecular dynamics simulations in this work show that the surface diffusivity is enhanced when (i) the Hamaker constant is smaller than a critical value prescribed by the interfacial surface energy and particle dimensions, and (ii) the nanoparticle is adsorbed at specific metastable separations of molecular dimensions away from the wall. Understanding and controlling this phenomenon can have significant implications for technical applications involving mass, charge, or energy transport by nanomaterials dispersed in liquids under micro/nanoscale confinement, such as membrane-based separation and ultrafiltration, surface electrochemistry and catalysis, and interfacial self-assembly.

Experimental verification of seismic vibration control of high-rise buildings with friction-type multiple tuned mass dampers

In recent decades, tuned mass damper (TMD) devices have been implemented in numerous high-rise buildings in the world. The vibration of tall buildings caused by natural or man-made dynamic loading poses a challenge. In this study, to ensure structural safety and resident comfort, a friction-type multiple TMD (FT-MTMD) system was investigated and its ability to reduce the seismic response of high-rise buildings was evaluated. The proposed FT-MTMD system comprises multiple TMD units in a parallel arrangement and has a greater frequency bandwidth than a conventional TMD system. To address practical issues, a prototype FT-MTMD system was designed and fabricated to control a scale-down test model which has similar fundamental modal properties to a real 36-story building. Because of the nonlinearity of friction, the parameters of the FT-MTMD system were determined using a proposed optimal design method. First, a component test was conducted to ensure that the parameters of the FT-MTMD agreed with the designed values. Then, the FT-MTMD was installed on the long-period test model and its control performance was experimentally evaluated. Shaking table test results indicated that the FT-MTMD system favorably reduced the seismic response in the test model, indicating that the proposed optimal design method is reliable. A theoretical structure–MTMD model was also developed to simulate the system response with unsynchronized stick-slip motion of the FT-MTMD system. The predicted system response agreed well with the measured response. In addition, to avoid damage to the FT-MTMD system during a severe earthquake, a fail-safe device was employed to lock the TMD when its stroke reached the maximum allowable value.

Energy dissipation during homogeneous wetting of surfaces with randomly and periodically distributed cylindrical pillars

HypothesisUnderstanding contact angle hysteresis on rough surfaces is important as most industrially relevant and naturally occurring surfaces possess some form of random or structured roughness. We hypothesise that hysteresis can be described by the dilute defect model of Joanny & de Gennes [1] and that the energy dissipation occurring during the stick-slip motion of the contact line is key to developing a predictive equation for hysteresis. ExperimentsWe measured hysteresis on surfaces with randomly distributed and periodically arranged microscopic cylindrical pillars for a variety of different liquids in air. The inherent (flat surface) contact angles tested range from lyophilic (θe=33.8°) to lyophobic (θe=112.0°). FindingsA methodology for averaging the measured advancing and receding contact angles on random surfaces is presented. Based on these results correlations for roughness-induced energy dissipation are derived, and an equation for predicting the advancing and receding contact angles during homogeneous (Wenzel) wetting on random surfaces is presented. Equations that predict the onset of the alternate wetting conditions of hemiwicking, split-advancing, split-receding and heterogeneous (Cassie) wetting are also derived, thus defining the range of validity for the homogeneous wetting equation. A ‘cluster’ concept is proposed to explain the measurably higher hysteresis exhibited by structured surfaces compared to random surfaces.

Insight into enhancing foundation stability with rubber-soil mixtures: A nanofriction study

Ground vibration during earthquakes can lead to loss of soil strength and structural damage. Rubber-soil mixtures (RSM) show promise in mitigating the residual ground deformation under dynamic loading. The influence of clay minerals on soil frictional strength and system stability is essential in the context of earthquake mechanics. This study employs molecular dynamics (MD) simulations to investigate the friction behavior of the rubber-clay interface within the RSM system. The results indicate a direct correlation between normal stress and friction force, with denser soil systems exhibiting higher friction forces, analogous to natural soils. The increase in friction can be achieved by compacting the rubber and clay components in the RSM systems. The inclusion of rubber in the RSM significantly reduces the stick-slip motion at the montmorillonite-rubber interface, providing a damping effect that reduces the intensity of the stick-slip vibration during sliding. The friction force between the montmorillonite and rubber exhibits a velocity enhancement behavior. The higher the sliding velocity, the less the adaptation time for interfacial atoms, resulting in a higher friction force. The rubber/montmorillonite surface exhibits a higher friction coefficient at higher sliding velocities, effectively limiting the buildup of shear stress responsible for initiating stick-slip behavior. Comparisons with experimental data validate the accuracy of the calculated mechanical properties, work of adhesion, and friction coefficients. These results contribute to a better understanding of the friction behavior within the RSM system, facilitating its application in improving seismic resistance.

Evolution of force networks during stick-slip motion of an intruder in a granular material: Topological measures extracted from experimental data.

In quasi-two-dimensional experiments with photoelastic particles confined to an annular region, an intruder constrained to move in a circular path halfway between the annular walls experiences stick-slip dynamics. We discuss the response of the granular medium to the driven intruder, focusing on the evolution of the force network during sticking periods. Because the available experimental data do not include precise information about individual contact forces, we use an approach developed in our previous work [Basak et al., J. Eng. Mech. 147, 04021100 (2021)0733-939910.1061/(ASCE)EM.1943-7889.0002003] based on networks constructed from measurements of the integrated strain magnitude on each particle. These networks are analyzed using topological measures based on persistence diagrams, revealing that force networks evolve smoothly but in a nontrivial manner throughout each sticking period, even though the intruder and granular particles are stationary. Characteristic features of persistence diagrams show identifiable slip precursors. In particular, the number of generators describing the structure and complexity of force networks increases consistently before slips. Key features of the dynamics are similar for granular materials composed of disks or pentagons, but some details are consistently different. In particular, we find significantly larger fluctuations of the measures computed based on persistence diagrams and, therefore, of the underlying networks, for systems of pentagonal particles.

Development and analysis of magnet-engaged piezoelectric energy generator under friction-induced vibration

Piezoelectric energy transducers, which can be an efficient solution for the power supply of wireless devices, have been widely researched. This study investigated the characteristics of a magnet-engaged nonlinear piezoelectric energy generator stimulated by friction-induced vibration (FIV), in two distinct design configurations (in-parallel and in-series). A mathematical model was developed, and the dynamic response of the mechanical system and voltage output from the piezoelectric shear deformation were solved using an iterative method. A friction model considering the Stribeck effect was introduced to describe the friction motion. The emergence of a stick-slip motion induced limit cycle and its vanishing delineates the unstable and stable regions of the system, respectively. A critical sliding velocity vc splits the regions. When the sliding velocity exceeds vc, the system remains in stable region with exclusive slip friction behavior. Parameter studies were conducted to explore the effect of decay factor β, dynamic friction coefficient μk, static friction coefficient μstatic, and normal force FN on vc. The results indicate that increasing β and μk can reduce the unstable region and generation of FIV, whereas, increasing FN and μstatic can promote the occurrence of FIV. The energy generation was evaluated by a transient charging simulation that has been experimentally validated in a previous study. The influence of β, μk, μstatic, and FN on the energy generation was also investigated relative to the operating velocity range (OVR) and sum of root mean square charging power (SRCP). The in-parallel systems exhibit a higher SRCP within the same OVR, whereas the in-series systems are more likely to excite FIV with a wider OVR. Additionally, the simulation results of fluctuating working conditions show that both fluctuating FN and v0 have negative effects on the energy generation. The nonlinear in-series system exhibits better robustness with the least affected SRCP and almost unchanged OVR under fluctuating FN and v0.

Motion of a viscous slug on heterogeneous surfaces: crossover from stick–slip to steady sliding

We present a theoretical study of viscous slug motion inside a microscopically rough capillary tube, where pronounced stick–slip motion can emerge at slow displacement rates. The mathematical description of this intermittent motion can be reduced to a system of ordinary differential equations, which also describe the motion of a pendulum inside a fluid-filled rotating drum. We use this analogy to show that the stick–slip motion transitions to steady sliding at high displacement rates. We characterize this crossover with a simple scaling relation and show that the crossover is accompanied by a shift in the dominant energy dissipation mechanisms within the system.

Analysis of rail corrugation characteristics in the vehicle braking section of metro

To study the evolution characteristics of corrugation in the vehicle braking section of the metro, a three-dimensional wheel–rail transient contact finite element model is established, and the contact stick–slip characteristics and rail wear distribution features are analyzed. The results show that, under the braking condition, the interface has stick–slip motion, indicating that the system is in a state of instability; the longitudinal relative slip is unevenly distributed; the peak position of the initial corrugation has a large longitudinal relative slip; and the transverse relative slip in the initial corrugation area is significantly larger than that in other areas, indicating that the initial corrugation will continue to develop and have a remarkable transverse wear trend. Under the nonbraking condition, there is no stick–slip motion at the interface, and the longitudinal and transverse relative slip values are less than the corresponding results under the braking condition. The cause of corrugation in the vehicle braking section is the wheel–rail unstable stick–slip motion triggered by the vehicle braking, and the fixed operating mode of the train provides the wavelength-fixing condition for the development of the initial corrugation, which leads to its continuous deterioration.

Stick-Slip Movement in Driving Axles of Railway Vehicles equipped with Damping Devices

In this article, we carried out a study on the behaviour and efficiency of an oscillation-damping system, mounted on the driving axles of railway vehicles to mitigate stick-slip oscillations. The occurrence of the stick-slip phenomenon is particularly harmful in operation because it generates wear on the tread surfaces of the wheels and rails, generates fatigue stresses in the axles and diminishes locomotive performance. To reduce these inconveniences, we proposed installing on the axles a damping system to reduce stick-slip oscillations and studied the behaviour and the efficiency in the operation of this system.

Probing the wear characteristics of graphene on flexible polymer substrates using a heated atomic force microscopy tip

Graphene is a useful solid lubricant for flexible micro/nanoelectromechanical systems (MEMS/NEMS) because of its beneficial mechanical properties. However, understanding the tribological and wear characteristics of graphene on polymer substrates under high-temperature conditions is essential for predicting whether graphene will fail as a solid lubricant for flexible substrates in high-temperature environments. Herein, the friction and wear characteristics of monolayer graphene on flexible polydimethylsiloxane (PDMS) substrates are studied by atomic force microscopy using a heated tip. The friction of graphene before wear is more stable than that of PDMS, demonstrating that graphene can be used as a solid lubricant to stabilize the stick-slip motion of the tip on the flexible substrate at elevated temperatures. The friction of graphene shows an increasing trend with the heating temperature increasing due to an enlarged tip-graphene contact area. However, the friction of graphene considerably decreases with the tip sliding velocity increasing at a speed of less than 0.5 µm/s, resulting from a reduced tip-graphene contact area. The thermally-induced wear of graphene is caused by the coupling effect of the temperature and the sliding velocity. These results can provide an in-depth understanding of graphene as a solid lubricant for flexible polymer-based MEMS/NEMS devices in high-temperature environments.

Migration of Anomalous Displacements on the Flanks of a Preparing Earthquake Source: A Swing Model

The geomechanical modeling results on the stress-strain state dynamics before the 2019 M = 7.1 Ridgecrest earthquake, Southern California, show the alternating development of maximum displacements at the fault’s ends, which simulates the process of “swinging” of the epicentral zone of the earthquake. These results together with the existing theoretical ideas about the block structure of the Earth’s crust and the corresponding connections between blocks are used to construct a geomechanical “swing” model based on the stick-slip motion of three interconnected blocks. The model parameters are related to the rheological properties of the Earth’s crust in the region of the rupture of the bridging isthmus which determines the source size of the seismic event.

Molecular Alignment-Mediated Stick-Slip Poiseuille Flow of Oil in Graphene Nanochannels.

The flow behavior of oil in nanochannels has attracted extensive attention for oil transport applications. In most, if not all, of the prior theoretical simulations, oil molecules were observed to flow steadily in nanochannels under pressure gradients. In this study, non-equilibrium molecular dynamics simulations are conducted to simulate the Poiseuille flow of oil with three different hydrocarbon chain lengths in graphene nanochannels. Contrary to the conventional perception of steady flows of oil in nanochannels, we find that oil molecules with the longest hydrocarbon chain (i.e., n-dodecane) exhibit notable stick-slip flow behavior. An alternation between the high average velocity of n-dodecane in the slip motion and the low average velocity in the stick motion is observed, with a drastic, abrupt velocity jolt of up to 40 times occurring at the transition in a stick-slip motion. Further statistical analyses show that the stick-slip flow behavior of n-dodecane molecules originates from the molecular alignment change of oil near the graphene wall. The molecular alignment of n-dodecane shows different statistical distributions under stick and slip motion states, leading to significant changes of friction forces and thus notable velocity fluctuations. This work provides new insights into the Poiseuille flow behavior of oil in graphene nanochannels and may offer useful guidelines for other mass transport applications.