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The Prandtl–Tomlinson (PT) model has been widely applied to interpret the atomic friction mechanism of a single asperity. In this study, we present an approximate explicit expression for the friction force in the one-dimensional PT model under quasi-static conditions. The 'stick–slip' friction curves are first approximated properly by sawtooth-like lines, where the critical points before and after the 'slip' motion are described analytically in terms of a dimensionless parameter η. Following this, the average friction force is expressed in a closed form that remains continuous and valid for η > 1. Finally, an analytical expression for the load dependence of atomic friction of a single asperity is derived by connecting the parameter η with the normal load. With the parameters reported in experiments, our prediction shows good agreement with relevant experimental results. [ABSTRACT FROM AUTHOR]

This study investigates the modeling and dynamic analysis of three coupled electromechanical systems, emphasizing interactions between a magnetic linear drive and frictional contact with flat springs. The experimental setup includes a table driven by a three-phase permanent magnet linear synchronous motor (PMLSM) using an LMCA4 inductor, LMCAS3 magnetic track, and Xenus XTL controller. Mechanical phenomena such as stick-slip friction and impulsive loads are observed, particularly due to the rapid buckling of flat springs. These springs transition between sliding friction and fixation, impacting the motor’s operation during reciprocating velocity trajectories and generating acoustic emissions. Numerical simulations using COMSOL Multiphysics evaluate the magnetic field and system geometry in two- and three-dimensional spaces. Key findings include mechanical stick-slip vibrations, numerical modeling of the linear drive, and comparative analysis of experimental and simulated inductor current variations. Additionally, energy loss mechanisms under irregular loading conditions are assessed. The results highlight the coupling between friction-induced current changes and magnetic field variations, elucidating their impact on motor efficiency, vibration propagation, and acoustic emissions. The study provides insights into optimizing the design and reliability of coreless linear motors for precision applications under discontinuous loading.

A novel penalty contact constitution was developed to replicate the hysteresis memory effect observed in contact interfaces. On this basis, a refined finite element analysis (FEA) was performed to study the stick–slip friction contact behavior of bolted joint interfaces. The analysis was validated by comparing it with the experimental hysteresis loops in the literature. The simulated hysteresis loops were subsequently used to identify four parameters of the Iwan model. Additionally, the effects of bolt clamping, friction coefficient, and excitation amplitude were individually examined. It was found that the deterioration in bolt clamping performance resulted in a decrease in both the equivalent joint stiffness and energy dissipation. Similarly, the reduction in the friction coefficient yielded a comparable impact. Furthermore, the identified model parameters of critical stick–slip force and displacement exhibited a quasi-linear relationship to the bolt preload and friction coefficient. [ABSTRACT FROM AUTHOR]

A novel penalty contact constitution was developed to replicate the hysteresis memory effect observed in contact interfaces. On this basis, a refined finite element analysis (FEA) was performed to study the stick–slip friction contact behavior of bolted joint interfaces. The analysis was validated by comparing it with the experimental hysteresis loops in the literature. The simulated hysteresis loops were subsequently used to identify four parameters of the Iwan model. Additionally, the effects of bolt clamping, friction coefficient, and excitation amplitude were individually examined. It was found that the deterioration in bolt clamping performance resulted in a decrease in both the equivalent joint stiffness and energy dissipation. Similarly, the reduction in the friction coefficient yielded a comparable impact. Furthermore, the identified model parameters of critical stick–slip force and displacement exhibited a quasi-linear relationship to the bolt preload and friction coefficient.

Here we find the general and abnormal stick-slip friction of nanoconfined water by extensive molecular dynamics simulations. Specifically, water films exhibit general stick-slip behavior when confined below 1 nm, independent of the water phase, surface wettability, and solid lattice structure. However, at confinement distances of 0.7 and 0.9 nm water films are in liquid-like states, which contradicts the common belief that only solid-like lubricant films can produce stick-slip friction. This unexpected behavior is attributed to the nature of short-time-scale ordered but long-time-scale disordered. Further, we reveal the velocity dependence of friction, which is mainly linear at > = 1 nm, logarithmic at 0.8–0.9 nm, and plateau-like at 0.6–0.7 nm, and give theoretical descriptions by extending the Kramer's theory of activated processes. [Display omitted] • Liquid-like nanoconfined water films unexpectedly exhibit stick-slip friction. • Water films exhibit general stick-slip friction when confined below 1 nm. • The velocity dependence of friction of nanoconfined water is revealed. [ABSTRACT FROM AUTHOR]

The effect of fluid properties on hydraulic cylinder rod seal stick‐slip friction was studied. Breakaway and stick‐slip forces were measured for three ISO VG 32 fluids with slipper, U‐cup, and Vee‐pack seals. Breakaway forces increased exponentially with dwell time. Stick‐slip friction produced audible low‐frequency noise. Differences in the stick‐slip behavior of the fluids were observed. Fast Fourier transform analysis of sound, force, and mechanical vibrations was conducted. Stick‐slip friction increased the amplitude of low‐frequency vibrations in all three domains. Micro stick‐slip movement was elucidated via motion amplification technology. These findings provide a basis for the development of fluids that improve the control and safety of hydraulic equipment. [ABSTRACT FROM AUTHOR]

Humidity can affect the bulk behavior of fine hygroscopic powders at multiple levels and fewer mitigation approaches are presently available to counter its adverse effects. This work reports these approaches while investigating humidity influenced frictional behavior in fine cohesive starch powder flow under confined conditions. Interparticle friction and wall friction were examined under varying relative humidity (RH) using shear and wall friction tests in the quasi-static regime. The measured stress details from the bulk powder testing in the powder rheometer revealed increased stick-slip friction in the form of unsteady stresses at lower RH which gradually decreased with increase in RH. The surface texturing of particles and modifying contact stiffness through the dry coating alleviated the nonmonotonic powder flow at all the RH conditions. The stress oscillations and the consequent increase in measured friction were attributed to the discretely distributed surface moisture causing alternate sticking and slipping of the contacts. The lubricating effect of moisture at higher RH and the surface modification facilitated steady sliding, also accompanied by reduced coefficient of friction and wall friction angle. Furthermore, the different fluid film lubrication regimes were identified and highlighted the importance of fluid-particle interactions leading to undesirable bulk behavior in fine powders. [ABSTRACT FROM AUTHOR]

The cable-driven segmented manipulator with cable-constrained synchronous rotating mechanisms is a new type of continuum manipulator, which has large stiffness and fewer motors, and thus exhibits excellent comprehensive performance. This paper presents a dynamic modeling method for this type of manipulator to analyze the effect of the friction and deformation of the cables on the dynamical behaviors of the system. First, the driving cables are modeled based on the ALE formulation, strategies to detect stick–slip transitions are proposed by using a trial-and-error algorithm, and the stiff problem of the dynamic equations is released by a model smoothing method. Second, the dynamic modeling method for rigid links is presented using quaternion parameters. Third, the connecting cables are modeled by torsional spring–dampers, and the frictions between the connecting cables and conduits are considered based on a modified Coulomb friction model. Finally, numerical results are presented and verified by comparison with the experiment results. The study shows that friction and cable deformation play an important role in the dynamical behaviors of the manipulator. Due to these two factors, the constant curvature bending of the segments does not remain. [ABSTRACT FROM AUTHOR]

Several recent designs of soft robots feature locomotion mechanisms that entail orchestrating changes to intrinsic curvature to enable the robot's limbs to either stick, adhere, or slip on the robot's workspace. The resulting locomotion mechanism has several features in common with peristaltic locomotion that can be found in the animal world. The purpose of the present paper is to examine the feasibility of, and design guidelines for, a locomotion mechanism that exploits the control of intrinsic curvature on a rough surface. With the help of a quasi-static analysis of a continuous model of a soft robot's limb, we show precisely how locomotion is induced and how the performance can be enhanced by controlling the curvature profile. Our work provides a framework for the theoretical analysis of the locomotion of the soft robot and the resulting analysis is also used to develop some design guidelines.

The discovery and understanding of gecko 'frictional-adhesion' adhering and climbing mechanism has allowed researchers to mimic and create gecko-inspired adhesives. A few experimental and theoretical approaches have been taken to understand the effect of surface roughness on synthetic adhesive performance, and the implications of stick-slip friction during shearing. This work extends previous studies by using a modified surface forces apparatus to quantitatively measure and model frictional forces between arrays of polydimethylsiloxane gecko footpad-mimetic tilted microflaps against smooth and rough glass surfaces. Constant attachments and detachments occur between the surfaces during shearing, as described by an avalanche model. These detachments ultimately result in failure of the adhesion interface and have been characterized in this study. Stick-slip friction disappears with increasing velocity when the flaps are sheared against a smooth silica surface; however, stick-slip was always present at all velocities and loads tested when shearing the flaps against rough glass surfaces. These results demonstrate the significance of pre-load, shearing velocity, shearing distances, commensurability and shearing direction of gecko-mimetic adhesives and provide us a simple model for analysing and/or designing such systems.

The self-affine mode of ice softening during friction is investigated within the rheological model for viscoelastic medium approximation. The different modes of ice rubbing, determined by formation of surface liquid-like layer, are studied. The analysis of time series of friction force is carried out, namely Fourier analysis, construction of autocorrelation and difference autocorrelation functions. The spectral power law is detected for modes of crystalline ice as well as of a mixture of stable ice and metastable softening. The self-similarity and a periodic character of corresponding time series of friction force are proved. [ABSTRACT FROM AUTHOR]

Many recent designs of soft robots and nano-robots feature locomotion mechanisms that cleverly exploit slipping and sticking phenomena. These mechanisms have many features in common with peristaltic locomotion found in the animal world. The purpose of the present paper is to examine the energy efficiency of a locomotion mechanism that exploits friction. With the help of a model that captures most of the salient features of locomotion, we show how locomotion featuring stick-slip friction is more efficient than a counterpart that only features slipping. Our analysis also provides a framework to establish how optimal locomotion mechanisms can be selected.

The tribological properties between taut hair fibers in wet conditions were investigated to evaluate the tangling/detangling performance of shampoo formulations during washing (particularly rinsing). A new setup for friction measurements between taut hair fibers was established. Using the setup, tribological properties of hair fibers treated with two shampoo formulations, whose tangling performances were different, were investigated. The base formulation for the shampoos was the same; the only difference was the type of amino‐modified silicones used as conditioning agents. Shampoo (Sp) A (poor detangling performance) incudes water‐insoluble silicone, and Sp B (excellent detangling performance) includes water‐soluble silicone. The tribological behaviors between taut hair fibers treated with the diluted solutions of the Sp were very different; the Sp A‐treated hair exhibited stick‐slip sliding, whereas the Sp B‐treated hair exhibited smooth sliding. This difference presumably comes from the different coacervation behaviors in the diluted solutions and resulting structure of conditioning film formed on hair surfaces. The smooth sliding (ideal for detangling) of Sp B‐treated hair comes from the two‐layer structure of the conditioning film on hair; positively charged amino‐modified silicone dissolved in water adsorbed immediately on negatively charged hair surface, followed by the physical adsorption of coacervates on the adsorbed silicone layer. The outer coacervate layer is easily removed during sliding, and smooth sliding comes from the low friction of the silicone layer. The relationship between the type of amino‐modified silicones, conditioning film formation on the surface, and tribological properties was discussed, which gives insights into designing Sp formulations with excellent detangling performance. [ABSTRACT FROM AUTHOR]

• Scale effect generated longitudinal torsion of the yield frame support profile. • Torsion of the support profile increased dynamic unbalance forces 6 times. • Torsional dissipative structure reduced bearing capacity while stick–slip saved it. • Effective joints of yield frame and rock bolt were invented and tested underground. • New joints prevented torsion and increased frame's stability conserving bearing capacity. Yieldable frame support (YFS) is the most important primary component of a tunnel or underground roadway propping in a consequent set of multistage support technology, which is employed in the squeezing rock. This research aimed to enhance the efficiency of combined support using the synergetic effect of connecting YFS to the rock bolts/cables (YFSB). Employing the methods of actual measurements and survey, computer simulation, and underground testing of YFS, we investigated conditions that provoke a spontaneous torsion of the YFS profile, which caused YFS stability failure, loss of the bearing capacity and integrity. We revealed a longitudinal twist or torsion of the YFS profile as a new mode of YFS stability failure and demonstrated that the torsion is a consequence of a scale effect. Based on the thermodynamics of irreversible processes, we proved that this torsion is a form of dangerous dissipative structure that minimizes entropy production. We investigated the torsion parameters and developed a new joint between YFS and rock bolt, which is a key element of a novel lean technology that effectively prevents the YFS profile torsion. The joint and its optimal parameters were successfully tested in an underground condition that provided YFSB stability, increased its average resistance, conserved total bearing capacity, and integrity. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Vibration Engineering is the property of Nanjing University of Aeronautics & Astronautics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract This work proposes an analytical model for the stick-slip friction of a solid mass on oiled surfaces. The dynamic friction was described as F d = λAv , where λ is a parameter related to the surface conditions, A is the contact area and v is the sliding velocity. A mass-spring system with a dashpot with damping constant c (= λA) was used to determine the slip motions of the solids. The applicability of the model is examined by comparing the experimental slip displacements of rubber samples on oiled smooth glass surfaces. The model represents the important aspects of slip motions and suggested that an abrupt change in the acceleration force from positive to negative magnitudes was responsible for the unstable stick-slip phenomenon. [ABSTRACT FROM AUTHOR]

Pupae of numerous Papilionidae and Nymphalidae produce twitter sounds when wriggling in response to mechanical stimulation. The structural basis comprises distinct pairs of sound-producing organs (SPOs) located at intersegmental membranes of the abdomen. They differ—as the twitters do—in sampled taxa of Papilioninae, Epicaliini, and Heliconiini. The opposing sculptured cuticular sound plates (SPs) of each SPO appear structurally the same but are actually mirror-images of each other. Results suggest that sounds are not generated by stridulation (friction of a file and a scraper) but when these inversely sculptured and interlocking surfaces separate during pupal wriggling, representing a stick-slip mechanism. Twitter sounds comprise series of short broadband pulses with the main energy in the frequency range 3–13 kHz; they can be heard by humans but extend into ultrasonic frequencies up to 100 kHz. [ABSTRACT FROM AUTHOR]

Summary: This work is focused on the Newton‐Krylov technique for computing the steady cyclic states of evolution problems in nonlinear mechanics with space‐time periodicity conditions. This kind of problems can be faced, for instance, in the modeling of a rolling tire with a periodic tread pattern, where the cyclic state satisfies “rolling” periodicity condition, including shifts both in time and space. The Newton‐Krylov method is a combination of a Newton nonlinear solver with a Krylov linear solver, looking for the initial state, which provides the space‐time periodic solution. The convergence of the Krylov iterations is proved to hold in presence of an adequate preconditioner. After preconditioning, the Newton‐Krylov method can be also considered as an observer‐controller method, correcting the transient solution of the initial value problem after each period. Using information stored while computing the residual, the Krylov solver computation time becomes negligible with respect to the residual computation time. The method has been analyzed and tested on academic applications and compared with the standard evolution (fixed point) method. Finally, it has been implemented into the Michelin industrial code, applied to a full 3D rolling tire model. [ABSTRACT FROM AUTHOR]

This work is focused on fast techniques for computing the cyclic steady states of evolution problems in non-linear mechanics with space–time periodicity conditions. In industrial applications, in order to avoid the inversion of very large matrices, such a cyclic solution is usually computed as an asymptotic limit of the associated initial value problem with arbitrary initial data. However, when the relaxation time is high, convergence to the limit cycle can be very slow. In such cases nonetheless, one is not interested in the transient solution, but only in a fast access to the limit cycle. Thus, in this work we modify the problem, introducing the time-delayed feedback control, which is widely used for stabilization of unstable periodic orbits. In our framework it is applied to an initially stable system in order to accelerate its convergence to the limit cycle. Moreover, the control term, based on the space–time periodicity error, includes both shifts in time and in space. Our main result is the optimal form of the control term for a very general class of linear evolution problems, providing the fastest convergence to the cyclic solution, which has been further extended and studied in the non-linear case. Efficiency of the method increases with the problem’s relaxation time. The method has been tested using academic applications and compared to the non-controlled asymptotic convergence as well as to the Newton–Krylov shooting algorithm. Finally, the method has been implemented into the Michelin industrial code, applied to a full 3D rolling tyre model. [ABSTRACT FROM AUTHOR]

The fundamental questions of how lubricant molecules organize into a layered structure under nanometers confinement and what is the interplay between layering and friction are still not well answered in the field of nanotribology. While the phase transition of lubricants during a squeeze-out process under compression is a long-standing controversial debate (i.e., liquid-like to solid-like phase transition versus amorphous glass-like transition), recent different interpretations to the stick-slip friction of lubricants in boundary lubrication present new challenges in this field. We carry out molecular dynamics simulations of a model lubricant film (cyclohexane) confined between molecularly smooth surfaces (mica)--a prototypical model system studied in surface force apparatus or surface force balance experiments. Through fully atomistic simulations, we find that repulsive force between two solid surfaces starts at about seven lubricant layers (n = 7) and the lubricant film undergoes a sudden liquid-like to solid-like phase transition at n < 6 monolayers thickness. Shear of solidified lubricant films at three- or four-monolayer thickness results in stick-slip friction. The sliding friction simulation shows that instead of shear melting of the film during the slip of the surface, boundary slips at solid-lubricant interfaces happen, while the solidified structure of the lubricant film is well maintained during repeated stick-slip friction cycles. Moreover, no dilation of the lubricant film during the slip is observed, which is surprisingly consistent with recent surface force balance experimental measurements. [ABSTRACT FROM AUTHOR]

The tribological behaviors of soft materials are closely related to their surface chemistry and morphology. Thus, this study investigates the effects of surface chemistry and morphology on the stick-slip friction of polydimethylsiloxane (PDMS). Air plasma treatment is conducted to modify the surface chemistry, and the bionic shark skin texture is replicated on PDMS. The synergistic effect of the bionic shark skin texture and air plasma treatment on stick-slip friction is evaluated. The results show that air plasma treatment and bionic texture decrease the friction force. Various stick-slip features are observed under different numbers of pendant chains at the contact interfaces, which increase the adhesion force. This study provides fundamental insights into the stick-slip behaviors of other soft materials. [Display omitted] • Stick-slip patterns were proposed to analyze the stick-slip friction behavior of soft material such as PDMS. • Air plasma treatment was used to change surface chemistry of PDMS and decrease the friction of PDMS. • Bionic (shark skin) structure was replicated on PDMS to reduce the friction force and stick-slip effect. • Synergistic effect of surface chemistry and topography on friction of PDMS is analyzed and explained. [ABSTRACT FROM AUTHOR]

This paper, based on the real-time in-situ observation of white box test, aims to investigate the micro-contact characteristics and the friction and wear mechanisms of the GM-3 lining material on the rubbing interface. The results show that the friction coefficient is positively correlated with the actual contact area at different contact pressures and sliding speeds. When the sliding speed reaches 5 mm/s, there is a phenomenon of stick-slip fluctuation with the friction noise. The process of dynamic viscoelastic friction can be divided into four stages. And when it is worn, the viscoelastic lining material is easy to produce reel-like debris. [ABSTRACT FROM AUTHOR]

Apabila dua buah atau lebih benda yang mengalami kontak dan bergerak relatif satu sama lain maka akan menimbulkan gaya gesek yang dapat menyebabkan terjadinya keausan. Pada kecepatan tertentu, sering terjadi suatu fenomena dimana keausan yang terjadi lebih besar dibandingkan yang lain. Fenomena tersebut disebabkan oleh adanya Stick-Slip Friction. Namun, masih sedikit penelitian mengenai gesekan tersebut. Penelitian dilakukan dengan menganalisa kinematika gerakan spesimen untuk menentukan pada rasio kecepatan berapakah stick-slip terjadi. Kemudian, hal tersebut dibuktikan dengan pengambilan data volume keausan menggunakan tribometer tipe Pin-on-disk dengan material Ultra high molecular weight polyethylene (UHMWPE) sebagai pin uji dan Stainless steel sebagai disk, dimana masing-masing pin dan disk akan bergerak secara rotasi. Masing-masing pengujian divariasikan berdasarkan rasio kecepatan antara pin dengan disk, yaitu rasio kecepatan antara 4,2; 5; 6,5; 10; dan 20 rpm/rpm. Pengujian dilakukan dengan pin digesekkan sepanjang 2000 meter dan diberikan pembebanan 4kg serta diberikan variasi dari radius pin. Selanjutnya spesimen diamati struktur permukaannya menggunakan mikroskop optis dengan perbesaran 5x dan 10x sehingga diketahui mekanisme keausannya, sedangkan data hasil pengujian selanjutnya diolah untuk diketahui laju keausan (wear coefficient) dari spesimen uji. Hasil dari penelitian ini adalah Pada saat rasio kecepatan 4,2 daerah yang mengalami stick-slip terjadi pada radius 9 mm dari pusat pin, ketika rasio kecepatan 5 daerah yang mengalami stick-slip terjadi pada radius 8 mm dari pusat pin, saat rasio kecepatan 6,5 daerah yang mengalami stick-slip terjadi pada radius 6 mm dari pusat pin, kemudian saat rasio kecepatan 10 daerah yang mengalami stick-slip terjadi pada radius 4 mm dari pusat pin, dan saat rasio kecepatan 20 daerah yang mengalami stick-slip terjadi pada radius 2 mm dari pusat pin. Laju keausan benda yang mengalami stick-slip friction lebih tinggi jika dibandingkan dengan benda yang mengalami uni-directional contact friction. Mekanisme keausan yang terjadi pada saat fenomena stick-slip terjadi adalah keausan abrasif dan adhesif.

Molecular dynamics simulations of an atomic force microscope (AFM) probe scanning the surface of a five-layer graphene were conducted. The AFM-like scanning probe was modeled by a capped single-wall carbon nanotube. Note that interference with the graphene surface induced frictional behavior; moreover, the effects on the friction system of scanning velocity, probe direction and temperature were investigated. Wrinkling of the graphene surface became more apparent at higher temperatures, while stick-slip friction was more apparent at a lower temperature and a slower scanning velocity. The friction coefficient of the system was approximately 0.001. The molecular dynamics simulations were performed to study the friction characteristics of graphene layers. The effects on the friction system of scanning velocity, probe direction, and temperature were investigated. Wrinkling of the graphene surface became more apparent at higher temperatures, while stick-slip friction was more apparent at a lower temperature and a slower scanning velocity. [ABSTRACT FROM AUTHOR]

Although atomic stick-slip friction has been extensively studied since its first demonstration on graphite, the physical understanding of this dissipation-dominated phenomenon is still very limited. In this work, we perform molecular dynamics (MD) simulations to study the frictional behavior of a diamond tip sliding over a graphite surface. In contrast to the common wisdom, our MD results suggest that the energy barrier associated lateral sliding (known as energy corrugation) comes not only from interaction between the tip and the top layer of graphite but also from interactions among the deformed atomic layers of graphite. Due to the competition of these two subentries, friction on graphite can be tuned by controlling the relative adhesion of different interfaces. For relatively low tip-graphite adhesion, friction behaves normally and increases with increasing normal load. However, for relatively high tip-graphite adhesion, friction increases unusually with decreasing normal load leading to an effectively negative coefficient of friction, which is consistent with the recent experimental observations on chemically modified graphite. Our results provide a new insight into the physical origins of energy corrugation in atomic scale friction. [ABSTRACT FROM AUTHOR]

Several recent designs of soft robots feature locomotion mechanisms that entail orchestrating changes to intrinsic curvature to enable the robot׳s limbs to either stick, adhere, or slip on the robot׳s workspace. The resulting locomotion mechanism has several features in common with peristaltic locomotion that can be found in the animal world. The purpose of the present paper is to examine the feasibility of, and design guidelines for, a locomotion mechanism that exploits the control of intrinsic curvature on a rough surface. With the help of a quasi-static analysis of a continuous model of a soft robot׳s limb, we show precisely how locomotion is induced and how the performance can be enhanced by controlling the curvature profile. Our work provides a framework for the theoretical analysis of the locomotion of the soft robot and the resulting analysis is also used to develop some design guidelines. [ABSTRACT FROM AUTHOR]

Intermittent sliding (stick-slip motion) between solids is commonplace (e.g., squeaking hinges), even in the presence of lubricants, and is believed to occur by shear-induced fluidization of the lubricant film (slip), followed by its resolidification (stick). Using a surface force balance, we measure how the thickness of molecularly thin, model lubricant films (octamethylcyclotetrasiloxane) varies in stick-slip sliding between atomically smooth surfaces during the fleeting (ca. 20 ms) individual slip events. Shear fluidization of a film of five to six molecular layers during an individual slip event should result in film dilation of 0.4-0.5 nm, but our results show that, within our resolution of ca. 0.1 nm, slip of the surfaces is not correlated with any dilation of the intersurface gap. This reveals that, unlike what is commonly supposed, slip does not occur by such shear melting, and indicates that other mechanisms, such as intralayer slip within the lubricant film, or at its interface with the confining surfaces, may be the dominant dissipation modes. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Vibration Engineering is the property of Nanjing University of Aeronautics & Astronautics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents an approach to predict and evaluate the dynamic characteristics of the transmission system in conveying equipment under various working conditions. To solve the problems of varying mass and load, the space, which the transmission system locates, is divided into multiple space-fixed finite control volumes according to the material distribution as well as motion pattern. Each volume is further discretized into a series of finite elements. System-governing equations are obtained by the assembly of all the individual elements’ dynamic equations and the topological structure of the transmission system. Karnopp model is utilized as the basis to render the duty resistance induced by friction. As an illustrative example, the present method is applied to model a large-scale armoured face conveyor, and the corresponding simulation code is developed based on Matlab/Simulink. Simulation results show that the start-up and stop processes with empty load are relatively smooth, which is beneficial to protect the components of the system, especially the chains. Furthermore, the resulted chain-steady velocity, chain-load spectrum and minimum tension force can be directly used to predict the conveying capacity, evaluate chain strength and optimise the pretension force. [ABSTRACT FROM PUBLISHER]

Abstract: Modern bicycle disk-brake systems often induce vibration and noise in bike components such as brake rotors, wheels, and even bike frames. When the vibration or noise are excessive, brake performance can be perceived as unsatisfactory. Previous research incorporating bike frame structural dynamics and brake friction modeling has shown that stick-slip friction is likely the cause of much of this vibration and noise. Bicycle design parameters such as brake friction behavior and bike component structural properties are central in producing and/or sustaining these vibrations. The predicted dynamics of these models has correlated reasonably well with the testing of braking systems. This research extends the modelling of previous efforts to improve correspondence with brake noise/vibration testing and gain further understanding into the contributors and possible cures of this unwanted vibration. Specifically, the extended model incorporates torsional wheel dynamics (including rotor/hub, rim, and tire inertias, and spoke, rotor, and tire stiffnesses) into previous models. This new model allows the dynamics of the bike frame and wheel to couple through braking application. To support and validate the modelling, motion/vibration measurements are recorded during noisy braking with a non-contact laser vibrometer in the laboratory and with an accelerometer in field tests. Vibration measurements are studied along with model predictions toward the goal of connecting unwanted noise/vibration with specific design parameters of the bicycle brake-frame-wheel system. [Copyright &y& Elsevier]

Atomic-scale friction measurements were performed on a metallic glass in corrosive solutions using an atomic force microscope. An irregular stick-slip motion was observed and attributed to the amorphous structure of corroded surfaces. The friction data are interpreted based on the Prandtl-Tomlinson model by considering the disordered surface interaction potential. The transition between different stick-slip regimes, namely smooth sliding, slips over a basic lattice distance or multiple lattice sites, is a position-dependent characteristic on the amorphous surface. The stronger corrosion causes a significant increase in the probability of multiple slips accompanied by larger maximal forces and leads to a higher average friction. Our findings contribute to the understanding of atomic-scale friction on amorphous surfaces and fundamental friction mechanisms in corrosive conditions. • Irregular stick-slip friction is observed by AFM on a metallic glass in corrosive solutions. • The effect of corrosion on friction is explained by frictional slip over multiple lattice sites. • An analytical model is proposed to interpret nanoscale stick-slip friction on amorphous surfaces. [ABSTRACT FROM AUTHOR]

The focus of this study is to experimentally investigate the effect of debonding stress, the interface between the fibers and the polymer matrix, on the damping properties of the short fiberglass reinforced polymer composites. In this study, short fiberglass reinforced polycarbonate composite materials were fabricated and characterized for their tensile properties by varying the fiberglass loading fraction. The debonding stress was evaluated by coupling the acoustic emission technique with the tensile testing. After the determination of the debonding stress was completed, dynamic cyclic testing was performed in order to investigate the effect of debonding on the damping properties of the polymer composites. It was experimentally observed in this study that the debonding can facilitate the stick-slip friction under cyclic loadings, which then gives rise to better damping performance in the fiberglass composites. [ABSTRACT FROM AUTHOR]

In this paper, the dynamic response of a planar rigid multi-body system with stick-slip friction in revolute clearance joints is studied. LuGre friction law is proposed to model the stick-slip friction at the revolute clearance joints. This is because using this law, one can capture the variation of the friction force with slip velocity, thus making it suitable for studies involving stick-slip motions. The effective coefficient of friction is represented as a function of the relative tangential velocity of the contacting bodies, that is, the journal and the bearing, and an internal state. In LuGre friction model, the internal state is considered to be the average bristle deflection of the contacting bodies. By applying the LuGre friction law on a typical slider-crank mechanism, the friction force in the revolute joint having clearance is seen not to have a discontinuity at zero slip velocity throughout the simulation unlike in static friction models. In addition, LuGre model was observed to capture the Stribeck effect which is a phenomenon associated directly with stick-slip friction. The friction forces are seen to increase with increase in input speed. The effect of stick-slip friction on the overall dynamic behavior of a mechanical system at different speeds was seen to vary from one clearance joint to another. [ABSTRACT FROM AUTHOR]

In this paper, a phenomenon is presented that severely restricts control of end-point force via actuation at the other end in a constrained very flexible single-link arm. This limitation is different from and can be more severe than its known non-minimum-phase characteristic. The link flexibility, contact compliance, and stick–slip friction forces at the hub and end-point areas are incorporated into a unique dynamic model and individual effects of friction forces at the hub and the tip on the control performance are investigated. Experimental results are presented to verify the phenomenon and evaluate the validity of the proposed model. [ABSTRACT FROM PUBLISHER]

Abstract: The slow-motion control of an experimental hydraulically actuated robot with unknown friction forces and stick-slip oscillations is considered. A solution based on a design well-suited for engineering implementation is proposed. This consists of a double integral action controller with adequate stability margins. With such a configuration, harmful jerky motion is eliminated. Limited resolution of the sensors, friction forces and the integral actions of the controller give rise to stick-slip oscillations. The consideration of a switching control based on a linear observer designed for the closed-loop system makes the mechanism be free of these oscillations. Experimental results show the effectivity of the control scheme. The relevance of the solution here proposed is threefold: (a) well-known control engineering techniques are applied, (b) modelling and identification of elaborated friction force models usually required for more sophisticated controllers are not needed for the solution here proposed, and (c) the control system stability margin specifications considered are adequate. [Copyright &y& Elsevier]

In magnetic tape drives, lateral in-plane vibration of the tape leads to misalignment between data tracks and read/write head's position resulting in reduced storage capacity. To attenuate this lateral tape motion (LTM), surface guides—which include grooved, porous or roughened rollers—are used. The axial motion of the tape over the roller surface switches between two states: a sticking state when the axial force is smaller than the static frictional force; and a slipping state when the axial force is larger than the frictional force. A good understanding of the physical phenomena involved in this frictional interaction between the magnetic tape and surface friction guides will allow the appropriate and optimal choice of roller characteristics. We conduct a parametric study of frictional interaction between roller surface and the traveling magnetic tape by systematically varying the axial tension and transport velocity of the tape. An experimental setup is used to independently control these parameters and obtain lateral vibration measurements at two equidistant points—upstream and downstream—from the tape-roller interface. Techniques from spectral analysis are applied to the two signals to analyze and isolate the effect of stick-slip friction on LTM. It is noticed that the coherence function between the LTM signals provides valuable insight into the nature of stick-slip friction at the interface. We subsequently use it as a metric to construct and understand the “dynamic phase diagram,” i.e., to demarcate regions in the tension-velocity phase-space where predominance of stick or slip occurs. [ABSTRACT FROM PUBLISHER]

The melting of an ultrathin lubricating film during the friction of two solid atomically smooth surfaces is studied within the limits of the Lorentz model that approximates a viscoelastic medium, the deformation effect of the shear modulus being taken into account. It is shown that the action of a random force representing additive non-correlated noise results in the sustained oscillation mode that corresponds to stickslip friction. The numerical modeling of the process yields the ratios between the relaxation times at which the stick-slip mode is characterized by a high amplitude. The amplitude of stick-slip transitions is found to decrease as the shear modulus of the lubricant increases. [ABSTRACT FROM AUTHOR]

Melting of an ultrathin lubricant film confined between two atomically flat surfaces is studied using the rheological model for viscoelastic matter approximation. Phase diagram with domains, corresponding to sliding, dry, and two types of stick-slip friction regimes has been built taking into account additive noises of stress, strain, and temperature of the lubricant. The stress time series have been obtained for all regimes of friction using the Stratonovich interpretation. It has been shown that self-similar regime of lubricant melting is observed when intensity of temperature noise is much larger than intensities of strain and stress noises. This regime is defined by homogenous distribution, at which characteristic stress scale is absent. We study stress time series obtained for all friction regimes using multifractal detrended fluctuation analysis. It has been shown that multifractality of these series is caused by different correlations that are present in the system and also by a power-law distribution. Since the power-law distribution is related to small stresses, this case corresponds to self-similar solid-like lubricant. [ABSTRACT FROM AUTHOR]

This paper proposes an arbitrary Lagrange Euler (ALE) method for dynamic modeling and simulation of cable-driven mechanisms considering stick–slip frictions. The dynamic equations of the cables are presented based on the ALE formulation. The frictional forces acting at the Eulerian nodes are derived from the Coulomb dry friction model. The detections for stick–slip motions of different contact points between the cables and the holes are carried out independently through a trial-and-error method. The stiff problems yielded by the high stiffness of the cables are released by using a model smoothing method. The dynamic equations of the system are integrated by an explicit solver, avoiding the calculation of Jacobian matrix of the dynamic equations with respect to state variables, which is nonexistent in the stick–slip transition points. The effectiveness and correctness of the proposed method are verified by comparison with previous studies and with experiments. The proposed method not only can capture stick–slip motions, which are consistent well with experiments, but also has a high calculation efficiency. • An ALE method for dynamic modeling and simulation of cable-driven mechanisms is presented. • The stick–slip frictions between the cable and the holes/rings/pulleys are considered. • The stiff problems are released by using modeling smoothing method. • The proposed method can capture stick–slip motions consistent with experiments well. • The proposed method has a high calculation efficiency. [ABSTRACT FROM AUTHOR]

Frictional energy dissipation inside the foil structure is considered as a key factor in improving the stability of the gas foil bearing (GFB) rotor system. However, the effect and mechanism of friction on the stability of bump-type GFB rotor systems have remained partially addressed. This study aims to develop a novel comprehensive model to investigate the stability and frictional dissipation mechanism of the GFB rotor system. The LuGre dynamic friction model is adopted to capture accurate stick–slip states. The model order reduction technique and simultaneous solution framework are applied to improve the computational efficiency. The effect of friction on linear and nonlinear stability is investigated based on the proposed model, and an analysis of frictional dissipation is performed to explain the mechanism. The results reveal that the dissipation capacity of the foil structure is directly governed by the stick–slip states that are affected by the friction coefficient and disturbance magnitude, so the optimal friction coefficient for nonlinear stability is higher than the one for linear stability of the GFB rotor system. A further comparison between different friction models greatly highlights the necessity of the ability of the friction model to capture accurate stick–slip states. [Display omitted] • LuGre dynamic friction model is adopted to capture accurate stick–slip states. • The order reduction and simultaneous solution are applied to improve efficiency. • The dissipation capacity of the foil is directly related to the stick–slip states. • Friction has different effects on linear and nonlinear stability of foil bearing. • Ability to capture accurate stick–slip states is imperative for bearing design. [ABSTRACT FROM AUTHOR]

A novel multiple time scale approach is proposed which combines dynamic and static atomistic methods in one numerical simulation. The method is especially effective for modeling processes that consist of two distinct phases: the slow phase when atomic equilibrium positions barely change and the fast phase associated with a rapid change of the system’s configuration. In this case, the slow phase can be effectively modeled using static energy minimization while molecular dynamics (MD) can be applied when specific dynamic effects have to be captured. Compared to direct MD simulations, the new method allows for computational cost savings, and eventually simulation timescale extension, since the major part of the simulation can be modeled as static, without the need to follow vibrations of individual atoms and comply with the critical time step requirement of molecular dynamics. As a result, this approach may allow for modeling loading velocities and strain rates that are more realistic than those currently attainable through direct MD simulations. The fundamental issues in developing this method include the correlation between the MD time scale and quasi-static step-like procedure as well as finding effective criteria for switching between the static and dynamic regimes. The method was inspired by and is applied to simulations of atomic-scale stick-slip friction. Possible applications of the new method to other nano-mechanical problems are also discussed. [ABSTRACT FROM AUTHOR]

Abstract: Within the framework of Lorentz model for description of viscoelastic medium the influence of deformational defect of the shear modulus is studied on melting of ultrathin lubricant film confined between the atomically flat solid surfaces. The possibility of jump-like and continuous melting is shown. Three modes of lubricant behavior are found, which correspond to the zero shear stress, the Hooke section of loading diagram, and the domain of plastic flow. Transition between these modes can take place according to mechanisms of first-order and second-order phase transformations. Hysteresis of dependencies of stationary stresses on strain and friction surfaces temperature is described. Phase kinetics of the system is investigated. It is shown that ratio of the relaxation times for the studied quantities influences qualitatively on the character of the stationary mode setting. [Copyright &y& Elsevier]

Large-scale molecular dynamics simulations are applied to study the sliding friction of amorphous silicon carbide on amorphous silicon carbide, amorphous silicon carbide on diamond, nano--crystalline silicon carbide on diamond, and crystalline silicon on diamond systems. The friction coefficient and structural evolution of these systems are investigated as functions of sliding velocity, temperature, and normal load. Based on our results, the physics of atomic-scale sliding friction in crystalline, nanocrystalline, and amorphous materials under investigation is clarified. The established regularities are validated with available experimental results. [ABSTRACT FROM AUTHOR]

Abstract: A dynamic fuzzy logic-based adaptive algorithm is proposed for reducing the effect of stick–slip friction and for the compensation of backlash. The control scheme proposed is an online identification and indirect adaptive control, in which the control input is adjusted adaptively to compensate the effect of these non-linearities. A tuning algorithm for fuzzy logic parameters is used to ensure stable performance. The efficacy of the proposed algorithm is verified on a one degree of freedom (1-DOF) mechanical mass system with stick–slip friction and on a one-link robot manipulator with backlash. [Copyright &y& Elsevier]