Friction Control Research Articles

Corrosion-Resistant Metal-Ceramic Composite Coatings for Tribological Applications

Abstract Effective design of corrosion-resistant coatings is critical for the protection of metals and alloys. Many state-of-the-art corrosion-resistant coatings are unable to satisfy the challenges in extreme environments for tribological applications, such as elevated or cryogenic temperatures, high mechanical loads and impacts, severe wear, chemical attack, or a combination of these. The nature of challenging conditions demands that coatings have high corrosion and wear resistance, sustained friction control, and maintain surface integrity. In this research, multi-performance metal-ceramic composite coatings were developed for applications in harsh environments. These coatings were developed with an easy to fabricate, low-cost, and safe procedure. The coating consisted of boron nitride, graphite, silicon carbide, and transition metals such as chromium or nickel using epoxy as vehicle and bonding agent. Salt spray (SS) corrosion tests showed that 1010 carbon steel (1/4 hard temper) substrates lost 20–100 × more mass than the coatings. The potentiodynamic polarization study showed better performance of the coatings by seven orders of magnitude in terms of corrosion relative to the substrate. Additionally, the corrosion rates of the coatings with Ni as an additive were five orders of magnitude lower than reported. The coefficient of friction (COF) of coatings was as low as 0.1, five to six times lower than that of epoxy and lower than a wide range of epoxy resin-based coatings found in literature. Coatings developed here exhibited potential in applications in challenging environments for tribological applications.

Vibrational Transportation on a Platform Subjected to Sinusoidal Displacement Cycles Employing Dry Friction Control.

Currently used vibrational transportation methods are usually based on asymmetries of geometric, kinematic, wave, or time types. This paper investigates the vibrational transportation of objects on a platform that is subjected to sinusoidal displacement cycles, employing periodic dynamic dry friction control. This manner of dry friction control creates an asymmetry, which is necessary to move the object. The theoretical investigation on functional capabilities and transportation regimes was carried out using a developed parametric mathematical model, and the control parameters that determine the transportation characteristics such as velocity and direction were defined. To test the functional capabilities of the proposed method, an experimental setup was developed, and experiments were carried out. The results of the presented research indicate that the proposed method ensures smooth control of the transportation velocity in a wide range and allows it to change the direction of motion. Moreover, the proposed method offers other new functional capabilities, such as a capability to move individual objects on the same platform in opposite directions and at different velocities at the same time by imposing different friction control parameters on different regions of the platform or on different objects. In addition, objects can be subjected to translation and rotation at the same time by imposing different friction control parameters on different regions of the platform. The presented research extends the classical theory of vibrational transportation and has a practical value for industries that operate manufacturing systems performing tasks such as handling and transportation, positioning, feeding, sorting, aligning, or assembling.

Light-Fueled Polymer Film Capable of Directional Crawling, Friction-Controlled Climbing, and Self-Sustained Motion on a Human Hair.

Recent efforts in stimuli‐responsive soft materials have enabled wirelessly controlled actuation with increasing degrees of freedom, yielding miniature robots capable of various locomotion in open environments such as on a plane or inside fluids. However, grand challenges remain in harnessing photomechanical deformation to induce locomotion and control of friction during the movement, especially for robotic actuations within constrained spaces. Here, the authors report a centimeter‐long polymer strip made of a liquid crystal network that is capable of versatile light‐fueled motions along a human hair. The soft polymer robot can translocate directionally upon temporally modulated excitation and climb vertically through friction control with light. A self‐oscillating strip is demonstrated to continuously translocate along the hair upon a constant light stimulus, and its gaiting is associated to the smoothness of the hair surface. The results offer new insights to small‐scale photo‐actuator, mechanical control, and automation in soft micro robotics.

Surface Engineering Development Trends and Impact of Surface Coatings and Textures on Automotive Powertrain Friction and Wear Control

Abstract The global automotive industry is facing higher energy costs, more legislative pressure, and an ever-increasing environmental awareness to achieve fuel efficiency and environmental sustainability. In recent years the automotive industry has undergone a revolution in hardware and materials. Among these approaches, engine friction reduction and wear control by surface engineering are the most effective approaches. In this paper, surface engineering and its impact of surface coatings and texture technologies on powertrain components will be reviewed. Recently the lightweight nonferrous alloy and nanocomposites are being incorporated into the emerging powertrain technologies—including a wide range of surface coating materials such as thermal sprayed aluminum liners, diamond-like carbon-coated valve train components, and hard nitride piston rings or composite coatings toward energy-efficient and wear-resistant systems. The major section of this paper will discuss the future development trends of engine friction reduction and wear control by surface modification such as friction-reducing and wear-resistant coatings or surface textures in powertrain components. The impact of surface coatings or surface textures on tribological characteristics will be reviewed. Specifically, this review paper will address the impact of these emerging technologies on engine material requirements. The connection between surface engineering and the emerging powertrain technologies will be described. In summary, this paper will review the impact of emerging surface engineering technologies on tribological performance and future trends for advanced powertrain components. In addition, the bench and engine wear and scuffing assessments will be reviewed in terms of wear and scuffing resistance for a variety of surface coatings or textures applied to engine components. This paper also addresses the interactions between powertrain components and surface coatings or textures and their effects on friction, wear, and engine durability. The increasing importance of surface coatings and textures in engine component design and tribological performance will be fully illustrated.

Near-Infrared-Light-Modulated Lubricating Coating Enabled by Photothermal Microgels.

As a micro-/nano-sized hydrogel, polymeric microgel not only has three-dimensional (3D) molecular networks but also displays the small-size effect, which has been widely used in various fields, such as drug nanocarrier, photonic crystal, functional coating, and aqueous lubrication. In this work, a photothermal lubricating coating was prepared using polymeric/inorganic hybrid microgels and its surficial friction was deliberately modulated by the remote irradiation of near-infrared (NIR) light. Specifically, a photothermal hybrid microgel, Fe3O4@poly(N-isopropylacrylamide-co-polyacrylic acid) (Fe3O4@PNA), was first fabricated and then sprayed onto poly(ethyleneimine) (PEI)-modified substrate to form a lubricating microgel coating. At room temperature, this microgel coating was hydrophilic and achieved good hydration lubrication with relatively low friction. After the introduction of NIR light, the photothermal microgel coating converted light energy into heat energy for increasing its own temperature rapidly. Due to the thermosensitive PNA shell, the wettability of the coating was transformed to hydrophobicity above the lower critical solution temperature (LCST), resulting in a remarkable increase in friction. In other words, the surficial friction of this microgel coating could be reversibly modulated using NIR light. This work expands the application scope of microgels in the field of aqueous lubrication and introduces the functional microgels into making the smart lubricating coating for the first time. This basic research in the field of friction control may provide an efficient strategy for the design of interfacial sensing, controlled transmission, and intelligent manipulator.

Active Control of Boundary Lubrication of Ceramic Tribo-Pairs in Sodium Dodecyl Sulfate Aqueous Solutions

The objective of the study is to actively control friction between engineering ceramics in underwater applications. By designing a proper electrode system and applying an external electric field, the active control of friction between Al2O3 plate and ZrO2 ball in sodium dodecyl sulfate (SDS) aqueous solutions has been realized, which is different from the previous studies of potential-controlled boundary lubrication where at least one part of tribo-pairs is a conductor. Reversible change of friction coefficient has been observed in the range from 0.12 to 0.35. An indirect electric field-assisted adsorption/desorption model has been proposed to explain the observed phenomena. The addition of inorganic salts containing counterions to the SDS solution or increasing the concentration of SDS can shorten the response time of friction to the variation of the applied electric field by facilitating the formation of SDS micelles. This opens a new way to realize the active control of friction for insulative tribo-pairs without corrosion.

Friction control by tailoring deformation mechanism of interfacial grains in metals

Micro-scale stick-slip motion of metals is closely related to interfacial plasticity. However, previous studies about the effect of interfacial plasticity on the stick-slip motion only focused on the role of asperity plasticity while ignored the role of grain size of interfacial grains. This study focuses on the stick-slip motion of coarse-grain (CG), ultrafine grain (UFG), nanograin (NG), and heterogeneous grain structure Ti–6Al–4V alloys. Micro-scale stick-slip motion controlled by tailoring grain size of interfacial grains was discovered for the first time. When interfacial materials are coarse-grains (CGs) and ultrafine grains (UFGs), the friction mode is mixed regime (stick-slip competed). When interfacial material is nanograins, the friction mode shows slip regime (slip dominated). When interfacial material is heterogeneous grain structure, the friction mode displays partial slip regime (stick dominated). Notched micro-cantilever tests show that dislocation slip in CGs contributes to large plasticity and high fracture toughness, and that grain boundary migration in NGs results in limited plasticity and low fracture toughness. The plasticity and fracture toughness affected by deformation mechanism play an important role in micro-scale stick-slip motion. The nature of the stick-slip motion control by tailoring grain size of interfacial grains is that the change of grain size can affect the deformation mechanism. This study may provide a new design strategy of micro-scale stick-slip motion control by tailoring deformation mechanism of interfacial grains in metals.

A Combined Analytical Method for Intelligent Control of Friction Damped Structures

Controlling structures and increasing the prognosis of their behaviour before natural disasters are the most critical issues in structural engineering. To that end, predicting the destructive effects of earthquakes on both acceleration and displacement of structures would be beneficial. This paper suggests an intelligent control system that realises simultaneous control of acceleration and displacement parameters. There are two modules in the system. First, the preserving module aims to estimate the crisis thresholds of acceleration and displacement based on the historical seismic data of each area. Second, the processing module finds the optimum value of the slip load of the friction damper so that both acceleration and displacement are controlled. We introduce an analytical method based on a matrix analysis approach and heuristic algorithm (MAHA) as a core of the processing module. MAHA would analyse the structure response, and the friction damper would determine the optimum slip load. The numerical and software simulation results for various one-bay and two-bay steel structures show that the proposed intelligent control system applies to multiple frictions damped structures under different earthquake records. In addition, a control level of 80% in acceleration and displacement of structures is achieved compared to an uncontrolled state. Moreover, the mentioned system enables the engineers to find appropriate friction dampers during the design of structures.

Manipulation of Miniature and Microminiature Bodies on a Harmonically Oscillating Platform by Controlling Dry Friction

Currently used nonprehensile manipulation systems that are based on vibrational techniques employ temporal (vibrational) asymmetry, spatial asymmetry, or force asymmetry to provide and control a directional motion of a body. This paper presents a novel method of nonprehensile manipulation of miniature and microminiature bodies on a harmonically oscillating platform by creating a frictional asymmetry through dynamic dry friction control. To theoretically verify the feasibility of the method and to determine the control parameters that define the motion characteristics, a mathematical model was developed, and modeling was carried out. Experimental setups for miniature and microminiature bodies were developed for nonprehensile manipulation by dry friction control, and manipulation experiments were carried out to experimentally verify the feasibility of the proposed method and theoretical findings. By revealing how characteristic control parameters influence the direction and velocity, the modeling results theoretically verified the feasibility of the proposed method. The experimental investigation verified that the proposed method is technically feasible and can be applied in practice, as well as confirmed the theoretical findings that the velocity and direction of the body can be controlled by changing the parameters of the function for dynamic dry friction control. The presented research enriches the classical theories of manipulation methods on vibrating plates and platforms, as well as the presented results, are relevant for industries dealing with feeding, assembling, or manipulation of miniature and microminiature bodies.

Phototribology: Control of Friction by Light.

In dry sliding, the coefficient of friction depends on the material pair and contact conditions. If the material and operating conditions remain unchanged, the coefficient of friction is constant. Obviously, we can tune friction by surface treatments, but it is a nonreversible process. Here, we report active control of friction forces on TiO2 thin films under UV light. It is reversible and stable and can be tuned/controlled with the light wavelength. The analysis of atomic force microscopy signals by wavelet spectrograms reveals different mechanisms acting in the darkness and under UV. Ab initio simulations on UV light-exposed TiO2 show a lower atomic orbital overlapping on the surface, which leads to a friction reduction of up to 60%. We suggest that photocontrol of friction is due to the modification of atomic orbital interactions from both surfaces at the sliding interface.

Nonprehensile Manipulation of Parts on a Horizontal Circularly Oscillating Platform with Dynamic Dry Friction Control

This paper presents a novel method for nonprehensile manipulation of parts on a circularly oscillating platform when the effective coefficient of dry friction between the part and the platform is being dynamically controlled. Theoretical and experimental analyses have been performed to validate the proposed method and to determine the control parameters that define the characteristics of the part’s motion. A mathematical model of the manipulation process with dynamic dry friction control was developed and solved. The modeling showed that by changing the phase shift between the function for dynamic dry friction control and the function defining the circular motion of the platform, the part can be moved in any direction as the angle of displacement can be controlled in a full range from 0 to 2π. The nature of the trajectory and the mean displacement velocity of the part mainly depend on the width of the rectangular function for dynamic dry friction control. To verify the theoretical findings, an experimental setup was developed, and experiments of manipulation were carried out. The experimental results qualitatively confirmed the theoretical findings. The presented analysis enriches the classical theories of nonprehensile manipulation on oscillating platforms, and the presented findings are relevant for mechatronics, robotics, mechanics, electronics, medical, and other industries.

Directional anisotropy of friction in microscale superlubric graphite/ hBN heterojunctions

Structural superlubricity is one of the most fascinating tribological concepts, describing the state of almost vanishing friction, which arises from the cancellation of the lateral interactions between incommensurate rigid surfaces. In this paper, the dependence of friction on sliding directions is experimentally studied under ambient conditions using state of the art friction force microscopy of misaligned microscale heterogeneous contacts between the single crystalline $h\mathrm{BN}$ and graphite. The observed minor frictional anisotropy (\ensuremath{\le}20%) demonstrates that the microscale superlubric translational motion is maintained along all sliding directions. With atomistic simulations, we further show that the frictional anisotropy results from a change in the corrugation of the sliding potential energy surface with changing the sliding direction. Our results validate the robustness of the structural superlubricity against the sliding direction, and provide an effective approach to precise friction control.

Reversible Underwater Adhesion for Soft Robotic Feet by Leveraging Electrochemically Tunable Liquid Metal Interfaces.

Soft crawling robots have potential applications for surveillance, rescue, and detection in complex environments. Despite this, most existing soft crawling robots either use nonadjustable feet to passively induce asymmetry in friction to actuate or are only capable of moving on surfaces with specific designs. Thus, robots often lack the ability to move along arbitrary directions in a two-dimensional (2D) plane or in unpredictable environments such as wet surfaces. Here, leveraging the electrochemically tunable interfaces of liquid metal, we report the development of liquid metal smart feet (LMSF) that enable electrical control of friction for achieving versatile actuation of prismatic crawling robots on wet slippery surfaces. The functionality of the LMSF is examined on crawling robots with soft or rigid actuators. Parameters that affect the performance of the LMSF are investigated. The robots with the LMSF prove capable of actuating across different surfaces in various solutions. Demonstration of 2D locomotion of crawling robots along arbitrary directions validates the versatility and reliability of the LMSF, suggesting broad utility in the development of advanced soft robotic systems.

Effect of Noninteracting Intercalants on Layer Exfoliation in Transition-Metal Dichalcogenides

The control of friction at the atomic scale is fundamental to optimize the exfoliation of layered materials. To this aim, we report a density-functional investigation of how intercalated molecules affect the nanoscale friction of van der Waals transition-metal dichalcogenides. We find that the molecule does not interact with the electronic density of the layers directly; nonetheless it determines the features of the valence band of the system. In particular, the valence-band width appears to be a promising parameter to correlate the electronic properties with the nanofrictional response; it then constitutes a guide for the automatic search of intercalation molecules suitable for layer exfoliation. The present outcomes also constitute a theoretical tool for future investigations of the effect that intercalated species have on the nanoscale friction in layered materials.

Numerical Study of Stress-Strain State of Workpiece in Contact Problem of Surface Mandrel Drilling

In recent years, the economic factor has played an increasingly important role in the selection of technologies for manufacturing machine parts with specified values of normalized parameters of geometric accuracy and quality of working surfaces. As applied to surface plastic deformation processes, this is noticeably manifested in the search for effective friction control methods in the “tool – workpiece” pair, which ultimately determines the distribution pattern and the magnitude of stresses and strains in the workpiece and the tool. It is not possible to obtain a rigorous analytical solution to the problem of establishing a connection between surface conditions, friction, and the stress-strain state of the contacted bodies. In this regard, the construction of mathematical models comes to the fore, the solution of which is possible by numerical methods. The paper presents the results of a numerical study (computational experiment) of a finite-element model of workpiece deformation under various conditions of contact interaction and friction by one of the methods of surface plastic deformation – surface mandrel drilling. The friction coefficient has been chosen as the criterion for assessing the conditions of contact interaction and friction. It is shown that a change in the friction coefficient in the process of surface mandrel has no noticeable effect on the formation of a stress field in the deformable workpiece both in the axial, and in the radial and circumferential directions. At the same time, with an increase in the value of the friction coefficient in the “tool – workpiece” pair and with the associated increase in the force of mechanical resistance to deformation of the workpiece, their growth is observed. A computational experiment has confirmed the presence of non-contact deformations of the workpiece and tool during surface mandrel drilling, as well as as a decrease in the value of residual deformations in the workpiece with a decrease in the coefficient of friction. Balance assessment of contact surface displacements in the workpiece (the inner surface of the hole to be machined) and the tool (mandrel) has shown that the deformations of the tool in the elastic region can lead to a significant decrease in the real tightness of surface mandrel drilling.

Controlling the Friction of Gels by Regulating Interfacial Oxygen During Polymerization

Hydrogel surfaces are of great interest in applications ranging from cell scaffolds and transdermal drug-delivery patches to catheter coatings and contact lenses. In this work, we propose a method to control the surface structure of hydrogels, thereby tailoring their frictional properties. The method is based on oxygen inhibition of the free-radical polymerization reaction during synthesis and enables (i) control of friction over more than an order in magnitude and (ii) spatial control of friction as either a continuous gradient or a distinct pattern. The presented method has successfully been applied to acrylamide-, diacrylate- and methacrylate-based gels, illustrating the universality of the presented method, and its potential use in the above-mentioned applications.Graphical

Adaptive Sliding Mode Control for a Robotic Manipulator with Unknown Friction and Unknown Control Direction

This paper is aimed at addressing the tracking control issue for an n-DOF manipulator regardless of unknown friction and unknown control direction. In order to handle the above issues, an adaptive sliding mode control (ASMC) is developed with a Nussbaum function. The sliding mode control (SMC) in the proposed control guarantees the tracking problem and fast responses for the manipulator. Additionally, there are adaptive laws for the robust gain in the SMC to deal with the unknown external disturbance and reduce the chattering effect in the system. In practice, the mistakes in the connection between actuators and drivers, named unknown control direction, cause serious damage to the manipulator. To overcome this issue, the Nussbaum function is multiplied by the ASMC law. A Lyapunov approach is investigated to analyze the stability and robustness of the whole system. Finally, several simulations are implemented on a 3-DOF manipulator and their results are compared with those of the existing controllers to validate the advantages of the proposed method.

FRICTION UNDER LARGE-AMPLITUDE NORMAL OSCILLATIONS

Building on a recently proposed contact-mechanical theory of friction control by external vibration, the case of large-amplitude normal oscillation is revisited. It is shown that the coefficient of friction can be expressed in particularly simple form if the waveform of the displacement oscillation is triangular or rectangular, and the contact stiffness is constant. The latter requirement limits the scope of the exact solutions to contacts between a plane and a flat-ended cylinder or a curved shape with a wear flat, but the adopted methodology also enables efficient numerical solution in more general cases.

Observer-based interval type-2 fuzzy friction modeling and compensation control for steer-by-wire system

This paper studies the tracking control of the SbW system with unknown nonlinear friction torque and the unmeasured angular velocity. An observer-based adaptive interval type-2 fuzzy logic system controller is proposed to eliminate the adverse influence of the friction torque on the SbW system. Firstly, the angular velocity of the front wheels is estimated via the observer, such that the system sensitivity to measurement noise, the hardware cost, and the structural complexity are reduced. Then, an interval type-2 fuzzy logic system (IT2 FLS) is used to model the friction torque, in which the model and parameters are not effectively identified. IT2 FLS has a more exceptional ability to deal with uncertainties than the traditional type-1 fuzzy logic system (T1 FLS), so the friction modeling based on IT2 FLS has more satisfactory effect in practical application. Finally, an adaptive interval type-2 fuzzy logic system controller is proposed to achieve excellent tracking performance. The tracking error can be guaranteed to converge asymptotically to zero by the Lyapunov stability theory. The numerical simulations and hardware-in-loop (HIL) experiments verify the effectiveness and superiority of the proposed friction modeling method and control strategy.

Nanoscale friction and growth of surface oxides on a metallic glass under electrochemical polarization

Metallic glasses are excellent materials for micromechanical systems, where miniature components involving mechanical contact require control of friction at the microscopic scale. We report on an in-situ study of the structure of oxide films formed upon electrochemical polarization and their role in nanoscale friction on a metallic glass in aqueous environment using atomic force microscopy. The oxide film has a bilayer structure, as revealed by repeated scanning with the tip of an atomic force microscope. The dependence of friction on electrochemical potential reveals the growth mechanism and highlights the role of the oxide films for the frictional response of metallic glasses. The chemical sensitivity of nanotribology studies under electrochemical control contributes to the understanding of corrosion mechanisms on metallic glasses.