Lateral Friction Force Research Articles

Influence of friction between wood and support elements in the design of timber structures for roofing

Throughout history, wood has played a crucial role in all phases of building construction. Despite existing prejudices in Brazil regarding its use in structural systems, primarily due to the lack of dissemination of technical information, wood is gradually gaining more space in the market as a viable and environmentally sustainable alternative. With exceptional mechanical properties, wood is compatible with other widely used construction materials in the Brazilian structural market, such as concrete and steel. In this context, this research aims to analyze the influence of considering the friction coefficient caused by the sliding of the support with free horizontal displacements in isostatic trusses, investigating its impact on the design of the components that make up the truss. Such sliding generates a lateral friction force that promotes a restraining effect on the structure, potentially relieving stresses on the lower chord members. For this purpose, the Finite Element Method (FEM) is used as an analytical tool, supported by the iTruss verification software to validate the obtained results. By considering the frictional force generated on the support links of the analyzed trusses, the numerical results revealed changes in the design of structural profiles for all existing wood strength classes (D20, D30, D40, D50, and D60) in situations of friction between wood and wood, and between wood and concrete. A reduction in the volume of wooden pieces was observed, ranging from 5.88% to 8.54%, suggesting that the inclusion of the friction coefficient during structural calculations can result in savings, not only from a financial standpoint but also promoting environmental benefits by encouraging a more responsible use of wood in civil construction.

Analysis of water droplet motion on hydrophobic surfaces with different microstructures

AbstractThe influence of material surface microstructure on interface properties is crucial for the preparation and development of special functional materials. In this paper, polydimethylsiloxane‐based superhydrophobic surfaces of varying roughness and surface energy are prepared using the template method and a spraying technique, and the effect of surface microstructure on lateral friction is studied using a lateral friction detection system. The experimental results indicate that as the surface roughness of a sample decreases, it is observed that the water droplets transition from a Cassie state to a Wenzel state. When the roughness changes from 4.619 μm, reduce to 3.512 μm, the maximum static friction force increases from 33.59 μN increased to 51.52 μN. The lateral sliding friction force ranges from 15.87 ± 1.9 μN increases to 40.91 ± 1.2 μN. For a given surface roughness, when the surface energy is reduced, the water droplets on the surface can be seen to transition from a Wenzel state to a Cassie state, the maximum static friction force increases from 19.32 μN dropped to 9.23 μN, and the lateral sliding friction force increases from 15.26 ± 1.6 μN dropped to 3.47 ± 2.1 μN. However, this behavior is distinct from that observed when changing the roughness of the sample. Studying the influence of the surface microstructure on the lateral friction force observed at a solid–liquid interface can provide important insights into novel geometries that may be used in new, advanced functional surfaces.

Effects of indentation depth and grain size on scratching behavior of nanograin FCC Fe polycrystalline substrate

Owing to their high grain boundary (GB) density, nanograin materials have excellent mechanical and physicochemical properties. The variation of GB density can dominate their plastic deformation mechanism. This work investigated the effects of indentation depth and mean grain size (MGS) on the scratching plastic deformation of FCC Fe nanograin substrates by molecular dynamics method. The contact strengths of the models with MGSs of 2.05 and 8.71 nm were the smallest (9.26 GPa) and largest (11.67 GPa), respectively. When the MGS was refined smaller than the critical size (5.07 nm), the Hall–Petch breakdown occurred in the nanograin polycrystalline substrate. With the increase in the indentation depth, plastic deformation became dominant, and abrasion volume first increased and then decreased with a decrease in the MGS. The lateral friction force and normal forces (including their increments) increased with the indentation depth. Models with moderate grain sizes could maintain larger "acceleration" of friction and normal force increments. After grain refinement, dislocations increased during the scratching process, and all of them were short dislocations limited by grain boundaries; in particular, there was no long straight stair-rod dislocation. The shear strain in ultrafine grain model was distributed along GBs. Grain lattice rotation extends throughout small grains with the MGS decrease to 2.05 nm. The deformation mechanism changed from dislocation-mediated mechanism to that involving grain lattice rotation and GBs sliding. This work can provide a theoretical basis for the design, machining, and performance prediction of nanograin polycrystalline materials.

A Classical Molecular Dynamics Study of the Effect of the Atomic Force Microscope Tip Shape, Size and Deformation on the Tribological Properties of the Graphene/Au(111) Interface

Atomic force microscopes are used, besides their principal function as surface imaging tools, in the surface manipulation and measurement of interfacial properties. In particular, they can be modified to measure lateral friction forces that occur during the sliding of the tip against the underlying substrate. However, the shape, size, and deformation of the tips profoundly affect the measurements in a manner that is difficult to predict. In this work, we investigate the contribution of these effect to the magnitude of the lateral forces during sliding. The surface substrate is chosen to be a few-layer AB-stacked graphene surface, whereas the tip is initially constructed from face-centered cubic gold. In order to separate the effect of deformation from the shape, the rigid tips of three different shapes were considered first, namely, a cone, a pyramid and a hemisphere. The shape was seen to dictate all aspects of the interface during sliding, from temperature dependence to stick–slip behavior. Deformation was investigated next by comparing a rigid hemispherical tip to one of an identical shape and size but with all but the top three layers of atoms being free to move. The deformation, as also verified by an indentation analysis, occurs by means of the lower layers collapsing on the upper ones, thereby increasing the contact area. This collapse mitigates the friction force and decreases it with respect to the rigid tip for the same vertical distance. Finally, the size effect is studied by means of calculating the friction forces for a much larger hemispherical tip whose atoms are free to move. In this case, the deformation is found to be much smaller, but the stick–slip behavior is much more clearly seen.

Path tracking of varying-velocity 4WS autonomous vehicles under tire force friction ellipse constraints

In this paper, a control scheme is presented to solve the problem of path tracking for varying-velocity autonomous vehicles with higher robust performance while friction force constraints of vehicle tires and ground are considered to avoid appearing the steering lost situation actively in the limit of the tire friction forces by using four wheel steering. To achieve these goals, a new expression of the tire forces and a new controlled system are proposed for the three degree of freedom vehicle model. A longitudinal input-saturation controller is designed to track the desired longitudinal velocity and attenuate the influence of lateral and yaw motions. The virtual control input method is used to design the input-saturation controller and get the desired steering angles to track the desired path for the lateral and yaw motions while a new control problem with desired forces tracking is considered to autonomously avoid the limit of lateral tire friction forces and the steering lost situation appearing. To test these results, lane changing, U-corner turning and straight-line driving for a varying-velocity vehicle are simulated with external disturbances and model uncertainties. Simulation results show that the higher robustness and precise path tracking performances are obtained.

Experimental study on the dynamic wetting of silica nanofluids

Nanofluids are recently discovered nanomaterials with improved thermophysical properties that can enhance the efficiency and reliability of heat transfer systems. Their relevant properties for describing heat transfer, thin film flows, droplet impingements, or microfluidics are surface tension and wettability. A thorough investigation on this topic of research is crucial to understand the root cause of the factors affecting the degree of wetting of nanofluids on solid surfaces. In the present work, silica (SiO2) nanofluids with different mass fractions and types of surfactants based on deionized water were prepared using a simple and cheap two-step method. The effect of surface tension changes on the lateral friction force of the nanofluid was studied using a solid–liquid interface lateral friction force detection system. According to the findings, an increase in the mass fraction of silica nanoparticles led to the larger surface tension of the nanofluid, resulting in a linear decrease in the lateral friction of the latter on the hydrophobic surface of PDMS. The use of ionic surfactants as dispersants caused a dramatic decrease in surface tension and static angle of SiO2 nanofluid (by 20% and 30% after adding SDS and by 40% and 50% after adding CTAB, respectively). This exerted a noticeable impact on the lateral friction force of the fluid. On the contrary, polymeric surfactants (NaPSS) had a small effect on the lateral friction of SiO2 nanofluid. Meanwhile, the lateral friction after stable motion differed from the maximum static friction to a small extent.

Hot Briquetting Technology for Ferrous Metal Waste in Molds with Movable Matrix

The paper describes the technology of hot briquetting of structurally heterogeneous metalworking waste in molds with a movable matrix, which differs from known analogues in the possibility of improving the quality of briquettes with a minimum number of preparatory operations. The aim of the work is to improve the process of hot briquetting. The tasks to be solved are to develop a technological scheme and a physical and mathematical model of the process, reduce the forces of contact friction and tool wear, and optimize the energy-power parameters according to the criteria for the density and strength of briquettes. The technological scheme of briquetting is represented by a mold with a movable matrix, in which compressed air is used as an elastic support. During the briquetting process, the matrix and the pressed metal move in the same direction. The lateral friction force is active, directed towards the briquetting force. As a result, the force and work of briquetting, mold wear are reduced, and the briquette itself is of high quality – uniform in density and without internal defects.As a result of the numerical calculation of the model, the dependences of the stress state of the pressing and pressing pressure on the coordinates and density on the contact surfaces and in the depth of the material were obtained, which makes it possible to calculate the strength of the mold parts and select equipment for the briquetting process. The regularities of formation of the briquette structure are studied, the advantages of using the proposed technological scheme in comparison with briquetting in a fixed matrix are shown. The proposed technology eliminates the implementation of the preliminary operation of coolant removal by centrifugation or other known methods. Coolant is removed by thermal sublimation, partially burned in the furnace firebox, partially condensed in the “wet” cleaning system.

Stability Analysis of Shield Excavation Surface with Curved Body Model

Currently, the limit equilibrium method of wedge shape is generally adopted for the stability of the excavation surface in shield tunnel construction. In this method, the sliding surface is approximated by a plane, and the lateral friction force of the sliding surface is estimated and assumed to be a known quantity to derive the equilibrium equation and calculate the support force of the excavation surface. However, it is difficult to accurately estimate the lateral friction force of the sliding surface because of many factors that affect such friction, for example, soil arching. In this paper, a sliding block model of curved surface body composed of a semicircular platform and a partial sphere is proposed for the stability of the excavation surface in shield tunnel construction. By using the symmetry of the surface body model, there is no need for estimating the friction force of the sliding surface during the stability analysis of the excavation surface, and the calculation accuracy of the limit support pressure is improved. Furthermore, the force analysis of the semi-circular platform surface model above the tunnel vault is carried out. Considering the variation of the lateral pressure coefficient caused by the deflection of the principal stress under the soil arch effect, the analytical solution of the vertical stress in the soil is derived when the sliding crack surface is curved. Finally, we present a sensitivity analysis of various parameters affecting the support force of the excavation face through the study of examples. The influencing factors and changing rules related to the support force of the excavation face are also discussed.

Straining of atomically thin WSe2 crystals: Suppressing slippage by thermal annealing

The atomically thin two-dimensional (2D) transition-metal dichalcogenide (e.g., MoS2) material can withstand large strains up to 11% to change its energy band structure, thereby further tuning its optical, electrical, and other physical properties. However, the slippage of 2D materials on substrate hammers the further strain tuning of the properties of 2D materials. Hereby, a facile three points approach combined with a dry transfer method that can apply uniaxial strain to two-dimensional materials is provided. The slippage of WSe2 on polycarbonate (PC) substrate can be suppressed by thermally annealing WSe2/PC in low pressure Ar atmosphere above 100 °C for 3 h. Straining cycle evolution experiments revealed that the thermal annealing of (1L) WSe2 could suppress slippage from the surface of the PC. The spectral gauge factor of 1L WSe2 is found to be around -60 meV/%. After thermal treatment, WSe2/PC stacking can survive in DI water for at least 24 h without the degradation of the spectral gauge factor. Dome structures are formed after thermal treatments with the interplay of the viscoelasticity and surface tension of the PC and the 0.4% tensile strain on WSe2, and the RMS roughness of WSe2/PC increased from 820 to 1292 pm, indicating that there could be larger lateral friction force to suppress slippage following thermal annealing. Our findings enrich the strain engineering of 2D materials and their device applications.

Fluctuational electrodynamics in and out of equilibrium

Dispersion forces between neutral material bodies are due to fluctuations of the polarization of the bodies. For bodies in equilibrium these forces are often referred to as Casimir–Lifshitz forces. For bodies in relative motion, in addition to the Casimir–Lifshitz force, a lateral frictional force (“quantum friction”, in the zero temperature limit) comes into play. The widely accepted theory of the fluctuation-induced forces is based on the “fluctuational electrodynamics”, when the Maxwell equations are supplemented by random current sources responsible for the fluctuations of the medium polarization. The first part of our paper touches on some conceptual issues of the theory, such as the dissipation-less limit and the link between Rytov’s approach and quantum electrodynamics. We point out the problems with the dissipation-less plasma model (with its unphysical double pole at zero frequency) which still appears in the literature. The second part of the paper is devoted to “quantum friction”, in a broad sense, and it contains some novel material. In particular, it is pointed out that in weakly dissipative systems the friction force may not be a stationary process. It is shown, using an “exact” (nonperturbative) quantum treatment, that under appropriate conditions, an instability can occur when the kinetic energy (due to the relative motion between the bodies) is transformed into coherent radiation, exponentially growing in intensity (the instability gets eventually limited by nonlinear effects). We also discuss a setup when the two bodies are at rest but a constant electric current is flowing in one of the bodies. One may say that only the electron component of one body is dragged with respect to the other body, unlike the usual setup when the two bodies are in relative motion. Clearly, there are differences in the frictional forces between the two setups.

A novel estimation scheme of tyre–road friction characteristics based on parameter constraints on varied-µ roads

On varied-µ roads, most of the current research on the estimation of tyre-road characteristic parameters and peak friction coefficient lack consideration of parameter constraints. To improve the estimation accuracy, in this study, a novel estimation scheme of tyre-road friction characteristics based on parameter constraints is proposed: based on estimating the longitudinal and lateral friction force, a data preprocessing method is proposed to obtain the constraint region of parameters. Then, the nonlinear least square method is used to preliminarily estimate the parameters. Finally, a constrained auxiliary particle filter algorithm is proposed to correct the estimated parameters. To verify the superiority of the proposed scheme, the estimation performances of friction characteristics of four schemes are compared on low/high speed varied-µ roads, respectively. The results demonstrate that the proposed scheme has the best estimation performance. Simultaneously, compared with the scheme without considering parameter constraints, the proposed scheme can significantly reduce the estimation error.

A Novel Method for Surface Exploration by 6-DOF Encountered-Type Haptic Display Towards Virtual Palpation

Surface exploration in virtual reality has a large potential to enrich the user's experience. It could for example be used to train and simulate medical palpation. During palpation, users tap, indent, and rub the surface of a sample to estimate the underlying properties. However, up to now there is no good approach to render such intricate interaction realistically. This paper introduces 6 degrees of freedom (DoF) encountered-type haptic display technology for simulating surface exploration tasks. Among the different phases of exploration, this article focuses on the 'in-contact sliding' phase. Two novel control approaches to render sliding over a virtual surface are elaborated. A first rendering method generates lateral frictional forces as the finger slides over the surface. A second method adjusts the inclination of the end-effector to render tissue properties. With both methods a stiff nodule embedded in a soft tissue was prepared. User experiments were carried out to find proper parameter and intensity ranges and to confirm the feasibility of the new rendering schemes. Participants indicated that both rendering schemes felt realistic. Compared to earlier work, where only the vertical stiffness was altered, lower thresholds to detect and localise embedded virtual nodules were found. Users also made fewer errors in detecting nodule edges. Furthermore, the method that used end-effector inclination allowed faster discovery of the nodule's edges. It is expected that approaches that combine both rendering methods could provide an even more realistic feel.

The role of charge distribution on the friction coefficients of epitaxial graphene grown on the Si-terminated and C-terminated faces of SiC

The friction coefficients of single-layer epitaxial graphene grown on the Si-terminated and C-terminated faces of Silicon Carbide (SiC) substrate were measured under ambient conditions using Friction Force Microscope (FFM). The lateral friction force measurements acquired in the applied normal force range between 4.0 and 16.0 nN showed that the friction coefficient of graphene on the C-terminated face of SiC is about two times smaller than the one grown on its Si-terminated face. The lateral friction was found to be decreased as the average of root mean square roughness increases suggesting the observed difference in the friction coefficients cannot be related to the roughness of the graphene layers. DFT calculations demonstrated that the altered periodicity of charge distribution on graphene due to the specific interactions with two distinct polar faces of SiC substrate might explain the observed difference in the friction coefficients.

Controlled pipeline lateral buckling by reeling induced curvature imperfections

Expansion of pipelines installed on the sea floor due to the passage of high temperature and pressure hydrocarbons leads to lateral buckling. Interaction with a frictional sea floor can result in localization of such buckles, which must be controlled to ensure that the local bending is within acceptable limits. Periodic geometric imperfections introduced to a pipeline installed by reeling using the Residual Curvature Method are modeled and their effectiveness as expansion loops is evaluated. The imperfections are generated by allowing chosen lengths of the line to retain a small curvature by judicious action at the straightener. The model properly accounts for the complex interactions between geometric and material nonlinearities with frictional forces. It is demonstrated that as the temperature increases, the line can buckle in a snap-through manner, or can grow stably usually causing plastic deformation in its crest. The behavior is governed by the length, curvature, amplitude and periodicity of the imperfection, and by the lateral and axial frictional forces that develop. The effect of each of these variables is studied parametrically. Overall, the Residual Curvature Method is found to be a viable and effective method of controlling lateral buckling. The results provide guidance on the optimal periodicity, how to avoid snap-through buckling, and how to simultaneously minimize plastic bending.

Investigation of longitudinal friction characteristics of an omnidirectional wheel via LuGre model

SUMMARYIn recent years, omnidirectional wheels have found more applications in the design of automated guided vehicles (AGV). In this work, LuGre friction model is used for an omnidirectional wheel. A test setup that includes a single omnidirectional wheel is designed and constructed to identify the model parameters. With the help of the constructed test setup, the longitudinal friction characteristic of the omnidirectional wheel is obtained, and the model is verified via validation tests. In addition, for the first time, the effect of lateral frictional force on longitudinal motion is examined for an omnidirectional wheel through experiments.

Internal Force of the Anti-slide Pile in Soil Based on the Deep Beam Model

According to the deep beam model, the bury conditions, the geometry characteristics and the load condition, we established a load transfer model based on the tie rod arch and an internal force model for the loaded and anchored segments of the anti-slide pile. Then, we analyzed the shear, bending shear and local compressive failures of the pile, caused by the equivalent concentrated thrust force, the lateral frictional force, active earth pressure, and passive earth pressure, etc. With the laboratory results of the deep beam model, the relation between the shear span ratio and the tie rod arch was presented. According to the mechanical balance conditions of the cantilever beam, we obtained the power function curve of the tie rod arch and the influence factors. Subsequently, we established the equations of the horizontal displacement and the deflection angle at the bearing segment by superposing the load and the displacement of the strip nodes. According to the deformation characteristics of the Timoshenko deep beam element, the equations of the horizontal displacement and the deflection angle at the anchored segment were proposed. With the established calculation model and the material mechanics, the displacement, shear force and bending moment curves at the loaded and anchored segment of the anti-slide pile were proposed. Finally, the case study indicates that the displacement and the internal forces are nonlinear in the pile. The results obtained using the preliminary beam are larger than the numerical results, which is the smallest results than the other two methods.

Dynamic model of a logistic train with different steering systems and tire models

Abstract Logistic train is one of the recent solutions applied in the intralogistics. It bases on the concept of the “milk-run” delivery method. The main problem in the implementation of intralogistics trains is the possibility to determine whether the train is able to pass the given path without a colliding with surrounding objects. Dynamic model presented in this paper was performed for the three most common steering systems for the trolleys: double Ackermann steering system and two drawbar systems: conventional and virtual clutch. The dynamic model was developed following Lagrange’s theorem including the possibility of lateral slip. The system of differential equations was numerically solved. In order to calculate the lateral friction forces we used three different tire models: simplified, sigmoidal and Pacejka Magic formula. The results obtained for different tire models and steering systems are presented in the form of animations presenting train run in various conditions. The analyses have shown that the use of simplified tire models is justified under certain conditions.

Innovative structural and technological developments of pile foundation engineering

The paper considers innovative structural and technological solutions for precast piles, which significantly increase their load-bearing capacity: a transformable pile and a pile with “pockets” (recesses) on the side surface for use in loose soils. In the first case, in the manufacture of precast reinforced concrete piles in the center they set plastic cone-shaped cruciform brake detail with length 0.75 of the pile length, in which after driving the piles destructive non-explosive substance is poured, that increasing in volume in 2-3 times, transforms prismatic pile into a pyramid one. In the second case, when making precast concrete piles, they provide for the arrangement along the side faces of “pockets” (recesses). The liquid hardening compound located in the “pockets” penetrates into the soil of the pile during the driving process and secures it, which significantly increases the lateral friction force of the pile and its load-bearing capacity and reduces the energy of the pile sinking. The considered design and technological solutions allow reducing the energy of pile driving, while increasing their load-bearing capacity.

Improved Tactile Perception of 3D Geometric Bumps Using Coupled Electrovibration and Mechanical Vibration Stimuli

Abstract At present, the tactile perception of 3D geometric bumps (such as sinusoidal bumps, Gaussian bumps, triangular bumps, etc.) on touchscreens is mainly realized by mapping the local gradients of rendered virtual surfaces to lateral electrostatic friction, while maintaining the constant normal feedback force. The latest study has shown that the recognition rate of 3D visual objects with electrovibration is lower by 27$\%$ than that using force-feedback devices. Based on the custom-designed tactile display coupling with electrovibration and mechanical vibration stimuli, this paper proposes a novel tactile rendering algorithm of 3D geometric bumps, which simultaneously generates the lateral and the normal perceptual dimensions. Specifically, a mapping relationship with the electrostatic friction proportional to the gradient of 3D geometric bumps is firstly established. Then, resorting to the angle between the lateral friction force and the normal feedback force, a rendering model of the normal feedback force using mechanical vibration is further determined. Compared to the previous works with electrovibration, objective evaluations with 12 participants showed that the novel version significantly improved recognition rates of 3D bumps on touchscreens.

Design and testing of a new dual-axial underfloor piezoelectric energy harvester

This paper presents the design, fabrication, and testing of a dual-axial underfloor piezoelectric energy harvester based on piezoelectric stack. Usually, an underfloor energy harvester can only scavenge the energy from vertical force excitation. In addition to vertical pressure, the floor also suffers from lateral friction force during human walking. One uniqueness of the designed underfloor energy harvester lies in that it can collect energy from both vertical and horizontal excitation forces. To amplify the input force to get a larger output power, a flexure-based two-stage force amplifier is introduced and optimally designed. In order to transmit the two-directional (2-D) input force into the single direction that can be received by the force amplifier, the conical transmission mechanisms and slider mechanisms are introduced. Position limiters are adopted to protect the proposed mechanism. A prototype has been fabricated and tested. Experimental results indicate that the fabricated dual-axial piezoelectric energy harvester can provide an average output power up to 1.25 mW with a load resistance of 12 kΩ from 5 Hz force excitation of 100 N in two directions. With a load resistance of 26 kΩ, the harvested energy per walking footstep is derived as 7.00 mJ for the underfloor energy harvester.