Influence Of Friction Forces Research Articles

A Science Friction Story: Molecular Interactions in Semiflexible Polymer Networks

AbstractEstablished model theories, developed to capture the mechanical behavior of soft, complex materials composed of semiflexible polymers, assume that entropic interactions between filaments are primarily responsible for determining the mechanical response. In recent studies, the generally accepted tube model has been challenged in terms of this basic assumption about filament–filament interactions, but also because of its predictions regarding the frequency dependence of the elastic modulus in the intermediate frequency regime. A central question is how molecular interactions and friction between network constituents influence the rheological response of isotropic entangled networks of semiflexible polymers. It has been previously shown that friction forces between aligned pairs of actin filaments are not negligible. Here, the influence of friction forces and attractive interactions on network rheology is systematically investigated by means of targeted surface modification. It is shown that these forces have a qualitative and quantitative influence on the viscoelastic properties of semiflexible polymer networks and contribute to their response to nonlinear deformations. By comparing two polymer model systems with respect to their surface compositions, a possible explanation is given about the origin of acting forces on a molecular level.

Design and verification of low-friction and high-performance monotube magnetorheological damper

The frictional force of the suspension damper is an essential factor affecting vehicle ride comfort. As an important basic component of intelligent suspension, magnetorheological (MR) damper has the advantages of simple structure and adjustable damping performance. However, the frictional force of the MR damper is excessively high, due to the high-pressure gas to avoid the cavitation effect. If the frictional force of MR damper can be reduced, the vibration isolation performance of the intelligent suspension based on the MR damper will be further improved. In this study, a monotube MR damper with low friction and high performance is proposed and investigated. Firstly, the structural design of the low-friction MR damper is carried out, and the mathematical model of its controllable damping force and uncontrollable damping force is established. Secondly, the key structural parameters of the MR piston are optimized, and the valve system is matched based on the optimized mechanical characteristics of the piston to avoid the cavitation effect. Thirdly, bench tests are carried out on the developed low-friction MR damper. The experimental results show that the frictional force of the MR damper is very low, and no cavitation effect occurs. Finally, the system performance simulation analysis is carried out on the 1/4 vehicle semi-active suspension using the MR damper, and the influence of frictional force on the performance evaluation indexes of passive and semi-active suspensions is investigated. The simulation results indicate that the influence of frictional force on semi-active suspension is higher than that of passive suspension, and reducing the frictional force of the MR damper is of great significance to improve the performance of the semi-active suspension.

The Influence of Friction Force and Hysteresis on the Dynamic Responses of Passive Quarter-Car Suspension with Linear and Non-Linear Damper Static Characteristics

Abstract Vehicle passive suspensions consist of two major elements generating force – spring and passive damper. Both possess non-linear characteristics, which are quite often taken into account in simulations; however, the friction forces inside the hydraulic damper and the damping force’s hysteresis are usually left out. The researchers in this paper present the results of examination of the influence of using complex damper models – with friction and hysteresis; and with linear and non-linear static characteristics – on the chosen dynamic responses of a suspension system for excitations in the typical exploitation frequency range. The results from the simulation tests of the simplified and advanced versions of the damper model – different transfer functions and their relation to the reference model’s transfer functions – are compared. The main conclusion is that friction and hysteresis add extra force to the already existing damping force, acting similar to damping increase for the base static characteristics. But this increase is not linear – it is bigger for smaller frequencies than for higher frequencies. The research shows the importance of including non-linear characteristics and proposed modules in modelling passive dampers.

Wave propagation in a cylindrical body in the presence of surface forces depending on the relative displacement

Studies of wave propagation in extended bodies with external friction have a wide range of applications and are significant for various engineering and scientific fields. They contribute to the development of new technologies, improve the design and construction of structures, and expand our understanding of the physical processes occurring in various materials and media. In this article, axisymmetric two-dimensional problems of the propagation of longitudinal waves in a cylindrical body are numerically solved in the presence of surface friction forces of the Winkler and Kelvin-Voigt types. For the numerical solution, the Wilkins scheme of the finite difference method was used. The influence of friction forces on the wave parameters is revealed. It is determined that the results of the considered problems are between solutions using slippery contact without friction and with friction according to the Coulomb law. A 5-7% deviation of the hypothesis of flat sections is shown, which makes it possible to reduce such a problem to a one-dimensional formulation.

Hot crimping in a special profile matrix of axisymmetric hollow workpieces from high carbon steel

Using the finite element method, mathematical models were created and studies were carried out of direct and reverse methods of hot crimping in a matrix of a special profile of hollow workpieces made of high-carbon steel with a variable wall thickness along the height. A plastic model of metal and cylindrical coordinates are used. By calculation, the shape and dimensions of the initial workpiece for crimping were established, which provided the required dimensions of the product. Before crimping, a part of the billet was heated along the height, which was subject to deformation in the matrix. The use of a matrix of a special profile with a deforming surface made with annular protrusions made it possible to obtain a product in one step due to a decrease in the influence of friction forces during shaping. The deformation rate is determined to comply with the hot deformation mode during the crimping. The dependences of the axial force on the deforming tool on the movement of punches and the distribution of specific forces on the contact surfaces are established. The use of direct crimping leads to a decrease in forces modes and specific forces on the tool. The final stress-strain state of the metal, the shape and dimensions of the product are determined. According to the distribution of strain intensity, an assessment was made of the elaboration of the metal structure by plastic deformation. Based on the simulation data, a design of the general view of the die tooling for direct crimping has been developed.

Experimental validation of a constant-force mechanism and analysis of its performance with a calibrated multibody model

The potential applications of constant-force mechanisms (CFMs) have increased in recent years with the development of new designs. This paper focuses on the experimental evaluation and the mathematical modelling of a CFM. The mechanism is based on the use of cams, rollers and springs, which allows for a large stroke and user-adjustable force value. The evaluation and validation of the mechanism is carried out by performing a series of tests examining the constancy of the input force, and where the influence of friction forces and the manufacturing process on the performance of the mechanism is revealed. A multibody model of the constant-force mechanism is developed and calibrated with the help of the experimental results. This model is based on the assumption of rolling without sliding between the cam and the roller, what makes the multibody model to include velocity constraints. The calibration of the model pursues the development of a mathematical tool to study the performance of the mechanism in conditions that are different from those of the experiments presented. The CFM model is used to perform a sensitivity analysis of some important design parameters of the mechanism.

Influence of sea wave shock on transient start-up performance of water-lubricated bearing

The water-lubricated bearing in ship propulsion system is easily impacted by sea wave shock, which is a great threat to the smooth start-up of the bearing system. Therefore, in the present research, the Euler equations, average Reynolds equation, and sea wave shock function are combined together to build the start-up model of water-lubricated bearing. The influences of amplitude, direction, and entry time of sea wave shock on the start-up performance of bearing are studied. The result shows that the shaft has a strong instantaneous vibration under the influence of friction force at the initial start-up stage, and the shock load with appropriate direction and amplitude can suppress or even eliminate this vibration phenomenon. The earlier the shock enters the start-up process, the more serious asperity contact gets, and the worse the system’s stability becomes. The increase of the shock load amplitude and the advance of the shock load entry time can help the shaft rapidly lift off. This study can provide a reference for the smooth start-up of ship propulsion system in a sea wave environment.

An improved mesh stiffness model of helical gear pair considering axial mesh force and friction force influenced by surface roughness under EHL condition

An improved mesh stiffness calculation model of helical gear pair is proposed, in which the transverse gear tooth stiffness, transverse gear foundation stiffness, in addition to axial gear tooth stiffness, axial gear foundation stiffness, that influenced by surface roughness under elastohydrodynamic lubrication (EHL) condition are fully considered. The time varying friction coefficients are obtained by elastoplastic model under varying surface roughness, and then the influence of friction force on mesh stiffness calculation are investigated. The results show that the improved mesh stiffness calculation model could obtain the mesh stiffness under actual lubrication condition compared with conventional method, in which the axial mesh forces and friction forces acting on the gear tooth and gear foundation are always ignored in the mesh stiffness calculation for helical gear pair.

Modeling and Experimental Verification of a Cable-Constrained Synchronous Rotating Mechanism Considering Friction Effect

Cable-Constrained Synchronous Rotating Mechanism (CCSRM) has an important application prospect in the field of cable-driven robots, which can greatly reduce the number of driving motors while ensuring the light and slender body. However, there are obvious cable friction effect and elastic deformation in CCSRM. These nonlinear characteristics have a significant impact on synchronous motion performance. In this letter, a model of CCSRM considering cable friction is proposed, which integrates the effects of cable pretension, elastic deformation, and friction between cable and pulley on system characteristics. The distribution law of cable tension under the influence of friction force and the phenomenon of motion hysteresis caused in reverse rotation are emphatically discussed. Then, an improved LuGre friction model is proposed to solve the problem of line contact friction between cables and pulleys. Further a dynamic model of CCSRM is established to simulate the motion characteristics of the whole process, including the discontinuous friction phenomenon in reverse rotation. Finally, an experimental prototype of two-axis synchronous rotating system is built, and the friction coefficient is identified. The experimental results show that the dynamic model can well simulate the motion characteristics of CCSRM.

Micro-debond Experiment and Analytical Model for Interfacial Fracture Toughness between Single Carbon Fiber and TiO2 Micro-droplet

To improve mechanical behaviors of the carbon fiber-reinforced metal matrix composites, TiO2-coated carbon fibers are usually used in the composites to protect the fiber from degradation. Thus, it is crucial to maintain both strong interfacial bonding at carbon fiber–TiO2 interlayer interface and high interfacial fracture toughness, which influence the damage tolerance of the composites as well as their energy absorption capacity. In this study, different single carbon fiber/TiO2 systems with and without modified carbon fiber were prepared at heat treatment temperatures of 80 and 700 °C, respectively, and an analytical modeling for evaluating interfacial fracture toughness from the micro-debond tests by using the tests that record only the debond and friction force as a function of the TiO2 micro-droplet length was implemented first, and then, the interfacial adhesion forces, interfacial fracture toughness and the influence of friction force and thermal residual stress on the fracture toughness of the systems were discussed in detail. From the experimental and theoretical results, heat treatment temperature and local strong bonding sites have a significant effect on the interfacial fracture toughness, while the interfacial morphology and functional groups are dominant in determining the interfacial adhesion forces. Meanwhile, the dominant factor of the interfacial fracture toughness will change as the heat treatment temperature increases. The friction force is a major contributor to the interfacial fracture toughness of the systems treated under lower temperature (80 °C), while the residual thermal stress is responsible for the toughness of the systems treated under higher temperature (700 °C). The results in this study can serve as reliable input data in multi-scale simulation of the carbon fiber-reinforced light metal matrix composites and offer exciting opportunities for further investigation of the microscopic deformation mechanisms in the composites.

Restoration of hydraulic cylinder rods by method of ESA

During the operation of equipment, its structural elements under the influence of frictional forces and the environment are exposed to various types of wear. To maintain the rolling stock in a working condition, it is necessary to systematically carry out a large set of measures, such as maintenance, current and overhaul repairs with periodic replacement and restoration of worn parts and assemblies. It is obvious that maintaining the performance of modern machines requires high technical knowledge and modern technology. It is not uncommon for special machinery, including tractors and various agricultural vehicles, to be equipped with hydraulic power systems to perform various heavy operations. The actuating mechanisms of such systems are hydraulic cylinders. One of the main features of their design and operation is that the main and very precise part - the rod in working order is in an unprotected environment, namely in the open air. The specificity of the work of heavy equipment is high dust content, gas pollution and the presence of various abrasive materials in the work area in the form of stones and soil. Under these conditions, the precision, polished rods are subject to significant wear. In this paper, the possibility of restoring hydraulic cylinder rods for small types of wear (scratches and dents of a depth of no more than 0,3 mm) is considered by the method of electrospark alloying (ESA), with the creation of coatings on their working surfaces that are identical in their characteristics to the new ones. Electrode materials and processing modes were selected. Research was carried out to determine the dynamic microhardness of the created coating.

Analysis of the Stress-Strain State of Ceramic Brick when Tested for Compressive Strength

The article analyzes the change in the stress-strain state of ceramic brick samples when tested in compression, depending on the variable parameters - the type of sample and the method of surface preparation. The experiment showed that the friction forces arising in the “sample-plate test press” zone of contact have a significant effect on the deformation conditions of the samples and lead to an uneven distribution of the breaking load over the surface. This in turn leads to an overestimation of the strength characteristics of the lot, and, consequently, to errors in the calculations of the bearing capacity of the structures. A numerical analysis of the stress distribution also showed that for the samples aligned by grinding and with the help of a mortar; the effect of compression caused by friction forces can be traced. Thus, the results of the numerical experiment are in good agreement with the results of the full-scale experiment. To increase the reliability of the test results, it is necessary to reduce the influence of friction forces and provide conditions for the realization of uniaxial compression. In this regard, it is necessary to adjust the standard test method, namely to use the technical felt gaskets as a method of preparing the surface.

ДЕФОРМАЦИОННЫЕ И УДАРНО-ВОЛНОВЫЕ ПРЕДСТАВЛЕНИЯ О ПРИРОДЕ ТРЕНИЯ И ИЗНАШИВАНИЯ

As the statistical analysis shows the main reason for the failure of the machines is not their breakdown, but the wear of mobile conjugation and working bodies under the influence of friction forces. However, when creating machines, practically no movable

To the question of the design of direct-flow gas pressure regulator direct actions

In this paper, issues that need to be considered when designing direct-flow gas pressure regulators of direct action are addressed. A constructive scheme of a piston type gas pressure regulator is presented. Experimental studies of gas pressure regulators of standard sizes DN50 and DN80 at the facility of the existing gas pipeline were conducted, and adjustment of regulators was carried out at the pneumatic stand of the university. The influence of friction forces on the quasi-harmonic low-frequency self-oscillations of the control system is shown. This phenomenon is due to the nature of friction when using rubber and fluoroplastic sealing rings in the moving elements of the regulator and the presence (or absence) of a film of lubricant. This is directly related to transients, stability conditions in transients during regulation due to changes in gas flow.

THE INFLUENCE OF FRICTION FORCES ON LONGITUDINAL WAVE PROPAGATION IN A STUCK DRILL STRING IN A BOREHOLE

A mathematical model and the computer software for the analysis of dynamic processes occurring in the drilling pipes in the borehole under stuck drill string release by means of an impact mechanism (a jerking device) or a pulse-wave installation, equipped with electric linear pulse motor are presented. The drill string with an impact mechanism, which is inserted over the stuck section after failure, is detected and is activated by lowering and taking the non-stuck upper part of the string by means of the drilling rig drive and is considered as a discrete-continuous mechanical system. As a result of the impact of the hammer on the body of the impact mechanism, wave processes are formed in the drill string, which helps to release the stuck drill string. The influence of friction forces on propagation of longitudinal waves in the drill pipe string is investigated. Practical recommendations are developed regarding the above-mentioned efficiency of drilling for oil and gas.

Model and Energy Aspects for Propagation of Strain and Mechanical Stresses in Textile Fabrics

We consider the influence of frictional forces between warp and weft yarns on the resistance of the fabric. We have established that when the fabric is stretched, the strain distribution is not uniform over the length of the sample. We have found that the major portion of the strain occurs in the section of yarns between their overlaps with weft yarns.

Анализ влияния сил трения в зацеплении на динамические нагрузки в зубчатых передачах

Анализ влияния сил трения в зацеплении на динамические нагрузки в зубчатых передачах

Downhill cycling symmetry breaking: how the rider foils experiment

In high-school teaching of mechanics, we deal, among other things, with the nature of static and kinetic friction, forces that are proportional to the normal force. Under the influence of frictional forces, a body moves down a rough sloped decline at a fixed rate of acceleration that is independent of its mass. This situation does not apply to cases where the frictional force is dependent upon velocity, such as bodies which are moving through a streaming fluid (such as raindrops falling to the ground). In this case the body moves with a continuously decreasing acceleration, eventually reaching a terminal velocity when the frictional and gravitational forces balance out. This velocity constraint is determined by the dependence of the frictional force on velocity and geometric parameters that determine the strength of the frictional force. We show here that a similar situation takes place when bicycles descend an incline with a fixed slope. We also investigated the dependence of the velocity constraint with mass, using bicycles equipped with sophisticated sensors that metamorphose them into data-processing laboratories.

ANALYSIS OF THE INFLUENCE OF FRICTION FORCE ON THE STRAINS OF GAS PIPELINE USING THE HILBERT-HUANG TRANSFORM

The aim of the study was to determine the effect of friction forces on strains of a gas pipeline pipe in conditions of static and dynamic load. The experiments were conducted on a 28-metre section of pipe laid in quartz sand haunching. The source of dynamic loads was artificially generated soil vibration of a pulse character, which can be interpreted as seismic-like waves of mining origin. The static loads were applied by means of an actuator, which allowed the setting of different values of tension force acting along the pipe axis. The dynamic strain and vibration acceleration of the pipeline were measured during the experiments at different values of tension forces. The recorded signals were subjected to the time-domain decomposition by using the Hilbert-Huang transform. The method allows for the correct decomposition of the primary signal that describes the non-stationary and nonlinear phenomena as a sum of quasi-harmonic components whose amplitudes and frequencies are the parametric functions of time. The analysis included the determination of the influence of friction force in contact between the pipe and the sand haunching on the parameters of dynamic strain signals.

An Experimental Study of Influence of Frictional Force, Temperature and Optimization of Process Parameters During Machining of Mild Steel Material

An Experimental Study of Influence of Frictional Force, Temperature and Optimization of Process Parameters During Machining of Mild Steel Material