Contact Spots Research Articles

Determination of the dependencies of the wear influence of the cylindrical brush on the operational characteristics of the garbage truck’s mounted sweeping equipment

The article is dedicated to the establishment of dependencies of the influence of the wear of the cylindrical brush on the operational characteristics of the mounted sweeping equipment of the garbage truck. By using the planning of the second-order experiment with the first-order interaction effects, using the Box-Wilson method, the adequate dependencies of the influence of the wear of the cylindrical brush on the performance characteristics of the mounted sweeping equipment of the garbage truck were determined. It was established that, according to the Student's criterion, among the investigated factors of influence, the wear of the cylindrical brush has the greatest effect on the deformation of the cylindrical brush, and the width of the contact spot has the least influence. The required pressing force of the cylindrical brush is most affected by the width of the contact spot, and the least by the wear of the cylindrical brush. The response surfaces of the target functions are shown – the amount of deformation and the required pressing force of the cylindrical brush and their two-dimensional cross-sections in the planes of influence parameters, which make it possible to visually illustrate the specified dependences of target function data on individual influence parameters. It was established that the wear of the cylindrical brush of 50% of cases leads to an increase in the deformation of the cylindrical brush by 1.3 times, and the necessary force of pressing of the cylindrical brush – by 3.1...3.6 times, depending on the width of the contact spot. It is shown the expediency of conducting further researches of the effect of antifriction materials on the wear of the friction pairs of the mounted sweeping equipment of the garbage truck.

ELEMENTS OF L. PETROV’S THEORY FOR A WHEEL-DRIVEN VEHICLE WITH EXTENDED TRACTION EFFORT

The rolling of a car wheel drive is accompanied by its loading by gravitational force in the area of the spot of contact with the supporting surface, which can lead to uneven tire rotation between the right and left sidewalls during its deformation, as well as a decrease in the power transmitted to the car’s wheel drives. The article deals with the research of the elements of the theory of a truck with an internally built-in mechanism. The purpose of the study is to improve the technological scheme of loading the wheel drive with the mechanism built into it when loading this mechanism with rotating inertial wheels, which allows the energy of rotational movement to be transferred to the wheel drive due to the flexible element kinematically connected to it. The scientific component of the wheel drive is that the inner part of the wheel drive is loaded with a dynamic mechanism, during the rotation of which the law of energy accumulation is applied on the inner surface of the disk, and this makes it possible to realize the traction moment on the wheel drive. Mathematical determination of the amount of additional force, which is formed during the rotation of movable inertial wheels and is related to the semi-axis of the car wheel, and this allows changing the speed of the car in a short period of time. A truck with an internally built-in wheel drive, which allows you to develop a design of a wheel drive with a portable internal effect, and this allows you to increase the dynamic stability of the vehicle itself. In the design of the wheel drive of the truck, the traction force vector is used in its inner surface in order to align it along the thrust between the left and right sides. The design of the car with an internally integrated moving mechanism in the wheel drive ensures the efficient use of engine power to create a tangential traction force on the wheel. Keywords: physical model, force, moving wheels, moment of inertia, kinetic energy, flexible element.

Numerical Simulation of Turbulent Fluid Flow in Rough Rock Fracture: 3D Case

We investigate both laminar and turbulent flow regimes in a 3D rock fracture via numerical CFD simulations. We construct our realistic fracture model from 3D scan data of a fractured rock sample and implement changes in both shear displacement and contact ratio, examining their effect on fracture permeability and friction factor. While previous studies were investigating either fully viscous Darcy or inertial Forchheimer laminar flow regimes, we chose to cover the wide Reynolds number range of 0.1–106\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^6$$\\end{document}. We introduce CFD simulation of a turbulent flow for realistic 3D fractures, implementing the RANS approach to turbulence modeling. We focus on 3D fracture geometries and implement changes in both shear displacement and contact ratio, systematically examining their effect on fracture permeability and friction factor in a manner similar to the fundamental studies of the flow in rough-walled pipes. Growing Re leads to first stationary–non-stationary and then laminar–turbulent transitions. The presence of contact spots severely disrupts the flow pattern and adversely affects the overall permeability of the fracture. Regardless of shear displacement, ‘no contact’ 3D models can be reasonably approximated by the 2D profiles. Depending on the fracture geometry, Forchheimer β\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta$$\\end{document} fitting for both laminar and turbulent regimes can be performed either by a single or by two parameter values.

On contact spots details of rough surface contact using morphologic image processing

In the rough surface contact research, the real contact area has long been the primary focus, however, the details of contact spots, such as the size, morphology, and distribution which directly impact thermal and electrical contact performance, are basically overlooked. In the present study, an efficient and straightforward method using morphological image processing is proposed to obtain the details of contact spots from rough surface contact solved by finite element simulation. This study shows that the present method can better evaluate the real contact area and enable to reveal the evolutions of contact spots, including the number, average area, variance, and average gap of contact spots. Three evolution stages of rough surface contact are identified as Involving, Growing, and Merging stages according to the critical number of contact spots. The effects of characteristic parameters of rough surfaces are also investigated.

Contact Reconstruction and Contact Spot Analysis of Microscopic Contact Surfaces Based on Feature Matching

Contact Reconstruction and Contact Spot Analysis of Microscopic Contact Surfaces Based on Feature Matching

A rough surface electrical contact model considering the interaction between asperities

A rough surface electrical contact model considering the asperity interaction is developed to study the electrical contact behavior. The rough surface is generated by using a two-dimensional Weierstrass-Mandelbrot function. First, the mechanical contact area of the rough surface is determined by the boundary element method in the absence of the electric potential. The electrical contact area is then calculated by a fitting function based on the mechanical contact area. The fitting data is provided by the single-asperity electrical contact model developed in our previous study. By using the electrical contact area of each asperity, the contact force, electrical contact resistance, electric current, and temperature rise on the asperities are calculated. Finally, the electrical contact behavior on the rough surface is thus determined by summarizing the contributions of each contact spot. The finite element simulation of electrical contact of rough surfaces is also conducted to validate the proposed model. The proposed model is used to investigate the effects of the electric potential, fractal surface parameters, and material parameters on the electrical contact behavior. The results illustrate that the developed model can accurately predict the multi-physics behavior of electrical contact.

Impact-aware task-space quadratic-programming control

Robots usually establish contacts at rigid surfaces with near-zero relative velocities. Otherwise, impact-induced energy propagates in the robot’s linkage and may cause irreversible damage to the hardware. Moreover, abrupt changes in task-space contact velocity and peak impact forces also result in abrupt changes in robot joint velocities and torques; which can compromise controllers’ stability, especially for those based on smooth models. In reality, several tasks would require establishing contact with moderately high velocity. We propose to enhance task-space multi-objective controllers formulated as a quadratic program to be resilient to frictional impacts in three dimensions. We devise new constraints and reformulate the usual ones to be robust to the abrupt joint state changes mentioned earlier. The impact event becomes a controlled process once the optimal control search space is aware of: (1) the hardware-affordable impact bounds and (2) analytically computed feasible set (polyhedra) that constrain post-impact critical states. Prior to and nearby the targeted contact spot, we assume, at each control cycle, that the impact will occur at the next iteration. This somewhat one-step preview makes our controller robust to impact time and location. To assess our approach, we experimented its resilience to moderate impacts with the Panda manipulator and achieved swift grabbing tasks with the HRP-4 humanoid robot.

Elasto-plastic partial slip contact modeling of graded layers

A calculation model is developed to solve elasto-plastic partial slip contact problems of graded layer-substrate systems. With the high dependence of contact stress on the local region near the contact spot, the graded layer-substrate system of interest is modeled as a homogeneous half-plane with an embedded, finitely long inclusion. Unlike the conventional finite element method, the elasto-plastic responses are solved within a considerably small region rather than an oversized truncated domain. The computational domain allows arbitrary distributions of elasto-plastic properties and is directly discretized without tedious separation and assembling skills. The resulting disturbance fields are calculated by the numerical equivalent inclusion method. Additionally, the plastic strain is determined via the return-mapping algorithm, and the generated residual responses are directly obtained based on the explicit theoretical solutions. The conjugate gradient method is utilized to solve surface tractions, and the induced elasto-plastic fields are calculated by the technique of fast Fourier transform. Some parametric studies are subsequently conducted based on the developed model to explore the effects of property inhomogeneity and friction coefficient on the elasto-plastic response.

Deterministic Model of Elastic Rough Contact Taking into Account the Mutual Influence of Asperities

The analytical solution of the elastic contact problem for the bodies with rough surfaces is presented using a deterministic description of the surface roughness. Particularly, a model of the normal contact of a periodic system of axisymmetric punches of different heights with an elastic half-space is developed. The solution is obtained taking into account the real contact pressure distribution only under nearby ones, and considering the action of remote ones as the nominal pressure (the localization method). The effect of the shape of the punches and their spatial positions on the dependencies of the real contact area and the contact pressure distribution at the contact spots on the applied load are studied. The additional displacement function, which characterizes the effect of surface roughness on the relative approach of contacting bodies at the macrolevel, is also analysed.

Substantiation of a rational program for the running-in of tribosystems

The paper presents the results of studies on the justification of a rational program for running-in of tribosystems. It is shown that the first component of the program is the fulfillment of the condition on the verge of loss of stability due to the appearance of accelerated wear, with the maximum load on the tribosystem and the minimum sliding speed. This mode performs the function of "training" the surface layers for future operating conditions due to deformation processes and changes in the roughness of the friction surfaces. The mode is characterized by minimum wear rate values and maximum friction coefficient values.
 The second component of the running-in program is the fulfillment of the condition on the verge of loss of stability due to the appearance of burrs on the friction surfaces, with minimal load on the tribosystem and maximum sliding speed. This mode performs the function of "adaptation" of the surface layers to the future operating conditions by increasing the rate of deformation of the materials of the surface layers on the spots of actual contact. The mode is characterized by maximum wear rate values and minimum friction coefficient values.
 The third mode of the program aims to form surface structures and roughness on the friction surfaces of tribosystems that correspond to operational modes. This mode performs the function of "sufficient adaptation" of the surface layers to the future operating conditions, and corresponds to the condition with the maximum value of the stability margin. The final result of the running-in process is the transition of the tribosystem from an unbalanced, thermodynamically unstable state to a stationary, equilibrium state, as a result of which such parameters as wear rate, friction coefficient, temperature and roughness of the friction surfaces are stabilized. Such a step-by-step transition is associated with the formation of a special, dissipative structure of the surface layers of triboelements as a result of self-organization.
 The use of the three-mode program will reduce the time for tribosystems to run in by 23.0 - 38.4% compared to other programs. The effectiveness of the developed three-mode program is proven by experimental studies with the calculation of the modeling error.

Simulation model of contact interaction during surface strengthening of steel parts

In the processes of surface strengthening of steel parts, the stress-strain state is decisive for explaining the physical processes of strengthening, forming the dimensions of the contact area. Analytical dependences of contact parameters are quite approximate. In this work, based on the Ansys software complex, a simulated model of the contact of a truncated torus with a cylinder is proposed, which demonstrates the kinetics of the process of pressing a hard alloy tool into a steel workpiece - a cylinder. The experiment was conducted for 4 seconds in order to determine the maximum level of stresses, the distribution of stresses and the amount of residual stresses after removing the load. The clamping force was applied mainly in the zone of elastic deformations. The results showed an uneven stress distribution with a maximum in the center of the contact spot of 1082 MPa. After changing the load direction, small residual deformations at the level of 0.00311 μm were observed in the center of the contact patch. This indicates a violation of the elastic region on a small contact area, which does not affect the general nature of the stress distribution and can be removed during the finishing process. The results of simulation of the stressed state are used for the correlation with the observed structural changes of the material during the action of thermal and power stresses. The stress peak was formed at a distance of 200 μm, which contributes to the formation of maximum values of microhardness at this depth.

Design and fluid analysis of the microsegment gear tooth profile for pump operating at high speed and high pressure

In order to solve the problem of oil trapping in involute gear pumps, a new tooth profile based on the microsegment tooth profile and incorporating the circular arc tooth profile theory has been designed in this study. Firstly, the tooth profile equation of the microsegment gear profile for the pump has been derived. Then, the spatial tooth surface equation of the helical microsegment gear for the pump has been derived, and the feasibility of the new tooth profile has been verified using the contact spot experiment. The characteristics of the new gear profile without oil trapping and the closed “8” type mesh line have been analyzed, from which the output flow rate of the microsegment gear pump has been verified to be constant. A conclusion has been drawn on the applicability of the microsegment gear tooth profile for the pumps. Further, the fluid analysis model of the microsegment gear pump has been proposed to analyze the oil pressure distribution and state of fluid motion at high pressures in the microsegment gear pump. A comparison of the performances of the involute and the microsegment gear pumps shows that the output pressure and maximum pressures of the microsegment gear pump are smoother than that of the involute gear pump. Analysis of the effect of the high rotational speed on the output oil pressure and the maximum pressure shows that the former increases, whereas the latter varies very little with the rotational speed.

Interference Assembly Stress of Wheel-Axle in B-type Subway

This paper aims to improve the reliability of train operation as well as to guarantee the safety of wheelset interference assembly. A finite element model of the wheel-axle interference fit is established with a metro B-type car as the research object. The finite element calculation software is used to simulate the static strength of the wheel-axle model under different working conditions, contact spots, and maximum/minimum interference. The effect of different interference and different working conditions on contact stress is studied. The study shows that the wheel meets the static strength requirements under all working conditions. The maximum equivalent stresses are located at the wheel hub bore under the maximum or minimum interference assembly. The full curved condition with maximum interference is the most dangerous condition among the working conditions.

On the contact between elasto-plastic media with self-affine fractal roughness

Modeling the elasto-plastic contact between rough interfaces may require high computational effort as real surfaces present broad roughness spectra. In this work, we propose an efficient multi-asperity model where each asperity follows Jackson and Green’s equations and both coupling and coalescence of contact spots are considered. In agreement with previous studies, the contact area A is found to rise linearly with the applied load. Moreover, under the assumption of yield stress independent of the asperity size, no differences are found with respect to the elastic contact solution for nanometric root mean square (rms) roughness amplitudes hrms. On the contrary, for micrometric hrms, the slope of the area-load relation is observed to increase when reducing the yield strength σY. We have also investigated the effect of increasing the rms roughness gradient of the surface hrms′ by adding fine-scale wavelengths to the roughness spectrum. Due to plastic deformations, the contact area A is found to be independent of the high-frequency cut-off of the roughness spectrum as it converges when increasing the number of roughness scales.

Effect of Third-Particle Material and Contact Mode on Tribology Contact Characteristics at Interface

A moving pair with two-body contact is the ideal situation assumed in previous analyses. However, all moving pairs are in a three-body contact state at the start of operation or immediately after the start of operation, such as bearings, ball-screws, gears and engines. This work studies the influence of wear particles (SUJ2), environmental particles (SiO2 and Al2O3) and nano-additives (CuO) on the tribological contact characteristics under different particle concentrations, particle sizes, surface roughnesses and contact modes. The three-body microcontact analysis revealed that the differences in the real contact area, particle contact area and separation of the four-particle materials in the three-body s–s and p–s contact modes are rather small. Under the three-body hybrid contact mode, the difference is relatively large and the sequence of the real contact area value obtained due to the elastic modulus for the four-particle material at this interface is Al2O3 > SUJ2 > CuO > SiO2. The order of the other two contact characteristics is reversed. The difference increases as the particle size or particle concentration increases. The order of the critical load required to transform three kinds of contact modes is SiO2 > CuO > SUJ2 > Al2O3. On the nearly initial three-body hybrid contact mode, the plastic contact area ratio at the interface first increases to a critical value and then decreases as the load increases because the original plastic contact spot area and contact spot number increases with the increase in load. At the same time, the elasto-plastic contact area ratio decreases to a low value and then increases. The elastic contact area ratio at the interface decreases as the load increases. Among the four third-particle materials, the experimental results and theoretical predictions show that the environmental particles, Al2O3, cause the maximum friction and wear observed at the interface.

Thermal and stress-strain state of friction pairs in ventilated disc brakes of lightweight vehicles

The work is dedicated to the thermal behavior and stress-strain state of ventilated disc brakes installed in the lightweight vehicles (scooters, electric bikes, ATVs, etc.) using ANSYS environment in various experiment modes. Modeling of the temperature distribution in the rotor (disc) and the corresponding brake pads is determined taking into account a number of factors and input parameters during the braking operation: the amount of rotation speed, the gap between the pads and the disc, the speed of load application, thermal expansion, etc. Numerical modeling of the transient thermal and the stress fields in the area of contact between the pads and the rotor is carried out by the method of sequential thermostructural connection of the intermediate calculation states of the brake model in the ANSYS Coupled Field Transient environment. For a comprehensive assessment of brake behavior, our research considers two load approaches: constant long-term (20 s) with an influence factor in the form of thermal expansion as a result of contact pair friction; linear load from the pads on the disс with a corresponding increase in pressure up to the moment when the rotation of the system is blocked. Our research presents an assessment of the rotor ventilation channels influence on the nature of the contact spot with the brake pads (open far-field contact, sliding contact, sticking contact, etc.). In addition, it is demonstrated that despite the linear increase in pads pressure on the rotor, the graphs of temperatures, volume (thermal expansion) and stresses are of parabolic character with a disproportionate increase in indicators. Such a result forces us to come to the conclusion that it is not possible to predict the behavior of the brakes based on the analysis during a short period of time of the experiment - conducting long-term analytical studies is extremely important in the case of brakes

Phenomenological Laws of Single Point Contact: Pre-Rolling Contact Resistance through Pendulum

The development results of a single-point contact system set up as a pendulum to study the laws of rolling resistance to contacting bodies at a distance significantly reduced compared to the elastic contact spot size. The designed device uses a physical pendulum sustained by only one ball on a flat polished surface. The problem of stability of the pendulum swing plane is solved. A phenomenological theory of rolling resistance is described. The surface tension of solids on the contact zone, parameters of the frequency-independent internal friction and the pressure of the adhesion forces are found.

Ultrasonic inspection technology of welded joints obtained by spot friction welding

Friction stir welding has found wide application in the aircraft and rocket industries, primarily due to the possibility of obtaining welded joints with a strength close to that of the base material. One of the most promising methods of such welding is friction stir spot welding, which can serve as an alternative to electric contact spot welding and riveting of joints. To introduce friction stir spot welding into the production of critical products, it is necessary to consider issues related to non-destructive quality control of welded joints obtained by this welding method. The purpose of this work is to substantiate the applicability of the ultrasonic echo method for quality control of welded joints obtained by friction stir spot welding. The relevance of the work is confirmed by the fact that today there is no sufficiently complete information on the results of experimental studies aimed at analyzing the characteristics of welded joints obtained by friction stir spot welding. The authors of the article proposed to use the ultrasonic echo method of control. The control was carried out using an ultrasonic flaw detector with a separate-combined piezoelectric transducer on samples of welds made using friction stir spot welding. Flaws such as lack of penetration and root sticking were found in three samples as a result of ultrasonic testing, which was confirmed by metallographic studies. Samples in which no defects were found were subjected to mechanical tests, as a result of which it was found that the strength of the obtained welded joints is comparable to the strength of the base metal of the samples. Metallographic studies were carried out on samples after the absence of defects in welded joints was confirmed through mechanical tests. Thus, the relationship between the results of ultrasonic testing, metallographic studies, and mechanical tests is shown, which makes it possible to justify the applicability of the ultrasonic echo method for quality control of welded joints obtained by friction stir spot welding.

The impact of hydrogen plasma on the structure and morphology of tin and lead micrometer sized particles

The stability of micrometer sized particles in hydrogen plasma is essential for extreme ultraviolet lithography, the ITER fusion program and the application of hydrogen plasma etching. We experimentally investigated the morphological evolution of tin (Sn), lead (Pb), and lead (II) oxide (PbO) micrometer sized particles on a surface that is exposed to a low pressure hydrogen plasma. Post exposure particle cross sections obtained by a scanning electron microscope accompanied by a focused ion beam demonstrated a significant influence of hydrogen plasma exposure on both the surface and the bulk material of the particles. Chemical sputtering at the surface and accumulation of pressurized hydrogen bubbles in cavities in the bulk material are the main drivers of the morphological changes. These mechanisms may influence the adhesion of particles to the surface through the introduction of asperities, increase of contact spot area, or fragmentation after the accumulation of mechanical stress.

Модель контакта и оценка молекулярной cоставляющей силы трения

According to the level of the measurement scale, the friction force changes its nature and is determined by different depend-encies. The paper views a procedure for determining a friction force molecular component based on the evaluation of specif-ic shearing resistance of molecular links un-der the elastic interaction of a silicon nitride cantilever needle having a steel sample, used for scanning a section of a sample surface in the nanometer range with an atomic force microscope (AFM) «FemtoScan» under low loads. A sensitive element (measuring device) of an atomic force microscope acts as a force sensor for measuring both: a normal load very roughly, and a change in the force, applied to the cantilever under known stiffness, including the value of the cantilever rod form alteration. It also changes the load on the sensitive element (to assess the mo-lecular component of the friction force, the route of the «smoothest» surface itself was chosen). The paper also provides an analytical assessment of the contact interaction parameters of a cantilever needle in a nano-scale, rep-resented as a spheri-cal indenter, with an elastic half-space as a surface under study, based on the Hertz theory. Analysis of the calculation and experiment data on measuring the resistance force of the indenter during scanning of the surface under study, showed good convergence of the results with a deviation of even values from the experimental data of no more than 7,5 %. Calculations using the established formulas showed that with an increase in the load on the contact at the nanoscale, the coefficient of friction decreases due to a faster growth of contact spots in the elastic state (provided that angularity of inequalities related to sub-roughness remains constant), which was also confirmed in the course of the experiment.