Pair Contact Research Articles

Simulation and validation of the transmission error, meshing stiffness, and load sharing of planetary spur gear transmissions

Although the load sharing between planets of sequentially phased planetary gear transmissions has been studied in the past, the required solving techniques based on the Finite Element Method result in long time consuming and high computational cost. This limits the possibilities of undertaking extensive studies that take into consideration a high number of cases allowing optimal solutions to be sought or general conclusions drawn. In addition, the determination of the curves of transmission error, time-varying mesh stiffness, and load sharing among tooth pairs in simultaneous contact are also complicated. In this work an analytical model has been developed for the simulation of the time-varying mesh stiffness, quasi-static transmission error, and load sharing ratio between planets and tooth pairs of planetary spur gear transmissions. It is based on similar models for external and internal spur gears previously developed and has been validated by comparison with a hybrid model based on the Finite Element Method and theoretic-experimental correlation.

Computerized generation, deviation correction and rapid tooth contact analysis of helical face gear

This paper delves into the generation of helical face gears using a grinding worm. It investigates the computerized generation process and explores the inherent geometric constraints associated with the application of a grinding worm for helical face gears. An approximate grinding method, tailored for helical face gears featuring large helix angles, is proposed, with an evaluation of the resulting theoretical deviations. Furthermore, a novel rapid computational approach for determining the bearing contact of helical face gear pairs is introduced and validated through Finite Element Analysis (FEA). The subsequent analysis comprehensively examines the effects of the machine tool positioning errors on tooth flank deviations, bearing contact, and transmission errors. A sensitivity matrix is developed to elucidate the relationship between machine tool positioning errors and the tooth flank deviations, leading to the proposition of a correction method for theoretical generating deviations. Finally, the paper introduces a tooth flank modification method for helical face gears and the meshing performance is highly improved.

Friction and Wear Performance of a Hydraulic Motor Roller/Piston Pair Contact lined with the Self-Lubricating Bearing Bush Modified by PEEK

Poly Ether Ether Ketone (PEEK) is a kind of special engineering plastic with excellent properties such as high-temperature resistance, self-lubrication, wear resistance, and high mechanical strength. However, its blending or composite modification applications still face numerous challenges. The primary objective of this research was to evaluate the friction and wear performance of a three-layer self-lubricating bearing bush, which was made from a modified material containing short carbon fiber and Poly Ether Ether Ketone (SCF/PEEK). The bearing bush is used as a surface contact layer on the pistons of a hydraulic motor in the interface with the cam roller. The bearing bush was processed using a 15% SCF-modified PEEK material, and the friction and wear test was conducted using a self-built friction test machine. This study aimed to assess the frictional and wear characteristics of the SCF/PEEK-modified material in the bearing bush. The results show that as the experimental pressure rises from 15 MPa to 25 MPa, the friction coefficient of the SCF-modified bearing bush experiences a significant decrease from 0.420 to 0.296. Furthermore, the stability of the frictional morphology of carbon fibers indicates its effective adaptability to low speed and high load conditions.

Nonlinear dynamic separation characteristics of friction pair and experimental analysis

This paper aims to reduce friction pair erosion of the clutch in the case of continuous shift; the dynamic separation process of the friction pair is investigated. The temperature of the friction pair, friction torque, and separation speed in the separation process are taken as the research objects, and the dynamics simulation model and finite element thermal coupling simulation model of the clutch separation process are established. The nonlinear dynamic separation characteristics of the friction pair are investigated by comparing and analyzing the effects of control parameters such as rotational speed difference, damping ratio, and lubricant viscosity on the friction torque, friction pair separation speed, separation gap, and contact stress during the separation process. The gap recovery coefficient is proposed as a response indicator for observing the separation process in response to the inability to observe the nonlinear dynamic motion of the friction pair during the separation process and to measure the end time of the separation. Finally, the clutch was subjected to a separation test. The results show that the proposed gap recovery coefficient accurately describes the separation process. The simulation model can simulate the clutch's separation and predict the trend of separation parameters.

Dry sliding wear and friction performance of zirconium dioxide tribopairs

Zirconium is an attractive engineering material owing to its commendable temperature, corrosion resistance, and excellent biocompatibility. Despite these merits, its industrial applicability is hindered by elevated wear and friction in tribological settings. Previous research has concentrated on unmatched pair contacts involving zirconium and alumina primarily due to the exceptional hardness. However, there is a noticeable dearth of literature on the matched pair contact condition for zirconium dioxide. Thermal oxidation is a promising and cost-effective method to address the suboptimal tribological performance and enhance the mechanical and electrochemical properties of zirconium. In this study, thermal oxidation is employed to produce a 6-μm-thick oxide layer in an air furnace at 650°C for 6 h. Subsequently, the resulting surface coating was tribologically tested using a pin-on-disc tribometer against two distinct counterface materials, namely, alumina and zirconium dioxide, in a dry and unlubricated environment. The findings reveal that matched contact between the zirconium dioxide tribopair is unfavorable, leading to elevated friction and wear rates. Consequently, this configuration should be avoided in dry contact situations characterized by high contact pressures. However, under lower contact pressures, the wear performance is acceptable. Furthermore, when combined with lubrication, this system may have potential applications in bio-tribological systems.

Mechanochemical Synthesis of Thiadiazole Functionalized COF as Oil-Based Lubricant Additive for Reducing Friction and Wear.

In this work, the functionalized covalent organic framework (COF) was prepared via a convenient ball milling process. The aldehyde group terminated COF-F reacted with amino thiadiazole in the ball milling jar under mechanical forces; hence, the thiadiazole functionalized COF-F was obtained and denoted as Thdz@COF-F. The as-prepared Thdz@COF-F serves as an oil-based lubricant additive and exhibits remarkable tribological properties, which can reduce the average friction coefficient of base oil from 0.169 to 0.102 and decrease the wear volume by 87.0%. The antifriction and antiwear performances are mainly due to the repairing effect of Thdz@COF-F nanoparticles and the protective tribo-film that averts the direct contact of friction pairs. In addition, through the ball milling method, triazole and thiazole functionalized COF-F were also prepared and represented good lubrication performance, demonstrating the feasibility of this mechanochemical synthesis method for functionalized COFs.

Dynamic modeling of spur gear system considering the coupling effect between bearing deflection and gear mesh stiffness

Bearing deflection has a direct impact on the mesh condition of gear systems via the center distance of the gear pair and corner contact. These factors need to be considered to accurately model the time-varying mesh stiffness and dynamic responses of gears. To address this issue, a spatial coordinate conversion is used to obtain the instantaneous spatial position of the gear pair under the bearing deflection. The tooth pair separation distance is derived through the geometric relationship analysis to model the corner contact effect. A dynamic model is established which employs a step-to-step time integration algorithm that considers the coupling effect between bearing deflection and time-varying mesh stiffness to obtain the dynamic response of the spur gear system. The simulation results of the proposed model show good agreement with the experimental results which demonstrate that the proposed model enables a proper analysis of the influence of bearing deflection on gear mesh behavior. This study provides an original dynamic model for analyzing the dynamic performance of the gear system considering the influence of bearing deflection.

Research on the Type Synthesis of a Regular Hexagonal Prism Rubik’s Cube Mechanism

The Rubik’s Cube mechanism (RCM) is a kind of reconfigurable mechanism with multiple characteristics such as multiple configurations, variable topology, strong coupling, and reconfigurability. Crossover research on the RCM with mathematics, chemistry, cryptography, and other disciplines has led to important breakthroughs and progress. It is obvious that the invention and creation of a new RCM can provide important ideological inspiration and theoretical guidance for the accelerated iterative updating of Rubik’s Cube products and the expansion of their applications. This paper investigates the type synthesis method for a regular hexagonal prism (RHP) RCM (RHPRCM). Through analysis of the reconfigurable movement process of the RCM, two mechanism factors are abstracted, a type synthesis process for the RHPRCM is proposed, a symmetry layout method for the RCM’s revolute axis based on the RHP space polyhedron is proposed, and an analysis method for the intersection of the revolute pair contact surfaces (RPCSs) based on the adjacency matrix is proposed. Taking a revolute axis passing through the center of an RHP and having only one RPCS for each revolute axis as an example, an RHPRCM with different topological structures is synthesized. The relevant research in this paper can provide methodological guidance for the synthesis of other spatial RCMs.

ANALYSIS OF RESEARCH ON THE PRODUCTION OF CARBON NANOPARTICLES AND THEIR APPLICATION IN TRIBOLOGY SYSTEMS

The article analyzes research on the production of carbon nanoparticles and their use in tribological systems. A comparison of the results of installations based on different methods of obtaining nanotubes and fullerenes shows that the purest and highest-quality product is obtained by laser evaporation of graphite, but this is a long, time-consuming and expensive process. The yield of useful products is up to 20 %. The thermal method has its advantages and disadvantages. The advantages include the availability and cheapness of carbon raw materials: from oil, carbon gases to municipal waste. All of them are sources of nanotubes and fullerenes when using the thermal method. The yield of useful nanoproducts is average, and the purity reaches 90-95 %. The simplest known method is the electric arc method for obtaining nanotubes and fullerenes. However, the yield of useful products does not exceed 15%. In addition, the large number of reactor designs for obtaining highly structured carbon nanoparticles indicates that an acceptable design has not yet been found that would guarantee obtaining a product with specified properties, stable parameters and in the required quantities. The article also analyzes research on the effect of carbon nanoparticles on the lubricating film, provides a calculation scheme for the interaction of a carbon nanoparticle with a metal surface in a friction pair, and provides a calculation model for the change in the adsorption time of carbon nanoparticles depending on the radius to the initial distance. Which showed that according to the experimental data of other researchers, the data obtained regarding the time of physical adsorption of individual molecules and their aggregates is about 10-9 to 10-6 seconds, which confirms the priority of the formation of the solvate shell, and only then the manifestation of the adsorption of carbon nanoparticles. The analysis of studies on the influence of carbon nanoparticles showed that there is a dependence for determining the intensity of wear of sliding friction pairs in elastic contact, which takes into account the concentration of carbon nanoparticles in the oil and the contact pressure. According to the obtained dependence, the intensity of wear is inversely proportional to the concentration of carbon nanoparticles, and directly proportional to the contact pressure.

Wear mechanism and evolution of tribofilm of ceramic on steel pairs under ester oil lubrication in wide temperature range

The ceramic-steel-pentaerythritol ester system has a broad application prospect under high temperature conditions, which are respectively in the fields of aviation, aerospace and advanced equipment manufacturing. However, a comprehensive understanding of the friction and wear mechanisms of this system across a broad temperature range remains elusive. The tribological properties of the system at 25–475 °C were studied. With the increase of temperature, the evolution of the tribofilm follows the sequence: discontinuous tribofilm → uniform tribofilm → tribofilm removal. At 200–300 °C, an approximately 100 nm thick amorphous PxOy compound tribofilm is formed, and its nanohardness and modulus are reduced by 81.33 % and 54.02 %, respectively, compared with base steel. The tribofilm effectively reduces shear resistance by blocking friction pair contact. When the temperature exceeds 300 °C, it will lead to high-temperature coking, which adversely affects the lubrication performance. It is worth noting that the system can endure short-term service at a maximum temperature of 475 °C. Therefore, this research can help achieve continuous, stable operation of high-temperature resistant systems, as well as short-term use under extreme conditions encountered by complex equipment.

Study of the nootropic effect of the extract of <i>Scutellaria baicalensis Georgi</i> in modeling anxiety and depressive disorders in rats during the development of a conditioned reflex of passive avoidance

Experimental study is devoted to the study of the nootropic effect of the extract Scutellaria baicalensis Georgi in normal conditions and in modelling anxiety-depressive disorders by creating "social" stress in rats during the development of a conditioned passive avoidance reflex. Materials and methods. The study was made of the extract obtained by maceration of the underground part (rhizomes with roots) of the plant Scutellaria baicalensis Georgi. The experimental work involved the study of the behavioural characteristics of laboratory animals (non-linear rats) in the amount of 159 males aged 7-9 months, divided into groups in accordance with the stages of the study. The study of nootropic activity in the norm formed the basis of the first stage and included work with animals divided into 4 groups: receiving water for injection (intact); Scutellaria baicalensis Georgi extract, medicinal product «Tetramethyltetraazocycloocyandione»; medicinal product «Piracetam+Cinnarizine». The creation of conditions providing for paired sensory contact of individuals, contributing to the development of inter-male confrontations, was achieved by modelling “social” stress in groups identical to the normal state at the second stage of experimental work. The use of the standard setting of the passive avoidance conditioned reflex made it possible to analyse the cognitive functions of the animals. Results. The nootropic effect of Scutellaria baicalensis Georgi extract has been proven. The decrease in the consequences of stress in the form of a deterioration in memorization and reproduction of a conditioned reflex of passive avoidance was shown when it was administered to laboratory animals. Extension of the latent period of entry into the dark chamber of the passive avoidance conditioned reflex test, an increase in the total time spent in the illuminated compartment, and a decrease in the percentage of animals that visited the dark "aversive" compartment under the influence of the extract were described. Conclusion. The preservation of a memory trace in laboratory animals after the introduction of an extract made on the basis of Scutellaria baicalensis Georgi has been established. The presence of a complex of various groups of biologically active substances in the composition of the Scutellaria baicalensis Georgi determines this plant object as a source of obtaining new drugs recommended for use as nootropic drugs that reduce the reactions that develop during “social” stress.

Tribological behavior of ultra-high molecular weight polyethylene (UHMWPE) for acetabular replacement under frictional heat based on molecular dynamics

Abstract Hip prostheses generate higher frictional heat than natural joints at the joint head-socket interface during in vivo service, resulting in higher temperatures of the contact surfaces and surrounding synovial fluid, which affects the frictional properties of the prosthetic material. In order to clarify the influence mechanism of frictional heat on the tribological behavior of ultra-high molecular weight polyethylene (UHMWPE) for acetabular replacement, the tribological tests of three contact pairs were carried out under different synovial fluid temperatures in this research. Furthermore, the movement processes of the molecular chain structure of UHMWPE during friction were simulated by Materials Studio (MS), and the mechanism of oxidative degradation was discussed. The results show that the temperature of synovial fluid has a significant effect on the friction and wear resistance of UHMWPE and the lubrication characteristics of synovial fluid. At the same time, the action mechanism of the proteins in the synovial fluid that gradually precipitate with the temperature rise to participate in the friction process is related to the friction pair material and contact mode. The synergistic effect of temperature rise and friction will accelerate the oxidative degradation reaction of UHMWPE and form ketone and alcohol oxides on its surface, thus reducing its wear resistance.

Расчет движения подвижного состава по железнодорожному пути сеточно-характеристическим методом

The application of a grid-characteristic method is proposed for numerical simulation of the movement of rolling stock along a railway track laid on an earth and a bridge. In the study, the railway track is presented using a dynamic system of equations of the theory of elasticity of hyperbolic type. The grid-characteristic method relies on the characteristic properties of the system under consideration and uses finite-difference schemes of high order of accuracy to obtain a space-time solution. The features of railway structures are considered by changing the boundary conditions and conditions at the contact borders. To simulate the areas of contact of wheel pairs of rolling stock with the rail – the "wheel-rail" system – a previously developed pressure boundary condition is applied, modified so as to consider multi-element rolling stock. As a result of computer simulation of the movement of rolling stock along the railway track of various types, full-wave stress distribution in the track structure is obtained, which makes it possible to predict dangerous sections of rolling stock movement.

Thermal Simulation of Ventilated Brake Disc Based on Complex Multifield Coupled Method

In this article, considering the coupled interaction of heat, stress, material wear, and wheel–rail force transmission in the disc-braking process, a complex multifield coupled method was proposed to study thermal mechanical properties and contact state of brake discs. First, a coupled dynamic model of train, track, and brake gear was established to analyze the force transmission between brake friction pairs and wheel–rail system. Based on the coupled dynamics simulation results, a thermomechanical wear coupled model of the friction pair was established. It is found that the track irregularity results in vertical relative displacements with a range of (–2.6 mm, 2.8 mm) and makes the maximum brake force increase to 24.1 kN. As a comparison, brake bench tests without wheel–rail interaction were carried out. This showed that there was no vertical relative displacement between the friction pair, and the braking force had a stable value of 22.5 kN. The simulation results of the brake disc temperature distribution, and the friction pair contact state are consistent with the bench test results. In addition, different thermal simulation methods of the brake disc were used to verify the validity of the complex multifield coupled simulation results.

An explicit finite element approach for simulations of transient meshing contact of gear pairs and the resulting wear

A 3D time-domain modelling approach is developed with the explicit finite element method to simulate transient meshing contact of gear pairs and the resulting wear. Taking a helical gear pair used in a locomotive as an example, the dynamic contact states of gear teeth are predicted for different speeds in consideration of actual geometries (including those of damaged teeth), time dependent torques, and structural and continuum vibrations of the gear system. The friction between mating teeth is taken into account by a non-Newtonian EHL friction model. A tiny time step of 4.5 × 10−8 s determined by conditional stability of the explicit time integration ensures the capture of transient effects. Based on detailed contact solutions during meshing, the dynamic wear on teeth is further calculated using an Archard wear model to predict tooth profile evolvement. Taking initial involute profiles and a speed of 120 km/h, the model is first validated for dynamic contact solutions. More results show that structural vibrations and worn profiles influence the dynamic meshing contact significantly, tooth wear increases as lubrication fails, and tooth pitting's influence is localized. This approach provides key load boundaries for detailed studies on mating gears, and may be employed for studies on tooth damages and as a reference for lumped parameter dynamic models of gear pairs.

Tribological investigation of contact pairs applied in metallic gate valve seals for onshore application

Valves are equipment used in fluid management in industrial processes. Among the components of a valve, the set considered most critical for its operation and performance is the obturator sealing system, whose function is to make the fluid tight. This paper aims to analyze the tribological performance of two pairs in contact used in gate valves for onshore applications in oil installations. The specimens were manufactured using martensitic stainless steel with 13Cr as base material, varying the surface hardening processes under the following conditions: (A) heat treated and (B) Stellite 6 deposited by Plasma Transferred Arc Welding (PTAW). Pin-on-disc tests (PoD) were executed to compare the tribological performance of A/B and B/B configurations. In disc A versus pin B, the predominant wear mechanism was adhesion, resulting in a material pullout. For disc B versus pin B, the wear mechanism started with adhesion, followed by transfer film formation, generating elongated abrasive marks in the direction of movement on the surfaces of the pin and disc. With the results obtained, it was found that pair B/B showed less wear and friction. Based on these results, it is possible to indicate the use of the B/B pair for applications in valves that commonly require more activations and lower efforts for equipment actuation.

Beyond activity coefficients with pairwise interacting surface (COSMO-type) models

Pairwise interacting surface models, like COSMO-RS and COSMO-SAC, are getting popular in the prediction of activity coefficients when experimental data is scarce. In this work an alternative derivation of the COSMO-SAC model is presented and pair contact probabilities as well as nonrandom factors are compared with classic models. By using these probabilities one can readily calculate the system internal energy (or enthalpy). The case of temperature dependent interaction energies and the potential inconsistencies in this case are discussed in detail. Many properties of the resulting equations are discussed, including the issue of distinguishable or indistinguishable segment types. An accompanying open-source code favoring readability over efficiency is also provided.

Lubrication behavior of fluorescent graphene quantum dots hybrid polyethylene glycol lubricant

Graphene quantum dots (GQDs) with a lattice structure and the size of 1.8–3.4 nm were prepared by a simple hydrogen peroxide-containing hydrothermal reaction method using graphene oxide (GO) as a precursor. The hydroxyl group with the cutting effect can cut GO into GQDs with a large number of oxygen-containing functional groups. As polyethylene glycol (PEG) additives, the photoluminescence (PL) properties of well-dispersed GQDs can reflect and monitor the lubrication state between the sliding interfaces because partial GQDs contributed to low friction/wear and occurred the structural transformation. As-modulated hybrid PEG with 0.04 wt% GQDs shows excellent wear reduction ability, and the wear rate is reduced by 40.5%. The formation of a dense disordered carbon film on the sliding surfaces and iron/iron oxide debris with attached GQDs between sliding interfaces contribute to filling the pits and hindering the direct contact of friction pairs, thereby enhancing the wear resistance. This work illustrates that GQDs as a polar lubricant additive have a great application potential in lubrication regulation and monitoring.

Tribological behavior of steel-steel pair: Influence of roughness and cutting parameters

Roughness characterizes the quality of the machined surfaces, mainly determined by the geometric tolerances and induced by the different factors involved in the cutting process. The aim of this paper is to study the influence of cutting parameters (cutting speed (Vc), feed rate (f), tool nose radius (Rc) and cutting depth (ap)), on the cylinder surface roughness, in order to value the friction coefficient (μ) and the wear rate (W) of the contact surfaces of steel-steel pair: 42CrMo4-20MnCr5. Full factorial design (DOE) of 9 tests is used, to develop theoretical model of the roughness of machined metal parts on turning. Hence, the influence of the cylinder roughness on the friction and wear behavior of the steel-steel pair contact is studied, using a pin-cylinder tribometer. The results revealed that the friction coefficient and wear rate, increases progressively by varying the surface roughness (cutting parameters). The processing and observations of the results were recorded using a profilometer, an optical microscope, a scanning electron microscopy (SEM) followed by an analysis in energy dispersive spectroscopy (EDS). However, the surface of the pin is plowed, cracked and plastically deformed, thus inducing more loss of material by adhesion and oxidation of the formed particles on the cylinder, which bring about a material transfer and formation of a metal oxide layer.

The Applicability of the Hertzian Formulas to Point Contacts of Spheres and Spherical Caps

Hertzian formulas are commonly used for the evaluation of deformation and pressure distribution of non-conformal and slightly conformal mechanical pairs to estimate component stiffness and durability. For the sake of simplicity, their use is extended even to those cases in which Hertz’s hypotheses do not hold. This paper summarizes Hertz’s theory and compares the results obtained with theoretical and finite element analysis of the point contact of non-conformal and conformal pairs made of spheres, caps, and spherical seats. This study was motivated by the non-Hertzian behavior of a tilting pad bearing ball-and-socket pivot conforming contact observed by the authors in previous experiments. In particular, the displacement and force relation were investigated by varying the geometrical parameters, the materials, the boundary conditions, and the friction coefficient. In the case of non-conformal contact, the parameter variations had negligible effect in agreement with Hertz’s theory while for conformal contact, the cap and seat height and width and the relative clearance were the most influential parameters on the non-Hertzian behavior. These novel results indicate that in conformal pairs, such as for tilting pad bearing ball-and-socket pivots, whenever Hertz’s hypotheses are not satisfied and the assessment of contact stiffness is crucial, Hertzian formulas should not be applied as done in common practice, instead more accurate numerical or experimental evaluation should be made.