Problems of Tribology

Implementation of the process of forming regular micro-reliefs on the working surfaces of connecting rod bearings

2026-09-01T20:50:21+03:00

The article presents the results of designing a technological operation for the formation of a Type II regular mesh micro-relief with triangular grooves, performed using a vibration-free method in a single pass on the inner cylindrical surface of connecting rod bearings. The technological operation is implemented utilizing a specially designed tool by machining a pair of connecting rod bearings within a split holding fixture. The connecting rod body for the specified bearing size was used as the holding fixture. The required depth of the micro-relief grooves is achieved through a dimensional analysis of the developed special tool designed for the plastic deformation of the connecting rod bearing surface. Relative micro-relief areas of 14.9% and 28.5% were obtained by determining the appropriate feed rate and tool rotational speed. Experimental samples of connecting rod bearings for a Volvo V50 1.6 HDI vehicle, with the geometric parameters D_ring = 47.0 mm and B_ring = 16.9 mm, were produced with the formed regular micro-relief. The process was executed at an axial tool feed rate of f_in = 19.43 mm/rev (for the 28.5% area) and f_in = 39.56 mm/rev for the 14.9% area, utilizing a HAAS VF-B/40HE CNC vertical milling machine. It has been established that this technological operation can be performed either during the finishing stage of machining the copper-lead base of the bearing (which has a thickness of 250–400 μm) immediately prior to the application of protective metal layers of nickel, copper, and/or composite materials, or after the application of the protective coating.

Transformation of groove area distribution non-uniformity in partially regular microrelief of the rotational type with increasing axial pitch

2026-09-01T21:04:48+03:00

The transformation of the groove shape in a rotary-type regular micro-relief with varying degrees of groove loop overlap, simulated by an increase in the rotary tool feed rate, is considered. A search was conducted to find the optimal groove shape for partially regular micro-reliefs formed by the rotary method, subject to ensuring the optimal value of the planar heterogeneity coefficient of the groove area distribution. Graphs illustrating the planar heterogeneity of the groove area distribution were constructed for groove shapes formed at tool feed rates of 2.5, and 3.5 mm/s. It was established that as the longitudinal spindle feed rate increases, the planar heterogeneity coefficient of the groove area distribution, decreases in both the axial direction and the direction perpendicular to it. Thus, it is proven that increasing the tool feed rate at a constant rotational speed leads to an increase in the heterogeneity of the groove area distribution for a partially regular micro-relief formed by the rotary method. Optimization of the micro-relief creates a favorable profile of compressive residual stresses, preventing the propagation of microcracks. As the tool feed rate increases, the number of groove intersections decreases from 4 to 2, and the shape itself becomes elongated in the axial direction. Correspondingly, the planar heterogeneity coefficients k_gX decrease from 0.69 to 0.48, and k_gY decrease from 0.71 to 0.6. The overall relative area of the micro-relief, F_n, drops sharply from 68.48% to 45.9%, which is a critical parameter for determining the load-bearing capacity of the component surfaces.

Numerical Rheological Modeling of Thin Lubricating Oil Films Considering Polymolecular Adsorption and ZDP

2026-09-01T21:15:56+03:00

A computational approach is proposed for evaluating the rheological and frictional behaviour of highly confined lubricant films, with particular attention to molecular adsorption and the formation of strongly structured interfacial regions. The viscosity variation between the opposing surfaces is represented using an adsorption-based formulation derived from the Polanyi potential concept. Near each solid boundary, the model introduces a quasi-solid lubricant region whose properties gradually approach those of the bulk oil with increasing distance from the surface. The integral response of the film is characterized by a harmonically averaged viscosity, calculated numerically by the trapezoidal method using 200 discretization intervals in Microsoft Excel. The shear-dependent rheology of the bulk lubricant is described by the C–Y relationship. Experimental friction data for I-20A base oil and formulations containing 1.25 and 2.5 wt% zinc dialkyldithiophosphate (ZDP) were used to determine the interfacial model parameters. Increasing the ZDP concentration produced substantial changes in the properties of the adsorbed lubricant region. The estimated surface viscosity increased from 0.14 to 1.68 Pa·s, while the characteristic attenuation length increased from 2.1 to 4.6 nm and the optimal thickness of the quasi-solid interfacial layer increased from 0.8 to 1.9 nm. Agreement between the simulations and experimental measurements was satisfactory, with mean relative deviations of 6.9–10.2%. The calculated minimum of the friction coefficient occurred at approximately 5 MPa for the base oil and shifted to about 8 MPa after ZDP addition. This shift suggests that the additive extends the range of operating conditions under which fluid-film lubrication can be maintained.

Dynamics of a Journal Bearing During Sudden Rotor Stoppage Considering Inertial Properties and Pressure-Dependent Lubricant Viscosity

2026-09-06T20:58:26+03:00

The dynamic behavior of a journal bearing during sudden rotor stoppage is investigated using a mathematical model that accounts for the inertial properties of the rotor and the pressure dependence of lubricant viscosity. The lubricant viscosity is described by the Barus law, and the pressure distribution in the lubricant film is determined from the Reynolds equation for one-dimensional flow with variable viscosity. The resultant hydrodynamic force is incorporated into the second-order equation of motion of the rotor–bearing system. A sinusoidal half-wave is used to represent the external impact load, and the resulting nonlinear differential equation is solved numerically. The transient variation of lubricant-film thickness and maximum lubricant-film pressure is analyzed during the impact and after removal of the load. For the investigated conditions, the maximum pressure in the lubricant film reaches approximately 74 MPa and subsequently decreases to low-amplitude oscillations around a mean value of about 14 MPa. The lubricant-film thickness remains sufficient to preserve film integrity throughout the considered transient process. Comparison with the approximate approach shows that the latter overestimates the displacement, velocity, and pressure responses. The proposed model can be used to assess the dynamic behavior and impact resistance of journal bearings under sudden rotor stoppage and impact loading

Characteristics of the lubricating action of oils under EHD conditions in the local friction contact zone

2026-09-07T20:28:04+03:00

Based on the newly developed interferometric test stand for evaluating lubricant film thickness — which enables the high-precision recording and analysis of transient processes under EHD lubrication conditions in the local friction contact zone of the non-conforming assemblies with varying actual contact geometries — across a wide range of operating (kinematic and load) parameters, an assessment was made of the influence of velocity, contact load, friction pair materials, the rheological properties of the lubricants and the geometry of the contact shape on the process of forming the minimum and central thicknesses of the lubricant film and the lubricating action of oils within the framework of determining the lubricant film parameter

Prediction and analysis of the Tribological Behaviors of hybrid Polymer Composites under reciprocating tribometer

2026-09-11T23:30:48+03:00

This study investigates the tribological behavior of polyether ether ketone (PEEK) composites with polytetrafluoroethylene (PTFE) as a solid lubricant filler under dry reciprocating sliding conditions. Polymer specimens (80% PEEK/20% PTFE and 30% PEEK/70% PTFE) were tested against a steel counterpart using a linear reciprocating tribometer. The Taguchi L4 (2³) orthogonal array was employed to evaluate the effects of load (100 N, 150 N), frequency (1.20 Hz, 2.30 Hz), and temperature (40°C, 80°C) on frictional force, coefficient of friction, and wear rate. Results showed that adding PTFE significantly reduced wear, with the 30% PEEK/70% PTFE composite achieving a minimum coefficient of friction (0.037) and wear rate (0.001 g) at 150 N, 30 Hz, and 40°C. ANOVA revealed load as the dominant factor for friction (61.28% contribution) and temperature for wear rate. Regression models predicted tribological outcomes with 99% accuracy. These findings highlight the potential of PEEK/PTFE composites for high-performance applications like bearings and seals

The impact of deposition method on wear mechanisms of NiAl-15 wt.% CrB2 coatings

2026-09-12T06:32:14+03:00

In this work, the effect of the deposition method on the wear mechanisms of NiAl–15% CrB₂ composite coatings was investigated. The wear rates of coatings produced by Plasma spraying, Detonation spraying and Electric-Spark Alloying (ESA) were evaluated using room-temperature “pin-on-disc” tribological tests. The worn surfaces and corresponding wear mechanisms were analyzed via SEM. The results demonstrate that incorporating CrB₂ into the NiAl matrix significantly enhances the wear resistance of the composite coatings, shifting the dominant wear mechanism from abrasive-adhesive to oxidative wear, regardless of the deposition technique.

Dependence of the quality indicators of transient processes in the hydraulic drive for rotation of the garbage truck manipulator arm on the wear of friction pairs

2026-09-12T22:15:39+03:00

This article is dedicated to determining the analytical relationships between the quality indicators of transient processes in the hydraulic drive of the manipulator arm rotation mechanism of a garbage truck, taking into account the wear of friction pairs, which can be used to develop an improved method for the design calculation of the parameters of the manipulator arm rotation mechanism during the loading of municipal solid waste. The drive for the working components of the garbage truck manipulator arm rotation mechanism is hydraulic, powered by the garbage truck’s pump station. During the operation of this drive, transient processes inevitably occur, associated with the operation of the control unit, the activation of the positive-displacement hydraulic pump, changes in the load on the actuator, and so on. These results showed that accounting for friction pair wear significantly affects the quality indicators of transient processes in the hydraulic drive of the garbage truck manipulator arm rotation mechanism. It was established that an increase in the wear of the friction pairs in the garbage truck manipulator arm rotation mechanism leads to a decrease in the quality indicators of the transient processes of its hydraulic drive.

Evaluation of the Stress-Strain State of Aircraft Spherical Plain Bearings Based on Titanium Alloys and Antifriction Composite Materials and the Feasibility of Their Use

2026-06-27T12:15:47+03:00

The paper presents an analysis of the use of titanium alloys for spherical bearings with antifriction composite materials. An analytical assessment of the use of titanium in spherical bearings is given. A model of the stress-strain state of spherical bearings with composite antifriction materials is presented. It was determined that Zedex ZX324VMT and Iglidur TX1 composite materials, when modeling the stress-strain state, reduce the maximum specific stress by 50 % in the material at loads of 3, 100 and 200 kN, compared to the base bearing on steel. Modeling the stress-strain state of spherical plain bearings with composite antifriction materials proved a reduction in specific stresses in the surface layers of bearing materials when using titanium alloys Ti5Al5V5Мо1Cr1Fe instead of bearing steel X105CrMo17 up to 20 %, depending on the material and load conditions. Economic calculations of the use of spherical plain bearings made of titanium alloys for aircraft were carried out. It was determined that under the conditions of operation of spherical plain bearings for 3000 hours of operation, the economic benefit is about 150 thousand dollars per aircraft. It was also determined that modified maintenance-free bearings with composite materials allow the operation of equipment to be closer to its technical condition by reducing maintenance costs when using aircraft.

Analysis of modern methods for reducing welding residual stresses

2026-09-15T06:21:30+03:00

This paper presents a systematic comparative analysis of the physical mechanisms governing internal stress generation in structural weldments, evaluates the efficiency of existing stress relaxation techniques, and provides scientific substantiation for promising dynamic approaches aimed at extending the operational life of welded structures. It was established that conventional post-weld tempering of creep-resistant alloy steels under prolonged holding leads to the dissolution of strengthening nano-carbides and their boundary coagulation, resulting in a 4 – 5-fold reduction in long-term creep resistance. Surface plastic deformation methods, such as weld rolling and ultrasonic impact treatment, induce beneficial compressive stresses but remain restricted to a shallow depth of 1.5–2.0 mm or require extreme contact loads, whereas standard electromechanical vibration treatment with monochromatic excitation proves ineffective for thick-walled, high-rigidity structures with natural frequencies exceeding 200 Hz. Consequently, the transition toward dynamic pulse excitation is substantiated, as it generates shock deformation waves with steep-fronted rise times, excites higher-order spatial poly-harmonics, refines primary solidification dendrites by 25–32%, and relieves peak macro-stresses by 60 – 80%. The scientific novelty lies in determining the physical regularities of multi-mode dynamic stress relaxation within welded concentration zones through non-linear wave processes and intensified dislocation mobility without prolonged resonant structural overloading. The practical significance of the obtained results enables the justified selection of resource-saving stress relief technologies for heavy-duty and thick-walled fabrications, eliminating expensive furnace annealing while minimizing dimensional distortion

Optimization of the composition of the composite material of contact inserts for electric vehicles based on the criterion of wear resistance

2026-09-15T06:39:05+03:00

The paper considers the problem of reusing spent graphite contact inserts of electric transport and improving their functional properties by modifying the composition of the composite material. Modern approaches to the formation of graphite and copper-graphite electrical contact composites, the influence of the granulometric composition, conductive and solid lubricating additives on the electrical and tribological characteristics are analyzed. The prospects for using secondary graphite as the main raw material are shown, provided that the structural integrity and electrically conductive contacts between particles are restored. The feasibility of using carbon black to form an additional conductive network, copper powder to reduce contact resistance, and molybdenum disulfide to stabilize friction and reduce wear is substantiated. It has been established that the properties of such composites are multifactorial and nonlinear in nature, therefore the choice of composition requires comprehensive optimization with simultaneous consideration of the electrical resistance, wear resistance of the insert, and the effect on the contact wire.

Kinetics of boundary layers in non-conformal contact under non-stationary conditions

2026-09-15T21:38:38+03:00

The tests were carried out according to the roller-on-roller scheme on an SMC-2 rig, the specimens being cylindrical rollers of steel 45 with hardness HRC 32. The studies were performed in the mode of frequent starts and stops: acceleration 4 s, stop 3.5 s, the cycles following one another without pauses. The total rolling speed was 1.91 m/s, the slip 20 %, the contact stress 550 MPa, the total number of operating cycles N = 2350. The lubricant layer thickness was determined by the voltage drop method in the normal glow discharge mode. A mechanism of the formation and adaptation of boundary adsorption layers on friction surfaces under conditions of frequent starts and stops has been revealed, which consists in the fact that activation of the metal surfaces under multi-cycle action and polarization of hydrocarbon molecules by the electric field of the solid phase initiate the formation of the layer, while its subsequent failure exposes the nascent metal surface, and the escape of electrons from it (exoelectron emission) creates conditions for the formation of anions and radicals and the growth of chemisorbed films. The obtained dependences of the boundary layer thickness on the number of operating cycles make it possible to predict the lubrication regime of non-conformal friction units under conditions of frequent starts and stops and to choose the concentration of the fullerene additive in a justified way.

Microscopic studies of the degradation processes of dental composite materials

2026-09-17T22:08:16+03:00

The article addresses the strength of dental composite materials, with particular emphasis on their resistance to compression. This type of loading is predominant in the anterior and posterior chewing teeth of humans. Understanding the mechanisms of initiation and development of internal stresses in materials used for restorative procedures is essential for the informed selection of materials and the further improvement of their properties. The dental composite materials Estelite Asteria and Estelite Posterior, manufactured by Tokuyama Dental, were used in the experiments. A specimen preparation technique for compression loading was considered, and experimental studies were conducted with the recording of ultimate forces and stresses. The fractured specimens were examined to determine the type of failure. It was established that the plastic component during the deformation process is practically absent, while the load–deformation relationship is quasi-linear.

For further investigation, fragments of the materials were embedded in epoxy resin, after which cubic specimens were prepared. Based on these specimens, metallographic sections were produced for a detailed examination of the mechanisms of damage accumulation and the formation and propagation of microcracks within the material structure. It was found that the fracture mechanisms and microcrack configuration depend on the size of the inorganic fillers in the composites. It was demonstrated that the avalanche-like loss of structural integrity of a composite material occurs when a certain microcrack density is reached, defined as the total crack length per unit area.

Tribological Characteristics of Pulse-Anodized Layers on Aluminum

2026-09-21T22:06:38+03:00

This study develops advanced electrochemical synthesis methods for high-performance hard anodic coatings on Al-Cu-Mg alloy (AA2024/D16) substrates. The research systematically investigates the synergistic effects of chemical electrolyte modification via hydrogen peroxide or ozone additions, high-voltage pulse hard anodizing (PHA) modes, and post-synthetic thermal treatments on the coating kinetics and phase composition. It was established that lowering the electrolyte temperature to -5 °C suppresses acid-induced chemical surface dissolution, promoting the steady growth of a dense monohydrated boehmite phase (Al₂O₃⋅H₂O) with significantly enhanced microhardness. Conversely, elevating the synthesis temperature above 0 °C triggers a structural phase transition toward a trihydrated gibbsite phase (Al₂O₃⋅3H₂O). Tribological evaluations under dry sliding and boundary lubrication conditions (mineral and synthetic oils) revealed a unique self-lubricating mechanism: the lower-hardness gibbsite phase undergoes mechanical shearing during sliding contact and forms a continuous, self-replenishing tribo-transfer solid lubricant film on both steel and ceramic counterfaces. The pulse modulation effectively mitigates local thermal concentrations within the pore channels, enabling optimal tribomechanical responses under diverse wear modes. Objective: To enhance the durability of aluminum alloys using surface engineering methods. Research methodology: A novel approach involving pulse-mode anodizing was employed to form a surface layer on the aluminum alloy; the physicochemical properties and wear resistance of this layer under friction conditions were investigated. Scientific novelty: Synthesis conditions and electrolyte composition were determined for forming an anodized layer with a specific phase composition. Practical significance: Pulse-mode anodizing and heat treatment ensure improved wear resistance of the aluminum alloy