Search

The dynamic wetting and dewetting of a water droplet on a hydrophobic solid surface with an equilibrium contact angle of approximately 100° was investigated using molecular kinetic (MK) theory to model the extension–contraction experiment and numerically calculate the radius of the contact line circle between the solid and liquid, contact line velocity, and dynamic contact angle. Furthermore, the numerical calculation results were examined in terms of various coefficients of the contact line friction to evaluate the mobility of the contact line. The calculation results of wetting and dewetting were in quantitative agreement with our previous experimental results, indicating that our constructed model was appropriate. Therefore, the MK theory can be applied to explain the characteristics of dynamic wetting and dewetting of droplets on hydrophobic surfaces, as with hydrophilic surfaces.

Large-diameter slewing bearings are capable of supporting high loads and moments. They find typical usage in applications requiring extensive rotational movements, such as cranes, excavators, and wind turbines. Engineered to endure significant loads, these bearings offer low friction and maintenance requirements. With diameters often reaching several meters and featuring wide raceways, large-diameter slewing bearings are important components. In case of a failure a delivery of a new bearing can take several weeks, due to their large dimensions. Therefore, a process chain was developed, which ensures the repair of damaged raceways of the large-diameter slewing bearings. Remanufacturing aims not only to prolong the lifespan of the slewing bearings but also to minimize waste, presenting a sustainable alternative to purchasing new units. The repair process chain consists of several steps. Commencing with a damaged bearing raceway, a cladding material with sufficient chemical and physical properties is applied on the damaged surface by plasma-transferred-arc welding (PTA). Afterwards the slewing bearing undergoes a heat treatment, followed by surface pre-machining to achieve the nominal dimensions. An incremental forming process is performed to adjust the rolling bearing properties and induce compressive residual stresses. The last step of the repair process chain contains service life investigation of the repaired bearings on a rolling bearing test rig. In this first study, the fundamental feasibility of the process chain was evaluated using smaller axial bearing washers of type 81212. Therefore, plasma transferred arc welding were applied to repair the damaged raceways of the bearing washers by surface cladding. Following the repair, the bearing washers underwent a heat treatment process. Challenges in repair welding can arise from various factors, including the type of material being repaired, the location and accessibility of the repair area, and the required level of precision and quality. The repair welding process was evaluated according to different criteria. To evaluate the quality of the welding processes the repaired bearings were examined by using metallography, scanning ultrasonic microscopy, scanning electron microscopy, 3D scanning and x-ray diffraction. Furthermore, hardness measurements were carried out to investigate the properties and characteristics of the cladded layer and base material. The investigations demonstrated the feasibility of repairing the damaged raceways and showed that the new cladded raceway could welded without any macro pores or other defects.

It is important to understand tribological characteristics of components operating in a hydrogen atmosphere. For instance, piston rings used in reciprocating compressors require strength, heat resistance and wear resistance, hence resins containing fillers are used. Particularly at high-pressure stages, PEEK- or polyimide (PI)-type composite resins are often introduced. In this study, focusing on PI and its composites, we investigated sliding properties of the resin in the hydrogen environment and the structure of transfer film. It was confirmed that some PI without fillers had good sliding properties and this unfilled PI exhibited sliding properties which was equivalent to other graphite-filled PI. A cross-sectional TEM EELS analysis revealed that the transfer film was a layer mainly composed of carbon. Raman analysis suggested that, in case of unfilled PI, the transfer film of carbon was formed by the decomposition of the PI due to wear, whereas in case of graphite-rich PI resin, the film was created mainly by decomposition of graphite. These results suggest that the carbon layer of the transfer film, which comes from sliding in the hydrogen environment, improves friction and wear properties, indicating that the origin of the layer may be irrespective of whatever it is (e.g., PI, graphite, etc.).

The study focuses on the prediction technology of rubber block friction properties on ice. The 2-D simplified block model with sipes (narrow grooves) and the mechanical analysis methodology are applied to understand the complex tribological phenomena and improve winter tire grip on icy roads. The friction forces on ice are assumed to consist of adhesion force, viscous drag of water film, and ploughing effects of sipe edges. Based on this assumption, the ice temperature distribution and friction coefficient in the contact patch are predicted. The effects of sipe density and block stiffness on tire tread pattern are evaluated. Experimental results partially validated the predicted friction coefficients. The study also proposed new sipe structures with high-density short sipes to improve ice performance. Tentative test results indicate the effectiveness of these new structures.

Friction and wear collectively account for nearly a quarter of the world’s energy consumption, resulting in over eight Gigatons of CO2 emissions annually. With increasing mobility and industrial activity, the adverse effects of friction and wear on energy, the environment, the global economy, and sustainability will undoubtedly intensify. Unless we reverse this unsustainable trend, our planet could face a major ecological and environmental catastrophe. Fortunately, significant strides have been made in reducing friction to almost undetectable levels, with friction coefficients below 0.001. These remarkable achievements have resulted from numerous collaborative efforts and global initiatives focused on developing novel materials, surfaces, and interfaces that exhibit minimal or near zero friction, even at macro or engineering scales. This paper provides a comprehensive overview of the factors that contribute to and hinder superlubric sliding conditions, examining the impact of both intrinsic and extrinsic factors that are integral parts of the test conditions and environments. Drawing from recent analytical, experimental, and computational findings, underlying mechanisms most responsible for superlubricity are also discussed. The paper discusses recent mechanistic studies on highly ordered 2D materials, such as graphene, MoS2, h-BN, MXene, etc., and thin solid coatings such as diamond-like carbon or DLCs, as well as liquids, and discusses their potential for the development of large-scale mechanical systems. These exciting advancements pave the way for designing and producing next-generation engineering systems that can minimize friction in practical applications, thus conserving energy, enhancing durability, and protecting the environment for a sustainable future.

Rolling element bearings in a particular application experience premature failure accompanied with white structure in steel. A possible cause of the failure is diffused hydrogen in steel which is generated by the decomposition of lubricant. This paper studied hydrogen generation from lubricant under rolling-sliding contact. A two-roller test was conducted in a sealed chamber, where the sliding speed and the lubricant temperature were controlled. The material of the roller was bearing steel and ceramic. Hydrogen gas concentration in the chamber was measured with a gas chromatograph. It was found that the hydrogen generation due to rolling-sliding contact depended on the lubricating conditions when the bearing steel specimens were used. The hydrogen generation increased by increasing the sliding speed and the oil temperature and decreasing the oil film parameter. Moreover, hydrogen generation was hardly observed under pure rolling condition. Another finding was that when ceramic specimens were used, the hydrogen generation was much smaller than when bearing steel specimens were used. These results suggest that nascent steel surface caused by the combination of metal-to-metal contact and slip accelerates the lubricant decomposition to generate hydrogen.

This paper presents a numerical simulation of an impulse gas seal. Impulse gas seals are mechanical seals equipped with feeding grooves on the stator and chambers on the rotor. During rotation, the chambers are fed with high-pressure gas when facing the feeding grooves and then release the high-pressure gas to maintain a gas film between the seal surfaces. The effect of operating conditions and chamber volume on the gas film thickness is studied. It is shown that the gas film thickness variation with pressure, speed, and chamber volume can be described with a power law of a duty parameter. Similar results are obtained for the mass flow rate and friction torque.

The accurate prediction of friction coefficients is crucial for the maintenance of sliding mechanical components to enable the timely detection of potential failures. Traditional methods rely on sensors like load cells and strain gauges to measure friction coefficients. However, these conventional techniques face challenges in real-time measurement during machine operation owing to physical constraints associated with sensor placement. To address this limitation, this study investigates the application of laser speckle patterns for predicting friction coefficients through a novel approach using convolutional neural networks (CNNs). The laser speckle technique offers rich surface condition data, while CNNs, which are particularly advanced in managing vast datasets, excel in establishing relationships between diverse factors for precise inference, classification, and prediction. Utilizing ResNet, a leading CNN architecture, a new friction tester capable of concurrently recording friction coefficients and speckle patterns in a cylinder-on-disk friction test was developed. The findings reveal that the CNN-based method, especially with ResNet, attained a coefficient of determination (R2) of 0.758, demonstrating its effectiveness in the accurate prediction of friction coefficients. This study significantly advances the field of friction coefficient prediction, highlighting the innovative application of laser speckle methodologies combined with machine learning techniques.

This research study investigates how incorporating soft nanoparticles affect the wear behavior and the characteristics of the materials in three-body mixed lubrication conditions. A disk-on-block tribometer was used to revealed a positive correlation between plasticity index and wear rates, indicating that increased plastic deformation leads to higher wear. The size and concentration of copper oxide (CuO) nanoparticles significantly influenced wear behavior. The study found that for block materials with a hardness of 27 HRC and 43 HRC paired with a disk of 58 HRC, increasing nanoparticle concentration and using larger nanoparticles relative to surface roughness (larger nanoparticle size and surface roughness ratio) resulted in reduced wear. The larger nanoparticles can more effectively fill the gaps on the smoother surface, increasing contact area and minimizing plastic deformation during sliding, especially when the contact is more elastic. However, when the counteracting block material is significantly harder than the disk, the effect of nanoparticles might be reversed, potentially leading to increased wear. These findings suggest a complex interplay between material properties, nanoparticle characteristics, and wear resistance, influenced by the relative hardness of contacting surfaces. This research offers valuable insight for developing materials with improved wear performance in applications involving sliding friction in third-body contact.

It is widely known that the impact of atmospheric humidity on tribological phenomena is significant, particularly in the context of dry sliding. Previous reviews have comprehensively addressed various cases within this domain and this article aims to complement these reviews with recent findings. The review covers a wide spectrum of humidity levels, ranging from trace amounts of water in the order of a few vol ppb to the relative humidity levels experienced in daily life. It delineates the forms of adsorbed water on solid surfaces within each humidity range and explores the potential physical lubrication mechanism of the adsorbed water and its effects on tribological phenomena. In the past, explanations for this influence have tended to be qualitative, primarily viewed from the perspective of chemical reactions. This discussion seeks to broaden the understanding by considering the influences from a physical lubrication perspective. Concluding the review, recent research findings are presented, shedding light on instances where trace amounts of water present in gases such as hydrogen exert an influence on tribological phenomena.

The effect of an electrospun (ES) film on the reduction of micro-drilling cutting force required for SUS304 plate was investigated. ES films were fabricated using the electrospinning method with polyvinyl alcohol (PVA) and polymethyl methacrylate (PMMA) as raw materials. The results of ATR-FTIR spectroscopy showed that there was no difference in the composition of the raw polymers and the fabricated ES films, and that the polymers were not altered. The diameters of the PVA and PMMA nanofibers were approximately 0.069–0.30 and 7.2 μm, respectively. The drill thrust force and run-out when using the nanofiber ES films were lower than those on an uncoated JIS SUS304 plate during the drilling. High-speed camera images showed that PMMA nanofibers pulverized by the cutting process adhered to the drilling tool surface and were guided into the drilling hole. This suggests that ES films made of organic polymer compounds, such as PMMA, are promising candidates for stable drilling, as they suppress drill run-out and act as an excellent lubricant during cutting.

Tribological machine elements, such as rolling element bearings and gears, are often used in mechanical components and various industrial applications. The contact interfaces and sliding parts fundamentally consist of two solid and one liquid lubricant, and they are operated under a thermal elastohydrodynamic lubrication (TEHL) condition. The TEHL solution characteristics depend on the operating conditions and lubricant physical properties, as well as the surrounding environment, including the temperature along the solid surfaces and pressure adjacent to lubricated contact. Herein, we numerically examine the influence of both solid temperature and ambient pressure on TEHL solutions at the nominal line contact and discuss the synergistic effects. Any changes in the physical properties of the lubricants are considered either together or separately as functions of temperature and pressure. The high ambient pressure enhances the effects of the solid temperatures on the resultant TEHL solutions. Regardless of the solid temperature and ambient pressure conditions, the TEHL solutions for all the lubricant models are grouped into two in terms of thermal conductivity.

A railway wheel flat occurs when the wheel locks and slides along the rail, forming a white etching layer (WEL) just under the flat surface where rolling contact fatigue cracks often form that can propagate into the wheel and spall during service. This study comprehensively investigated the influencing factors on wheel crack propagation that lead to spalling. Experiments were conducted to test wheel specimens with WELs of various dimensions, and simulations were performed to evaluate the stresses near the WELs as well as the rate and direction of crack propagation.

We measured the adhesion force between a sphere and a plane in water using a surface force apparatus that can measure the adhesion force with ultra-high accuracy. In particular, we focused on the relationship between the withdrawal speed and the adhesion force as one of the dynamic characteristics of the surface force. PDMS (Polydimethylsiloxane) was used as a spherical probe, and PEEK (Poly Ether Ether Ketone) and Si were used as plane samples. The results revealed that the adhesion forces depended on the withdrawal speed in water. This dependence was found to be qualitatively the same as that observed in a vacuum, indicating the influence of the viscoelasticity of PDMS on the adhesion forces. Furthermore, a comparison of the adhesion forces in air and water showed that they are dependent on the combination of materials. We deduced that the wettability of the material affected the adhesion forces. Specifically, the low affinity of the two surfaces to water resulted in hydrophobic attraction, while a hydration repulsion acts when one surface becomes hydrophilic.

Gas foil bearings, which are oil-free and exhibit low energy losses, are used in high-speed rotating machinery. Because gas is used as the working fluid, there is a need to improve damping performance using support structures. Additionally, the support structure, which becomes increasingly complex shaft performance, needs to be simplified. This study proposes a new bump mesh foil bearing focusing on the support structure and experimentally verifies its static and dynamic characteristics. The bump metal mesh foil bearing is a simple structure that combines a bump shape and metal mesh. Static load and hammering tests were conducted to evaluate the static characteristics, and the frictional torque and vibration at high-speed rotation were measured to evaluate the dynamic characteristics. The bump metal mesh foil bearing exhibited excellent damping performance owing to the friction damping caused by the bump shape and metal mesh; however, the rigidity of the bump metal mesh foil bearing was reduced. The bump metal mesh foil bearing exhibited the same level of lifting performance as the bump foil bearing, and vibration reduction at high-speed rotation was confirmed. Thus, the combination of the bump foil and metal mesh bearings yielded good results in terms of vibration characteristics.

Segmented radial seals are modern technologies used in aeronautic engines and space turbopumps. They consist of several circumferential segments assembled as an annular ring freely mounted on the rotor. A circumferential (garter) spring tightens the segments around the shaft. The segments can move radially relative to each other, sliding against a casing and following the dynamic displacements of the rotor. Two similar segmented seals made of different materials were tested. The results showed different leakage flow rates and different correlations between leakage and wear rate. For example, the leakage rate decreases with wear for one seal and increases for the other. For explaining these results, wear was correlated with the microstructure of the materials of the two seals. Profilometric analyses were made for the two seals, highlighting that wear was not localised in the same areas. Raman spectra maps were taken on the pads of the segment in contact with the rotor and microstructural changes caused by friction were enlightened. The evolution of residual stresses was measured for new and worn segments. These findings strengthen the results obtained from profilometric wear analyses. They also allow a more precise understanding of tribological degradation scenarios depending on the operating conditions and the properties of the material.

Catheter surgery is an effective treatment for vascular disease and has been investigated from a tribological perspective to prevent vascular damage. Endothelial glycocalyx layer (EGL), which is present on the most superficial surface of vascular endothelial cells plays an important role in maintaining vascular homeostasis, but, during catheter surgery, they are affected by frictional stimulation caused by direct contact with the catheter. In this study, to investigate and discuss the effects of frictional stimulation on the surface properties of vascular endothelial cells, we conducted nano friction tests using atomic force microscopy (AFM) on the surface of vascular endothelial cells. and evaluated mechanical properties, interaction structure, and surface properties of vascular endothelial cells and EGL. The results show that the elastic modulus of endothelial cells increased after the nano friction test. It was also found that EGL was worn away after several slides and the friction coefficient of vascular endothelial cells increased with the wear of the EGL. Furthermore, the adhesion force of endothelial cells increased by the wear of EGL. Besides that, the amount of adsorption to fatal bovine serum (FBS) was also examined using the QCM-D method, and a trend toward increased adsorption was observed for cells without EGL compared to cells with EGL.

Hydrophobic textured surfaces are studied for their low wettability and their capacity to create a ‘slippery’ fluid on the surface during lubrication. To this end, the flow between two parallel surfaces is numerically addressed by computing two dimensional numerical simulations. One of the surfaces moves with a uniform rectilinear motion, while the other is fixed, with a cavity in the middle. The steady-state flow is laminar and monophasic with a low Reynolds number. The reduction of the wall shear stress caused by a vortex in the cavity, with respect to a Couette flow, looks like the creation of an equivalent slip of the fluid on the wall at a macroscopic scale. Three methods are used to calculate the slip length: one is based on the wall shear stress and the other two are based on the speed of the fluid flow. When the slip length is calculated according to these three methods, the obtained results differ. The differences show that the slip often used in the literature is a macroscopic representation of local effects that are not necessarily slippery. The speed profiles and the streamlines are then discussed, in order to propose an explanation for this difference.

The world cannot counter climate change without the automobile industry becoming far more environmentally sustainable than it is today. With the realization that electrified mobility will take decades, not years, and that internal combustion engines (ICE) will continue to power vehicles in the near future, we need to step up the focus on improving fuel efficiency of ICE vehicles. In this report, we have confirmed that, in timing chains for automobile engines, the sliding area can be reduced by changing the arrangement of the arms & guides from continuous contact to a segmented one and by using an aromatic polyimide (PI) that can withstand the high contact surface pressure, thereby reducing friction loss. Through bench test monitoring, we confirmed that the friction loss was reduced in comparison to that by the conventional arms & guides in ICEs. The conventional arms & guides in the layout of the timing chains are placed with a curvature of ~ R2000 mm (at least R500 mm). In this study, the layout of the arms & guides was investigated. Each arm or guide is divided into two or three segments in the direction of travel and each curvature is reduced to about R100 mm. In addition, the material has been changed from polyamide (PA66) to PI. By these changes, the contact surface is decreased, and the surface pressure is increased. This means that on the Stribeck diagram, the lubrication conditions move in the direction of the smaller Sommerfeld number and the friction loss decreases. The use of the high compressive modulus material reduces the amount of deformation of the arms & guides contact surface, leading to the reduction of the friction loss.

The effects of Polymethacrylate (PMA)-series polar compounds on the friction and wear characteristics and on tribofilm formation in fully formulated low-viscosity engine oil have been studied. Optical microscopy, AFM, and element analyses by EPMA, AES, and XPS were used to determine the coexisting effects. The results showed that common additives in fully formulated (FF) oil had blocking effects that reduced the formation of ZnDTP-based tribofilm. PMA0 showed a blocking effect in preventing uniform tribofilm formation in FF low-viscosity oil. PMA-N showed comprehensive effects by forming a lower-quality uniform tribofilm in FF low-viscosity oil. PMA-OH and PMA-COOH showed a concerted effect by forming a lower S/P ratio and a higher Ca/Zn ratio uniform tribofilm in FF

In swash plate type axial piston pumps, slipper/swash plate sliding surfaces is subject to high fluctuating load. Therefore, the slippers are required to provide stable operation and reduce losses due to sliding. The behavior of the slipper fluctuates in a complex manner due to changes in the hydraulic pressure in the cylinder and inertial forces caused by the reciprocating motion of the piston. However, the time variation of the oil film thickness distribution of the slipper has not been measured. Furthermore, there are no measurements of the movement of the spherical joint connecting the slipper and piston, which affects the slipper behavior. In this study, the visualized sliding test rig with a sapphire glass swash plate was developed. The oil film thickness distribution of the slipper and the rotation of the slipper and the piston were measured continuously during one rotation of the pump.

The design calculation of crane metal structures is usually performed according to load combinations, for which the dynamic coefficients are strictly defined in the regulatory documentation. In fact, these coefficients depend on the departure and the length of the suspension of the load, they are different when lifting loads of different weights. A review of the literature has revealed a clear gap in the studies of the dynamics of gantry cranes, which are characterized by a change in the characteristics of their design even during one cycle of their operation. In this paper, to study the influence of the parameters of the gantry crane system on the magnitude of the dynamism coefficients, a dynamic model consisting of the mass of the crane’s metal structure brought to the point of suspension of the load and the weight of the load is applied. The weight of the rope, the elasticity of the lifting mechanism, and the damping of vibrations are not taken into account, and the characteristic of the drive is considered absolutely rigid. A method for determining the parameters of a dynamic model such as structural rigidity, its reduced masses is presented, and the results of calculating the dynamism coefficients for the metal structure of a crane and a rope suspension under various parameters and operating modes are presented. Calculations for a gantry crane with a lifting capacity of 10 tons have shown that with small departures, the dynamic load coefficient in the rope is always less than for a metal structure, while its value is maximum. For large departures, the values of the dynamics coefficients are close to those accepted for calculations according to regulatory documents. These circumstances should be taken into account both in the static calculation of portal cranes and in the calculation of their elements for durability, which will increase their reliability in determining the loading of metal structures.

Vibration protection for heavy equipment operators is important. Exposure to vibration is harmful to health. Vibration protection seats are used for protection. Reliable passive systems with quasi-zero stiffness are promising. For the developed design of the seat on the basis of parallelogram mechanism, spring, cable and rollers, the study of vibration-protective properties is carried out. The design scheme has been developed, key parameters have been selected, and their study on vibration protection parameters has been carried out. The static force response was approximated by three linear segments with a horizontal mean. The known dynamic model describing forced oscillations of the mass was used. The displacement of the base was given by a harmonic function. Vibration protection systems with three-segment and with one-segment static force response were compared. The comparison was carried out in terms of transmission coefficients, accelerations and suspension displacement. The results of the computational experiment are presented in the form of graphs: amplitude-frequency characteristics in the form of transmission coefficients in acceleration and displacement, at different amplitudes of base vibrations, damp-ing and stiffness coefficients. Dependences of average values of transmission coefficients in the investigated frequency range are given. Vibration damping is effective when the maximum suspension travel does not exceed the middle section of the static characteristic. The most effective vibration damping, according to the average value of the acceleration transfer coefficient, is achieved at minimum, and for a single-segment characteristic — zero values of the stiffness coefficient. The presence of extreme segments in the characteristic significantly increases the average values of the accelera-tion and displacement transfer coefficients of the suspension. Seat vibration protection systems in real conditions should have a limitation of suspension displacement for ergonomic reasons. The values of the stiffness coefficients of the extreme parts of the static force response, according to the criterion of minimizing the average value of the acceleration transfer coefficient, should be minimized. To substantiate the optimal values of the stiffness coefficients of the extreme sections of the characteristic and viscous friction coefficients, it is advisable to conduct additional studies under step and stochastic impacts.

The known variants of volumetric hydraulic drives of lifting and technological mechanisms are considered and analyzed. The areas of application of pumping and accumulator hydraulic drives, with various types of regulation, and options for their implementation as drives of a cargo winch of a bridge crane are considered. It is shown that the operation of the volumetric hydraulic drives of the cargo winch, along with volumetric and throttle control, can be performed by a relay method. It is noted that the cyclical operation of lifting mechanisms during lifting and lowering of cargo allows for mechanical and hydraulic energy recovery within the working cycle, which is a promising way to significantly increase the efficiency of their work. The analysis of the existing designs of hydraulic drives of technological machines, allowing to recover the potential energy of working bodies with cargo, is carried out. It is proposed as an alternative to the known hydraulic drives of the cargo winch of the bridge crane, a hydraulic drive with relay control. The efficiency of such a drive is shown, according to the indicators of the nominal pressure utilization coefficient and the energy intensity of the working fluid, in the case of the implementation of mechanical and hydraulic energy recovery in the working cycle in it. The mechanical and hydraulic circuits of such a drive are examined. An algorithm of mathematical model of its operation with consideration of different phases of cargo movement is proposed and its investigation is carried out. The possibility of fulfilling the safety conditions of operation of a hydraulic drive with relay control, in terms of ensuring the requirements for the uniformity of cargo movement, is analyzed.

The efficiency of using logging machines on a steep slope depends on many factors, including the working area of the manipulator, which can be implemented in various technological modes of operation. The geometric parameters of the implemented working area are determined by the working position of the machine in the appropriate technological mode, that is, the place of installation of the machine relative to the tree or group of trees to be harvested. Optimization of the manipulator’s working area, formed during the operation of a logging machine, is one of the most effective ways to increase its productivity. In this article, based on a previously developed mathematical model for optimizing the structural dimensions of the links of a four-link articulated hydraulic manipulator designed for spatial manipulation of the harvester head when cutting and stacking trees for further transportation to the loading area, an analysis of the influence of the main geometric and power characteristics of the harvester on the optimal size of the working area is performed.

The failure of the slewing support leads to significant economic damage associated with long downtime of equipment due to the impossibility of replacing it with a new one as a result of the imposition of sanctions by unfriendly countries. If earlier, before the introduction of restrictive sanctions (measures), the failure of the was less painful and took from 15 days to one month maximum, now it stretches to 3… 5 months. One of the reasons for the failure of equipment is the wear of the teeth of the wheel and gear of the rotary bearing, which leads to a change in the stress-strain state of the cassettes with rolling elements. There is uneven wear of the wheel in height, with the upper part of the wheel wearing out to a greater extent than the lower part, which leads to slippage between the gear teeth in the upper part to a greater extent than in the lower part. Wear of the teeth of the gear and the turntable leads to uneven and increased wear of the cassettes and cages of the slewing support and, accordingly, to the loss of rolling elements. The established unevenness of wheel wear in its various segments makes it possible to make proposals for improving the wheel design. The studies of the wear of cassettes and rollers made it possible to establish changes in the stress-strain state in the contact zone of the cassette and the roller, which in the future will improve the method of their calculation and make a proposal to improve the connection between the cassette and the roller.

Different types of models are used to study the stress-strain behavior of asphalt concrete mixture during compaction. For modeling it is necessary to know the values of model parameters in the whole range of changes in the characteristics of the compacted material. The aim of the paper is to develop a methodology for determining model parameters based on the results of laboratory creep-recovery testing of asphalt-concrete mixture. In the paper, a model reflecting elastic, visco-elastic and visco-fluid properties of the compacted material is adopted. A differential equation representing the law of behavior of the asphalt-concrete mixture layer under load is obtained. The stages of creep-recovery testing are analytically described, namely: rapid loading with a constant load and deformation under this load; load removal and recovery. Initial conditions for the mentioned stages are determined. Taking into account the initial conditions, analytical expressions of the laws of deformation of the model under the action of a constant load and in the process of recovery are obtained. The methodology of laboratory experiments on creep-recovery is described, according to the results of which the required values of the model parameters with minimum absolute error are obtained. The developed methodology allows to determine the parameters of the model describing the stress-strain behavior of asphalt-concrete mixture of different density and temperature. Consequently, it is possible to simulate the behavior of the asphalt concrete mixture layer at the preliminary, main and final stages of compaction in order to determine the effective operating modes of compaction equipment.

This scientific article discusses the possibilities of using Anylogic software to simulate transportation using transformable containers. The main attention is paid to the analysis of the unique characteristics of the transformable container, including its ability to transform, mobile warehouse technology, as well as modification of Anylogic software tools to develop models for improving loading and unloading, transport, transshipment and warehouse operations, based on new technical design solutions containers that increase the efficiency of transport and technological systems. The article analyzes specific functions and data libraries of the Anylogic program, which allow taking into account the unique characteristics of transformable containers when modeling transportation by improving production processes, including loading and unloading, transport, transshipment and warehouse operations. Original algorithms are proposed to optimize loading and unloading, as well as tools for planning routes taking into account the specific use of such containers. Ways to integrate these approaches into existing logistics systems are proposed and the potential benefits of their application to achieve higher efficiency and sustainability of urban transport and technological systems are described.

The results of the analysis of the manifestation of drought in the Faizabad region based on calculations of the standardized precipitation and evapotranspiration index (SPEI) are presented. It has been established that there is no definite pattern in the occurrence of drought, even for a long period. By comparing the number and duration of droughts in the Fayzabad district with the climatic characteristics of the Fayzabad district, a close dependence of drought on the average annual temperature and precipitation has been established.

The mechanisms of chemical mechanical polishing (CMP) of copper (Cu) surface using a slurry containing hydrogen peroxide (H2O2) and silica abrasive grains were theoretically investigated. First, molecular dynamics (MD) simulations using ReaxFF were used to analyze reactions that remove Cu atoms from the Cu(111) surface. At the Cu/H2O2 interface, Cu atoms were oxidized by forming Cu-O atoms were oxidized. In the second pathway, the atomic arrangement around the oxidized Cu atoms was disordered caused by surface vacancies. In relation to the first reaction pathway, activation energies were calculated to study the effects of the oxidation of Cu atoms on the Cu removal reactions. The results showed that the lowest activation energy was obtained when the structure in which neighboring Cu atoms were most oxidized, which supported the results of the MD simulations. The findings of this study indicate that the oxidation degree of adjacent Cu atoms and the atomic arrangement of the Cu surface affect the Cu removal reactions.

High-speed deep-groove ball bearings for the eAxle of electric vehicles must adapt to higher rotational speed conditions, because eAxle motor speed increases to downsize the unit. Therefore, it is necessary to clarify the lubrication process of ball bearings at the high rotational speeds to prevent seizure and wear. The oil-film thickness between outer-ring and ball, and the oil distribution around balls in 6008 deep-groove ball bearings incorporating experimental quartz outer rings were measured under high-speed conditions, with speeds exceeding 20,000 min−1. These measurements were carried out by employing the three-wavelength flash-light optical interferometry method and the UV-LED light-induced fluorescence method. It was found that the oil-film thickness did not increase even when the rolling speeds increased, which is in contrast to the EHL theory under sufficient lubrication condition. Contrary to the EHL theory, these phenomena can be attributed to the oil starvation and lowering effective viscosity of oil containing bubbles resulting from aeration under high-speed conditions.

Under low-speed or start/stop conditions, the rubbing of top foil in foil journal bearing (FJB) prompting the application of heat treatment to improve the rubbing behavior of the foil bearing. During heat treatment, various factors can influence the thermo-physical properties of foil. Therefore, the present study is carried out to analyze the impact of heat treatment variables on the rubbing behavior of FJB. To obtain it, bump-type FJBs are fabricated using SS 316 foil material with a corrugated die. Subsequently, experimental investigations of the developed bump-type FJB are conducted based on response surface methodology. The rubbing behavior of the FJB, including wear rate and surface roughness, is evaluated under various heat treatment conditions. The results indicate that both the wear rate and surface roughness of bump-type FJB decrease with increasing HT time duration. Furthermore, it is observed that the temperature distribution of the heated foil becomes more uniform with longer HT time durations. At the optimal HT variables of 500°C and 3 hours, the surface roughness and rubbing temperature of bump-type FJB are measured at 1.295 μm and 55.20°C, respectively. Additionally, the rubbing temperature of bump-type FJB is thoroughly evaluated.

It is well known that the friction coefficient of viscoelastic solids against the drive speed exhibits a bell shape. In previous theoretical studies on viscoelastic friction, we can find two origins for the bell shape. One is due to the material response (i.e., the bell-shaped rheology of viscoelastic solids), and the other is due to the mechanical response (i.e., the vertical lift of the counter surface with asperities). Although these two origins do not contradict each other, their relationship seems unclear. This paper theoretically examines the friction coefficient for the steady sliding contact between a rigid probe and a viscoelastic foundation exhibiting the standard linear solid viscoelasticity. Capitalizing on the strength of the simple model, we successfully find the complete set of dimensionless numbers and master curves describing the velocity dependence of the friction coefficient. Comparing them with the dimensionless numbers and master curves for the Kelvin-Voigt viscoelasticity, we clarify two origins for the bell-shaped velocity-dependent friction coefficient and their relationship.

Polyester base oil has good lubricating properties and biodegradability, which meets the requirements of green and sustainable development. In this work, polypropylene adipate (PPA) was synthesized with spherical nano-MoS2/sericite (SMS) as catalyst. SMS did not need to be separated from PPA after the reaction and could be retained in PPA as a lubricant additive. The SMS precipitated slowly in the SMS/PPA suspension during standing storage, and after 7 days, there was still 1236 mg/L SMS in the PPA. Compared with PPA synthesized without SMS, the friction coefficient of the SMS/PPA suspension after standing for 7 days was reduced by 13.9%. Moreover, the suspension also decreased the wear volumes of the steel ball and the steel disc by 59% and 94%, respectively. The characterization results showed that SMS participated in the formation of tribofilm, and decomposed into silicon and oxygen-rich compounds filled in the peeling caves. This study provides an alternative path for the synthesis of polyester base oil, and also expands the potential application range of MoS2 lubricant additives.

Machining processes hold a pivotal place in the sphere of modern manufacturing. Thus, constant advancements to enhance their efficiency and sustainability are warranted. This review paper discusses the recent advancements in machining with Minimum Quantity Lubrication and a combination of Nano-Fluids with Minimum quantity lubrication (Nano-Fluid MQL). Recent developments are assessed with particular emphasis on critical parameters such as cutting temperatures, tool wear, and surface quality. In addition, the environmental and economic aspects of using MQL in combination with nano-fluids are discussed. This combinatory approach is evaluated as a sustainable solution in machining. This paper also presents the literature survey of nano-fluids and the application of nano-fluids in MQL.

The low-friction mechanism of graphene oxide-dispersed lubricants remains to be elucidated. In this study, pin-on-disk friction tests were conducted on specimens with various surface properties to clarify the effect of the lubrication condition of the contact point on the low-friction by dispersing graphene oxide (GO) particles into lubricating oil. The relationship between the lubrication state and the friction coefficient was investigated using Λ ratio calculated from the surface roughness of the sliding area after the test and the calculated minimum oil film thickness. The friction coefficient decreased as Λ ratio increased, that is, as the lubrication state approached fluid lubrication. For the disk specimen containing pit shapes on the surface, the friction coefficient was significantly reduced by up to 70% for the graphene oxide-dispersed lubricant compared to the base oil alone. On the other hand, the friction reduction was only 20% for the specimen without pits. The composite surface roughness of the sliding area after the test was significantly improved for the disk with pits, which indicates that the progress of running-in process during the test affects the friction properties of the GO containing lubricant.

This paper proposes a method of topographical characterization for tribo-surface textures based on contact asperities. BEM (boundary element method) simulation using the Boussinesq-Cerruti theory was employed to estimate the contact condition. Parameters such as contact area ratio, contact pressure, radius of curvature, etc., were evaluated from the contact condition. The proposed method was applied for understanding the mechanism of higher friction for a belt-CVT (continuously variable transmission). Results showed that the contact summit density and mean contact summit area have clear correlations with the coefficient of friction obtained by experiments.

The present study describes an improvement of damping performance of a mechanical tensioner driven by friction force at the power spring interface, used for the timing chain system for an internal combustion engine. The mechanical tensioner consists of a power spring subjected to face-to-face contact with a reciprocal motion and a leaf spring to apply the reaction load. The concave and convex surface texture was fabricated with an electrochemical etching on the power spring surfaces. Since the reaction load is affected by the friction force at the power spring interface, the damping performance is evaluated from a hysteresis loop resulting in the reaction load and the plunger displacement trajectory. Superior stabilization of the reaction load and a remarkable decrease of the wear loss including the restriction of the oxidation was found on the convex textured tensioner in lubricated condition. The tensioner performance was also evaluated in staved lubricating conditions. Results showed that the change of the reaction load of the convex textured tensioner was small just before the stiction occurrence. In contrast, the reaction load of the concave textured tensioner increased with the increase in the number of cycles. Therefore, the applicability of the convex surface texture to the power spring surface of the tensioner was confirmed. It was also estimated that the discharge of the wear debris is an important factor in maintaining the tensioner performance.

Friction control is the most fundamental and important issue in the field of tribology. In recent years, friction control technology, which aims to reduce the energy loss in mechanical systems to address global environmental issues, has received significant attention. Friction control involves minimizing the friction coefficients and maintaining high frictional forces, such as in power transmissions and brakes. Surface texturing plays a crucial role in controlling the friction of tribological elements. In the future, technologies for active friction control at the interface between living organisms and artifacts will be indispensable for realizing a collaborative society with the coexistence of humans and robots. This article reviews the role and key findings of surface texturing and outlines its potential and future trends.

The 9th International Tribology Conference, Fukuoka 2023 was held on 25–30 September 2023 at Fukuoka International Congress Center in Fukuoka City, Japan. The number of participants was 975 from 30 countries and regions, and the number of papers presented was 676. We thank all the people who joined and contributed to ITC. Papers submitted to this special issue went through peer-review process. Twenty papers were already published in Part 1, and 19 papers were accepted for publication in this Part 2. On behalf of the Organizing Committee, we would like to thank all the authors for their contributions, and also thank the editors, reviewers and the editorial office of Tribology Online for their efforts. Taking this opportunity, we would like to include in the next page the manuscript of the congratulatory speech delivered by Professor Masato Tanaka in Banquet on Thursday, 28 September, 2023

It is possible to calculate the oil film thickness and the pressure distribution on the Hertzian contact surface of bearings, gears, traction drives, etc. by the EHL theory by Dowson et al.. For these calculations, it is important to determine the high pressure viscosity and high pressure density of lubricant. In a previous report, I constructed a theory of the relationship between viscosity, temperature and pressure. And the van der Waals type viscosity equation was derived. Similarly, in this study, I constructed a theory of the relationship between density, temperature and pressure. As a result, it was found from the dimensional analysis that 1/3 power of density (line density) was negatively proportional to temperature. This linear equation was found to be a van der Waals type line density equation which consists of three eigen constants: absolute zero line density ρt=01/3, line density constant 1/G and pressure constant H/G. Furthermore, the pressure constant H/G of the line density equation is equivalent to the PR of the liquid state equation and the pressure constant C/B of the van der Waals type viscosity equation. And I report the results of estimating the high pressure density of various lubricants by the line density equation.

This study examined the effects of polytetrafluoroethylene (PTFE) and Eichhornia crassipes carboxymethyl cellulose (EC-CMC) polymers in base jatropha lubricant and employed commercial shell lubricant as the reference. Wear reduction and coefficient of friction (COF) were measured using 1 mass% polymer concentrations. Characterization analysis showed that the formulation processes required functional groups like carbonyl, alkene, aliphatic CH2 and CH3 group that the Fourier Transmission Infrared (FT-IR) studies indicated were necessary for lubrication. According to the frictional analysis, the polymers’ tribological performance was influenced by changes in both load and operational speed. At 40 kg and 1200 rpm, PTFE and EC-CMC reduced COF by 53.7% and 49.8%, respectively, compared to base jatropha. However, commercial shell oil produced exceptional performance.

The durability of super-low friction of hydrogenated carbon nitride (CNx:H) coatings sliding against Si3N4 balls in high-vacuum (HV) environments and the phenomena that occur at the interface were clarified. In an HV, CNx:H achieved super-low friction (µ

Indentations in rolling bearings from particle contamination introduce surface damage because they disturb lubrication and produce stress concentrations. In this article, a methodology is proposed where non-failed bearings that have been running in the field are inspected, indentations are counted and their geometry is characterized. With this information and the use of a mathematical model previously developed, the inferred damage in the bearing can be estimated and with this also the actual contamination parameter, ηc as described in the ISO 281 standard. In this way giving more certainty on the real contamination conditions in the application than other indirect assessment methods.

Within the framework of the put forward hypothesis that energy costs of working movements of the links of racking stacker cranes are inextricably linked to the shape of the working area of the warehouse in which the crane operates, to reduce energy costs, it was pro-posed to use a rotating boom in the design of the stacker crane. With the help of program implementations of mathematical models of stacker cranes of traditional bicycle design and the proposed design with a rotating boom, it became possible to determine the average energy costs for all possible movements of loads of the same mass within the corresponding working areas of these designs. For this purpose, systems of differential equations in Cauchy form were developed, where dissipation of energy was taken into account. The total value of work of crane drives during acceleration and braking was determined. The latter were carried out with constant accelerations, and the movement after acceleration — with constant speeds. The developed simulation mathematical models of cranes of traditional design and the proposed design with a rotating boom allow to determine the energy costs in the drives when moving the crane links along the given trajectories. According to the criterion of average total energy costs, adopted for all possible combinations of movements within areas of the same capacity of one hundred square meters, the stacker crane of the proposed design has an advantage over the crane of traditional design. This makes it possible to significantly reduce energy costs when using such cranes in warehouses and hangars. It is reasonable to recommend the use of a stacker crane of the developed design in warehouses of round shape — it will allow to reduce significantly the energy costs when using such cranes in warehouses and hangars.

The factors of resistance to the movement of the bridge trolley as a system consisting of many elements that are in structural and functional relationships with each other and change little during the operation of the system are considered and their parametric models are compiled. At the same time, the interdependent influence of structural, technological and operational factors in the system is considered taking into account their manifestation in various physical effects. A multi-level hierarchical structural-functional-parametric model of the system has been compiled, formed on the principle of a sequential two-level hierarchy, as well as parametric models of various levels applied to the periods of the most intense change in the states and transformation of the system in the process of functioning: resistance from rolling friction; resistance from friction in the axle boxes; resistance from the current supply; resistance from slope; resistance from inertia. A constructive method of reducing the resistance to the movement of the crane is considered by introducing elements of elastic suspension of the crane bridge into the design, which ensures the formation of a negative slope, characterized as a «kinematic slope», the value of which varies in proportion to the change in the position of the cargo trolley. The concept of parametric reliability is defined, applied to the drag system of the bridge crane trolley, as a time function characterizing the probability of fulfilling the condition of finding its numerical values in the limits set by the technical conditions.

The article presents the results of research activities in 2023 by scientists of the Academician I.G. Petrovskii Bryansk State University in the field of developing promising domestic designs of single-span mobile ropeways of various designs — based on autonomous self-propelled wheeled chassis with high load capacity and cross-country ability and based on modular airmobile units. The results of the creation of scientifically based methods for their design and computer modeling of operational processes are also presented. The article describes the results of the creation of a theory of design and modeling of work processes for harvesters equipped with rope anchoring equipment for logging operations when working on steep slopes in highly rugged or mountainous terrain.

A printing press is a complex technical system that includes a large number of rotating parts (shafts, gears, etc.), including bearings and support rollers. The appearance of defects in bearing assemblies can lead to serious consequences, such as equipment failure and jamming of shafts, which will lead to a halt in production or the appearance of defective printed products. The purpose of the work was to study defects in the support roller of the gripper shaft, which is responsible for transferring the sheet inside the printing section. The defects of the outer ring of the support roller are considered in the article. With the help of a control and measuring machine, the changes that occur in its geometry are studied. The research was carried out on the new roller, as well as on the rollers that came out of operation, the changes that occur during operation were revealed. Also, with a tenfold increase, defects that occur on the surface of the ring that appeared during operation, such as abrasive wear, traces of fatigue, were studied.

The increasing requirements for the accuracy of construction work lead to the need to create modern control systems that will eliminate the human operator from the process of controlling road construction machines, increase the energy efficiency and productivity of these machines, as well as the quality of the finished construction object. The use of unmanned control systems has become an absolute technological break-through. Improving the accuracy of work with the help of unmanned control systems is an urgent and complex area of research. This is due to the need to improve algorithms and improve sensors to more accurately de-termine the coordinates of the machine and make decisions. Only by possessing high accuracy, modern unmanned vehicles are able to minimize errors in construction work and associated safety risks. To do this, it is necessary to provide the ability to recognize and analyze various factors, such as moving objects, weather conditions, terrain, etc. The article presents the results of a functional analysis of a number of road construction machines, defines the range of tasks that a modern unmanned control system should solve, describes a possible implementation option for such a system, and shows the differences in flowcharts of working processes of construction machines both without automatic control systems and equipped with standard and developed automatic control systems.