Friction Conditions Research Articles

Targeted assembly of hierarchical sea-urchin inspired NiPS@LDH architecture for enhanced toughness, wear-resistance and fire-safety of epoxy composites

Epoxy resin (EP) is a versatile material widely used in fields such as electronic encapsulation, coatings, adhesives, and composites. The targeted assembly of nanomaterials to optimize the flame retardancy, mechanical properties, and interfacial properties of composite materials is a prominent research hotspot in the field of EP. Therefore, a hierarchical sea-urchin inspired architecture (NiPS@LDH), based on layered double hydroxide (LDH) nanosheets grown on nickel phyllosilicate (NiPS), was rationally constructed as a functional filler for EP with a view to building high-performance EP composites. The addition of 1 wt% NiPS@LDH increased the tensile strength, modulus of elasticity, and elongation at break of EP by 44.1 %, 27.6 %, and 66.2 %, respectively, showing excellent strengthening and toughening effects. Meanwhile, under dry friction conditions, the wear rate of the composites was 0.86 mm3·N−1·m−1, reduced by 87.8 % compared to that of pure EP, indicating excellent wear resistance. Besides, the pHRR, THR, pSPR, TSP, pCO and pCO₂ of EP/NiPS@LDH-3 composites were found to be significantly reduced by 54.0 %, 61.9 %, 50.7 %, 54.4 %, 51.2 %, and 58.2 %, respectively. The LOI value of the composites increased to 26.4 %, and the maximum weight loss (Rmax) was reduced by 27.7 %. This study provides an innovative strategy for the targeted assembly of nanomaterials, paving the way for the preparation of high-performance EP nanocomposites.

Experimental investigations of the wear behaviour of railway brake block raw materials

Abstract Passenger and freight transport by rail is gaining ground not only in Europe, but in many countries around the world. At the same time, due to the increased traffic, the need to investigate the effects of rail transport on the environment and to reduce the harmful effects is also increasing. One of the recurring problems is the reduction of the noise that occurs during the braking of railway cars, as well as the mitigation of particles released during braking and, as a result, the reduction of their health-damaging effects. In more and more European countries, the so-called Noise Differentiated Track Access Charges (NDTAC) is being introduced, where the cost depends on the amount of noise emitted during braking. For this reason, the examination of the friction conditions of the materials used in railway brakes and the finding of materials with the most favourable properties is a priority area of research. In this paper, the initial investigations of a recently started research project on the subject are presented, the aim of which is to develop and test new layered composite materials that may be used in the future to produce railway brake blocks. The paper presents the main objectives of the project, the principles, and tools of the friction tests to be applied, as well as the test measurements carried out, during which the friction characteristics of copper alloy and aluminium control materials along with the currently used cast iron and composite brake blocks were examined.

Features of Increasing the Wear Resistance of 90CrSi Tool Steel Surface under Various Electrophysical Parameters of Plasma Electrolytic Treatment

The paper investigates the feasibility of plasma electrolytic treatment (PET) of 90CrSi tool steel to enhance hardness and wear resistance. The influence of electrophysical parameters of PET (polarity of the active electrode, chemical-thermal treatment, and polishing modes) on the composition, structure, morphology, and tribological properties of the surface was studied. Tribological tests were carried out under dry friction conditions according to the shaft-bushing scheme with fixation of the friction coefficient and temperature in the friction contact zone, measurements of surface microgeometry parameters, morphological analysis of friction tracks, and weight wear. The formation of a surface hardened to 1110–1120 HV due to the formation of quenched martensite is shown. Features of nitrogen diffusion during anodic PET and cathodic PET were revealed, and diffusion coefficients were calculated. The wear resistance of the surface of 90CrSi steel increased by 5–9 times after anodic PET followed by polishing, by 16 times after cathodic PET, and up to 32 times after subsequent polishing. It is shown that in all cases, the violation of frictional bonds occurs through the plastic displacement of the material, and the wear mechanism is fatigue wear during dry friction and plastic contact.

FSW of AA2024: effects of tool wear on energy consumption

ABSTRACT This study shows that the progressive adhesion of weld material to the tool in friction stir welding AA 2024-T3, up to tool saturation, brings about a decrease in power consumption until a plateau is reached. The cause of this behavior is the hindering of the stirring action of the tool due to the material accumulated on it. The built-up material changes the nature of the tool/material interaction and then the friction condition at their interface. The direct consequence is a decrease in the shearing strain and therefore in the heat generated by friction. Bits of this adhering material break off from the tool at intervals. Macro and micro detachments are identified. Micro-detachments happen continuously at small periodic intervals and produce vibrations. The amplitude of these vibrations increases in all their characteristic spectral components up to tool saturation. Macro-detachments generate oscillations in power consumption and leave galling on the weld bead.

Effect of raceway surface topography based on solid lubrication on temperature rise characteristics of HIPSN full ceramic ball bearings

PurposeThis study aims to understand the influence of raceway surface topography on the temperature rise characteristics of silicon nitride (Si3N4) full ceramic ball bearing and improve its service life.Design/methodology/approachThe arithmetic average height Sa, skewness Ssk and kurtosis Sku in the three-dimensional surface roughness parameters are used to quantitatively characterize the surface topography of the raceway after superfinishing. The bearing life testing machine is used to test the Si3N4 full ceramic ball bearing using polytetrafluoroethylene (PTFE) cage under dry friction conditions, and the self-lubricating full ceramic ball bearing heat generation model is established.FindingsWith the decrease of Sa and Ssk on the raceway surface and the increase of Sku, the average height of the raceway surface decreases, and the peaks and valleys tend to be symmetrically distributed on the average surface, and the surface texture becomes tighter. This kind of raceway surface topography is beneficial to form a thin and uniform filamentous PTFE transfer film with a wide coverage area on the raceway surface based on consuming less cage materials and improving the temperature rise characteristics of hot isostatic pressing silicon nitride full ceramic ball bearings.Originality/valueThe research results provide a theoretical basis for the reasonable selection of Si3N4 ring raceway processing technology and have important significance for improving the working characteristics and service life of Si3N4 full ceramic ball bearings under dry friction conditions.

Wear Characteristics of Textured Floating Oil Seal Surfaces: A Simulation and Experimental Study

This study aimed to analyze the effects of surface texture on the wear amount of floating oil seals and how these effects are related to the texture parameters. To achieve this, a finite element model was constructed to simulate the frictional behavior of seal discs under both textured and non-textured conditions. The study focused on a specific set of texture parameters. The texture depth was held constant, while the area density and diameter of the textures were varied. Three different area densities were considered: 10%, 20%, and 30%. Similarly, three different texture diameters were included in the study: 100, 200, and 300 μm. For each combination of area density and diameter, three different texture depths were evaluated: 50, 100, and 150 μm. The results show that compared with the non-texture, the wear loss of the texture is significantly reduced, and the wear loss is reduced by 56.8%. As the texture depth increases, the corresponding increase in wear remains relatively small. In contrast, increasing the texture diameter and area density leads to a more significant increase in wear, indicating that these two parameters have a more significant effect on the wear behavior of the seal. Under the condition of dry friction, the average friction coefficient analysis shows that the texture area density is 30%, the texture diameter is 200 μm, and the minimum value is about 0.602. Under the lubrication condition, the lowest average friction coefficient is about 0.147, the texture area density is 20%, and the texture diameter is 300 μm.

Microstructure characterization and high-temperature wear mechanism of high-entropy alloy matrix composite coating fabricated by laser cladding

The development of diecasting technology requires hot die steels with high-temperature resistance. In this study, a high-entropy alloy (HEA) was combined with ceramic particles to generate a CoCrFeNiMo0.2Nb0.2/WC composite coating via laser cladding. The coating consisted of a face-centered cubic (FCC) matrix with unmelted WC particles, eutectics and nanoscale (Mo)NbC phases. With the strong lattice distortion caused by the sequestration of W atoms, a nanoscale amorphous layer existed between the Laves and HEA matrix phases. A transition layer with the same structure as the Laves phase was facilitated between the WC particles and the HEA matrix. Due to the hard phases in the HEA matrix and their interfaces, the composite coating with a high proportion of WC exhibited excellent wear resistance under high-temperature dry friction conditions. When the WC was 60 wt%, a minimum wear rate reached to 0.74 × 10−5 mm3/(N·m) at 600 ℃ and 1.46 × 10−5 mm3/(N·m) at 800 ℃. The destruction pattern of the composite coating at 600 ∼ 800 °C was due to the interaction of the adhesive, oxidative and abrasive wear. The composite coatings fabricated in this study provide a route to enhance the high-temperature wear resistance of die-casting molds.

Current-carrying tribological behavior and wear mechanism of CuW composites with different W content

CuW composites are widely used in the field of electrical contacts, such as high-voltage switch and microelectronic devices, and the service life of the key components is directly affected by its wear resistance and corrosion resistance. In this paper, the effects of loading current on the tribological behavior of CuW composites with different W content were studied, focusing on the variation of friction coefficient during friction, wear rate and the wear topography of the surface after friction, and the wear mechanism was discussed. The results indicate that the friction coefficient of CuW composites was larger under energized conditions than under dry friction conditions, and that the friction coefficient first increases and then decreases with the increasing current. The main reason for the decrease in friction coefficient is that the heat generated by increasing current creates a layer of molten lubricant on the contact surface. In addition, the wear rate of the CuW composites decreased as the W content increased. When loaded with a current of 15 A, the CuW80 composites exhibited the lowest wear rate of 8 × 10−3 mg/m, which was attributed to the improved wear resistance due to the ability of the high W content to resist plastic deformation. The wear forms of CuW composites under current loading include adhesion, abrasive wear and arc erosion, and fatigue wear was also associated with long-term high current conditions.

Tribological properties of ductile cast iron with in-situ textures created through abrasive grinding and laser surface ablation

This paper discusses the proposed abrasive grinding (AG) and laser surface ablation (LSA) method for creating in-situ textures on ductile cast iron (DCI) surfaces. LSA method removes spherical graphite of DCI’s surface, forming martensite and high residual stress on the matrix, thus increasing hardness. AG method uses Al2O3 abrasives to disrupt spherical graphite and form grinding-layer. Compared to LSA, AG method avoids residual stress and burrs, simplifies the processing technology. Tribological tests show that LSA-treated samples have a lower coefficient of friction (COF) and specific wear rate, especially under dry friction conditions, due to increased surface hardness. AG-treated samples have a more stable COF because the oxide layer reduces adhesive wear, grinding-layer provides solid lubrication and reduces localized contact stress.

Effect of Temperature on Thermal Oxidation Behavior of Ti-6Al-4V ELI Alloy.

In this paper, the morphological, micromechanical and tribological characteristics of the Ti-6Al-4V ELI alloy after thermal oxidation (TO) were identified. TO was carried out at temperatures of 848 K, 898 K and 948 K over a period of 50 h. Microscopic examination revealed that an increase in temperature resulted in an improved uniformity of coverage and an increased oxide grain size. Micromechanical tests showed that TO of the Ti-6Al-4V ELI alloy led to an increase in hardness and deformation resistance. Following oxidation, a decrease (by approximately 10-22%) was observed in the total mechanical work of indentation, Wtotal, compared to the as-received material. The formation of protective oxide films on the Ti-6Al-4V ELI alloy also led to the improvement of tribological characteristics, both when tested under dry friction conditions and in Ringer's solution. The sliding wear resistance increased with an increase in the oxidation temperature. However, a greater degree of wear reduction (by approximately 30-50%) was found for the lubricated contact in comparison with the dry friction tests. Surface roughness also increased with the increase in temperature.

КОНСТРУКТОРСКО-ТЕХНОЛОГИЧЕСКОЕ ОБЕСПЕЧЕНИЕ ТРИБОТЕХНИЧЕСКИХ ПАРАМЕТРОВ СОЕДИНЕНИЙ ТРЕНИЯ СКОЛЬЖЕНИЯ В ПРОЦЕССЕ ПРИРАБОТКИ ПРИ СТУПЕНЧАТОМ НАГРУЖЕНИИ

The paper deals with the issues of technological support to provide the load capacity index of cylindrical sliding friction joints during running-in under step stress. The load capacity of sliding friction joints is one of the tribological characteristics, depending on design and technological factors. The results of studying tribotechnical characteristics of cylindrical sliding friction pairs operating under boundary friction conditions are presented. The working surfaces of these triboelements after preliminary finishing (turning with composite 10 or grinding with the periphery of an abrasive wheel) were subjected to various technological methods of antifriction treatment. In particular, the following methods are considered: 1) application of break-in soft films on the surface of triboelements (shafts) by plating methods; 2) application of break-in soft copper-containing films on the surface of the triboelement (shafts) by friction brassing or chemical copper plating; 3) modification of the surfaces of triboelements with solid nitride-containing coatings (combined treatment) in combination with soft break-in films followed by finishing and hardening surface treatment by surface plastic deformation methods. The shafts were made of 45 steel with subsequent hardening, and the inserts were made of bearing materials recommended in the reference literature (antifriction cast iron ASF-1; babbit B -88; bronze BrOCC -5-5-5 ). Logical models of antifriction treatment methods under consideration and the rationale for their application are presented. Experimental studies were carried out by methods of active experiment on a special test bench having a wide range of changes in stresses on the model of the tested compound and relative sliding velocities of triboelements. Statistical treatment of experimental results made it possible to find out the influence of the studied design and technological factors and running-in conditions on the tribotechnical characteristics of the compounds. The research results are analyzed and on their basis practical recommendations for their use are given. Adequate models of forming the load capacity of joints are obtained, which are recommended to be taken into account at the stages of their design (selection of materials and coatings), machining and running-in.

Tribological Characteristics of Fibrous Polyphthalamide-Based Composites.

The aim of this study was to investigate the tribological characteristics of commercially available high-strength polyphthalamide-based composites with great contents (30-50 wt.%) of both carbon and glass fibers in point and linear contacts against metal and ceramic counterfaces under dry friction and oil-lubricated conditions at various loads and sliding speeds. The lengths of both types of fibers were varied simultaneously with their contents while samples were fabricated from granules by injection molding. When loading PPA with 30 wt.% SCFs at an aspect ratio (AR) of 200, the ultimate tensile strength and the elastic modulus increased up to 142.7 ± 12.5 MPa and 12.9 ± 0.6 GPa, respectively. In the composites with the higher contents of reinforcing fibers PPA/40CCF and AR~1000, the ultimate tensile strength and the elastic modulus were 240 ± 3 MPa and 33.7 ± 1.9 GPa, respectively. Under the applied test conditions, a composite reinforced with 40 wt.% carbon fibers up to 100 μm long at an aspect ratio of ~1000 possessed the best both mechanical properties and tribological characteristics. One of the reasons that should be considered for improving the tribological characteristics of the composite is the fatigue wear mechanism, which is facilitated by the high filling degree, the strong interfacial adhesion, and the great aspect ratio for fibers. Under the oil-lubricated conditions, both friction coefficients and wear rates decreased, so such friction units could be implemented whenever possible. The reported data can be used as practical recommendations for applying fibrous polyphthalamide-based composites as friction unit components.

High-temperature tribological properties of AlCrN coatings deposited on textured surfaces under dry friction

Linear textures and AlCrN coatings were produced on cemented carbides using laser and physical vapor deposition, respectively. Reciprocal sliding friction studies were conducted under dry friction conditions to examine the tribological properties of the AlCrN coatings placed on textured surfaces against Si3N4 ceramic balls at various temperatures. The findings demonstrated that at friction temperatures of 200 °C, 400 °C, and 600 °C, the average friction coefficient of the AlCrN coating samples placed on textured surfaces was lower than that of the samples deposited on smooth surfaces. This reduction occurred by 9.6%, 15.1%, and 23.9%, respectively. Meanwhile, because micro-textures trap wear debris, AlCrN coating samples put on textured surfaces had lower surface adhesions, indicating that micro-textures can improve the tribological properties of AlCrN coatings. Finally, the mechanisms of micro-texture improving tribological properties were investigated. Micro-textures can store wear debris, reducing friction coefficients and thereby minimizing abrasive wear. Micro-textures, on the other hand, can prevent coating oxidation by lowering the temperature of the friction area, resulting in less oxidative wear.

Experimental study of the end effect on the mechanical behaviors of rocks under true 3D compressions

AbstractIn true triaxial compression tests, all three principal stresses are imposed independently. This allows for a more comprehensive analysis of the material's mechanical properties. The end effect in true triaxial compression tests is a crucial phenomenon that impacts the accuracy and reliability of the test results. In this study, a series of true triaxial compression tests is conducted to examine the influence of the end friction on the mechanical properties. The laboratory results show that the presence of the end friction could bring about an apparent increase in rock strength and also restrict the deformation in each direction showing that the stiffness (the slope of the curves) increased slightly. The rock strength could be enhanced from 24.7 to 90.7 () when the end friction is increased, which is mainly caused by the lateral interface friction. The failure mode and fracture angle of the specimen are also influenced by the end effect, showing that under high friction conditions, the failure is more ductile, and a larger fracture angle is observed. At last, in comparison with the published experimental data, the actual specific friction angle (corresponding friction coefficient is about 0.19) for the direct specimen–metal contacts in a true 3D test is numerically identified, which is empirically reasonable and higher than the tested range 0.146–0.157 obtained from double‐shear test system.

Optimal Convergence of Thermoelastic Contact Problem Involving Nonlinear Hencky-Type Materials with Friction Conditions

Optimal Convergence of Thermoelastic Contact Problem Involving Nonlinear Hencky-Type Materials with Friction Conditions

A Detailed Understanding of Slow Self‐Arresting Rupture

AbstractRecent numerical simulation studies suggest the existence of a seismic type that is distinct from regular earthquakes—the slow self‐arresting rupture (SSAR). Unlike regular earthquakes that propagate dynamically following the initiation, The SSARs automatically arrest within the nucleation zone without interference. Additionally, numerical simulations indicate that SSARs exhibit a significantly lower energy release compared to regular earthquakes, while also exhibiting a relatively long source duration. Given these distinctive properties, comprehending the source processes of SSARs assumes great strategic importance. However, our current understanding of SSARs, particularly regarding their response to different frictional conditions and their correlation with natural phenomena, remains limited in scope. To further explore the intricacies of SSARs, we employ a three‐dimensional fully dynamic source model to simulate SSARs under various slip‐weakening frictional conditions. The findings indicate that SSARs occur in frictional environments characterized by large normalized critical slip distances, with the seismic source process being primarily influenced by this parameter. Apart from displaying significantly smaller average slip and stress drop, which are two to three orders of magnitude lower than those of regular earthquakes of comparable magnitude, SSARs also showcase a decrease in duration, seismic moment, slip rate, and stress drop as the normalized critical slip distance increases. The moment‐duration scaling law of SSARs exhibits a linear pattern. Moreover, the observation of slow earthquakes offers further implications for the presence of SSARs, indicating their potential association with a wider range of intricate seismic phenomena.

Condition monitoring for planetary journal bearings in wind turbine gearboxes by means of acoustic measurements and machine learning

The use of journal bearings instead of rolling bearings as planetary bearings in wind turbine (WT) gearboxes is advantageous for the power density of the drive train. In addition, they can increase the reliability of the gearboxes as they can be operated wear-free in hydrodynamic operation, i.e. with fluid friction. The dynamic loading conditions in wind turbines, as well as special conditions such as insufficient lubrication and particle contamination, can lead to mixed friction operation and consequently to wear in the journal bearings. If mixed friction is not detected, damage and failure of the journal bearing and consequently of the WT gearbox may occur. Therefore, it is required to develop a Condition Monitoring System (CMS) to detect mixed friction in the journal bearings during operation of the WT. Preliminary investigations have shown that various friction conditions can be detected by acoustic measurements in combination with machine learning classifiers. Current investigations on CMS methods for journal bearings using acoustic measurement methods are limited to component level applications. A condition monitoring methodology for wind turbine gearbox journal bearings does not currently exist. A major challenge for CMS development for journal bearings in WT gearboxes is the transfer of methods already proven at component level to gearbox applications. In preparation for CMS application at the gearbox level, this paper presents an approach for monitoring different friction conditions of journal bearings based on acoustic measurements at a component test rig. For the classification of the friction state, different machine learning (ML)-based approaches trained on the acquired acoustic measurement data are compared with respect to the achieved classification accuracy. Knowledge of the robustness of the classification method, e.g. with respect to the distance of the sensor to the bearing, provides the necessary basis for the use of the CMS at the gearbox level. The investigations are carried out under operating conditions typical for planetary bearings in wind turbines. Classification performance is evaluated using a validated elasto-hydrodynamic simulation model. The aim of the work is to develop a method that detects friction classes in the journal bearing based on structure-borne sound measurements. Here, simulation results are used to train the algorithms. Finally, the demonstrated method will be successfully applied to a test rig for wind turbine gearbox journal bearing. Based on the results, an ML approach will be selected for application in gearboxes.

Influence of wet wire drawing speed on the brass-plated steel cord properties

Steel cords are a reinforcing phase of the rubber-steel-canvas composite, and their properties, including strength, depend on the quality of the wires. The novelty of the work is a multi-parameter analysis of the cord production process, which showed that there is a relationship between the rheological properties of the lubricating emulsion, the friction conditions and deformation of the brass coating, and the properties of the wires and their resistance to cracking when braiding into a steel cord. It was shown that the friction conditions depend on the wire temperature and the rheological properties of the emulsion. As the drawing speed increases, the emulsion viscosity improves. The grease reaches its optimum at a specific drawing speed depending on the type of emulsion and the type of wire. Further increases in drawing speed result in an increase in temperature at the material/tool interface. This leads to a decrease in the viscosity of the emulsion and the breakdown of the lubricant film in the contact zone. Inappropriate selection of wet drawing speed contributes to a decrease in plastic properties and a reduction in the number of twists and bends of the wire, which leads not only to wire breakage at the stage of cord braiding but also to its premature breaking during the tensile test.

A Review on Galling of Aluminum in Cold Forming Processes

As world’s sustainability become the most influential topic, aluminum and its alloys are becoming the preferred material of the automotive industry because they allow vehicle weight to be reduced without compromising safety. Thus, aluminum has taken its place in the global industry as an alternative material that can be used instead of steel. The main drawback of forming aluminum at room temperature is galling. This phenomena in cold forming of aluminum not only affect the quality of the produced parts but also the lifespan of production tools. This paper reviews the galling of aluminum alloys during bulk and sheet cold forming processes along with friction conditions. The available testing methods in order to simulate the actual cold forming process are introduced. Effect of process parameters such as lubrication, tool surface finish and tool coatings are discussed in detail.

Tribological Research of Resin Composites with the Fillers of Glass Powder and Micro-Bubbles.

This study investigates the tribological properties of resin composites reinforced with the fillers of glass powder and micro-bubbles. Resin composites were prepared with varying concentrations from 1% to 5% wt of fillers. Tribological tests were conducted using a block-on-ring scheme under dry friction conditions. The measurements of friction coefficient and wear values were performed under variable rotation speeds and loading conditions. The study showed that resin composites with 2-3% glass powder fillers and resin composites with 3-4% micro-bubbles exhibited optimal tribological properties. The resin glass powder modifications reduce the wear by 63% and resin micro-bubbles reduce wear by 32%. SEM analysis of the surfaces revealed surface imperfections and structural damage mechanisms, including abrasive and fatigue wear. The study concludes that specific filler concentrations improve the friction and wear resistance of resin composites, highlighting the importance of material preparation and surface quality in tribological performance. The increased wear resistance on both composites would hopefully expand the usage of additive manufactured composite, namely industrial moving components such as polymer gear, wheel, pulley, etc.