Friction Coefficient Research Articles

INFLUENCE OF PLASMA ELECTROLYTIC OXIDATIONPARAMETERS ON TRIBOLOGICAL PROPERTIES OF LAYERSPRODUCED ON AZ31B MAGNESIUM ALLOY

The article discusses the effect of Plasma Electrolytic Oxidation (PEO) on the tribological properties of oxidelayers produced on the AZ31B magnesium alloy. The layers were formed using PEO (AC+DC) in an alkalineelectrolyte with a current density of 10 A/dm. The oxidation parameters (process time, cathodic voltage) wereselected based on a research plan. The tribological properties of the samples were tested on a T-17 tester in apin-on-plate test under technically dry friction conditions, using a pin made of PEEK-HPV polymer. The testsallowed the determination of the coefficient of friction, linear wear, and changes in the mass of the sampleand pin. Profilometric measurements were also made before and after the friction process. An increase in theoxidation time and cathodic voltage led to an increase in the thickness and roughness of the oxide layer. Thesample oxidized under the highest parameters exhibited the greatest thickness, as well as the highest amplitudeand Abbott–Firestone bearing ratio parameters. It was found that with increasing process time and cathodicvoltage, the coefficient of friction (μ) and polymer pin wear increased. Sample C, which had the highestprocessing parameters, showed the best tribological properties, with a coefficient of friction of 0.253 and a linearwear of 0.057 mm. Due to friction, a significant amount of opaque tribofilm was deposited on sample C, resultingin the highest mass wear of the pin (5.33 mg) and an increase in the mass of the sample by 0.74 mg.

INFLUENCE OF CONTACT TIME WITH LUBRICANTON POLYMER-POLYMER SLIDING PAIR INTERACTION

This paper presents tribological investigations of pairs of same-type construction polymers: PET, PA6, andPOM, which for different durations were in contact with a lubricant. Hydraulic oil HLP 68, used for heavilyloaded drive systems, was the lubricant. Test samples were subjected to storage in this lubricating mediumfor different lengths of time: ranging from no storage to 2 weeks of storage. The static friction coefficient,which has a significant bearing on the startup of systems, was studied. Furthermore, investigations aimed atidentifying the phenomena involved in the interaction of the polymer-polymer sliding pair were carried out.The duration of the storage of the polymeric materials in the lubricating medium has been found to have avisible effect on static friction coefficient values and surface hardness and condition.

Aloe Vera as a Printed Coating to Mitigate the Wear of Textiles

Aloe vera is well known for its biological properties as a bioflavonoid anti-inflammatory and antibacterial agent. It has been used frequently in the food sector as a food coating due to its hygroscopic properties and as an ingredient in the lucrative cosmetic industry. Studies have also included aloe vera as an eco-friendly green solution based on these properties. The current research focuses on the use of aloe vera gel in printing pastes as an alternative sustainable solution to synthetic thickeners, evaluating its wet performance and ease of fabric stitching, and has been inspired by studies that similarly used this substance and measured its effect on the fabric’s coefficient of friction and antimicrobial action. In the current study, printing pastes with natural colourants, such as saffron, curcumin, and annatto, and aloe vera gel thickener derived from natural leaves from Crete increased the fabric’s mechanical resistance to abrasion compared to the untreated pastes. The measured performance did not differ substantially from prints with traditional synthetic pastes, hence tolerating the substitution with the non-contaminant variant. The enhanced resistance to abrasion and wear extends the fabric’s serviceable life and resulting garments, decreasing the need for high industry processing volumes and, as a result, reducing pollution. The resistance to wear was evaluated using the dominant method in textile testing of the Martindale apparatus, which measured the cycles to failure, weight loss, and general appearance deterioration using the official photographic standards.

Benchmarking numerical simulation of induced fault slip with semi-analytical solutions

AbstractPore pressure fluctuation in subsurface reservoirs and its resulting mechanical response can cause fault reactivation. Numerical simulation of such induced seismicity is important to develop reliable seismic hazard and risk assessments. However, modeling of fault reactivation is quite challenging, especially in the case of displaced faults, i.e., faults with non-zero offset. In this paper, we perform a systematic benchmarking study to validate two recently developed numerical methods for fault slip simulation. Reference solutions are based on a semi-analytical approach that makes use of inclusion theory and Cauchy-type singular integral equations. The two numerical methods both use finite volume discretizations, but they employ different approaches to represent faults. One of them uses a conformal discrete fault model (DFM) while the other employs an embedded (non-conformal) fault model. The semi-analytical test cases cover a vertical frictionless fault, and inclined displaced faults with constant friction and slip-weakening friction. It was found that both numerical methods accurately represent pre-slip stress fields caused by pore pressure changes. Moreover, they also successfully cope with a vertical frictionless fault. However, for the case with an inclined displaced fault with a constant friction coefficient, the embedded method can not converge for the post-slip phase, whereas the DFM successfully coped with both constant and slip-weakening friction coefficients. In its current implementation, the DFM is therefore the model of choice when accurate simulation of local faulted systems is required.

Effect of load and pulling speed on the static coefficient of friction of cross-country skis on snow

Effect of load and pulling speed on the static coefficient of friction of cross-country skis on snow

Mitigating Low-Speed Crawling and Jitter in Telescopic Hydraulic Cylinders through Stick-Slip Dynamics Analysis and Friction Reduction Strategies

Abstract This study investigates the mechanisms of jittering in telescopic cylinders and proposes effective mitigation strategies. The focus is on the dynamic behavior of hydraulic cylinders under low-speed conditions, particularly the stick-slip phenomenon. Through finite element analysis using Abaqus and tribological tests, the impact of various factors on the friction and wear properties of cylinder components is examined. Findings reveal that optimizing the average friction coefficient, stick-slip amplitude, and stick-slip time can significantly reduce jitter and creep in hydraulic cylinders. The results provide valuable insights for improving the performance and longevity of hydraulic systems in engineering machinery.

Analysis of Water Film Distribution and Aerodynamic Performances of High-Speed Train Under Rainfall Environment

AbstractThe current research on the aerodynamic performance of the train running in rainy weather is primarily concerned with the trajectory of the raindrops and the aerodynamic variation of trains caused by raindrops. In fact, water film will generate on the train body when raindrops hit the train, which interacts with the flow field around the train, and would probably affect the aerodynamic performance of the train. In this paper, based on shear stress transport (SST) k-w turbulence model and Euler-Lagrange discrete phase model, the aerodynamic calculation model of a high-speed train under rainfall environment is established. The LWF (Lagrangian wall film) is used to simulate the water film distribution of the high-speed train under different rainfall intensities, and the aerodynamic performance of the train are studied. The calculation results show that raindrops will gather on the train surface and form water film under rainfall environment. With the extension of rainfall time, the thickness and coverage range of water film expand, and the maximum thickness of water film can reach 4.95 mm under the working conditions in this paper. The average thickness of water film on the train body increases with the rainfall intensity. When the rainfall intensity increases from 100 mm/h to 500 mm/h, the average water film thickness will increase by 3.26 times. The velocity of water film in the streamlined area of head car is larger than that in other areas, and the maximum velocity is 22.14 m/s. Compared with the rainless environment condition, the skin friction coefficient of the high-speed train increases and the average value will increase by 10.74% for a rainfall intensity of 500 mm/h. The positive pressure and resistance coefficient of the head car increase with the rainfall intensity. This research proposes a methodology to systematically analyze the generation of water film on the train surface and its influence on the train aerodynamic performance; the analysis can provide more practical results and can serve as a reference basis for the design and development of high-speed trains.

Slip Resistance (Friction) and Safe Walk Characteristics of Selected Shoe Soles on Floor Tiles in Nigeria

Slip-related accidents represent a significant public safety concern, particularly in environments where flooring may be exposed to various contaminants. This research investigates the slip resistance characteristics of selected shoe soles on different types of local floor tiles, employing the British Pendulum Tester (BPT) under diverse conditions, including: dry, sandy, wet, soapy, and oily surfaces. The study aims to provide quantitative data on friction coefficients to comprehensively assess the performance of different shoe sole and tile combinations. The results indicate varying levels of slip resistance across the tested combinations, with some shoe soles demonstrating superior performance under specific conditions. For instance, Poly-Urethane soles consistently showed higher friction coefficients in both dry and contaminated conditions, suggesting their suitability for environments prone to slip hazards. Conversely, certain tiles exhibited lower slip resistance when exposed to water and oily substances, highlighting the need for careful selection of both footwear and flooring materials in safety-critical applications. The findings underscore the importance of considering environmental factors in evaluating footwear performance, providing practical implications for improving safety standards in public and private spaces. The data generated from this research can inform recommendations for better footwear design, floor tile selection, and maintenance practices to mitigate slip hazards effectively. This study emphasizes the significance of evidence-based approaches in enhancing slip resistance standards, advocating for ongoing research and industry collaboration to ensure continuous improvement in safety protocols.

Macroscale Superlubrication Achieved with Shear-Thinning Semisolid Lubricants.

Macrosuperlubric materials are pivotal for reducing friction and wear in engineering applications. However, current solid superlubricants require intricate fabrication and specific conditions (e.g., vacuum or inert atmospheres), while liquid superlubricants are prone to creep, leakage, and corrosion. Here, a novel semisolid subnanometer nanowire (SNW) superlubrication material based on the shear-thinning effect is introduced to overcome these challenges. The SNWs achieve an exceptionally low friction coefficient (0.008-0.009) with silicon nitride (Si3N4) and polytetrafluoroethylene (PTFE) tribo-pairs, demonstrating a brief running-in period (≈39 s) and stable superlubrication over extended friction (12 h, >120000 cycles). The combination of the shear-thinning network structure mechanism, the adsorption membrane mechanism, and hydrodynamic effects provides a synergistic effect, playing a crucial role in achieving superlubricity. Additionally, SNWs can be combined with various base oils to create semisolid gel lubricants with superlubricating properties. This innovative approach addresses the limitations of current superlubrication systems and introduces a new category of semisolid gel lubricants, significantly expanding the applications of superlubrication materials.

Influence of dynamic complexity on serial robots with joint clearance based on a nonlinearity measure

Conditional monitoring and diagnosis of serial robots depend not only on the method used but also on the dynamic complexity of the robotic system itself. Previously, researchers have focused mainly on the analysis of dynamic behaviors with different parameters of a mechanical system with clearance. Although the indicators such as Root Mean Square (RMS), spectrum kurtosis (SK), Entropy have the potentiality to express the specific trend by different parameters, it can be noticed that they mainly depend on the values of the dynamic responses and neglect the information of the nonlinear characteristics in the responses of mechanical systems. In this paper, a nonlinearity measure-based method is proposed to analyze the impact of dynamic complexity on serial robots with joint clearance. The kinetic equations of a serial robot with joint clearance are established by considering the contact forces in the joint. The dynamic model of the robotic system is validated by experiments. A quantization method for dynamic complexity analysis is established based on the nonlinearity measure, and the influences of parameters on the dynamic complexity are analyzed via numerical computations for the validated dynamical models of the robotic system. A relationship is developed among the clearance radius, friction coefficient, and dynamic complexity. This shows that a larger clearance radius will lead to a more complex system and that friction coefficients within a certain range can reduce the dynamic complexity of the system. These results can guide methodological choices for condition monitoring and diagnosis of serial robotic systems.

Investigation on tribo‐properties of twaron pulp‐reinforced brake friction composites

AbstractDetermining the appropriate formulation in designing and developing brake friction materials is one of the most complex tasks. This study investigates the synergistic effect and optimization of twaron fiber on the fade and recovery performance of brake friction composites. For this purpose, a series of friction materials containing varying amounts of twaron between 1 and 9 wt% were developed, and their characterization and tribo evaluation were carried out. The tribo performance of the composites was evaluated in a Krauss‐type friction test machine in line with the ECE R90 procedure in terms of their fade and recovery behaviors. It was noted that the fade‐recovery friction response of composites was affected when fiber is added; that is, an increase in fiber content improved the fade performance, friction fluctuations decreased, and a higher recovery response was observed. The fade and average coefficient of friction were found to be the main determinants, while recovery was found to be the stabilizer. Analytical hierarchy process (AHP) was used to determine the priority of importance of criteria in the performance evaluation, and VIKOR (multi‐criteria optimization compromise solution) was used for ranking evaluation. The formulation with a concentration of twaron 7 wt% was found to have exhibited an optimal braking performance. The worn surfaces scanning electron microscope (SEM) study confirms the general friction and wear mechanisms of friction layers with fiber content.Highlights Development of twaron pulp‐reinforced eco‐friendly brake friction composites. Use of MCDM approach in the development of BFCs for braking applications. VIKOR optimization positioned 7 wt% twaron‐addition BFC as the optimal choice. It was observed that fiber amount is effective on the behaviors of composites.

Enhancement of friction and wear performance of polytetrafluoroethylene composites through the synergistic effect of hard fillers

AbstractThe Stirling engine is a high‐efficiency externally heating piston engine. The self‐lubricating properties of polytetrafluoroethylene (PTFE) are crucial for the operation of Stirling engines. Three PTFE composites filled with different contents of carbon fiber (CF), polyimide (PI) and nano‐zirconia (nano‐ZrO2) were prepared and their mechanical, friction and wear properties were investigated. The results showed that the density of CF‐containing PTFE composites was significantly reduced by 1.46% to 6.9% compared to neat PTFE. Meanwhile, the incorporation of fillers greatly enhanced the hardness by more than 21.4% over the hardness of neat PTFE. In addition, the friction coefficients of three PTFE composites were lower than those of neat PTFE, and the wear rate of these composites was three orders of magnitude lower than that of neat PTFE. In particular, the wear rate of PTFE filled with CF and PI at high pressure (2 MPa) and high velocity (4 m/s) was only 1.24 × 10–6 mm3/Nm. The wear morphology was also analyzed by scanning electron microscopy and energy‐dispersive x‐ray spectroscopy. It was found that the addition of CF and PI in PTFE has the most pronounced improvement on tribological performances. The synergistic effect of CF's mechanical reinforcement and PI's adhesive properties reduces the wear of the matrix, resulting in excellent wear resistance of PTFE composites.Highlights The compressive strength of PTFE was reinforced by CF and nano‐ZrO2. CF can lower the density and significantly enhance hardness of PTFE. Synergistic CF and PI enhance PTFE composites' friction & wear performance. Adhesive fillers & debris size key to forming uniform continuous transfer films.

Reversible and controllable reduction in friction of atomically thin two-dimensional materials through high-stress pre-rubbing.

Great efforts have been made to further reduce friction of atomically thin two-dimensional (2D) materials as solid lubricants due to their exceptional tribological properties and mechanical strength. In this work, the friction of atomically thin graphene is extensively and controllably reduced through pre-rubbing under high stress, resulting in a reduction of the friction coefficient by up to a factor of six compared to the pristine graphene. Also, this reduction can be reversed by reciprocating friction under moderate stress. Furthermore, high-stress pre-rubbing allows for patterning intentionally lubricating features on atomically thin graphene, such as nanometer-sized letters. This reduction in friction is attributed to the decreased sliding potential barrier yet increased contact stiffness, induced by the enhanced strength of graphene adhesion to the substrate due to interfacial charge transfer, as revealed by density functional theory (DFT) calculations. These findings present a practical methodology for optimizing and controlling the performance of 2D materials.

Use of Electrospun Cellulose Acetate/Silica Composites as Multifunctional Ingredients in Eco‐Friendly Semisolid Lubricant Formulations

ABSTRACTCellulose acetate/silica (CA/SIL) nanocomposites are prepared by electrospinning and investigated as multifunctional ingredients in eco‐friendly semisolid lubricant formulations. The structuring ability of these electrospun composites in castor oil and the antifriction and antiwear properties are examined through rheological and tribological experiments. The multifunctionality of CA/SIL composites arises from a balance between the silica content and the formation of nanofiber‐dominated structures. The linear viscoelasticity functions in the oleo‐dispersions increase by several orders of magnitude with both the spinning solution concentration and the CA:SIL ratio. However, the rheological response primarily depends on the morphology of the nanofiber mat obtained, specifically nanofiber diameter and the presence of beads. In contrast, the silica content significantly impacts the tribological performance of the oleo‐dispersions regardless of nanofiber morphology. For similar nanoarchitectures and rheological responses, the friction coefficient is reduced from 0.227 to 0.108 by incorporating silica in a 10:1 CA:SIL ratio, compared with the SIL‐free electrospun CA nanofibers, while wear is completely prevented. Increasing the composite concentration from 5 to 12.5 wt. % enhances wear protection and the gel strength of oleo‐dispersions, for example, the plateau modulus rises from 800 to 42,000 Pa using a composite with a 10:1 CA:SIL ratio.

Oleylamine-grafted carbon nanoparticles as the friction-reducing and anti-wear additives of aviation lubricating oils

Purpose This paper aims to try to develop new, environmentally friendly and efficient lubricating additives; study the compatibility of carbon-based additives with different base oils [Polyalphaolefin (PAO)-3, PAO-20 and NPE-2]; and explore the lubrication mechanism. Design/methodology/approach Oleylamine modified carbon nanoparticles (CNPs-OA) were prepared and the dispersion stability of CNPs-OA in PAO-3, PAO-20 and NPE-2 base oils was investigated by transmission electron microscopy, Fourier transform infrared, thermogravimetric analysis, energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Universal Mechanical Tester (UMT) platform was used to carry out experiments on the effects of different additive concentrations on the lubricating properties of base oil. Findings The mean friction coefficient of PAO-3, PAO-20 and NPE-2 reduced by 32.8%, 10.1% and 11.4% when the adding concentration of CNPs-OA was 1.5, 2.0 and 0.5 Wt.%, respectively. Generally, The CNPs-OA exhibited the best friction-reducing and anti-wear performance in PAO-3. Originality/value The agglomeration phenomenon of carbon nanoparticles as lubricating additive was improved by surface modification, and the lubricating effect of carbon nanoparticles in three synthetic aviation lubricating base oils was compared.

Artificial intelligence neural network and fuzzy modelling of unsteady Sisko trihybrid nanofluids for cancer therapy with entropy insights.

The main objective of the current endeavor is to monitor hypothetical processes utilizing a Sisko tri-hybrid fluid over a rotating disk with entropy generation suspended in Darcy-Forchheimer porous medium. Electro Magneto Hydro Dynamics (EMHD), non-linear thermal radiation and exponential and thermal- space dependent heat source/sink coefficients are considered with the intent of conceiving an Runge-Kutta-Fehlberg method with shooting procedures integrated with a combination of an Adaptive Neuro-Fuzzy Inference System (ANFIS) and Reptile Search Algorithm (RSA). Then, ANFIS-RSA, is used to predict the Nusselt number, skin friction co-efficient in radial and tangential velocities. Reliable self-similarity variables have reduced a non-linear partial differential set of equations into an ordinary differential equation. According to the empirical evidence, Sisko fluid parameter rises the radial velocity whereas for magnetic field and Darcy-Forchheimer the azimuthal and axial velocities visualizations decreasing trend, respectively. The entropy generation and Bejan number rises for electric and radiation effects. Also, ANFIS-RSA indicates that the model attained a high level of precision in terms of radial velocity (98.13%), tangential velocity (98.18%) and Nusselt number (98.91%). Thus, the longer rendering of the nanoparticles used here might, makes them potentially helpful for regulating the therapeutic impact in the management and treatment of cancer.

Energy Loss in Frictional Hertzian Contact Subjected to Two-Dimensional Cyclic Loadings

We investigate the effect of three different harmonically varying loads as a function of the friction coefficient on energy loss in a three-dimensional discrete uncoupled frictional contact problem. Three loading cases include (1) a normal force is constant and a tangential force varies, (2) normal and tangential forces both vary, but the loading and unloading curves are identical, and (3) normal and tangential forces both vary, but the loading and unloading curves are different. For a higher coefficient of friction, three loading cases show different characteristics. If a normal force is constant and a tangential force varies, there is always some slip, but dissipation tends asymptotically to zero at large coefficient of friction. If normal and tangential forces both vary, but the loading and unloading curves are identical, there is no slip and no dissipation above a critical coefficient of friction. If the loading and unloading curves are different, dissipation occurs for all values of the coefficient of friction, and we expect that the dissipation is asymptotic to the relaxation damping value as the coefficient of friction approaches infinity. For lowering coefficient of friction, the three loading cases show similar behavior. Dissipation increases and reaches a maximum just before a state where gross slip is possible.

Generation mechanism and anti-friction effect evaluation of continuous micro-groove texture machined by ball-end milling process

Abstract The tool path in ball-end milling process is flexible and controllable considering the structure characteristics and moving way of the cutter. This paper aims to reveal the generation method of continuous surface micro-groove texture by using ball-end milling process and evaluate the corresponding anti-friction performance by combining simulation and friction experiments. Results indicate that continuous micro-grooved surface texture can be obtained by combining small feed per tooth and large radial cutting depth. Radial depth of cut and tool radius affect aspect ratio of micro-groove. The bearing capacity of the oil film shows an increasing and then decreasing trend with the increase of radial depth of cut and orientation angle. Radial depth of cut increased from 0.1 mm to 0.3 mm, resulting in a maximum 4.87% increase in the bearing capacity of oil film because of the enhanced wedge effect. However, further increase in radial depth of cut leads to increased vortex, weakening the wedge effect. The oil film bearing capacity is reduced so that the friction coefficient increases by a maximum of 510%. Moreover, as the orientation angle increases from 10° to 20°, the bearing capacity of the oil film increases by 22.7%. The minimum friction coefficient currently is 0.0215. However, when the micro-groove orientation angle is further increased, the countercurrent effect is enhanced and the dynamic pressure effect is weakened, which finally leads to a decrease in the bearing capacity of the oil film. The friction coefficient has increased by 30.2% maximum. This study is of great significance which provides a new method for guiding the friction reduction on the die surface.

An Investigation on the High-Temperature Stability and Tribological Properties of Impregnated Graphite

Impregnated graphite is a common material for friction pairs in aeroengine seals, especially at high temperatures. For the convenience of the application of graphite materials in aeroengines, an SRV-4 tribometer and a synchronous thermal analyzer are employed to study the tribological properties and thermal stability of pure, resin-impregnated, metal-impregnated, and phosphate-impregnated graphite against stainless steel from room temperature to 500 °C. The results indicate that impregnations can improve the wear resistance and thermal stability of graphite at high temperatures. Compared with other impregnated graphite materials, the resin-impregnated graphite shows a good friction coefficient and poor wear rate and thermal stability over 300 °C, due to the degradation and oxidation of the resin-and-graphite matrix. The metal- and phosphate-impregnated graphite materials exhibit excellent wear resistance and thermal stability under 500 °C as a result of the protection of the impregnations, while the average friction coefficient of the metal-impregnated graphite is much greater than the phosphate-impregnated graphite, and even reaches 2.14-fold at 300 °C. The wear rates for the graphite impregnated with resin, metal, and phosphate are 235 × 10−7, 7 × 10−7, and 16 × 10−7 mm3N−1m−1 at 500 °C, respectively. Considering all aspects, the phosphate-impregnated graphite exhibits excellent tribological properties and thermal stability.

On the Influence of Microstructure and Properties of Direct Laser Deposited 50Cr6Ni2Y Coatings with Different TiC Contents

Three 50Cr6Ni2Y + x wt.% TiC (x = 1.5, 3.0, 4.5) alloy steel coatings were prepared using direct laser deposition (DLD) technology. The microstructure, microhardness, and wear resistance of DLD samples were studied. The results indicate that DLD coatings were composed of α-Fe (Fe-Cr-Ti), γ-Fe (Fe-Ni), and TiC. When the added TiC content was 3.0 wt.%, the DLD coating without cracks was fabricated, and TiC particles were well embedded in the sample. In addition, the coating demonstrated the best performance, with a microhardness of 758 ± 23.3 HV0.2, an average friction coefficient of 0.58, and a wear rate of 0.37 %. The addition of an appropriate amount of TiC as a reinforcing phase, on the one hand, had played a role in the second phase strengthening. On the other hand, the diffusion interfaces formed between TiC particles and the matrix allowed some Ti elements to melt into the matrix and formed a solid solution, playing a role in solid solution strengthening. The results could provide a reference for the preparation and repair of laser additive manufacturing high-performance wear-resistant parts.