Variation Of Friction Coefficient Research Articles

Influence of oil-water mixing conditions on the friction and wear performance of ship tail-bearing materials

This study addresses the lubrication challenges posed by oil-water mixtures that arise when vessels encounter adverse maritime conditions, including collisions, grounding, and reefing, which can lead to failures in lubrication systems during navigation. The research focuses on three representative ship tail-bearing composites: polymer material(K4), thordon material(SR), and tenmat material(FR). Various volume fractions of oil-water mixtures were prepared, and the rheological properties of these mixtures were examined using a rotational rheometer (MCR102). Additionally, the variation of friction coefficients of the composites about load and linear velocity under different oil-water mixtures was analyzed using a Ring-Block Friction and Wear Testing Machine. Following the experiments, the surface morphology of the composites was assessed, and the wear mechanisms were analyzed using a laser interferometric surface profiler (LI-type), a confocal laser microscope (CLSM), and a scanning electron microscope (SEM). The findings indicate that, under all lubrication conditions, the friction coefficients of the three materials exhibit a gradual decrease with increasing load and linear velocity.Furthermore, the wear of the materials initially increases and then decreases with rising oil content, with higher oil concentrations in the oil-water mixture correlating with reduced wear. The study reveals that the three materials experience significant abrasive and adhesive wear under adverse oil-water mixing conditions. This research offers valuable insights for developing friction substitutes for oil-water mixing bearings in specialized operational environments and guides the design of friction components in such bearings.

Electrotunable superlubricity of two-dimensional ZIF-8

Electric field control can actively, dynamically, and repeatably influence the interface friction behavior. The unique properties of two-dimensional (2D) ZIF-8 make it a promising lubricating material for electromechanical devices. The study on the electrotunable superlubricity of 2D ZIF-8 is carried out under longitudinal and transverse electric fields respectively, resulting in an order of magnitude variation in friction coefficient (μ: 0.0037–0.0124). Through the experiments and simulation, the regulation mechanism of electric fields on the lubricating properties of 2D ZIF-8 is attributed to the coupling effect of adhesion regulation and out-of-plane deformation regulation: The weakening of anchoring effect reduces the adhesion between probe and 2D ZIF-8; the tight binding of interfacial charge under longitudinal electric field as well as the increase in surface stiffness caused by lattice tension under transverse electric field, both restrain the out-of-plane deformation during friction. The electrotunable superlubricity of 2D ZIF-8 helps achieve rapid and flexible adjustment of the friction interface in electro-mechanical systems under charged conditions, illuminating the future development prospects for intelligent control.

A comprehensive investigation into the effect of vertical component of ground motion on response of sliding unanchored blocks

This study aims to quantify the effect of the vertical component of ground motion on the seismic response of sliding rigid blocks, in terms of maximum and residual displacements. A multi-stripe analysis approach is employed to examine the response with and without the vertical component under various levels of ground motion intensity. First, a parametric study is conducted using a Coulomb friction model with a constant coefficient of friction that does not account for any dependence of the friction coefficient on velocity or pressure. It is shown that the effect of the vertical component on maximum and residual displacement is more pronounced for ground motions that can barely initiate sliding. Moreover, the influence of the vertical component on the residual sliding displacement is higher than that on the maximum displacement. Subsequently, to account for the friction coefficient dependence on pressure and sliding velocity, two interface cases (steel-steel, and concrete-concrete) are analyzed. It is found that even when a variable coefficient of friction is used, the overall trends observed for a constant coefficient of friction do not change.

Effect of the infill percentage of 3D printed Polyetheretherketone under the dry sliding condition

Sliding bearings made of advanced polymers like Polyetheretherketone (PEEK) are preferred for medium and heavy-duty applications. The high-temperature additive manufacturing process permits the efficient fabrication of lighter porous parts using high-cost materials like PEEK. Customised geometries and surface features are easily achievable using an additive manufacturing process and facilitate design for the required performance. The 3D-print parameters employed affect the surface characteristics and are investigated. The variation in infill porosity is found to affect the crystallinity, hardness, modulus, and surface roughness of the printed samples. The friction coefficient variation, wear resistance, and temperature rise in the 3D-printed PEEK samples are studied when slid against steel discs under dry sliding conditions. The material transfer between surfaces varies based on the sample's surface properties and porosity, significantly affecting friction and wear behaviour. Accumulation and strong adhesion of wear debris in the groves of PEEK samples contribute to improved wear resistance. The temperature rise in the polymer sample also depends on the infill porosity, and a reduced temperature rise is observed in porous samples, which will improve the life when used in bearings.

Evolution of Lubrication Characteristics of Double-Nut Ball Screws Based on an Efficient Surface Roughness Modeling Method

Abstract Accurate prediction of lubrication characteristics, specifically film thickness and pressure distribution, is pivotal for ensuring optimal performance in ball screws. Despite its significance, there is a notable dearth of studies investigating the evolution of lubrication characteristics resulting from the changing surface roughness over prolonged operation of ball screws. Furthermore, obtaining the surface roughness of ball screws poses a challenge due to the limited loading capacity of measurement instruments. Traditional methods involving cutting the screw for surface roughness measurement are impractical for continuous monitoring during extended operation. To address this issue, the present study introduces an efficient approach to model the surface roughness of the raceway in double-nut ball screws. A profilometer is employed to measure profile roughness along two directions (parallel and perpendicular to the rolling direction) without the need to cut the screw raceway. The 2D power spectral densities and height probability densities of profile roughness are calculated to model the surface roughness, and the synthesized data are utilized to solve the Reynolds equation. The simulation method is validated through friction torque tests, demonstrating a calculation accuracy exceeding 92%. The study further explores the evolution of film thickness and pressure distribution in double-nut ball screws during running-in and steady wear stages, revealing severe asperity contact in the two nuts. Additionally, variations in load ratio, friction coefficient, and film thickness ratio (λ) are investigated. Considering the load ratio and λ of the slave nut, it can be inferred that boundary lubrication persists in the two nuts throughout the operation.

Numerical investigation on effects of swirl and offset ratio on hydro-thermal transport phenomena and irreversibility generation of turbulent jet flow

The combined influence of offset jet and imposition of swirling motion is crucial because many macro-level electronic devices and heat exchanger systems involve such types of configuration. The mutual impact of the offset ratio and swirl number along with a range of Reynolds numbers is taken into account to briefly discuss the primary laws (first and second) of thermodynamics associated with the prescribed problem. An open channel with variable nozzle height is assumed under forced convective flow conditions. The flow physics associated with the prescribed problem has been solved numerically with an improvised [Formula: see text] turbulent (shear stress transport) model. The intricate interplay between the swirl intensity and the offset upon the thermal and entropy generation characteristics has been revealed in the average Nusselt number, local variation of skin friction coefficient, and total entropy generation by varying the distinct embedded control parameters. The results indicate that a higher range of Reynolds number leads to a high value of average Nusselt number unrelatedly of swirl number and offset ratio. However, the improvement of thermal performance does not depend only upon the heat transfer characteristics but also the total irreversibility should be optimized. In that regard, a swirl ratio of 0.5 with an offset ratio of 3 provides optimized configurations irrespective of all other parameters.

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.

A New Method to Estimate and Predict the Variation of Dry Friction Coefficient in Ultra-Long Distance Rock Pipe Jacking: A Case Study in Guanjingkou

A New Method to Estimate and Predict the Variation of Dry Friction Coefficient in Ultra-Long Distance Rock Pipe Jacking: A Case Study in Guanjingkou

Forward and Inverse Modeling of Ice Sheet Flow Using Physics‐Informed Neural Networks: Application to Helheim Glacier, Greenland

AbstractPredicting the future contribution of the ice sheets to sea level rise over the next decades presents several challenges due to a poor understanding of critical boundary conditions, such as basal sliding. Traditional numerical models often rely on data assimilation methods to infer spatially variable friction coefficients by solving an inverse problem, given an empirical friction law. However, these approaches are not versatile, as they sometimes demand extensive code development efforts when integrating new physics into the model. Furthermore, this approach makes it difficult to handle sparse data effectively. To tackle these challenges, we use the Physics‐Informed Neural Networks (PINNs) to seamlessly integrate observational data and governing equations of ice flow into a unified loss function, facilitating the solution of both forward and inverse problems within the same framework. We illustrate the versatility of this approach by applying the framework to two‐dimensional problems on the Helheim Glacier in southeast Greenland. By systematically concealing one variable (e.g., ice speed, ice thickness, etc.), we demonstrate the ability of PINNs to accurately reconstruct hidden information. Furthermore, we extend this application to address a challenging mixed inversion problem. We show how PINNs are capable of inferring the basal friction coefficient while simultaneously filling gaps in the sparsely observed ice thickness. This unified framework offers a promising avenue to enhance the predictive capabilities of ice sheet models, reducing uncertainties, and advancing our understanding of poorly constrained physical processes.

A study on the effects of hybrid (SIC- PSSA) nano sized reinforcement on mechanical and tribological behaviour of Al alloy-based metal matrix composite produced by ultrasonic assisted stir casting

This study focuses on the effects of hybrid reinforcement consisting of nanosized particles of Palm Sprout Shell Ash (PSSA) and silicon carbide (SiC) on the mechanical and tribological properties of the Al-Cu-Mg alloy. Hybrid reinforced composites with different weight percentages of SiC and PSSA (0:0, 0:4, 1:3, 2:2, and 4:0 wt%) were prepared using the ultrasonic-assisted bottom-poured stir casting technique. Scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) were used to characterize the hybrid composite made of Al-Cu-Mg alloy. The optical and SEM microstructural analyses demonstrated an even distribution of SiC and PSSA nano size reinforcements within the matrix. The EDS analysis revealed SiC and PSSA reinforcement particles in the composite. The mechanical properties (tensile, flexural, and impact strength) and wear properties (wear rate and coefficient of friction) of the composites and alloys were evaluated according to the ASTM standards. The hybrid reinforced composites outperformed the base alloy. Among all composites, the 2:2 wt% SIC and PSSA hybrid reinforced composites exhibited a significant enhancement in both tensile and flexural strength, with a 29.15% and 27.64% increase in strength, respectively. However, the inclusion of these reinforcements led to a reduction in the ductility and impact strength of the Al-Cu-Mg alloy composite. The 0:4 wt% SiC- and PSSA-reinforced composites experienced the largest reductions in ductility and impact strength, with decreases of 47.67% and 3.56%, respectively. For the 2:2 wt% SiC and PSSA composites, these reductions were 23.64% and 3.16%, respectively. The SEM analysis of the fractured surfaces of the composites tested for mechanical properties revealed evidence of both ductile and brittle fracture mechanisms in the tensile, flexural, and impact tests. The wear behaviour of the prepared samples was evaluated, and all composites exhibited superior performance compared with the base alloy, demonstrating adhesive and abrasive wear mechanisms and varying friction coefficients. Among all the composites, the 2:2 wt% SiC- and PSSA-reinforced composites exhibited high wear resistance and a lower coefficient of friction than the other fabricated composites.

Effect of the dynamic contact angle on electromagnetically driven flows in free liquid films

We study the effect of a dynamic contact angle on an electromagnetically driven flow in a horizontal free electrolyte film stretched between two coaxial cylindrical electrodes and placed in a uniform magnetic field. The flow dynamics and film deformation are described using the reduced hydrodynamic model derived in the lubrication approximation in [A. Pototsky and S. A. Suslov, J. Fluid Mech., 984, A75 (2024)]. The linearized molecular kinetic model is used to relate the dynamic and static contact angles to the wetting-line friction coefficient. Steady azimuthal flow is found for arbitrary static contact angles. Linear stability of the base azimuthal flow with respect to azimuthally invariant perturbations is studied using the numerical continuation method. We find that the flow stability is highly sensitive to variations of the wetting-line friction coefficient and the static contact angle. The least stable azimuthal flow is found for the frictionless contact line corresponding to a free film that remains perpendicular to the surface of the electrodes. The azimuthal flows are found to experience a supercritical Hopf bifurcation upon which they transition to a stable oscillatory dynamic regime characterized by alternating squeezing and swelling of the film near the inner and outer electrodes.

Simulations of Texture Evolution in the Near-Surface Region During Aluminum Rolling

Prediction of texture changes during cold rolling is important because they affect the recrystallization and anisotropy of an aluminum sheet during successive forming steps. During cold rolling of aluminum alloys, the through-thickness textural change in the subsurface layer depends heavily on the shear stresses exerted on the material. The intensity of this shear stress is determined by the value of and change in the coefficient of friction as the contact length between the rolls and metallic sheet changes. The quality of the texture prediction under constant and variable coefficients of friction are assessed for three established texture models: the grain interaction (GIA) model, the viscoplastic self-consistent (VPSC) approach, and the full-field crystal plasticity Düsseldorf Advanced Material Simulation Kit (DAMASK) code. The simulation results are compared with subsurface layer textures obtained from conducting experimental cold-rolling trials on an aluminum alloy, which are designed to maximize shear in a single rolling pass. The formulation of a variable coefficient of friction is crucial for ensuring both the reasonable prediction of rolling forces and changes in texture. GIA and DAMASK yield the best texture prediction results for a variable coefficient of friction model.

Performance-based seismic design of sliding gusset plate braced frames incorporating thermodynamic models

A sliding gusset plate braced frame (SGBF) is proposed to enhance the seismic resilience of steel concentrically braced frames (CBFs). The symmetric friction connection (SFC) is used at the brace-to-gusset plate connection to create a sliding gusset plate brace. The sliding gusset plate brace offers high initial stiffness to withstand wind and service level earthquake loads. It also absorbs energy through friction beyond service level earthquakes, which mitigates performance degradation caused by brace buckling. Besides, replaceable links are added to the beam ends where plastic hinges are anticipated to form, creating a dual system that allows for damage control and rapid repair. The paper first presents the design concepts and performance objectives of SGBFs. Subsequently, a thermodynamic model is established to reveal the energy–temperature–coefficient of friction (CoF) (E-T-μ) relationship based on quasi-static tests of SFCs. The model partially tackles and addresses the challenge of temperature-dependent variations in CoF during sliding. By incorporating the model into performance-based seismic design, the overstrength ratio of SFC due to temperature-induced hardening can be quantified, according to the energy absorption demand of a specific SGBF during an earthquake. In this manner, unexpected damage and failure of members adjacent to the SFC and sliding gusset plate braces can be avoided. To demonstrate the application of the thermodynamic model and verify the seismic performance of SGBF, a prototype is designed based on a practical four-story hospital and validated through an excessive array of nonlinear dynamic analyses. The results show that the proposed SGBF can achieve the targeted performance objectives under different seismic shaking intensities. In addition, the SGBF has a sufficient margin of safety against collapse. Hence, the proposed SGBF can be used as an efficient and resilient structural system in high seismic zones.

Investigation of friction induced vibrations on a nonlinear two degree of freedom mathematical model and experimental validation

This article investigates the dynamic behavior of a low order nonlinear mathematical model, which is developed based on an existing mass-sliding belt experiment. First, the proposed model is developed with kinematic and friction nonlinearities, and the corresponding governing equations are obtained. Governing equations are then solved numerically for certain operating parameters, and the characteristics of different dynamic responses are investigated. It is observed from the numerical solutions that the dynamic response of the system can be deterministic or chaotic based on the set of operating parameters. Furthermore, the period doubling mechanism is found to be the path from deterministic to chaotic behavior. Second, experiments are performed at a wide range of operating parameters in order to calculate the dynamic friction coefficient, which are used in artificial neural network models for the generation of friction models as functions of operating parameters. It is observed that these operating parameters have significant influence on the variation of the dynamic friction coefficient. Third, the friction models developed with artificial neural network approach are implemented in the nonlinear mathematical model, and numerical solutions are obtained at the same operating parameters. Finally, the numerical results of the low order nonlinear mathematical model are compared to the experimental data, and it is concluded that there is a good correlation between the model predictions and measurements from the perspectives of fundamental frequencies and the characteristics of the dynamic responses. Hence, a better insight about the dynamic response behavior of the mass-sliding belt experiment is achieved through the bifurcation analyses.

Melting heat transfer and irreversibility analysis in Darcy-Forchheimer flow of Casson fluid modulated by EMHD over cone and wedge surfaces

The present mathematical model analyses the melting heat transfer and irreversibility in Darcy-Forchheimer flow of Casson fluids modulated by the electroosmosis and magnetohydrodynamic mechanisms over the wedge and cone surfaces. The effects of thermal radiation, thermal buoyancy and heat generation/absorption are taken into consideration. Appropriate similarity transformations are utilized to establish a system of ordinary differential equations which are non-linear. The model has been numerically simulated using shooting approach in conjunction with the fourth order Runge-Kutta method under the bvp4c tool of MATLAB. Numerical results are computed for fluid velocity, fluid temperature, Nusselt number and Bejan number for analysing the fluid flow behaviour and heat transfer characteristics for the Casson fluid. A comparative analysis is performed to determine the irreversibility and heat transfer in the absence and presence of melting parameters, respectively. Variations in skin friction coefficient, local Nusselt number and Bejan number have also been examined under the effects of key parameters. Key findings of the present study indicate enhanced velocity distribution with increasing zeta potential and electric field parameters, while it diminishes with higher Prandtl number and Forchheimer terms. Moreover, fluid temperature reduces with rising zeta potential, while the Bejan number escalates with greater thermal radiation in the core region of geometries. The findings of the model may be useful in various applications of thermal systems.

Simulation of fretting wear in steel wires under variable coefficient of friction and variable wear coefficient

In this paper, the fretting wear behaviour of steel wires working in coal mining technology is studied numerically. In past studies, the fretting process of steel wires was carried out numerically considering that the coefficient of friction (COF) and wear coefficient (WC) are constant parameters. However, it has been noticed experimentally that COF increases up to a certain number of fretting cycles and then becomes constant, i.e. a steady-state stage, depending on the loading conditions. This increase in COF during the fretting process is also known as the running-up stage. The fretting wear model is modified to evaluate the influence of the varying coefficient of friction (VCOF), which is associated with the variable wear coefficient (VWC), so the influence of VWC is also considered. The subroutine UMESHMOTION used to implement the wear law is also modified to study the effect of VCOF and VWC. Therefore, in this study, the numerical results of a three-dimensional finite element (FE) model are compared, with analytical results of contact area and contact stresses, and with experimental results of peak wear depth. After validating the FE model, the wear scar, the increasing wear depth, wear volume, and the decreasing contact stress with increasing fretting cycles are determined numerically considering VCOF and VWC using cycle jump approach. The energy dissipation effect of frictional force and fretting amplitude is also studied for varying interaction properties of fretting wear models. The numerical simulations are performed by considering both elastic and plastic material properties to analyse the influence of varying interaction properties on fretting wear models at the running-up stage. The results indicate that the VWC model exhibits comparable impacts on both the elastic and plastic models. The results also show that the VWC fretting wear model leads to higher wear scar, wear volume, and wear depth values at the running-up stage as well as at the steady state stage, which are close to the experimental data.

Hybrid modeling prediction of residual stresses in turned Ti6Al4V considering frictional contact

Residual stress plays a pivotal role in assessing the surface quality of machined components, influencing characteristics such as fatigue performance, corrosion resistance, and mechanical strength. Ti6Al4V, a critical material in the nuclear sector, the generation of residual stresses during machining has attracted significant attention. A model for variable friction coefficient model is proposed to accurately characterize the complex plastic deformation behavior of the material. This model takes into account variables such as the relative sliding velocity, contact pressure, and temperature. A subroutine has been developed using the VFRIC interface to enhance precise cutting simulation and modeling. Using the friction model, a new hybrid prediction model for surface residual stresses is developed by integrating finite element analysis and analytical methods. The reliability of both the hybrid and friction models is confirmed through the evaluation of cutting forces, chip morphology, and residual stress. The findings suggest that the novel friction model produces simulation results with higher accuracy compared to traditional Coulomb friction models. The variations in cutting force amount to 5.8% and 13.7%, the error in chip serration is 12.4%, and the deviation in predicting the maximum residual compressive stress is 10.3%. This study contributes to the advancement of friction models and methodologies used in predicting residual stress.

Effects of Proline on Internal Friction in Simulated Folding Dynamics of Several Alanine-Based α-Helical Peptides.

We have studied in silico the effect of proline, a model cosolvent, on local and global friction coefficients in (un)folding of several typical alanine-based α-helical peptides. Local friction is related to dwell times of a single, ensemble-averaged hydrogen bond (HB) within each peptide. Global friction is related to energy dissipated in a series of configurational changes of each peptide experienced by increasing the number of HBs during folding. Both of these approaches are important in relation to future atomic force microscopic-based measurements of internal friction via force-clamp single-molecule force spectroscopy. Molecular dynamics (MD) simulations for six peptides, namely, ALA5, ALA8, ALA15, ALA21, (AAQAA)3, and H2N-GN(AAQAA)2G-COONH2, have been conducted at 2 and 5 M proline solutions in water. Using previously obtained MD data for these peptides in pure water as well as upgraded theoretical models, we obtained variations of local and global internal friction coefficients as a function of solution viscosity. The results showed the substantial role of proline in stabilizing the folded state and slowing the overall folding dynamics. Consequently, larger friction coefficients were obtained at larger viscosities. The local and global internal friction, i.e., respective, friction coefficients approximated to zero viscosity, was also obtained. The evolution of friction coefficients with viscosity was weakly dependent on the number of concurrent folding pathways but was rather dominated by a stabilizing effect of proline on the folded states. Obtained values of local and global internal friction showed qualitatively similar results and a clear dependency on the structure of the studied peptide.

Friction coefficient of sliding isolators in icing conditions

This paper investigates the variation in static friction coefficient of a double curved surface slider (DCSS) due to low temperature exposure. In the experimental campaign, a full-scale DCSS was subjected to displacement controlled cyclic motions after exposure to different temperatures (20, 0 and −20 °C) for different levels of exposure times (3, 12 and 24 hrs). Tests were repeated for several normal stresses (40, 60 and 80 MPa) and maximum loading velocities (250, 500 and 750 mm/s). Force-displacement curves obtained from the tests were used to calculate static friction coefficients. It is revealed that exposure of DCSS to low temperature leads to formation of an ice layer on the sliding surface. The corresponding sliding is no more a function of properties representative of dry-dry friction, but the ice layer behaves as a lubricant. Thus, static friction coefficient decreases in case of an ice layer on the sliding surface.

Effects of tribological and material properties of wire rope on the motion synchronization of a precision flexible transmission device

During the long-term service process of a precision flexible transmission device driven by a wire rope, the tribological and material properties of the rope changes and causes a motion synchronization degradation. In this paper, a finite element model and a transmission error model of the device are built with the considerations of the surface wear of the rope, the variations in the rope-pulley friction coefficient, elastic modulus and Poisson’s ratio of the rope material. The evolutions of transmission error, elongation, stress state, and the output torque of the device as well as the tension distribution along the rope are solved. The results show that the motion synchronization degradation results from the surface wear, the decrements in the friction coefficient and elastic modulus, and the increment in the Poisson’s ratio. The rope tension decreases in the wrapping section around the guide pulley, and increases in most other positions due to wear. An increment in the friction coefficient causes reduced tensions in the wrapping section around the active pulley and the free section between guide pulleys, and worsens the tension uniformity and output torque performance of the device. The maximum stress of the rope increases with increasing elastic modulus and decreasing Poisson’s ratio.