Variation Of Friction Coefficient Research Articles

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.

Wheel-rail contact wear analysis on curved lubricated track for heavy haul locomotive studies

The effect of lubrications on a curved track to heavy-haul wheel-rail contact wear is studied. To analyse wheel-rail contact wear damage due to existing high-adhesive AC locomotive, a methodology for investigation is proposed, and the locomotive models are required to run at 20 km/h under maximum traction efforts, and the simulations include a DC locomotive for comparison. An extended creep force model, which was developed by Polach and has been widely used for the wheel-rail contacts under dry and wet conditions with variable friction coefficients, is further extended to apply for the typical low-coefficient-friction modifier, oil, and grease lubricant conditions. The wear models from two pairs of wheel-rail materials are used to predict the wear rates, and the wear numbers Tγ are presented for discussions. The simulations show that the lubricants significantly reduce the wheel-rail contact wear.

Lubricious yet tough fabric composites at cryogenic temperature by sulfonated polyether-ether-ketone reinforcement

A novel PTFE/Nomex fiber fabric composite reinforced by sulfonated polyether-ether-ketone (PN-SPEEK) was designed and fabricated, which has comprehensive properties with self-lubricity, high strength and toughness at wide cryogenic temperature range. The tensile strength and toughness were increased by 16.9 % and 64.3 % at −160 °C compared to conventional phenolic-formaldehyde-reinforced fabric (PN-PF), and the wear rate dramatically reduced to 2.7 × 10-16m3/(N•m). Within the temperature range of −160 °C to 25 °C, the variation of friction coefficient for PN-SPEEK was flattened between 0.086 and 0.126, which increased dramatically to approximately 0.2 with decreasing temperatures for PN-PF. The transfer film was analyzed comprehensively and thoroughly, demonstrating that the improved stable lubricity was primarily attributed to favorable formation of tribofilm composed of plenty of PTFE and strong chelation between SPEEK and iron base in transfer film. The developed PN-SPEEK is greatly expected for engineering applications.

Fretting fatigue crack nucleation analysis under a variable coefficient of friction

Fretting fatigue is a phenomenon that occurs when two surfaces come into contact and experience oscillatory stresses and displacements of small amplitude. This can lead to a significant reduction in mechanical parts’ lifetime. The complexity of this type of problems relies on the many variables that can affect the results. One of its most important variables is the Coefficient of Friction (CoF), which has been observed to vary throughout a single fretting test. However, this variation is rarely considered in fretting fatigue finite element analyses. In order to analyse the effects of a Variable Coefficient of Friction (VCoF) on nucleation lifetime, a cylinder-on-plane finite element model is developed. To predict nucleation lifetime, two critical plane damage parameters, Fatemi-Socie (FS) and Findley parameter (FP), are used along with an evolving CoF during the first stress cycles. These parameters are evaluated by calculating initiation lifetime where the maximum value of the damage parameter occurs (hotspot method) and by the quadrant averaging method, because of its capability of predicting lifetime with relative accuracy and negative crack angles. To simulate the evolution of the CoF, a Python script that changes the value of CoF before each simulation is developed. This coefficient varies between 0.3633 and 0.65, following arbitrary points on the coefficient’s evolution curve. Once the simulation is concluded, the script evaluates the damage parameters and their equivalent lifetime throughout the contact surface and saves those values in an accumulation parameter that follows Miner’s rule. This process is repeated until CoF reaches its maximum value. The lifetime to nucleation is statistically analysed for all methodologies. The results suggest that, regarding the hotspot method, FP values remain within ± 3 N deviations from the experimental results, while FS results are nearer, within ± 2 N deviations. In addition, the quadrant method results remain at ± 3 N deviations, but providing more accurate results for the FP parameter. The application of a VCoF to these methods leads to less conservative and less deviated results, providing more accuracy for conservative approaches and more consistency for predictions in general. It is concluded that VCoF analysis is an interesting tool to determine more accurately nucleation lifetime for conservative approaches. Additionally, it reduces the predictions variation for differently loaded fretting setups regardless the desired approach.

Insect-Scale Biped Robots Based on Asymmetrical Friction Effect Induced by Magnetic Torque.

Multimodal and controllable locomotion in complex terrain is of great importance for practical applications of insect-scale robots. Robust locomotion plays a particularly critical role. In this study, a locomotion mechanism for magnetic robots based on asymmetrical friction effect induced by magnetic torque is revealed and defined. The defined mechanism overcomes the design constraints imposed by both robot and substrate structures, enabling the realization of multimodal locomotion on complex terrains. Drawing inspiration from human walking and running locomotion, a biped robot based on the mechanism is proposed, which not only exhibits rapid locomotion across substrates with varying friction coefficients but also achieves precise locomotion along patterned trajectories through programmed controlling. Furthermore, apart from its exceptional locomotive capabilities, the biped robot demonstrates remarkable robustness in terms of load-carrying and weight-bearing performance. The presented locomotion and mechanism herein introduce a novel concept for designing magnetic robots while offering extensive possibilities for practical applications in insect-scale robotics.

Control of a Path Following Cable Trench Caterpillar Robot Based on a Self-Coupling PD Algorithm

Underground cable trench inspection robots work in narrow, variable friction coefficient, and complex road environments. The running trajectory easily deviates from the desired path and leads to a collision, or even the destruction of the robot or cable. Addressing this problem, a path-following control method for the dual-tracked chassis robot based on a self-coupling PID (SCPID) control algorithm was developed. The caterpillar robot dynamics were modelled and both the unknown dynamics and external bounded disturbances were defined as sum disturbances, thus mapping the nonlinear system into a linearly disturbed system, then the self-coupling PD (SCPD) controller was designed. The system proved to be a robust stability control system and only one parameter, the velocity factor, needed to be tuned to achieve parameter calibration. Meanwhile, to solve the problem that the error-based speed factor is not universal and to improve the adaptive ability of the SCPD controller, an iterative method was used for adaptive tuning. The simulation results showed that the SCPID can achieve better control. The field test results showed that the SCPD’s maximum offset angle was 56.7% and 10.3% smaller than incremental PID and sliding mode control (SMC), respectively. The inspection time of the SCPD was 20% faster than other methods in the same environment.

Microstructural evolution and mechanical properties of FeCrNiCuTix high entropy alloys

In this study, the microstructural evolution and mechanical properties of a series of FeCrNiCuTix (x = 0, 0.2, 0.4, 0.6, 0.8, and 1, in mole ratio) high entropy alloys (HEAs) were analyzed in detail to study the influence of Ti content on the HEAs. The microstructures of the alloys transformed from single-phase face-centered cubic (FCC) phase structure to FCC and body-centered cubic (BCC) diphase, finally to FCC, BCC and intermetallic compound (Fe2Ti) phase with the increase of Ti content. The addition of Ti element significantly refined the grain of the alloys. The hardness, strength and tribology tests of the alloys were also carried out. The results indicated that the Vickers hardness, yield strength, and fracture strength increased first and then decreased, the average friction coefficient variation law was just the opposite, and the plastic strain reduced monotonically, with the increase of x values for the alloys. At x = 0.4, the maximum yield strength and fracture strength of the alloy were 1646.89 MPa and 1947.09 MPa, respectively, and the average friction coefficient was a minimum of 0.47, with a hardness value of HV 489.68 and a plastic strain of 13.98%. The maximum hardness value of the alloy was HV 656.19 at x = 0.8. The fracture mechanism of the alloys was from ductile fracture to brittle fracture and the wear mechanism was form of abrasive wear. Accordingly, the FeCrNiCuTi0.4 alloy obtained the optimal mechanical properties overall. This research is of great significance for the development of engineering and structural materials with excellent mechanical properties.

New insight in characterization of red wine astringency using soft tribology method

AbstractThe variation of friction coefficient (μ) of model wine and model saliva mixtures with entrainment speed (VR) on simulated oral surfaces was evaluated by oral tribology. Combined with techniques of dynamic light scattering (DLS), atomic force microscopy (AFM), rheometer, and quartz crystal microbalance with dissipation monitoring (QCM‐D), the correlation between characteristics of the model wine and model saliva mixtures (particle size and morphology, suspension viscosity, adsorption film thickness, and viscoelasticity) and the oral lubrication loss was established. The results showed that the higher the concentration of tannin in the model wine, the larger the size of the complexes with the model saliva, and the higher the thickness, viscoelasticity, and roughness of the adsorption film formed, which resulted in the increase of friction coefficient in the boundary lubrication regime. Different from previous results, it is found that the maximum value of the friction coefficient (μmax) in the boundary regime has the best positive correlation with the astringency perception intensity of the model wine accordingly.

Fast-response mechanism for regulating friction coefficients induced by microviscosity in polymer-based aqueous lubrication systems

Controlling the friction coefficient is crucial for smart friction management and the reduction of energy consumption. The exploration of the mechanisms for regulating friction coefficients is at the core of this issue. In this study, it is proposed that microviscosity plays a pivotal role in influencing the rapid response of the friction coefficient variation in polymer-water-based lubrication systems. The change in microviscosity induced by salt ions was investigated using fluorescent probes and molecular dynamic simulation. The friction contact region was divided into core, corona and blank regions based on functional specificity to investigate microviscosity. The results of the study showed that the microviscosity exhibited by salt ions which are more readily adsorbed in the corona region is the key to determining changes in the friction coefficient. The high microviscosity in the core region of the polymer coating serves as the basis for maintaining a low friction coefficient. The blank region ensures low shear viscosity during friction. Therefore, the regulation of the friction coefficient can be achieved by controlling the microviscosity in the corona region using salt ions. This study not only presents a novel method for characterizing microviscosity but also establishes a theoretical basis for the intelligent regulation of friction.

A comparative study of original equipment manufacturer brake pads using tribological testing and hybrid ranking for enhanced decision making and cost effectiveness

Tribological test and hybrid ranking techniques are employed to evaluate brake pads from original equipment manufacturers for Indian passenger cars. The study was conducted for four brake pads designated as OE1, OE2, OE3, and OE4. The assessment integrates the analytical hierarchy process with various ranking methods including Extension Evaluation Method, Complex Proportional Assessment, Preference Selection Index, and Technique for Order of Preference by Similarity to Ideal Solution. Brake pad samples undergo testing according to the standard IS2742 part 1-4 of 1994, generating crucial performance parameters such as performance coefficient of friction, hot coefficient of friction, normal coefficient of friction, fade percentage, recovery percentage, variation in coefficient of friction, wear thickness loss percentage, wear mass loss percentage, and time taken to reach maximum temperature. These performance metrics are technically analyzed and ranked using hybrid ranking techniques to enhance the decision-making process. The results show that OE4, a budget-friendly brake pad ranked first, is the best performer. OE2, a more expensive alternative, is placed second, and OE1 and OE3, which are more affordable possibilities, are ranked third and fourth, respectively. This research serves as a valuable resource for selecting brake pads for Indian passenger cars, especially in scenarios where technical specifications and cost-effectiveness are crucial considerations.

Carbon-carbon composite material in friction units when lubricated with hydraulic fluid

The paper deals with the issues related to the friction of carbon-carbon composite against steel in the medium of hydraulic fluid. Variation of friction coefficient from load, speed and temperature is analyzed. Comparison of antifriction properties of Hardcarb TP material with fluoroplastic modified by radiation treatment is performed. It is established that under the conditions of the experiments, the carbon composite has a higher friction coefficient than the fluoroplastic, but acceptable (f = 0.12) for use in friction units. Hardcarb TP material is promising for application in sliding friction friction units in lubrication with AMg-10 working fluid under conditions of increased requirements for the reliability and service life of hydraulic pumps.

Measuring applied force and energy consumption in deep drawing die Sets: An experimental and numerical analysis of CrN and CrTiN PVD coating effects

Excessive forming loads ultimately result in wear during the deep drawing process. This study uses an innovative test rig on a universal testing machine to monitor force–time variations during deep drawing. The rig captures force changes, workpiece/die friction, and energy consumption. The research explores how varying friction coefficients between the die and workpiece, lubrication conditions, and different PVD coatings on the die surfaces affect production performance in deep drawing. Various coatings were applied to 1.2379 cold work steel samples, and their friction behavior was examined. The performance of PVD-coated die sets was evaluated through experimental and numerical methods. The abrasive wear test revealed that the CrN coating had 46 % less wear volume than uncoated specimens. In contrast, the CrTiN coating showed 70 % more abrasion volume at 15 N load and 96.4 % less at 30 N load compared to CrN. Adhesive wear tests demonstrated that CrTiN had 9.09 % less wear at 6 N load and 27.66 % less at 10 N compared to CrN. Numerical simulations explored friction's impact on deep drawing; CrTiN die set used least energy, forming with lowest max force, while CrN set reduced max force by 0.56 %. CrTiN coating showcased better wear resistance, lower forming forces, and reduced energy consumption than CrN and uncoated dies under various friction conditions.

Dynamic Response Analysis of Wedge-Shaped Rock Slopes under Harmonic Wave Action

In dynamic disasters involving rock slopes, wedge failures formed by complex structural discontinuities are more predominant, and the dynamic response associated with them remains a classic concern in rock slope engineering. To address this concern, this paper utilized refined modeling to analyze a wedge-shaped rock slope by inputting horizontal harmonics as loads. We conducted dynamic response analyses by varying the inclination of the structural surface on the wedge-shaped rock slope, the axial offset angle, the friction coefficient, and the configuration of the single sliding surface. The results in this paper indicate that for wedge-shaped and single-sliding-surface configurations of rock slopes, with an increase in the structural surface inclination angle, the dynamic response of the sliding body, stress distribution, excellent frequency, and spectrum values all increase. Furthermore, wedge-shaped rock slopes’ dynamic responses are more significant than those of single-sliding-surface rock slopes. For wedge-shaped rock slopes, increases in the axial offset angle and structural surface friction coefficient reduce the dynamic response, excellent frequency, and spectrum values. Meanwhile, within the context of the axial offset angle conditions in wedge-shaped rock slopes, the dynamic response, excellent frequency, and spectrum values are better than the variations in the structural surface friction coefficient. Under the influence of these factors, stress concentration occurs at the sliding fronts of rock slopes.

Mixed Convection Flow Analysis of Carreau Fluid Over a Vertical Stretching/Shrinking Sheet

The current investigation aspires to unravel the steady mixed convection flow of Carreau fluid over a permeable vertical stretching/shrinking sheet near a stagnation point. The system of governing equations is reduced into ODEs utilizing appropriate similarity transformations. The similarity transformations are obtained via the Lie scaling group of transformations. Dual similarity solutions are detected depending on the opposing flow parameter for stretching and shrinking cases. The effects of pertinent parameters on the skin friction coefficient, Nusselt number, velocity, and temperature fields are examined in detail. The influence of the suction parameter on the variations of skin friction coefficient for the stretching case shows various behavior than in the shrinking case. However, on the variations of the Nusselt number, a similar trend in both the stretching and shrinking cases is observed. The fluid velocity decreases, and the temperature rises with the increment of non-Newtonian parameter in the upper branch, whereas the lower branch depicts opposite trends. Due to the different characteristics of the lower branch than the upper branch, it is necessary to find a physically reliable solution branch. Thus, a linear temporal stability analysis is conducted based on the sign of the smallest eigenvalue. The smallest eigenvalues are determined numerically using the shooting technique, revealing that the upper branch is the only stable solution branch.

Dual solution of melting heat transfer efficiency in radiative hybrid (Cu-[formula omitted]/water) nanofluid flow

Hybrid nanofluids have been proposed as a new class of nanofluids, whose thermal properties and potential utility have been identified to serve the purpose of enhancing heat transfer rates. The main objective of the present analysis is to study the emerging unsteady hybrid nanofluid flows through porous medium with the impacts of melting temperature and slip velocity on the surface. Additionally, the heat transportation is analyzed with the presence of, thermal radiation, Joule heating and heat source/sink over a stretched/shrunk surface. Here two distinct nanoparticles (Cu- Al2O3) considered to examine the flow field over the shrinking/stretching surface. The Navier-Stokes equations are used in the process of developing the mathematical model under the mentioned assumptions. By utilizing the suitable transformations, the modeled equations are converted into non-linear ordinary differential equations. The formulated mathematical differential system is solved numerically by bvp4c technique in MATLAB. Dual nature study is focused in which solid lines show the first solution and dash lines for the second solutions. The behavior of hybrid nanofluids in terms of velocity and temperature distribution have been visualized graphically. For better understanding of the flow features and heat transfer rate, variation in skin friction coefficients and the Nusselt number of hybrid nanofluids are closely examined. We find from the present study that the rate of heat transfer is enhanced in the hybrid nanofluids by the impact of melting temperature. Moreover, in the first solution, skin friction coefficient rises with the enlargement of magnetic field parameter while heat transfer rate reduces in this situation. Additionally, the velocity profile reduces by the influence of unsteadiness parameter in the first solution while rises in the second solution. The heat transfer process at the surface is improved when a stronger Melting temperature is taken into account.

Shear performance investigation of recycled concrete load-bearing blocks for sustainable masonry

PurposeRecycled concrete is an economical and environmentally friendly green material. The shear performance of recycled concrete load-bearing masonry is studied, which is great of significance for its promotion and application and also has great significance for the sustainable development of energy materials.Design/methodology/approachIn total, 30 new load-bearing block masonry samples of self-insulating recycled concrete are subjected to pure shear tests, and 42 samples are tested subjected to shear-compression composite shear tests. According to the axial design compression ratio, the test is separated into seven working conditions (0.1–0.8).FindingsAccording to the test results, the recommended formula for the average shear strength along the joint section of recycled concrete block masonry is given, which can be used as a reference for engineering design. The measured shear-compression correlation curves of recycled concrete block masonry are drawn, and the proposed limits of three shear-compression failure characteristics are given. The recommended formula for the average shear strength of masonry under the theory of shear-friction with variable friction coefficient is given, providing a valuable reference for the formulation of relevant specifications and practical engineering design.Originality/valueSimulated elastoplastic analysis and finite element modeling on the specimens are performed to verify the test results.