Maximum Friction Coefficient Research Articles

Experimental study on the maximum static friction coefficient of fiber winding based on semi‐geodesic method

Experimental study on the maximum static friction coefficient of fiber winding based on semi‐geodesic method

Effect of Fucoidan on Conformation of Xanthan Gum and Its Tribo-Rheological Properties.

This study sought to explore the rheological and tribological properties of fucoidan-xanthan gum (XG) mixtures at different fucoidan concentrations. A conformational transition of XG from disordered to ordered forms was observed with an increasing fucoidan concentration, as determined by intrinsic viscosity measurements and Fourier transform infrared analysis. All mixtures exhibited non-Newtonian flow behavior with the yield stress. The mixture sample with 0.5% fucoidan displayed higher apparent viscosity at 100 s-1, yield stress, and viscoelastic moduli values than XG alone, suggesting viscoelastic synergism between the two biopolymers. However, these values exhibited a decreasing trend with higher fucoidan concentrations (0.5-2.0%), indicating a nullification of synergism. While XG alone exhibited antithixotropic behavior, fucoidan-XG mixtures showed thixotropic behavior, most pronounced at 1.0% fucoidan. A decreasing trend was observed in the maximum friction coefficient as the fucoidan concentration increased, indicating better lubricant properties. Collectively, our findings may enable widespread adoption and application of fucoidan in various industries.

Discrete element parameter calibration during cottonseed crushing process

In order to address the current deficit in research on discrete elements within the context of the cotton seed pressing process, a combination of physical tests and simulation experiments were conducted on Xinluzao 84 cottonseed. The Plackett-Burman experimental design was employed to identify the parameters that had a significant impact on the accumulation angle. Subsequently, the Box-Behnken design was employed to establish a second-order regression model for the accumulation angle and the significant parameters. This resulted in the optimal parameter combination for the maximum friction coefficient, minimum sliding friction coefficient and critical shear stress being 0.207, 0.388, and 5×10⁶ Pa, respectively. In order to calibrate the cottonseed bonding parameters, a Box-Behnken test was designed based on the results of the cottonseed particle crushing test. The optimal parameter combinations of normal stiffness, tangential stiffness, and bond radius were obtained as 1.25×10⁹ N/m², 7.57×10⁸ N/m², and 0.727 mm, respectively. The obtained parameters were verified by the simulation of stacking angle and the crushing test simulation. The relative error was 0.84% and 0.46%, respectively. This serves to validate the cottonseed bonding model and simulation parameters, thereby providing a foundation for optimising the core structural parameters of the cottonseed shelling machine.

Reliability assessment of an aircraft locking mechanism considering tribocorrosion and correlated failure modes in a marine environment

Landing gear door locking mechanisms are critical for aircraft safety, as their failure can lead to severe accidents. Therefore, these mechanisms must meet stringent reliability requirements. This study introduces a reliability evaluation method for a locking mechanism operating in a marine environment, which integrates dynamic simulation with a tribocorrosion experiment of the joints. Initially, a multibody dynamic model of the locking mechanism was developed to establish the boundary conditions for the joints. Subsequently, an accelerated tribocorrosion experiment was performed to assess the tribocorrosion behavior of these joints. Based on the experimental outcomes, the motion torque and output of the locking mechanism were determined. Considering the correlation between failures due to insufficient accuracy and jamming, an improved response surface methodology utilizing cross-utilization of experimental points was developed. Reliability of the locking mechanism was subsequently confirmed. The present findings indicated that the maximum wear depth in the corrosive environment increased by 25.28 μm (37.15 %) compared to a non-corrosive, dry friction environment. Similarly, the maximum friction coefficient in the corrosive environment increased by 0.0818, which corresponds to an increase of approximately 11.76 %. Furthermore, the proposed reliability evaluation method proved to be 33 % more efficient than the traditional response surface method.

A Novel Technosol Formulation for Sustainable Landfill Top Covers Using Non-Hazardous Wastes

This study explores the potential of non-hazardous wastes for crafting an engineered soil-like material (Technosol) suitable for landfill capping applications. Three distinct materials—waste foundry sand (WFS), washing aggregate sludge (WAS), and composted biosolids (CBS)—were strategically combined to develop this innovative Technosol. The formulation process involved a comprehensive analysis of their physical–chemical properties, mineral composition, leachate quality, and a series of geotechnical assessments to ensure compliance with landfill top cover construction standards. The blend 90WFS/10WAS showed optimal geotechnical properties for constructing a protective layer, including maximum dry density (1.77 g cm−3), void ratio (0.4), CBR index (23.2), cohesive strength (40 kPa), internal friction (ϕ = 30°), and permeability coefficient (k = 1.48 × 10−6 cm s−1). Further enhancement was achieved by adding 10% CBS, resulting in the development of a functional organo-mineral topsoil horizon (81WFS/9WAS/10CBS). Importantly, leachate analysis confirmed the negligible environmental footprint of this Technosol. Moreover, a pot-based experiment with Brassica juncea planting validated its capacity to support plant growth and establish a vegetative cover on the landfill surface.

Tribological Behaviour of Short Carbon Fiber Reinforced Polyethersulfone Composites with PTW Filler

In various applications like bearings, gear pairs, and brake pads, understanding how polymer composites interact with harder counterparts during sliding motions is crucial. A challenge arises from the heat generated during sliding friction, which has the potential to raise the contact temperature. This temperature increase, if it exceeds the material's glass transition temperature, can compromise the thermal stability of the composites, leading to rapid material wear. In the present investigation, dry sliding wear test was performed on 25 wt. % of short carbon fiber (SCF) reinforced polyethersulfone (PES) composites filled with 2.5 and 5.0 wt. % of potassium titanate whisker (PTW) using pin-on-disc tribometer. Wear test was planned and executed according to the experiment design formulations obtained by central composite design method. Contact temperature at the interface between composite pin and steel disc was monitored with an infrared thermal camera. Wear resistance was found to increase with the addition of fibers and fillers. PTW filled composites exhibited minimum wear with maximum coefficient of friction. Morphology studies were carried out on worn surfaces of the composites using scanning electron microscope to identify and describe the mechanism of wear involved. This investigation sheds light on the intricate behavior of polymer composites during sliding interactions.

An experimental and numerical study on the shear performance of friction-type high-strength bolted connections used for CLT-steel hybrid shear walls

One type of friction-type high-strength bolted connections (FHBCs) was developed to connect steel frames to the infilled cross-laminated timber (CLT) shear walls. In the FHBC, an opening was cut in the CLT near the wall-to-beam interface. Two predrilled holes existed within the CLT panel, running vertically from the bottom surface of the opening to the wall-to-beam interface. Two slotted holes were also predrilled on the top flange of the steel beam. Two high-strength bolts were attached to the upper anchor plate installed in the opening and the bottom anchor plate placed below the top flange of the steel beam. By applying the pretension force on the bolts, the CLT panel was pressed against the steel beam, forming the static friction force to resist the shear force along the wall-to-beam interface. In the study, cyclic tests were conducted to evaluate the friction properties of the interface between the infilled CLT wall and the steel beam. The CLT-steel friction coefficient was carefully investigated, which was a critical parameter for determining the maximum static friction force of the FHBCs. Three-dimensional solid finite element models were developed to predict the load-slip behaviors of the FHBCs, and their multi-stage load-slip behaviors were analyzed using the step-by-step method. It is found that the CLT-to-steel interface can perform with considerable shear-resisting capacity and shear stiffness in the pre-sliding friction as well as stable energy-dissipating capacity in its post-sliding behavior. The maximum static friction coefficient and the dynamic friction coefficient of the interface are recommended as 0.55 and 0.50, respectively. When the pretension force is enhanced from 40 kN to 80 kN, for the FHBCs with the three-layer CLT and those with the five-layer CLT, their ultimate shear-resisting capacity increases by 75.85% and 35.67%, respectively. The load-slip curves from the FHBC models exhibit a similar pre-sliding behavior with considerable shear stiffness and shear-resisting capacity. Whereas, the numerical load-slip curves of the post-sliding stage are distinctive between the FHBCs with the three-layer CLT and those with the five-layer CLT.

Comparative study of copper nanoparticles over radially stretching sheet with water and silicone oil

Abstract Copper nanoparticles are widely used in many sectors and research endeavors owing to their unique properties, including a large surface area, catalytic capabilities, and high thermal and electrical conductivity. The selection of the base fluid for copper nanoparticles should be contingent upon the anticipated application requirements since various fluids exhibit distinct characteristics that could potentially impact the mobility of the nanoparticles. The present investigation analyzes heat transfer phenomena occurring across a radially stretched surface. The research explores the effects of different states of Cu nanoparticles when combined with base fluids, such as water and silicone oil, on the heat transfer process. The momentum and energy equations are transformed into nonlinear ordinary differential equations by applying the similarity transformation. The boundary value problem-fourth-order (BVP4C) method numerically solves the governing ordinary differential equation for the modeled problem. In addition, the influence of various factors such as the slip parameter, solid volume fraction, Eckert number, Prandtl number, and unsteadiness parameter are examined. It has been discovered that blade-shaped nanoparticles transfer heat as quickly as possible via silicone oil and water. However, for platelet-shaped nanoparticles, a minimum heat transfer rate has been noted. The maximum skin friction coefficient is observed in platelet-shaped nanoparticles, while blade-shaped nanoparticles have the lowest skin friction coefficient.

High temperature lubrication performance of chlorophenyl silicone oil

Most studies of liquid lubricants were carried out at temperatures below 200 °C. However, the service temperature of lubricants for aerospace and aeroengine has reached above 300 °C. In order to investigate the friction mechanism and provide data for high temperature lubrication, the friction and wear properties of chlorophenyl silicone oil (CPSO)-lubricated M50 steel and Si3N4 friction pairs were investigated herein. Ball-on-disk experimental results show that the lubrication performance of CPSO varies significantly with temperature. Below 150 °C, coefficient of friction (COF) remains at 0.13–0.15 after the short running-in stage (600 s), while the COF in the running-in stage is 0.2–0.3. At 200 °C and above, the running-in time is much longer (1,200 s), and the initial instantaneous maximum COF can reach 0.5. Under this condition, the COF gradually decreases and finally stabilizes at around 0.16–0.17 afterwards. This phenomenon is mainly due to the different thickness of boundary adsorption film. More importantly, the wear rate of M50 steel increases significantly with the temperature, while the wear rate barely changes at temperatures above 200 °C. The anti-wear mechanism is explained as tribochemical reactions are more likely to occur between CPSO and steel surface with the increased temperature, generating the FeCl2 protective film on the metal surface. Accordingly, FeCl2 tribochemical film improves the lubrication and anti-wear capacity of the system. At high temperatures (200–350 °C), FeCl2 film becomes thicker, and the contact region pressure becomes lower due to the larger wear scar size, so the wear rate growth of M50 steel is much smaller compared with that of low temperatures (22–150 °C). The main findings in this study demonstrate that CPSO lubricant has good anti-wear and lubrication capacity, which is capable of working under temperatures up to 350 °C.

Efficient seismic fragility assessment method for a frictional isolated bridge constrained by shape memory alloy cables under pulse-like ground motion

Utilizing shape memory alloy (SMA) cables to constrain frictional isolated bridges is considered an efficient approach to limit bearing displacement and prevent serious earthquake damage. Accurate seismic fragility assessments of this kind of structure are crucial for aseismic decision making. However, traditional assessment methods cannot quantitatively describe the impact of the pulse effect on pulse-type seismic motions, which may lead to inaccurate assessment results. Therefore, this study deduced a novel equation for seismic fragility assessment that considers the pulse effect. Firstly, the impact of the pulse effect is quantified. Then, a multivariable probabilistic seismic demand model (MV-PSDM) is developed that is conditioned on the pulse period, peak ground velocity, structural period, maximum friction coefficient and SMA consumption. Based on the MV-PSDM, an effective approach for predicting structural seismic vulnerability is recommended, which does not require finite element modeling or nonlinear time-history analysis. Finally, a novel equation for calculating the intensity measure corresponding to 50% damage probability is deduced. The results indicate that increased friction coefficients and SMA consumption can enhance structural seismic safety under pulse-type ground motions. However, when the ratio of pulse period to structural period is too small, increased friction coefficients or SMA consumption have no meaningful effect on the seismic fragility of the structure.

Particle size and concentration of ground rice on tribological properties and in vitro starch digestibility of rice porridge

ABSTRACT Rice porridge is a food for general consumption; however, it may vary in food texture and starch digestibility depending on particle sizes and concentrations. This study investigated the tribological properties, steady shear flow, and in vitro starch digestibility of rice porridge with different particle sizes of ground rice (small size, <0.2 mm; large size, 0.2–0.45 mm; based on sieving) and concentrations (5, 7.5, or 10% w/v). The results showed that a high concentration of large-sized ground rice promoted lubrication properties, with the maximum friction coefficient reducing from ~ 0.7 in the 5% w/v concentration to ~ 0.4 in the 10% w/v concentration. In addition, the reduction in the friction started at a sliding speed of ~ 2 mm/s for the high concentration ground rice compared to ~ 20 mm/s for the low concentration rice. The results of high viscosity, small hysteresis loops, and swollen rice particles under morphological observation showed greater porridge stability for the high concentration, thus promoting its lubrication properties. These physical characteristics of the porridge could also play a role in starch digestibility during in vitro gastric digestion. Therefore, the management of ground rice to obtain a large size and a high concentration in rice porridge could benefit food preparation for the elderly and people having difficulty swallowing.

Tribological behavior of styrene butadiene rubber conveyor belts: effects of applied load and rotational speed

Conveyor belts are used for material transportation in the mining and construction industries. The friction and wear properties of the styrene butadiene rubber (SBR) used in conveyor belts are investigated, including the effects of the applied load and rotational speed on the friction coefficient and weight loss. The sliding wear mechanism of the SBR is analyzed using scanning electron microscope, energy dispersive spectrometer, and Fourier transform infrared spectrometer. The results demonstrate that the friction coefficient and total weight loss of SBR increase as a function of rotational speed, whereas the friction coefficient decreases and the total weight loss increases as a function of increasing applied load. The maximum friction coefficient occurred at a loading of 10 N and a speed of 120 revolutions·min−1, and the maximum total weight loss occurred at a loading of 20 N and a speed of 120 revolutions·min−1. In comparison to the unworn surface, the worn surface of the SBR exhibits melting, adhesive, and abrasive wear characteristics. The increases in the hardness, yellowing, oxygen content, and the number of complex structures, such as hydroxyl, aldehyde, ketone, and ether groups, occur simultaneously.

Analysis of micromechanical and tribotechnical properties of fluoropolymers during friction on 40Kh steel

The paper presents the results of micromechanical and tribotechnical tests of samples of polytetrafluoroethylene, radiation-modified (PTFE – RM according to modes A and B), coked in comparison with the PTFE standard (Fluoroplast -F4). The influence of the surface roughness of a 40Kh steel counter-tile on the coefficients of friction against time at a constant sliding speed is considered. Micromechanical tests were carried out using the method of instrumental indentation with a triangular Berkovich diamond pyramid. Tribotechnical tests were performed on a friction machine with a vertical axis of rotation of the spindle according to the scheme “the end of the sample of the fluoropolymer disk is the end of the counter-flange of the annular sleeve (steel 40Kh)” without lubrication and when the friction pair is lubricated with MGE-10A hydraulic oil. It was found that during friction without lubrication, PTFE samples had the maximum friction coefficients, and F4K20 samples had the minimum friction coefficients when working with 40X steel counter-tiles treated with P180 sandpaper. PTFE-RM (A) samples had the best wear resistance, followed by decreasing F4K20, PTFE – RM (B) and PTFE under friction without lubrication. In the presence of lubricant, the samples of the PTFE standard were inferior in wear resistance to the F4K20 samples, but were 5-7% better than the samples of PTFE-RM (B) and (A), respectively.

Enhancing friction and wear performance in hybrid aluminum composites through grey relational analysis

Hybrid aluminum metal matrix composites (AMMCs) include qualities including being lightweight, very effective, and highly resistant to wear, and corrosion. The process used in this study to maximize friction and minimize wear of hybrid AMMCs involves applying grey relational analysis (GRA) to optimize the process features. Stir-casting was used to create hybrid AMMCs of the Al-6061 alloy reinforced with graphene (Gr) and silicon carbide (SiC). The experiment used Taguchi's L27 design, and three process parameters—normal load, sliding distance, and sliding speed—were combined with GRA to produce the maximum coefficient of friction and lowest wear rate. Al-6Gr-6SiC obtained the maximum hardness of 128 VHN and 253 MPa as tensile strength, further coefficient of friction, and wear were analyzed for the same composite., respectively. The ideal mixture of graphene (6 weight percent) and silicon carbide (6 weight percent) as reinforcement in Al-6061 alloy obtained the optimum value of frictional coefficient (0.29766) and wear (0.002588 mm3/m), respectively.

Effect of alumina content on the thermal, mechanical and tribological properties of resin‐based friction materials

AbstractTo investigate the effect of alumina on the thermal, mechanical, and tribological properties of resin‐based friction materials, five friction materials with different alumina contents were prepared by the hot press molding process. The experimental results showed denser friction materials possessed higher hardness, while compressive strength and compression modulus dropped as alumina decreased. Friction material with 6 wt% alumina exhibited outstanding impact strength and great heat resistance. It also showed excellent friction stability, with a maximum mean coefficient of friction (COF) steady between 0.408 and 0.425 at various braking speeds. The wear resistance of friction materials had a positive relationship with the stability of the COF, and the greater the stability of the COF, the better the wear resistance and the lower the corresponding wear rate. The morphology of the worn surface indicated multiple sources of friction at different braking speeds, and large areas of dense friction films were beneficial to stabilizing the COF and reducing the wear rate.Highlights The sample with 6 wt% alumina showed excellent heat resistance, with a residual value of 83.5% at 800°C. The highest compressive strength and compression modulus were achieved in the sample with 8 wt% alumina. The sample containing 6 wt% alumina exhibited the highest COF and the lowest wear rate. The maximum subsurface temperature of the friction materials basically rose as braking speed increased. Large areas of dense friction films were beneficial to stabilizing the COF and reducing the wear rate.

Lubrication analysis of low-speed and heavy-load journal bearing in wind turbine gearbox under different operating conditions

Aiming at the working conditions of frequent starting, low speed and heavy load, and yaw tilting of radial sliding bearings in wind turbine gearboxes, a numerical analysis model of the lubrication performance coupled with instantaneous starting and operating conditions of radial sliding bearings was established based on the average Reynolds equation, and the start-up phase was analyzed. The motion trajectory of the shaft diameter and the axis center was used to obtain the change state of the bearing film thickness from the start-up to the stable stage; the influences of the comprehensive surface roughness, the journal inclination angle, and the journal rotation speed on the lubrication performance of the bearing during the whole stage of start-up and stable operation were studied respectively. The results show that the eccentricity has a maximum value in the starting stage, and the risk of film rupture caused by rough contact is the greatest. With the increase of the comprehensive surface roughness, the bearing capacity and friction coefficient both increase, and the maximum bearing capacity and friction coefficient in the starting stage are higher than those in the stable stage, which increase by about 13.62% and 131.58% respectively. With the increase of the inclination angle of the shaft diameter, the bearing capacity and friction coefficient both increase, and the maximum load capacity and friction coefficient in the starting stage are about 30% and 116% higher than those in the stable stage on average. With the increase of the speed, the bearing capacity of the bearing increases and the friction coefficient decreases, which is beneficial to improve the bearing performance. The calculation results provide an important basis for evaluating the wear risk of sliding bearings under frequent starting conditions, and provide a reference for the structural design and selection of sliding bearings, operating temperature, oil film pressure, etc.

Substantiation of a rational program for the running-in of tribosystems

The paper presents the results of studies on the justification of a rational program for running-in of tribosystems. It is shown that the first component of the program is the fulfillment of the condition on the verge of loss of stability due to the appearance of accelerated wear, with the maximum load on the tribosystem and the minimum sliding speed. This mode performs the function of "training" the surface layers for future operating conditions due to deformation processes and changes in the roughness of the friction surfaces. The mode is characterized by minimum wear rate values and maximum friction coefficient values.&#x0D; The second component of the running-in program is the fulfillment of the condition on the verge of loss of stability due to the appearance of burrs on the friction surfaces, with minimal load on the tribosystem and maximum sliding speed. This mode performs the function of "adaptation" of the surface layers to the future operating conditions by increasing the rate of deformation of the materials of the surface layers on the spots of actual contact. The mode is characterized by maximum wear rate values and minimum friction coefficient values.&#x0D; The third mode of the program aims to form surface structures and roughness on the friction surfaces of tribosystems that correspond to operational modes. This mode performs the function of "sufficient adaptation" of the surface layers to the future operating conditions, and corresponds to the condition with the maximum value of the stability margin. The final result of the running-in process is the transition of the tribosystem from an unbalanced, thermodynamically unstable state to a stationary, equilibrium state, as a result of which such parameters as wear rate, friction coefficient, temperature and roughness of the friction surfaces are stabilized. Such a step-by-step transition is associated with the formation of a special, dissipative structure of the surface layers of triboelements as a result of self-organization.&#x0D; The use of the three-mode program will reduce the time for tribosystems to run in by 23.0 - 38.4% compared to other programs. The effectiveness of the developed three-mode program is proven by experimental studies with the calculation of the modeling error.

Unraveling Tribochemistry and Self-Lubrication Mechanism of Polytetrafluoroethylene by Reactive Coarse-Grained Molecular Dynamics Simulations.

Lubrication of polymeric materials generally involves processes of atomic-scale chemical bond forming/breaking at the interface and mesoscale chain reorientation, disentanglement, and so forth. However, it is difficult to describe the important aspects of tribochemical reactions by conventional coarse-grained molecular dynamics (CGMD) simulations. Here, reactive CGMD simulations were conducted based on the ReaxFF force field to study the tribochemical interactions between polytetrafluoroethylene (PTFE) and iron. The chemical bond forming/breaking between the molecular chain and countersurface was fitted through the bond dissociation energies of specific reaction sites from all-atom ReaxFF-MD simulations. This enabled a quantitative description of tribochemical reactions in a macromolecule system. First, the number of anchoring bonds between PTFE molecules and the countersurface showed a strong correlation with the friction coefficient. The shearing process induced breaking of the interfacial anchoring bonds as well as chain disentanglement in the matrix, which consequently led to ordering reorientation of molecular chains toward sliding direction and hence decrease of friction. Second, two competitive factors were clarified to affect polymer friction with varying temperatures. The decrease of interfacial anchoring reactivity and molecular chain mobility at low temperature prohibited reorientation of molecular chains and increased the friction coefficient. On the other hand, the hardening of PTFE and the reduction in effective contact area at low temperatures decreased the friction coefficient. This led to a turning point with a maximum friction coefficient around 100 K. These results shed light on the essential role of tribochemical reactions on polymer lubrication, especially under low temperatures, which provides design guidance of polymeric lubrication systems for engineering applications.

Evaluation of blue Cupressus Arizona cone in automotive brake pad biocomposite

Recently, new brake pads have been developed using sustainable materials that are not harmful to the environment. In this study, the effect of using blue-colored Cupressus arizonica cones was determined as a friction modifier in brake pad composites. Four different samples were prepared by grinding the cone material. The samples’ physical and chemical properties and performances were compared, and finally, their microscopic analyses were visualized by scanning electron microscopy. Maximum friction coefficient and minimum wear rate are required for brake pads. The maximum friction coefficient of 0.39 and the minimum wear rate of the samples containing Cupressus arizonica were obtained in the 0.124X10-7 cm3/Nm BCA3 sample. When the brake pads developed from lignocellulosic biomass were compared, it was determined that the BCA3 sample met the most reasonable performance values.

Macro-micro mechanical study of principal stress rotation in granular materials using DEM simulations of hollow cylinder test

The dependency of sand behavior anisotropy on microstructure reveals the importance of macro-micro mechanical analysis of the principal stresses rotation effect on the strength-deformation response of granular material. In this study multi-scale analysis of the granular material's behavior using three-dimensional discrete element method simulations of the hollow cylinder test was presented. The effect of principal stresses rotation (α) on the macro-mechanical behavior of the soil was investigated from the micro-mechanical anisotropy aspect. It was observed that principal stress rotation affects the anisotropy coefficient and directional distribution of all micro-parameters which can change the soil's behavior according to loading conditions. The stress-force-fabric relationship was used to analyze the microstructure's stress state based on micro-parameters anisotropy coefficients. In addition to the good agreement between stress-force-fabric and general stress tensors, the decreasing trend of the maximum deviator stress and internal friction coefficient angle with increasing α can be observed for both stress tensors.