Friction Properties Of Materials Research Articles

Effect of Iron Powder Type on Friction and Wear Properties of Copper-Based Friction Powder Metallurgy Material

The sintered copper-based friction materials for high-speed train brake pads have a complex composition that should possess good physical, mechanical, and tribological properties in practical applications. For this article, four kinds of friction materials were prepared by powder metallurgy technology and the effects of iron powders on the microstructural and tribological properties of copper-based friction materials were characterized using a scanning electron microscope (SEM) and x-ray diffraction (XRD). The results showed that iron powder as an enhancing component could effectively change the friction and wear properties of the experimental materials. The copper-based friction materials containing hydroxy iron (1–5 μm) have a relatively higher coefficient of friction: The friction coefficient was significantly improved by 16.8% compared with reduced iron under a rotation speed of 4000 r/min. The friction coefficient of friction material containing water-atomized iron powder is relatively reliable with 3000–7000 r/min speed range. In a high-speed environment, the friction surface of material containing reduced iron or hydroxy iron (1–5 μm) mainly has cracks and brittle fractures, and the material containing hydroxy iron (10 μm) or water-atomized iron has an obvious layered structure and shows fatigue wear.

Experimental investigation of three-body wear for rubber seals in abrasive slurry environment

Three-body wear is a complex phenomenon occurring when abrasive particles present between two material surfaces. By developing a new experimental setup, we systematically study wear at the contact between stainless steel and three different rubbers (TPU, NBR and LSR) in a slurry environment, i.e. water containing sand particles. Results showed that wear on both metal and rubber pads increases exponentially with the sliding speed, while a weak correlation was observed with the applied normal load for the given range of load. Wear analysis showed that the stainless steel experienced the most wear when in contact with NBR and the least when in contact with LSR. The TPU rubber pads experienced the most wear, whereas the LSR pads barely exhibit any wear when in contact with the stainless steel. Furthermore, frictional measurements indicated an inverse relationship between the system coefficient of friction and the amount of wear observed on the rubber elements. These observations are discussed in terms of the probability of the sand particles being clung to the rubber pads, after which they abrade the steel surface. This probability is justified as a function of the rubber material properties and the system friction coefficient. The findings in this study suggest new directions for minimizing three-body wear at the contact between metals and rubbers.

Temperature dependent tensile fracture strength model of rubber materials based on Mooney-Rivlin model

With the increasingly widespread application of rubber in many fields, the demand for quantitative characterization of temperature dependent mechanical properties in service environments over a wide temperature range is increasing. Tensile fracture strength is one of the most important mechanical properties of rubber materials, but its temperature dependent model without fitting parameters is still rarely reported. In this work, based on Mooney-Rivlin hyperelastic constitutive model, a strain energy expression that explicitly includes tensile fracture strength is derived, and a temperature dependent tensile fracture strength model for rubber materials without fitting parameters is further developed in combination with the Force-Heat Equivalence Energy Density Principle. The prediction results of the model in a wide temperature range are in good agreement with the experimental results. Furthermore, a quantitative analysis of the effect of elastic modulus on tensile fracture strength at different temperatures is conducted. Finally, based on the above conclusions, some useful suggestions on the selection of rubber materials for service in a wide temperature range are proposed.

Comparison of the theoretical and experimental coefficient of friction for the brake disc-brake pad system

Contact between the automotive brake pad and the disc is mathematically modelled to estimate the coefficient of friction (COF). The mathematical model is proposed for the prognosis of the COF of brake pad material, by considering the contact mechanics between the interfacing surface and their material properties. The Greenwood-Williamson contact model is applied for rough contact surfaces for the estimation of the real contact radius. A MATLAB program has been formulated for generating the surface of brake pad material by considering its material properties which aid in the analytical evaluation of the COF. The proposed model is further validated with experimentation on pin-on-disc apparatus, as it is considered suitable for friction pad product testing according to previous research. The 25 pins were fabricated as per the ASTM G99 test for testing under varying loads and speeds. The obtained results showed that the range of COF has been between 0.2 and 0.4. The investigation presents an analytical approach for estimating COF and contact radius for brake disc and brake pad, which can be used to design an efficient automotive brake disc-brake pad system under the given load and rotational speed. The artificial neural network (ANN) is modelled for predicting the values of the COF for brake disc-brake pad systems, which can be further used for determining the tribological properties of new friction materials and their compatibility for efficient brake systems.

Железнодорожный дисковый тормоз с термоизолированными узлами трения, содержащими материалы с различными фрикционными свойствами

Purpose: Description of the design of the disc brake with thermally insulated friction units and the peculiarities of its manufacture. Methods: Analysis of the properties of friction materials for friction units of the railway disc brake. Results: The design of disc brake with thermally insulated friction units is proposed, a characteristic feature of which is thermal insulation of friction units A and B from each other. In addition, different friction materials are used in friction units – brake discs and brake linings. The basic principle of the disc brake is to compensate for the friction force of the friction assembly A in low temperature conditions where the carbonbased friction material is placed. Features of brake manufacturing are given. It is noted that the recommended material for thermally insulated working parts of the disc brake is chrysotile-asbestos. This material has a low thermal conductivity and an acceptable cost. It is recommended to use adhesive joints based on ABRO TM-185 glue by thermal insulation of brake discs. Practical significance: The design and features of the manufacture of a disc brake with thermally insulated friction units are described, as well as the best friction materials for it are determined. The results of the study can be used in specialized and locomotive manufacturing enterprises in order to eliminate the existing drawbacks regarding the friction characteristics of the friction materials used, as well as to reduce the cost of manufacturing a carbon-based disc brake.

Effects of Pre-Curing on the Structure and Properties of Paper-Based Materials.

Paper-based friction material is a typical paper-based composite that is usually cured via hot-pressing. This curing method does not account for the effect of pressure on the matrix resin, resulting in uneven distribution of resin in the material and reducing the mechanical properties of friction materials. To overcome the above shortcomings, a pre-curing method was introduced before hot-pressing, and the effects of different pre-curing degrees on the surface morphology and mechanical properties of paper-based friction materials were studied. The pre-curing degree significantly affected the resin distribution and interfacial bonding strength of the paper-based friction material. When the material was cured at 160 °C for 10 min, the pre-curing degree reached 60%. At this point, most of the resin was in a gel state, which could retain abundant pore structures on the material surface without causing mechanical damage to the fiber and resin matrix during hot-pressing. Ultimately, the paper-based friction material exhibited improved static mechanical properties, decreased permanent deformation, and reasonable dynamic mechanical properties.

Effect of carbon black components on rolling mechanical properties of tread rubber material by using improved digital image correlation

AbstractThe rolling and sliding state of the tread rubber material within contact patch was very important to the handling stability and safety of the vehicle. In this paper, first, the absolute coordinate system was introduced into the digital image correlation method, which improved the ability of the traditional digital image correlation method to solve the large deformation of polymer material surface. Second, a new calculation method of rolling friction coefficient based on the brush model was proposed. Third, a non‐contact full‐field rolling dynamics experimental device was developed to study the effects of carbon black components, rotational speed and vertical load on the rolling mechanical characteristics of tread rubber material. On this basis, the rolling mechanical characteristics of tread rubber material with different formulations were obtained by analyzing the distribution properties of global strain rate, full‐field longitudinal speed and full‐field longitudinal acceleration and the variation laws of transverse/longitudinal strain rate, trajectory of marked points, stress‐strain hysteresis curve and rolling friction coefficient. Finally, the influence mechanism of carbon black composition on rolling mechanical properties of tread rubber material was revealed.

An Interval Prediction of Chloroprene Rubber Crack Propagation Characteristics Based on Thermal Accelerated Aging.

Thermo-oxidative aging plays an important role in changing the properties of rubber materials; it significantly decreases the fatigue life of air spring bags and further causes safety hazards. However, due to the great uncertainty of rubber material properties, an effective interval prediction model has not been established considering the effect of aging on airbag rubber properties. To solve the problem, this study proposes an interval parameter correlation model that can more accurately describe rubber crack propagation characteristics by considering material uncertainty. Furthermore, an aging prediction model of the rubber crack propagation characteristic region is established based on the Arrhenius equation. The effectiveness and accuracy of the method are verified by comparing the test and prediction results under the temperature spectrum. The method can be used to determine the variations in the interval change of the fatigue crack propagation parameters during rubber aging and can guide fatigue reliability analyses of air spring bags.

Corrosion Stiction in Automotive Braking Systems.

This review paper targets the corrosion-stiction phenomenon that can occur in automotive braking systems under static conditions in aggressive environments. The corrosion of gray cast iron discs can lead to a strong adhesion of the brake pad at the pad/disc interface that can impair the reliability and performance of the braking system. The main constituents of friction materials are initially reviewed in order to highlight the complexity of a brake pad. Corrosion-related phenomena, including stiction and stick-slip, are considered in detail to discuss the complex effect of the chemical and physical properties of friction materials on these phenomena. In addition, testing methods to evaluate the susceptibility to corrosion stiction are reviewed in this work. Electrochemical methods, including potentiodynamic polarization and electrochemical impedance spectroscopy, are useful tools for a better understanding of corrosion stiction. The development of friction materials with low susceptibility to stiction should follow a complementary approach targeting an accurate selection of the constituents, control of local conditions at the pad-disc interface, and the use of specific additives or surface treatments to reduce the corrosion susceptibility of gray cast-iron rotors.

High‐damping ultralow−gel nonpolar elastomeric polymer through thiol−ene photo−click chemistry reaction

AbstractWith the increasing demand for high‐performance damping rubber material in various fields, improving the damping performance of existing nonpolar rubber has garnered tremendous scientific and industrial interest. However, it remains a long‐standing challenge to improve the damping properties of nonpolar rubber materials due to their low intrinsic glass transition temperature (Tg) and incompatible surface energy with high‐damping polar polymers or fillers. To solve this conundrum, ultra‐low gel multifunctional carboxy‐functional high vinyl polybutadiene HVBR (HVBR/COOH‐x%) was prepared by grafting 3‐mercaptopropionic acid (3PMA) onto HVBR via thiol−ene photo−click. The effects of reaction parameters including molecular weight, 1,2‐vinyl content, photoinitiators, reaction time, thiol and photoinitiator dosage on gel content and carboxyl grafting ratio were investigated. The HVBR/COOH‐x% demonstrate a controllable grafting ratio range from 2% to 73%. Furthermore, the increased Tg and intermolecular force resulted in excellent performance, including high‐glass transition temperature of 26.3°C, tensile strength of 15.52 MPa, and elongation at break of 396.16%. Particularly with a wide range of effective damping temperatures above 46.6°C. Meanwhile, COOH endowed the HVBR with better self‐viscosity, but also equipped it with stronger mutual viscosity. Therefore, this experiment proposes a feasible path to high damping and high adhesion in nonpolar rubber materials.

Effects of Lignocellulose Contents in Bamboo Charcoal on Mechanical and Thermal Properties of Polybenzoxazine-based Friction Materials

The objective of this research is to study mechanical and thermal properties of polybenzoxazine-based friction materials (PFMs) filled with 10 wt% bamboo charcoal particles (BC) containing residual lignocellulose content of 0-10wt% (BC0-10%), 10-20wt% (BC10-20%) and 20-30wt% (BC20-30%). The PFMs filled with synthetic graphite particles was also prepared to compare the properties. The obtained results showed that the mechanical properties, i.e., flexural strength and flexural modulus of the PFMs were improved with an increase of the residual lignocellulose content, and tended to be higher than that of the PFMs filled with synthetic graphite particles. Thermal stability monitored by the degradation temperature at 5% weight loss (Td5) of the PFMs revealed a decrease with an increasing residual lignocellulose content in BC. However, the Td5 of the PFMs filled with BC is still higher than the generated heat during the braking, which has temperatures around 350 °C. The results suggested that the obtained composite material is a promising candidate for car brake pads.

Study on Friction and Wear Properties of 3D Braided Carbon Fiber

In this paper, the friction and wear properties of 3D braided carbon fiber wet friction material at 2550r/min, 3800r/min and 5100r/min were studied with MM3000 friction and wear tester, and the wear mechanism was studied with SEM. The results show that the average static friction coefficient of friction materials is 0.153; With the increase of rotating speed, the dynamic friction coefficient decreases from 0.095 to 0.087; The volume wear rate decreased from 9.46*10−8cm3/J to 2.58*10−8cm3/J; The friction torque curves at three different speeds are relatively stable, showing the material has good braking stability. 3D braided carbon fiber friction material has fiber fracture and crack on the raised surface of the material after 1500 times of jointing at three different speeds. The mechanism of friction and wear is abrasive wear and fatigue wear.

Microstructure and properties of carbon fiber-H62 brass matrix composites prepared by friction stir processing

Carbon fibre (CF) reinforced H62 brass matrix composites were fabricated by friction stir process (FSP). The influence of CF compound amount and welding speed on the microstructure and properties of CF-H62 brass matrix composites was investigated by variable orthogonal experiments by drilling CF filled holes in H62 brass plates. Under the set experimental process parameters, the stirred friction processed composites with good surface formation, all without macroscopic defects, no loosening or holes. Optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the microstructure of the joints. The microstructure is a fine isometric crystal that is the result of dynamic recrystallisation. As the welding speed increased from 20 mm/min to 60 mm/min, the average grain size at the weld in the weld zone decreased from 5 μm to 2 μm. When the hole depth of the filled CF was 1.5 mm and the welding speed was 40 mm/min, the CF was most uniformly distributed in the composite area. This paper uses the orthogonal test method to optimise the formulation design of a variety of reinforcement fibre contents. The friction and wear properties as well as the physical properties of the two friction material samples were tested using a constant speed friction tester, a shear strength tester and a Rockwell hardness tester. The influence of each fibre and content on the friction material properties was investigated by extreme difference analysis; The best fibre ratio formulation was selected by combining a fuzzy comprehensive evaluation method. ANOVA was used to investigate the changes in friction material properties after the addition of graphene.

Effect of Polymer Ether Ketone Fibers on the Tribological Properties of Resin-Based Friction Materials

Resin-based friction materials (RBFM) are widely used in the fields of automobiles, agriculture machinery and engineering machinery, and they are vital for safe and stable operation. In this paper, polymer ether ketone (PEEK) fibers were added to RBFM to enhance its tribological properties. Specimens were fabricated by wet granulation and hot-pressing. The relationship between intelligent reinforcement PEEK fibers and tribological behaviors was investigated by a JF150F-II constant-speed tester according to GB/T 5763-2008, and the worn surface morphology was observed using an EVO-18 scanning electron microscope. The results showed that PEEK fibers can efficiently enhance the tribological properties of RBFM. A specimen with 6 ωt% PEEK fibers obtained the optimal tribological performance, the fade ratio was -6.2%, which was much higher than that of the specimen without the addition of PEEK fibers, the recovery ratio was 108.59% and the wear rate was the lowest, which was 1.497 × 10-7 cm3/(Nm)-1. The reason for the enhancing tribological performance was that, on the one hand, PEEK fibers have a high strength and modulus which can enhance the specimens at lower temperatures; on the other hand, molten PEEK at high temperatures can also promote the formation of secondary plateaus, which are beneficial for friction. The results in this paper can lay a foundation for future studies on intelligent RBFM.

UKF-Based Observer Design for the Electric Brake Booster in Situations of Disturbance

The motor-driven electric brake booster (E-Booster) can replace the traditional vacuum booster to realize the braking power assistance and active braking. Independent of extra sensors, this paper proposes a full-state observer for E-Booster based on Unscented Kalman Filter (UKF) in the presence of a driver’s input force disturbance. The electro-hydraulic system is first modeled, which includes a nonlinear hydraulic model and the reaction disk’s rubber model. The pre-compression is designed to produce linear power assistance based on the properties of rubber material. With the existence of the disturbance, the linear quadratic regulator (LQR) algorithm is used to track the pre-compression of the reaction disk so that E-Booster is developed into a closed-loop system to achieve power assistance. The proposed UKF observer can online estimate the states considering the controller input and disturbance input. To reduce the process error, the hydraulic p-V characteristic is fitted using the recursive least squares (RLS) method before observation. Furthermore, the simulation test and vehicle tests are performed to validate the observation effect. In the closed-loop test, UKF decreases residual error by 16% when compared to the typical Extended Kalman Filter (EKF). The simulation results remain consistent with the experimental results, demonstrating the effectiveness of the proposed method.

Modelling the dynamic physical properties of vulcanised polymer models by molecular dynamics simulations and machine learning

The performance trade-off of rubber materials is a major barrier to their development. Thus, to overcome such limitations, there is a strong need to understand the mechanisms related to the influence of the polymer structure on the physical properties of rubber materials. Although a number of studies have analysed the relationship between the structures of monomers and the properties of polymers, few studies have focused on the contribution of polymer dynamics to property analysis. Thus, we performed molecular dynamics simulations on vulcanised natural rubber to calculate the dynamic structural features and physical properties. Machine learning was used to analyse the effect of changes in the polymer structure (i.e., sulfur crosslinking) on the physical properties. Furthermore, the structural parameters involved in the physical properties were extracted. These findings provide clues to understanding the mechanism of simultaneous control of multiple properties in a trade-off relationship, which has previously been considered difficult.

Effects of Hybrid Rockwool–Wood Fiber on the Performance of Asbestos-Free Brake Friction Composites

The present study explores the physical-mechanical and tribological properties of hybrid wood fiber and rockwool-reinforced asbestos-free resin-based friction materials. We developed asbestos-free brake friction composites with different contents of hybrid fiber (wood and rockwool fiber) at a total fixed fiber loading of 30%. Then, the developed composites were investigated on the physical, mechanical, and tribological properties according to the industry standards. The results show that, with the increase in wood fiber, the density, hardness, and strength decrease, and the water absorption increases. Meanwhile, rockwool fiber can improve the coefficient of friction and enhance friction stability, while wood fiber has a significant impact on wear resistance. The sample with 5% wood fiber and 25% rockwool fiber presented the best performance in terms of the coefficients of friction, wear rate, and fade–recovery behavior. It provides a new idea for the research of asbestos-free composites.

Experimental characterization of friction properties of materials for innovative beam-to-column dissipative connection for low-damage RC structures

Low-damage design of structures in seismic-prone areas is becoming an efficient strategy to obtain “earthquake-proof” buildings, i.e. buildings that, even in the case of severe seismic actions, experience a low or negligible amount of damage. Besides the safeguard of human lives, this design strategy aims also to limit the downtime of buildings, which represents a significant source of economic loss, and to ensure an immediate occupancy in the aftermath of an earthquake. In this context, focusing on moment-resisting frames (MRFs), several solutions have been developed for the beam-to-column connections (BCCs) of steel and precast/prestressed concrete structures, but very few for cast-in-situ reinforced concrete (RC) structures. This paper focuses on a recently-proposed friction-based BCC for MRFs made with hybrid steel-trussed concrete beams (HSTCBs). The latter are made by a spatial lattice built using V-shaped rebars and a steel bottom plate, which eases the introduction of a friction dissipative device. HSTCBs are usually characterized by a small effective depth, which leads to a large amount of longitudinal rebars. The latter, together with a small-sized beam-column joint, make it potentially subjected to severe damage, which reduces its dissipative capacity. The shear force acting on the joint can be reduced by endowing the BCC with a friction device, with the aim of increasing the lever arm of the bending moment transferred between beam and joint, preventing the latter from damage. To evaluate the mechanical performance of the above connection, two experimental programs have been carried out at the Structures Laboratory of the University of Palermo. The first one focused on the characterization of the friction properties of two different materials (thermal sprayed aluminum and brass), by means of a linear dissipative device subjected to cyclic load. The second one tested a beam-to-column subassembly endowed with the recently-proposed connection in which the dissipative device was made with the best performing friction material tested before. The results of the cyclic tests are presented and commented, showing the promising performance of such connection in providing a low-damage behavior and a satisfactory dissipative capacity.

Modeling of Hyper-Viscoelastic Properties of High-Damping Rubber Materials during the Cyclic Tension and Compression Process in the Vertical Direction.

With the rapid development of the economy and urbanization, the construction of the urban rail transit system has had a great impact on the work, life, and health of residents in buildings along the rail transit line. Thus, it is particularly urgent and necessary to develop base isolation technologies to control and reduce the impact of vibrations of rail transit systems on building structures. High-damping rubber isolation bearings have shown significant effectiveness in the reduction of this impact, and their isolation performance mainly depends on the mechanical and damping energy dissipation characteristics of the high-damping rubber material. This paper aims to investigate the hyper-viscoelastic properties of the high-damping rubber material used for high-damping rubber isolation bearings during the cyclic tension and compression process in the vertical direction. These properties include hyperelastic parameters, viscoelastic coefficients, and the relaxation times of the material. For this purpose, uniaxial cyclic tension and compression tests were conducted. A three-element Maxwell rheological model combining a strain energy density function was proposed for modeling the hyper-viscoelastic behaviors of the materials during the cyclic tension and compression process. Based on the obtained results, an iterative identification procedure was used to determine the constitutive parameters of the material for each loading-unloading cycle. The aforementioned parameters were further expressed as a function of the number of cycles. New insights into hyper-viscoelastic property changes in this high-damping rubber material during the cyclic tension and compression process were gained in this work. These investigations could facilitate the development of computational tools, which would regulate fundamental guidelines for the better controlling and optimization of the isolation performance of the high-damping rubber material used for high-damping rubber isolation bearings, which have a wider perspective of applications in the urban rail transit system.

Analysis of High-Temperature Wideband Dielectric Properties of ATH-Filled Silicone Rubber Used for On-Site Insulation of Bare Overhead Conductors

Due to its excellent electrical and mechanical properties, and easy to cure at room temperature, room temperature vulcanizing silicone rubber is currently used in the on-site insulation of bare overhead conductors in the distribution system. The dielectric properties of silicone rubber materials have a great impact on power loss, which is vital to the transmission lines. Therefore, in this article, the dielectric properties of silicone rubber with the addition of different aluminum hydroxide contents are investigated by broadband dielectric spectroscopy in wide broadband range and wide temperature ranges, and the influence of aluminum hydroxide filler on the dielectric response is analyzed using a modified Cole–Cole model which takes the low-frequency dispersion process into account. It is found that the relationship of the dc conductivity and the low-frequency dispersion strength with temperature follows the Arrhenius equation law. The low-frequency dielectric response is influenced by dipoles’ polarization and electrode polarization. Moreover, the relaxation time decreases with the increase in temperature, and its mechanism can be revealed by the double-well model. The characteristic parameters obtained in this article can provide a reference for on-site insulating of bare overhead conductors.