Friction Materials Research Articles

Experimental Wear Characterization and Durability Enhancement of an Aeronautic Braking System

This paper is focused on the experimental wear characterization of an electromagnetic braking system used for helicopters. The characterization was performed through the evaluation of some monitoring parameters during endurance tests on a test bench and through the visual analysis of the worn surfaces after the tests. The monitoring parameters were the engagement threshold voltage, the release threshold voltage, the inductance, and the braking torque, which are directly correlated with the wear progress. The visual analysis allowed the assessment of the wear extent and the distribution of wear particles at the interfaces. The test performed on the initial base configuration, having ten springs and carbon fibers as friction materials, demonstrated that the braking system had insufficient durability in terms of actuation cycles. The results allowed the design of two new configurations based on different brake architectures and on different friction pairs. One of the new configurations was based on a reduction in the number of springs (eight-spring configuration), and the second one was based on the employment of a different friction material (NAO configuration). Both of these optimized configurations showed enhanced durability and wear resistance, but only the second one showed sufficient durability with respect to the requirements and was defined as acceptable. The final results showed a durability of 3000 actuation cycles for the base configuration, 4385 for the eight-spring configuration, and 35,223 for the NAO configuration. Nevertheless, the analysis of results allowed the cause of the wear phenomena to be studied and eventual further improvements in the system to be suggested.

Experimental studies of truck transport brake pads materials friction properties

The work presents the results of experimental systematic studies of "wheel-brake pad" friction pairs wear resistance and the effect of the wear-resistant coating on the wear, in particular, from metal-ceramic friction materials (ФМК-8), carbon composite materials (ВВКМ) in comparison with carbon steel of grade 45. It was established that the instantaneous values of brake pads friction coefficients during the tests on inertial stand are random in nature and require the use of mathematical statistics methods for their analysis. Change nature in pads and wheels friction force instantaneous values is determined by pressing forces. It is shown that the mathematical expectation of the friction coefficients values is within the normalized permissible interval. The probability of friction coefficients instantaneous values matching into the normalized interval at a pressing force of 10kN is 0,6-0,8 for speeds up to 60 km/h, for the rest is more than 0,8 at pressing force of 20kN, the specified probability exceeds 0,85 for the entire range of speeds. With a pressing force of 20kN, the probability of values exceeding the normalized interval does not exceed 0,15, with a pressing force of 10kN, the friction coefficients exceeded the maximum normative values more than 0,35 for speeds up to 40 km/h. It has been established that the most wear-resistant pads are coated with metal-ceramic material (ФМК-8) and carbon-carbon composite materials (ВВКМ). It is shown that the described technique based on the mathematical statistic application allows to perform more in-depth analysis of freight wheeled road trains brake pads frictional properties.

Tunable Thermal, Mechanical, and Tribological Properties of Polybenzoxazine-Based Composite for Vehicle Applications

In this study, a series of composites comprising polyether ether ketone (PEEK) and carbon fiber (CF)-reinforced polybenzoxazine for high-temperature friction materials for vehicle brake applications were developed using a high-temperature compression molding technique. The objective of this research was to systematically investigate the thermal, mechanical (tensile and flexural), and tribological performance of friction materials made from polybenzoxazine-based composites by varying the PEEK/CF mass ratio. Our study reveals the substantial improvement effect of the increased content of PEEK fibers on the thermal conductivity, the coefficient of friction, and the friction strength of the polybenzoxazine-based composite materials. Meanwhile, the introduction of carbon fibers was found to have a monotonic positive effect on the mechanical (tensile and flexural) properties and wear performance of the polybenzoxazine-based composites. The polybenzoxazine-based composites exhibit high mechanical strength, with a tensile strength of 50.1–78.6 MPa, Young’s modulus of 10.2–24.3 GPa, a flexural strength of 62.1–88.3 MPa, and a flexural modulus of 13.1–27.4 GPa. In addition, the polybenzoxazine-based composite with a PEEK/CF mass ratio of 75:25 exhibits a high and stable coefficient of friction (0.33) and a specific wear rate (1.79 × 10−7 cm3/Nm at room temperature). Subsequent to the wear test at ambient temperature, the worn surfaces of five polybenzoxazine-based composite samples with various PEEK/CF mass ratios were studied using electron microscopy technology (SEM). The observation of small cracks and tiny grooves on the worn surfaces indicates a combined abrasive and adhesive wear mechanism of the material. Our experimental results clearly reveal superior mechanical properties and excellent tribological characteristics. As a result, these composites show promising potential for the application of friction materials in terms of vehicle braking system applications.

A numerical framework for modelling tire mechanics accounting for composite materials, large strains and frictional contact

We present a general framework for the analysis and modelling of frictional contact involving composite materials. The study has focused on composite materials formed by a matrix of rubber and synthetic or metallic fibres, which is the case of standard tires. We detail the numerical treatment of incompressibility at large deformations that rubber can experience, as well as the stiffening effect that properly oriented fibres will induce within the rubber. To solve the frictional contact between solids, a Dual Augmented Lagrangian Multiplier Method is used together with the Mortar method. This ensures a variationally consistent estimation of the contact forces. A modified Serial-Parallel Rule of Mixtures is employed to model the behaviour of composite materials. This is a simple and novel methodology that allows the blending of constitutive behaviours as diverse as rubber (very low stiffness and incompressible behaviour) and steel (high stiffness and compressible behaviour) taking into account the orientation of the fibres within the material. The locking due to the incompressibility constraint in the rubber material has been overcome by using Total Lagrangian mixed displacement-pressure elements. A collection of numerical examples is provided to show the accuracy and consistency of the methodology presented when solving frictional contact, incompressibility and composite materials under finite strains.

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.

Fabrication and Process Optimization of Chinese Fir-Derived SiC Ceramic with High-Performance Friction Properties.

In this study, a novel friction material with biomass-ceramic (SiC) dual matrixes was fabricated using Chinese fir pyrocarbon via the liquid-phase silicon infiltration and in situ growth method. SiC can be grown in situ on the surface of a carbonized wood cell wall by mixing and calcination of wood and Si powder. The samples were characterized using XRD, SEM, and SEM-EDS analysis. Meanwhile, their friction coefficients and wear rates were tested to study their frictional properties. To explore the influence of crucial factors on friction performance, response surface analysis was also conducted to optimize the preparation process. The results showed that longitudinally crossed and disordered SiC nanowhiskers were grown on the carbonized wood cell wall, which could enhance the strength of SiC. The designed biomass-ceramic material had satisfying friction coefficients and low wear rates. The response surface analysis results indicate that the optimal process could be determined (carbon to silicon ratio of 3:7, reaction temperature of 1600 °C, and 5% adhesive dosage). Biomass-ceramic materials utilizing Chinese fir pyrocarbon could display great promise to potentially replace the current iron-copper-based alloy materials used in brake systems.

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.

Wear Performance of Multi-Walled Carbon Nanotubes Grafted Hybrid Fiber (Carbon–Aramid) Friction Materials

Wear Performance of Multi-Walled Carbon Nanotubes Grafted Hybrid Fiber (Carbon–Aramid) Friction Materials

Cyclic behavior and seismic control performance of SMA friction damper

Using superelastic shape memory alloy (SMA) bars and non-asbestos organic friction material, this study developed an innovative self-centering friction damper (SCFD). This hybrid passive control device consists of the self-centering device using SMA bars and the friction energy dissipation device which can provide excellent self-centering ability and energy-absorbing ability to meet the requirements of civil engineering applications. To explore the feasibility and hysteretic properties of the SCFD, experimental tests under cyclic loading were conducted. According to the experimental results, the proposed SCFD exhibited a stable and repeatable flag-shaped hysteretic response, which can achieve the recovered displacement of 76.07% and dissipated energy of 6.04 kJ at 42 mm. The finite element model of the SCFD using ABAQUS software was established and validated by experimental results. And a series of numerical simulations with different parameters were performed, which enables a more in-depth interpretation of the SCFD. Additionally, a system-level nonlinear time-history analysis was performed on a three-story steel frame equipped with and without SCFDs. The dynamic analysis results indicated that the SCFDs could effectively reduce structural damage and enhance post-earthquake recoverability under rare earthquakes.

Analisa Pengaruh Variasi Pelumas terhadap Keausan Baja St 60 dengan Tribometer Pin-On-Disc

Pin-On-Disc is a tool used to test a material's friction and wear levels. This tool is also one of the tribometer components. Pin-on-Disc uses a ball-shaped pin and a disk of ST 60 wrought iron as a disc in this test. This test aims to see or determine the volume of wear produced by pins with SAE40 and SAE140 lubricants and the importance of pin wear without lubrication. Lubrication influences the material or test specimen in this tribometer test. In this test, they are using a simple Pin-on-Disc Tribometer. The results obtained from this test are that the test without using lubricant shows at coordinates 0.0704 N, while the test with SAE40 lubricant shows at coordinates 0.07027 N, and testing with SAE140 lubricant is at coordinates 0.0703N.

Sustainable, recyclable, and highly wear-resistant wood matrix as a new paper-based friction material

Sustainable, recyclable, and highly wear-resistant wood matrix as a new paper-based friction material

Mechanical and tribological properties of C/C–SiC ceramic composites with different preforms

Abstract The C/C–SiC composites were fabricated by the liquid silicon infiltration method. The mechanical and tribological properties of C/C–SiC composites were assessed and compared based on different C/C densities and the carbon fiber textile architecture. The results demonstrated that the bending and shear strengths of C/C–SiC were lower than those of C/C composites, which resulted from the carbon fibers being corroded during the process of infiltration of liquid silicon. In contrast to C/C composites, the compressive strength of C/C–SiC exhibited higher values due to the presence of SiC ceramics. Moreover, the mechanical strength of C/C composites increased gradually with the increase of the C/C preform density. The tribological properties of various C/C–SiC composites showed a stable friction phase at an intermediate braking stage. When the density of C/C preforms was around 1.78 g/cm3, the C/C–SiC composites exhibited excellent friction coefficients (0.438 and 0.465), and low wear rates (linear and weight wear rates were 0.450 µm/time and 0.123 g/cycle, respectively). Furthermore, the C/C–SiC composites fabricated with non-woven carbon fiber needling preforms showed relatively a higher friction value and wear rate than those of C/C–SiC with PANOF integral C/C preforms. Therefore, C/C–SiC composites have been considered promising friction materials for braking system applications.

Influence of Varying Concentrations of Epoxy, Rice Husk, Al2O3, and Fe2O3 on the Properties of Brake Friction Materials Prepared Using Hand Layup Method.

Brake friction materials (BFMs) have a critical role in ensuring the safety as well as the reliability of automotive braking systems. However, traditional BFMs, typically made from asbestos, are associated with environmental and health concerns. Therefore, this results in a growing interest in developing alternative BFMs that are eco-friendly, sustainable, and cost-effective. This study investigates the effect of varying concentrations of epoxy, rice husk, alumina (Al2O3), and iron oxide (Fe2O3) on the mechanical and thermal properties of BFMs prepared using the hand layup method. In this study, the rice husk, Al2O3, and Fe2O3 were filtered through a 200-mesh sieve. Note that the BFMs were fabricated using different combinations and concentrations of the materials. Their mechanical properties, such as density, hardness, flexural strength, wear resistance, and thermal properties, were investigated. The results suggest that the concentrations of the ingredients significantly influence the mechanical and thermal properties of the BFMs. A specimen made from epoxy, rice husk, Al2O3, and Fe2O3 with concentrations of 50 wt.%, 20 wt.%, 15 wt.%, and 15 wt.%, respectively, produced the best properties for BFMs. On the other hand, the density, hardness, flexural strength, flexural modulus, and wear rate values of this specimen were 1.23 g/cm3, 81.2 Vickers (HV), 57.24 MPa, 4.08 GPa, and 8.665 × 10-7 mm2/kg. In addition, this specimen had better thermal properties than the other specimens. These findings provide valuable insights into developing eco-friendly and sustainable BFMs with suitable performance for automotive applications.

RECENT PROGRESS AND EVOLUTION IN THE DEVELOPMENT OF NON-ASBESTOS BASED AUTOMOTIVE BRAKE PADS- A REVIEW

Asbestos has been a significant reinforcement material in producing automobile friction components due to its physical and mechanical properties. However, the replacement of asbestos and other toxic metals employed in producing conventional friction components has been called for due to health and environmental concerns. Research in this area has led to the development of more efficient non-asbestos-based organic friction materials for automobiles. In this study, recent progress in the manufacture of non-asbestos-based, eco-friendly automotive brake pads is reviewed. A thorough classification of conventional and non-conventional friction materials used in the development of brake pads is presented, and the production method and the roles of friction materials in the mechanical and tribological properties of the manufactured pads are discussed. The study shows that the performance of brake pads manufactured from plants, animals, or plants and animal materials (hybrid) varies depending on the physical, chemical and mechanical properties of the plants and animals.

Synergistic optimization of mechanical and tribological properties of TiC modified copper-graphite composites by direct current in-situ sintering

The application of Cu-graphite composites in the field of friction materials is limited by the poor wettability between Cu and graphite and weakened mechanical properties. In this work, in-situ TiC layers were generated by interfacial resistance sintering with direct current to manipulate the interfacial bonding of the composites and enhance their comprehensive properties. The Ti added to the composites would react with graphite at the interface to generate TiC layers and form strong Cu–TiC-graphite interfaces due to interfacial reactions. When the added Ti content is 6 wt%, the composite demonstrates the most excellent mechanical properties and tribological characteristics, i.e., yield strength (168 MPa) and wear rate (2.7 × 10−10 m2/N) are 93.1% higher and 29.7% lower than those of the Cu-graphite composite without Ti addition, respectively. The dense TiC layer induces the strengthening of the Cu matrix and serves as the reinforcing phase to optimize the interfacial bonding and stress transfer, which not only greatly enhances the mechanical properties of the composite but also enables the composite to take full advantage of the hard TiC and graphite phases to obtain stable friction coefficient and low wear rate. This work provides a simpler technique to prepare modified Cu-graphite composites with excellent performance and contributes to the in-depth understanding of the enhancement mechanism of hard ceramic layers on the mechanical and tribological properties of composites.

Effect of special-shaped texture on tribological properties of PTFE-based friction material/CuSn6 friction pair

In this paper, special-shaped textures with different sizes and densities were fabricated on the surface of CuSn6 by laser, and the friction and wear properties were tested by a multifunctional friction and wear tester. The experimental results show that different friction coefficients can be obtained in the vertical and inclined planes of the special-shaped texture. When the special-shaped texture size is 600 μm, the friction coefficient ring increases gradually with the increase of special-shaped texture density. The wear loss of Polytetrafluoroethylene (PTFE) based friction materials decreases gradually, effectively improving the wear resistance of PTFE-based friction materials.

Iron-based friction materials fabricated by in situ carbothermic reactions and vacuum sintering with Cr addition

In this study, we fabricated iron-based friction materials directly by in situ selective carbothermic reaction and vacuum sintering from vanadium-bearing titanomagnetite concentrate and evaluated the effects of Cr on the microstructure, properties, and tribological behavior. The results reveal that Cr dissolves in the Fe matrix and contributes to the formation and refinement of pearlite, thereby improving the sintering densification and properties of the material. After adding moderate Cr, the microstructure becomes denser and more homogeneous, with improved sintering densification, hardness, and tribological properties. The dominant wear mechanism changes from severe abrasive and oxidative wear to mild abrasive and oxidative wear, indicating a decreasing wear degree. However, for Cr content exceeding 2 wt%, the sintering densification and properties slightly deteriorate. In particular, the material with 2 wt% Cr exhibits the optimal overall properties, with a much lower friction coefficient and wear rate than the sample without Cr. This work provides practical guidelines for further research on the properties improvement of the friction material.

Multifunctional composite fabric with outstanding self-cleaning and high photothermal effect for biomechanical energy harvester

Flexible fabrics have gained widespread attention in thermal management and energy harvesting recently due to their fascinating merits of flexibility and breathability. However, the simple and efficient integration of multiple functions into a single fabric remains a challenge. Herein, a multifunctional fabric was prepared by in-situ polymerized polyaniline (PANI) and polypyrrole (PPy) onto air-laid paper (AP), followed by wrapping with hydrophobic reagent. The synergistic effect of PANI and PPy networks endowed the composite fabric with excellent photothermal performance. Additionally, the smart fabrics exhibited the terrific self-cleaning property. More promisingly, triboelectric nanogenerator (TENG) based on the smart fabrics as effective positive friction material could transform electrical signal with through collecting energy from small human movement, delivering charge of 82.7 nC, open circuit voltage of 213.6 V, and short circuit current of 14.7 μA. This work provides new insights for the study of the next generation lightweight, portable thermal management fabric.

Effect of blending cashew oil modified phenolic resin and nitrile rubber on thermal, mechanical, and tribological performance of friction materials

AbstractThis study aims to investigate the effects of blending cashew nutshell oil modified phenolic resin and nitrile rubber (NBR) on the thermal, mechanical, and tribological performance of brake friction materials. The friction materials, which have a total binder of 25 wt% and different ratios of cashew nutshell oil modified phenolic resin and NBR, were prepared by hot press molding process. The experimental results show that NBR is beneficial to improve the hardness and compression modulus of the brake friction materials. The coefficient of friction (COF) is proportional to the wear rate, when the ratio of cashew nutshell oil modified phenolic resin and NBR is 13:12, the friction material has good heat resistance and exhibits excellent friction stability in the braking process, and the COF is steady between 0.420 and 0.448 at different braking speeds, while the wear resistance of material is optimal. The worn surfaces of the friction materials were examined by scanning electron microscope, and it was determined that the friction film is predominantly secondary plateaus, which can stabilize the COF and reduce the wear rate.

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.