Friction Materials Research Articles

The Influence of Configuration Parameters of the Planetary Drive of Crank Presses on its Dynamic and Energy-Consumption Characteristics

Introduction. The planetary drive has been widely found in the activation systems of crank presses as it improves working conditions of friction units and reduces press metal consumption and energy consumption.Problem Statement. For studying the planetary motion of its main parts, it is advisable to consider its operation as four periods characterized by different patterns of changes in external loads and, consequently, different patterns of motion of core parts. The periods between switching the brakes when one link has not stopped, while other one starts moving is of the greatest interest. The problem of dynamic and energy-consumption parameters of the drive in transient conditions still remain a little open.Purpose. The purpose of this research is to qualitatively assess the influence of configuration parameters on the dynamics of the processes of switching and stopping the planetary drive.Material and Methods. The parameters of the experimental pilot plant, a model planetary drive with a nominal load of 400 kN, have been calculated. The minimum speed of the central gear has been estimated depending on the moments of inertia of the leading mass and the outer gear. The obtained dependences have been processed with the use of a standard mathematical apparatus.Results. It has been found that the energy-consumption and dynamic parameters of the drive are significantly influenced by such characteristics as moments of inertia and braking moments, while decreasing angular velocity of the drive flywheel does not depend on the moments of inertia of the stopped links. The rate of braking processes is determined by the elastic properties of the friction materials and the parameters of the brake springs, not by the parameters of compressed air outflow.Conclusions. The obtained analytical and graphical dependences have allowed not only qualitative, but also quantitative assessment of the influence of the parameters on the dynamics of processes. These recommendations can be used at the design stage, to select the optimal parameters of the drive with the predicted properties.

Tribological behavior of shape memory cyanate ester materials and their tunable friction mechanism

High-performance polymer friction materials with tunable tribological behavior to fit varied work conditions remain a challenge of widespread interest for a variety of applications. Shape memory polymer exhibits morphing and modulus changing over temperature changing provides a promising material to adjust the friction process. Herein, we investigated the tribological properties of shape memory cyanate ester (SMCE) under different conditions. The SMCE exhibits the tribological behavior of good friction material with stable high coefficient of friction (COF) and a low wear rate. Besides, the COF increases and wear rate decreases with the temperature increasing show the tunable friction property of the SMCE. We propose a new model of wear-compensation through shape recovery to explain the adjustable friction behavior of thermal-responsive polymer from the aspect of shape recovery and energy conversion. This study provides a high-performance friction material and paves the route for the application of shape memory polymer (SMP) in tribology field with tunable property.

The MD simulation of friction heat dissipation and generation in high-speed dry sliding system

3D non-equilibrium molecular dynamics simulations are performed to investigate the friction heat dissipation and generation of high-speed sliding system. A sliding simulation model with two blocks is built. The friction heat generation with different materials, different velocities are studied. The mechanism of the heat dissipation at the interface is investigated. The heat partition of different friction system is obtained. The results show that more friction heat will be produced with higher sliding velocity. But in the case with more plastic deformation, less friction heat will be generated. The heat partition is mainly influenced by the friction material and the velocity ratio. The material which has the similar thermodynamic properties will be easier to produce phonon with similar spectrum.

Understanding friction and wear properties of carbon fiber/epoxy stitched composites

Due to its low friction coefficient and wear rate, and good self-lubrication, carbon fiber reinforced polymer (CFRP) composite is used as friction material. The easy interlaminar delamination and low impact damage tolerance of conventional CFRP laminates lead the friction materials to wear seriously, which causes the early-stage failure. Here, carbon fiber/epoxy stitched composites were prepared by the resin transfer molding technology. Effects of load and stitch parameters on the friction and wear properties of stitched composites under dry conditions were investigated through experiment and simulation. The coefficients of friction (COFs) of composites increase linearly at the initial stage, and then decrease from a maximum peak to a relatively stable state value. Samples with a high stitch density and a small stitch spacing along the sliding direction has low COF values and wear rates. With the increase of the normal load, COFs and the wear rate both decrease first and then increase. The wear tracks on the surface of CF/EP stitched composites are generated by comprehensive effects of cutting, adhesive and fatigue wears. This study provides comprehensive characterization and deep understanding of friction and wear properties of carbon fiber/epoxy stitched composites, which will broaden the CFRP application as frication material.

The influence of the addition of different kinds of slags on the friction and emission behavior of a commercially employed friction material formulation

Keeping sustainability and the circular economy in mind, numerous studies have been conducted on the feasibility of the utilization of industrial wastes in friction material formulations for braking applications. One such highly produced waste is slags from blast furnaces. The present work focuses on the friction, wear, and emissions behavior of a commercially employed friction material formulation observing the inclusion of three kinds of slags. Two types of slags were obtained from a blast furnace; the difference was the cooling method. The third type of slag was collected from a basic oxygen steel furnace. The prepared samples were tested in the form of pins on a pin on disc equipment at 1.51 m/s, 1 MPa, and ambient conditions to replicate a mild braking scenario. Irrespective of the type of slag, the addition of the wastes observed either a decrease or similar emissions when compared to the virgin formulation. The friction and wear were in the range comparable to that of the reference composition; the CoF for slag specimens ranged between 0.49 and 0.51 compared to 0.45 for the reference composition. On the other hand, by inspection of the worn surfaces of the pins, it was seen that the slag-containing specimens had compact and expansive secondary contact plateaus with the inclusion of slag particles in their composition. Through this preliminary analysis, the possibility of the utilization of different slags is highlighted, especially in an already implemented commercial formulation, paving the path for further testing and validation.

Experiment and Analysis on Friction Damage and Energy Loss Characteristics of Potatoes

In view of the problem that the research of potato friction damage is not sufficiently systematic and the characteristics of potato friction damage and energy loss are not clear, this paper investigates the initial height, potato mass, potato varieties, friction materials and temperature as experimental factors and the epidermal damage proportion as the evaluation index, filtering for significant factors by a factorial test. On this basis, the proportion of epidermal damage and the ratio of energy consumption loss were used as evaluation indicators to conduct a single factor test for significant factors. Thereby, the influence of these factors on friction damage and energy loss characteristics of potato were further investigated. The results show that the initial height, potato mass and potato varieties were the significant factors affecting the proportion of epidermal damage of potatoes. With the increase in initial height, the proportion of epidermal damage and ratio of energy consumption loss gradually increased. With the increment in potato mass, the proportion of epidermal damage gradually increased, and the energy consumption loss ratio gradually decreased. The epidermal damage proportion and energy consumption loss ratio of potato varieties were ranked as Xisen 1 > Jizhang 12 > Xisen 6 > Xuechuanhong > Netherlands 15, and Netherlands 15 > Xisen 6 > Xisen 1 > Xuechuanhong > Jizhang 12, respectively. The energy loss ratio and epidermal damage proportion were highly correlated at initial height and potato mass. A mathematical model for predicting the proportion of epidermal damage using energy consumption loss ratio is proposed: η1 = 0.8861ζ − 0.2062 (R2 = 0.8626), η2 = −0.5813ζ + 0.2394 (R2 = 0.8537).

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.

Size effect of CrFe particles on tribological behavior and airborne particle emissions of copper metal matrix composites

Brake wear particles emitted from vehicles during friction have become an important source of airborne particulate matter (PM) that causes adverse health effects. Particle emissions might be reduced by optimizing the composition of friction materials. Effects of CrFe particle size on tribological behavior and airborne particle emissions of copper metal matrix composites (Cu-MMCs) were investigated using a pin-on-disc tribometer at sliding speeds ranging from 2.5 to 5.0 m/s. The results indicate that the frictional properties, particle emission behavior and worn surface characteristics of Cu-MMCs were strongly influenced by the size of CrFe particles. With decreasing the CrFe particle size, the friction coefficient was relatively stable at 3.8 m/s, decreased gradually at 2.5 m/s, and decreased first then increased at 5.0 m/s. Basically, Cu-MMCs with medium-sized CrFe particles (100–150 mesh) produced the highest levels of particle emissions, followed by Cu-MMCs with large-sized CrFe particles (60–100 mesh), and then Cu-MMCs with small-sized CrFe particles (150–250 mesh) in succession. The level of particle emissions from Cu-MMCs increased substantially with increasing sliding speed. The obtained results were explained considering the evolution of the worn surface characteristics during the friction process.

Mechanical and Tribological Performance of HDPE Matrix Reinforced by Hybrid Gr/TiO2 NPs for Hip Joint Replacement.

Hip joint collapse is a very common health problem. Many cases need a joint replacement, so nano-polymeric composites are an ideal alternative solution. Due to its mechanical properties and wear resistance, HDPE might be considered a suitable alternative to frictional materials. The current research focuses on using hybrid nanofiller TiO2 NPs and nano-graphene with various loading compositions to evaluate the best loading amount. The compressive strength, modules of elasticity, and hardness were examined via experiments. The COF and wear resistance were evaluated via a pin-on-disk tribometer. The worn surfaces were analyzed based on 3D topography and SEM images. The HDPE samples with various compositions of 0.5%, 1.0%, 1.5%, and 2.0 wt.% filling content of TiO2 NPs and Gr (with a ratio of 1:1) were analyzed. Results revealed that hybrid nanofiller with a composition of 1.5 wt.% exhibits superior mechanical properties compared to other filling compositions. Moreover, the COF and wear rate decreased by 27.5% and 36.3%, respectively.

An organic semiconductor/metal Schottky heterojunction based direct current triboelectric nanogenerator windmill for wind energy harvesting

In this work, we design and fabricate a miniature direct current (DC) windmill generator based on dynamic semiconductor/metal Schottky triboelectric nanogenerators (TENGs), demonstrating a novel way for DC electrical power generation by harvesting wind energy. The semiconducting Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) film and metallic Al foil are designed as the positive-negative friction pair in the DC-TENG, and the softness as well as workability of the friction materials provides excellent flexibility for the design and tailor of a windmill DC-TENG. We systematically studied the effect factors on the output performance of the device, including wind speed, external load, and dimensions of the friction layers. Our device achieves an optimal output performance with a maximum open-circuit voltage (Voc) of 0.6 V and a maximum short-circuit current (Isc) of 3.6 μA at the wind speed of 7 m/s for the friction layer area at 2.5 cm2. To improve the wear resistance of the devices, we introduce a few lubricating materials at the PEDOT:PSS /Al interface and Polyalphaolefin 4 (PAO 4) can improve both the abrasiveness as well as the Voc and Isc. Our work presents a possible strategy for fabricating miniature windmill DC-TENG and provides a potential supplemental for the traditional electrical magnet windmill with heavy equipment.

Study on the Influence of Friction and Wear Properties of High-Speed Rail Brake Materials under Humidity Environment and Temperature Conditions

A multi-functional friction and wear testing machine was used to test the pin disk wear of high-speed railway brake friction material under different disk temperatures (20 °C, 100 °C, and 200 °C) and different ambient humidities (55%, 95%). The test results show that the change in the disk temperature and different ambient humidities have significant effects on the frictional wear performance of the high-speed railway brake material. Under the conditions of 20 °C, 100 °C and 200 °C, the instantaneous friction coefficient and wear rate of the brake material decreased as the ambient humidity increased. The different ambient humidity caused severe surface damage to the brake materials, but the damage mechanisms were dramatically different. At constant temperature, the higher the ambient humidity, the lower the maximum equilibrium temperature of the disc.

Self-healable, stretchable triboelectric nanogenerators based on flexible polyimide for energy harvesting and self-powered sensors

Self-healing triboelectric nanogenerators (TENGs) are new, stable and durable energy harvesters. Polyimide (PI) is a promising negatively charged material that has been widely developed as a negative friction material for TENGs, but self-healing PI-based TENGs are currently vacant. Here, we reported a self-healing TENG device fabricated by self-healing PI for energy harvesting and motion sensing. The designed and fabricated PI-based TENGs exhibited excellent intrinsic self-healing and shape tailorability properties. The self-healing properties are derived from the dynamic disulfide bond exchange and flexible PDMS fragments in the PI backbone, which can recover its damage and output performance at 100 °C for 3 h. The output performance of the fabricated 6FDA-4PDA-PDMS-PI-based TENG was double that of the normal PI-based TENG due to CF3 electron-absorbing groups and siloxane fragments in the PI backbone. Finally, the applications of self-healing PI-based TENGs to harvest energy to drive commercial electronic devices and joint motion sensing were demonstrated. This work provides theoretical guidance for the fabrication of self-healing TENGs with reliable output performance and practical applications, contributing to the future of sustainable energy and wearable electronics.

Influence of Natural Fiber Content on the Frictional Material of Brake Pads—A Review

Research into the use of eco-friendly materials, such as natural fibers, in brake pads has gained momentum in the last few decades. This can be attributed to the potential of natural fibers to replace traditional materials in tribological applications such as braking pads. The harmful impact of the commonly-used brake pad materials, such as metal and mineral fibers, on human health and the environment necessitates the development of eco-friendly alternatives. Natural fibers, such as banana peels, palm kernels, and palm slag, have been shown to be a viable replacement for traditional brake pad materials. This article reviews the literature on the use of different natural fibers in brake pads and their impact on the physical, mechanical, and tribological properties. Trends for density, porosity, hardness, coefficient of friction (COF), and wear rate are observed. The recommended formulations to yield the optimum properties, according to the perspective of several studies, are showcased. In addition, the effect of asbestos material and natural fibers on life-cycle assessment and CO2 emission is highlighted. This article is an attempt to provide a foundation for future researchers in the field of natural fiber-reinforced composites for brake pad applications.

Biowaste Eggshell Membranes for Bio-triboelectric Nanogenerators and Smart Sensors.

In this study, we used a simple and cost-effective method to fabricate triboelectric nanogenerators (TENGs) based on biowaste eggshell membranes (EMs). We prepared stretchable electrodes with various types of EMs (hen, duck, goose, and ostrich) and employed them as positive friction materials for bio-TENGs. A comparison of the electrical properties of the hen, duck, goose, and ostrich EMs revealed that the output voltage of the ostrich EM could reach up to 300 V, due to its abundant functional groups, natural fiber structure, high surface roughness, high surface charge, and high dielectric constant. The output power of the resulting device reached 0.18 mW, sufficient to power 250 red light-emitting diodes simultaneously, as well as a digital watch. This device also displayed good durability when subjected to 9000 cycles at 30 N at a frequency of 3 Hz. Furthermore, we designed an ostrich EM-TENG as a smart sensor for the detection of body motion, including leg movement and the pressing of different numbers of fingers.

An investigation into the physical, mechanical, tribology, thermal and durability performance of commercial brake material for rail transportation

Brake friction materials play a crucial role to enable effective deceleration on the moving rail vehicle. Unfortunately, particulate matters generated by brake wear as well as during the brake manufacturing process are affecting the environment and human health. Due to this, the development of green friction material is important to improve environmental health, safety, and human health. To develop new environmental-friendly friction materials, it is important to understand the commercial brake block material components and their tribological performance. Characterisation techniques such as hardness test, pin-on-disc wear test, durability test, thermogravimetric analysis, morphology, density and porosity were performed on the commercial brake block, the obtained results were then compared with the existing literature. The experiment results showed that the performance of the commercial sample is superior to the available green friction composite materials. This indicates the necessity of a new formulation for the development of green friction brake block material that can give better or similar performance as commercial material. The results from this article can be referenced to develop the new formulation.

Robust salt-shelled metal halide for highly efficient photoluminescence and wearable real-time human motion perception

All-inorganic metal halide perovskites (MHPs) with the formula CsPbX3 (X = Cl-, Br-, I-) have excellent photophysical properties and low-cost fabrication, offering exciting opportunities for flexible electronics. However, the suboptimal quantum yield and inferior stability of solid-state MHPs impede their diverse wearable applications. Here, a straightforward water evaporation crystallization strategy for the preparation of salt-shelled metal halide solids is proposed. The well-designed CsPbBr3@KBr material exhibits narrow green photoluminescence (full-width at half-maximum ∼ 20 nm), high quantum yield (87.3 %), and favourable light irradiation and thermal stability. Thus, their applications in waterborne transparency inks and flexible photoluminescent films are demonstrated. Especially, they can be employed as fillers of polyvinyl alcohol (PVA) for high-performance positive friction materials in triboelectric nanogenerators (TENGs), and the output performance of the TENG is 2.3 times higher than the pristine one. As a proof-of-concept, a wearable photoluminescent sensor with a voltage response range of 0–100 kPa and a response time of 125 ms is constructed, which can potentially be served as a passive sensor-in-screen configuration to detect motions of various parts of the human body. It is believed that such metal halides will unleash the possibility of a broad variety of applications in lightweight and multifunctional wearable electronics.

Interplay Between Friction and Cohesion: A Spectrum of Retrogressive Slope Failure

AbstractRetrogressive failures occur in slopes consisting of sensitive materials such as snow or quick clay. They can be triggered by a small disturbance at the slope toe, but can cause propagated failure spreading miles away. Understanding the physical mechanism and predicting the retrogressive failure process are particularly important. Previous studies have discussed the failure criteria, the soil properties or the method of numerical modeling of retrogressive slope failure. However, little attention has been paid to the microscopic failure mechanism, especially relating to various possible failure patterns. In this study, multiscale modeling is incorporated to study the physical mechanism of different retrogressive failure patterns, including earth flow, flowslide and spread failure, within a unified framework. Utilizing multiscale analysis, we found that earth flow failure is related to the shear failure of granular materials. In contrast, the development of macroscopic shear bands is accompanied by tensile failure. As shear and tension failures are typical failure mechanisms of frictional and cohesive materials, it is deduced that friction and cohesion effects play key roles in different retrogressive failure patterns. Therefore, the distributions of attractive and repulsive contact forces are explored and a novel parameter η is proposed to quantify the interplay between friction and cohesion. Further analysis proves that η can capture the effect of friction and cohesion and distinguish different retrogressive failure patterns. Finally, a spectrum of retrogressive failures for a granular slope is established, in which the failure mechanism is explained by the changeable dominant effect, that is, frictional or cohesive in soil.

Disc Brake Design with Carbon Friction Material

Disc Brake Design with Carbon Friction Material

Effect of limestone usage on tribological properties in copper and asbestos-free brake friction materials

PurposeThis study aims to determine the braking performance of limestone as a filler in brake friction materials.Design/methodology/approachSamples containing limestone material (30-35-40%), which can be an alternative to brake friction material filler, were produced. The samples were weighed on precision scales, mixed homogeneously and produced using the hot molding method. The physical and tribological properties of the produced samples were determined, and their microscopic analyzes were made with scanning electron microscopy.FindingsAs the amount of limestone increased, the density of the samples decreased. The friction coefficient and wear rates were close to each other and within the optimum limits for all samples. Limestone materials can be used instead of barite materials studied in the literature on brake linings. Microcracks were observed only in samples containing 30% and 35% limestone in microscopic images.Originality/valueIn this study, the wear rate, coefficient of friction and microstructures on the friction surfaces of brake friction materials containing limestone were investigated. The usability of limestone as a filler in brake friction materials provides valuable information to researchers and industrial organizations in the brake friction material field.

On Friction, Heat Input, and Material Flow Initiation during Friction Stir Welding: Tool and Process Optimization

The Friction Stir Welding (FSW) process depends entirely upon mechanical contact between the tool and the workpiece. As a result of this, all process phenomena and process outcomes such as weld geometry and mechanical properties are governed by FSW’s frictional system. The following work characterizes this system with a focus on process initialization, heat input and material flow. For this purpose, an experimental program for the isolated investigation of the frictional system was carried out. Short-term effects such as contact initiation, run-in behavior and frictional transitions are considered as well as the influences of process parameters and geometry. The system and its behavior are analyzed quantitatively and qualitatively by experiments altering the normal pressure, relative velocity, and tool geometry. The experiments demonstrate a self-similar behavior of the process, including an important wear transition which initiates the material flow, and a subsequent equilibrium of forces, heat balance, and temperatures. The interaction between the tool and the welded material is described, as is the link between the frictional interface and material flow initialization. Based on these findings, recommendations are provided for process optimization and tool design.