Friction Materials Research Articles

Performance assessment of agricultural waste based eco‐friendly brake friction composites

AbstractThere has been growing interest in using sustainable and eco‐friendly products to produce engineering materials. For this purpose, composite material applications obtained from agricultural wastes are gaining popularity. This study examines the synergistic effect of rice husk and rice stalk wastes on the fade and recovery performance of brake friction composites. Brake friction materials were developed using rice husk and rice stalk separately and in two different weight percentages as a 5–10 ratio in the formulation. For comparison purposes, a reference brake pad using copper as a substitute and a commercially available brake pad were used. Various physical, mechanical and thermal properties were analyzed. The tribological behavior of friction composites was evaluated on the Krauss test device in line with the ECE R90 procedure. The worn surface properties were analyzed using scanning electron microscopy. Tribo test results of friction composites were taken as criteria for performance optimization. While the importance weight of the criteria was determined by AHP, the VIKOR method was used in the sorting of alternatives. The experimental results have revealed that rice husk‐added friction composites had a good coefficient of friction value with better fade and recovery performance compared to rice stalk‐added ones. Increasing the amount of rice husk and rice stalk in the formulation tended to decrease the fade performance; however, it has increased the wear rate and recovery properties. Optimization results have shown that the brake friction composite containing 5 wt % rice husk ranks first in meeting the desired tribological criteria.Highlights Cu‐free rice husk and rice stalk‐added friction composites were developed. Fibrous structure in the matrix developed the contact plateaus. Rice husk‐based tribo‐layer protected the composite from further wear damage. The addition of agro‐waste to friction composites exhibited good potential.

Pin-on-disc tribological characterization of single ingredients used in a brake pad friction material

Researchers have long been studying the effects of the modification of friction material compositions on their tribological properties. Predictive models have also been developed, but they are of limited use in the design of new compositions. Therefore, this research aims to investigate the tribological behaviour of single ingredients in friction materials to develop a tribological dataset. This dataset could then be used as a foundation for a cellular automaton (CA) predictive model, intended to be a tool for designing friction materials. Tribological samples were almost entirely composed of four distinct friction material ingredients, and one sample composed of their mixture was successfully produced. Pin-on-disc (PoD) tribometer testing and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDXS) analysis were used for the tribological characterization. Each material showed distinct tribological properties and evolution of the contact surface features, and the synergistic effect of their mutual interaction was also demonstrated by their mixture.

An enhanced analytical and numerical thermal model of frictional clutch system using functionally graded materials

Abstract When a component was built from a functionally graded material (FGM), the temperature of contact was determined using an analytical model (FGM). The analytical solution is applied using the concept of equivalent properties. In order to fully examine the dynamic of the equivalent property principle, a numerical analysis was done. The FGM (silicon carbide and aluminum) friction liner was used. It focuses on a few characteristics that have an impact, such as load, velocity, friction material type, and slip time, which appear in dimensionless form. The results show that for loads and velocities, the ratio of the rate of dissipation to the rate of generation of heat transfer is one, whereas the behavior differs for friction material and slip time. Furthermore, this study’s chosen FGM exhibits superior thermal behavior compared to Al and Sic, bolstering its viability as a friction liner in the clutch system.

Large Scale Simulation of 3D Fault Rupture Subjected to Far‐Field Loading With PDS‐FEM: Application to the 2018 Palu Earthquake

AbstractSimulating dynamic rupture of fault systems can be computationally demanding, as it requires reproducing complex fault geometry and accurately capturing waves propagating away from the rupture front. It is in particular challenging to predict an initial stress state consistent with fault geometries, heterogeneous distribution of surrounding materials, and far‐field tectonic loading. While standard techniques such as contact analysis and Lagrangian multipliers can be used to model the fault, it can lead to significant computational overhead in FEM. We extended Particle Discretization Scheme‐FEM, which provides numerically efficient crack treatment, without requiring contact analysis, to simulate dynamic fault rupture as a frictional crack propagating along a pre‐existing shear crack surface. Initial stress, which is consistent with initial frictional forces, material distribution and fault geometry, is derived using Coulomb friction and far‐field boundary conditions. The study first demonstrates the ability of the numerical method to reproduce a 2D ideal supershear scenario, and the underlying Burridge‐Andrew rupture mechanism. The methodology is then applied to the large scale simulation of the 2018 Palu earthquake on the Palu‐Koro fault. The simulation successfully reproduces the early and sustained supershear rupture which was observed for the Palu earthquake. Also, it indicates that the presence of an off‐fault damage zone can contribute to the low rupture velocity measured during the earthquake. Unlike sub‐Rayleigh earthquakes, the shockwave propagation was observed to lead to significant amplitudes of the ground motion even far from the fault.

Evaluation of mechanical and tribological properties of Cu-based friction materials reinforced by 3D mesh structure

Cu-based friction materials (CBFMs) are widely used in brake system such as High-Speed Trains and Wind Power Generation, its mechanical and tribological properties are of vital importance for the stable and safe operation. In this study, CBFMs holding 3D mesh structure were designed and fabricated by wet granulation and particle coating technology. Stress and temperature fields were obtained by finite element simulation. After that, the mechanical and tribological properties were investigated. The results showed that 3D mesh structure can enhance the compressive strength of CBFMs to 34.56 % and reduce wear rate to a large extent. This study was expected to open up a new direction in enhancing comprehensive performances of CBFMs without changing its composition.

Conversion of images of 3D friction maps to study the coupling between coefficient of friction, velocity and contact temperature of the disc brake

The coefficient of friction during braking is not constant. Determining its variability requires measurements in real conditions. This paper presents a methodology of conversion of the measured time profiles of the sliding velocity Veq, contact temperature T, and coefficient of friction f, into analytical formulation of two variables z = f(x,y). This was executed in the following steps: 1) creating a three-column table Veq, T, f from experimental measurements; 2) interpolation using Kriging; 3) creating a contour map of the coefficient of friction dependent on the sliding velocity and temperature, 4) import of a grey scale image of the friction map into the finite element (FE) software, and 5) definition of a function z = f(x,y). The studies were carried out for five composite organic friction materials and cast-iron brake disc of a railway vehicle. The developed five friction maps for each friction pair were based the data from the full-scale bench tests during braking from the initial vehicle velocity of 80 kmh−1, 120 kmh−1, 140 kmh−1, 160 kmh−1, 200 kmh−1 to a stop. In the second part of the study the initial-value problem for the equation of motion combined with the heat conduction problem were formulated and solved numerically using special functionalities of the FE software, e.g. Deformed Geometry, Mathematics. Changes in the vehicle velocity and time profiles of the coefficient of friction were determined from the solution of the coupled thermal problem. The computational FE model was verified by comparing the measured and calculated changes in the vehicle velocity, coefficient of friction and evolutions of the brake disc temperature during single braking. The maximum calculated temperature 1 mm under the contact surface of the brake disc, during braking from initial vehicle velocity of 80 kmh−1, was obtained for the base friction material and was equal to T1,3,5Num.= 72 °C. The corresponding experimental value was T1-6Exp.= 66.1 °C. When braking from 140 kmh−1, for the same material it was T1,3,5Num.= 129.7 °C and T1-6Exp.= 130.7 °C. The obtained differences in braking times calculated and measured did not exceed 1.7 %. The corresponding temperature differences of the disc at the stopping time were lower than 5.5 %.

High-output solid[sbnd]liquid triboelectric nanogenerator enhanced by the regulation of interfacial wettability

Triboelectric nanogenerators (TENGs), as a new strategy for harvesting energy from nature, have attracted widespread attention in the field of water droplet energy capture. As a friction layer material, the solidliquid electrification phenomenon of coatings has been studied. However, little attention is paid to the influence of the surface wettability of the coating itself on the electrical signal of the droplet generator. In this study, alkyl/phenyl pure silicone resin was utilized as a substitute for fluorine-containing polymer materials. This substitution not only mitigated the risk of environmental pollution from TENG friction materials but also resulted in varying wettability of the silicone resin coating through plasma and surface structure treatment. The droplet-based Double-electrode (D-TENG) and Single-electrode (S-TENG) coating-based triboelectric nanogenerators were fabricated. Through the integration of a high-speed camera and ammeter, the motion state of water droplets on surfaces with different wettability closely correlates with their charged behavior. This correlation is utilized to observe the motion state of water droplets on hydrophilic-hydrophobic surfaces in four stages: contact, spreading, contraction, and sliding. Under the double-electrode structure, as the water contact angle of the coating increased from 6.84° to 139.77°, the short-circuit current initially increased and then decreased, peaking at 466 µA when the contact angle was 98.48°, representing a 677-fold increase from the initial 0.689 µA. In the single electrode structure, the short-circuit current increased from 2.66 nA to 700 nA, indicating a 263-fold increase. Studying the varied wettability of the surface of silicone resin coating aids in comprehending the application of the coating material in solid-liquid friction electrification for energy collection. Furthermore, it offers insight into selecting appropriate coating materials for friction coatings in future applications.

Multi-scale morphological analysis of brake lining surface and load-bearing arrangement in the contact

In the case of braking, a diversity of friction mechanisms occurs at the interface, caused by the heterogeneity of the composition, properties, and thermal phenomena. After friction, the obtained surfaces of the brake lining materials are highly heterogeneous. Load-bearing plates which are also called contact plateaus are formed with a compacted third body and constitute the sites of energy dissipation and sliding velocity accommodation. Their arrangement and preferential localizations in the contact constitute a key factor for the understanding of friction-induced phenomena and braking performance. Within this framework, a morphological characterization method has been set up based on several measurement techniques to explore the macroscopic and microscopic contact situation of the pad-disc system. The results show that exploiting Abbott curve parameters combined with roughness parameters is an effective way to give a detailed and comprehensive morphological description of the brake pad friction surface. It can be seen that the contact plateaus have preferential locations which give a particular load-bearing arrangement in the pad-disc interface which can be explained by friction and wear mechanisms. Results reveal also the main encountered difficulties, especially regarding the significance of scales and parameters describing the morphology of the friction material surface and the load-bearing plates disposition.

Advances in brake friction materials: A comprehensive review of ingredients, processing methods, and performance characteristics

AbstractThe crucial significance of brake friction materials lies in ensuring automobile safety and performance. This drives the ongoing development of these materials to meet rigorous criteria. Recent developments in friction materials have improved the effectiveness of braking systems, resulting in increased safety and comfort. Modern society has increasingly adopted environmentally friendly friction materials, replacing conventional alternatives. The advancements in brake friction material development primarily focus on improving braking performance while simultaneously reducing environmental pollution caused by dangerous substances in brake pads. Understanding the different formulations of brake pads and the impact of the materials used is essential due to the complex and expert‐dependent nature of the brake pad manufacturing process. This review aims to fill knowledge gaps surrounding the basic formulations of brake pads and provide insights to researchers on the impact of different ingredients in creating friction brake pads. This research not only highlights the influence of various components on the friction and wear characteristics of brake pads but also addresses the importance of a comprehensive understanding of their fundamentals. The novelty of this review is justified by the lack of up‐to‐date, thorough reviews on brake friction materials, particularly in light of the recent advancements in the field. This review focuses on the developments and innovations in brake friction materials over the last 15 years. It aims to bridge the knowledge gaps regarding the basic formulations of brake pads and provide valuable insights into the influence of various components on their friction and wear characteristics. By addressing both the performance improvements and environmental considerations, this review offers a timely and essential resource for researchers and practitioners in the automotive industry.Highlights Exploration of various ingredients used in the brake friction composites. Ingredients influence on the various characteristics of brake friction composites. Different formulations and its usage in the brake friction composites. Recycled materials usage in the friction composites‐waste to wealth approach.

Preparation and Properties of Brake Friction Materials Reinforced with Coconut Fiber and Dypsis Lutescens Fiber.

Brake friction material reinforced with coconut fiber and dypsis lutescens fiber was designed and prepared in this study. Specimens incorporating 0-8 wt.% of coconut fibers or dypsis lutescens fibers were fabricated. The effect of the content of these reinforcing fibers on the overall properties of brake friction materials was systematically investigated. The results indicate that the inclusion of reinforcing fibers in the formulation of brake friction materials can improve the physical properties and friction and wear properties of brake friction materials. The specimen incorporating 6 wt.% plant fiber obtained the optimal comprehensive performance with excellent fade resistance and recovery properties, and better wear resistance. In order to further investigate their performance, nine hybrid fiber brake friction materials were designed using the golden section method and orthogonal test method. The study indicated that the F-6 hybrid fiber-reinforced brake friction materials have better physical properties, thermal degradation resistance, recovery properties, and abrasion resistance than the single-fiber-reinforced brake friction materials. This study provides new concepts for the preparation of fiber-reinforced brake friction materials as well as formulation optimization.

Effect of mullite on the friction stability of carbon fiber-reinforced friction material

PurposeThe purpose of this paper is to investigate the effect of mullite on the mechanical properties and friction of carbon fiber (CF)-reinforced friction material.Design/methodology/approachCF-reinforced friction materials with varying content of mullite were fabricated by hot press molding, and then the tribological properties were tested on the MRH-3-type tribometer under ambient conditions with the ring-on-block configuration.FindingsThe experimental results indicated that the addition of mullite increased the density and compressive strength of friction material. However, the flexural strength of friction material decreased by 16% with the addition of 15 Wt.% mullite. The friction coefficient was proportional to the mullite content. Friction material with 12.5 Wt.% mullite showed the highest friction stability under different loads, whereas friction material with 10 Wt.% mullite exhibited the highest friction stability under different sliding speeds.Originality/valueBy boosting the resistance to deformation under load and increasing the specific heat capacity, mullite contributed significantly to the friction stability of the friction material.

Molecular Dynamics Simulation and Experimental Study of Friction and Wear Characteristics of Carbon Nanotube-Reinforced Nitrile Butadiene Rubber

Nitrile butadiene rubber (NBR) and its various composite materials are widely employed as friction materials in mechanical equipment. The use of carbon nanotube (CNT) reinforcement in NBR for improved friction and wear characteristics has become a major research focus. However, the mechanisms underlying the improvement in the friction and wear characteristics of NBR with different CNT contents remain insufficiently elucidated. Therefore, we conducted a combined analysis of NBR reinforced with varying CNT contents through molecular dynamics (MD) simulations and ring–block friction experiments. The aim is to analyze the extent to which CNTs enhance the water-lubricated friction and dry wear properties of NBR and explore the improvement mechanisms through molecular chain characteristics. The results of this study demonstrate that as the mass fraction of CNTs (0%, 1.25%, 2.5%, 5%) increases, the water-lubricated friction coefficient of NBR continuously decreases. Under water-lubricated conditions, CNTs improve the water storage capacity of the NBR surface and enhance lubrication efficiency. In the dry wear state, CNTs help reduce scratch depth and dry wear volume.

Enhanced tribological performance of MoS2 and hBN-based composite friction materials: Design of tribo-pair for automotive brake pad-disc systems

This research comprehensively analyzes the friction and wear behavior of composite friction materials when dry sliding against grey cast iron and laser-clad nickel-based (LC1) and iron-based (LC2) alloy discs. The composite friction materials (P1, P2, P3, P4, P5, and P6) under investigation contain graphite, MoS2, and hBN-based solid lubricant synthesized through the powder metallurgy technique. Tribological tests were conducted using a pin-on-disc configuration to simulate the dynamic interaction between the composite materials and the laser-clad grey cast iron discs. The tests were performed at a 60 N load, 6283.19 m sliding distance, and 2.094 m/s sliding velocity under dry sliding conditions. The results provide valuable insights into the effectiveness of MoS2 and hBN-based solid lubricant composites in reducing friction and wear when in contact with iron and nickel alloy-based laser-clad grey cast iron surfaces. The study elucidates the mechanisms governing tribological behavior, including the formation of friction plateaus and the role of laser-clad counter-discs in reducing wear. The specific wear rate of the nickel-based laser-clad counter disc (LC1) and iron-based laser-clad (LC2) system improved by 63.76 % and 48.32 %, respectively, compared to the conventional grey cast iron disc system when using the hBN-based pin (P6). Additionally, the specific wear rate of the hBN-based pin was 38.49 % lower than the conventional graphite-based pin when sliding against the grey cast iron counter-disc. Artificial Neural Network (ANN) was used to validate the wear rate of the best-performing tribological pair, namely the hBN-based pin (P6) and LC2 counter discs, through supervised learning.

Highly Moisture-Resistant Flexible Thin-Film-Based Triboelectric Nanogenerator for Environmental Energy Harvesting and Self-Powered Tactile Sensing.

Triboelectric nanogenerator (TENG) has been demonstrated as a sustainable energy utilization method for waste mechanical energy and self-powered system. However, the charge dissipation of frictional layer materials in a humid environment severely limits their stable energy supply. In this work, a new method is reported for preparing polymer film as a hydrophobic negative friction material by solution blending poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and polyvinyl chloride (PVC), doping with titanium dioxide (TiO2) nanoparticles, and further surface patterning modification. The P-TENG composed of the PVDF-HFP/PVC/TiO2 composite film with optimized hydrophobic performance (WCA = 124°) achieved an output voltage of 235 V and a short-circuit current of 35 μA, which is approximately three times that of the bare PVDF-HFP-based TENG. Under charge excitation, the transferred charge of the P-TENG can reach 35 nC. When the external load resistance is 5.5 MΩ, the output peak power density can reach 1.4 W m-2. Meanwhile, the hydrophobic surface layer with a rough surface structure enables the device to overcome the influence of water molecules on charge transfer in a humid environment, quickly recover, and maintain a high output. The P-TENG can effectively monitor finger flexibility and strength and realize real-time evaluation of the exercise state and hand fatigue of the elderly and rehabilitation trainers. It has broad application prospects in self-powered intelligent motion sensing, soft robotics, human-machine interaction, and other fields.

A semi-conservative depth-averaged material point method for fast flow-like landslides and mudflows

We present a two-dimensional semi-conservative variant of the depth-averaged material point method (DAMPM) for modeling flow-like landslides. The mathematical model is given by the shallow water equations, derived from the depth-integration of the Navier–Stokes equations with the inclusion of an appropriate bed friction model and material rheology, namely Voellmy and the depth-integrated Bingham viscoplastic stress model, respectively. After assessing the accuracy and performance of the proposed numerical method by means of several idealized benchmarks, we test its behavior in a realistic scenario.

Experimental Comparison of Manufacturing Parameters in Automotive Friction Materials

In this study, a fixed automotive friction material content was determined and the mechanical and tribological effects of manufacturing parameters on friction materials were investigated. Parameters; pre-forming time (1-3-5 min) and pre-forming pressure (8-10-12 MPa), hot pressing time (5-10-15 min) hot pressing pressure (8-10-12 MPa) and hot pressing temperature (125-150-175 °C), curing time (4-8-12 h) and curing temperature (120-150-180 °C) were determined. The friction test of the produced samples was carried out under 0.551 MPa pressure and 7 m/s rotation speed for 90 min. In addition, the average COF, friction stability, specific wear rate, density and hardness values of the samples were calculated. According to the results obtained, the average COF value increased as the pre-forming time and pressure increased. The lowest specific wear rate among all specimens was calculated as 7.622x10-6 cm3/Nm in PFP-12 specimen. With the increase in hot pressing time, the tribological properties of friction materials improved. The highest friction stability among all samples was calculated as 79.42% in the HPT-15 sample. Although there was an increase in the average COF value with increasing hot pressing pressure and temperature, the specific wear rates increased in these parameters. The highest average COF value among all samples was obtained in the CT-12 sample with a value of 0.553. The specific wear rate increased with the increase in curing time and temperature. The highest specific wear rate among all samples was calculated 10,743x10-6 cm3/Nm in the CTe-180 sample. Finally, it has been suggested that 3 min for pre-forming time, 12 MPa for pre-forming pressure; 15 min for hot pressing time, 12 MPa for hot pressing pressure, and 150°C for hot pressing temperature; and a curing time of 8 h and curing temperature of 150 °C may be sufficient.

The self-lubrication property of single-phase high-entropy carbide ceramic under tribo-induced effect

Self-lubricating ceramic materials are mainly achieved through the addition of lubrication phases. Although incorporating lubrication phases can improve their tribological performances, the mechanical properties are consistently compromised. Thus, designing and fabricating single-phase ceramic with favorable self-lubricity is the relentless pursuit of researchers. In this study, the single-phase high-entropy ceramic of (Hf0.2Mo0.2Nb0.2Ta0.2Ti0.2)C exhibits self-lubricating properties and which closely relates to the testing condition. The wear rate and friction coefficient decrease with the increasing of loads (not above 30 N). And the friction coefficient of (Hf0.2Mo0.2Nb0.2Ta0.2Ti0.2)C samples against Si3N4 balls is as low as 0.3 under 30 N and 5 Hz. This originates from the carbon-rich tribo-film with self-lubricity, which is generated through diffusion and enrichment under the effect of tribo-induced. Single-phase self-lubricating ceramics—using own constituent elements to form a lubricating tribo-film—are expected to open up a new research field on the high-performance friction materials.

All-Cellulose Nanofiber-Based Sustainable Triboelectric Nanogenerators for Enhanced Energy Harvesting.

Triboelectric nanogenerators (TENGs) show promising potential in energy harvesting and sensing for various electronic devices in multiple fields. However, the majority of materials currently utilized in TENGs are unrenewable, undegradable, and necessitate complex preparation processes, resulting in restricted performance and durability for practical applications. Here, we propose a strategy that combines straightforward chemical modification and electrospinning techniques to construct all-cellulose nanofiber-based TENGs with substantial power output. By using cellulose acetate (CA) as the raw material, the prepared cellulose membranes (CMs) and fluorinated cellulose membranes (FCMs) with different functional groups and hydrophobic properties are applied as the tribopositive and tribonegative friction layers of FCM/CM-based triboelectric nanogenerators (FC-TENGs), respectively. This approach modulates the microstructure and triboelectric polarity of the friction materials in FC-TENGs, thus enhancing their triboelectric charge densities and contact areas. As a result, the assembled FC-TENGs demonstrate enhanced output performance (94 V, 8.5 µA, and 0.15 W/m2) and exceptional durability in 15,000 cycles. The prepared FC-TENGs with efficient energy harvesting capabilities can be implemented in practical applications to power various electronic devices. Our work strengthens the viability of cellulose-based TENGs for sustainable development and provides novel perspectives on the cost-effective and valuable utilization of cellulose in the future.

Investigation on microstructure of Cu-VC-Al2O3-graphite composites fabricated by a novel in-situ reactive synthesis

Cu-graphite composites play an important role as friction materials used in many fields. However, weak bonding of copper with graphite and low strength of copper are significant limitations. In this study, our focus on fabricating high-density Cu-VC-Al2O3-graphite composites by using V2AlC as a modifier for the Cu-graphite systems. The microstructure and interface properties of the composites were thoroughly examined by SEM, EDS, and XRD techniques. The results indicate the in-situ synthesis of VC and Al2O3, which exhibit good compatibility with the copper matrix in the composites. Furthermore, the formation of a VC layer facilitates enhanced interfacial bonding between the copper matrix and graphite. In addition, the resulting composite materials show desirable density and hardness, boasting a relative density of 94.5 % and a hardness of 80.6 HV.

The impact of dual ceramic components (WC/B4C) on the friction performance of copper-based powder metallurgy friction materials and wear mechanism

The copper-based powder metallurgy friction material, modified with dual ceramic components (WC/B4C), underwent friction experiments paired with custom-made carbon ceramic discs. The overall findings are as follows: The judicious addition of dual ceramic components (WC/B4C) can enhance the mechanical, thermal, and frictional performance of copper-based powder metallurgy friction materials. When the WC/B4C ratio is 5:3, the material exhibits the optimal mechanical, thermal, and frictional properties. B4C and WC, after braking, form friction films of B2O3 and WO3. Additionally, the friction film of copper-based powder metallurgy friction materials can be categorized into an oxide layer, a deformation layer, and a matrix layer. The oxide layer primarily consists of Fe2O3, the deformation layer is mainly composed of WO3 and B2O3, and the matrix layer is primarily composed of CuO and Cu2O. With the increase in the WC/B4C ratio, the primary wear mechanisms of copper-based powder metallurgy friction materials shift from abrasive wear to mild fatigue wear, mild fatigue wear progressing to severe fatigue wear, adhesive wear, and fatigue wear, accompanied by a gradual intensification of oxidative wear.