Friction Pads Research Articles

Experimental study of rotational friction damper for seismic response control: friction material comparison and configuration optimization

Rotational friction dampers (RFDs) can be incorporated into structures flexibly as energy-dissipation devices for seismic response control. However, the basic primary form of RFD has three main challenges and objectives in enhancing its performance: (1) avoiding strength fluctuation and jittering, namely, improving the stability of the performance, (2) enhancing the strength, and (3) relieving the basic assumption that the clamping pressure is uniformly distributed on the friction pads and ensuring the accuracy of the theoretical equation. To address these issues, this study proposes four potential approaches: (1) selecting a friction material with a stable performance, (2) increasing the friction coefficient, (3) increasing the clamping force, and (4) optimizing key configurations. Based on these concepts, two sets of experimental studies, including 27 friction pad material comparison tests and 17 lug plate and clamping bolt configuration optimization tests, were conducted. According to the test results, the fiber-reinforced resin-based composite (FRRC) material was found to be better than H62 brass and 7075 aluminum alloy in realizing a high friction coefficient and stable performance, as well as achieving uniformly distributed pressure. The four-bolt lug plate and six-bolt lug plate with stiffening ribs were found to be effective in realizing a high clamping force and, thus, a high RFD strength, as well as in achieving a uniformly distributed pressure. In contrast, the single-bolt lug plate could not realize a high clamping force because of the tightening torque limit. A six-bolt lug plate can cause pressure concentration and edge damage to the friction pad.

Investigation on the failure mechanism of friction-based self-centering timber beam-column joint considering bolt bearing effect: Experimental study and theoretical analyses

For friction-based self-centering timber structures, the bearing between friction bolts and the edge of holes is inevitable, due to machining inaccuracies and significant deformations at the beam-column joints. However, this issue has yet to be addressed in existing research. A limit state investigation was conducted on these friction-based self-centering timber beam-column joints under extensive deformation to analyze the failure mechanism and the loss of pretension force throughout the loading process. The influence of bolt bearing behavior on the residual deformation, loading capacity, energy dissipation capacity, and stiffness of the joint was studied. Finally, a theoretical prediction model considering single bolt and multi bolts bearing was proposed incorporating theoretical analysis and experimental results. The results indicate that the damage of the joint is concentrated on the compression deformation at the edge of bolt holes in friction pads and timber beams. The joint ultimately fails due to the end face of the column being crushed by the anchor used to fix post-tensioned (PT) strands. The joint exhibits good hysteresis characteristics within a 4 % drift and still demonstrates good recoverability within a 6 % drift. The loss rate of pretension force is below 15 % when the drift is lower than 4 %, but it increases significantly after the drift exceeds 5 %. When the drift is less than 4 %, the joints primarily exhibit single bolt bearing mode, resulting in only a slight increase in stiffness for the joints. When the drift exceeds 8 %, the joints primarily exhibit a multi bolt bearing mode, resulting in a maximum increase of approximately 64.5 % in joint stiffness. The theoretical bolt bearing model derived can better predict the position of bolts bearing the edge of holes and the damage state of friction-based self-centering timber beam-column joints.

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.

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.

Laboratory Tests on the Possibility of Using Flax Fibers as a Plant-Origin Reinforcement Component in Composite Friction Materials for Vehicle Braking Systems.

Braking systems are extremely important in any vehicle. They convert the kinetic energy of motion into thermal energy that is dissipated into the atmosphere. Different vehicle groups have different nominal and maximum speeds and masses, so the amount of thermal energy that needs to be absorbed by the friction pads and then dissipated can vary significantly. Conventional friction materials are composite materials capable of withstanding high temperatures (in the order of 500-600 °C) and high mechanical loads resulting from braking intensity and vehicle weight. In small vehicles traveling at low speeds, where both the amount of thermal energy and its density are limited, the use of slightly weaker friction materials with better ecological properties can be considered. This work proposes a prototype composite friction material using flax fibers as reinforcement instead of the commonly used aramid. A number of samples were prepared and subjected to laboratory tests. The samples were prepared using components of plant origin, specifically flax fibers. This component acted as reinforcement in the composite friction material, replacing aramid commonly used for this purpose. The main tribological characteristics were determined, such as the values of the coefficients of friction and the coefficients of abrasive wear rate. For this purpose, an authorial method using ball-cratering contact was used. The results were analyzed using statistical methods. It was found that the composite material using flax fibers does not differ significantly in its tribological properties from conventional solutions; so, it can be assumed that it can be used in the vehicle's braking system.

Metal 3D-Printed Bioinspired Lattice Elevator Braking Pads for Enhanced Dynamic Friction Performance.

The elevator industry is constantly expanding creating an increased demand for the integration of high technological tools to increase elevator efficiency and safety. Towards this direction, Additive Manufacturing (AM), and especially metal AM, is one of the technologies that could offer numerous competitive advantages in the production of industrial parts, such as integration of complex geometry, high manufacturability of high-strength metal alloys, etc. In this context, the present study has 3D designed, 3D printing manufactured, and evaluated novel bioinspired structures for elevator safety gear friction pads with the aim of enhancing their dynamic friction performance and eliminating the undesired behavior properties observed in conventional pads. Four different friction pads with embedded bioinspired surface lattice structures were formed on the template of the friction surface of the conventional pads and 3D printed by the Selective Laser Melting (SLM) process utilizing tool steel H13 powder as feedstock material. Each safety gear friction pad underwent tribological tests to evaluate its dynamic coefficient of friction (CoF). The results indicated that pads with a high contact surface area, such as those with car-tire-like and extended honeycomb structures, exhibit high CoF of 0.549 and 0.459, respectively. Based on the acquired CoFs, Finite Element Models (FEM) were developed to access the performance of braking pads under realistic operation conditions, highlighting the lower stress concentration for the aforementioned designs. The 3D-printed safety gear friction pads were assembled in an existing emergency progressive safety gear system of KLEEMANN Group, providing sufficient functionality.

Evaluation of the Degree of Degradation of Brake Pad Friction Surfaces Using Image Processing

The improvement of drilling rig systems to ensure a reduction in unproductive time spent on lowering and lifting operations for replacing drilling tools and restoring the performance of drilling equipment units is an important task. At the same time, considerable attention is paid to the reliable and efficient operation of the braking systems of drilling rig winches. In the process of operation, the polymer pads periodically come into contact with the outer cylindrical surface of the metal pulley during braking, work in extreme conditions and wear out intensively, so they need periodic replacement. Tests were carried out on a modernized stand and in industrial conditions for the brakes of drilling winches. A methodology for evaluating the degradation of the brake pad friction surface during its operation is proposed. The assessment of the degradation degree is carried out based on the image of the brake pad surface using image processing techniques. Geometric transformations of the input image were performed to avoid perspective distortions caused by the concave shape of the brake pads and the spatial angle at which the image is acquired to avoid glares. The crack detection step was implemented based on the scale-space theory, followed by contour detection and skeletonization. The ratios of the area and perimeter of segmented and skeletonized cracks to the total area were chosen as integral characteristics of the degradation degree. With the help of scanning electron microscopy, the character of the destruction of the friction surface and the degradation of the polymer material was investigated. Experimental studies were performed, and the application of the proposed method is illustrated.

Friction Coefficient of Wet Clutches as a Function of Service Mileage

As a core component for efficient variable speed transmission and energy saving, wet clutches are widely used in the transmission systems of energy-saving and new energy vehicles. However, with an increase in the service mileage of the wet clutch, the friction coefficient undergoes alterations. This leads to a deterioration of the control accuracy of the clutch transmission torque, which ultimately has a negative impact on the dynamic characteristics and driving safety of the entire vehicle. In order to understand the service behavior of the friction coefficient in a wet clutch, wet clutches with different service mileages were investigated experimentally and theoretically. The results show that as the service mileage increased, the hydrodynamic lubrication phase was extended. Analyses of the three-dimensional profile of the friction plate and the theoretical simulation of the friction revealed that the edge ridges of the friction pads were flattened. This increased the clutch engagement force when the asperities on the separator and friction plates came into contact.

Structural and Tribological Analysis of Brake Disc–Pad Pair Material for Cars

The study of the tribological behavior of the braking system in auto vehicles requires knowing the characteristics of the material in contact and, in the work process, the friction pair brake disc pads. Material structural analysis is necessary because the wear process depends both on the friction-pair chemical composition (brake disc pads) and on the work process parameters (pressing force, rotational speed, traffic conditions, etc.). The material of the brake discs is generally the same, gray cast iron, and the brake pads can be semimetallic (particles of steel, copper, brass, and graphite, all united with a special resin), organic materials (particles of rubber, glass, and Kevlar, all joined with the help of a resin), composite materials that contain different constituents, and ceramic materials (rarely have small copper particles). Therefore, the purpose of this paper is to analyze the crystalline structure, tribological behavior (at friction and wear), and the mechanical properties of the materials of the brake disc–pad friction pair specific to the field through study and analysis.

Assessment of benzoxazine resins as brake pad friction material binder: Tribological properties and PM emission

This study explores benzoxazine resins as alternative binders for brake pad friction materials, comparing them to the established phenolic resins. Benzoxazine resins feature great thermal properties, alongside industrially-attractive properties such as forgiving storage conditions and extended shelf life. Tribological Pin-on-Disc tests were conducted at different temperatures, with airborne emission monitoring. The characterization of the samples and their worn surfaces was carried out through TGA, SEM, and EDXS analyses. The results revealed promising tribological performance for benzoxazine-bound materials, suggesting potential environmental benefits, especially in high-temperature conditions. This research builds upon a preliminary study focusing on the processing aspects of benzoxazine resins.

Research on point-supported rotational semi-rigid energy-dissipation connection for precast-cladding-panel at connection level

A novel point-supported rotational semi-rigid energy-dissipation connection for precast cladding panels (PRSEC) is proposed in this paper. The PRSEC, utilizing combined mechanical mechanisms involving friction and bending parts, could transform from a rigid connection into a flexible energy-dissipative connection as the seismic action increased. Theoretical predictions of PRSEC are presented, followed by a coordinated design method with the precast cladding panels. Subsequently, monotonic and cyclic loading tests are conducted to investigate the semi-rigid characteristic of PRSEC. Two distinctive working stages, the static friction stage and the sliding friction stage, are clearly captured in the monotonic test results. Additionally, the cyclic tests reveal that the PRSEC specimens exhibit favorable hysteretic performance, characterized by a stable load capacity, favorable deformation ability, and efficient energy dissipation capacity. The NAO friction pads exhibit a fragmented damage pattern, while the brass friction pads demonstrate a linear scratch damage pattern. No cracks or tears are observed on the surface of the bending part, which demonstrated a track-like deformation mode. Both PRSEC specimens with NAO and brass friction pads show satisfactory low-cycle fatigue performance. Furthermore, finite element analyses are conducted using Abaqus to reveal the working mechanism of the friction and bending parts. The influence of the relative parameters is also summarized based on both experimental and numerical analyses. Subsequent research would be conducted to analyze the interaction between PRSEC and precast cladding panels at the structural level to provide a reference for the design of structures employing PRSEC.

Mechanisation in the production process of the technical station - ensuring the safety of train traffic

The article is devoted to the replacement of brake pads at railway infrastructure car maintenance facilities. This article studies the problem of replacing friction pads in passenger cars, when the checks jam under the influence of external dynamic and temperature factors during operation. According to the standard technology the replacement of the defective pad is carried out with the use of manual devices, which does not meet modern requirements. A new screw puller for replacing the brake pads of wagons is proposed. The screw pair is calculated and its rational parameters are specified.

MODELING THE RESOURCE OF HAUL MECHANISMS OF PASSENGER VEHICLES WITH THE PROMINATION OF THEIR FRICTIONS

The article considers the process of wear of the friction surfaces of disc brakes, taking into account their designparameters, the coefficient of wear resistance of materials, the initial braking speed of the car, the amount of mileage andits braking distance during this period, which are used to estimate the resource of braking mechanisms.For this, a systematic approach was used, a rational combination of experimental research and analysis of knowntheoretical scientific results of I.V. Kragelsky on the theory of friction and wear.It is known that in order to estimate the resource of braking mechanisms of motor vehicles, it is important to establishthe amount of permissible wear of friction surfaces that form frictional contact.The authors established the regularity of changes in the wear of the friction surfaces of disc brake mechanismsdepending on the friction radius, the kinematic rolling radius of the wheel, the amount of drive pressure and the brakingdistance of the car.It is important to assess the service life of brake mechanisms of passenger cars in operation is to establish thepermissible relative wear of individual parts and couplings of brake mechanisms. Since the most responsible part of thecar's braking system, which is the brake mechanism, works in different conditions of wear, then establishing the relativewear of the coupled parts that create friction, depending on the change in its geometric parameters and operating modesduring operation, is an urgent task.A predictive assessment of the resource of brake mechanisms of the front and rear axles of passenger cars is provided,which is proposed to be carried out based on the indicator of the relative wear of the friction surfaces. It is shown on theexample of Chevrolet Aveo passenger cars that the relative wear of the brakes of the front axle is maximum and variesbetween 22.5-26.1%, while the relative wear of the brakes of the rear axle is 21.0-22.5%. The resource of the brake discis 4.44 times greater than the resource of the friction pad, while this indicator is 4.76 for the rear axle.

Iron Oxide and Hydroxide Speciation in Emissions of Brake Wear Particles from Different Friction Materials Using an X-ray Absorption Fine Structure

Iron (Fe), the main component of non-exhaust particulates, is known to have variable health effects that depend on the chemical species of iron. This study characterized the possible contribution of iron oxides and hydroxides to airborne brake wear particles under realistic vehicle driving and braking conditions with different brake pad friction materials. We found significant differences in wear factors and PM10 and PM2.5 emissions between non-asbestos organic (NAO) and European performance (ECE) brake pads. Iron was the dominant contributor to PM10 and PM2.5 brake wear particles for both NAO and ECE. The iron concentration ratio in the particle mass (PM) was comparable to the disc-to-pads ratio measured by wear mass. The fact that magnetite, which is of interest with respect to health effects, was less abundant in NAO than in ECE suggested that tribo-oxidations occurred in NAO. Metallic iron is generated not only from abrasive wear but also from tribo-chemical reduction with magnetite as the starting material. We found that there were differences in PM emissions between brake friction materials, and that the phase transformations of iron differed between friction materials. These differences were apparent in the distribution of iron oxides and hydroxides. Heat, tribo-oxidation, and tribo-reduction are intricately involved in these reactions.

Development and optimization of a novel response‐amplified friction damper with different friction pairs

AbstractIn order to improve the efficiency of friction dampers, a shear‐type response‐amplified friction damper (RAFD) was proposed, which utilized a lever mechanism to amplify the shear displacement and increase the sliding distance of friction pairs. Cyclic loading tests were conducted on 12 RAFD specimens to evaluate the effects of machining processes, friction materials, loading protocols, and bolt pretension on the mechanical performance of the specimens. The results showed that the RAFD specimens with NAO and brass friction pads exhibited plump hysteresis loops, and the bearing capacity, effective stiffness, energy dissipation, and equivalent viscous damping ratio all met the stability requirements of FEMA 356 for the friction damper. Reducing the clearance between pins and holes and strengthening the hole edges shortened the plateau near zero resistances of the hysteresis loops by 75%–90%. Furthermore, combined with rotational analysis of the lever, a design methodology for the RAFD specimen was developed. Based on the response amplification factor R, key mechanical indices such as bearing capacity and equivalent friction coefficient were derived, and a theoretical hysteresis model for the RAFD was constructed, which matched well with experimental results.

Increasing the Repair Efficiency of Clutch Plates by Development of an Appliance for the Adhesion of Friction Pads

Increasing the Repair Efficiency of Clutch Plates by Development of an Appliance for the Adhesion of Friction Pads

Research on hysteretic performance of a semi-rigid energy dissipation connection for precast cladding panels

A novel semi-rigid energy dissipation connection (SEDC), capable of transitioning the precast cladding panel from a rigid connection to a flexible connection with the primary structure as the seismic action increases, is proposed in the present study. The combination of the bending part and friction part endows the connection with the ability to provide adjustable sliding force and sufficient energy dissipation for the precast cladding panel. The design methods of SEDC, including the elastic stiffness, the yield force, the yield displacement, and the bear capacity, are proposed, followed by a coordinated design method between the precast cladding panels and the primary structure based on SEDC. Fourteen SEDC specimens are designed and tested under monotonic and cyclic loading tests to investigate the semi-rigid workability of SEDC and to evaluate the influence of design parameters of the bending and friction parts. Two working processes, which are the static friction process and the sliding friction process, are clearly reflected by the monotonic test results. The cyclic test results indicate that the SEDC specimens demonstrate satisfactory plastic development with full hysteretic curves, stable load capacity, reliable deformation ability, and favorable energy dissipation ability. The U-shaped bending plates exhibited a track-like deformation pattern without any observed tears or cracks. The NAO friction pads demonstrated a fragmented damage pattern, while the Brass friction pads demonstrated a linear scratch damage pattern. SEDC specimens equipped with Brass friction pads exhibited better low-cycle fatigue performance, which can be attributed to the favorable wear resistance of the Brass material. In addition, finite models of SEDCs are established and validated based on Abaqus. The combined working mechanism of SEDC, including the contribution ratio of load capacity and dissipated energy from the bending part and the friction part, is clearly revealed. Furthermore, the influence of parameters including the thickness (t), width (B), straight section length (l), radius (R), and height (h) of the bending part, as well as the pre-tightening force (pc) and the friction coefficient (f) of the friction part, are also summarized based on both the experimental and numerical analyses. Further discussions, including the calculation of the seismic behavior factor and the measurements for accurate construction, are conducted.

Thermal Field Simulation and Thermal Capacity Influence Factor Analysis of Disc Brake Based on Thermal-structure Coupling

The matching and heat dissipation capacity of the brake have an important impact on the braking performance of the vehicle. During braking, most of the driving kinetic energy of the vehicle is converted into the internal energy of the brake disc through friction heat generation, resulting in a quick rise in the temperature of the brake disc, thus causing a complex thermal-solid coupling problem. This paper takes the disc brake of a certain vehicle as the analysis object, establishes the finite element model of the disc brake through hypermesh, and analyzes the distribution characteristics of the contact pressure between the friction pad and the brake disc under clamping and torsion braking behaviors. A thermal-solid coupling simulation analysis method considering the actual heat flow and heat transfer boundary of the brake disc is proposed. Compared with the temperature field of the bench test, the simulation accuracy reaches 97%. Finally, three types of brake discs with point rib, rotation rib and straight rib are designed, and the influence of brake disc thickness, shape and number of ventilation rib on the thermal capacity of brake disc is analysed. It provides guidance for the structural design of brake discs and can replace partial tests and shorten the brake disc development cycle.

On the impact of pad material ingredients on particulate wear emissions from disc brakes

Besides friction and wear, airborne particle emission has become a central parameter when evaluating disc brake performance due to its potential adverse health effects as component of ambient air pollution. The pad friction material of brake system is composed of a mixture of ingredients grouped into four material categories: abrasives, reinforcing fibres, lubricants, and fillers. Some other ingredients which do not typically belong to aforementioned categories can be attributed to “fixed material”, such as aramid fibre, which is usually added into brake pad to harmonize the overall tribological properties. There is a gap of knowledge about how one ingredient from one category contributes to the emissions of particle number (PN) and mass (PM2.5, PM10). To investigate this, one ingredient from each category was chosen and produced as pins. As a reference, pins made of a commercial European brake friction material were also produced. The pins were tested using a pin-on-disc tribometer designed for airborne emission studies. Coefficient of friction, particle mass and number concentrations were measured during the tests. The results indicate that the abrasive and metal fibre have PN, PM2.5, and PM10 emission factors that are orders of magnitude higher than the lubricant and aramid fibre.

Wear-friction properties of friction pairs in disc-pad brakes

This paper reports data on the dynamic coefficient of friction and wear of materials of different types of friction pads and brake discs obtained from experimental research during braking under bench conditions. It was established that on the basis of the chemical composition of the materials of the friction pads with codes, in the temperature range of 100–450 °C with a step of 50 °C, the ratio of the maximum to the minimum wear of the disc varies from 6.0 to 10.0. The value of the disc wear ratio at 800 and 1000 brakings, respectively, in the temperature range of 100–250 °C and 100–450 °C was 7.6 and 14.0. This indicates that for pad materials of type A, B, C, and D under the second thermal regime, the linear wear of the working surfaces of the discs is greater than under the first thermal regime. And for the pad materials of type E and F, the wear of the discs was the same. This indicates that the use of traditional pads is characterized by a higher thermal tension of the disc brake friction pair; the absolute temperature values are in the unfavorable zone of 400–700 °C. That, in turn, could lead to both phase changes and thermal fatigue aging of materials and, as a result, to the deterioration of their tribological and thermophysical characteristics in operation. Thus, the implementation of the method of selecting pad components could improve the performance of disc brake devices of cars