Wear Of Friction Materials Research Articles

T–01M TESTER ADAPTATION FOR WEAR DEBRIS COLLECTIONAND ANALYSIS

The article describes the need to collect and analyse data on stereological features of car tire and brakesystem friction material wear products, as required under new European Union regulations and by the projectto expand the existing T–01M tester with a separation chamber and equipment enabling their capture. Thestructure of the chamber is described and the conditions for measuring the average diameter of particlesemitted by the tested contacts are presented. The basic task of the additional chamber is to separate thesurroundings of the tested friction node from environmental influences and to enable the capture of wearproducts to measure stereological features and analyse their chemical composition. A unidirectional filteredair flow towards the friction node is provided in the separation chamber in order to limit the deposition of wearproducts on the tester components. Mounting the separation chamber does not require any interference in thestructure of the T–01M tester, because it is mounted on a sealed base frame screwed to the station plate. Thechamber is equipped with holders for mounting a replaceable filter at the air inlet and a removable cycloneparticles separator with a container for wear debris collected.

Coupled thermomechanical FE model of a railway disc brake for friction material wear calculations

The article presents a fully coupled 3D thermomechanical model of a railway vehicle disc brake for calculations of temperature, stress, contact pressure and wear distributions. Five specially designed composite organic friction materials associated with a cast-iron ventilated brake disc were analyzed. The performed computer simulations correspond to the operational parameters of braking carried out on a full scale dynamometer test stand at constant braking power and constant vehicle velocity. These conditions were obtained by correcting the clamping force in relation to changes in the coefficient of friction. In the finite element (FE) model of the disc brake, the pad wear depth distribution was determined on the basis of the Archard's law taking into account the specific wear rate, contact pressure and sliding velocity. To create the numerical model with the geometry deformation allowing for friction material loss due to wear, advanced techniques were adapted. The geometric model of the brake includes the complex shapes of the brake pad holder, brake pad and ventilated disc. The wear constants of the tested friction material were obtained by means of the FE simulation and the measurement of the pad weight loss before and after the test on a full scale dynamometer test stand. The distributions of temperature, stresses, contact pressure and accumulated wear depth, obtained from the finite element analysis, in combination with the measured changes in the clamping force and coefficient of friction during braking, enabled to establish relationships between the properties of materials, operational parameters of braking and geometrical features of the brake components.

Research progress of temperature field calculation of disc brake braking interface based on numerical analysis

Disc brakes are the most widely used key components in the braking system of various types of machinery and equipment. When it works, it converts kinetic energy into thermal energy, which will make the braking interface overheat, thus leading to thermal recession of the brake disc and brake pad, which will eventually seriously affect the service life of the machine. The study of temperature changes at the working interface of disc brakes during braking is of great significance to the selection of brake friction pairs and the setting of braking parameters, and is an important theoretical guarantee for improving the service life of brakes. Currently, there are extensive researches on the analysis of temperature fields at the working interface of disc brakes. This paper summarizes the latest numerical research progress of the friction interface temperature field of disc brakes, and evaluates the research status of the friction interface temperature field model, temperature field solution method, and thermodynamics. The review finds that the current numerical method has become the most common method for conducting thermal analysis of disc brakes. The finite element analysis based on thermal modeling, thermal-mechanical coupling methods, and temperature distribution is able to provide more research basis for studying the thermal failure of brake friction pairs, thermal damage mechanisms, and friction material wear mechanisms. Improving the accuracy of the thermal model calculation will be an important research direction for the future numerical analysis of the temperature field of disc brakes.

Friction material wear: Effects and interactions between service brake temperature, lining contact pressure, and vehicle speed

International standards and original equipment manufacturers (OEM) procedures usually define wear tests in organic materials focusing on the brake lining temperature. The current work presents an approach combining different brake pads temperatures, vehicle speeds, and brake pressures for analyzing their effects and interactions in the friction material wear through dynamometer tests. Therefore, mechanical properties were evaluated, where internal shear strength had the most significant influence on wear; furthermore, compressive strength and flexural strength did not considerably change with variations on the test parameters. A 23 factorial design of the experiment (DOE) showed that the brake temperature alone was not the main factor for increasing wear, and the primary wear mechanism was abrasion. Furthermore, higher vehicle speed (80 km/h) along with greater brake pressure (3 bar) promoted the highest friction material mass loss (10.8 g).

Analysis of the Accuracy of Mass Difference-Based Measurement of Dry Clutch Friction Material Wear.

The paper demonstrates that the dry clutch friction plate wear rate, measured based on the plate mass difference method, exhibits a transient behavior after each change of friction interface temperature level. The effect is hypothesized to be caused by a temperature-dependent change in the moisture content/mass level in the friction material. To test this hypothesis, a series of synchronized characterization experiments have been conducted by using two friction plates, one for wear tests and the other for drying in an oven under the same temperature conditions. Based on the analysis of test results, a moisture content compensation procedure, which reduces the transient wear rate from being 100% to being 50% higher compared to stabilized wear rate, is proposed and verified. The gained insights are used to set recommendations on the organization of routine wear characterization experiments aimed at avoiding the effect of moisture content influence on the accuracy of wear measurement. The main recommendations are to minimize the number of temperature target level changes through proper design of the experiment, insert a run-in test after every long test pause, and execute a pre-heat, blind wear test at the beginning of each test day.

Susceptibility of eco-friendly brake-pads to noise-vibration emanation due to siloxane treatment on alumina particles

In case of friction materials (FMs), contribution towards desired friction level and counter-face rejuvenation during braking is manipulated by adding abrasives such alumina, silica, zirconia, SiC etc. in adequate level. However, such particles have less adhesion with the resin and hence are easily dug out during braking contributing to the higher wear and to propensity to the noise-vibration. If efforts are made to enhance the filler-matrix adhesion, not only the wear of FMs would reduce, the friction performance would also improve. This is due to the fact that they will stay for a longer time on the tribo-surface of the FM to contribute fully towards controlling the µ and avoiding three-body abrasion phenomena to the extent possible. Finally, this is expected to enhance the noise-vibration (NV) performance of the brake-pads. The first part of the hypothesis has been validated in the authors’ laboratory by including siloxane-treated alumina particles in brake-pads. However, the second aspect (influence on NV performance) that was not considered in the earlier work is addressed in the current paper.Two types of NAO Cu-free brake-pads were developed keeping all the parent formulation identical using alumina (2 wt%) as a theme ingredient (siloxane treated and untreated). An additional type of a brake-pad without abrasive particles was also developed to analyse the effect of abrasive particles on the NV performance. The present study focusses on a detailed experimental investigation for the evaluation of NV performance based on the noise and vibration data obtained from an NV test-rig according to SAE J2521 standard. It was observed that siloxane treatment influenced the NV performance of brake-pads in a beneficial way and an average reduction of 2–3 dB(A) in the overall sound pressure level (SPL) was observed.

An experimental and molecular dynamics study of the superlubricity enabled by hydration lubrication

Recently, hydration lubrication has emerged as a promising approach to macroscale liquid superlubricity. However, the reported methods till now exhibit a long running-in process that features high and fluctuating friction evolution. Herein, we have employed glycerol aqueous solutions as the model to reveal the mechanism governing the achievement of superlow friction by hydration lubrication, aiming to erase the long and disturbing running-in. Through experimental investigations and molecular dynamics simulations, it is found that the initial high friction of dilute glycerol aqueous solution with the water/glycerol weight ratio of 2.0 is due to the ineffective film formation between the tribopairs, and the superlow low friction after the long running-in is attributed to the synergetic effect of increased viscosity due to water evaporation, increased film thickness due to higher speeds, reduced contact pressure due to the wear of friction materials, and the adsorbed molecular layers on steel surfaces. To improve the initial lubricating condition that is responsible for the high coefficient of friction at the start of the test, the formula has been modified with the water/glycerol weight ratio reduced to 0.2, and its friction performances have been further investigated. Surprisingly, remarkable and robust superlow friction appears almost as soon as the test starts. Molecular dynamics sliding simulation reveals the formation of shearing layers or hydration layers near the surfaces and the load-supporting layers between them. The results in this work are helpful to expand the understanding of the superlubricity mechanism enabled by hydration lubrication, and it also provides a novel strategy to liquid superlubricity using aqueous media that features vanished running-in.

Functionalization of alumina particles to improve the performance of eco-friendly brake-pads

Abrasives, such as oxides of alumina (Al), silica (Si), zirconia (Zr), chromium (Cr) etc., are added to raise the friction level and also to remove the glaze on the disc so that surface will be rejuvenated continuously during braking and will contribute to maintain the desired friction level. However, these inorganic particles have less adhesion with the resin/binder and hence are easily dug out during wearing process contributing to higher wear. If efforts are made to enhance the filler-matrix adhesion, not only the wear of friction material (FM) should reduce, the particles may stay for a longer time on the tribo-surface of the pads to contribute fully towards controlling the coefficient of friction (μ). In the present study, alumina particles were selected for siloxane treatment to improve the filler-matrix adhesion. Two types of eco-friendly (free from asbestos and Cu) brake-pads were developed using alumina as a theme ingredient (treated and untreated) keeping all the parent formulation identical. An additional type of brake-pads without alumina particles was also developed to observe the effect of abrasive particles on the tribo-performance. The performance properties (physical, mechanical, and tribological) of brake-pads were compared when evaluated in identical conditions. The tribo-testing was done on full-scale brake inertia dynamometer following the procedure in Japanese automobile standard (JASO C 406). It was observed that siloxane treatment affected both friction and wear of brake-pads in a beneficial way. Wear resistance got increased 35% for siloxane treated pads. Worn surfaces were analysed using scanning electron microscopy (SEM) and energy dispersive X-ray (EDAX) technique.

Exploring the tribo-potential of nano and micron-sized particles of potassium titanate in PAEK based composite

Structural and mechanical integrity, as well as friction and wear performance of a composite designed for tribological application (hereafter called as tribo-composite) depends on a precise selection and potent combination of fillers, fibers, and polymer matrix along with right processing technique. Modern day research is primarily focused on exploring the suitability and potential of new ingredients, which are better than the conventional ones, in enhancing the friction and wear performance of a tribo-composite. In-depth laboratory scale study on the tribo-performance evaluation of these ingredients is a key to explore their potential and use at an industrial level. Particles of potassium titanate (KT) is one of such ingredients which helps in reducing wear of friction materials. However, its role in influencing the wear performance of anti-friction materials is still unexplored. In the present work, the potential of KT particles (10 wt%) in two sizes (micron and a combination of micrometer and nanometer, 7 + 3 wt%) has been evaluated. In all, three tribo-composites based on two fixed ingredients viz. polyaryletherketone (PAEK) and short glass fibers (GF-30 wt%) were developed. The first composite contained 10 wt% graphite, while the other two composites contained additional 10 wt% KT particles. It was observed that KT particles acted as a solid lubricant despite not having a layer-lattice structure. Tribo-composites with nanoparticles of KT as a filler proved more effective at severe sliding conditions (PVlimit 168 MPa m s−1) compared to that filled with micron-sized particles (PVlimit 112 MPa m s−1 respectively). Based on this study, it was concluded that KT proved as a filler having the potential to enhance the tribo-performance of PAEK based composites and nano-sized particles proved more efficient compared to the micro-sized one.

Tribological properties of textured stator and PTFE-based material in travelling wave ultrasonic motors

This study fabricated textures on the stator surface of a traveling wave ultrasonic motor (USM) using laser and investigated the tribological behavior of a polytetrafluoroethylene (PTFE) composite friction material and stator. Initially, the effect of textures with different densities was tested. As the results suggested, the generation of large transfer films of PTFE composite was prevented by laser surface texturing, and adhesive wear reduced notably despite the insignificant decrease in load capacity and efficiency. Next, the 100-h test was performed to further study the effects of texture. Worn surface and wear debris were observed to discuss wear mechanisms. After 100 h, the form of wear debris changed into particles. The wear mechanisms of friction material sliding against the textured stator were small size fatigue and slight abrasive wear. The wear height of friction material decreased from 3.8 μm to 1.1 μm. This research provides a method to reduce the wear of friction materials used in travelling wave USMs.

Mechanical and electrical characteristics of traveling wave ultrasonic motors during the whole life of friction material

It is difficult to evaluate the characteristics of traveling wave ultrasonic motors (TWUSMs) during the whole life of friction material (FM) because the wear of FM is quite slow. To solve this problem, an accelerated life test method was proposed and the mechanical and electrical characteristics of TWUSMs in the whole life of FM were analyzed systematically. The results show that the mechanical characteristics including speed and efficiency have a decline trend after an ascent with the increase of FM thickness, especially when the load torque is great. When the load torque is greater than 0.4 Nm, the optimum range of FM thickness is 0.10–0.20 mm. When the residual FM thickness is less than 0.17 mm, holding torque is greater than stall torque. Electrical characteristics of TWUSM show monotonicity in the whole life of FM. Therefore, the variations of electrical characteristics could be the wear indicator of FM. Based on experiment analysis, mechanism of interactions and couplings in the energy transfer process of the TWUSM system was explored. The energy transfer process of TWUSM was divided into four subprocesses. The wear of FM is in the intermediate subprocess, which has influence on both output performance and drive circuit of TWUSM. The four subprocesses interact and couple with each other closely. Consequently, the mechanical part and electrical part of TWUSM should be not isolated, and not only the forward action, but also the backward action in energy transfer process should be considered for a more realistic theoretical model of TWUSM.

Properties of carbon fiber reinforced poly(vinylidene fluoride)‐based friction materials of ultrasonic motors

In order to improve output properties and anti‐irradiation capability of ultrasonic motors (USMs), which are driven by friction forces of friction material between the stator and rotor, a type of friction material is fabricated by composite materials consist of carbon fiber (CF) and polyvinylidene fluoride (PVDF). The effects of different contents of CF on the mechanical and tribological properties of PVDF‐based friction materials are studied, and the mechanical features of the relative USMs are measured. Further, the worn surface morphology of PVDF composites is observed by means of scanning electron microscope and the wear mechanisms are also discussed. In addition, the anti‐irradiation capability of the type of friction materials is measured by the γ‐ray irradiation at room temperature environment with the total radiation dose of 4.0X rad (Si). The experimental results show that the incorporation of CF into PVDF can effectively improve the friction and wear properties of the friction materials, and the mechanical properties of TRUM‐60 used by relative PVDF composites are also increased with the increase of CF. For TRUM‐60, both the no‐load speed and holding torque of the USMs were high, and the wear of friction material was lowest, when the CF content is 15 wt%. The experiment results also show that this PVDF‐based friction material has a good anti‐irradiation property. Therefore, the composite materials consist of CF and PVDF are beneficial for the applications in USMs, especially for some radiation environment. POLYM. COMPOS., 37:547–552, 2016. © 2014 Society of Plastics Engineers

Experimental Characterization and Modeling of Dry Dual Clutch Wear

Clutch wear is dominantly manifested as the reduction of friction plate thickness. For dry dual clutch with positioncontrolled electromechanical actuators this affects the accuracy of normal force control because of the increased clutch clearance. In order to compensate for the wear, dry dual clutch is equipped with wear compensation mechanism. The paper presents results of experimental characterization and mathematical modeling of two clutch wear related effects. The first one is the decrease of clutch friction plate thickness (i.e. increase of clutch clearance) which is described using friction material wear rate experimentally characterized using a pin-on-disc type tribometer test rig. The second wear related effect, namely the influence of the clutch wear compensation mechanism activation at various stages of clutch wear on main clutch characteristics, was experimentally characterized using a clutch test rig which incorporates entire clutch with related bell housing. Finally, the previously proposed and experimentally validated physical clutch model, which was focused on the clutch actuator and axial dynamics, is extended to capture both wear related effects as a further step towards a more comprehensive overall clutch dynamics model.

Research on the Performance Influence of Partly Granulation Technology for Friction Materials

This paper experimentally investigated the friction, wear performance, density, hardness and impact performance of pelletizing friction material. The research was used partly granulation process for prepare friction material. Experiments showed that: When the proportion of partly granulation friction material and powder was mixed with 2:1, the friction coefficient was better, which compared to 1:1 and 1:2. The friction coefficient of partly granulation friction material was higher than the powder friction material, and it also increase along with the temperature rise. The best friction material was made by diameter particle mixed the powder with 2:1, of which particle in diameter of 1-10mm. Without the particle diameter of 1-3mm, the friction material wear rate was lower than when the other diameter levels particle and powder were mixed with 2:1. The wear rate of the partly granulated friction material reduced by 10.9-39.47%, which compared to ungranulated friction material. Furthermore, the friction material that was the mixture of powder and particles, the impact strength will decrease following the increasing proportion. At the same range, the impact strength was relatively large when the particles and the powder was mixed with 1:2. The minimum impact strength was 0.0984J cm2 which the particle diameter was 8-10mm and the ratio was 2:1. The friction material density first increased and then decreased as the particle size increasing. The density whose granules and powders ratio was 1:2 was greater than the density between 1:1 and 2:1 at the same level. The minimum density,which occured in 8-10mm particle friction material, was 1.101659 g/cm3. The hardness of part of the granulated friction material increases as the particles size increases, but the range is limited. The hardness value is 102HRR of the maximum hardness of the friction material, which made with 8-10mms diameter particle and powder that ratio was 2:1, The minimum hardness is 80HRR. The friction material formed by mixing particles and the powder occurred rough surface and obvious porosity and a crack after the abrasion test. When the ration was 1:1 and 1:2, the surface scratched obviously, emerged cutting and furrows. The results showed that when Granules and powder mixed with 2:1, the worn surface of the sample is relatively flat. It also showed the main wear form of the friction material was abrasive wear and fatigue wear.

Effects of wear of friction material on performance of ultrasonic motor

Friction material is one of the key components in an ultrasonic motor. The wear of the material affects the contact friction and output performance of the motor. A method which utilizes the equivalent wear of friction material to simulate the wear during operation is proposed based on the wear characteristics of the ultrasonic motor’s contact interface. A relationship between wear and performances of the ultrasonic motor is constructed. The influences of wear on output performance, friction coefficient of the contact interface, and wear morphology are researched in the experiments. According to the experiment’s results, with wear of friction material (decreasing thickness), the output performance of the ultrasonic motor presents a downward trend, the friction coefficient between contact interfaces decreases gradually, the friction-reducing ratio between contact interfaces increases gradually, and the wear between contact interfaces decreases. The results are helpful to understand operating performance, design, and select friction material of ultrasonic motor.

Effect of Contact Characteristics on the Friction and Wear Behaviors of Stainless Steel/Copper-Impregnated Metalized Carbon under Electric Current

Influence of the support stiffness and contact force on friction and wear behaviors of stainless steel rubbing against copper-impregnated metalized carbon under electric current was researched on an improved friction and wear test machine. The result indicates that the support stiffness and the contact force significantly affect the friction coefficient of contact pairs, wear and surface roughness of pin samples. The appropriated support stiffness and contact force can effectively reduce friction material wear of contact couple.

Optimization of manufacturing process effects on brake friction material wear

Manufacturing parameters of brake friction materials have a crucial impact on its friction and wear behavior. The effects of manufacturing parameters on wear have been modeled aiming at the optimization of facing behaviors. The influences of the five most important manufacturing parameters, such as molding pressure, molding time, molding temperature, heat-treatment temperature, and heat-treatment time, have been investigated. Their effects have been investigated on different formulations of the friction material and under different brake interface temperatures. The neuro-genetic optimization model was developed to be able to predict and optimize the effects of manufacturing parameters on the brake friction material wear.

Gradient Design Model of Contact Interface for Ultrasonic Motor

Ultrasonic motor is a new type of motor driven by friction force between the contact interface of rotor and stator. Friction material is an important part of contact interface. Its design and wear control are key problems for ultrasonic motor. A simplified model of ultrasonic motor is established. Effect of wear of friction material on contact parameters and driving friction force is studied. The properties that worn friction material should have are obtained by keeping stable contact width between rotor and stator. Design principle and theoretical structure model of gradient friction material for ultrasonic motor are proposed. The simulation analysis shows that normal elastic modulus of friction material pasted on rotor should gradually decline from the extenior to the interior. This type of friction material can maintain the output properties and increase performance lifetime of ultrasonic motor. And a new field is opened up for choosing and reasearching friction material for ultrasonic motor.

Morphology and Toughness of Abrasive Particles and Their Effects on the Friction and Wear of Friction Materials: A Case Study with Zircon and Quartz

This study examined the friction and wear of brake friction materials containing two different abrasives: zircon and quartz. Commercial grade abrasives with two different sizes (fine and coarse) were compared in terms of the effects of the size, shape, and toughness of the abrasive particles on the friction and wear of the friction material and counter discs. The results showed that the morphology of the abrasives has a considerable effect on the friction effectiveness and wear of the friction couple. The level of friction was higher in the case of using quartz than zircon, and smaller particles were more effective in increasing the coefficient of friction. The toughness of the abrasives also played important roles in determining the friction effectiveness. Improved heat resistance at elevated temperatures was achieved when coarse zircon was used. The wear of the friction material was also dependent on the morphology and toughness of the abrasives and the large abrasive particles produced more wear on the gray iron disc.

Relationship between wear of friction materials and dissipated power density

Specific tribometric tests showed both the effect and relevance of the power dissipated by friction upon the transition from mild wear to severe wear for friction materials. The dissipated power density could be viewed as an important variable either to identify the critical wear characteristics of friction materials or to make comparisons among different types of friction materials. The scanning electron microscopy analysis showed some correspondence between the sliding surface morphology after the friction tests and the wear rate obtained. Moreover, the phenomena observed are related to known mechanochemical wear mechanisms.