Дисертації з теми "Brake Wear"

Passenger vehicle disk brakes produce large amounts of wear debris that needs to be analyzed to verify its environmental and health impact because its effects are amplified by the massive extent of vehicular transportation around the world. An efficient and thorough method for wear debris analysis should be derived from this research to assist brake manufacturers and researchers in understanding the characteristics of wear particulates being released from current brake materials. In addition, a test method allowing inspection of brake formulations in development phase should be provided and several model "environmentally friendly" brake lining materials should be developed. The most hazardous constituents in a known brake lining formula should be replaced with non-hazardous materials that will obtain performance specifications comparable to the original formula. The brake manufacturing industry and general public should be notified of important findings from this research. Model brake linings fabricated on-site with known constituents were run through an AO4D performance dynamometer test to collect airborne and non-airborne wear debris that is comparable to wear debris produced by an average passenger vehicle. Based on previous experience with analysis of brake linings, this wear debris will be analyzed with scanning electron microscopy equipped with energy dispersive X-ray microanalysis (SEM-EDX), transmission electron microscopy with EDX (TEM-EDX), X-ray diffraction (XRD), polarized light microscopy (PLM), X-ray fluorescence (XRF), and laser scattering particle size distribution analyzer (LSPSDA). Research presented in this report indicates clearly that the previous work published by several groups is lacking sufficient information and the findings should be corrected. For instance the particle size distribution detected by particle size analyzers and impactors (recommended by EPA) is not accurate and TEM as well as SEM studies allowing direct observation of wear particles revealed considerable differences between sizes detected by these analyzers and realistic particle size. EDX in combination with XRF and XRD allows for reliable identification of chemical species and crystalline phases present in wear debris. True airborne wear debris should be sampled from brake exhaust from an appropriate distance. Degummed hemp shows promising results as a copper replacement in low-metallic friction material.

Vid användandet av en skivbroms på ett tåg frigörs partiklar i friktionskontakten mellan skiva och belägg. Beroende på den aerodynamiska diametern blir partiklar luftburna, och de anses vara farliga för människans andningssystem. Att fånga upp partiklarna och på så vis förbättra luftkvaliteten är därför fördelaktigt.Olika metoder för uppsamling av de luftburna partiklarna utvärderades och den mest lämpliga valdes för vidareutveckling. En konceptuell lösning, för applicering av denna metod på en Reginaboggi, genererades och utformades.Resultatet är en partikelfångare som renar luft med hjälp av filter med tillräcklig uppsamlingseffektivitet. En central uppsamlingsenhet monteras på boggin, och ansluts med rörledningar till insug monterade vid bromsbeläggen. En fläkt genererar ett luftflöde som transporterar partiklarna genom rörsystemet och filtren.
In a train disc brake, the frictional contact will generate wear particles in different size ranges. Depending on the aerodynamic diameter some of the particles become airborne; these are considered to be harmful to the human respiratory system. It is therefore beneficial to collect the airborne particles to improve the air quality.Different methods of gathering airborne particles were evaluated and the most suitable was selected. A conceptual solution in how to apply this on a Regina train bogie was then formulated and designed.The result is a particle collector that purifies the air using filters with sufficient efficiency for the application. A central collection unit is fitted on the bogie, connected by tubes to intakes mounted at the brake pads. The system utilizes airflow created by a fan to transport the particles through the tubing and filters.

In recent decades, significant requirements of changes in composition of brake friction materials in order for faster and more reliable transportation as well as their environmental friendly characterizations attracted attentions. However, the relation between performance and formulation/composition is not clear since friction processes are accompanied by many complex problems such as instability in the coefficient of friction, noise, vibration and wear. Creep-groan is a low frequency vibration which could originate in different part of the system (vehicle). The resulting resonant vibration in the passenger compartment causes discomfort and often leads to complaints of customers and related increase of warranty costs covered by manufacturers. In spite of relatively large amount of publications addressing the creep-groan phenomena, there is not an universal solution addressing the engineering aspects of brake/vehicle design. In addition, Relevance of wear occurring in brake materials increased particularly with relation to the released chemicals and corresponding health and environmental hazards. It is well known that humidity can considerably modify the adhesion of rubbing counterfaces by creating menisci and increasing the contact area. The chemistry, morphology and phase composition of the friction layers (third body) generated on the friction surfaces could play a determining role when amounts of adsorbed water on brake surfaces is concerned. The friction layer is typically a complex mix of numerous materials and, as a rule, contains the agglomerated or sintered nanoparticles. Hence, quantum effects could further modify the adsorption of water. This work addresses the impact of humidity on wear and creep groan of two commercial brake material types: the so called i) "non-asbestos organic" (NAO) and the ii) "semi-metallic" (SM) brake materials rubbed against pearlitic gray cast iron rotors typically used in the passenger vehicles. The friction and wear tests were performed with the Universal Mechanical Tester (UMT) manufactured by Bruker and the wear surfaces/mechanisms were studied by using of scanning electron microscopy, energy dispersive X-ray microanalysis, and optical topography methods. The applied wear testing conditions were designed as a series of particularly designed drag tests and were performed at several different relative humidity levels ranging between 50% and 80%. The major findings confirmed the considerable effect of humidity on wear of brake materials. Both pad types wore noticeably less at increased humidity. This was ascribed to a better capacity to form a protective friction layer. The complex wear mechanisms including abrasive, adhesive, fatigue, and corrosion wear were observed on both material types, irrespectively of humidity levels, and they dependent on the chemistry and phase composition of the friction layer. Humidity also influenced the level of friction.

Wear is an ubiquitous phenomenon affecting an extremely wide number of technological system, often determining their premature failure. In this regard, wear and friction behavior of friction materials and the characterization of wear debris from brake disc system is an important step to understand the dominant wear mechanisms active in a given tribological system, in order to improve its performances and to increase the expected lifetime. In the thesis, four tribological task has been performed, under the code name Case I, II, III & IV. This thesis present the work on the development of a characterization methodology of a wear debris from brake pad-disc system, M1 and M2 friction materials at elevated temperatures and study of the wear and frictional behavior of a heat treated cast iron disc. In Case I, the dry sliding behavior of two friction materials (M1 & M2) have been investigated. The sliding tests were carried out on a pin-on-disc test rig, using a cast iron disc as a counterface, under mild conditions (the applied nominal pressure was 2 MPa and the sliding speed was 3.14 m/s). The results shows that friction material M2 is characterized by a lower friction coefficient than friction material M1, and the friction coefficient is stable during the test. In addition, friction material M2 shows a lower wear rate than M1. The results were explained by considering the characteristics of the friction layer that is established during the test. On the bases of the experimental observations, the lower friction and wear of friction material M2 was attributed to the formation a quite uniform and well compacted friction layer, due to the presence of ingredients, such as Zr oxides, able to form small particles during sliding that are compacted and held together by the presence of metallic ingredients, such as copper. The absence of Zr-oxides in the formulation of M1friction material and the presence, in their place, of hard and abrasives Mg, Zn and Al-oxides, impeded the formation of wide covering friction layer, increasing friction and wear. The different frictional properties of the brake pads determine their driving performances, and the different wear behavior determine their in-service deterioration and also their attitude to emit particulate matter in the environment, which is nowadays a concern of increasing importance. Under the Case II, a streamline characterization protocol for wear debris emitted under wear testing conditions (Case I - M1 friction material) used for disc brake assemblies is presented. An important aspect of the experimental test methodology concerns the powder collection methodology on different substrates: aluminum foil, for a gravitational integral collection, and polycarbonate filters of an ELPI+ impactor equipment, on which particles are selectively trapped, according to their average size. The protocol is based on the application of different materials characterization tools, like scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The deliberate aim of the study was to identify suitable selection parameters, like specimen availability and average particle size, for an effective and smart application of the mentioned experimental techniques so to optimize testing times and obtain statistical reliable results. The proposed characterization approach could be profitably employed also in other contexts, like environmental and health monitoring, as far as particulate matter, even from other sources than brake systems, is concerned. We extended the work in Case I by investigating further wear mechanisms of M1 & M2 pins at elevated temperatures i.e., 170°C, 200°C, 250°C, 300°C and 350°C, under Case III. The results showed a clear evolution of frictional parameters with temperature. For M1, the working temperature were 155°C, 200°C, 250°C and 300°C, the absence of frictional parameters with temperature and wear behavior of M1 is higher than M2 with one degree higher order of magnitude. Wear tracks on the discs form from the piling up of wear fragments produced both by the tribo-oxidation of the disc itself and from the wearing out of the pin materials. This accumulation of wear debris on the disc surface nearly compensate for the weight loss associated with disc wear. The observed tribological behaviour is very much influenced by the thermal degradation of the phenolic binder of the friction material. The thermal decomposition kinetics was confirmed by thermogravimetric analyses, conducted on purpose on the pin material, and by Raman spectroscopy results, that confirmed the presence of carbonaceous products on the worn out pin surface. For M2, the working temperature were 170°C, 200°C, 250°C, 300°C and 350°C, above 170°C a transition from mild to severe wear was observed. Correspondingly, the friction layers, in particular, the secondary plateaus, which develop on the pins and disc surface during sliding displayed quite different features, as proved by electron microscopy observations and X-ray spectroscopy analyses. As concerns the pins, at 25°C and 170°C, the friction layer consists of primary and well compacted secondary plateaus. At 200°C and above, a progressive reduction of the pin surface coverage by the secondary component of the friction layer and a corresponding thinning of this component are observed. Secondary plateaus are barely present on the samples tested at 350°C. Although referring to rather extreme conditions and simplified sliding conditions, the results obtained in this study provide useful indications on the role that the thermal stability of the organic component may have in determining wear rate in brake systems in which the temperature rise may be induced by actual operational conditions. The Case IV work aims at illustrating the role of conventional heat-treatments on the friction and wear behavior of the above system. Wear rates of both disc and M2 friction material were reduced by almost one order of magnitude when the disc is preliminarily heat-treated and then grinded to remove the surface decarburized layer that forms during the adopted treatment cycle. Heat-treatment and heat-treatment plus ground results in the reduction of the friction coefficient, which was comparatively low for the grounded samples (grinded to remove the surface decarburized layer). The friction and wear behavior along with the contact temperature evolutions were rationalized according to the materials characteristics and the observed wear mechanisms.

Since the investigation of wear particles from rail transport started in the late 1910s, the high mass concentrations of these particles have prompted concern among researchers interested in air quality. However, effective action has yet to be taken because relevant knowledge is still missing. This thesis provides knowledge of airborne wear particles originating from rail transport. Some aspects of their characteristic parameters, such as size, mass concentration, number concentration, and morphology, were investigated in the field and in laboratory tests. We also discuss means to mitigate non-exhaust emissions, as well as the advantages and disadvantages of various test set-ups in the seven appended journal papers:Paper A reviews recent studies of exhaust and non-exhaust emissions from rail vehicles. The results, measurements, adverse health effects, and proposed or applied solutions presented in this literature are summarized in this paper.Paper B summarizes the results of field tests we conducted. The effects of curve negotiation and braking under different real conditions were investigated in a field test in which on-board measurements were made. The elemental composition and morphology of the particles emitted and their potential sources were also investigated.Paper C describes how a pin-on-disc machine can be used to reproduce real operating conditions during mechanical train braking in a controlled laboratory setting. The results were validated by comparing the field test results with the results of laboratory studies.Paper D presents comprehensive results of laboratory studies of airborne particles from different braking materials. A new index is introduced in this paper, which can be used as a quantitative metric for assessing airborne wear particle emission rates.Paper E describes the effects of using various friction modifiers and lubricants on the characteristics of airborne particles from wheel–rail contact under lubricated and unlubricated conditions.Paper F reports work to simulate thermoelastic instability in the cast-iron braking material. We simulated the fluctuation of the flash temperature by considering the temperature dependency of the material properties and the transformation of the contact state due to thermomechanical phenomena and wear.Paper G reviews new full- and sub-scale measurements of non-exhaust emissions from ground transport. The advantages and disadvantages of on-board measurements, pin-on-disc tests, dynamometer tests, and test rig studies are discussed in this paper.

QC 20131025

on mechanical brakes. The electric regenerative brakes can thus be used as normal service brake with minimum time loss.The first part of the study aims at developing a method to calculate wear on train brake pads. This is done by using a reformulated version of Archard’s wear equation with a temperature dependent wear coefficient and a temperature model to predict the brake pad temperature during braking. The temperature model is calibrated using trustworthy data from a brake system supplier and full-scale test results.By performing simulations in the program STEC (Simulation of Train Energy Consumption), energy consumption for different cases of high-speed train operations is procured and significant data for the wear calculations are found. Simulations include both “normal driving techniques” and “eco driving”. The driving styles were decided through interviews with train drivers and experts on energy optimized driving systems.The simulations show that more powerful drive systems reduce both energy consumption and travel time by permitting higher acceleration and energy regeneration while braking. Calculations show that since the electric motors could carry out more of the braking the wear of the mechanical brakes becomes lower.Eco driving techniques can help to further reduce the energy consumption and mechanical brake wear. This driving style can require some time margins though, since it takes slightly longer time to drive when using coasting and avoiding speed peaks. However, if used properly this should not have to affect the actual travel time, partly because some time margins are always included in the timetable.Even if new, more powerful, trains would have the ability to reduce energy consumption and brake wear it is also necessary to have an appropriate slip control system for the electric brakes, making it possible to use them also under slippery conditions. In this context it is important that the adhesion utilization is modest, about 12 – 15 % for speeds up to 100 km/h and lower at higher speeds.

The fundamental theories of heat generation and transfer at the friction interface of a brake assume either matching or not matching surface temperatures by having a varying or uniform heat partition ratio respectively. In the research presented the behaviour of heat partition has been investigated in a fundamental study based on experimental measurements of temperature and the associated modelling and simulation of heat transfer in a brake friction pair. For a disc brake, an important parameter that was identified from the literature study is the interface tribo-layer (ITL), which has been modelled as an equivalent thermal resistance value based on its thickness and thermal conductivity. The interface real contact area was also an important parameter in this investigation, and it has been found to affect heat partitioning by adding its own thermal resistance. A 2-dimensional (2D) coupled-temperature displacement Finite Element (FE) model is presented, based on which a novel relationship which characterises the total thermal resistance (or conductance) at the friction interface has been characterised based on the ITL thermal properties, the contact area, and the contact pressure at the interface. Using the model the effect of friction material wear on the total thermal resistance (or conductance) at the friction interface was predicted and a comparison of the Archard and Arrhenius wear laws in predicting the wear of a resin bonded composite friction material operating against a cast iron mating surface is presented. A 3-dimensional (3D) model is also presented. This model has represented a small scale disc brake test rig which has been used in parallel with the simulation for validation in a drag braking scenario. Two simulation conditions with different pad surface states were investigated, the first having a nominally flat surface, and the second an adjusted (worn) pad surface based on bedding-in data. The Arrhenius wear model was applied to significance of including wear on the total thermal resistance at the friction interface over a short brake application. A sensitivity analysis on the interface thermal conductance, the location of heat generation, and the magnitude of contact pressure has identified the importance of each factor in determining the total thermal resistance (or conductance) at the friction interface during any friction brake application. It is concluded that the heat partitioning is insensitive on the location of heat generation, and that the most sensitive parameter is the contact pressure.
Institution of Mechanical Engineers (IMechE)

The fundamental theories of heat generation and transfer at the friction interface of a brake assume either matching or not matching surface temperatures by having a varying or uniform heat partition ratio respectively. In the research presented the behaviour of heat partition has been investigated in a fundamental study based on experimental measurements of temperature and the associated modelling and simulation of heat transfer in a brake friction pair. For a disc brake, an important parameter that was identified from the literature study is the interface tribo-layer (ITL), which has been modelled as an equivalent thermal resistance value based on its thickness and thermal conductivity. The interface real contact area was also an important parameter in this investigation, and it has been found to affect heat partitioning by adding its own thermal resistance. A 2-dimensional (2D) coupled-temperature displacement Finite Element (FE) model is presented, based on which a novel relationship which characterises the total thermal resistance (or conductance) at the friction interface has been characterised based on the ITL thermal properties, the contact area, and the contact pressure at the interface. Using the model the effect of friction material wear on the total thermal resistance (or conductance) at the friction interface was predicted and a comparison of the Archard and Arrhenius wear laws in predicting the wear of a resin bonded composite friction material operating against a cast iron mating surface is presented. A 3-dimensional (3D) model is also presented. This model has represented a small scale disc brake test rig which has been used in parallel with the simulation for validation in a drag braking scenario. Two simulation conditions with different pad surface states were investigated, the first having a nominally flat surface, and the second an adjusted (worn) pad surface based on bedding-in data. The Arrhenius wear model was applied to significance of including wear on the total thermal resistance at the friction interface over a short brake application. A sensitivity analysis on the interface thermal conductance, the location of heat generation, and the magnitude of contact pressure has identified the importance of each factor in determining the total thermal resistance (or conductance) at the friction interface during any friction brake application. It is concluded that the heat partitioning is insensitive on the location of heat generation, and that the most sensitive parameter is the contact pressure.

Estudos recentes mostram que o cobre oriundo do desgaste de materiais de fricção de freio automotivo é a principal fonte do depósito deste metal em rios e lagos, afetando negativamente o meio ambiente. Consequentemente, novas legislações de agências governamentais internacionais têm imposto uma redução drástica da utilização do cobre em materiais de fricção nos próximos anos, sendo esta uma tendência a ser seguida por governos de todo o mundo. Embora o cobre seja largamente utilizado em materiais de fricção, a compreensão dos mecanismos de ação deste metal para esta aplicação ainda é bastante limitada. Este trabalho tem como intuito contribuir para uma melhor compreensão do papel do cobre em pastilhas de freio automotivo no que diz respeito ao coeficiente de atrito e ao desgaste. Ensaios de frenagens foram realizados no tribômetro do Laboratório de Tribologia da UFRGS, onde três tipos de pastilhas de freio (contendo 0%, 10% e 30% de cobre cada) foram testadas em diferentes temperaturas (100 ºC, 200 ºC e 300 ºC). Foram aplicados métodos para avaliar o coeficiente de atrito, desgaste de pastilha, desgaste de disco, parâmetros morfológicos de platôs de contato e depósito de filme no disco O material sem cobre em sua composição apresentou valores de coeficiente de atrito maiores do que os materiais com cobre para os três patamares de temperatura. O material com 10% de cobre apresentou maior sensibilidade do atrito em função da velocidade de deslizamento do que os outros dois materiais. Correlação inversa forte foi observada entre desgaste de pastilha e desgaste de disco. A quantidade de platôs de contato foi o parâmetro morfológico que mais se correlacionou com o coeficiente de atrito em diferentes temperaturas. Em alguns ensaios foi observada uma variação abrupta do coeficiente de atrito em determinadas frenagens dos materiais sem cobre e com 10% de cobre. Juntamente com esta variação, foi constatada uma perturbação do filme depositado sobre o disco, onde este é removido quando ocorre o aumento repentino do atrito. Entretanto, este fenômeno ocorreu apenas para a temperatura de 100 ºC, indicando que esta variação de atrito e perturbação do filme ocorre apenas em baixas temperaturas, e independente do percentual de cobre.
Previous studies have shown that the copper originated from the wear of automotive brake friction materials is the main source of the deposit of this metal in rivers and lakes, leading to environmental impacts. As a result, recent legislations from international governmental agencies have forced a drastic reduction of the copper used in friction materials in next years, which is likely to be followed by other governments in the world. Although the copper is widely used in friction materials, the understanding of the action mechanisms of this metal in friction materials is quite limited. This work aims to contribute to a better understanding of the role of copper in automotive brake pads in terms of friction and wear. Tests were carried out in the tribometer of the Laboratory of Tribology of UFRGS, where three kinds of brake pads (with 0%, 10% and 30% of copper each) were subjected to different temperatures (100 ºC, 200 ºC e 300 ºC). Methodologies to evaluate friction, wear of brake pads, wear of discs, morphological parameters of contact plateaus and deposit of film on disc surface were used. The sample without copper presented higher friction than the samples with copper for the three temperature levels. The material with 10% of copper presented higher friction sensibility due the sliding speed than other samples. Strong inverse correlation between wear of brake pads and wear of discs was observed. Quantity of contact plateaus was the parameter that presented the higher correlation with the friction in different temperatures. An abrupted variation of friction was observed in some experiments for samples without copper and with 10% of copper. At the same time, it was observed a disturbance of the film deposited on the disc surface, where the film was removed when the sudden increase of the friction occurs. However, this phenomenon occurred only at 100 °C, indicating that the variation of friction and the disturbance of film occurs only at low temperatures, and seems to be regardless of percentage of copper.

The continuous increase of human activities produced new sources of pollution. The increase in specific contaminants bound to atmospheric PM involves a serious risk factor influencing the ecosystems global balance. The question arises about what can happen when well-known ubiquitous pollutants interact with emerging ones, and considering as a reference matrix the PM generated by the abrasion of the brake systems. The focus was paid of the effects of air pollution on aquatic and edaphic ecosystems, identifying the biological effects by developing biomarkers at different levels of functional complexity, suitable in monitoring the stress syndrome evolution from sub-cellular levels up to organism/population dysfunctions. First, the cytotoxic effects of b[a]p and fullerene-C60 were evaluated in relation to the triggering of autophagic pathways on M. galloprovincialis. The lysosomal membrane stability, the increase in the lysosome/cytoplasm ratio, the production of lipofuscins and neutral lipids have been verified. The results were used for immunohistochemical investigations to detect alterations in the mTOR kinase complex pathway, strictly related to autophagy. The possibility that co-exposure of b[a]p and fullerenec60 could generate a "Trojan Horse effect" was also evaluated. Subsequent investigations of a more holistic nature were carried out to study the environmental impact of the brake wear's nano-micro PM that directly affect the quality of the air but, following transport and deposition phenomena, it can determining risks for edaphic and aquatic ecosystems. An industrial research to obtain more eco-friendly braking systems served as a contour to the present study. To assess the impact of the commercial/experimental technology employed, a battery of ecotoxicological assays has been prepared with model organisms of terrestrial and aquatic ecosystems at different trophic levels, evaluating lethal and sublethal endpoints and the possible onset of genotoxicity.

The transportation sector is responsible for the majority of airborne particles and global energy consumption in urban areas. Its role in generating air pollution in urban areas is even more critical, as many visitors, commuters and citizens travel there daily for various reasons. Emissions released by transport fleets have an exhaust (tailpipe) and a non-exhaust (brake wears ) origin. Both exhaust and non-exhaust airborne particles can have destructive effects on the human cardiovascular and respiratory systems and even lead to premature deaths. This dissertation aims to estimate the amount of exhaust and brake emissions in a real case study by proposing an innovative methodology. For this purpose, different levels of study have been introduced, including the subsystem level, the system level, the environmental level and the suprasystem level. To address these levels, two approaches were proposed along with a data collection process. First, a comprehensive field survey was conducted in the area of Buonconsiglio Castle and data was collected on traffic and non-traffic during peak hours. Then, in the first approach, a state-of-the-art simulation-based method was presented to estimate the amount of exhaust emissions generated and the rate of fuel consumption in the case study using the VISSIM traffic microsimulation software and Enviver emission modeler at the suprasystem level. In order to calculate the results under different mobility conditions, a total of 18 scenarios were defined based on changes in vehicle speeds and the share of heavy vehicles (HV%) in the modal split. Subsequently, the scenarios were accurately modelled in the simulation software VISSIM and repeated 30 times with a simulation runtime of three hours. The results of the first approach confirmed the simultaneous effects of considering vehicle speed and HV % on fuel consumption and the amount of exhaust emissions generated. Furthermore, the sensitivity of exhaust emissions and fuel consumption to variations in vehicle speed was found to be much higher than HV %. In other words, the production of NOx and VOC emissions can be increased by up to 20 % by increasing the maximum speed of vehicles by 10 km/h. Conversely, increasing the HV percentage at the same speed does not seem to produce a significant change. Furthermore, increasing the speed from 30 km/h to 50 km/h increased CO emissions and fuel consumption by up to 33%. Similarly, a reduction in speed of 20 or 10 km/h with a 100% increase in HV resulted in a 40% and 27% decrease in exhaust emissions per seat, respectively. In the second approach, a novel methodology was proposed to estimate the number of brake particles in the case study. To achieve this goal, a downstream approach was proposed starting from the suprasystem level (microscopic traffic simulation models in VISSIM) and using a developed mathematical vehicle dynamics model at the system level to calculate the braking torques and angular velocities of the front and rear wheels, and proposes an artificial neural network (ANN) as a brake emission model, which has been appropriately trained and validated using emission data collected through more than 1000 experimental tribological tests on a reduced-scale dynamometer at the subsystem level (braking system). Consideration of this multi-level approach, from tribological to traffic-related aspects, is necessary for a realistic estimation of brake emissions. The proposed method was implemented on a targeted vehicle, a dominant SUV family car in the case study, considering real driving conditions. The relevant dynamic quantities of the targeted vehicle (braking torques and angular velocities of the wheels) were calculated based on the vehicle trajectory data such as speed and deceleration obtained from the traffic microsimulation models and converted into braking emissions via the artificial neural network. The total number of brake emissions emitted by the targeted vehicles was predicted for 10 iterations route by route and for the entire traffic network. The results showed that a large number of brake particles (in the order of billions of particles) are released by the targeted vehicles, which significantly affect the air quality in the case study. The results of this dissertation provide important information for policy makers to gain better insight into the rate of exhaust and brake emissions and fuel consumption in metropolitan areas and to understand their acute negative impacts on the health of citizens and commuters.

This document is final report of an expertise project lead for ALPHA Company. The project focuses on the machinability characterization and comparison of various lamellar cast irons metallurgies. The comparison is performed in order to improve the casting process and the cast irons composition of brake and hub disk, to increase their machinability. The characterization of the metallurgies was made by tool life test with measurements of the cutting forces. Hardness and surface roughness measurements were performed too. Several Silicon nitride tools were tested. First an adjustment test has been performed to validate the machining parameters, and the methodology of characterization. Secondly, a reference test on Alpha’s cast iron brought reference data for the comparison of the various metallurgies to be tested. This test has improved the method of characterization. Cutting forces recording appeared as the most relevant and irrelevant measurements such as surface roughness were eliminated from the method. A test performed on a second cast iron showed that it has a lower machinability. Project succeeded to characterize and compare cast irons’ machinabilities, allowing the improvement of the composition by further tests.

During braking, both the disc and pads in disc brakes are worn. Since disc brakes are not sealed,some of the wear particles generated can become airborne. Several studies have found anassociation between adverse health effects and the concentration of particles in the atmosphere,so it is of interest to improve our knowledge of the airborne wear particles generated by discbrakes. This thesis deals with experimental and computational methods focusing on airborne wearparticles from disc brakes. The eight appended papers discuss the possibility to both measure andnumerically determine the concentration and size distribution of airborne wear particles thatoriginate from the pad-to-disc contact. The objective is to increase the scientific knowledge ofairborne wear particles generated from disc brakes. Papers A, B and C describe tests of disc brake materials conducted in a modified pin-on-discmachine. The results show that the test set-up can be used to measure and rank disc brakematerials with respect to the concentration of airborne particles generated. Ultrafine (nanosized),fine and coarse airborne wear particles that contain metals such as iron, copper and tin werefound. Papers D and E describe a novel disc brake assembly test stand and tests of disc brake materialsconducted in it. The results show that the test set-up can be used to measure the concentrationand size distribution of airborne wear particles generated from disc brake materials. The resultsalso indicate an ability to rank different pad/disc combinations with respect to the concentrationof airborne wear particles. Furthermore, the results suggest that this test stand can be used tostudy rust layer removal from the disc and that airborne particles are generated even at low brakepressures, such as used to remove dirt from the disc. Paper F compares measurements made in passenger car field tests with measurements made in adisc brake assembly test stand and in a pin-on-disc machine. A promising correlation between thethree different test methods is found. Paper G presents and discusses a simulation methodology that numerically determines theconcentration and size distribution of airborne wear particles generated from the pad-to-disccontact in disc brakes by using general-purpose finite element software. Paper H discusses a cellular automaton model that describes the microscopic contact situationbetween the pad and disc in disc brakes. This model is used to numerically determine the amountof wear that leaves the contact. The results correlate qualitatively with experimental observationsfound in the literature.
QC 20110317

During braking, both the rotor and the pads in disc brakes are worn. Since disc brakes are not sealed, some of the wear particles generated can become airborne. Several studies have found an association between adverse health effects and the concentration of particles in the atmosphere, so it is of interest to improve our knowledge of the airborne wear particles generated by disc brakes. However, in field tests it is difficult to distinguish these particles from others in the surrounding environment, so it may be preferable to use laboratory test stands and/or simulation models to study the amount of airborne wear particles generated.

This thesis deals with a simulation methodology for prediction of airborne wear particles from disc brakes and three experimental methods for testing disc brake materials with focus on airborne wear particles. The four appended papers discuss the possibility to both measure and predict the number and size distribution of airborne wear particles that originate from the pad to rotor contact. The objective is to develop a simulation methodology that predicts the number and size distribution of airborne wear particles from disc brakes.

Paper A describes how a modified pin-on-disc machine was used to study airborne wear particles originating from different disc brake materials. The results indicate that the test setup can be used to measure and rank the number concentration and size distribution of the airborne wear particles generated.

Paper B describes a disc brake assembly test stand for measurements of airborne wear particles from disc brakes. The results indicate that the test setup can be used to measure the number concentration and size distribution of airborne wear particles generated from disc brake materials. The results also indicate a promising ability to rank different pad/rotor material combinations with respect to the number concentration of airborne wear particles.

Paper C compares measurements made in passenger car field tests with measurements made in a disc brake assembly test stand and in a pin-on-disc machine. A promising correlation between the three different test methods is found.

Paper D presents a simulation methodology for predicting the number and size distribution of airborne wear particles using finite element analysis (FEA). The simulated number distribution is compared with experimental measurements at component level. The result indicates that the proposed methodology may be used to predict the number concentration and size distribution of airborne particles generated in the pad-to-rotor contact.

During braking, both the rotor and the pads in disc brakes are worn. Since disc brakes are not sealed, some of the wear particles generated can become airborne. Several studies have found an association between adverse health effects and the concentration of particles in the atmosphere, so it is of interest to improve our knowledge of the airborne wear particles generated by disc brakes. However, in field tests it is difficult to distinguish these particles from others in the surrounding environment, so it may be preferable to use laboratory test stands and/or simulation models to study the amount of airborne wear particles generated. This thesis deals with a simulation methodology for prediction of airborne wear particles from disc brakes and three experimental methods for testing disc brake materials with focus on airborne wear particles. The four appended papers discuss the possibility to both measure and predict the number and size distribution of airborne wear particles that originate from the pad to rotor contact. The objective is to develop a simulation methodology that predicts the number and size distribution of airborne wear particles from disc brakes. Paper A describes how a modified pin-on-disc machine was used to study airborne wear particles originating from different disc brake materials. The results indicate that the test setup can be used to measure and rank the number concentration and size distribution of the airborne wear particles generated. Paper B describes a disc brake assembly test stand for measurements of airborne wear particles from disc brakes. The results indicate that the test setup can be used to measure the number concentration and size distribution of airborne wear particles generated from disc brake materials. The results also indicate a promising ability to rank different pad/rotor material combinations with respect to the number concentration of airborne wear particles. Paper C compares measurements made in passenger car field tests with measurements made in a disc brake assembly test stand and in a pin-on-disc machine. A promising correlation between the three different test methods is found. Paper D presents a simulation methodology for predicting the number and size distribution of airborne wear particles using finite element analysis (FEA). The simulated number distribution is compared with experimental measurements at component level. The result indicates that the proposed methodology may be used to predict the number concentration and size distribution of airborne particles generated in the pad-to-rotor contact.

Thesis (Ph.D.)--Southern Illinois University Carbondale, 2006.
"Department of Mechanical Engineering and Energy Processes." Includes bibliographical references (leaves 77-81). Also available online.

Six sets of subscale carbon–carbon composite rotors and stators for aircraft brakes were manufactured to provide friction and wear test samples at six different densities. The friction and wear tests used energies to represent the service energy of the Boeing 767 aircraft. A functional relationship between fiction coefficient and porosity/density was made. This relationship was used to minimise manufacturing cost by providing the minimum densification of the carbon–carbon composite brake discs needed to meet design friction coefficient.

Le rôle des constituants au sein des matériaux de friction pour garniture de frein est encore mal connu du fait, d'une part de la complexité des formulations de ces matériaux composites organiques, d'autre part de la sollicitation induite par le freinage qui engendre de multiples phénomènes physiques. Il s'avère donc particulièrement difficile d'établir les liens entre la composition d'une garniture et ses performances. Les travaux ont concerné une garniture de frein industrielle pour véhicule poids lourd. Une étude préalable a été réalisée du point de vue de sa microstructure et de ses constituants, de ses propriétés, de son élaboration et de ses performances en freinage. La démarche expérimentale adoptée a reposé sur le développement i) d'une formulation " modèle ", déduite de la formulation industrielle par simplification de la composition, ii) d'un essai d'usure représentatif de sollicitations de freinage, pour aborder le fonctionnement tribologique des constituants dans une configuration simplifiée. Deux constituants ont été plus particulièrement étudiés, des particules de laiton et des fibres de verre introduites dans la formulation modèle prise en référence. L'analyse des performances a porté sur la compréhension des liens entre les mécanismes de frottement et d'usure, la microstructure et les propriétés des matériaux et leur comportement tribologique

Embreagens de prensas mecânicas, principalmente as de forja a quente se caracterizam por um intenso regime de trabalho com espaços muito curtos entre acionamentos. Muitas das embreagens apresentam desgaste acentuado obrigando a paradas frequentes para manutenção. Neste trabalho são discutidos os princípios de funcionamento de prensas excêntricas e os parâmetros de projeto de embreagens e freios. Pontos importantes são: o balanço entre torque de operação, número de inserções por minuto e a dissipação de calor. É feita uma breve revisão da literatura sobre compósitos, lonas e seu comportamento. Discute-se a diferença das premissas de projeto de uma lona automotiva e a lona para uso industrial com alto número de aplicações por minuto. Apresenta-se um pressuposto quanto ao processo de transmissão de calor na embreagem e o que influência no desgaste da mesma, relacionando-o com a pressão de contato. Nas manutenções se verificam resíduos (debris) diferentes sugerindo regimes diferentes de desgaste. Há um resíduo preto que caracteriza um regime severo de desgaste. Pode-se associar esse resíduo ao fenômeno da degradação da base polimérica que compõe a lona. A degradação da base polimérica é causada pela alta temperatura de operação dessas embreagens. Em ensaios simples de pino e disco consegue-se reproduzir desgaste das lonas, que comprova o observado na prática e as condições que isso ocorre. Finalmente são apresentadas sugestões para o dimensionamento das embreagens e cuidados necessários no projeto de freios e embreagens.
Mechanical press clutches, especially clutches for hot forging presses have a hard working cycle with a little time between engagements. Many of those clutches present a severe lining wear, needing frequent maintenance stops. This work is discusse, the basics of eccentric presses and the clutch design parameters. Important points are: the balance between operation torque, engagements per minute and heat dissipation. This also presents a short literature review regarding composites and linings. It is discussed the design baselines differences between automotive linings and this specific case. It is presented a hypothesis about the heat transfer process in the clutch and how its related with wear, associating it with the contact pressure. In maintenance it is found different kinds of wear debris, suggesting more than one wear regime. The black debris indicates a severe wear regime. This debris can be associated to the lining polymeric matrix degradation. The polymeric matrix degradation is caused by the high op eration temperatures in these clutches. Based on simple pin-on-disc tests can be obtained results that show what is practical observed and the conditions this occurs, proving the hypothesis. Finally are presented suggestions for clutch dimensioning and necessary project cares.

Thesis (M.S.)--Southern Illinois University Carbondale, 2005.
"Department of Mechanical Engineering and Energy Processes." Includes bibliographical references (leaves 84-86). Also available online.

Les matériaux composites organiques pour garniture de frein à friction sont le fruit d’une élaboration complexe, composée d’une succession d’étapes (mélange de constituants, préformage à froid, moulage à chaud, post-cuisson) ce qui rend difficile la maitrise du lien entre procédé, propriétés et comportement de ces matériaux en particulier du fait des synergies entre les constituants formant le mélange d’une part, et entre la composition et le procédé de fabrication d’autre part. Les travaux de thèse se sont focalisés sur deux étapes de fabrication, le moulage à chaud et la post cuisson, avec l’objectif de mieux comprendre l’influence de certains paramètres du procédé de fabrication sur les performances des matériaux : la température et la durée de moulage à chaud, la durée de post cuisson. L’analyse a porté sur la compréhension des liens entre la microstructure, les propriétés, le comportement tribologique et les mécanismes de frottement et d’usure, par le biais d’une démarche expérimentale fondée sur des formulations matériaux simplifiées ainsi que sur des essais d’usure élémentaires, spécifiques aux sollicitations de freinage
Organic composite friction materials for brake lining result from a complex elaboration made up of successive stages (mixture of constituents, cold preforming, hot molding, post-curing) that makes difficult the mastery of the link between process, properties and behaviour of friction material, especially because of synergies between constituents on one hand, and between composition and manufacturing process on the other hand. Two manufacturing stages were involved in this study, the hot molding and the post-curing, with the aim of a better understanding of the influence of certain parameters of the manufacturing process: the temperature and the duration of hot molding, and the duration of post curing. The analysis has focused on the understanding the relationship between microstructure, properties, tribological behaviour and friction and wear mechanisms of materials.The experimental approach was based on the development of simplified formulations of friction material, and on an elementary wear test specifically designed for braking loadings

碩士
國立中興大學
機械工程學系所
106
Recently, the Public Bicycle System is using Roller Brake System to reduce the maintenance cost. The lifespan of the bicycle brake devices has been cut down because of the uneven wear. The main purpose of this thesis is to discuss the wear of brake pads for Roller Brake. Through experiments and Computer-Aided Engineering analysis to understand the wear distribution and the design model are improved to achieve uniform wear for brake pads. At the first of this study, aim to understand the braking range of Roller Brake and to confirm if it complies with EN specification, thus we do braking performance test. After that, used Computer-Aided Engineering software to complete the simulation model of Roller Brake, and analyzed the equivalent stress values of the coupled Thermal-Mechanical during braking, then have wear simulation procedure based on Archard’s wear law. Finally, compared the experiment of wear and the result of simulation, the improvement model would be proposed. From the experiment and analysis of this study, we could see the uneven wear of the brake pads. The improvement model changes the position of restraint of the brake pads and makes the structure symmetrical. By this design, the maximum stress value can be reduced by 9% to 46% compared with the original design, the stress distribution of the three brake pads is similar, and the stress values of the brake pads are evener than the original design.

碩士
國立臺北科技大學
車輛工程系所
101
Harsh driving behaviors or poor vehicle maintenance can easily cause un-uniform wear on the brake pad or disc and lead to vibration or noise problems of the brake system. This research focuses the brake vibration that is due to the pad wear. The study uses the commercial finite element code package, HyperWorks, to create the major components and sub-systems of a brake system, and to analyze and to predict the wear of the brake pad. The analysis results of this study are compared with the data of literature. They show good consistency with each other. Design improvement is made by choosing different heat treatment for the pad to enhance the surface toughness. The wear of the pad is reduced by 15.3%, and the vibration amplitude of the brake system is improved around 78%. It is a quick, easy and practical way to improve the brake vibration and pad wear problems for the vehicles which are on the market.

no
The migration of hot banding is the phenomenon whereby hot bands or hot spots on the brake disc surface periodically migrate radially inward and outward. These migrations can cause the undesired brake torque variation (BTV) and further induce vibration problems such as brake judder. To investigate the forming and migration of hot banding problem, transient thermal mechanical finite element models of repetitive braking considering the effects of wear have been performed. The displacement, temperature, stress, and contact pressure distribution against time were obtained in this model. The thermal buckling, thermo-elastic instability (TEI) and hot band migration phenomena have been captured and investigated. The results suggest a cause-effect chain of radial hot band migration. Its determinants include mechanical loading, disc thermal buckling, and most importantly the transient interactions between TEI and wear.

Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra
A finalidade dos travões é desacelerar o veículo, através da transformação da energia cinética em calor, dissipando para o meio através do atrito. Os materiais de travagem fazem parte integrante de veículos pesados ou ligeiros e, têm, por isso, requisitos específicos, tais como: a resistência à corrosão, peso reduzido, longa vida, baixo ruído, atrito estável, baixa taxa de desgaste, e uma relação aceitável entre custo e desempenho. Existem dois tipos de sistemas de travagem – travões de tambor/calços e travões de disco/pastilhas. De modo a atingir o desempenho necessário, a maior parte dos materiais de atrito não são constituídos por um único elemento ou composto, antes são materiais compósitos. Mais de 2000 materiais diferentes e suas variantes são actualmente usados em componentes comerciais para pastilhas de travão. No que diz respeito à sua função, os materiais de travagem são classificados em quatro categorias principais: matriz, conhecido como material de ligação, fibras, modificadores de atrito e materiais de enchimento/reforço [1]. A matriz é o núcleo do compósito pois tem a função de aglomerar firmemente todos os ingredientes, de modo a que cada um desempenhe a sua função de material de atrito. As fibras, por sua vez, são adicionadas para uma maior resistência, enquanto os modificadores de atrito são usados para manipular a gama de coeficiente de atrito desejado. Os materiais de enchimento/reforço pretendem manter o coeficiente de atrito numa gama elevada de temperaturas, e também, reduzir custos. Os fabricantes de material de atrito reivindicam excelente resistência ao desgaste mas não dão garantias de uma determinada vida útil dos seus produtos, e, raramente publicam dados relativamente ao desgaste dos materiais por eles produzidos. Os ensaios à escala de material de travagem é muito demorado e muito custoso. Deste modo, existem inúmeros testes a escala reduzida que permitem a comparação, mais rápida, de diferentes formulações. Este tipo de equipamento não permite simular e obter resultados idênticos aos obtidos pelos materiais em serviço. Para além da complexidade dos materiais de atrito para travagem, a sua caracterização mecânica e tribológica também é difícil. A presente dissertação tem, como objectivo principal, a caracterização mecânica e tribológica de quatro materiais de desgaste de travagem - pastilhas - para veículos pesados, sendo estes o ACERCHINA, o ATV 55, o FRASLE FLE1749 e o JURID FF29. Para o efeito foi usado um equipamento a uma escala reduzida que permitiu variar os parâmetros que mais influenciam a travagem, e, controlar a temperatura e a força de atrito das pastilhas em estudo. Nos ensaios tribológicos foram usadas três velocidades de travagem e três forças normais. Como outputs foram obtidas as temperaturas das pastilhas e a força de atrito ao longo do ensaio. O desgaste de cada conjunto de pastilhas ensaiado foi determinado através de pesagem. A comparação do desempenho das formulações foi realizada através da representação gráfica de força e coeficiente de atrito ao longo da distância de escorregamento, bem como os volumes de desgaste de todas as condições e materiais. Por forma a complementar a caracterização tribológica, e para auxiliar a compreensão dos resultados, foram determinados os valores de dureza, densidade e o módulo de elasticidade para várias temperaturas. As amostras ensaiadas foram também observadas através de microscopia óptica e microscopia electrónica de varrimento. Genericamente, observou-se, para todos os materiais, que o volume de desgaste, para a mesma pressão, sofria um aumento quando a velocidade de escorregamento aumentava. O volume desgastado aumentava ainda mais quando se mantinha a velocidade e se aumentava a pressão. Em alguns materiais, mas apenas em algumas condições de ensaios, ocorreu uma diminuição abrupta da força de atrito e consequentemente diminuição da temperatura da pastilha. Outros materiais registaram um ruído agudo na maior parte dos ensaios. No que concerne às propriedades mecânicas, o módulo de elasticidade de todas as pastilhas diminuiu com o aumento da temperatura. Com o aumento da dureza das pastilhas verifica-se um aumento do desgaste específico [mg/MJ]. As formulações com melhor desempenho foram: o JURID no coeficiente de atrito, por registar valores mais elevados; o ATV na temperatura, por dissipar melhor a energia térmica; e o FRASLE no volume de desgaste, por ter valores mais reduzidos de desgaste volúmico e o único dentro dos valores de referência do desgaste específico.
The main purpose of brakes is to decelerate vehicles, by dissipating the kinetic energy into heat to the environment through friction. Braking materials are an integral part of heavy or light vehicles, and therefore have specific requirements, such as corrosion resistance, low weight, long life, low noise, stable friction, low wear rate, and an acceptable relation between cost and performance. There are two types of braking systems - brake drum/shoes and brake disc/pads. In order to achieve the required performance, most of the friction material are not constituted by a single element or compound, but by several components, they are composite materials. More than 2000 different variants of materials are currently used in commercial components for brake pads. With regard to its function, brake materials are classified into four major categories: matrix or binder material, fibers, friction modifiers, and fillers/reinforcements. Binder is the heart of a system which binds the ingredients firmly so that they can perform the desired function in the friction materials. Fibers in combination are added mainly for strength, while friction modifiers are used to manipulate the desired range of friction. Fillers/reinforcements are intended to maintain the friction coefficient in a high temperature range and also reduce costs. Friction material manufacturers claim excellent wear resistance but do not guarantee a certain life span of their products, and, rarely publish data regarding the wear of the materials they produce. Braking material test to scale are time consuming and very expensive. Thus, there are numerous small scale tests which allow a faster and inexpensive comparison between different formulations. This type of equipment cannot simulate and obtain results identical to those obtained for the materials in service. In addition to the complexity of brake friction material its tribological and mechanical characteristics is also problematic. The main objective of the present work is the mechanical and tribological characterization of four braking wear materials - pads - for heavy vehicles. Regarding this objective, a small scale tribometer was used to allow a parametric study on braking, and to control pads temperature and the friction force. In the tribological tests were used three sliding speeds and three normal forces. Pads temperature and friction force were the outputs of the tests. Wear volumes for each set of pads tested was determined by weighing. The performance comparison of formulations was done by plotting the friction force versus slip distance, and the evaluation of material removed by wear of all wear conditions and material formulation. In order to complement the tribological characteristics, and aid the understanding of the results, hardness values and density were determined. The elastic modulus was determined for various temperatures. The test samples were also observed in an optic microscope and a scanning electron microscope. Generally, all materials have an increase in wear volume, for the same normal pressure, when the sliding speed increases. A bigger amount of volume was worn when, at constant sliding speed, the normal pressure increased. Some materials, for determined test conditions, have a clear decrease of the friction force and consequently decreasing in pads temperature. Other materials squealed in most tests. For what mechanical properties concerns, the elastic modulus of all the pads decreased with increasing temperature. An increase in pads hardness presented an increase in specific wear [mg/MJ]. The formulations with best performances were: JURID in friction coefficient, for the higher achieved values; ATV in temperature, due to dissipate the thermal energy better than the other formulations; and FRASLE for volume wear, for being the one with the lowest values of volume worn during the tests and the only one to keep its values within the ideal in specific wear.