Comparison Between Different Investigation Methods of Quasi-Static and Dynamic Brake Pad Behaviour

<div class="section abstract"><div class="htmlview paragraph">This work pioneers the development of eco-friendly brake pads using coconut fiber and sawdust as reinforcement materials, combined with abrasives and friction modifiers. The innovation lies in the utilization of these natural fibers, which are not only cost-effective and abundantly available but also contribute to the sustainability of brake pad manufacturing. The study aims to explore the feasibility and performance of these organic fibers in brake pad applications. Coconut fiber and sawdust were chosen for their unique properties, such as high strength-to-weight ratio and thermal stability, making them ideal candidates for enhancing brake pad performance. The inclusion of abrasives and friction modifiers further optimizes the braking efficiency and durability of the pads. Comprehensive testing was conducted, including hardness, compression, wear (using a pin-on-disc apparatus), and thermogravimetric analysis (TGA), to thoroughly evaluate the mechanical properties and thermal stability of the fabricated brake pads. The results demonstrated that the brake pads possess satisfactory hardness, compression strength, and wear resistance, aligning with industry standards for organic brake pads. Notably, the TGA indicated excellent thermal stability, even under elevated temperatures, underscoring the material’s robustness. This project underscores the potential of using coconut fiber and sawdust in the formulation of organic brake pads, offering a sustainable and high-performance alternative to conventional materials. The novelty of this work lies in the strategic selection and combination of natural fibers with advanced testing to validate their application in automotive braking systems. Future research will focus on optimizing the composition and refining the manufacturing processes to further enhance performance and environmental benefits, paving the way for more sustainable practices in the automotive industry.</div></div>

<div class="section abstract"><div class="htmlview paragraph">The Los Angeles City Traffic (LACT) brake test is well known acclaimed procedure used by many vehicle manufacturers to assess the brake pad wear behavior and to investigate the Noise, Vibration and Harness (NVH) performance of the brake system. The LACT driving route consists of a set of real-world driving conditions, which has been considered representative of the US passenger vehicle market.</div><div class="htmlview paragraph">The scope of this study is to mimic the LACT test using finite element analysis (FEA) to calculate the wear displacement based on Rhee’s theory. The Leading-edge and trailing edge of the brake pad’s wear tendency is also predicted from the simulation. The finite element model for wear simulation consists of brake system viz., Rotor, Knuckle, Pads, Anchor bracket, Piston, and Caliper. Various braking scenarios consist of different driving characteristics (Number of brake applications, vehicle speed, brake pressure, rotor temperature, and brake rotor interface friction variation) based on LACT Route traffics are replicated in FEA.</div><div class="htmlview paragraph">The wear displacement results from the finite element analysis are in good agreement with physical test results. Further, based on the wear displacement values, the brake pad’s life span is calculated and correlated well with the test measurements.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Brake pads employing innovative hydraulic inorganic binders in place of common state-of-the-art thermosetting phenolic resins have been produced by means of a unique prototypal equipment and a distinctive manufacturing process. The unicity of the process enables us to exclude completely any thermal cycle in the manufacturing steps, with a considerable positive energy balance compared to the standard counterpart. Realized brake pads have indeed been successfully tuned to meet the braking performances of phenolic counterparts. In the present work our latest efforts in this field are illustrated, focusing our attention to three main areas of interest: performance, energy consumption, volatile organic emissions. One selected exponent of our cementitious-based material is reported, demonstrating its capability of matching both standard OE and AM braking performances (investigated through a full scale brake dynamometer by SAE J2522 procedure), and its feasibility to be released as an actual AM material according to ECE R90 regulation (road test on vehicle). The energetic evaluation of the employed technology in term of prototypal manufacturing process and employed raw materials has been established, demonstrating the advantages of this new system compared to the standard one. Our investigation finally reports selected thermo-chemical analysis (TG-EGA and pyrolysis PY-GC/MS) devoted at identifying the key organic compounds potentially/eventually emitted during braking at various temperatures. Our material shows a dramatic drop of the volatile hazardous/organic compounds (VHCs/VOCs) released by a standard phenolic homologous, thus increasing the favorable characteristics of such inorganic hydraulic-binder brake pads and related technology.</div></div>

<div class="section abstract"><div class="htmlview paragraph">The effects of particle size and composition of platelet titanates, including potassium titanate and potassium-magnesium titanate, were investigated to determine their friction stability, wear resistance, and transfer film formation. The composition and properties of titanates were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), and particle size analysis. Tribological properties were evaluated using a tribometer (MFT-5000), while the worn surfaces were analyzed with scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS).</div><div class="htmlview paragraph">Results indicate that the transfer film characteristics are significantly influenced by the particle size and composition of platelet titanates. Brake pads containing potassium-magnesium titanates formed a more uniform transfer film, leading to improved friction stability and reduced wear rates. In contrast, potassium titanates increased friction levels but also resulted in higher wear on the brake friction materials.</div><div class="htmlview paragraph">These findings demonstrate the importance of carefully controlling titanate composition and particle size to enhance brake pad performance. This research provides valuable insights for designing more durable and stable brake materials.</div></div>

<div class="section abstract"><div class="htmlview paragraph">To date, no generally valid statements can be made about the service life of brake pads, which may be due to factors such as driving style, the friction material used or the varying vehicle weight. While dynamic friction models including friction history are already established [<span class="xref">1</span>], the investigation of wear and wear dust behavior is currently in the focus of many research projects. One example is the investigation of calculation models for brake pad wear while neglecting the temperature development in the brake [<span class="xref">2</span>].</div><div class="htmlview paragraph">In cars, temperatures of up to 800°C occur in the brake under high loads, which leads to a significant increase in wear. Accordingly, the question arises how an estimation of brake pad wear can be applied to highly dynamic load cases. To do this, however, the processes taking place in the boundary layer between pad and disc must first be comprehensively understood and described. For this purpose, high-precision measurement technology is necessary, which was developed and optimized over several years at the Institute of Dynamics and Vibrations (IDS) in the form of the Automated Universal Tribotester (AUT).</div><div class="htmlview paragraph">In cooperation with Volkswagen AG, several test procedures have therefore been developed for the AUT, which provide information about the factors influencing the wear of brake pads under non-stationary conditions. For example, a previously developed stationary test procedure is carried out with four different temperature levels, which demonstrates a different temperature sensitivity depending on the pad material. In addition, decreasing velocity profiles with equivalent idle work to the stationary test procedure have been investigated in order to be able to analyze the influence of the dynamics of braking on wear more precisely. Depending on the friction pairing used, both the tendency and the absolute generated wear show differences with respect to the stationary reference measurement. The obtained results therefore represent a starting point for the better understanding of the influencing factors on brake pad wear.</div></div>

<div class="section abstract"><div class="htmlview paragraph">The moisture adsorption kinetics of copper-free brake pads was studied to confirm an earlier finding that the adsorption weight gain follows a logarithmic relationship with respect to the square root of humidity exposure time and the relationship is linear in the beginning. When the pad cure temperature was raised from 120 to 180 and 240 °C, the adsorption rate increased. The 180 °C cure produced the highest pad modulus. With increasing moisture adsorption, the pad compression modulus increased just like the pad dynamic modulus, meaning decreasing compression/compressibility while the ISO ‘compressibility’ determined after 3 compressions under 160 bars increased in contradiction. It is concluded that the ISO ‘compressibility’ is a destructive hardness measurement like the Gogan or Rockwell hardness: the key difference is the indenter covers the entire surface of the pad. The true compressibility must be determined as an inverse function of bulk modulus. It is recommended that the pad compression modulus should be measured under low pressures like 10 bars for the purpose of determining the initial quality of virgin pads if the current ‘compressibility’ machines are to be used. Compression tangent modulus and dynamic modulus measurements produce the same results, meaning that one could replace the other. Pad cure temperature affects friction coefficient and moisture adsorption influences friction coefficient in opposite direction for moderate-speed snubs of 80 km/h vs. low-speed stops of 5 km/h.</div></div>

The effect of directional orientation of Chopped steel wool fiber in a friction material matrix / Brake pads that influences Friction, Wear and Mechanical properties of the Brake pads have been evaluated in a phenolic resin-based asbestos-free semi-metallic friction material composition. </p><p>Brake pad compositions widely use chopped steel wool fibers having a nominal length of less than 10 mm; diameter of about 500 microns; carbon content between 0.05 – 0.15 % as reinforcement. During compounding and mixing of friction material formulation, chopped Steel wool fibers along with dozen other raw materials are mixed/homogenized using plough shear mixer resulting in the steel fibers dispersed and oriented randomly in different plan and direction in the mixture and so over the final brake pad matrix too. </p><p>Trials have been carried out in Fricmart’s prototype Lab to orient chopped steel wool fiber in an uni directional plan in various semi-metallic formulations and progress has been achieved only in a medium- steel brake pad formulation that contains about 25% chopped steel fibers. Fricmart’s S-428 grade Steel wool fiber conforming to the above said specification has been used in the experiments. Fibers were initially classified using a set of sieves to remove the fines having diameter and length less than 200 microns and 3 mm respectively to meet the desired loose density / bulk density limit of 0.55 – 0.70 gm/cc to support the process of orientation. Further, a brake pad model that has rectangular geometry ( Merc. W-123 Pad) with an area of about 50 sq. cm was chosen to conduct the trials and to support the process of orientation. Brake pads were molded using conventional compression molding process at temp. of 150 deg. C with specific pressure of 250 bar and 6 minutes curing followed by 4 hours step curing ( post-baking ) to max. temp. of 180 deg. C in an air oven . Preparation of Samples: Sample 1 -By employing bi-directional magnetic field coupled with other special charging chute and dispersing techniques, the desired orientation of chopped steel wool fiber that was targeted to be parallel to the sliding direction of the brake (pad) was achieved to a level of more than 90% evenly oriented throughout the layer and matrix of the brake pad. Fricmart’s PLM – Stereo Microscope surveillance facility is used to ascertain percentage orientation during trials. Sample - 2: Brake pads processed as above by “parallel orientation to sliding direction’’ have later been used to study the effect of “orientation in perpendicular to the sliding direction’’ just by “inverting the new sample” specimen at the time of testing. Sample - 3: One set of brake pads were processed as per industries standard using the same batch/composition of raw materials with a random distribution of chopped steel wool fiber under identical process condition without carrying out directional orientation. Testing & Evaluation:The samples were cut from the brake pad and tested in Chase Type Friction Tester as per SAE J661 – small sample testing and the following are the observations. Internal shear measured as per ISO 6311 of sample -1 was significantly higher than sample – 2 & least in the case of sample 3 Faster bedding or faster adaptability to the disc in case of the sample- 1. 80% bedding achieved within 10 minutes of burnishing as compared to 20 minutes in case of samples- 2 & 3. The coefficient of friction is also dependent on the fiber orientation and µ for the developed pad ranges between 0.35 and 0.40. Fade resistance for samples 1 & 2 is superior when compared to sample 3.</p><p>Further, it was observed that as temperature increases, initially there was abrasion/plowing and on a further rise in temperature, a transfer film was developed making the steady-state friction. The wear rates decreased if the sliding path/direction changes from parallel to the perpendicular direction. The worn surface morphology was studied using FESEM and found that wear resistance is found to relate to the stability of the developed film. Sample 1 with the fibers oriented parallel to the sliding direction exhibited smoother running whereas sample 2 created undesirable judder noise. Hence it can be concluded that the Orientation of fibers with respect to sliding direction is preferable to the randomly oriented fibers towards frictional characteristics.

This study aims to develop asbestos-free and environmentally friendly brake pads using apus bamboo powder (Gigantochloa apus). In the experiments, bamboo powder, resin, and catalyst were used as the raw materials and varied to ensure the quality of the prepared brake pads. To analyze the performance of brake pads, the fabricated brake pads are subjected to physicochemical tests (such as microscopic tests and functional group analysis) and mechanical tests (such as puncture tests, compression tests, and friction tests). The research results showed that adjusting the composition of the raw materials allowed a change in the performance of the brake pad, including porosity, morphological structure, and mechanical properties. Indeed, the condition of the low porosity on the inside of the brake pad strategically optimizes the compression strength of the material, making this design ideal for applications that require high resistance to compression loads. This study shows the possibility of apus bamboo powder as an alternative to asbestos in the production of non-asbestos brake pads, offering a safer and environmentally friendly solution as well as giving ideas for supporting current issues in the sustainable development goals (SDGs).

This study investigates the sustainable utilization of fly ash, palm slag and Cement By-Pass Dust (CBPD) waste as alternative materials for environmentally friendly brake pad development. These waste materials, with compositions similar to Asbestos, historically used in brake pad composites, present an eco-conscious solution. Integrating industrial waste in brake pad production offers substantial environmental benefits, technological progress, and commercial advantages. The compaction value and particle size distribution significantly impact brake pad mechanical properties. Adjusting these factors is crucial for meeting desired mechanical property requirements. A large particle size distribution enhances material density and hardness poses challenges in maintaining performance stability at high temperatures despite good recovery values. This paper highlights the potential of waste materials for sustainable brake pad development and underscores the need for careful optimization for high-temperature stability.

<div class="htmlview paragraph">A comprehensive strategy for applying quasi-static and dynamic tests in the development of automobile side impact protection systems is presented. The approach is geared towards providing an understanding of how vehicle components relate to occupant protection as measured by the FMVSS 214 dynamic side impact test. These test methods are viewed as being complimentary, rather than competitive, tools to be employed in the overall strategy.</div> <div class="htmlview paragraph">The approach begins with obtaining detailed data from an FMVSS 214 dynamic test. Additional instrumentation is required so that the results of the test can be used to form the basis for setting conditions for subsequent quasi-static and dynamic tests.</div> <div class="htmlview paragraph">The Composite Test Procedure (CTP) is an integral part of the process. As described here, the CTP can be conducted under three different methods; three step procedure, continuous computer control, and continuous manual control. The principal value of the CTP method is to obtain spatial relationships within the door structure, overall force-deflection properties of the vehicle body structure, and input for a simplified, linear spring mass model to represent the FMVSS 214 dynamic test.</div> <div class="htmlview paragraph">Door structures are tested to provide a preliminary evaluation of door modifications, including both structure and trim panel, without resorting to full vehicle body development and build. The methods for door tests include both quasi-static, where the door structure and trim panel are evaluated, and dynamic (sled), where door trim panels are evaluated. Results obtained from these component tests can be related to full scale crash testing through mathematical modelling.</div> <div class="htmlview paragraph">The complimentary nature of these test methods is then discussed relative to improving performance in an FMVSS 214 dynamic test. A flow chart showing the relationship to a complete vehicle development program is presented and discussed.</div>

<div class="htmlview paragraph">This paper reports the progress that has been made to date on a research program that has as its focus to describe the mechanism of metal pick-up generation on passenger car disc brake pads in correlation with deep rotor scoring. In contrast to other existing generation theories, the new investigation considers other aspects of the initial onset of the metal pick-up.</div>

A modified phenolic resin was designed and developed in our laboratory to manufacture friction material with high performance. The potential application of the resin as a binder for hybrid-fibers reinforced brake pads for railroad passenger-coach braking was evaluated on a full-scale test bench according to Standard of China Railway Ministry TB/T 3118-2005 “The brake lining made of composite materials for rolling stock”. The test results indicated that the physical and mechanical properties, the braking performance and wear resistance of the brake pad fully met the corresponding requirements; the whole polymer structure survived after the severe braking tests. This result may be due to the metal fibers and/or particles in the friction material that can effectively export frictional heat during the braking process, and the heat stability of the formed tribochemical products. The brake pad with this new binder has achieved practical application for passenger-coach braking in China.

<div class="htmlview paragraph">Today's fragmentary and heterogeneous regulation regarding vehicle and components, static and dynamic tests, suggest a new trend for a global evaluation of the vehicle by means of collision tests between the vehicle, with dummies on board, and dynamometric deformable moving barrier.</div> <div class="htmlview paragraph">Such moving barrier (always the same) is used in the front collision test as well as in side and rear collision tests.</div> <div class="htmlview paragraph">The new Fiat Safety Center is designed not only to enable it to carry out the tests required by present regulations, but also with a view to future test trend.</div> <div class="htmlview paragraph">Covering 27 acres, the installation provides for any type of test, with 1370-ft tracks giving a terminal speed of 97 mph for cars and 62 mph for trucks of up to 20 Tons.</div> <div class="htmlview paragraph">Vehicle are propelled by a two-ton trolley, rolling on angled rails in a culvert below the surface. This is driven by a closed loop of 1-in cable powered by a 2300 hp eletric motor, the speed of which is held within a tolerance of 0.25 % by a central computer, programmed for each particular crash test.</div> <div class="htmlview paragraph">Crash data are transmitted to the control room by a 60-channel cable and a 96-channel radio telemetry system. Signals are processed by computer, with recordings on magnetic tape or digital print-outs.</div>

Understanding the wear behavior of Cu-based brake pads, which are used in high-speed railway trains and aircraft, is essential for improving their design and safety. Therefore, the wear mechanism of these pads has been studied extensively. However, most studies have focused on the changes in their composition and not the effects of their manufacturing conditions. In this study, we fabricated commercial Cu-based brake pads containing Fe, graphite, Al2O3, and SiO2 using spark plasma sintering under different conditions. The microstructures and mechanical properties of the pads were investigated. The pads were tribo-evaluated using the ball-on-disc test under various load conditions. Their worn surfaces were analyzed using X-ray diffraction analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and confocal microscopy in order to elucidate their wear mechanism. In addition, the dynamometer test was performed to confirm whether their wear behavior would be similar under actual conditions. Finally, a comparative analysis was performed using the ball-on-disc test. The results indicated that the brake pads with the same composition but fabricated under different sintering conditions exhibited different wear characteristics. We believe that this research is of great significance for understanding the wear mechanism of Cu-based brake pads and improving their design and hence their performance.

<div class="section abstract"><div class="htmlview paragraph">Metal foil is a widely used material in the automobile industry, which not only is the honeycomb barrier material but is also used as current collectors in Li-ion batteries. Plenty of studies proved that the mechanical property of the metal foil is quite different from that of the metal sheet because of the size effect on microscopic scale, as the metal foil shows a larger fracture stress and a lower ductility than the metal sheet. Meanwhile, the fracture behavior and accurate constitutive model of the metal foil with the consideration of the strain rate effect are widely concerned in further studies of battery safety and the honeycomb. This article conducted experiments on 8011H18 aluminum foil, aiming to explore the quasi-static and dynamic tension testing method and the anisotropic mechanical behavior of the very thin foil. Two metal foil dog-bone specimens and three types of notched specimens were tested with a strain rate ranging from 2 × 10<sup>−4</sup>/<i>s</i> to 40/<i>s</i> and various stress states. It was shown that the metal foil has an obvious anisotropic behavior and the stress level increases with the strain rate. An anisotropic material model, which combined the Yld2000-2d plasticity model and the rate-dependent plasticity framework, was used to describe the mechanical behavior of the metal foil. Meanwhile, the fracture behavior of the metal foil was calibrated with an anisotropic fracture initiation model. The results of the constitutive model reproduced the strain rate effect and the anisotropic behavior of the metal foil, which have a good agreement with the experimental data.</div></div>