Waste clam shell was evaluated as an eco-friendly filler ingredient for brake friction materials and was compared with standard filler, like calcite and barite. The raw shell crystalline structure, morphology, and thermal stability were characterized. It was subsequently milled to 25-45 mu m and incorporated into brake pad formulations in concentrations of 15 wt% and 30 wt%. Pin-on-disc tests at room temperature, 200 degrees C, and 400 degrees C under mild wear conditions were conducted. Seashell and calcite obtained coefficient of friction (CoF) similar to barite at room temperature and at 200 degrees C. At 400 degrees C, 15 wt% seashell or calcite reduced the CoF with respect to barite, whereas 30 wt% increased the CoF. Wear coefficients increased with temperature. Samples containing only barite showed the lowest wear at room temperature. On the other hand, at 400 degrees C samples with 15 wt% seashell or calcite showed the lowest wear, with seashell being equivalent to calcite and outperforming barite. Seashell and calcite formed a protective tribofilm on the disc at elevated temperature, which reduced disc wear. The emissions were found to be proportional to the wear of the samples. Life cycle assessment showed that replacing calcite for seashell reduces the environmental impact over all categories. Overall, seashell powder had comparable performance to calcite and barite, and 15 wt% seashell offered the best balance between friction stability, wear resistance, and emissions. This highlights the potential of seashell waste as a sustainable filler in friction materials.

Noise assessment of brake materials is typically conducted using a full-scale dynamometer or vehicle testing due to its complex and system-dependent nature. However, reduced-scale setups are of strong interest for their flexibility and cost-effectiveness. This study applied the SAE J2521 squeal procedure to a reduced-scale dynamometer using two specific configurations differing in damping and stiffness properties. The reference setup is a fully supported configuration, typical of pin-on-disk setups. In the second, we introduced a mechanical spacer between the disk and its support, where disk vibrations are less constrained, offering a closer representation of real application conditions. Both configurations exhibited squeal events at frequencies of 3.8-4 kHz, 11 kHz, and 12.4 kHz, whereas the spaced configuration showed additional frequencies at 7.0 kHz and 14.7 kHz, and exhibited higher squeal occurrence and amplitude. Experimental modal analysis revealed that the spaced setup exhibits, on average, about 25% lower modal damping than the reference setup. The differences between the two systems are discussed in relation to their dynamics obtained by experimental characterization using frequency response function (FRF) measurements. The study also investigates the influence of braking parameters, pressure, velocity, and temperature, on the squeal propensity.

Brake emissions have gained increasing attention over the past twenty years. Still, due to the inherently transient and complex nature of brake emissions, advanced modeling techniques are necessary but remain limited in the existing literature. In this study, randomized tests were conducted on a reduced-scale dynamometer with braking parameters within the domain of the Worldwide Harmonized Light Vehicles Test Procedure (WLTP). Emissions were measured using an Optical Particle Sizer (0.3-10 mu m) and modeled with a Neural Network (RNN) featuring an ad hoc recurrent architecture. The RNN model comprises: 1) an Internal State, s, which describes the beddingin process and surface-state transitions caused by changes in braking parameters, and 2) a stationary component, e0, which depends solely on dissipated energy and brake deceleration. WLTP data were used to test the model. Additional randomized tests were then conducted, yielding strong R2 values ranging from 0.96 to 0.99 for cumulative emissions and lower values of 0.55 to 0.60 for individual events.

In this study, three friction materials were analyzed to evaluate the tribological behavior of novel, sustainable abrasives derived from steelmaking slags. A reference formulation containing alumina was compared with two alternative formulations incorporating Electric Arc Furnace (EAF) and Ladle Furnace (LF) slags. Tribological tests assessed friction stability, wear, and particulate emissions, while detailed characterization of worn surfaces and cross-sections provided insight into wear mechanisms. All materials formed secondary plateaus mainly composed of compacted iron oxides, as common in systems employing cast iron disc counterfaces. While all abrasives contributed to the generation of Fe-rich wear debris, EAF slag particles showed superior performance due to their ability to fragment and integrate into the friction layer, enhancing its compactness and reducing wear and emissions. LF slag particles, in contrast, did not fragment and failed to bond effectively with the friction layer. The results highlight the potential of EAF slag as an effective, eco-friendly abrasive in brake pads. Further validation under realistic conditions is recommended through inertia dynamometer testing.

The warm and hot deformation behavior of a 6060 aluminum alloy was investigated through compression tests conducted at temperatures ranging from 100 °C to 400 °C (homologous temperature range of 0.41–0.75) and strain rates of 0.001 and 0.1 s−1. The flow stresses were correlated with strain rate and temperature using a hyperbolic sine equation, and the activation energy was calculated for both deformation regimes. The modeling parameters were linked to the active plastic deformation mechanisms: strain hardening in the warm regime and dynamic recrystallization in the hot regime. A strong correlation between the experimental and calculated data was observed when the equation was applied separately to the stresses measured in the warm and hot temperature ranges.

This work explores two approaches aimed at improving the sustainability of automotive brake systems: incorporating rice husk as renewable raw material and using benzoxazine resins as an alternative binder in brake pad friction material formulations. The automotive brake system generates wear and PM emission during operation, contributing significantly to the traffic-related pollution. The need for the brake industry to address these emissions has been further promoted by the EURO 7 legislation, prompting a shift towards more sustainable brake systems. Rice husk and benzoxazine resins were chosen considering some attractive properties related to the friction material application but also to an actual industrial implementation, such as their favourable storing requirements. Four different friction material compositions underwent tribological testing on a reduced-scale dynamometer, also monitoring the airborne emissions. The contact surfaces were characterized through SEM, EDXS and XRD analysis. RH showed promising results towards a commercial application, and benzoxazine resin meaningfully lowered the wear of the friction material.

Friction-induced vibrations in an automotive braking system are of serious concern, leading to different repercussions. Numerous conventional and unconventional methods have been proposed to curb these vibrations, which are also observed to be directly related to generating non-exhaust particulate matter emissions. In this study, an in-house formulated friction material, tested in the form of pins, was subjected to internal damping by adding rubber content from 0 to 3 wt% and external damping by wrapping the different pins in rubber tape. The DMTA showed a decrease in storage modulus and an increase in loss factor with the increase in rubber content. The pin density decreased with the increase in the rubber content. Dry sliding friction, wear, emissions, and vibrations tests were conducted on a pin on disc tribometer with relevant attachments to measure emissions and vibrations. A large drop in vibrations was observed with the rubber content, irrespective of external damping. On the other hand, a significant reduction in wear, emissions, and vibrations was observed with the sample containing the highest rubber addition and with the damping tape. This study showed the feasibility of employing the combination of internal and external damping, emphasizing the optimum rubber content in friction material formulations.

Magnetic fraction isolated from steel furnace slag was tested as a component of Cu-free friction composites. The friction–wear performance and production of wear particles during their testing using a pin-on-disc tester against a cast iron disc were evaluated. To compare the effect of the magnetic fraction on the parameters studied, the composite with alumina and the composite with original steel furnace slag were also prepared and tested. All composites showed a comparable friction coefficient. The composite with original steel furnace slag, and the composite with a magnetic fraction showed higher wear resistance compared to the composite containing alumina. The positive effect of the magnetic fraction on the extent of the emission of wear particles was observed and explained by the decreased aggressiveness of this composite to the cast iron disc. The influence of the phase composition of the steel furnace slag and the magnetic fraction on the friction film formation was also indicated, and its effect on the production of wear particles was proposed.

With sustainability dominating the industry, recycling the generated waste from different processes is becoming increasingly important. This study focuses on recycling waste generated during aluminum anodizing waste (AAW) in friction material formulations for automotive braking applications. However, before utilization, the waste needs to be pre-treated, which mainly involves drying. Hence, four different industrial drying methods were studied to dry the AAW, and the corresponding characteristics were observed by evaluating its residual humidity and crushability index. The waste powders were further characterized using FT-IR and SEM/EDXS to understand their constituents. The initial analysis showed that the waste subjected to the drying process P2 and P1 with the lowest final humidity fetched the most desirable results, with P1 having the simpler drying procedure. The AAW powders were added in a commercial friction material formulation at 6 and 12 wt.% and subjected to friction, wear, and non-exhaust particulate matter analysis. The worn surfaces were analyzed using SEM/EDXS evaluation to understand the extension and composition of the deposited secondary contact plateaus. It was seen that the 12 wt.% addition of waste processed using the P1 technique provided the most satisfactory friction, wear, and emission characteristics, along with expansive secondary contact plateaus with a good contribution of the waste in its formation. This study showed a good relationship between the processing method and a formulation’s tribological and emission characteristics, thereby paving the way for using this drying method for other waste requiring pre-treatment.

The deposition of hard coatings on the surfaces of brake discs can significantly decrease the wear and related particulate matter of brake materials. Considering that brake materials, along with low emissions, have to guarantee excellent brake performance, the present work investigates the brake performance of a Co-free WC–FeCrAlY cermet-coated disc. The coating was deposited by the High-Velocity Oxygen Fuel technology. The influence of the braking conditions was investigated with tribological tests on a sub-scale dynamometer in a wide range of contact pressure (0.7-4.8 MPa), initial sliding speed (8-21 m/s) and temperature (above 900 °C). Under high temperature and velocity conditions, tribo-oxidative processes were high enough to control the frictional behavior through the formation of very large glazes on the pad surfaces. However, under high temperature and low velocity, the coated disc revealed an insufficient source of iron for the formation of extended glazes, thus the interaction was highly adhesive and associated with friction instability.

The development of modern brake systems requires the assessment of multiple aspects. Among these, parameters related to the tribological behaviour, vibration, and particulate matter emission are typically evaluated using inertia dynamometers and tribometers. While these two testing systems have been previously compared regarding emissions and tribological behaviours, vibrations were not compared, nor have all these aspects been examined simultaneously. This study investigates the scale effects between a pin-on-disc tribometer and a reduced-scale dynamometer operating under dragging conditions with two levels of pressure and velocity, and a disc temperature not exceeding 260 degrees C. Regarding the vibration, the pin-on-disc exhibited higher and broader values in the normal direction, 1.3-15.5 m/s2, 2 , than the reduced-scale dynamometer, 0.37-0.42 m/s2, 2 , while the tangential vibrations exceeded those in the normal direction in both systems. The wear rates in the two systems were overall similar, in the range of 1-4 e-14 m2/N. 2 /N. During the tests the disc temperature in the dynamometer increased at a higher rate compared to the pin-on-disc, affecting the tribological and emission behaviours: steady state values were obtained only in the pin-on-disc tests. The particulate concentration values observed during dynamometer tests better correlated with the peak values from pin-on-disc tests rather than with the steady-state values. This study highlights the importance of including transient values in the evaluation of pin-on-disc testing.

This study aims to investigate the outcomes of carbonaceous products, derived from the decomposition of the components of vehicular brake materials, under high-temperature wear tests. Pin-on-disc (PoD) wear tests were conducted by using cast iron discs against pins made of commercially available low-steel friction material. Tests were carried out at different temperatures: 155 °C, 200 °C, 250 °C, and 300 °C. The characterization of the sliding plateaus on worn pin surfaces was based on X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. It was noted that at temperatures above 200 °C, the thermal degradation of the inorganic resin, used as a material binder, occurs. An interesting observation was recorded at 300 °C; the brake pin material’s friction curve showed higher stability despite having an excessive wear rate. However, the brake pin’s specific wear coefficient was higher at this temperature than was observed in the other friction tests. A detailed study of the friction plateaus on the worn-out pins at 300 °C revealed that the decomposed carbon resin product, i.e., the distorted graphite, was widespread over the surface of the pin. Lubricant stabilization can be expected, as established by the observed values of the coefficient of friction (CoF), retaining values within the 0.4–0.6 range, even at high temperatures. Other friction material components may have contributed to the formation of this ubiquitous carbonaceous interface film.

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

The study focuses on the characterization of aluminum anodizing waste (AAW) in different friction material formulations. AAW was observed to have a dominant presence of hydroxide, sulfate hydrate, and a fraction of alumina. After heat treatment at 400 degrees C for 4.5 hours, the AAW also constituted of AlOx, obtained from the conversion of hydroxides. The AAW was included in two kinds of friction material compositions - a basic composition (BC) with few constituents, and a commercial composition (CFM), wherein, the AAW was added at 12, 24, and 32 wt.% of variation, and subjected to friction, wear, and emission analysis. The tests were conducted on a pin on disc testing equipment, in mild conditions and at room temperature. The analysis with BC revealed the mild abrasive nature of the AAW, along with acceptable friction, wear, and emission characteristics. With the CFM, the permissible CoF, pin and disc wear, and desirable emission characteristics were observed with 12 wt.% addition of AAW. Higher AAW content led to the degradation of wear and emission characteristics of the CFM specimens. Through this preliminary investigation, the possibility of the recycling/ utilization of AAW in friction materials was explored, paving the path for further exploration and feasibility analysis of the inclusion of AAW in braking applications.

The tribological behavior of new green friction materials with rice husk (RH) and rice husk ash (RHA) is discussed in the current paper. Two formulations developed, one with 6% RH and one with 6% RHA, were compared with a reference formulation with alumina under the AK Master test, through a braking tribometer. Formulation with RHA showed tribological performance equal to or better than the reference material, especially in high temperature applications where the RHA particles assisted in the building of the contact plateaus. Adding RH reduced the abrasive action of the composite, allowing the formation of a more homogeneous tribofilm on the disc than in the other formulations.

Recent studies have indicated the positive aspects of adding blast furnace (BF) slags on the friction and wear properties of different composite materials. However, the corresponding studies on the extremely important particulate matter (PM) emissions characteristics are seldom explored. This one-of-a-kind study examined the PM characteristics of two types of BF slags in detail. The slags were added in an in-house formulated friction material formulation with limited constituents to highlight the role of the added slags. Pin on disc tests were conducted at a mild wear testing condition with added attachments to the equipment to count and collect emitted particles at different particle size range. A significant reduction in pin wear and collected emitted particles were seen with the slag presence. The friction coefficient of the slag specimens was slightly lower than the reference sample. Through SEM and TEM analysis, it was seen that the slags actively contributed to and supported the formation of smooth, compacted, and extended secondary contact plateaus. From this study, the utilization of slags for specific applications is further evaluated, paving the path for subsequent inclusion/ replacement of conventional constituents in friction material compositions.