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Technical Paper

Use of Hexagonal Boron Nitride in Automotive Friction Materials

The major goal of this research study was to address the possible replacement of copper and selected solid lubricants by environmentally friendly hexagonal boron nitride (h-BN). Model friction samples were manufactured and subjected to friction assessment and screening tests (FAST) and full scale automotive brake dynamometer (Dyno) tests. The SAE recommended J2430 procedure provided the necessary data for the Brake Effectiveness Evaluation Procedure (BEEP) by Brake Manufacturers' Council. The obtained results indicate that the overall coefficient of friction, as detected in FAST, increased with respect to baseline with a 1:1 substitution of h-BN for either Cu or metal sulfides (Sb₂ S₃ and MoS₂). The thickness losses in FAST tests were similar or lower when h-BN was being used to replace copper and metal sulfides, except for the HCR type of h-BN.
Journal Article

Toxicity of the Airborne Brake Wear Debris

Particulate air pollution from road traffic currently represents significant environmental and health issue. Attention is also paid to the “non-exhaust pollution sources,” which includes brake wear debris. During each brake application, the airborne and nonairborne particles are emitted into the environment due to wear. High temperatures and pressures on the friction surfaces initiate chemical and morphological changes of the initial components of brake pads and rotating counterparts. Understanding of impact of matter released from brakes on health is vital. Numerous studies clearly demonstrated that particulate matter caused potential adverse effects related to cytotoxicity, oxidative stress, stimulation of proinflammatory factors, and mutagenicity on the cellular level. This paper compiles our main results in the field of genotoxicity, immunotoxicity, and aquatic toxicity of airborne brake wear particles. The brake wear particles were generated using an automotive brake dynamometer.
Technical Paper

Performance of Low-metallic Cu-free Brake Pads with Two Different Graphite Types

Automotive brake lining materials are complex composites consisting of numerous ingredients allowing for their optimal performance. Since regulations are increasingly limiting Cu content in brake pads and Cu exhibits extremely high thermal conductivity, graphites being excellent heat conducting materials themselves, are often considered for use as potential Cu replacement. This paper surveys the role of two types of carbons (Superior Graphite) with high thermal conductivity but different mechanical properties and morphology: the so-called i) purified flake graphite (PFG) and the ii) resilient graphitic carbon (RGC). A successful “high-end” commercial low-metallic brake pad was re-formulated (SIU Carbondale) by removing of over 20 wt. % of Cu and replacing it with a cocktail of ingredients including 15 wt. % of these two graphite types (RGC and PFG).
Journal Article

Optimization of Brake Friction Materials Using Mathematical Methods and Testing

Brake linings have complex microstructure and consist of different components. Fast growing automotive industry requires new brake lining materials to be developed at considerably shorter time periods. The purpose of this research was to generate the knowledge for optimizing of brake friction materials formula with mathematical methods which can result in minimizing the number of experiments/test, saving development time and costs with optimal friction performance of brakes. A combination of processing methods, raw materials and testing supported with the Artificial Neural Network (ANN) and Taguchi design of experiment (DOE) allowed achieving excellent results in a very short time period. Friction performance and wear data from a series of Friction Assessment and Screening Test (FAST) were used to train an artificial neural network, which was used to optimize the formulations. The averaged COF, COF variation and wear were used as the output parameters.
Journal Article

Influence of the Automotive Brake Wear Debris on the Environment - A Review of Recent Research

Automotive brake linings are complex composite materials. Some raw materials used by manufacturers or the compounds created during the friction process might be potentially hazardous and may cause various adverse effects. Different fractions of the brake wear debris can be released during braking: i) the airborne and ii) the nonairborne. Due to the small size and minimum gravitational action, the airborne particles could be spread for long distances from a source and typically remain suspended in the air for long periods of time. Our previous research demonstrated that the airborne fraction contains considerable amounts of different nanoparticulates. On the other hand, the emitted nonairborne fraction typically settles on vehicle/brake hardware surfaces and in the vicinity of roads. The nonairborne particles are considered to be relatively large, but it was shown that nano-sized particles readily attach to them and can be released later.
Journal Article

Identification of Organic Compounds Released from Low-Metallic Automotive Model Brake Pad and its Non-Airborne Wear Particles

The brake wear contribution to the environmental pollution has been extensively discussed, with major focus on asbestos and heavy metals released to the environment. Only limited attention was paid to released organic compounds generated during friction processes, although the organic and carbonaceous components are not the minor part in brake lining formulations. Friction processes in brakes are associated with relatively high temperatures and high pressures on the friction surfaces which relates to the thermal decomposition of the organic components in friction materials and to brake lining thermal fade. Thus, this study focuses on the identification of organic compounds released from a model low metallic brake material.
Technical Paper

Friction and Wear Responses with Metallic Composite Materials to Replace Copper and Copper Alloys in Brake Pad Formulations

Copper and copper alloys are widely used in friction materials such as brake pad formulations as one of key ingredients by providing good thermal conductivity and high temperature friction stability to achieve desired friction performance, fade and wear resistance. However, the use of copper or copper containing material is being restricted in brake pads due to environment and health concerns. Extensive works have been made to explore the copper substitutes but most of these efforts became ineffective and failed with issues either thermal fade or excessive pad/rotor wear. In this paper, friction and wear responses were examined when a metallic composite material was used as the copper substitute in NAO and Low-met brake formulations where the copper and copper alloys were added 8% and 22% respectively.
Journal Article

Friction Performance of Eco-Friendly Cu-Free Brake Materials with Geopolymer Matrixes

Besides elimination of copper, the eco-friendly brake materials are developed using geopolymer matrix and natural fibers to replace phenolic resin and synthetic fibers, respectively. The objectives are to diminish i) the amount of volatile organic compounds (VOCs) being released from the brake materials when subjected to temperatures higher than 300 °C; and ii) release the potentially hazardous wear debris particles to the environment. Brake materials were fabricated in university and tested using SAE J2430 test procedure and full scale automotive brake dynamometer (Dyno). Dyno test results indicate that the average friction level of the eco-friendly Cu-free materials (µ ∼ 0.30 to 0.33) was only slightly lower when compared to the baseline material containing Cu (µ ∼ 0.35). All tested materials have passed the Brake Effectiveness Evaluation Procedure (BEEP).
Technical Paper

Development of Cu-Free Brake Materials

The purpose of this research study was to develop Cu-free automotive brake materials. Model brake material samples were manufactured and subjected to full scale automotive brake dynamometer (Dyno) tests using SAE J2430 test procedure. The SAE recommended J2430 test procedure provided the necessary data for the Brake Effectiveness Evaluation Procedure (BEEP) by the Brake Manufacturers' Council. The Dyno results indicate that the friction level of the all four Cu-free samples was similar to the baseline material. All tested brakes have passed the Brake Effectiveness Evaluation Procedure (BEEP). The average effectiveness of Baseline (BL), GT1, GT2, T401 and T402 samples is 0.32, 0.31, 0.30, 0.31 and 0.31, respectively. The Dyno results show that the Cu-free samples had similar or better performance compared to the baseline material as the temperature of the brake increased in the fade section. However, the Cu-free samples exhibit slightly higher wear rate in Dyno tests.
Technical Paper

Automotive Brake Lining Characterization

A number of brake lining materials representative of original equipment in US, Japanese and European automobiles were characterized in order to determine their composition and microstructure. Their frictional performance was subsequently determined using the Friction Assessment and Screening Test (FAST machine). The goal of this work was to identify each constituent of the friction material, to deduce their individual role in the friction process and to determine the effect of the microstructure on the wear properties.
Journal Article

Application of Extension Evaluation Method in Development of Novel Eco-friendly Brake Materials

Extenics is a new cross discipline to study rules and methods of solving contradictory problems in the real world. The basic concepts and theoretical frame of extenics are briefly introduced in this paper. Based on the merit of extenics, the extension evaluation method was applied to evaluate the brake materials according to a five-grade criterion established in this study. Considering the results computed by the original and simplified models, the similar conclusions were made: all four brake samples, marked A - D, were evaluated in the first grade based on the calculated dependence degrees, and sample B was judged as the best performing friction material with the highest dependence degree and the lowest wear rate.