Research and/or engineering questions/objectives (100 words): Substantial research has been dedicating to investigating new materials to replace GCI brake rotors to offer a reduction in emissions, wear, and corrosion. However, these may give rise to other problems, such as worsened environmental impacts at manufacturing phase. This research applies a developed Life Cycle Assessment model to quantify the environmental impacts of a lightweight PEO aluminium alloy rotor compared to GCI across the full life cycle. The objective is to assess the benefits of weight reduction within a braking system from an environmental viewpoint, as well as ensuring no problem shifting occurs. 

Methodology: Life Cycle Assessment (LCA) is a cradle-to-grave methodology to assess and quantify the environmental impacts of a product. The LCA has been applied to a Lightweight PEO Aluminium Alloy rotor and a traditional uncoated GCI rotor for a baseline comparison. The serviceability of the rotors is defined using a functional unit for a fair comparison. This is the decelerating of a vehicle over a specified lifetime based on the WLTP cycle. The emissions and impacts are allocated by mass of the products/by-products. 

Results: A self-built Matlab model has been used to produce the results, making it forwards compatible with testing other brake rotor materials and adjusting to new legislation. This paper presents the results for the full life cycle of both rotors, indicating the benefits of lightweight rotor materials. These results provide a breakdown as to how the environment is affected at each stage of the life cycle, displaying a detailed overview of how problem shifting can be avoided to ensure the full life cycle offers reductions in environmental impacts. The potential benefits of recycling a rotor through recoating can also be demonstrated to reduce impacts associated with manufacture. 

Limitations of the study: The main limitation of any LCA study is data availability. A big restriction is the confidentiality and complexity of the constituents that go into making a brake pad. Due to the emissions and performance being very dependent on the frictional interface the pad was included within the study. Assumptions are made that the manufacturing phase of the pad is consistent between rotors in terms of energy usage and emissions. Therefore, with this being a comparative study these can be assumed to be same between the two rotors and so omitted. The section of life cycle where they will differ is during use. With the testing having been done in house at University of Leeds, data is not an issue for both components here. 

What does the paper offer that is new in the field in comparison to previous research: There has been significant research investigating the benefits of new materials within a braking system to overcome the drawbacks of GCI and to meet new legislation. However, investigation into the whole life cycle is limited. The benefit of this is to understand, if any, problem shifting occurs between life cycle phases. Currently the existing LCA applications have been limited to coated GCI rotors and do not investigate the benefits of a lightweight material. This paper also builds on previous research by the same authors that focused on the development of the methodology for a brake rotor application. The methodology has now been applied on the full life cycle of both rotors, providing a detailed breakdown of environmental impacts at each stage. 

Conclusion: Results show a detailed breakdown of environmental Impacts at each stage of the life cycle. These results indicated the potential environmental benefits of a lightweight material for a brake rotor as well as those associated with the ability for closed loop recycling through recoating rotors.

Mr. Asmawi Sanuddin, University of Leeds, UNITED KINGDOM

Prof. David Barton, University of Leeds, UNITED KINGDOM

Dr. Peter Brooks, University of Leeds, UNITED KINGDOM

Dr. Carl Gilkeson, University of Leeds, UNITED KINGDOM

Dr. Shahriar Kosarieh, University of Leeds, UNITED KINGDOM

Prof. Suman Shrestha, Keronite International Ltd, UNITED KINGDOM

Lightweight disc brake rotors have become a popular alternative to conventional grey cast iron (GCI). The thermal and tribological response of these brake rotors will differ during a braking operation. This may result in the generation of particulate wear debris with different characteristics, which can affect the environment and human health to different degrees. Studies have shown a relationship between adverse health effects and the characteristics of airborne particulate matter such as particle size, concentration and chemical composition. In this study, the particulate matter released from a novel lightweight disc brake rotor is compared to that released from the conventional grey cast iron rotor. The lightweight brake rotor was made of aluminium alloy (Al6082) and its rubbing surfaces were treated using the Plasma Electrolytic Oxidation (PEO) process. The process produced hard, dense, wear-resistant and well-adhered alumina coatings of approximate thickness 50 microns.

A novel test rig was developed based upon the existing Leeds full-scale disc brake dynamometer. An enclosure was constructed around the brake assembly and ducting was carefully designed to ensure the cleanliness of the intake air to the system. Both brake rotors were tested under drag-braking conditions of constant sliding speed and applied braking pressure. Three braking test conditions with hydraulic pressures of 5, 10 and 15 bar at a constant speed of 135 rpm were selected from initial brake dynamometer tests. Braking test parameters of rotor rubbing surface temperature and coefficient of friction were measured during the tests and their effect on the brake wear particle characteristics were investigated. To measure and collect airborne brake wear particles, the Dekati ELPI+ unit was utilised along with a custom-made probe. This probe was made of stainless steel and its geometry was tailored to comply with the isokinetic concept. A scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDX) system was utilised to investigate the morphology and chemical composition of the airborne brake wear particles collected by the Dekati unit.

The initial comparison results showed that the PEO-treated lightweight aluminium alloy (PEO-Al) rotor has the potential not only to significantly reduce the unsprung mass of the vehicle but also reduce particulate matter emissions compared with the standard GCI rotor. The results also revealed that the percentage of iron contained in the PEO-Al debris was about threefold lower than that from the GCI rotor under all steady-state drag braking conditions studied which may have important health implications.

Mr. Fabian Limmer, University of Leeds, UNITED KINGDOM

Prof. David Barton, University of Leeds, UNITED KINGDOM

Dr. Carl Gilkeson, University of Leeds, UNITED KINGDOM

Dr. Peter Brooks, University of Leeds, UNITED KINGDOM

Dr. Shahriar Kosarieh, University of Leeds, UNITED KINGDOM

The brake industry is currently on the search for lighter, corrosion-resistant and more eco-friendly brake systems. Apart from health and environmental issues, the main drivers for this development are the changing load profiles arising from the megatrends of electrification and autonomous driving. As the brake disc and brake pad together represent a tribological system, both components must be adjusted in order to achieve optimal functionality.

Testing of brake friction couples, however, is usually a very costly, energy and time-consuming process, that only allows for a very limited range of material concepts to be considered. This is where testing friction materials on a small-scale level has great advantages because much time and money can potentially be saved in sample generation, testing and post-test analysis compared with full-scale testing.

A novel small-scale test bench has been developed at the University of Leeds which aims to screen friction materials under realistic braking conditions. The foundation of the setup is the Bruker UMT TriboLab tribometer operating in a modified pin-on-disc type configuration. Popular full-scale cycles such as the WLTP based real-world driving cycle have been implemented to replicate current everyday driving scenarios as well as custom cycles that aim to simulate possible future load profiles. A full enclosure around the friction couple has been designed using CFD to allow for controlled airflow and subsequent wear debris capture and analysis. The wear particles generated during braking operation are sampled under isokinetic conditions using the well-known Dekati ELPI+ instrument.

The paper will report on the scaling approach used to design the test bench and the conversion of the WLTP based real-world driving cycle to a non-inertial system. Details of the CFD analysis as well as preliminary test results will also be presented.