Research Questions / Objective Brake callipers are generally produced by processes like casting, forging or milling; typically in aluminium or spherical graphite iron. With the current shift towards electric propulsion systems, the load spectrum of brake callipers can be reduced due to regenerative braking. Therefore, alternative materials such as carbon-fibre reinforced plastics are imaginable for components like for example brake callipers. Within this paper, a carbon-fibre reinforced Sheet Moulding Compound (CF-SMC) is applied within a novel calliper design. The main challenges are, besides ensuring function and stiffness of the system, to provide engineering processes for the design of such a thick-walled CF-SMC component. Methodology CF-SMC is commonly used for thin-walled bracings, reinforcements, bodywork and aerodynamic devices. These parts e.g. support a car’s chassis, for example as strut bars, or guide the airflow, as e.g. diffusers, wing elements or endplates. Thick-walled components, however, are not yet established in CF-SMC technology. The complex stress situation of a brake calliper and the exposure to brake fluid combined with high temperatures poses a completely new application. Hence, the design is executed in such a way that a beneficial flow of forces and efficient manufacturing could be combined. Additionally, tests are performed to ensure the chemical resistance of the thermoset material to DOT4 brake fluid. Hand in hand with that, material flow simulations, curing simulations and structural FEM-simulations determine the optimal way to arrange the stiffeners on the calliper, the layers of pre-impregnated carbon fibre in the mould and the parameters to run the process. Results The iterative design process results in a two-piece fixed brake calliper, which will be manufactured with special attention to the material flow and the resulting orientation of carbon-fibres. Metallic inserts are added in the model to handle various tasks such as guiding the brake pistons or enabling the transfer of tangential forces via fitting bolts. A physical prototype will be produced and tested in the upcoming months, with first results presented at EuroBrake 2023. By applying the aforementioned simulation-methods in an iterative design approach, a weight saving of about 20 %, compared to a high-volume sports bike brake calliper, is reached. Limitations of this study Currently, the prototypes are still in the manufacturing phase and not tested yet. Strength and stiffness are only evaluated by simulative measures, showing also a limited stiffness of the parts compared to an aluminium reference calliper. An AK Master test is planned, to compare the stiffness performance to the simulations and evaluate the material behaviour at high temperatures. What is new in this paper? So far, CF-SMC has not been used neither for brake callipers, nor for thick-walled components in general. Therefore, this study shows absolutely novel approaches regarding design and simulation techniques for CF-SMC. Conclusion Using carbon-fibre reinforced polymers for brake callipers is a bold idea. However, considering the increasing ability for regen braking in with battery electric and hybrid vehicles, the brake system is facing reduced loads during customer-typical driving cycles. Therefore, this area of use is opened up for previously uncommon materials. Nonetheless, the challenges related to thermal capability, chemical resistance and structural capacity are still large. The presented work explores the boundaries of thick-walled CF-SMC components. It shall be seen as an incentive to further exploit the potential of this group of high-potential lightweight materials.
Mr. Alexander Fidler, Junior Researcher, Institute of Automotive Engineering, Graz University of Technology; Dipl.-Ing. Severin Huemer-Kals, University Assistant, Institute of Automotive Engineering, Graz University of Technology; Dipl.-Ing. Andreas Kapshammer, University Assistant, Institute for Polymer Product Engineering, Johannes Kepler University; Mr. Kepa Zulueta, Researcher, Leartiker; Prof. Dr. Peter Fischer, Head of Institute, TU Graz; Ms. Aimourza Altemirov, R&D Engineer, GD Tech; Ms. Michaela Stiefman, Research Project Manager, Ipoint-systems gmbh; Ms. Maria Dos Santos, Team Lead Results & Innovation, Ipoint-systems gmbh; Mr. Michael Bruyneel, Scientific Director, GD Tech