Carbon Fibre Reinforced Sheet Moulding Compound in Brakes: Manufacturing and Testing of a Lightweight Motorcycle Brake Calliper

With regen braking on the rise, thermal and mechanical loading of friction brake components is reduced. Novel materials, such as fibre reinforced polymers, can be feasible for structural brake parts. Their high specific stiffness and strength paired with their chemical resistance identify them as an appropriate substitute material. However, composites still present challenges in engineering. This paper continues previous research on the design of a thick-walled carbon fibre reinforced sheet moulding compound (CF-SMC) brake calliper. It focuses on the manufacturing process, the validation of various simulations through testing and quality control, and the environmental impact in a cradle-to-grave (ctg) approach.
Multiple CF-SMC brake calliper prototypes were made from pre-impregnated (pre-preg) carbon fibre sheet moulding compound by compression moulding (CM). Diverse testing methods on a static test bench are applied to gather insights on function fulfilment, stiffness, acoustics and bursting strength. A life cycle assessment (LCA) is conducted to track the processes with the highest energy demand and to evaluate the calliper’s environmental impact. A cradle-to-grave approach was chosen, since it is essential to consider all life cycle stages from resource extraction to recycling. The results are then compared to those of a conventional aluminium brake calliper. Furthermore, the high automation potential of pre-preg CF-SMC material processed in CM, due to fast curing resins and the absence of hand lamination, is examined.
The prototype tests prove the capability of the concept. Computed tomography (CT) scans visualize the fibre orientation, a result from material flow during compression moulding. Moreover, the CT scans are compared to manufacturing simulations to validate the accuracy of the predicted fibre orientations, obtained by a velocity gradient procedure. Static strength tests indicate that the maximum calliper displacement is close to the outcome of coupled FEM simulations, which are based on an integrative simulation workflow to consider the fibre orientation in the numerical model. The performance of the CF-SMC calliper is compared to that of the aluminium reference component. Considering the LCA, the most energy-intensive operation was found to be manufacturing of primary carbon fibres. As a consequence, the focus is on recycling processes, improving the current potential for environmental sustainability. Further static/dynamic tests are currently in progress, providing a more profound insight in material and component performance. Hence, no statement can be made about the thermal behaviour yet. Moreover, the results must be statistically analysed due to the initial randomly-arranged, discontinuous reinforcement fibres and a certain scatter in performance.
Building on design and simulation techniques from the preceding publication, this work demonstrates the feasibility of CF-SMC brake callipers. The application of a carbon fibre reinforced sheet moulding compound brake calliper on a test bench is an unprecedented innovation. To fully exploit the material’s benefits, it is essential to consider the unique characteristics throughout all stages of the engineering process. With the presented comprehensive approach, involving dedicated simulations, material tests and quality control, the potential of thick-walled carbon fibre reinforced composites is shown. Systematic action in recycling can resolve the remaining challenges, allowing more cost-effective and sustainable large-scale production. Thus, it is likely that CF-SMC usage will increase, especially in thick-walled applications, like brake callipers.