During my travel around Singapore delivering plastic bags to various shops, I noticed that there is a nascent trend of using carbon fibre as material of construction for cars’ axles and suspension unit. Specifically, while carbon fibre is a strong material capable of withstanding significant amount of load before failure, its catastrophic mode of failure where it breaks into different parts meant that it is a dangerous material of construction that, upon impact failure, could lead to more serious damage to the car and fatalities.
Carbon fibre draws its strength from its ability to withstand tensile stress. In relation to compressive stress such as direct exertion of force on the material, carbon fibre remains a strong material, but it tends to shatter into small pieces upon failure, which would lead to further disintegration of the structure. Hence, in applications requiring material strength, carbon fibre is not suitable as a material of construction.
However, carbon fibre has been widely deployed for various strength applications in motor racing and high performance yacht racing such as the renowned Volvo Ocean Race. Hence, why is it not used, on a widespread and frequent basis, as a high performance material in road cars and other daily use products. The key lies in its lack of durability and resilience to shock waves under a variety of conditions.
Specifically, carbon fibre is acceptable as a lightweight and high performance structural material in Formula 1 and the construction of Volvo Open 70 race boats of the Volvo Ocean Race. And, race performance data, whether in Formula 1 cars and Volvo Ocean Race yachts, suggests that carbon fibre structures performed admirably and up to specifications under severe high load race scenarios. However, a bugbear of carbon fibre lies in its relative lack of resilience against high impact forces and, most importantly, its tendency to shatter into small fragments of myriad shape and size upon collision; thus, making it unsafe as a structural member.
From a daily use item’s perspective, durability, robustness, resilience and ability to withstand high load forces under a variety of working conditions are key considerations for selecting a particular material for use as structural member or component. While carbon fibre affords high performance in strength and is lightweight for a given load to support, it critically lacks durability. Specifically, long term use of carbon fibre as structural member for repetitive, high load applications has shown that it tends to degrade in performance and resilience against high loads with progressive usage, especially under high temperature and pressure. Therefore, long term use of carbon fibre as structural material in load applications, such as in road cars, is not advisable.
Taking the above points into account, evaluating the use of carbon fibre as structural member of car axle and suspensions highlights the clear possibility that repetitive, long term load under braking and cruising over undulating terrain, would most likely result in progressive structural deterioration of carbon fibre at the microscopic level. Specifically, a combination of delamination of different adhesive sheets of carbon fibre, and breakage of long chain of carbon molecules reduce the resilience of the material against sudden high load condition such as a collision. Hence, for durability applications such as the axle and suspension of road cars, carbon fibre is not suitable as a structural component.
Category: materials, materials engineering, mechanical engineering, physics,
Tags: carbon fibre, structural member, axle, suspension, delamination, microscopic damage, durability, repetitive high load,
Acknowledgement: Ng Wenfa thank Seah Kwi Shan for co-authoring this blog post.