Left: Carbon fibre crankset with 53/39 rings. Right: Aluminium crankset with 53/39 rings. Photo credit: John Rees

Before getting into the comparison, it’s important to clarify that we’ll be using generalizations. There are many different types of aluminium and many types of carbon fiber, each with their own properties. Unless stated otherwise, when we talk about carbon fiber, we mean a composite made of carbon fibers and epoxy resin, and for aluminium, something like 6061 or similar. We’ll focus on the most representative properties of each material to keep the comparison as fair as possible.

Comparison between carbon fiber and aluminium

In the table below, we compare some of the most relevant properties of each material to give a clearer picture of their differences.

When is carbon fiber clearly superior to aluminium?

As mentioned earlier, it depends on the specific project. But if we simplify, we can say that when strength-to-weight ratio or stiffness-to-weight ratio are critical, carbon fiber is usually the better option.

On top of that, carbon fiber is anisotropic, which makes it especially effective in applications where the main loads are directional. Another key advantage of composites is their resistance to corrosion, while aluminium can experience galvanic corrosion depending on the environment and the materials it’s in contact with.

When is aluminium clearly superior to carbon fiber?

Again, simplifying things, aluminium is the better choice when heat dissipation matters, since it has very high thermal conductivity. It’s also generally easier to scale for large-volume industrial production.

Aluminium boat hull. Photo credit: NearEMPTiness

Aluminium behaves in a very predictable way under impact—it bends or dents instead of suddenly breaking, which is a big advantage in certain products. And while it depends on the application, it’s usually more affordable, which can be a deciding factor in many projects.

Where do they compete?

There are plenty of industries where both materials are solid options, but here are three common examples. They show pretty clearly that materials are just one part of the equation in engineering—choosing the right one depends on a lot of specific factors.

Aviation

Metals have traditionally been the go-to materials for aircraft manufacturing, especially aluminium. However, composites are becoming more popular thanks to the efficiency gains they offer and advantages like improved fatigue resistance in certain cases.

Carbon fiber light aircraft fuselage. Photo credit: Matti Blume

Bicycles

Carbon fiber bikes have been around for years and dominate the high-performance segment, but aluminium is still very popular among many riders. Generally speaking, carbon bikes are lighter, while aluminium ones tend to handle crashes and rough use better.

Wheels

Most bikes, motorcycles, and cars use aluminium alloy wheels, although high-performance models increasingly use carbon fiber wheels or offer them as an option. Aluminium wheels offer a great balance of strength, cost, and weight, while carbon fiber wheels deliver top performance with the lowest possible weight.

When should hybrid carbon fiber and aluminium parts be used?

A growing engineering approach is to use hybrid structures combining carbon fiber and aluminium to take advantage of both materials. For example, using carbon fiber outer layers attached to aluminium frameworks, or aluminium structures reinforced with CFRP, or directly joining a carbon fiber structure to an aluminium one. This allows engineers to benefit from lightweight stiffness along with the ductility and energy absorption of metal.

Alfa Romeo 4 C combination of carbon fiber and aluminium. Photo credit: youkeys

However, these combinations need careful design, since it’s usually necessary to avoid direct contact between the two materials to prevent galvanic corrosion in aluminium. Another important factor is thermal expansion—aluminium expands much more with temperature than carbon fiber, so the design has to accommodate that difference.

TL:DR

Aluminium is more ductile, isotropic, usually more affordable, and better suited for large-scale production. Carbon fiber is stiffer, lighter, anisotropic, and enables designs that aren’t possible with metal.

Depending on the project, one will be a better fit than the other. In some cases, the best solution is actually a hybrid design that combines both materials.

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We think about carbon fiber composites as very stiff, however, as the authors suggest, when this material is manufactured thin enough, it can withstand very high deformations! The resulting high tensile and compressive strains require accurate modeling of the fiber-dominated non-linear effects to predict the mechanical response.

These thin, unidirectional carbon fiber composite shells can be folded to impressively small bending radii without failure. The ability to elastically sustain and recover large deformations makes these materials highly beneficial for applications like deployable space structures, future medical devices, or shape adaptable meta-materials.

Interested in learning more about this topic? Here is the link to the publication: https://lnkd.in/e_ywKNZ

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During the development stage, the company faced several problems with the torsional stiffness of the aluminum honeycomb chassis. The prototype chassis was losing a fifth of its torsional stiffness after 30,000 kilometers of testing, and the test drivers were noticing poor vehicle handling. To solve this problem, Bugatti invested in a new carbon fiber chassis that was developed and supplied by Aerospatiale, giving the car the stiffness it needed to achieve its performance targets. History was made when the EB 110 became the first production car to have a carbon fiber monocoque.

Another version of the EB 110 was also released. Named »Super Sport», this variant was lighter than the original by 150 kg. This was achieved by the use of carbon fiber body panels on the exterior and in the interior.

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Madrid, 28^th of April 2022 – Managing Composites, the engineering company specialized in composite materials projects, today announced the close of a 1,5M€ financing round by Bouwen Sistemas Industriales, holding of Itera Mobility Engineering, Hidragrup and Sinfiny.

The investment will enable Managing Composites to continue providing best in class engineering composite services while facing bigger challenges, boosting the lightweighting transformation of traditional industries, as well as, opening new markets. The company is already providing services to world-class hypercar and automotive brands, electric airplanes, space applications, underwater robots and sports material. In addition, the investment will allow the company to keep on transforming some of the services and R&D activities into products. Managing Composites projects portfolio already have The Native Lab, a composites EdTech company and two R&D projects close to be commercialized (SaaS for automatic defect analysis and a revolutionary reusable and full recyclable resin) as own initiatives.

“We are thrilled by Bouwen’s support, who sees the composites growing market as a one of the future key technology drivers in all the new mobility scheme” said Lluc Marti, founder and Managing Composites CEO. “The need of experts in composites has never been greater, especially with the need of lightweighting in new transportation solutions. This is the time for Managing Composites to continue growing and realize our vision of spreading composites word while making it more sustainable, affordable, and technically accessible.”

The use of composites and its knowhow, especially outside the aerospace world, has been developed privately in workshops/factories in a learning by doing process. For that reason, the companies that have the know-how are hesitant to share it. Managing Composites’ founding team has been involved throughout the complete value chain and understands that sharing the knowledge is key to help developing the industry.

The Managing Composites adventure started at the end of 2019 and since then has grown with pure bootstrapping, achieving 1,3M€ of turnover in 2021. The company plans to exceed 2,2M€ in 2022.

Bouwen Sistemas Industriales, is a holding of industrial companies. They have a well stablished engineering company in the automotive and railway industry, Itera Mobility Engineering, a hydraulic presses and industrial equipment manufacturer, Hidragrup, and one company specialized in the automatization of industrial processes, Sinfiny Smart Solutions. This way, Bouwen covers the whole value chain, starting with the conceptualization and development of products, going through the construction of machinery, the design, automatization, and set-up of processes and ending with on-site engineering support during serial life.

Bouwen started its journey back in 2003 and since then, the company has kept on growing, both organically and inorganically, incorporating companies that complemented their capabilities. Bouwen targets 20M€ sales for 2022 and 200 employees, that includes the extension of the operations to North America.

What started as a collaboration project between Managing Composites and Itera Mobility Engineering, ended one year later with Bouwen (Itera’s owner) becoming a shareholder in Managing Composites, trusting on the current management team, and understanding what can be delivered with further resources.

 “For Bouwen has been a strategic investment. Given the increasing need of the main OEMs in keep on reducing weight, especially for the electrical vehicles and our aim on always offering innovative solutions, we consider the incorporation of Managing Composites into our group can be a perfect complement to the services we are providing to our current and future customers. Being together will allow synergies among the different companies in our portfolio and facilitating making available composites technologies developed in niche sectors, today ready to be implemented in big OEMs and TIERs” says Héctor Corral, Bouwen CEO.

 “We were not looking for investment. Nevertheless, after some months of project meetings, possible synergies with other companies from the holding, both sides realised that it will be a win-win situation. We will have the capacity to grow faster with the unevaluable experience from Bouwen who grew from scratch an engineering company to become a market reference. And for Bouwen, we are opening doors to a new engineering and industrial fast-moving market” says Alex Batán, CPO at Managing Composites.

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Why make them so thin?

In short, carbon fibers are manufactured through the stabilization, carbonization and graphitization of a precursor (generally polyacrylonitrile or petroleum pitch). The crystal structure of graphite consists of sp2 hybridized carbon atoms arranged two-dimensionally in a honeycomb structure in the x-y plane. The layers, termed graphene layers, are stacked parallel to each other in a 3D structure.

A precursor with a smaller fiber diameter allows for a higher graphitization degree. In other words, the carbon fiber will have greater graphite content. This way, the probability of having a concentration of defects in the 3D structure is considerably reduced. That is why the mechanical properties of fibers are inversely proportional to their filament diameter.

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AIMPLAS recently reported that it has made progress in regards to the EU-funded RECOTRANS project, which focuses on integrating unconventional manufacturing technologies to obtain cost-effective recyclable multi-material composites suitable for the transport sector at high production rates.

In particular, new thermoplastic composites have been developed through the integration of microwaves and laser welding. It has been demonstrated that microwaves can be used to optimize the curing process of composites in resin transfer moulding (RTM) and pultrusion, which reduces the energy consumed, shortens manufacturing times and helps produce better quality parts.

It has also been shown that laser technology can be used to obtain stable joints between the composite and metal, thus making it possible to eliminate riveted joints, which typically increase structural weight. Finally, studies were carried out on the recyclability of the thermoplastic composite by using it to manufacture a new part.

AIMPLAS says these results were validated through the manufacture of three life-size demonstration samples using various either carbon or glass fiber reinforcement and a thermoplastic acrylic resin, and one demo sample from the recycling material:

• A glass fiber-reinforced thermoplastic rear suspension system for a truck cab, manufactured by integrating microwaves into the RTM process; the composite-metal joint employed laser welding.
• Carbon fiber-reinforced thermoplastic automotive door panel, manufactured via microwave integration with C-RTM.
• Glass fiber-reinforced thermoplastic interior panel for the rail industry manufactured by using microwaves in the pultrusion process.

The joint between the composite and metal parts was made using laser welding. In addition, the recyclability of the materials was validated by manufacturing a demo sample of a car door handle made of 50% recycled material.

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