Carbon fibre or fibreglass? Kim Sjödahl advises how to pick the best composite for your application
You wouldn’t attempt to delicately manicure a bonsai tree with a chainsaw, even if it would be entertaining to watch. This may seem obvious, but there are many fields where selecting the right tool is a vital ingredient to success. In the composites industry, customers often request carbon fibre when in fact fibreglass is a better suited high-performance material for their needs.
Carbon fibre is often hailed as the material of the future. When people think of carbon fibre, they’re likely to envision slick sports cars with doors that open vertically or, if they are industry focused, wind turbine blades longer than previously imaginable. For most composite producers, carbon fibre is the material that gets customers and their design engineers interested in composites – before they realise that other composites such as fibreglass are better suited to their project.
Sports cars, road bikes and professional tennis rackets are all extensively made using carbon fibre. This is because these applications require a low density and high ultimate tensile strength material to maximise weight advantages. However, this doesn’t mean that carbon fibre is perfect for every application.
Raising the bar with fibreglass composites
In many cases when clients are looking for carbon fibre, the material that better suits their needs is fibreglass. In fact, it could be said that fibreglass was the first ever high-performance material, with its conception dating back to before the Second World War. Fibreglass has proven its usefulness over and over, from use in door or window frame profiles to telescoping poles, in automotive applications to rail joints and telecommunications radomes. If you have the impression that fibreglass is reserved for making rowing boats, it may be time to take another look at what else it can achieve.
Fibreglass has a very good ultimate tensile strength, higher than most metals. It’s a great insulator, with a very low coefficient of thermal expansion, and it is corrosion and weather resistant. For example, the ITER fusion reactor, a tokamak style fusion reactor being developed by 35 collaborating nations, uses fibreglass composite pre-compression rings (PCR) to hold the reactor together.
The ITER fusion reactor uses the PCRs to absorb the deformation and fatigue from magnets that hold the plasma, which is heated to 150,000,000 °C, in place. Fibreglass was selected for the PCRs because of the material’s specific high-performance mechanical properties.
Fibreglass has withstood the test of time. Since its early uses in World War II, the material has yet to be replaced with a better alternative. This is largely due to the material’s mechanical properties combined with its competitive cost and design flexibility.
With composites, it is also important to note that the choice is not binary. Exel Composites offers a range of pultruded and pull-wound composite solutions. It manufactures many carbon fibre products along with fibreglass and hybrid combinations, where it uses both carbon and glass fibres.
Deciding on the best material choice requires a clear understanding of the desired application and product specifications, and the company first works with customers to develop a mutual understanding. Based on this understanding, the composites supplier should use its materials science expertise to design the end user’s ideal composite product. This discussion should include costs, particularly as raw carbon fibre materials come at a higher cost point than fibreglass.
Tailoring a composite can range from a specific mix of fibres to give certain properties, to managing the fibre alignment and resin formulation. For example, a fibreglass tube could require extra reinforcements along one side of the geometry. In this case, carbon fibres could be strategically incorporated into the tube along with the fibreglass at the point of manufacturing to create a strong hybrid structure that meets design requirements while considering cost optimisation.
Having the correct tool at your disposal is important whether you are trying to prune a bonsai tree or upgrade a piece of infrastructure. Although it may seem more appealing to use a chainsaw, or carbon fibre, lower-key choices can sometimes be the better option for the task at hand.
Kim Sjödahl is senior vice president, R&D and Technology at Excel Composites