The usage of carbon fiber reinforced plastics (CFRP) has skyrocketed since their first commercial application in the 1970s. Initially used for fishing poles, golf clubs and tennis rackets, other industries soon picked up on the promising material.
Why the ever-increasing interest in CFRP?
CFRPs offer huge benefits when compared to the ubiquitous steel: their strength-to-weight ratio is 5 times that of steel, meaning that they use about 20 percent of the mass of steel yet are equally as strong and stiff. This makes them the perfect material for every application where lightweight and high-performance requirements need to be met -aerospace, wind turbines, cars, bikes and even marine applications such as sport yachts. CFRPs are light-weight and extremely strong, resistant to corrosion, have low thermal expansion coefficients and an extremely high load alternation resistance and therefore high longevity.
Their design is relatively simple, especially when compared to the various benefits they offer. Carbon fibers (filaments) are used as bundled rovings, filament yarns or woven fabric. They are then impregnated with a thermoset or thermoplastic resin. The fibers give the finished product the desired strength while the hardened polymer matrix keeps the them in place. The key factor of these composite materials is that they can transmit forces very efficiently along the direction of the fibers due to their tensile strength. However, they lack this ability in any other direction. (anisotropy)
There is a wide range of manufacturing processes that create prepreg (pre-impregnated) materials, like tows, tapes, or multidirectional sheets. Because of the anisotropic properties of CFRPs, composite parts need to be designed in a way that optimizes force transmission along all necessary directions, meaning that multiple layers of different orientations of these prepregs need to be layered on top of each other, forming a stack (or stacking).
Figure 2: A simple laminate designed in the CAESA Composites TapeStation. In this stacking of multiple angles, different colors indicate different layup angles. The tows of the layers have been cut to show the vertical structure.
While multidirectional sheets are already made up of multiple angles, they can only be draped on relatively simple surfaces, since they lack flexibility and will start to wrinkle when draped onto complex geometries like moulds.
Tows and tapes are fixed width material stripes. Tows are up to 1’’ wide, while tapes are usually wider. The advantage of tows and tapes over sheets is that they can be laid on more complex surfaces without wrinkling since they are narrower. This increases their flexibility and opens possibilities to manufacturing very complex curved parts. This however requires more complex machinery to manufacture laminates, closely resembling the final part. The laminate will, in most cases, be a multi-directional (quasi-isotropic) layer structure that needs to be “baked” in an autoclave to harden the resin (plastic) and bring the part to its final state. From then on it can be used in the specific application it has been designed for.
The big challenge of this still-developing technology is to create manufacturing opportunities that are competitive to well-established materials and processes. Using state-of-the-art CAD and CAM solutions for designing parts and laminates proves to be a good way of increasing manufacturing productivity and performance of CFRP components in all applications.
In the following posts, we will go into detail about how the manufacturing processes of CFRP parts work and how CAM software helps to improve these. Until then, stay safe and stay tuned.