Carbon fiber composites are currently used in many different applications due to its superior properties in comparison to other materials, such as aluminium alloys, titanium alloys and steels. It is mainly the stiffness and strength to weight ratio, but also EMC properties, corrosion resistance, moulding advantages amongst others. This article reviews composite material properties and how their adoption can improve your products.
What is a composite material?
The advantage of a composite material is that the properties of the composite material are better than those of its constituents. This is true if the material is well designed and manufactured. Bold Valuable Technology has experience in both to offer our customers the advantages of composite materials.
Classification of composite materials
There are four common categories for composite materials. Carbon fiber can be found amongst them:
- Fibrous composite materials that combine fibers with a matrix: an example of these type of fibrous composite materials would be city buses bodywork. For this type of application, the fibers of choice are fiberglass in a matt form with a polyester resin.
- Laminated composite materials: layers of continuous fibrous materials in a stack. For example, carbon fibers with an epoxy matrix. A Formula 1 chassis is made of carbon fiber / epoxy material. Within carbon fibers there are a number of different fibers and matrixes which offer a huge variety of properties for the final composite material.
- Particulate composite materials in a matrix: this type would be similar to fibrous composite materials, except the reinforcement material (i.e. carbon fiber) is no longer a fiber but a particle. An example of these kind of materials are metal matrix composites (MMC) which are used in high performance applications such as aerospace and motorsport. The reinforcement materials are currently SiC, TiB2, Al2O3, B4C, used within different aluminium alloys.
- Combinations of some or all of the above.
What is carbon fiber?
Carbon fibers are widely used for structural applications mainly due to its high specific strength and stiffness to weight ratio. Typically carbon fibers can be classified into three groups: High modulus, High strength and Intermediate modulus.
Carbon fibers are made from an organic precursor produced from a polymer that undergoes a process of carbonization. Most of the carbon fibers used for automotive and aerospace applications are PAN fibers. Another type of carbon fiber is Pitch, but it is used in smaller quantities.
Properties of carbon fiber
Some properties that relate to composite materials, in particular the ones using carbon fiber as one of its constituents, are shown below:
- Strength
- Stiffness
- Corrosion resistance
- EM Transparency
- Attractiveness
- Low density
- Fatigue life
- Thermal conductivity
Benefits of carbon fiber
When describing the properties of carbon fiber one must make a comparison with other materials available for manufacturing components to be able to comprehend the actual benefits. Obvious choices for manufacturing components are metals, of which competitors to carbon fibers are aluminium alloys, titanium alloys and steels. For structural applications, the relationship between stiffness and strength to weight is the most critical factor for the designer.
Cost is an important factor too, however for vehicle applications the performance of the material usually outdoes the cost factor in the lifespan of the vehicle. All three mentioned metals have a specific stiffness ratio around 25 (GPa / g/cm3). Carbon fibre composites range from 66 to 150 (GPa / g/cm3), depending on orientation and type of reinforcement. This is around a factor of 3 to 6 times better.
Ref. http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/strength-density/NS6Chart.html
In terms of strength, the properties window of different alloys is significant, but considering the much lower density of carbon fiber (1,5 g/cm3) to metals (aluminium 2,8, titanium 4,5, and steel 7,8 g/cm3) one can see it is better most of times. To extract the best performance of the material it is important to ensure the designer is experienced with the specific composite material design techniques and tools, such as FEA (Finite Element Analysis).
Bold has Nastran FEA package that can simulate nonlinear and orthotropic materials. These features are required to study composite materials. Unlike metals, which are mostly isotropic, composite materials have different properties in each main axis of the material. That makes structural simulation more complex.
What are carbon fiber composites?
Carbon fibre composites come in different shapes and forms. The most common format for structural applications that Bold uses are prepregs. These are layers of material that have resin and reinforcement (usually epoxy resin with carbon fiber fabrics). In a prepreg, the two constituents are already “pre-mixed” and ready to lay up in a mould. The picture below shows how the carbon fiber is supplied, before laminating it into the mould. After the material is laminated in the mould, heat and pressure are applied to cure the matrix and to create a component.
How can carbon fiber composites help your business?
Fiber composites in motorsport and automotive markets
As discussed before, carbon fiber offers significant advantadges for vehicular applications. In automotive, due to cost constrains of mainstream market, composite materials are mostly found in the sports cars to hyper cars categories, and motorsport. For example, more than 80% of a Formula 1 car is carbon fiber.
Bold Valuable Technology has designed and produced components for motorsport in different areas of the car. One example of work that Bold designed was a series of structural rear wings, where the structures were tested to 1000 kg (10 kN) and weighed only 3,5 kg.
Another example was for an EMI (Electro Magnetic Insulation) application. Carbon fiber was combined with special technical fibers to create a Faraday Cage to protect sensitive electronics of a battery pack.
Fiber composites in space and aeronautics markets
The push for lower fuel emissions in the aeronautic market has transformed the materials used to build passenger airliners. For decades, planes where made from aluminium but in the last 15 years, carbon fiber has been the king in the air. Examples of these are the A350 from Airbus and B787 from Boing.
Source: https://www.comsol.com/blogs/protecting-aircraft-composites-from-lightning-strike-damage/
Bold is currently designing and engineering an ultra-lightweight structure to carry sensing electronics on a UAV. This structure is so light that will weight less than 800 gr and is almost 1000 mm long. The fuselage of the craft will less than 0,1 mm thick on most of the area to achieve the weight target. For this type of application, there is no other material that can match the performance of carbon fiber.
Fiber composites in other industries
Bold is working with a number of industrial partners to introduce carbon fiber for specific applications.
These include fast moving devices, pick and place end effectors, and insulation materials. In terms of pick and place, the advantages are:
- Weight reduction compared to metals or 3D printing which can lead faster speeds and increase in productivity
- Attractive aesthetics of carbon fiber are eye-catching
- Stronger than 3D printing and machined Polyamide (Nylon), PEEK and other technical plastics.
- Fast turnaround. Bold is extremely flexible with tooling sourcing and choice. Some customers produce tooling for us using their machining or 3D printing capability. Otherwise we produce tooling to make from 1 off to hundreds of units. We have inhouse machining capacity too.