Composite materials

If you are still debating whether composite materials are worth the extra cost, we believe you will be convinced they are indeed worthwhile after examining Bold Valuable Tech’s comparative study we carried out for a recent project. A noteworthy discovery in this project is the major weight difference between aluminum and a composite material we measured side by side. The assembly in question is an inverter enclosure. This is the unit which contains the battery and allows it to communicate with other parts, principally with the motor.

Aluminum as a first pick

Aluminum has long been the building material of choice for this component. Afterall, it is only natural to turn to this material for its widespread familiarity. Yet, as the saying goes, ‘familiarity breeds contempt’. We let ourselves get used to always turning to aluminum without giving composites a second look. Composite materials are just as effective as aluminum but with the obvious advantage of creating a structure that is significantly lighter. It does stand to reason that a team putting together all the components at the start of a project is keen to keep costs down, which may be why composites are overlooked in the designing stages of power electronics and batteries.

No one wants to be the bearer of bad news when presenting the price quote for this material alternative. While we firmly believe in staying on budget, we would like to reiterate the fact that the material’s performance will eventually trump the cost factor. This could even translate into savings throughout the lifespan of the vehicle. In contrast to aluminum alloys, titanium alloys and steels which have a stiffness ratio of around 25 (GPa/g/cm3), carbon fiber composites range from 66 to 150 (Gpa/g/cm3). This makes for an advantage of 3 to 6 times more than metals. The actual focus should be on the important benefits from reducing the weight which do pay themselves off in the long run for specific applications, for example in high level motorsport.

Classification of composite materials

There are four common categories for composite materials applied across numerous sectors. Carbon fiber can be found amongst them:

• Fibrous composite materials that combine fibers with a matrix: an example of this type of fibrous composite materials would be in bodywork for city buses. 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 several 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 like fibrous composite materials, except for the reinforcement material (i.e., carbon fiber) is no longer a fiber but a particle. An example of these kinds 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 aluminum alloys.
• Combinations of some or all of the above.

Once the right composite has been determined, the next step is to decide on the right shape. Carbon fiber composites come in different shapes and forms. The most common format for structural applications that Bold uses more often 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 already start off “pre-mixed” and ready to lay up in a mold. After the material is laminated in the mold, heat and pressure are applied to cure the matrix and to create a component. Overall, carbon fiber offers significant advantages for vehicular applications. Yet, due to cost constrains of mainstream market, composite materials are mostly found in the sports cars to hyper cars categories as well as motorsport.

Advantages of composite materials

Going back to Bold’s research while working on the inverter enclosure project, we shed new light on the current weight of the assembly using aluminum in contrast with potentially replacing it with carbon fiber. In this study, we did not scrutinize the structure as the one made of aluminum was not optimized. We would also like to emphasize that these outcomes would be similar in any other study done between carbon fiber and other commonly used metal manufacturing components such as aluminum alloys, titanium alloys and steels. The astounding reduction of weight turned out to be 91% lighter than its aluminum counterpart. One of the chassis alone weighed 6,746 grams compared to the carbon fiber version which was a mere 616 grams. This is nearly 11 times lighter than manufacturing the part with aluminum.

This is just the most visible improvement when replacing the material with carbon fiber, but it is not the only one. There are other considerable improvements that come with opting for carbon fiber that pay off in the course of time. Compared to its metallic equivalent, carbon fiber offers the following benefits which can even result in cost-saving features:

• Easy to electrically insulate internal and/or external surfaces with addition of layers of different materials. This is important for HV applications where safety might be a concern in crash events or due to catastrophic failures to the unit
• Ease to achieve a full Faraday Cage for EMC requirements
• Metallic inserts can be electrically connected amongst them as with metals
• No corrosion with composites
• Embedding of sensor in composite material structure (laminated in)

Deciding factor

When it comes to motorsport vehicles, one major factor that will give your competitors a run for their money is eliminating excess weight. The other benefits that using composites entail all add up to being the better bet against choosing to make a metallic component. The team at Bold is familiar with these alternatives and are pleased to look into the right composition the application you are looking to create or tweak to gain a competitive edge. Get in touch with us to discover your options.