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Utilizing Lightweight Thermoset Composites in EVs

Striking the right balance between strength and weight is crucial in any automotive application.

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iStock/Ralf Hahn

Striking the right balance between strength and weight is crucial in any automotive application. Electric vehicles (EVs) take these concerns to new heights, as they’re often heavier than conventional cars, leading to increased tire wear. In addition, the ever-present issue of range anxiety pushes demand for motor efficiency — and, thus, lighter weight — higher.

Thermoset composites have emerged as an ideal component material in response to these trends, but using them in your designs isn’t always as straightforward as it may seem. Choosing the right one and applying it effectively requires attention to a few key factors.

Weight reduction

The most obvious material property to consider when designing thermoset composite parts is their weight. EV batteries are heavy — the electric Hummer’s is just 22 pounds lighter than a Toyota Corolla — so other components must be as light as possible to offset this mass.

Thermoset composites have successfully reduced weight and efficiency in other sectors. Carbon nano-reinforced polymers proved 30% lighter than conventional materials in aerospace applications, leading to more fuel-efficient planes. Using the same materials in EV components could produce similar results.

Of course, not every thermoset composite is equally lightweight. Carbon fiber-reinforced polymers tend to be lighter than those using glass fibers, making them better suited for automotive applications. Similarly, epoxies have a higher strength-to-weight ratio than polyesters but are more prone to corrosion, introducing unique concerns.

Heat dissipation

While being lightweight is crucial for EV applications, thermoset composite parts must also dissipate heat well. Electric motors don’t get as hot as internal combustion engines, but they still generate heat — enough to warp some conventional plastics. Reducing on-motor heat would also make EVs more efficient.

Thermoset composites enable unique structures that can dissipate motor-related heat more efficiently than conventional means. German researchers at the Fraunhofer Institute for Chemical Technology ICT successfully dissipated over 80% of heat losses by using flat cooling wires and a polymer housing. The lightweight housing left more room for efficient movement, letting the cooling wires transfer heat energy without needing a liquid coolant.

The specific materials you use impact these factors, too. Silicone-based composites are generally preferable, as their high thermal stability enables efficient heat waste routing.

Structural strength

As helpful as plastics are for weight reduction and heat transfer, these factors sometimes come at a tradeoff for strength. That’s not acceptable when a failing component could cause a car to break, so you must also consider how your material impacts your part’s structural integrity.

The glass fibers that make up 90% of thermoset reinforcements have tensile strengths up to 500,000 psi, which is respectable but less than carbon fiber’s. Carbon fiber reinforcements also have a much higher strength-to-weight ratio, so this structural stability comes without making parts heavier. At the same time, carbon fiber is brittle in some directions, so it’s not ideal for all applications.

You can mix and match reinforcements depending on the specific EV component in question. Carbon fiber is great for high-intensity but minimal-impact applications, like housing motor components. Kevlar reinforcements are a more reliable option for parts toward the exterior, which may withstand more impact.

Form factor

Similarly, you should consider your thermoset composite parts’ form factors. The size and shape of your components can make up for some material weaknesses, or limit their benefits depending on how you design them.

Thick shielding may be a good way to insulate sensitive circuit components from heat and mechanical stress, but it also takes up more room. Space is limited in an EV and weight comes at a premium, so it’s best to avoid that wherever possible. Using lighter but more resilient composites for these applications can help you strike the right balance.

Space constraints can get difficult when considering how EV battery cells expand and contract. Part manufacturers like Marian Inc. have found ways around this by using neoprene and silicone-based thermosets to maintain compression while relaxing stress instead of using a more rigid material in an inflexible form factor.

Sustainability

Finally, EV composite components must also be sustainable. One of the biggest selling points for an electric car is it’s more eco-friendly than fossil fuel alternatives. However, extending that sustainability to all parts of the vehicle — especially notoriously harmful plastics — can be challenging.

Part of the solution is to design EV circuity and parts to last longer. The more your components can withstand repeated pressures by virtue of stronger, more heat-resistant thermoset housings, the less plastic ends up in a landfill.

Recent material advances offer another solution through eco-conscious alternatives to conventional thermosets. Petrochemical manufacturer SABIC has found a way to recycle plastics repeatedly without property losses by breaking them down to the molecular level. Other researchers have found distributing certain materials throughout a thermoset makes them easier to break down and recycle.

EVs require unique material considerations

As battery technology advances and climate awareness grows, EVs will present an increasingly promising opportunity for electronics engineers. However, you must consider these machine’s unique material considerations to take advantage of this market effectively.

The housings you use in EV components must be lightweight, strong, sustainable and have high heat dissipation, and deliver these results in a small form factor. Achieving that requires an understanding of different thermoset composites and their unique properties. Once you gain that knowledge, you can capitalize on this growing opportunity.

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