Shape makes case for curved, pultruded profile on Corvette

The 2020 Chevrolet Corvette Stingray that General Motors Co. unveiled in July has a curved, multihollow pultruded carbon fiber bumper beam. It's a first for the automotive industry, according to Shape Corp., the Grand Haven, Mich.-based Tier 1 supplier that engineered and manufactured the part.

"It's groundbreaking," said Toby Jacobson, plastic materials and process manager of Shape's research and development team, the Advancement Product Development Group. "For the first time ever, we've been able to make a curved carbon fiber pultruded profile."

Jacobson started the project in 2013. His role was to research different ways to make composite parts for automotive applications.

"That's really how the project started because Shape historically hadn't really done any thermoset composites. We've done some thermoplastic injection molding with fiber … but it's not thermoset composites with continuous fiber," he said in a phone interview.

Jacobson researched different ways to convert the potentially highly attractive properties of the raw materials into a cost-effective part, ultimately settling on pultrusion. In late 2013, Shape engineers started prototyping pultruded profiles with an undisclosed regional supplier.

Testing, manufacturing and material development initially began on a straight part. This garnered attention from GM and launched the collaboration on the Corvette. Shape targeted straight front beams, but quickly recognized that certain performance and package requirements were going to be challenging to meet within the constraints of the material and straight part applications.

"That's when we started targeting the rear, but the rear was curved," Jacobson said.

Shape prototyped the curved bumper beam and developed the process with Thomas GmbH & Co. Technik + Innovation KG, a German fiber composite pultrusion company that has a patented radius pultrusion process. This enables the production of curved profiles.

On the Corvette, the bumper beam uses a thermoset resin system including roughly 60 percent carbon fiber and 40 percent resin — a urethane acrylate, Jacobson said — by mass. Bumper beams are traditionally made from various grades and processes of steel or aluminum.

Despite the high cost of carbon fiber, Jacobson said Shape was able to find a mass, cost and performance solution that was acceptable for GM.

"It's been quite a long journey for the team to develop this bumper application," Roger Townsend, Shape's vice president of technology, said in a phone interview. "We put a lot of investments and energy into looking at where composites — and, particularly, carbon fiber technologies — might fit on the vehicle. And Shape has a heritage, a very strong heritage, in bumpers."

The automotive industry has pultruded straight parts for a long time, he explained. The missing link was making those parts curved.

Townsend said merging Shape's knowledge of bumper design and crash management systems paired with the unique radius pultrusion process allowed the company to better understand GM's needs and the context for the part application.

"Understanding that context and putting that together with Toby's R&D work really enabled us to show our customer that we have both the application understanding and the material and process development to make this a good fit," Townsend said.

The continuous processing and low tooling cost of the pultrusion process can also offset some of the traditional costs of competing carbon fiber technologies, he added.

The Corvette is a premium segment vehicle, so it's typical of the automotive industry for new technologies to launch on high-end applications before cascading to more broad-based ones, Townsend said, but material cost still remains a hurdle.

"I think from here we still have to do a lot more work on the underlying costs of carbon fiber and composites, and find different resins, different fillers, because for this to become mainstream, there is still quite a big cost gap to address," he said.