To manufacture the cant rail structure, a layer of triaxial fabric is braided over a foam core in one shot. “Once we have braided the required amount of fabric over the foam, we load the preform into a tool and impregnate it with an epoxy matrix using a high-pressure resin transfer molding process,” says van der Putten. “In order to secure the position of the cant rail section, we embed the finished braided tube within the interior body side during the prepreg lay-up process, which in turn helps us integrate three parts into one. This is a very intricate process that requires extreme precision during manufacturing.”
The roof structure is thinner and stronger than a steel equivalent while still meeting safety and performance requirements, according to Polestar. It also allows for a lower roof line, creating a sleeker profile.
Polestar seems most excited about its unique floor reinforcement, which engineers call the “dragonfly.” It plays an instrumental role in creating the Polestar 1’s reactive dynamics by improving torsional stiffness at a critical point in the body structure, between the middle of the floor and rear construction, says van der Putten. He adds that the dragonfly couldn’t have been made with steel due to certain parameters of the platform.
“When you combine this strengthened framework with the CFRP body and roof structure, you get a stiff and communicative chassis which translates driver input into superb driving characteristics,” says Christian Samson, head of product creation at Polestar.
The design team was challenged to achieve the desired crash behavior, according to van der Putten. In contrast to a steel body, where bending helps the integrated crumple zones to reduce the crash energy that reaches the vehicle’s occupants, CFRP dissipates energy by cracking and shattering. During crash tests for the Polestar 1, the team paid close attention to the way the CFRP body reacted to extreme impact forces.
The Polestar 1 verification prototype was propelled into a stationary barrier at approximately 35 miles per hour, simulating a front collision. Most of the energy was absorbed by the car’s crash structure, with the remaining energy mitigated by the CFRP body panels into the body structure, which didn’t show signs of bending or misalignment after the crash. “The outcome of the first crash test validated the decision to build the body of Polestar 1 in carbon fiber,” says van der Putten. “It confirms that carbon fiber supports the highest safety standards.”