Driving Safety in Motorsports

Team Penske, an American professional auto racing organization, is competing in its 60^th season this year. The company fields cars for drivers in the NASCAR Cup Series, NTT INDYCAR Series and IMSA SportsCar Championship from its Mooresville, N.C., facility.

“We have a long history of racing in the United States,” says Andrew Miller, engineering manager for the team’s INDYCAR programs. “That includes more than 650 wins and nearly 50 total championships. Composite materials are a key component to the success – and safety – of the cars.”

NASCAR debuted its Next Gen vehicle for the Cup Series in 2022. Its specifications are built upon earlier cockpit enhancements that include transitioning from aluminum to composite seats.

“The next-generation car brought the opportunity for us to really make improvements in the design and functionality of the cockpit,” says Miller, who served as an advanced materials engineer for Team Penske during the redesign. “Our drivers need to not only be safe when they are pushing the car to the limit, but we want them to be as comfortable as possible so they can just focus on going fast.”

The primary component that Team Penske revamped was the knee knocker, a padded safety device that prevents the driver’s knees from hitting each other or the steering shaft during a crash or high g-force maneuvers. Previously, the knee knocker was made from two carbon fiber and aramid reinforced hybrid plates sandwiched between impact-absorbing foam and mounted to the steering column brackets. However, the knee knocker experienced partial fracture and delamination during large impacts, increasing the likelihood of injury.

To increase the strength and energy absorption of the knee knocker, Team Penske redesigned it as a continuous monolithic structure. The new component features a composite shell made from two plies of plain weave 60 GSM Kevlar^® fabric with a cast BSCI Energy Impact System (EIS) W50 foam interior with four fully integrated slots for mounting along the tubular steel dash bar. Extra plies of CFRP prepreg were added to the knee knocker near the steering column and where it mounts to the chassis to provide additional strength and stiffness.

Manufacturing the tooling for the monolithic part was challenging. Internal bladder tooling wasn’t feasible due to the complex geometry and slot integration, so Team Penske opted for 3D-printed tooling. They used Stratasys fused deposition modeling (FDM) technology to create an ST-130 soluble mold. Team Penske also manufactured stereolithography (SLA) molds for two-piece silicone intensifiers.

“Using the SLA molds, we cast silicone intensifiers that go on the knee knocker after lamination is completed,” says Miller. “That gives us a smooth finish on the driver interfacing component.”

Casting the two-part expanding polyurethane foam into the knee knocker was also challenging. “It took a while to figure out how much foam to pour in each time and get the expansion rate right,” says Miller. “We didn’t want to scrap any of these parts, so we spent a lot of time validating our foam casting process.”

In addition to redesigning the knee knocker, Team Penske made several other changes, including integrating the monolithic prepreg composite shin guard into the steering column hangers and eliminating some openings in the cockpit.

“We had restraints to keep the driver’s legs within the cockpit during an accident, but there were some openings in the leg restraints close to the front firewall,” says Miller. “We closed those to make it safer.”

Team Penske performed in-house testing to evaluate the previous and new cockpit designs. The results revealed that the redesign was three times stronger and three times more energy absorbent than its predecessor.

The company also conducted simulation testing with NASCAR, using the results to quantify the impact load. “The amount the old knee knocker moved during impact was significant, and the new one had much less movement and maintained its structural integrity even after impact,” says Miller.

While the next-generation cockpit is safer, Team Penske is always looking to the future. NASCAR has a finite element model of the driver that could allow the company to learn more about the failure mode of its designs and make improvements.

“NASCAR is interested in continually evolving safety, and so are we,” says Miller.

 Susan Keen Flynn is managing editor of Composites Manufacturing magazine. Email comments to sflynn@keenconcepts.net.