Development and Validation of Rear Head Surround Foam Performance Specification for Stock Car Racing

Over the last two decades many improvements have been made in stock car racing driver safety. The head surround of the NASCAR (National Association for Stock Car Auto Racing, LLC) seating environment serves as an effective restraint for head protection during lateral and rear impacts. However, previous rear head foam material specifications did not address low severity impacts that occur frequently during typical driving, such as race restart vehicle nose to tail contact. This study focused on developing a test methodology for comprehensive evaluation of rear head surround foam materials for repeated helmet-to-foam impacts of varying severity. Specifically, this study aimed to formulate a specification that maintains previous material performance at high speed, while decreasing head accelerations at low speed. Quasi-static and dynamic drop tower testing of sample materials was used to analyze the energy absorption capabilities of various foams and served to develop finite element material models to assess the effects of foam thickness on head kinematics. Component level testing was followed by anthropomorphic test device sled testing to analyze foam response in the NASCAR seating environment. In drop testing, the new materials achieved nearly a 33% reduction in peak acceleration for 5 mph impacts compared to the baseline foams while maintaining peak acceleration and rebound velocity performance at 13 mph. Sled testing confirmed equal performance to the baseline foams at high velocity, as well as a 5 to 15 G decrease in peak resultant head acceleration at low speed depending on foam materials being compared. Sled testing results aligned well with ATD response from numerical simulations using both the baseline and newly developed foam materials. Findings resulted in updates to the NASCAR rulebook including increasing the minimum thickness of the original rear head surround foam material and the use of the newly specified foam materials in the field.