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

<div class="section abstract"><div class="htmlview paragraph">Over the last two decades many improvements have been made in stock car racing driver safety. One of these is the head surround, which is rigidly secured to and an integral part of the NASCAR (National Association for Stock Car Auto Racing, LLC) seating environment and serves as an effective restraint for head protection during lateral and rear impacts. However, previous head impact material specifications were optimized for moderate to severe impacts and 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 materials for low, moderate and severe impacts. Specifically, this study aimed to formulate a specification that maintains previous material performance during high speed impacts, while decreasing head accelerations at low speed impacts. Quasi-static and dynamic drop tower testing of sample materials were used to analyze the energy absorption capabilities of various materials. Finite element material models were developed to assess the effects of foam thickness on head kinematics. Anthropomorphic test device (ATD) empirical sled testing was used to analyze material responses in the full NASCAR seating environment. In drop tower testing, the new materials achieved nearly a 33% reduction in peak acceleration for 2.2 m/s (5 mph) impacts compared to the baseline materials while maintaining original peak acceleration and rebound velocity performance at 5.8 m/s (13 mph). Empirical sled testing confirmed equal performance to the baseline materials at high velocity, as well as a 5 to 15 G decrease in peak resultant head acceleration at low speed depending on comparison samples. Study 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 alternate foam materials in the field. The alternate foams drop test requirements include 24 total drop tests on 12 test samples per material evaluation, at two speeds (2.2 and 5.8 m/s) and two temperatures (21° and 50° C). The repeated impacts are conducted at the same test speed, for each temperature, on the same sample. Material performance evaluations include peak acceleration, maximum rebound velocity, and flame retardancy.</div></div>