Evaluation of Automotive Roof Strength and Pretensioner Performance on the Occupant Neck Load

Roof intrusion is a major cause of neck injury to belted occupants during rollover accidents. The correlation of reduced head room with increased injury risk has been demonstrated by the National Highway Traffic Safety Administration (NHTSA) and others such as the Insurance Institute of Highway Safety (IIHS). The current FMVSS 216 standard requires the vehicle roof, when loaded with a platen of prescribed geometry and application vector, to resist 1.5 times the vehicle empty weight before deforming 127mm. This standard was developed to ensure a modest level of safety of the vehicle in rollover. This paper demonstrates the relation between roof intrusions, available head room and belt pretension on occupant neck loads. A validated finite element model of a 2001 Ford Taurus is used to conduct an inverted drop simulation. The vehicle’s roof impacts an ideally rigid surface with 5 deg of roll and 10 deg of pitch. A 95^th percentile Hybrid III ATD (Anthropomorphic Test Device) is used to simulate a large occupant. The simulations are conducted both for a production roof and a modified stiffer, stronger roof. The production roof is modified by addition of extra material in the B-pillars and A-pillars to enhance strength. A seatbelt pretensioner is also modeled to demonstrate the effectiveness of belt pretension in attenuating neck loads. This study demonstrates the inadequate performance of the subject production roof in preventing neck injury. The stronger roof in association with the belt pretensioner reduces the magnitude of the neck loads sufficiently to prevent injury. This study indicates that strong, non-deforming roofs along with belt pretension diminishes neck injury.