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Rollover accidents account for a large number of serious to fatal injuries annually. In the past, these injuries were often the result of unrestrained occupant ejection. Subsequent to mandatory belt use laws, a larger percentage of these injuries occur inside the vehicle, and the head and neck areas sustain a substantial number of these injuries. Rollovers have been characterized as violent events, roof crush as the natural consequence of such violence. Further, head and neck injury have been thus considered unavoidable, even with occupant use of the production restraints. This paper will describe the relationship between the three dimensional extent (severity) of roof crush and the equivalent drop test contact velocity as derived from physical experiments and tests. The drop test contact velocity is directly related to the cumulative change of velocity experienced by a vehicle as a result of roof contact deformation during a rollover accident by validated computer simulations.

Inverted drop testing of vehicles is a methodology that has long been used by the automotive industry and researchers to test roof integrity. In our laboratory, the inverted drop test methodology was employed on late model production vehicles to simulate the damage incurred by a real world rollover accident. The extent and shape of residual damage matched well with the corresponding accident damage. Modified vehicles were reinforced based upon previously documented techniques. Incorporation of these techniques demonstrated a significant increase in roof strength and corresponding reduction in roof crush with minor weight addition. Finally, a production vehicle and structurally enhanced vehicle were drop tested with instrumented Hybrid-III occupants. This pair of tests confirms that reduction of roof intrusion and increased headroom can significantly enhance occupant protection. It also highlights the need to maintain adequate survival space for the vehicle’s occupants.

The government, automotive industry and scientific community are currently scrutinizing the adequacy of the FMVSS #216 roof crush standard in the United States. As a result of concern about the ability of FMVSS #216 to enforce reasonable protection to occupants in rollovers, The National Highway Traffic Safety Administration (NHTSA) has recently published a Request For Comments in the Federal Register regarding updating this standard1. The inverted drop test methodology is a promising alternative test procedure to evaluate the structural integrity of roofs and is being considered by NHTSA as a possible compliance test. Recent testing on many different vehicle types indicates that damage consistent with field rollover accidents can be achieved through inverted drop testing at very small drop heights. Drop tests matrices were performed on 9 pairs of vehicles representing the majority of personal transportation vehicle types.

Experimental results from three point bending and axial compression tests of common automotive roof elements are presented. Modifications of these components were also tested to evaluate the effect of structural reinforcements and void filling. Under three-point bending, an open hat section side header (or side rail) was tested and failed in a manner consistent with observed failures in real world accidents. Modifying the hat section to create a closed section increased load capacity and energy absorption, and demonstrated some gains in strength to weight performance. Two epoxy compounds in a similar closed section configuration resulted in substantial increases in peak load, energy absorption and strength-to-weight ratio. In the axial compression tests, a open “c” section front header were tested in axial compression and failed just past a sheet metal reinforcement consistent with observed failures in real world accidents.