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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.

Contemporary production emergency locking seatbelt retractors (ELRs) have been proven very effective in the crash environment for which they have been primarily designed and most adequately tested, that is, in the full frontal crash mode. However, researchers have documented spool out during offset, angled, override, underride, and rollover crashes where seatbelt retractors are subject to acceleration pulses in varying directions, including the vertical plane. Occupant motions during these real world accident modes may also impart loads into the belts and belt hardware (webbing and buckle assemblies) that may not be immediately apparent in the frontal barrier test mode. Numerous laboratory studies have demonstrated that the inertial sensor can be held in the neutral position when an overriding opposing force is applied to the retractor, resulting in webbing spool out. Various ELR designs include ball and cage sensors, pendulum, and disk systems.

In this study we continue and build upon previous research conducted with various production three-point restraint systems; studying resulting vertical excursion on restrained inverted occupants. Vertical excursions will be reported for various sized occupants restrained by both production vehicle belt systems as well as systems incorporating alternative designs. Vertical excursions have been reduced by an average of 77% with optimized belt geometry combined with belt pretensioning.

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.