Different roof strength methods are applied on the 2003 Ford Explorer finite element (FE) model to achieve the current Federal Motor Vehicle Safety Standard (FMVSS) 216 requirements. Two different modification approaches are utilized. Additionally, the best design of each approach is tested dynamically, in rollover and side impact simulations.
In the first approach, several roll cage designs are integrated in all pillars, roof cross-members, and in the side roof rails. A roll cage design with a strength-to-weight ratio (SWR) of 3.58 and 3.40 for driver and passenger sides, respectively, with a weight penalty of 18.54 kg is selected for dynamic test assessments.
The second approach investigates different localized reinforcements to achieve a more reasonable weight penalty. A localized reinforcement of the B-pillar alone with a tube meets the new FMVSS 216 requirements with a weight penalty of 4.52 kg and is selected for dynamic analyses.
The two selected reinforcement designs are tested in a dynamic unconstrained rollover crash under different pitch angles while using common rollover initial conditions. Based on the limited dynamic analysis, the localized reinforcement has proved to be an effective approach for front row seat protection. However, passengers in the rear seats are better protected by the roll cage solution.
Additionally, side impact analysis is examined for both approaches. Overall, the influence of both reinforcement methods on the side impact is small and therefore deemed acceptable.
These methods can be incorporated in vehicle's roof structure or taken into consideration for future vehicle designs.