Using CAE to evaluate a structural foam design for increasing roof strengh

In recent years, there has been increased discussion of the strength of vehicle roofs in rollover crashes. NHTSA recently revised the federal roof strength requirement and the IIHS has published an even more stringent roof strength goal. While working to increase roof strength, automakers are also working to reduce vehicle mass for improved fuel economy and other benefits. Developing technology to achieve both of these goals is challenging. This paper investigates the use of CAE to evaluate the addition of structural foam to an existing design to maintain or increase roof strength. A concept solution that combines nylon and structural foam material was developed and analyzed using an explicit finite element model and later tested on a body-in-white to evaluate the CAE predictions. The main evaluation method was the FMVSS 216 test procedure. Through CAE analysis and actual testing, the modifications were found to have increased roof strength. A performance target was set and a conceptual steel-only assembly was created in CAE to meet this target. The foam/steel assembly met the performance target but at a reduced weight compared to the steel-only assembly. These analyses demonstrated that CAE is useful for predicting the performance of foam/steel assemblies and that foam/steel assemblies can yield greater strength with lower mass than a steel-only assembly. Questions regarding field performance and the feasibility of mass-production must still be addressed.