Light-weight design of vehicle roof panel for stiffness and crash analyses

Vehicle crashworthiness refers to proper designing of the vehicle structure to reduce the risk of death and injury during the vehicle accidents. In the recent years, due to the enforcement of new EU normative, the interest of all the car manufacturers in producing lightweight vehicles is progressively increased as the combustion engine optimization has already used most of the improvements they had and the residual ones are becoming more and more difficult and costly. Based on this auto industry’s interest, lightweight materials such as composite have absorbed lots of attention due to their superior characteristic of high stiffness to weight ratio. In this thesis, efforts have been made to present a broad research on the light-weight design of vehicle roof panel for stiffness and crash analyses. The first part of the analyses belongs to the vehicle chassis static and dynamic stiffness analyses via the finite element code with the specific focus on substituting the steel roof panel with the lightweight materials of aluminum and composites. The structural response of the vehicle roof panel, made of different solutions, in full frontal crash with respect to NHTSA standard has been investigated at the second step. The effects of increasing the vehicle roof panel thickness at the both steps have been tested and compared for different solutions. At the third step an innovative design solution for the vehicle roof structure has been developed and tested in rollover crash analysis. In order to perform this task, After determining the performance of tubes made of steel, composite and composite foam-filled solutions under the three points bending test and proving the efficiency of composite-foam design; the same idea is implemented on the vehicle roof panel during the roof quasi-static crush test. Besides the composite solutions, the sandwich design consists of composite face-sheets and foam core are tested in the roof crushing test based on the FMVSS 216 standard. After assessment of the sandwich roof panel in crushing test, the geometrical optimization of the foam core is implemented to determine the optimum design with respect to vehicle strength-to-weight ratio and mass reduction percentages. Besides different foam core configurations that have been tested, the final optimization have been implemented using the foam core with various densities and also the optimum face-sheets thickness has been determined. At the last chapter, challenges of vehicle composite roof panel assembly have been discussed. Results in the case of stiffness and frontal crash analyses at step one and step two proved that although the composite solutions have lower energy absorption capacity in comparison with the steel one, they have large contribution to the weight reduction of the vehicle roof panel and still stays in the acceptable range of structural performance. Using the new design of sandwich solutions in roof crushing test have proved that while theses designs have reduced the vehicle roof panel weight by 68%, they have the same structural performance as the steel solution and could be considered as interesting solutions. Evaluating the behavior of the vehicle roof structure made of different solutions with various configurations under distinct analyses of stiffness and crashworthiness will help to improve the vehicle roof structure performance.