The goal of this study was to determine the detailed design of a greenhouse structure (roof and pillars), such that when it is loaded in a static roof crush test the force-displacement response mimics that of a modern full-size crossover vehicle. This study was carried out using finite element analysis with the goal of identifying a specific design to be fabricated for use with a rollover test buck in dynamic rollover crash testing. A multi-tiered design approach was used consisting first of a simple beam element model, followed by a more complex model meshed with shell and solid elements. A truss-like structure consisting of steel tubing for the pillars, headers and roof rails, connected by steel bars (“plastic joints”) at the intersections was used for the initial design. Individual structure parameters (tubing cross-sections, wall thicknesses, material types, etc.) that did not affect the overall geometry were optimized in repeated simulations of a static roof crush test to ensure that the response of the buck roof matched the response defined by a strength-to-weight ratio of 4.0 for a 2268 kg vehicle. Additionally, different design solutions were examined, e.g. curving the B-pillar, adding a windshield or roof cross beams. The influence of the friction coefficient between the loading platen and the roof was also investigated. Model predictions were validated on component-level by comparing model behavior to three-point bending tests on the plastic joints. The resulting design, including curved B-pillars with additional stiffness elements, was then subjected to a dynamic rollover computer simulation to facilitate qualitative evaluation of the dynamic response in a rollover crash.

Further modification of the design may be necessary to improve the response beyond the peak quasi-static test force, but full scale fabrication and testing will be performed first to examine actual response at these levels before implementing additional changes.