Application of Simplified Load Path Models for BIW Development

Simplified load path models (SLMs) of the body in white (BIW) are an important tool in the body structure design process providing a highly flexible, idealized concept model to explore the design space through load path evaluation, material selection, and section optimization with rapid turnaround. In partnership with Altair Engineering, the C123 process was used to create and optimize SLMs for BIW models at FCA US LLC. These models help structures engineers to develop efficient load paths, sections, and joints for improved NVH as ultra-high-strength steels enable thinner gauges throughout the body structure. A few key differences in the SLM modeling method are contrasted to previous simplified BIW modeling methods. One such example is the parameterization of cross sections through response surface models rather than using contemporary finite element descriptions of arbitrary cross sections. Another difference is the modeling of structural joints as 1-D spring elements rather than high-fidelity shell models or superelements. To validate the new process, two BIW-level correlation studies are presented. The first study presents the correlation of an entire BIW SLM when compared to a high-fidelity shell model, and the second study uses a hybrid model approach, wherein the upperbody is comprised of an SLM and the underbody is a high-fidelity shell model. Both models’ normal mode and deflection global stiffness attributes correlated well to their high-fidelity, shell model counterparts. A case study of extending the rear header is explored on an SLM as an example of a typical use case for an SLM in a concept development environment. An optimization study is also performed on this model to understand and illustrate the benefits and effort required to provide optimized weight and performance data early in the vehicle’s development process.