Development of vehicle body-in-white section optimization framework for crash performance by introducing a combined collapse capacity criterion

Enhancing the stiffness and crash characteristics of the vehicle body structure is among the most important concerns of auto manufacturers. Typically, enhancing these attributes leads to an increase in the vehicle’s mass, and as a result, a suitable optimization scheme is needed. In crash scenarios, collapsing of a section causes the load path to lose its load-carrying capability and degrades the crash safety of the vehicle. As a result, the sections should be designed accordingly, so that their collapse capacities be as high as possible. Although there are some research works that deal with the analysis and optimization of thin-walled members for stiffness or crash objectives, utilization of optimization methods for the design of vehicle sections against collapsing is still absent in the literature. In this regard, the present paper proposes an optimization framework that takes into account the collapse capacity and stiffness of the sections and optimizes their weight. Analytic formulations are derived to calculate the collapse capacity of sections under pure axial force and bending moment. The formulations are verified via finite element (FE) simulations. It is shown that the average absolute difference between the formulation results and explicit FE solver is less than 12%. Considering the highly nonlinear nature of the problem, this is a reasonably accurate approximation. Moreover, a combined collapse capacity criterion (CCCC), as a handy design guide for engineers, is also proposed for the first time to take into account the combination of axial and bending load cases. It is based on the FE analyses of numerous automotive sections in different load cases. To facilitate the optimization process, a new software interface named “JSec Design” is developed and introduced that is much faster than existing FE-based optimizers. Finally, as a case study, an automotive A-pillar section is designed under a combination of axial force and bending moment.