## 3 Multi-Objective Optimization of the Body-in-White Structure  
### Optimization Parameters Selection and Design Objectives  
The side pole impact simulation reveals severe structural vulnerabilities: significant B-pillar deformation, extensive body frame and foundational beam collapse, and weak  
Figure 8: The original design scheme B-pillar and the main observation points near the threshold beam changes in the amount of intrusion.  
Figure 7: B-pillar observation point position.  
Figure 9: Deformation of battery pack in side pole impact simulation of original vehicle.  
lateral body resistance to deformation. The root causes stem from low steel strength in critical load transfer components and insufficient reinforcement structures along energy transmission paths.  
Through detailed analysis of load transfer paths, seven key components were identified as closely related to collision deformation. Therefore, this study proposes to optimize the vehicle body structure by selecting high-strength steel and increasing the thickness of specific components.  
This study optimizes seven key components shown in Figure 10 based on the original design to improve crashworthiness while minimizing overall vehicle mass. The optimization targets include B-pillar abdominal intrusion (\(L_{1}\)), lower sill intrusion (\(L_{2}\)), total absorbed energy (\(E\)) of the optimized components; and total mass (\(M\)) of the optimized components. The design variables are the thicknesses of the seven components, with the value ranges provided in Table 2. Its range is determined by material properties, manufacturing process capabilities and existing material specifications.  
The optimal Latin hypercube experimental method was used for data sampling within the design variable range, resulting in 75 sample points. These sample points were imported into LS-DYNA 2022 software for calculation and the experimental samples and simulation results are recorded in Table 3 (detailed data are shown in Appendix A, Table A1).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Design** & **Corresponding** & **Lower** & **Initial** & **Upper** \\
**Variables** & **Components** & **Limit/mm** & **Value/mm** & **Limit/mm** \\ \hline \(t_{1}\) & B-pillar outer panel & 0.5 & 0.65 & 2.0 \\ \(t_{2}\) & B-pillar reinforcement plate & 1.0 & 1.2 & 2.0 \\ \(t_{3}\) & B-pillar inner plate & 0.8 & 1.0 & 2.0 \\ \(t_{4}\) & Lower sill inner plate & 0.8 & 1.0 & 1.5 \\ \(t_{5}\) & Sill reinforcement beam & 1.0 & 1.5 & 2.5 \\ \(t_{6}\) & Sill outer plate & 0.5 & 0.65 & 1.2 \\ \(t_{7}\) & Upper beam inner plate & 0.6 & 0.7 & 1.5 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Range of design variables.  
Figure 10: Optimize the design of components. 1—B-pillar outer panel; 2—B-pillar reinforcement plate; 3—B-pillar inner plate; 4—threshold reinforcement beam; 5—lower threshold inner plate; 6—sill outer plate; 7—upper beam inner plate.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Title 1** & **\(t_{1}\)/mm** & **\(t_{2}\)/mm** & **\(t_{3}\)/mm** & **\(t_{4}\)/mm** & **\(t_{5}\)/mm** & **\(t_{6}\)/mm** & **\(t_{7}\)/mm** & **\(M\)/kg** & **\(L_{1}\)/mm** & **\(L_{2}\)/mm** & **\(E\)/J** \\ \hline
1 & 1.80 & 1.89 & 1.32 & 1.07 & 1.16 & 1.01 & 1.37 & 39.47 & 304.09 & 262.45 & 11,766.6 \\
2 & 1.96 & 1.80 & 1.40 & 1.24 & 1.41 & 0.57 & 1.03 & 38.00 & 305.56 & 256.29 & 12,202.0 \\
3 & 1.21 & 1.46 & 1.95 & 1.19 & 1.55 & 1.16 & 1.44 & 38.29 & 314.94 & 269.53 & 12,060.6 \\
4 & 1.03 & 1.08 & 1.01 & 0.80 & 1.47 & 0.86 & 0.93 & 32.02 & 329.68 & 285.61 & 10,852.2 \\ \(\cdots\) & \(\cdots\) & \(\cdots\) & \(\cdots\) & \(\cdots\) & \(\cdots\) & \(\cdots\) & \(\cdots\) & \(\cdots\) & \(\cdots\) & \(\cdots\) \\
75 & 0.87 & 1.72 & 1.82 & 0.98 & 2.10 & 1.15 & 0.81 & 36.67 & 316.42 & 265.37 & 10,847.9 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Test samples and simulation results.