## 2 Materials and Methods  
### Finite Element Modeling of the Baseline Subframe  
The baseline subframe material is SAPH440 steel, with its fundamental material properties detailed in Table 1. The reference subframe for comparative design has a mass of 33.73 kg, and its finite element model is shown in Figure 1. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Material**} & **Density** & **Elastic Modulus** & **Poisson’s** & **Yield Strength** \\  & **(g/cm\({}^{3}\))** & **(MPa)** & **Ratio** & **(MPa)** \\ \hline SAPH440 & 7.85 & 210,000 & 0.3 & 306 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Material parameters. The areas indicated by the red arrows in Figure 1 are loading points, and there are four loading points. The white triangular area represents the fixed constraint points. Figure 2 shows the unit quality information. According to the information in the figure, all information standards comply with industry standards. The following are the definitions and reasonable value ranges of each standard:  
1. Max Size refers to the maximum side length or diameter of the cell, which is used to control the refinement degree of the grid. The selection of Max Size is based on the specific requirements of the model and does not exceed \(1/20\) of the feature size. 2. Aspect Ratio is the ratio of the length of the longest side to the length of the shortest side of a unit, which is used to measure the uniformity of the unit. Set value: The aspect ratio shall not exceed 5, and in the optimal case, it is close to 1. Set the value from 1 to 5 as the qualified standard. 3. Warpage is mainly used to evaluate the flatness of quadrilateral elements. Ideally, the quadrilateral elements should be completely located on one plane. Set value: In HyperMesh, a warpage of no more than 5% (i.e., 0.05) is considered a qualified standard. 4. Skew measures the degree to which an element deviates from its ideal shape. Quadrilateral: It is usually calculated based on the maximum deviation of the interior angles of the elements. Triangle: Calculated based on the ratio of the maximum interior angle to the minimum interior angle. The smaller the distortion value, the better the unit quality. Set the distortion value not to exceed 0.85. 5. The Jacobian is an important indicator for describing the degree of deformation of an element. It reflects the degree of deformation of an element from its ideal shape (such as a square or an equilateral triangle) to its actual shape. The ideal range of the Jacobian value is [0, 1]. The closer the value is to 1, the closer the unit shape is to the ideal state. Negative value: If the Jacobian value is negative, it indicates that the unit has been flipped, which is absolutely unacceptable and requires immediate correction. The setting value: A Jacobian value greater than 0.6 is considered a qualified standard. 6. Max Angle and Min Angle, respectively, refer to the maximum and minimum values among all the angles within the unit. Set the standard Max Angle Quad: The maximum angle should generally not exceed 135 degrees. Min Angle Quad: The minimum angle is generally not less than 45 degrees. Max Angle Tria: The maximum angle should generally not exceed 150 degrees. Min Angle Tria: The minimum angle should generally not be less than 15 degrees. 7. Taper is typically used to assess the shape quality of triangular elements, especially for non-equilateral triangles. The smaller the Taper value, the better the unit quality. Set a Taper value not exceeding 0.8 as the qualified standard. Figure 1: Finite element model of the subframe. The above is the quality information of the grid cells. According to these design standards, the divided grids were inspected. After modification, it can be seen from the figure that the quality of all these grids fully meets the standards and requirements for grid division.