# Novel Bionic Design Method for Skeleton Structures Based on Load Path Analysis
## 4 Results and Discussion  
The FEM of both the initial model and the bionic model are established in commercial FEA software ANSYS 18.0. The material properties shown in Table 1 are assigned, and the loads and constraints shown in Figure 8 are applied to two model.  
Because the bionic model is more complex than the initial model, the meshing convergence is verified firstly by calculating the maximum displacement and stress with different element sizes. The variation trends under 1\(\sim\)4.5 mm element size are shown in Figure 17. From Figure 17a, the maximum displacements of the two models are constant under different element size, the value of initial model is 0.0611 mm, while the value of bionic model is 0.0230 mm. However, the maximum stress varies with the element size. The smaller the element size, the greater the local stress value in Figure 17b. The main reason is that too small element size is easy to cause stress concentration. However, the larger the element size, the lower the calculation accuracy. So, the convergence solutions of the two models can be obtained when the element size is 3 mm, as shown in Figure 18.  
Figure 16: The samples of the control arm: (**a**) initial model (1.01 kg); (**b**) bionic model (0.76 kg).  
Figure 17: Verification of meshing convergence: (**a**) maximum displacement; (**b**) maximum stress.  
Then, the FEA is carried out. The displacement and stress distribution are shown in Figures 19 and 20, and the comparisons of mechanical performance are shown in Table 4. It can be seen that the maximum displacement (0.023 mm) of bionic model is significantly reduced compared with that of the initial model (0.061 mm). The maximum stress (18.69 MPa) is far less than the material yield strength (220 MPa). Although the maximum stress of the bionic model is slightly larger than that of the original model, but the value is only one tenth of the yield strength of the material, that is, the safety factor of the bionic model is 11.77, which shows that the structure is absolutely safe. In addition, it is difficult to ensure the same stress when the structure is lighter. Under the design criteria, it is more reasonable to deteriorate the whole stress and greatly improve the structural stiffness and weight. Besides, it can be seen that the stress distribution of the bionic model is more uniform from Figures 19b and 20b.  
Figure 19: The finite element analysis (FEA) results of the initial model: (**a**) displacement distribution; (**b**) stress distribution.  
Figure 20: The FEA results of the bionic model: (**a**) displacement distribution; (**b**) stress distribution.  
As the strength of the control arm is far less than the material yield strength, it is not considered the main factor, while the stiffness directly affects the stability and sensitivity of the vehicle during driving. Therefore, the high stiffness design of the control arm is the focus in this case, and more materials should be distributed in the area of large load and deformation, rather than the area of stress concentration. So, we can conclude that the material distribution of the bionic model is more reasonable than the initial model. The stiffness is increased by 62.3% while the weight is reduced by 24.75%.  
In this study, the new control arm is tested on a real vehicle to further verify the mechanical performances. The sample is installed in a new formula car for vehicle testing, including two extreme conditions: wheel side impact on the obstacle, vehicle side slip and brake, as illustrated in Figure 21. The test results show that the control arm can meet the requirements of stiffness, strength and sensitivity in a normal driving process.