# Novel Bionic Design Method for Skeleton Structures Based on Load Path Analysis
## 5 Conclusions  
A novel bionic design method for the skeleton structures is proposed by the bio-inspired idea of main-branch and sub-branch. The main-branch of the bionic structure is obtained by the load path analysis, which can get a clear load transfer skeleton. The loads on a given structure are equivalent to the main-branch of the bionic structure and the bionic prototype is selected from three aspects: load similarity, structural similarity and manufacturability. The efficiency of selecting a bionic prototype is improved by the local similarity of the main-branch instead of the whole similarity. Then, the sub-branch of the bionic structure is established based on the cross-sectional characteristics of a bionic prototype, and the size optimization provides detailed size value for each parameter that achieve secondary lightweight.  
Taking a control arm of automobile suspension system as a case, the results of bionic design show that the material distribution of the bionic model is more reasonable than the initial model, and structural stiffness is increased by 62.3%, while the weight is reduced by 24.75%. This method combines the load path theory with biological feature, which can realize the lightweight design of more complex structure compared with the traditional bionic method.  
In addition, the selection of bionic prototype mainly focuses on load similarity and then the structural similarity, which can expand the selection range of biological prototype. The manufacturability is considered firstly in bionic design. Although the selected bionic prototype is still subject to certain constraints in this study, in the future, the selection range of bionic prototype will be further expanded under the development of additive manufacturing. For example, the cross-section characteristics of bamboo, wheat straw and bone will also be used for the main-branch of the control  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Max Displacement (mm)** & **Max Stress (MPa)** & **Mass (kg)** \\ \hline Initial model & 0.061 & 17.42 & 1.01 \\ Bionic model & 0.023 & 18.69 & 0.76 \\ Variation & \(-\)62.3\% & \(+\)7.3\% & \(-\)24.75\% \\ \hline \hline \end{tabular}
\end{table}
Table 4: Mechanical performances of the new control arm.  
Figure 21: Real vehicle test of the new control arm.  
arm. Therefore, this method can also be used for the skeleton structures of other fields including automobile, aerospace and civil engineering.  
**Author Contributions:** Bionic design method, Z.W. and F.W.; the theory of load path analysis, Z.W., N.W. and Q.W.; bionic design of the control arm, Z.W., Y.L. and Q.Y.; numerical simulation, Z.W. and Q.Y.; validation, Z.W. and F.W.; writing, review and editing, Z.W., Q.W. and N.W. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was supported by the Chinese National Key Research and Development Program (2016 YFC0802900), the Key Natural Science Projects of Hebei Provincial Department of Education (ZD2020156), the Science and Technology Research Project of Colleges and Universities in Hebei Province (Grant NO. QN2018228).  
**Conflicts of Interest:** The authors declare no conflict of interest.