Design Optimization Of A Novel Bio-inspired Hierarchical Porous Structure For Crashworthiness

Triply Periodic Minimal Surface（TPMS）is a surface whose mean curvature of zero at every point on the surface and periodicity in three independent directions.TPMS sheet structure is obtained through the replication and expansion of triply periodic minimal surface,which has been widely used in automobile,ship,aerospace and other industrial fields due to its lightweight and excellent energy absorption characteristics.Therefore,the mechanical properties of TPMS sheet structure have been studied by many researchers in the field of lightweight structure design.Over a long period time of biological evolution,there are a large number of hierarchical organisms in nature,and related studies have shown that hierarchical design can improve the mechanical properties of structures.However,the research on hierarchical design are mainly focuses on the traditional honeycomb structure and few investigates have been done on the TPMS sheet structures.Therefore,a novel hierarchical porous structure is created based on the triply periodic minimal surface in this study and the following research works have been carried out:（1）Construction of hierarchical porous structure.Based on the complexity of triply periodic minimal surface,it is difficult to obtained its 3D model by the general drawing software.Thus,the basis TPMS unit-cell of hierarchical porous structure is first obtained through the mathematical software K3DSURF and reverse design software BLENDER.Then,a new hierarchical porous structure is created by applying the idea of hierarchical design to TPMS.（2）Verify the accuracy of finite element model of hierarchical porous structure.In order to ensure the accuracy of the finite element analysis result,the TPMS sheet structures with material of CX stainless steel are manufactured through 3D printing technology in this study.Then,the quasi static axial compression experiment for TPMS sheet structures are executed through the universal material testing machine.Last,the experiment results are compared with the finite element analysis results to verify the accuracy of the finite element model of hierarchical porous structure.（3）Study on crashworthiness of hierarchical porous structure.In this study,the nonlinear finite element method is used to investigate the effect of cell number m,rib number n,rib wall thickness t₁,surface wall thickness t₂,distance D between internal and external walls,different impact velocity and impact angles on crashworthiness of hierarchical porous structure and the deformation mode is analyzed.According to the results of the influence of various variables on hierarchical porous structure,two parameters with great influence are chosen as the optimization design variables.Based on the above results,a multi-objective optimization method employing the Kriging surrogate modeling and Non-Dominated Sorting Genetic Algorithm II（NSGA-II）is used to obtain the optimal hierarchical porous structure.In addition,the crashworthiness of hierarchical porous structure is compared with that of TPMS sheet structure under the same mass.The results show that the hierarchical porous structure has better energy absorption characteristics than the TPMS sheet structure.Thus,it can be concluded that hierarchical porous structure is able to be applied in the field of impact engineering as an energy absorption structure.