Hierarchical Gradient Structure Design And Energy Absorption Mechanism

Improving the crashworthiness of the body structure promotes occupant safety and the maintenance economy of the body structure.Thin-walled metal energy-absorbing structures have been widely used in body structures because of their advantages of light weight and low price.Therefore,thin-walled energy-absorbing structures are of great significance in the crashworthiness design of car bodies.Focusing on the innovative design of thin-walled energy-absorbing structures,this paper proposes and studies a variety of new thin-walled energy-absorbing structures by comprehensively using various research methods such as theoretical analysis,experimental technology,numerical simulation and multi-objective optimization,and carries out systematic crashworthiness research.The main contents of the study are as follows:（1）Study on crashworthiness and optimization of rhombic hierarchical gradient multicellular hexagonal tube（RHGMHT）under axial impact.A series of new RHGMHTs are designed based on hierarchical gradients.The reliability of the finite element simulation is verified by experiments.Secondly,the influence of gradient distribution and non-gradient distribution of cross-section configuration and the crashworthiness of other structures are compared.Subsequently,a parametric study was carried out on RHGMHT,and the effects of wall thickness,hierarchy and different rib wall thickness were analyzed.Parametric studies show that the highest specific energy absorption（SEA）of 2^ndorder RHGMHT is 57.89%higher than that of 0^th order hexagonal tubes.The mean crushing force（MCF）of RHGMHT under different parameters was predicted by the theory of simplified super folding element（SSFE）.Finally,optimization is sought by the second-generation non-dominated sorting genetic algorithm（NSGA-II）.（2）Study on double-gradient hierarchical hexagonal tubes（DGHHT）crashworthiness under multiple loads.A new type of DGHHT was obtained through a double-gradient hierarchical design.Firstly,it is compared with Single-gradient hierarchical hexagonal tubes（SGHHT）to verify its crashworthiness under multiple loads.Subsequently,parametric studies were carried out to analyze the effects of wall thickness,hierarchy and impact angle on its crashworthiness.Finally,in contrast to conventional structures,its ability to resist global bending at higher impact angles is highlighted.（3）Study on bio-inspired hierarchical gradient multi-cell tubes（BHGMT）crashworthiness under axial impact.A series of BHGMTs were designed through the distribution characteristics of plant microstructure.Firstly,the reliability of the finite element simulation is verified by experiments.Subsequently,parametric studies of BHGMT were carried out.Parametric studies have shown that the SEA of the 4^th order BHGMT is 2.43 times higher than that of the square tube.Finally,the MCF of BHGMT under different parameters is predicted by SSFE theory.（4）Study on energy absorption performance of novel hierarchical gradient re-entrant honeycomb under in-plane impact.A new type of novel re-entrant honeycomb（NREH）is proposed.Firstly,comparing the three NRHEs and finding thatσ_m and SEA are not much different during in-plane impact,while the Poisson’s ratio of NREH-3 is smaller.Subsequently,parametric analysis of NREH-3 are carried out.Analyzing the change in NREH-3 angleθfound thatθis between 60°and 90°,and SEA increased with increasing angle.Between 90°and 120°,it decreases with increasing angle.Among them,NREH-3-80 has a41.46%improvement over NREH-3-60’s SEA,while the Poisson’s ratio is almost unchanged.