Bionic design and multi-objective optimization for variable wall thickness tube inspired bamboo structures

This study introduces an energy absorbing structure called a variable thickness structure (VTS) inspired by the gradient of thickness and the inter-nodal distance along the growth direction of bamboo. A series of VTSs under axial impact load were investigated to study the influence of the bionic factors on the energy absorption through a simulation analysis. It was determined that the wall thickness ratio and inter-nodal length ratio of a VTS have a significant effect on the crashworthiness of the structure. In order to obtain an optimal VTS, these factors were optimized through a multi-objective optimization method and polynomial regression (PR) meta-model. We found that the crashworthiness of some VTSs are better than that of a circular tube. In addition, a VTS with an inter-nodal length ratio of 1/2/1 and wall thickness of 3/2.47/1.78 mm was shown to be the optimal structure. A comparison between the optimal VTS and circular tube showed that the specific energy absorption of the VTS increased by 6.2%, whereas the peak crushing force showed a 28.23% decrease. Moreover, the crushing force efficiency increased by 7.48%, the mass decreased by 19.3%, and the VTS deformed more stably in terms of the overall crashing behaviours or collapse modes.