Geometrical effects in the crush behaviour of lotus stem-inspired composite tubes

This study presents an investigation into the energy absorbing characteristics and failure mechanisms in composite nR multicellular tubes inspired by the macro- and micro-structure of a lotus stem. A 1/n three-dimensional progressive damage model is developed using a user-defined VUMAT subroutine within the Abaqus/Explicit platform, with material parameters being obtained through mechanical property tests. Numerical simulations demonstrate that the 1/n finite element model provides significant computational efficiency improvements over full-scale models, while maintaining a high degree of accuracy. Furthermore, the three-dimensional progressive meshing strategy outperforms conventional global meshing in balancing computational precision and efficiency. A damage degree parameter is introduced to quantitatively assess material degradation. The results reveal a strong correlation between the damage severity and the load-bearing curve, with the degree of fibre damage exhibiting a significant influence on the energy absorbing characteristics. Subsequently, the effects of geometric parameters on the energy absorption characteristics of composite multicellular tubes are analysed, including rib number (n) and inner diameter (d). Parametric studies highlight a coupled interaction of both parameters on energy absorption. The findings highlight excellent energy absorption characteristics, in cases when the inner diameter and the number of ribs are small, and when they are large.