Post-impact damage tolerance and residual crashworthiness of lotus-stem-inspired composite multi-cell tubes

Low-velocity impact can compromise the residual crashworthiness of lightweight composite energy absorbers used in aerospace structures. This study aims to quantify how a transverse impact affects the residual energy absorption, damage mechanisms, and location sensitivity of circular and lotus stem-inspired multi-cell composite tubes. Experimental results were used to validate finite element analyses, in which intralaminar damage, interlaminar delamination, and permanent deformation were transferred from the impact model to the axial-crushing model through damage mapping. The models reproduced the experimental peak impact load and the maximum displacement with errors no greater than 5.2%. The results show that the intact and impacted multi-cell tubes absorb 110% and 172% more energy, respectively, than their circular counterparts. The prior impact reduces the residual energy-absorption capacity by approximately 61% for the circular tube but only 23% for the multi-cell tube. The mechanism analysis further reveals that the interlaminar damage dominates energy dissipation during the impact phase, whereas the intralaminar failure is the primary energy-absorbing mechanism during axial crushing. Furthermore, the impact-location analysis shows that the circumferential impact position mainly alters local damage, whereas the impact height has a greater influence on global residual performance, with the mid-height impact being the most detrimental. This study provides a useful reference for the damage-tolerant design of lightweight aerospace composite energy absorbers.