Damage tolerance and residual crashworthiness of bio-inspired composite multi-cell tubes for lightweight aerospace energy absorbers

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Abstract
Lightweight composite energy-absorbing structures are increasingly required in aerospace vehicles, where in-service low-velocity impacts may compromise their residual crashworthiness and damage tolerance. This study investigates the damage behaviour and residual crashworthiness of lotus stem-inspired multi-cell composite tubes containing transverse impact damage using a combined experimental and numerical approach. An efficient residual-performance prediction framework is developed by employing an impact damage-mapping technique, which enables the accurate transfer of intralaminar damage, interlaminar delamination, and permanent deformation between different analysis models. To further elucidate the energy-absorption mechanisms during impact and subsequent axial crushing, energy absorption and dissipation calculations are integrated into a VUMAT subroutine. The finite element model demonstrates a high level of predictive accuracy for both the transverse impact response and the post-impact compressive behaviour. Using this framework, the effects of circumferential and height impact locations on residual performance are systematically examined. The results show that transverse impact loading markedly affects the energy-absorption characteristics of composite tubes, while the multi-cell configuration reduces the degradation caused by prior impact damage. The residual energy-absorption capacity of the circular tube decreases by approximately 61 %, whereas the multi-cell tube exhibits a more moderate reduction of approximately 23 %. During the impact phase, interlaminar damage dominates energy dissipation, whereas during axial crushing intralaminar failure represents the primary energy-absorbing mechanism. Although circumferential impact locations produce different local responses, their effect on global residual performance is limited; in contrast, impact height has a significant influence on the remaining load-bearing capacity and ensuing failure modes. The proposed framework provides a methodological basis for the damage-tolerant design of lightweight aerospace composite energy-absorbing structures.

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