A multi-scale mechanical model of multilevel helical structures with filament damage

Multilevel helical structures are widely used in biology and engineering fields. The multilevel helical structure exhibits interesting and complex mechanical behaviors due to the hierarchical feature and interactions between various structural scales. Herein, by extending the straight filament shear-lag model, a multi-scale damage mechanical model including the helical filament and sub-cable scales is established to investigate the mechanical behavior of the multilevel helical structure. The effect of filament breakage, contact interactions, and helical characteristics on the mechanical responses of the sub-cable is investigated. It is found that helical filaments have the higher deformation flexibility than straight filaments, thus weakening the stress transferring capacity and inhibiting filament breakage. The stress-strain curve of the helical filament exhibits a plateau region by adjusting laying angles. It is demonstrated for the helical structure level that the axial tension stiffness can be enhanced by increasing laying angles of the filament bundle and sub-cable. Axial coupling stiffness with filament damage exhibits the non-monotonic variation with sub-cable laying angles. The effectiveness of the present model is also verified by comparison with axial tensile experiments of composite wires. This research seeks to elucidate the intertwined impacts of filament damage and helical characteristics on the mechanical behaviors of multilevel helical structures.