Microscopic instability-induced tunable configuration and shear-wave bandgap in soft fiber-reinforced composites

Controlling instability and understanding buckled configurations in soft composites is a key challenge in designing functional metamaterials. In particular, the post-buckling behavior and acoustic properties of fiber-reinforced soft composites remain insufficiently explored, despite their potential in wave control. This paper extends the instability analysis of soft FCs composed of neo-Hookean phases into the post-buckling domain. With an evaluation metric for specifying fiber shape, the evolution of buckled fiber morphology and corresponding shear-wave (S-wave) bandgap versus deformation and spacing ratio is examined. Our simulations demonstrate that the alternation of buckling direction and fiber morphology can be realized by tuning fiber periodicity and post-buckling deformation. Particularly, the transition between buckling directions allows the fiber to form diverse helical structures. The instability-induced microstructure transformations activate the onset of the bandgap for S-waves. By tuning the helix of the fiber, the filtering of shear waves with single or double polarization can be achieved. This explored the potential of soft FCs in wave control and provided a pathway for designing reconfigurable functional materials. We further examined the implementation of various geometric imperfections to induce buckling behavior in simulations, aiming to assist in clarifying the unexplored aspects in the open area of modeling complex post-buckling behavior.