Lateral dynamic crushing of skeletal muscle-inspired hierarchical celled structures

In this paper, a bionic structure made of skeletal muscle-inspired hierarchical (MH) unit cells is proposed. The mechanical properties and energy absorption (EA) characteristics of MH-celled structures with different geometric dimensions under various impact speeds were explored and compared with conventional circular-celled structures using finite element (FE) models in ABAQUS/Explicit. Quasi-static and dynamic tests were conducted to validate the FE modelling approach. Numerical investigations reveal that the hierarchical configuration significantly enhances EA compared to conventional designs. This improvement is attributed to the deformation behaviour of transverse localised bands, which form perpendicular to the crushing direction at the junctions between layers in the MH-celled structure. These bands effectively distribute stress, enhance plastic deformation, and promote frictional energy dissipation. Compared to the conventional structure, the MH-celled structure exhibited increases of 54.3% in SEA and 65.4% in plateau stress under low-speed impact (0.5 m s^-1). Under medium-velocity impact, these increases reached 55.4% and 57.5%, respectively. Moreover, it was found that the deformation mode of MH-celled structures is governed by the relative density of the structure and the impact velocity, which can be categorised into quasi-static mode, transition mode and dynamic mode. Parametric studies revealed that both the specific EA and plateau stress of MH-celled structures are enhanced with the increase in the relative density or the impact velocity. The results also demonstrate an exponential relationship between plateau stress, impact velocity, and relative density.