Fractal order-dependent nonlinear energy absorption mechanism of Menger sponge-inspired composite structures under blast loading

Fractal structures, with their multi-scale self-similarity, exhibit distinctive geometric advantages and broad application potential in blast-resistant engineering. As a classic fractal model featuring a high specific surface area and low volume fraction, the Menger sponge has been widely used in acoustics and biomedicine. While existing research on Menger sponge structures has been largely limited to quasi-static compression and low-velocity impact, their application in blast loaded composite structures still offers considerable scope for exploration. To address this gap, this study proposes a novel Menger sponge-inspired fractal composite structure for blast protection, aiming to simultaneously optimize lightweight performance and energy absorption efficiency. A numerical simulation model validated via impact tests was established to systematically investigate the effects of key parameters on the dynamic response and energy absorption characteristics of the proposed structure under blast loading. The results indicate that concrete-based Menger sponge fractal structure is a promising core-layer candidate, achieving a favorable balance between lightweight and energy absorption. Increasing the fractal order enhances cavity complexity and inter-unit coordinated deformation, thereby improving energy absorption capacity. Circular cavities demonstrate superior energy-absorbing performance compared to their square counterparts. These findings validate the superior potential of the proposed fractal structure as a blast-resistant core layer and provide valuable guidance for the design of next-generation protective composite structures.