Bio-inspired design and 4D Printing of Multi‐stiffness Wavy Metamaterial Energy Absorbers/Dissipators with Shape Recovery Features
Ramin Hamzehei, Mahdi Bodaghi, Nan Wu
Abstract
This study proposes a four-dimensional (4D) printing design of novel wavy metamaterials for energy absorption/dissipation applications. When designing energy absorbers (EAs), ensuring stability, high energy absorption capacity, and shape memory behavior becomes a pivotal consideration. The conventional re-entrant metamaterial is reformulated by replacing the oblique supports of the unit cells with wavy struts, and various curvatures and arrangements of these supports are analyzed for their impact on the mechanical behavior of the metamaterials. The straight horizontal beams of the lattice metamaterials are replaced with wavy connections with inspiration from the cactus fiber to further enhance the material ductility and strength before and after inner contacts, respectively. A finite element analysis (FEA) simulates the deformation patterns and shows mechanical stress distributions within the structures under quasi-static compression. Following this, the lattice structures are additively manufactured from polylactic acid (PLA) silk ultra to validate the FEA results. A good correlation is observed between the FEA and experiments. From both experiments and simulations, a direct relation between the curvature of the wavy ligaments and the stress values is noticed showing the lower the stiffness and stress concentration with the higher curvature. Due to the dependency of structural stiffness on the curvature of the wavy ligaments, multi-stiffness wavy unit cells containing different curvatures can be combined to introduce a hybrid design containing low and high-stiffness unit cells. Under quasi-static compression, the hybrid design leads to a layer-by-layer yield and corresponding multi-plateau region related to each yield on force-displacement relation. In addition, during lattice deformation, the wavy design facilitates earlier contact points and frictional interactions between the walls. These mechanisms enable stress redistribution across broader surfaces, significantly enhancing energy absorption and dissipation through contact-based mechanisms. Due to these newly introduced energy absorption and dissipation capabilities of the proposed metamaterials, multiple applications of the proposed metamaterials can be considered such as in airplane wings, crash boxes, and bio-protection devices. • Wavy metamaterials inspired by cactus fiber enhance energy dissipation property. • Adjusting cell curvatures causes earlier densification and high inner friction. • Functional graded wavy cell design leads to quasi-zero stiffness behavior. • Hybrid metamaterial design realizes stability under compression. • Fully shape-recoverable behavior was noticed via a heating-cooling process.