Lightweight origami sandwich structures with gradient design for improved energy absorption capacity

Origami structures, as typical mechanical metamaterials, have garnered extensive attention due to their lightweight, high strength, and customizable mechanical properties, making them highly promising for applications in aerospace, automotive engineering, and protective equipment. However, many conventional origami structures, especially those based on uniform tessellation, face limitations in mechanical tunability and adaptability due to their relatively fixed folding patterns and limited capacity for graded deformation, which restrict their broader functional application. To overcome these limitations, we propose a controllable gradient origami sandwich structure design method, drawing inspiration from the hierarchical and gradient characteristics of natural materials. This approach integrates the Miura-origami folding pattern with gradient design principles. The mechanical properties of gradient origami sandwich structures are validated through finite element methods, experiments utilizing 3D printed physical models, and theoretical analysis. Results show that most gradient structures outperform their uniform counterparts, with the highest improvements in specific energy absorption (SEA) and mean compressive force (MCF) reaching 35 % and 41 %, respectively. The introduction of gradients can significantly modulate the internal stress propagation mechanisms and reconfigure the deformation modes of origami sandwich structures compared with non-gradient structure. Additionally, gradient structures exhibited higher peak forces and better energy absorption capabilities in three-point bending tests. These findings systematically highlight the influence of gradient design on the energy absorption and deformation behavior of origami sandwich structures, supported by theoretical analysis, numerical simulations, and experimental validation.