Low-velocity impact resistance of double-layer folded gradient sandwich structure

Gradient design is incorporated into a double-layer folded sandwich structure to enhance its low-velocity impact resistance. The impact behavior of the V-shaped folded core is investigated using finite element simulations validated by experiments. Gradients are achieved by varying the height and wall thickness of the upper and lower core layers. Key performance indicators – peak impact force, energy absorption, and top panel displacement – are analyzed under different impact energies and gradient rates. Results show that while energy absorption remains largely unchanged compared to homogeneous structures, a positive gradient rate (q > 0) within a certain range increases structural stiffness and reduces peak contact force, especially at lower impact energies. Conversely, a negative gradient rate (q < 0) decreases stiffness but prolongs contact time and increases top panel displacement, offering enhanced cushioning. Thus, by studying the impact resistance and cushioning performance of gradient designs, this study demonstrated the feasibility of using gradient designs to meet the performance requirements of specific structures.