On the influence of thickness, stiffness, and soft interfaces in heterogeneous multilayered structures

This study examines the mechanical performance of spicule-inspired structures (SISs) modeled after the multilayered architecture of Euplectella aspergillum sponge spicules. Using finite element simulations validated by experiments on 3D-printed prototypes, we explore how variations in thickness distribution, modulus contrast, and the introduction of soft interfacial layers affect stress distribution, deformation, and energy absorption. Our results show that SISs with thinner outer layers and strategic modulus gradients—particularly those with stiff cores and soft outer layers—demonstrate enhanced flexibility, improved load transfer, and greater energy absorption compared to uniformly layered designs. The addition of soft, thin interfaces between layers further reduces stress concentrations, especially when interface modulus is tuned appropriately. These findings establish design principles that emphasize functional gradients and targeted material placement over simple layering, offering a framework for engineering lightweight, resilient structures for applications in aerospace, civil infrastructure, and bioinspired systems.