Stiffness-Independent Toughening of Beams through Coaxial Interfaces.

To be of engineering relevance, it is essential for stiff and strong materials to possess also high toughness. However, as these properties are typically mutually exclusive, they are rarely found in nature and synthetic replications are extremely limited. Here, an elegant albeit simple physical principle that enables ligaments in cellular networks to possess these mechanical properties simultaneously is presented. The underlying architecture consists of multiple, coaxially aligned layers separated by interfaces that prevent crack propagation, hence increasing the energy required for complete rupture. The results show that the fracture strain and toughness can be increased by over 100%, when compared to conventional reference struts, while fully maintaining the density, stiffness, and strength. The bioinspired and highly versatile approach is scale-independent under the absence of shear, applicable to various geometries, and complementary to existing approaches. It can, therefore, significantly improve safety and reduce cost and environmental impact in numerous applications, such as packaging, sports equipment, and transportation.