Specimen size effect on the fracture energy of architected stretchable materials

Architected stretchable materials with well-organized micro-architectures evolve very rapidly due to their potential in customizing mechanical properties and achieving exotic functions. In many applications, the architected stretchable materials are required to sustain large deformation, and their fracture is size-dependent. However, the size effect on the fracture of architected stretchable materials is still elusive. Here, we study this issue by experiment and finite element calculation. It is found that the fracture energy of architected stretchable materials increases with the specimen size ratio, H/h, within a range. When H/h reaches a transition ratio, R_t, the fracture energy approaches a plateau. This transition ratio differentiates the size-dependent and size-independent fracture behavior of architected stretchable materials. The mechanical properties of constituent material only have a minor effect on the transition ratio. The degree of constraint and stress concentration at the node, which are affected by the geometry of the unit-cell, dominate the specimen size effect. The result gives a practical guidance in choosing the specimen size to measure the steady state fracture energy of this class of materials. This work provides insights into the fracture of architected stretchable materials and design for fracture-resistant architected stretchable devices.