Interplay of various fracture mechanisms in bio-inspired staggered structure

Staggered structures have materialized to be an exquisite configuration possessing stiffness, strength and toughness, simultaneously. Various biocomposites such as nacre, teeth and bone display aforesaid properties consisting of hard phase in the form of platelets embedded in soft matrix. Platelet fracture, matrix fracture, and platelet-matrix interface debonding are found to be primary mechanisms behind emergent mechanical behaviors. However, the interaction of these fracture mechanisms needs to be fully exploited for design of bioinspired composites. Therefore, in this study, we present the mathematical framework to simulate the staggered structure that seamlessly accounts the platelet and matrix fractures along with debonding of the interfaces. Adopting phase field fracture, we model the bulk failure, while classical cohesive zone model (CZM) has been utilized to capture the debonding of vertical and horizontal interfaces. In order to validate the numerical scheme, a simplified shear-lag model with imperfectly bonded platelet-matrix interfaces has also been developed for the unit cell of staggered structure. Later, a staggered structure consisting multiple platelets has been examined for various interface and geometric parameters. The present study shows that type of interface and platelet's aspect ratio strongly influence the fracture behavior resulting in emanant stiffness, strength and toughness properties. Thus, the present findings provide design map of bio-inspired staggered composite for achieving the stiffness and toughness together.