Notch sensitivity of metamaterial with snapping microstructure

Abstract

The purpose of this project is to examine the notch sensitivity to the strength of a mechanical metamaterial comprising a periodic arrangement of snapping units. A unit cell of the metamaterial consists of two centrally connected wavy-shape segment (a snapping segment and a bearing segment). Since the unit cell possesses two stable deformation states in a certain load range, the nominal strain is rapidly increased by snap-through instabilities (snap-through deformation) when the applied load reaches a critical value. In the tensile experiment of specimens comprised of 30×30 unit cells under quasi-stick conditions, the cells on a certain row snap, and this results in a macroscopic load drop. As the applied deformation increases the snap-through deformation propagates to the adjacent cell. The cells snap through row-by-row with relatively small increases and decreases, until fracture occurs in the specimen. This process brings about a large macroscopic ductility of the metamaterial. Subsequently, a center-hole notch is introduced into the specimen and tensile experiments are performed. Although the snap-through deformation preferentially occurs at the notch root, it propagates to the other cells row-by-row without fracture because a stress concentration at the notch root is relaxed by the snapping. The snapping metamaterial possesses low defect susceptibility and high embrace as a structural material.