In-plane impact resistance enhancement with a graded cell-wall angle design for auxetic metamaterials

Auxetic metamaterials have demonstrated promising applications in crushing energy absorption. This paper proposes cell-wall angle graded auxetic metamaterials and investigates the potential benefits to in-plane impact resistance by using dynamic finite element analysis. It is the first study on enhancing impact resistant ability of auxetic metamaterials by using the cell-wall angle graded design. Firstly, the effectiveness of this graded design for enhanced energy absorption is uncovered and the underlying mechanism is discussed. Then, various influencing factors, including impact velocity, magnitude of cell-wall angle gradient, cell-wall thickness, are explored in details, and the results for the graded structures and uniform structures are compared. The experiment testing is also conducted to validate the initial simulation model by using a 3D printed specimen of the graded design. It is discovered that for the impact with a quasi-static or low velocity, the angle graded design could always deliver an enhanced energy absorption. Also, with the increase of the impact speed, the enhanced energy absorption could only happen when the crushing direction is along the structural weak-to-strong direction. The results shed light on a new approach to realize the application potential of mechanical metamaterials.