Lianchao WANG : "Mechanical Properties of 3D Auxetic Metamaterials"

Abstract : Rationally designed artificial porous structures and materials can achieve counter-intuitive mechanical properties, i.e., mechanical metamaterials, that are inaccessible to ordinary materials. Among the most popular mechanical metamaterials, auxetics have been widely investigated in the past few decades due to their unique lateral deformation. In this thesis, I focus on the investigation of the effective elastic constants (effective Poisson's ratio and Young's modulus) of 3D auxetics. In the first chapter, I introduce the concepts of mechanical metamaterials and the development of artificial auxetics. In the second chapter, based on the inspiration of the longitude and latitude, a 3D structure with partial auxeticity is proposed and studied. In the third chapter, directional instability is introduced and used to enhance the auxeticity of the structure investigated in the previous chapter. Then, in the fourth chapter, the structure proposed in Chapter 2 is utilized to design a new 3D structure that shows full auxeticity in the three main directions and a multi-step mechanical behavior. Specifically, this metamaterial has elementary auxeticity for small compressive strains but superior auxeticity for large strains. More importantly, the effective Young's modulus exhibits a parallel trend, i.e., it becomes larger with increasing compressive strain. In the last chapter, the curved beams in the structure are replaced by straight beams, and 3D auxetics with even better mechanical properties are obtained. Moreover, the elastically-stable continuous phase transition of the Poisson's ratio is reported.

Jury Composition :

Vincent LAUDE, Directeur de recherche, Université Bourgogne Franche-Comté, PhD Director

Gengkai HU, Professeur, Beijing Institute of Technology, Reporter

Corentin COULAIS, Associate Professor, Universiteit van Amsterdam, Reporter

Bing WANG, Professor, Harbin Institute of Technology, PhD Co-Director

Muamer KADIC, Associate Professo, Université Bourgogne Franche-Comté, PhD Co-Director

Andrew ALDERSON, Professor, Sheffield Hallam University, Reviewer

Linzhi WU, Professor, Harbin Institute of Technology, Reviewer

Localization : HIT Science Park No.2 Yikuang Street 150001, Harbin CHINE - salle 316, Building A