Séminaire SIMM : Tetsuo Yamaguchi (Kyushu University, Fukuoka, Japan)

6 septembre 2019 14:00 » 15:00

Possibilities of new toughening strategies for sparse elastic networks

Tetsuo Yamaguchi
Department of Mechanical Engineering, Kyushu University, Fukuoka, Japan

The toughening of sparse elastic networks, such as hydrogels, meshes, nets, and knitted fabrics, is one of the most important problems in materials science. For example, hydrogels were considered brittle materials because of their sparse structures, and many efforts have been made by polymer scientists to improve the toughness. Owing to their efforts, novel types of tough hydrogels have been developed in the last decade, and the toughening mechanisms such as “sacrificial bonds” [1] and “movable crosslinking points” [2] are known to work well. However, little attention has been paid to other aspects.
In this study, we propose two new strategies for toughening ; A) topology of elastic networks, and B) rotational degrees of freedom in mechanical metamaterials. In our experiments, we create model networks made of springs and connecters, and then conduct fracture experiments of such model networks with various topological structures and with different arm length of a crosslinker. As a result, we find that systematic modifications in local coordination (functional) number exhibit great improvement in toughness compared with regular square lattices [3] (see Figure), and also that rotation of a cross-linker causes compensation of opening displacement for a tensile crack [4]. In both cases, numerical simulations confirm that stress concentration at the crack tip can be significantly suppressed or disappear even without sacrificial bonds nor slide rings. This suggest a possibility of stress concentration-free design by considering topology or internal structures of sparse elastic networks.

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