As an important class of natural biocomposite materials, mollusk shells possess remarkable mechanical strength and toughness as a consequence of their hierarchical structuring of soft organic and hard mineral constituents through biomineralization. Strombus gigas conch, one of the toughest aragonitic mollusk shells commonly known as the giant pink queen conch, contains a high density of nanoscale {110} growth twins in its third order aragonite lamellae, the basic building block of the material. Although the existence of nanotwinned aragonite has been known for decades, its roles and functions in mechanical behaviors and properties of biological materials have received little attention, in spite of worldwide interests in biomimetic materials and numerous studies in recent years aimed to investigate the relationship between mechanical properties (e.g., moduli, strength and toughness) and the elegant nano- and hierarchical structures of biological materials.

 

We have been interested in the toughening mechanism governed by nanoscale twins in the Strombus gigas conch shell. A combination of in situ fracture experiments inside a TEM, large-scale atomistic simulations and finite element modelling by Prof. Huajian Gao’s group demonstrate that the twin boundaries can effectively block crack propagation by inducing phase transformation and delocalization of deformation around the crack tip. This mechanism leads to an increase in fracture energy of the basic building block by one order of magnitude, and contributes significantly to that of the overall structure via structural hierarchy.