Investigation to the nano crossed structure of Chamidae shell

The observation of scanning electron microscope (SEM) on a Chamidae´s shell showed that the shell consists of aragonite layers and collagen protein matrix. All aragonite layers are parallel with the surface of the shell and consist of many long and thin aragonite sheets. These aragonite sheets are perpendicular to the layers where they are located. The observation also showed that the aragonite sheets in different layers possess different orientations, which compose a kind of crossed microstructure of the sheets. More careful observation showed that the aragonite sheets consist further of lesser aragonite microsheets. The thickness of the aragonite microsheets possesses nanometer scale. The maximum pullout force of the crossed microstructure was investigated and compared with that of the parallel microstructure based on their representative models. It showed that the crossed microstructure can markedly increase the pullout force of the microsheets and improve the fracture toughness of the shell.