The mollusk shells constitute a large group of biocomposite materials playing a key role in protecting of the animal against the predators. They consist of ~95% of brittle CaCO3 ceramic phase (either in calcite or aragonite crystallographic form) and ~5% of soft and ductile organic material. The outer part of the shells presents characteristic complex architecture containing prisms or lamellas arranged in the way that should secure withstanding a significant static and dynamic loading. Therefore, in the present work, the mechanical response of mollusk shells was evaluated through static and dynamic loading. The former were experiments performed through uniaxial static compression and nanohardness tests along two perpendicular loading directions, while the latter encompassed the dynamic indentation. In addition, before and after the mechanical tests, the microstructure observations were carried out with the help of SEM microscope in order to document the propagation of cracks under loading of mollusk shells.
The static loading in the uniaxial compression test proved a strong anisotropy in mechanical behavior of the shells. If the compression of the sample was performed on the section perpendicular to the shell growth direction a brittle cracking was observed, while an atypical shape of stress-strain curve was documented when a load was applied to the section parallel to the growth direction. In the static indentation experiment the cracks were formed near to the corners of the indents and propagated in the ceramic material to the organic phase where most of them stopped, as it was documented through SEM microstructure observations. It suggest that the layer of soft and ductile organic phase serves as an obstacle for crack propagation.
It is believed that thorough characterization of mollusk shells may be the first step for construction of synthetic materials imitating natural designs in order to achieve extraordinary mechanical properties.