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The microstructures of Veined rapa whelk shell were characterized, and a series of compression tests were carried out on the shell with the compressive loading direction making different angles (0°, 30°, 60° and 90°) with the shell spiral lines. Weibull analysis of the experiment results shows that the compressive strength is generally the highest for the sample with 0°-orientation but the lowest for that with 60°-orientation, which means that the strength shows an obvious anisotropy and the strongest orientation represents the direction parallel to the spiral lines of the shell. Such a phenomenon is closely related to the distinctive microscopic arrangements of different-order aragonite lamellae. The interfaces of different-level lamellae in the adjacent macro-layers yield effects on the mechanical behavior of the shell in a coordinated fashion. [ABSTRACT FROM AUTHOR]

The microstructures and mechanical properties of Clinocardium californiense shell were investigated in relation to the different parts of shell. It is found that the shell can be divided into three parts, that is, the dorsal side, body part, and marginal side based on the variation of microstructures along the longitudinal cross section. Specifically, all areas exhibit a cross-lamellar structure on the dorsal side, and a hierarchical structure comprising three layers including inner (with a cross-lamellar structure), middle (with a complex cross-lamellar structure), and outer (with a prismatic structure) layers was observed on the body part, whereas on the marginal side, the orientation of aragonite sheets shows an obvious deflection. The structural architecture, the dimensions of different-order lamellae in the same kind of structure and the orientation between the indenting direction and aragonite sheet all contribute to the unique mechanical properties of this shell. It is also found that a low value of the ratio of hardness-to-Young's modulus ( H/ E) corresponds to an improved indentation toughness. The middle layer with the densest and most complicated structure on the body part shows the lowest H/ E ratio and the highest hardness and Young's modulus. [ABSTRACT FROM AUTHOR]