Fracture of the interlayer junction of the shell from a deep-sea hydrothermal vent gastropod
Author(s)Wheeler, Kevin (Kevin R.), S. B. Massachusetts Institute of Technology
Massachusetts Institute of Technology. Dept. of Materials Science and Engineering.
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There is considerable amount of interest in the hierarchical nanomechanical processes that contribute to property amplification of biomaterials. An investigation of these processes and the quantification of the mechanical properties and structure of a biomaterial multilayer is determined. The multilayer was composed of an inner, aragonite-like layer and a middle, compliant layer with a gradient layer between the two exhibiting a non-uniform composition and structure. It was found that the hardness of the middle, compliant layer was 0.186±0.007 GPa, while the inner, aragonite-like had a hardness of 2.1±0.22 GPa. The hardness was found to be 1.66±0.44 GPa within the gradient layer. The indentation toughness of the inner layer was found to be 0.307+0.097 MPa*m1/2 . It was also found that cracks propagated along the grain boundaries within the inner and gradient layers. Crack growth was thus driven by the separation of the grains. The formation of multiple cracks ahead of the crack tip suggested the formation of bands analogous to dilatation bands observed in nacre under certain stress-states. Thus, the mechanisms behind grain separation, the micro-architecture of the anisotropic aragonite grains and other constituents, and the gradual compositional change observed in the tougher gradient layer all acted as toughening mechanisms and contributed to overall property amplification of the shell.
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.Cataloged from PDF version of thesis.Includes bibliographical references (p. 29).
DepartmentMassachusetts Institute of Technology. Dept. of Materials Science and Engineering.
Massachusetts Institute of Technology
Materials Science and Engineering.