Fracture of the interlayer junction of the shell from a deep-sea hydrothermal vent gastropod

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.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Materials Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2008

Author dc:creator

• Wheeler, Kevin (Kevin R.), S. B. Massachusetts Institute of Technology

Advisor dc:contributor.advisor

• Christine Ortiz.

• Materials Science and Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/58274

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/58274