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dc.contributor.advisorChristine Ortiz.en_US
dc.contributor.authorBruet, Benjamin J. F. (Benjamin Jean Fernand), 1980-en_US
dc.contributor.otherMassachusetts Institute of Technology. Dept. of Materials Science and Engineering.en_US
dc.date.accessioned2005-09-27T18:50:09Z
dc.date.available2005-09-27T18:50:09Z
dc.date.copyright2004en_US
dc.date.issued2004en_US
dc.identifier.urihttp://hdl.handle.net/1721.1/28878
dc.descriptionThesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004.en_US
dc.descriptionIncludes bibliographical references (p. 82-83).en_US
dc.description.abstract(cont.) revealed jagged and branched crack fronts at plate interface, tortuous crack paths, non-uniform angles of polygons (suggesting possible intrinsic deformability and displacement/sliding). The technique of nanoindentation was carried out on individual aragonite tablets using a diamond-coated Berkovich probe tip (end-radius of 70 nm, tip angle of 142.3 degrees), at a rate of indentation of 10 [micro]N/s (load controlled), forces from 10 to 1000 [micro]N and indentation depths from 10 to 97 nm. AFM inspection of the indented region showed the existence of extensive plastic deformation within the tablet and suggested that occluded biomacromolecules may play a significant role in the deformation at loads below 100 [micro]N. Using the contact elastic theory, a Young modulus of 112.3 GPa and a hardness of 10.5 GPa were found for an individual platelet. This study shows that a biocomposite principally composed of a poor ceramic (aragonite) can achieve surprisingly good macroscopic mechanical properties thanks to a complex hierarchical structure allowing an extraordinary variety of energy-dissipating mechanisms. Our aim is to continue to formulate multiscale structure-property relationships to eventually aid in the design and advancement of new synthetic biologically inspired lightweight, hard body armor technologies.en_US
dc.description.abstractThe inner columnar nacreous layer of the gastropod mollusk Trochus Niloticus is a nanostructured biocomposite with outstanding and unique mechanical properties. It is composed of [approximately]95% wt of hexagonal aragonite plates (width=5.8±0.4 [micro]m, thickness=0.87±0.07 [micro]m), stacked [approximately]40 nm apart, and [approximately]5% wt of a biomacromolecular "glue" which exists between and within the individual plates. Atomic force microscopy (AFM) revealed a dense array of nanoasperities on the top and sides of the aragonite plates ([approximately]120 nm wide). A multiscale theoretical and experimental approach was taken to identify, understand, and predict the complex deformation mechanisms and mechanical behavior of this fascinating material. Macroscopic 3-point bend tests yielded an in-plane Young modulus of 68.0 ± 11.4 GPa and 65.4 ± 9.6 GPa for freshly cut samples and samples soaked for 10 weeks respectively. A fracture strength of 231 ± 34 MPa and 213 ± 42 MPa respectively were measured. Samples soaked for 10 weeks, even if slightly less strong, exhibited major non-linearities in the stress-strain curves, emphasizing the greater toughness of hydrated nacre. Uniaxial compression yielded Young moduli of 63.8 ± 14.7 GPa for samples with the brick layers oriented parallel to the load, 19.1 ± 3.4 GPa when oriented perpendicular to it and fracture strengths of respectively 225 ± 44 and 663 ± 71 MPa. The discrepancy between the compression moduli emphasizes that very distinct deformation mechanisms prevail during these tests, which is confirmed by the fact that fracture occurs also in three different ways (respectively through thickness, interlaminar and shatter). Scanning electron microscopy (SEM) and AFM of fractured samplesen_US
dc.description.statementofresponsibilityby Benjamin J.F. Bruet.en_US
dc.format.extent83 p.en_US
dc.format.extent4147986 bytes
dc.format.extent4156885 bytes
dc.format.mimetypeapplication/pdf
dc.format.mimetypeapplication/pdf
dc.language.isoen_US
dc.publisherMassachusetts Institute of Technologyen_US
dc.rightsM.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.en_US
dc.rights.urihttp://dspace.mit.edu/handle/1721.1/7582
dc.subjectMaterials Science and Engineering.en_US
dc.titleMultiscale mechanical studies of nacre from gastropod mollusk Trochus Nilocitusen_US
dc.typeThesisen_US
dc.description.degreeS.M.en_US
dc.contributor.departmentMassachusetts Institute of Technology. Dept. of Materials Science and Engineering.en_US
dc.contributor.departmentMassachusetts Institute of Technology. Department of Materials Science and Engineering
dc.identifier.oclc60425696en_US


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