Mapping of elastic modulus and hardness in Trochus niloticus seashell nacre by nanoindentation
Name
228658260-MIT.pdf
Description
Full printable version
Size
5.09 MB
Format
Adobe PDF
Checksum (MD5)
5dc36175ec9f983bb9c9a145dbcf8503
Author(s)
Villarreal, Julián Enrique
Advisor(s)
Christine Ortíz.
Date Issued
2007
Publisher
Massachusetts Institute of Technology
Abstract
Positionally-sensitive nanoindentation was carried out in the freshly-cleaved nacre found in the shell of the gastropod mollusk Trochus niloticus. Nacre is a hierarchical biocomposite composed of mineral tablets of 95 weight % calcium carbonate (CaCO3) in the aragonite mineral form and a biomacromolecular organic matrix. Nanoindentation was carried out in a pattern of square grids of 256 indents at maximum loads of 1 mN and 500 gN. The average elastic modulus and hardness for the 1 mN indents were found to be 97.8 GPa + 6.41 GPa and 5.41 GPa ± 0.49 GPa, respectively, and for the 500 gN indents average elastic modulus of 94.8 GPa ± 7.28 GPa and hardness of 4.89 GPa ± 0.53 GPa. Maps of the 2-D spatial distribution of elastic modulus and hardness for the indent areas were generated. Tapping mode Atomic Force Microscopy was performed on the indented nacre after a treatment of surface etching, which revealed the tablet boundaries in order to correlate qualitatively the topographical features with the properties distribution. The properties distribution maps revealed a non-uniform distribution of nanomechanical properties as well as highly-localized regions in which the values of the properties differed from the average values. Future studies may point to a direct correlation between structural heterogeneity and the properties distribution.
Description
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, June 2007.
Includes bibliographical references ( p. 22).
Subjects
Materials Science and Engineering.
MIT Department
Massachusetts Institute of Technology. Department of Materials Science and Engineering
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