2026-09-18T22:33:24Zhttps://dspace.mit.edu/server/oai/request

oai:dspace.mit.edu:1721.1/421642022-01-13T07:54:33Zcom_1721.1_7582com_1721.1_7581col_1721.1_131024

Christine Ortíz. Villarreal, Julián Enrique Massachusetts Institute of Technology. Dept. of Materials Science and Engineering. Massachusetts Institute of Technology. Department of Materials Science and Engineering 2008-09-03T14:46:12Z 2008-09-03T14:46:12Z 2006 2007 http://hdl.handle.net/1721.1/42164 228658260 Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, June 2007. Includes bibliographical references ( p. 22). 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. by Julián Enrique Villarreal. S.B. : eng Massachusetts Institute of Technology 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. http://dspace.mit.edu/handle/1721.1/7582 Materials Science and Engineering. Mapping of elastic modulus and hardness in Trochus niloticus seashell nacre by nanoindentation Thesis application/pdf Publication unknown unknown <Publication xmlns="https://www.openaire.eu/cerif-profile/1.1/" id="82970008-81f1-4ee5-8fcb-1cdba6c916f3"> <Type xmlns="https://www.openaire.eu/cerif-profile/vocab/COAR_Publication_Types">http://purl.org/coar/resource_type/c_1843</Type> <Language>eng</Language> <Title>Mapping of elastic modulus and hardness in Trochus niloticus seashell nacre by nanoindentation</Title> <PublishedIn> <Publication> </Publication> </PublishedIn> <PublicationDate>2007</PublicationDate> <Authors> <Author> <DisplayName>Villarreal, Julián Enrique</DisplayName> <Affiliation> <OrgUnit> </OrgUnit> </Affiliation> </Author> </Authors> <Editors> </Editors> <Publishers> <Publisher> <DisplayName>Massachusetts Institute of Technology</DisplayName> <OrgUnit /> </Publisher> </Publishers> <License>http://dspace.mit.edu/handle/1721.1/7582</License> <Keyword>Materials Science and Engineering.</Keyword> <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.</Abstract> <Access xmlns="http://purl.org/coar/access_right" > </Access> </Publication>