Nanoscale Deformation and Toughening Mechanisms of Nacre

We found direct evidence that a single-crystal-like aragonite platelet is essentially assembled with aragonite nanoparticles. The aragonite nanoparticles are readily oriented and assembled into pseudo-single-crystal aragonite platelets via screw dislocation and amorphous aggregation, which are two dominant mediating mechanisms between nanoparticles during biomineralization. The heat treatment burned out the biopolymer in nacre, leaving nanoscale holes at the aragonite platelet boundaries and on the platelet surfaces. By directly probing the biopolymer nanostrands using an atomic force microscope, we unveiled that the biopolymer in nacre has the capability to strengthen itself during deformation. An elastic modulus of 10.57 GPa was determined for nacre biopolymer matrix for the first time. Under high strain rate compression, nacre exhibits surprisingly high fracture strength and relatively marked plastic deformation excursion compared with those in the quasi-static loading mode. We discovered a new deformation mechanism that the emission of partial dislocation and the onset of deformation twinning jointly play a dominated role in the increased fracture strength and ductility. This project has supported 1 postdoctoral researcher and 3 PhD students. Five papers have been published or submitted for publication in prestigious referred journals. The work has been presented at 16 international conferences. (a) Papers published in peer-reviewed journals (N/A for none) Xiaodong Li and Zaiwang Huang, "Unveiling the Formation Mechanism of Pseudo-Single Crystal Aragonite Platelets in Nacre," Physical Review Letters, 102 (2009) 075502. Zaiwang Huang and Xiaodong Li, "Nanoscale Structural and Mechanical Characterization of Heat Treated Nacre," Materials Science and Engineering C, 29 (2009) 1803-1807. List of papers submitted or published that acknowledge ARO support during this reporting period. List the papers, including journal references, in the following categories: (b) Papers published in non-peer-reviewed journals or in conference proceedings (N/A for none) 2.00 Number of Papers published in peer-reviewed journals: Number of Papers published in non peer-reviewed journals: (c) Presentations 0.00 Xiaodong Li, "Unveiling the Strengthening and Toughening Mechanisms of Nacre Lessons from Nature," 2011 ASME Annual Conference, International Mechanical Engineering Congress & Exposition (IMECE), Denver, Colorado, November 1117, 2011 (invited keynote). Xiaodong Li, "Unveiling Deformation and Toughening Mechanisms of Nacre," 35th International Conference and Exposition on Advanced Ceramics and Composites (ICACC’11), Daytona Beach, Florida, January 23-28, 2011 (invited). Xiaodong Li, "Deformation and Toughening Mechanisms of Natural Biological Nanocomposites Lessons from Nature," 3rd International Conference on One-dimentional Nanomaterials (ICON 2009), Atlanta, Georgia, December 79, 2009 (invited). Xiaodong Li and Zaiwang Huang, "Unveiling the Formation Mechanism of Pseudo Single-Crystal Aragonite Platelets in Nacre," MS&T’09, Material Science & Technology 2009 Conference & Exhibition, Pittsburgh, PA, October 25-29, 2009 (invited). Xiaodong Li, "What Roles do Nanostructures Play in the Strengthening and Toughening of Nacre?," MS&T '08, Material Science & Technology 2008 Conference & Exhibition, Pittsburgh, PA, October 5-9, 2008 (invited). Xiaodong Li, "Nanomechanics of Biological Systems," 2008 MRS Spring Meeting, San Francisco, CA, March 24-28, 2008 (invited). Xiaodong Li, "Deformation and Toughening Mechanisms of Nanograins Lessons from Nature," TMS 2008, 137th Annual Meeting & Exhibition, New Orleans, LA, March 9-13, 2008 (invited). Xiaodong Li, "Deformation and Toughening Mechanisms of Natural Nanocomposites Lessons from Nature," 32nd International Conference & Exposition on Advanced Ceramics & Composites, Daytona Beach, Florida, January 27-February 1, 2008 (invited). Haoze Li, Zhi-Hui Xu, and Xiaodong Li, "Nanoscale Structural and Mechanical Characterization of Conch Shells," 2011 ASME Annual Conference, International Mechanical Engineering Congress & Exposition (IMECE), Denver, Colorado, November 1117, 2011. Xiaodong Li, "Unveiling the Deformation and Toughening Mechanisms of Nacre – Lessons from Nature," TMS 2011, 140th Annual Meeting & Exhibition, San Diego, California, February 27 March 3, 2011. Xiaodong Li and Zaiwang Huang, "Unveiling the Formation Mechanism of Pseudo Single-Crystal Aragonite Platelets in Nacre," TMS 2010, 139th Annual Meeting & Exhibition, Seattle, WA, February 14-18, 2010. Xiaodong Li and Zaiwang Huang, "Unveiling the Formation Mechanism of Nanostructured Aragonite Platelets in Nacre," 2009 MRS Fall Meeting, Boston, MA, November 30 – December 4, 2009. Zaiwang Huang and Xiaodong Li, "Nanoscale Structural and Mechanical Characterization of Heat Treated Natural Nanoparticle-based Material – Nacre," MS&T '09, Materials Science & Technology 2009 Conference & Exhibition, Detroit, Michigan, October 25-29, 2009. Zaiwang Huang and Xiaodong Li, Temperature Effect on the Structure and Mechanical Properties of Nacre, TMS 2009, 138th Annual Meeting & Exhibition, San Francisco, CA, February 15-19, 2009. Xiaodong Li, Zhi-Hui Xu, Zaiwang Huang, Wei-Che Chang, Yuh J. Chao, Rizhi Wang, and Min Chang, Deformation and Toughening Mechanisms of Nacre, 2008 ASME Annual Conference, International Mechanical Engineering Congress & Exposition (IMECE), Boston, MA, October 31November 6, 2008. Xiaodong Li, Zhi-Hui Xu, Wei-Che Chang, Yuh J. Chao, Rizhi Wang, and Min Chang, Nanoscale Structural and Mechanical Characterization of Nacre, 2008 SEM Annual Conference, Orlando, FL, June 2-5, 2008. Number of Presentations: 16.00 Non Peer-Reviewed Conference Proceeding publications (other than abstracts): Number of Non Peer-Reviewed Conference Proceeding publications (other than abstracts): 0 Peer-Reviewed Conference Proceeding publications (other than abstracts): Zhi-Hui Xu and Xiaodong Li, "Deformation Strengthening of the Biopolymer Matrix of Nacre," submitted for publication. Zhi-Hui Xu, Yingchao Yang, Zaiwang Huang, and Xiaodong Li, "Elastic Modulus of Biopolymer Matrix in Nacre Measured Using Coupled Atomic Force Microscopy Bending and Inverse Finite Element Techniques," submitted for publication. Zaiwang Huang, Haoze Li, Zhiliang Pan, Qiuming Wei, and Xiaodong Li, "New Deformation Mechanism in Nacre," submitted for publication. (d) Manuscripts Number of Peer-Reviewed Conference Proceeding publications (other than abstracts): 0 Number of Manuscripts: 3.00