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Direct Quantification of the Mechanical Anisotropy and Fracture of an Individual Exoskeleton Layer via Uniaxial Compression of Micropillars
Journal article   Peer reviewed

Direct Quantification of the Mechanical Anisotropy and Fracture of an Individual Exoskeleton Layer via Uniaxial Compression of Micropillars

Lin Han, Lifeng Wang, Juha Song, Mary C. Boyce and Christine Ortiz
Nano letters, v 11(9), pp 3868-3874
01 Sep 2011
PMID: 21755939

Abstract

Chemistry Chemistry, Multidisciplinary Chemistry, Physical Materials Science Materials Science, Multidisciplinary Nanoscience & Nanotechnology Physical Sciences Physics Physics, Applied Physics, Condensed Matter Science & Technology Science & Technology - Other Topics Technology
A common feature of the outer layer of protective biological exoskeletons is structural anisotropy. Here, we directly quantify the mechanical anisotropy and fracture of an individual material layer of a hydroxyapatite-based nanocomposite exoskeleton, the outmost ganoine of Polypterus senegalus scale. Uniaxial compression was conducted on cylindrical micropillars of ganoine fabricated via focused ion beam at different orientations relative to the hydroxyapatite rod long axis (theta = 0 degrees, 45 degrees, 90 degrees). Engineering stress versus strain curves revealed significant elastic and plastic anisotropy, off-axial strain hardening, and noncatastrophic crack propagation within ganoine. Off-axial compression (theta = 45 degrees) showed the lowest elastic modulus, E (36.2 +/- 1.6 GPa, n >= 10, mean +/- SEM), and yield stress, sigma(Y) (0.81 +/- 0.02 GPa), while compression at theta = 0 degrees showed the highest E (51.8 +/- 1.7 GPa) and sigma(Y) (1.08 +/- 0.05 GPa). A 3D elastic-plastic composite nanostructural finite element model revealed this anisotropy was correlated to the alignment of the HAP rods and could facilitate energy dissipation and damage localization, thus preventing catastrophic failure upon penetration attacks.

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Web of Science research areas
Chemistry, Multidisciplinary
Chemistry, Physical
Materials Science, Multidisciplinary
Nanoscience & Nanotechnology
Physics, Applied
Physics, Condensed Matter
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