Journal
ACTA BIOMATERIALIA
Volume 9, Issue 4, Pages 5876-5889Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.actbio.2012.12.026
Keywords
Scale; Flexible armor; Structure; Fracture resistance; Fracture mechanism
Funding
- National Science Foundation [DMR-1006931]
- UC Lab Research Program [09-LR-06-118456-MEYM]
- Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, of the US Department of Energy [DE-AC02-05CH11231]
- Department of Energy
- Division Of Materials Research
- Direct For Mathematical & Physical Scien [1006931] Funding Source: National Science Foundation
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The alligator gar is a large fish with flexible armor consisting of ganoid scales. These scales contain a thin layer of ganoine (microhardness similar to 2.5 GPa) and a bony body (microhardness 400 MPa), with jagged edges that provide effective protection against predators. We describe here the structure of both ganoine and bony foundation and characterize the mechanical properties and fracture mechanisms. The bony foundation is characterized by two components: a mineralized matrix and parallel arrays of tubules, most of which contain collagen fibers. The spacing of the empty tubules is similar to 60 mu m; the spacing of those filled with collagen fibers is similar to 7 mu m. Using micromechanical testing of such scales in a variable-pressure scanning electron microscope, we identify interactions between propagating cracks and the microstructure, and show that the toughness of the scales increases with crack extension in a classical resistance-curve response from the activation of extrinsic toughening mechanisms. We demonstrate how mechanical damage evolves in these structures, and further identify that the reinforcement of the mineral by the network of collagen fibers is the principal toughening mechanism resisting such damage. Additionally, we define the anisotropy of the toughness of the scales and relate this to the collagen fiber orientation. Published by Elsevier Ltd. on behalf of Acta Materialia Inc.
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