Biological Structures Mitigate Catastrophic Fracture Through Various Strategies |
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Authors: | R Ballarini R Kayacan F-J Ulm T Belytschko A H Heuer |
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Affiliation: | (1) Case Western Reserve University, Civil Engineering, 10900 Euclid Avenue, Cleveland, OH 44106-7201, USA;(2) Suleyman Demirel University, Turkey;(3) Massachusetts Institute of Technology, USA;(4) Northwestern University, USA |
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Abstract: | Gao et al. (PNAS, 100, 5597–5600 (2003)) have argued that load-bearing mineralized hard tissues, including bones, shells, and teeth, are nanocomposites,
in which the mineral phase has nanoscale dimensions that ensure optimum strength and flaw tolerance. In particular, it has
been claimed that the thickness of these brittle building blocks, being smaller than a critical size, h*, of the order of tens of nanometers, renders them insensitive to the presence of crack-like flaws and enables them to achieve
near-theoretical strength, which is why Nature employs nanoscale features in mineralized biological composites. We find this
point of view, which Gao et al. and others have quoted in subsequent publications and presentations, unpersuasive and present
several counterexamples which show that biological structures, as a result of being comprised of relatively fragile constituents
that fracture at stress levels several orders of magnitude smaller than the theoretical strength, adopt various strategies
to develop mechanical responses that enable them to mitigate catastrophic failure. Nanoscale structural features are not a
result of an innate resistance to very high stresses. |
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Keywords: | Biological structures crack bridging flaw-intolerance flaw-tolerance nanoscale structures toughening |
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