On the fracture toughness of advanced materials

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Few engineering materials are limited by their strength; rather they are limited by their resistance to fracture or fracture toughness. It is not by accident that most critical structures, such as bridges, ships, nuclear pressure vessels and so forth, are manufactured from materials that are comparatively low in strength but high in toughness. Indeed, in many classes of materials, strength and toughness are almost mutually exclusive. In the first instance, such resistance to fracture is a function of bonding and crystal structure (or lack thereof), but can be developed through the design of appropriate nano/microstructures. However, the creation of tough ... continued below

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Launey, Maximilien E. & Ritchie, Robert O. November 24, 2008.

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Few engineering materials are limited by their strength; rather they are limited by their resistance to fracture or fracture toughness. It is not by accident that most critical structures, such as bridges, ships, nuclear pressure vessels and so forth, are manufactured from materials that are comparatively low in strength but high in toughness. Indeed, in many classes of materials, strength and toughness are almost mutually exclusive. In the first instance, such resistance to fracture is a function of bonding and crystal structure (or lack thereof), but can be developed through the design of appropriate nano/microstructures. However, the creation of tough microstructures in structural materials, i.e., metals, polymers, ceramics and their composites, is invariably a compromise between resistance to intrinsic damage mechanisms ahead of the tip of a crack (intrinsic toughening) and the formation of crack-tip shielding mechanisms which principally act behind the tip to reduce the effective 'crack-driving force' (extrinsic toughening). Intrinsic toughening is essentially an inherent property of a specific microstructure; it is the dominant form of toughening in ductile (e.g., metallic) materials. However, for most brittle (e.g., ceramic) solids, and this includes many biological materials, it is largely ineffective and toughening conversely must be developed extrinsically, by such shielding mechanisms as crack bridging. From a fracture mechanics perspective, this results in toughening in the form of rising resistance-curve behavior where the fracture resistance actually increases with crack extension. The implication of this is that in many biological and high-strength advanced materials, toughness is developed primarily during crack growth and not for crack initiation. This is an important realization yet is still rarely reflected in the way that toughness is measured, which is invariably involves the use of single-value (crack-initiation) parameters such as the fracture toughness K{sub Ic}.

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  • Journal Name: Advanced Materials

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  • Report No.: LBNL-1467E
  • Grant Number: DE-AC02-05CH11231
  • Office of Scientific & Technical Information Report Number: 952579
  • Archival Resource Key: ark:/67531/metadc935384

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  • November 24, 2008

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  • Nov. 13, 2016, 7:26 p.m.

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  • Oct. 2, 2017, 5:32 p.m.

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Launey, Maximilien E. & Ritchie, Robert O. On the fracture toughness of advanced materials, article, November 24, 2008; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc935384/: accessed June 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.