Microstructure-Properties: I Fracture Toughness - Materials Science ...
Microstructure-Properties: I Fracture Toughness - Materials Science ...
Microstructure-Properties: I Fracture Toughness - Materials Science ...
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24<br />
Zone Shielding: 2A transformation toughening<br />
Objective<br />
Overview<br />
Crack<br />
Minimztn.<br />
Energy<br />
Absrptin.<br />
• Various mechanisms exist for shielding crack tips from some<br />
of the applied (and concentrated) stress.<br />
• The best known mechanism is transformation toughening.<br />
• This applies to both metals (stainless steels, Hadfield steels)<br />
and ceramics (zirconia additions).<br />
• The principle on which the toughening is based is that of<br />
including a phase that is metastable at the service<br />
temperature and which will transform when loaded (but not<br />
otherwise).<br />
• The transformation always has a volume change associated<br />
with the change in crystal structure, which can be written as a<br />
strain. The product of stress and strain is then the work done<br />
or expended during the (stress-induced) transformation.
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