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Scaling relations for crack-tip plasticity

: Hartmaier, A.; Gumbsch, P.


Philosophical magazine. A 82 (2002), Nr.17/18, S.3187-3200
ISSN: 0031-8086
Fraunhofer IWM ()
fracture; dislocation activity; scoling relation; brittle-to-ductile transition

The fracture toughness of semibrittle materials such as bcc transition metals or semiconductor crystals strongly depends on loading rate and temperature. If crack-tip pasticity is considered to be thermally activated, a strong correlation between these quantities is expected. An Arrthenius-like scaling relation between the loading rate and the brittle-to-ductile transition temperature has already been reported. In the present work, two-dimensional discrete dislocation dynamics simulations of crack-tip plasticity are employed to show that the different combinations of loading rates and termperatures which yield the same fracture toughness are indeed correlated by a scaling relation. This scaling relation is closely related to the law used to describe dislocation motion. A strong correlation between loading rate and temperature is found in the entiere temperature regime in which crack-tip plasticity is controlled by dislocation mobility. This shows the importance of dislocation mobility for fracture thoughness below the brittle-to-ductile transition and for the transition itself. The findings of our simulations are consistent with experimental data gathered on tungsten single crystals and suggest that non-screw dislocations are dominating crack-tip plasticity in the semibrittle regime of this material.