Mobility of non-planar screw dislocations ahead of a mode III crack tip

Conference · Sun Aug 01 04:00:00 EDT 1999

OSTI ID:364051

Ngan, A H.W. ^[1]; Zhang, H F ^[2]

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1. Univ. of Hong Kong (Hong Kong). Dept. of Mechanical Engineering
2. Central Iron and Steel Research Inst., Beijing (China). Dept. of Advanced Materials

A necessary though not sufficient condition for brittle-to-ductile transition (BDT) to occur is that dislocations can emanate from the crack tip. The problem of dislocation emission from a crack tip has been studied by a number of authors who have considered in detail the force required to gradually form a dislocation from zero to unit Burgers vector content and the competition between such mode of dislocation nucleation and crack cleavage. In the incipient process considered by these authors, the dislocation is assumed to have a planar core, and no lattice friction is assumed to exist once the dislocation is fully formed and begins to move away from the crack tip. The omission of friction stress during the incipient process is perhaps not important for close-packed slip systems because the lattice friction can be supposed to be small. However, for the bcc structure for which BDT is particularly important, screw dislocation cores are non-planar and so lattice friction should not be neglected a priori in a satisfactory treatment on crack-tip emission. The present work is therefore an attempt to remedy this deficiency. The generalized Peierls-Nabarro model is used to study the transformation of screw dislocation cores from the three-fold, non-planar state to the planar, glissile state ahead of a mode III crack tip.

• OSTI ID: 364051
• Report Number(s): CONF-981104--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BRITTLE-DUCTILE TRANSITIONS
CRACKS
DISLOCATIONS
MATERIALS
MATHEMATICAL MODELS
SLIP