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Modelling plastic zones and the brittle-ductile transition

1997; Royal Society; Volume: 355; Issue: 1731 Linguagem: Inglês

10.1098/rsta.1997.0101

1471-2962

P. B. Hirsch, Steve Roberts,

High-Velocity Impact and Material Behavior

Many crystalline solids fail by cleavage at low temperatures and by plastic processes at high temperatures. In the transition region, cleavage failure occurs at stresses increasing with increasing temperature, reflecting a decrease in yield stress and a consequent increase of plasticity around the crack tip. Crack tip plasticity blunts the crack and shields it through the compressive stresses in the plastic zone. This competition between cleavage and plastic flow can be modelled in terms of the generation (from a source), motion and interaction of dislocations moving on the slip plane containing the crack tip, obeying a velocity–stress–temperature law. Assumptions have to be made about the criterion for cleavage fracture and the density and strength of dislocation sources. While the temperature range and strain-rate sensitivity of the transition depend on the velocity law, the form of the transition (sharp or gradual) depends on spacing of the dislocation sources and thus the transition is structure sensitive. Static equilibrium arrays of discrete dislocations have also been modelled and these are compared with continuum plasticity models of the plastic zone.