Dynamic simulation of dislocation microstructures in mode III cracking

Journal Article · Mon Sep 01 04:00:00 EDT 1997 · Acta Materialia

DOI:https://doi.org/10.1016/S1359-6454(97)00029-3· OSTI ID:540955

Zacharopoulos, N; Srolovitz, D J ^[1]; Lesar, R ^[2]

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1. Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Materials Science and Engineering
2. Los Alamos National Lab., NM (United States)

The authors have developed a new, self-consistent simulation method for modeling crack growth with dislocation generation and motion in constant-loading-rate, Mode-III fracture. The dislocation emitted from the crack initially self-organize and propagate in very sharply defined lines. These lines undergo bifurcations, forming multiple new branches and shortening the initial line. The growth and bifurcation of these lines occurs repeatedly. Away from the crack, a highly structured plastic zone is formed that is approximately elliptical in shape with a dislocation free zone along its mid-plane. The rate of generation of new dislocations is limited by the rate at which previously generated dislocations move away from the crack up. this rate is controlled by the crack loading rate {dot K}{sub III} and the dislocation mobility. The size of the plastic zone scales as (K{sub III}{sup 2}/{dot K}{sub III}){sup 2 3}. The crack tip stress intensity factor K{sub tip} is very much smaller than the applied stress intensity factor. K{sub tip} increases sub-linearly with the load and exhibits both jumps and serrations corresponding to instabilities in the dislocation microstructure. K{sub tip} increases, however, with increasing loading rate at fixed load and a transition is seen between brittle and ductile behavior with decreasing loading rate. Crack propagation occurs when dislocations cannot be generated at the crack tip at a rate sufficient to counterbalance the increasing loading. This generation rate increases with increasing dislocation mobility. Since dislocation motion is thermally activated, this demonstrates that the brittle-to-ductile transition is ultimately controlled by dislocation migration.

• OSTI ID: 540955
• Journal Information: Acta Materialia, Journal Name: Acta Materialia Journal Issue: 9 Vol. 45; ISSN 1359-6454; ISSN ACMAFD
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BRITTLE-DUCTILE TRANSITIONS
CRACK PROPAGATION
DISLOCATIONS
FRACTURE MECHANICS
FRACTURE PROPERTIES
MATERIALS
MICROSTRUCTURE
SIMULATION
STRESS INTENSITY FACTORS