Strain rate dependence of the transition of dislocation sources from crack tips to grain boundaries based on the development of internal defect's stress field

Tomotsugu Shimokawa, Masaki Tanaka, Kenji Higashida

Research output: Contribution to journalArticle

Abstract

In order to investigate the mechanism behind the improvement of fracture toughness in ultrafinegrained metals at low temperatures, the strain rate dependence of the transition of dislocationsources from crack tips to grain boundaries is studied by the combination of molecular dynamicssimulations and the linear elastic theory. As the strain rate decreases, grain boundaries becomeanother stress consented site due to the pile-up of dislocations against the grain boundaries. Theamount of stress concentration became larger than that of crack tip as the number of dislocationsemitted from the crack tip increases. It was clearly indicated that dislocations were impinged intothe grain boundary when a new dislocation was emitted from there. It indicates the transition ofdislocation sources from the crack tip to grain boundaries at lower applied stresses. The distributionof dislocations between the crack tip and grain boundary is strongly related to the strain rate ; namely, a larger number of dislocations are distributed very close to the crack tip as the strain rate increases.It induces the smaller stress concentration at the grain boundary since the number of piling-updislocations is decreased around the grain boundary. Consequently, as the strain rate increases, thematerial becomes brittle, indicating that it will fail in a brittle mode and no longer deform plastically.

Original languageEnglish
Pages (from-to)169-174
Number of pages6
JournalZairyo/Journal of the Society of Materials Science, Japan
Volume61
Issue number2
DOIs
Publication statusPublished - Feb 1 2012

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crack tips
Dislocations (crystals)
Crack tips
stress distribution
strain rate
Strain rate
Grain boundaries
grain boundaries
Defects
defects
stress concentration
Piles
Stress concentration
piles
fracture strength
Fracture toughness
Metals
metals

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

Cite this

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abstract = "In order to investigate the mechanism behind the improvement of fracture toughness in ultrafinegrained metals at low temperatures, the strain rate dependence of the transition of dislocationsources from crack tips to grain boundaries is studied by the combination of molecular dynamicssimulations and the linear elastic theory. As the strain rate decreases, grain boundaries becomeanother stress consented site due to the pile-up of dislocations against the grain boundaries. Theamount of stress concentration became larger than that of crack tip as the number of dislocationsemitted from the crack tip increases. It was clearly indicated that dislocations were impinged intothe grain boundary when a new dislocation was emitted from there. It indicates the transition ofdislocation sources from the crack tip to grain boundaries at lower applied stresses. The distributionof dislocations between the crack tip and grain boundary is strongly related to the strain rate ; namely, a larger number of dislocations are distributed very close to the crack tip as the strain rate increases.It induces the smaller stress concentration at the grain boundary since the number of piling-updislocations is decreased around the grain boundary. Consequently, as the strain rate increases, thematerial becomes brittle, indicating that it will fail in a brittle mode and no longer deform plastically.",
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AB - In order to investigate the mechanism behind the improvement of fracture toughness in ultrafinegrained metals at low temperatures, the strain rate dependence of the transition of dislocationsources from crack tips to grain boundaries is studied by the combination of molecular dynamicssimulations and the linear elastic theory. As the strain rate decreases, grain boundaries becomeanother stress consented site due to the pile-up of dislocations against the grain boundaries. Theamount of stress concentration became larger than that of crack tip as the number of dislocationsemitted from the crack tip increases. It was clearly indicated that dislocations were impinged intothe grain boundary when a new dislocation was emitted from there. It indicates the transition ofdislocation sources from the crack tip to grain boundaries at lower applied stresses. The distributionof dislocations between the crack tip and grain boundary is strongly related to the strain rate ; namely, a larger number of dislocations are distributed very close to the crack tip as the strain rate increases.It induces the smaller stress concentration at the grain boundary since the number of piling-updislocations is decreased around the grain boundary. Consequently, as the strain rate increases, thematerial becomes brittle, indicating that it will fail in a brittle mode and no longer deform plastically.

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