Phase-Field Analysis of Fracture-Induced Twinning in Single Crystals

Abstract

Deformation twinning at the tip of a straight crack or notch is analyzed using a phase-field method that seeks equilibrium twin morphologies via direct minimization of a free energy functional. For isotropic solids, the tendency to twin under mode I or mode II loading is found to depend weakly on Poisson s ratio and elastic nonlinearity and strongly on surface energy and twinning shear (i.e., eigenstrain). Depending on the coherent twin boundary energy, anisotropy of surface energy is important for mode I loading but less so for mode II. Model predictions for several single crystals are in agreement with experimental observations. Calcite demonstrates a preference for mode I cleavage crack extension over crack tip twinning. Magnesium shows a likelihood for tensile twinning from a pre-existing crack on the basal plane. In sapphire, a preference for rhombohedral twins over basal twins is apparent, with the latter thinner in shape than the former.

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Document Details

Document Type
Technical Report
Publication Date
Jul 01, 2013
Accession Number
ADA585924

Entities

People

  • J. Knap
  • John D. Clayton

Organizations

  • United States Army Research Laboratory

Tags

Communities of Interest

  • Energy and Power Technologies

DTIC Thesaurus Topics

  • Anisotropy
  • Boundaries
  • Computational Science
  • Coordinate Systems
  • Crack Tips
  • Cracks
  • Crystal Structure
  • Crystallography
  • Crystals
  • Free Energy
  • Materials
  • Mechanics
  • Physical Properties
  • Single Crystals
  • Surface Energy
  • Three Dimensional
  • Two Dimensional

Readers

  • Materials Science and Engineering.
  • Structural Health Monitoring of Composite Structures.