High angle grain-boundary effects and microstructurally induced failure mechanisms in crystalline materials

Conference · Sun Dec 31 04:00:00 EST 1995

OSTI ID:175400

Zikry, M A; Kao, M ^[1]

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1. North Carolina State Univ., Raleigh, NC (United States)

An investigation of the thermo-viscoplastic finite strain slip deformation and failure of crystalline materials has been conducted. A theoretical and a computational constitutive formulation are introduced to characterize material failure on the micromechanical scale needed to determine the failure mode in crystalline materials separated by high angle tilt grain boundaries. A thermo-mechanical methodology is developed for the prediction of the formation and the evolution of material damage that may arise due to dislocation pile-ups at the grain boundary. The failure model is based on the interaction of the dislocations at the grain-boundary with the plastic slip on the active slip systems in each grain. The coupled effects of grain boundary orientation, dislocation densities, strain hardening, strain rate sensitivity, and geometrical and thermal softening are shown to be the dominant mechanisms in the evolution of failure in crystalline materials. The major objective of the present study is to deter-mine the influence of a class of high angle grain-boundary orientations on the deformation and the failure of metallic f.c.c. and b.c.c. crystalline materials. The constitutive formulation is based on a crystal line plasticity multiple-slip formulation, where the flow stresses are coupled to the dislocation densities at the grain-boundary. Estimates are obtained, based on limiting values of the dislocation densities, to deter-mine the conditions that govern shear-band formation and cleavage fracture in crystalline materials. Results from the present analysis and comparisons with experimental studies and observations, indicate that transgranular fracture, intergranular fracture, and shear band formation can be characterized in terms of the material competition between the strengthening and the softening mechanisms of the crystalline structure.

• OSTI ID: 175400
• Report Number(s): CONF-950686--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CRYSTAL STRUCTURE
CRYSTALS
DEFORMATION
DISLOCATIONS
GRAIN BOUNDARIES
MATERIALS
PLASTICITY
SENSITIVITY
SHEAR
SLIP
STRAIN HARDENING
STRAIN RATE
STRESSES