Author(s): Harold J. Frost; Timothy R. Smith
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Abstract: In this paper we report both experimental observations of crack nucleation and modeling of the crack nucleation process. In the experiments, cracks were generated in both fresh-water columnar ice and saline columnar ice by pulsed, biaxial loading in directions perpendicular to the columns. Cracks originate from the triple junctions where three grain boundaries meet, and they usually follow one of the boundary planes. Cracks may be observed optically in bulk specimens of fresh-water ice, or in thin sectioning for saline ice. Crack nucleation at triple points during high strain-rate deformation is expected to result from stress singularities which are due to the anisotropy of the elastic constants. We have modeled this process to discover how the various elements of microstructure should effect the stresses required for nucleation. We find that the nucleation stress should scale with grain size according to the exponent which describes the stress singularities at the triple points, which is generally different from the commonly expected scaling relationship of inverse square-root of grain size.
Year: 1992