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Mode I Large Strain Viscoelastic Crack Behavior in Nitrile Rubber Sheets.
ARMY RESEARCH LAB WATERTOWN MA MATERIALS DIRECTORATE
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A finite element analysis of a Mode I crack in a viscoelastic, hyperelastic, and incompressible material was performed under relaxation conditions. Loading of the finite element model was applied until the far field strain reached 50 the viscoelastic material was then allowed to relax for 15 minutes. The numerical results were compared to experimental material behavior. The applied load and stretch ratio histories obtained from the finite element analysis agreed closely with experimental results. The S22 stress component was the dominant stress and possessed a singularity of or-1, similar to the asymptotic solution for a mechanical crack tip stress field, which does not include viscoelasticity, in a hyperelattic material. The order of the singularity did not change with relaxation. Examination of the crack tip stress field showed that maximum stresses were found close to the crack surface suggesting that crack propagation should initiate above and below the deformed crack tip. MM
APPROVED FOR PUBLIC RELEASE