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The fracture behavior of a polyurethane elastomer in a hydrostatic tensile field has been experimentally studied via the ``poker-chip test.'' Microscopic examination of the material revealed residual gaseous bubbles, which were taken as fracture nucleation points. A study of the cavity behavior up through fracture initiation and propagation led to a determination of the fracture stress level, the identification of two regimes, or modes, of fracture, and the associated velocities of propagation.
Gerald H. Lindsey (Wed,) studied this question.