HYDROSTATIC TENSILE FRACTURE OF A POLYURETHANE ELASTOMER
Final rept. Oct 1964-Oct 1965
CALIFORNIA INST OF TECH PASADENA GRADUATE AERONAUTICAL LABS
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The investigation of fracture of polymeric materials in hydrostatic tensile fields constitutes an avenue of approach to the study of fracture in more general three-dimensional environments. The advantages created by the symmetry of the stress field are considerable and, on one of the cases studied, facilitates a theoretical treatment that includes large deformations, which are characteristic of this class of materials. The analysis is developed through the concept of fracture originating from a flaw, which in this instance is taken to be a spherical cavity. Through the application of energy principles, a theoretical prediction of ultimate strength is made for hydrostatic tensile fields. Experiments were conducted to demonstrate the existence of such flaws and to evaluate the theory. Results of the tests on specimens containing both residual flaws and artificially inserted ones indicate a fundamental difference in behavior as contrasted with cracks. An explanation is given linking experimental results and theoretical predictions. It is based on the concept that a flaw grows in the material under load using the cavity as a nucleating point. Upon this hypothesis is built a theory of rupture in which planar cracks grow radially from the center of the cavity in the form of Saturn- ring cracks.
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