Procedure to Experimentally Estimate the Long-Term Strength of Polymer Materials Using the Test Results for Ring Specimens

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A number of results obtained during the numerical finite element analysis of a procedure to test the ring specimens of polymer materials under internal pressure are discussed. The internal pressure is produced by the compression of an inset made of an incompressible material in the cavity of the specimen under test. The analysis is performed for the ring polyarylate specimens. The stress distributions in the specimen are obtained under constant load. It is shown that the stress distribution in the cross section of the specimen is not uniform for this type of loading. The effect of the elastic modulus and Poisson’s ratio of the loading inset on the tensile stresses in the specimen is studied. It is also shown that it is possible to use the maximum stress value or the stress intensity to estimate the long-term strength of polymer rings. The numerical results are used to estimate the durability of polyarylate sealing rings obtained by pressure casting at various temperature values. The experimental dependencies of time before fracture are given as functions of the maximum stress for the polymer specimens manufactured at the temperatures equal to 310 and 350° C. A new exponential dependence is proposed to approximate the experimental curves.