A procedure for experimental estimation of the long-term strength of polymer materials using the test results of ring specimens

The results of numerical analysis of stress state of annular specimens of a polymer material under internal pressure are presented. The internal pressure is produced by the mean of compression of an incompressible inset in the inner cavity of the specimen. The calculations were carried out for ring specimens of polyarylate. The calculated stress distribution in specimen was obtained at a constant load. It was shown that the stress distribution in the cross-section of the specimen is not uniform for the considered type of loading. The effect of the elastic modulus and the Poisson's ratio of the loading inset on the tensile stresses in the specimens 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 evaluate the durability of polyarylate sealing rings produced by injection molding at different values of the polymer melt temperature. The experimental time dependencies before fracture on the maximum stress value are presented for specimens manufactured at the temperatures of 310 and 350$^{\circ}$ C. A new exponential equation is proposed for the approximation of experimental curves.