Fatigue performance analysis of GRE composite pipes by conducting tension-tension tests on the rings cut from the pipe

The main purpose of this study is to analyze the fatigue behavior of an industrial (±55°)₉ filament-wound glass reinforced epoxy pipe. Fatigue tests are conducted in accordance with ASTM D2992, Standard Practice for Obtaining Hydrostatic or Pressure Design Basis for Fiberglass (Glass-Fiber-Reinforced Thermosetting-Resin) Pipe and Fittings, but instead of the entire pipe, rings cut from the pipe are used in the tests. This standard proposes a frequency of 0.42 Hz and stress ratio of R=0.05. Tension-tension fatigue tests are performed on the rings at different load levels from 60 to 90 % of the ultimate hoop strength of the pipe. After the tests, the maximum pressure and maximum hoop stress curves versus the number of cycles to fatigue failure are presented. A comprehensive discussion about the importance of substituting the ring test method with ASTM D2992 standard test methods to determine the long-term performance of the composite pipes in the future is presented. The microscopic fatigue failure mechanisms of the rings are also characterized and interpreted using a scanning electron microscope.