AN EFFECTIVE STRESS PARAMETER FOR LONG-TERM FATIGUE-STRENGTH OF FIBER-REINFORCED PLASTIC PIPES

The currently used American Society for Testing and Materials (ASTM) p rocedure and a modified American Petroleum Institute (API) method for cyclic pressure strength of fibre reinforced plastic (FRP) pipes are c ritically discussed together with the test results generated by Battel le. In addition, two new damage parameters, recently proposed by the a uthors, are examined using the Battelle tests as a database. An equiva lent stress range damage parameter, Delta<(sigma)over bar>, is recomme nded which combined the loading condition, hoop stress range and norma lized mean stress, and FRP pipe material properties. The proposed dama ge parameter, Delta<(sigma)over bar>, can be used in the engineering e valuation of fatigue performance of pressured fiberglass pipes. The De lta<(sigma)over bar> provides substantial improvement over the ASTM re commended parameter, hoop stress range. Using the Delta<(sigma)over ba r>, the fatigue data for different mean pressures are consolidated int o a narrow scatter band.