Flexural creep tests and long-term mechanical behavior of fiber-reinforced polymeric composite tubes

An experimental investigation of the long-term creep behavior of fiber reinforced polymeric composite tubes subjected to flexural loading was performed. The tubes were first tested under a three-point bending scheme at room temperature to determine the ultimate flexural strength (UFS) and to identify the characteristic failure mode and possible failure locations. Creep tests were then carried out at stress levels of 45%, 55%, 65%, and 75% of the UFS at constant temperatures ranging from −60 °C to 100 °C for 500 h, and strain measurements over time were recorded. The tubes were further tested at varying temperatures by applying 22.5 thermal cycles between −60 °C and 100 °C and 9.5 thermal cycles between −160 °C and 80 °C. Similar flexural loads were applied simultaneously on the tubes. Long-term creep deformation of the tube was evaluated using the time-temperature-stress superposition principle, the derived creep main curves, and the Findley model. Finally, the creep deformation and mechanical strength of the tube at expected service conditions over its entire lifetime were predicted.