Study on fatigue failure of glass fibre-reinforced thermoplastic pipe

The long-term fatigue performance of a glass fibre-reinforced thermoplastic pipe (RTP) is mainly determined by that of its glass fibre reinforcement layer. Glass fibre has an irregular network structure consisting of SiO4 tetrahedrons. In this network structure, there exists numerous defects. Under cyclic loading, cracks are initiated at these defects and grow steadily and perhaps even disruptively, ultimately leading to the fracture of the glass fibre. The mean stress corresponding to the occurrence of disruptive crack propagation is referred to as the critical fatigue stress. When the mean cyclic load is smaller than the critical value, the growing cracks stop propagating when in contact with high-energy chemical bonds. When the mean cyclic load is larger than the critical value, the glass fibre is doomed to fracture. In the present study, a series of fatigue tests was performed on a RTP subjected to cyclic loadings of different mean stresses. The numbers of cycles to failure at different mean stresses obtained from the tests were then used to estimate the critical fatigue stress of the RTP. The mechanism underlying the fatigue failure was analysed using fatigue mechanics and chemical bond theories.