Effects of elevated temperature, hydraulic pressure and fatigue loading on the property evolution of a carbon/glass fiber hybrid rod

Abstract

A carbon fiber core (CFC) and glass fiber shell (GFS) hybrid rod (HFRP) with the diameter of 22 mm was developed to replace the steel rod in the application of underground oil extraction. In the present study, the variation in the properties of the hybrid rod served for 553 days was investigated subjected to the coupling conditions of elevated temperature (T), hydraulic pressure (P) and fatigue load (L)/stress level peak (S), one exposure condition, closed to the ground (T = 25 °C, P = 0.5 MPa, Lmax/S = 70 kN/11.1%) and another in the underground oil-well up to 2600 m (T = 90 °C, P = 18 MPa, Lmax/S = 50 kN/7.9%). Exposed in the deep oil-well condition led to an extra degradation of interface shear strength (ISS) compared to the ground exposure. The degradation mechanism of ISS was attributed to the hydrolysis and plasticization of resin owing to formed multiple hydrogen bonds between the water molecule and chain structures of resin. The removal of free water from the hybrid rod brought about an average increase percentage of ISS, ~10.0% for the upper rod and ~7.4% for the bottom rod. Furthermore, the maximum recovery of ISS was observed for the removal of bound water for the drying at 100 °C for 14 days. The fatigue performance evaluation of hybrid rod exposed in underground oil-well condition showed the optimal rod diameter for the present fatigue load condition (Lmax/S = 70 kN/11.1%) was 19 mm with the service life of ~50 years. Furthermore, the applied maximum fatigue load was obtained to be 114.3 kN with the fatigue life of 22.6 years for the present hybrid rod.