Combined effects of temperature, hydraulic pressure and salty concentration on the water uptake and mechanical properties of a carbon/glass fibers hybrid rod in salty solutions

Pultruded unidirectional large-diameter (19 mm) carbon/glass fiber hybrid rods were used to investigate the coupling effects of elevated temperature and hydraulic pressure on water uptake and mechanical properties in salty solutions. Salty solutions with different salty concentrations at 60 °C and 80 °C with and without a hydraulic pressure of 20 MPa were selected as immersion media and the hybrid rods were immersed for half of a year. A self-designed hydraulic pressure device was applied for immersion and a new testing device was designed to obtain the interface shear strength (ISS) of the fiber and epoxy. Radial and longitudinal water uptakes of the hybrid rods were found to follow the classic Fick law. Elevated temperature and hydraulic pressure accelerated the diffusion of water molecules; while the salty concentration exhibited a negligible effect. The radial diffusivity in the hybrid rods was larger than longitudinal diffusivity due to the absence of “fiber barrier action”. Elevated temperatures led to an obvious decrease in the interface shear strength of the glass fiber shell, carbon fiber core, and shell–core interface. The interface shear strength of the shell–core interface was most susceptible to the immersion, and long-term stable retention was predicted to be ~54.2%, regardless of the immersed temperature and hydraulic pressure.