Influence of immersion in water under hydraulic pressure on the interfacial shear strength of a unidirectional carbon/glass hybrid rod

A pultruded unidirectional carbon/glass (core/shell) hybrid rod of 19 mm in diameter was developed for marine applications. To understand the long-term evolution of the mechanical properties of the rod in service, a pressure chamber device with adjustable hydraulic pressure and a self-designed interfacial shear strength (ISS) setup were developed. Immersion in water was performed at 20 degrees C, 40 degrees C, and 60 degrees C without hydraulic pressure or at 60 degrees C with a hydraulic pressure of 20 MPa for one year. Dynamic mechanical analysis (DMA) was conducted to analyse the thermal properties of the hybrid rod. Post curing, indicated by the increase in the glass transition temperature (T-g), was pronounced during immersion. ISS of the shell, core and shell/core interfaces was sensitive to water immersion and decreased after 360 days. A linear decrease of ISS with the exposure temperature was observed. The hydraulic pressure had a positive effect on ISS, especially for the GFRP shell. The evaluation of the long-term behaviour indicated that ISS will decrease to a stable level of 74.8% for glass fibre/resin, 57.8% for carbon fibre/resin and 69.9% for the interface between the carbon fibre core and the glass fibre shell.