Long-Term Degradation Behavior and Mechanism of Mechanical and Thermal Performance of C/GFRP Hybrid Rods

The hygrothermal resistance of fiber-reinforced polymer (FRP) is essential for civil engineering applications. In the present paper, carbon and glass fiber-reinforced polymer hybrid rods are immersed in distilled water to investigate the long-term degradation behavior and mechanism, and the influence of hybrid modes on hygrothermal resistance is evaluated. The research results show that the debonding of the fiber-resin interface induced by hygrothermal stress and plasticization impairs the cooperation among longitudinal fibers, resulting in a marked decline in tensile strength (10%–34%) and short beam shear strength (13%–47%). The combined effects of plasticization, resin hydrolysis, and interfacial debonding decrease the energy required for segmental movement of the resin matrix, leading to a 12%–42.1% drop in T_g retention. The degradation of mechanical performance strongly depends on fiber hybrid mode, CGH and UDH rods present higher short beam shear strength (SBSS) and tensile strength retention, respectively. Meanwhile, the dynamic thermal mechanical performance of hybrid rods is unaffected by the hybrid mode, as it relies entirely on the long-term hygrothermal resistance of the resin matrix.