Effect of hygrothermal and bending loading coupling on the long-term durability of C/GFRP hybrid rods

The long-term bending loading is a key influence factor on hygrothermal durability of fiber reinforced polymer (FRP), which decreases the long-term service performances of FRP and its reinforced structures. In the present study, the effect of bending loading on water absorption behavior and the evolution of thermal and mechanical performances of C/GFRP hybrid rods is investigated. The acceleration mechanism of bending loading on the degradation of mechanical performances is conducted through microstructure characterization analysis. The long-term life prediction model is established to evaluate the hydrothermal and bending loading resistance of hybrid rods. The research results show that the resin cracking and interfacial debonding damage caused by long-term bending loading provides more diffusion space for water molecules, which results in the water absorption curve of GFRP and GFRP shell-CFRP core coated hybrid (CGH) rods deviating from the Fick's diffusion behavior. The more ingression of water molecules significantly weakens the fiber-resin interfacial performance, and the shear strength of the fiber-resin interface degrades 22.2–29.0 % after aging for 180 days under 50 % stress level. Furthermore, the interfacial debonding leads to the fiber instability in the compressive zone, which results in 11.2–87.1 % degradation for bending strength of hybrid rods after aging for 180 days under 50 % stress level. The debonding of the fiber-resin interface is the main factor leading to the degradation of the mechanical performances of hybrid rod, and the instability of the fiber in the compression zone under bending loading further aggravates the degradation of the mechanical performances. The effect of hybrid mode on long-term bending performance of hybrid rods is significantly, the uniform dispersion hybrid (UDH) and CFRP shell-GFRP core coated hybrid (CGH) rods avoid the severe damage in the compression zone, which shows superior hygrothermal and bending loading resistance. The life prediction shows that the stable retention of bending strength of CFRP,GFRP,UDH,GCH and CGH rods is 52.8 %,30.2 %,66.1 %,0 % and 89.0 %, respectively. The prediction results provide key parameters for the durability design of hybrid rods under bending loading.