Prediction of Interfacial Performance of Fiber Reinforced Hybrid Rods: Time–Temperature Equivalence and Diffusion Theory

The penetration of water molecules reduces the interfacial shear strength (ISS) of fiber-reinforced polymer composites, diminishing their long-term operational effectiveness. This study investigates the water absorption behavior and the time-dependent evolution of the ISS in a pultruded carbon-glass fiber-reinforced hybrid rod. The life evolution of ISS for the hybrid rod under water immersion was predicted while employing the time–temperature equivalence principles and diffusion theory. The results show that higher aging temperatures enhanced the diffusion process of water molecules and reduced ISS. Hygrothermal aging induced resin plasticization and interfacial debonding, resulting in a reduction of ISS retention by up to 8.6%–32% after immersion for 403 days, while ISS retention increased by 5.6%–11.8% after drying for 90 days. The prediction model in the time–temperature equivalence theory was derived from the empirical analysis of experimental data, while the diffusion theory examined the quantitative impact of water molecules on ISS. The diffusion-based prediction results exhibited greater agreement with water diffusion behavior and more accurately reflected the actual ISS degradation in the service environment compared to the time–temperature equivalence theory. The time–temperature equivalence and diffusion-based models predicted similar stable ISS retention values of 65.15% and 65.67%, respectively. Moreover, the first stage of water immersion had a significant effect on interfacial performance, and a stable retention of ISS was achieved upon saturation of the hybrid rod with water.