Guijun Xian

Durability study of pultruded carbon fiber reinforced polymer plates subjected to water immersion

Pultruded carbon fiber reinforced polymer plates have been widely used for structural rehabilitation due to their excellent mechanical properties. Even though, the long-term durability performance of carbon fiber reinforced polymer plates is still a concern, especially when subjected to harsh environmental conditions (e.g. water immersion). In the present study, the effects of water immersion at 23°C, 40°C, and 60°C on the degradation of the pultruded carbon fiber reinforced polymer plates were investigated in terms of water uptake and mechanical properties. To elucidate the degradation mechanisms, the resin matrix and the fiber and resin adhesion were also assessed in the same conditions. The test results indicated that water immersion, especially at higher temperatures, leads to serious fiber debonding, and thus the carbon fiber reinforced polymer samples absorb much more water than the resin matrix. In addition, the transverse flexural strength of the carbon fiber reinforced polymer plates, closely correlated to the fiber–resin adhesion, reduced significantly at high temperatures. On the contrary, the resin matrix and carbon fiber reinforced polymer plates show much less degradation subjected to the same immersion conditions. Therefore, to comprehensively understand the long-term durability of a carbon fiber reinforced polymer material, it is necessary to test the variation of the bonding strength between fiber and resin matrix, in addition to the tensile performances in fiber directions of the carbon fiber reinforced polymer plates.

Comparative Study of the Durability Behaviors of Epoxy- and Polyurethane-Based CFRP Plates Subjected to the Combined Effects of Sustained Bending and Water/Seawater Immersion

In many applications, carbon fiber reinforced polymer (CFRP) composite materials suffer from the combined effects of sustained bending and immersion. In the present study, pultruded epoxy- and polyurethane (PU)-based CFRP plates were studied for their long-term performances, subjected to the combined effects of water/seawater immersion and sustained bending (0%, 30%, and 58% of the ultimate strain). The water uptake and the evolution of the mechanical properties were investigated. In addition, the service lives of the CFRPs were predicted using the Arrhenius method. Generally, the sustained bending led to a decrease in the water uptake, and reduced the mechanical properties. A diffusion model, dividing the cross-section of CFRPs into the “less resin area” and “rich resin area”, was proposed to elucidate the variation of water uptake and mechanical properties. Compared to epoxy-based CFRPs, although PU-based CFRPs possessed a significantly higher water uptake, they exhibited better long-term performances in terms of mechanical properties.

Effects of surface grafting of copper nanoparticles on the tensile and bonding properties of flax fibers

Abstract In the present work, functionalized copper nanoparticles (FCuNPs) were grafted onto flax fibers, and the effects on the tensile properties, bonding strength to an epoxy resin, as well as the properties of the flax fiber-epoxy model composites were investigated. The copper nanoparticles were synthesized at ambient temperature by a chemical reduction method. The reduction of solution of copper chloride salt in the polyvinylalcohol medium was done by using sodium borohydrate. Ultraviolet-visible spectroscopy, transmission electron microscopy, and X-ray diffraction studies were used to characterize the size of the synthesized particles. The synthesized copper nanoparticles were applied to saturate the unidirectional flax natural fibers, whose surfaces were previously tailored with the cationic agent triethylammonium chloride. A remarkable improvement in the tensile strength by 75% and modulus by 50% for FCuNPs grafted flax fibers was found. Thermo-mechanical properties of the flax fiber reinforced epoxy composites were studied using DMTA. Finally, the anti-microbial analysis for composites was also conducted against Aspergillus niger spores, and enhanced anti-microbial performance was observed for treated fiber-based composites.

Modeling of moisture diffusion in CFRP strengthened concrete based on thermal-moisture analogy

In this paper, the thermal-moisture analogy schemes were applied to simulate moisture diffusion in an epoxy resin and CFRP strengthened concrete system numerically. The two thermal-moisture analogy schemes were adopted for homogeneous material (e.g., epoxy adhesive) or multi-component material systems. The direct analogy (DA) is only valid for the homogeneous material system and can simulate the moisture diffusion in an epoxy adhesive accurately. The normalized analogy (NA) was proved be an effective tool for the CFRP-concrete system. In addition, based on NA, the interfacial stress and swelling stress induced by water can be simulated accurately