Durability Study Of Pultruded CFRP Plates Under Sustained Bending Immersed In Water And Seawater

Fiber reinforced polymers (FRP) are used in almost every type of advancedengineering structure, with their usage ranging from aircraft, helicopters, spacecraft andcivil engineering infrastructures. FRPs are lightweight, exhibit high specific strengthand specific stiffness, and can be tailored to satisfy various performance requirements.However, lack of data for long term durability limits the usage of FRP compositematerials in various service environments such as marine and water immersions.Numerous studies have been carried out to study the durability of FRP composites underhygrothermal conditions only and very few attempts have been made to study thecombined effects of immersion and sustained bending strain on durability of CFRP.In this study, the durability of unidirectional pultruded CFRP plates immersed inwater and seawater at room temperature, under sustained bending strains of30%and50%of ultimate strain was investigated. The synergic effects of water absorption andsustained bending strain on mechanical properties and visco-elastic properties of thecomposite were assessed over20week of immersion. The effects of sustained bendingstrain on water absorption kinetics were investigated in relation to the changes in freevolume fraction of the composite. The tensile, short beam shear and DMA based testswere employed to study the variation of tensile properties and visco-elastic propertiesi.e., storage modulus and the variations of glass transition temperature with wateringress.It was found that increasing level of sustained bending strain can cause reduction inwater uptake due to the reduction in free volume fraction of the polymer matrix. Theequilibrium moisture content of seawater was shown to be slightly higher than waterimmersed samples, and this is attributed to the blister induced damages as result of thegalvanic action between carbon fibers and active metals in seawater. The diffusioncoefficient of CFRP in seawater immersion was indicated to be lower than waterimmersion due to the high concentration of dissolved particles in seawater that retardmoisture diffusion by osmosis. Both water and seawater immersed samples exhibitedprogression of postcuring with water ingress which improved tensile properties, storagemodulus and glass transition temperature of CFRP composite.It was revealed that the increase in water content in both water and seawater tendsto degrade the composite tensile properties, interlaminar shear strength, and glasstransition temperature and storage modulus by plasticization in a short term and resinhydrolysis in a long term. High rate of degradation of interlaminar shear strength wasindicated in seawater in the initial stage of immersion.