Effects of moisture on glass fiber-reinforced polymer composites

Abstract

Glass fiber polymer composites are used in wind turbine blades because of their high-specific strength and stiffness, good fatigue properties, and low cost. The wind industry is moving offshore to satisfy economies of scale with larger turbines. High humidity in this environment degrades mechanical performance of wind turbine blades over their lifetime. Here, environmental moisture conditions were simulated by immersing glass fiber-reinforced polymer specimens in salt water for a period of up to 8 years. The mechanical properties of specimens were analyzed before and after immersion to evaluate the degradation mechanisms. Single-fiber tensile testing was also performed at different moisture conditions. The water-diffusion mechanism was studied to quantify the diffusion coefficients as a function of salt concentration, sample geometry, and fiber direction. Three degradation mechanisms were observed: polymer plasticization, fiber stress corrosion, and interface degradation, where the latter was found to be the most detrimental for wind-industry applications.

Hygrothermal chamber aging effect on mechanical behavior and morphology of glass fiber-epoxy-nanoclay composites

“…Similarly, the reduction in tensile modulus decreased to 17 and 15% at 40 wt%, 15 and 11% at 50 wt%, and 10 and 8% at 60 wt% of glass fiber. Epoxy's resistance to moisture absorption is increased by incorporating both glass fiber and nanoclay, which can be attributed to an improvement in the tortuosity path for water molecules to penetrate [36,37]. Table 6 shows that the weight percentage increase in glass fiber has improved the flexural properties of GFENCs.…”

Research needs concerning the performance of fiber reinforced (FR) composite retrofit systems for buildings and infrastructure

“…Furthermore, moisture-induced degradation, or hydrolysis, of the glass fiber coating (also called a sizing) that promotes fiber/matrix adhesion, can decrease the adhesion between the glass fibers and the matrix [32,33]. Stress corrosion, or moisture-induced degradation of fibers while under static fatigue, is another issue in which water molecules can extract cations from glass (i.e, leaching) to facilitate hydrolysis reactions (e.g., bond-breaking within glass structure with loss of water) of glass fibers (and glass fiber sizings) often at defect sites/microcracks, causing these defect sites/microcracks to expand [33,34]. The severity of both moisture-induced degradation mechanisms can be enhanced under both acidic and alkaline conditions (Table 2.1) [34].…”

“…For fibers, the UV-resistance of glass and carbon reinforcing fibers are typically better than polymer fibers (aramid fiber like Kevlar) [33,34].…”

“…For the FRP composite (fibers + polymer matrix), environmental degradation processes can lead to debonding between the fiber and matrix, matrix cracking, and interlaminar debonding, or debonding between the FRP composite layers [87]. For all fibers, moisture uptake can disrupt the interfacial regions between the polymer matrix and the fiber sizings (i.e., coatings for fiber/matrix compatibility) or surface treatments [33,88]. For glass fibers in particular, moisture can even hydrolyze silane-based sizings, which can detrimentally affect fiber/matrix adhesion [33,34].…”

“…For all fibers, moisture uptake can disrupt the interfacial regions between the polymer matrix and the fiber sizings (i.e., coatings for fiber/matrix compatibility) or surface treatments [33,88]. For glass fibers in particular, moisture can even hydrolyze silane-based sizings, which can detrimentally affect fiber/matrix adhesion [33,34].…”