Monitoring of water absorption and its effects on mechanical performance of thick GFRP structures by integrated smart sensors
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In many applications, such as offshore, marine, or wind energy industry, the aging of composites is an
important issue, as the structures are exposed to severe environmental conditions. Typically, moisture
gradients evolve from the surfaces in contact with moisture or water into the material. The underlying
diffusion process depends on the ambient temperature and the specific material selection (e.g. the
chemical structure of the polymeric resins). In this context, fiber reinforced polymers (FRP) are often
assumed to exhibit approximately Fickian diffusion behavior. Long term predictions are based on
isothermal aging tests, which are usually accelerated by full immersion of coupons in water with
higher temperatures than the service temperature [1]. Design parameters are derived from small-scale
coupon tests with saturated specimens. However, for FRP structures of several millimeter thickness in
real operating conditions, it takes years until the laminates are fully saturated. As it is well known that
especially glass fiber reinforced polymers (GFRP) can experience significant reductions in mechanical
properties due to moisture absorption, a reliable determination of the current moisture condition at
various points in the structures is beneficial. Precise knowledge about the effects of moisture on the
mechanical behavior of the composites can, furthermore, extend the service life and prevent failure.
Consequently, a method for monitoring local moisture absorption in thick GFRP laminates is
presented in this work. Therefore, an integrated sensor system based on single carbon fiber (CF)
bundles and impedance measurements as developed by Buggisch et al. [2] was evolved. Additionally,
the mechanical effects of single-sided moisture absorption (only through thickness) are evaluated
using four-point bending (FPB) and interlaminar shear strength (ILSS) tests
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