Experimental/numerical study of anisotropic water diusion in glass/epoxy composites

Abstract

In this work a glass/epoxy composite commonly used in wind turbine blades is exposed to a humid environment at an elevated temperature. To research the anisotropic di_usion behaviour observed in unidirectional composite specimens, experimental results of slices cut along the three directional planes of the laminate immersed in demineralised water at 50_C are coupled with numerical modelling. The weight of the slices was measured at regular intervals, from which the uptake behaviour could be deduced. The process was modelled using a 3-dimensional RVE of the material, where di_usion is modelled as steady-state and the di_usivity in each direction was measured by applying concentration gradients to the model. The experimental data shows similar water uptake behaviour for samples in both transverse directions, while the water uptake in the _bre direction was signi_cantly faster. A proper _t according to Fick's law was obtained for the transverse direction, while this was not possible for the samples in _bre direction, suggesting a strong dependency of the di_usion behaviour on the _bre orientation. Results from the proposed numerical models show that the geometric e_ect of _bres acting as barriers for the water movement is indeed responsible for part of the observed anisotropy.