Effects of Cold Temperature, Moisture and Freeze-Thaw Cycles on the Mechanical Properties of Unidirectional Glass Fiber-Epoxy Composites

Abstract

´The durability of composite materials used for wind turbines blades exposed to a northern climate presents uncertainties as their behavior for very cold temperature applications is not completely understood. The goal of this project is to confront actual theories to experimental results for mechanical properties of unidirectional glass-epoxy composites exposed to moisture, cold temperature and freeze-thaw cycles. Tests were made at ambient temperature and -40℃ on four sample families. The families consisted of either dry or moisture saturated specimens, of which half of the families were further conditioned with 100 freeze-thaw cycles between -40℃ and 40℃. Tensile, compressive and short beam shear tests were conducted. Results showed the inadequacy of classical theories for predicting strength of the specimens exposed to low temperature and/or moisture. Contrary to the results presented in most of the literature, freeze-thaw cycles did not significantly change the strength or modulus of the test specimens. However, low temperature provided an important increase in strength while modulus was retained. Moisture had a stronger effect on properties than models would predict but there was no evidence of a synergistic effect between moisture and temperature. Comparison of the results with those presented in the literature shows that the behavior of composites exposed to low temperatures or freezethaw cycles is very sensitive to the nature of the constituents and the molding process used to produce the parts.