Abstract
This work evaluates the mechanical properties of the glass fiber reinforced polymer (GFRP) material taken from an out of service 100 KW power wind turbine blade which has been in service life of 20 years old. Investigated samples were taken from two positions of undamaged regions at 1.6 m and 5.4 m from the rotor hub, respectively. Microstructure investigation and lay-up analysis were carried out. Fiber weight fraction of the investigated samples was ranging between 0.55–0.60. Tensile and compression tests were carried out at the temperature range from −10 °C to +50 °C on specimens which were machined so as to be loaded in the blade length direction LD, transverse to the blade length TD and off axis; 45° to the blade length. Tensile elastic modulus of the investigated GFRP was determined in the three direction tested. The number of fiber fabric layers found to be decreasing along the blade length away from the root and the density of the fibers along the length is the highest (858 gm/mm2) and in the transverse direction is the lowest (83 gm/mm2). The microstructure of the GFRP composite showed good wetting for the fiber by the polymer with some features of lack of penetration at the high density fiber bundles and some production porosity in the matrix. The tensile Properties at room temperature (RT) and high temperature are almost similar with the highest properties for the samples aligned with the blade length. The compressive strength is highest at the transverse direction samples and lowest at the blade length direction and decreasing with the increase of the test temperature. The bending properties are significantly affected by the fiber orientation with the highest properties for samples aligned with the blade length and the lowest for the samples with the transverse direction.
Highlights
The stacking sequence of the fiberglass fabric layers from the bottom layer which represents the internal surface of the blade to the gelcoating which represents the outer surface is shown in Figure 2, for sample 2
It can be noted that the total number of fiber fabric layers in this sample is 13 layers with the orientation shown in the figure
That the number of the fiber fabric layers found to be 11, 13, and 19 for samples 1, 2 and 3, respectively, which correspond to sample thicknesses of 4.8 mm, 5.6 mm, and ~8.6 mm, respectively
Summary
The high material stiffness is required to maintain optimal aerodynamic performance, the low density is required to reduce self-loading and gravity forces, and the long-fatigue life is required to reduce material failure and degradation [1]. To meet these requirements, the material of choice is based on fiber-reinforced polymers, wood, and combinations of them [2]. The laminated fabrics are combined in layered structure using thermosetting polymers, such as polyester, or epoxy [1,2,3] This composite material is commonly referred to as glass fiber reinforced polymer (GFRP) [1]
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