Determination of as-built properties of fiber reinforced polymers in a wind turbine blade using scanning electron and high-resolution X-ray microscopy

The fiber volume fraction (FVF) and porosity in fiber reinforced polymers (FRPs) depends strongly on the manufacturing process. These parameters influence the mechanical properties and thus the performance of an FRP. For this research, an epoxy-pre-impregnated glass FRP was investigated to determine the FVF and matrix mass fraction taking into consideration all material constituents, including sizing, stitching thread, as well as the porosity, the area density and the fiber orientations of each lamina, the filament fiber diameter, and the inter-laminar void size and shape. Therefore, samples from a commercially manufactured wind turbine rotor blade were experimentally investigated using scanning electron (SEM) and high-resolution X-ray microscopy (micro-CT), as well as a standardized calcination method and geometric measurements. Post-processing techniques such as thresholding and edge detection were used to analyze the images. There was good FVF agreement between SEM and the method of calcination. Micro-void cross-sectional shapes were well captured by SEM while meso- and macro-voids were volumetrically resolved with a reproducible void size distribution for two sample volumes by micro-CT.