Interfacial Evaluation of Wind Blade Carbon Spar-Cap Depending on Elimination Method of Intermediate Medium

An Ultrasonic Test (UT), a type of non-destructive test, is used to inspect the manufacturing integrity of carbon spar-caps of wind blades. When performing a UT, an intermediate medium is used to improve the signal detection ability between the inspection target and the probe. However, if the intermediate-medium residue is not removed, it acts as a contaminant in the interface between the spar-cap and the blade skin. This has a negative effect on the adhesion characteristics. A quantitative method is required for removing the intermediate medium and peel ply after the UT. After the UT, the interfacial characteristics of the spar-cap surface are examined according to the method of removing the intermediate medium in this study. The static contact angle and the work of adhesion (Wa) were measured according to various surface treatment conditions. In addition, shear strength of the Carbon Fiber-Reinforced Plastic (CFRP) spar-cap was evaluated by the lap shear test. An optimized method of peel-ply removal combined with an intermediate medium was found in this study. An optimal guideline for intermediate-medium treatment could be proposed when evaluating the manufacturing integrity of real wind blade spar-caps using UT.