Development of surface preparation procedure recommendations for wind turbine blade field repairs
Lusty, Ariel Francis
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Wind turbine blades necessitate reliable field repairs. However, the effects of current wind turbine field repair surface preparation techniques were not well- documented. Poorly informed surface preparation procedures lead to poor quality repairs, so surface preparation procedure recommendations for wind turbine blade field repairs were developed. The effectiveness of current surface preparation techniques, the effects of contaminants, and alternative techniques were evaluated. Current surface preparation techniques involve using solvent wiping to remove contamination. Results indicated that solvent wiping does not significantly affect bond strengths, but solvents can gel resin surfaces. Measuring the changes in bond strengths due to contamination from composite dust and hydraulic oil with time indicated that contamination diffusion effects along bond lines were negligible, but that composite dust and hydraulic oil diminished bond strengths. Contaminants should thus be removed from bond line surfaces prior to repairs. The goal of considering alternative techniques was to increase and equalize the surface energy of repair surfaces using plasma or sizing. There were significant drops in contact angles on composite surfaces treated with plasma, so plasma treatments should continue to be considered for composite surface preparation methods. To examine sizing effects, sizing was applied to scarfed surfaces and specimens were tested in tension. Applying sizing to tapered surfaces prior to scarf repairs did not affect scarf tension ultimate stress values, failure modes, or failure surface elemental composition. In addition, there was a stiffness reduction in the scarfed specimens compared to unscarfed specimens, indicating that the scarf tension repair did not fully restore the composite plate's original properties. Scarf tension experiments were simulated using finite element analysis and results had good agreement between the experiments and the model. The surface preparation recommendation is to test whichever surface preparation methods and adhesive-substrate combinations are used for a repair prior to implementation in the field. Implementing testing of surface preparation methods with adhesive-substrate combinations into surface preparation procedures will decrease lifetime costs and increase energy production for wind turbines, which will ultimately reduce reliance on fossil fuels for societal energy needs.