Feasibility of up-tower repair concepts for pultruded carbon spar cap planks in wind turbine blades

Abstract. While modern wind turbine blades utilize pultruded carbon-fiber-reinforced polymer (CFRP) planks for structural integrity in spar caps, these materials can sustain damage from operational stresses, leading to potential failures if unaddressed. Traditional down-tower repairs result in significant costs related to dismantling and transporting, especially for offshore installations, emphasizing the need for efficient up-tower repair methods. This research utilizes a finite-element model of an 81.6 m rotor blade designed for a 7 MW offshore turbine, subjected to aeroelastic simulations to evaluate load conditions during maintenance. The analysis focuses on a step-wise increased repair zone, assessing susceptibility to buckling, cyclic strains, and permissible wind speeds. Results indicate that while substantial repairs can endanger structural stability, turbulence-induced strain amplitudes are manageable. Recommendations include installing temporary pretensioning and buckling support structures to enhance safety during repairs. Various innovative support concepts are proposed for installation from both inside and outside the blade, aimed at improving structural integrity during up-tower repairs.