Structural integrity assessment of blade's subcomponents using acoustic emission monitoring

Abstract

Since the power generation capacity of a wind turbine has a direct correlation with increased blade length there is a general trend in the wind industry to move towards larger blades. Critical design issues associated with larger blades are: weight, strength and blade stiffness, reliability, manufacturing, installation and service costs and testing. Definitely, full scale testing becomes quite expensive. Therefore, testing components reduced in size and containing critical parts like adhesive bond lines seems to be an interesting alternative. As the adhesives are one of the main load carrying materials in many modern wind turbine blades, the bond line strength investigation is of vital importance. Recently, linking the gap between coupon size material characterization and the material performance on a blade structure, a lot of effort has been invested in the development of sub-component tests for structural evaluation prior to the construction of a prototype. In the present study, two GFRP I-beams are loaded incrementally to failure. The particular subcomponents simulate the complex stress state developed in the adhesive bonding between the spar cap and the shear web connection of a blade. The bond line has a thickness of 5 mm. Typical Acoustic Emission (AE) load-hold proof tests are performed at intermediate loading stages, in order to locate and characterize damage processes at relatively low loads.