Bridging the gap between coupon tests and full-scale blade tests

The current certification process for rotor blades of wind turbines starts out by performing coupon tests for establishing the material properties, as is the case for structural designs in most other industries. However, the next step does not consist of testing structural details, but skips directly to a full scale blade test to check the validity of the design of the blade by subjecting the fully built blade to a number of static and dynamic loads which exceed the design loads. The paper starts out with the backgrounds involved and outlines the project between DNV-GL and Fraunhofer IWES aimed at establishing practical guidelines for the testing of subcomponents and their use in the certification process of wind turbine blades. The project aims to establish a "catalogue of blade details" and their appropriate testing options. In order to check the validity of this approach, "certification tests" on two blade details: the bond line between spar cap and shear web and the trailing edge are foreseen, so as to verify the practical problems in application of the catalogue and use the knowledge gained to improve the descriptions in the detail catalogue. As an example in this paper, the beam test representing the bond line between spar cap and shear web is presented. Due to the high cost pressure in the industry, the need for a high reliability and the relative short time to market for new developments the certification process is a crucial step in the development of new products.