33 Sub-components of Wind Turbine Blades: Proof of a Novel Trailing Edge Testing Concept 269 Fig. 33.2 Finite element model showing extruded SHELL281 elements of the tested 3 m section (a), a zoom into the trailing edge bond-line modelled with SOLID186 elements (b), the load frame representation by CERIG elements and the load introduction via a master node (c) and its structural strain response (d). The color scale shows the longitudinal strain εz along the specimen at 20 % load level of the final test load of the leading-to-trailing edge (LTT) load case Fig. 33.3 Test rig overview (a) and specimen view (b). The hydraulic actuator is shown on the left introducing the loading into a hinged vertical beam. The specimen is mounted via ball joints between the vertical beam and a strong wall on the right. In the front two of the four DIC cameras are seen facing the suction side of the specimen The positions of the load introduction points at the specimen edges (Fig. 33.2d) were determined using the analytical model of the full and the cut cross-section. The structural response of the static full-scale leading-to-trailing edge (LTT) load case was chosen as reference. 33.2.3 Experimental 33.2.3.1 Setup The test concept described in Sec. 33.2.1 was set up on a strong floor with two adjustable strong walls (Fig. 33.3). The hydraulic actuator was used in displacement control and had a nominal load of 210 kN with a maximum stroke displacement range of 600 mm. A benefit of this setup is that relatively small variations in specimen length can be compensated by the stroke displacement. The ball joints used were designed for a nominal load of 400 kN. The gravity load constrains the 3 m long specimen’s rotational degree of freedom about its length axis. While mounting the specimen, it finds its stable position depending on the position of both joints R and T within the cross-section. 33.2.3.2 Specimen Preparation The specimen was cut along the spar cap and ground at the load introduction zones (Fig. 33.4a) both to improve the adhesion with the load frames and enhance visual inspections during testing (Fig. 33.4b). Wooden frames were milled according to the outer and inner surface of the specimen. In a casting process (Fig. 33.4c) the frames were glued to the specimen with an epoxy system. The curing of the epoxy resin was performed approximately for 12 h at 65◦C.
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