PSI - Issue 57

Philipp Ulrich Haselbach et al. / Procedia Structural Integrity 57 (2024) 169–178 P. U. Haselbach and P. Berring / Structural Integrity Procedia 00 (2023) 000–000

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Table 4. SEER and E ff ective Energy Release Ratio given for di ff erent dual- / multi-axial load sequences, where the shear web / spar cap bond is experiencing di ff erent loads caused by combinations of Suction towards Pressure side (STP), Leading Towards Trailing edge (LTT), Pressure Towards Suction side (PTS) and / or Trailing Towards Leading Edge (TTL) load combinations. Load case Loading flapwise Loading edgewise SERR mode I SERR mode II SERR mode III e ff . SERR ratio

0.12 J / m 2 0.76 J / m 2

532.63 J / m 2 236,28 J / m 2 56.57 J / m 2 165.77 J / m 2

425.38 J / m 2 34.38 J / m 2 8.62 J / m 2 20.14 J / m 2

Compression-compression STP Compression-compression STP Compression-compression PTS Compression-compression PTS

LTT TTL TTL LTT

1.181

0.54 1.06 0.38

132.99 J / m 2 16.34 J / m 2

Fig. 5. Defect design of the shear web / spar cap debond of the DTU 12.6 blade with an initial debonding between r = 1.45 m and r = 2.55 m, enclosed by low bonded and medium bonded areas to both sides, each individual region with a length of 0.45 m in length.

3.2. Manufacturing

The initial debonding between the shear web to spar cap is created by using slip foils, leading to fully debonded region. Perforated slip foils are used to represent low and medium bonds with 30% and 50% slip foil area content, respectively. Figure 6 shows the use and placing of the slip foils and perforated slip foils with 30% and 50% slip foil area content between the spar cap region and the rear shear web during the blade assembly process. After placing and bonding the rear shear web to the spar cap region on the upwind shell of the wind turbine, a Digital Image Correlation (DIC) system was prepared and installed to track by image registration techniques accurately measurements of the crack front and the anticipated crack growth in the bondline between the spar cap region and the rear shear web (see Figure 7).

4. Conclusion

The numerical predictions as well as the manufactured and instrumented blade sets the framework for subsequently to execute experimental tests of the damage growth in the adhesive joint in order to compare numerical and exper imental data. The experimental demonstration will allow to understand better the complexity of damage growth of composite structures under fatigue loading and the necessity of accurate numerical prediction tools for reliable prog nostic health management systems. Moreover, it will allow to investigate whether existing methods can monitor the damage growth rates and sizes and also allow to predict numerically the expected growth rates and sizes as for di ff erent load scenarios in order to establish a reliable PHM systems.