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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of 0.02. The wind turbine is been designed according to wind class IA from IEC 61400-1 (2019) and hence, the average wind speed, the reference wind speed, and the reference wind turbulence intensity used are 10 m / s, 50m / s and 0.16 [-], respectively. Six di ff erent turbulence seeds are used for each wind speed, together with three di ff erent yaw miss-alignments consisting of 0° , 10° and -10° angles. Each individual DLC has an e ff ective duration of 600 s after discarding the first 100 seconds in order to avoid initial transients a ff ecting the aeroelastic simulation simulation results as described in Haselbach, P. U. et al. (2020). The analysis of the aeroelastic load calculations lead to LifeTime Damage Equivalent Loads (DEL) with root bending moments (radial position R = 0 m) of M x = 120 . 52 kNm and M y = 64 . 05 kNm in amplitude for the pitch controlled wind turbine and 500,000 load cycles. According to IEC 61400-1 (2019), the loads are multiplied with a Partial Safety Factor (PSF) of 1.35 taken into account for uncertainties in the aeroelastic calculations. The loads have been separated into a bending moment coming from the part of the blade before truncation ( r ≥ 5 m ) and forces introduced to the blade at the load point. These loads have been applied for the subsequently conducted simulations and are used as basis for the fatigue load tests as defined in Table 2. Table 2. Load parameters defining the LifeTime Damage Equivalent Loads applied at the superior load point at radial blade position r = 5m. Force in x-direction Force in y-direction Bending moment M x Bending moment M y ± 5780 N ± 10 , 000 N ± 30 , 500 Nm ± 14 , 250 Nm In total, four di ff erent load scenarios are investigated. Here, combinations of flap- and edgewise loading are ap plied by alternating the sign, namely compression-compression, compression-tension, tension-tension and tension compression. The wind turbine blade consists of UD and BIAX glass fibre fabrics embedded into an epoxy resin system and its subcomponents are adhesively bonded together with an structural epoxy based adhesive (Haselbach, P. U. et al. (2020)). The material properties are given in Table 3. Table 3. Assumed material properties of the used UD and BIAX glass fibre epoxy resin material system, the polymore foam and the applied structural epoxy based adhesive paste ( ρ as the density, E i j as the Young’s modulus, ν i j as Poison’s ratio and G i j as the shear modulus). Design parameters UD Biax Adhesive paste Polymore foam 2.4. Material properties

1947 . 74 kg / m 3

1942 kg / m 3 13.92GPa 13.92GPa 13.92GPa

3750 kg / m 3

220 kg / m 3 0.055GPa

ρ

E 11 E 22 E 33 ν 12 ν 13 ν 23 G 12 G 13 G 23

42.71GPa 12.59GPa 12.59GPa

3.42GPa

0.257 0.257

0.533 0.533 0.257

0.3

0.4

0.364014 4.61GPa 4.61GPa 4.61GPa

11.50GPa 11.50GPa 5.536GPa

1.315GPa

0.0196GPa

In order to predict the damage initiation and growth in the bond between the shear web and spar cap, several DCB UBM (Double Cantilever Beam loaded with Uneven Bending Moments) experiments for static and on coupon level under fatigue tension-tension loading (R = 0.1) were conducted. Here, di ff erent load ratios (Mode I to Mode II) and specimens with low bonds (30%), medium bonds (50%) and fully bonded (100%) surfaces were tested, allowing to create a common fatigue crack propagation curve (Paris curve) for the adhesively bonded joints under steady state crack growth conditions. Here, the crack growth rate (da / dN) against the strain energy release rate plot indicates steady state crack growth at a lowest level of approximately 150 J / m 2 for opening Mode I and 500 J / m 2 under shear Mode II / Mode III conditions for adhesive joints with low bonds (30%). These fracture parameters are used to define