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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Fig. 1. The DTU 12.6m blade exposed to suction towards pressure side static loading includig PSF (1.35 PSF for the aeroelastic load calculations and 1.1 PSF for experimental loading for blade to blade variation).

For the design of the debonding failure, the original blade model is truncated at radial position of r = 5 m and is modified to establish a finer mesh in the region that represents the adhesive between the rear shear web and the spar cap on the upwind side of the airfoil, where an initial debonding will be placed. This step is necessary in order to simulate the crack initiation and growth and to reduce the computational costs. Figure 2 shows a cross section of the modified DTU 12.6 m blade model. The modified blade section is discretized with 260,190 elements, where rows with two elements through the thickness discretize the adhesive bond between the rear shear web and the spar cap. The two row of elements representing the adhesive bondline are separated in the middle and their surfaces are connected with interactive contact conditions and tie constraints, respectively. The constraints allow to easily modify regions, where crack growth should be enabled and regions, which are rigidly tied together and do not enable crack growth. Moreover, simulating the debonding process in the middle of the adhesive bondline layer allows modelling crack growth and simultaneously avoiding bi-material interfaces and consequently also elements length dependencies as described by Eder, M. A. and Bitsche, R. D. (2015). The two rows representing the adhesive layer are connected using tie-constraints to the shear web and spar cap region, respectively. Then, the adjacent surface between the two rows of elements through the thickness of the adhesive are split into di ff erent regions, allowing to assign di ff erent interaction behaviour. From r = 0m to r = 0.55m and from r = 3.45 m to r = 5 m, no debonding should happen and thus, these regions are rigidly bonded using tie constraints.

Fig. 2. Cross section of the DTU 12.6m blade with its 59 di ff erent regions (section assignments) per cross section and two rows of solid elements representing the adhesive layer between the rear shear web and the spar cap region of the upwind (pressure) side of the wind turbine blade.