PSI - Issue 57

Philipp Ulrich Haselbach et al. / Procedia Structural Integrity 57 (2024) 169–178

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P. U. Haselbach and P. Berring / Structural Integrity Procedia 00 (2023) 000–000

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Then, regions, where no initial debonding was simulated but crack growth is allowed, are defined by the means of surface to surface contact allowing small sliding but without secondary adjustment or clearance specifications using VCCT contact interactions properties. Here, the friction-less tangential behaviour, ”hard contact” for normal contact behaviour, allowing separation after contact and a fracture criterion of type VCCT are used to define the contact interactions. Figure 3 shows schematically the VCCT contact interaction regions placed in the shear web / spar cap bondline. The parameters defining the fracture criterion of type VCCT are presented in Table 1 using the Benzeggagh Kenane (BK) mixed mode behaviour. The region, where initial debonding is assumed, is modelled as friction-less contact conditions with the same tangential and normal contact behaviour as defined above.

Table 1. Parameters defining the fracture criterion of type VCCT. Type Mode I Mode II

Mode III

Exponent

Tolerance

Viscosity

150 J / m 2

500 J / m 2

500 J / m 2

VCCT

2.284

0.2

0.0001

At the blade root cross section, all nodes are connected to a reference point (superior node) in the center (blade coordinate system origin) and all degrees of freedoms are constrained using a kinematic coupling constraint. The reference node is fully constrained. At the truncated blade end at r = 5 m, all nodes (inferior nodes) are connected and coupled to a reference point in the aeroelastic center of the blade cross section. All degrees of freedom of the inferior nodes are constrained to follow the reference point’s movement. The loads are applied to the superior node.

2.3. Loads

The debonding of the shear web / cap region is supposed to growth under fatigue loading conditions in either uni axial or multi-axial excitement. Thus, the Design Load Case (DLC) 1.2, referring to standard operational design situation as fatigue analyses with normal turbulence wind conditions according to the IEC 61400-1 (2019), is used to calculate the design load. The Lifetime Damage Equivalent Load is based on the aeroelastic simulation using DTU’s HAWC2 (Horizontal Axis Wind turbine simulation Code 2nd generation), which is an aeroelastic code intended for calculating wind turbine responses in the time domain (Larsen, T. J. et al. (2019)). For that purpose, the structural blade model is represented by a fully populated matrix, building up the full rotor of the 3-bladed regulated wind turbine. In this multi-body simulation code, the rotor is mounted at the top of a 24 m flexible tower and linked to a 150 KW generator with a synchronous speed of 1500 rpm and a nominal slip

Fig. 3. Schematically respresentation of the VCCT contact interaction regions placed in the shear web / spar cap bondline of the DTU 12.6m blade.