Validation of crack initiation model by means of cyclic full-scale blade test

• Published in: Journal of physics. Conference series Vol. 2265; no. 3; pp. 32045 - 32058
• Main Authors: Rosemeier, M, Melcher, D, Krimmer, A, Wroblewski, W, Antoniou, A
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.05.2022
• Subjects: Amplitudes; Axial stress; Crack initiation; Cross-sections; Dynamic loads; Equivalence; Failure modes; Fatigue life; High cycle fatigue; Limit states; Physics; Residual stress; Rotor blades; Rotor blades (turbomachinery); Shear stress; Wind turbines
• ISSN: 1742-6588; 1742-6596
• DOI: 10.1088/1742-6596/2265/3/032045

Wind turbine rotor blades are subject to highly dynamic loads and designed for life cycles of at least 20 years, which means that materials are subjected to high-cycle fatigue. Fatigue is a design-driving loading for current and future blades. Bond lines of blades are exposed to a multi-axial stress-state due to the anisotropic thin-walled blade structure and curved, tapered, twisted, and airfoil-shaped blade geometry. To eliminate undesirable failure modes and thus increase the reliability of wind turbine rotor blades, standards and guidelines recommend that the multi-axial stress-states be taken into consideration for the limit state analysis. In addition, thermal residual stresses that develop during manufacture can have a significant impact on the fatigue life of the bond line. By means of a cyclic full-scale blade test of a commercial 81.6m long offshore blade, we validate a crack initiation model, which takes into account multi-axial thermal and mechanical stress-states, as well as the probabilistic stress-life, to predict the edge of crack initiation in the adhesive as well as the span-wise position. Both observations agreed well with the simulations. All residual normal stress components and cross-sectional plane shear stress made up the major part of the mean equivalent stress, while the mechanical stress amplitude components - longitudinal, peel, and cross-sectional plane shear stress - made up the major part of the equivalent stress amplitude.