Abstract
For a reliable design of wind turbine systems all of their components have to be designed to withstand the loads appearing in the turbine's lifetime. When performed in an integral manner this is called systems engineering, and is exceptionally important for components that have an impact on the entire wind turbine system, such as the rotor blade. Bondlines are crucial subcomponents of rotor blades, but they are not much recognized in the wind energy research community. However, a bondline failure can lead to the loss of a rotor blade, and potentially of the entire turbine, and is extraordinarily relevant to be treated with strong emphasis when designing a wind turbine.Modern wind turbine rotor blades with lengths of 80 m and more offer a degree of flexibility that has never been seen in wind energy technology before. Large deflections result in high strains in the adhesive connections, especially at the trailing edge. The latest edition of the DNV GL guideline from end of 2015 demands a three-dimensional stress analysis of bondlines, whereas before an isolated shear stress proof was sufficient. In order to quantify the lack of safety from older certification guidelines this paper studies the influence of multi-axial stress states on the ultimate and fatigue load resistance of trailing edge adhesive bonds. For this purpose, detailed finite element simulations of the IWES IWT-7.5-164 reference wind turbine blades are performed. Different yield criteria are evaluated for the prediction of failure and lifetime.The results show that the multi-axial stress state is governed by span-wise normal stresses. Those are evidently not captured in isolated shear stress proofs, yielding non-conservative estimates of lifetime and ultimate load resistance. This finding highlights the importance to include a three-dimensional stress state in the failure analysis of adhesive bonds in modern wind turbine rotor blades, and the necessity to perform a three-dimensional characterization of adhesive materials.
Highlights
Rotor blades of modern multi-megawatt wind turbines reach lengths of 80 m and more [1]
Considering that failure of a blade may potentially lead to the loss of an entire wind turbine, the reliable design of rotor blade bondlines is crucial for designing reliable wind turbines, and highly relevant for wind turbine systems engineering
The simulation results support the recent modifications of the design guidelines, highlight the necessity to account for multi-axial stress states, and potentially open a discussion on the real failure mechanisms appearing in adhesive connections of wind turbine rotor blades
Summary
To cite this article: Pablo Noever Castelos and Claudio Balzani 2016 J. View the article online for updates and enhancements. - Formability analysis of sheet metals by cruciform testing B Güler, K Alkan and M Efe. - Influence of stacking fault energy on friction of nanotwinned metals J J Zhang, Z F Wang, T Sun et al. - Micro-Raman spectroscopic analysis of single crystal silicon microstructures for surface stress mapping Nobuyuki Naka, Shinsuke Kashiwagi, Yuji Nagai et al. This content was downloaded from IP address 194.95.157.206 on 17/01/2018 at 08:42. Leibniz Universitat Hannover, Institute for Wind Energy Systems, Hannover, 30167, Germany
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