Materials of large wind turbine blades: recent results in testing and modeling

Abstract

The reliability of rotor blades is the pre‐condition for the development and wide use of large wind turbines. In order to accurately predict and improve the wind turbine blade behavior, three main aspects of the reliability and strength of rotor blades were considered: (i) development of methods for the experimental determination of reliable material properties used in the design of wind turbine blades and experimental validation of design models, (ii) development of predictive models for the life prediction, prediction of residual strength and failure probability of the blades and (iii) analysis of the effect of the microstructure of wind turbine blade composites on their strength and ways of microstructural optimization of the materials. By testing reference coupons, the effect of testing parameters (temperature and frequency) on the lifetime of blade composites was investigated, and the input data for advanced design of wind turbine blades were collected. For assessing the residual strength and stiffness of wind turbine blades subjected to irregular cyclic loads, a shell‐based finite element numerical methodology was developed, taking into account the non‐linear response of plies, and experimentally validated. Two methods of structural reliability estimation of the blade, which take into account the stochastic nature of the anisotropic material properties and loads, were developed on the basis of the response surface method and the Edgeworth expansion technique, respectively. The effects of fiber clustering, misalignments, interface properties and other factors on the strength and lifetime of the wind turbine blade materials were investigated in the micromechanical finite element simulations. The results described in this paper stem from the Rotor Structure and Materials task of the UPWIND project. Copyright © 2011 John Wiley & Sons, Ltd.

Reduction of wind turbine structural loads caused by rotor asymmetries

“…Newly introduced description of structural loads (14), has certain similarities with the description of load oscillations (2), where no rotor asymmetries were assumed. For harmonics k = 1, 4, 7 .…”

“…Due to rotation of the wind turbine rotor, rotor blades are subjected to oscillatory structural loads which increase the fatigue and shorten the wind turbine expected lifetime [1], [2]. The main reasons for such oscillations of the structural loads are the gravity and variations of wind speed over the wind turbine rotor area due to effects such as wind shear, tower shadow, yaw misalignment etc.…”

Development of robust and adaptive controller for blade testing machine

“…This depends on many factors, of which the load history, manufacturing method and blade size are among the most notable [4]. Moreover, the anisotropic characteristics of a composite blade can largely complicate fatigue analysis [5].…”

Microscale damage mechanisms and degradation of fiber-reinforced composites for wind energy applications: results of Danish–Chinese collaborative investigations

“…Generally, a wind turbine should work for 20-25 years without having to be repaired and with minimum maintenance. 1,2 The potential costs of maintenance, repair and replacement of damaged 100 m large wind turbines, standing offshore, can be huge and should be kept as low as possible.…”