Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Condition monitoring for wind turbine blades

Three-dimensional stress and strain fields are used to determine the degree of mechanical integrity of composite wind turbine rotor blades. The objective of this project was therefore to combine together existing testing techniques and use synergy to develop novel methodologies for the non-destructive testing (NDT) and condition monitoring of wind turbine blades. Three different, but complementary NDT methodologies have been developed, which together cover the dynamic and steady state properties of wind turbine blades under fatigue loading. The dynamic point test methodology relies on visco-elastic and thermo-visco-elastic measurements to test macroscopic and microscopic behaviour, in order to identify regions of weakness in the structure and determine damage accumulation. The steady state methodology uses photo-elastic, thermo-elastic and infrared thermographic measurements to analyse the steady state stress pattern. The 3-dimensional dynamic methodology in its pioneering stage combines simultaneous Moire interferometric, photo-elastic, strain gauge, thermal and acoustic emission measurements. The usefulness of these combined methodologies is demonstrated by the fatigue testing of plate specimens and, finally by a full-scale blade test.

Four new theories have also been developed and tested. They characterise the fundamental behaviour of non-linear, thermo-visco-elasticity, damage accumulation and lifetime prediction for wind turbine composite materials under arbitrary loadings. This project is the first to successfully measure 3-dimensional deformation over a 10 square metre area to an accuracy of 1 in 1000 in combination with photo-elastic stress measurements, and also to simultaneously measure and analyse mechanical and thermal effects in fatigue testing. Data have also been used to develop a fundamental theory for the damage accumulated in a sample under an arbitrary loading history in order to predict life-time, incorporating the time-dependent properties of the materials under test.

The results show that the 3 non-destructive testing methodologies developed, when combined and analysed together, have the potential to extract more information than that obtainable using the individual techniques in isolation. The thermodynamic variables acting when materials are fatigued have therefore been unravelled and analysed in order to gain insight into the nature of the fatigue and damage process. A generic methodology for condition monitoring of wind turbine blades has therefore been developed and these NDT methodologies were also able to extract information on non-linear visco-elasticity thermo-visco-elasticity and combined 3-dimensional properties.


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