Abstract
As manufacturing defects, voids in wind turbine blades may cause damage under fatigue loads. In this paper, the internal energy storage is used as an indicator to identify the critical moment when a defect evolves into damage. The heat transfer equation of composites material containing void defects is derived based upon the theory of the thermodynamics of irreversible processes. In order to obtain the numerical calculation model of the internal energy storage of the evolving process, the thermal conductivity along the transverse direction is homogenized as the temperature date along this direction is acquired by a thermal camera. Specimens with different void fractions are tested with infrared thermal imaging under fatigue load, during which the stress, strain and temperature data are acquired to establish the curve of internal energy storage against the fatigue cycle. This relationship curve can be used to identify the critical moment when void defects evolve into damage. The feasibility of this method is proven by microscopic observation.
Highlights
As a new type of clean energy, wind energy can be exploited and utilized by producing electricity with wind turbines [1]
Of particular interest in this paper is to investigate the void defects of the main girder in wind turbine blades
The quantitative identification method is developed to detect the local damage of a defect in the wind blade so that the accurate state parameters can be provided for the initial damage state during the fatigue test
Summary
As a new type of clean energy, wind energy can be exploited and utilized by producing electricity with wind turbines [1]. Comparing to other parts of the wind turbine, its blade is the most important part of the wind turbine to capture wind energy. The blade is easy to damage in the terrible working environment [2,3]. The maintaining and replacement of the blade is hard to carry out because of its heavy weights [4]. It is essential to develop the health monitoring technology of the blade to adapt the development of the wind power industry. It is difficult to detect the early damage of a particular blade. The manufacturing defects may reduce the strength of the blade especially in the defect region. The defective blade can still be sold even though it contains voids, because the overall strength can meet the requirements of the ex-factory inspection standards. The fibers around the defect area will break under loads, leading to the interlayer cracking and the actual damage
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