| Summary: | 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.
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