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Effects of Localized Manufacturing-Induced Porosity Defects on the Fatigue of Wind Turbine Blades—Experiment and Modeling



In the absence of credible models to provide insight on the relationship between the state of porosity and its impact on the ultimate compressive strength and compressive fatigue strength, blade manufacturers, OEMs and wind farm operators are unable to make well-informed decisions for the disposition of wind turbine blades with such manufacturing-induced defects. In the current research, a lab-scale methodology to replicate the types of local porosity defects that occur during wind blade manufacturing was developed and was used to make 35-ply composite blocks for experimental investigation and modeling. Each block represents a typical section cut from the spar cap region of a blade. Coupons were cut from the blocks then sorted into high-, medium-, low-, and “baseline”-porosity density groups as characterized by optical microscopy, SEM and CT scan. Axial compression and compression-compression fatigue tests were conducted to evaluate the compressive strength and fatigue life as a function of porosity classification, respectively. A complimentary finite element model of a representative unit volume (RUV) of the lab-manufactured block was built from the 3D reconstruction model using CT scan images. The test data and the complementary finite element models are to be used to guide the development of simple empirical models for predicting the fatigue life for the composite material system as a function of the state of porosity.


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