Wind turbine blade certification tests often generate sudden audible cracking sounds from somewhere within the blade, without the operators being able to locate the noise source or to evaluate the existence or the extent of any damage. It would be beneficial to be able to detect any damage incurred by the blade, whether it is accompanied by audible noise or not. The current project, named AEGIS, is looking at the possibility of using acoustic emission monitoring during testing of fiber composite blades to detect the source of damage events and assess the blade condition. The test methodology is discussed in the context of the blade certification procedure and results are presented from a series of static and fatigue blade tests to failure in the laboratory.

Wind turbine blade certification tests, comprising a static test, a fatigue test, and finally a residual strength test, often involve sudden audible cracking sounds from somewhere within the blade, without the operators being able to locate the noise source, or to determine whether damage (minor or major) has occurred. A current EC-funded research project is looking at the possibility of using acoustic emission (AE) monitoring during testing of fibre composite blades to detect such events and assess the blade condition. AE can both locate and characterise damage processes in blades, starting with non-audible signals occurring due to damage propagation at relatively low loads. The test methodology is discussed in the context of the blade certification procedure and results are presented from a series of static and fatigue blade tests to failure in the laboratory. Inferences are drawn about small differences in the manufacture of the nominally identical blades and conclusions are presented for the application of the methodology.

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For large off-shore wind turbines, blades with relative low blade mass are becoming more important. The economic use of large-tow carbon fibers can help achieve lower blade masses. Basic material design data have been established for two promising material combinations, including the fatigue properties for Panex33/epoxy. Blade root joints have been developed in a carbon/glass combination, resulting in a better price performance ratio. The initial cost assessment on a blade dominated by severe fatigue loads shows that application of carbon fibers in the spar leads to cost reductions.