Acoustic emission monitoring of a wind turbine blade during a fatigue test

Abstract

A fatigue test of a wind turbine blade was conducted a t the National Renewable Energy Laboratory in the fall of 1994. Acoustic emission monitoring of the test was performed, starting with the second loading level. The acoustic emission data indicated that this load exceeded the strength of the blade. From the first cycle a t the new load, an oil can type of deformation occurred in two areas of the upper skin of the blade. One of these was near the blade root and the other was about the middle of the tested portion of the blade. The emission monitoring indicated that no damage was taking place in the area near the root, but in the deforming area near the middle of the blade, damage occurred from the first cycles a t the higher Ioad. The test was stopped after approximately one day and the blade was declared destroyed, although no gross damage had occurred. Several weeks later the test was resumed, to be continued until gross damage occurred. The upper skin tofe approximately one half hour after the cycling was restarted.

On the Fatigue Analysis of Wind Turbines

“…Additional applications of standard and non-standard NDT and NDE techniques to wind turbine components, in both laboratory and field environments, have been explored [209,210,214,215].…”

“…General descriptions of techniques and applications exist in the literature [206,207]. A well as applications of these techniques to wind turbines [208][209][210].…”

Non-Destructive Evaluation of Damage Mechanisms in Composite Sandwich Structure

“…At this stage, it is believed that the technique could benefit blade development and manufacturing, as well as inspection and maintenance. Future experiments will develop upon the testing procedures shown, as well as introducing other aspects such as acoustic emissions (AE) monitoring, which has been receiving a lot of attention from research groups experimenting in the wind turbine field recently, [11][12][13]. What has been demonstrated generally is that AE is capable of giving early indication of some damage in a composite structure, with potentially some indication of the type of damage incurred.…”

Comprehensive testing of NedWind 12-meter wind turbine blades at NREL

“…8 Although this is not standard practice at NREL, SNL is often invited to join tests if it is of mutual benefit to the laboratories and the blade client. Sensors placed along the blade measured high frequency emissions that may be related to incipient blade damage during the test.…”