Static test until structural collapse after fatigue testing of a full-scale wind turbine blade

The effect of fatigue damage on the residual strength of a large wind turbine blade is a very important issue in the wind industry. To test the residual strength after fatigue testing, this study prepared a test specimen, a 48.3 m wind turbine blade that had experienced initial static tests and then fatigue tests in accordance with the technical specification IEC TS 61400-23. The prepared specimen was loaded sequentially along the positive flapwise, the positive edgewise, and the negative flapwise direction, while video-recording the test situations. The wind turbine blade was able to sustain the loads in the first two tests, but the blade collapsed in the third test when the negative flapwise load reached 70% of the maximum target value, a value representing 50% of the most severe load in the first test. Based on the recorded information and the fracture patterns at the blade's broken section, the collapse processes were analyzed. From this analysis we suggest a modified laminate pattern that can enhance the residual strength of a fatigue damaged wind turbine blade.