Environmental Engineering Reference
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Fig. 9.18 Photo of the blade failure
Fig. 9.19 Photograph of the fatigue damage process, a gel-coat cracks appearance, b gel-coat
cracks development, c adhesive joint failure, d blade failure
lost its structural integrity and the top and bottom halves flattened before allowing
the blade to fold (as shown in Fig. 9.18 ).
Figure 9.19 shows the fatigue damage process of the blade. Starting at about
40,000 cycles, a multitude of fine gel-coat cracks developed on the high-pressure
(upward facing) side and the cracks were most apparent at the 70-80 cm span of
the blade, which was the high strain region of the blade according to the strain
distribution obtained by the DPP-BOTDA system in the statist test. From 80,000 to
260,000 cycles, these gel-coat cracks progressed in length and gap width. Some of
the gel-coat cracks near the high strain region turned to larger visible cracks.
Between 260,000 and 300,000 cycles, adhesive joint failure between skins at the
leading edge was visually identified at 75 cm from the root. As the crack of
adhesive joint failure progressed in length, the blade lost its structural integrity and
failed at about 310,000 cycles.
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