Environmental Engineering Reference
In-Depth Information
Fig. 9.22 Differences in the fitted BGS along the leading edge at different fatigue cycle counts:
a results in point a, b results in point b, c results in point c, d results in point d.
single peak Lorenz shape. As the development of the gel-coat cracks (from 40,000 to
80,000 cycles), the stiffness degradation and accumulated cracks reduced the local
flexural stiffness and changed the local strain gradient, which broadened the width of
the BGS near the damaged region. As shown in the test results of 80,000 cycles, the
width of the BGS near the damage region (point C) changed significantly, while
the BGS near the undamaged region kept its initial shape. The test results reveal that
fatigue damage introduced local strain gradient change will broaden the width of the
BGS, which can be used to detect and locate fatigue damage. As these gel-coat
cracks progressed in length and gap width, from 80,000 to 260,000 cycles, the local
flexural stiffness near the damaged region further decreased, which resulted in a
steeper strain gradient. Hence, the shape of the BGS further changed. As shown in
the test results of 260,000 cycles, the BGS near the damage region (point C) changed
from single peak to double peak, which indicated a very steep local strain gradient
and high nonuniform strain. The appearance of the double-pick BGS indicated
further damage in this region. Then, the adhesive joint failure was visually identified
at point C, between 260,000 and 300,000 cycles, which further validates the
effectiveness of damage detection base on the BGS shape change.
9.4 Damage Detection under Static Loading Using PZT
Sensors
9.4.1 Test Description
The glass fiber reinforced plastic composite wind turbine blade in this test was a
prototype of a 2.1 meter blade. During the test, the blade was mounted horizontally
in a flap direction with its attached to a rigid steel mounting assembly. An actuator
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