Environmental influence on the fatigue behavior of wind turbine rotor blades
- KEMA Nederland B.V., Arnhem (Netherlands)
Generally, the lifetime of Wind Turbine blades is limited by the (mechanical) fatigue resistance, which in turn is lowered by environmental aspects such as humidity and temperature (changes). At this time, not much knowledge on the combined influence of both fatigue and environmental aspects is available, which leads to arbitrary safety factors being used by Wind Turbine designers and manufacturers, which in turn results in low cost effectiveness. To predict the life time under both fatigue and environmental loading, KEMA has developed an accelerated (50x) environmental test for Wind Turbine blades. This test is based on climatological data from different sites in the Netherlands for periods up to four years. The acceleration factors were taken from the procedures proposed in ASTM D-1183 and EN-STAFF, and based on some common knowledge. The accelerated weathering test was evaluated using data on total moisture content and moisture profile from actual glass reinforced polyester blades weathered for a prolonged period outdoors. The accelerated environmental test was adapted where necessary using WW8GAIN, a software program to simulate the effect of humidity and temperature changes on the moisture content and moisture profile for composite materials. The resulting accelerated test procedure has been used to pre-condition a number of test specimens which are thereafter tested in fatigue loading according to a constant amplitude and WISPER-spectrum. Preliminary tests indicate that the precondition on its own does not significantly influence the life time of the glass fiber reinforced samples. However, when samples are continuously kept in contact with water during fatigue loading a drastic reduction of the life time is found correspondingly to a considerably larger design safety factor than the factor 1.25 currently used.
- OSTI ID:
- 122770
- Report Number(s):
- CONF-950521--; ISBN 1-56676-313-4
- Country of Publication:
- United States
- Language:
- English
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