| Summary: | In the wind turbine industry, damage occurs in many parts of the wind turbine,
such as the tower, the gearbox, the shaft and the rotor blade etc., but the most
common damage occurs in the rotor blade and the tower. More attention required
on the structural health of the rotor blades since they play a significant role in the
wind turbine system, accounting for 15-20% of the entire turbine cost and
resulting in an expensive repair cost when damage occurs. The most common
causes of rotor blade damage are wind gusts, heavy rainfall and lightning strikes.
Over 30% is affected by thunderstorms or lightning strikes, 28.21% by heavy
rainfall and 15.3% by strong winds. Wind turbines are susceptible to lightning
strikes since their size is becoming larger and it is predictable that they will be
more exposed to lightning strikes in the future. Therefore, this thesis focused on
lightning strike behaviour with respect to rotor blades for both composite and
biocomposite material. The literature review highlighted wind energy, lightning
damage on rotor blades and the types of damage detection used. The main
objective of this thesis is to determine the lightning strike behaviour with respect
to biocomposite, hybrid and composite material. The study adopted two
techniques: firstly, Failure Modes and Effect Analysis (FMEA) to recognise the
failure modes and potential causes for blade damage, and secondly, the fuzzy
Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) for
assessing the potential causes that have been identified. It was found that the
most dominant potential causes of blade damage is caused by lightning strike.
Lightning tests were conducted for the coupon specimens and the blade
specimens for both composite and biocomposite materials. The materials tested
for coupon specimens are kenaf fibre, flax fibre and fibreglass with different
configurations; without wire mesh, embedded wire mesh and outer-ply wire
mesh in order to find the best configuration for wind turbine blade fabrication.
The fibres were reinforced with a polyester (PE) matrix. Four types of damage
detection were used to assess the severity of lightning damage on the composite
and biocomposite blades, i.e. visual inspection, liquid dye-penetrant testing, ultrasonic guided wave, and laser-based ultrasonic scan. Based on the NDT
tests performed on the coupon specimens, the best configurations are either
made of flax fibre or fibreglass with embedded wire mesh. Three different types
of blade specimens; i.e. fibreglass, flax-fibreglass, flax were fabricated and
subjected to lightning strike. It was found that the flax blade suffers the least
lightning damage compared to the blade containing fibreglass. This means that,
natural fibre can be a good alternative to synthetic fibre in wind turbine blade
fabrication. All the techniques can detect the lightning damage in the overall
tested materials and blade structural systems but, the most effective technique
are ultrasonic laser-based scan because the damage size and location of the
damage can be observed clearly.
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