Early studies on raindrop erosion
of the material and coating of aviation objects were launched with the
invention of rocket-powered aircrafts and missiles around the WWII. Raindrop
impacts impose a high magnitude force on the target that can damage the surface
or dislodge the bulk material. Set-ups to simulate the raindrop impact on such
vehicles are therefore focused on very high-speed liquid-solid impacts.
Another field where raindrop
impact has received a lot of attention in recent years is the wind turbine
industry. To make energy production more efficient the wind turbines and their
rotor diameter are getting bigger. Presently the largest rotor diameter is 170
m with 8 MW capacity. Rotor diameters of 250 m with 20 MW capacity are anticipated.
Maximum tip speed of the present wind turbine blades is 100 m/s, which might be
higher for larger wind turbines.
Composite wind turbine blades are
designed to last for about 20-25 years in the field. However, the composite
materials are susceptible to heat, moisture, UV radiation, and especially
erosion from both solid particles and rain. If repairs are not done at the early
stages, damage to the underlying laminate will be present as early as after
five years. The break down mechanisms are not fully understood, however apart
from the protecting materials ability to withstand a single impact also the
relation between the raindrop impact period and the relaxation time is
The industrial standard to
investigate simulated impact from raindrops is the so-called whirling arm
erosion test rig or rain erosion test (RET). In this set-up, the raindrops are
colliding with the painted sample mounted on a rotating arm. One attempt to
make this test method simpler is the principle based on a provoked water jet
driven by a high-pressure pump.
of the project:
The purpose of this project is to develop and
evaluate a new test method for assessment of the coatings against water impact
erosion. Experiments are performed with this set-up to quantify the lifetime of
the coating and to correlate it with the established RET method.
Literature study on coating
water impact erosion and test methods
Investigate and report the
standard protocols for performing the rain erosion tests
Correlation of the coatings
erosion resistance results from the new set-up with RET results
Experimental determination of
the coating life time