Safety is a primary concern of aircraft manufacturing. A failure in the air can mean tragedy, so aerospace engineers must design to prevent worst-case scenarios. However, such high standards come at a high cost.
What if there was a way to better identify design flaws and reduce wasteful redundancy?
Jet engine turbine blades are protected from intense heat and wear by ceramic thermal barrier coatings. Currently, even if the coatings are applied under the exact same conditions, there is no accurate way to predict how long the blades will last—ranging anywhere from 1,000 to 10,000 hours at maximum thrust.
Because of safety demands, turbines must be replaced at the minimum expected lifetime, even if they are in good working order. This new test could more accurately estimate the lifetime of individual turbine blades. That means less engine maintenance while upholding the same standard of safety.
A collaboration between Rolls-Royce and researchers at Heriot-Watt University, the method works by placing a test material under controlled tensile strain and observing changes in the material’s refractive index with a polariscope. The team aims to develop this technique into a setup that can analyze an entire part, providing data to more accurately predict when the part will fail.
Refractive index is a measure of how light travels through a transparent material.
So how can researchers see through opaque ceramic? The answer is gigahertz frequency illumination of the subject. These wavelengths can penetrate some opaque materials that visible light cannot. In this test, the GHz beam passes through the ceramic coating and reflects off the underlying metal into the polariscope.
Next, the team believes they can improve resolution of the test by cranking illumination frequency up to terahertz levels.
Currently, the apparatus is only capable of analyzing single points on the material, but an imaging setup could analyze an entire blade. Once blades that have been imaged with this system are used and worn out, the real-world wear can be compared to the imaging data. More data is needed to correlate the test data to lifetime estimates.
The method can also help design new ceramic coatings in other industries, like nuclear power and automotive.
More accurate analysis of ceramic thermal coatings, in aerospace applications or otherwise, will not only save manufacturing and service costs, but could also lead to new coatings that improve efficiency, leading to fuel savings and reduced pollution.
For more information, check out the research team’s paper on the subject here.