• Question: what kind of problems do you encounter when inspecting/testing jet engines??

    Asked by jamesbrough93 to Katy on 19 Mar 2010 in Categories: .
    • Photo: Katy Milne

      Katy Milne answered on 20 Mar 2010:


      Where do I start?

      We do inspections while the engine is on wing. In that case one of the biggest issues is access. We do not take the engine apart and often we have to send a probe down a narrow pipe in order to carry out the inspection. A 10mm diameter pipe is not much room. Often we want to send down an ultrasonic probe into the engine, water to couple the probe to the component that we are inspecting (like the gel they put on pregnant women’s stomachs), and a video camera to see what we are doing. And we only have a 10mm diameter gap! It is a pretty hard problem but we are getting very good at it.

      We also develop inspections for new types of components. Then the problem is finding small things. Defects like fatigue cracks normally grow slowly over time. That is because they experience cyclic loads in the engine. If we can find something really small, then we are improving the safety of the engine and we can also increase the time between inspections, which saves money for whoever owns the aeroplane. Finding small things is very difficult.

      Modern materials such as composites can be difficult to inspect. For instance, we use ultrasonic inspection often. Ultrasound is a high frequency sound wave. The wave propagates by vibrating molecules in the solid that you are inspecting. You can think about ultrasound like light. Composites are made up of two types of material. If you shine light through a forest (which is made up of trees and air) then you can’t see all the way through. This is like shining an ultrasonic beam on a composite material. The wave is reflected like light off a mirror from the interfaces between different materials. It is difficult to separate defects from reflections within the materials. However, we are now getting very good at this. We use advanced signal processing methods to improve our sensitivity.

      Geometry is also a problem. Imagine that you are looking straight down a corridor but you want to see visually if there is someone standing in a room off the corridor. The door is closed. This is analogous to the problem of inspecting components with different geometries or components. We have to solve problems like this using physics every day.

Comments