Spotting the cracks

An Australian company – Structural Monitoring Systems – has developed a novel structural health monitoring system for aircraft that provides real-time monitoring of crack initiation and propagation.

About ten years ago, retired airline pilot Ken Davey developed a novel structural health monitoring system for aircraft that provides real-time monitoring of crack initiation and propagation.

Now, an Australian company – Structural Monitoring Systems (SMS) – has brought the so-called Comparative Vacuum Monitoring (CVM) technology to market and today it’s being evaluated by leading aerospace manufacturers worldwide.

The CVM system itself, which is so sensitive that it can detect a crack measuring 1/10,000 of an inch, consists of three main components: an inert sensor that can be adhered to the structure or embedded within the structure during manufacture, a flow meter and a vacuum source.

The CVM technique measures the differential pressure between low vacuum passages in the sensor called ‘galleries’ that alternate with similar ‘galleries’ that are kept at atmospheric pressure.

If no flaw is present in the material that the sensor is attached to, the vacuum will remain at a stable level. If a flaw develops, air will flow through the passage created from the atmosphere to the vacuum galleries. This throws the system out of balance as the sensor no longer contains the same vacuum level as the reference value. It is at this point that the crack is detected.

Commonly, the sensors themselves are flat, self-adhesive and made of polymer but SMS can also design and manufacture sensors in a range of configurations to conform to two and three- dimensional surfaces.

Presently, a number of manufacturers are evaluating the new technique. Airbus, for example, are investigating the use of the CVM technology in the A380 aircraft, while British Aerospace (BAE) and Messier Dowty in the UK are using CVM to test Airbus landing gear components.

In the USA, the first CVM system was installed on a commercial passenger airliner – a Boeing DC 9 aircraft – on 16 February this year.