By Ian Randall
For most people, it’s considered rather eccentric to talk to inanimate objects – and if the objects seem to be talking back, then it’s probably time to seek medical advice! Not, however, for Alex Ng and his colleagues at the University of Adelaide in Australia, who are working on a way to “chat” to buildings, bridges, aeroplanes and other structures, so they can report back on their structural health.
Ng’s team is particularly interested in things made from fibre-composite laminates. These laminates comprise individual layers of high-strength fibre in a ceramic, metallic or polymer matrix and are becoming increasingly popular as building materials. Their internal structure provides strength and stiffness, while also being lighter than alternative materials. They can be used for such wide-ranging purposes as building construction, aerospace design and even sports goods. For example, Boeing’s 787 Dreamliner aircraft is made of 80% composite materials by volume.
However, it can be very difficult to measure the structural integrity of components made from laminates. This is because it is often impossible to assess the internal layers of a structure for damage without doing destructive testing.
To overcome this problem, Ng and his team of engineers are developing a system of electrical transducers that can probe the integrity of such structures using sound waves. Sound travels through the laminate materials like ripples on the surface of a pond. Data are gathered on the waves that are reflected back to the source, and this information is analysed to reveal the presence of damage or defects throughout the structure.
Ng’s transducers could either be integrated into the composite materials during construction, or connected to their surface afterwards. This would offer the possibility of round-the-clock, automatic monitoring of the structure at minimal expense.
While the project is only in its early stages, the team has already succeeded at creating a system in their laboratory that emits and receives sound waves within the target structures. “Right now, we can only detect where the damage is,” Ng says, explaining that eventually the team expects to be able to detect the exact size and shape of any defects. “It will allow us to talk to the structure… just like someone going to the doctor for a health check.”
The same method should also be applicable to other structural materials, such as steel – which can also be difficult to assess without destructive testing.