When steel and other metals, reinforced concrete and composites are subjected to cyclic stress, they will after a time form small cracks called fatigue cracks. Initially these will be in the order of tenths of a millimetre in size. When cracking occurs, very small sound signals are given off.
Acoustic Emission Technology (AET) is regarded as a “passive” system which listens for these sounds.
This is unlike ultrasonic testing which projects sound signals into steel and looks at the reflected signal to see if there are physical defects present.
While interest in acoustic emission as an inspection method started to develop in the 1960s it was not until the 1990s that there was a better understanding of the fundamentals affecting crack growth and measuring that with acoustic emission and acoustic emission technology became a credible method for inspecting structures with many learned papers and the writing of international standards.
In the decade of 2000 to 2010 acoustic emission technology has been used to successfully on North Sea Oil rigs, in the British Nuclear industry, in Aerospace and the marine industry.
The technology is used for both asset management and safety