For aluminium aircraft, visual inspection is used to monitor damage, but this is often not possible for composite structures where, for example, matrix cracking or delamination can occur without any indication of damage on the surface. With composite use becoming increasingly common in modern aircraft, a solution to this problem is keenly awaited.
Acoustic emission monitoring is thought to offer a means of detecting such internal damage as it happens by listening to the acoustic waves emanating from the event and triangulating to locate the damage. However, conventional piezo acoustic emission techniques are largely unsuited to aerospace due to their electromagnetic sensitivity, relatively massive cabling, the inability for dense multiplexing and inability to provide safe operation in explosive zones near the fuel system.
Fibre optic sensing has long promised to offer a solution that overcomes these advantages yet, to date, no commercial solution exists. Smart Fibres has been involved in the effort to bring such a solution to market, initially through the 2010-2012 Research Project MACH, in which a fibre laser based solution was developed and a prototype system evaluated. More recently, Smart Fibres is working on a quasi-distributed acoustic emission monitoring system using FBGs for oil & gas industry applications. This solution shows great promise to become the long sought-after commercial solution to this monitoring requirement.