Abstract
Acoustic emission (AE) is an in situ Structural Health Monitoring (SHM) technique, where a structure is monitored for the ultrasonic waves produced due to crack growth. A major challenge with AE when applied to aircraft, and other complex structures, is that wave propagation is significantly affected by stiffeners, holes, thickness changes and other complexity. This reduces the accuracy of traditional source location techniques, that are based on a singular propagating wave speed. The Delta-T method enables higher levels of accuracy by mapping the structure and accounting for these changes. In this work AE monitoring equipment was installed on a section of an aluminium Airbus A320 wing. Location trials showed the Delta-T technique improved the average error from 85mm to 23mm, for artificial Hsu-Nielson sources, compared to the commercial standard technique. Testing under fatigue however demonstrated the challenges encountered when inspecting 3D structures (due to multiple signal paths) with significant levels of background noise. Of two cracks identified in the structure, the first of these was successfully detected and located, whilst the other was missed due to high machine noise and unrepresentative loading.
Highlights
Many aircraft structures, such as much of the wing, are designed to be damage tolerant; this ensures that any damage within the structure is detected significantly before any failure occurs
Acoustic emission (AE) is an in situ Structural Health Monitoring (SHM) technique, where a structure is monitored for the ultrasonic waves produced due to crack growth
This paper presents the results of a fatigue test on a section of aluminium A320 aircraft wing, where AE is been located using the commercial Time of Arrival (TOA) technique and the advanced Delta-T technique developed at Cardiff University (Baxter et al, 2007)
Summary
Many aircraft structures, such as much of the wing, are designed to be damage tolerant; this ensures that any damage within the structure is detected significantly before any failure occurs. Prior to flight all aircraft undergo substantial testing of components and entire airframes, in both static and fatigue tests, to ensure failure will not occur in service. In addition to substantial testing prior to commercial flights, aircraft undergo regular inspections Some of these are quick, visual inspections, others require the aircraft to be taken out of service for weeks, allowing a thorough inspection of the entire airframe. This costs the operator, both in terms of the cost of Maintenance, Repair and Overhaul (MRO) which typically account for 12%-15% of the total operating costs of an aircraft, and the loss of revenue whilst the aircraft is not in service (Rodrigues Vieira and Loures, 2016)
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