Overview of the European FP 7 Project “Aircraft Integrated Structural Health Assessment II†with Focus on the Detection of Corrosive and Hydraulic Liquids by Gauges Based on the Collapse of Percolation Conductivity

Abstract

The European project “Aircraft Integrated Structural Health Assessment II†AISHA II focuses on the development of structural health monitoring systems for aircraft with a relatively high technology readiness level (TRL). As full-scale parts aluminium alloy-based floor beams, stringer-stiffeners structures, slat-tracks made of maraging steel and helicopter tailbooms consisting of monolithic and sandwich CFRP were selected. The applied NDT technologies are based on ultrasonics as well as on electrical and electrochemical impedance measurements. Due to the dominance of platestructures, guided ultrasonic waves are used, such as Lamb waves and Rayleigh waves. In this context, mode conversion effects are exploited and detected with appropriated sensors arrays. Another promising candidate is high-end time-of-flight detection of Lamb waves using chirp technology. Such ultrasonic systems were used for helicopter tailbooms, slat tracks and aluminium sheet structures. For more local damage detection, the interruption of electrical signals by fatigue crack formation (slat tracks and aluminium sheet structures) or by leaking corrosive liquids (floor beams) appears to be successful. Finally, electrochemical and electric impedance spectroscopy is used for detecting corrosion in floor beams and cracks in doubler repairs. For all systems proposed, durability and robustness is a major concern. Since April 2011 a first sensor system for detecting aqueous liquids in floor beams was implemented in an operational airliner Boeing 737-500 (Lufthansa).