Development of a structural health and load monitoring system and its implementation into an aircraft flying demonstrator

Many common metal structures of industrial applications are recently optimized or even replaced by lightweight substitutes. Lightweight structures yield less weight at high stiffness and excellent fatigue resistance. Environmental pollution as well as operational and maintenance costs can thus be reduced in many areas, for example in automotive or aircraft sector. However, the persistence of components built of lightweight structures like carbon fiber reinforced plastics could be seriously affected by impact damages and lead to fatal failure within short, unpredictable time. To handle this concern, lightweight structures have to be monitored consistently by appropriate sensors and all structural information should be collected and analyzed by a suitable system. In this paper, the design and development of a comprehensive monitoring system for aircraft lightweight structures and the final implementation into a flight demonstrator is presented. An ATR 72 has been used as in-flight demonstration platform, thanks to the common work and support of Finmeccanica and ATR. This system combines two monitoring techniques: piezo-based structural health and optical Fiber Bragg grating-based load monitoring. The structural health monitoring approach is based on broadband acousto-ultrasonic measurements. Here, the structure to be monitored is excited to vibration in a broad frequency band and in parallel the transmitted structural response is acquired and analyzed. Structural changes are reflected in the acquired transfer functions. Damage is detected by the means of correlation functions between current and baseline measurements. For load monitoring optical fibres with integrated Bragg gratings collect strains applied to the monitored structure at crucial points. In this way a load history required for the estimation of the remaining structural service life is provided. Both methodologies have been implemented and tested under real flight conditions.