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AISHA
Aircraft Integrated Structural Health Assessment

Background

The structural health of engineering structures is increasingly threatened by material degradation. Reliable means of health monitoring are therefore required for safe operation. Based on this monitoring, maintenance actions can be undertaken. Whereas a time-based inspection scheme has resulted in excellent reliability records for aircraft, there is an economic drive for more innovative health monitoring procedures. Recently, it has been proposed to switch from time-based towards condition-based procedures, where maintenance is only performed when a component is known to be degraded. This requires a means of continuously assessing the structural integrity of the aircraft by a continuous damage monitoring system.

Project objectives

This project aims to develop aircraft monitoring technology by exploring ultrasonic waves as the basic sensing principle. Both active and passive wave inspection will be explored, using the innovative concept of multimode wave generation and reception. The information from these waves, combined with signal analysis routines and models for remaining lifetime prediction, will ultimately be used in a full-scale testing action during which the possibilities for large-scale application will be explored. A consortium with broad and multidisciplinary expertise has been formed, with contributions from high tech SMEs, university research groups, end-users and a certification laboratory.

Wing with extended slat tracks during MRO. The transition from time-based to condition-based maintenance, based on Lamb wave ultrasonic inspection, will be the focus of AISHA.
Wing with extended slat tracks during MRO. The transition from time-based to condition-based maintenance, based on Lamb wave ultrasonic inspection, will be the focus of AISHA.

Description of the work

It is suggested to use a limited number of Lamb wave modes in the detection process. As a first step in the project, optimum Lamb wave mode sets will be selected, taking into account the material under investigation, loading condition and damage type. Novel sensors/actuators will be developed for selectively generating and detecting Lamb wave modes. Methodologies for the integration of sensors and actuators into the structure will be explored. A major part of the project will be devoted to establishing quantitative relations between growing damage phenomena and detected signals. This step will be aided by the development of automated signal analysis strategies, which aim to provide either a visualisation of the data or a multidimensional analysis. A separate action will be devoted to providing the link between the monitored results and the actual structural condition. Based on a sound knowledge of the amount of damage present, a conclusion will have to be drawn about the fitness for service of the structure and the need for repair. This will require an adequate modelling of damage states, calculating residual properties and predicting the remaining lifetime. A final research action will be devoted to a full-scale testing of the obtained laboratory results.

Expected results

On the way towards the main project goals described above, a number of results are being generated through co-operation in the consortium. A digital and searchable database has been constructed, containing common structural aircraft materials together with their relevant properties and degradation mechanisms. An important result of the project will be the understanding of the interaction of propagating Lamb waves with material defects in metals and long fibre composite materials. The use of this knowledge is not confined to the study of aircraft materials, but can also be used for the inspection of other structural parts that exhibit defect formation, such as chemical process installations with corrosion cracks or structural composites that are subject to impact or fatigue damage evolution. Towards the end of the project, a way of monitoring will be tested at full scale, giving additional information on the issues encountered while scaling up lab techniques. In addition, the concepts predicting the remaining lifetime of structures during damage generation and evolution can be used for other applications.



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