Health Monitoring of Aircraft by Nonlinear Elastic Wave Spectroscopy
Nonlinear Elastic Wave Spectroscopy (NEWS) and related acoustic and ultrasonic methods comprise a new class of innovative non-destructive techniques that provide extreme sensitivity in detecting and imaging incipient damage in the form of microcracks or delaminations, weakening of adhesive bonds, thermal and chemical damage, etc. The sensitivity and applicability of nonlinear methods to damage are superior to those obtained by currently used technologies. NEWS methods are in various stages of development and have not yet been applied to aircraft health monitoring.
The project's goal was to examine, confirm and exploit the successful results of these techniques, using fundamental materials research on fatigue loading, and to apply them to the particular field of aeronautics.
The project included progressive microdamage and fatigue monitoring of aircraft components and structures, sensor engineering, development of NEWS-based imaging methods, and fundamental research on the modelling of meso-scale damage phenomena. It aimed to investigate the relation of these studies to the macroscopic behaviour of progressively fatiguing materials, and formulate the design of a unique system for microdamage inspection, including remote control and communication tools, and the completion of a full-scale model validation.
The long-term goal of the project (5-10 years) is to monitor while in operation, the integrity of airframes and aircraft engines, and helicopter rotor systems. The development of this innovative NEWS-based technology and its engineering applications to aeronautics, will result in an enhanced, reliable and integrated measurement system and protocol for microcrack diagnostics of aircraft components and structures. This development is expected to result in a significant increase in aircraft and passenger safety while contributing to substantial cost savings through a decrease in maintenance and operating times.
The AERONEWS project integrated activities in three sections:
- fundamental and applied research
- technological development and innovation related activities
- validation and training.
The emphasis of the project methodology is on the development and perfection of suitable techniques and knowledge enhancement of NEWS so that it can be used for both the current and extended non-destructive evaluation (NDE) methods and applications in the field of aeronautics.
The working flow-chart of the project incorporates all the steps required for the practical implementation of NEWS technology. Activities dealt with:
- fundamental and applied research;
- technological developments;
- validation of the proposed product;
- dissemination activities.
AERONEWS' overall result was to provide an enhanced, reliable and integrated prototype measurement system and protocol for microcrack diagnostics of selected aircraft components and structures, through the development and preliminary verification of an innovative NEWS-based non-destructive testing (NDT) technology and its engineering applications in aeronautics. Several intermediate results were used:
- AERONEWS identified and selected critical parts and structures of interest to aeronautics NDT and on identifying several of the most common failure scenarios. This work led to an extensive database of available testing material. In so doing, AERONEWS also built an extensive database on the type of damage (failure scenarios), from weak bonding to single cracks, localised and extended microcracked regions, and corrosion.
- AERONEWS developed diagnosis techniques, including non-linear wave propagation, non-linear wave modulation, impact modulation, and non-linear reverberation spectroscopy. The results were promising, showing both global and local signatures of damage. To prove the increased sensitivity of non-linear techniques in NDT evaluations, an extensive monitoring experiment was planned and executed on a field test site. Moreover, the experience gained using the NEWS techniques allowed for the setting up of a database of the most important characteristics, requirements and limitations of the various techniques.
- AERONEWS provided numerical support for the experiments, and developed, through intensive NEWS modelling, two methodologies for a NEWS technology-based imaging system: NEWIMAGE and MUMONRAS (Multi Mode Non-linear Resonance Acoustic Spectroscopy). The main conclusion from this third result is that numerical simulations have indeed supported the developments on the experimental level for NEWS-based imaging techniques of micro-damage.
- Concerning the design of smart transducer/sensing systems, AERONEWS conducted a survey on current and emerging sensor and transducer technologies and a mapping of these technologies to the specific demands of NEWS and NEWIMAGE. The conclusion of this study made clear that no single transducer/sensor would be the answer for all techniques since the techniques themselves are different in nature and have different requirements.
- The project developed prototypes for transducer/sensing systems, including specific hardware design (ceramic elements, cheap optical/piezoelectric transducers, smart surface contact transducers and syst
- The conclusion of the 'Experimental week', in which the field tests were carried out, was that, although the various techniques were not yet optimised for the use on extended and complex samples, results were overall positive and provided useful guidance as to how the technique can be improved.
- Due to the increased sensitivity of the technology, it is expected that this development will result in a significant increase in aircraft and passenger safety while contributing to substantial cost savings through a decrease in maintenance and operating times. The long term goals are the engineering of a standard measurement system based on NEWS for continuous health monitoring and early-stage damage diagnosis.
- However, all developments (software and hardware) carried out under the AERONEWS framework and successfully tested will finally lead to commercial exploitation. Therefore, AERONEWS developments fully comply with current standards and regulations, with the aim of being installed in airborne systems.
From a policy point of view, the sheer scope and mandate of the AERONEWS project, as well as the number and level of partners involved, is an indication of the level of success that can be achieved within European coordination.
- As part of a 'Dissemination' programme, AERONEWS carried out high-level scientific international projects, including more than 25 special sessions at several international conferences, and the publication of about 50 scientific papers in international reviewed journals. Recommendations were specified for follow-up NEWS technology standardisation and maturation in view of the implementation of the system on aircrafts, and the resulting patent proposals.
- The exploitable products resulting from the AERONEWS project, as part of the general domain of Ultrasonic Non destructive testing equipment, have a wide sectoral application, namely:
- Aeronautical & Civil engineering;
- Marine & Rail transport;
- Materials' Manufacturing;
- Inspection Pharmaceuticals;
- Food Industry.