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AISHA II
Aircraft Integrated Structural Health Assessment II

Tags: Air

State of the Art - Background

Today's aircraft inspection procedures are excellent, but too expensive and not appropriate for all situations. A cheaper alternative for damage detection is offered by 'structural health monitoring'(SHM). With such SHM systems, a permanent sensor network, comparable to the nervous system in a human body, is placed at crucial structural components of an aircraft. In this project, guided ultrasonic waves (Lamb waves) are used to detect different kinds of defects.

However, this apparently easy solution requires a quite complex research and implementation effort using well-coordinated collaborations of many disciplines and expertise in Europe. The European Research Area establishes the ideal platform for such a collaborative undertaking, and the considerable financial risks can be reduced by a substantial amount by appropriate funding from dedicated European research programmes.

During the last few years, a number of SHM solutions have been presented at laboratory scale, and even partially implemented in real aircraft parts. There is thus, in principle, enough experimental evidence that such systems are able to deliver all the required information. However, the final implementation is still in an early phase and is partially hindered by a number of obstacles (technical immaturity, lack of acceptance by end-users, etc.).

Objectives

It will not be possible within this project to present a large-scale integrated technical solution to overcome all the challenges related to structural health monitoring. However, the following strategies have been chosen to put the operating systems into practice.

It appears that the best strategy to overcome the above-mentioned obstacles is to develop a SHM system for selected, isolated problems which can easily be followed and validated by conventional methods. If this technique appears to be trustworthy, a broader field of application will be created.

AISHA II therefore intends to focus on hot-spot monitoring instead of large-area screening. From operational experiences it is known that defects usually occur at well-defined locations. There are thus isolated problems in maintenance where a simple SHM can give reasonable added value, without screening the whole aircraft.

Description of Work

This project will use a limited number of carefully selected ultrasonic Lamb wave modes in the detection process. Lamb mode selection, both active and passive, is, however, not an easy process. As one of the main innovative aspects, the principle of controlled Lamb wave selection will be used as the basis of an aircraft health monitoring system, both for active and passive Lamb wave testing. In practice, this will mean that the amount and type of Lamb wave modes to be used in the monitoring process will depend on the type of material and damage to be detected and will thus have to be controllable by the user. Other NDT technologies will also be applied, such as electrochemical monitoring and eddy current.

Other work includes:

- opening the initial phase with the establishment of detailed specification sheets where the different demands on damage detection are clearly defined. The respective full-scale part will be studied by the assigned NDT groups, the different aspects of feasibility explored and the final plan for SHM implementation developed;

- implementing the selected SHM systems will be carried out in close collaboration with all partners. Using the transducer, hardware and software required, the approved concepts will be implemented following the detailed road map defined in the design phase;

- an extended test programme will be run to check all operational aspects.

Expected Results

The expected progress that the proposed project will bring with respect to the state of the art will be the following:

- A selection of very specific aircraft components (representing isolated 'hot spots') in collaboration with the aircraft operators and aircraft manufacturers. The expected cost savings from using SHM must be considerable;

- A systematic research on durable sensor connections ensured by collaborating with a specified research institute;

- If proved useful, the introduction of the pseudo-defect technique for automated validation. This enables a dramatic enhancement in the efficiency of the validation tests leading to a fine-tuning of data analysis techniques;

- The application of combined sensor groups (ultrasonic sensor + parametric sensors for temperature and strain), electrochemical monitoring and thermography. These techniques are beyond the application of ultrasonic Lamb waves, but they help to facilitate the interpretation of signal-damage relationships.

AISHA II - Sensor network
AISHA II - Sensor network

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