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Early detection and progress monitoring and prediction of corrosion in aeronautic Al alloys through calibrated Ultrasonic CorROSion Sensors application

Periodic Reporting for period 2 - U-CROSS (Early detection and progress monitoring and prediction of corrosion in aeronautic Al alloys through calibrated Ultrasonic CorROSion Sensors application)

Reporting period: 2021-04-01 to 2022-09-30

The need of reducing aircraft weight, to in turn decrease fuel consumption, is pushing the aerospace industry to incorporate light materials, such as Aluminium alloys. One of the main drawbacks of Al alloys, which is limiting its greater use, is that they are sensitive to microstructural localized corrosion, generating corrosion events such as pits. Corrosion is an important consideration here since it can lead to material loss and is often the precursor of fatigue cracking among other failure mechanism, affecting aircraft availability, security and operational issues.
Nowadays, aircraft operators attempt to reduce the maintenance costs by implementing different approaches to detect/monitor corrosion. Among them, probably the most challenging is the indirect measurements using non-destructive sensors, where calibration is needed to minimize as much as possible false positive or negative signals during maintenance actions.
The main impact of U-CROSS, regarding the industry field, is an estimated saving of up to 50%. This cost-efficiency enhance the competitiveness of many industrial big companies.
On the other hand, regarding the environmental impact, U-CROSS project will indirectly contribute to ACARE 2020 objectives. The future implementation of U-CROSS results in other industries is also relevant, as the potential redesign for lighter parts will mean also less fuel consumption in the airplane. Lighter aircraft would mean less fuel, less CO2, less emissions, etc.
The target of the WP1 was related with the selection of aircraft components and damages worthy to monitoring, defining methodologies and defining the systems under test, which have to be used in the following WPs.
Then, during WP2, the sensitivity of different acoustic/ultrasonic detectors in different scenarios and test rig design for each type of corrosion was determined.
The WP3 focalised on the calibration process. In particular, the activities of the WP3 were addressing the preparation of systems to test, the monitoring of the systems under study by means the corrosion sensors, and analysis through data processing.
On the WP4, the consortium has prepared real structures/components to test in external ambient, and validate the corrosion sensors.
Finally, the WP5 is addressing the degradation model of coatings and the software of calibration (ultrasonic corrosion sensor).
Currently, at industrial application level, some unsolved questions related with the evaluations of the corrosion in aero structures are going to be addressed by U-CROSS project:
- It does not exist a standard procedure for corrosion forms creation to manufacture reference blocks.
- NDT for corrosion detection is only limited to damage such as crack and loss of thickness.
- There is not correlation between laboratory tests and in service conditions.
At academic level, the main progresses beyond the state-of-the-art associated to U-CROSS concerns the development of an experimental strategy for triggering the different corrosion forms, the determination of the signature of signals for each corrosion form, the validation of the calibration methodology for Ultrasound Corrosion Sensor (UCS), and the development of a prediction software taking into acount the ageing of the coatings.
AE monitoring of corrosion process on coated aluminium