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Development of Integrated MEasurement Systems

Periodic Reporting for period 1 - DIMES (Development of Integrated MEasurement Systems)

Reporting period: 2019-01-01 to 2019-12-31

The aim of the project is to develop advanced integrated testing methods that have the capability to detect a crack or delamination in a metallic or composite structure and have the potential to be deployed as part of an on-board structural health monitoring system for passenger aircraft. The project seeks to incorporate a new philosophy for monitoring damage in which the disturbance to the strain field in the structure caused by the damage is used to identify significant damage and to track its propagation. Recently, this approach has been demonstrated to be at least as effective in composite structures as traditional non-destructive evaluation techniques and, in CS2 project INSTRUCTIVE using infrared technology, it has been shown to be capable of identifying smaller cracks in metallic structures than any other available technique. In this project, these innovations are being amalgamated with established techniques, such as strain gauges and fibre Bragg gratings, to demonstrate an integrated testing method. The objectives are designed to mature technologies from TRL 4 to 6 that are likely to have a disruptive impact on the structural health monitoring of next generation large passenger aircraft. The objectives are: i) to develop a robust and innovative concept for integrating a diverse set of sensors and data acquisition systems for detecting and monitoring damage in an aircraft assembly; ii) to produce an integrated system of sensors and data acquisition systems deployed on a test bench representing an aircraft assembly, and; iii) to conduct prototype demonstration and evaluation tests of the integrated system and test bench using independent systems. The primary outcome will be the demonstration, on a test bench section of aircraft, of an integrated measurement system for ‘on-line’ detecting and monitoring damage based on a diverse range of sensor systems.
At the mid-point in the project, DIMES is on-schedule to complete all of its deliverables and to achieve its objectives. The consortium is working together effectively and has a strong working relationship with its Topic Manager, Airbus, at whose facilities a major structural test will take place in the second half of the project, which will include the implementation and demonstration of the project outputs. From a technical perspective, the project has already delivered (i) the outcomes from a rational-decision-making process for an integrated measurement system for detecting and monitoring damage in aircraft structures; (ii) a set of robust and innovative conceptual designs that integrate a diverse set of sensors and data acquisition systems for detecting and monitoring damage in an aircraft assembly (project objective [a]); and (iii) prototypes of an integrated system of sensors and data acquisition systems deployed on a test-bench representing an aircraft assembly (project objective [b]). Good progress is being made toward delivering the final objective of the project: to conduct prototype demonstration and evaluation tests of the integrated system and test bench using independent measurement systems to verify the outcomes. The dissemination of the outputs from the project is underway. A conference presentation has been made and archived journal papers are being planned. A series of posts on an engineering blog have been published and the first video short has been released. A workshop was held at Airbus in Filton in January 2019 and another is planned for March 2020 at Airbus in Toulouse.
Farrar and Worden [Phil Trans R Soc A, 365:303-315, 2007] identified five questions that need to be answered in order to describe the damage state of a system: (i) Is there damage? (ii) Where is the damage? (iii) What kind of damage is present? (iv) How severe is the damage? (v) How much useful life remains? These questions are increasingly more difficult to answer. Many structural health monitoring (SHM) systems cannot progress beyond the first two questions, while some non-destructive evaluation (NDE) approaches can address all, except the final question. Structural health monitoring is associated with 'on-line' damage identification, whereas non-destructive evaluation is usually performed 'off-line', in the sense that the component is taken out of service, which allows a wider range of techniques to be deployed including radiography, thermal imaging and ultrasound. In the DIMES project, these concepts are being integrated in a system that uses non-destructive testing and inspection approaches to perform structural health monitoring and thereby deliver answers to four of the five questions identified by Farrar and Worden - its implementation built around small, low-cost devices represents a significant advance on the state-of-the-art.

Recent work in the Clean Sky 2 INSTRUCTIVE project has shown that representative flight cycle loading can be used to generate a thermal signal which is sufficient to detect the initiation of damage in metallic components based on the thermoelastic effect. At the same time, compact low-cost microbolometer systems have become available for thermoelastic stress analysis; so that it is viable to translate thermoelastic stress analysis into the structural health monitoring domain by combining these developments to allow whole-field detection of damage during flight-cycle loading without any special surface preparation. In the DIMES project, this capability has been delivered in an instrumented test bench at EMPA that includes a section of an Airbus wing and represents an advance on the state-of-the-art.

In the next stage of the project, the capabilities of the prototype integrated measurement system will be verified and the system will be demonstrated on an assembled A320 wing subject to deformation due to loads representative of flight cycles at the topic manager's site and will represent a substantial advance in the state-of-the-art relative to these prior studies which have used flat or near-flat reinforced panels about 1x1 metre.

The development of an automated system, which integrates data acquisition from a diverse set of sensors with a user interface and allows continuous operation during a structure test, will result in state-of-the-art instrumentation. And, the requirement for the system to allow multi-interface options with Commercial-Off-The-Shelf (COTS) sensors and automated linking to the test control system, is likely to lead to instrumentation for which there will be a market in the worldwide aerospace industry and that could be further developed for other industries, such as the power generation industry. The demonstration in an industrial environment of the multi-faceted technologies in the integrated measurement system is likely to provide a boost to further fundamental research on sensor technology, data acquisition and processing methodologies and development of more efficient design prototyping. Consequently, the proposed research represents a significant and generic advance in the technology and methodologies used to test prototype structures and perform on-line structural health monitoring which is likely to be of benefit to the European aerospace industry, in the first instance, but subsequently to a wider range of industrial sectors.
DIMES project team and the wing-based test bench at EMPA, see