Overview
The continued growth in air traffic has placed an increasing demand on the aerospace industry to manufacture aircraft at lower costs, while, at the same time, ensuring the products are efficient to operate, environmentally friendly and maintain the required level of safety. The primary objective of the aero-space industry is to offer products that not only meet the operational criteria, in terms of pay-loads and range, but also in terms of significantly reduced direct operating cost, which is to the benefit of their customers, the airlines.
The ultimate aim of the SMIST project was to develop and validate monitoring technologies able to deliver certain cost savings for maintenance and enable innovative structural design for metals and composites. For this purpose, the objective was to allow the most advanced sensing technologies to become an integral part of the aircraft structure and thus implement Structural health monitoring (SHM) into aircraft structural design in order to minimise maintenance costs, increase aircraft availability and minimise weight.
The project itself was split into three parts (Work Packages), dealing with:
- Work Package 1 - specifications;
- Work Package 2 - technology development, and;
- Work Package 3 - application and validation tests.
The project included nine sensor and monitoring technologies of different natures, which, at the end of the project, had to prove their applicability with regard to the objectives and specifications set. Due to their different natures, not all the technologies met all of the objectives and specifications. However, all the objectives were addressed and hopefully met by the different technologies involved. Providing different solutions to meeting the objectives guaranteed that the merging of different technologies into one system would still be possible in the end, and that lead to a system meeting all of the objectives being addressed. It was possible that none of the technologies presented were able to meet the objectives set at this stage.
The monitoring technologies to be proven were:
- Fibre Optic Bragg Gratings;
- Sensitive Coatings;
- Environmental Degradation Monitoring Sensors;
- µ-wave Antennas;
- Acousto-Ultrasonics;
- Comparative Vacuum Measurement;
- Acoustic Emission;
- Imaging Ultrasonics;
- Eddy Current Foil Systems.
Funding
Results
The main achievements of the projects were subsumed into the following eight fields:
Fibre Bragg gratings (FBGs)
- application procedure using patches was established and filed for patenting;
- connectors for embedding Fibre optic (FO) sensors have been developed;
- panels for damage monitoring on composite structures were manufactured;
- finite element analysis was performed and verified by small scale test.
Acousto-ultrasonic (AU) technologies
- the damage detection capability in metal structures was shown and a better understanding of signal processing was achieved;
- hardware with regard to transducers was investigated and new sensors were developed;
- the first environmental tests were successfully finalised;
- the first common testing on composite structures was performed.
Comparative vacuum monitoring (CVM) - systems
- an application procedure was established and an installation sheet compiled;
- tailored sensors for several applications were developed;
- a service bulletin was published allowing the use of these sensors on service aircraft;
- the first environmental and mechanical durability tests were successfully performed;
- a Probability of detection (PoD) was achieved;
- the first detection capability tests on composite panels were successfully performe.
Acoustic emission (AE) systems
- two patents have been filed, the first one concerned new types of transducers and the other one concerned the testing procedure for the damage assessment of small Carbon fibre-reinforced polymer (CFRP) coupon specimens subject to AE-monitored fatigue loading including the algorithms for processing AE data;
- the AE BALRUE software was improved;
- work was completed to develop AE analysis for complex three-dimensional (3D) structures;
- a study on the use of FBG sensors for AE was completed.
Sensitive coatings (SCs) and Environmental degradation monitoring systems (EDMS)
- Direct write (DW) Radio-frequency identification (RFID), Strain Gauge (SG), Crack wire (CW) and micro-environmental sensors were developed and tested under mechanical and environmental conditions;
- one new sensor system for crack detection was filed for patenting;
- a study on environmental degradation monitoring systems was completed.
Technical Implications
The main innovation through SMIST will be to equip aero-structures with an integrated sensing function by adaptation of advanced sensor technologies to SHM systems, with the SHM systems being ready to be adapted to virtually any type of real aircraft structure and under a real in-service environment