The project was divided into 2 main areas and was carried out by two partners, the German Aerospace Center and the Netherland Aerospace Center. The first focus with about one third of the budget was the evaluation of technologies. These technologies were developed in the second focus of DEMETER and in two sister projects of CleanSky 2. The evaluation should compare the previously assumed technological advantages with those achieved in the projects. Therefore an evaluation concept based on questionnaires and evaluation matrices was developed. The evaluation approach was developed together with M2P from the AIRMES project. Therefore all technical results from both projects were collected and evaluated with the AirTobs tool. The overall results were described in deliverables 4.1 and 4.2.
In the second part of DEMETER, which accounts for about two thirds of the budget, research was conducted on usage and structural health monitoring systems. Usage monitoring uses flight data and converts them into usable information with the help of simulation models. This enables the real usage at selected positions of the aircraft to be analyzed and thus to change the maintenance interval from a previously fixed planning to a variable usage-based planning. In DEMETER, different models such as flight simulation, stress calculation, structural fatigue assessment and maintenance planning were networked and analyses were carried out. The input data for the flight maneuvers can be extracted from the flight recorders or, in the case of DEMETER, data from Flight Radar24. The considered Use Case was the engine mount. It could be shown that such a usage monitoring evaluation chain can be built up in a decentralized, modular way. The modules are flexibly exchangeable and the respective partial services can be offered separately in the future. The developed data exchange concept is flexible and expandable.
While a Usage Monitoring System uses existing data to make an assessment, Structural Health Monitoring Systems use sensors at specific positions in the structure to monitor it. Two systems were considered. First, strain sensors (Fibre Bragg Sensors) were used to check load paths. Here, the engine mount was also used as a use case. If a load path fails due to damage, the system automatically reports the need for repair. The second technological approach is based on the area-wide monitoring of structures using guided ultrasonic waves. A concept evaluation showed that 5% structural mass can be achieved with such a system due to an adapted aircraft design. In the project this technology was further developed to compensate for environmental influences and to detect the damage by means of machine learning algorithms. Once the damage has been detected, an evaluation of the damage itself is helpful in deciding whether a repair is necessary. For this purpose, methods have been further developed to make this possible. It is possible to transfer impact damages based on structural health monitoring systems and classical non-destructive testing methods into a model. By analyzing the damage, the residual strength can be calculated and evaluated if a repair is necessary.
