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ROSA Résumé de rapport

Project ID: 270590
Financé au titre de: FP7-JTI
Pays: Germany

Periodic Report Summary 1 - ROSA (Reliability Oriented Optimisation of Structural Replacement Strategies for Aircraft Structures)

Project Context and Objectives:

The optimization of maintenance schemes for aircraft structures is a major technical and economic issue in the aerospace industry. There is a strong interest to further optimise and customize maintenance activities, aiming at reducing costs directly and indirectly associated with unnecessary inspections and replacement actions. Recent technical developments in Structural Heath Monitoring (SHM) have provided new possibilities for inspecting engineered structures in general. Knowledge of the “damage level” of the structure and forecasting of its development on a probabilistic basis allows the intelligent system to plan removal from service of the aircraft when the requirement for maintenance is specifically justified.

The methodology and the corresponding codes developed in the ROSA project facilitate the quantification of the impact of SHM information on maintenance planning and the optimization of the life-cycle costs. The framework developed enable the quantification of the effect of changes in the design of the structural components as well as the SHM design on the inspection / maintenance cost and consequently the overall life-cycle cost.

Project Results:

This is the first and final formal (online) periodic report for the ROSA project and therefore the final results are given in the next section.

Potential Impact:

Final results:

All relevant models for the problem description have been presented, developed and implemented into a code. Main achievements of the ROSA project are summarized as follows:

• A mechanical meta-model for the description of the damage growth on stiffened composite material due to different impact scenario has been identified and implemented.
• A procedure for the inclusion of the monitoring system has been investigated. Models for the probability of detection and the receiver operating characteristic have shown to be essential in the perspective of the Bayesian damage update, at the basis of this report.
• The method for the evaluation of the capacity loss due to the damage detected by the monitoring system can be extended in order to include an alarm system for decision support.
• Complex structures, as the aircraft wing in final report, can be easily handled by the method, accounting for simplified structural effects on the element capacity.
• The ROSA strategy has been implemented for specific models but it can easily be adapted to more complex models, due to the modularity of the methodology.

Sensitivity analysis has been presented by changing the most relevant parameters. It has been shown that the quality of the monitoring system, expressed by the Receiver Operating Characteristic (ROC) curves is central to the optimization of the optimal interval between consecutive inspections.

The expected life-cycle cost analysis has been presented. The analysis evidenced that the probability of false alarm of the structural health monitoring systems plays an essential role in the total expected maintenance element cost.

The theory has been implemented in standalone a code and details, examples of runs and results have been provided. The possibility of interfacing the code with the software Strurel has been examined and conceptual solution has been given.

Potential Impact:

Structural health monitoring (SHM) technologies such as embedded sensors provide large potential for cost savings during the operation of an aircraft due to reduced down-time of the aircraft associated with inspections. The associated economic benefits will lead to operators requesting such aircrafts in the future. However, due the fact that SHM is a novel technology, practical experiences are lacking. For these technologies to be successful, it is essential that their impact on safety and maintenance cost can be determined analytically and can be demonstrated to the operators prior to installing them. This project provided a methodology and associated software tools towards achieving this goal and will thus enhance the implementation of the novel technologies in the industry.

Although ROSA did not focus on the improvement of composite structure design, it is expected to have an indirect beneficial influence on it. As ROSA contributes to the goal of making embedded sensors technologies practical, efficient and reliable, it is expected to provide simultaneously more potential for light-weight design by means of increasing design allowables, especially for specific aspects of composite structures that are currently designed in a very conservative way in order to account for the different uncertainties that can reduce structural strength (e.g. a barely visible defect due to impact damage). In particular, the renewal modeling of the life-cycle of aircraft structural components as a function of operational utilization, structural integrity, internal condition and performance can provide valuable insight on the structure performance and room for future improvements of the structural design. The ROSA software modules can potentially be related to flight conditions and performance and can be fed back to on-going design activities for improving the engineering models, test organizations for analysis, verification, and validation for next-generation structures.

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