STRAINMON

Strain Monitoring in Composite Stiffened Panels Using Sensors

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 Obiettivo del progetto (Objective)

'STRAINMON aims to develop and establish a methodology for the strain monitoring of composite fuselage stiffened panels using embedded and/or bonded Fiber-Optic Bragg Grating (FOBG) sensors and strain gauges. The proposed work-programme of STRAINMON is summarized as follows: 1. Definition of the FOBG system requirements and specifications based on the nature of the problem and the available technology using progressive damage modeling. The number of sensors will be decided and the network of sensors will be designed. 2. Description of the methodology for integration of sensors related to the autoclave manufacturing process by ensuring measurement capability of the sensors, integrity of sensors, and integrity of the parent composite material. 3. Design of the test plan and design and fabrication of the test-rig, 4. Execution of the series of the following tests to establish the proposed SHM methodology: -Compression tests to failure on undamaged panels to characterize their reference compressive behavior, -Low velocity impact tests on selected critical locations of the panel in order to create impact damage, -Compression tests to failure on the impact-damaged panels to evaluate the residual stiffness and strength of the panels, -Fatigue of impact-damage panels up to a certain number of cycles in order to create additional fatigue damage, -Compression tests to failure of panels subjected to impact and fatigue to evaluate the residual stiffness and strength data of the impacted and fatigued panels. After each test series, NDT inspection of the panels will be conducted in order to detect the type, extent and location of damage induced. Each of the above tasks meet an activity of the topic. A reliable and effective data acquisition system will be build to take sensor measurements at appropriate rates during the whole duration of the testing scheme and from all sensors placed on the panels simultaneously. STRAINMON's consortium comprises VZLU (CZ) and UNIPatras (GR).'

Introduzione (Teaser)

An EU project developed and proved a lightweight system for monitoring aircraft structural integrity. The system involves fibre-optic sensors installed into a specially stiffened panel.

Descrizione progetto (Article)

The air transportation industry has been responding to public concerns about pollution and climate change. Clean Sky is a multi-project joint initiative between the aviation industry and the European Commission aimed at developing and marketing new green aircraft technologies.

Funded by the EU, the project 'Strain monitoring in composite stiffened panels using sensors' (STRAINMON) was part of Clean Sky. The project aimed to develop procedures for implementation of a structural health monitoring system, based on fibre-optic Bragg grating (FOBG) sensors and strain gauges. The new system was to be installed onto a carbon-fibre reinforced polymer fuselage stiffened panel. The purpose of the FOBG sensor was to monitor structural integrity of impacted and fatigued panels under compression loading. The advantage of the new technology over current monitoring systems is weight-saving. The two-member consortium ran from January to August 2012.

The project set eight technical goals, amounting to defining system requirements, manufacturing a test rig and testing. Work resulted in the team developing a method for embedding the sensors in the structure, which is related to the autoclave manufacturing process. In developing the method, the group paid special attention to entry/exit points, and to definition of appropriate sensors. A suitable testing plan was developed, then associated testing rigs were designed and built. Two panels were struck with low-force impact, and subjected to static and fatigue testing using the project's system. The FOBG data matched conventional testing systems, meaning that the FOBG sensors may be an adequate alternative.

STRAINMON successfully demonstrated that FOBG sensors can be integrated into composite aircraft structures, while also effectively monitoring structure strain. Use of the sensors will mean weight reduction, meaning savings on fuel and reduced pollution, and reduced maintenance intervals.