A thin foil optical strain gage based on silicon-on-insulator microresonators - art. no. 661914

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Photonic skins for optical sensing:highlights of the PHOSFOS project

PHOSFOS (Photonic Skins For Optical Sensing) is a research project funded by the European Commission's 7th Framework Programme. The project aims at developing a flexible and stretchable foil that integrates highly advanced optical fibre sensing elements as well as optical and electrical powering functionalities and read-out of the sensors. This skin-like foil can be wrapped around or attached to irregularly shaped objects or bodies and will allow quasi-distributed sensing of mechanical quantities such as deformation and pressure. The applications targeted can be found in the fields of structural health monitoring and healthcare

Delamination detection with fibre Bragg gratings based on dynamic behaviour

The influence of a delamination on the resonance frequencies of laminated composite beam is investigated. A model, proposed by Mujumdar and Suryanarayan [Mujumdar PM, Suryanarayan S. Flexural vibrations of beams with delamination. J Sound Vib 1988;125(3):441–61], of the dynamic properties of delaminated isotropic beams is extended to anisotropic laminated beams. Parameter studies show that the resonance frequencies are a function of both delamination parameters (location and size) and laminate lay-up. Experimental and analytical resonance frequencies for undamaged and delaminated test samples show good agreement. The resonance frequencies of carbon-PEI laminated cantilever beams were measured using embedded fibre Bragg grating strain sensors. High frequency measurements were performed by using a slope-filter based interrogator. \u

The use of optical fibers for fatigue testing of fiber-reinforced thermoplastics

This study investigates the possibility of using optical fibers with Bragg gratings for measurements under fatigue loading conditions. Detailed information is given on the principle of optical fiber measurements, the embedding process and the fatigue tests. To verify the strain derived from the optical fiber, the strain is compared with extensometer measurements. Furthermore, X-ray micro-tomography is discussed and used for the visualisation of the optical fibers and damage in the composite material. The material used for this study was a carbon fiber-reinforced polyphenylene sulphide. It can be concluded that the optical fiber survives over half a million loading cycles, without de-bonding of the fiber. Furthermore, the resolution of the micro-tomography is high enough to visualise not only the optical fiber, but also damage in the material

Arrays of regenerated fiber bragg gratings in non-hydrogen-loaded photosensitive fibers for high-temperature sensor networks

We report about the possibility of using regenerated fiber Bragg gratings generated in photosensitive fibers without applying hydrogen loading for high temperature sensor networks. We use a thermally induced regenerative process which leads to a secondary increase in grating reflectivity. This refractive index modification has shown to become more stable after the regeneration up to temperatures of 600 °C. With the use of an interferometric writing technique, it is possible also to generate arrays of regenerated fiber Bragg gratings for sensor networks. © 2009 by the authors

Non-destructive evaluation of composite structures using an innovative Bragg sensor

This paper discusses a new sensor design based on optical fibre Bragg gratings which is being developed in the framework of the MASSFOS-project ('Multi-Axial Stress and Strain sensing of thermo hardened composite elements using Fibre Optic Sensors'-project). The objective of this ESA co-funded project is to develop a monitoring system which measures dynamically the multi-axial stress and strain plus temperature in thermo hardened composite elements. The sensor consists of a 'High Birefringence'-fibre in which two gratings have been inscribed; each grating yields two distinct Bragg peaks. The first grating is sensitive to the total stress field in the material, while the second one is isolated from transverse stress components. By measuring the four Bragg peaks of the sensor, it is theoretically possible to determine the total strain field, plus the temperature inside a composite material. A Static tensile test has already been carried out to prove the feasibility of the sensor embedded in a composite laminate

Feasibility study of an embedded Multi-Axial fibre bragg grating sensor

This paper discusses a new sensor design based on optical fibre Bragg gratings which is being developed in the framework of the MASSFOS-project ('Multi-Axial Stress and Strain sensing of thermo hardened composite elements using Fibre Optic Sensors'-project). The objective of this ESA co-funded project is to develop a monitoring system which measures dynamically the multi-axial stress and strain plus temperature in thermo hardened composite elements. The sensor consists of a 'High Birefringence'-fibre in which two gratings have been inscribed; each grating yields two distinct Bragg peaks. The first grating is sensitive to the total stress field in the material, while the second one is isolated from transverse stress components. By measuring the four Bragg peaks of the sensor, it is theoretically possible to determine the total strain field, plus the temperature inside a composite material. Static experiments (a tensile test and a compressive test) have already been carried out to prove the feasibility of the sensor embedded in a composite laminate

Strain monitoring of FRP elements using an embedded fibre optic sensor

This paper presents a strain monitoring approach for following up FRP elements (in this case a [90] CFRP laminate) using an embedded fibre optic sensor. The sensor exists of two fibre Bragg gratings (FBGs) written in a polarization maintaining fibre (PMF). First, the strain response of the non-embedded sensor is determined which makes it possible to relate the different bragg peak shifts with the induced strain field in the core of the optical fibre. Secondly, a transfer coefficient matrix is presented and calculated using finite element simulations which relates the measured strain field of the sensor with the adjacent one existing in the structure as if no sensor would be present