Evaluation of Rugged 'Smart Patch' Fibre-Optic Strain Sensors

Fibre-optic sensors have advantages over existing electrical sensors in many strain and stress monitoring applications. However, bare optical fibres are fragile and packaging techniques must be developed before these sensors can be used more widely. One such method is the Smart Patch, in which the fibre Bragg grating is encapsulated between plies of glass-reinforced epoxy where rugged cables are anchored. This forms a flat flexible patch in which the fibre is protected from mechanical and environmental damage. However, it is important that the mechanical strength of the patch is not achieved at the expense of good strain transfer characteristics. To confirm this, fibre Bragg gratings with acrylate and polyimide coatings were embedded in a glass-epoxy patch that was bonded to an aluminium tensile specimen. An electrical strain gauge was also bonded to the specimen to provide a strain reference. Tests were carried out at different loading rates and at temperatures from -30°C to +80°C. There was good agreement between the fibre-optic sensors and the electrical strain gauge demonstrating that the patch performed in a practically identical manner to the conventional gauges. A second experiment on a representative part of ship structure demonstrated the versatility of the patch.

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Evaluation of Strain Transition Properties between Cast-In Fibre Bragg Gratings and Cast Aluminium during Uniaxial Straining

Sensors ◽

10.3390/s20216276 ◽

2020 ◽

Vol 20 (21) ◽

pp. 6276

Author(s):

Florian Heilmeier ◽

Robert Koos ◽

Michael Singer ◽

Constantin Bauer ◽

Peter Hornberger ◽

...

Keyword(s):

Bragg Gratings ◽

Tensile Specimen ◽

Strain Sensors ◽

Fe Model ◽

Plastic Strains ◽

Closing The Gap ◽

Optical Strain ◽

Structural Parts ◽

Fibre Bragg Gratings

Current testing methods are capable of measuring strain near the surface on structural parts, for example by using strain gauges. However, stress peaks often occur within the material and can only be approximated. An alternative strain measurement incorporates fibre-optical strain sensors (Fiber Bragg Gratings, FBG) which are able to determine strains within the material. The principle has already been verified by using embedded FBGs in tensile specimens. The transition area between fibre and aluminium, however, is not yet properly investigated. Therefore, strains in tensile specimens containing FBGs were measured by neutron diffraction in gauge volumes of two different sizes around the Bragg grating. As a result, it is possible to identify and decouple elastic and plastic strains affecting the FBGs and to transfer the findings into a fully descriptive FE-model of the strain transition area.We thus accomplished closing the gap between the external load and internal straining obtained from cast-in FBG and generating valuable information about the mechanisms within the strain transition area.It was found that the porosity within the casting has a significant impact on the stiffness of the tensile specimen, the generation of excess microscopic tensions and thus the formation of permanent plastic strains, which are well recognized by the FBG. The knowledge that FBG as internal strain sensors function just as well as common external strain sensors will now allow for the application of FBG in actual structural parts and measurements under real load conditions. In the future, applications for long-term monitoring of cast parts will also be enabled and are currently under development.

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Leak detection on water pipelines in unsaturated ground by discrete fibre optic sensing

Structural Health Monitoring ◽

10.1177/1475921719881979 ◽

2019 ◽

Vol 19 (4) ◽

pp. 1219-1236 ◽

Cited By ~ 2

Author(s):

Schalk Willem Jacobsz ◽

Sebastian Ingo Jahnke

Keyword(s):

Unsaturated Soil ◽

Ground Deformation ◽

Bragg Gratings ◽

Leak Detection ◽

Bragg Grating ◽

Fibre Bragg Grating ◽

Fibre Optic ◽

Temperature Changes ◽

Water Leak ◽

Fibre Bragg Gratings

The article describes a study using discrete fibre optic sensing as a means of leak detection on water distribution pipes installed in unsaturated ground. A short length of pipe fitted with artificial leak points was installed, to which a fibre optic cable with fibre Bragg gratings was attached. An optical fibre with fibre Bragg gratings was also installed in the ground parallel to but separate from the pipe. Thermistors were installed at selected locations to measure temperature changes independent of strain. It was found that a simulated water leak resulted in clearly detectable temperature changes and thermally induced fibre Bragg grating wavelength changes in the ground around the pipe. However, significantly larger deformation-induced fibre Bragg grating wavelength changes were measured on the pipe walls and also in the initially unsaturated ground in response to leaks. A wetting front originating from a water leak propagating through unsaturated soil is associated with significant effective stress changes because the infiltrating water alters the ambient matric suction in the soil. This effective stress change is associated with significant ground deformation resulting in a fibre Bragg grating response which significantly exceeds the thermal response associated with (usually) colder water leaking into unsaturated soil. The study illustrates advantages of measuring ground deformation-induced fibre Bragg grating wavelength changes over pure temperature changes as an efficient means of leak detection in unsaturated ground. However, due to the limited number of fibre Bragg gratings that can be monitored along a single optical fibre, a leak detection system suitable for practical implementation should be based on distributed fibre optic strain sensing, an aspect requiring further research.

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Composite Structural Element Characterisation Using Fibre Optic Strain Sensors

Advanced Composites Letters ◽

10.1177/096369359700600501 ◽

1997 ◽

Vol 6 (5) ◽

pp. 096369359700600

Author(s):

R. P. Kenny ◽

E. Gutierrez ◽

M. P. Whelan ◽

A. C. Lucia

Keyword(s):

Strain Sensors ◽

Fibre Bragg Grating ◽

Structural Elements ◽

Application Area ◽

Fibre Optic ◽

Structural Element ◽

Fibre Optic Sensor ◽

Optic Sensor ◽

On Line ◽

Passive Techniques

Fibre optic sensor systems have been developed for characterisation and monitoring of structural elements. The particular application area reported here is on testing of pultruded composite beams. Demodulation schemes for in-fibre Bragg grating strain sensors using either Acousto-Optic tuneable filters or passive techniques are described. It is found that the fibre optic sensor measurements correspond well with those of standard electrical gauges, and demonstrate their potential as on-line structural diagnostic devices.

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Comparison of shearography and optical fibre Bragg grating strain sensors with resistance foil strain gauge measurements

10.1117/12.611887 ◽

2005 ◽

Cited By ~ 1

Author(s):

Roger M. Groves ◽

Edmon Chehura ◽

Weilai Li ◽

Stephen E. Staines ◽

Stephen W. James ◽

...

Keyword(s):

Optical Fibre ◽

Strain Gauge ◽

Strain Sensors ◽

Bragg Grating ◽

Fibre Bragg Grating ◽

Strain Gauge Measurements

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Dual Measurement of Strain and Temperature Using the Combination of Er3+ -Doped Fibre Fluorescence Lifetime and a Fibre Bragg Grating

Measurement and Control ◽

10.1177/002029400103400606 ◽

2001 ◽

Vol 34 (6) ◽

pp. 175-178 ◽

Cited By ~ 3

Author(s):

S.A. Wade ◽

D.I. Forsyth ◽

Q. Guofu ◽

X. Chen ◽

T. S. Chuan ◽

...

Keyword(s):

Fluorescence Lifetime ◽

Bragg Gratings ◽

Bragg Grating ◽

Fibre Bragg Grating ◽

Fibre Optic ◽

Erbium Doped ◽

Fibre Bragg Gratings ◽

Dual Measurement

Fibre optic sensing devices have been produced for the dual measurement of strain and temperature using the combined properties of fibre Bragg gratings and the fluorescence lifetime of erbium-doped fibre. Two different sensors were constructed with the fibre Bragg grating written in normal fibre and also written directly in the Er3+-doped fibre. Results obtained indicate that this technique can be used to measure strains and temperatures with accuracies of approximately 1.2°C and 20.4 με

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Comparison of optical fibre Bragg grating strain sensors with shearography and resistance foil strain gauge measurements

10.1117/12.624218 ◽

2005 ◽

Author(s):

Edmon Chehura ◽

Roger M. Groves ◽

Weilai Li ◽

Stephen E. Staines ◽

Stephen W. James ◽

...

Keyword(s):

Optical Fibre ◽

Strain Gauge ◽

Strain Sensors ◽

Bragg Grating ◽

Fibre Bragg Grating ◽

Strain Gauge Measurements

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Study of reliability of fibre Bragg grating fibre optic strain sensors for field-test applications

Sensors and Actuators A Physical ◽

10.1016/j.sna.2012.06.026 ◽

2012 ◽

Vol 185 ◽

pp. 8-16 ◽

Cited By ~ 26

Author(s):

Frederic Surre ◽

Richard H. Scott ◽

Pradipta Banerji ◽

P.A.M. Basheer ◽

Tong Sun ◽

...

Keyword(s):

Field Test ◽

Strain Sensors ◽

Bragg Grating ◽

Fibre Bragg Grating ◽

Fibre Optic

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Experimental qualification and validation of fibre optic strain sensors

10.1117/12.968801 ◽

2012 ◽

Author(s):

Constanze Schilder ◽

Nadine Kusche ◽

Vivien G. Schukar ◽

Wolfgang R. Habel

Keyword(s):

Strain Sensors ◽

Fibre Optic

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Self-monitoring Properties of Concrete Columns with Embedded Cement-based Strain Sensors

Journal of Intelligent Material Systems and Structures ◽

10.1177/1045389x10396573 ◽

2011 ◽

Vol 22 (2) ◽

pp. 191-200 ◽

Cited By ~ 21

Author(s):

Huigang Xiao ◽

Hui Li ◽

Jinping Ou

Keyword(s):

Cyclic Load ◽

Failure Modes ◽

Concrete Structures ◽

Concrete Columns ◽

Strain Sensors ◽

Strain Sensing ◽

Self Monitoring ◽

Good Strain ◽

Displacement Transducers ◽

Monotonic Load

Cement-based strain sensors (CBCC sensor) were fabricated by taking the advantage of piezoresistivity of CB-filled CBCC. CBCC sensors were centrally embedded into concrete columns (made with C40 and C80 concretes, respectively) to monitor the strain of the columns under cyclic load and monotonic load by measuring the resistance of CBCC sensors. The comparison between the monitored results of CBCC sensors and that of traditional displacement transducers indicates that CBCC sensors have good strain-sensing abilities. Meanwhile, CBCC sensors exhibit different failure modes that break later than C40 concrete columns, but a little earlier than C80 concrete columns. Therefore, the strength-matching principle between embedded CBCC sensors and concrete columns is proposed in this article to guarantee the sensing capacity of CBCC sensors in various concrete structures. The analytical results agree well with the experimental phenomena.

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