Use of Fiber Optic Sensors for Monitoring Crack Growth in Fatigue and Corrosion-Fatigue Tests

Fibre Bragg Gratings (FBGs) are optical strain gages manufactured directly inside the fiber core. They provide several advantages with respect to conventional strain gages. In particular it is possible to put several FBGs along the same fibre (multiplexing), they are immune to corrosive environments and to electromagnetic interferences. They can be embedded in almost all types of materials and are very useful in Structural Health Monitoring. An innovative approach for testing specimens in this area is reported in this work. An aluminium alloy 2024-T3 CT specimen has been manufactured with one small feed-through hole and a superficial groove. Two FBG sensors, multiplexed on the same fibre, have been glued one inside the hole and one inside the groove. Fatigue test has been carried out monitoring the crack length both with standard measure system and with the FBG strain sensors placed in front of the crack tip.

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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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we bolted BGK-FBG-4150 sensors on wireless strain sensors on the specimen the specimen instead of welding on it, with 502 plastic. This four kinds of we pasted MOI FBG sensors on the sensors are arranged in the middle specimen with the help of AB glue, and position of the specimen in order to we pasted FLA-5-11 strain sensor and ensure the unity, as shown in Fig.1;

Structural Health Monitoring and Integrity Management ◽

10.1201/b18510-94 ◽

2015 ◽

pp. 292-295

Keyword(s):

Strain Sensor ◽

Strain Sensors ◽

Fbg Sensors

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Strains in Aluminum-Adhesive-Ceramic Trilayers

Journal of Electronic Packaging ◽

10.1115/1.2904381 ◽

1990 ◽

Vol 112 (4) ◽

pp. 288-302 ◽

Cited By ~ 15

Author(s):

P. M. Hall ◽

F. L. Howland ◽

Y. S. Kim ◽

L. H. Herring

Keyword(s):

Elastic Modulus ◽

High Speed ◽

Theoretical Study ◽

Alumina Ceramic ◽

Strain Gages ◽

Wire Bonds ◽

Large Expansion ◽

Trilayer Structure ◽

Almost All ◽

Increasing Temperature

In many of today’s high speed, high density circuits, there is a need to remove large amounts of heat. To facilitate this removal of heat, it is common to adhere a sheet of a high thermal conductivity material (such as aluminum or copper) to the substrate (which may be alumina ceramic). This can result in large expansion mismatches which cause stresses and bowing, with the possibility of delamination, cracking, stressing solder joints, loss of hermeticity, or shorting of a metal lid to wire bonds inside a cavity. One approach to this problem is to use a compliant adhesive to decouple the materials. The present paper is an experimental and theoretical study of the strains as a function of temperature from −40° C to 140° C in a trilayer structure of 0.030 in. or 0.76 mm thick aluminum, 0.006 in. or 0.15 mm thick adhesive, and 0.021 in. or 0.5 mm thick low-temperature cofired (glassy) ceramic. The strains are analyzed using E. Suhir’s theory, and they are measured using strain gages for three adhesives: an epoxy, a fabric-reinforced epoxy, and a silcone elastopolymer. If the adhesive has an elastic modulus below 10 psi or 70 kPa, theory predicts almost complete de-coupling. Between 100 and 105 psi or 700 kPa and 700 MPa, there is partial decoupling, depending on the in-plane dimensions. Above 10,000 psi or 700 MPa, the decoupling is negligible, and the same bowing results for any elastic modulus between 10,000 and 1,000,000 psi or 70 MPa and 7 GPa. For temperatures below 80° C, only the elastomer has enough compliance to provide any de-coupling. Above 80° C, the elastomer de-couples the most, and the unreinforced epoxy the least. Almost all of the observed effects are understandable in terms of the Suhir theory, along with the fact that the elastic modulus of the epoxy materials decreases with increasing temperature. In particular, when there is some decoupling of the materials, the amount of decoupling depends on the in-plane dimensions of the sample.

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Optical Strain Gages for Use at Elevated Temperatures

Symposium on Elevated Temperature Strain Gages ◽

10.1520/stp45033s ◽

2009 ◽

pp. 51-51-6

Author(s):

H. K. Howerton

Keyword(s):

Elevated Temperatures ◽

Strain Gages ◽

Optical Strain

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Implementation of a Mobile Platform Based on Fiber Bragg Grating Sensors for Automotive Traffic Monitoring

Sensors ◽

10.3390/s20061567 ◽

2020 ◽

Vol 20 (6) ◽

pp. 1567 ◽

Cited By ~ 7

Author(s):

Kivilcim Yuksel ◽

Damien Kinet ◽

Karima Chah ◽

Christophe Caucheteur

Keyword(s):

Fiber Optic ◽

Traffic Monitoring ◽

Fiber Optic Sensors ◽

Mobile Platform ◽

Vehicle Speed ◽

Distributed Monitoring ◽

Fiber Bragg Grating Sensors ◽

Weigh In Motion ◽

Monitoring Applications ◽

Fbg Sensors

Instrumentation techniques, implementation and installation methods are major concerns in today’s distributed and quasi-distributed monitoring applications using fiber optic sensors. Although many successful traffic monitoring experiments have been reported using Fiber Bragg Gratings (FBGs), there has been no standardized solution proposed so far to have FBG seamlessly implemented in roads. In this work, we investigate a mobile platform including FBG sensors that can be positioned on roads for the purpose of vehicle speed measurements. The experimental results prove the efficiency of the proposed platform, providing a perspective toward weigh-in-motion systems.

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Fatigue Life Estimation of Aeronautical Joints Based on Stress Severity Factor

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1135.128 ◽

2016 ◽

Vol 1135 ◽

pp. 128-139

Author(s):

Roberto da Silva Gonçalves ◽

Carlos E. Chaves

Keyword(s):

Fatigue Life ◽

Fatigue Tests ◽

Lap Joints ◽

Severity Factor ◽

Application Range ◽

Aircraft Fuselage ◽

Bending Effect ◽

Fatigue Life Estimation ◽

Recorded Data ◽

Almost All

The goal of the present work is to investigate the validity limits and safe application range of Stress Severity Factor methodology in estimating fatigue life of aircraft fuselage joints. Fatigue tests were conducted and recorded data from aluminum alloys joints was subjected to analytical evaluation. FE models were created to obtain fasteners load distribution and determine normal stress due to secondary bending. Severity Factor method conservatively estimated fatigue life of 74% for the analyzed joints. Its robustness was verified for lap joints fatigue life estimative, but for almost all single strap joints, secondary bending effect were significant. Thus for this kind of joints, a term accounting for bending stress was added to the original severity factor formulation to increase level of safety in fatigue life estimates.

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Monitoring Stress/Strain in Buried Pipelines Through the Use of Fiber Bragg Grating Sensors

ASME 2015 International Pipeline Geotechnical Conference ◽

10.1115/ipg2015-8540 ◽

2015 ◽

Author(s):

Juan David Betancur Ríos ◽

Camilo Eliécer Torres ◽

Jaime Hernan Aristizabal ◽

Adriana Galvis ◽

Ronald Andrés Díaz ◽

...

Keyword(s):

Strain Sensors ◽

Strong Impact ◽

Buried Pipelines ◽

Stress Strain ◽

Fiber Bragg Grating Sensors ◽

Pipeline Program ◽

Integrity Management ◽

Optical Strain ◽

External Forces ◽

Rain Precipitation

ECOPETROL S.A. has been working since 2006 in Pipeline Integrity Management Process. In that process, the threat related to climate and external forces play an important role, because of the vulnerability of ECOPETROL pipelines to this threat, not only by the geomorphology of Colombia, but also because of the strong impact of climate phenomenon such as “La Niña”, that consists in an unusual quantity of rain precipitation, represented in the increasing of slopes instability that affects the rights of way. Due to these events and the evolution of optical strain sensors monitoring technology, ECOPETROL has introduced an instrumentation pipeline program for monitoring the strain and advanced in the understanding of the behavior of pipelines. This paper describes the technology selected, the criteria used to select the monitoring sites and the thresholds stress/strain. The results of monitoring are discussed for a particular case.

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