Simulation of fibre Bragg grating (FBG) reflection spectrums using OptiGrating

Birch, Byrenn James Colin ORCID: (2013) Simulation of fibre Bragg grating (FBG) reflection spectrums using OptiGrating. [USQ Project]


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Fibre composite materials for use in structural applications are becoming more common. However the sudden failures they are susceptible to creates a need for structural health monitoring to ensure safe use. Mechanical fibre composite structures such as wind turbine blades and airframes are desirable to have in operation as long as possible, therefore any structural health monitoring technology capable of operating when the structure is in service is advantageous. This technology is optical sensors, specifically fibre Bragg grating sensors. Fibre Bragg grating sensors can be embedded in composite materials to measure the strain and temperature at a specific location. These measurements can be compared with historical data to assess the health of the structure.

The data is viewed as the reflection spectrum which visually shows the trends and can be analysed numerically. This research intends to reproduce the reflection spectrum using a combination of finite element analysis (FEA) software and OptiGrating. This has the potential to extend academic knowledge and be a step in the development of methods to calculate the actual strain field to which a sensor is subject.

Three different sample were manufactured with known defects and tested. The zero load reflections were imported to OptiGrating and solved using inbuilt functions. Finite element analysis yielded good correlation to the strain calculated from the Bragg wavelength of each physical test. However, when the FEA strain was applied to a virtual sensor in OptiGrating the data did not correlate with the real tests, nor the FEA data.

This was investigated and it was discovered that a fundamental programming error was present in OptiGrating for calculating the strain-optic coefficient. Further
examination found that this error could be compensated for, thus OptiGrating analysis was repeated. Following the correction the Bragg wavelength correlation was good but due to limitations with the inverse scattering solver and FEA made replicating the behaviour of sidelobes impossible at this stage.

OptiGrating was contacted about these issues. They have confirmed the error in calculating the strain-optic coefficient and are currently developing a version that corrects the issue.

Recommendations were made to revisit the project upon OptiGrating releasing a new or updated version with an improved inverse scattering solver and corrected strain optic coefficient formulae. With these improvement it is likely the method would be much more effective. However at this point in time it was concluded that the process used was not an effective method of reproducing and simulating Bragg reflection spectrums.

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Item Type: USQ Project
Item Status: Live Archive
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Mechanical and Electrical Engineering (1 Jul 2013 - 31 Dec 2021)
Supervisors: Epaarachchi, Jayantha
Date Deposited: 23 Feb 2014 07:02
Last Modified: 07 Oct 2020 00:53
Uncontrolled Keywords: simulation; fibre bragg grating; reflection spectrums; optigrating
Fields of Research (2008): 09 Engineering > 0912 Materials Engineering > 091202 Composite and Hybrid Materials
Fields of Research (2020): 40 ENGINEERING > 4016 Materials engineering > 401602 Composite and hybrid materials
Socio-Economic Objectives (2008): B Economic Development > 86 Manufacturing > 8699 Other Manufacturing > 869999 Manufacturing not elsewhere classified
B Economic Development > 86 Manufacturing > 8615 Instrumentation > 861501 Industrial Instruments

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