- freely available
Appl. Sci. 2017, 7(2), 188; https://doi.org/10.3390/app7020188
2. Basic Theory
3. Theoretical Strain Transfer Analysis
- The optical fiber is linearly elastic with its m-segment and n-segment having the same mechanical properties. The mechanical properties of optical fiber are impacted by taking advantage of phase masks and ultraviolet irradiation methods when processing FBG writing. The FBG sensor does not carry the external force directly, and the axial strain is supposed to transfer from the host material to the optical fiber by the interlayer shear deformation.
- The interlayer is a hollow cylinder, which is homogeneously coated on the fiber surface to undergo the shear deformation, regardless of its axial deformation.
- There is no relative slip between the FBG sensor and the interlayer.
3.1. Strain Transfer Rate Distribution of the m-Segment of the Optical Fiber
3.2. Strain Transfer Rate Distribution of the n-Segment of the Optical Fiber
4. Theoretical Analysis Results
4.1. Strain Transfer Rate of a Clamped FBG Sensor
4.2. Main Factors Affecting the Strain Transfer Rate
4.2.1. Effect of the Gauge Ratio
4.2.2. Effect of the Interlayer Thickness
5. Experimental Verification
- Specimen is clamped by supports on the testing machine. The pre-loading applied to the specimen is 30 kN, and the step loading is 5 kN every ten seconds until the total loading of 60 kN.
- In ten seconds pause time, the resistances of the strain sensor and FBG demodulators are acquired as the immediate data.
- Parameter error: The strain transfer rate of the theoretical model involves the elastic modulus of the optical fiber, shear modulus of the interlayer, Poisson ratio, etc. This may generate errors because of the difference between the used and actual values in testing conditions.
- Model error: Some assumptions of the theoretical model lead to model errors. For example, the defect of the n-segment optical fiber appears in the writing process, which could alter the mechanical properties.
- Test error: This is one important error source including sensor zero drift, asynchronous acquisition and the artificial reading error.
Conflicts of Interest
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|Elastic modulus of optical fiber/MPa||Eg||72,000|
|Elastic modulus of interlayer/MPa||Ej||30|
|Radius of optical fiber/μm||rg||62.5|
|Gauge ratio parameter||A||1.25|
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