Abstract
Clamped fiber Bragg grating (FBG) sensors have been widely applied in engineering strain measurements due to their advantages of high flexibility and efficiency. However, due to the existence of the interlayer, the strain measured by the encapsulated FBG sensor is not equal to the strain of the host material, which causes strain measurement errors. In this paper, the strain transfer analysis of a clamped FBG sensor based on the shear-lag theory is conducted to improve the accuracy of strain measurements. A novel theoretical model for the axial strain distribution of a clamped FBG sensor is proposed. It is also discussed how the gauge ratio and interlayer thickness affect the strain transfer rate. The accuracy of the proposed theoretical model is verified by experimental tensile tests. The theoretical value of the strain transfer rate matches well with the tested value.
Highlights
Fiber Bragg grating (FBG) sensors have attracted wide attention from the civil and mechanical research community because of its many merits such as small size, high sensitivity, and immunity to electromagnetic interference [1]
Results revealed that when the elastic modulus of the coated layer was equal to the average elastic modulus of the host material and optical fiber, the maximum strain can be sensed by the FBG sensor
Strain transfer rate distribution of the m-segment of the optical fiber is from Equation (23), while the other part is calculated from Equation (27)
Summary
Fiber Bragg grating (FBG) sensors have attracted wide attention from the civil and mechanical research community because of its many merits such as small size, high sensitivity, and immunity to electromagnetic interference [1]. The error caused by the strain transfer rate between the host material and the FBG sensor cannot be ignored, especially in real applications. Results revealed that when the elastic modulus of the coated layer was equal to the average elastic modulus of the host material and optical fiber, the maximum strain can be sensed by the FBG sensor. The creep constitutive relation of concrete was introduced to analyze the strain transfer and the finite element method was used to verify the theoretical analysis results. Experimental and simulation results show that the length and the middle layer thickness have the dominating effect on the strain transfer rate of FBG sensors. It should be noted that in the abovementioned previous studies, the strain transfer analysis theories are based on the models of surface pasted or embedded FBG sensors. The theoretical analysis results are verified by experimental tensile tests
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