Numerical analysis of the strain values obtained by FBG embedded in a composite material using assumptions about uniaxial stress state of the optical fiber and capillary on the Bragg grating

Abstract

One of the issues in the strain measurement with the help of fiber-optic sensors based on Bragg gratings is the calculation of the strain based on the information from the sensor and its correspondence to the material strain. Relationships between the data measured by the sensor and the strain in the Bragg grating have a unique solution under the condition of uniaxial stress state of the fiber, which are not fulfilled when the fiber is embedded in the material. The paper presents the results of numerical simulations with an example of a model problem for a polymer composite material with an embedded optical fiber, which can be surrounded by a resin pocket. The presented results allow to estimate the error of the strain values calculated on the basis of uniaxial stress state assumption of the optical fiber. Based on numerical calculations, parameters of a capillary on an optical fiber in the Bragg grating zone are estimated, ensuring uniaxial stress state of the fiber in the Bragg grating zone. To ensure these conditions, the cross section of the capillary in an isotropic material is a circle, and in an anisotropic material, good results can be obtained with an elliptical cross section.

Strain State Detection in Composite Structures: Review and New Challenges

“…Fiber optic temperature (FOT) sensors were inserted into the sample to track temperature gradient at each step of the curing process. A futher paper [63] presents the results of numerical simulations with reference to a polymer composite material with an embedded optical fiber, which can be surrounded by a resin pocket, Figure 10. The presented outcomes allowed for estimating the error of the strain values calculated on the basis of 1D stress state assumption of the optical fiber.…”

The study of internal structure of woven glass and carbon fiber reinforced composite materials with embedded fiber-optic sensors

“…Spectral distortions can be caused by curing pressure, which leads to residual transverse strains of the optical fiber, and/or the non-uniform strain distribution along the length of the optical fiber that also occurs during the manufacturing process. There are several ways to overcome such problem, among which are the implementation of more advanced algorithms of calculating the spectrum change [31] and the use of additional mechanical protection of the Bragg grating area [32].…”