Design of Polarization-Maintaining FBGs Using Polyimide Films to Improve Strain-Temperature Sensing in CFRP Laminates

Abstract

Uniform Fiber Bragg Grating sensors based on Polarization-Maintaining fibers are designed for simultaneous longitudinal strain and temperature measurement of Carbon Fiber Reinforced Polymer laminates. Panda, Bow tie and Pseudo-rectangle optical fiber shape sections are investigated employing three different embedding methods, for each optical fiber. The simulation accurately takes into account that the fibers are embedded in unidirectional Carbon Fiber Reinforced Polymer and covered between two adhesive polyimide films. An exhaustive, accurate and robust investigation of the mechanisms originating Bragg wavelength shift is developed by considering a complete multiphysical model including: the propagation modes and their interaction, the birefringence, the optomechanical and thermal behaviour of both the optical fiber and the embedding composite material. For the first time, the use of polyimide films is proposed to obtain an increase of temperature sensor sensitivity, reducing the stress-transfer, due to thermal expansion, between the composite laminate and the sensing element. The designed Fiber Bragg Grating sensors are compared and their potential application, for simultaneous strain and temperature measurement of Carbon Fiber Reinforced Polymer is discussed.

Design of Microstructured Flat Optical Fiber for Multiaxial Strain Monitoring in Composite Materials

“…The refractive index change due to the applied stress has been calculated according to [2]. The propagation constants and the electromagnetic field distribution of the propagating modes have been simulated as described in Section II.…”

“…1(b). The CFRP is modelled considering the micromechanical analysis of the unit cell, leading to the computation of the elasticity matrix [E] m [2]. The evaluated strains are employed to calculate the refractive index variation Δn of the optical guiding structure [2].…”

“…The CFRP is modelled considering the micromechanical analysis of the unit cell, leading to the computation of the elasticity matrix [E] m [2]. The evaluated strains are employed to calculate the refractive index variation Δn of the optical guiding structure [2]. The effective refractive index of fundamental modes n ef f guided in the two eyelets can be computed through 2D-FEM mode analysis and used as input data for calculating the Bragg wavelength λ B shift via TMM [41].…”

“…A micromechanical analysis on a single unit cell, made of carbon fiber and resin (carbon fiber-resin volume fraction v f = 0.6), has been performed to evaluate the elasticity matrix [E] m of a layer as in [2].…”

High temperature and strain dual-parameters fiber sensing based on intermodal interference and femtosecond laser fabricated fiber Bragg grating

“…As a typical type of PCF, GPCF has many amazing properties such as controllable nonlinearity, endlessly single-mode characteristics, low bending loss, large mode area [14][15][16], and so on. Compared with bow tie panda fiber [17,18], high birefringence PCF [19] and other types of PCFs [20,21], the tri-hole PCF used has larger air holes, smaller core and better interference signal quality. The optical field distribution is contained within the PCF's fiber core due torefractive index difference between its fiber core and air holes.…”