Real-time through-thickness and in-plane strain measurement in carbon fibre reinforced polymer composites using planar optical Bragg gratings

Abstract

A new strain sensor is proposed which can measure both through-thickness and in-plane strains within a laminated fibre-reinforced composite material. The planar sensor uses novel embedded planar optic sensors and is demonstrated on a carbon fibre composite test coupon. The planar optical sensor was fabricated via flame hydrolysis deposition and was physically machined to reduce the substrate thickness to < 50 μm. Strain components are decoupled through monitoring the transverse electric and transverse magnetic effective refractive indices of two orthogonal planar waveguides. The work investigates if the embedded planar sensors have any mechanical knockdown effects on the composite structure and demonstrates their effectiveness at decoupling three orthogonal strain components.

Health Monitoring of Aerospace Structures Utilizing Novel Health Indicators Extracted from Complex Strain and Acoustic Emission Data

“…Most specimens display increasing behaviors over time for both cumulative hits and RA. Interestingly, and unlike the strain-based HIs, the failure values of the AE-based HIs have less scatter (higher prognosability), making it easier to set a failure threshold compared to Recently, interest has been shown in thickness strain measurements with embedded FBGs [39]. Embedding sensors into composite materials is a highly interesting concept, and may significantly improve the sensitivity of the sensors, in addition to the HIs, and also provide extra information regarding the degradation from the out-of-plain strains.…”

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

“…From our tests, embedding polyimide coated optical fibers in composites does not produce critical problems in structural integrity. The adhesion quality depends upon the polymer considered in the matrix and on the diameter of the fibre, as reported in [8]- [11]. For these reasons, polyimide coated optical fibers are an excellent choice for the construction of embedded FBG strain and temperature sensors.…”

“…The detection of in-plane and through-thickness strains of composite has been realized by using polarized light in embedded optical fiber sensors and embedded planar optics [8], [12]- [14]. In order to prevent subsurface delamination between plylayers, it is useful to take into account through-thickness strains.…”

Wavelength Characteristic Analysis of a FBG Array Embedded in Quaternary Unconsolidated Strata during a Deep Borehole Installation

“…Fiber Bragg gratings can be embedded in composite material or structural systems or can be used for real-time monitoring of internal stress, strain, and displacement distributions of a material or structure [1][2][3], temperature distributions [4], and humidity distributions [5]. Research has also been conducted using laboratory tests and simulations [6,7] on the transfer of fiber optic sensor strain [8,9] and the fiber Bragg grating transverse effects [10]. Overall however, fiber optic sensing technology is still considered being in the experimental stage.…”