Measurement of Mechanical and Thermal Strains by Optical FBG Sensors Embedded in CFRP Rod

Abstract

The present study intends to provide the photoelastic coefficient and thermal expansion coefficient needed to use an FBG-embedded CFRP rod (smart rod) as strain sensor. Due to the monolithic combination of the FBG sensor with a CFRP rod, the smart rod is likely to exhibit thermal and mechanical properties differing from those of the bare FBG sensor. A tensile test showed that the photoelastic coefficient of the smart rod is 0.204, which is about 7.3% lower than the 0.22 value of the bare optical FBG. Moreover, the thermal expansion coefficient of the smart rod obtained through a thermal test appeared to be negative with a low value of −0.190×10−6/°C. Consequently, the temperature dependence of the smart rod is mainly expressed by means of the thermooptic coefficient. Compared to the bare FBG sensor, the smart rod is easier to handle and can measure compressive strains, which make it a convenient sensor for various concrete structures.

Cantilever-Based Sensor Utilizing a Diffractive Optical Element with High Sensitivity to Relative Humidity

“…The RH as an analyte was selected for a number of reasons: first—low-cost, highly sensitive sensors to RH are still under development and in demand; second—measuring RH involves using a non-toxic analyte, and it is a suitable model analysis from a proof-of-concept perspective, third—the previous experience in developing flat holographic sensors for RH [ 47 , 48 ] allowed for a direct comparison with the existing holographic sensor technology. Opto-mechanical sensors have been previously explored, for example, sensors based on photoelastic effect [ 48 , 49 , 50 , 51 , 52 ]. The novelty of this work relies on the conversion of a minute mechanical signal into a strong optical signal induced by the response of a holographic diffractive structure.…”

Highly sensitive temperature-independent FBG-based sensor embedded in thermoplastic polyurethane using 3D printing technology for the measurements of torsion

“…The CTE for TPU95A is 100.0 × 10 -6 m. C-1 [38], which is 2 times higher than the CTE of PVC pipe (supporting material) with a value of 50.4 × 10 -6 m. C-1 [39]. The CTE for silica glass is 0.5 × 10 -6 m. C-1 [31,40,41]. The FBG T was also embedded in the TPU similarly to FBG 1, 2, 3, and 4.…”

Dual-FBG arrays hybrid measurement technology for mechanical strain, temperature, and thermal strain on composite materials

“…Generally, some strategies such as special package design of FBG sensors and combination configuration of FBG sensors, have been presented to distinguish the cross-sensitivity effect between strain and temperature [9][10][11][12][13][14][15][16][17]. A number of similar techniques for simultaneously measuring temperature and strain have been proposed [9][10][11][12], including the use of two types of FBGs, such as a pair of etched and un-etched polymer FBG functions as a sensor [11], the combination of a FBG and two PM-PCF with different coatings [10], a FBGembedded CFRP rod [12]. While these methods may be able to distinguish a cross-sensitivity between strain and temperature, most of them require the use of different fibre types and FBGs or any extrinsic special techniques [11].…”