Feasibility use of in-line Mach–Zehnder interferometer optical fibre sensor in lightweight foamed concrete structural beam on curvature sensing and crack monitoring

Abstract

This article presents a novel study on curvature sensing and crack monitoring in lightweight foamed concrete structural beam using the packaged fibre-based in-line Mach–Zehnder interferometer curvature sensor. The Mach–Zehnder interferometer sensors which consist of two abrupt biconic tapers were fabricated and packaged into polypropylene slabs to protect the sensors under harsh condition of the real sensing environment, as the sensors were embedded into lightweight foamed concrete structural beams for field tests. Pretest characterizations of Mach–Zehnder interferometer sensors based on the packaging thicknesses at different operating wavelengths (1310, 1490 and 1550 nm) were done before the field tests. Three packages with different thicknesses were prepared to justify the effect of the packaging thicknesses on the curvature sensitivity of sensors. Results showed that the Mach–Zehnder interferometer sensor with a thicker bottom slab has the highest sensitivity of up to 3.53 µW m−1 which is capable of detecting a minimum curvature of 0.25 km−1 and a maximum curvature radius of up to 4 km. In the field tests, three Mach–Zehnder interferometer sensors were embedded into the lightweight foamed concrete structural beams with different polypropylene percentages (0.4%, 0.25% and 0%, respectively) to characterize the sensor performance according to the concrete environments with different tensile capacities. Mach–Zehnder interferometer sensor managed to hold up to a maximum loading force of 26 kN in the concrete environment before stopping functioning. Optical powers in response to the loading forces imposed to the beams were mapped to the strains measured by the lead wire alloy foil strain gauges (brand: TML, model: FLK-6-11) with a good correlation value of up to 0.968. Furthermore, the double-sided sensing property of Mach–Zehnder interferometer sensors preponderates over the conventional strain gauges in detecting the internal cracking within the concretes before any earlier sighting of the macrocracks.

Sensitivity Enhancement of Curvature Fiber Sensor Based on Polymer-Coated Capillary Hollow-Core Fiber

“…We should highlight that the sensor 5 (based on ARROW effect) has a high sensitivity, but only measures large curvatures within a narrow curvature range. Based on these parameters, this sensor will not exhibit good performance for structural health monitoring applications where low curvatures are measured [30]. The sensor 3 shows a similar curvature range, but it requires further processing for the taper and has a lower sensitivity.…”

“…It must be pointed out that the thickness of the polymer layer was 2 mm, and the sensor was set in the middle of this polymer layer (this position inside the material is called the neutral axis). This axis does not suffer any elongation when the segment is bent [30]. We decided to put the sensor in this position to guaranty that it does experience any strain due to the polymer.…”

“…Different parameters have been measured using ARROW sensors such as temperature [18], pressure [19,20], magnetic field [21][22][23], relative humidity [24], torsion [25], liquid level [26], displacement [27], and curvature [28] just to mention a few. In particular, measuring curvature is a crucial task that needs to be implemented in different areas such as robotic arms [29] and structural health monitoring [30], which includes the monitoring of bridges, buildings, airplanes, and other structures. In the above applications, fiber optic curvature sensors have been widely employed due to their easy integration, portability, and multiplexing capabilities.…”

Crack detection using fusion features‐based broad learning system and image processing

“…With the development of various types of contact sensors, some contact sensor-based crack detection methods have been studied (Narayanan et al, 2018;Yan et al, 2019). Leung et al (2000) and Png et al (2018) developed a new fiber optic sensor for cracks detection. Experimental results showed that the sensor can detect tiny cracks of about 0.1 mm.…”

An ultra-thin printable nanocomposite sensor network for structural health monitoring

“…1 Early detection of undersized damage in the scale of several millimeters has been facilitated by numerous damage detection methods developed in recent decades, typified as eddy current nondestructive testing, laser interferometry measurement, and ultrasonics-based structural health monitoring (SHM), to name a few. [2][3][4][5][6] Among these approaches, ultrasonics-based SHM has been widely utilized to implement real-time monitoring of the operation and health status of engineering assets, using various piezoelectric sensors such as piezoelectric lead zirconate titanate (PZT) and transducers that can be utilized to perceive guided ultrasonic waves (GUWs). However, certain drawbacks of these piezoelectric sensors have limited the further development of SHM.…”