Muneesh Maheshwari

Effect of the location and size of a single crack on first fundamental frequency of a cantilever beam using fiber optic polarimetric sensors and characterisation of FBG sensors

Fiber Optics Polarimetric Sensors (FOPS), utilizing first fundamental frequency mode and its harmonics, have already been used as damage detection tool. The FOPS technology is attractive in damage detection as it facilitates us with real time non-destructive health monitoring of different mechanical and civil structures. In this paper, the effects of the size and the location of a single crack on the frequency of first fundamental mode of a cantilever beam have been studied. A relation between the relative size of a crack and relative change in the first fundamental frequency has been established theoretically and then verified experimentally. Further, it has been shown that the cracks, close to the fixed end of the cantilever beam, have significant effect on the frequency of first fundamental mode and as the crack moves away from the fixed end, the effect on the frequency starts becoming diminished. Also the sensitivity of Fiber Bragg Grating (FBG) sensor against a single crack has been studied along both the directions; parallel to the axis of FBG sensor and perpendicular to the axis of FBG sensor. Experimental results show that the range of sensitivity in both the directions is almost the same bur FBG is more efficient along its axis.

Crack monitoring using multiple smart materials; fiber-optic sensors & piezo sensors

ABSTRACT This article focuses on health monitoring of structures using multiple smart materials. In this research, two fiber-optic sensors, namely fiber Bragg grating (FBG) and fiber-optic polarimetric sensor (FOPS), are investigated for damage detection in the beam specimen. FBG is used for local strain measurement while FOPS is used for global strain measurement. Both FBG and FOPS show significant changes in the strain due to damages in the specimen. Also, at the center of the specimen, piezoelectric wafer active sensor (PWAS) is attached. The electromechanical admittance (EMA) signature of the specimen beam is recorded by PWAS. The changes in the amplitudes of the peaks obtained at various frequencies in this EMA signature are analyzed, and it is shown that the peak amplitudes respond differently to damages and to change in loading. Thus, multiple smart materials (FBG, FOPS, and PWAS) are used to get improved information on the health of the beam.

FBG and FOPS for local and global structural health monitoring on a single fiber

Fiber Bragg grating (FBG) sensors and fiber optic polarimetric sensors (FOPS) have been widely researched and implemented for structural health monitoring (SHM). FBG essentially provides localized strain information, while FOPS gives a global indication of the structural health of materials. An FBG written on the polarization maintaining (PM) fiber can thus be used for both global structural monitoring and local strain sensing. However each sensor has to be used with its own hardware and processing. For gratings written on PM fibers two Bragg reflections, corresponding to two modes of polarization, are observed. While both Bragg wavelengths shift under longitudinal strain in unison, their relative peak amplitude does not change. In this paper, a novel concept is proposed which makes the peak amplitudes responsive to the longitudinal strain. This relative amplitude of both the peaks is used for the first time to determine the state of polarization (SOP) with no additional optical systems. With this additional information on SOP, PM?FBGs can be used for both, local and global SHM simultaneously. Further, a new design has been proposed which gives improved information on the damaged location in beam structures. This can be further extended to other complex geometries.

Fibre optic sensors for load-displacement measurements and comparisons to piezo sensor based electromechanical admittance signatures

Structural health monitoring techniques using smart materials are on rise to meet the ever ending demand due to increased construction and manufacturing activities worldwide. The civil-structural components such as slabs, beams and columns and aero-components such as wings are constantly subjected to some or the other forms of external loading. This article thus focuses on condition monitoring due to loading/unloading cycle for a simply supported aluminum beam using multiple smart materials. On the specimen, fibre optic polarimetric sensor (FOPS) and fibre Bragg grating (FBG) sensors were glued. Piezoelectric wafer active sensor (PWAS) was also bonded at the centre of the specimen. FOPS and FBG provided the global and local strain measurements respectively whereas, PWAS predicted boundary condition variations by electromechanical admittance signatures. Thus these multiple smart materials together successfully assessed the condition of structure for loading and unloading tests.

Failure assessment of aluminum liner based filament-wound hybrid riser subjected to internal hydrostatic pressure

The present study describes the burst behavior of aluminum liner based prototype filament-wound hybrid riser under internal hydrostatic pressure. The main objective of present study is to developed an internal pressure test rig set-up for filament-wound hybrid riser and investigate the failure modes of filament-wound hybrid riser under internal hydrostatic burst pressure loading. The prototype filament-wound hybrid riser used for burst test consists of an internal aluminum liner and outer composite layer. The carbon-epoxy composites as part of the filament-wound hybrid risers were manufactured with [±55 o ] lay-up pattern with total composite layer thickness of 1.6 mm using a CNC filament-winding machine. The burst test was monitored by video camera which helps to analyze the failure mechanism of the fractured filament-wound hybrid riser. The Fiber Bragg Grating (FBG) sensor was used to monitor and record the strain changes during burst test of prototype filament-wound hybrid riser. This study shows good improvements in burst strength of filament-wound hybrid riser compared to the monolithic metallic riser. Since, strain measurement using FBG sensors has been testified as a reliable method, we aim to further understand in detail using this technique.

A buoyancy-based fiber Bragg grating tilt sensor

In this paper, a novel design of fiber Bragg grating tilt sensor is proposed. This tilt sensor exhibits high angle sensitivity and resolution. The presented tilt sensor works on the principle of the force of buoyancy in a liquid. It has certain advantages over the other designs of tilt sensors. The temperature effect can be easily compensated by using an un-bonded or free FBG. An analytical model is established which correlates the Bragg wavelength (λB) with the angle of inclination. This model is then validated by the experiment, where the experimental and analytical results are found in good agreement with each other.

Combined fiber Bragg grating and fiber optic polarimetric sensors on a single fiber for structural health monitoring of two-dimensional structures

Fiber optic sensors have a lot to offer in the field of structural health monitoring. The most widely investigated and implemented fiber optic sensors for structural health monitoring are fiber Bragg grating and fiber optic polarimetric sensor. Fiber Bragg grating sensors provide localized strain data, thereby providing local damage information, while fiber optic polarimetric sensors are known for their capabilities of global damage monitoring for both static and dynamic loadings. However, each sensor has to be used with its own instrumentation and processing system. In this article, it is shown that an fiber Bragg grating written on a polarizing maintaining fiber can discern information from both fiber Bragg grating and fiber optic polarimetric sensors using only one decoding system. This reduces costs and complexities. Furthermore, by proper multiplexing the polarizing maintaining-fiber Bragg grating sensor, it is possible to predict the damage location in plates. The results demonstrate that the damage site can be located in two-dimensional structures using this multiplexed sensing array.

Damage monitoring using fiber optic sensors and by analysing electro- mechanical admittance signatures obtained from piezo sensor

Damage monitoring is the need of the hour in this age of infrastructure. Many methods are being used for damage monitoring in different mechanical and civil structures. Some of them are strain based methods in which abruptly increased strain signifies the presence of damage in the structure. This article focuses on crack monitoring of a fixedfixed beam using fiber optic sensors which can measure strain locally or globally. The two types of fiber optic sensors used in this research are fiber Bragg grating (FBG) and fiber optic polarimetric sensors (FOPS). FBG and FOPS are used for local strain monitoring (at one point only) and global strain monitoring (in the entire specimen) respectively. At the centre of the specimen, a piezoelectric wafer active sensor (PWAS) is also attached. PWAS is used to obtain electromechanical admittance (EMA) signatures. Further, these EMA signatures are analysed to access the damage state in the beam. These multiple smart materials together provide improved information on damages in the specimen which is very valuable for the structural health monitoring (SHM) of the specimen.

Fibre Bragg grating sensors for in-situ measurement of resin pressure in curing composites

A fibre optic sensor was developed for in-situ pressure measurement based on the principle of differential pressure in liquids. This sensor system is very simple and consists of fibre Bragg grating (FBG) done on a fibre with core diameter of 9 μm. A calibration study was carried out with a water column and the pressure sensitivity was found to be 1.636 × 10 -2 MPa -1 . The results show that response of FBG to the rise of water level is linear and agrees well with the theoretical results. The reliability of the sensors is confirmed by repeating the measurements for three times. The sensor is useful in applications that involve in-situ resin pressure measurement in manufacturing of laminated composite materials.