scholarly journals Diagnostics of impregnation defects of reinforcing filaments of polymer composite with built-in fibre-optic sensor with distributed Bragg grating

2020 ◽  
pp. 60-72
Author(s):  
A. A Pan’kov
Keyword(s):  
Composite Material ◽  
Optical Fiber ◽  
Density Function ◽  
Strain Distribution ◽  
Distribution Density ◽  
Optical Fiber Sensor ◽  
Fiber Sensor ◽  
Distribution Density Function ◽  
Optic Sensor ◽  
Probability Of Presence

Mathematical model of unidirectional fibrous polymer composite material with optical fiber sensor built into reinforcing fiber (filament of elementary fibers) with distributed Bragg grating is developed in order to diagnoste defects of filament impregnation - finding probability of impregnation defect as relative length of local sections of filament without impregnation, i.e. without filling binder of space between its elementary fibers. The technique of digital processing of reflection spectrum according to the solution of the integral Fredholm equation of the 1st kind is used in order to find the desired informative function of density of distribution of axial strains along the length of the sensitive section of the fibre-optic sensor. The approach assumes that the optical fiber sensor is embedded in the composite material at the stage of its manufacture, wherein the low-reflective nature of the sensitive portion of the optical fiber allows linear summation of reflection coefficients from its various local portions regardless of their mutual positions. Algorithm of numerical processing of strain distribution density function is developed for finding of sought probability of presence of impregnation defects along filament length. It has been revealed that the distribution density function has pronounced informative pulses, from the location and value of which the sought-after values of probability of presence of impregnation defects along the length of the filament can be found. The results of diagnostics of different values of the sought probability of the filament impregnation defect are presented based on the results of numerical simulation of the measured reflection spectra and the sought function of strain distribution density along the length of the sensitive section of the optical fiber sensor at different values of the volume fraction of the filaments, combinations of transverse and longitudinal loads of the representative domain of the unidirectional fibrous composite material in comparison with graphs for the case without load.

Novel Measurement System With Optical Fiber Sensor for Strain Distributions in Welded Tubular Joints

2008 ◽  
Author(s):  
Hideaki Murayama ◽  
Kazuro Kageyama ◽  
Kohei Ohara ◽  
Kiyoshi Uzawa ◽  
Makoto Kanai ◽  
...  
Keyword(s):  
Optical Fiber ◽  
Spatial Resolution ◽  
Measurement System ◽  
Strain Distribution ◽  
Welded Joint ◽  
Optical Fiber Sensor ◽  
Weld Line ◽  
Fiber Sensor ◽  
Strain Monitoring ◽  
Tubular Joint

Defects and damage in a structural joint can trigger a critical degradation or collapse of the structure. Among joints, welded joints have many uncertainties, such as remaining stress, initial defects, and heat-affected zone. Such uncertainties in a welded joint can also induce a strain fluctuation, when they are subjected to a load. Conversely, the strain fluctuation along the weld line may represent the presence of uncertainties in the welded joint. This means that monitoring strain distribution along the weld line can be good way to assess their integrity and improve reliability of the structure. We have developed a novel distributed strain measurement technique which can measure strain distributions along fiber Bragg gratings (FBG) in an optical fiber and has the high spatial resolution and we applied it to strain monitoring of a welded tubular joint. The spatial resolution o is less than 1 mm and it was confirmed by measurement simulations and experiments. Then, we measured the strain distributions along the weld line of the tubular joint of a steel pipe subjected to a tensile load by the developed measurement system. We could successfully measure the development of the strain distribution along the weld line, where the sharply fluctuating strain distributions resulting from some defects were observed. In this paper, we describe the measurement principle and performance of the optical fiber sensor, and then show the results of strain monitoring in the welded joint.

Evaluation of Bolt Strength Characteristics in Bolted Joints Using an Optical Fiber Sensor System

2019 ◽  
Author(s):  
Atsushi Shirakawa ◽  
Toshiyuki Sawa
Keyword(s):  
Optical Fiber ◽  
Strain Distribution ◽  
Force Measurement ◽  
Optical Fiber Sensor ◽  
Effective Cross Section ◽  
Tensile Load ◽  
Bolted Joints ◽  
Strength Characteristics ◽  
Sensor System ◽  
Fiber Sensor

Abstract Bolted joints are used in many industrial products such as mechanical structures, automobiles, airplanes, chemical plants, and so on. In many cases, after the design of new products is finished, various tests on the bolt and bolted joints are carried out using actual parts to prevent accidents due to bolt loosening and fracture. At the same time, in the strength tests, external force measurement, axial bolt force measurement and so on are included. However, there are no advanced tests in which axial bolt strain distribution or bolt elongation in actual parts and so on are measured. Therefore, in this research, a new method for evaluating bolt strength characteristics using an optical fiber sensor system capable of measuring actual parts is demonstrated. First, a tensile strength test using an optical fiber sensor is carried out to measure strain distribution in a bolt, and a maximum strain value position in the measured clamp load-strain curve is shown. Then, the elongation at each part of the bolt is shown. Next, yield clamp bolt force is found using this sensor system in torque/clamp force testing. In addition, the measured yield clamp bolt force is compared with the values in the conventional measurement method and in the estimation formula. Also, discussed is the effective cross section area by which the stress at the engaged threads is calculated under tensile load. Finally, another case where an optical fiber sensor system is used for bolt fastening evaluation is discussed.

An Optical Fiber Sensor for Measuring Light Absorption in Suspension Solutions

2011 ◽  
Vol 121-126 ◽  
pp. 2509-2513
Author(s):  
Fei Bing Xiong ◽  
N Djeu ◽  
Wen Zhang Zhu
Keyword(s):  
Optical Fiber ◽  
Glassy Carbon ◽  
Fiber Optic ◽  
Optical Fiber Sensor ◽  
Fiber Optic Sensor ◽  
Fiber Sensor ◽  
Graphite Flake ◽  
Chemical Information ◽  
Carbon Particles ◽  
Optic Sensor

An optical fiber sensor based on attenuated total reflectance (ATR) for extraction chemical information from highly scattering turbid materials has been evaluated. The influence of particles on bulk absorption and ATR transmitted spectra of micron-sized graphite flakes and spherical glassy carbon suspensions were investigated. The ATR transmitted spectra of coiled fiber-optic sensor in those suspensions with various concentrations are insensitive to scattering of suspended particles, especially for graphite flake suspensions. The reason for different influence of graphite flakes and spherical glassy carbon particles suspensions on e ATR spectra analyzed. This study demonstrates that fiber-optic sensor based on ATR technique is a feasible technique in application for monitoring turbid suspensions.

Real-Time and In Situ Monitoring of FRP by Rayleigh Scattering-Based Distributed Sensing

2020 ◽  
Vol 843 ◽  
pp. 39-44
Author(s):  
Tatsuro Kosaka
Keyword(s):  
Optical Fiber ◽  
Process Monitoring ◽  
Strain Distribution ◽  
Rayleigh Scattering ◽  
Damage Identification ◽  
Optical Fiber Sensor ◽  
In Situ Monitoring ◽  
Fiber Sensor ◽  
Flow Front

In-situ monitoring method of FRP (Fiber Reinforced Plastics) by built-in sensors is a key technology for developing future and high-reliable composite structures. The Rayleigh scattering-based distributed optical fiber sensor has high spatial resolution of 1mm and good embeddability into FRP and then it can be considered that the sensor is very suitable to in-situ monitoring of FRP. In the present paper, process monitoring and damage identification of FRP were conducted. In the process monitoring, flow-front of silicon oil impregnating into glass textile during VaRTM (Vacuum-assisted Resin Transfer Molding) process was measured. Comparing to visual observation results, it appeared that the maximum slope position of strain distribution showed flow-front position. In the health monitoring, damage identification of cross-ply GFRP laminates with delamination by the attached distribution optical fiber sensors was carried on. From the results, it was found that the strain varied largely on the delaminated section and then the delamination was detectable from the surface strain distribution measured by the optical fiber sensor.

Method of Measuring Tendon Force using Optical Fiber Sensor

2018 ◽  
Vol 56 (1) ◽  
pp. 94-99
Author(s):  
N. Sogabe ◽  
S. Nakaue ◽  
K. Chikiri ◽  
M. Hayakawa
Keyword(s):  
Optical Fiber ◽  
Optical Fiber Sensor ◽  
Fiber Sensor ◽  
Tendon Force
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