scholarly journals The application of distributed optical strain sensing to measure the strain distribution of ground support members

FACETS ◽  
2018 ◽  
Vol 3 (1) ◽  
pp. 195-226 ◽  
Author(s):  
Bradley Forbes ◽  
Nicholas Vlachopoulos ◽  
Andrew J. Hyett
Keyword(s):  
Optical Fiber ◽  
Strain Distribution ◽  
Shear Loading ◽  
Strain Sensing ◽  
Micro Scale ◽  
Ground Support ◽  
Frequency Domain Reflectometry ◽  
Optical Strain ◽  
Mining Works ◽  
Cable Bolt

A distributed optical strain-sensing technique is presented as a solution for measuring the strain distribution along ground support members used in tunnelling and mining works. The technique employs a Rayleigh optical frequency domain reflectometry technology, which measures strain at a spatial resolution of 0.65 mm along the length of a standard optical fiber. A rationale for selecting this technology as a potential monitoring technique for ground support elements over alternative commercially available technologies is discussed. The development of a technique to couple optical fiber sensors with rock bolt, umbrella arch, and cable bolt support members is also demonstrated. A robust laboratory investigation of such optically instrumented support members demonstrated the capability of the technique to capture the expected in situ support behaviour in the form of coaxial, lateral, and shear loading arrangements as would be anticipated in the field. Moreover, the micro-scale data obtained by this optical sensing technique are shown to provide unprecedented insight into the local/micro-scale geomechanistic complexities associated with the bearing capacity of ground support members, especially when compared with data obtained by discrete strain-sensing technologies.

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.

Investigation of PDC Cutter Interface Geometry Using 3D FEM Modelling

2017 ◽  
Vol 29 ◽  
pp. 45-53 ◽  
Author(s):  
Seyed Ali Heydarshahy ◽  
Shivakumar Karekal
Keyword(s):  
Strain Distribution ◽  
High Stress ◽  
Polycrystalline Diamond ◽  
Shear Loading ◽  
Stress And Strain ◽  
3D Fem ◽  
Interface Shear ◽  
Interface Elements ◽  
Premature Failure ◽  
Stress And Strain Distribution

Polycrystalline Diamond Compact (PDC) cutters have been popularly used in recent times due to their resistance against mechanical and thermal wear. This paper was focused on interface geometries between the substrate and the diamond table. Various types of interfaces were designed, to investigate how different interface geometries influence distribution of stress and strain under shear loading. The interface geometries examined in this paper included castle interface, dent interface, honeycomb interface and chase interface. Parallel to the interface, shear loading was applied to the top of diamond table to mimic the shear loading component from the rock cutting. To apply the shear loading, two locations were considered for each of the geometries. These locations differed depending on the interface features. Stress and strain distribution and values across different interface geometries were analysed with the aid of 3D Finite Element Method (FEM). The numerical simulations indicated that stress and strain magnitudes and distribution patterns varied in relation to different geometries. Some substrates showed relatively lower plastic strain representing higher durability of the geometries. Concentration of stress and strain distribution showed the areas where one could expect weakness. It also implies that rotating the PDC cutter assemblies around their cylindrical axis helps avoiding fatigue of interface elements in regions of high stress concentration; and thus, preventing premature failure of interface elements.

GROWTH MONITORING OF DELAMINATION AND ADHESIVE DEBONDING OF CFRP STRUCTURES BY RAYLEIGH SCATTING-BASED DISTRIBUTION SENSORS

2021 ◽  
Author(s):  
KAZUKI OHNISHI ◽  
TATSURO KOSAKA ◽  
GENKO FUJIOKA
Keyword(s):  
Optical Fiber ◽  
Strain Distribution ◽  
Rayleigh Scattering ◽  
Adhesive Layer ◽  
Optical Fiber Sensors ◽  
Surface Strain ◽  
Growth Monitoring ◽  
Monitoring Method ◽  
Fiber Sensors ◽  
Measured Strain

Since delamination of CFRP laminates is generated by impact or fatigue in aircraft operation, identification method of the delamination is a very important technology to ensure safety of aircraft. Recently, built-in sensors are paid attention as a real-time monitoring method of initiation and growth of delamination. Optical fiber sensors are promised as built-in sensors of FRP due to their high strength, durability and embeddability. In this paper, we applied a Rayleigh scattering-based distribution sensor to detect delamination and debonding of CFRP structures. This optical fiber sensor can measure strain distribution along a fiber with wide area range, high spatial and strain resolutions. The optical fiber sensors attached on the surface of laminates were used to detect delamination and adhesive debonding of DCB, ENF and SLJ (single lap joint) specimens. Pre-crack were formed by inserting a Teflon films between the layers or the laminate and adhesive layer during manufacturing. The experimental results of DCB tests showed that the position of delamination edge could be identified precisely from the measured sharp peak of strain distribution. From the results of ENF tests, it appeared that the strain distribution showed the maximum at the delamination edge and the detected delamination edge positions agreed very well with the observed positions. The measured strain distributions were almost same as simulated results by FEM. From the tensile test results of SLJ specimen, it appeared that strain distribution showed extremum at debonding edge. It was also shown that the measured strain distribution agreed well with simulated results by FEM. From the above results, it appeared that the open delamination and debonding could be easily identified from surface strain distribution measured by the Rayleigh scattering-based sensor.

scholarly journals Truly Distributed Optical Fiber Sensors for Structural Health Monitoring: From the Telecommunication Optical Fiber Drawling Tower to Water Leakage Detection in Dikes and Concrete Structure Strain Monitoring

2010 ◽  
Vol 2010 ◽  
pp. 1-13 ◽  
Author(s):  
Jean-Marie Henault ◽  
Gautier Moreau ◽  
Sylvain Blairon ◽  
Jean Salin ◽  
Jean-Robert Courivaud ◽  
...  
Keyword(s):  
Optical Fiber ◽  
Optical Fibers ◽  
Brillouin Scattering ◽  
Optical Fiber Sensors ◽  
Leakage Detection ◽  
Strain Sensing ◽  
Water Leakage ◽  
Fiber Sensors ◽  
Practical Applications ◽  
Water Leakage Detection

Although optical fiber sensors have been developed for 30 years, there is a gap between lab experiments and field applications. This article focuses on specific methods developed to evaluate the whole sensing chain, with an emphasis on (i) commercially-available optoelectronic instruments and (ii) sensing cable. A number of additional considerations for a successful pairing of these two must be taken into account for successful field applications. These considerations are further developed within this article and illustrated with practical applications of water leakage detection in dikes and concrete structures monitoring, making use of distributed temperature and strain sensing based on Rayleigh, Raman, and Brillouin scattering in optical fibers. They include an adequate choice of working wavelengths, dedicated localization processes, choices of connector type, and further include a useful selection of traditional reference sensors to be installed nearby the optical fiber sensors, as well as temperature compensation in case of strain sensing.

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.

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