scholarly journals Study on Strain Characterization and Failure Location of Rock Fracture Process Using Distributed Optical Fiber under Uniaxial Compression

Sensors ◽  
2020 ◽  
Vol 20 (14) ◽  
pp. 3853
Author(s):  
Shiang Xu ◽  
Shuangming Wang ◽  
Pingsong Zhang ◽  
Duoxing Yang ◽  
Binyang Sun
Keyword(s):  
Rock Mass ◽  
Optical Fiber ◽  
Uniaxial Compression ◽  
Circumferential Strain ◽  
Rock Fracture ◽  
Test System ◽  
Dynamic Strain ◽  
Strain Response ◽  
Strain Characterization ◽  
Distributed Optical Fiber

A rock fracture test is a very important method in the study of rock mechanics. Based on the Mechanics Test System (MTS), the dynamic strain response of the failure process of cylindrical granite specimens under uniaxial compression was observed by using distributed optical fiber strain sensors. Two groups of tests were designed and studied for rock sample fracturing. The main comparison and analysis were made between the distributed optical fiber testing technology and the MTS testing system in terms of the circumferential strain response curve and the evolution characteristics of strain with time. The strain characterization of distributed optical fiber in the process of rock fracturing was obtained. The results show that the ring strains measured by the distributed optical fiber sensor and the circumferential strain gauge were consistent, with a minimum ring strain error of 1.27%. The relationship between the strain jump or gradient band of the distributed optical fiber and the crack space on the sample surface is clear, which can reasonably determine the time of crack initiation and propagation, point out the location of the rock failure area, and provide precursory information about rock fracture. The distributed optical fiber strain sensor can realize the linear and continuous measurement of rock mass deformation, which can provide some reference for the study of macro damage evolution and the fracture instability prediction of field engineering rock mass.

scholarly journals Distributed Dynamic Strain Sensing Based on Brillouin Scattering in Optical Fibers

Sensors ◽  
2020 ◽  
Vol 20 (19) ◽  
pp. 5629
Author(s):  
Agnese Coscetta ◽  
Aldo Minardo ◽  
Luigi Zeni
Keyword(s):  
Optical Fiber ◽  
Brillouin Scattering ◽  
Traffic Monitoring ◽  
Optical Fiber Sensors ◽  
Dynamic Strain ◽  
Dynamic Measurements ◽  
Research Activity ◽  
Fiber Sensors ◽  
Railway Traffic ◽  
Distributed Optical Fiber

Over the past three decades, extensive research activity on Brillouin scattering-based distributed optical fiber sensors has led to the availability of commercial instruments capable of measuring the static temperature/strain distribution over kilometer distances and with high spatial resolution, with applications typically covering structural and environmental monitoring. At the same time, the interest in dynamic measurements has rapidly grown due to the relevant number of applications which could benefit from this technology, including structural analysis for defect identification, vibration detection, railway traffic monitoring, shock events detection, and so on. In this paper, we present an overview of the recent advances in Brillouin-based distributed optical fiber sensors for dynamic sensing. The aspects of the Brillouin scattering process relevant in distributed dynamic measurements are analyzed, and the different techniques are compared in terms of performance and hardware complexity.

scholarly journals Experimental and Numerical Investigation on the Strain Response of Distributed Optical Fiber Sensors Bonded to Concrete: Influence of the Adhesive Stiffness on Crack Monitoring Performance

Sensors ◽  
2020 ◽  
Vol 20 (18) ◽  
pp. 5144
Author(s):  
Ismail Alj ◽  
Marc Quiertant ◽  
Aghiad Khadour ◽  
Quentin Grando ◽  
Benjamin Terrade ◽  
...  
Keyword(s):  
Optical Fiber ◽  
Concrete Structure ◽  
Crack Opening ◽  
Mechanical Tests ◽  
Elastic Behavior ◽  
Peak Strain ◽  
Strain Response ◽  
Rayleigh Backscattering ◽  
Crack Monitoring ◽  
Distributed Optical Fiber

The present study investigated the strain response of a distributed optical fiber sensor (DOFS) sealed in a groove at the surface of a concrete structure using a polymer adhesive and aimed to identify optimal conditions for crack monitoring. A finite element model (FEM) was first proposed to describe the strain transfer process between the host structure and the DOFS core, highlighting the influence of the adhesive stiffness. In a second part, mechanical tests were conducted on concrete specimens instrumented with DOFS bonded/sealed using several adhesives exhibiting a broad stiffness range. Distributed strain profiles were then collected with an interrogation unit based on Rayleigh backscattering. These experiments showed that strain measurements provided by DOFS were consistent with those from conventional sensors and confirmed that bonding DOFS to the concrete structure using soft adhesives allowed to mitigate the amplitude of local strain peaks induced by crack openings, which may prevent the sensor from early breakage. Finally, the FEM was generalized to describe the strain response of bonded DOFS in the presence of crack and an analytical expression relating DOFS peak strain to the crack opening was proposed, which is valid in the domain of elastic behavior of materials and interfaces.

scholarly journals Discerning Localized Thermal Heating from Mechanical Strain Using an Embedded Distributed Optical Fiber Sensor Network

Sensors ◽  
2020 ◽  
Vol 20 (9) ◽  
pp. 2583 ◽  
Author(s):  
R. Brian Jenkins ◽  
Peter Joyce ◽  
Adam Kong ◽  
Charles Nelson
Keyword(s):  
Carbon Fiber ◽  
Optical Fiber ◽  
Rapid Detection ◽  
Composite Structures ◽  
Epoxy Composite ◽  
Thermal Response ◽  
Strain Response ◽  
Energy Laser ◽  
Distributed Optical Fiber ◽  
Carbon Fiber Epoxy

Prior research has demonstrated that distributed optical fiber sensors (DOFS) based on Rayleigh scattering can be embedded in carbon fiber/epoxy composite structures to rapidly detect temperature changes approaching 1000 °C, such as would be experienced during a high energy laser strike. However, composite structures often experience mechanical strains that are also detected during DOFS interrogation. Hence, the combined temperature and strain response in the composite can interfere with rapid detection and measurement of a localized thermal impulse. In this research, initial testing has demonstrated the simultaneous response of the DOFS to both temperature and strain. An embedded DOFS network was designed and used to isolate and measure a localized thermal response of a carbon fiber/epoxy composite to a low energy laser strike under cyclic bending strain. The sensor interrogation scheme uses a simple signal processing technique to enhance the thermal response, while mitigating the strain response due to bending. While our ultimate goal is rapid detection of directed energy on the surface of the composite, the technique could be generalized to structural health monitoring of temperature sensitive components or smart structures.

scholarly journals Monitoring of Strain and Temperature in an Open Pit Using Brillouin Distributed Optical Fiber Sensors

Sensors ◽  
2020 ◽  
Vol 20 (7) ◽  
pp. 1924 ◽  
Author(s):  
Chiara Lanciano ◽  
Riccardo Salvini
Keyword(s):  
Rock Mass ◽  
Optical Fiber ◽  
Test Site ◽  
Optical Fiber Sensors ◽  
Open Pit ◽  
Rock Falls ◽  
Fiber Sensors ◽  
Geotechnical Monitoring ◽  
Distributed Optical Fiber ◽  
Marble Quarries

Marble quarries are quite dangerous environments in which rock falls may occur. As many workers operate in these sites, it is necessary to deal with the matter of safety at work, checking and monitoring the stability conditions of the rock mass. In this paper, some results of an innovative analysis method are shown. It is based on the combination of Distributed Optical Fiber Sensors (DOFS), digital photogrammetry through Unmanned Aerial Vehicle (UAV), topographic, and geotechnical monitoring systems. Although DOFS are currently widely used for studying infrastructures, buildings and landslides, their use in rock marble quarries represents an element of peculiarity. The complex morphologies and the intense temperature range that characterize this environment make this application original. The selected test site is the Lorano open pit which is located in the Apuan Alps (Italy); here, a monitoring system consisting of extensometers, crackmeters, clinometers and a Robotic Total Station has been operating since 2012. From DOFS measurements, strain and temperature values were obtained and validated with displacement data from topographic and geotechnical instruments. These results may provide useful fundamental indications about the rock mass stability for the safety at work and the long-term planning of mining activities.

Influence exerted by underground excavation shape and by effective stresses on the formation of a tensile strain zone at a depth greater than 1 km

2020 ◽  
pp. 67-75
Author(s):  
Van Min Nguyen ◽  
V. A. Eremenko ◽  
M. A. Sukhorukova ◽  
S. S. Shermatova
Keyword(s):  
Rock Mass ◽  
Cross Sections ◽  
Tensile Strain ◽  
Rock Fracture ◽  
Strain Analysis ◽  
Surrounding Rock ◽  
Underground Excavation ◽  
Secondary Stress ◽  
Principal Stresses ◽  
Mining Depth

The article presents the studies into the secondary stress field formed in surrounding rock mass around underground excavations of different cross-sections and the variants of principal stresses at a mining depth greater than 1 km. The stress-strain analysis of surrounding rock mass around development headings was performed in Map3D environment. The obtained results of the quantitative analysis are currently used in adjustment of the model over the whole period of heading and support of operating mine openings. The estimates of the assumed parameters of excavations, as well as the calculations of micro-strains in surrounding rock mass by three scenarios are given. During heading in the test area in granite, dense fracturing and formation of tensile strain zone proceeds from the boundary of e ≥ 350me and is used to determine rough distances from the roof ( H roof) and sidewalls ( H side) of an underground excavation to the 3 boundary e = 350me (probable rock fracture zone). The modeling has determined the structure of secondary stress and strain fields in the conditions of heading operations at great depths.

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