OFDR-based rock surface strain field test method and system

Abstract

The invention provides an OFDR-based rock surface strain field test method and system, and particularly relates to the technical field of rock dynamic failure monitoring, the method comprises the following steps: winding a distributed optical fiber on the outer surface of a rock sample to obtain an annular optical fiber and a spiral optical fiber, and applying a compression force to the rock sample to obtain a strain field of the rock surface strain field; according to the optical signals in the circumferential optical fiber and the spiral optical fiber, circumferential strain distribution and axial strain distribution are obtained through calculation, and the method solves the problem that it is difficult to dynamically monitor the surface strain change of the test piece in the failure deformation process in real time with high precision. The effect of real-time dynamic high-precision monitoring of the surface strain of the test piece in the damage deformation process of the test piece is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of rock dynamic damage monitoring, and in particular to a testing method and system for rock surface strain field based on OFDR. Background Art

[0002] At present, there is still a lack of understanding of the disaster-causing mechanism, rock mechanical properties and crack expansion of deep surrounding rocks, which seriously restricts the safe and efficient production of coal. Geotechnical engineering projects mainly rely on laboratory uniaxial compression tests to obtain geomechanical properties, which are crucial for studying the impact of mining on underground projects.

[0003] At present, the existing methods all use indirect measurement to monitor the deformation and failure process of the specimen. The acoustic signals, electrical signals, temperature and other signals during the deformation and failure of the specimen are used to monitor and characterize its failure deformation. It is rare to directly measure the surface strain changes of the specimen. Therefore, it is necessary to seek a new monitoring method that can measure the surface strain changes of the specimen in real time.

[0004] In summary, how to achieve real-time dynamic and high-precision monitoring of the specimen surface strain during the specimen failure deformation process is a problem that needs to be solved in this field. Summary of the invention

[0005] The main purpose of the present invention is to provide a testing method and system based on OFDR rock surface strain field, so as to solve the problem that it is difficult to realize real-time dynamic and high-precision monitoring of the specimen surface strain during the specimen failure and deformation process, and realize the effect of real-time dynamic and high-precision monitoring of the specimen surface strain during the specimen failure and deformation process.

[0006] In order to achieve the above objectives, the present invention provides a testing method for rock surface strain field based on OFDR, so as to save storage space and improve retrieval efficiency.

[0007] In a first aspect, the present invention provides a testing method based on OFDR rock surface strain field, which is applied to an OFDR testing system. The method comprises:

[0008] Obtain rock samples and distributed optical fiber;

[0009] Winding the distributed optical fiber on the outer surface of the rock sample to obtain the circumferential optical fiber and the spiral optical fiber;

[0010] A compressive force is applied to the rock sample, and the annular strain distribution and the axial strain distribution are calculated based on the optical signals in the annular optical fiber and the spiral optical fiber.

[0011] Optionally, the step of winding the distributed optical fiber on the outer surface of the rock sample to obtain the circumferential optical fiber and the spiral optical fiber comprises:

[0012] Winding the distributed optical fiber on the outer surface of the rock sample in a first winding manner to obtain the circumferential optical fiber;

[0013] The distributed optical fiber is wound on the outer surface of the rock sample in a second winding manner to obtain the spiral optical fiber.

[0014] Optionally, applying a compressive force to the rock sample and calculating the annular strain distribution and the axial strain distribution according to the optical signals in the annular optical fiber and the spiral optical fiber include:

[0015] The optical signal in the circumferential optical fiber is collected and converted by an optical fiber sensor to obtain a circumferential electrical signal, the circumferential electrical signal is processed by optical frequency domain reflection technology to obtain a circumferential strain, and the circumferential strain distribution is calculated according to the circumferential strain;

[0016] The optical signal in the spiral optical fiber is collected and converted by an optical sensor to obtain a spiral electrical signal, the spiral electrical signal is processed using an optical frequency domain reflection technology to obtain the axial strain, and the axial strain distribution is calculated based on the axial strain.

[0017] Optionally, the rock sample is a cylinder, and the step of winding the distributed optical fiber on the outer surface of the rock sample in a first winding manner to obtain the circumferential optical fiber comprises:

[0018] After the distributed optical fiber is horizontally wound around the first end of the outer surface of the rock sample for the first time, some loose optical fiber is left and then the second time is wound around after an interval of 20 mm until it is wound around the second end of the outer surface of the rock sample to obtain the annular optical fiber, wherein the loose optical fiber refers to the distributed optical fiber that is not in contact with the outer surface of the rock sample between each circle of the annular optical fiber.

[0019] Optionally, the step of winding the distributed optical fiber on the outer surface of the rock sample in a second winding manner to obtain the spiral optical fiber comprises:

[0020] The distributed optical fiber is closely attached to the second end of the outer surface of the rock sample and is spirally wound toward the second end until it is wound to the first end of the outer surface of the rock sample to obtain the spiral optical fiber.

[0021] Optionally, the calculating and obtaining the hoop strain distribution includes:

[0022] The hoop strain distribution is calculated using the hoop strain formula, which can be expressed as:

[0023]

[0024] Among them, ε Lis the annular strain distribution, θ1 is the inclination angle of the annular optical fiber, θ2 is the angle formed by the annular optical fiber and the spiral optical fiber, ε1 is the annular strain, and ε2 is the axial strain.

[0025] Optionally, the calculating and obtaining the axial strain distribution includes:

[0026] The axial strain distribution is calculated using the axial strain formula, which can be expressed as:

[0027]

[0028] Among them, ε A is the axial strain distribution, θ1 is the inclination angle of the annular optical fiber, θ2 is the angle formed by the annular optical fiber and the spiral optical fiber, ε1 is the annular strain, and ε2 is the axial strain.

[0029] In a second aspect, the present invention provides an optical fiber monitoring system using the testing method described in the first aspect, comprising:

[0030] A press unit, the press unit being used to apply pressure to the rock sample;

[0031] A press loading system unit, the press loading system unit is connected to the press unit and is used to control the pressure applied by the press unit to the rock sample;

[0032] An optical fiber strain collection system unit, wherein the optical fiber strain collection system unit is connected to the press unit and is used to collect strain information in the press unit.

[0033] In a third aspect, the OFDR demodulation device applied to the monitoring system described in the second aspect comprises:

[0034] A data line for transmitting strain information in the press unit;

[0035] Strain dynamic signal acquisition software, used to obtain the strain information through the data line;

[0036] A collection host, the collection host is connected to the data line, and the collection host is used to provide hardware support for the variable dynamic signal collection software;

[0037] The acquisition host is applied to the optical fiber strain acquisition system unit, and the strain dynamic signal acquisition software is configured in the acquisition host.

[0038] The present application provides a testing method and system based on OFDR rock surface strain field. The method obtains the circumferential optical fiber and the spiral optical fiber by winding the distributed optical fiber on the outer surface of the rock sample, applies a compressive force to the rock sample, and calculates the circumferential strain distribution and the axial strain distribution according to the optical signals in the circumferential optical fiber and the spiral optical fiber. The method solves the problem that the existing technology is difficult to monitor the surface strain changes of the test piece in the process of destruction and deformation in real time and with high precision. The effect of real-time dynamic and high-precision monitoring of the surface strain of the test piece during the process of destruction and deformation of the test piece is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0040] Figure 1 Schematic diagram of the testing method based on OFDR rock surface strain field provided in this application Figure 1 ;

[0041] Figure 2 Schematic diagram of the testing method based on OFDR rock surface strain field provided in this application Figure 2 ;

[0042] Figure 3 A three-dimensional schematic diagram of the optical fiber layout based on OFDR rock surface strain field provided for this application;

[0043] Figure 4 Schematic diagram of the structure of the optical fiber monitoring system based on OFDR rock surface strain field provided in this application.

[0044] The above drawings have shown clear embodiments of the present application, which will be described in more detail later. These drawings and text descriptions are not intended to limit the scope of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solutions and advantages of this application clearer, the technical solutions in this application will be clearly and completely described below in conjunction with the drawings in this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0046] The terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in sequences other than those illustrated or described herein.

[0047] In the present invention, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in this application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0048] As China's dominant energy source, coal plays an important role in primary energy generation. At present, there is still a lack of understanding of the disaster mechanism, rock mechanical properties and crack expansion of deep surrounding rocks, which seriously restricts the safe and efficient production of coal. Geotechnical engineering projects mainly rely on laboratory uniaxial compression tests to obtain geomechanical properties, which are crucial for studying the impact of mining on underground engineering.

[0049] At present, the existing methods all use indirect measurement to monitor the deformation and failure process of the specimen. The acoustic signals, electrical signals, temperature and other signals during the deformation and failure of the specimen are used to monitor and characterize its failure deformation. It is rare to directly measure the surface strain changes of the specimen. Therefore, it is necessary to seek a new monitoring method that can measure the surface strain changes of the specimen in real time.

[0050] In summary, achieving real-time dynamic and high-precision monitoring of the specimen surface strain during the specimen failure and deformation process is a problem that needs to be solved in this field.

[0051] The present application provides a testing method based on OFDR rock surface strain field. The method obtains the circumferential optical fiber and the spiral optical fiber by winding the distributed optical fiber on the outer surface of the rock sample, applies a compressive force to the rock sample, and calculates the circumferential strain distribution and the axial strain distribution according to the optical signals in the circumferential optical fiber and the spiral optical fiber. The method solves the problem that the existing technology is difficult to monitor the surface strain changes of the test piece in the process of damage and deformation in real time and with high precision. The effect of real-time dynamic and high-precision monitoring of the surface strain of the test piece during the process of damage and deformation of the test piece is achieved.

[0052] The technical solution of the present application and how the technical solution of the present application solves the above-mentioned technical problems are described in detail below with specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0053] Figure 1 Schematic diagram of the testing method based on OFDR rock surface strain field provided in this application Figure 1 The execution subject of this embodiment is the OFDR test system, such as Figure 1 As shown, the present embodiment provides a testing method based on OFDR rock surface strain field, the method comprising:

[0054] S101: Obtain rock samples and distributed optical fibers.

[0055] The rock sample may be in the shape of a cuboid or a cylinder. The distributed optical fiber includes a circumferential optical fiber and a spiral optical fiber, which are wound around the outer surface of the rock sample. The distributed optical fiber is used as both a sensing element and a transmission element. The distributed optical fiber uses the scattering principle of light in the optical fiber to perform continuous distributed measurement of external parameters distributed along the axial direction of the optical fiber, and obtains the spatial distribution state of the measured physical quantity (temperature, strain, etc.) and information on its change over time.

[0056] As can be understood, representative rock samples are selected, usually standard cylinders or square prisms, to ensure consistency in sample size, shape and material properties.

[0057] S102: Winding the distributed optical fiber on the outer surface of the rock sample to obtain a circumferential optical fiber and a spiral optical fiber.

[0058] Among them, Figure 3 As shown, the annular optical fiber 310 refers to the distributed optical fiber being closely attached to the first end of the outer surface of the rock sample and then horizontally wound for the first circle, leaving loose optical fiber in the air, and then winding for the second circle after 20mm, until winding to the second end of the outer surface of the rock sample to obtain the annular optical fiber 310, wherein the loose optical fiber 330 refers to the distributed optical fiber that does not fit the outer surface of the rock sample between each circle of the annular optical fiber 310. The spiral optical fiber 320 refers to the distributed optical fiber being closely attached to the second end of the outer surface of the rock sample and then spirally wound toward the second end, until winding to the first end of the outer surface of the rock sample to obtain the spiral optical fiber 320. L1, L2, L3, L4, L5 are used to represent the annular optical fiber 310 of each circle of the distributed optical fiber wound around the rock sample; S1, S2, S3, S4 are used to represent the spiral optical fiber 320 of each circle of the distributed optical fiber wound around the rock sample.

[0059] The specific implementation method may be: select a high-precision optical fiber cable suitable for optical frequency domain reflection technology as a distributed optical fiber, and wind and lay the distributed optical fiber along the outer surface of the rock sample to ensure that the distributed optical fiber is in close contact with the outer surface of the rock sample. When laying, it is necessary to pay attention to the neat arrangement of the optical fiber to avoid bending and breakage. Use epoxy resin and curing agent or other fixing devices to firmly attach the optical fiber to the outer surface of the rock sample. The present invention uses a standard cylindrical rock sample with a size of φ50×100mm. A distributed optical fiber is wound around the rock sample, and loose optical fibers 330 are left at the ends. The optical fiber is first wound horizontally to obtain a circumferential optical fiber 310, and then spirally wound to obtain a spiral optical fiber 320. The horizontal winding has an interval of 20mm per circle. The rock sample with the distributed light is installed on a uniaxial compression device to ensure that the central axis of the rock sample is aligned with the loading direction, connect the optical fiber sensor to the OFDR measurement system, and check the stability of the connection system.

[0060] S103: applying a compressive force to the rock sample, and calculating the annular strain distribution and the axial strain distribution according to the optical signals in the annular optical fiber and the spiral optical fiber.

[0061] The compression force applied to the rock sample can be applied using a compression fixture of a testing machine in a uniaxial compression experiment. The method for calculating the annular strain distribution and the axial strain distribution based on the optical signals in the annular optical fiber 310 and the spiral optical fiber 320 is: collecting and converting the optical signals in the annular optical fiber 310 through an optical sensor to obtain annular electrical signals, using optical frequency domain reflection technology to process the annular electrical signals to obtain annular strain, and calculating the annular strain distribution based on the annular strain, wherein the specific implementation method of calculating the annular strain distribution is: using the annular strain formula to calculate the annular strain distribution, the annular strain formula can be expressed as:

[0062]

[0063] Among them, ε L is the hoop strain distribution, θ1 is the inclination angle of the hoop optical fiber 310, θ2 is the angle formed by the hoop optical fiber 310 and the spiral optical fiber 320, ε1 is the hoop strain, and ε2 is the axial strain.

[0064] The optical signal in the spiral optical fiber 320 is collected and converted by an optical sensor to obtain a spiral electrical signal, and the spiral electrical signal is processed by optical frequency domain reflection technology to obtain the axial strain, and the axial strain distribution is calculated according to the axial strain. The specific implementation method of calculating the axial strain distribution is: using the axial strain formula to calculate the axial strain distribution, and the axial strain formula can be expressed as:

[0065]

[0066] Among them, ε A is the axial strain distribution, θ1 is the inclination angle of the annular optical fiber 310, θ2 is the angle formed by the annular optical fiber 310 and the spiral optical fiber 320, ε1 is the annular strain, and ε2 is the axial strain.

[0067] The annular strain ε1 and axial strain ε2 in this step are obtained by using optical frequency domain reflection technology. In specific implementation, the OFDR distributed optical fiber sensing device can be directly used to process the spiral electrical signal and the annular electrical signal to obtain the annular strain ε1 and the axial strain ε2. θ1 is the inclination angle of the annular optical fiber 310, and θ2 is the angle formed by the annular optical fiber 310 and the spiral optical fiber 320. In specific implementation, it is obtained according to the angle measurement during winding.

[0068] It can be understood that the optical frequency domain reflectometry (OFDR) in this step is a new type of distributed optical fiber sensing technology developed in recent years with the goal of high precision and high spatial resolution. It can obtain the Rayleigh scattering information of the entire optical fiber, and invert the strain distribution of each position of the entire optical fiber by measuring the changes in the position and intensity of the Rayleigh scattering signal. The uniaxial compression experiment used in this step is a commonly used material mechanics test method, which is used to study the deformation and failure characteristics of materials under stress. In the uniaxial compression experiment, the sample is placed between the compression fixtures of the testing machine, and a force perpendicular to the axial direction of the sample is applied to compress the sample in one direction. At present, the uniaxial compression experiment is one of the basic and widely used laboratory test methods for monitoring rock mechanical properties and failure mechanisms through strain measurement.

[0069] The following are the general steps for a uniaxial compression experiment:

[0070] (1) Sample preparation: Prepare samples that meet standard specifications according to experimental requirements. Usually, the sample is in the shape of a cuboid or cylinder, and the size and proportion must comply with relevant standards or research requirements.

[0071] (2) Test setup: Place the specimen between the compression fixtures of the testing machine and set the appropriate loading rate and loading method according to the test requirements. Generally, the loading rate of the specimen should comply with the provisions of the relevant standards to ensure the accuracy and comparability of the test results.

[0072] (3) Test conduct: Start the testing machine, apply a compressive load perpendicular to the axis of the specimen, and record the deformation and load response data of the specimen during the loading process. During the test, the strain and deformation of the specimen, as well as the loading force applied by the testing machine, are usually continuously monitored.

[0073] (4) Data acquisition: The test data is collected in real time through sensors or measuring equipment, including the strain, deformation, load and other parameters of the specimen. These data can be used for subsequent analysis and research.

[0074] (5) End of test: When the preset termination condition is reached, the loading is stopped and the test data is recorded. Generally, the test end condition is when the specimen reaches the failure point or reaches the set maximum load value.

[0075] (6) Data analysis: Analyze and process the test data, including drawing stress-strain curves, calculating mechanical properties parameters such as elastic modulus, yield strength, ultimate strength, etc., and conducting research and comparative analysis.

[0076] Through the uniaxial compression experiment of rock mechanics, the mechanical properties, deformation characteristics and failure behavior of the rock mass can be evaluated, and the quantitative characterization and analysis of the damage of coal rock mass by distributed optical fiber can be realized. The results can provide guidance for the engineering application of soil and rock mass, the support design of underground engineering, etc., thereby improving the safety and reliability of underground mining.

[0077] As can be understood, optical frequency domain reflectometry (OFDR) technology, as a high-precision distributed fiber optic sensing technology, is widely used in rock mechanics testing because of its ability to achieve high spatial resolution and high sensitivity strain measurement. In uniaxial compression experiments, OFDR technology provides a new method for continuous and real-time monitoring of rock surface strain distribution.

[0078] (1) Experimental preparation

[0079] Select representative rock samples, usually standard cylinders or square prisms, to ensure consistency in sample size, shape and material properties.

[0080] (2) Fiber Optic Laying

[0081] Select high-precision optical fiber cables suitable for OFDR technology, and lay the distributed optical fiber along the surface of the sample to ensure close contact between the optical fiber and the rock sample. When laying out, pay attention to the neat arrangement of the optical fiber to avoid bending and damage. Use epoxy resin and curing agent or other fixing devices to firmly attach the optical fiber to the surface of the sample.

[0082] (3) Test equipment

[0083] A high-precision uniaxial compression press is used to apply a stable and uniform compressive force. The system includes a loading controller and a data acquisition system that can record the applied pressure and displacement data in real time.

[0084] (4) Experimental procedures

[0085] 1) System initialization

[0086] ① Equipment calibration: Ensure that the initial status of the press and OFDR system is accurate and perform necessary calibration work.

[0087] ② Parameter setting: Set appropriate measurement parameters in the OFDR system, including light source power, scanning frequency, sampling interval, etc.

[0088] 2) Sample installation

[0089] ① Install the rock sample with optical fiber on the uniaxial compression device to ensure that the central axis of the sample is aligned with the loading direction.

[0090] ② Connect the optical fiber sensor to the OFDR measurement system and check the stability of the connection system.

[0091] 3) Loading and measurement

[0092] ① Preload: Apply an initial preload to eliminate relaxation factors in the specimen and the press.

[0093] ②Formal loading: Apply compression force gradually according to the set loading rate, and start the OFDR system for real-time strain monitoring.

[0094] ③Data acquisition: synchronously record loading force, displacement and optical fiber strain signals to ensure data integrity and accuracy.

[0095] 4) Data processing and analysis

[0096] ① Data processing: Use the OFDR system-specific software to demodulate, filter and analyze the collected optical fiber strain signal.

[0097] ②Result analysis: Compare and analyze the strain distribution at different loading stages, obtain the circumferential strain and axial strain of each specimen, and evaluate the deformation characteristics and rupture process of the specimen.

[0098] By applying OFDR optical frequency domain reflectometry in uniaxial compression experiments, high-precision and continuous monitoring of rock surface strain can be achieved. This technology not only helps to deeply understand the mechanical behavior of rock under compression conditions, but also provides a scientific basis for rock stability evaluation and support design in engineering practice.

[0099] The testing method based on OFDR rock surface strain field provided in the embodiment of the present application is to obtain the annular optical fiber 310 and the spiral optical fiber 320 by winding the distributed optical fiber on the outer surface of the rock sample, apply a compressive force to the rock sample, and calculate the annular strain distribution and the axial strain distribution according to the optical signals in the annular optical fiber 310 and the spiral optical fiber 320. This method solves the technical problem of difficulty in real-time dynamic and high-precision monitoring of the surface strain of the test piece during the process of damage and deformation. The effect of real-time dynamic and high-precision monitoring of the surface strain of the test piece during the process of damage and deformation of the test piece is achieved.

[0100] Figure 2 Schematic diagram of the testing method based on OFDR rock surface strain field provided in this application Figure 2 ,like Figure 2 As shown, in this embodiment Figure 1 and Figure 3 Based on the embodiment, the testing method of rock surface strain field based on OFDR is described in detail, as follows: Figure 2 As shown, the present embodiment provides a testing method based on OFDR rock surface strain field, the method comprising:

[0101] S201: Obtain rock samples and distributed optical fibers.

[0102] The rock sample may be in the shape of a cuboid or a cylinder. The distributed optical fiber includes a circumferential optical fiber 310 and a spiral optical fiber 320. The circumferential optical fiber 310 and the spiral optical fiber 320 are distinguished according to the winding method. The circumferential optical fiber 310 refers to the distributed optical fiber being horizontally wound around the first end of the outer surface of the rock sample for the first circle, leaving a loose optical fiber 330 in the air, and then winding the second circle after 20 mm, until the circumferential optical fiber 310 is obtained by winding around the second end of the outer surface of the rock sample. The loose optical fiber 330 refers to the distributed optical fiber that does not fit the outer surface of the rock sample between each circle of the circumferential optical fiber 310. The spiral optical fiber 320 refers to the distributed optical fiber that is closely attached to the second end of the outer surface of the rock sample and is spirally wound toward the second end until it is wound to the first end of the outer surface of the rock sample to obtain the spiral optical fiber 320. The distributed optical fiber serves as both a sensing element and a transmission element. It utilizes the scattering principle of light in the optical fiber to perform continuous distributed measurement of external parameters distributed along the axial direction of the optical fiber, and obtains the spatial distribution state of the measured physical quantity (temperature, strain, etc.) and information on its changes over time.

[0103] As can be understood, representative rock samples are selected, usually standard cylinders or square prisms, to ensure consistency in sample size, shape and material properties.

[0104] S202: Winding the distributed optical fiber on the outer surface of the rock sample in a first winding manner to obtain a circumferential optical fiber 310.

[0105] Among them, the first winding method refers to horizontally winding the distributed optical fiber close to the first end of the outer surface of the rock sample for the first circle, leaving loose optical fiber 330 in the air, and then starting to wind the second circle after 20 mm until it is wound to the second end of the outer surface of the rock sample.

[0106] Further, after the distributed optical fiber is horizontally wound around the first end of the outer surface of the rock sample for the first turn, a loose optical fiber 330 is left, and then the second turn is wound after an interval of 20 mm until it is wound to the second end of the outer surface of the rock sample, thereby obtaining the annular optical fiber 310, wherein the loose optical fiber 330 refers to the distributed optical fiber that does not fit the outer surface of the rock sample between each turn of the annular optical fiber 310. The specific implementation method is as follows: after a distributed optical fiber is horizontally wound around the first end of the outer surface of a cylindrical rock sample for the first turn, a loose optical fiber 330 is left, and then the second turn is wound at a position 20 mm vertically away from the first turn until it is wound to the second end of the outer surface of the cylindrical rock sample, thereby obtaining the annular optical fiber 310, wherein the loose optical fiber 330 refers to the distributed optical fiber that does not fit the outer surface of the cylindrical rock sample between each turn of the annular optical fiber 310.

[0107] It can be understood that the first winding method is to horizontally wind the distributed optical fiber closely around the surface of the rock sample in order to measure the annular strain on the surface of the cylindrical rock sample.

[0108] S203: Winding the distributed optical fiber on the outer surface of the rock sample in a second winding manner to obtain the spiral optical fiber 320.

[0109] The second winding method refers to starting to spirally wind the distributed optical fiber close to the second end of the outer surface of the rock sample toward the second end until it is wound to the first end of the outer surface of the rock sample.

[0110] Furthermore, the distributed optical fiber is closely attached to the second end of the outer surface of the rock sample and is spirally wound toward the second end until it is wound to the first end of the outer surface of the rock sample, and the specific implementation method of obtaining the spiral optical fiber 320 is as follows: after a distributed optical fiber in step S203 completes the first winding method of winding, the remaining distributed optical fiber is closely attached to the second end of the outer surface of the cylindrical rock sample and is spirally wound toward the second end until it is wound to the first end of the outer surface of the rock sample, thereby obtaining the spiral optical fiber 320.

[0111] It can be understood that the second winding method is to spirally wind the distributed optical fiber horizontally and closely around the surface of the rock sample so as to measure the axial strain on the surface of the rock sample.

[0112] S204: collecting and converting the optical signal in the annular optical fiber 310 by means of an optical sensor to obtain an annular electrical signal, processing the annular electrical signal by means of an optical frequency domain reflection technique to obtain annular strain, and calculating the annular strain distribution according to the annular strain.

[0113] Among them, the processes of collecting data through optical sensors and processing using optical frequency domain reflectometry technology are both technical means commonly used by technicians in this field. In specific implementation, the OFDR distributed optical fiber sensing equipment can be directly used to process the circumferential electrical signal to obtain the circumferential strain, and the circumferential strain distribution can be calculated.

[0114] Furthermore, the specific implementation method of calculating the hoop strain distribution is: using the hoop strain formula to calculate the hoop strain distribution, the hoop strain formula can be expressed as:

[0115]

[0116] Among them, ε L is the hoop strain distribution, θ1 is the inclination angle of the hoop optical fiber 310, θ2 is the angle formed by the hoop optical fiber 310 and the spiral optical fiber 320, ε1 is the hoop strain, and ε2 is the axial strain.

[0117] The annular strain ε1 and axial strain ε2 in this step are obtained by using optical frequency domain reflection technology. In specific implementation, the OFDR distributed optical fiber sensing device can be directly used to process the spiral electrical signal and the annular electrical signal to obtain the annular strain ε1 and the axial strain ε2. θ1 is the inclination angle of the annular optical fiber 310, and θ2 is the angle formed by the annular optical fiber 310 and the spiral optical fiber 320. In specific implementation, it is obtained according to the angle measurement during winding.

[0118] S205: Collect and convert the optical signal in the spiral optical fiber 320 by means of an optical sensor to obtain a spiral electrical signal, process the spiral electrical signal by means of an optical frequency domain reflection technique to obtain an axial strain, and calculate the axial strain distribution according to the axial strain.

[0119] Among them, the processes of collecting data through optical sensors and processing using optical frequency domain reflection technology are both technical means commonly used by technicians in this field. In specific implementation, the OFDR distributed optical fiber sensing equipment can be used to directly process the spiral electrical signal to obtain the axial strain, and the axial strain distribution can be obtained based on the axial strain calculation.

[0120] Furthermore, the specific implementation method of calculating the axial strain distribution is: using the axial strain formula to calculate the axial strain distribution, the axial strain formula can be expressed as:

[0121]

[0122] Among them, ε A is the axial strain distribution, θ1 is the inclination angle of the annular optical fiber 310, θ2 is the angle formed by the annular optical fiber 310 and the spiral optical fiber 320, ε1 is the annular strain, and ε2 is the axial strain.

[0123] The annular strain ε1 and axial strain ε2 in this step are obtained by using optical frequency domain reflection technology. In specific implementation, the OFDR distributed optical fiber sensing device can be directly used to process the spiral electrical signal and the annular electrical signal to obtain the annular strain ε1 and the axial strain ε2. θ1 is the inclination angle of the annular optical fiber 310, and θ2 is the angle formed by the annular optical fiber 310 and the spiral optical fiber 320. In specific implementation, it is obtained according to the angle measurement during winding.

[0124] The testing method based on OFDR rock surface strain field provided in the embodiment of the present application is to obtain the annular optical fiber 310 and the spiral optical fiber 320 by winding the distributed optical fiber on the outer surface of the rock sample, apply compressive force to the rock sample, collect and convert the optical signal in the annular optical fiber 310 by an optical sensor to obtain an annular electrical signal, use optical frequency domain reflection technology to process the annular electrical signal to obtain annular strain, and calculate the annular strain distribution according to the annular strain, collect and convert the optical signal in the spiral optical fiber 320 by an optical sensor to obtain a spiral electrical signal, use optical frequency domain reflection technology to process the spiral electrical signal to obtain axial strain, and calculate the axial strain distribution according to the axial strain. This method solves the technical problem that it is difficult to monitor the surface strain of the test piece in the process of destruction and deformation in real time and dynamic with high precision. The effect of real-time dynamic and high-precision monitoring of the surface strain of the test piece during the process of destruction and deformation of the test piece is achieved.

[0125] Figure 4 This is a schematic diagram of the structure of the optical fiber monitoring system based on OFDR rock surface strain field provided in this application. Figure 4 As shown, the optical fiber monitoring system 500 of rock surface strain field based on OFDR provided by the present application includes: a press unit 10, a press loading system unit 30, and an optical fiber strain acquisition system unit 20;

[0126] The press unit is used to apply pressure to the rock sample 13; the press unit 10 comprises: a rock sample 13, a press 11, and a distributed optical fiber 12, wherein the rock sample 13 is placed in the middle of the press 11, and the press 11 is used to apply pressure to the rock sample 13; the distributed optical fiber 12 is wound around the surface of the rock sample 13, and is used to sense and transmit stress and strain information of the rock sample 13;

[0127] The press loading system unit 30 is connected to the press unit 10 and is used to control the pressure applied by the press 11 to the rock sample 13; wherein, the press loading system unit 30 refers to the press loading system, which refers to the system that provides power to the press 11 and controls its workload. It is a key part of the press to achieve various processing functions and can be provided by the press manufacturer; the connection method between the press loading system unit 30 and the press unit 10 varies depending on the type, design and specific application requirements of the press, but generally speaking, the connection between them mainly involves power transmission, control signal transmission and coordination of mechanical structures. The following connection methods can be used in specific implementation:

[0128] 1. Power transmission connection

[0129] Electric motor drive: For hydraulic or mechanical presses, the electric motor is the main power source. The electric motor is connected to the driving components of the press (such as hydraulic pump, crankshaft, etc.) through a transmission device such as a belt, chain or coupling to achieve power transmission.

[0130] Hydraulic system: In a hydraulic press, the hydraulic energy generated by the hydraulic pump is transmitted to the cylinder or actuator through hydraulic components such as oil pipes and joints to load the workpiece. The connection of the hydraulic system needs to ensure good sealing to prevent oil leakage.

[0131] 2. Control signal transmission

[0132] Electrical control: The loading system of the press is usually connected to the electrical control system, which can accurately control the loading process by controlling the start and stop of the motor and adjusting the opening and closing of the hydraulic valve. The electrical control connection includes power lines, signal lines, control cables, etc., which are connected to the control system of the press through sockets, plugs, terminals and other components.

[0133] Sensors and feedback: In order to monitor the loading status of the press in real time, the loading system is also connected to various sensors (such as pressure sensors, displacement sensors, etc.). The sensors transmit the detected signals to the control system, and the control system adjusts the loading parameters according to the feedback signals to ensure the stability and accuracy of the loading process.

[0134] 3. Mechanical structure coordination

[0135] Mechanical connectors: The actuators of the loading system (such as oil cylinders, air cylinders, mechanical arms, etc.) need to be connected to the main structure of the press through mechanical connectors (such as bolts, pins, keys, etc.). These connectors need to withstand the huge forces generated during the loading process, so high-strength, wear-resistant materials must be selected and the connection must be firm and reliable.

[0136] Guide rails and slides: In a mechanical press, the actuator of the loading system may slide or move on the main frame of the press through mechanical structures such as guide rails and slides to load the workpiece. The cooperation between the guide rails and slides needs to be precise and stable to ensure the smooth progress of the loading process.

[0137] The optical fiber strain acquisition system unit 20 is connected to the press unit 10, and the optical fiber strain acquisition system unit 20 is used to collect strain information in the press unit 10. Among them, the optical fiber strain acquisition system unit 20 refers to the optical fiber strain acquisition system, which is a system that uses optical fiber sensing technology to monitor and collect strain information in real time. The system is based on optical fiber as a sensing element, and infers the size and distribution of strain by measuring the changes in optical signals in the optical fiber. The optical fiber strain acquisition system can be developed by yourself or purchased on the market. The optical fiber strain acquisition system unit 20 can be connected to the press unit 10 through a signal line or a data line. The specific connection method is determined according to actual needs and is not limited here.

[0138] The present application also provides an application Figure 4 The OFDR demodulation device of the monitoring system in the embodiment includes:

[0139] A data line for transmitting strain information in the press unit;

[0140] Strain dynamic signal acquisition software, used to obtain the strain information through the data line;

[0141] A collection host, the collection host is connected to the data line, and the collection host is used to provide hardware support for the variable dynamic signal collection software;

[0142] Wherein, the acquisition host is applied to the optical fiber strain acquisition system unit, and the strain dynamic signal acquisition software is configured in the acquisition host. The strain information is used to indicate the optical signal in the circumferential optical fiber 310 and the spiral optical fiber 320. OFDR demodulation device (Optical Frequency Domain Reflectometry Demodulation Device) is a high-precision demodulation device for optical fiber sensing system, mainly used in the field of distributed sensing. OFDR technology emits an optical signal whose frequency changes linearly with time through a tuned laser, transmits it to the optical fiber, and monitors the returned scattered signal. Since the reflection and scattering inside the optical fiber will produce corresponding phase and amplitude changes with the change of frequency, the OFDR device can analyze these changes in the frequency domain to obtain the distribution information of strain, temperature or other physical quantities at each point in the optical fiber. The collection of distributed optical fiber data uses the OSI-D optical fiber demodulator produced by Wuhan Haoheng Technology Co., Ltd., which mainly includes an acquisition host, strain dynamic signal acquisition software, and a data cable. The acquisition host is mainly based on the OFDR sensing principle, and the internal strain of the sample can be monitored in real time by connecting the optical fiber to the test instrument. The instrument has a spatial resolution of up to 0.64mm and a maximum measuring length of 120m. It has the characteristics of short-distance and high-precision measurement and can achieve fully distributed millimeter-level high-precision strain measurement.

[0143] It should be noted that, for the aforementioned method embodiments, for the sake of simplicity, they are all expressed as a series of action combinations, but those skilled in the art should be aware that the present application is not limited by the described order of actions, because according to the present application, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all optional embodiments, and the actions and modules involved are not necessarily required by the present application.

[0144] It should be understood that the above-mentioned device embodiments are only illustrative, and the device of the present application can also be implemented in other ways. For example, the division of units / modules in the above-mentioned embodiments is only a logical function division, and there may be other division methods in actual implementation. For example, multiple units, modules or components can be combined, or can be integrated into another system, or some features can be ignored or not executed.

[0145] In addition, unless otherwise specified, each functional unit / module in each embodiment of the present application may be integrated into one unit / module, each unit / module may exist physically separately, or two or more units / modules may be integrated together. The above-mentioned integrated unit / module may be implemented in the form of hardware or in the form of a software program module.

[0146] It should be understood that the present application is not limited to the precise structures that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A testing method for rock surface strain field based on OFDR, characterized in that: Applied to an OFDR test system, the method comprises: Obtain rock samples and distributed optical fiber; The distributed optical fiber is wound around the outer surface of the rock sample to obtain a circular optical fiber and Helical optical fiber; A compressive force is applied to the rock sample, and the annular strain distribution and the axial strain distribution are calculated based on the optical signals in the annular optical fiber and the spiral optical fiber.

2. The method according to claim 1, characterized in that The step of winding the distributed optical fiber on the outer surface of the rock sample to obtain the circumferential optical fiber and the spiral optical fiber comprises: The distributed optical fiber is wound on the outer surface of the rock sample in a first winding manner Obtaining the annular optical fiber; The distributed optical fiber is wound on the outer surface of the rock sample in a second winding manner The helical optical fiber is obtained.

3. The method according to claim 1, characterized in that The step of applying a compressive force to the rock sample and calculating the annular strain distribution and the axial strain distribution according to the optical signals in the annular optical fiber and the spiral optical fiber comprises: The optical signal in the circular optical fiber is collected and converted by an optical fiber sensor to obtain A circumferential electrical signal, wherein the circumferential electrical signal is processed by using an optical frequency domain reflectometry technique to obtain a circumferential strain, and a circumferential strain distribution is calculated based on the circumferential strain; The optical signal in the spiral optical fiber is collected and converted by an optical sensor to obtain a spiral electrical signal, the spiral electrical signal is processed using an optical frequency domain reflection technology to obtain the axial strain, and the axial strain distribution is calculated based on the axial strain.

4. The method according to claim 2, characterized in that: The rock sample is a cylinder, and the step of winding the distributed optical fiber on the outer surface of the rock sample in a first winding manner to obtain the circumferential optical fiber comprises: After the distributed optical fiber is horizontally wound around the first end of the outer surface of the rock sample for the first time, some loose optical fiber is left and then the second time is wound around after an interval of 20 mm until it is wound around the second end of the outer surface of the rock sample to obtain the annular optical fiber, wherein the loose optical fiber refers to the distributed optical fiber that is not in contact with the outer surface of the rock sample between each circle of the annular optical fiber.

5. The method according to claim 2, characterized in that: The step of winding the distributed optical fiber on the outer surface of the rock sample in a second winding manner to obtain the spiral optical fiber comprises: The distributed optical fiber is closely attached to the second end of the outer surface of the rock sample and is spirally wound toward the second end until it is wound to the first end of the outer surface of the rock sample to obtain the spiral optical fiber.

6. The method according to claim 3, characterized in that The calculation to obtain the hoop strain distribution includes: The hoop strain distribution is calculated using the hoop strain formula, which can be expressed as: Among them, ε L is the annular strain distribution, θ1 is the inclination angle of the annular optical fiber, θ2 is the angle formed by the annular optical fiber and the spiral optical fiber, ε1 is the annular strain, and ε2 is the axial strain.

7. The method according to claim 3, characterized in that The calculating and obtaining the axial strain distribution includes: The axial strain distribution is calculated using the axial strain formula, which can be expressed as: Among them, ε A is the axial strain distribution, θ1 is the inclination angle of the annular optical fiber, θ2 is the angle formed by the annular optical fiber and the spiral optical fiber, ε1 is the annular strain, and ε2 is the axial strain.

8. An optical fiber monitoring system using the testing method according to any one of claims 1 to 7, characterized in that: include: A press unit, the press unit being used to apply pressure to the rock sample; A press loading system unit, the press loading system unit is connected to the press unit and is used to control the pressure applied by the press unit to the rock sample; An optical fiber strain collection system unit, wherein the optical fiber strain collection system unit is connected to the press unit and is used to collect strain information in the press unit.

9. An OFDR demodulation device applied to the monitoring system as claimed in claim 8, characterized in that: include: A data line for transmitting strain information in the press unit; Strain dynamic signal acquisition software, used to obtain the strain information through the data line; A collection host, the collection host is connected to the data line, and the collection host is used to provide hardware support for the variable dynamic signal collection software; The acquisition host is applied to the optical fiber strain acquisition system unit, and the strain dynamic signal acquisition software is configured in the acquisition host.

Images