A true triaxial electric blasting fracturing multi-field visualization monitoring system and method

Abstract

The application discloses a true triaxial electric blasting fracturing multi-field visual monitoring system and method, and belongs to the technical field of testing or analyzing materials by measuring physical properties of the materials. The system comprises a true triaxial servo loading host, a visual pressure-bearing assembly, a composite fracturing excitation source, a multi-field synchronous monitoring module and an electromagnetic shielding control module. The visual pressure-bearing assembly comprises a grid pressure-bearing frame and an embedded transparent observation window, the end surface of the observation window is lower than the pressure-bearing end surface of the frame to form a micro-gap avoiding layer for load sharing of the ground stress and the fracturing pressure. The multi-field synchronous monitoring module integrates a high-speed camera, a three-dimensional DIC full-field strain gauge, an acoustic emission array and an in-hole dynamic pressure measuring unit. The electromagnetic shielding control module weakens the electromagnetic radiation of high-voltage electric blasting through an optoelectronic isolation circuit and a shielding copper mesh. The application solves the problem of field of view shielding caused by a closed pressure head of a traditional device, and realizes multi-field synchronous testing of a composite fracturing process under stress clamping.

Description

Technical Field

[0001] This invention relates to the technical field of testing or analyzing materials by measuring their physical properties, and particularly to a true triaxial electro-explosion-induced multi-field visualization monitoring system and method. Background Technology

[0002] With the continuous exploitation of deep resources, deep rock masses are generally in complex in-situ environments with high three-dimensional geostress, exhibiting significant high compressive strength and high integrity. Traditional explosive blasting faces significant safety hazards and strong disturbance problems, and the single liquid state... Phase change fracturing technology, under deep high confining pressure, faces difficulties in initiating fracturing due to slow pressure rise rates and weak initial impact kinetic energy, leading to phenomena such as cylinder blockage or directional propagation of a single fracture. In recent years, to overcome the limitations of single-energy fracturing, high-voltage pulse electro-explosion combined with liquid phase change fracturing has been developed. Phase transformation coupled with phase transformation, this composite fracturing technology combines microsecond-level strong dynamic loading for fracturing with millisecond-level quasi-static gas wedge propagation in the gas phase, making it a cutting-edge technology for overcoming the problem of non-explosive fracturing in deep rock masses.

[0003] To investigate this electrically induced liquid state The fracture evolution mechanism and fracture bifurcation law of phase transformation combined fracturing under deep geostress require true triaxial loading fracturing simulation tests on rock samples of different sizes in the laboratory. However, existing rock mechanics experimental testing equipment has the following technical shortcomings when dealing with the combined impact of strong dynamic load and high-pressure fluid:

[0004] (1) Traditional true triaxial testing systems suffer from severe black box effects and are incompatible with optical full-field monitoring. Existing true triaxial servo loading equipment uses heavy, enclosed solid high-strength alloy steel plates for its loading heads in order to provide and withstand extremely high three-dimensional principal stresses. The specimen is completely covered and concealed during pressurization, making it impossible for high-speed cameras to obtain the visual channel of the specimen surface. Current research only conducts full-field strain observation of DIC under unconfined conditions, which is detached from the real physical boundary conditions of deep three-dimensional high ground stress strongly constraining the cracks; in addition, monitoring only through acoustic means cannot intuitively capture the dynamic manifold evolution of the main crack from the inside of the specimen to the surface and the branching.

[0005] (2) Difficulty in synchronous triggering of multiphysics fields at the microsecond level and low precision of timing decoupling. The stress wave action time of electric explosion-induced stress waves is on the order of microseconds, while... Phase change gas wedge propagation is maintained on the order of milliseconds. Existing testing systems mostly operate independently and lack an integrated control center capable of high-precision time-series alignment across time scales for the high-voltage pulse discharge terminal, the three-dimensional DIC optical capture system, and the acoustic emission (AE) array. This results in the inability to accurately capture the critical mechanical response at the moment of alternation between dynamic and static loads.

[0006] (3) Interference of high-voltage electric explosion transient strong electromagnetic radiation on precision monitoring instruments. The high-voltage pulse power supply generates extremely high amplitude spatial electromagnetic pulses and ground surges at the moment of breaking down the metal wire. Conventional true triaxial and monitoring equipment do not have special isolation design. This strong electromagnetic radiation can easily cause serious signal crosstalk and waveform distortion in the surrounding broadband acoustic emission probes and high-frequency dynamic pressure sensors, which limits the fidelity and security of multi-source heterogeneous data.

[0007] In summary, there is an urgent need to develop a visualized true triaxial loading and multi-field synchronous monitoring system for the electro-explosion-induced phase transformation fracturing process. This system would be suitable for rock mechanics and deep-earth engineering experimental equipment, overcoming the technical limitations of the mutual exclusion between high-stress loading and optical full-field observation. It would provide key hard-core testing equipment for elucidating the complex fracturing mechanism in deep in-situ environments. Summary of the Invention

[0008] (a) Technical problems to be solved

[0009] To address the shortcomings of existing technologies, this invention provides a true triaxial electro-explosive fracturing multi-field visualization monitoring system. The structural features of this invention are as follows:

[0010] I. A visual composite pressure-bearing structure for direct optical observation under stress constraint was set up. By combining a grid pressure-bearing frame with an embedded transparent observation window with a 0.5mm to 2.0mm clearance micro-gap, the time-series load sharing of static stress loading and dynamic response pressure was realized. While applying three-dimensional geostress to the rock sample, the field of view obstruction of the closed loading head was reduced, which is used to observe the process of internal rock fracture penetrating to the surface under stress constraint.

[0011] Second, a multi-physics field timing adjustment and anti-interference synchronization mechanism is set up. The electromagnetic shielding control module with integrated opto-isolation circuit is used to attenuate the interference of electromagnetic pulses and ground surges generated during discharge on weak current monitoring instruments. The timing alignment of high-speed camera, acoustic emission array and pressure acquisition is achieved through multi-channel adjustable TTL level delay.

[0012] Third, an integrated multi-energy composite cracking full life cycle monitoring system is established, which combines the full-field strain evolution of the three-dimensional DIC surface, the location of microcrack initiation inside the AE, and the transient pressure fluctuation curve inside the hole for monitoring, in order to analyze the evolution process of composite cracking under in-situ stress environment constraints.

[0013] (II) Technical Solution

[0014] To achieve the above objectives, the present invention provides the following technical solution: a true triaxial electro-explosive fracturing multi-field visualization monitoring system, comprising a true triaxial servo loading host, a composite fracturing excitation source, a visualization pressure-bearing component, a multi-field synchronous monitoring module, and an electromagnetic shielding control module;

[0015] The true triaxial servo loading host is equipped with a loading chamber for placing rock samples and includes hydraulic cylinders arranged in three-dimensional orthogonal directions for independently applying triaxial principal stress to the rock samples.

[0016] A pre-fabricated blind hole is machined in the middle of the rock sample along a direction perpendicular to the observation surface, and the fracturing tube of the composite fracturing excitation source is inserted into the pre-fabricated blind hole; the composite fracturing excitation source also includes a high-voltage pulse power supply that is electrically connected to the internal electrode of the fracturing tube.

[0017] The visualization pressure-bearing component is located at the end of at least one principal stress loading direction of the true triaxial servo loading host, and is pressed against the loaded end face of the rock sample facing the bottom of the prefabricated blind hole, and is used to provide an optical observation channel while transmitting axial load;

[0018] The multi-field synchronous monitoring module includes an optical acquisition architecture set on the outside of the visual pressure-bearing component, and an acoustic acquisition architecture uniformly pasted on the remaining non-transparent load-bearing end face of the rock sample.

[0019] The electromagnetic shielding control module is electrically connected to the high-voltage pulse power supply, the optical acquisition architecture, and the acoustic acquisition architecture, respectively, and is used to issue timing control commands to realize the coordinated triggering of multi-source heterogeneous monitoring devices in the system and the shielding of transient spatial electromagnetic pulses during discharge.

[0020] As a preferred embodiment, the loading chamber and the assembly dimensions of the visualization pressure-bearing component of the true triaxial servo loading host are adjustable to accommodate rock samples of different sizes, including 200mm×200mm×200mm cubic samples or 500mm×500mm×260mm cuboid samples.

[0021] As a preferred embodiment, the diameter of the prefabricated blind hole is 30mm to 50mm and the axial depth is 150mm to 200mm; a complete rock layer with a preset thickness of 50mm to 100mm is left between the bottom of the prefabricated blind hole and the inner side of the visualized pressure-bearing component. This complete rock layer serves as the targeted exposure surface for stress wave reflection stretching and gas wedge splitting penetration generated instantaneously by composite fracturing.

[0022] As a preferred embodiment, the visualization pressure-bearing component includes a grid pressure-bearing frame and an embedded transparent observation window. The periphery of the grid pressure-bearing frame is fixedly connected to the end of the hydraulic cylinder of the true triaxial servo loading host, and a through optical observation hole is opened at its center. The inner pressure-bearing end face of the grid pressure-bearing frame is rigidly fitted with the end face of the rock sample to bear the three-dimensional static stress loading load of the main body. The embedded transparent observation window is embedded in the optical observation hole, and its inner end face is 0.5mm to 2.0mm lower than the inner pressure-bearing end face of the grid pressure-bearing frame, thereby forming a micro-gap structure avoidance layer between the embedded transparent observation window and the initial end face of the rock sample, which is used to achieve flexible contact with the rock sample after the end face bulges and deforms under load.

[0023] As a preferred embodiment, the inlaid transparent observation window is made by alternating layers of high-transmittance sapphire glass plates and polycarbonate buffer films through hot pressing and curing; an annular damping and shock-absorbing washer is embedded between its axial outer wall and the inner wall of the optical observation hole of the grid pressure frame, which is used to flexibly absorb and attenuate the dynamic shock wave energy transmitted outward at the moment of composite cracking.

[0024] As a preferred embodiment, the multi-field synchronous monitoring module includes a three-dimensional DIC observation unit, an acoustic emission monitoring array, and an in-hole dynamic pressure measurement unit. The three-dimensional DIC observation unit includes two dynamic high-speed cameras and flicker-free LED supplementary lights. The two cameras are positioned axially outside the visualization pressure-bearing component, with their lens optical axes forming a preset convergence angle with the central axis of the inlaid transparent observation window, aimed at the pre-fabricated speckle area on the end face of the rock sample. The acoustic emission monitoring array includes multiple broadband piezoelectric acoustic emission probes, evenly attached to the remaining five loaded end faces of the rock sample where the visualization pressure-bearing component is not located. The in-hole dynamic pressure measurement unit includes a piezoelectric pressure sensor and a piezoresistive pressure sensor, encapsulated at the tail end of the fracturing tube and extending into the sealed reaction chamber inside the fracturing tube.

[0025] As a preferred embodiment, the electromagnetic shielding control module includes a central control microprocessor, a multi-channel TTL level delay distributor, an opto-isolation circuit, and an overall shielding copper mesh cover. The central control microprocessor is connected to the input terminals of the two high-speed cameras and the acoustic emission monitoring array's acquisition card via the multi-channel TTL level delay distributor. The opto-isolation circuit is connected in series between the central control microprocessor and the discharge trigger terminal of the high-voltage pulse power supply. The overall shielding copper mesh cover is installed around the 3D DIC observation unit, the acoustic emission monitoring array, and related transmission cables, and is grounded at a single point.

[0026] This invention also proposes a true triaxial electro-explosive fracturing multi-field visualization monitoring method, comprising the following steps:

[0027] Step 1: Sample preparation and speckle pattern preparation

[0028] Select a 200mm×200mm×200mm cubic rock sample or a 500mm×500mm×260mm rectangular rock sample according to the test requirements, and process a pre-made blind hole at the center of the sample so that a complete rock layer with a preset thickness of 50mm to 100mm is left at the bottom of the hole; uniformly spray a black and white micro-mechanical speckle pattern on the outer surface of the rock sample facing the complete rock layer, and attach acoustic emission probes to the other five non-transparent load-bearing end faces.

[0029] Step 2: Excitation source placement and sealing assembly

[0030] The interior is filled with liquid The fracturing tube consisting of metal wire and constant pressure shear plate is slid into the prefabricated blind hole and is rigidly sealed and locked to the rock sample by the hole thread constraint device.

[0031] Step 3: True Three-Axis Alignment Loading and Calibration

[0032] Based on the size of the selected rock sample, the corresponding specification of the visualization pressure-bearing component is assembled on the true triaxial servo loading host; the assembled sample is pushed into the loading chamber, so that the complete rock layer end face sprayed with speckle pattern is aligned and fitted with the inner pressure-bearing surface of the grid pressure-bearing frame, and a micro-gap structure avoidance layer of 0.5mm to 2.0mm is maintained between the inlaid transparent observation window and the sample end face; three-dimensional orthogonal initial geostress is uniformly applied to the sample through the hydraulic cylinder, and the rock sample undergoes end face bulging deformation after being compressed and fills the micro-gap structure avoidance layer until the speckle pattern and the inlaid transparent observation window are flexibly fitted; the angle and focal length of the two high-speed cameras on the outside are adjusted, and the three-dimensional spatial coordinate calibration of the binocular camera is completed through the inlaid transparent observation window;

[0033] Step 4: Timing Setting and Anti-interference Pre-triggering

[0034] In the electromagnetic shielding control module, timing parameters are set so that the main trigger signal sent by the multi-channel TTL level delay distributor to the high-speed camera and acoustic emission acquisition card is 50μs to 100μs ahead of the trigger discharge command sent to the high-voltage pulse power supply, so that the weak current monitoring instrument enters the high-frequency sampling lock state in advance.

[0035] Step 5: Multi-energy superposition excitation and synchronous data acquisition

[0036] The electromagnetic shielding control module is activated, and the opto-isolation circuit triggers a high-voltage pulse power supply that outputs a large current, causing the metal wire inside the tube to break down and explode electrically, subsequently inducing a liquid explosion. Phase change blasting; the system reduces electromagnetic pulse and ground surge interference during discharge transients through built-in opto-isolation circuits and an external overall shielding copper mesh cover;

[0037] A high-speed camera penetrates an inlaid transparent observation window to continuously record, at a microsecond time resolution, the transient fracture full-field strain images of the intact rock strata at the bottom of the blind borehole under the reflection and stretching of the electric shock wave, and continuously records at millisecond levels. The crack opening and bifurcation morphology driven by the gas wedge of the deflagration gas; the acoustic emission monitoring array and the dynamic pressure measurement unit in the borehole synchronously capture the acoustic positioning and reaction chamber pressure change curves.

[0038] Step Six: Multi-Field Temporal Alignment and Inversion Analysis

[0039] The calibrated optical speckle image, acoustic emission three-dimensional spatiotemporal data and pressure curve were exported. The time sequence alignment of the multi-source heterogeneous data was performed with the initial control command signal issued by the electromagnetic shielding control module as the absolute time zero point. The fluid-structure interaction fracture evolution characteristics of the rock under deep in-situ environmental constraints from dynamic load transient initiation to gas phase quasi-static propagation were inverted and restored.

[0040] (III) Beneficial Effects

[0041] Compared with the prior art, the present invention provides a true triaxial electro-explosion-induced fracturing multi-field visualization monitoring system and method, which has the following beneficial effects:

[0042] I. Solving the problem of true triaxial fully enclosed loading obstruction and realizing pressure-bearing visualization observation. By setting up an embedded transparent observation window with micro-gap of 0.5mm to 2.0mm and a grid-bearing frame, the pressure-bearing frame bears the main static load during the static pressure stage, reducing the risk of stress concentration at the edge of the observation window; during the testing stage when the sample is compressed and bulges and fits into the observation window, the observation window provides a field of view for light, meeting the visualization observation needs of the entire process of rock fracture from internal to surface penetration.

[0043] II. Physical shielding against electromagnetic interference ensures high-fidelity signals across multiple fields. To address the radiated interference generated by high-voltage pulse discharge, the system incorporates an electromagnetic shielding control module. Its built-in opto-isolation circuit blocks the ground surge path in the trigger circuit, while the external overall shielding copper mesh reduces the radiated impact of spatial electromagnetic pulses on surrounding low-voltage instruments, lowering the probability of signal crosstalk and distortion between the high-speed camera and acoustic emission probe at the moment of electrical explosion.

[0044] Third, precise decoupling at the microsecond level enables synchronous capture of the entire cycle of the fracture manifold. The system's integrated multi-channel TTL level delay distributor can distribute trigger pulses to the optical, acoustic, and pressure monitoring units according to the set advance amount, enabling each monitoring device to smoothly enter the high-frequency sampling lock state before the electric explosion is triggered. This meets the requirement for synchronous acquisition of multi-channel signals during the alternation of microsecond-level electric explosion dynamic load and millisecond-level fluid-gas wedge phase.

[0045] IV. Targeted exposure of bottom plate cracks, providing a direct view of multi-energy composite mechanisms. By preserving an intact rock stratum at the bottom of a prefabricated blind borehole as the targeted exposure surface, and placing an embedded transparent observation window directly on top of this rock stratum, the system directly records the initial lamination morphology of the bottom rock stratum under stress wave reflection and tension, as well as the subsequent opening and bifurcation of cracks, effectively supplementing the shortcomings of conventional side observation methods.

[0046] V. Compatible with rock specimens across different scales, broadening the equipment's applicability. The system employs a true triaxial loading chamber with adjustable assembly dimensions and is equipped with modular replacement parts of various specifications for the visualized pressure-bearing components. This allows it to adapt to rock specimens of different sizes, helping to reduce boundary effects on small-sized specimens during testing and improving the system's applicability. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the overall structure and test topology of the present invention;

[0048] Figure 2 This is a schematic diagram of the internal cross-sectional structure of the assembly of the prefabricated blind hole and the fracturing tube in the rock sample of the present invention.

[0049] Figure 3 This is a partially enlarged cross-sectional schematic diagram of the pressure-bearing component in this invention;

[0050] Figure 4 This is a block diagram of the signal isolation and multi-channel TTL delay triggering logic of the electromagnetic shielding control module in this invention;

[0051] Figure 5 This is a flowchart of the multi-field synchronous monitoring method of the present invention.

[0052] In the picture:

[0053] 1. True three-axis servo loading host; 101. Loading chamber; 102. Hydraulic cylinder; 2. Visual pressure-bearing component; 201. Grid pressure-bearing frame; 202. Embedded transparent observation window; 203. Damping and vibration-damping washers; 204. Optical observation hole; 3. Composite fracturing excitation source; 301. High-voltage pulse power supply; 302. Fracturing tube; 303. Liquid 4. Filling system; 5. Multi-field synchronous monitoring module; 6. Three-dimensional DIC observation unit; 7. High-speed camera; 8. Flicker-free LED supplementary light; 9. Acoustic emission monitoring array; 10. Dynamic pressure measurement unit inside the borehole; 11. Electromagnetic shielding control module; 12. Central control microprocessor; 13. Opto-isolation circuit; 24. Multi-channel TTL level delay distributor; 35. Overall shielded copper mesh cover; 46. Rock sample; 57. Prefabricated blind hole; 68. Intact rock strata; 79. Scattered pattern. Detailed Implementation

[0054] To better understand the purpose, structure, and function of this invention, the following description, in conjunction with the accompanying drawings, will further illustrate a true triaxial electro-explosion-induced fracturing multi-field visualization monitoring system and method of this invention.

[0055] Example 1: Overall Structure and Mechanical Connections of the Test System

[0056] This embodiment provides a true triaxial electro-explosive fracturing multi-field visualization monitoring system. Combined with... Figure 1 , Figure 2 and Figure 3 As shown, the system includes a true triaxial servo loading host 1, a visual pressure-bearing component 2, a composite crack induction source 3, a multi-field synchronous monitoring module 4, and an electromagnetic shielding control module 5.

[0057] The true triaxial servo loading host 1 has a loading chamber 101 for placing the rock sample 6. The true triaxial servo loading host 1 includes hydraulic cylinders 102 arranged along three-dimensional orthogonal directions. Each hydraulic cylinder 102 includes a pair of vertically oriented hydraulic cylinders facing each other in the vertical direction, and two pairs of horizontally oriented hydraulic cylinders orthogonal to each other in the horizontal direction. Each hydraulic cylinder 102 is independently controlled by a servo proportional valve to independently apply triaxial stress to the rock sample 6, recreating the in-situ stress environment of deep underground engineering.

[0058] The visualization pressure-bearing component 2 is used to replace at least one conventional solid loading head in the horizontal direction of the true three-axis servo loading host 1. The visualization pressure-bearing component 2 includes a grid pressure-bearing frame 201 and an embedded transparent observation window 202. The periphery of the grid pressure-bearing frame 201 is fixedly connected to the push rod end of the hydraulic cylinder 102 by bolts or high-strength pins. The grid pressure-bearing frame 201 has a segmented reinforcing rib grid structure, is integrally forged from alloy steel, and has a fully through optical observation hole 204 at its central axis position.

[0059] The inlaid transparent observation window 202 is embedded in the optical observation hole 204, and the inner end face of the inlaid transparent observation window 202 is 0.5mm to 2.0mm lower than the inner pressure-bearing end face of the grid pressure-bearing frame 201. In the initial state where no static stress is applied to the system, the inner pressure-bearing end face of the grid pressure-bearing frame 201 is tightly bonded to the end face of the rock sample 6, while an axial micro-gap of 0.5mm to 2.0mm is maintained between the inlaid transparent observation window 202 and the end face of the rock sample 6, forming a micro-gap structure clearance layer. The inlaid transparent observation window 202 is made of three layers of sapphire glass plates and two layers of high-molecular polycarbonate films alternately laminated, and hot-pressed and cured at a temperature of 300℃ to 400℃ and a pressure of 30MPa to 50MPa, with an overall axial thickness of 30mm to 60mm. An annular damping washer 203 is embedded between the outer axial sidewall of the inlaid transparent observation window 202 and the inner stepped surface of the optical observation hole 204 of the grid bearing frame 201. The damping washer 203 is made of hydrogenated nitrile rubber with a Shore hardness of 85-90 degrees and is used for interface sealing and attenuation of high-frequency shock wave vibration energy.

[0060] A pre-fabricated blind hole 601 is machined in the middle of the rock sample 6. The fracturing tube 302 of the composite fracturing induction source 3 is inserted into the pre-fabricated blind hole 601. The front end of the fracturing tube 302 is sealed, and the inside is filled with metal wire and liquid. The fracture-inducing tube 302 is sealed and locked to the rock sample 6 via a threaded confinement device. The composite fracture-inducing excitation source 3 also includes a high-voltage pulse power supply 301, which is electrically connected to the metal wire inside the fracture-inducing tube 302 via a high-voltage coaxial cable and a sealed electrode.

[0061] The multi-field synchronous monitoring module 4 includes a three-dimensional DIC observation unit 401, an acoustic emission monitoring array 404, and an in-hole dynamic pressure measurement unit 405. The three-dimensional DIC observation unit 401 includes two microsecond-level dynamic high-speed cameras 402 and a flicker-free LED supplementary light 403. The two high-speed cameras 402 are arranged outside the visualization pressure-bearing component 2, with their lens optical axes forming a preset convergence angle of 15° to 30° with the center line of the inlaid transparent observation window 202, and focusing on the pre-fabricated speckle pattern 603 on the end face of the rock sample 6. The acoustic emission monitoring array 404 includes 8 to 16 broadband piezoelectric acoustic emission probes, uniformly attached to the non-transparent surface of the rock sample 6.

[0062] Combination Figure 4As shown, the electromagnetic shielding control module 5 includes a central control microprocessor 501, an opto-isolation circuit 502, a multi-channel TTL level delay distributor 503, and an overall shielding copper mesh cover 504. The signal output terminal of the central control microprocessor 501 is communicatively connected to the hardware trigger terminal of the high-speed camera 402 and the input terminal of the acoustic emission monitoring array 404 through the multi-channel TTL level delay distributor 503. The opto-isolation circuit 502 is connected in series between the central control microprocessor 501 and the discharge trigger terminal of the high-voltage pulse power supply 301. The overall shielding copper mesh cover 504 is a double-layer mesh metal cover with a thickness of not less than 1.5mm, which is wrapped around the outer layer of external weak current monitoring equipment and transmission cables, and is grounded at a single point.

[0063] Example 2: Cross-scale specimen compatibility and yield adaptive load sharing mechanism

[0064] Based on Example 1, this embodiment provides a structural control scheme with cross-scale sample compatibility.

[0065] In this embodiment, the grid pressure-bearing frame 201 and the inlaid transparent observation window 202 of the visualization pressure-bearing component 2 are equipped with two sets of replacement parts with different geometric specifications, namely the first pressure-bearing specification replacement part and the second pressure-bearing specification replacement part.

[0066] The end face dimensions of the grid pressure-bearing frame 201 corresponding to the first pressure-bearing specification replacement part are 200mm×200mm, which is used to fit with the 200mm×200mm×200mm cubic rock sample 6. At this time, the pre-fabricated blind hole 601 has a diameter of 30mm and an axial depth of 150mm. A complete rock layer 602 with an absolute thickness of 50mm is left between the bottom of the pre-fabricated blind hole 601 and the inner end face of the embedded transparent observation window 202.

[0067] The end face dimensions of the grid pressure-bearing frame 201 corresponding to the second pressure-bearing specification replacement part are 500mm × 260mm, which is used to fit with the 500mm × 500mm × 260mm cuboid rock sample 6. At this time, the pre-fabricated blind hole 601 has a diameter of 50mm and an axial depth of 200mm. A complete rock layer 602 with an absolute thickness of 100mm is left between the bottom of the pre-fabricated blind hole 601 and the inner end face of the embedded transparent observation window 202.

[0068] The intact rock stratum 602 with a preset thickness of 50mm or 100mm faces the embedded transparent observation window 202. In the initial stage of true triaxial static loading, due to the presence of the micro-gap structure avoidance layer, the axial static load applied by the true triaxial host is borne by the grid bearing frame 201. As the in-situ stress increases, the rock sample 6 exhibits a Poisson effect under compressive constraint, causing its end face facing the optical observation hole 204 to undergo outward axial bulging deformation. This deformation gradually squeezes and fills the micro-gap structure avoidance layer, causing the outer surface of the intact rock stratum 602 to adhere to the inner end face of the embedded transparent observation window 202.

[0069] When the high-voltage pulse power supply 301 discharges and triggers an electrical explosion inside the fracture tube 302, the resulting compressive stress wave propagates axially downwards, reaching the contact section between the intact rock stratum 602 and the embedded transparent observation window 202. Due to the difference in material wave impedance, the compressive wave is reflected at the contact section, generating a reverse tensile wave. When the combined tensile stress exceeds the dynamic tensile strength of the rock sample 6, tensile delamination occurs on the outer surface of the intact rock stratum 602 (i.e., the Hopkinson effect), manifested as bulging and crack initiation at the center of the exposed surface. Subsequently, the high-pressure gas generated by the phase change and deflagration in the reaction chamber performs quasi-static gas wedge splitting on the initial fracture. At this time, the embedded transparent observation window 202 independently bears the dynamic axial thrust brought by the fluid ejection, and the crack expands radially and penetrates in all directions.

[0070] Example 3: Multi-field synchronous monitoring process and operation procedure

[0071] This embodiment provides a method for simultaneous multi-field monitoring of multi-energy composite fracture using the systems described in Embodiments 1 and 2 above. Combined with... Figure 5 As shown, the method specifically includes the following steps:

[0072] Step 1: Sample preparation and speckle pattern preparation

[0073] Based on the experimental scale requirements, a 200mm cubic rock sample 6 or a 500mm×260mm rectangular rock sample 6 was selected. A pre-fabricated blind hole 601 (30mm or 50mm in diameter, 150mm or 200mm in depth) was machined at the center of the geometric cross-section of the rock sample 6 along the predetermined observation direction, leaving a 50mm or 100mm thick intact rock layer 602 at the bottom of the hole. A mechanical speckle pattern 603 with alternating black and white colors and a particle size distribution of 2–5 pixels was uniformly sprayed onto the outer surface of the rock sample 6 facing the intact rock layer 602 using quick-drying matte white and matte black paint. Acoustic emission probes were rigidly attached to the remaining five non-transparent bearing surfaces of the rock sample 6 using epoxy resin.

[0074] Step 2: Insertion and sealing assembly of the excitation source.

[0075] In a laboratory-specific filling fixture, a metal wire is pre-placed into the sealed reaction chamber of the fracturing tube 302, followed by the filling of energetic metal powder, and a constant-pressure shear plate with a pre-set fracture threshold is installed. Then, saturated liquid is injected into the fracturing tube 302 through the filling valve. Then close the valve. Slide the filled fracturing tube 302 into the prefabricated blind hole 601 of the rock sample 6, and use the hole clamp and sealing nut to thread-lock the tail end of the fracturing tube 302 to the hole opening to ensure that there is no lateral fluid leakage during the reaction process.

[0076] Step 3: True three-axis centering loading and spatial calibration.

[0077] According to the specifications of the selected rock sample 6, the corresponding size of the grid bearing frame 201 and the embedded transparent observation window 202 are assembled onto the end of the true triaxial hydraulic cylinder. The rock sample 6 with the assembled excitation source is pushed into the loading chamber 101, so that the end face of the complete rock layer 602 sprayed with speckle pattern 603 is precisely aligned and tightly fitted with the inner plane of the grid bearing frame 201, maintaining a micro-gap structure avoidance layer of 0.5mm to 2.0mm between the embedded transparent observation window 202 and the end face of the sample. The hydraulic cylinder 102 is activated, and the initial geostress is applied to the three-dimensional orthogonal direction of the rock sample 6 at a loading rate of 0.5MPa / s to the set value in stages; during this compression process, the rock sample 6 undergoes axial bulging deformation and fills the micro-gap until the speckle pattern 603 and the embedded transparent observation window 202 are flexibly fitted together.

[0078] The high-frequency flicker-free LED supplemental light 403 is turned on to illuminate the speckle area through the embedded transparent observation window 202. The objective lens focal length, focal plane, and aperture of the two external high-speed cameras 402 are adjusted to ensure that the speckle pattern 603 is clearly imaged in the digital image fields of the two cameras. A standard 3D DIC calibration board is placed outside the observation window, and multiple sets of calibration board images with different spatial postures are acquired through control software to complete the spatial coordinate calibration of the internal parameters and external relative geometric position of the binocular cameras.

[0079] Step 4: Timing setting and pre-triggering.

[0080] Activate the synchronous triggering and electromagnetic shielding control module 5. Input timing configuration parameters into the multi-channel TTL level delay distributor 503 via control software. Set the emission time of the first TTL trigger signal (connected to two high-speed cameras 402) and the second TTL trigger signal (connected to the acoustic emission acquisition card) to lead the third trigger discharge signal (connected to the trigger terminal of the high-voltage pulse power supply 301 via opto-isolation circuit 502) by 80μs. Set the recording mode of the high-speed camera 402 to external trigger loop buffer mode, and the shooting frame rate to 500,000fps; set the sampling frequency of the acoustic emission monitoring array 404 to 10MHz.

[0081] Step 5: Multi-energy superposition excitation and synchronous data acquisition.

[0082] When the start switch of the synchronous trigger and electromagnetic shielding control module 5 is pressed, the central control microprocessor 501 issues a control command: the multi-channel TTL level delay distributor 503 first distributes advance pulse signals to the high-speed camera 402 and the acoustic emission system, so that the optical and acoustic weak current monitoring instruments enter the high-frequency sampling lock and data coverage state in advance.

[0083] After a delay of 80μs, the central control microprocessor 501 converts the electrical trigger pulse into an optical signal via a high-speed optocoupler diode inside the opto-isolation circuit 502. This signal is then restored to a trigger level by the receiver and sent to the gap switch of the high-voltage pulse power supply 301. The high-voltage pulse power supply 301 discharges instantaneously, puncturing the metal wire inside the rupture tube 302 and causing an electrical explosion. Because of the opto-isolation circuit 502 between the discharge circuit and the control microprocessor 501, the ground surge of the high-current discharge and the high-frequency electromagnetic pulse in space are physically cut off. Simultaneously, the external overall shielding copper mesh cover 504 absorbs and guides the electromagnetic waves radiated from space into the ground, reducing the impact of electromagnetic radiation on the external high-speed camera 402 and acoustic emission equipment.

[0084] The plasma shock wave generated by the electrical explosion of the metal wire inside the rupture tube 302 successively induced liquid... Supercritical phase transition and powder deflagration occur. The transient pressure inside the tube rises rapidly. When the pressure reaches the shear yield limit of the constant pressure shear plate, the shear plate breaks transiently, and the high-pressure fluid medium is ejected through the vent, impacting the bottom and surrounding walls of the pre-fabricated blind hole 601.

[0085] Two high-speed cameras 402 penetrate the embedded transparent observation window 202 to record in real time the initial speckle abrupt change on the surface of the intact rock strata 602 at the bottom of the blind hole under the tensile action of the electric shock wave reflection, the full-field strain field generated by the shear slip zone, and continuously record the subsequent millisecond-level data. The two-dimensional radial crack opening displacement and volumetric crack network bifurcation morphology under continuous driving of the deflagration gas wedge were measured. The acoustic emission monitoring array 404 and the in-hole dynamic pressure measurement unit 405 synchronously captured the elastic waves generated by the initiation of the internal microcrack group and the cavity pressure drop curve.

[0086] Step 6: Multi-field temporal alignment and broken manifold inversion.

[0087] After the experiment, the three-dimensional geostress was unloaded and rock sample 6 was removed. The calibrated high-speed optical speckle sequence image, acoustic emission three-dimensional spatiotemporal positioning point set, and high-frequency dynamic pressure measurement data were exported from the data storage. Using a digital image correlation matching algorithm, with the initial trigger time level signal issued by the synchronous trigger and electromagnetic shielding control module 5 as the absolute zero point, the data lines of each monitoring channel were time-aligned on the same microsecond-level time axis.

[0088] By calculating the lateral displacement field U and longitudinal displacement field V of the speckle image, the full-field dynamic evolution cloud map of the principal strain and maximum shear strain on the surface of the intact rock stratum 602 was obtained through inversion. Combining the spatial clustering of AE three-dimensional positioning density and the dynamic pressure inflection point, the fracture evolution law and fracture mechanics energy dissipation constitutive relation of rock sample 6 under complex static load clamping, from the transient initiation of microsecond-level electro-explosive dynamic load to the long-range propagation stage of millisecond-level fluid-structure coupling phase change gas wedge, were decoupled and presented.

[0089] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A true triaxial electro-explosive fracturing multi-field visualization monitoring system, characterized in that, include: A true triaxial servo loading host (1) is used to apply three-dimensional independently adjustable in-situ static stress to a rock sample (6) placed in its internal loading chamber (101); The visualization pressure-bearing component (2) is set in at least one principal stress loading direction of the true triaxial servo loading host (1) and is pressed against the loaded end face of the rock sample (6) to provide an optical observation channel while transmitting axial load; The composite fracturing excitation source (3) has a fracturing tube (302) that fits into a prefabricated blind hole (601) inside the rock sample (6). The composite fracturing excitation source (3) also includes a high-voltage pulse power supply (301) that is electrically connected to the internal electrode of the fracturing tube (302) for applying an impact load to the hole wall of the rock sample (6). The multi-field synchronous monitoring module (4) is arranged on the outside of the true triaxial servo loading host (1) and on the non-transparent loaded end face of the rock sample (6) to collect optical speckle images, acoustic emission signals and dynamic pressure inside the hole during the fracturing process. The electromagnetic shielding control module (5) is electrically connected to the high-voltage pulse power supply (301) and the multi-field synchronous monitoring module (4) respectively, and is used to issue timing control commands to realize the coordinated triggering of multi-source heterogeneous monitoring equipment and the shielding of transient spatial electromagnetic pulses of discharge.

2. The true triaxial electro-explosive fracturing multi-field visualization monitoring system according to claim 1, characterized in that, The visualization pressure-bearing component (2) includes a grid pressure-bearing frame (201) and an inlaid transparent observation window (202); the periphery of the grid pressure-bearing frame (201) is fixedly connected to the end of the hydraulic cylinder (102) of the true triaxial servo loading host (1), and a through optical observation hole (204) is opened at its center position; the inner pressure-bearing end face of the grid pressure-bearing frame (201) is rigidly attached to the end face of the rock sample (6); The inlaid transparent observation window (202) is embedded in the optical observation hole (204), and the inner end face of the inlaid transparent observation window (202) is 0.5mm to 2.0mm lower than the inner end face of the grid pressure-bearing frame (201), thereby forming a micro-gap structure avoidance layer between the inlaid transparent observation window (202) and the initial end face of the rock sample (6).

3. The true triaxial electro-explosive fracturing multi-field visualization monitoring system according to claim 1, characterized in that, The inlaid transparent observation window (202) is made by alternating layers of high light transmittance sapphire glass plates and polycarbonate buffer films and hot pressing and curing. An annular damping shock absorber (203) is embedded between the axial outer wall of the inlaid transparent observation window (202) and the inner wall of the optical observation hole (204) of the grid pressure-bearing frame (201).

4. The true triaxial electro-explosive fracturing multi-field visualization monitoring system according to claim 2, characterized in that, The multi-field synchronous monitoring module (4) includes a three-dimensional DIC observation unit (401), an acoustic emission monitoring array (404), and an in-hole dynamic pressure measurement unit (405). The three-dimensional DIC observation unit (401) includes a high-speed camera (402) and a flicker-free LED supplement light (403). The two high-speed cameras (402) are arranged on the outer side of the visualization pressure-bearing component (2), and the optical axis of the lens is aligned with the prefabricated speckle pattern (603) on the end face of the rock sample (6) at a preset convergence angle with the central axis of the inlaid transparent observation window (202). The acoustic emission monitoring array (404) includes multiple broadband piezoelectric acoustic emission probes, which are uniformly pasted on the remaining non-transparent load-bearing end face of the rock sample (6) without the visualization pressure-bearing component (2); The in-hole dynamic pressure measurement unit (405) is integrated into the tail end of the fracturing tube (302) and extends into the reaction chamber inside the fracturing tube (302).

5. The true triaxial electro-explosive fracturing multi-field visualization monitoring system according to claim 4, characterized in that, The electromagnetic shielding control module (5) includes a central control microprocessor (501), a multi-channel TTL level delay distributor (503), an opto-isolation circuit (502), and an overall shielding copper mesh cover (504). The central control microprocessor (501) is connected to the input terminals of the acquisition cards of the two high-speed cameras (402) and the acoustic emission monitoring array (404) respectively through the multi-channel TTL level delay distributor (503); The opto-isolation circuit (502) is connected in series between the central control microprocessor (501) and the discharge trigger terminal of the high-voltage pulse power supply (301); The overall shielding copper mesh cover (504) is wrapped around the outside of the three-dimensional DIC observation unit (401), the acoustic emission monitoring array (404) and the signal transmission cable and is grounded.

6. The true triaxial electro-explosive fracturing multi-field visualization monitoring system according to claim 1, characterized in that, The loading chamber (101) of the true triaxial servo loading host (1) and the assembly dimensions of the visual pressure-bearing component (2) are both adjustable to accommodate 200mm×200mm×200mm cubic rock samples or 500mm×500mm×260mm rectangular rock samples.

7. The true triaxial electro-explosive fracturing multi-field visualization monitoring system according to claim 1, characterized in that, A complete rock layer (602) of a preset thickness is left between the bottom of the prefabricated blind hole (601) and the inner pressure bearing surface of the visualized pressure bearing component (2). The preset thickness is 50mm to 100mm, which is used as a targeted exposure surface for generating stress wave reflection stretching and gas wedge splitting penetration.

8. A method for real triaxial electro-explosive fracturing multi-field visualization monitoring as described in any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Sample preparation and speckle pattern preparation: A pre-fabricated blind hole (601) is processed at the center of the rock sample (6) so that a complete rock layer (602) with a preset thickness of 50mm to 100mm is left at the bottom of the hole; a black and white micro-mechanical speckle pattern (603) is uniformly sprayed on the outer surface of the rock sample (6) facing the complete rock layer (602), and an acoustic emission probe is attached to the remaining non-transparent load-bearing end face; Step Two: Insertion and Sealing Assembly of the Excitation Source: Insert the liquid source into the sealed assembly. The fracturing tube (302) of the metal wire and constant pressure shear plate is fitted and slid into the prefabricated blind hole (601), and is sealed and locked with the rock sample (6) by the hole thread constraint device; Step 3: True triaxial centering loading and calibration: Push the assembled sample into the loading chamber (101) so that the end face with the speckle pattern (603) is facing the embedded transparent observation window (202) of the visualization pressure-bearing component (2). Apply three-dimensional orthogonal initial ground stress to the sample through the hydraulic cylinder (102) so that the rock sample (6) is compressed and undergoes lateral bulging deformation and fills the micro-gap structure avoidance layer; complete the three-dimensional spatial coordinate calibration of the two high-speed cameras (402); Step 4: Timing setting and anti-interference pre-trigger: Set the timing parameters in the electromagnetic shielding control module (5) so that the main trigger signal sent by the multi-channel TTL level delay distributor (503) to the high-speed camera (402) and the acoustic emission acquisition card is 50us ahead of the discharge trigger command sent to the high-voltage pulse power supply (301); Step 5: Multi-energy superposition excitation and data synchronous acquisition: Start the electromagnetic shielding control module (5), the opto-isolation circuit (502) triggers the high-voltage pulse power supply (301) output current to break down the metal wire inside the fracture tube (302) and cause an electrical explosion, which in turn induces liquid... Phase change and powder deflagration; the system weakens electromagnetic pulse interference during discharge transients through an overall shielded copper mesh cover (504); a high-speed camera (402) penetrates the embedded transparent observation window (202) to record the full-field strain image of the fracture on the surface of the intact rock layer (602); the acoustic emission monitoring array (404) and the dynamic pressure measurement unit in the borehole (405) capture the acoustic positioning and reaction chamber pressure curves; Step 6: Multi-field time-series alignment and data analysis: Export speckle images, acoustic emission tri-form data and pressure curves, and perform time-series alignment of multi-source heterogeneous data based on the initial control command time issued by the electromagnetic shielding control module (5) to analyze the fracture evolution characteristics of rocks under composite impact loads.

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