Device and method for generating three-dimensional controllable cracks in rock based on high-voltage pulse discharge

Abstract

The invention discloses a rock internal three-dimensional controllable crack generation device and method based on high-voltage pulse discharge, and relates to the technical field of rock mechanics experiments and engineering. The device comprises a high-voltage pulse discharge system which comprises an electric pulse generator, an electrode and a conductive fixing frame, the electrode is used for being inserted into a to-be-measured rock guide hole and connected with the negative electrode of the electric pulse generator, the conductive fixing frame is used for fixing the to-be-measured rock and connected with the positive electrode of the electric pulse generator, and the electric pulse generator is used for generating high-voltage pulse discharge; cracks are formed in the rock; the track control module is used for controlling the electrode to move in the to-be-detected rock guide hole so as to guide the crack to extend along a preset track; the medium circulation module is used for injecting a liquid medium into the to-be-measured rock guide hole; and the feedback control module is used for monitoring the crack propagation signal and adjusting the discharge parameter according to the monitoring result. According to the method, the controllability of the fractal characteristics of the cracks and the directional expansion of the cracks in a three-dimensional space can be realized.

Description

Technical Field

[0001] The present invention relates to the technical fields of rock mechanics experiments and engineering technologies, and particularly relates to a device and method for generating three-dimensional controllable cracks inside rocks based on high-voltage pulsed discharge. Background Art

[0002] In rock mechanics experiments and engineering practices, artificially prefabricating internal cracks is an important technical means for studying the failure mechanism of rock masses and optimizing energy extraction schemes. However, traditional methods mainly adopt contact loading methods such as indirect tension method and mechanical pre-cracking method, and these technologies have significant limitations. First of all, it is difficult to precisely control the depth and spatial distribution characteristics of cracks during the mechanical loading process, and the crack morphology shows great randomness under the influence of boundary conditions. Secondly, high stress concentration easily leads to irreversible damage on the rock surface, and even causes the overall rupture of the specimen, seriously affecting the reliability of subsequent experimental data. More critically, the cracks generated by existing methods are mostly limited to two-dimensional plane expansion, and it is impossible to construct a three-dimensional crack network that conforms to real geological conditions.

[0003] In addition, the applicable range of existing technologies is strictly restricted by material properties, and effective crack generation can only be achieved in rock-like materials or low-strength rock samples. For natural rocks with high tensile strength such as granite and shale, conventional loading methods often have difficulty in forming internal cracks with a predetermined morphology due to insufficient energy transfer efficiency. Chinese patent document CN110687253A discloses a method for fabricating internal cracks in rock samples and quantitatively evaluating the grouting effect. Although this scheme has improvements in crack detection, its core still relies on the indirect tension method to prepare initial cracks, resulting in uncontrollable crack fractal characteristics and inability to achieve three-dimensional spatial directional expansion. At the same time, the traditional hydraulic fracturing method has high energy dissipation, seriously restricting its application value in precision experiments. Summary of the Invention

[0004] One of the purposes of the present invention is to provide a device that uses high-voltage pulsed discharge technology to generate three-dimensional controllable cracks inside rocks through non-contact energy transfer, so as to achieve the controllability of crack fractal characteristics and the directional expansion of cracks in three-dimensional space.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: A device for generating three-dimensional controllable cracks inside rocks based on high-voltage pulsed discharge, comprising:

[0006] A high-voltage pulsed discharge system, including an electrical pulse generator, an electrode, and a conductive fixing frame. The electrode is used to be inserted into the guide hole of the rock to be tested and connected to the negative pole of the electrical pulse generator, and the conductive fixing frame is used to fix the rock to be tested and connected to the positive pole of the electrical pulse generator. The electrical pulse generator is used to generate high-voltage pulsed discharge to form cracks inside the rock;

[0007] A trajectory control module, which is used to control the movement of the electrode in the pilot hole of the rock to be measured, so as to guide the crack to expand along a predetermined trajectory;

[0008] A medium circulation module, which is used to inject a liquid medium into the pilot hole of the rock to be measured;

[0009] A feedback control module, which is used to monitor the crack expansion signal and adjust the discharge parameters according to the monitoring results.

[0010] Furthermore, the electrode adopts a three-layer composite structure, which consists of a tungsten steel inner core, a copper-nickel alloy conductive layer and a polyimide insulating layer from the inside to the outside, and the tip of the electrode is processed to form a discharge focusing end.

[0011] Furthermore, the trajectory control module includes a displacement controller and a telescopic component connected thereto, and the telescopic component is connected to the electrode and drives the electrode to move in the pilot hole of the rock to be measured.

[0012] Furthermore, the medium circulation module includes a deionized water exchanger, which is used to inject deionized water into the pilot hole of the rock to be measured.

[0013] Furthermore, the medium circulation module includes an ultrasonic oscillator, which is used to eliminate the bubbles in the pilot hole of the rock to be measured.

[0014] Furthermore, the feedback control module includes an acoustic emission detector and an acoustic emission probe. The acoustic emission probe is used to be fixed on the rock to be measured, and the elastic wave signal generated by the crack expansion is monitored through the acoustic emission detector. The acoustic emission detector is electrically connected to the control end of the electric pulse generator.

[0015] Furthermore, the feedback control module adjusts the discharge parameters by combining the quantitative correlation model of the acoustic emission energy release rate and the crack expansion rate;

[0016] The quantitative correlation model is as follows:

[0017]

[0018] Wherein, v(t) is the real-time crack expansion rate, with the unit of mm / s; is the acoustic emission energy release rate, with the unit of μJ / s; β is the material energy conversion coefficient, with the unit of μJ / mm.

[0019] Furthermore, the discharge parameters include at least one of the discharge voltage and the pulse interval time.

[0020] Another object of the present invention is to provide a method for generating three-dimensional controllable cracks inside a rock based on high-voltage pulsed discharge. This method uses the above-mentioned device and includes the following steps:

[0021] Step 1: Drill a guide hole in the rock to be tested, fix the rock to be tested on a conductive fixing bracket, insert electrodes into the guide hole, and connect the conductive fixing bracket and the electrodes to the positive and negative electrodes of an electric pulse generator respectively;

[0022] Step 2: Inject a liquid medium into the guide hole through the medium circulation module;

[0023] Step 3: Select the working mode of the electric pulse generator, including single discharge mode or continuous pulse mode;

[0024] Step 4: Generate initial microcracks inside the rock to be tested through high-voltage pulsed discharge;

[0025] Step 5: The trajectory control module controls the displacement of the electrodes in the guide hole to guide the crack to expand along a predetermined trajectory;

[0026] Step 6: The feedback control module monitors the crack expansion signal in real time and adjusts the discharge parameters of the electric pulse generator according to the monitoring results to achieve three-dimensional directional expansion of the crack.

[0027] Further, in Step 3, select the working mode of the electric pulse generator according to the rock type: for rocks with a tensile strength less than 3 MPa, use the single discharge mode; for rocks with a tensile strength greater than or equal to 3 MPa, use the continuous pulse mode.

[0028] Different from the previous rock fracturing technologies, the present invention mainly uses high-voltage pulsed discharge technology to generate three-dimensional controllable cracks inside the rock through non-contact energy transfer. Specifically, the present invention uses an electric pulse generator to generate high-voltage pulsed discharge, thereby forming cracks inside the rock. At the same time, a liquid medium is injected into the guide hole of the rock to be tested through the medium circulation module to optimize the discharge environment. In addition, the present invention also uses the trajectory control module to control the displacement of the electrodes in the guide hole to guide the crack to expand along a predetermined trajectory. And, the feedback control module monitors the crack expansion signal and adjusts the discharge parameters in real time according to the monitoring results. Through these technical means, the present invention realizes the controllable generation of three-dimensional cracks, effectively solving the problems of uncontrollable crack fractal characteristics and inability to achieve three-dimensional spatial directional expansion in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural diagram of a device for generating three-dimensional controllable cracks inside a rock based on high-voltage pulsed discharge.

[0030] In the figure:

[0031] 1 - Rock to be tested 1a - Guide hole

[0032] 2 - Electric pulse generator 3 - Positive electrode

[0033] 4——Negative electrode 5——Pulse adjustment knob

[0034] 6——Electrode 7——Conductive fixing bracket

[0035] 8——Deionized water exchanger 9——Soft insulating conduit

[0036] 10——Hard insulating conduit 11——Ultrasonic oscillator

[0037] 12——Acoustic emission detector 13——Acoustic emission probe 1

[0038] 14——Acoustic emission probe 2 15——Displacement controller

[0039] 16——Telescopic inner rod 17——Telescopic outer rod Detailed implementation mode

[0040] For the convenience of those skilled in the art to better understand the improvements of the present invention over the prior art, the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0041] The high-voltage pulse discharge technology has significant advantages in terms of accuracy, controllability, and non-destructiveness. Moreover, the technical components are mature and the experimental verification is sufficient, with high feasibility. However, the current technical system still faces challenges in the dimension of energy control: existing equipment lacks a quantitative correlation mechanism between discharge parameters and crack morphology, making it difficult to actively control the fractal dimension of cracks through energy regulation. These technical bottlenecks make the existing devices unable to meet the refined requirements for the preparation of three-dimensional complex crack networks in fields such as deep resource exploitation and engineering disaster prevention and control.

[0042] Therefore, the present invention proposes a device and method using the high-voltage pulse discharge technology to generate three-dimensional controllable cracks inside rocks through non-contact energy transfer. This technology can effectively overcome the defects of existing rock internal crack preparation technologies, such as low control accuracy, large energy loss, and insufficient three-dimensional expansion ability, and is applicable to fields such as underground engineering disaster prevention and control and energy exploitation optimization.

[0043] Specifically, a device for generating three-dimensional controllable cracks inside rocks based on high-voltage pulse discharge (the structure of which can be seen in Figure 1 ), includes:

[0044] A high-voltage pulse discharge system includes an electric pulse generator 2 (such as a modular Marx generator equipped with a pulse adjustment knob 5 for adjusting the working mode of the generator), an electrode 6 (such as a micro coaxial electrode), and a conductive fixing bracket 7 (such as a metal fixing bracket). The electrode 6 is used to be inserted into the borehole 1a of the rock to be measured and connected to the negative electrode 4 of the electric pulse generator 2. The conductive fixing bracket 7 is used to fix the rock to be measured and connected to the positive electrode 3 of the electric pulse generator 2. The electric pulse generator 2 is used to generate high-voltage pulse discharge to form cracks inside the rock;

[0045] A trajectory control module is used to control the movement of the electrode 6 in the borehole 1a of the rock to be measured to guide the crack to expand along a predetermined trajectory;

[0046] A medium circulation module is used to inject a liquid medium into the borehole 1a of the rock to be measured to optimize the discharge environment;

[0047] A feedback control module is used to monitor the crack expansion signal and adjust the discharge parameters according to the monitoring results.

[0048] In the above device, the electric pulse generator 2 can adopt a modular Marx generator, and the precise regulation of 5 - 50 kV voltage is realized through an insulated gate bipolar transistor (IGBT) switch array. With the adjustable capacity design (1 - 10 kJ) of the oil-immersed energy storage capacitor bank, it can not only meet the single-precision discharge requirement but also support the construction of a crack network in the continuous pulse mode.

[0049] In the above device, the electrode 6 can adopt a three-layer composite structure, which is successively a tungsten steel inner core, a copper-nickel alloy conductive layer, and a polyimide insulating layer from the inside to the outside. And the tip of the electrode 6 is processed to form a discharge focusing end with a size of 0.1 - 0.5 mm (such as 0.2 mm ± 0.02 mm). This electrode 6 adopts a tungsten steel reinforced inner core and a gradient insulation structure design. While ensuring a bending strength of 1800 MPa, the spatial focusing of the discharge energy is realized through the 0.1 - 0.5 mm precision grinding tip. Its three-layer composite structure (polyimide insulating layer / copper-nickel alloy conductive layer / tungsten steel reinforcement layer) enables the electrode 6 to still maintain a positioning accuracy at the 0.01 mm level after 10^4 discharge cycles. Among them, the tungsten steel inner core (tungsten steel reinforcement layer) can provide high-strength support, the copper-nickel alloy conductive layer can achieve efficient electric energy transmission, and the polyimide insulating layer can ensure the insulation performance of the electrode.

[0050] In the above device, the trajectory control module includes a displacement controller 15 and a telescopic component connected thereto, the telescopic component is connected to the electrode 6 and drives the electrode 6 to move in the rock guide hole 1a to be tested. Specifically, the telescopic component includes a telescopic inner rod 16 and a telescopic outer rod 17 that are nested with each other. The telescopic inner rod 16 can slide axially in the telescopic outer rod 17, thereby realizing the telescopic function. The displacement controller 15 is installed on the telescopic outer rod 17 to control the telescopic movement of the telescopic inner rod 16. The end of the telescopic inner rod 16 is connected to the electrode 6 after being bent and extended. Through the drive of the displacement controller 15, the telescopic inner rod 16 can move in the telescopic outer rod 17, thereby driving the electrode 6 to achieve precise displacement control.

[0051] In the above device, the design of the medium circulation module breaks through the fluid control limitations of traditional hydraulic fracturing technology and constructs a medium circulation system with secondary purification and dynamic defoaming functions. The core component of this module is the deionized water exchanger 8, which is connected to the rock guide hole 1a to be tested through a soft insulating conduit 9 and a hard insulating conduit 10. The hard insulating conduit 10 is directly inserted into the rock guide hole 1a to be tested to ensure that the deionized water can be accurately injected into the rock. The deionized water exchanger 8 can stably control the conductivity of deionized water below 1μS / cm through the synergistic effect of a 5μm ceramic filter element and a mixed bed ion exchange resin. This purification process not only ensures the high purity of the liquid medium injected into the rock guide hole, but also can flush the rock fragments knocked down by the electric pulse to the outside of the rock sample, thereby keeping the guide hole 1a clean. In addition, the medium circulation module is also equipped with a 40kHz ultrasonic oscillator 11 for real-time elimination of microbubbles in the rock guide hole 1a to be tested. Through the high-frequency vibration of ultrasound, bubbles in the liquid can be effectively destroyed, further improving the uniformity of the discharge channel medium to more than 98%, providing a more ideal environment for high-voltage pulse discharge. In order to accurately control the flow of the liquid medium, the medium circulation module also includes a flow control system, which uses a micro diaphragm pump and can achieve linear flow adjustment of 0.1 to 5 mL / s. This flexible flow adjustment capability not only ensures the directional transmission efficiency of shock wave energy, but also can adjust the injection speed of the liquid medium in real time according to experimental requirements, thereby optimizing the entire crack generation process.

[0052] In the above device, the feedback control module includes an acoustic emission detector 12 and two acoustic emission probes (acoustic emission probe 1 13 and acoustic emission probe 2 14). The two acoustic emission probes are respectively fixed on the upper and lower end faces of the rock 1 to be tested, and are used to monitor the elastic wave signals generated during the crack propagation process in real time. These signals are transmitted to the acoustic emission detector 12 and analyzed and processed by it. The acoustic emission detector 12 is electrically connected to the control end of the electric pulse generator 2 so as to dynamically adjust the discharge parameters of the electric pulse generator 2 according to the monitored crack propagation conditions, thereby realizing accurate control of the crack propagation process.

[0053] In the above device, the feedback control module adjusts the discharge parameters in combination with the quantitative correlation model between the acoustic emission energy release rate and the crack propagation rate, and the discharge parameters include at least one of the discharge voltage and the pulse interval time.

[0054] The quantitative correlation model is as follows:

[0055]

[0056] Wherein, v(t) is the real-time crack propagation rate, with the unit of mm / s; is the acoustic emission energy release rate, with the unit of μJ / s; β is the material energy conversion coefficient, with the unit of μJ / mm.

[0057] The calculation formula of the material energy conversion coefficient β is as follows:

[0058]

[0059] Wherein, a is the final crack length, and E is the cumulative acoustic emission energy.

[0060] Furthermore, the information feedback control module establishes an adaptive adjustment mechanism for the discharge parameters through the deep coupling of acoustic emission feature extraction and the crack propagation dynamics model. The acoustic emission array captures the elastic wave signals of crack propagation in real time, and based on the hypothesis of the linear relationship between the acoustic emission energy release rate and the crack propagation rate, a quantitative correlation model between the crack propagation rate and the acoustic emission energy is established. Through real-time monitoring and feedback adjustment, the feedback control module can avoid abnormal crack propagation caused by over-discharge or insufficient energy, thereby reducing energy loss. In addition, it can effectively reduce the experimental errors introduced by uncontrollable crack propagation, and improve the accuracy and repeatability of experimental data.

[0061] Among them, the acoustic emission energy release rate is measured in real time by the acoustic emission probe. The material energy conversion coefficient is calibrated through experiments and reflects the acoustic emission energy released per unit crack propagation length.

[0062] Experimental calibration:

[0063] Calibration experiments are carried out on specific rock types (such as granite, shale), and the following are measured under different discharge parameters:

[0064] Final crack length: a (through CT scan or cross-section analysis);

[0065] Cumulative acoustic emission energy: E (integrated acoustic emission signal amplitude or energy count).

[0066] Calculation Take the average value of multiple experiments.

[0067] Specifically, a three-dimensional controllable crack generation method inside rocks based on high-voltage pulsed discharge uses the above-mentioned device and includes the following steps:

[0068] Step 1: Drill a guide hole 1a in the rock 1 to be measured, fix the rock 1 to be measured on the conductive fixing frame 7, insert the electrode 6 into the guide hole 1a, and connect the positive electrode 3 and the negative electrode 4 of the electric pulse generator 2 to the conductive fixing frame 7 and the electrode 6 respectively;

[0069] Step 2: Inject a liquid medium (such as deionized water) into the guide hole 1a through the medium circulation module to optimize the discharge environment;

[0070] Step 3: Select the working mode of the electric pulse generator 2, including a single discharge mode or a continuous pulse mode;

[0071] Step 4: Generate initial microcracks inside the rock 1 to be measured through high-voltage pulsed discharge;

[0072] Step 5: The trajectory control module controls the displacement of the electrode 6 in the guide hole 1a to guide the crack to expand along a predetermined trajectory;

[0073] Step 6: The feedback control module monitors the crack expansion signal in real time and adjusts the discharge parameters of the electric pulse generator 2 according to the monitoring results to achieve three-dimensional directional expansion of the crack.

[0074] Optional, Step 7: After the crack is generated, withdraw the electrode 6 to avoid mechanical disturbance to the generated crack.

[0075] In Step 3, the working mode of the electric pulse generator 2 can be selected according to the rock type: for rocks with a tensile strength less than 3 MPa (such as shale), the single discharge mode is adopted; for rocks with a tensile strength greater than or equal to 3 MPa (such as granite), the continuous pulse mode is adopted.

[0076] The following is further illustrated by specific examples.

[0077] In this embodiment, a diamond drill bit is used to process a pilot hole 1a with a diameter of 1.5 mm and a depth of 30 mm in the rock sample 1 to be tested at a preset coordinate point. The rock 1 to be tested is fixed to the conductive fixing frame 7. After removing the rock powder in the pilot hole 1a through the vacuum adsorption device, the electrode 6 is inserted into the bottom of the hole, and the exposed length of the tip of the electrode 6 is controlled within 0.2 mm ± 0.02 mm. The acoustic emission probe 13 and the acoustic emission probe 14 are respectively installed on the upper and lower surfaces of the rock sample 1. The probe and the rock surface 1 are coupled through a vacuum coupling agent, and the contact pressure is controlled within the range of 0.6 - 0.8 MPa to ensure the signal transmission efficiency. After the system is started, the probe continuously collects elastic wave signals at a sampling rate of 1 MHz. After the deionized water exchanger 8 is started, the purified deionized water is injected into the pilot hole 1a at a flow rate of 1.2 mL / s. At the same time, the 40 kHz ultrasonic oscillator 11 continuously eliminates the bubbles with a diameter > 10 μm in the water body to ensure that the medium uniformity reaches more than 98%. The electric pulse generator 2 selects different working modes through the pulse adjustment knob 5 according to the rock type: for shale with a tensile strength < 3 MPa, the single discharge mode is adopted; for high-strength rocks such as granite, the continuous pulse mode is enabled, and the single pulse energy is adjusted to an interval time of 50 ms. The electrode 6 is connected to the negative electrode 4 (negative electrode) of the electric pulse generator 2, and the conductive fixing frame 7 is connected to the positive electrode 3 (positive electrode) of the electric pulse generator 2 to ensure good contact. During the discharge process, the electrode 6 releases a pulsed current with a peak voltage of 35 kV within 5 μs, forming a local plasma channel at the tip of the electrode 6 and diffusing around, forming initial microcracks inside the rock.

[0078] In the crack propagation stage, the displacement controller 15 drives the telescopic inner rod 16 and the telescopic outer rod 17 to advance the electrode 6 at a step size of 0.05 mm according to the preset trajectory parameters, inducing the crack to fractally expand in three-dimensional directions. The system collects E(t) through the acoustic emission probe and calculates the instantaneous energy release rate. Substitute into the formula to reverse v(t). If v(t) deviates from the preset value, the discharge voltage or pulse interval is automatically adjusted. When it is monitored that the characteristic frequency deviation exceeds the set value, it is determined as an ideal crack initiation signal, and the control terminal automatically triggers the parameter adjustment protocol to realize the closed-loop control of the crack propagation path. The system automatically executes the decoupling program, and then slowly withdraws the electrode 6 at a rate of 2 cm / s to avoid mechanical disturbance to the generated cracks.

[0079] In summary, through the non-contact energy transfer mechanism and the multi-physical field collaborative control strategy, the present invention realizes the sub-millimeter spatial positioning, adjustable fractal dimension, and crack network construction of internal cracks in rocks, and solves the technical bottlenecks of traditional mechanical loading methods in crack morphology control, energy utilization rate, and experimental repeatability.

[0080] The above embodiments are preferred implementation solutions of the present invention, and any obvious substitution without departing from the concept of the technical solution is within the protection scope of the present invention.

Claims

1. A three-dimensional controllable crack generation device inside a rock based on high-voltage pulsed discharge, characterized in that, Comprising: A high-voltage pulsed discharge system, including an electric pulse generator, an electrode, and a conductive fixing frame. The electrode is used to be inserted into the guide hole of the rock to be measured and connected to the negative electrode of the electric pulse generator. The conductive fixing frame is used to fix the rock to be measured and connected to the positive electrode of the electric pulse generator. The electric pulse generator is used to generate high-voltage pulsed discharge to form cracks inside the rock; A trajectory control module, used to control the movement of the electrode in the guide hole of the rock to be measured to guide the crack to expand along a predetermined trajectory; A medium circulation module, used to inject a liquid medium into the guide hole of the rock to be measured; A feedback control module, used to monitor the crack expansion signal and adjust the discharge parameters according to the monitoring result.

2. The three-dimensional controllable crack generation device inside a rock based on high-voltage pulsed discharge according to claim 1, characterized in that: The electrode adopts a three-layer composite structure, which is successively a tungsten steel inner core, a copper-nickel alloy conductive layer, and a polyimide insulating layer from the inside to the outside, and the electrode tip is processed to form a discharge focusing end.

3. The three-dimensional controllable crack generation device inside a rock based on high-voltage pulsed discharge according to claim 1, characterized in that: The trajectory control module includes a displacement controller and a telescopic component connected thereto. The telescopic component connects the electrode and drives the electrode to move in the guide hole of the rock to be measured.

4. The three-dimensional controllable crack generation device inside rock based on high-voltage pulse discharge according to claim 1, characterized in that: The medium circulation module includes a deionized water exchanger, used to inject deionized water into the guide hole of the rock to be measured.

5. The three-dimensional controllable crack generation device inside rock based on high-voltage pulse discharge according to claim 1 or 4, characterized in that: The medium circulation module includes an ultrasonic oscillator, used to eliminate the bubbles in the guide hole of the rock to be measured.

6. The three-dimensional controllable crack generation device inside rock based on high-voltage pulsed discharge according to claim 1, characterized in that: The feedback control module includes an acoustic emission detector and an acoustic emission probe. The acoustic emission probe is used to be fixed on the rock to be measured and monitor the elastic wave signal generated by the crack expansion through the acoustic emission detector. The acoustic emission detector is electrically connected to the control end of the electric pulse generator.

7. The three-dimensional controllable crack generation device inside a rock based on high-voltage pulsed discharge according to claim 1 or 6, characterized in that: The feedback control module adjusts the discharge parameters by combining the quantitative correlation model of the acoustic emission energy release rate and the crack expansion rate; The quantitative correlation model is as follows: Among them, v(t) is the real-time crack propagation rate, with the unit of mm / s; is the acoustic emission energy release rate, with the unit of μJ / s; β is the material energy conversion coefficient, with the unit of μJ / mm.

8. The three-dimensional controllable crack generation device inside a rock based on high-voltage pulsed discharge according to claim 1, characterized in that: The discharge parameters include at least one of the discharge voltage and the pulse interval time.

9. A three-dimensional controllable crack generation method inside rocks based on high-voltage pulsed discharge, characterized in that: Using the device according to any one of claims 1-8, and including the following steps: Step 1: Process a guide hole on the rock to be measured, fix the rock to be measured on the conductive fixing frame, insert the electrode into the guide hole, and connect the conductive fixing frame and the electrode to the positive and negative electrodes of the electric pulse generator respectively; Step 2: Inject a liquid medium into the guide hole through the medium circulation module; Step 3: Select the working mode of the electric pulse generator, including a single discharge mode or a continuous pulse mode; Step 4: Generate initial micro-cracks inside the rock to be measured through high-voltage pulsed discharge; Step 5: The trajectory control module controls the displacement of the electrode in the guide hole to guide the crack to expand along a predetermined trajectory; Step 6: The feedback control module monitors the crack expansion signal in real time and adjusts the discharge parameters of the electric pulse generator according to the monitoring result to achieve three-dimensional directional expansion of the crack.

10. The method for generating three-dimensional controllable cracks inside rocks based on high-voltage pulsed discharge according to claim 9, characterized in that: In step 3, select the working mode of the electric pulse generator according to the rock type: for rocks with a tensile strength less than 3 MPa, adopt the single discharge mode; for rocks with a tensile strength greater than or equal to 3 MPa, adopt the continuous pulse mode.

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