A deep rock tension-shear mixed dynamic fracture three-dimensional visualization test system

Abstract

The application discloses a deep rock tension-shear mixed dynamic fracture three-dimensional visualization test system, and belongs to the field of rock mechanics and dynamic test technology. The system comprises a base, wherein a first support, a supporting seat, a gas gun and a second support are arranged on the base; an axial loading actuator is arranged on the first support; a plurality of supporting seats are used for supporting a transmission rod and an incident rod; a sample is located between the transmission rod and the incident rod; the axial loading actuator presses the sample on the incident rod through the transmission rod; the incident rod is connected with the second support through a first flange plate; the gas gun comprises an impact bullet, the impact bullet is sleeved on the incident rod, and the impact bullet impacts on the first flange plate when the gas gun fires the impact bullet. In the dynamic test, the system realizes clear and stable true triaxial high ground stress environment simulation and provides a stress condition close to the real one; the loading path of static pressure first and then dynamic tension scientifically simulates a deep engineering stress scene of a high ground stress background and dynamic disturbance.

Description

Technical Field

[0001] This invention belongs to the field of rock mechanics and dynamic testing technology, specifically relating to a three-dimensional visualization test system for dynamic fracture of deep rock under tension and shear. Background Technology

[0002] Brittle fracture of rocks mainly exhibits two basic modes: tension and shear. Theoretical studies show that these two modes constitute a continuous fracture spectrum. However, the transitional mode, namely mixed tension-shear fracture, remains unclear in experimental formation and observation. Deep rock masses exist in complex environments with high geostress and high temperatures. Their fracture is the result of the combined effects of static and dynamic forces (excavation disturbance, blasting), often manifesting as a mixed tension-shear fracture mode. Traditional rock mechanics testing machines often cannot simultaneously simulate the true triaxial static stress field and dynamic disturbance loads in deep rock masses. Furthermore, observations of the fracture process are mostly limited to the sample surface or the final state, making it difficult to capture the three-dimensional dynamic propagation process of internal cracks in situ and in real time. Therefore, there is an urgent need to develop an advanced testing system that can integrate true triaxial static loading, dynamic impact, and full-process three-dimensional visualization observation to reveal the dynamic fracture mechanism of mixed tension-shear fracture in deep rocks.

[0003] Currently, rock tensile shear testing devices generally adopt hydraulic servo control, as seen in Chinese invention patent applications with publication numbers CN118294293A, CN115753441A, CN112014243A, and CN110018052A. Static tensile shear testing devices have significant shortcomings in simulating the mechanical behavior of deep rock masses. (1) The loading rate is low, making it impossible to simulate the strain rate range included in dynamic disturbances such as blasting and rockburst, resulting in a large gap with the dynamic response in deep engineering. (2) The simulation of stress is not realistic enough: traditional devices often cannot simulate the true triaxial stress state of deep rock masses, and their confining pressure loading method is relatively simple, resulting in a gap with the realism of the deep high-stress environment.

[0004] Currently, the Hopkinson bar test technique is mainly used to test the dynamic mechanical properties of rocks. This technique generates tensile stress pulses in the bar through specific loading methods (such as reflection, rotary, or direct impact) to study the mechanical properties of materials under high strain rates. For example, Chinese invention patent applications and utility model patents with publication numbers CN115046868A, CN212483222U, CN118961465A, CN120009089A and CN119198395A. However, this technique still has obvious limitations in simulating the complex stress environment and specific failure modes of deep rock masses: (1) Traditional Hopkinson bar devices are mainly designed to achieve unidirectional dynamic tension of materials, and their loading path is relatively simple. To achieve tensile-shear combined failure, special design of the specimen is usually required (such as pre-fabricated cracks or specific geometries). Under dynamic load, it tends to cause simple tensile or splitting failure along the direction of maximum tensile stress, rather than the expected tensile-shear combined failure. (2) Conventional Hopkinson bar test apparatus is usually carried out under conditions of no confining pressure or simple confining pressure, and its confining pressure loading method is difficult to simulate the non-uniform three-dimensional stress state of deep rock mass. Summary of the Invention

[0005] The technical problem solved by this invention is to provide a three-dimensional visualization test system for dynamic tensile-shear hybrid fracture of deep rocks, which realizes a high static stress environment inside the sample that approximates the deep strata. On this static stress background, controllable dynamic tensile disturbance is applied to simulate engineering disturbance and induce real tensile-shear hybrid failure.

[0006] Technical Solution: To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A three-dimensional visualization test system for dynamic fracture of deep rock involving tension and shear includes a base, on which are provided a first support, a support seat, an air gun, and a second support. The first support is provided with an axial loading actuator. Multiple support seats are used to support a transmission rod and an incident rod. The test sample is located between the transmission rod and the incident rod. The axial loading actuator presses the test sample onto the incident rod through the transmission rod. The incident rod is connected to the second support through a first flange. The air gun includes an impact bullet, which is sleeved on the incident rod. When the air gun fires the impact bullet, the impact bullet impacts the first flange.

[0008] Preferably, the test sample is located inside the confining pressure assembly, which includes an inner confining pressure chamber and an outer confining pressure chamber sleeved outside the inner confining pressure chamber. Hydraulic oil is provided in the inner confining pressure chamber. One end of the transmission rod passes through the outer confining pressure chamber and the inner confining pressure chamber and abuts against the test sample. One end of the incident rod passes through the outer confining pressure chamber and the inner confining pressure chamber and abuts against the test sample.

[0009] Preferably, the test sample includes a first end, a second end, and an intermediate segment connecting the first end and the second end. The cross-sectional area of ​​the intermediate segment gradually increases from the middle towards the first end, and the cross-sectional area of ​​the intermediate segment also gradually increases from the middle towards the second end.

[0010] Preferably, the middle section has a circular cross-section, and the first and second ends also have circular cross-sections.

[0011] Preferably, the outer pressure chamber is provided with a first observation window, and the inner pressure chamber is provided with a second observation window.

[0012] Preferably, multiple connecting rods are provided between the first support, the air cannon, and the second support.

[0013] Preferably, strain gauges are connected to both the transmission rod and the incident rod, and the strain gauges are connected to a dynamic strain gauge.

[0014] Preferably, the inner pressure chamber is connected to a hydraulic pump.

[0015] Preferably, the test system includes the following steps when it is in operation:

[0016] S1. The test sample is placed in the inner confining pressure chamber, with the first end of the test sample in contact with the transmission rod and the second end of the test sample in contact with the incident rod.

[0017] S2. The axial loading actuator pushes the transmission rod according to the preset force or displacement rate. The transmission rod applies axial preload to the test sample. The axial preload is transmitted to the incident rod through the test sample. The axial preload is the axial force F.

[0018] S3. While applying axial preload, hydraulic oil is injected into the inner confining pressure chamber to raise the internal pressure of the inner confining pressure chamber to a preset value. The internal pressure is the confining pressure P. The confining pressure P acts on the circumference of the specimen. At this time, the specimen is in a state of static stress equilibrium under triaxial compression, and its stress state is characterized as follows:

[0019] σ1=C, σ2=P, σ3=P

[0020] Where σ1 is the axial stress at the narrowest point of the middle section, σ2 is the first lateral constraint stress, σ3 is the second lateral constraint stress, and C is the equivalent stress resulting from the combined action of the compressive stress generated by the axial force F in the middle section of the specimen and the variable cross-sectional geometry of the specimen.

[0021]

[0022] In the formula, A t Let A be the cross-sectional area at the narrowest point of the middle section. h The cross-sectional area of ​​the first or second end;

[0023] S4. The air cannon fires an impact projectile. The impact projectile is ejected at a predetermined velocity and strikes the first flange, generating a tensile stress pulse incident wave σ in the incident rod. i The incident wave σ of the tensile stress pulse i The stress propagates along the incident rod to the sample and superimposes with the existing static stress field within the sample. The dynamic stress state of the sample is calculated by the following formula:

[0024]

[0025] In the formula, σ d (t) represents the dynamic axial tensile stress of the sample at time t, E b A represents the elastic modulus of the materials of the incident and transmitting rods. b ε represents the cross-sectional area of ​​the incident or transmitting rod. i (t) represents the incident wave strain signal measured by the strain gauge on the incident rod at time t, ε r (t) represents the strain signal of the reflected wave measured by the strain gauge on the incident rod at time t, ε t (t) represents the strain signal of the transmitted wave measured by the strain gauge on the transmission rod at time t, A t This is the cross-sectional area at the narrowest point of the middle section;

[0026] S5, Tensile stress pulse incident wave σ i After the action, the effective first principal stress σ′1 = σ1 - σ d It increases sharply, where σ d This represents the dynamic axial tensile stress of the specimen. When this stress difference exceeds the specimen's strength criterion, it induces a mixed tensile-shear fracture.

[0027] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0028] 1. By setting up a first support, a transmission rod, an incident rod, and a second support, and using an axial loading actuator to push the transmission rod, the transmission rod applies axial preload to the test sample. The incident rod supports the test sample and is balanced by the second support. The incident rod passes through the air cannon. The impact bullet is fitted on the incident rod. When working, the impact bullet generates a tensile stress pulse incident wave in the incident rod, which can effectively and repeatedly induce tensile-shear mixed failure.

[0029] 2. The test sample was located in the outer pressure chamber and the inner pressure chamber. In the dynamic test, a clear and stable true triaxial high ground stress environment simulation was achieved, which provided a near-real stress condition for studying the mechanical behavior of deep rock masses. The loading path of static pressure followed by dynamic tension was adopted to scientifically simulate the stress scenario of deep engineering under high ground stress background and dynamic disturbance.

[0030] 3. The test sample is designed with a shape that is narrow in the middle and thick at both ends. Under the loading conditions of static pressure followed by dynamic tension, the cross-sectional area of ​​the middle section is small, and the effective stress (the superposition of static pressure stress and dynamic stress) it bears is the largest. This can ensure that the tensile-shear mixed failure of the rock occurs in the middle of the visual observation area, rather than at the end that is in contact with the rod. By adjusting the area ratio of the middle section to the two ends, the static stress level of the middle section can be precisely controlled, making it easier to induce a specific tensile-shear mixed failure mode when dynamic tensile waves are applied.

[0031] 4. Observation windows are set on the outer and inner pressure chambers, which is conducive to the in-situ, three-dimensional quantitative observation of the entire process of rock fracturing from initiation to penetration. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the overall structure of an embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of the outer and inner pressure chambers of the embodiment;

[0034] Figure 3 This is a schematic diagram of the internal structure of the outer pressure chamber and the inner pressure chamber in the embodiment;

[0035] Figure 4 This is a schematic diagram of the sample structure in the embodiment;

[0036] Figure 5 This is a sample size diagram of the embodiment;

[0037] Figure 6 This is a schematic diagram of the strain gauge bonding position in the embodiment;

[0038] Figure 7 This is a graph showing the loading force curve of the axial loading actuator in an embodiment.

[0039] Figure 8 This is a confining pressure loading curve of the confining pressure chamber in the embodiment;

[0040] Figure 9 This is a time history curve of the axial stress generated in the middle section of the test sample under axial compression in the embodiment.

[0041] Figure 10 This is the stress time history curve of embodiment σ1;

[0042] Figure 11 This is a schematic diagram of the internal structure of the air cannon in the embodiment. Detailed Implementation

[0043] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0044] Example

[0045] like Figure 1 As shown, a three-dimensional visualization test system for dynamic fracture of deep rock under tension and shear includes a base 1, which is a horizontally fixed elongated base. The base 1 is sequentially equipped with a first support 3, a support seat 5, an air gun 10, and a second support 13. The first support 3 is connected to one end of the base 1 and is slidably connected to the base 1 via a guide rail (the bottom of the first support 3 is equipped with a guide slider, whose position is adjusted by sliding along the guide rail on the base 1, and then locked to the base 1 by high-strength bolts after adjustment). This facilitates adjustment of the left and right positions. The second support 13 is fixedly connected to the other end of the base 1 (the second support 13 is rigidly fixed to the end of the base 1 by bolts or welding, serving as the axial force reaction wall of the system). Multiple support seats 5 are provided, positioned on the base 1 between the first support 3 and the second support 13. The support seats 5 are slidably connected to the base 1 via the guide rail on the base 1, allowing for axial adjustment to meet the support requirements of the rods, and are locked by bolts. The air gun 10 is positioned in the middle right of the base 1.

[0046] like Figure 1As shown, an axial loading actuator 2 is mounted on the first support 3. The first support 3 is a rectangular plate. The axial loading actuator 2 is located on the outside of the first support 3. The first support 3 has a central hole corresponding to the axial loading actuator 2. The piston rod of the axial loading actuator 2 passes through the central hole of the first support 3. The axial loading actuator 2 adopts an existing electro-hydraulic servo actuator, which is supplied with oil by a hydraulic pump station and can provide a constant axial static load. The axial loading actuator 2 is connected to a hydraulic servo system, which adopts an existing electro-hydraulic servo control system, such as the FlexTest series control system from MTS or a domestically produced servo loading system with equivalent performance. This hydraulic servo system mainly consists of a high-pressure hydraulic pump station, an electro-hydraulic servo valve, a pressure sensor, a displacement sensor, and a control computer. Its main function is based on the PID closed-loop control algorithm, receiving feedback signals from sensors in real time and adjusting the opening of the servo valve to precisely control the output force or piston displacement of the axial loading actuator 2. During the test, the hydraulic servo system can achieve smooth switching between force control and displacement control modes, providing the test sample 14 with a long-term, high-precision and numerically constant axial static load to simulate the overburden pressure on deep rocks. The support seat 5 is provided with a first through hole, and multiple support seats 5 are used to support the transmission rod 7 and the incident rod 9. The transmission rod 7 and the incident rod 9 are supported by the support seat 5 after passing through the first through hole on the support seat 5. The transmission rod 7 and the incident rod 9 are both cylindrical and have the same diameter. When the transmission rod 7 and the incident rod 9 are supported by the support seat 5, their axes coincide. The transmission rod 7 is located at one end of the first support 3, and the incident rod 9 is located at one end of the second support 13. The piston rod of the axial loading actuator 2 abuts against the first end of the transmission rod 7, and the tail end of the incident rod 9 is connected to the second support 13 through the first flange 12.

[0047] like Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5As shown, the sample 14 is located between the transmission rod 7 and the incident rod 9. The sample 14 is taken from rock material in deep strata, such as brittle rocks like granite, sandstone, marble, or limestone. The sample 14 includes a first end 141, a second end 142, and a middle section 143. The middle section 143 connects the first end 141 and the second end 142. The middle section 143 is narrowest at the middle. The cross-sectional area of ​​the middle section 143 gradually increases from the middle towards the first end 141 and from the middle towards the second end 142. The cross-section of the middle section 143 is circular. The area of ​​the circular cross-section increases outward from the narrowest point in the middle. The first end 141 and the second end 142 are cylinders with equal diameters, so the cross-sections of the first end 141 and the second end 142 are circular. The maximum diameter of the middle section 143 is equal to the diameters of the first end 141 and the second end 142. In this embodiment, the total length of the sample 14 is 90mm, the length of the first end 141 and the second end 142 is 10mm, the length of the middle section 143 is 70mm, the diameter of the first end 141 and the second end 142 is 40mm, and the diameter of the narrowest part of the middle section 143 is 30mm.

[0048] like Figure 1 , Figure 2 , Figure 3 and Figure 4The axial loading actuator 2 presses the test sample 14 onto the incident rod 9 via the transmission rod 7. The test sample 14 is located inside the confining pressure assembly, which includes an inner confining pressure chamber 15 and an outer confining pressure chamber 8 fitted outside the inner confining pressure chamber 15. The outer confining pressure chamber 8 is connected to the base 1 via an external support (the external support is omitted in the figure). The inner confining pressure chamber 15 is located inside the outer confining pressure chamber 8, and the two confining pressure chambers are coaxial. The inner confining pressure chamber 15 is filled with hydraulic oil and is connected to an existing external confining pressure servo loading system via a high-pressure oil-resistant pipeline. This confining pressure servo loading system mainly consists of a high-pressure hydraulic pump, an electro-hydraulic servo valve, a precision pressure sensor, and a control host. The working process is as follows: Before the test begins, the control host issues a pressurization command, the high-pressure hydraulic pump draws in and pressurizes the hydraulic oil, and after the flow rate is regulated by the electro-hydraulic servo valve, it is injected into the inner confining pressure chamber 15 through the pipeline; the pressure sensor installed on the pipeline or the inner confining pressure chamber 15 monitors the internal oil pressure signal in real time and feeds it back to the control host; the control host, based on the PID closed-loop control algorithm, compares the feedback pressure with the preset confining pressure value P, and dynamically adjusts the opening of the servo valve to compensate for pressure loss, so that the inner confining pressure chamber 15 can quickly establish and maintain a constant and precise hydrostatic pressure environment until the test ends and the pressure is released. One end of the transmission rod 7 passes through the end cap of the outer pressure chamber 8 and the inner confining pressure chamber 15 and is pressed against one end of the test sample 14, and one end of the incident rod 9 passes through the end cap of the other end of the outer pressure chamber 8 and the inner confining pressure chamber 15 and is pressed against the other end of the test sample 14. The sealing between the transmission rod 7 and the incident rod 9 and the confining pressure chamber adopts a multi-seal structure built into the end cap. Both the outer pressure chamber 8 and the inner pressure chamber 15 have through holes at the center of their metal end caps. The inner walls of these through holes are machined with two or more annular sealing grooves, into which O-ring rubber seals and anti-extrusion retaining rings are sequentially embedded. During pressurization, the O-rings expand under pressure and press tightly against the surfaces of the rods (transmission rod 7 and incident rod 9) to prevent oil leakage; simultaneously, the anti-extrusion retaining rings prevent the seals from being squeezed into the mating gap under high pressure. This structure ensures zero leakage under confining pressures up to several megapascals while allowing axial displacement of the rods at the moment of impact. Before the test begins, connect and seal one end cap of the inner confining pressure chamber 15 to the intermediate cylinder. Place the test sample 14, wrapped with an oil-proof film, inside the intermediate cylinder of the inner confining pressure chamber 15, and install the other end cap of the inner confining pressure chamber 15 to form a closed chamber. Place the assembled inner confining pressure chamber 15 on the fixed seat inside the outer pressure chamber 8, insert the incident rod 9 and the transmission rod 7, and adjust the position of the test sample 14 to ensure close contact with the end faces of the rods. Tighten the clamps (saddle clamps, omitted in the figure) on the outside of the outer pressure chamber 8 to complete the installation. The axial length of the inner confining pressure chamber 15 is greater than the length of the test sample 14. The inner confining pressure chamber 15 forms a closed cavity spanning the test sample 14. The sealing rings in the through holes at both ends of the inner confining pressure chamber 15 act directly on the outer circumferential sidewalls of the incident rod 9 and the transmission rod 7, rather than directly contacting the test sample 14. This design ensures that even if the test sample 14 breaks under high confining pressure, the dynamic sealing structure between the inner confining pressure chamber 15 and the rod remains intact, preventing high-pressure hydraulic oil leakage.To prevent hydraulic oil in the inner pressure chamber 15 from seeping into the rock sample 14 and affecting its mechanical properties, the surface of the sample 14 is wrapped with an oil-proof heat-shrink tubing (or flexible rubber film) before the test. The two ends of the heat-shrink tubing extend to cover the connection between the ends of the incident rod 9 and the transmission rod 7, and are secured with metal wire or elastic rubber rings, thereby forming a flexible protective layer on the outside of the sample 14 that is isolated from the hydraulic oil.

[0049] like Figure 1 and Figure 2 As shown, a first observation window 16 is provided on the outer pressure chamber 8, and a second observation window 17 is provided on the inner pressure chamber 15. The first and second observation windows 16 and 17 are made of high-strength sapphire or transparent ceramic materials, which together withstand the internal high pressure and ensure excellent optical transparency. Multiple high-speed cameras (not shown in the figure, but existing digital industrial cameras can be used) are provided outside the outer pressure chamber 8. The high-speed cameras are supported by camera brackets. Multiple high-speed cameras are used to photograph the sample 14 from different angles. By setting up two observation windows and high-speed cameras arranged at different angles, combined with digital image correlation (DIC) technology, the full-field deformation image of the surface of the sample 14 is recorded in real time at a high frame rate for subsequent reconstruction of the three-dimensional displacement field and strain field, and accurate analysis of crack dynamic propagation behavior.

[0050] like Figure 1 and Figure 11 As shown, the air cannon 10 has a second through hole corresponding to the incident rod 9. The incident rod 9 passes through the second through hole and penetrates the air cannon 10. The air cannon 10 includes a high-pressure gas storage chamber, a launch tube, and an impact bullet 11. The launch tube is located at the end of the air cannon 10 near the second support 13. The high-pressure gas storage chamber is connected to the inside of the launch tube. A quick-release solenoid valve is provided at the connection between the high-pressure gas storage chamber and the launch tube. The incident rod 9 passes through the launch tube, and the impact bullet 11 is sleeved on the incident rod 9 and located inside the launch tube. Working principle: During the test, the high-pressure gas storage chamber is pre-filled with nitrogen or compressed air at a set pressure. After the launch signal is triggered, the quick-release solenoid valve opens instantaneously, and the high-pressure gas quickly enters the launch tube, pushing the impact bullet 11 located inside the launch tube to accelerate axially. The impact bullet 11 is a tubular bullet (i.e., a hollow cylindrical bullet) specifically used for the Hopkinson's lever (SHTB) test. Specific Structure: The impact projectile 11 is made of high-strength alloy steel (such as 40CrNiMo), with an inner diameter slightly larger than the diameter of the incident rod 9 and an outer diameter slightly smaller than the inner diameter of the air cannon 10's firing tube. Assembly and Function: The impact projectile 11 is coaxially and slidably sleeved on the outside of the incident rod 9 and located inside the firing tube of the air cannon 10. When the air cannon is fired, the tubular impact projectile 11 slides forward at high speed, and its end face impacts the first flange 12 fixed to the end of the incident rod 9, thereby generating a tensile stress wave in the incident rod 9 pointing towards the sample 14.

[0051] like Figure 1As shown, multiple connecting rods 6 are provided between the first support 3, the air cannon 10, and the second support 13. In this embodiment, four connecting rods 6 are provided, with one connecting rod 6 corresponding to each of the four corners of the first support 3 and the four corners of the second support 13. The connecting rod 6 passes through the first support 3 and is connected to the first support 3 by a nut (the two ends of the connecting rod 6 have a certain length of thread to facilitate adaptation to different left and right positions of the first support 3; the connecting rod 6 clamps and fixes the first support 3 by a nut after passing through the first support 3). The connecting rod 6 passes through the second support 13 and is also connected to the second support 13 by a nut. The base 1, first support 3, second support 13, and four connecting rods 6 are connected to form an integral frame, improving overall stability. The air cannon 10 is provided with a third through hole corresponding to the connecting rod 6. The connecting rod 6 passes through the air cannon 10 through the third through hole. This design allows the connecting rod 6 to freely connect the first support 3 and the second support 13 into a force-bearing whole to bear the axial static load. The bottom of the air cannon 10 is independently fixed to the base 1 by bolts. The two do not interfere with each other, avoiding the transfer of static load to the air cannon 10 shell, and also isolating the impact of firing vibration on the static loading frame.

[0052] like Figure 6 As shown, strain gauges are attached to the outer walls of both the transmission rod 7 and the incident rod 9 via adhesive bonding. These strain gauges are connected to a dynamic strain gauge. Existing resistance strain gauges are used, such as the high-precision resistance strain gauge BFH120-5AA-D150, with a standard resistance of 120Ω and a sensitivity coefficient of 2.0±1%. The dynamic strain gauge is an existing ultra-dynamic strain gauge with a frequency response range covering DC to 1500kHz (-3dB), ensuring complete capture of extremely short-duration (microsecond-level) shock wave signals in Hopkinson bar tests and guaranteeing no distortion of high-frequency signals. It features multi-level gain adjustment (10, 30, 100, 300, 1000 times) and integrates a low-pass filter (adjustable cutoff frequency 10kHz~1500kHz), effectively filtering out high-frequency electromagnetic noise and significantly improving the signal-to-noise ratio (SNR > 40dB). It can completely record the strain-time history of the incident, reflected, and transmitted waves.

[0053] The testing system operates by including the following steps:

[0054] S1. The test sample 14 is placed in the inner pressure chamber 15. The first end 141 of the test sample 14 is in contact with the transmission rod 7, and the second end 142 of the test sample 14 is in contact with the incident rod 9.

[0055] The two ends of the test sample 14 are in close contact with the transmission rod 7 and the incident rod 9, respectively, and the axis of the test sample 14 coincides with the axis of the transmission rod 7 and the incident rod 9.

[0056] S2, Axial loading actuator 2 pushes transmission rod 7 according to preset force or displacement rate, transmission rod 7 applies axial preload to test sample 14, axial preload is transmitted to incident rod 9 through test sample 14, axial preload is axial force F;

[0057] When the axial preload is transmitted to the incident rod 9 through the test sample 14, it is finally balanced by the second support 13. During this process, the axial force F acting on both ends of the test sample 14 is monitored in real time. The axial force F is monitored in real time by a precision force sensor integrated at the output end of the axial loading actuator 2. The force sensor feeds back the collected force signal to the electro-hydraulic servo control system, and adjusts the output of the axial loading actuator 2 through the PID closed-loop control algorithm to ensure that the axial force F applied to the test sample 14 remains constant during the static load stage before the air gun 10 is fired.

[0058] S3. While applying axial preload, hydraulic oil is injected into the inner confining pressure chamber 15 to raise the internal pressure of the inner confining pressure chamber 15 to a preset value, which is the confining pressure P. The confining pressure P acts on the circumference of the test sample 14. At this time, the test sample 14 is in a state of static stress equilibrium under triaxial compression, and its stress state is characterized as follows:

[0059] σ1=C, σ2=P, σ3=P

[0060] Where σ1 is the axial stress at the narrowest point of the middle section 143, σ2 is the first lateral constraint stress, σ3 is the second lateral constraint stress, and C is the equivalent stress resulting from the combined action of the compressive stress generated by the axial force F in the middle section 143 of the specimen 14 and the variable cross-sectional geometry of the specimen 14.

[0061]

[0062] In the formula, A t Let A be the cross-sectional area at the narrowest point of the middle section 143. h The cross-sectional area is the first end 141 or the second end 142; this formula clarifies that the axial stress is determined by the axial force F (direct load) and the confining pressure P through the geometrical variation (A) of the specimen 14. h -A t The equivalent loads generated by these components together constitute the total load.

[0063] At this point, a uniform and stable triaxial static pressure state simulating deep strata is established inside the sample 14.

[0064] S4. The air cannon 10 fires an impact projectile 11. The impact projectile 11 is ejected at a predetermined velocity and strikes the first flange 12, generating a tensile stress pulse incident wave σ in the incident rod 9. i The incident wave σ of the tensile stress pulse iThe stress propagates along the incident rod 9 to the sample 14, where it superimposes with the existing static stress field within the sample 14. The dynamic stress state of the sample 14 is calculated by the following formula:

[0065]

[0066] In the formula, σ d (t) represents the dynamic axial tensile stress of sample 14 at time t, E b A represents the elastic modulus of the material of the elastic rods (i.e., incident rod 9 and transmission rod 7). b ε represents the cross-sectional area of ​​the elastic rods (i.e., incident rod 9 and transmission rod 7). i (t) represents the incident wave strain signal measured by the strain gauge on the incident rod 9 at time t, ε r (t) represents the strain signal of the reflected wave measured by the strain gauge on the incident rod 9 at time t, ε t (t) represents the transmitted wave strain signal measured by the strain gauge on the transmission rod 7 at time t, A t This represents the cross-sectional area at the narrowest point of section 143 in the middle of the sample.

[0067] S5, Tensile stress pulse incident wave σ i After the action, the effective first principal stress σ′1 = σ1 - σ d It increases sharply, where σ d This indicates the dynamic axial tensile stress of specimen 14. When this stress difference exceeds the strength criterion of the rock (the rock material of specimen 14), it induces a mixed tensile-shear fracture.

[0068] According to the one-dimensional stress wave theory, the dynamic load acting on the specimen 14 will be superimposed with the static load, causing a rapid dynamic change in the axial resultant force F on the specimen 14. This change causes the axial stress σ1 at the narrowest point of the middle section 143 to decrease sharply, resulting in a sudden change in the maximum principal stress difference inside the specimen 14. The stress state rapidly enters the critical region of tensile-shear combined failure, thereby inducing tensile-shear mixed fracture of the specimen.

[0069] At the instant of impact, all data acquisition units are simultaneously triggered: strain gauges attached to the incident rod 9 and the transmission rod 7 record the strain-time history of the incident wave, reflected wave, and transmitted wave. Simultaneously, through two observation windows in the outer pressure chamber 8 and the inner pressure chamber 15, high-speed cameras positioned at different angles, combined with digital image correlation (DIC) technology, record the full-field deformation images of the sample 14 surface at a high frame rate in real time. These images are then used to reconstruct the three-dimensional displacement and strain fields, enabling precise analysis of crack dynamic propagation behavior.

[0070] After the test, the confining pressure (the pressure generated by the hydraulic oil in the inner confining pressure chamber 15) and the axial pressure (the pressure generated by the axial loading actuator 2) were released slowly in sequence. The axial loading actuator 2 was controlled to drive the transmission rod 7 to move axially backward to separate the test sample 14 and make room for operation. The drain valve of the inner confining pressure chamber 15 was opened to drain the internal hydraulic oil back to the oil tank. Then, a special tool was used to loosen and remove the sealing end caps at the ends of the outer pressure chamber 8 and the inner confining pressure chamber 15, thereby opening the outer pressure chamber 8 and the inner confining pressure chamber 15. The broken test sample 14 was then taken out from the open cavity. By combining dynamic stress-strain data with three-dimensional full-field deformation time-series images, the evolution law of crack initiation stress threshold, propagation rate, fracture surface angle, and tensile and shear stress components can be quantitatively analyzed, thereby revealing in depth the tensile-shear mixed fracture mechanism of deep rocks under dynamic and static combined loads.

[0071] like Figure 7 , Figure 8 , Figure 9 and Figure 10 As shown, the diameter of the end of the sample 14, the diameter of the incident rod 9, and the diameter of the transmission rod 7 are all 40 mm. The diameter of the narrowest part of the middle section of the sample is 30 mm. The cross-sectional area A of the end of the sample 14, the incident rod 9, and the transmission rod 7 is... h =π×(40 / 2) 2 =400π≈1256.64mm 2 The cross-sectional area A at the narrowest point of the middle section t =π×(30 / 2) 2 =225π≈706.86mm 2 During the test, the axial loading actuator 2 was preset with a force F of 14.14 kN and a confining pressure P of 90 MPa. Both were loaded from time t=0 s to the preset values ​​at time t=60 s and remained unchanged.

[0072] according to After loading, the stresses in the middle section 143 of the sample 14 are σ1=90MPa, σ2=σ3=90MPa, respectively. Figure 7 The curve shows the loading force of the axial loading actuator 2, with the horizontal axis representing the loading time and the vertical axis representing the pressure value. Figure 8 The confining pressure loading curve is shown on the horizontal axis, where the loading time is represented by the horizontal axis, and the circumferential stress value generated by the confining pressure on the specimen is represented by the vertical axis. Due to the axial pressure, the confining pressure is applied synchronously, and the triaxial stress in the middle section 143 of specimen 14 also increases synchronously. Its stress-time history curve is shown in the figure. Figure 9 As shown, Figure 9 The horizontal axis represents the loading time, and the vertical axis represents the axial stress value generated by the axial compression on the middle section of the test sample.

[0073] After the loading stabilizes, the tubular impact projectile 11 fired by the air cannon 10 strikes the first flange 12 at the end of the incident rod 9, generating a tensile stress pulse wave that propagates along the incident rod 9. This tensile wave propagates to the region of the sample 14 and undergoes dynamic superposition with the existing static compressive stress field. The axial stress σ1 stress-time history curve at the narrowest point of the middle section 143 is shown below. Figure 10 As shown, Figure 10 The horizontal axis represents time, and the vertical axis represents the σ1 stress value. By offsetting (reducing) the axial compressive stress, the specimen 14 experiences a sudden change in stress path from high pressure to low pressure or even tension, thereby precisely inducing dynamic tensile-shear fracture of rock under a deep high-stress background. To accurately determine the failure load, the experiment employs high-speed photography and dynamic stress acquisition synchronization technology: the precise time point of specimen fracture is identified through high-speed photographic images, and then mapped back to the axial stress-time curve to accurately extract the axial force value corresponding to the instant of failure of specimen 14.

[0074] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A three-dimensional visualization test system for dynamic fracture of deep rock involving tensile and shear forces, characterized in that, The device includes a base (1), on which a first support (3), a support seat (5), an air cannon (10), and a second support (13) are provided. An axial loading actuator (2) is provided on the first support (3). Multiple support seats (5) are used to support a transmission rod (7) and an incident rod (9). A test sample (14) is located between the transmission rod (7) and the incident rod (9). The axial loading actuator (2) presses the test sample (14) onto the incident rod (9) through the transmission rod (7). The incident rod (9) is connected to the second support (13) through a first flange (12). The air cannon (10) includes an impact bullet (11). The impact bullet (11) is sleeved on the incident rod (9). When the air cannon (10) fires the impact bullet (11), the impact bullet (11) impacts the first flange (12).

2. The three-dimensional visualization test system for deep rock tensile-shear hybrid dynamic fracture according to claim 1, characterized in that, The test sample (14) is located inside the confining pressure assembly, which includes an inner confining pressure chamber (15) and an outer confining pressure chamber (8) sleeved outside the inner confining pressure chamber (15). The inner confining pressure chamber (15) is filled with hydraulic oil. One end of the transmission rod (7) passes through the outer confining pressure chamber (8) and the inner confining pressure chamber (15) and abuts against the test sample (14). One end of the incident rod (9) passes through the outer confining pressure chamber (8) and the inner confining pressure chamber (15) and abuts against the test sample (14).

3. The three-dimensional visualization test system for deep rock tensile-shear hybrid dynamic fracture according to claim 2, characterized in that, The test sample (14) includes a first end (141), a second end (142), and an intermediate section (143) connecting the first end (141) and the second end (142). The cross-sectional area of ​​the intermediate section (143) gradually increases from the middle towards the first end (141), and the cross-sectional area of ​​the intermediate section (143) also gradually increases from the middle towards the second end (142).

4. The three-dimensional visualization test system for deep rock tensile-shear hybrid dynamic fracture according to claim 3, characterized in that, The middle section (143) has a circular cross-section, and the first end (141) and the second end (142) also have circular cross-sections.

5. The three-dimensional visualization test system for deep rock tensile-shear hybrid dynamic fracture according to claim 2, characterized in that, The outer pressure chamber (8) is provided with a first observation window (16), and the inner pressure chamber (15) is provided with a second observation window (17).

6. The three-dimensional visualization test system for deep rock tensile-shear hybrid dynamic fracture according to claim 1, characterized in that, Multiple connecting rods (6) are provided between the first support (3), the air cannon (10), and the second support (13).

7. The three-dimensional visualization test system for deep rock tensile-shear hybrid dynamic fracture according to claim 3, characterized in that, Both the transmission rod (7) and the incident rod (9) are connected to strain gauges, which are connected to a dynamic strain gauge.

8. The three-dimensional visualization test system for deep rock tensile-shear hybrid dynamic fracture according to claim 2, characterized in that, The inner pressure chamber (15) is connected to a hydraulic pump.

9. The three-dimensional visualization test system for deep rock tensile-shear hybrid dynamic fracture according to claim 3, characterized in that, The testing system operates by including the following steps: S1. The test sample (14) is placed in the inner confining pressure chamber (15). The first end (141) of the test sample (14) is in contact with the transmission rod (7), and the second end (142) of the test sample (14) is in contact with the incident rod (9). S2, Axial loading actuator (2) pushes transmission rod (7) according to preset force or displacement rate. Transmission rod (7) applies axial preload to test sample (14). Axial preload is transmitted to incident rod (9) through test sample (14). Axial preload is axial force F. S3. While applying axial preload, hydraulic oil is injected into the inner confining pressure chamber (15) to raise the internal pressure of the inner confining pressure chamber (15) to a preset value. The internal pressure is the confining pressure P. The confining pressure P acts on the circumference of the test sample (14). At this time, the test sample (14) is in a state of static stress equilibrium under triaxial compression. Its stress state is characterized as follows: σ1=C, σ2=P, σ3=P; Where σ1 is the axial stress at the narrowest point of the middle section (143), σ2 is the first lateral constraint stress, σ3 is the second lateral constraint stress, and C is the equivalent stress resulting from the combined action of the compressive stress generated by the axial force F in the middle section (143) of the specimen (14) and the variable cross-section geometry of the specimen (14): ； In the formula, A t A is the cross-sectional area at the narrowest point of the middle segment (143). h The cross-sectional area of ​​the first end (141) or the second end (142); S4. The air cannon (10) fires an impact bullet (11). The impact bullet (11) is fired at a predetermined speed and strikes the first flange (12), generating a tensile stress pulse incident wave σ in the incident rod (9). i The incident wave σ of the tensile stress pulse i The stress propagates along the incident rod (9) to the test sample (14), and superimposes with the existing static stress field within the test sample (14). The dynamic stress state of the test sample (14) is calculated by the following formula: ； In the formula, σ d (t) represents the dynamic axial tensile stress of the test sample (14) at time t, E b A represents the elastic modulus of the materials of the incident rod (9) and the transmitting rod (7). b ε represents the cross-sectional area of ​​the incident rod (9) or the transmitting rod (7). i (t) represents the incident wave strain signal measured by the strain gauge on the incident rod (9) at time t, ε r (t) represents the strain signal of the reflected wave measured by the strain gauge on the incident rod (9) at time t, ε t (t) represents the transmitted wave strain signal measured by the strain gauge on the transmission rod (7) at time t, A t The cross-sectional area at the narrowest point of the middle section (143); S5, Tensile stress pulse incident wave σ i After the action, the effective first principal stress σ′1 = σ1 - σ d It increases sharply, where σ d The dynamic axial tensile stress of the test sample (14) is indicated. When this stress difference exceeds the strength criterion of the test sample (14), a mixed tensile-shear fracture is induced.

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