A triaxial six-directional impact test simulation method and system based on F-DEM

Abstract

The application provides a triaxial six-direction impact test simulation method and system based on F-DEM, the triaxial six-direction impact test simulation method based on F-DEM comprises a full-size model frame establishing step, an F-DEM coupling step, a model dynamic solving step and an automatic data post-processing step, and the application also provides a triaxial six-direction impact test simulation system based on F-DEM, a three-dimensional full-scale numerical model is established based on the basic parameters of a waveguide rod and a rock sample in a TEHB test system, and the three-dimensional full-scale numerical model comprises a discrete element rock sample model and a finite element waveguide rod model. The application realizes efficient coupling modeling of the finite element waveguide rod and the discrete element rock sample, has good stress wave propagation accuracy, can accurately simulate the dynamic response behavior of the rock sample under triaxial six-direction loading, and provides efficient and verifiable technical support for impact response analysis and engineering application research of rock mass in a complex stress environment.

Description

Technical Field

[0001] This invention relates to the field of rock impact test simulation technology, specifically to a triaxial six-axis impact test simulation method and system based on F-DEM. Background Technology

[0002] Rock masses are often subjected to complex stress and high strain rate environments, and loads such as engineering disturbances and earthquakes can significantly alter their mechanical behavior. Rock dynamics is an important branch of research that studies the mechanical behavior and fracture mechanisms of rock masses under dynamic loads. It involves core issues such as material instantaneous response, energy transfer, and failure evolution. Its research is of great significance for understanding the formation mechanisms of geological hazards, guiding blasting and support design, and ensuring the safety of engineering structures.

[0003] In recent years, the development of the True Triaxial Electromagnetic Hopkinson Bar (TEHB) testing system has provided an advanced experimental platform for studying rock mass response under multiaxial dynamic loading conditions. It can achieve triaxial six-axis impact loading that more closely approximates engineering realities and acquire stress-strain response data with high spatiotemporal resolution. However, the TEHB testing system suffers from high equipment costs, long sample preparation and debugging cycles, and reliance on manual control, limiting its experimental efficiency and parameter coverage. To improve research efficiency and promote the expansion and verification of TEHB experimental results under a wider range of working conditions, it is urgent to construct a reliable numerical simulation method and system as an extension and supplement to the experiment.

[0004] Currently, numerical simulation methods applicable to split Hopkinson bar tests are mainly based on the finite element method (FEM) or discrete element method (DEM) for single modeling, and most are limited to two-dimensional models. It is difficult to balance wave propagation accuracy and fracture response accuracy between the two types of methods. Especially under the triaxial six-axis high strain rate loading conditions involved in the TEHB test system, the existing modeling methods are difficult to meet the dual requirements of fine modeling and experimental feedback analysis. Summary of the Invention

[0005] To address the problems in the prior art, this invention provides a triaxial six-axis impact test simulation method based on F-DEM.

[0006] The present invention provides a triaxial six-axis impact test simulation method based on F-DEM, comprising the following steps:

[0007] Steps for establishing a full-scale model framework: Based on the basic parameters of the waveguide rod and the rock sample to be tested in the triaxial six-axis dynamic true triaxial electromagnetic Hopkinson bar TEHB test system, a three-dimensional full-scale numerical model including the rock sample and the six-axis waveguide rod is established. The three-dimensional full-scale numerical model includes a discrete element rock sample model and a finite element waveguide rod model.

[0008] F-DEM coupling steps: Based on the actual contact state between the waveguide rod and the rock sample, a coupling relationship is established between the discrete element rock sample model and the finite element waveguide rod model at the contact interface. The physical parameters of the contact surface are set, and a dynamic coupling interface is constructed between the discrete element rock sample model and the finite element waveguide rod model. In the coupling mechanism, the finite element waveguide rod model provides the velocity boundary input, while the discrete element rock sample model provides real-time feedback of the contact force, forming a continuous and consistent waveguide rod-rock sample coupled physical field, realizing the bidirectional transmission of velocity and contact force.

[0009] Model dynamic solution steps: Apply a certain impact load to the loading end of the three-dimensional full-scale numerical model to simulate the propagation process of stress wave in the waveguide rod and rock sample;

[0010] Automated data post-processing steps: Collect strain monitoring data in the waveguide rod, and based on the strain monitoring data, obtain the dynamic response index of the impact test to quantify the dynamic response characteristics of the rock sample under impact load.

[0011] Furthermore, the full-size model framework establishment steps include discrete element rock sample model establishment step A1 and finite element waveguide rod model establishment step A2.

[0012] The processing method for step A1 of establishing the discrete element rock sample model is as follows:

[0013] A101: Constructing a discrete element rock sample model: Construct a cube-shaped three-dimensional rock sample model, and divide the three-dimensional rock sample model into several discrete blocks using the complete triangulation method to form a discrete element rock sample model.

[0014] A102: Setting model parameters: Set the block material parameters and contact surface parameters of the discrete element rock sample model, and iteratively simulate the indoor uniaxial compressive strength test process through trial and error, repeatedly adjusting the parameters until the numerical results match the test results;

[0015] The processing method for step A2 of the finite element waveguide rod model establishment is as follows:

[0016] A201: Constructing a finite element waveguide model: Six symmetrically distributed, square finite element waveguides are arranged in the positive and negative directions of the X, Y, and Z coordinate axes, respectively. The cross-section of the finite element waveguides is consistent with the dimensions of each face of the three-dimensional rock sample model. According to the set dimensions, the finite element waveguides are meshed in three dimensions. The element type after three-dimensional meshing is an eight-node hexahedral element, forming a finite element waveguide model.

[0017] A202: Setting waveguide rod material parameters: Based on the actual indoor parameters, set the mechanical parameters of the waveguide rod to make it have the wave transmission characteristics required by the composite requirements and match the physical performance of the experimental equipment. The mechanical parameters include elastic modulus, density and Poisson's ratio.

[0018] Further, in step A101, the size of the three-dimensional rock sample model is 50mm×50mm×50mm, and in step A201, the size of the finite element waveguide is 2800mm×50mm×50mm. The finite element waveguide is three-dimensionally partitioned using a 280×5×5 mesh.

[0019] Furthermore, the processing method for the F-DEM coupling step includes the following sub-steps:

[0020] B1: Define the boundary of the coupling region: In the contact area between the waveguide rod and the rock sample, identify the boundary surfaces and node sets of the finite element waveguide rod model and the discrete element rock sample model, respectively, to provide a geometric basis for the subsequent interface establishment;

[0021] B2: Establish coupling interface relationship: Bind the boundary elements of the finite element waveguide rod model region to the block nodes of the discrete element rock sample model region to construct a coupling interface that supports the transmission of contact force and velocity;

[0022] B3: Set up the contact mechanics model: Define interface properties to achieve weak frictional contact and simulate the effect of applying a medium to reduce end-face effect to the contact interface in indoor tests;

[0023] B4: Perform static solution: Apply zero-velocity boundary constraints and a gravity field in the unloaded direction of the waveguide rod, and perform static iterative solution to obtain the initial stress equilibrium state of the three-dimensional full-scale numerical model.

[0024] Furthermore, the processing method for the dynamic solution step of the model includes the following sub-steps:

[0025] C1: Reset system state variables: Clear the velocity and displacement after static solution, and retain the initial stress equilibrium state;

[0026] C2: Set loading boundary conditions: On the end face of each waveguide rod away from the rock sample, set viscous and stress boundaries, and simultaneously program the amplitude, frequency, and loading time of the custom dynamic loading waveform. The calculation formula is as follows:

[0027]

[0028] In the formula: Represents amplitude. Represents frequency, Represents time, This represents the loading time, which is the duration of the half-sine wave.

[0029] C3: Conduct the dynamic solution process: Start the dynamic analysis, set the damping coefficient to 0, and record the strain monitoring data in the six-way waveguide rod in real time.

[0030] Furthermore, the processing method for the automated data post-processing step includes the following sub-steps:

[0031] D1: Based on the strain monitoring data, analyze the time-series signal captured on the waveguide rod to identify and distinguish between incident waves and reflected waves;

[0032] D2: Based on the incident wave and the reflected wave, extract dynamic response indicators, including strain rate, dynamic stress, and dynamic balance coefficient.

[0033] D3: Based on the dynamic response index, plot the dynamic stress-strain curve, stress-time curve, and strain-strain curve to analyze the dynamic response characteristics of the rock sample under impact load.

[0034] Furthermore, in step D2, the calculation method for each dynamic response index is as follows:

[0035]

[0036] in, represent Strain rate on the shaft, and These represent the incident wave velocity and the length of the rock sample, respectively. and Represent Strain of the incident wave in the positive and negative directions of the axis and Represent Strain of the reflected wave in the positive and negative directions of the axis represent Strain of the shaft represent Stress on the shaft, and These represent the cross-sectional areas of the waveguide rod and the rock sample, respectively. The elastic modulus of the waveguide rod. represent The balance coefficient of direction, and Represent The stress in the positive and negative directions of the axis, where dt represents the time infinitesimal element.

[0037] This invention also provides a triaxial six-axis impact test simulation system based on F-DEM, used to implement the aforementioned triaxial six-axis impact test simulation method based on F-DEM, comprising:

[0038] Full-scale model framework establishment module: used to establish a three-dimensional full-scale numerical model including the rock sample and the six-way waveguide rod based on the basic parameters of the waveguide rod and the rock sample to be tested in the triaxial six-way dynamic true triaxial electromagnetic Hopkinson rod TEHB test system. The three-dimensional full-scale numerical model includes a discrete element rock sample model and a finite element waveguide rod model.

[0039] The F-DEM coupling module is used to establish the coupling relationship between the discrete element rock sample model and the finite element waveguide rod model at the contact interface based on the actual contact state between the waveguide rod and the rock sample. It also sets the physical parameters of the contact surface and constructs a dynamic coupling interface between the discrete element rock sample model and the finite element waveguide rod model. In the coupling mechanism, the finite element waveguide rod model provides the velocity boundary input, while the discrete element rock sample model provides real-time feedback of the contact force, forming a continuous and consistent waveguide rod-rock sample coupled physical field, realizing the bidirectional transmission of velocity and contact force.

[0040] The model dynamic solution module is used to apply a certain impact load to the loading end of the three-dimensional full-scale numerical model to simulate the propagation process of stress waves in the waveguide rod and rock sample.

[0041] Automated data post-processing module: used to collect strain monitoring data in the waveguide rod, and based on the strain monitoring data, obtain the dynamic response index of the impact test, and quantify the dynamic response characteristics of the rock sample under impact load.

[0042] Compared with existing technologies, the advantages of this invention are as follows: Addressing the challenge of modeling the experimental process of a dynamic true triaxial electromagnetic Hopkinson bar (TEHB) system under triaxial six-directional impact loading conditions, this invention proposes a triaxial six-directional impact test simulation method and system based on F-DEM. This method accurately reconstructs the propagation path and waveform characteristics of stress waves in the waveguide bar and achieves full-scale reproduction of the rock mass response process under multi-axis synchronous loading boundaries. Combining the modeling advantages of finite element method (FEM) for continuous wave processes with the crack capture capabilities of discrete element method (DEM), stable load and velocity transfer is achieved between the rock sample and the waveguide bar by setting coupling interface properties, significantly improving the physical consistency and boundary control accuracy of the overall model response. The system incorporates measured parameters from the TEHB test system for model material parameter inversion, ensuring a high degree of correspondence between the model and the actual device in terms of geometry, materials, and loading methods. Simultaneously, an automated post-processing module is integrated, which can automatically identify incident and reflected waves from strain monitoring data and extract response indicators such as strain rate, dynamic stress, and stress balance coefficient, providing an efficient means for multi-directional response evaluation under dynamic loading conditions. In summary, this invention constructs a triaxial six-axis impact test simulation technology path that combines accuracy, efficiency, and scalability, providing strong support for the study of rock mass dynamics, interpretation of TEHB test data, assessment of engineering impact disturbances, and disaster prevention and control. Attached Figure Description

[0043] To more clearly illustrate the solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a flowchart of the triaxial six-axis impact test simulation method based on F-DEM of the present invention;

[0045] Figure 2 This is a block diagram of the system structure of the present invention;

[0046] Figure 3 This is a schematic diagram illustrating the establishment of the full-size model framework of the present invention;

[0047] Figure 4 A schematic diagram of the structure of a dynamic true triaxial electromagnetic Hopkinson bar (TEHB) test system.

[0048] Figure 5 This is a schematic diagram of the material parameter correction results for the numerical model.

[0049] Figure 6 This is a schematic diagram of the F-DEM coupling structure;

[0050] Figure 7 This is a schematic diagram of the waveform data processing results in the automated data post-processing step.

[0051] Figure 8(a) is a schematic diagram of the calculation results of the mechanical response index in the X-axis direction in the automated data post-processing step;

[0052] Figure 8(b) is a schematic diagram of the calculation results of the mechanical response index in the Y-axis direction in the automated data post-processing step;

[0053] Figure 8(c) is a schematic diagram of the calculation results of the mechanical response index in the Z-axis direction in the automated data post-processing step;

[0054] Figure 9 This is a comparison chart of numerical simulation results and indoor test results in an embodiment of the present invention.

[0055] Figure label:

[0056] 1-X + To the auxiliary slide rail, 2-X + To support the platform, 3-X + 4-X Confining Pressure Loading Actuator + Apply pressure to the end baffle, 5-X + To the confining compression loading frame, 6-X + To the electromagnetic pulse gun, 7-X + Support base for electromagnetic pulse gun, 8-X + To the connecting rod support rod, 9-X + 10-Waveguide rod, 11-Central frame, 12-Central support platform, 13-X - To the waveguide rod, 13-X - To the connecting rod support rod, 14-X - To the confining pressure loading end baffle, 15-X - To the auxiliary slide rail, 16-X - To support platform, 17-X - Electromagnetic pulse gun support base, 18-X - To the electromagnetic pulse gun, 19-X - To the confining compression loading frame, 20-Y + To the auxiliary slide rail, 21-Y + To support platform, 22-Y + To the confining pressure loading end baffle, 23-Y + To the confining compression loading frame, 24-Y + To the waveguide rod, 25-Y + To the connecting rod support rod, 26-Y + Applying confining pressure to the actuator, 27-Y + Electromagnetic pulse gun support base, 28-Y - To the electromagnetic pulse gun, 29-Y -To the auxiliary slide rail, 30-Y - To support platform, 31-Y - To the confining pressure loading end baffle, 32-Y - To the confining compression loading frame, 33-Y - To the electromagnetic pulse gun, 34-Y - Electromagnetic pulse gun support base, 35-Y - To the waveguide rod, 36–Y - To the connecting rod support rod, 37-Z + Confining pressure loading actuator, 38-Z + Vertically fixed and supported platform, 39-Z + Electromagnetic pulse gun support base, 40-Z + To the auxiliary slide rail, 41-Z + To the electromagnetic pulse gun, 42-Z + To the waveguide rod, 43-Z - Vertically fixed and supported platform, 44-Z - Electromagnetic pulse gun support base, 45-Z - To the electromagnetic pulse gun, 46-Z - Towards the waveguide rod, 47 - coupling interface, 48 - waveguide rod. Detailed Implementation

[0057] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and foregoing drawings are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification, claims, or foregoing drawings are used to distinguish different objects, not to describe a particular order.

[0058] In this invention, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment to other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0059] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0060] like Figure 1As shown, the triaxial six-axis impact test simulation method based on F-DEM of the present invention includes the following steps:

[0061] S1: Steps for establishing a full-size model framework.

[0062] This invention establishes a three-dimensional full-scale numerical model containing the rock sample and the waveguide rod in the triaxial six-axis dynamic true triaxial electromagnetic Hopkinson rod (TEHB) test system, based on the basic parameters of the waveguide rod and the rock sample to be tested, as well as the macroscopic mechanical properties of the rock sample. The three-dimensional full-scale numerical model (hereinafter referred to as the numerical model) includes a discrete element rock sample model (DEM model) and a finite element waveguide rod model (FEM model).

[0063] S2: F-DEM coupling steps.

[0064] Based on the actual contact state between the waveguide rod and the rock sample during the experiment, a coupling relationship between the finite element method (FEM) and the discrete element method (DEM) is established at the contact interface between the two, and the physical parameters of the contact surface are set to form a continuous and consistent waveguide rod-rock sample coupled physical field.

[0065] S3: Steps for dynamic solution of the model.

[0066] The characteristics of the input dynamic load in the TEHB test system were reproduced. A custom half-sine function form of impact load was applied to the loading end of the three-dimensional full-scale numerical model to simulate the propagation process of stress wave in the waveguide rod and the specimen, and the response behavior of rock mass under impact was obtained.

[0067] S4: Automated data post-processing steps.

[0068] Strain monitoring data is collected from the waveguide rod. The incident wave and the reflected wave are identified by the algorithm. Key dynamic response indicators such as strain rate, dynamic stress, and dynamic balance coefficient are calculated to quantify the dynamic response characteristics of the rock sample under impact load.

[0069] like Figure 2 As shown, the present invention also provides an F-DEM-based triaxial six-axis impact test simulation system corresponding to the aforementioned F-DEM-based triaxial six-axis impact test simulation method, used to implement the F-DEM-based triaxial six-axis impact test simulation method. The F-DEM-based triaxial six-axis impact test simulation system includes:

[0070] Full-scale model framework construction module: Used to construct a three-dimensional full-scale model including a rock sample and six-axis waveguides. In this example, the rock sample is 50 mm × 50 mm × 50 mm in size, and irregular polyhedral elements are generated using complete triangulation. The rock material parameters are determined through a trial-and-error method. One waveguide is placed in each of the positive and negative X, Y, and Z axes. In this example, the waveguide is 2800 mm × 50 mm × 50 mm in size. Then, eight-node hexahedral elements are used for meshing, and the basic mechanical parameters of the waveguide are set to complete the model construction and material property initialization.

[0071] The F-DEM coupling module is used to establish and define the coupling interface between the FEM and DEM at the contact surface between the waveguide rod and the rock sample. It achieves connections between mesh points, uses a "weak friction contact" coupling interface, applies boundary constraints, performs static solutions, solves for the initial equilibrium state of the system, and verifies the effectiveness of the coupling interface.

[0072] The model dynamic solution module is used to set the dynamic load input side interface as viscous and stress boundaries on the basis of the established coupled model, set strain monitoring points in the waveguide rod, and apply dynamic impact load to simulate the entire process of stress wave propagation and reflection in the waveguide rod and rock sample.

[0073] Automated data post-processing module: Used to automatically process signals collected from strain monitoring points, identify and separate incident and reflected waves, and calculate dynamic response parameters, including strain rate, dynamic stress, dynamic strain and stress balance coefficient, to provide a basis for evaluating the dynamic behavior of rock samples and comparing and analyzing parameters.

[0074] This invention addresses the challenge of modeling the experimental process of a dynamic true triaxial electromagnetic Hopkinson bar (TEHB) system under triaxial six-directional impact loading conditions. It proposes a triaxial six-directional impact test simulation method and system based on F-DEM, which can accurately reconstruct the propagation path and waveform characteristics of stress waves in the waveguide bar and achieve full-scale reproduction of the rock mass response process under multi-axis synchronous loading boundaries. Combining the advantages of finite element method (FEM) in modeling continuous wave processes with the ability of discrete element method (DEM) in crack capture, stable load and velocity transfer is achieved between the rock sample and the waveguide bar by setting coupling interface properties, significantly improving the physical consistency and boundary control accuracy of the overall model response. The system incorporates measured parameters from the TEHB test system for model material parameter inversion, ensuring a high degree of correspondence between the model and the actual device in terms of geometry, materials, and loading methods. Simultaneously, an automated post-processing module is integrated, which can automatically identify incident and reflected waves from strain monitoring data and extract response indicators such as strain rate, dynamic stress, and stress balance coefficient, providing an efficient means for multi-directional response evaluation under dynamic loading conditions. In summary, this invention constructs a triaxial six-axis impact test simulation technology path that combines accuracy, efficiency, and scalability, providing strong support for the study of rock mass dynamics, interpretation of TEHB test data, assessment of engineering impact disturbances, and disaster prevention and control.

[0075] The implementation steps of the present invention will be described in detail below with reference to specific embodiments.

[0076] like Figure 3 As shown, the full-size model framework establishment steps include discrete element rock sample model establishment step A1 and finite element waveguide rod model establishment step A2.

[0077] The processing method for step A1 of establishing the discrete element rock sample model is as follows:

[0078] A101: Constructing Discrete Element Rock Sample Models

[0079] A three-dimensional rock sample model of a cube is constructed, and the three-dimensional rock sample model is divided into several discrete blocks by the complete triangulation method to form a discrete element rock sample model.

[0080] The rock sample used in this example has a size of 50 mm × 50 mm × 50 mm and is divided into 6858 discrete blocks using a complete Delaunay triangulation to simulate the microstructure inside the rock. See details below. Figure 3 The subgraph (b) is shown.

[0081] A102: Setting Model Parameters

[0082] The parameters of the discrete block material (elastic modulus, Poisson's ratio) and contact surface parameters (normal, tangential stiffness, etc.) are set. The indoor uniaxial compression test process is simulated iteratively through a trial-and-error method, and the parameters are repeatedly adjusted until the numerical results match the experimental results. In this example, after selecting the initial mechanical parameters, a numerical uniaxial compression test is carried out, and the results are compared with the measured mechanical parameters in the laboratory. Through repeated adjustments to match the peak strength and failure mode, the model parameters are inverted.

[0083] The processing method for step A2 of the finite element waveguide rod model establishment in this example is as follows:

[0084] A201: Constructing a Finite Element Waveguide Model

[0085] Six symmetrically distributed finite element waveguide rods are arranged along the positive and negative directions of the X, Y, and Z coordinate axes. Each waveguide rod has dimensions of 2800 mm × 50 mm × 50 mm and is three-dimensionally meshed using a 280 mm × 5 mm × 5 mm mesh. The element type is an eight-node hexahedral element, specifically a 10 mm × 10 mm × 10 mm cube, forming a finite element waveguide rod model. This finite element waveguide rod model includes 420,000 elements. Figure 3 The (c) subgraph is shown.

[0086] A202: Set waveguide rod material parameters

[0087] A script for automatically calculating wave velocity was written to set the mechanical parameters of the waveguide rod in combination with actual indoor parameters, so that it has the wave transmission characteristics required for the composite and matches the physical performance of the experimental equipment. The mechanical parameters include elastic modulus, density and Poisson's ratio.

[0088] The waveguide material parameters (elastic modulus, density, and Poisson's ratio) in this example are set based on measured data from the TEHB testing system. To improve parameter accuracy and consistency with wave propagation characteristics, the system integrates an automatic wave velocity calculation script. Based on multiple monitoring points deployed in the waveguide, the wave velocity is calculated by identifying the time difference of waveform propagation and the known point spacing. The results are used to verify the consistency of the waveguide material parameters and the accuracy of the mesh generation.

[0089] This embodiment verifies the effectiveness of the numerical modeling system based on indoor test data, employing the unique triaxial six-axis synchronous impact test of the TEHB testing system for verification and monitoring. The structure of the TEHB testing system is as follows: Figure 4 As shown, the rock sample is placed within the central frame 10 on the central support platform 11. Since this structure is existing, it will not be described in detail here.

[0090] This example is set up as follows: Figure 3Following the numerical model shown, waveguide rods with a length of 2800 mm and a cross-section of 50 mm × 50 mm were arranged in the X, Y, and Z directions. These waveguide rods were made of non-magnetic TC21 titanium alloy. The rock sample dimensions were 50 mm × 50 mm × 50 mm, using yellow sandstone, consistent with the dimensions used in the laboratory physical experiments. The waveguide rods were internally divided into regular hexahedral elements using the finite difference method and were set as fully elastic elements, meaning they did not undergo plastic deformation during impact loading. The rock sample was constructed into multiple irregular block sets using the Delaunay triangular mesh algorithm to accurately simulate its discontinuous fracture characteristics. Regarding material parameters, the waveguide rods were set with an elastic modulus of 110 GPa, a density of 4500 kg / m³, and a Poisson's ratio of 0.33. The uniaxial compressive strength of the rock sample in the numerical model was 61 MPa, and the elastic modulus was 7 GPa. These parameters were determined through repeated comparison with experimental curves using a trial-and-error method, and the calibration results are shown below. Figure 5 As shown.

[0091] The integrated automatic wave velocity calculation script in the numerical model enables accurate identification of the sound velocity in the waveguide rod material. The principle is as follows: multiple monitoring points are set up inside the waveguide rod, strain waveforms are extracted, and the wave velocity value is calculated by identifying the time difference between the waveforms reaching each monitoring point and combining this with the known distance between two monitoring points. This allows for dynamic feedback and model verification of the propagation velocity of the loaded wave.

[0092] like Figure 6 As shown in sub-figure (a), after constructing the full-size model framework, interface coupling is performed on the interaction area between different calculation principles, namely the coupling interface 47 between the waveguide rod 48 and the rock sample, to correctly transmit force and velocity. The specific execution method of the F-DEM coupling step in step S2 is as follows:

[0093] B1: Define the boundary of the coupling region

[0094] In the contact area between the waveguide rod and the rock sample, the boundary surfaces and node sets of the finite element and discrete element regions are identified by the ZONE FACE GROUP and BLOCK GP GROUP commands, respectively, providing a geometric basis for the subsequent interface establishment.

[0095] B2: Establish coupling interface relationships

[0096] By calling the ZONE-BLOCK CREATE command, the boundary elements of the FEM model region are bound to the block nodes of the DEM model region, thus constructing a coupled interface that supports force and velocity transmission.

[0097] B3: Setting the Contact Mechanics Model

[0098] Define interface properties to achieve "weak frictional contact". Set parameters such as internal friction angle, cohesion, and tensile strength of the contact surface to 0 to simulate the effect of applying Vaseline to the contact interface to reduce the end-face effect in the indoor test.

[0099] B4: Perform static solution

[0100] Zero-velocity boundary constraints were applied in the unloaded direction of the waveguide rod using the ZONE FACE APPLY VELOCITY command. Then, the MODEL GRAVITY command was used to apply the gravity field, and the MODEL CYCLE command was executed to perform static iterative solution to obtain the initial stress equilibrium state of the three-dimensional full-scale numerical model and verify the stability and consistency of force and velocity transmission at the coupling interface.

[0101] Static solution results are as follows Figure 6 As shown in subfigure (b), the waveguides along the X, Y, and Z axes form a completely symmetrical displacement field. The waveguide along the Z axis is subject to gravity, and its displacement is slightly larger than that along the X and Y axes. A completely continuous regional displacement field is formed between the waveguides along the X, Y, and Z axes and the rock sample, indicating that the force and velocity at the coupling interface are correctly transmitted.

[0102] After completing the numerical model construction and coupling effectiveness check, the dynamic solution step is performed. In step S3, the specific execution method for dynamic model solution is as follows:

[0103] C1: Reset system state variables

[0104] Remove the velocity and displacement values ​​from the static solution, but retain the initial stress state for subsequent dynamic loading analysis.

[0105] C2: Set load boundary conditions

[0106] A "viscous boundary" and a "stress boundary" are set at the loading end of the waveguide rod away from the rock sample. Simultaneously, the amplitude, frequency, and loading time of the custom dynamic wave pattern are programmed. A strain monitoring point is set in the waveguide rod 1.5m from the end face of the rock sample. Of course, the location and number of strain monitoring points can be arranged according to actual needs.

[0107] C3: Conduct the dynamic solution process

[0108] Initiate dynamic analysis, set the damping coefficient to 0, and record the strain data in the six-way waveguide rod in real time.

[0109] like Figure 7 As shown in Figures 8(a), 8(b), and 8(c), the specific execution method of the automated data post-processing step in step S4 is as follows:

[0110] D1: Signal Decomposition and Identification Processing

[0111] The time-series signals captured on the waveguide are analyzed to automatically distinguish between incident and reflected waves. The incident and reflected waves distinguished by the six-way waveguide are as follows: Figure 7 As shown.

[0112] D2: Extracting dynamic response indicators

[0113] The dynamic equilibrium coefficient, strain rate, stress-strain curve, and other mechanical parameters of the rock specimen under impact loading are calculated using the following formulas:

[0114]

[0115] in, represent Strain rate on the shaft, and These represent the incident wave velocity and the sample length, respectively. and Represent Strain of the incident wave in the positive and negative directions of the axis and Represent Strain of the reflected wave in the positive and negative directions of the axis represent Strain of the shaft represent Stress on the shaft, and These represent the cross-sectional areas of the waveguide rod and the sample, respectively. The elastic modulus of the waveguide rod. represent The balance coefficient of direction, and Represent The stress in the positive and negative directions of the axis, where dt represents the time infinitesimal element.

[0116] The results of the triaxial six-axis synchronous impact test obtained by the present invention through the above steps S1-S4 are compared with the results of the indoor test as follows: Figure 9 As shown, the mechanical response characteristics of the rock in the impact test were accurately reproduced.

[0117] It should be noted that the dynamic stress-strain curves in the laboratory tests exhibit a compaction stage, i.e., a nonlinear ascending range. This is because natural rocks have initial microscopic defects that close under low stress, causing the apparent elastic modulus to increase with stress. Conventional dynamic impact tests calculate the elastic modulus based on the slope of the linear elastic stage. The results obtained from the simulation system differ from those from the laboratory samples by 3.2%. The dynamic response indices calculated by the numerical system differ from the laboratory test results by less than 6%, as shown in Table 1. Furthermore, as... Figure 9As shown in (b) and (c), the numerical system calculation results show that the rock sample after impact was mainly deformed, and the surface was not significantly damaged, which is consistent with the results of the laboratory test.

[0118] Table 1 Comparison of numerical model calculation results and indoor test results

[0119] Feature indicators Indoor test Numerical model error / % Peak stress / MPa 204 194 5.1 Elastic modulus / GPa 24.6 24.2 3.2

[0120] This invention, through a verification example, illustrates the effectiveness and accuracy of the proposed method in simulating the TEHB triaxial six-axis test. Comparative verification shows that the F-DEM-based triaxial six-axis impact test simulation method proposed in this invention can accurately reproduce the loading boundary and wave propagation path in the TEHB test system, and accurately capture the key mechanical response parameters of rock under impact load. This invention achieves a high degree of automation and process integration in key aspects such as waveguide modeling, material parameter setting, and post-processing of monitoring data, significantly improving the efficiency and consistency of model construction and analysis. This method can quickly obtain the impact response characteristics of rock mass under various loading conditions, possessing good versatility and scalability. Especially in situations where experimental conditions are limited, sample processing is difficult, or extreme conditions are difficult to reproduce, it can effectively supplement physical tests, expand the load combination forms, save experimental costs, improve research efficiency, and has high engineering adaptability and application value.

[0121] The specific embodiments described above are preferred embodiments of the present invention and are not intended to limit the specific scope of the present invention. The scope of the present invention includes, but is not limited to, these specific embodiments. All equivalent changes made in accordance with the present invention are within the protection scope of the present invention.

Claims

1. A triaxial six-directional impact test simulation method based on F-DEM, characterized in that, The method comprises the following steps: A full-size model framework establishment step: based on the basic parameters of the waveguide rod in a triaxial six-direction dynamic true triaxial electromagnetic Hopkinson bar (TEHB) test system and a rock sample to be tested, a three-dimensional full-scale numerical model containing the rock sample and the six-direction waveguide rod is established, and the three-dimensional full-scale numerical model comprises a discrete element rock sample model and a finite element waveguide rod model; An F-DEM coupling step: according to the actual contact state between the waveguide rod and the rock sample, a coupling relationship between the discrete element rock sample model and the finite element waveguide rod model is established at the contact interface between the two, and a contact surface physical parameter is set, a dynamic coupling interface between the discrete element rock sample model and the finite element waveguide rod model is constructed, in the coupling mechanism, the finite element waveguide rod model side provides a velocity boundary input, and the discrete element rock sample model side feeds back a contact force in real time, a continuous and consistent waveguide rod-rock sample coupling physical field is formed, and bidirectional transmission of velocity and contact force is realized; A model dynamic solving step: a certain impact load is applied to the loading end of the three-dimensional full-scale numerical model, and the propagation process of stress waves in the waveguide rod and the rock sample is simulated; An automatic data post-processing step: strain monitoring data in the waveguide rod are collected, dynamic response indexes of the impact test are obtained based on the strain monitoring data, and dynamic response characteristics of the rock sample under the impact load are quantified, In the full-size model framework establishment step, a discrete element rock sample model establishment step A1 and a finite element waveguide rod model establishment step A2 are included, The processing method of the discrete element rock sample model establishment step A1 is as follows: A101: constructing a discrete element rock sample model: a three-dimensional rock sample model of a cube is constructed, and the three-dimensional rock sample model is divided into a plurality of discrete blocks by a complete triangular division method to form a discrete element rock sample model; A102: setting model parameters: the block material parameters and the contact surface parameters of the discrete element rock sample model are set, a uniaxial compression test process in a laboratory is iteratively simulated by a trial-and-error method, and the parameters are repeatedly adjusted until the numerical results are consistent with the test results; The processing method of the finite element waveguide rod model establishment step A2 is as follows: A201: constructing a finite element waveguide rod model: six symmetrical square finite element waveguide rods are arranged in the positive and negative directions of the X, Y and Z coordinate axes, the cross section of the finite element waveguide rod is consistent with the size of each face of the three-dimensional rock sample model, the finite element waveguide rod is three-dimensionally divided in a grid division manner according to the set size, the element type after three-dimensional division is an eight-node hexahedral element, and a finite element waveguide rod model is formed; A202: setting waveguide rod material parameters: the mechanical parameters of the waveguide rod are set in combination with the actual parameters in a laboratory, so that the waveguide rod has composite required wave transmission characteristics and matches the physical performance of the experimental equipment, and the mechanical parameters include an elastic modulus, a density and a Poisson's ratio.

2. The F-DEM-based triaxial six-directional impact test simulation method according to claim 1, characterized in that: In step A101, the size of the three-dimensional rock sample model is 50mm*50mm*50mm, and in step A201, the size of the finite element waveguide rod is 2800mm*50mm*50mm, and the finite element waveguide rod is three-dimensionally divided by using a grid division mode of 280*5*5.

3. The F-DEM-based triaxial six-directional impact test simulation method according to claim 1, characterized in that: The processing method of the F-DEM coupling step includes the following sub-steps: B1: defining the coupling region boundary: in the contact region of the waveguide rod and the rock sample, the boundary surface and the node set of the finite element waveguide rod model and the discrete element rock sample model region are respectively identified, to provide a geometric basis for subsequent interface establishment; B2: establishing a coupling interface relationship: binding the boundary element of the finite element waveguide rod model region and the block node of the discrete element rock sample model region, and constructing a coupling interface supporting the transmission of contact force and velocity; B3: setting a contact mechanics model: defining the interface properties, realizing weak friction contact, and simulating the operation effect of smearing a medium for reducing the end face effect in the contact interface in the laboratory test; B4: performing static solving: applying zero velocity boundary constraints and gravity field in the non-loading direction of the waveguide rod, and performing static force iterative solving to obtain the initial stress equilibrium state of the three-dimensional full-scale numerical model.

4. The F-DEM-based triaxial six-directional impact test simulation method according to claim 3, characterized in that: The processing method of the model dynamic solving step includes the following sub-steps: C1: resetting the system state variables: clearing the velocity and displacement after static force solving, and retaining the initial stress equilibrium state; C2: setting the loading boundary condition: setting the viscous boundary and stress boundary on the end face of each waveguide rod away from the rock sample, and programming the amplitude, frequency and loading time of the self-defined dynamic loading waveform, and the waveform calculation formula is as follows: In the formula: represents the amplitude, represents the frequency, represents the time, represents the loading time, i.e. the duration of the half-sine wave; C3: carrying out dynamic solving process: starting the dynamics analysis, setting the damping coefficient to 0, and recording the strain monitoring data in the six-directional waveguide rod in real time.

5. The F-DEM-based triaxial six-directional impact test simulation method according to claim 4, characterized in that: The processing method of the automatic data post-processing step includes the following sub-steps: D1: based on the strain monitoring data, analyzing the time series signals captured on the waveguide rod, and identifying and distinguishing incident waves and reflected waves; D2: based on the incident waves and reflected waves, extracting dynamic response indicators, including strain rate, dynamic stress and dynamic balance coefficient; D3: based on the dynamic response indicators, drawing dynamic stress-strain curves, stress-time curves and strain-strain curves, and analyzing the dynamic response characteristics of the rock sample under impact load.

6. The F-DEM-based triaxial six-directional impact test simulation method according to claim 5, characterized in that: In step D2, the calculation method of each dynamic response indicator is: wherein, represents the strain rate in the and represent the wave velocity of the incident wave and the length of the rock sample, respectively, and represent the strain of the incident wave in the positive and negative directions of the and represent the strain of the reflected wave in the positive and negative directions of the represents the strain in the represents the stress in the and represent the cross-sectional area of the waveguide rod and the rock sample, respectively, represents the elastic modulus of the waveguide rod, represents the equilibrium coefficient in the and represent the stress in the positive and negative directions of the dt represents a time infinitesimal.

7. A F-DEM-based triaxial six-directional impact test simulation system for implementing the F-DEM-based triaxial six-directional impact test simulation method according to any one of claims 1 to 6, characterized in that, including: a full-size model framework establishment module: for establishing a three-dimensional full-scale numerical model containing a rock sample and a six-directional waveguide rod based on the basic parameters of the waveguide rod and the rock sample to be tested in a triaxial six-directional dynamic true triaxial electromagnetic Hopkinson bar (TEHB) test system, the three-dimensional full-scale numerical model including a discrete element rock sample model and a finite element waveguide rod model; The F-DEM coupling module is used for establishing a coupling relationship between the discrete element rock sample model and the finite element waveguide rod model at a contact interface between the waveguide rod and the rock sample according to an actual contact state between the waveguide rod and the rock sample, setting a physical parameter of the contact surface, constructing a dynamic coupling interface between the discrete element rock sample model and the finite element waveguide rod model, providing a velocity boundary input on the side of the finite element waveguide rod model in the coupling mechanism, and feeding back a contact force on the side of the discrete element rock sample model in real time, so that a continuous and consistent waveguide rod-rock sample coupling physical field is formed, and bidirectional transmission of the velocity and the contact force is realized. The model dynamic solving module is used for applying a certain impact load to a loading end of the three-dimensional full-scale numerical model, simulating propagation of a stress wave in the waveguide rod and the rock sample. The automatic data post-processing module is used for collecting strain monitoring data in the waveguide rod, obtaining a dynamic response index of the impact test based on the strain monitoring data, and quantifying dynamic response characteristics of the rock sample under the impact load.

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