A method for determining the reasonable aspect ratio of coal and rock samples in the split-Hopkinson pressure bar test

Abstract

The present invention proposes a method for determining a reasonable aspect ratio of coal and rock samples in a separate Hopkinson pressure bar test, the method comprising the following steps: selecting a sample, and processing the structure, shape and size of the selected sample according to experimental requirements, analyzing based on the number of stress wave propagation times, determining the number of times the stress wave propagates back and forth in the sample during the rising edge stage, analyzing based on dynamic stress balance, synchronously collecting dynamic stress waveform data at both ends of the sample, comparing the overlap of the dynamic stress waveforms at both ends of the sample, using an error evaluation index to quantify the difference in waveform curve overlap, analyzing based on a discrete type of dynamic parameters, and analyzing based on the ease of sample processing. The method for determining a reasonable aspect ratio of coal and rock samples in a separate Hopkinson pressure bar test of the present invention can improve the accuracy and reliability of test data and reduce the difficulty of processing experimental coal samples.

Description

Technical Field

[0001] The invention relates to the technical field of coal rock dynamic mechanical property testing, and in particular to a method for determining a reasonable aspect ratio of a coal rock sample in a split Hopkinson pressure bar test. Background Art

[0002] As an important material dynamic mechanical property test method, the Split Hopkinson Pressure Bar (SHPB) test is widely used in the study of dynamic mechanical properties of coal, rock, concrete, etc. In the SHPB test, the aspect ratio of coal and rock samples is an important factor affecting the test results. However, there is no unified standard for the aspect ratio of coal and rock samples in the SHPB test at home and abroad. The aspect ratio range recommended by the International Society for Rock Mechanics and Engineering is relatively wide, and there is no distinction between coal and rock of different categories or different physical and mechanical properties, which is not conducive to comparative analysis and standardized operations by industry scholars. Summary of the invention

[0003] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, an embodiment of the present invention proposes a method for determining a reasonable aspect ratio of a coal-rock sample in a split-Hopkinson pressure bar test, which can improve the accuracy and reliability of test data and reduce the difficulty of processing experimental coal samples.

[0004] The method for determining the reasonable aspect ratio of a coal-rock sample in a split-Hopkinson pressure bar test according to an embodiment of the present invention comprises the following steps:

[0005] Select samples and process the structure, shape and size of the selected samples according to experimental requirements;

[0006] Based on the number of stress wave propagation, the number of times the stress wave propagates back and forth in the specimen during the rising edge stage is determined;

[0007] Based on the dynamic stress balance analysis, the dynamic stress waveform data at both ends of the specimen are collected synchronously, the coincidence of the dynamic stress waveforms at both ends of the specimen is compared, and the difference in waveform curve coincidence is quantified using the error evaluation index;

[0008] Based on the analysis of the discrete type of dynamic parameters, the impact test of the sample was carried out and the dynamic mechanical parameters were fitted by nonlinear regression method, and the fitting correlation coefficient was calculated.

[0009] For discrete evaluation, the dynamic comprehensive correlation coefficient is proposed , comprehensively considering the fitting effects of different dynamic mechanical parameters, quantitatively evaluating the influence of the aspect ratio of the specimen on the discreteness of the dynamic mechanical parameters, the calculation method is as follows:

[0010]

[0011] Where: is the correlation coefficient for fitting different dynamic mechanical parameters, is the sample size;

[0012] The analysis is based on the ease of sample processing.

[0013] The method for determining the reasonable aspect ratio of coal and rock samples in the split-Hopkinson pressure bar test of the embodiment of the present invention recommends the aspect ratio of samples with smaller discreteness by analyzing the discreteness of dynamic mechanical parameters, thereby improving the regularity of the test results. In addition, by statistically analyzing the processing failure rates of samples with different aspect ratios, the aspect ratio of samples with higher processing success rates is recommended, thereby facilitating the early preparation work of the split-Hopkinson pressure bar test.

[0014] In some embodiments, the impact test on the sample also includes the following steps: selecting multiple groups of dynamic mechanical parameters of the sample for fitting analysis.

[0015] In some embodiments, the dynamic mechanical parameters include: peak stress-average strain rate relationship curve, peak strain-average strain rate relationship curve, maximum strain-average strain rate relationship curve, crushing energy-incident energy relationship curve and crushing energy-average strain rate relationship curve.

[0016] In some embodiments, the analysis based on the number of stress wave propagation times further includes the following steps:

[0017] Calculate the reflection coefficient of the stress wave propagating from the rod to the specimen. That is, according to the law of stress wave propagation, the incident wave, reflected wave, and transmitted wave have the following relationship:

[0018] ;

[0019] ;

[0020] ;

[0021] in, is the stress of the reflected wave, is the stress of the transmitted wave, is the stress of the incident wave, and are the densities of the specimen and the elastic rod, respectively, and are the wave velocities of the specimen and the elastic rod respectively, and the reflection coefficient of the stress wave propagating from the specimen to the rod is , the transmission coefficient is .

[0022] In some embodiments, the method for determining the reasonable aspect ratio of a coal-rock sample in a split-Hopkinson pressure bar test of an embodiment of the present invention further comprises the following steps:

[0023] The incident rod-sample interface and the sample-transmission rod interface are respectively The stress at the moment is expressed as , , then the two end surfaces of the specimen are Relative value of stress difference at time for:

[0024] ,

[0025] in, is the time taken for the stress wave to propagate from the incident end face of the specimen to the other end face, n is the number of times the stress wave propagates back and forth in the specimen for a certain loading time t, and , take an integer.

[0026] In some embodiments, for medium-hard rock, the relative value of the stress difference is within 2% to meet the stress wave propagation number condition; for soft rock and coal, the relative value of the stress difference is within 5% to meet the stress wave propagation number condition.

[0027] In some embodiments, the method for determining the reasonable aspect ratio of a coal-rock sample in a split-Hopkinson pressure bar test of an embodiment of the present invention further comprises the following steps:

[0028] The physical and mechanical parameters of the sample can be obtained through laboratory tests, and the reflection coefficient of the wave propagating from the rod to the sample can be obtained. , and the two end faces of the specimen are Relative value of stress difference at time , get the number of propagation n, and then according to:

[0029]

[0030] In the formula, is the duration of the rising edge of the stress wave, It is the maximum value of the specimen length that satisfies the stress wave propagation number condition.

[0031] In some embodiments, the analysis based on the sample processing difficulty further includes the following steps:

[0032] The processing failure rates of samples with different aspect ratios were statistically analyzed, and the influence of the aspect ratio of the sample on the processing difficulty was analyzed.

[0033] In some embodiments, the method for determining the reasonable aspect ratio of a coal-rock sample in a split-Hopkinson pressure bar test of an embodiment of the present invention further comprises the following steps:

[0034] The qualified number and unqualified reasons of specimens with different aspect ratios in the actual processing process are counted, and the processing unqualified rate of specimens with different aspect ratios is calculated based on the qualified number and the total processing quantity.

[0035] In some embodiments, the method for determining the reasonable aspect ratio of a coal-rock sample in a split-Hopkinson pressure bar test of an embodiment of the present invention further comprises the following steps:

[0036] According to the analysis results, the reasonable aspect ratio of the experimental coal sample in the split Hopkinson pressure bar test is given. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic flow chart of a method for determining a reasonable aspect ratio of a coal-rock sample in a split-Hopkinson pressure bar test according to an embodiment of the present invention.

[0038] Figure 2 It is a stress waveform diagram at both ends of a coal sample with an aspect ratio of 1.0 according to an embodiment of the present invention.

[0039] Figure 3 It is a stress waveform diagram at both ends of a coal sample with an aspect ratio of 0.8 according to an embodiment of the present invention.

[0040] Figure 4 It is a stress waveform diagram at both ends of a coal sample with an aspect ratio of 0.6 according to an embodiment of the present invention.

[0041] Figure 5 It is a stress waveform diagram at both ends of a coal sample with an aspect ratio of 0.5 according to an embodiment of the present invention. DETAILED DESCRIPTION

[0042] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0043] like Figure 1 As shown, the method for determining the reasonable aspect ratio of coal and rock samples in the split-Hopkinson pressure bar test of an embodiment of the present invention includes the following steps: selecting a sample, and processing the structure, shape and size of the selected sample according to experimental requirements.

[0044] It is understood that the selected sample (i.e., the test coal sample) is cut and polished to conform to the shape and size required for the subsequent experiment, that is, the sample can be processed by using cutting and polishing tools (such as a cutter, a grinder, etc.). Preferably, the two ends of the sample are parallel to reduce the end face friction effect in the test.

[0045] Based on the analysis of the stress wave propagation times, the number of times the stress wave propagates back and forth in the specimen during the rising edge stage is determined.

[0046] In some embodiments, performing analysis based on stress wave propagation times further includes the following steps:

[0047] Calculate the reflection coefficient of the stress wave propagating from the rod to the specimen. That is, according to the law of stress wave propagation, the incident wave, reflected wave, and transmitted wave have the following relationship:

[0048] , formula 1;

[0049] , formula 2;

[0050] , formula 3;

[0051] in, is the stress of the reflected wave, is the stress of the transmitted wave, is the stress of the incident wave, and are the densities of the specimen and the elastic rod, respectively, and are the wave velocities of the specimen and the elastic rod respectively, and the reflection coefficient of the stress wave propagating from the specimen to the rod is , the transmission coefficient is .

[0052] In addition, the loading time is Stress wave , using a continuous function Indicates that It can be expressed as follows:

[0053] , formula 4;

[0054] In some embodiments, the method for determining the reasonable aspect ratio of a coal-rock sample in a split-Hopkinson pressure bar test of an embodiment of the present invention further comprises the following steps:

[0055] The incident rod-sample interface and the sample-transmission rod interface are respectively The stress at the moment is expressed as , , then the two end surfaces of the specimen are Relative value of stress difference at time for:

[0056] , formula 5;

[0057] in, is the time taken for the stress wave to propagate from the incident end face of the specimen to the other end face, n is the number of times the stress wave propagates back and forth in the specimen for a certain loading time t, and , take an integer.

[0058] It should be noted that It is the time taken for the stress wave to propagate from the incident end face of the specimen to the other end face, and is calculated as follows:

[0059] , Formula 6;

[0060] in, is the length of the specimen, so the time required for the stress wave to propagate back and forth in the specimen is , then the value of n is calculated based on the number of times the load needs to propagate back and forth in the sample for a certain loading time t.

[0061] Preferably, for medium-hard rock, the relative value of the stress difference is within 2% to meet the stress wave propagation number condition; for soft rock and coal, the relative value of the stress difference is within 5% to meet the stress wave propagation number condition.

[0062] In some embodiments, the method for determining the reasonable aspect ratio of a coal-rock sample in a split-Hopkinson pressure bar test of an embodiment of the present invention further comprises the following steps:

[0063] The physical and mechanical parameters of the sample can be obtained through laboratory tests, and the reflection coefficient of the wave propagating from the rod to the sample can be obtained. , and the two end faces of the specimen are Relative value of stress difference at time , get the number of propagation n, and then according to:

[0064] , Formula 7;

[0065] In the formula, is the duration of the rising edge of the stress wave, It is the maximum value of the specimen length that satisfies the stress wave propagation number condition.

[0066] That is to say, according to the above analysis based on the number of stress wave propagation, the length of the specimen that satisfies the condition of the number of stress wave propagation can be obtained. The maximum value of , that is, the maximum aspect ratio that satisfies this condition.

[0067] Based on the dynamic stress balance analysis, the dynamic stress waveform data at both ends of the specimen are collected synchronously, the coincidence of the dynamic stress waveforms at both ends of the specimen is compared, and the error evaluation index is used to quantify the difference in waveform curve coincidence.

[0068] It is understandable that the acquisition and analysis of waveforms can be achieved relatively easily through existing data analysis software and programming languages. And by synchronously acquiring and comparing the dynamic stress waveforms at both ends, the dynamic mechanical behavior of coal and rock samples can be understood more accurately. In addition, through quantitative indicators, the waveform overlap can be objectively evaluated to reduce the error caused by subjective judgment.

[0069] That is to say, according to the error evaluation index results, the dynamic stress balance degree of specimens with different aspect ratios is analyzed so that the aspect ratio of the specimen with better dynamic stress balance state can be recommended.

[0070] Based on the analysis of the discrete type of dynamic parameters, the impact test of the sample is carried out to fit the dynamic mechanical parameters using methods such as nonlinear regression, and the fitting correlation coefficient is calculated.

[0071] For discrete evaluation, the dynamic comprehensive correlation coefficient is proposed , comprehensively consider the fitting effects of different dynamic mechanical parameters, and quantitatively evaluate the influence of the aspect ratio of the specimen on the discreteness of the dynamic mechanical parameters. The calculation method is as follows:

[0072] , formula 8;

[0073] Where: is the correlation coefficient for fitting different dynamic mechanical parameters, is the sample size.

[0074] Preferably, the impact test on the sample also includes the following steps: selecting multiple groups of dynamic mechanical parameters of the sample for fitting analysis.

[0075] It is understandable that according to calculations, the dynamic comprehensive correlation coefficient The larger the value, the higher the correlation of the test results and the better the regularity of the test data.

[0076] In some embodiments, the dynamic mechanical parameters include: peak stress-average strain rate relationship curve, peak strain-average strain rate relationship curve, maximum strain-average strain rate relationship curve, crushing energy-incident energy relationship curve and crushing energy-average strain rate relationship curve.

[0077] It can be understood that the peak stress-average strain rate relationship curve represents the stress value when the material reaches the peak stress (i.e., maximum stress) at different average strain rates. The peak stress is the maximum stress value that the material can withstand during the loading process, and the average strain rate is the average rate at which the material strain changes over time. This curve can help us understand the effect of strain rate on material strength, that is, whether the material exhibits higher strength when the loading rate is faster.

[0078] The peak strain-average strain rate curve shows the strain value when the material reaches peak stress at different average strain rates. Peak strain refers to the strain when the material reaches the maximum stress. This curve helps to analyze the effect of strain rate on the ductility of the material, that is, how the strain rate changes the material's ability to deform before failure.

[0079] The maximum strain-average strain rate relationship curve describes the maximum strain at material failure at different average strain rates. The maximum strain refers to the strain experienced by the material when it is completely destroyed or fails. Through this curve, the influence of strain rate on the material failure mode and the failure behavior of the material under high-speed loading can be analyzed.

[0080] The crushing energy-incident energy relationship curve shows the relationship between the energy consumed by the material crushing and the incident energy applied to the specimen in the SHPB test or similar impact test. The crushing energy refers to the energy absorbed by the material during the crushing process, while the incident energy is the total energy when the shock wave enters the specimen. This curve can be used to evaluate the energy absorption capacity and impact resistance of the material.

[0081] The relationship between crushing energy consumption and average strain rate describes the energy consumed by the material at different average strain rates. This relationship can reveal the effect of strain rate on the energy absorption efficiency of the material, that is, how the material's ability to absorb and dissipate energy changes at different loading rates.

[0082] That is, these curves are often used to analyze the dynamic mechanical properties of materials, especially their behavior under high-speed impact loading conditions. Through these relationship curves, researchers can better understand and predict how materials will perform in practical applications.

[0083] Analysis based on the processing difficulty of the sample. In some embodiments, analysis based on the processing difficulty of the sample further includes the following steps: counting the processing failure rates of samples with different aspect ratios, and analyzing the influence of the aspect ratio of the sample on the processing difficulty.

[0084] In some embodiments, the method for determining the reasonable aspect ratio of coal and rock samples in the split-Hopkinson pressure bar test of an embodiment of the present invention also includes the following steps: counting the qualified number and unqualified reasons of samples with different aspect ratios during the actual processing process, and calculating the processing unqualified rate of samples with different aspect ratios based on the qualified number and the total processing number.

[0085] In some embodiments, the method for determining the reasonable aspect ratio of coal and rock samples in the split-Hopkinson pressure bar test of an embodiment of the present invention also includes the following steps: based on the analysis results, a reasonable aspect ratio of the experimental coal sample in the split-Hopkinson pressure bar test is given.

[0086] In summary, based on the analysis results of the above four aspects, a reasonable aspect ratio of the split-Hopkinson compression bar test specimen can be given.

[0087] Therefore, the method for determining the reasonable aspect ratio of coal and rock samples in the split-Hopkinson pressure bar test of the embodiment of the present invention recommends the aspect ratio of samples with smaller discreteness by analyzing the discreteness of dynamic mechanical parameters, thereby improving the regularity of the test results. In addition, by counting the processing failure rates of samples with different aspect ratios, the aspect ratio of samples with higher processing success rates is recommended, which facilitates the early preparation work of the split-Hopkinson pressure bar test.

[0088] In addition, the method for determining the reasonable aspect ratio of coal and rock samples in the split-Hopkinson pressure bar test of the embodiment of the present invention also improves the accuracy and repeatability of test data by ensuring that the sample reaches a state of radial stress uniformity and dynamic stress equilibrium before failure.

[0089] like Figure 2-Figure 5 As shown, in some embodiments, the above method is used to determine the reasonable aspect ratio of a coal sample from a mine when conducting a split Hopkinson pressure bar test. The aspect ratios of the compared coal samples are 0.5, 0.6, 0.8, and 1.0. Among them, Figure 2 The stress waveform at both ends of the coal sample with an aspect ratio of 1.0 is shown. Figure 3 The figure shows the stress waveform at both ends of the coal sample with an aspect ratio of 0.8. Figure 3 The figure shows the stress waveform at both ends of the coal sample with an aspect ratio of 0.6. Figure 4 The stress waveform at both ends of the coal sample with an aspect ratio of 0.5 is shown.

[0090] Step 1: Obtain coal samples from the site, obtain various physical and mechanical parameters of the coal samples through laboratory experiments, and substitute them into formula (3) to obtain the reflection coefficient ;Will Substituting into formula (5), the relative value of stress difference is calculated as Minimum number of propagations less than 5% ,Will Substituting into formula (6) we can get the specimen length that satisfies the stress wave propagation times: For a coal sample with a diameter of 50 mm, the reasonable aspect ratio under this condition should be less than 0.82.

[0091] Step 2: Draw the stress waveform at both ends of the sample, introduce the mean absolute error index to quantify the difference in waveform curve overlap, and obtain the mean absolute errors of the stress wave curves at both ends of the coal samples with aspect ratios of 0.5, 0.6, 0.8, and 1.0 as 7.991, 11.557, 18.857, and 27.765, indicating that samples with small aspect ratios are easier to achieve a better dynamic stress equilibrium state. Based on this condition, the order of reasonable aspect ratios of SHPB test coal samples is obtained as follows: .

[0092] Step 3: Carry out impact test on coal samples to obtain the correlation coefficients of dynamic peak stress-average strain rate, dynamic peak strain-average strain rate, dynamic maximum strain-average strain rate, crushing energy-incident energy, and crushing energy-average strain rate fitting. Substitute the coefficients of each aspect ratio into formula (8), and the dynamic comprehensive correlation coefficients of coal samples with aspect ratios of 0.5, 0.6, 0.8, and 1.0 are 0.9377, 0.9069, 0.9446, and 0.8972, respectively. Based on this condition, the order of reasonable aspect ratios of SHPB test coal samples is obtained as follows: .

[0093] Step 4: The unqualified rates of coal samples with aspect ratios of 0.5, 0.6, 0.8, and 1.0 in the actual processing process are 41.2%, 28.6%, 16.7%, and 16.7%, respectively. Based on this condition, the order of reasonable aspect ratios of SHPB test coal samples is obtained as follows: .

[0094] Step 5: Comprehensive analysis. Based on the analysis of stress wave propagation times, the aspect ratio of the specimen must be less than 0.82 to meet the requirements, so it is not recommended. ; Based on the analysis of dynamic stress balance, the error evaluation index of the specimen with an aspect ratio of 1.0 is relatively large, so it is not recommended Based on the discrete analysis of dynamic mechanical parameters, the dynamic comprehensive correlation coefficient of the specimens with aspect ratios of 1.0 and 0.6 is significantly smaller than that of the specimens with aspect ratios of 0.5 and 0.8, so it is not recommended. and Based on the analysis of the difficulty of specimen processing, the specimens with aspect ratios of 0.5 and 0.6 have a low processing success rate, and the reasons for failure are less affected by human factors and equipment. In order to facilitate the preliminary preparation of the SHPB test, it is not recommended. and Based on the above analysis, the reasonable aspect ratio of the SHPB test coal sample is 0.8.

[0095] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0096] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0097] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0098] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0099] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0100] Although the above embodiments have been shown and described, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those of ordinary skill in the art are all within the scope of protection of the present invention.

Claims

1. A method for determining the reasonable aspect ratio of coal and rock samples in a split Hopkinson pressure bar test, characterized in that: The following steps are involved: Select samples and process the structure, shape and size of the selected samples according to experimental requirements; Based on the number of stress wave propagation, the number of times the stress wave propagates back and forth in the specimen during the rising edge stage is determined; Based on the dynamic stress balance analysis, the dynamic stress waveform data at both ends of the specimen are collected synchronously, the coincidence of the dynamic stress waveforms at both ends of the specimen is compared, and the difference in waveform curve coincidence is quantified using the error evaluation index; Based on the analysis of the discrete type of dynamic parameters, the impact test of the sample was carried out and the dynamic mechanical parameters were fitted by nonlinear regression method, and the fitting correlation coefficient was calculated. For discrete evaluation, the dynamic comprehensive correlation coefficient is proposed , comprehensively considering the fitting effects of different dynamic mechanical parameters, quantitatively evaluating the influence of the aspect ratio of the specimen on the discreteness of the dynamic mechanical parameters, the calculation method is as follows: Where: is the correlation coefficient for fitting different dynamic mechanical parameters, is the sample size; The analysis is based on the ease of sample processing.

2. The method for determining the reasonable aspect ratio of coal and rock samples in the split Hopkinson pressure bar test according to claim 1 is characterized in that: The impact test on the sample also includes the following steps: selecting multiple groups of sample dynamic mechanical parameters for fitting analysis.

3. The method for determining the reasonable aspect ratio of coal and rock samples in the split Hopkinson pressure bar test according to claim 2 is characterized in that: The dynamic mechanical parameters include: peak stress-average strain rate relationship curve, peak strain-average strain rate relationship curve, maximum strain-average strain rate relationship curve, crushing energy consumption-incident energy relationship curve and crushing energy consumption-average strain rate relationship curve.

4. The method for determining the reasonable aspect ratio of coal and rock samples in the split Hopkinson pressure bar test according to claim 1 is characterized in that: The analysis based on the number of stress wave propagation times also includes the following steps: Calculate the reflection coefficient of the stress wave propagating from the rod to the specimen. That is, according to the law of stress wave propagation, the incident wave, reflected wave, and transmitted wave have the following relationship: ； ； ； in, is the stress of the reflected wave, is the stress of the transmitted wave, is the stress of the incident wave, and are the densities of the specimen and the elastic rod, respectively, and are the wave velocities of the specimen and the elastic rod respectively, and the reflection coefficient of the stress wave propagating from the specimen to the rod is , the transmission coefficient is .

5. The method for determining the reasonable aspect ratio of coal and rock samples in the split Hopkinson pressure bar test according to claim 4 is characterized in that: The following steps are also included: The incident rod-sample interface and the sample-transmission rod interface are respectively The stress at the moment is expressed as , , then the two end faces of the specimen are Relative value of stress difference at time for: ， in, is the time taken for the stress wave to propagate from the incident end face of the specimen to the other end face, n is the number of times the stress wave propagates back and forth in the specimen for a certain loading time t, and , take an integer.

6. The method for determining the reasonable aspect ratio of coal and rock samples in the split Hopkinson pressure bar test according to claim 5 is characterized in that: For medium-hard rock, the relative value of stress difference is within 2% to meet the stress wave propagation number condition; for soft rock and coal, the relative value of stress difference is within 5% to meet the stress wave propagation number condition.

7. The method for determining the reasonable aspect ratio of coal and rock samples in the split Hopkinson pressure bar test according to claim 6 is characterized in that: The following steps are also included: The physical and mechanical parameters of the sample can be obtained through laboratory tests, and the reflection coefficient of the wave propagating from the rod to the sample can be obtained. , and the two end faces of the specimen are Relative value of stress difference at time , get the number of propagation n, and then according to: In the formula, is the duration of the rising edge of the stress wave, It is the maximum value of the specimen length that satisfies the stress wave propagation number condition.

8. The method for determining the reasonable aspect ratio of coal and rock samples in the split Hopkinson pressure bar test according to claim 1, characterized in that: The analysis based on the sample processing difficulty also includes the following steps: The processing failure rates of samples with different aspect ratios were statistically analyzed, and the influence of the aspect ratio of the sample on the processing difficulty was analyzed.

9. The method for determining the reasonable aspect ratio of coal and rock samples in the split Hopkinson pressure bar test according to claim 8, characterized in that: The following steps are also included: The qualified number and unqualified reasons of specimens with different aspect ratios in the actual processing process are counted, and the processing unqualified rate of specimens with different aspect ratios is calculated based on the qualified number and the total processing quantity.

10. The method for determining the reasonable aspect ratio of coal and rock samples in the split Hopkinson pressure bar test according to any one of claims 1 to 9, characterized in that: The following steps are also included: According to the analysis results, the reasonable aspect ratio of the experimental coal sample in the split Hopkinson pressure bar test is given.

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