Rock impact test method considering cyclic damage history

Abstract

The invention discloses a rock impact test method considering cyclic damage history, which comprises the following steps: (1) under a preset quasi-static graded cyclic loading-unloading path, selecting an impact insertion opportunity according to a dimensionalized cyclic phase; (2) realizing a target dynamic strain rate and peak stress by adopting pulse shaping and energy calibration; (3) carrying out data processing by using a three-wave method and static-dynamic energy decomposition; (4) taking force balance and strain rate stability as receiving criteria; and (5) constructing a unified evaluation framework of the coupling energy index and the damage variable so as to obtain the strength / rigidity degradation, energy dissipation and damage mode evolution law of the material under the combined action of multiple cycle history and transient impact. According to the method, only the process and parameter control are limited, the specific device structure is not limited, and the method has the advantages that the process can be copied, parameters can be traced back, and indexes can be quantified, and is suitable for experimental research and standardized comparison of stability and impact resistance evaluation of underground engineering surrounding rocks.

Description

Technical Field

[0001] This invention belongs to the field of dynamic testing technology of rocks and brittle materials, specifically involving a rock mechanics testing method based on cyclic loading and split Hopkinson bar (SHPB) impact coupling, which can be used for mechanical response research and engineering comparability evaluation of deep rock masses under the combined action of cyclic disturbance and transient impact. Background Technology

[0002] In deep tunnels, mining, and underground energy storage projects, the surrounding rock is subjected to both quasi-static cyclic stress (such as mining-induced stress adjustment and equipment start-up and shutdown) and transient impacts (blasting and rockburst). Existing rock mechanics testing methods do not simultaneously address this, and their main problems include: 1. Cyclic loading tests reveal low-speed hysteresis and cumulative damage, but lack high-speed dynamic response characteristics; 2. Traditional SHPB tests typically only study the "first impact response," neglecting the influence of existing material damage on re-impact sensitivity; 3. Inconsistent test pathways, energy calibration, and data processing across different laboratories, lacking a standardized, repeatable, and comparable process. Therefore, it is necessary to propose a procedural, parameterized, and verifiable testing method that organically couples the cyclic loading history with the SHPB impact process to construct a unified energy and damage evaluation framework. Summary of the Invention

[0003] The present invention aims to provide a repeatable and verifiable SHPB-cyclic loading coupled test method, which can realize impact insertion timing control, energy calibration and damage quantification assessment under a unified phase coordinate, and ensure comparability between different materials and working conditions.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a rock impact testing method considering cyclic damage history, comprising the following steps:

[0005] S0. Sample preparation and calibration: Prepare cylindrical rock samples with parallelism of no more than 0.02 mm at both ends and surface roughness Ra of no more than 0.8 μm, and mark them to ensure consistent clamping orientation.

[0006] S1. Static Load Path Design and Cyclic Phase Definition: Design the quasi-static loading-unloading path and set the cyclic peak stress. Minimum stress And the loading rate, define the cycle phase φ, and load one cycle. Peak → Unload "Closure" normalized to The loading start point φ=0, the cycle peak point φ=0.5, and the unloading end φ=1.0;

[0007] S2. Static load graded cyclic loading and unloading: Perform graded cyclic tests according to the set cyclic peak stress and loading rate, and record the hysteresis curve and stress-strain data;

[0008] S3. Impact Insertion and Pulse Shaping: Pause the static load change at the predetermined cycle phase φ, maintain the current stress level or unload to a safe low load, and perform one or two micro-cycle calibrations to ensure the sample condition is stable. If the calibration result is consistent with the previous cycle... If the difference exceeds 5%, recalibrate.

[0009] After calibration, one or more SHPB impacts are triggered at a predetermined cyclic phase φ, and the waveform is adjusted by a pulse shaping plate and the impact intensity is controlled by energy calibration.

[0010] S4. Data Acquisition and Processing: Acquiring the incident wave Reflected waves Transmitted strain wave The waveform was preserved and the original signal was measured using the three-wave method. , , Dispersion correction was performed to obtain the sample stress. strain rate With strain And energy data;

[0011] S5. Mechanical validity determination: The force balance condition and strain rate stability are used as the acceptance criteria. If the acceptance criteria are met, the next step is executed. Otherwise, return to S3 and repeat the impact test. If the criteria are not met, the impact data is invalid. The parameters need to be adjusted and the test is repeated on a new sample or within the allowable range of the current sample.

[0012] S6. Energy Decomposition and Coupling Calculation: Calculate the static hysteresis energy and dynamic energy components, and define the coupling energy index. To characterize the combined effect of cyclic loading and impact, the sample was reloaded into the static load system and micro-cyclic calibration was performed to obtain the secant modulus after impact. ;

[0013] If | - | / If the percentage is less than 5%, the sample is considered to have minor damage; otherwise, it is considered to have significant damage. To impact the secant modulus of the previous cycle.

[0014] S7. Calculation of damage variables: Define the cumulative damage variable before impact intervention as D, and analyze the cumulative evolution law of damage variable D with cycle number n, as well as the abrupt change characteristics of damage increment ΔD under different impact phases φ; (Note: There is no formula relationship between D and cycle number and impact phase, so it is not quantitatively analyzed here) , The damage variables were measured after microcirculation calibration following the impact.

[0015] S8. Adaptive Iteration: Based on the coupling energy index κ and damage increment ΔD (defined as the difference between the damage variable before and after impact), adjust subsequent cycle or impact parameters: If κ is below the set threshold and damage increment ΔD is small (e.g., ΔD≈0 or in the linear accumulation region, indicating the sample is in a stable stage), increase the impact intensity or adjust to a sensitive phase (e.g., unloading phase); if κ is greater than or equal to the threshold or damage increment ΔD is significant (e.g., a sudden change in crack propagation occurs, indicating the sample has entered an unstable crack propagation period), decrease the impact intensity or postpone the phase. Repeat steps S2 to S7 until the sample fails or the termination condition is met; if If ΔD is within the target range, then maintain the current impact parameters and continue to the next cycle.

[0016] S9. Results Output and Report: Output includes reports on static-dynamic energy decomposition curves, coupling indices, and failure modes.

[0017] As an improvement, the cyclic phase φ is defined by normalization according to a complete load-unload cycle, and during the S3 impact insertion, φ∈{0.5, 0.75, 1.0}.

[0018] As an improvement, the impact strength in S3 is controlled by energy calibration: with the target dynamic strain rate [50,300] With the target peak stress As an indicator, pulse shaping and iterative approximation of driving gas pressure are used until the target is met. ≤10%.

[0019] As an improvement, the energy data in S4 includes static energy data and dynamic energy data, wherein the static energy data is calculated using the hysteresis energy of each cycle:

[0020]

[0021] In the formula, The static energy data is represented by σ, where σ is the axial stress of the specimen and ε is the axial strain of the specimen.

[0022] Volume normalization, dynamic energy The three-wave method is used for calculation:

[0023]

[0024]

[0025] In the formula, Indicates incident energy, Indicates reflected energy, Indicates transmission energy. Let these represent the cross-sectional area, elastic modulus, and elastic wave velocity of the Hopkinson column, respectively. for The abbreviation of .

[0026] As an improvement, the characteristic is that the sample stress in S4 is... strain rate With strain The calculation is as follows:

[0027]

[0028]

[0029]

[0030] As an improvement, the receiving criterion in S5 is to simultaneously satisfy the force balance condition and strain rate stability.

[0031] Force equilibrium conditions:

[0032] Strain rate stability:

[0033]

[0034]

[0035] In the formula, , and and represent the contact surface force at the incident end of the sample, the contact surface force at the transmission end of the sample, and the average force inside the sample at time t, respectively.

[0036] As an improvement, the coupling energy index κ in S5 is:

[0037]

[0038] In the formula, This represents the hysteresis energy of the previous complete quasi-static cycle before the impact intervention. This represents the static hysteresis energy of the previous complete cycle before the impact. "static" refers to the quasi-static loading condition, and "prev" refers to the previous sequence in terms of time.

[0039] As an improvement, the sample damage variable in S6 Defined as the secant modulus degradation rate:

[0040]

[0041] in, The initial secant modulus, Let be the secant modulus of the i-th iteration.

[0042] As an improvement, the dispersion correction in S4 is achieved through frequency domain phase compensation: the phase velocity-frequency relationship obtained from the calibrated impact is used to perform zero-phase deconvolution or bandwidth limiting on the strain signal, and multi-channel synchronization is achieved by aligning the maximum values ​​of cross-correlation.

[0043] Compared with the prior art, the present invention has at least the following beneficial effects:

[0044] 1. This invention solves the problem of timing alignment and quantitative evaluation under multi-field coupling: This invention defines a normalized cyclic phase φ∈[0,1] in step S1, and accurately controls the timing of impact insertion based on this phase in step S3, thus solving the problems of mismatch between dynamic and static loading time scales and high randomness in traditional experiments.

[0045] 2. Achieved unified calibration of dynamic and static energy and damage decoupling: By constructing the coupling energy index κ in step S6, the quasi-static hysteresis energy consumption and dynamic impact energy consumption are compared under the same framework; combined with the micro-circulation calibration in step S7, the damage increment ΔD caused solely by impact can be separated, thereby accurately and quantitatively characterizing the influence of "historical damage" on "transient impact sensitivity".

[0046] 3. An adaptive standardized test procedure was established: A feedback adjustment mechanism based on κ and ΔD was introduced in step S8, enabling test parameters (such as impact pressure and phase) to be dynamically adjusted according to the real-time state of the sample. This not only avoids data loss due to premature sample failure but also prevents insignificant effects due to insufficient impact, ensuring the comparability and repeatability of data from different batches and different laboratories.

[0047] 4. This invention achieves precise spatiotemporal coupling between "quasi-static prestressing" and "transient impact," solving the problems of uncontrollable and unrepeatable test conditions. In existing technologies, the timing of impact insertion is often random, making it impossible to distinguish whether differences in test results stem from the material itself or different loading states. This invention, by establishing normalized cyclic phase coordinates (φ∈[0,1]), precisely defines the specific timing of impact intervention (such as peak stress point, unloading midpoint, etc.). This effect makes the test highly repeatable and comparable, accurately reproducing the specific working conditions of "mining-induced high-stress unloading" and "blasting disturbance" superimposed in deep engineering, providing a standardized operational paradigm for studying the differences in the dynamic response of rocks at different stress history stages.

[0048] 5. A unified "energy-damage" quantitative evaluation system was constructed, solving the problem of decoupling and quantitatively comparing material damage under dynamic and static loads. Traditional methods struggle to compare long-cycle quasi-static hysteresis energy dissipation with millisecond-level dynamic impact energy on the same dimension. This invention achieves a key effect by introducing a "coupled energy index (κ)" and a "micro-circulation calibration" step: it can separate the transient damage increment (ΔD) caused by impact from cumulative fatigue damage. This not only quantifies the degree of degradation of rock mechanical properties by a single impact but also establishes a quantitative mapping relationship (ΔD-κ) between energy input and micro-damage propagation, thus enabling a more sensitive capture of the abrupt damage characteristics of materials before critical failure.

[0049] 6. An adaptive testing process based on real-time feedback was established, solving the problem of premature sample failure or invalid data caused by blind impact. Existing tests often use fixed-parameter impacts, which easily leads to polarized situations such as "excessive impact causing sample crushing" or "insufficient impact resulting in no response." The adaptive iterative mechanism designed in this invention (step S8) dynamically adjusts subsequent parameters based on the coupling index and damage state of the previous cycle. This effect greatly improves the efficiency and completeness of test data, ensuring that full life-cycle evolution data of the sample from "compaction - elasticity - stable crack propagation - unstable failure" can be obtained, avoiding the waste of valuable rock samples due to improper parameter settings.

[0050] 7. It provides end-to-end data quality control and standardized interfaces, improving the reliability and universality of data across different laboratories. Through three-wave dispersion correction, dual acceptance criteria of force balance and strain rate stability (step S5), and clear discard / retest standards, the results eliminate interference from equipment system errors and human error, providing a universal benchmark for test results of different sizes and lithologies. This facilitates the establishment of a large database and industry standards for deep rock mechanical behavior. Attached Figure Description

[0051] Figure 1 This is a simplified flowchart of the method of the present invention.

[0052] Figure 2 A schematic diagram for defining the cyclic phase. Detailed Implementation

[0053] The following examples are only used to illustrate the operability of the method and parameter selection, and do not limit the device structure. The parameters can be adjusted as needed within the stated range.

[0054] S0. Sample Preparation and Calibration: Prepare cylindrical rock samples with a diameter of (50±0.5) mm and an aspect ratio of 0.5~1.0. The parallelism of both end faces should not exceed 0.02 mm, and the surface roughness Ra should not exceed 0.8 μm. Mark the samples to ensure consistent clamping orientation. Establish a baseline along the axial direction and mark the incident end to ensure consistent clamping orientation. Perform initial loading and unloading on a static load machine to obtain the reference secant modulus E0.

[0055] S1. Static Load Path Design and Cyclic Phase Definition: Design the quasi-static loading-unloading path and set the cyclic peak stress. Minimum stress And the loading rate, define the cycle phase φ, and load one cycle. Peak → Unload "Closure" normalized to The loading start point φ=0, the cycle peak point φ=0.5, and the unloading end φ=1.0; the impact insertion phase table is determined according to the test purpose, such as φ=0.5, 0.75, or 1.0.

[0056] S2. Static load graded cyclic loading and unloading: Perform graded cyclic tests according to the set cyclic peak stress and loading rate, and record the hysteresis curve and stress-strain data; at the end of each cycle, calculate the hysteresis energy and secant modulus to characterize the cumulative damage state.

[0057] S3. Impact Insertion and Pulse Shaping: Pause the static load change at the predetermined cycle phase φ, maintain the current stress level or unload to a safe low load, and perform one or two micro-cycle calibrations to ensure the sample condition is stable. If the calibration result is consistent with the previous cycle... If the difference exceeds 5%, recalibrate. If the difference exceeds 5%, extend the static stabilization time or repeat the mechanical break-in until the difference is less than 5% before impact. To ensure comparability, perform micro-cycle calibration with the same amplitude on the static load system before and after each impact. If the secant modulus deviation exceeds 5% after impact, discard the impact data and recalibrate.

[0058] After calibration, one or more SHPB impacts are triggered at a predetermined cycle phase φ. The waveform is adjusted using a pulse shaper, and the impact intensity is controlled by energy scaling. During impact insertion, φ∈{0.5, 0.75, 1.0}. This is to compare the sensitivity during peak loading, the middle of unloading, and the end of the cycle.

[0059] In practice, pre-impact calibration and state freeze are performed first: Static load changes are paused at the planned impact cycle phase φ, maintaining the current stress level or unloading to a safe low load. One or two micro-cycle calibrations (with the same amplitude) are performed to ensure the specimen's state is stable. If the calibration result is consistent with the previous cycle... If the difference exceeds 5%, recalibrate.

[0060] Specifically, the impact intensity is controlled by energy calibration: based on the target dynamic strain rate. [50,300] With the target peak stress As an indicator, pulse shaping and iterative approximation of driving gas pressure are used until the target is met. ≤10%.

[0061] After calibration, impact insertion and pulse shaping are performed: the shaping sheet material and thickness are selected according to the target dynamic strain rate, the driving air pressure is adjusted to trigger the SHPB impact, and the error between the incident wave peak stress and the target value is made not more than 10% by energy calibration method.

[0062] S4. Data Acquisition and Processing: Acquiring the incident wave Reflected waves Transmitted strain wave The waveform was preserved and the original signal was measured using the three-wave method. , , Dispersion correction was performed, and frequency domain analysis was conducted on the acquired signals. Zero-phase compensation and bandwidth limiting were implemented using the phase velocity-frequency relationship. Multi-channel time alignment was achieved by using the maximum cross-correlation value, and the sample stress was calculated. strain rate With strain And energy data:

[0063] .

[0064] Energy data includes static energy data and dynamic energy data, where static energy data is calculated using the hysteresis energy of each cycle:

[0065] Calculate the incident energy separately Reflected energy Transmission energy Hysteresis energy Energy data includes static energy data and dynamic energy data. Static energy data is calculated using the hysteresis energy of each cycle, while dynamic energy data... The three-wave method is used for calculation:

[0066]

[0067]

[0068]

[0069]

[0070] Where σ is the axial stress of the specimen, and ε is the axial strain of the specimen. Let these represent the cross-sectional area, elastic modulus, and elastic wave velocity of the Hopkinson column, respectively. for abbreviation, Indicates the length of the rock sample.

[0071] In this step, dispersion correction is achieved through frequency domain phase compensation: the phase velocity-frequency relationship obtained from the calibrated impact is used to perform zero-phase deconvolution or bandwidth limiting on the strain signal, and multi-channel synchronization is achieved by aligning the maximum values ​​of cross-correlation.

[0072] S5. Mechanical validity determination: Conditions one and two must be satisfied simultaneously.

[0073] Condition 1: The equilibrium condition is that the force difference between the incident and transmitted ends does not exceed 10% of the average force. ;

[0074] Condition 2: The duration of the strain rate stabilization period is ≥ 30% of the total loading time.

[0075] Force balance refers to the approximate numerical equality of the pressures experienced by the incident end (left end) and the transmission end (right end) of the specimen during impact loading. Stress homogeneity assumption: The SHPB theory is based on the assumption that the specimen is a point mass with uniformly distributed internal stress. Only when the forces at both ends of the specimen are equal can we say that the internal stress of the specimen is effective. If the force at the incident end is much greater than the force at the transmitting end ( This indicates that the sample is undergoing violent acceleration (Newton's second law). The data measured at this point includes the inertial force of the sample, not the strength of the material itself. Rock is a brittle material with a relatively low velocity of sound. If the rising edge of the shock wave is too steep (square wave), the front end of the sample may break before the shock wave reaches the end. It is necessary to allow the wave to reflect back and forth multiple times inside the sample to homogenize the stress.

[0076] During the main plastic deformation or failure of the specimen, the rate of deformation (i.e., strain rate) remains constant, rather than fluctuating. Throughout the loading process, there must be a sufficiently long period (at least 30% of the total time) during which the strain rate is essentially stable (the reflected wave is flat). Only when failure occurs within this stable period can the measured peak strength be considered a reliable "constant strain rate strength".

[0077] Force equilibrium conditions:

[0078] Strain rate stability:

[0079] S6. Energy decomposition and coupling calculation: Calculate the static hysteresis energy and dynamic energy components, and define the coupling energy index κ to characterize the combined effect of cyclic loading and impact.

[0080] The sample was reloaded into the static load system and micro-circulation calibration was performed to obtain... like If the damage is minor, it is recorded as minor damage; otherwise, it is recorded as significant damage.

[0081] Define the coupling energy index: .

[0082] : Coupling Energy Index. Meaning: This is a dimensionless index used to characterize the combined effect of "quasi-static cyclic loading history" and "transient impact". Function: As a normalization benchmark.

[0083] When κ is small, it indicates that the energy input by the impact is small relative to the current cumulative damage state (static hysteresis) of the specimen, causing only a slight disturbance; when κ is large, it indicates that the impact energy significantly exceeds the static energy dissipation capacity of the specimen, which may cause severe crack propagation or destruction.

[0084] In step S8 (adaptive iteration), it is used as the basis for determining the intensity of the next impact.

[0085] Dynamic Dissipated Energy. Calculation method: Based on the law of conservation of energy, calculated using three-wave data.

[0086] (That is: incident energy - reflected energy - transmitted energy)

[0087] Physical meaning: Represents the energy absorbed by a rock sample during a single transient impact. This energy is mainly used for the dynamic propagation of microcracks within the rock, the formation of new surfaces, and plastic deformation.

[0088] The static hysteresis energy of the previous complete cycle before impact, calculated by finding the area of ​​the aligning static stress-strain hysteresis curve. Physical meaning: It represents the cumulative damage state or damping characteristics of rock before it is subjected to impact. It reflects the energy dissipation capacity of the material itself in the current cycle stage (such as the compaction stage or crack propagation stage), serving as a "baseline" for assessing the intensity of impact energy.

[0089] Secant modulus before impact, defined as the stiffness (secant modulus) of the specimen measured after one cycle of loading on a static load testing machine before the SHPB dynamic impact. Significance: Represents the healthy state of the specimen immediately before impact (initial baseline).

[0090] Secant modulus after impact, defined as the specimen stiffness (secant modulus) measured after the SHPB dynamic impact is completed and the specimen is returned to the static load tester, and the same cyclic loading is performed again. Meaning: Represents the residual state of the specimen after impact.

[0091] S7. Calculation of damage variables and coupling indices: Static energy is taken as the hysteresis of the first complete cycle before impact. Define damage variables : ;

[0092] Combined with energy indicators Calculate the damage increment after impact .in The cumulative damage variable prior to impact intervention. This represents the damage variable measured after microcirculation calibration following the impact. ΔD and There is a positively correlated coupling relationship (usually exhibiting linear or nonlinear growth), i.e., the unit coupling energy exponent. The input is converted into a corresponding damage increment ΔD, which reflects the impact sensitivity of the material at a specific cycle stage.

[0093] ΔD is the input relative energy intensity, and ΔD is the output structural damage result. The two are positively correlated, and their slope reflects the impact sensitivity of the rock in its current state. Calculating ΔD has the following significance: 1. It separates the damage caused by dynamic impact from the static fatigue history for independent evaluation; 2. It serves as a criterion for the adaptive iteration in step S8, guiding subsequent experimental parameter adjustments and preventing premature sample failure; 3. It quantifies the differences in impact sensitivity under different phases, providing a basis for the safety evaluation of deep engineering projects.

[0094] The cumulative damage variable after impact refers to the total degree of damage measured on the specimen after the impact has occurred.

[0095] Evaluate the coupling effect of the cycle number n and phase φ on κ and D.

[0096] S8. Adaptive Iteration: Adjust subsequent cycle or impact parameters based on the coupling energy index κ and damage increment ΔD. If κ is below the threshold (e.g., 0.2) and the damage increment ΔD is small (indicating the specimen is in a stable stage), the impact intensity can be increased or the phase can be adjusted to a more sensitive region (e.g., the unloading stage). If κ is greater than or equal to the threshold or the damage increment ΔD increases significantly (indicating the specimen has entered the unstable crack propagation stage), the impact intensity is reduced or the phase is delayed to the compaction stage to obtain more complete process data. Repeat steps S2 to S7 until the specimen fails or the termination condition is met.

[0097] S9. Data Statistics and Comparison: Set up multiple sets of comparative experiments with different materials or phases, and statistically analyze the significant differences between the coupling energy index and damage variables. Use analysis of variance or regression methods to verify the regularity.

[0098] S101. Results Reporting and Archiving: Output includes static-dynamic energy decomposition curves; force equilibrium and strain rate stability segments; damage evolution diagrams and failure photographs; three-wave signals and data processing scripts. A standardized data archiving format is established to facilitate comparison and reproduction between different laboratories.

[0099] In practice, the static load rate is 0.1–1 MPa / s, the number of cycles is 5–30, the number of impacts is 1–5, and the interval between any two impacts must span at least one complete static cycle.

[0100] Example 1: Peak phase interpolation, granite baseline

[0101] Material and dimensions: Fine-grained granite, .

[0102] Static load path: Loading / unloading rate Repeat 10 times, then press... There are three levels of classification.

[0103] Impact: At the peak points of the 3rd, 6th, and 9th cycles Insert three impacts, target

[0104] implement:

[0105] S3: Microcirculation calibration before each impact, record.

[0106] S4-S6: Strain rate stabilization is achieved by using shaping plates to control the rising edge. Force balance .

[0107] S7: After impact, return to the stationary microcirculation system and measure... .

[0108] S8: Calculation and .

[0109] Typical results:

[0110] Dynamic energy According to the cycle number Increase and rise:

[0111] and Nearly linear relationship: ;

[0112] The secant modulus degrades significantly after the 9th iteration, entering the strong nonlinear region.

[0113] Example 2: Unloading mid-section insertion, sandstone to north ratio

[0114] Material and dimensions: Medium-grained sandstone .

[0115] Static load path: rate Repeat 12 times.

[0116] Impact: Mid-unloading phase during the 4th and 8th cycles Two impacts were inserted.

[0117] Observation: Same Down, Phase-induced Higher than This indicates that the microcracks in the unloading path are more easily amplified by impact.

[0118] Example 3: Energy Closed-Loop Control

[0119] Objective: To make each impact maintain .

[0120] Strategy: If The next impact will increase the driving strength. ; like , reduce .

[0121] Result: After three iterations It converges to the target range, significantly improving the comparability of input energy across samples.

[0122] Data processing:

[0123] 1. Three-wave method

[0124]

[0125] 2. Energy decomposition

[0126]

[0127] 3. Static hysteresis energy (from the previous complete cycle)

[0128]

[0129] 4. Criteria

[0130] Force balance:

[0131] Strain rate steady-state segment: ; changed to 0.30

[0132] Re-measured stiffness deviation: They are considered comparable in state.

[0133] 5. Dispersion Correction: Perform FFT on the lattice waveform and adjust the phase velocity according to the calibration. Phase compensation is performed to suppress high-frequency noise. Frequency band limiting; finally, the channel clock is aligned with the cross-correlation peak of the force time history at the incident end and the transmitted end.

[0134] This invention presents a rock mechanics testing method based on cyclic loading and split Hopkinson bar (SHPB) impact coupling. This standardized coupled testing method completes a closed-loop process—from phased timing design, energy calibration, three-wave processing, mechanical criterion coupling index, adaptive iteration, and statistical comparison—without limiting the specific device structure. This method can quantitatively characterize the sensitivity of cyclic history to impact response, providing a unified... The scale enables comparison of different materials and working conditions, and ensures data quality and reduces experimental dispersion through receiving criteria. It provides a reproducible and generalizable experimental path and evaluation framework for material behavior under cyclic disturbance + transient impact scenarios in deep engineering.

[0135] Appendix 1: Explanation of Symbols

[0136]

Claims

1. A rock impact testing method considering cyclic damage history, characterized in that, Includes the following steps: S0. Sample preparation and calibration: Prepare cylindrical rock samples with parallelism of no more than 0.02 mm at both ends and surface roughness Ra of no more than 0.8 μm, and mark them to ensure consistent clamping orientation; S1. Static Load Path Design and Cyclic Phase Definition: Design the quasi-static loading-unloading path and set the cyclic peak stress σ. max Minimum stress σ min and loading rate, define the cycle phase Normalize a single "load → peak → unload → closure" process to The loading starting point Cyclic peak point Uninstallation complete S2. Static load graded cyclic loading and unloading: Perform graded cyclic tests according to the set cyclic peak stress and loading rate, and record the hysteresis curve and stress-strain data. S3, Impact Insertion and Pulse Shaping: In a predetermined cycle phase Pause static load changes, maintain the current stress level or unload to a safe low load, perform one or two micro-cycle calibrations to ensure the sample condition is stable. If the calibration result is consistent with the previous cycle E i If the difference exceeds 5%, recalibrate. After calibration, at the predetermined cyclic phase One or more SHPB impacts are triggered, and the waveform is adjusted by a pulse shaping plate and the impact intensity is controlled by energy scaling. S4. Data Acquisition and Processing: Acquiring the incident wave ε i (t), reflected wave ε r (t), transmitted strain wave ε t (t) waveform and save the original signal, then use the three-wave method to determine ε. i (t), ε r (t), ε t (t), dispersion correction is performed to obtain the sample stress σ. s (t), strain rate With strain ε s (t) and energy data; S5. Mechanical validity determination: The force equilibrium condition and strain rate stability are used as acceptance criteria. If the acceptance criteria are met, the next step is continued. If not, the impact data is invalid and the parameters need to be adjusted before retesting a new sample or within the allowable range of the current sample. S6. Energy decomposition and coupling calculation: Calculate the static hysteresis energy and dynamic energy components, and define the coupling energy index κ to characterize the combined effect of cyclic loading and impact. The sample was reloaded into the static load system and micro-circulation calibration was performed to obtain the secant modulus E after impact. sec,post ; If |E sec,post -E sec,pre | / E sec,pre If the percentage is less than 5%, the sample is considered to have minor damage; otherwise, it is considered to have significant damage. (E) sec,pre To impact the secant modulus of the previous cycle; S7. Calculation of Damage Variables: Define the cumulative damage variable before impact intervention as D, and calculate the damage at different impact phases. The abrupt change characteristics of the damage increment ΔD; ΔD = D' – D, where D' is the damage variable measured after microcirculation calibration following the impact; S8. Adaptive Iteration: Adjust subsequent cycle or impact parameters based on the coupling energy index κ and damage increment ΔD: If κ is below the set threshold and the damage increment ΔD is small, increase the impact intensity or adjust to the sensitive phase; if κ is greater than or equal to the threshold or the damage increment ΔD is significant, decrease the impact intensity or postpone the phase; if κ and ΔD are in the target range, maintain the current impact parameters and continue to the next cycle. Repeat steps S2 to S7 until the sample is destroyed or the termination condition is met. S9. Results Output and Report: Output includes reports on static-dynamic energy decomposition curves, coupling indices, and failure modes.

2. The rock impact testing method considering cyclic damage history according to claim 1, characterized in that, The cyclic phase According to the normalized definition of a complete load-unload cycle, during the S3 impact insertion...

3. A rock impact testing method considering cyclic damage history according to claim 1 or 2, characterized in that, The impact strength in S3 is controlled by energy calibration: based on the target dynamic strain rate. With the target peak stress As an indicator, pulse shaping and iterative approximation of driving gas pressure are used until the target is met. and 4. A rock impact testing method considering cyclic damage history according to claim 3, characterized in that, The energy data in S4 includes static energy data and dynamic energy data, wherein the static energy data is calculated using the hysteresis energy of each cycle: IN static =∮σdε In the formula, W static This represents static energy data, where σ is the axial stress of the specimen and ε is the axial strain of the specimen. According to volume normalization, dynamic energy E diss The three-wave method is used for calculation: AND diss =And in -AND ref -AND tra In the formula, E in Indicates incident energy, E ref Represents reflected energy, E tra A represents the transmission energy. b E b c b Let ε represent the cross-sectional area, elastic modulus, and elastic wave velocity of the Hopkinson column, respectively. i,r,t (t) is ε i (t), ε r (t), ε t (t) is an abbreviation.

5. A rock impact testing method considering cyclic damage history according to claim 4, characterized in that, The stress σ of the sample in S4 s (t), strain rate With strain ε s The calculation of (t) is as follows: ε s (t)=∫ε s (t)dt。 6. A rock impact testing method considering cyclic damage history according to claim 5, characterized in that, The acceptance criterion in S5 is that both the force balance condition and strain rate stability are satisfied simultaneously. Force equilibrium conditions: Strain rate stability: F in (t)=(E b A b )(ε i (t)-ε r (t)) F out (t)=(E b A b )ε t (t) In the formula, F in (t), F out (t) and F avg (t) and represent the contact surface force at the incident end of the sample, the contact surface force at the transmission end of the sample, and the average force inside the sample at time t, respectively.

7. A rock impact testing method considering cyclic damage history according to claim 6, characterized in that, The coupling energy index κ in S5 is: k=E diss / W static,prev In the formula, W prev W represents the hysteresis energy of the previous complete quasi-static cycle before the impact intervention. static,prev This represents the static hysteresis energy of the previous complete cycle before the impact.

8. A rock impact testing method considering cyclic damage history according to claim 7, characterized in that, In S6, the sample damage variable D is defined as the secant modulus degradation rate: Where E0 is the initial secant modulus, E i Let be the secant modulus of the i-th iteration.

9. A rock impact testing method considering cyclic damage history according to claim 3, characterized in that, In S4, dispersion correction is achieved through frequency domain phase compensation: the phase velocity-frequency relationship obtained from the calibrated impact is used to perform zero-phase deconvolution or bandwidth limiting on the strain signal, and multi-channel synchronization is achieved by aligning the maximum values ​​of cross-correlation.

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