Change In Loading Rate Research Articles

Simulation of lunar soil compressive strength performance test based on grey correlation analysis

Detecting water ice in the permanent shadow area of the lunar south pole is an important task of China's Chang'e-7. For this purpose, a simulation study was carried out under the earth environment, and a test sample of polar water-containing simulated lunar soil was prepared. The mechanical properties of the lunar soil simulant were tested under ultra-low temperature conditions, and the changes in water content, relative density, temperature, loading rate, and base material ratio with compressive strength were analyzed. The results show that the compressive strength of the frozen lunar soil simulant increases with the increase of water content, increases with the increase of density, and increases with the decrease of temperature. It is less affected by the change of loading rate. The order of compressive strength affected by different base material ratios is: 100%anorthosite, <90%anorthosite, +10%basalt <70%, +30%anorthosite <100%, basalt, lunar soil simulant. Finally, the correlation between the basic physical properties of lunar soil simulant such as water content, relative density, temperature, loading rate, and ratio and compressive strength is explored through grey correlation analysis. The correlation order is: water content> density> temperature> ratio> loading rate. This paper prepared and tested the mechanical properties of hydrated lunar soil, and proposed a more systematic and standardized implementation plan. It serves as the basis for studying the properties of hydrated lunar soil in the polar region, and provides a theoretical basis and reference for subsequent lunar soil simulation research.

Non-redundant metagenome-assembled genomes of activated sludge reactors at different disturbances and scales

Metagenome-assembled genomes (MAGs) are microbial genomes reconstructed from metagenomic data and can be assigned to known taxa or lead to uncovering novel ones. MAGs can provide insights into how microbes interact with the environment. Here, we performed genome-resolved metagenomics on sequencing data from four studies using sequencing batch reactors at microcosm (~25 mL) and mesocosm (~4 L) scales inoculated with sludge from full-scale wastewater treatment plants. These studies investigated how microbial communities in such plants respond to two environmental disturbances: the presence of toxic 3-chloroaniline and changes in organic loading rate. We report 839 non-redundant MAGs with at least 50% completeness and 10% contamination (MIMAG medium-quality criteria). From these, 399 are of putative high-quality, while sixty-seven meet the MIMAG high-quality criteria. MAGs in this catalogue represent the microbial communities in sixty-eight laboratory-scale reactors used for the disturbance experiments, and in the full-scale wastewater treatment plant which provided the source sludge. This dataset can aid meta-studies aimed at understanding the responses of microbial communities to disturbances, particularly as ecosystems confront rapid environmental changes.

Effect of temperature on damage mechanism and fracture behavior of LiH ceramic under 3-point bending at different loading rates

The damage mechanism and fracture behavior of lithium hydride (LiH) ceramic are key to its design and application at elevated temperature in nuclear engineering. LiH ceramic is tested in a loading rate range of 0.001–2 mm/min from room temperature (RT) to 600 °C using digital image correlation (DIC) method combined with high-speed photography. At low temperature (up to 300 °C), LiH ceramic undergoes brittle fracture. At high temperature (up to 600 °C), LiH ceramic undergoes creep fracture at low loading rate and ductile fracture at high loading rate. The main crack growth rate of LiH ceramic with ductile fracture is higher than that of LiH ceramic with creep fracture, and is lower than that of LiH ceramic with brittle fracture. With the change of temperature and loading rate, three damage mechanisms, fatigue damage corresponding to SCG of inherent flaws, creep damage represented by creep microcracks and ductile damage symbolled by dimples, occur simultaneously and show competitive characteristics, one of which dominates the failure. At low loading rate, there is a transition of the dominant damage mechanism from fatigue to creep damage with increasing temperature. At high temperature, the dominant damage mechanism changes from creep to ductile damage with the increase of loading rate.

DUAL MODE FRACTURE BASED ON LOADING RATE DURING SLIDING INDENTATION OF Si–C–N HARD COATINGS ON 304SS SUBSTRATES

Scratch tests were performed on thermal-resistant hard Si–C–N coatings deposited on steel (SS) 304, by radio frequency (RF) magnetron sputtering. The abrasion and wear properties were studied by analyzing the changing failure complexion inside the scratch showing a mixture of ductile and brittle properties. The change in loading rate caused noticeable changes in the failure mode. The plasticity was found to have a peripheral domination initially with an increase in load but was replaced by brittle failure on increasing the loading rate. The work of adhesion and wear rate were determined.

How to walk to reduce footstep noise in multi-story residential buildings

Loud footsteps from upstairs cause disturbance to downstairs neighbours in multi-story residential buildings. In this experiment, we examined how participants walk when asked to walk quietly and evaluated the efficiency of their quiet walking patterns. Changes in vertical impact loading rates during the early stance phase, walking speed, and lower limb muscle activity when asked to walk quietly were evaluated from twenty-six young participants. Study data show that participants who struck the ground with the rearfoot reduced the impact loading rate by 44.6% with 29.3% slower walking speed than normal walking. Those who struck with the fore- or mid-foot reduced the impact loading by 69.2% with a 23.4% decrease in speed. Quiet walking with the non-rearfoot strike pattern reduced the impact loading by 48.7%, even when asked to walk as fast as normal walking. The results support the non-rearfoot strike pattern as an efficient walking strategy for lowering footstep impact. Practitioner summary: Data of this study show that voluntary gait alteration, such as adopting a non-rearfoot strike pattern, can reduce footstep impact. The study results propose that implementing such changes could be beneficial in addressing floor noise issues of multi-story residential buildings. Abbreviations: RFS: Rearfoot strike; NRFS: non-rearfoot strike; COP: Center of pressure; NW: Normal walking; QWs: Quiet walking at a preferred slower speed; QWn: Quiet walking at the speed of normal walking; EMG: Electromyography; BW: Body weight; iNEMG: integrated normalized EMG.

Energy Behavior of Sandstone Containing Weak Filling Joints with Multiple Angles under Dynamic Splitting Loads

The impact of weak filling joints with multiple angles on the energy dissipation mechanism is significant for surrounding rock engineering to prevent and mitigate disasters. In the present study, the sandstone samples containing weak filling joints were prefabricated, and dynamic splitting tests were conducted under three nominal loading rates with a modified Split Hopkinson Pressure Bar system. The effects of nominal loading rates and joint angles on time-based curves and energy-based curves were investigated systematically. The test results indicated that the nominal loading rate and joint angle had remarkable influences on energy dissipation characteristics. The sample containing a larger joint angle preferred brittle failure, whereas the sample with a smaller joint angle failed with a plastic feature. Moreover, the reflection energy decreased as the joint angle increased, which was opposite to the evolution tendencies of transmission energy and absorption energy. The transmission energy and absorption energy had different sensitivities to changes in joint angle and nominal loading rate. The exponential function could excellently describe the dependence of transmission energy, reflection energy, and absorption energy on joint angles. With the incremental joint angle, the energy reflection ratio had a contrary tendency to the energy transmission ratio.

A refined first-order shear deformation theory for large dynamic and static deflection investigations of abruptly/harmonically pressurized/blasted incompressible circular hyperelastic plates

In this paper, nonlinear large-deformation dynamic and static responses of the suddenly and harmonically pressurized or blasted compliant incompressible hyperelastic circular plates are investigated through the development of a novel enhanced circular plate theory that in contrast to the available plate theories, utilizes transverse normal strains whose order is much higher than those of the in-plane strains. For this reason, no shear correction factor is needed for the new plate theory. The deformation gradient and Green's strain tensors are first determined based on the first-order shear deformation plate theory as predictors and then, corrected by simultaneously including the transverse compliance and volume conservation concepts in the neo-Hookean framework of hyperelasticity. The equations of motion are obtained using Hamilton's principle. The resulting highly nonlinear equations that include both large deformation and constitutive nonlinearities are solved by a hybrid iterative/updating technique that utilizes a combination of the differential quadrature (DQ) spatial-discretization and Newmark's time-marching methods, after an exhaustive order analysis for the identification of the extremely small terms. The effects of the changes in geometric parameters, material properties, and loading rate and type are investigated on the dynamic lateral deflection of the plate and the approximate fundamental natural frequency. Results reveal that the contribution of the higher vibration modes in the responses is much more remarkable in the high-rate and high-frequency loadings. Furthermore, the deformed shape of the plate that indicates the superimposed effects of the higher vibration modes is plotted for successive time instants.

Hydrodynamic behavior and start-up performance in a periodic anaerobic baffled reactor treating traditional Chinese medicine wastewater for different operation patterns

In order to explore the effect of operation pattern on performance, hydrodynamic behavior and start-up performance including molecular weight distribution (MWD) of soluble organic compounds in a periodic anaerobic baffled reactor (PABR) handling traditional Chinese medicine (TCM) wastewater. Residence time distribution test with tap water in the clean PABR was carried out at a certain hydraulic residence time of 48 h in experiments and in computational fluid dynamics (CFD) simulations, both of which were in good agreement for the ‘every second’ (switching period T = 48 h), the ‘clockwise sequential’ (T = 96 h), and the ‘no switching’ (T = ∞) operation pattern. The CFD model output visualized the hydrodynamic-mass transport, which heavily influenced by operation pattern, successfully inside a PABR. The PABRs run in those three operation patterns were subjected to three successive step changes in average organic loading rate at about 1, 2, 4 and 6 kg COD m−3 d−1 for 12, 24, 24 and 6 d, respectively. Pollutants in the TCM wastewater had the longest time to be digested and degraded within PABR run in the ‘every second’ operation pattern, resulting in a most stable performance among the three. Performance of PABR was consistent with the variation in MWD of soluble organic compounds no matter what the operation pattern was. High- MW species (93–130 kDa) broke down into simpler intermediate- MW solutes (7–56 kDa) by the metabolism of anaerobic flocs sludge mostly in the compartment which contributed most to the total COD removal of PABR. Then, intermediate- MW solutes were mineralized step by step into low- MW solutes (100 Da) and biogas in the follow-up compartments in the sequence of flow pattern.

Influence of loading rates and feeding conditions on hybrid constructed wetlands integrated with microbial fuel cells

The present study had as objective to evaluate the influence of different operation conditions on two treatment systems composed of anerobic biofilter (AF) and hybrid constructed wetlands (CWs). Both treatment lines had as the first treatment stages an 1450 L AF unit and a CW designed as a Floating Treatment Wetland. Then, a pump directed half of the wastewater flow for each of the treatment lines. One of the lines was composed of a Vertical Flow CW incorporated with microbial fuel cells (CW-MFC), called Configuration 1 (C1), whereas the other line consisted of a Vertical Flow CW (VFCW) and a Horizontal Flow CW (HFCW), named Configuration 2 (C2). The treatment system was fed with wastewater generated in a university campus and monitored for 13 months, with three operation conditions tested: 3 pulses per day with 50 L each (20.5 L/m2day); 4 pulses with 75 L each (41 L/m2day) and 6 pulses with 75 L each (61.6 L/m2day). In addition, the potential bioenergy generated was monitored. For the last operation condition, C1 efficiently reduced BOD5 (88.7%) and turbidity (84.4%). On the other hand, for the nutrients the treatment efficiencies were lower, with 40.3% (TP) and 46.6% (N−NH3). Overall, similar results were obtained with the C2, with mean removal efficiencies of BOD5 (87.3%), turbidity (93.1%), and lower TP (10.4%) reduction. The treatment performance presented similar tendencies even with the changes in loading rates and in hydraulic retention times. Regarding the voltage monitoring, a peak of 687 mV was obtained considering a mean loading rate of 15.6 gCOD/m2day, whereas the maximum power density was 0.25 mW/m. Future research should focus on reducing the internal resistance of the CW system, thus increasing the bioelectricity generated and in treating wastewater with higher organic matter content.

Process stability in expanded granular sludge bed bioreactors enhances resistance to organic load shocks

Environmental perturbations such as changes in organic loading rate (OLR) can have deleterious effects on the anaerobic digestion process, leading to VFA accumulation and process failure. However, the operational history of a reactor, such as prior exposure to VFA build up, can impact a reactor's resistance to shock loads. In the present study, the effects of long term (>100 days) bioreactor (un)stability on OLR shock resistance were assessed. Three 4 L EGSB bioreactors were subjected to varying levels of process stability. Operational conditions such as OLR, temperature and pH were maintained stable in R1; R2 was subjected to a series of minor OLR perturbations and R3 was subjected to a series of non-OLR perturbations, including ammonium, temperature, pH and sulfide. The effect of these different operational histories on each reactor's resistance to a sudden 8-fold increase in OLR were assessed by monitoring COD removal efficiency and biogas production. The microbial communities of each reactor were monitored using 16S rRNA gene sequencing to understand the relationship between microbial diversity and reactor stability. It was determined that the stable (un-perturbed) reactor performed best in terms of its resistance to a large OLR shock, despite its lower microbial community diversity.

Study on Crack Propagation of Rock Bridge in Rock-like Material with Fractures under Compression Loading with Sudden Change Rate

In order to study the influence of sudden change of loading rate on crack propagation and failure mode of rock bridge of fractured rock mass, the specimens used in this paper were rock-like materials containing two prefabricated fractures. The mechanical properties and the failure mode of the specimens under different constant loading rates and sudden changes in loading rate were tested. The photographic monitoring and acoustic emission were carried out at the same time. The results show that: (1) In the process of sudden change loading, the specimen shows the characteristics of approximate elastic deformation, and the stress-strain curve after sudden loading is similar to the corresponding stress-strain curve at the corresponding constant loading rate. (2) Combined with acoustic emission detection, it is found that when the loading rate is not much different before the mutation, the loading rates is the same after the mutation and the stress-strain curve of the specimen is similar. In the low-speed loading stage, the acoustic emission count is generally low, while in the high-speed loading stage, the acoustic emission count is generally high. The sudden change from low-speed loading to high-speed loading easily induces stress drop, resulting in crack generation and increase of acoustic emission count. (3) The rate of the specimen during the crack development period plays a decisive role in the failure mode of the specimen. Before the sudden change of loading rate, the low-speed loading within a certain range has little effect on the specimen. When the high-speed loading is carried out when the stress is low in the early stage of the mutation, the acoustic emission count of the specimen is high, which will cause some damage inside the specimen. As a result, even if the rate is the same after the mutation, the final peak stress and failure mode may be different.

Coupled thermo‐viscoplastic fracture model for ductile‐brittle failure of amorphous glassy polymers with phase‐field approach

AbstractAmorphous glassy polymers have an extensive use in the industrial sectors including micro‐electronics, medical industry and aerospace, therefore their design and usage have become a significant task nowadays. The fracture response of these polymers may vary from ductile to brittle depending on several factors such as entanglement density, temperature level and external loading rate. The ductile response is driven by diffuse shear zones exhibiting volume–preserving inelastic deformations while the brittle response is manifested by very small crack‐like defects composed of a sequence of fibrillar bridges separated by micro‐voids, thereby connotating void formation consisting of nucleation and propagation steps. The presents study is focused on the description of shear yielding and crazing phenomenon in terms of their respective evolution equations. In addition, an extension towards the modelling of the fracture is employed via the crack phase–field approach, considering ductile and brittle failure simultaneously. This is provided by the novel failure criterion that features a critical amount of plastic strain and void volume fraction. Since the proposed approach unitedly models the macroscopic crack initiation and propagation for ductile or brittle failure, it is asserted to be more physically grounded compared to present models in the literature. Constitutive formulations for shear yielding, crazing, and void volume fraction are derived with their specific forms starting with the local and conductive component of the dissipation inequality. The performance of model is evaluated after developing the local and global Newton–type update algorithms for the dissipative internal and primary field variables, respectively and it has been analysed by fitting of several experimental data of homogeneous and inhomogeneous tests. The findings reveal the remarkable temperature dependency on the type of failure as well as the interaction between loading rate and temperature change owing to dissipative heating in the solid.

Analysis of sensitivity of elastic characteristics of unidirectional carbon fiber specimens with thermoplastic matrix to loading rate at high temperature

The problem of assessing the sensitivity of unidirectional carbon fiber reinforced plastics to loading rate is considered. As a rule, when the loading rate changes, the stress-strain curves for unidirectional CFRP specimens under loading at different off-axis angles change due to the rheological properties and physical nonlinearity. An attempt is made to reveal the degree of anisotropy sensitivity of a unidirectional carbon fiber reinforced plastic with thermoplastic matrix at an elevated temperature in the range of changes in the loading rate by two orders of magnitude both in stress and in strain.

Loading Rate and Temperature Interaction Effects on the Mode I Fracture Response of a Ductile Polyurethane Adhesive Used in the Automotive Industry.

Due to their high elongation at failure and damping capacity, polyurethanes are one of the main types of adhesives used in automotive structures. However, despite the wide range of applications of adhesives, their fracture mechanics behavior is still poorly studied in the literature, especially when both the loading rate and ambient temperature change. Accordingly, the main aim of the current work is to deal with the research gap. In the current research, mode I fracture energy of a ductile polyurethane adhesive with adaptive properties for its industrial application is determined at different test speeds and temperatures. Tests were done at quasi-static, intermediate, and high-speed levels and each at three different temperatures, including low, high, and room temperature. Mode I fracture toughness was determined using DCB tests. Increasing the loading rate from quasi-static to 6000 mm/min was found to significantly increase the maximum strength of the tested DCBs (from 1770 N to about 4180 N). The greatest sensitivity to the loading rate was observed for the DCBs tested at room temperature, where the fracture energy increased by a factor of 3.5 from quasi-static (0.2 mm/min) to a high loading rate (6000 mm/min). The stiffness analysis of the DCB samples showed that the transition from below the Tg to room temperature decreases the bond stiffness by about 60%, while a further temperature increase (from 23 °C to 60 °C) has no significant effect on this parameter. Since polyurethane-bonded joints often experience a wide range of temperatures and loading rates in service, the obtained results can be used to design these joints more securely against such loading/environmental conditions.

Study on K0 consolidation triaxial test of remolded saturated loess

Experimental study on K0 consolidation test of remolded saturated loess is carried out by GDS static triaxial apparatus. The deformation characteristics of specimens, under different loading rates, are discussed and the test results are compared and analyzed. The results show that the changing trend of the curve modeling the relation between the axial stress and the axial strain of the sample is consistent even with the change in loading rates. Thus, under this same context, the larger the loading rate is, the greater the axial strain will be, when the axial stress reaches the same value. Moreover, under different loading rates, the trend of the relationship curve between the lateral pressure coefficient K0 and the axial strain of the soil sample is basically consistent. The stability value of the lateral pressure coefficient K0 of the sample varies with the loading rate, but only within a fixed range.

Characteristic Analysis on Temporal Evolution of Granulation in a Modified Anaerobic Digestion System

In the present study, the surface morphology, particle size distribution, sedimentation performance, and fractal characteristics of sludge flocs in a modified anaerobic baffled reactor (mABR) during start-up were analyzed by digital image analysis technology. The results showed that the special structure of mABR enabled successful start-up and granular sludge formation in a relatively short time. After the granular sludge was mature, the COD removal rate could quickly recover to the level before the change in organic loading rates (OLRs) within just six days, increasing from the lowest value of 76.8% to 80.2%, which indicated that the granular sludge could maintain a relatively stable micro-environment and make the metabolic process continue when the influent conditions changed suddenly. It was expected that this paper would be helpful for researchers to further develop a unified theory for anaerobic granulation and technology for expediting the formation of mABR granules.

Responsiveness of an activity tracker as a measurement tool in a knee osteoarthritis clinical trial (ACTIVe-OA study).

In osteoarthritis (OA) clinical trials, reliable and responsive outcome measures to document physical and functional improvements are limited. This study aimed to assess whether the use of an activity tracker in an OA clinical trial is a responsive measurement tool. Secondary objectives assessed feasibility and validity. We recruited 65 participants in a prospective cohort study nested in a placebo-controlled clinical trial of platelet-rich plasma injection in knee OA. Participants wore an activity tracker (Fitbit Flex 2), and a smartphone was preloaded with a mobile application (OApp) designed to monitor load rates as a surrogate of knee loading. Participants used the systems for 7 days at baseline and for 7 days before the 2-month follow-up assessment. Effect size (ES) and standardised response mean (SRM) were calculated for change in step count and knee loading rate and regularly used knee OA outcome measures. Correlation coefficients (r) were calculated to examine the strength of the association between outcome measures. . Step count showed a trivial ES and SRM and mean knee loading rate measurements a moderate ES and SRM. We found a weak but significant correlation between change in mean steps per day and global improvement overall (r=0.28) and Western Ontario and McMaster Universities Osteoarthritis Index function (r=-0.28). Compliance was high with the activity trackers. Despite good feasibility, this study did not show significant responsiveness or validity of the activity trackers as compared with currently recommended outcome measures in OA clinical trials. The main challenge is the lack of a gold standard outcome measure to validate against, and because of the complex interplay between pain and measured function, a lack of correlation does not necessarily represent a failed validation in this context. ACTRN12617000853347. This trial is a substudy of the "Platelet-rich plasma as a symptom-and disease-modifying treatment for knee osteoarthritis - the RESTORE trial".

Efficient nitrogen removal from onsite wastewater by a novel continuous flow biofilter

Soil-based passive biofiltration system is an economically feasible technology for nitrogen removal from onsite wastewater. However, the conventional design requires a large system footprint with limited treatment capacity. In this study, a novel continuous flow biofilter (CFB) with adjustable recirculation and continuous flow pattern was developed for onsite wastewater treatment with a small footprint. Efficient total nitrogen removal (80.1–97.5%) was observed at various hydraulic loadings (0.03–0.12 m3 m−2 d−1), nitrogen loadings (1.1–8.6 g N m−2 d−1) and recycle ratios (2–3) when treating septic tank effluent (STE), with low effluent TN (0.7–13.6 mg N L−1). Nitrous oxide was observed in the denitrification effluent indicating incomplete denitrification at elevated dissolved oxygen levels (3.3–5.8 mg L−1). Nitrogen removal rate (2.9–7.0 g N m−2 d−1) and ammonium removal rate (2.4–7.2 g N m−2 d−1) were positively correlated with nitrogen loadings increase (1.1–8.6 g N m−2 d−1) but were not significantly impacted by the hydraulic loading rate change (0.08–0.12 m3 m−2 d−1). The total biomass abundance and nitrifying microorganisms decreased significantly as the nitrification columns depth increased, while homogeneous microbial distribution was observed in the denitrification columns. The abundance of ammonium oxidizing archaea (AOA) increased significantly at increased hydraulic and nitrogen loading rate, while the ammonium oxidizing bacteria (AOB) abundance remained steady. The abundance of functional genes involved in denitrification process (nirS, nirK and nosZ) responded differently when hydraulic and nitrogen loading rate changes. Collectively, this study suggested the CFB could efficiently remove nitrogen from onsite wastewater with fluctuating influent compositions and various hydraulic loadings.

Multiday load carriage decreases ability to mitigate ground reaction force through reduction of ankle torque production

The aim of this study was to examine the impact of backpack load carriage on lower limb strength and loading rate change in a cohort that match military recruit profiles. Twenty-six participants walked on a treadmill either carrying a military load carriage system (32 kg) or unloaded for 2 h on two consecutive days. Participants ground reaction forces and strength measures were assessed using a force platform and dynamometry, respectively. Testing included assessments before and after treadmill walking on days one and two, and 24 h following day 2. When assessed by mixed methods ANOVA (alpha: 0.05) statistically significant interaction effects were observed for loading peak (p = 0.031), loading rate (p = 0.035) and plantarflexor torque dynamometry variables at 60°s−1 (p = 0.011) and 120°s−1 (p = 0.024). Repeated measures correlation highlighted associations between plantarflexor torque at 60°s−1 and loading rate (r = −0.901, p < 0.001). Load carriage reduced lower limb torque which did not recover between days. Plantarflexor torque reductions were associated with increases in loading rate. Practitioners should consider that load bearers are more likely to experience lower limb injury during multi-day load carriage. Future work should develop protocols to reduce plantarflexor torque loss in order to reduce ground reaction force change.

Experimental Study on Mechanical Properties and Seepage Laws of Raw Coal under Variable Loading and Unloading Rates

This manuscript studied the effects of variable axial pressure loading rate and variable confining pressure unloading rate on the deformation behavior and seepage characteristics of raw coal under alternate loading and unloading of axial pressure and confining pressure. It believed that as axial stress increases, axial strain ε 1 decreases, radial strain ε 3 increases, and permeability k decreases, and ε 1 ′ , ε 3 ′ , and k ′ increase when confining pressure is decreases. With the loading of axial stress and the unloading of confining pressure, the variation amplitudes of ε 1 ′ , ε 3 ′ , and k ′ values reduce gradually. During axial stress loading, the rise in the amplitude of ε 1 is larger than that of ε 3 and the reduction in the amplitude of k , indicating that ε 1 is more sensitive to axial stress than ε 3 and k . During unloading of confining pressure, the increase rate of ε 3 is larger than that of ε 1 and k ; also, ε 3 showed a high sensitivity to confining pressure. In the stage of axial stress loading and confining pressure unloading, the evolution law of deformation and permeability parameters is basically consistent with the change in loading and unloading rate.