Compressive and sealing characteristics of PTFE under cyclic loading-unloading at room temperature are studied in order to evaluate the cyclic sealing performance of control valve comprehensively. The unloading charac...Compressive and sealing characteristics of PTFE under cyclic loading-unloading at room temperature are studied in order to evaluate the cyclic sealing performance of control valve comprehensively. The unloading characteristics are different from the loading ones, therefore there is hysteresis between the unloading and loading curves. Compressive hysteresis is the main factor that causes sealing hysteresis. The leakage rate of PTFE complies with the power law before it enters the relatively stable region. Lastly, the effect of working pressure on the compressive and sealing characteristics is discussed. The experimental results show that the working pressure has little effect on compressive deformation but has a great influence on leakage rate.展开更多
High-altitude cold regions exhibit complex geological and environmental conditions,fostering steep rock slopes with macroscopic joints and mesoscopic freeze-thaw(F-T)damage.Cyclic loading further exacerbates rock inst...High-altitude cold regions exhibit complex geological and environmental conditions,fostering steep rock slopes with macroscopic joints and mesoscopic freeze-thaw(F-T)damage.Cyclic loading further exacerbates rock instability,yet the fracture mechanisms and load response relationships remain poorly understood.This study prepared intact and fractured sandstone specimens,subjected them to F-T cycles and graded loading-unloading,and monitored their structural evolution via X-ray computed tomography.First,the progressive failure process was investigated from both qualitative morphologic features and quantitative void parameters.The results showed that intact and fractured sandstone instability behaviors are determined by F-T damage and joint arrangement,respectively.However,both indicate that precursory localization of failure can only be detected when heterogeneous damage exists in advance.Furthermore,the void parameters of undamaged intact sandstone exhibit power-law acceleration,while damaged sandstones are characterized by a trend of initial decrease followed by an increase.Subsequently,a damage constitutive model for freeze-thawed fractured sandstone under graded loading-unloading was established.This model is based on the Lemaitre strain equivalence hypothesis and defines the coupled damage variable through multivariable indicators.In this framework,the material damage induced by fractures and F-T is unified and characterized by void parameters;while the load-induced damage is integrated with the energy linear allocation law and defined by damage energy.Thus,the stress-strain theoretical relationship is depicted,and the model is validated as reliable.Finally,a conceptual model of rock damage due to F-T and loading-unloading was proposed by combining the microscopic testing results from X-ray diffraction and scanning electron microscopy.展开更多
The deteriorated bearing capacity and nonlinear expansion deformation of weakly cemented Xiyu conglomerate under complex water environments and stress disturbances pose significant risks to the safety of stratum engin...The deteriorated bearing capacity and nonlinear expansion deformation of weakly cemented Xiyu conglomerate under complex water environments and stress disturbances pose significant risks to the safety of stratum engineering construction.In this study,to precisely comprehend the influences of pore pressure(P_(w))and stress path on the deformation characteristics,dilation behavior,and damage evolution of Xiyu conglomerate,a series of triaxial monotonic loading and cyclic loading-unloading tests were conducted on saturated Xiyu conglomerate with varied confining pressures(σ_(3))and pore pressures.The results indicate that as P_(w)increases,the secant modulus,unloading modulus,and loading modulus decrease,but increase with risingσ_(3).Additionally,P_(w)accelerates the onset of dilatancy,whereasσ_(3)delays it.Asσ_(3)increases,the peak stress,crack damage stress,and residual strength increase,while these parameters decrease with increasing P_(w).A positive correlation exists between the effective confining pressure and the effective axial stress.Furthermore,an increase in P_(w)results in a greater maximum dilation angle,which decreases with increasingσ_(3).The failure mode is mainly a tensile-shear mixed failure mode.The high pore pressure and cyclic loading stress path aggravate the deterioration of strength and failure mode of the weakly cemented Xiyu conglomerate.Finally,a new damage variable and conceptual model are proposed and discussed.The findings provide insight into the damage and failure mechanism of the Xiyu conglomerate under pore pressure and cyclic disturbance,offering a crucial experimental foundation for the design and construction of hydropower projects in the Xiyu conglomerate layer.展开更多
Among various architectures of polymers,end-group-free rings have attracted growing interests due to their distinct physicochemical performances over the linear counterparts which are exemplified by reduced hydrodynam...Among various architectures of polymers,end-group-free rings have attracted growing interests due to their distinct physicochemical performances over the linear counterparts which are exemplified by reduced hydrodynamic size and slower degradation.It is key to develop facile methods to large-scale synthesis of polymer rings with tunable compositions and microstructures.Recent progresses in large-scale synthesis of polymer rings against single-chain dynamic nanoparticles,and the example applications in synchronous enhancing toughness and strength of polymer nanocomposites are summarized.Once there is the breakthrough in rational design and effective large-scale synthesis of polymer rings and their functional derivatives,a family of cyclic functional hybrids would be available,thus providing a new paradigm in developing polymer science and engineering.展开更多
In contrast to cyclic polymers with ring-like backbones,side-chain cyclization is another intriguing structural feature that has not been extensively studied.In this study,a library of orthogonally protected monomers ...In contrast to cyclic polymers with ring-like backbones,side-chain cyclization is another intriguing structural feature that has not been extensively studied.In this study,a library of orthogonally protected monomers featuring monocyclic,dicyclic,or tricyclic pendant motifs was designed and prepared based on malic acid derivatives.Polyesters with precise chemical structures and uniform chain lengths were prepared modularly through iterative growth.Meticulous control over the chemical details allows for a close investigation of the topological effects on the polymer properties.Compared to their linear side chain counterparts,the presence of cyclic pendant groups has a significant impact on chain conformation,leading to a reduction in hydrodynamic volume and an enhancement in the glass transition temperature.These results underscore the potential of tailoring polymer properties through rational engineering of side chain topology.展开更多
Drilling and blasting tunneling is a cyclic process in which tunnel rock undergoes repeated blast loading,affecting its dynamic characteristics,energy evolution,and damage progression.To explore the dynamic mechanical...Drilling and blasting tunneling is a cyclic process in which tunnel rock undergoes repeated blast loading,affecting its dynamic characteristics,energy evolution,and damage progression.To explore the dynamic mechanical properties and damage mechanisms of carbonaceous slate under cyclic impact loads of varying intensities,cyclic dynamic tests are conducted using a triaxial split Hopkinson pressure bar.This study analyzes the stress-strain relationship,energy damage evolution,and macro-to-micro failure characteristics.The results show that peak stress and strain are significantly influenced by impact intensity and the number of impacts.The initial dynamic stress is positively correlated with the impact intensity,but with more impact,the dynamic stress decreases while the peak strain increases.Energy evolution follows a pattern of"slow growthfluctuating growthrapid growth,"with the crack initiation stress and its proportion decreasing.CT and SEM analyses reveal that as the impact intensity increases,failure becomes more chaotic,the fracture volume increases,and the fracture mode shifts from interlayer and intergranular to through-layer and trans-granular fractures.These findings provide an experimental basis for soft rock tunnel stability analysis.展开更多
The outstanding performance of O3-type NaNi_(1/3)Fe_(1/3)Mn_(1/3)O_(2)(NFM111)at both high and low temperatures coupled with its impressive specific capacity makes it an excellent cathode material for sodium-ion batte...The outstanding performance of O3-type NaNi_(1/3)Fe_(1/3)Mn_(1/3)O_(2)(NFM111)at both high and low temperatures coupled with its impressive specific capacity makes it an excellent cathode material for sodium-ion batteries.However,its poor cycling,owing to highpressure phase transitions,is one of its disadvantages.In this study,Cu/Ti was introduced into NFM111 cathode material using a solidphase method.Through both theoretically and experimentally,this study found that Cu doping provides a higher redox potential in NFM111,improving its reversible capacity and charge compensation process.The introduction of Ti would enhance the cycling stability of the material,smooth its charge and discharge curves,and suppress its high-voltage phase transitions.Accordingly,the NaNi_(0.27)Fe_(0.28)Mn_(0.33)Cu_(0.05)Ti_(0.06)O_(2)sample used in the study exhibited a remarkable rate performance of 142.97 mAh·g^(-1)at 0.1 C(2.0-4.2 V)and an excellent capacity retention of 72.81%after 300 cycles at 1C(1C=150 mA·g^(-1)).展开更多
Large-scale geological energy storage plays a crucial role in balancing the intermittency of renewable energy.As an energy storage medium,soaked sandstone has a wide range of applications in geological energy storage....Large-scale geological energy storage plays a crucial role in balancing the intermittency of renewable energy.As an energy storage medium,soaked sandstone has a wide range of applications in geological energy storage.Understanding the damage characteristics in soaked sandstones is essential for ensuring the stability and longevity of these energy storage systems.This study involved multi-stage cyclic loading tests conducted on soaked sandstone to explore the damage evolution throughout the loading process.The findingsreveal several important insights:(1)The plastic hysteresis loops observed during multi-stage cyclic loading evolved from dense to sparse.An increase in stress level led to greater damage in the rock,as evidenced by an increase in accumulated peak/plastic strains.(2)Energy density and stress level are related by quadratic polynomial relationships.The elastic and dissipated energy densities are related by a linear law.The average energy storage coefficientdecreased by up to 24.1%with increasing stress amplitude,reflectingchanges in energy dynamics within the samples.(3)AE counts,amplitude,and frequency provided critical insights into rock damage and fracture patterns.The greater the loading rate and stress amplitude,the lower the proportion of high-amplitude,high-peak frequency,and shear-type fractures.Increasing stress amplitude caused a maximum 16.63%reduction in the AE bvalue,indicating shifts in fracture behavior under varying stress conditions.(4)The increase in loading rate and stress amplitude promotes the transformation of micropores and mesopores to macropores/microcracks.(5)Damage variables,definedin terms of cumulative dissipation energy,aligned closely with the fatigue damage model under multi-stage cyclic loading.Accelerated damage primarily occurred during the finalstages of fatigue loading,highlighting critical periods in the degradation of soaked sandstones.This study can offer guidance for designing operational parameters for energy storage geological bodies dominated by soaked sandstones.展开更多
This study presents and verifies a hybrid methodology for reliable determination of parameters in structural rheological models(Zener,Burgers,and Maxwell)describing the viscoelastic behavior of polyurethane specimens ...This study presents and verifies a hybrid methodology for reliable determination of parameters in structural rheological models(Zener,Burgers,and Maxwell)describing the viscoelastic behavior of polyurethane specimens manufactured using extrusion-based 3D printing.Through comprehensive testing,including cyclic compression at strain rates ranging from 0.12 to 120 mm/min(0%-15%strain)and creep/relaxation experiments(10%-30%strain),the lumped parameters were independently determined using both analytical and numerical solutions of the models’differential equations,followed by cross-verification in additional experiments.Numerical solutions for creep and relaxation problems were obtained using finite element analysis,with the three-parameter Mooney-Rivlin model and Prony series employed to simulate elastic and viscous stress components,respectively.Energy dissipation per cycle was quantified during cyclic compression tests.The results demonstrate that all three models adequately describe material behavior within the 0%-15%strain range across various strain rates.Comparative analysis revealed the Burgers model’s superior performance in characterizing creep and stress relaxation at low strain levels.While Zener and Burgers model parameters from uniaxial compression showed limited applicability for energy dissipation calculations,the generalized Maxwell model effectively captured viscoelastic properties across different strain rates.Notably,parameters derived from creep tests provided a more universal assessment of dissipative properties due to optimization based on characteristic curve regions.Both parameter sets described polyurethane’s elastic-hysteretic behavior with approximately 20%error,proving significantly more accurate than the linear strain-time dependence hypothesis.Finite element analysis(FEA)complemented numerical modeling by demonstrating that while the generalized Maxwell model effectively describes initial rapid stress-strain changes,FEA provides superior characterization of steady-state processes.This computational approach yields more physically representative results compared to simplified analytical solutions,despite certain limitations in transient analysis.展开更多
During deep coal mining,an instability failure of coal usually occurs under the combined effect of initial damage and triaxial cyclic loading and unloading(TCLU).Therefore,this study investigated the impact of initial...During deep coal mining,an instability failure of coal usually occurs under the combined effect of initial damage and triaxial cyclic loading and unloading(TCLU).Therefore,this study investigated the impact of initial damage on mechanical behavior and acoustic emission(AE)characteristics of coal under TCLU.Initial damage variables(IDVs)of coal specimens were quantified using preloading,followed by TCLU experiments to assess the deformation,energy distribution,and fracture development.The results revealed that the increase in IDVs significantly reduced the structural integrity of coal specimens,increased the cumulative irreversible strain,and enhanced the dissipated energy owing to microfracture expansion.Moreover,AE monitoring showed earlier activation of fractures and a higher occurrence of large-scale rupture events of coal specimens with high IDVs,which correlated with decreasing AE b values(reflecting the different scales of fracture within specimens)and increasing S values(reflecting the AE activity within specimens).Additionally,computed tomography analysis revealed intensified fracture networks and increasing three-dimensional fractal dimensions of coal specimens with higher IDVs.Finally,the coupling effect of TCLU and initial damage on the weakening mechanism of coal was investigated.Initial damage significantly reduced the structural integrity of coal by increasing the number of weak planes within coal specimens,contributing to the earlier activation and rapid expansion of fractures at low stress levels under TCLU and eventually accelerating the weakening process of coal.This study provides a scientific basis and theoretical support for the prevention and control of dynamic disasters in deep coal mining.展开更多
In the process of engineering construction such as tunnels and slopes,rock mass is frequently subjected to multiple levels of loading and unloading,while previous research ignores the impact of unloading rate on the s...In the process of engineering construction such as tunnels and slopes,rock mass is frequently subjected to multiple levels of loading and unloading,while previous research ignores the impact of unloading rate on the stability of rock mass.A number of uniaxial multi-level cyclic loading-unloading experiments were conducted to better understand the effect of unloading rate on the deformation behavior,energy evolution,and damage properties of rock-like material.The experimental results demonstrated that the unloading rate and relative cyclic number clearly influence the deformation behavior and energy evo-lution of rock-like samples.In particular,as the relative cyclic number rises,the total strain and reversible strain both increase linearly,while the total energy density,elastic energy density,and dissipated energy density all rise nonlinearly.In contrast,the irreversible strain first decreases quickly,then stabilizes,and finally rises slowly.As the unloading rate increases,the total strain and reversible strain both increase,while the irreversible strain decreases.The dissipated energy damage was examined in light of the aforementioned experimental findings.The accuracy of the proposed damage model,which takes into account the impact of the unloading rate and relative cyclic number,is then confirmed by examining the consistency between the model predicted and the experimental results.The proposed damage model will make it easier to foresee how the multi-level loading-unloading cycles will affect the rock-like materials.展开更多
To evaluate the columnar jointed basalts in the dam site of Baihetan hydropower station in southwest China, we developed a basic conceptual model of single jointed rock mass. Considering that the rock mass deformation...To evaluate the columnar jointed basalts in the dam site of Baihetan hydropower station in southwest China, we developed a basic conceptual model of single jointed rock mass. Considering that the rock mass deformation consists of rock block deformation and joints deformation, the linear mechanical characteristics of the cell (including the elastic joints and the nonlinear mechanical behaviors of the cell) with a combined frictional-elastic interface were analyzed. We developed formulas to calculate the rock block deformation, which can be adapted for multiple jointed rock mass and columnar jointed basalts. The formulas are effective in calculating the equivalent modulus of multiple jointed rock mass, and precisely reveal the anisotropic properties of columnar jointed basalts. Furthermore, the in situ rigid bearing plate tests were analyzed and calculated, and the types of loading-unloading curves and the equivalent modulus along different directions of columnar jointed basalts were obtained. The analytical results are in close compliance with the test results.展开更多
The unified hardening(UH)model proposed by Yao et al.(Geotechnique 2009)is the constitutive model which can consider the influence of the complex stress path and stress history on the deformation and strength of clays...The unified hardening(UH)model proposed by Yao et al.(Geotechnique 2009)is the constitutive model which can consider the influence of the complex stress path and stress history on the deformation and strength of clays reasonably.Firstly,the loading-unloading criterion of material model is defined as the change law of the intersection of current yield surface and the p axis,which makes the loading-unloading in the process of hardening and softening can be unified considered in UH model.Then,the Newton-Raphson method is adopted to attain the nonlinear problems solution in the finite element method of UH model,and the semi-implicit return mapping method is adopted to update stress.The application of the UH model in the finite element is realized.And then,the analyses of triaxial test are performed using the unit prediction and finite element method.The results of the unit prediction method are compared with the experimental results to illustrate the rationality of the UH model.Comparing the results with the unit prediction method and the finite element method,the correctness of the finite element program of the UH model is iUusttated.Further,Ae three-dimensional firdte element andysis of embankment on soft soil is performed by the program.The comparison between the results calculated by the UH model and the modified Cam-clay(MCC)model and the experimental data shows that the UH model is rational in analyzing the actual embankment engineering on soft soil.展开更多
Using in-situ measurements from the Cassini spacecraft in 2013, we report an Earth substorm-like loading-unloading process at Saturn's distant magnetotail. We found that the loading process is featured with two di...Using in-situ measurements from the Cassini spacecraft in 2013, we report an Earth substorm-like loading-unloading process at Saturn's distant magnetotail. We found that the loading process is featured with two distinct processes: a rapid loading process that was likely driven by an internal source and a slow loading process that was likely driven by solar wind. Each of the two loading processes could also individually lead to an unloading process. The rapid internal loading process lasts for ~ 1-2 hours; the solar wind driven loading process lasts for ~ 3-18 hours and the following unloading process lasts for ~1-3 hours. In this letter, we suggest three possible loadingunloading circulations, which are fundamental in understanding the role of solar wind in driving giant planetary magnetospheric dynamics.展开更多
Designing catalysts with high catalytic activity and stability is the key to achieve the commercial application of MgH_(2).Herein,the sulfur doped Ti_(3)C_(2)(S-Ti_(3)C_(2))was successfully prepared by heat treatment ...Designing catalysts with high catalytic activity and stability is the key to achieve the commercial application of MgH_(2).Herein,the sulfur doped Ti_(3)C_(2)(S-Ti_(3)C_(2))was successfully prepared by heat treatment of Ti_(3)C_(2)MXene under Ar/H_(2)S atmosphere to facilitate the hydrogen release and uptake from MgH_(2).The S-Ti_(3)C_(2)exhibited pleasant catalytic effect on the hydriding/dehydriding kinetics and cyclic stability of MgH_(2).The addition of 5 wt%S-Ti_(3)C_(2)into MgH_(2)resulted in a reduction of 114℃in the starting dehydriding temperature compared to pure MgH_(2).MgH_(2)+5 wt%S-Ti_(3)C_(2)sample could quickly release 6.6 wt%hydrogen in 17 min at 220℃,and 6.8 wt%H_(2)was absorbed in 25 min at 200℃.Cyclic testing revealed that MgH_(2)+5 wt%S-Ti_(3)C_(2)system achieved a reversible hydrogen capacity of 6.5 wt%.Characterization analysis demonstrated that Ti-species(Ti0,Ti^(2+),Ti-S,and Ti^(3+))as active species significantly lowered the dehydrogenation temperature and promoted the re-/dehydrogenation kinetics of MgH_(2),and sulfur doping can effectively improve the stability of Ti0 and Ti^(3+),contributing to the improvement of cyclic stability of MgH_(2).This study provides strategy for the construction of catalysts for hydrogen storage materials.展开更多
A cyclic quenching treatment(CQT)succeeded in turning a 2.3 GPa maraging steel with a Charpy impact energy of 9 J into a new grade with the same strength but a Charpy impact energy of 20 J upon 4 cyclic treatments.The...A cyclic quenching treatment(CQT)succeeded in turning a 2.3 GPa maraging steel with a Charpy impact energy of 9 J into a new grade with the same strength but a Charpy impact energy of 20 J upon 4 cyclic treatments.The improvement of mechanical properties is attributed to the refinement and increased chemical heterogeneity of the martensitic substructure,rather than the refinement of prior austenite grain(PAG),as well as the Transformation-Induced Plasticity(TRIP)effect facilitated by small austenite grains.The role of local segregation of Ni during CQT in the formation of Ni-rich austenite grains,Ni-rich martensite laths and Ni-poor martensite laths,was investigated and verified by DICTRA simulations.This study highlights the important influence of Ni partitioning behavior during CQT,providing insights into microstructural evolution and mechanical properties.展开更多
To completely recover valuable elements and reduce the amount of waste,the impact of phosphoric acid on the decomposition of rare earth,fluorine and phosphorus during cyclic leaching was studied based on the character...To completely recover valuable elements and reduce the amount of waste,the impact of phosphoric acid on the decomposition of rare earth,fluorine and phosphorus during cyclic leaching was studied based on the characteristics of low-tempe rature sulfuric acid deco mposition.When a single monazite was leached using 75 wt% H_(2)SO_(4) solution with phosphoric acid,the size and number of monazite particles in the washing slag gradually decrease with the increase in phosphoric acid content in the leaching solution.The monazite phase can hardly be found in the slag when the phosphoric acid content reaches 70 g/L,which indicates that phosphoric acid is favorable for monazite decomposition.The mixed rare earth concentrate was leached by 75 wt% H_(2)SO_(4) containing 70 g/L phosphoric acid,the mineral compositions of the washing slag are only gypsum and unwashed rare earth sulfuric acid.After cyclic leaching of75 wt% H_(2)SO_(4),the mineral compositions of the primary leaching washing slag are mainly undecomposed monazite,rare earth sulfate and calcium sulfate.However,monazite is not found in the mineral phase of the second and third leaching washing slag.The leaching rates of rare earth and phosphorus gradually increase with the increase in cyclic leaching times.In addition,the phosphoric acid content in the leaching solution increases with the increase in the number of cyclic leaching time.However,the rising trend decreases when the phosphoric acid content reaches 50 g/L by adsorption and crystallization of phosphoric acid.A small amount of water can be used to clean the leaching residue before washing to recover the more soluble phosphorus acid according to the difference of dissolution between phosphoric acid and rare earth sulfuric acid.展开更多
基金Funded by the Fund of the State Key Laboratory of Technologies in Space Cryogenic Propellants(No.SKLTSCP1210)
文摘Compressive and sealing characteristics of PTFE under cyclic loading-unloading at room temperature are studied in order to evaluate the cyclic sealing performance of control valve comprehensively. The unloading characteristics are different from the loading ones, therefore there is hysteresis between the unloading and loading curves. Compressive hysteresis is the main factor that causes sealing hysteresis. The leakage rate of PTFE complies with the power law before it enters the relatively stable region. Lastly, the effect of working pressure on the compressive and sealing characteristics is discussed. The experimental results show that the working pressure has little effect on compressive deformation but has a great influence on leakage rate.
基金supported by the National Natural Science Foundation of China(Grant Nos.11972283 and 42277182).
文摘High-altitude cold regions exhibit complex geological and environmental conditions,fostering steep rock slopes with macroscopic joints and mesoscopic freeze-thaw(F-T)damage.Cyclic loading further exacerbates rock instability,yet the fracture mechanisms and load response relationships remain poorly understood.This study prepared intact and fractured sandstone specimens,subjected them to F-T cycles and graded loading-unloading,and monitored their structural evolution via X-ray computed tomography.First,the progressive failure process was investigated from both qualitative morphologic features and quantitative void parameters.The results showed that intact and fractured sandstone instability behaviors are determined by F-T damage and joint arrangement,respectively.However,both indicate that precursory localization of failure can only be detected when heterogeneous damage exists in advance.Furthermore,the void parameters of undamaged intact sandstone exhibit power-law acceleration,while damaged sandstones are characterized by a trend of initial decrease followed by an increase.Subsequently,a damage constitutive model for freeze-thawed fractured sandstone under graded loading-unloading was established.This model is based on the Lemaitre strain equivalence hypothesis and defines the coupled damage variable through multivariable indicators.In this framework,the material damage induced by fractures and F-T is unified and characterized by void parameters;while the load-induced damage is integrated with the energy linear allocation law and defined by damage energy.Thus,the stress-strain theoretical relationship is depicted,and the model is validated as reliable.Finally,a conceptual model of rock damage due to F-T and loading-unloading was proposed by combining the microscopic testing results from X-ray diffraction and scanning electron microscopy.
基金This work was supported by the Central University Basic Research Fund of China(B230201059and No.B240201155)the water science and technology special fund of Xinjiang Uygur Autonomous Region(No.XSKJ-2023-30)funded by China Power Construction Group research project(Grant No.DJ-HXGG-2023-16).
文摘The deteriorated bearing capacity and nonlinear expansion deformation of weakly cemented Xiyu conglomerate under complex water environments and stress disturbances pose significant risks to the safety of stratum engineering construction.In this study,to precisely comprehend the influences of pore pressure(P_(w))and stress path on the deformation characteristics,dilation behavior,and damage evolution of Xiyu conglomerate,a series of triaxial monotonic loading and cyclic loading-unloading tests were conducted on saturated Xiyu conglomerate with varied confining pressures(σ_(3))and pore pressures.The results indicate that as P_(w)increases,the secant modulus,unloading modulus,and loading modulus decrease,but increase with risingσ_(3).Additionally,P_(w)accelerates the onset of dilatancy,whereasσ_(3)delays it.Asσ_(3)increases,the peak stress,crack damage stress,and residual strength increase,while these parameters decrease with increasing P_(w).A positive correlation exists between the effective confining pressure and the effective axial stress.Furthermore,an increase in P_(w)results in a greater maximum dilation angle,which decreases with increasingσ_(3).The failure mode is mainly a tensile-shear mixed failure mode.The high pore pressure and cyclic loading stress path aggravate the deterioration of strength and failure mode of the weakly cemented Xiyu conglomerate.Finally,a new damage variable and conceptual model are proposed and discussed.The findings provide insight into the damage and failure mechanism of the Xiyu conglomerate under pore pressure and cyclic disturbance,offering a crucial experimental foundation for the design and construction of hydropower projects in the Xiyu conglomerate layer.
基金Supported by the National Natural Science Foundation of China(Nos.52293472,22473096 and 22471164)。
文摘Among various architectures of polymers,end-group-free rings have attracted growing interests due to their distinct physicochemical performances over the linear counterparts which are exemplified by reduced hydrodynamic size and slower degradation.It is key to develop facile methods to large-scale synthesis of polymer rings with tunable compositions and microstructures.Recent progresses in large-scale synthesis of polymer rings against single-chain dynamic nanoparticles,and the example applications in synchronous enhancing toughness and strength of polymer nanocomposites are summarized.Once there is the breakthrough in rational design and effective large-scale synthesis of polymer rings and their functional derivatives,a family of cyclic functional hybrids would be available,thus providing a new paradigm in developing polymer science and engineering.
基金financially supported by the National Natural Science Foundation of China(No.22273026)Scientific Research Innovation Capability Support Project for Young Faculty(No.ZYGXQNJSKYCXNLZCXM-I15)+3 种基金Basic and Applied Basic Research Foundation of Guangdong Province(2024A1515012401)GJYC program of Guangzhou(No.2024D03J0002)the China Postdoctoral Science Foundation(No.2024M750938)Postdoctoral Fellowship Program of CPSF(No.GZC20240492)for their financial support。
文摘In contrast to cyclic polymers with ring-like backbones,side-chain cyclization is another intriguing structural feature that has not been extensively studied.In this study,a library of orthogonally protected monomers featuring monocyclic,dicyclic,or tricyclic pendant motifs was designed and prepared based on malic acid derivatives.Polyesters with precise chemical structures and uniform chain lengths were prepared modularly through iterative growth.Meticulous control over the chemical details allows for a close investigation of the topological effects on the polymer properties.Compared to their linear side chain counterparts,the presence of cyclic pendant groups has a significant impact on chain conformation,leading to a reduction in hydrodynamic volume and an enhancement in the glass transition temperature.These results underscore the potential of tailoring polymer properties through rational engineering of side chain topology.
基金support from the Joint Funds of the National Natural Science Foundation of China(Grant No.U23A2060)the National Natural Science Foundation of China(Grant Nos.42177143 and 52474150).
文摘Drilling and blasting tunneling is a cyclic process in which tunnel rock undergoes repeated blast loading,affecting its dynamic characteristics,energy evolution,and damage progression.To explore the dynamic mechanical properties and damage mechanisms of carbonaceous slate under cyclic impact loads of varying intensities,cyclic dynamic tests are conducted using a triaxial split Hopkinson pressure bar.This study analyzes the stress-strain relationship,energy damage evolution,and macro-to-micro failure characteristics.The results show that peak stress and strain are significantly influenced by impact intensity and the number of impacts.The initial dynamic stress is positively correlated with the impact intensity,but with more impact,the dynamic stress decreases while the peak strain increases.Energy evolution follows a pattern of"slow growthfluctuating growthrapid growth,"with the crack initiation stress and its proportion decreasing.CT and SEM analyses reveal that as the impact intensity increases,failure becomes more chaotic,the fracture volume increases,and the fracture mode shifts from interlayer and intergranular to through-layer and trans-granular fractures.These findings provide an experimental basis for soft rock tunnel stability analysis.
基金supported by the Low-Cost Long-Life Batteries program,China(No.WL-24-08-01)the National Natural Science Foundation of China(No.22279007)。
文摘The outstanding performance of O3-type NaNi_(1/3)Fe_(1/3)Mn_(1/3)O_(2)(NFM111)at both high and low temperatures coupled with its impressive specific capacity makes it an excellent cathode material for sodium-ion batteries.However,its poor cycling,owing to highpressure phase transitions,is one of its disadvantages.In this study,Cu/Ti was introduced into NFM111 cathode material using a solidphase method.Through both theoretically and experimentally,this study found that Cu doping provides a higher redox potential in NFM111,improving its reversible capacity and charge compensation process.The introduction of Ti would enhance the cycling stability of the material,smooth its charge and discharge curves,and suppress its high-voltage phase transitions.Accordingly,the NaNi_(0.27)Fe_(0.28)Mn_(0.33)Cu_(0.05)Ti_(0.06)O_(2)sample used in the study exhibited a remarkable rate performance of 142.97 mAh·g^(-1)at 0.1 C(2.0-4.2 V)and an excellent capacity retention of 72.81%after 300 cycles at 1C(1C=150 mA·g^(-1)).
基金sponsored by National Natural Science Foundation of China(Grant Nos.U22B6003 and 52304070)Key Laboratory of Geomechanics and Geotechnical Engineering Safety,Chinese Academy of Sciences(Grant No.SKLGME-JBGS2404).
文摘Large-scale geological energy storage plays a crucial role in balancing the intermittency of renewable energy.As an energy storage medium,soaked sandstone has a wide range of applications in geological energy storage.Understanding the damage characteristics in soaked sandstones is essential for ensuring the stability and longevity of these energy storage systems.This study involved multi-stage cyclic loading tests conducted on soaked sandstone to explore the damage evolution throughout the loading process.The findingsreveal several important insights:(1)The plastic hysteresis loops observed during multi-stage cyclic loading evolved from dense to sparse.An increase in stress level led to greater damage in the rock,as evidenced by an increase in accumulated peak/plastic strains.(2)Energy density and stress level are related by quadratic polynomial relationships.The elastic and dissipated energy densities are related by a linear law.The average energy storage coefficientdecreased by up to 24.1%with increasing stress amplitude,reflectingchanges in energy dynamics within the samples.(3)AE counts,amplitude,and frequency provided critical insights into rock damage and fracture patterns.The greater the loading rate and stress amplitude,the lower the proportion of high-amplitude,high-peak frequency,and shear-type fractures.Increasing stress amplitude caused a maximum 16.63%reduction in the AE bvalue,indicating shifts in fracture behavior under varying stress conditions.(4)The increase in loading rate and stress amplitude promotes the transformation of micropores and mesopores to macropores/microcracks.(5)Damage variables,definedin terms of cumulative dissipation energy,aligned closely with the fatigue damage model under multi-stage cyclic loading.Accelerated damage primarily occurred during the finalstages of fatigue loading,highlighting critical periods in the degradation of soaked sandstones.This study can offer guidance for designing operational parameters for energy storage geological bodies dominated by soaked sandstones.
文摘This study presents and verifies a hybrid methodology for reliable determination of parameters in structural rheological models(Zener,Burgers,and Maxwell)describing the viscoelastic behavior of polyurethane specimens manufactured using extrusion-based 3D printing.Through comprehensive testing,including cyclic compression at strain rates ranging from 0.12 to 120 mm/min(0%-15%strain)and creep/relaxation experiments(10%-30%strain),the lumped parameters were independently determined using both analytical and numerical solutions of the models’differential equations,followed by cross-verification in additional experiments.Numerical solutions for creep and relaxation problems were obtained using finite element analysis,with the three-parameter Mooney-Rivlin model and Prony series employed to simulate elastic and viscous stress components,respectively.Energy dissipation per cycle was quantified during cyclic compression tests.The results demonstrate that all three models adequately describe material behavior within the 0%-15%strain range across various strain rates.Comparative analysis revealed the Burgers model’s superior performance in characterizing creep and stress relaxation at low strain levels.While Zener and Burgers model parameters from uniaxial compression showed limited applicability for energy dissipation calculations,the generalized Maxwell model effectively captured viscoelastic properties across different strain rates.Notably,parameters derived from creep tests provided a more universal assessment of dissipative properties due to optimization based on characteristic curve regions.Both parameter sets described polyurethane’s elastic-hysteretic behavior with approximately 20%error,proving significantly more accurate than the linear strain-time dependence hypothesis.Finite element analysis(FEA)complemented numerical modeling by demonstrating that while the generalized Maxwell model effectively describes initial rapid stress-strain changes,FEA provides superior characterization of steady-state processes.This computational approach yields more physically representative results compared to simplified analytical solutions,despite certain limitations in transient analysis.
基金supported by the National Key R&D Program of China(Grant No.2022YFC3004704)the National Natural Science Foundation of China(Grant No.52174166)Graduate Research and Innovation Foundation of Chongqing,China(Grant No.CYB23031),which were gratefully acknowledged.
文摘During deep coal mining,an instability failure of coal usually occurs under the combined effect of initial damage and triaxial cyclic loading and unloading(TCLU).Therefore,this study investigated the impact of initial damage on mechanical behavior and acoustic emission(AE)characteristics of coal under TCLU.Initial damage variables(IDVs)of coal specimens were quantified using preloading,followed by TCLU experiments to assess the deformation,energy distribution,and fracture development.The results revealed that the increase in IDVs significantly reduced the structural integrity of coal specimens,increased the cumulative irreversible strain,and enhanced the dissipated energy owing to microfracture expansion.Moreover,AE monitoring showed earlier activation of fractures and a higher occurrence of large-scale rupture events of coal specimens with high IDVs,which correlated with decreasing AE b values(reflecting the different scales of fracture within specimens)and increasing S values(reflecting the AE activity within specimens).Additionally,computed tomography analysis revealed intensified fracture networks and increasing three-dimensional fractal dimensions of coal specimens with higher IDVs.Finally,the coupling effect of TCLU and initial damage on the weakening mechanism of coal was investigated.Initial damage significantly reduced the structural integrity of coal by increasing the number of weak planes within coal specimens,contributing to the earlier activation and rapid expansion of fractures at low stress levels under TCLU and eventually accelerating the weakening process of coal.This study provides a scientific basis and theoretical support for the prevention and control of dynamic disasters in deep coal mining.
基金the Water Conservancy Science and Technology Major Project of Hunan Province,China(Project XSKJ2019081-10)the China Scholarship Council(Grant No.202006370344)the First-class Project Special Funding of Yellow River Laboratory,China(Grant No.YRL22YL07).
文摘In the process of engineering construction such as tunnels and slopes,rock mass is frequently subjected to multiple levels of loading and unloading,while previous research ignores the impact of unloading rate on the stability of rock mass.A number of uniaxial multi-level cyclic loading-unloading experiments were conducted to better understand the effect of unloading rate on the deformation behavior,energy evolution,and damage properties of rock-like material.The experimental results demonstrated that the unloading rate and relative cyclic number clearly influence the deformation behavior and energy evo-lution of rock-like samples.In particular,as the relative cyclic number rises,the total strain and reversible strain both increase linearly,while the total energy density,elastic energy density,and dissipated energy density all rise nonlinearly.In contrast,the irreversible strain first decreases quickly,then stabilizes,and finally rises slowly.As the unloading rate increases,the total strain and reversible strain both increase,while the irreversible strain decreases.The dissipated energy damage was examined in light of the aforementioned experimental findings.The accuracy of the proposed damage model,which takes into account the impact of the unloading rate and relative cyclic number,is then confirmed by examining the consistency between the model predicted and the experimental results.The proposed damage model will make it easier to foresee how the multi-level loading-unloading cycles will affect the rock-like materials.
基金Project (Nos. 50911130366 and 2011CB013504) supported by the National Natural Science Foundation of Chinathe Postdoctoral Advanced Research Programs Class Ⅱ of Zhejiang Province (No. BSH1302013), China
文摘To evaluate the columnar jointed basalts in the dam site of Baihetan hydropower station in southwest China, we developed a basic conceptual model of single jointed rock mass. Considering that the rock mass deformation consists of rock block deformation and joints deformation, the linear mechanical characteristics of the cell (including the elastic joints and the nonlinear mechanical behaviors of the cell) with a combined frictional-elastic interface were analyzed. We developed formulas to calculate the rock block deformation, which can be adapted for multiple jointed rock mass and columnar jointed basalts. The formulas are effective in calculating the equivalent modulus of multiple jointed rock mass, and precisely reveal the anisotropic properties of columnar jointed basalts. Furthermore, the in situ rigid bearing plate tests were analyzed and calculated, and the types of loading-unloading curves and the equivalent modulus along different directions of columnar jointed basalts were obtained. The analytical results are in close compliance with the test results.
基金supported by the National Natural Science Foundation of China(Grants 11672015,51808547,and 51808548)the Central University Basic Scientific Research Business Expenses Funded Project(Grant 3122014C014)+1 种基金the Civil Aviation University Airport Engineering Base Open Fund(Grant JCGC2019KFJJ003)Tianjin Municipal Education Commission Scientific Research Project(Grant 2019KJ124)。
文摘The unified hardening(UH)model proposed by Yao et al.(Geotechnique 2009)is the constitutive model which can consider the influence of the complex stress path and stress history on the deformation and strength of clays reasonably.Firstly,the loading-unloading criterion of material model is defined as the change law of the intersection of current yield surface and the p axis,which makes the loading-unloading in the process of hardening and softening can be unified considered in UH model.Then,the Newton-Raphson method is adopted to attain the nonlinear problems solution in the finite element method of UH model,and the semi-implicit return mapping method is adopted to update stress.The application of the UH model in the finite element is realized.And then,the analyses of triaxial test are performed using the unit prediction and finite element method.The results of the unit prediction method are compared with the experimental results to illustrate the rationality of the UH model.Comparing the results with the unit prediction method and the finite element method,the correctness of the finite element program of the UH model is iUusttated.Further,Ae three-dimensional firdte element andysis of embankment on soft soil is performed by the program.The comparison between the results calculated by the UH model and the modified Cam-clay(MCC)model and the experimental data shows that the UH model is rational in analyzing the actual embankment engineering on soft soil.
基金supported by the National Science Foundation of China (41525016,41404117)
文摘Using in-situ measurements from the Cassini spacecraft in 2013, we report an Earth substorm-like loading-unloading process at Saturn's distant magnetotail. We found that the loading process is featured with two distinct processes: a rapid loading process that was likely driven by an internal source and a slow loading process that was likely driven by solar wind. Each of the two loading processes could also individually lead to an unloading process. The rapid internal loading process lasts for ~ 1-2 hours; the solar wind driven loading process lasts for ~ 3-18 hours and the following unloading process lasts for ~1-3 hours. In this letter, we suggest three possible loadingunloading circulations, which are fundamental in understanding the role of solar wind in driving giant planetary magnetospheric dynamics.
基金supported by the National Natural Science Foundation of China(U22A20120,52071135,51871090,U1804135,and 52301269)the Natural Science Foundation of Hebei Province for Innovation Groups Program(C2022203003)Fundamental Research Funds for the Universities of Henan Province(NSFRF220201).
文摘Designing catalysts with high catalytic activity and stability is the key to achieve the commercial application of MgH_(2).Herein,the sulfur doped Ti_(3)C_(2)(S-Ti_(3)C_(2))was successfully prepared by heat treatment of Ti_(3)C_(2)MXene under Ar/H_(2)S atmosphere to facilitate the hydrogen release and uptake from MgH_(2).The S-Ti_(3)C_(2)exhibited pleasant catalytic effect on the hydriding/dehydriding kinetics and cyclic stability of MgH_(2).The addition of 5 wt%S-Ti_(3)C_(2)into MgH_(2)resulted in a reduction of 114℃in the starting dehydriding temperature compared to pure MgH_(2).MgH_(2)+5 wt%S-Ti_(3)C_(2)sample could quickly release 6.6 wt%hydrogen in 17 min at 220℃,and 6.8 wt%H_(2)was absorbed in 25 min at 200℃.Cyclic testing revealed that MgH_(2)+5 wt%S-Ti_(3)C_(2)system achieved a reversible hydrogen capacity of 6.5 wt%.Characterization analysis demonstrated that Ti-species(Ti0,Ti^(2+),Ti-S,and Ti^(3+))as active species significantly lowered the dehydrogenation temperature and promoted the re-/dehydrogenation kinetics of MgH_(2),and sulfur doping can effectively improve the stability of Ti0 and Ti^(3+),contributing to the improvement of cyclic stability of MgH_(2).This study provides strategy for the construction of catalysts for hydrogen storage materials.
基金sponsored by the National Natural Science Foun-dation of China(Grant Nos.52271122,52203384).
文摘A cyclic quenching treatment(CQT)succeeded in turning a 2.3 GPa maraging steel with a Charpy impact energy of 9 J into a new grade with the same strength but a Charpy impact energy of 20 J upon 4 cyclic treatments.The improvement of mechanical properties is attributed to the refinement and increased chemical heterogeneity of the martensitic substructure,rather than the refinement of prior austenite grain(PAG),as well as the Transformation-Induced Plasticity(TRIP)effect facilitated by small austenite grains.The role of local segregation of Ni during CQT in the formation of Ni-rich austenite grains,Ni-rich martensite laths and Ni-poor martensite laths,was investigated and verified by DICTRA simulations.This study highlights the important influence of Ni partitioning behavior during CQT,providing insights into microstructural evolution and mechanical properties.
基金support by the National Natural Science Foundation of Inner Mongolia (2022SHZR1885)Natural Science Foundation of Hebei province (E2022402101,E2022402105)。
文摘To completely recover valuable elements and reduce the amount of waste,the impact of phosphoric acid on the decomposition of rare earth,fluorine and phosphorus during cyclic leaching was studied based on the characteristics of low-tempe rature sulfuric acid deco mposition.When a single monazite was leached using 75 wt% H_(2)SO_(4) solution with phosphoric acid,the size and number of monazite particles in the washing slag gradually decrease with the increase in phosphoric acid content in the leaching solution.The monazite phase can hardly be found in the slag when the phosphoric acid content reaches 70 g/L,which indicates that phosphoric acid is favorable for monazite decomposition.The mixed rare earth concentrate was leached by 75 wt% H_(2)SO_(4) containing 70 g/L phosphoric acid,the mineral compositions of the washing slag are only gypsum and unwashed rare earth sulfuric acid.After cyclic leaching of75 wt% H_(2)SO_(4),the mineral compositions of the primary leaching washing slag are mainly undecomposed monazite,rare earth sulfate and calcium sulfate.However,monazite is not found in the mineral phase of the second and third leaching washing slag.The leaching rates of rare earth and phosphorus gradually increase with the increase in cyclic leaching times.In addition,the phosphoric acid content in the leaching solution increases with the increase in the number of cyclic leaching time.However,the rising trend decreases when the phosphoric acid content reaches 50 g/L by adsorption and crystallization of phosphoric acid.A small amount of water can be used to clean the leaching residue before washing to recover the more soluble phosphorus acid according to the difference of dissolution between phosphoric acid and rare earth sulfuric acid.
