Efficient lubrication of magnesium alloys is a highly challenging topic in the field of tribology.In this study,magnesium silicate hydroxide(MSH)nanotubes with serpentine structures were synthesized.The tribological b...Efficient lubrication of magnesium alloys is a highly challenging topic in the field of tribology.In this study,magnesium silicate hydroxide(MSH)nanotubes with serpentine structures were synthesized.The tribological behavior of AZ91D magnesium alloy rubbed against GCr15 steel was studied under lubricating oil with surface-modified MSH nanotubes as additives.The effects of the concentration,applied load,and reciprocating frequency on the friction and wear of the AZ91D alloy were studied using an SRV-4 sliding wear tester.Results show a decrease of 18.7–68.5%in friction coefficient,and a reduction of 19.4–54.3%in wear volume of magnesium alloy can be achieved by applying the synthetic serpentine additive under different conditions.A suspension containing 0.3 wt.%MSH was most efficient in reducing wear and friction.High frequency and medium load were more conducive to improving the tribological properties of magnesium alloys.A series of beneficial physical and chemical processes occurring at the AZ91D alloy/steel interface can be used to explain friction and wear reduction based on the characterization of the morphology,chemical composition,chemical state,microstructure,and nanomechanical properties of the worn surface.The synthetic MSH,with serpentine structure and nanotube morphology,possesses excellent adsorbability,high chemical activity,and good self-lubrication and catalytic activity.Therefore,physical polishing,tribochemical reactions,and physicalchemical depositions can occur easily on the sliding contacts.A dense tribolayer with a complex composition and composite structure was formed on the worn surface.Its high hardness,good toughness and plasticity,and prominent lubricity resulted in the improvement of friction and wear,making the synthetic MSH a promising efficient oil additive for magnesium alloys under boundary and mixed lubrication.展开更多
This article investigates the mechanical responses and acoustic emission(AE)characteristics of sandstone under the triaxial differential cyclic loading(DCL)at different unloading rates of confining stress.The test res...This article investigates the mechanical responses and acoustic emission(AE)characteristics of sandstone under the triaxial differential cyclic loading(DCL)at different unloading rates of confining stress.The test results indicate that strength of rock specimens under different stress paths of triaxial unloading confining stress-differential cyclic loading(TUCS-DCL)can be fitted by the Mohr–Coulomb,Hoek–Brown,and Bieniawski criteria.The confining stress unloading rate can dominate the radial strain rate,while the axial DCL pattern has an unpronounced effect.The confining stress unloading rate affects the energy evolution in radial and axial directions of specimens,with the ratio of radially released energy to axially consumed energy fluctuating more significantly during the fast unloading of confining stress,the valley value of the ratio can serve as a precursor for failure.The confining stress unloading rate has no significant effect on stress–strain phase shift,while axial rapid-loading-slow-unloading can correspond to a larger magnitude of phase shift.AE signals begin to significantly increase after the confining stress is unloaded to zero,and a notable Kaiser effect is observed during cyclic loading preceding the failure.展开更多
This work presents experimental tests based on coal collected from a coal mine based underground water reservoir(CMUWR).The mechanical responses of dry and water-soaked coal samples under the complex normal and shear ...This work presents experimental tests based on coal collected from a coal mine based underground water reservoir(CMUWR).The mechanical responses of dry and water-soaked coal samples under the complex normal and shear stresses under multi-amplitude and variable frequency is investigated.The experimental results reveal the effects of stress path,water soaking and frequency on deformation,energy dissipation,secant modulus and shear failure surface roughness.The experimental results show that when normal and shear stresses are applied simultaneously,there is a significant competitive relationship between them.On the dominant side,the strain rate will be significantly increased.The sample under a loading frequency of 0.2 Hz exhibits a longer fatigue life.During the cyclic shear test,the shear strain of the water-soaked sample is higher than that of the dry samples.The average roughness coefficient of failure surface exhibits an increasing pattern with increase in shear strength,the elevated roughness of a shear surface is advantageous in constraining shear displacements of specimens,thereby lowering the energy dissipation.This study can provide theoretical and practical implications for a long-term safety evaluation of CMUWR.展开更多
This work presents particle-based numerical simulations on coal pillars in a coal mine based underground water reservoir(CMUWR).We aim to replicate the stress-strain characteristics and present the acoustic emission b...This work presents particle-based numerical simulations on coal pillars in a coal mine based underground water reservoir(CMUWR).We aim to replicate the stress-strain characteristics and present the acoustic emission behavior of the coal under complex dynamic stress paths.The study reveals failure characteristics of coal exposed to monotonic/cyclic shear load under constant/cyclic normal loads.Based on the evolution of stress-time-dependent bond diameter implemented in particle model,different damage paths are established for dry and water-immersed samples under two loading frequencies.Furthermore,the numerical Gutenberg-Richter's b-value was calculated from the released energy emanating from bond failure,and this work presents the evolution of numerical Gutenberg-Richter's b-value.The numerical simulation contributes to a micromechanical understanding of the failure mechanisms of coal under water-immersion and cyclic stress,providing valuable insights for strength prediction of CMUWR.展开更多
基金support from the National Natural Science Foundation of China(grant number 52075544)Innovation Funds of Jihua Laboratory(X220971UZ230)+1 种基金Basic and Applied Basic Research Foundation of Guangdong Province(2022A1515110649)Funds from Research Platforms of Guangdong Higher Education Institutes(2022ZDJS038).
文摘Efficient lubrication of magnesium alloys is a highly challenging topic in the field of tribology.In this study,magnesium silicate hydroxide(MSH)nanotubes with serpentine structures were synthesized.The tribological behavior of AZ91D magnesium alloy rubbed against GCr15 steel was studied under lubricating oil with surface-modified MSH nanotubes as additives.The effects of the concentration,applied load,and reciprocating frequency on the friction and wear of the AZ91D alloy were studied using an SRV-4 sliding wear tester.Results show a decrease of 18.7–68.5%in friction coefficient,and a reduction of 19.4–54.3%in wear volume of magnesium alloy can be achieved by applying the synthetic serpentine additive under different conditions.A suspension containing 0.3 wt.%MSH was most efficient in reducing wear and friction.High frequency and medium load were more conducive to improving the tribological properties of magnesium alloys.A series of beneficial physical and chemical processes occurring at the AZ91D alloy/steel interface can be used to explain friction and wear reduction based on the characterization of the morphology,chemical composition,chemical state,microstructure,and nanomechanical properties of the worn surface.The synthetic MSH,with serpentine structure and nanotube morphology,possesses excellent adsorbability,high chemical activity,and good self-lubrication and catalytic activity.Therefore,physical polishing,tribochemical reactions,and physicalchemical depositions can occur easily on the sliding contacts.A dense tribolayer with a complex composition and composite structure was formed on the worn surface.Its high hardness,good toughness and plasticity,and prominent lubricity resulted in the improvement of friction and wear,making the synthetic MSH a promising efficient oil additive for magnesium alloys under boundary and mixed lubrication.
基金funded by NSFC(52204086,52474122)Guangdong Provincial Department of Science and Technology(2025B1515020067,2022A1515240009).
文摘This article investigates the mechanical responses and acoustic emission(AE)characteristics of sandstone under the triaxial differential cyclic loading(DCL)at different unloading rates of confining stress.The test results indicate that strength of rock specimens under different stress paths of triaxial unloading confining stress-differential cyclic loading(TUCS-DCL)can be fitted by the Mohr–Coulomb,Hoek–Brown,and Bieniawski criteria.The confining stress unloading rate can dominate the radial strain rate,while the axial DCL pattern has an unpronounced effect.The confining stress unloading rate affects the energy evolution in radial and axial directions of specimens,with the ratio of radially released energy to axially consumed energy fluctuating more significantly during the fast unloading of confining stress,the valley value of the ratio can serve as a precursor for failure.The confining stress unloading rate has no significant effect on stress–strain phase shift,while axial rapid-loading-slow-unloading can correspond to a larger magnitude of phase shift.AE signals begin to significantly increase after the confining stress is unloaded to zero,and a notable Kaiser effect is observed during cyclic loading preceding the failure.
基金funded by Open Fund of State Key Laboratory of Water Resource Protection and Utilization in Coal Mining(GJNY-20-113-03)Funds from NSFC(52204086)+2 种基金Funds from Joint National-Local Engineering Research Center for Safe and Precise Coal Mining(EC2021004)Funds from State Key Laboratory of Coal Resources in Western China(SKLCRKF20-07)Funds from Humboldt Research Fellowship.
文摘This work presents experimental tests based on coal collected from a coal mine based underground water reservoir(CMUWR).The mechanical responses of dry and water-soaked coal samples under the complex normal and shear stresses under multi-amplitude and variable frequency is investigated.The experimental results reveal the effects of stress path,water soaking and frequency on deformation,energy dissipation,secant modulus and shear failure surface roughness.The experimental results show that when normal and shear stresses are applied simultaneously,there is a significant competitive relationship between them.On the dominant side,the strain rate will be significantly increased.The sample under a loading frequency of 0.2 Hz exhibits a longer fatigue life.During the cyclic shear test,the shear strain of the water-soaked sample is higher than that of the dry samples.The average roughness coefficient of failure surface exhibits an increasing pattern with increase in shear strength,the elevated roughness of a shear surface is advantageous in constraining shear displacements of specimens,thereby lowering the energy dissipation.This study can provide theoretical and practical implications for a long-term safety evaluation of CMUWR.
基金funded by Open Fund of State Key Laboratory of Water Resource Protection and Utilization in Coal Mining(GJNY-20-113-03)Funds from NSFC(52204086)+2 种基金Funds from Joint National-Local Engineering Research Center for Safe and Precise Coal Mining(EC2021004)Funds from State Key Laboratory of Coal Resources in Western China(SKLCRKF20-07)Fund from Alexander von Humboldt Stiftung.
文摘This work presents particle-based numerical simulations on coal pillars in a coal mine based underground water reservoir(CMUWR).We aim to replicate the stress-strain characteristics and present the acoustic emission behavior of the coal under complex dynamic stress paths.The study reveals failure characteristics of coal exposed to monotonic/cyclic shear load under constant/cyclic normal loads.Based on the evolution of stress-time-dependent bond diameter implemented in particle model,different damage paths are established for dry and water-immersed samples under two loading frequencies.Furthermore,the numerical Gutenberg-Richter's b-value was calculated from the released energy emanating from bond failure,and this work presents the evolution of numerical Gutenberg-Richter's b-value.The numerical simulation contributes to a micromechanical understanding of the failure mechanisms of coal under water-immersion and cyclic stress,providing valuable insights for strength prediction of CMUWR.
