This paper investigates the temperature and loading rate dependencies of the critical stress intensity fac-tor(KIC)for dislocation nucleation at crack tips.We develop a new KIC formula with a generalized form by incor...This paper investigates the temperature and loading rate dependencies of the critical stress intensity fac-tor(KIC)for dislocation nucleation at crack tips.We develop a new KIC formula with a generalized form by incorporating the atomistic reaction pathway analysis into Transition State Theory(TST),which cap-tures the KIC of the first dislocation nucleation event at crack tips and its sensitivity to temperature and loading rates.We use this formula and atomistic modeling information to specifically calculate the KIC for quasi-two-dimensional crack tips located at various slant twin boundaries in nano-twinned TiAl al-loys across a wide range of temperatures and strain rates.Our findings reveal that twinning dislocation nucleation at the crack tip dominates crack propagation when twin boundaries(TBs)are tilted at 15.79°and 29.5°.Conversely,when TBs tilt at 45.29°,54.74°,and 70.53°,dislocation slip becomes the preferred mode.Additionally,at TB tilts of 29.5°and 70.53°,at higher temperatures above 800 K and typical exper-imental loading rates,both dislocation nucleation modes can be activated with nearly equal probability.This observation is particularly significant as it highlights scenarios that molecular dynamics simulations,due to their time scale limitations,cannot adequately explore.This insight underscores the importance of analyzing temperature and loading rate dependencies of the KIC to fully understand the competing mechanisms of dislocation nucleation and their impact on material behavior.展开更多
To find the deformation properties of chloride saline soil under the influence of a low temperature environment and different loads,two types of chloride saline soil were selected and their deformation process was tes...To find the deformation properties of chloride saline soil under the influence of a low temperature environment and different loads,two types of chloride saline soil were selected and their deformation process was tested in the laboratory and analyzed during the cooling process in the sensitive cryogenic temperature range.The research results show that high-chloride-salt saline soil underwent little volume change under the no-load condition during the cooling process.Under staticload and dynamic-load conditions,different degrees of settlement deformation occurred;throughout the entire cooling process,another chloride saline soil with a high proportion of sulfate salt underwent volume expansion under no-load and static-load conditions.Under the no-load condition,a certain degree of settlement deformation occurred.Deformation properties were evaluated at different time points during the cooling process for two kinds of chloride saline soil.Finally,deformation characteristics of chloride saline soil were analyzed from the perspective of salt type and crystallization variation under the action of a low-temperature environment and different loads.展开更多
Ultra-high speed machining technology enables high efficiency, high precision and high integrity of machined surface. Previous researches of hybrid bearing rarely consider influences of solid particles in lubricant an...Ultra-high speed machining technology enables high efficiency, high precision and high integrity of machined surface. Previous researches of hybrid bearing rarely consider influences of solid particles in lubricant and ultra-high speed of hybrid bearing, which cannot be ignored under the high speed and micro-space conditions of ultra-high speed water-lubricated hybrid bearing. Considering the impact of solid particles in lubricant, turbulence and temperature viscosity effects of lubricant, the influences of particles on pressure distribution, loading capacity and the temperature rise of the lubricant film with four-step-cavity ultra-high speed water-lubricated hybrid bearing are presented in the paper. The results show that loading capacity of the hybrid bearing can be affected by changing the viscosity of the lubricant, and large particles can improve the bearing loading capacity higher. The impact of water film temperature rise produced by solid particles in lubricant is related with particle diameter and minimum film thickness. Compared with the soft particles, hard particles cause the more increasing of water film temperature rise and loading capacity. When the speed of hybrid bearing increases, the impact of solid particles on hybrid bearing becomes increasingly apparent, especially for ultra-high speed water-lubricated hybrid bearing. This research presents influences of solid particles on the loading capacity and the temperature rise of water film in ultra-high speed hybrid bearings, the research conclusions provide a new method to evaluate the influence of solid particles in lubricant of ultra-high speed water-lubricated hybrid bearing, which is important to performance calculation of ultra-high speed hybrid bearings, design of filtration system, and safe operation of ultra-high speed hybrid bearings.展开更多
The uniaxial compression tests for mudstone specimens are carried out with four different loading rates from room temperature to 400℃ by using the Rock Mechanics Servo-controlled Testing System MTS810 and high temper...The uniaxial compression tests for mudstone specimens are carried out with four different loading rates from room temperature to 400℃ by using the Rock Mechanics Servo-controlled Testing System MTS810 and high temperature furnace MTS652.02.The mechanical properties of mudstone with various loading rates are studied under different temperature conditions.The results show that when temperature increases from room temperature to 400℃ and loading rate is less than 0.03 mm/s,the peak strength of mudstone specimen decreases as loading rate increases,while the various peak strengths show significant differences when loading rate exceeds 0.03 mm/s.At room temperature,the elastic modulus decreases at the first time and then increases with loading rate rising.When the temperature is between200 and 400℃,the elastic modulus presents a decreasing trend with increasing loading rate.With increasing the loading rate,the number of fragments in mudstone becomes larger and even the powder is observed in mudstone with higher loading rate.Under high loading rate,the failure mode of mudstone specimens under different temperatures is mainly conical damage.展开更多
It is important to analyze the damage evolution process of surrounding rock under different water content for the stability of engineering rock mass.Based on digital speckle correlation(DSCM),acoustic emission(AE)and ...It is important to analyze the damage evolution process of surrounding rock under different water content for the stability of engineering rock mass.Based on digital speckle correlation(DSCM),acoustic emission(AE)and electromagnetic radiation(EMR),uniaxial hierarchical cyclic loading and unloading tests were carried out on sandstones with different fracture numbers under dry,natural and saturated water content,to explore the fracture propagation,failure precursor characteristics and damage response mechanism under the influence of water content effect.The results show that with the increase of water content,the peak stress and crack initiation stress decrease gradually,and the decreases are 15.28%-21.11%and 17.64%-23.04%,respectively.The peak strain and crack initiation strain increase gradually,and the increases are 19.85%-44.53%and 19.15%-41.94%,respectively.The precracked rock with different water content is mainly characterized by tensile failure at different loading stages.However,with the increase of water content,the proportion of shear cracks gradually increases,while acoustic emission events gradually decrease,the dissipative energy and energy storage limits of the rock under peak load gradually decrease,and the charge signal increases significantly,which is because the lubrication effect of water reduces the friction coefficient between crack surfaces.展开更多
To investigate the wear resistance of ZG42CrMo in industrial application,the wear behaviors under different normal loads,sliding speeds and ambient temperatures were simulated by an MMU-5G abrasion tester to acquire t...To investigate the wear resistance of ZG42CrMo in industrial application,the wear behaviors under different normal loads,sliding speeds and ambient temperatures were simulated by an MMU-5G abrasion tester to acquire the friction coefficients and wear rates,with the morphology of worn surface observed by scanning electron microscopy(SEM)and chemical composition of worn surface and debris analyzed by X-ray energy dispersive spectroscopy(EDS).Combine with the theory of tribology,finally the regular of environmental factors’influence on material wear behaviors is determined.The results show that the increase of load decreases wear resistance significantly,when the pressure reaches a certain extent,severe spalling occurs on the worn surface;the changes of speed result in the changes of size of abrasive debris,and then effect the wear behaviors,in the increasing process of speed,the wear rate increases firstly and then decreases;the rise of temperature causes changes in wear mechanism,bring forth oxidation film on the worn surface,which leads to significant improvement of the wear resistance of materials under high temperature compared to that under low temperature.展开更多
In this paper, the influence of loading rate and specimen height on flexural strength of Al2O3 at high temperatures has been studied by three-point bending method. The experimental results show that the flexural stren...In this paper, the influence of loading rate and specimen height on flexural strength of Al2O3 at high temperatures has been studied by three-point bending method. The experimental results show that the flexural strength of Al2O3 decreases with increasing specimen height at room temperature, and it tends to stability when height increases to a certain degree (h=5mm in this paper), while the flexural strength of Al2O3 variates unapparently at high temperature with increasing height. There is a critical loading rate R . c. When loading rate R . is less than R . c, the flexural strength of Al2O3 increases with increasing loading rate and it drops sharply when loading rate is higher than R . c. The sensitivity of flexural strength to the loading rate decreases with elevating temperatures.展开更多
Owing to some excellent properties(such as large transmission ratio, high reliability, high precision,large stiffness, small volume and long service life), filtering reducers are suitable for occasions with high requi...Owing to some excellent properties(such as large transmission ratio, high reliability, high precision,large stiffness, small volume and long service life), filtering reducers are suitable for occasions with high requirements(e.g. space equipment). However, the tough working condition in space(including frequent changes of temperature, and large temperature difference combined with shock loads) may significantly affect the reliability.In this paper, the expressions of the minimal and maximal instantaneous transmission ratios(ITRs) considering temperature correction are developed. The minimal and maximal ITRs from simulation are used to verify the accuracy. Moreover, the reliability of a filtering reducer under different temperatures and the shock load are calculated, respectively. The research is beneficial to the design of spacecraft mechanism.展开更多
To predict the failure loads of adhesive joints under different stress states over the service temperature range of automobiles,adhesively bonded carbon fiber reinforced plastic( CFRP)/aluminum alloy joints under shea...To predict the failure loads of adhesive joints under different stress states over the service temperature range of automobiles,adhesively bonded carbon fiber reinforced plastic( CFRP)/aluminum alloy joints under shear stress state( thickadherend shear joints,TSJ),normal stress state( butt joints,BJ) and combined shear and normal stress states( scarf joints with scarf angle 45°,SJ45°) were manufactured and tested at-40,-20,0,20,40,60 and 80 ℃,respectively. The glass transition temperature Tgof the adhesive and CFRP,failure loads and fracture surfaces were used to analyze the failure mechanism of CFRP/aluminum alloy joints at different temperatures. A response surface,describing the variations of quadratic stress criteria with temperature,was established and introduced into the cohesive zone model( CZM) to carry out a simulation analysis. Results show that the failure of CFRP/aluminum alloy joints was determined collectively by the mechanical performances of adhesive and CFRP. Besides,reducing temperature or increasing the proportion of normal stress of adhesive layer was more likely to cause fibre tear or delamination of CFRP,resulting in a more obvious effect of CFRP. The validity of the prediction method was verified by the test of scarf joints with the scarf angle of 30°( SJ30°) and 60°( SJ60°) at-10 and 50 ℃.展开更多
This paper presents the results of fatigue performance tests performed up to 10 million cycles on a load-measuring pot bearing with built-in load cell to verify its field applicability and proposes an empirical temper...This paper presents the results of fatigue performance tests performed up to 10 million cycles on a load-measuring pot bearing with built-in load cell to verify its field applicability and proposes an empirical temperature correction formula. In Part I of this work, various measurement performances of the load-measuring pot bearing were evaluated through static and dynamic loading tests. Bridge bearings are subjected to the effect of fatigue caused by the repeated application of moving loads and exposed to harsh site conditions including cold and hot weathers differently to laboratory conditions. Accordingly, the durability of the load-measuring pot bearing with built-in load cell shall be secured and the environmental effects like temperature shall be minimized for its application on field. This study conducted fatigue tests up to 10 million cycles on a load-measuring pot bearing with the capacity of 1000 kN to examine eventual degradation of the measurement accuracy with respect to the number of fatigue loading cycles. In addition, the experimental temperature correction procedure is proposed to obtain the temperature correction formula enabling to correct the effect of temperature on the load measurement.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
Preexisting cracks inside tight sandstones are one of the most important properties for controlling the mechanical and seepage behaviors.During the cyclic loading process,the rock generally exhibits obvious memorabili...Preexisting cracks inside tight sandstones are one of the most important properties for controlling the mechanical and seepage behaviors.During the cyclic loading process,the rock generally exhibits obvious memorability and irreversible plastic deformation,even in the linear elastic stage.The assessment of the evolution of preexisting cracks under hydrostatic pressure loading and unloading processes is helpful in understanding the mechanism of plastic deformation.In this study,ultrasonic measurements were conducted on two tight sandstone specimens with different bedding orientations subjected to hydrostatic loading and unloading processes.The P-wave velocity was characterized by a similar response with the volumetric strain to the hydrostatic pressure and showed different strain sensitivities at different loading and unloading stages.A numerical model based on the discrete element method(DEM)was proposed to quantitatively clarify the evolution of the crack distribution under different hydrostatic pressures.The numerical model was verified by comparing the evolution of the measured P-wave velocities on two anisotropic specimens.The irreversible plastic deformation that occurred during the hydrostatic unloading stage was mainly due to the permanent closure of plastic-controlled cracks.The closure and reopening of cracks with a small aspect ratio account for the major microstructure evolution during the hydrostatic loading and unloading processes.Such evolution of microcracks is highly dependent on the stress path.The anisotropy of the crack distribution plays an important role in the magnitude and strain sensitivity of the P-wave velocity under stress conditions.The study can provide insight into the microstructure evolution during cyclic loading and unloading processes.展开更多
The influeuce of temperature on rheological characteristics of lubricants is analyzed. The constitutive equation, which describes the non-Newtonian properties of lubricants caused by thermal effect, is founded and cou...The influeuce of temperature on rheological characteristics of lubricants is analyzed. The constitutive equation, which describes the non-Newtonian properties of lubricants caused by thermal effect, is founded and coupled with equations or continuity and momentum of fluid to calculate the load carrying capacity of thrust bearings. The results or numerical solution show that lubricants have ultimate shear strength as a result or nou-Newtonian effect of temperature, and the thermal effect plays an.important role in load carrying capacity of thrust bearings The mechanism of film failure in thrust bearings is investigated initially’ Theoretlcal bases for predicting the lubrication situatlon and improving the design of thrust bearings are provided in this paper.展开更多
A series of tests were conducted to analyze temperature field distribution and thawing settlement of a thawing soil under static and dynamic loading at various cooling and thawing temperatures. The results demonstrate...A series of tests were conducted to analyze temperature field distribution and thawing settlement of a thawing soil under static and dynamic loading at various cooling and thawing temperatures. The results demonstrate： （1） the temperature field distribution of the thawing soil was not significantly influenced by the loading form under the tested loading conditions; similar results were obtained for samples at different dynamic loading frequencies and different dynamic loading ampli- tudes, which verified the independence of loading form and temperature field; （2） changed temperature field distributions were found in thawing soil with different cooling and thawing temperatures, and the cooling and thawing temperature of the samples were the main factors affecting their temperature distributions; （3） under the tested conditions, thawing set- tlements were little influenced by the thawing temperature and the dynamic loading frequency; and （4） a linear relation- ship existed between the thawing settlement and the cooling temperature, and a logarithmic function could be used to describe the relationship between the thawing settlement and the loading amplitude.展开更多
The influence of temperature-dependent properties on temperature response and optimum design of newly developed ceramic-metal functionally graded materials under cyclic thermal loading and high temperature gradient en...The influence of temperature-dependent properties on temperature response and optimum design of newly developed ceramic-metal functionally graded materials under cyclic thermal loading and high temperature gradient environment is studied. The thermal conductivity of the material is considered to be dependent on the temperature. In this paper, the temperature response of the material is calculated using a nonlinear finite element method. Emphasis is placed on the influence of temperatue-dependent properties on the thermal response and insulation property of the material render the different graded compositional distributions and different heat flux magnitudes. Through the analysis, it is suggested that the influence of temperature-dependent properties can not be neglected in the temperature response analysis and the optimum design process of the material must be based on the temperature-dependent temperature analysis theory.展开更多
To obtain frequency-temperature compensation in a sapphire loaded cavity for hydrogen maser, a dielectric named SrTiO3 is employed whose temperature coefficient of permittivity is opposite to that of sapphire. Based o...To obtain frequency-temperature compensation in a sapphire loaded cavity for hydrogen maser, a dielectric named SrTiO3 is employed whose temperature coefficient of permittivity is opposite to that of sapphire. Based on theoretical analysis and computer simulation, a TE011 mode of a sapphire loaded cavity associated with two small rings of SrTiO3 with different thickness is solved, and the useful parameters that influence the temperature coefficient of cavity are calculated. Finally an experiment is brought forward and its results are very close to the computing results. When the thickness of SiTiO3 dielectric is 7 mm and the diameter is 17 mm in configuration b, the temperature coefficient of cavity is decreased from -58.8 kHz/K to -8.2 kHz/K and the quality factor is 40248.展开更多
Conventional nuclear fusion occurs in plasma at temperatures greater than 10^(7)℃ or when energy higher than 10 keV is applied.We report a new result of anomalous neutron emission,also called cascade neutron burst em...Conventional nuclear fusion occurs in plasma at temperatures greater than 10^(7)℃ or when energy higher than 10 keV is applied.We report a new result of anomalous neutron emission,also called cascade neutron burst emission,from deuterium-loaded titanium and uranium deuteride samples at room temperature.The number of neutrons in the large bursts is measured as up to 2800 in less than a 64-μs interval.We suggest that the anomalous cascade neutron bursts are correlated with deuterium-loaded metals and probably the result of nuclear reactions occurring in the samples.展开更多
Anomalous ^(3)He/^(4)He ratios in deuterium-loaded titanium samples are observed to be about 1-4×10^(-1),much greater than the values (≤10^(-4)) in natural objects.Control experiments with the deuterium-unloaded...Anomalous ^(3)He/^(4)He ratios in deuterium-loaded titanium samples are observed to be about 1-4×10^(-1),much greater than the values (≤10^(-4)) in natural objects.Control experiments with the deuterium-unloaded titanium sample and original industrial deuterium gas are also carried out,but no anomalous 3He/4He values are observed.In addition,anomalous tritium in deuterium-loaded titanium samples are also observed.To explain the excess 3He and tritium in the deuterium-loaded titanium samples,it is required that the deuteron-induced nuclear reaction occurs in the samples at low temperature.展开更多
Ammonium overloading is a common response of aquatic organisms to air exposure during transport. This study elucidated the relationship between ammonium overloading and mortality of crab Portunus trituberculatus. Addi...Ammonium overloading is a common response of aquatic organisms to air exposure during transport. This study elucidated the relationship between ammonium overloading and mortality of crab Portunus trituberculatus. Additionally, we also explored the effects of emersion time and air temperature on ammonium loading and concomitant physiological change. To test the air temperature effect, the crab was exposed to 16, 23 and 30℃ in air for 3 h, respectively, and then recovered in seawater at 23℃ for 12 h. To test the emersion time effect, crab was exposed to 23℃ in air for 0.5 and 3 h, respectively, and then recovered in seawater at 23℃ for 12 h. In the control group, crab was always immersed at 23℃. At each time interval(0.5, 1.5 and 3 h during air exposure and 0.5, 2, 4 and 12 h during recovery), ammonium excretion rate, level of total ammonium, total free amino acids and urea concentration in hemolymph and the hepatopancreas enzyme activity involved in detoxifying ammonium were analysed. Results showed that crab mortality was positively related with emersion time and temperature while ammonium loading was lower at 16 and 30℃ than at 23℃. For crab experiencing thermal inconsistence of culture media(i.e., 16 or 30℃), they were higher in ammonium excretion rate and activities of ammonium detoxification enzymes, which may be the reason that they had a lower ammonium loading. Prolonged emersion time(3.0 h vs. 0.5 h) increased the ammonium overloading and the activity of ammonium detoxification pathways in crab. Our results demonstrated that emersion-induced ammonium overloading may not be the main reason leading to P. trituberculatus death during air exposure and subsequent recovery. When the culture medium changed, thermal variation, compared with constant temperature, could reduce ammonium overloading in crab by elevating the activities of ammonium detoxification enzymes and ammonium excretion rate during recovery period.展开更多
A complete road-soft ground model is established in this paper to study the dynamic responses caused by vehicle loads and/or daily temperature variation.A dynamic thermo-elastic model is applied to capturing the behav...A complete road-soft ground model is established in this paper to study the dynamic responses caused by vehicle loads and/or daily temperature variation.A dynamic thermo-elastic model is applied to capturing the behavior of the rigid pavement,the base course,and the subgrade,while the soft ground is characterized using a dynamic thermo-poroelastic model.Solutions to the road-soft ground system are derived in the Laplace-Hankel transform domain.The time domain solutions are obtained using an integration approach.The temperature,thermal stress,pore water pressure,and displacement responses caused by the vehicle load and the daily temperature variation are presented.Results show that obvious temperature change mainly exists within 0.3 m of the road when subjected to the daily temperature variation,whereas the stress responses can still be found in deeper places because of the thermal swelling/shrinkage deformation within the upper road structures.Moreover,it is important to consider the coupling effects of the vehicle load and the daily temperature variation when calculating the dynamic responses inside the road-soft ground system.展开更多
基金supported by the China Scholarship Council(Grant No.202007865002)the National Natural Science Foundation of China(Grant Nos.51865027,52065036,and 52065037)+2 种基金the Educational Unveiling Leadership Project of Gansu Province of China(Grant No.2021jyjbgs01)the support by JSPS KAKENHI(Grant No.JP23K20037)MEXT Programs(Grant Nos.JPMXP1122684766,JPMXP1020230325,and JPMXP1020230327).
文摘This paper investigates the temperature and loading rate dependencies of the critical stress intensity fac-tor(KIC)for dislocation nucleation at crack tips.We develop a new KIC formula with a generalized form by incorporating the atomistic reaction pathway analysis into Transition State Theory(TST),which cap-tures the KIC of the first dislocation nucleation event at crack tips and its sensitivity to temperature and loading rates.We use this formula and atomistic modeling information to specifically calculate the KIC for quasi-two-dimensional crack tips located at various slant twin boundaries in nano-twinned TiAl al-loys across a wide range of temperatures and strain rates.Our findings reveal that twinning dislocation nucleation at the crack tip dominates crack propagation when twin boundaries(TBs)are tilted at 15.79°and 29.5°.Conversely,when TBs tilt at 45.29°,54.74°,and 70.53°,dislocation slip becomes the preferred mode.Additionally,at TB tilts of 29.5°and 70.53°,at higher temperatures above 800 K and typical exper-imental loading rates,both dislocation nucleation modes can be activated with nearly equal probability.This observation is particularly significant as it highlights scenarios that molecular dynamics simulations,due to their time scale limitations,cannot adequately explore.This insight underscores the importance of analyzing temperature and loading rate dependencies of the KIC to fully understand the competing mechanisms of dislocation nucleation and their impact on material behavior.
基金supported by National Natural Science Foundation of China (No. 41501062)
文摘To find the deformation properties of chloride saline soil under the influence of a low temperature environment and different loads,two types of chloride saline soil were selected and their deformation process was tested in the laboratory and analyzed during the cooling process in the sensitive cryogenic temperature range.The research results show that high-chloride-salt saline soil underwent little volume change under the no-load condition during the cooling process.Under staticload and dynamic-load conditions,different degrees of settlement deformation occurred;throughout the entire cooling process,another chloride saline soil with a high proportion of sulfate salt underwent volume expansion under no-load and static-load conditions.Under the no-load condition,a certain degree of settlement deformation occurred.Deformation properties were evaluated at different time points during the cooling process for two kinds of chloride saline soil.Finally,deformation characteristics of chloride saline soil were analyzed from the perspective of salt type and crystallization variation under the action of a low-temperature environment and different loads.
基金Supported by National Natural Science Foundation of China(Grant No.51275395)Major National Basic Research Program of China(973 Program,Grant Nos.2009CB724304-2,2009CB724404)
文摘Ultra-high speed machining technology enables high efficiency, high precision and high integrity of machined surface. Previous researches of hybrid bearing rarely consider influences of solid particles in lubricant and ultra-high speed of hybrid bearing, which cannot be ignored under the high speed and micro-space conditions of ultra-high speed water-lubricated hybrid bearing. Considering the impact of solid particles in lubricant, turbulence and temperature viscosity effects of lubricant, the influences of particles on pressure distribution, loading capacity and the temperature rise of the lubricant film with four-step-cavity ultra-high speed water-lubricated hybrid bearing are presented in the paper. The results show that loading capacity of the hybrid bearing can be affected by changing the viscosity of the lubricant, and large particles can improve the bearing loading capacity higher. The impact of water film temperature rise produced by solid particles in lubricant is related with particle diameter and minimum film thickness. Compared with the soft particles, hard particles cause the more increasing of water film temperature rise and loading capacity. When the speed of hybrid bearing increases, the impact of solid particles on hybrid bearing becomes increasingly apparent, especially for ultra-high speed water-lubricated hybrid bearing. This research presents influences of solid particles on the loading capacity and the temperature rise of water film in ultra-high speed hybrid bearings, the research conclusions provide a new method to evaluate the influence of solid particles in lubricant of ultra-high speed water-lubricated hybrid bearing, which is important to performance calculation of ultra-high speed hybrid bearings, design of filtration system, and safe operation of ultra-high speed hybrid bearings.
基金supported by the National Natural Science Foundation of China(Nos.51104128,51322401,51304201 and 51204159)Jiangsu Province Prospective industry-UniversityResearch Cooperation Research Program of China(No.BY2012085)+2 种基金Doctor Station Fund of China(No.20120095110013)333 Project Program of Jiangsu Province of China"Blue Project" Program of Jiangsu Province of China
文摘The uniaxial compression tests for mudstone specimens are carried out with four different loading rates from room temperature to 400℃ by using the Rock Mechanics Servo-controlled Testing System MTS810 and high temperature furnace MTS652.02.The mechanical properties of mudstone with various loading rates are studied under different temperature conditions.The results show that when temperature increases from room temperature to 400℃ and loading rate is less than 0.03 mm/s,the peak strength of mudstone specimen decreases as loading rate increases,while the various peak strengths show significant differences when loading rate exceeds 0.03 mm/s.At room temperature,the elastic modulus decreases at the first time and then increases with loading rate rising.When the temperature is between200 and 400℃,the elastic modulus presents a decreasing trend with increasing loading rate.With increasing the loading rate,the number of fragments in mudstone becomes larger and even the powder is observed in mudstone with higher loading rate.Under high loading rate,the failure mode of mudstone specimens under different temperatures is mainly conical damage.
基金financially supported by National Natural Science Foundation of China(No.52304136)Young Talent of Lifting Engineering for Science and Technology in Shandong,China(No.SDAST2024QTA060)Key Project of Research and Development in Liaocheng(No.2023YD02)。
文摘It is important to analyze the damage evolution process of surrounding rock under different water content for the stability of engineering rock mass.Based on digital speckle correlation(DSCM),acoustic emission(AE)and electromagnetic radiation(EMR),uniaxial hierarchical cyclic loading and unloading tests were carried out on sandstones with different fracture numbers under dry,natural and saturated water content,to explore the fracture propagation,failure precursor characteristics and damage response mechanism under the influence of water content effect.The results show that with the increase of water content,the peak stress and crack initiation stress decrease gradually,and the decreases are 15.28%-21.11%and 17.64%-23.04%,respectively.The peak strain and crack initiation strain increase gradually,and the increases are 19.85%-44.53%and 19.15%-41.94%,respectively.The precracked rock with different water content is mainly characterized by tensile failure at different loading stages.However,with the increase of water content,the proportion of shear cracks gradually increases,while acoustic emission events gradually decrease,the dissipative energy and energy storage limits of the rock under peak load gradually decrease,and the charge signal increases significantly,which is because the lubrication effect of water reduces the friction coefficient between crack surfaces.
基金Sponsored by High Technology Research and Development Program of China(2009AA04Z143)New Century Excellent Talents in University of China(NCET-09-0117)
文摘To investigate the wear resistance of ZG42CrMo in industrial application,the wear behaviors under different normal loads,sliding speeds and ambient temperatures were simulated by an MMU-5G abrasion tester to acquire the friction coefficients and wear rates,with the morphology of worn surface observed by scanning electron microscopy(SEM)and chemical composition of worn surface and debris analyzed by X-ray energy dispersive spectroscopy(EDS).Combine with the theory of tribology,finally the regular of environmental factors’influence on material wear behaviors is determined.The results show that the increase of load decreases wear resistance significantly,when the pressure reaches a certain extent,severe spalling occurs on the worn surface;the changes of speed result in the changes of size of abrasive debris,and then effect the wear behaviors,in the increasing process of speed,the wear rate increases firstly and then decreases;the rise of temperature causes changes in wear mechanism,bring forth oxidation film on the worn surface,which leads to significant improvement of the wear resistance of materials under high temperature compared to that under low temperature.
文摘In this paper, the influence of loading rate and specimen height on flexural strength of Al2O3 at high temperatures has been studied by three-point bending method. The experimental results show that the flexural strength of Al2O3 decreases with increasing specimen height at room temperature, and it tends to stability when height increases to a certain degree (h=5mm in this paper), while the flexural strength of Al2O3 variates unapparently at high temperature with increasing height. There is a critical loading rate R . c. When loading rate R . is less than R . c, the flexural strength of Al2O3 increases with increasing loading rate and it drops sharply when loading rate is higher than R . c. The sensitivity of flexural strength to the loading rate decreases with elevating temperatures.
基金the Open Foundation of the State Key Laboratory of Mechanical Transmissions of Chongqing University(No.SKLMT-KFKT-201601)
文摘Owing to some excellent properties(such as large transmission ratio, high reliability, high precision,large stiffness, small volume and long service life), filtering reducers are suitable for occasions with high requirements(e.g. space equipment). However, the tough working condition in space(including frequent changes of temperature, and large temperature difference combined with shock loads) may significantly affect the reliability.In this paper, the expressions of the minimal and maximal instantaneous transmission ratios(ITRs) considering temperature correction are developed. The minimal and maximal ITRs from simulation are used to verify the accuracy. Moreover, the reliability of a filtering reducer under different temperatures and the shock load are calculated, respectively. The research is beneficial to the design of spacecraft mechanism.
基金The National Natural Science Foundation of China(No.51775230)
文摘To predict the failure loads of adhesive joints under different stress states over the service temperature range of automobiles,adhesively bonded carbon fiber reinforced plastic( CFRP)/aluminum alloy joints under shear stress state( thickadherend shear joints,TSJ),normal stress state( butt joints,BJ) and combined shear and normal stress states( scarf joints with scarf angle 45°,SJ45°) were manufactured and tested at-40,-20,0,20,40,60 and 80 ℃,respectively. The glass transition temperature Tgof the adhesive and CFRP,failure loads and fracture surfaces were used to analyze the failure mechanism of CFRP/aluminum alloy joints at different temperatures. A response surface,describing the variations of quadratic stress criteria with temperature,was established and introduced into the cohesive zone model( CZM) to carry out a simulation analysis. Results show that the failure of CFRP/aluminum alloy joints was determined collectively by the mechanical performances of adhesive and CFRP. Besides,reducing temperature or increasing the proportion of normal stress of adhesive layer was more likely to cause fibre tear or delamination of CFRP,resulting in a more obvious effect of CFRP. The validity of the prediction method was verified by the test of scarf joints with the scarf angle of 30°( SJ30°) and 60°( SJ60°) at-10 and 50 ℃.
文摘This paper presents the results of fatigue performance tests performed up to 10 million cycles on a load-measuring pot bearing with built-in load cell to verify its field applicability and proposes an empirical temperature correction formula. In Part I of this work, various measurement performances of the load-measuring pot bearing were evaluated through static and dynamic loading tests. Bridge bearings are subjected to the effect of fatigue caused by the repeated application of moving loads and exposed to harsh site conditions including cold and hot weathers differently to laboratory conditions. Accordingly, the durability of the load-measuring pot bearing with built-in load cell shall be secured and the environmental effects like temperature shall be minimized for its application on field. This study conducted fatigue tests up to 10 million cycles on a load-measuring pot bearing with the capacity of 1000 kN to examine eventual degradation of the measurement accuracy with respect to the number of fatigue loading cycles. In addition, the experimental temperature correction procedure is proposed to obtain the temperature correction formula enabling to correct the effect of temperature on the load measurement.
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supported by the National Natural Science Foundation of China(Grant No.U2244215)the Knowledge Innovation Program of Wuhan-Basic Research(Grant No.2022010801010159)the Major Project of Inner Mongolia Science and Technology(Grant No.2021ZD0034).
文摘Preexisting cracks inside tight sandstones are one of the most important properties for controlling the mechanical and seepage behaviors.During the cyclic loading process,the rock generally exhibits obvious memorability and irreversible plastic deformation,even in the linear elastic stage.The assessment of the evolution of preexisting cracks under hydrostatic pressure loading and unloading processes is helpful in understanding the mechanism of plastic deformation.In this study,ultrasonic measurements were conducted on two tight sandstone specimens with different bedding orientations subjected to hydrostatic loading and unloading processes.The P-wave velocity was characterized by a similar response with the volumetric strain to the hydrostatic pressure and showed different strain sensitivities at different loading and unloading stages.A numerical model based on the discrete element method(DEM)was proposed to quantitatively clarify the evolution of the crack distribution under different hydrostatic pressures.The numerical model was verified by comparing the evolution of the measured P-wave velocities on two anisotropic specimens.The irreversible plastic deformation that occurred during the hydrostatic unloading stage was mainly due to the permanent closure of plastic-controlled cracks.The closure and reopening of cracks with a small aspect ratio account for the major microstructure evolution during the hydrostatic loading and unloading processes.Such evolution of microcracks is highly dependent on the stress path.The anisotropy of the crack distribution plays an important role in the magnitude and strain sensitivity of the P-wave velocity under stress conditions.The study can provide insight into the microstructure evolution during cyclic loading and unloading processes.
文摘The influeuce of temperature on rheological characteristics of lubricants is analyzed. The constitutive equation, which describes the non-Newtonian properties of lubricants caused by thermal effect, is founded and coupled with equations or continuity and momentum of fluid to calculate the load carrying capacity of thrust bearings. The results or numerical solution show that lubricants have ultimate shear strength as a result or nou-Newtonian effect of temperature, and the thermal effect plays an.important role in load carrying capacity of thrust bearings The mechanism of film failure in thrust bearings is investigated initially’ Theoretlcal bases for predicting the lubrication situatlon and improving the design of thrust bearings are provided in this paper.
基金provided by National Natural Science Foundation of China (NSFC) under Grant Nos.41001036 and 41171064
文摘A series of tests were conducted to analyze temperature field distribution and thawing settlement of a thawing soil under static and dynamic loading at various cooling and thawing temperatures. The results demonstrate： （1） the temperature field distribution of the thawing soil was not significantly influenced by the loading form under the tested loading conditions; similar results were obtained for samples at different dynamic loading frequencies and different dynamic loading ampli- tudes, which verified the independence of loading form and temperature field; （2） changed temperature field distributions were found in thawing soil with different cooling and thawing temperatures, and the cooling and thawing temperature of the samples were the main factors affecting their temperature distributions; （3） under the tested conditions, thawing set- tlements were little influenced by the thawing temperature and the dynamic loading frequency; and （4） a linear relation- ship existed between the thawing settlement and the cooling temperature, and a logarithmic function could be used to describe the relationship between the thawing settlement and the loading amplitude.
基金This work was supported by the National Science Foundation of China
文摘The influence of temperature-dependent properties on temperature response and optimum design of newly developed ceramic-metal functionally graded materials under cyclic thermal loading and high temperature gradient environment is studied. The thermal conductivity of the material is considered to be dependent on the temperature. In this paper, the temperature response of the material is calculated using a nonlinear finite element method. Emphasis is placed on the influence of temperatue-dependent properties on the thermal response and insulation property of the material render the different graded compositional distributions and different heat flux magnitudes. Through the analysis, it is suggested that the influence of temperature-dependent properties can not be neglected in the temperature response analysis and the optimum design process of the material must be based on the temperature-dependent temperature analysis theory.
文摘To obtain frequency-temperature compensation in a sapphire loaded cavity for hydrogen maser, a dielectric named SrTiO3 is employed whose temperature coefficient of permittivity is opposite to that of sapphire. Based on theoretical analysis and computer simulation, a TE011 mode of a sapphire loaded cavity associated with two small rings of SrTiO3 with different thickness is solved, and the useful parameters that influence the temperature coefficient of cavity are calculated. Finally an experiment is brought forward and its results are very close to the computing results. When the thickness of SiTiO3 dielectric is 7 mm and the diameter is 17 mm in configuration b, the temperature coefficient of cavity is decreased from -58.8 kHz/K to -8.2 kHz/K and the quality factor is 40248.
基金Supported by the President Foundation of the China Institute of Atomic Energy(No YZ-0704).
文摘Conventional nuclear fusion occurs in plasma at temperatures greater than 10^(7)℃ or when energy higher than 10 keV is applied.We report a new result of anomalous neutron emission,also called cascade neutron burst emission,from deuterium-loaded titanium and uranium deuteride samples at room temperature.The number of neutrons in the large bursts is measured as up to 2800 in less than a 64-μs interval.We suggest that the anomalous cascade neutron bursts are correlated with deuterium-loaded metals and probably the result of nuclear reactions occurring in the samples.
基金Supported by President Foundation of the China Institute of Atomic Energy(No YZ-0704).
文摘Anomalous ^(3)He/^(4)He ratios in deuterium-loaded titanium samples are observed to be about 1-4×10^(-1),much greater than the values (≤10^(-4)) in natural objects.Control experiments with the deuterium-unloaded titanium sample and original industrial deuterium gas are also carried out,but no anomalous 3He/4He values are observed.In addition,anomalous tritium in deuterium-loaded titanium samples are also observed.To explain the excess 3He and tritium in the deuterium-loaded titanium samples,it is required that the deuteron-induced nuclear reaction occurs in the samples at low temperature.
基金supported by the National Natural Science Foundation of China (No.31972784)the Shandong Province Natural Science Fund Project (No.ZR2018M C028)+4 种基金the High-level Talents Research Fund of Qingdao Agricultural University (No.663/1119032)the Scientific Research Project of Tianjin Education Commission (No.2017KJ186)the Shrimp & Crab Innovation Team of Shandong Agriculture Research System (No.SDAIT-15-011)the 'First Class Fishery Discipline' programme in Shandong Province, ChinaMarine and Fishery Science and Technology Innovation Project of Shandong Province (No.2017YY20)。
文摘Ammonium overloading is a common response of aquatic organisms to air exposure during transport. This study elucidated the relationship between ammonium overloading and mortality of crab Portunus trituberculatus. Additionally, we also explored the effects of emersion time and air temperature on ammonium loading and concomitant physiological change. To test the air temperature effect, the crab was exposed to 16, 23 and 30℃ in air for 3 h, respectively, and then recovered in seawater at 23℃ for 12 h. To test the emersion time effect, crab was exposed to 23℃ in air for 0.5 and 3 h, respectively, and then recovered in seawater at 23℃ for 12 h. In the control group, crab was always immersed at 23℃. At each time interval(0.5, 1.5 and 3 h during air exposure and 0.5, 2, 4 and 12 h during recovery), ammonium excretion rate, level of total ammonium, total free amino acids and urea concentration in hemolymph and the hepatopancreas enzyme activity involved in detoxifying ammonium were analysed. Results showed that crab mortality was positively related with emersion time and temperature while ammonium loading was lower at 16 and 30℃ than at 23℃. For crab experiencing thermal inconsistence of culture media(i.e., 16 or 30℃), they were higher in ammonium excretion rate and activities of ammonium detoxification enzymes, which may be the reason that they had a lower ammonium loading. Prolonged emersion time(3.0 h vs. 0.5 h) increased the ammonium overloading and the activity of ammonium detoxification pathways in crab. Our results demonstrated that emersion-induced ammonium overloading may not be the main reason leading to P. trituberculatus death during air exposure and subsequent recovery. When the culture medium changed, thermal variation, compared with constant temperature, could reduce ammonium overloading in crab by elevating the activities of ammonium detoxification enzymes and ammonium excretion rate during recovery period.
基金funding support from the National Natural Science Foundation of China(Grant Nos.42077262 and 42077261).
文摘A complete road-soft ground model is established in this paper to study the dynamic responses caused by vehicle loads and/or daily temperature variation.A dynamic thermo-elastic model is applied to capturing the behavior of the rigid pavement,the base course,and the subgrade,while the soft ground is characterized using a dynamic thermo-poroelastic model.Solutions to the road-soft ground system are derived in the Laplace-Hankel transform domain.The time domain solutions are obtained using an integration approach.The temperature,thermal stress,pore water pressure,and displacement responses caused by the vehicle load and the daily temperature variation are presented.Results show that obvious temperature change mainly exists within 0.3 m of the road when subjected to the daily temperature variation,whereas the stress responses can still be found in deeper places because of the thermal swelling/shrinkage deformation within the upper road structures.Moreover,it is important to consider the coupling effects of the vehicle load and the daily temperature variation when calculating the dynamic responses inside the road-soft ground system.
