The degradation of the shear stress between pile-clay interface caused by undrained cyclic jacking affects the jacking force.A series of large displacement monotonic shear,cyclic shear and post-cyclic monotonic steel ...The degradation of the shear stress between pile-clay interface caused by undrained cyclic jacking affects the jacking force.A series of large displacement monotonic shear,cyclic shear and post-cyclic monotonic steel plate-clay interface shear te sts were performed under the constant normal load(CNL)condition to inve stigate the effects of normal stre ss,cyclic amplitude,and number of cycles on a steel plate-clay interface using the GDS multi-function interface shear tester.Based on the experimental results,in monotonic shear tests,change of shear stress took place in the specimen,the shear stress rapidly reached the peak value at shear displacement of 1 mm,and then abruptly decreased to the residual value.In cyclic shear te sts,accumulated displacement was a better parameter to describe the soil degradation characteristics,and the degradation degree of shear stress became greater with the increasing of normal stress and accumulated displacement.Shear stress in post-cyclic monotonic shear tests did not generate a peak value and was lower than that in monotonic shear tests under the same normal stress.The soil was completely disturbed and reached the residual strength when the cumulative displacement approached 6 m.An empirical equation to evaluate shear stress degradation mechanism was formulated and the procedure of parameter identification was presented.展开更多
The study of frictional properties of human skin is important for medical research, skin care products and textile exploi- tation. In order to investigate the influence of normal load and sliding speed on the friction...The study of frictional properties of human skin is important for medical research, skin care products and textile exploi- tation. In order to investigate the influence of normal load and sliding speed on the frictional properties of skin and its possible mechanism, tests were carded out on a multi-specimen friction tester. When the normal load increases from 0.1 N to 0.9 N, normal displacement and the friction coefficient of skin increase. The friction coefficient is dependent on the load, indicating that both adhesion and deformation contribute to the friction behaviour. The deformation friction was interpreted using the plough model of friction. When sliding speed increases from 0.5 mm·s^-1 to 4 mm·s^-1, the friction coefficient increases and "stick-slip" phenomena increase, indicating that hysteretic friction contributes to the friction. The hysteretic friction was in- terpreted using schematic of energy translation during the rigid spherical probe sliding on the soft skin surface, which provides an explanation for the influence of the sliding speed on the frictional characteristics of the skin.展开更多
The dynamic frictional behaviors of natural discontinuities(joints,fractures,faults)play an important role in geohazards assessment;however,the mechanisms of the dynamic fault weakening/strengthening are still unclear...The dynamic frictional behaviors of natural discontinuities(joints,fractures,faults)play an important role in geohazards assessment;however,the mechanisms of the dynamic fault weakening/strengthening are still unclear.In this paper,a dynamic shear box was used to perform direct shear tests on saw-cut(planar)and natural(rough)granite fractures,with different normal load oscillation amplitudes.Based on the recorded shear forces and normal displacements,the shear forces,apparent friction coefficients and normal displacements are found to change periodically with oscillated normal loads and are characterized by a series of time shifts.The observed changing patterns are similar for the rough and planar fractures.Compared with the test data under constant normal load(CNL),small/large normal load oscillation amplitude enhances/reduces the peak shear strength,with a critical point.The magnitude of critical normal load oscillation for the rough fractures is smaller than the planer fractures.The results imply that dynamic fault weakening/strengthening can be achieved by both normal load oscillation amplitudes and slip surface topography.The rough fractures with larger normal oscillation amplitude can easily cause frictional weakening under stress disturbance.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
Slide-hold-slide(SHS)test is an essential experimental approach for studying the frictional stability of faults.The origin SHS framework was established based on a consistent constant normal stress,which cannot truly ...Slide-hold-slide(SHS)test is an essential experimental approach for studying the frictional stability of faults.The origin SHS framework was established based on a consistent constant normal stress,which cannot truly reflect the stress disturbance around fault zones.In this paper,we conducted a series of'dynamic SHS tests',which includes normal stress oscillations in the relaxation stage with different oscillation amplitudes and frequencies on synthetic quartz gouge using a double direct shear assembly.The experimental results reveal that the amplitude of the normal load oscillation has a remarkable effect on the frictional relaxation and healing patterns.However,the frequency of the normal load oscillation has a minor effect.Additionally,the shear loading rate is proportional to the normal loading rate during the relaxation stage,and the normal stiffness of the quartz layer remains nearly constant under various loading conditions.The creep rate during the hold phase is not obviously affected by the normal load oscillation,while the precursory slip is also sensitive to the oscillation amplitude.This study provides insights into the evolution of frictional stability in discontinuities and is beneficial for controlling relative disasters in fault zones.展开更多
This paper investigates the frictional behavior of the infilled rock fracture under dynamic normal stress.A series of direct shear tests were conducted on saw-cut granite fractures infilled with quartz using a selfdev...This paper investigates the frictional behavior of the infilled rock fracture under dynamic normal stress.A series of direct shear tests were conducted on saw-cut granite fractures infilled with quartz using a selfdeveloped dynamic shear apparatus,and the effects of normal load oscillation amplitude,normal load oscillation period and sliding velocity were studied.The test results reveal that the shear response can be divided into three stages over a whole loading-unloading process,characterized by different time spans and stress variations.Generally,a smaller oscillation amplitude,a longer oscillation period and a fast shear velocity promote the stability of the friction system,which is also confirmed by the Coulomb failure criterion calculated based on the observed periodic apparent friction coefficient.The dynamic strengthening/weakening phenomenon is dependent on the oscillation amplitude and product of sliding velocity and oscillation period(vT).Also,the rate and state friction law incorporating the parameter a that characterizes the normal stress variation is employed to describe the dynamic friction coefficient but exhibits an incompetent performance when handling intensive variation in normal stress.Finally,the potential seismicity induced by oscillating normal stress based on the observed stress drop is analyzed.This work helps us understand the sliding process and stability evolution of natural faults,and its benefits for relative hazard mitigation.展开更多
The scratch test is used for quality control mostly in phenomenological ways,and whether fracture toughness can be obtained from this test is still a matter of debate requiring further elucidation.In this paper,values...The scratch test is used for quality control mostly in phenomenological ways,and whether fracture toughness can be obtained from this test is still a matter of debate requiring further elucidation.In this paper,values of the fracture toughness of copper obtained by different scratch-based approaches are compared in order to examine the applicability of scratch-based methodologies to characterize the fracture toughness of soft metals.The scratch response of copper to a Rockwell C diamond indenter is studied under a constant normal load condition.The variations of penetration depth,residual depth,and residual scratch width with applied normal load are quantified from spherical to sphero-conical contact regimes by piecewise functions.A newly proposed size effect law is found to be the most suitable for scratch-based approaches to characterizing the fracture toughness of soft metallic materials with significant plasticity.A simple expression relating the nominal stress to the penetration depth is proposed for the spherical contact regime and gives almost the same value of fracture toughness.The residual scratch width provides useful information on pile-up of material and on the spherical tip radius of the indenter.It is found that the values of the fracture toughness obtained from the microscratch test are influenced by the data range for analysis.展开更多
随着建筑物能源消耗的不断升高,高精度与高泛化能力的非侵入式负荷监测技术的研究具有重大意义。针对当前负荷分解方法存在的问题,提出了一种基于多尺度特征融合与多任务学习框架的非侵入式负荷监测方法。将实例-批归一化网络与U形网络...随着建筑物能源消耗的不断升高,高精度与高泛化能力的非侵入式负荷监测技术的研究具有重大意义。针对当前负荷分解方法存在的问题,提出了一种基于多尺度特征融合与多任务学习框架的非侵入式负荷监测方法。将实例-批归一化网络与U形网络结合,提取总负荷数据的上下文信息,并利用跨越连接实现对不同尺度的细节特征与全局特征的融合。针对多特征特点,引入高效通道注意力网络,使模型聚焦重要特征。引入多任务学习框架与后处理操作,去除输出的假阳性片段,实现对目标电器的精准识别。将所提模型与几种代表性模型在UK-DALE(UK domestic appliance-level electricity)数据集与REDD(reference energy disaggregation data set)上进行对比实验,结果表明,所提模型的性能优于对比模型,具有出色的负荷分解能力与状态识别能力。展开更多
基金financially supported by the Fundamental Research Funds for the Study on Formation and Evolution Mechanism of Soil Plug of Jacked Pipe Pile Cyclic Penetration in Clay (Grant No.52078483)。
文摘The degradation of the shear stress between pile-clay interface caused by undrained cyclic jacking affects the jacking force.A series of large displacement monotonic shear,cyclic shear and post-cyclic monotonic steel plate-clay interface shear te sts were performed under the constant normal load(CNL)condition to inve stigate the effects of normal stre ss,cyclic amplitude,and number of cycles on a steel plate-clay interface using the GDS multi-function interface shear tester.Based on the experimental results,in monotonic shear tests,change of shear stress took place in the specimen,the shear stress rapidly reached the peak value at shear displacement of 1 mm,and then abruptly decreased to the residual value.In cyclic shear te sts,accumulated displacement was a better parameter to describe the soil degradation characteristics,and the degradation degree of shear stress became greater with the increasing of normal stress and accumulated displacement.Shear stress in post-cyclic monotonic shear tests did not generate a peak value and was lower than that in monotonic shear tests under the same normal stress.The soil was completely disturbed and reached the residual strength when the cumulative displacement approached 6 m.An empirical equation to evaluate shear stress degradation mechanism was formulated and the procedure of parameter identification was presented.
基金This work was supported by the National Natural Science Foundation of China(grant No.50475164 and 50535050)by the Science Foundation of China University of Mining and Technology(grant No.2005B034).
文摘The study of frictional properties of human skin is important for medical research, skin care products and textile exploi- tation. In order to investigate the influence of normal load and sliding speed on the frictional properties of skin and its possible mechanism, tests were carded out on a multi-specimen friction tester. When the normal load increases from 0.1 N to 0.9 N, normal displacement and the friction coefficient of skin increase. The friction coefficient is dependent on the load, indicating that both adhesion and deformation contribute to the friction behaviour. The deformation friction was interpreted using the plough model of friction. When sliding speed increases from 0.5 mm·s^-1 to 4 mm·s^-1, the friction coefficient increases and "stick-slip" phenomena increase, indicating that hysteretic friction contributes to the friction. The hysteretic friction was in- terpreted using schematic of energy translation during the rigid spherical probe sliding on the soft skin surface, which provides an explanation for the influence of the sliding speed on the frictional characteristics of the skin.
基金the funding support from the National Natural Science Foundation of China (Grant No. 51904359)the Guangdong Provincial Department of Science and Technology (Grant No. 2019ZT08G090)the Open Research Fund of the State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology (CUMT) (Grant No. SKLCRSM20KF002)
文摘The dynamic frictional behaviors of natural discontinuities(joints,fractures,faults)play an important role in geohazards assessment;however,the mechanisms of the dynamic fault weakening/strengthening are still unclear.In this paper,a dynamic shear box was used to perform direct shear tests on saw-cut(planar)and natural(rough)granite fractures,with different normal load oscillation amplitudes.Based on the recorded shear forces and normal displacements,the shear forces,apparent friction coefficients and normal displacements are found to change periodically with oscillated normal loads and are characterized by a series of time shifts.The observed changing patterns are similar for the rough and planar fractures.Compared with the test data under constant normal load(CNL),small/large normal load oscillation amplitude enhances/reduces the peak shear strength,with a critical point.The magnitude of critical normal load oscillation for the rough fractures is smaller than the planer fractures.The results imply that dynamic fault weakening/strengthening can be achieved by both normal load oscillation amplitudes and slip surface topography.The rough fractures with larger normal oscillation amplitude can easily cause frictional weakening under stress disturbance.
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
基金supported by Fundamental Research Funds for the Central Universities (22dfx06)Natural Science Foundation of Guangdong Province-Joint Program for Offshore Wind Power (2022A1515240009).
文摘Slide-hold-slide(SHS)test is an essential experimental approach for studying the frictional stability of faults.The origin SHS framework was established based on a consistent constant normal stress,which cannot truly reflect the stress disturbance around fault zones.In this paper,we conducted a series of'dynamic SHS tests',which includes normal stress oscillations in the relaxation stage with different oscillation amplitudes and frequencies on synthetic quartz gouge using a double direct shear assembly.The experimental results reveal that the amplitude of the normal load oscillation has a remarkable effect on the frictional relaxation and healing patterns.However,the frequency of the normal load oscillation has a minor effect.Additionally,the shear loading rate is proportional to the normal loading rate during the relaxation stage,and the normal stiffness of the quartz layer remains nearly constant under various loading conditions.The creep rate during the hold phase is not obviously affected by the normal load oscillation,while the precursory slip is also sensitive to the oscillation amplitude.This study provides insights into the evolution of frictional stability in discontinuities and is beneficial for controlling relative disasters in fault zones.
基金the National Natural Science Foundation of China(Nos.51904359,51978677 and 52111530089)the Guangdong Provincial Department of Science and Technology(No.2019ZT08G090)+2 种基金the Enhanced National Key Basic Research Program(No.2019-JCJQ-ZD-352-00-04)the Science and Technology Program for Sustainable Development of Shenzhen(No.KCXFZ202002011008532)the Open Research Fund of the State Key Laboratory of Coal Resources and Safe Mining,CUMT(No.SKLCRSM20KF002).
文摘This paper investigates the frictional behavior of the infilled rock fracture under dynamic normal stress.A series of direct shear tests were conducted on saw-cut granite fractures infilled with quartz using a selfdeveloped dynamic shear apparatus,and the effects of normal load oscillation amplitude,normal load oscillation period and sliding velocity were studied.The test results reveal that the shear response can be divided into three stages over a whole loading-unloading process,characterized by different time spans and stress variations.Generally,a smaller oscillation amplitude,a longer oscillation period and a fast shear velocity promote the stability of the friction system,which is also confirmed by the Coulomb failure criterion calculated based on the observed periodic apparent friction coefficient.The dynamic strengthening/weakening phenomenon is dependent on the oscillation amplitude and product of sliding velocity and oscillation period(vT).Also,the rate and state friction law incorporating the parameter a that characterizes the normal stress variation is employed to describe the dynamic friction coefficient but exhibits an incompetent performance when handling intensive variation in normal stress.Finally,the potential seismicity induced by oscillating normal stress based on the observed stress drop is analyzed.This work helps us understand the sliding process and stability evolution of natural faults,and its benefits for relative hazard mitigation.
基金This work was supported by the National Natural Science Foundation of China(No.51705082)the Engineering Research Center for CAD/CAM of Fujian Provincial Colleges and Universities(No.K201705)+1 种基金the Development Center of Scientific and Educational Park of Fuzhou University in the City of Jinjiang(No.2019-JJFDKY-11)Fuzhou University Testing Fund of Precious Apparatus(No.2020T017).
文摘The scratch test is used for quality control mostly in phenomenological ways,and whether fracture toughness can be obtained from this test is still a matter of debate requiring further elucidation.In this paper,values of the fracture toughness of copper obtained by different scratch-based approaches are compared in order to examine the applicability of scratch-based methodologies to characterize the fracture toughness of soft metals.The scratch response of copper to a Rockwell C diamond indenter is studied under a constant normal load condition.The variations of penetration depth,residual depth,and residual scratch width with applied normal load are quantified from spherical to sphero-conical contact regimes by piecewise functions.A newly proposed size effect law is found to be the most suitable for scratch-based approaches to characterizing the fracture toughness of soft metallic materials with significant plasticity.A simple expression relating the nominal stress to the penetration depth is proposed for the spherical contact regime and gives almost the same value of fracture toughness.The residual scratch width provides useful information on pile-up of material and on the spherical tip radius of the indenter.It is found that the values of the fracture toughness obtained from the microscratch test are influenced by the data range for analysis.
文摘随着建筑物能源消耗的不断升高,高精度与高泛化能力的非侵入式负荷监测技术的研究具有重大意义。针对当前负荷分解方法存在的问题,提出了一种基于多尺度特征融合与多任务学习框架的非侵入式负荷监测方法。将实例-批归一化网络与U形网络结合,提取总负荷数据的上下文信息,并利用跨越连接实现对不同尺度的细节特征与全局特征的融合。针对多特征特点,引入高效通道注意力网络,使模型聚焦重要特征。引入多任务学习框架与后处理操作,去除输出的假阳性片段,实现对目标电器的精准识别。将所提模型与几种代表性模型在UK-DALE(UK domestic appliance-level electricity)数据集与REDD(reference energy disaggregation data set)上进行对比实验,结果表明,所提模型的性能优于对比模型,具有出色的负荷分解能力与状态识别能力。