Strain rate effects on the stress-strain behavior of sand were investigated by performing special plane strain and triaxial compression tests on saturated and air-dried sand specimens. In these tests, the loading stra...Strain rate effects on the stress-strain behavior of sand were investigated by performing special plane strain and triaxial compression tests on saturated and air-dried sand specimens. In these tests, the loading strain rate was changed many times by a factor of up to 1 000 during otherwise monotonous loading at a constant axial strain rate. Test results show that the stress jump upon a stepwise change in the strain rate decays with an increase in the irreversible strain when monotonous loading continues at the changed strain rate and the amount of stress jump is essentially proportional to the instantaneous stress. Based on the amount of these stress jumps, a parameter fl called the rate-sensitivity coefficient is introduced to represent the quantity of the observed viscous properties of sand, which equals 0.021 3 and 0.024 2 respectively for Hostun and Toyoura sands. Further analyses on the results indicate that the effect of the presence of pore water is deemed to be negligible with sand and the fl value is rather independent of loading method, wet condition and confining pressure.展开更多
Based on the traditional hydraulic bulging process,an improved hydraulic bulging process with axial feeding in the bulging process was proposed.The finite element simulation and experiment of bellows formed by the tra...Based on the traditional hydraulic bulging process,an improved hydraulic bulging process with axial feeding in the bulging process was proposed.The finite element simulation and experiment of bellows formed by the traditional and improved hydraulic bulging processes were conducted.The grid strain measurement system analysis results of strain and wall thickness distribution of the metal bellows,obtained from simulation and experiment,show that the maximum thinning rates of the wall thickness under the traditional and improved processes were 15%and 10%,respectively.And the wall thickness distribution of the metal bellows formed with improved process was more uniform.The strain values from the root to crown of the waveform increased gradually.However,the strain values were smaller than those of traditional process due to the axial feeding of the improved process in bulging process.展开更多
In order to describe and control the stress distribution and total deformation of bladed disk assemblies used in the aeroengine, a highly efficient and precise method of probabilistic analysis which is called extremum...In order to describe and control the stress distribution and total deformation of bladed disk assemblies used in the aeroengine, a highly efficient and precise method of probabilistic analysis which is called extremum response surface method(ERSM) is produced based on the previous deterministic analysis results with the finite element model(FEM). In this work, many key nonlinear factors, such as the dynamic feature of the temperature load, the centrifugal force and the boundary conditions, are taken into consideration for the model. The changing patterns with time of bladed disk assemblies about stress distribution and total deformation are obtained during the deterministic analysis, and at the same time, the largest deformation and stress nodes of bladed disk assemblies are found and taken as input target of probabilistic analysis in a scientific and reasonable way. Not only their reliability, historical sample, extreme response surface(ERS) and the cumulative probability distribution function but also their sensitivity and effect probability are obtained. Main factors affecting stress distribution and total deformation of bladed disk assemblies are investigated through the sensitivity analysis of the model. Finally, compared with the response surface method(RSM) and the Monte Carlo simulation(MCS), the results show that this new approach is effective.展开更多
The qualitative relationship between hydrogen concentration and notch tensile strength has been investigated for 5Ni-16Cr-Mo steel with different strength.The notch tensile strength was determined by means of slow str...The qualitative relationship between hydrogen concentration and notch tensile strength has been investigated for 5Ni-16Cr-Mo steel with different strength.The notch tensile strength was determined by means of slow strain rate test(SSRT)on circumferentially notched round bar specimens with the notch root radius of 0.15 mm after hydrogen charging.Meanwhile,the hydrogen diffusion behaviors of various strength steel were studied by thermal desorption spectroscopy(TDS)analysis.The SSRT results show that the T460 steel has higher susceptibility of hydrogen embrittlement in contrast with T520 steel.The activation energies and microstructure indicate that the dislocations and interfaces of martensitic laths are hydrogen traps in 5Ni-16Cr-Mo steel.By SSRT,the elastic limit of charged specimen loaded in air is higher than the flow stress without hydrogen charging before unloading,while the difference is defined as hydrogen-induced stress.The value of hydrogen-induced stress σ*increases linearly with hydrogen concentration:σ*=−0.622+2.015C_(0).The finite element analysis results of stress distributions near the notch tip have shown that the maximum principal stress increases with the notch root radius decreasing.展开更多
Hot-compression of aluminum alloy 5182 was carried out on a Gleeble- 1500 thermo-simulator at deformation temperature ranging from 350 ℃ to 500 ℃ and at strain rate from 0.01 s^-1 to 10 s^-1 with strain range from 0...Hot-compression of aluminum alloy 5182 was carried out on a Gleeble- 1500 thermo-simulator at deformation temperature ranging from 350 ℃ to 500 ℃ and at strain rate from 0.01 s^-1 to 10 s^-1 with strain range from 0.7 to 1.9. The microstructures and macro-textures evolution under different conditions were investigated by polarized optical microscopy and X-ray diffraction analysis, respectively. The basic trend is that the hot-compression stress increases with the decrease of temperature and increase of strain rate, which is revealed and elucidated in terms of Zener-Hollomon parameter in the hyperbolic sine equation with the hot-deformation activation energy of 143.5 kJ/mol. An empirical constitutive equation is proposed to predict the hot-deformation behavior under different conditions. As deformation temperature increases up to 400 ℃, at strain rate over 1 s^-1, dynamic recrystallization （DRX） occurs. Cube orientation { 100} （001） is detected in the recrystallized sample after hot-compression.展开更多
基金Project(50679056) supported by the National Natural Science Foundation of ChinaProject(06-0378) supported by Program for NewCentury Excellent Talents in University+1 种基金Project(05SG25) supported by the "Dawn" Program of Shanghai Education Commission, ChinaProject(B308) supported by the Shanghai Leading Academic Discipline, China
文摘Strain rate effects on the stress-strain behavior of sand were investigated by performing special plane strain and triaxial compression tests on saturated and air-dried sand specimens. In these tests, the loading strain rate was changed many times by a factor of up to 1 000 during otherwise monotonous loading at a constant axial strain rate. Test results show that the stress jump upon a stepwise change in the strain rate decays with an increase in the irreversible strain when monotonous loading continues at the changed strain rate and the amount of stress jump is essentially proportional to the instantaneous stress. Based on the amount of these stress jumps, a parameter fl called the rate-sensitivity coefficient is introduced to represent the quantity of the observed viscous properties of sand, which equals 0.021 3 and 0.024 2 respectively for Hostun and Toyoura sands. Further analyses on the results indicate that the effect of the presence of pore water is deemed to be negligible with sand and the fl value is rather independent of loading method, wet condition and confining pressure.
基金Project (51775479) supported by the National Natural Science Foundation of ChinaProject (E2017203046) supported by the Natural Science Foundation of Hebei Province,China
文摘Based on the traditional hydraulic bulging process,an improved hydraulic bulging process with axial feeding in the bulging process was proposed.The finite element simulation and experiment of bellows formed by the traditional and improved hydraulic bulging processes were conducted.The grid strain measurement system analysis results of strain and wall thickness distribution of the metal bellows,obtained from simulation and experiment,show that the maximum thinning rates of the wall thickness under the traditional and improved processes were 15%and 10%,respectively.And the wall thickness distribution of the metal bellows formed with improved process was more uniform.The strain values from the root to crown of the waveform increased gradually.However,the strain values were smaller than those of traditional process due to the axial feeding of the improved process in bulging process.
基金Projects(51375032,51175017,51245027)supported by the National Natural Science Foundation of China
文摘In order to describe and control the stress distribution and total deformation of bladed disk assemblies used in the aeroengine, a highly efficient and precise method of probabilistic analysis which is called extremum response surface method(ERSM) is produced based on the previous deterministic analysis results with the finite element model(FEM). In this work, many key nonlinear factors, such as the dynamic feature of the temperature load, the centrifugal force and the boundary conditions, are taken into consideration for the model. The changing patterns with time of bladed disk assemblies about stress distribution and total deformation are obtained during the deterministic analysis, and at the same time, the largest deformation and stress nodes of bladed disk assemblies are found and taken as input target of probabilistic analysis in a scientific and reasonable way. Not only their reliability, historical sample, extreme response surface(ERS) and the cumulative probability distribution function but also their sensitivity and effect probability are obtained. Main factors affecting stress distribution and total deformation of bladed disk assemblies are investigated through the sensitivity analysis of the model. Finally, compared with the response surface method(RSM) and the Monte Carlo simulation(MCS), the results show that this new approach is effective.
基金Project(3220024018)supported by the Fundamental Research Funds for the Luoyang Sunrui Special Equipment Co.,Ltd.,China。
文摘The qualitative relationship between hydrogen concentration and notch tensile strength has been investigated for 5Ni-16Cr-Mo steel with different strength.The notch tensile strength was determined by means of slow strain rate test(SSRT)on circumferentially notched round bar specimens with the notch root radius of 0.15 mm after hydrogen charging.Meanwhile,the hydrogen diffusion behaviors of various strength steel were studied by thermal desorption spectroscopy(TDS)analysis.The SSRT results show that the T460 steel has higher susceptibility of hydrogen embrittlement in contrast with T520 steel.The activation energies and microstructure indicate that the dislocations and interfaces of martensitic laths are hydrogen traps in 5Ni-16Cr-Mo steel.By SSRT,the elastic limit of charged specimen loaded in air is higher than the flow stress without hydrogen charging before unloading,while the difference is defined as hydrogen-induced stress.The value of hydrogen-induced stress σ*increases linearly with hydrogen concentration:σ*=−0.622+2.015C_(0).The finite element analysis results of stress distributions near the notch tip have shown that the maximum principal stress increases with the notch root radius decreasing.
基金Project(50905188) supported by the National Natural Science FoundationProject(2012CB619500) supported by Key Basic Research Program of China
文摘Hot-compression of aluminum alloy 5182 was carried out on a Gleeble- 1500 thermo-simulator at deformation temperature ranging from 350 ℃ to 500 ℃ and at strain rate from 0.01 s^-1 to 10 s^-1 with strain range from 0.7 to 1.9. The microstructures and macro-textures evolution under different conditions were investigated by polarized optical microscopy and X-ray diffraction analysis, respectively. The basic trend is that the hot-compression stress increases with the decrease of temperature and increase of strain rate, which is revealed and elucidated in terms of Zener-Hollomon parameter in the hyperbolic sine equation with the hot-deformation activation energy of 143.5 kJ/mol. An empirical constitutive equation is proposed to predict the hot-deformation behavior under different conditions. As deformation temperature increases up to 400 ℃, at strain rate over 1 s^-1, dynamic recrystallization （DRX） occurs. Cube orientation { 100} （001） is detected in the recrystallized sample after hot-compression.
