Direct numerical simulations（DNSs） of purely elastic turbulence in rectilinear shear flows in a three-dimensional（3D） parallel plate channel were carried out,by which numerical databases were established.Based on ...Direct numerical simulations（DNSs） of purely elastic turbulence in rectilinear shear flows in a three-dimensional（3D） parallel plate channel were carried out,by which numerical databases were established.Based on the numerical databases,the present paper analyzed the structural and statistical characteristics of the elastic turbulence including flow patterns,the wall effect on the turbulent kinetic energy spectrum,and the local relationship between the flow motion and the microstructures＇ behavior.Moreover,to address the underlying physical mechanism of elastic turbulence,its generation was presented in terms of the global energy budget.The results showed that the flow structures in elastic turbulence were 3D with spatial scales on the order of the geometrical characteristic length,and vortex tubes were more likely to be embedded in the regions where the polymers were strongly stretched.In addition,the patterns of microstructures＇ elongation behave like a filament.From the results of the turbulent kinetic energy budget,it was found that the continuous energy releasing from the polymers into the main flow was the main source of the generation and maintenance of the elastic turbulent status.展开更多
Based on mineral component and in-situ vane shear strength of deep-sea sediment, four kinds of simulative soils were prepared by mixing different bentonites with water in order to find the best simulative soil for the...Based on mineral component and in-situ vane shear strength of deep-sea sediment, four kinds of simulative soils were prepared by mixing different bentonites with water in order to find the best simulative soil for the deep-sea sediment collected from the Pacific C-C area. Shear creep characteristics of the simulative soil were studied by shear creep test and shear creep parameters were determined by Burgers creep model. Research results show that the shear creep curves of the simulative soil can be divided into transient creep, unstable creep and stable creep, where the unstable creep stage is very short due to its high water content. The shear creep parameters increase with compressive stress and change slightly or fluctuate to approach a constant value with shear stress, and thus average creep parameters under the same compressive stress are used as the creep parameters of the simulative soil. Traction of the deep-sea mining machine walking at a constant velocity can be calculated by the shear creep constitutive equation of the deep-sea simulative soil, which provides a theoretical basis for safe operation and optimal design of the deep-sea mining machine.展开更多
Alternating shear stress is a critical factor in the accumulation of damage during rolling contact fatigue,severely limiting the service life of bearings.However,the specific mechanisms responsible for the cyclic shea...Alternating shear stress is a critical factor in the accumulation of damage during rolling contact fatigue,severely limiting the service life of bearings.However,the specific mechanisms responsible for the cyclic shear fatigue damage in bearing steel have not been fully understood.Here the mechanical response and microstructural evolution of a model GGr15 bearing steel under cyclic shear loading are investigated through the implementation of molecular dynamics simulations.The samples undergo 30 cycles under three different loading conditions with strains of 6.2%,9.2%,and 12.2%,respectively.The findings indicate that severe cyclic shear deformation results in early cyclic softening and significant accumulation of plastic damage in the bearing steel.Besides,samples subjected to higher strain-controlled loading exhibit higher plastic strain energy and shorter fatigue life.Additionally,strain localization is identified as the predominant damage mechanism in cyclic shear fatigue of the bearing steel,which accumulates and ultimately results in fatigue failure.Furthermore,simulation results also revealed the microstructural reasons for the strain localization(e.g.,BCC phase transformation into FCC and HCP phase),which well explained the formation of white etching areas.This study provides fresh atomic-scale insights into the mechanisms of cyclic shear fatigue damage in bearing steels.展开更多
The tumbling dynamics of individual absorbed polymer chains in shear flow is studied by employing multi-particle collision dynamics simulation techniques combined with molecular dynamics simulations.We find that the d...The tumbling dynamics of individual absorbed polymer chains in shear flow is studied by employing multi-particle collision dynamics simulation techniques combined with molecular dynamics simulations.We find that the dependence of tumbling frequencies on shear rate is independent of both adsorption strength and surface corrugate.展开更多
Rigid ellipsoidal objects(gravels and porphyroclasts)in ductile zone is an important factor to indicate the kinematics and dynamics.Jeffery’s theory(Jeffery G,1922),a quantitative research method,for the rotation oft...Rigid ellipsoidal objects(gravels and porphyroclasts)in ductile zone is an important factor to indicate the kinematics and dynamics.Jeffery’s theory(Jeffery G,1922),a quantitative research method,for the rotation ofthe rigid objects(no deformation)in the Newtonian fluid of the simple deformation field has been widely applied by geologists to the study of fabrics in rocks.The theory展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51276046 and 51506037)the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(Grant No.51421063)+2 种基金the China Postdoctoral Science Foundation(Grant No.2016M591526)the Heilongjiang Postdoctoral Fund,China(Grant No.LBH-Z15063)the China Postdoctoral International Exchange Program
文摘Direct numerical simulations（DNSs） of purely elastic turbulence in rectilinear shear flows in a three-dimensional（3D） parallel plate channel were carried out,by which numerical databases were established.Based on the numerical databases,the present paper analyzed the structural and statistical characteristics of the elastic turbulence including flow patterns,the wall effect on the turbulent kinetic energy spectrum,and the local relationship between the flow motion and the microstructures＇ behavior.Moreover,to address the underlying physical mechanism of elastic turbulence,its generation was presented in terms of the global energy budget.The results showed that the flow structures in elastic turbulence were 3D with spatial scales on the order of the geometrical characteristic length,and vortex tubes were more likely to be embedded in the regions where the polymers were strongly stretched.In addition,the patterns of microstructures＇ elongation behave like a filament.From the results of the turbulent kinetic energy budget,it was found that the continuous energy releasing from the polymers into the main flow was the main source of the generation and maintenance of the elastic turbulent status.
基金Project(51274251)supported by the National Natural Science Foundation of China
文摘Based on mineral component and in-situ vane shear strength of deep-sea sediment, four kinds of simulative soils were prepared by mixing different bentonites with water in order to find the best simulative soil for the deep-sea sediment collected from the Pacific C-C area. Shear creep characteristics of the simulative soil were studied by shear creep test and shear creep parameters were determined by Burgers creep model. Research results show that the shear creep curves of the simulative soil can be divided into transient creep, unstable creep and stable creep, where the unstable creep stage is very short due to its high water content. The shear creep parameters increase with compressive stress and change slightly or fluctuate to approach a constant value with shear stress, and thus average creep parameters under the same compressive stress are used as the creep parameters of the simulative soil. Traction of the deep-sea mining machine walking at a constant velocity can be calculated by the shear creep constitutive equation of the deep-sea simulative soil, which provides a theoretical basis for safe operation and optimal design of the deep-sea mining machine.
基金the Natural Science Foundation of China(No.52175188)the Key Research and Development Program of Shaanxi Province(No.2023-YBGY-434)+2 种基金the Open Fund of Liaoning Provincial Key Laboratory of Aero-engine Materials Tribology(No.LKLAMTF202101)the State Key Laboratory for Mechanical Behavior of Materials(No.20222412)the Fundamental Research Funds for the Central Universities.
文摘Alternating shear stress is a critical factor in the accumulation of damage during rolling contact fatigue,severely limiting the service life of bearings.However,the specific mechanisms responsible for the cyclic shear fatigue damage in bearing steel have not been fully understood.Here the mechanical response and microstructural evolution of a model GGr15 bearing steel under cyclic shear loading are investigated through the implementation of molecular dynamics simulations.The samples undergo 30 cycles under three different loading conditions with strains of 6.2%,9.2%,and 12.2%,respectively.The findings indicate that severe cyclic shear deformation results in early cyclic softening and significant accumulation of plastic damage in the bearing steel.Besides,samples subjected to higher strain-controlled loading exhibit higher plastic strain energy and shorter fatigue life.Additionally,strain localization is identified as the predominant damage mechanism in cyclic shear fatigue of the bearing steel,which accumulates and ultimately results in fatigue failure.Furthermore,simulation results also revealed the microstructural reasons for the strain localization(e.g.,BCC phase transformation into FCC and HCP phase),which well explained the formation of white etching areas.This study provides fresh atomic-scale insights into the mechanisms of cyclic shear fatigue damage in bearing steels.
基金supported by the National Natural Science Foundation of China (No. 21274153)
文摘The tumbling dynamics of individual absorbed polymer chains in shear flow is studied by employing multi-particle collision dynamics simulation techniques combined with molecular dynamics simulations.We find that the dependence of tumbling frequencies on shear rate is independent of both adsorption strength and surface corrugate.
文摘Rigid ellipsoidal objects(gravels and porphyroclasts)in ductile zone is an important factor to indicate the kinematics and dynamics.Jeffery’s theory(Jeffery G,1922),a quantitative research method,for the rotation ofthe rigid objects(no deformation)in the Newtonian fluid of the simple deformation field has been widely applied by geologists to the study of fabrics in rocks.The theory
