In microscale deformation, the magnitudes of specimen and grain sizes are usually identical, and size- dependent phenomena of deformation behavior occur, namely, size effects. In this study, size effects in micro- cyl...In microscale deformation, the magnitudes of specimen and grain sizes are usually identical, and size- dependent phenomena of deformation behavior occur, namely, size effects. In this study, size effects in micro- cylindrical compression were investigated experimentally. It was found that, with the increase of grain size and decrease of specimen size, flow stress decreases and inhomogeneous material flow increases. These size effects tend to be more distinct with miniaturization. Thereafter, a modified model considering orientation distribution of surface grains and continuity between surface grains and inner grains is developed to model size effects in micro- forming. Through finite element simulation, the effects of specimen size, grain size, and orientation of surface grains on the flow stress and inhomogeneous deformation were analyzed. There is a good agreement between experimental and simulation results.展开更多
Stability analyses of perfect and imperfect cylindrical shells under axial compression and torsion were presented. Finite element method for the stability analysis of perfect cylindrical shells was put forward through...Stability analyses of perfect and imperfect cylindrical shells under axial compression and torsion were presented. Finite element method for the stability analysis of perfect cylindrical shells was put forward through comparing critical loads and the first buckling modes with those obtained through theoretical analysis. Two typical initial defects, non-circularity and uneven thickness distribution, were studied. Critical loads decline with the increase of non-circularity, which exist in imperfect cylindrical shells under both axial compression and torsion. Non-circularity defect has no effect on the first buckling mode when cylindrical shell is under torsion. Unfortunately, it has a completely different buckling mode when cylindrical shell is under axial compression. Critical loads decline with the increase of thickness defect amplitude, which exist in imperfect cylindrical shells under both axial compression and torsion, too. A greater wave number is conducive to the stability of cylindrical shells. The first buckling mode of imperfect cylindrical shells under torsion maintains its original shape, but it changes with wave number when the cylindrical shell is under axial compression.展开更多
This study aims to investigate the effects of heat treatment on the corrosion resistance and antimicrobial activity of Mg-Zn-Ag-xCa alloys under simulated physiological conditions.The focus of this research is to unde...This study aims to investigate the effects of heat treatment on the corrosion resistance and antimicrobial activity of Mg-Zn-Ag-xCa alloys under simulated physiological conditions.The focus of this research is to understand how to optimize the biomedical performance of the alloy by adjusting its composition,particularly its stability in simulated body fluids and its ability to counteract microbes.The corrosion behavior and antibacterial properties of silver-containing magnesium alloys with different calcium contents after solution treatment were studied.The results show that the addition of calcium affects the microstructure of the alloy,including grain refinement and the distribution of the second phase.It acts as a barrier at the microscopic scale,which helps to prevent the invasion of the corrosive agent,thereby improving the overall corrosion resistance of the material.The gradual increase in calcium initially has a positive effect on the properties of the alloy,especially in terms of corrosion resistance.However,when the calcium content increases to 1.5Ca,although the initial corrosion potential of the alloy increases,excessive calcium may lead to excessive accumulation of the second phase in the microstructure,which will have a negative impact on the long-term stability and corrosion resistance of the material.After corrosion,when the calcium content is 1.0 wt%,the surface roughness of the sample is 1.65μm,with the surface being the smoothest,and the corrosion rate is 0.25 mm·year-1.However,when the calcium content increases to 1.5 wt%,the sample exhibits the fastest corrosion rate at 0.45 mm·year-1.The antibacterial properties of magnesium alloy were optimized by adding silver.展开更多
The conversion of intermittent renewable electrical energy to chemical energy is of great importance which can not only mitigate current energy and environmental crisis but also contribute to the ongoing carbon neutra...The conversion of intermittent renewable electrical energy to chemical energy is of great importance which can not only mitigate current energy and environmental crisis but also contribute to the ongoing carbon neutrality national strategy.Electrocatalysis is serving as a low-carbon conversion technology that enables green and efficient energy conversion mainly through hydrogen evolution reaction(HER),carbon dioxide reduction reaction(CO_(2)RR),and nitrogen reduction reaction(NRR).The core of electrocatalysis is the design and construction of low-cost high-activity and high-stability electrocatalyst to drive reaction thermodynamics and kinetics.The employment of polyoxometalates(POMs)as platforms or precursors to construct different types of electrocatalysts has been widely reported.Herein,we systematically summarized the recent advances in POM-derived nanostructures for electrocatalysis application.The strategies for precursor design and electrocatalyst synthesis were briefly introduced.The morphology control,phase control,composite modulation,and heterostructure engineering in POM-derived nanostructures were presented in detail.The structure–activity relationship of POM-derived nanostructures is fully discussed for HER CO_(2)RR,and NRR applications.Finally,the current challenges and future outlooks of POM-derived nanostructures are summarized to provide insights toward high-efficiency electrocatalysts for energy conversion technologies.展开更多
To model the strain-inducedγ→α′phase transformation for the Cr-Mn metastable austenitic stainless steel,the 201Cu steel was chosen as the analytical material and the cylindrical samples of this steel with size ofϕ...To model the strain-inducedγ→α′phase transformation for the Cr-Mn metastable austenitic stainless steel,the 201Cu steel was chosen as the analytical material and the cylindrical samples of this steel with size ofϕ5 mm×10 mm were compressed at strains of 0.2–0.6 in the temperature range of 25–150℃ and in the strain rate range of 0.1–5.0 s^(−1).The flaky samples were prepared by wire cutting from the cylindrical samples and the volume fraction of the strain-inducedα′phase was detected in the test point of the flaky samples.The volume fraction changing with the process parameters was modeled,and the critical temperatures and the critical strains to preventγ→α′phase transformation were calculated as other different process parameters changed.The linear fitting goodness of the model between the calculated volume fraction values and the tested ones is 0.986 and the validity of the model was verified by application in cold and warm rolling experiments.展开更多
The longitudinal compressive buckling of long and thin-walled cylinders in yield region is analyzed with the incremental and finite forms of the endochronic constitutive equation, respectively. The relations between t...The longitudinal compressive buckling of long and thin-walled cylinders in yield region is analyzed with the incremental and finite forms of the endochronic constitutive equation, respectively. The relations between the critical stress σ_(cr)versus the ratio of R (the radius) versus h (the thickness of the wall) are derived. The critical stress of the thin-walled cylinders made of abuminum alloys AMГ and 1T are analyzed and compared with the experimental data and the analytical results based on traditional theory of plasticity. It is seen that. except that the σ_(cr) of the cylinders made of 1Tpredicted by the finite form of the endochronic theory seems a little more conservative than that by traditional deformation theory of plasticity, in most cases, both forms of the endochornic constitutive equation provide more satisfactory results.展开更多
基金financially supported by the National Natural Science Foundation of China (Nos. 50835002 and 51105102)
文摘In microscale deformation, the magnitudes of specimen and grain sizes are usually identical, and size- dependent phenomena of deformation behavior occur, namely, size effects. In this study, size effects in micro- cylindrical compression were investigated experimentally. It was found that, with the increase of grain size and decrease of specimen size, flow stress decreases and inhomogeneous material flow increases. These size effects tend to be more distinct with miniaturization. Thereafter, a modified model considering orientation distribution of surface grains and continuity between surface grains and inner grains is developed to model size effects in micro- forming. Through finite element simulation, the effects of specimen size, grain size, and orientation of surface grains on the flow stress and inhomogeneous deformation were analyzed. There is a good agreement between experimental and simulation results.
基金Project(11102163)supported by the National Natural Science Foundation of ChinaProjects(JC20110218,JC20110260)supported by Foundation for Fundamental Research of Northwestern Polytechnical University,China
文摘Stability analyses of perfect and imperfect cylindrical shells under axial compression and torsion were presented. Finite element method for the stability analysis of perfect cylindrical shells was put forward through comparing critical loads and the first buckling modes with those obtained through theoretical analysis. Two typical initial defects, non-circularity and uneven thickness distribution, were studied. Critical loads decline with the increase of non-circularity, which exist in imperfect cylindrical shells under both axial compression and torsion. Non-circularity defect has no effect on the first buckling mode when cylindrical shell is under torsion. Unfortunately, it has a completely different buckling mode when cylindrical shell is under axial compression. Critical loads decline with the increase of thickness defect amplitude, which exist in imperfect cylindrical shells under both axial compression and torsion, too. A greater wave number is conducive to the stability of cylindrical shells. The first buckling mode of imperfect cylindrical shells under torsion maintains its original shape, but it changes with wave number when the cylindrical shell is under axial compression.
基金supported by Wenhai Program of the S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology(No.2021WHZZB2301)Hainan Provincial Joint Project of Sanya Yazhou Bay Science and Technology City(No.2021CXLH0005)Overseas Science and Education Centers of Bureau of International Cooperation Chinese Academy of Sciences(No.121311KYSB20210005-2).
文摘This study aims to investigate the effects of heat treatment on the corrosion resistance and antimicrobial activity of Mg-Zn-Ag-xCa alloys under simulated physiological conditions.The focus of this research is to understand how to optimize the biomedical performance of the alloy by adjusting its composition,particularly its stability in simulated body fluids and its ability to counteract microbes.The corrosion behavior and antibacterial properties of silver-containing magnesium alloys with different calcium contents after solution treatment were studied.The results show that the addition of calcium affects the microstructure of the alloy,including grain refinement and the distribution of the second phase.It acts as a barrier at the microscopic scale,which helps to prevent the invasion of the corrosive agent,thereby improving the overall corrosion resistance of the material.The gradual increase in calcium initially has a positive effect on the properties of the alloy,especially in terms of corrosion resistance.However,when the calcium content increases to 1.5Ca,although the initial corrosion potential of the alloy increases,excessive calcium may lead to excessive accumulation of the second phase in the microstructure,which will have a negative impact on the long-term stability and corrosion resistance of the material.After corrosion,when the calcium content is 1.0 wt%,the surface roughness of the sample is 1.65μm,with the surface being the smoothest,and the corrosion rate is 0.25 mm·year-1.However,when the calcium content increases to 1.5 wt%,the sample exhibits the fastest corrosion rate at 0.45 mm·year-1.The antibacterial properties of magnesium alloy were optimized by adding silver.
基金financially supported by Shandong Provincial Natural Science Foundation(No.ZR2019BB025)。
文摘The conversion of intermittent renewable electrical energy to chemical energy is of great importance which can not only mitigate current energy and environmental crisis but also contribute to the ongoing carbon neutrality national strategy.Electrocatalysis is serving as a low-carbon conversion technology that enables green and efficient energy conversion mainly through hydrogen evolution reaction(HER),carbon dioxide reduction reaction(CO_(2)RR),and nitrogen reduction reaction(NRR).The core of electrocatalysis is the design and construction of low-cost high-activity and high-stability electrocatalyst to drive reaction thermodynamics and kinetics.The employment of polyoxometalates(POMs)as platforms or precursors to construct different types of electrocatalysts has been widely reported.Herein,we systematically summarized the recent advances in POM-derived nanostructures for electrocatalysis application.The strategies for precursor design and electrocatalyst synthesis were briefly introduced.The morphology control,phase control,composite modulation,and heterostructure engineering in POM-derived nanostructures were presented in detail.The structure–activity relationship of POM-derived nanostructures is fully discussed for HER CO_(2)RR,and NRR applications.Finally,the current challenges and future outlooks of POM-derived nanostructures are summarized to provide insights toward high-efficiency electrocatalysts for energy conversion technologies.
基金the financial support from the Open Project provided by the State Key Laboratory of Development and Application Technology of Automotive Steels(Baowu Steel Group)(Grant No.Y21ECEQ17Y).
文摘To model the strain-inducedγ→α′phase transformation for the Cr-Mn metastable austenitic stainless steel,the 201Cu steel was chosen as the analytical material and the cylindrical samples of this steel with size ofϕ5 mm×10 mm were compressed at strains of 0.2–0.6 in the temperature range of 25–150℃ and in the strain rate range of 0.1–5.0 s^(−1).The flaky samples were prepared by wire cutting from the cylindrical samples and the volume fraction of the strain-inducedα′phase was detected in the test point of the flaky samples.The volume fraction changing with the process parameters was modeled,and the critical temperatures and the critical strains to preventγ→α′phase transformation were calculated as other different process parameters changed.The linear fitting goodness of the model between the calculated volume fraction values and the tested ones is 0.986 and the validity of the model was verified by application in cold and warm rolling experiments.
文摘The longitudinal compressive buckling of long and thin-walled cylinders in yield region is analyzed with the incremental and finite forms of the endochronic constitutive equation, respectively. The relations between the critical stress σ_(cr)versus the ratio of R (the radius) versus h (the thickness of the wall) are derived. The critical stress of the thin-walled cylinders made of abuminum alloys AMГ and 1T are analyzed and compared with the experimental data and the analytical results based on traditional theory of plasticity. It is seen that. except that the σ_(cr) of the cylinders made of 1Tpredicted by the finite form of the endochronic theory seems a little more conservative than that by traditional deformation theory of plasticity, in most cases, both forms of the endochornic constitutive equation provide more satisfactory results.
