Numerous experimental evidences show that the grain size may significantly alter the yield strength of metals.Similarly,innickel-based superalloys,the precipitate size also influences their yield strength.Then,how to ...Numerous experimental evidences show that the grain size may significantly alter the yield strength of metals.Similarly,innickel-based superalloys,the precipitate size also influences their yield strength.Then,how to describe such two kinds of size effects on the yield strength is a very practical challenge.In this study,according to experimental observations,a collinear micro-shear-bands model is proposed to explore these size effects on metal materials’yield strength.An analytical solution for the simple model is derived.It reveals that the yield strength is a function of average grain-size or precipitate-size,which is able to reasonably explain size effects on yield strength.The typical example validation shows that the new relationship is not only able to precisely describe the grain-size effect in some cases,but also able to theoretically address the unexplained Hall-Petch relationship between theprecipitate size and the yield strength of nickel-based superalloys.展开更多
Microrolling experiments and uniaxial tensile tests of pure copper under different annealing conditions were carried out in this paper. The effects of grain size and reduction on non-uniform deformation, edge cracking...Microrolling experiments and uniaxial tensile tests of pure copper under different annealing conditions were carried out in this paper. The effects of grain size and reduction on non-uniform deformation, edge cracking, and microstructure were studied. The experimen- tal results showed that the side deformation became more non-uniform, resulting in substantial edge bulge, and the uneven spread increased with increasing grain size and reduction level. When the reduction level reached 80% and the grain size was 65 μm, slight edge cracks occurred. When the grain size was 200 μm, the edge cracks became wider and deeper. No edge cracks occurred when the grain size was 200 μm and the reduction level was less than 60%; edge cracks occurred when the reduction level was increased to 80%. As the reduction level increased, the grains were gradually elongated and appeared as a sheet-like structure along the rolling direction; a fine lamellar structure was obtained when the grain size was 20 lam and the reduction level was less than 60%.展开更多
The influence of Al content on microstructure characterization and indentation hardness testing behavior of Mg-8Sn-x Al(x=1 wt%, 2 wt%, 3 wt%)-1Zn alloys was investigated by optical microscope, Pandat software, X-ray ...The influence of Al content on microstructure characterization and indentation hardness testing behavior of Mg-8Sn-x Al(x=1 wt%, 2 wt%, 3 wt%)-1Zn alloys was investigated by optical microscope, Pandat software, X-ray diffraction, scanning electron microscope, differential scanning calorimetry and a microhardness testing equipment. The results can be summarized as follows: when the Al content is 1 wt%, the alloy is composed of α-Mg and Mg2 Sn phases; while the new phase of Mgx(Al Zn)1-x can be observed and the morphology of Mg2 Sn phase transfers from the semi-continuous network to the dispersed particles with further addition of Al content to 2 wt% and 3 wt%. The dendrite arm spacing(DAS) deceases firstly and then slightly increases with the increase of Al content. The micro-hardness of Mg-8Sn-x Al(x=1 wt%, 2 wt%, 3 wt%)-1Zn also increases with increasing of Al content. Moreover, the indentation size effect(ISE) in Vickers hardness for Mg-8Sn-1Al-1Zn alloy was observed with the applied test load ranging from 0.490 to 4.903 N.展开更多
The linear and nonlinear torsional free vibration analyses of functionMly graded micro/nuno-tubes （FGMTs） are analytically investigated based on the couple stress theory. The employed non-classical continuum theory ...The linear and nonlinear torsional free vibration analyses of functionMly graded micro/nuno-tubes （FGMTs） are analytically investigated based on the couple stress theory. The employed non-classical continuum theory contains one material length scale parameter, which can capture the small scale effect. The FGMT model accounts for the through-radius power-law variation of a two-constituent material. Hamilton＇s principle is used to develop the non-classical nonlinear governing equation. To study the effect of the boundary conditions, two types of end conditions, i.e., fixed-fixed and fixed-free, are considered. The derived boundary value governing equation is of the fourthorder, and is solved by the homotopy analysis method （HAM）. This method is based on the Taylor series with an embedded parameter and is capable of providing very good approximations by means of only a few terms, if the initial guess and the auxiliary linear operator are properly selected. The analytical expressions are developed for the linear and nonlinear natural frequencies, which can be conveniently used to investigate the effects of the dimensionless length scale parameter, the material gradient index, and the vibration amplitude on the natural frequencies of FGMTs.展开更多
基金supported by the National Natural Science Foundation of China (41630634)the China Postdoctoral Science Foundation (2017M623213)
文摘Numerous experimental evidences show that the grain size may significantly alter the yield strength of metals.Similarly,innickel-based superalloys,the precipitate size also influences their yield strength.Then,how to describe such two kinds of size effects on the yield strength is a very practical challenge.In this study,according to experimental observations,a collinear micro-shear-bands model is proposed to explore these size effects on metal materials’yield strength.An analytical solution for the simple model is derived.It reveals that the yield strength is a function of average grain-size or precipitate-size,which is able to reasonably explain size effects on yield strength.The typical example validation shows that the new relationship is not only able to precisely describe the grain-size effect in some cases,but also able to theoretically address the unexplained Hall-Petch relationship between theprecipitate size and the yield strength of nickel-based superalloys.
基金finically supported by the National Natural Science Foundation of China (No. 51474127)the Chinese Scholar Council (No. 201408210289)the Key Laboratory Open Project of Liaoning Province (USTLKFSY201504)
文摘Microrolling experiments and uniaxial tensile tests of pure copper under different annealing conditions were carried out in this paper. The effects of grain size and reduction on non-uniform deformation, edge cracking, and microstructure were studied. The experimen- tal results showed that the side deformation became more non-uniform, resulting in substantial edge bulge, and the uneven spread increased with increasing grain size and reduction level. When the reduction level reached 80% and the grain size was 65 μm, slight edge cracks occurred. When the grain size was 200 μm, the edge cracks became wider and deeper. No edge cracks occurred when the grain size was 200 μm and the reduction level was less than 60%; edge cracks occurred when the reduction level was increased to 80%. As the reduction level increased, the grains were gradually elongated and appeared as a sheet-like structure along the rolling direction; a fine lamellar structure was obtained when the grain size was 20 lam and the reduction level was less than 60%.
基金Supported by National Natural Science Foundation of China(Nos.51404166 and 51401144)Shanxi Province Science Foundation for Youths(No.2013021013-4)+2 种基金Research Project Supported by Shanxi Scholarship Council of China(No.2014-023)Technological Innovation Programs of Higher Education Institutions in Shanxi(No.2014120)the Advanced Programs of Department of Human Resources and Social Security of Shanxi Province for Returned Scholars(No.2013101)
文摘The influence of Al content on microstructure characterization and indentation hardness testing behavior of Mg-8Sn-x Al(x=1 wt%, 2 wt%, 3 wt%)-1Zn alloys was investigated by optical microscope, Pandat software, X-ray diffraction, scanning electron microscope, differential scanning calorimetry and a microhardness testing equipment. The results can be summarized as follows: when the Al content is 1 wt%, the alloy is composed of α-Mg and Mg2 Sn phases; while the new phase of Mgx(Al Zn)1-x can be observed and the morphology of Mg2 Sn phase transfers from the semi-continuous network to the dispersed particles with further addition of Al content to 2 wt% and 3 wt%. The dendrite arm spacing(DAS) deceases firstly and then slightly increases with the increase of Al content. The micro-hardness of Mg-8Sn-x Al(x=1 wt%, 2 wt%, 3 wt%)-1Zn also increases with increasing of Al content. Moreover, the indentation size effect(ISE) in Vickers hardness for Mg-8Sn-1Al-1Zn alloy was observed with the applied test load ranging from 0.490 to 4.903 N.
文摘The linear and nonlinear torsional free vibration analyses of functionMly graded micro/nuno-tubes （FGMTs） are analytically investigated based on the couple stress theory. The employed non-classical continuum theory contains one material length scale parameter, which can capture the small scale effect. The FGMT model accounts for the through-radius power-law variation of a two-constituent material. Hamilton＇s principle is used to develop the non-classical nonlinear governing equation. To study the effect of the boundary conditions, two types of end conditions, i.e., fixed-fixed and fixed-free, are considered. The derived boundary value governing equation is of the fourthorder, and is solved by the homotopy analysis method （HAM）. This method is based on the Taylor series with an embedded parameter and is capable of providing very good approximations by means of only a few terms, if the initial guess and the auxiliary linear operator are properly selected. The analytical expressions are developed for the linear and nonlinear natural frequencies, which can be conveniently used to investigate the effects of the dimensionless length scale parameter, the material gradient index, and the vibration amplitude on the natural frequencies of FGMTs.
