Size effects on plastic deformation behaviors in uniaxial micro tension of pure nickel fine wires were investigated experimentally, including flow stress and inhomogeneous deformation behaviors. It is found that with ...Size effects on plastic deformation behaviors in uniaxial micro tension of pure nickel fine wires were investigated experimentally, including flow stress and inhomogeneous deformation behaviors. It is found that with the increase of grain size or the decrease of number of grains across the diameter, the flow stress decreases and inhomogeneous deformation degree increases. When there are less than 9.3 grains across the diameter, the flow stress decreases quickly with the increase of grain size. Then, the flow stress size effect in micro tension of fine wires is revealed by a proposed model by introducing the grain boundary size factor. These results also indicate that both the fracture strain and stress decrease with the increase of grain size. When there are less than 14.7 grains across the diameter, both the fracture strain and stress decrease quickly. This indicates that the inhomogeneous deformation degree in micro tension increases with the decrease of the number of grains across the diameter. The fracture topography tends to be more and more irregular with the decrease of the number of grains across the diameter. Then, the formation mechanism of irregular fracture topography was analyzed considering the inhomogeneous distribution of microstructure when there are a few grains across the diameter.展开更多
Process of warm tube hydroforming was experimentally investigated for forming an AZ31B magnesium alloy tubular part with a large expansion ratio. Effects of temperature on the mechanical properties and formability wer...Process of warm tube hydroforming was experimentally investigated for forming an AZ31B magnesium alloy tubular part with a large expansion ratio. Effects of temperature on the mechanical properties and formability were studied by uniaxial tensile test and hydraulic bulge test. Total elongation increases with temperature up to 250℃, but uniform elongation and maximum expansion ratio get the highest value at 175℃. Different axial feeding amounts were applied in experiments to determine the reasonable loading path. A preform with useful wrinkles was then realized and the tubular part with an expansion ratio of 50% was formed. Finally, mechanical condition to produce useful wrinkles is deduced and the result illustrates that useful wrinkles are easier to be obtained for tube with higher strain hardening coefficient value and tubular part with smaller expansion ratio.展开更多
Different from conventional mechanical systems with single degree of freedom (DOF), the main idea of the system of hybrid-driven precision press is to combine the motion of a constant speed motor with a servomotor via...Different from conventional mechanical systems with single degree of freedom (DOF), the main idea of the system of hybrid-driven precision press is to combine the motion of a constant speed motor with a servomotor via a two-DOF mechanism to provide flexible output. In order to make the feasibility clear, this paper studies theoretically the dynamic characteristics of this hybrid-driven mechanical system.Firstly,the dynamics model of the whole electromechanical system is set up by combining dynamic equations of DC motors with those of two-DOF nine-bar mechanism deduced by the Lagrange′s formula. Secondly through the numerical solution with the fourth Runge-Kutta, computer simulation about the dynamics is done, which shows that the designed and optimized hybrid-driven precision press is feasible in theory. These provide theoretical basis for later experimental research.展开更多
The effects of homogenization parameters on the microstructure evolution and tensile behavior of a balanced Al−Mg−Si alloy were investigated using the optical microscope,scanning electron microscope,X-ray diffraction,...The effects of homogenization parameters on the microstructure evolution and tensile behavior of a balanced Al−Mg−Si alloy were investigated using the optical microscope,scanning electron microscope,X-ray diffraction,electron probe microanalyzer,differential scanning calorimetry,electrical conductivity test,and tensile test.The results show that Mg_(2)Si andβ-AlFeSi are the main intermetallic compounds in the as-cast structure,and Mg solute microsegregation is predominant inside the dendrite cell.The prediction of the full dissolution time of Mg_(2)Si by a kinetic model is consistent with the experiment.Theβ-AlFeSi in the alloy exhibits high thermal stability and mainly undergoes dissolution and coarsening during homogenization at 560℃,and only a small portion is converted toα-AlFeSi.The optimal homogenization parameters are determined as 560℃and 360 min,when considering the evolution of microstructure and resource savings.Both the strength and ductility of the alloy increased after homogenization.展开更多
基金Projects(51375111,51375113,51505101)supported by the National Natural Science Foundation of ChinaProject(2015M571407)supported by the China Postdoctoral Science Foundation
文摘Size effects on plastic deformation behaviors in uniaxial micro tension of pure nickel fine wires were investigated experimentally, including flow stress and inhomogeneous deformation behaviors. It is found that with the increase of grain size or the decrease of number of grains across the diameter, the flow stress decreases and inhomogeneous deformation degree increases. When there are less than 9.3 grains across the diameter, the flow stress decreases quickly with the increase of grain size. Then, the flow stress size effect in micro tension of fine wires is revealed by a proposed model by introducing the grain boundary size factor. These results also indicate that both the fracture strain and stress decrease with the increase of grain size. When there are less than 14.7 grains across the diameter, both the fracture strain and stress decrease quickly. This indicates that the inhomogeneous deformation degree in micro tension increases with the decrease of the number of grains across the diameter. The fracture topography tends to be more and more irregular with the decrease of the number of grains across the diameter. Then, the formation mechanism of irregular fracture topography was analyzed considering the inhomogeneous distribution of microstructure when there are a few grains across the diameter.
基金Project(NCET-07-0237) supported by New Century Excellent Talents Program in Chinese University
文摘Process of warm tube hydroforming was experimentally investigated for forming an AZ31B magnesium alloy tubular part with a large expansion ratio. Effects of temperature on the mechanical properties and formability were studied by uniaxial tensile test and hydraulic bulge test. Total elongation increases with temperature up to 250℃, but uniform elongation and maximum expansion ratio get the highest value at 175℃. Different axial feeding amounts were applied in experiments to determine the reasonable loading path. A preform with useful wrinkles was then realized and the tubular part with an expansion ratio of 50% was formed. Finally, mechanical condition to produce useful wrinkles is deduced and the result illustrates that useful wrinkles are easier to be obtained for tube with higher strain hardening coefficient value and tubular part with smaller expansion ratio.
文摘Different from conventional mechanical systems with single degree of freedom (DOF), the main idea of the system of hybrid-driven precision press is to combine the motion of a constant speed motor with a servomotor via a two-DOF mechanism to provide flexible output. In order to make the feasibility clear, this paper studies theoretically the dynamic characteristics of this hybrid-driven mechanical system.Firstly,the dynamics model of the whole electromechanical system is set up by combining dynamic equations of DC motors with those of two-DOF nine-bar mechanism deduced by the Lagrange′s formula. Secondly through the numerical solution with the fourth Runge-Kutta, computer simulation about the dynamics is done, which shows that the designed and optimized hybrid-driven precision press is feasible in theory. These provide theoretical basis for later experimental research.
基金financially supported by State Grid Corporation of China (No.5500-202128250A-0-0-00)。
文摘The effects of homogenization parameters on the microstructure evolution and tensile behavior of a balanced Al−Mg−Si alloy were investigated using the optical microscope,scanning electron microscope,X-ray diffraction,electron probe microanalyzer,differential scanning calorimetry,electrical conductivity test,and tensile test.The results show that Mg_(2)Si andβ-AlFeSi are the main intermetallic compounds in the as-cast structure,and Mg solute microsegregation is predominant inside the dendrite cell.The prediction of the full dissolution time of Mg_(2)Si by a kinetic model is consistent with the experiment.Theβ-AlFeSi in the alloy exhibits high thermal stability and mainly undergoes dissolution and coarsening during homogenization at 560℃,and only a small portion is converted toα-AlFeSi.The optimal homogenization parameters are determined as 560℃and 360 min,when considering the evolution of microstructure and resource savings.Both the strength and ductility of the alloy increased after homogenization.
