Alternating extrusion(AFE)is a new way to effectively alter the texture and enhance the mechanical properties of the extruded bars.However,the mechanisms of microstructure evolution and enhancement of hardness are sti...Alternating extrusion(AFE)is a new way to effectively alter the texture and enhance the mechanical properties of the extruded bars.However,the mechanisms of microstructure evolution and enhancement of hardness are still unknown by different extrusion ratios(ERs)during extrusion.This work systematically investigated the microstructure and hardness of AZ31 alloy with various extrusion ratios of 8.1,15.6,and 24.8 by electron backscattered diffraction.The most striking result to emerge from the data is that when the ERs were increased from 8.1 to 15.6,the grain size was refined to 7.13μm.However,when the ER reached 24.8,the average grain size was 11.43μm.The proportion of recrystallization was only 2.92%,there was a continuous rotation of sub-grains at coarse grain boundaries,and non-basal slip<a>dislocations were activated and enriched near low-angle grain boundaries.At present,the recrystallization has not been completed.The grains of the product are coarsened,and the hardness is reduced.Whenλ=15.6,the AFE has a significant grain refinement effect and the highest hardness value.展开更多
(FePt)85Cu15 nanoparticles were successfully prepared by alternate reduction of metal salts in aqueous medium.Detailed investigations on the correlation between the magnetic and structural properties of these nanopart...(FePt)85Cu15 nanoparticles were successfully prepared by alternate reduction of metal salts in aqueous medium.Detailed investigations on the correlation between the magnetic and structural properties of these nanoparticles are presented as a function of annealing temperature.Both the X-ray diffraction patterns and the magnetic hysteresis loop measurements show the existence of L10-FePt phase at a relative low annealing temperature.It is proved that the Cu additive and alternate reduction are very effective methods in reducing the ordering temperature of FePt nanoparticles.展开更多
A 9-story concrete-filled steel tubular frame model is used to analyze the response of joints due to sudden column loss. Three different models are developed and compared to study the efficiency and feasibility of sim...A 9-story concrete-filled steel tubular frame model is used to analyze the response of joints due to sudden column loss. Three different models are developed and compared to study the efficiency and feasibility of simulation, which include substructure model, beam element model and solid element model. The comparison results show that the substructure model has a satisfying capability, calculation efficiency and accuracy to predict the concerned joints as well as the overall framework. Based on the substructure model and a kind of semi-rigid connection for concretefilled square hollow section steel column proposed in this paper, the nonlinear dynamic analyses are conducted by the alternate path method. It is found that the removal of the ground inner column brings high-level joint moments and comparatively low-level axial tension forces. The initial stiffness and transmitted ultimate moment of the semi-rigid connection are the main factors that influence the frame behavior, and their lower limit should be guaranteed to resist collapse. Reduced ultimate moment results in drastic displacement and axial force development, which may bring progressive collapse. The higher initial stiffness ensures that the structure has a stronger capacity to resist progressive collapse.展开更多
基金supported by the National Natural Science Foundation of China(No.51975166)the Natural Science Foundation of Heilongjiang Province(No.JQ2022E004).
文摘Alternating extrusion(AFE)is a new way to effectively alter the texture and enhance the mechanical properties of the extruded bars.However,the mechanisms of microstructure evolution and enhancement of hardness are still unknown by different extrusion ratios(ERs)during extrusion.This work systematically investigated the microstructure and hardness of AZ31 alloy with various extrusion ratios of 8.1,15.6,and 24.8 by electron backscattered diffraction.The most striking result to emerge from the data is that when the ERs were increased from 8.1 to 15.6,the grain size was refined to 7.13μm.However,when the ER reached 24.8,the average grain size was 11.43μm.The proportion of recrystallization was only 2.92%,there was a continuous rotation of sub-grains at coarse grain boundaries,and non-basal slip<a>dislocations were activated and enriched near low-angle grain boundaries.At present,the recrystallization has not been completed.The grains of the product are coarsened,and the hardness is reduced.Whenλ=15.6,the AFE has a significant grain refinement effect and the highest hardness value.
基金supported by the National Key Research and Development Program(2016YFB1100101)the National Natural Science Foundation of China(51471135)+1 种基金Shaanxi Science and Technology Program(2017KW-ZD-07)Shenzhen Fundamental Research Program.
文摘(FePt)85Cu15 nanoparticles were successfully prepared by alternate reduction of metal salts in aqueous medium.Detailed investigations on the correlation between the magnetic and structural properties of these nanoparticles are presented as a function of annealing temperature.Both the X-ray diffraction patterns and the magnetic hysteresis loop measurements show the existence of L10-FePt phase at a relative low annealing temperature.It is proved that the Cu additive and alternate reduction are very effective methods in reducing the ordering temperature of FePt nanoparticles.
基金Supported by National Natural Science Foundation of China (No.50878066)Natural Science Foundation of Heilongjiang Province (No.ZJG0701)Heilongjiang Postdoctoral Science Foundation
文摘A 9-story concrete-filled steel tubular frame model is used to analyze the response of joints due to sudden column loss. Three different models are developed and compared to study the efficiency and feasibility of simulation, which include substructure model, beam element model and solid element model. The comparison results show that the substructure model has a satisfying capability, calculation efficiency and accuracy to predict the concerned joints as well as the overall framework. Based on the substructure model and a kind of semi-rigid connection for concretefilled square hollow section steel column proposed in this paper, the nonlinear dynamic analyses are conducted by the alternate path method. It is found that the removal of the ground inner column brings high-level joint moments and comparatively low-level axial tension forces. The initial stiffness and transmitted ultimate moment of the semi-rigid connection are the main factors that influence the frame behavior, and their lower limit should be guaranteed to resist collapse. Reduced ultimate moment results in drastic displacement and axial force development, which may bring progressive collapse. The higher initial stiffness ensures that the structure has a stronger capacity to resist progressive collapse.
