Silicon carbide ceramics with different thicknesses/diameter ratios were prepared by using ultra-fine silicon carbide powder with the sintering additives of 1.0 wt% boron and 1.5 wt% carbon. The influence of thickness...Silicon carbide ceramics with different thicknesses/diameter ratios were prepared by using ultra-fine silicon carbide powder with the sintering additives of 1.0 wt% boron and 1.5 wt% carbon. The influence of thickness/diameter ratio on the microstructure and density of SiC ceramics was investigated in detail. The experimental results show that the addition of boron and carbon sintering aids can promote the densification process of SiC ceramic, leading to the low sintering temperature and improve mechanical properties. At 1950 ℃, SiC ceramic with a density of 99% exhibits Young's modulus, hardness, and flexural strength of 476 MPa, 28.3 GPa, and 334 MPa, respectively. It is found that long holding time has a positive effect on the uniformity of the microstructure and density distribution of SiC ceramics with large thickness/diameter ratios. Additionally, the sintering additive of boron can solid-solve into SiC, and then facilitate the phase transformation of SiC to form 6H-SiC and 4H-SiC composite ceramics.展开更多
An elastic vibration model for high length diameter ratio spinning rocket with attitude control system which can be used for trajectory simulation is established. The basic theory of elastic dynamics and vibration dy...An elastic vibration model for high length diameter ratio spinning rocket with attitude control system which can be used for trajectory simulation is established. The basic theory of elastic dynamics and vibration dynamics were both used to set up the elastic vibration model of rocket body. In order to study the problem more conveniently, the rocket's body was simplified to be an even beam with two free ends. The model was validated by simulation results and the test data.展开更多
An experiment was conducted on hydroforming a double-diameter aluminum alloy tubular part.The influence of loading paths,i.e.the relation between internal pressure and axial feeding,on the forming results was emphasiz...An experiment was conducted on hydroforming a double-diameter aluminum alloy tubular part.The influence of loading paths,i.e.the relation between internal pressure and axial feeding,on the forming results was emphasized with fixed total axial feeding length.The loading paths were analyzed together with the corresponding diagram of stress and strain.Two kinds of bursting phenomenon occurred in the experiment.Sound part can be formed whether there are wrinkles or not.It is indicated by the experiment results that the loading path has great effect on the distribution of material during axial feeding.The thickness distribution is more even for the part formed with wrinkles than that without wrinkles.展开更多
基金Funded by the National Key Research and Development Plan of China (No.2017YFB0310400)the National Natural Science Foundation of China (No.5167020705)
文摘Silicon carbide ceramics with different thicknesses/diameter ratios were prepared by using ultra-fine silicon carbide powder with the sintering additives of 1.0 wt% boron and 1.5 wt% carbon. The influence of thickness/diameter ratio on the microstructure and density of SiC ceramics was investigated in detail. The experimental results show that the addition of boron and carbon sintering aids can promote the densification process of SiC ceramic, leading to the low sintering temperature and improve mechanical properties. At 1950 ℃, SiC ceramic with a density of 99% exhibits Young's modulus, hardness, and flexural strength of 476 MPa, 28.3 GPa, and 334 MPa, respectively. It is found that long holding time has a positive effect on the uniformity of the microstructure and density distribution of SiC ceramics with large thickness/diameter ratios. Additionally, the sintering additive of boron can solid-solve into SiC, and then facilitate the phase transformation of SiC to form 6H-SiC and 4H-SiC composite ceramics.
文摘An elastic vibration model for high length diameter ratio spinning rocket with attitude control system which can be used for trajectory simulation is established. The basic theory of elastic dynamics and vibration dynamics were both used to set up the elastic vibration model of rocket body. In order to study the problem more conveniently, the rocket's body was simplified to be an even beam with two free ends. The model was validated by simulation results and the test data.
基金This work is financially supported by the National Natural Science Fund for Distinguished Young Scholars ( No 50525516)the Specialized Research Fund for the Doctoral Program of Higher Edu-cation (No 20050213041)
文摘An experiment was conducted on hydroforming a double-diameter aluminum alloy tubular part.The influence of loading paths,i.e.the relation between internal pressure and axial feeding,on the forming results was emphasized with fixed total axial feeding length.The loading paths were analyzed together with the corresponding diagram of stress and strain.Two kinds of bursting phenomenon occurred in the experiment.Sound part can be formed whether there are wrinkles or not.It is indicated by the experiment results that the loading path has great effect on the distribution of material during axial feeding.The thickness distribution is more even for the part formed with wrinkles than that without wrinkles.
