To analyze fracture mechanism of propellant grain and study the mechanical properties of propellant grain, the press and fracture processes of propellant grain with and without initial defects are modeled using the di...To analyze fracture mechanism of propellant grain and study the mechanical properties of propellant grain, the press and fracture processes of propellant grain with and without initial defects are modeled using the discrete element method. On the basis of the appropriate constitutive relationships, the discrete element model of the propellant grain was established. Compared with experimental measurements, the micro-parameters of the bonded-particle model of the propellant grain under unconfined uniaxial compression tests were calibrated. The propellant grains without initial defects, with initial surface defects, and with initial internal defects were studied numerically through a series of unconfined uniaxial compression tests. Results show that the established discrete element model is an efficient tool to study the press and fracture processes of the propellant grain. The fracture process of the propellant grain without initial defects can be divided into the elastic deformation phase, crack initiation phase, crack stable propagation phase, and crack unstable propagation phase. The fracture mechanism of this grain is the global shear failure along the direction of the maximum shear stress. Initial defects have significant effects on both the fracture mechanism and peak strength of the propellant grain. The major fracture mechanism of the propellant grain with initial surface defects is local shear failure, whereas that of the propellant grain with initial internal defects is global tensile failure. Both defects weaken the peak strengths of the propellant grain. Therefore, the carrying and filling process of the propellant grain needs to minimize initial defects as far as possible.展开更多
The mechanism of high pressure roll grinding on improvement of compression strength of oxidized hematite pellets was researched by considering their roasting properties. The results indicate that oxidized hematite pel...The mechanism of high pressure roll grinding on improvement of compression strength of oxidized hematite pellets was researched by considering their roasting properties. The results indicate that oxidized hematite pellets require higher preheating temperature and longer preheating time to attain required compression strength of pellets compared with the common magnetite oxidized pellets. It is found that when the hematite concentrates are pretreated by high pressure roll grinding （HPRG）, the compression strengths of preheated and roasted oxidized hematite pellets get improved even with lower preheating and roasting temperatures and shorter preheating and roasting time. The mechanism for HPRG to improve roasting properties of oxidized pellets were investigated and the cause mainly lies in the increase of micro-sized particles and the decrease of dispersion degree for hematite concentrates, which promotes the hematite concentrate particles to be compacted, the solid-phase crystallization, and finally the formation of Fe203 bonding bridges during subsequent high temperature roasting process.展开更多
This review highlights very recent achievements and new developments of severe plastic deformation(SPD) technology for producing bulk ultrafine-grain(UFG) and even nanocrystalline(nc) materials.These numerous modified...This review highlights very recent achievements and new developments of severe plastic deformation(SPD) technology for producing bulk ultrafine-grain(UFG) and even nanocrystalline(nc) materials.These numerous modified and novel SPD methods include cyclic forward-backward extrusion,axi-symmetric forward spiral extrusion,vortex extrusion,simple shear extrusion,planar twist extrusion,tubular channel angular pressing,cone-cone method,high-pressure tube twisting,tube channel pressing and elliptical cross-section spiral equal-channel extrusion.According to classification,these new methods are categorized into the extension of equal-channel angle pressing(ECAP),high-pressure torsion(HPT),twist extrusion(TE) and constrained groove pressing(CGP),respectively.The principles of various new SPD technologies are described in detail.In addition,the microstructure revolution characteristics and mechanical properties of materials produced by SPD process,as well as the applications of SPD techniques to UFG materials,are also reported.Furthermore,this article reviews recent progresses in determining the refinement and/or deformation mechanisms,e.g.dislocation deformation mechanism,twin deformation mechanism and grain boundary sliding and torsional deformation mechanism,and further orientation of SPD technology.展开更多
Stress granules(SGs) are intracellular granules formed when cellular translation is blocked and have been reported to be involved in a variety of viral infections. Our previous studies revealed that SGs are involved i...Stress granules(SGs) are intracellular granules formed when cellular translation is blocked and have been reported to be involved in a variety of viral infections. Our previous studies revealed that SGs are involved in the coxsackievirus B(CVB)infection process, but the role of SGs in CVB infection has not been fully explored. In this study, we found that CVB type 3(CVB3) could induce SG formation in the early phase of infection. Results showed that levels of CVB3 RNA and protein were significantly inhibited during the early stage of CVB3 infection by the elevated formation of SGs, while viral RNA and protein synthesis were significantly promoted when SG formation was blocked. Our findings suggest that SG formation is one of the early antiviral mechanisms for host cells against CVB infection.展开更多
基金The National Key Research and Development Program of China(No.2018YFD1100401-04)the National Natural Science Foundation of China(No.11772091)+1 种基金the Priority Academic Program Development of Jiangsu Higher Education Institutions(No.CE01-2)the Open Research Fund Program of Jiangsu Key Laboratory of Engineering M echanics(No.LEM16A08)
文摘To analyze fracture mechanism of propellant grain and study the mechanical properties of propellant grain, the press and fracture processes of propellant grain with and without initial defects are modeled using the discrete element method. On the basis of the appropriate constitutive relationships, the discrete element model of the propellant grain was established. Compared with experimental measurements, the micro-parameters of the bonded-particle model of the propellant grain under unconfined uniaxial compression tests were calibrated. The propellant grains without initial defects, with initial surface defects, and with initial internal defects were studied numerically through a series of unconfined uniaxial compression tests. Results show that the established discrete element model is an efficient tool to study the press and fracture processes of the propellant grain. The fracture process of the propellant grain without initial defects can be divided into the elastic deformation phase, crack initiation phase, crack stable propagation phase, and crack unstable propagation phase. The fracture mechanism of this grain is the global shear failure along the direction of the maximum shear stress. Initial defects have significant effects on both the fracture mechanism and peak strength of the propellant grain. The major fracture mechanism of the propellant grain with initial surface defects is local shear failure, whereas that of the propellant grain with initial internal defects is global tensile failure. Both defects weaken the peak strengths of the propellant grain. Therefore, the carrying and filling process of the propellant grain needs to minimize initial defects as far as possible.
基金Project(50725416) supported by the National Natural Science Funds for Distinguished Young Scholars of China
文摘The mechanism of high pressure roll grinding on improvement of compression strength of oxidized hematite pellets was researched by considering their roasting properties. The results indicate that oxidized hematite pellets require higher preheating temperature and longer preheating time to attain required compression strength of pellets compared with the common magnetite oxidized pellets. It is found that when the hematite concentrates are pretreated by high pressure roll grinding （HPRG）, the compression strengths of preheated and roasted oxidized hematite pellets get improved even with lower preheating and roasting temperatures and shorter preheating and roasting time. The mechanism for HPRG to improve roasting properties of oxidized pellets were investigated and the cause mainly lies in the increase of micro-sized particles and the decrease of dispersion degree for hematite concentrates, which promotes the hematite concentrate particles to be compacted, the solid-phase crystallization, and finally the formation of Fe203 bonding bridges during subsequent high temperature roasting process.
基金supported by the Aeronautical Science Foundation of China(Grant No. 2011ZE53059)the Graduate Starting Seed Fund of Northwestern Polytechnical University (Grant No. Z2011006)
文摘This review highlights very recent achievements and new developments of severe plastic deformation(SPD) technology for producing bulk ultrafine-grain(UFG) and even nanocrystalline(nc) materials.These numerous modified and novel SPD methods include cyclic forward-backward extrusion,axi-symmetric forward spiral extrusion,vortex extrusion,simple shear extrusion,planar twist extrusion,tubular channel angular pressing,cone-cone method,high-pressure tube twisting,tube channel pressing and elliptical cross-section spiral equal-channel extrusion.According to classification,these new methods are categorized into the extension of equal-channel angle pressing(ECAP),high-pressure torsion(HPT),twist extrusion(TE) and constrained groove pressing(CGP),respectively.The principles of various new SPD technologies are described in detail.In addition,the microstructure revolution characteristics and mechanical properties of materials produced by SPD process,as well as the applications of SPD techniques to UFG materials,are also reported.Furthermore,this article reviews recent progresses in determining the refinement and/or deformation mechanisms,e.g.dislocation deformation mechanism,twin deformation mechanism and grain boundary sliding and torsional deformation mechanism,and further orientation of SPD technology.
基金supported by the Natural Science Foundation of China(Grant 81571999 to Z Zhong81672007 to W Zhao+1 种基金81772188 to Y Wang,31300144 to T Wang)support from Heilongjiang Provincial Key Laboratory of Pathogens and Immunity and Heilongjiang Provincial Science and Technology Innovation Team in Higher Education Institutes for Infection and Immunity of Harbin Medical University
文摘Stress granules(SGs) are intracellular granules formed when cellular translation is blocked and have been reported to be involved in a variety of viral infections. Our previous studies revealed that SGs are involved in the coxsackievirus B(CVB)infection process, but the role of SGs in CVB infection has not been fully explored. In this study, we found that CVB type 3(CVB3) could induce SG formation in the early phase of infection. Results showed that levels of CVB3 RNA and protein were significantly inhibited during the early stage of CVB3 infection by the elevated formation of SGs, while viral RNA and protein synthesis were significantly promoted when SG formation was blocked. Our findings suggest that SG formation is one of the early antiviral mechanisms for host cells against CVB infection.
