Carbon spheres with size of 50-300 nm were synthesized via a solvent-thermal reaction with calcium carbide and chloroform as reactants in a sealed autoclave.The morphologies and microstructures of carbon spheres befor...Carbon spheres with size of 50-300 nm were synthesized via a solvent-thermal reaction with calcium carbide and chloroform as reactants in a sealed autoclave.The morphologies and microstructures of carbon spheres before and after high temperature treatment(HTT) were characterized by X-ray diffractometry(XRD) ,scanning electronic microscopy(SEM) ,energy diffraction spectroscopy(EDS) ,and transmission electron microscopy(TEM) .The formation mechanism of carbon spheres was discussed.The results indicate that the carbon spheres convert to hollow polyhedron through HTT.Carbon spheres are composed of entangled and curve graphitic layers with short range order similar to cotton structure,and carbon polyhedron with dimension of 50-250 nm and shell thickness of 15-30 nm.The change of solid spheres to hollow polyhedron with branches gives a new evidence for formation mechanism of hollow carbon spheres.展开更多
为获取土壤离散元仿真模型的土壤颗粒物理参数和接触参数,本文采用试验与仿真相结合的方法,以桑园土壤为例,对土壤颗粒的接触参数进行了仿真标定。首先利用粉体仪、斜面仪、等应变直剪仪等,分析了试验地不同深度土壤的粒径分布,测量了...为获取土壤离散元仿真模型的土壤颗粒物理参数和接触参数,本文采用试验与仿真相结合的方法,以桑园土壤为例,对土壤颗粒的接触参数进行了仿真标定。首先利用粉体仪、斜面仪、等应变直剪仪等,分析了试验地不同深度土壤的粒径分布,测量了试验地不同深度土壤休止角、滑动摩擦角、剪应力、内聚力、内摩擦角;然后,根据实测土壤粒径分布,利用EDEM软件建立了非等直径土壤球形颗粒模型。在此基础上,以土壤颗粒间及土壤与65Mn钢间的静摩擦因数、滚动摩擦因数、恢复系数为试验因素,土壤休止角、土壤65Mn钢滑动摩擦角为目标值,建立了基于中心组合试验设计(CCD)方案,并利用Design-Expert软件对仿真试验结果进行了分析,得到了仿真标定的土壤土壤间静摩擦因数、滚动摩擦因数和恢复系数的最优值分别为0.89、0.45和0.43;标定的土壤65Mn钢间静摩擦因数、滚动摩擦因数和恢复系数的最优值分别为1.15、0.05和0.4。利用以上标定的最优参数对桑园土壤进行了休止角与滑动摩擦角仿真试验,试验结果表明,休止角仿真值与试验值相对误差为1.69%,土壤65Mn钢的滑动摩擦角仿真值与试验值相对误差为2.88%。在此基础上,依据实测的土壤剪应力,采用试错法,以实测土壤内摩擦角为目标值,优化标定了土壤土壤颗粒HertzMindlin with Bonding接触模型中的粘结参数,标定法向粘结刚度、切向粘结刚度分别为1×10^(8)、5×10^(7) N/m^(3),临界法向应力和临界切向应力均为10 kPa,接触半径为1.1倍颗粒半径,直剪仿真得到内摩擦角为30.24°,仿真值与直剪试验内摩擦角平均值相对误差为5.53%。本文提出的土壤颗粒建模方法、标定方法及其所标定的参数值,可用于砂质壤土桑园耕作机械触土部件与土壤相互作用的离散元仿真分析及其结构优化。展开更多
基金Project(2006CB600901) supported by the National Basic Research Program of ChinaProject(0991015) supported by Guangxi Natural Science Foundation,ChinaProject(200808MS083) supported by Guangxi Education Department Foundation,China
文摘Carbon spheres with size of 50-300 nm were synthesized via a solvent-thermal reaction with calcium carbide and chloroform as reactants in a sealed autoclave.The morphologies and microstructures of carbon spheres before and after high temperature treatment(HTT) were characterized by X-ray diffractometry(XRD) ,scanning electronic microscopy(SEM) ,energy diffraction spectroscopy(EDS) ,and transmission electron microscopy(TEM) .The formation mechanism of carbon spheres was discussed.The results indicate that the carbon spheres convert to hollow polyhedron through HTT.Carbon spheres are composed of entangled and curve graphitic layers with short range order similar to cotton structure,and carbon polyhedron with dimension of 50-250 nm and shell thickness of 15-30 nm.The change of solid spheres to hollow polyhedron with branches gives a new evidence for formation mechanism of hollow carbon spheres.
文摘为获取土壤离散元仿真模型的土壤颗粒物理参数和接触参数,本文采用试验与仿真相结合的方法,以桑园土壤为例,对土壤颗粒的接触参数进行了仿真标定。首先利用粉体仪、斜面仪、等应变直剪仪等,分析了试验地不同深度土壤的粒径分布,测量了试验地不同深度土壤休止角、滑动摩擦角、剪应力、内聚力、内摩擦角;然后,根据实测土壤粒径分布,利用EDEM软件建立了非等直径土壤球形颗粒模型。在此基础上,以土壤颗粒间及土壤与65Mn钢间的静摩擦因数、滚动摩擦因数、恢复系数为试验因素,土壤休止角、土壤65Mn钢滑动摩擦角为目标值,建立了基于中心组合试验设计(CCD)方案,并利用Design-Expert软件对仿真试验结果进行了分析,得到了仿真标定的土壤土壤间静摩擦因数、滚动摩擦因数和恢复系数的最优值分别为0.89、0.45和0.43;标定的土壤65Mn钢间静摩擦因数、滚动摩擦因数和恢复系数的最优值分别为1.15、0.05和0.4。利用以上标定的最优参数对桑园土壤进行了休止角与滑动摩擦角仿真试验,试验结果表明,休止角仿真值与试验值相对误差为1.69%,土壤65Mn钢的滑动摩擦角仿真值与试验值相对误差为2.88%。在此基础上,依据实测的土壤剪应力,采用试错法,以实测土壤内摩擦角为目标值,优化标定了土壤土壤颗粒HertzMindlin with Bonding接触模型中的粘结参数,标定法向粘结刚度、切向粘结刚度分别为1×10^(8)、5×10^(7) N/m^(3),临界法向应力和临界切向应力均为10 kPa,接触半径为1.1倍颗粒半径,直剪仿真得到内摩擦角为30.24°,仿真值与直剪试验内摩擦角平均值相对误差为5.53%。本文提出的土壤颗粒建模方法、标定方法及其所标定的参数值,可用于砂质壤土桑园耕作机械触土部件与土壤相互作用的离散元仿真分析及其结构优化。
