Synthesis and densification of magnesium aluminate spinel: effect of MgO reactivity

Stoichiometric magnesium aluminate spinel was synthesized by reaction sintering of alumina with caustic and sintered magnesia. The volume expansion of 5–7% during MgAl₂O₄ formation was utilized to identify the starting temperature of spinel formation and densification by high temperature dilatometry. The magnesia reactivity was determined by measurement of crystallite size and specific surface area. Caustic magnesia and sintered magnesia behave differently vis-à-vis phase formation and densification of spinel. Densification of stoichiometric Mag-Al spinel was carried out between 1650 and 1750 °C. Attempts were made to correlate the MgO reactivity with microstructure and densification of spinel.     

蜂窝式构件长细比的计算方法

为了进一步研究蜂窝构件稳定承载性能,以现有长细比计算理论为基础,结合蜂窝构件的受力机理和界面特性,提出了蜂窝构件长细比计算中相关参数的计算方法．同时,结合理论推导和数值分析结果,提出了蜂窝构件换算长细比建议计算公式．     

P110和P110SS钢在含CO_2/H_2S溶液的电化学腐蚀行为研究

为了对比普通和抗硫油套管在CO2和CO2/H2S环境的抗腐蚀性能,借助动电位极化和交流阻抗等电化学测试手段在70℃时对普通P110和抗硫P110SS两种材料进行了研究,同时利用ZsimpWin软件对交流阻抗谱进行了等效电路模型拟合,并对其动力学参数进行了分析与讨论.实验结果表明,少量的H2S(0.1%Na2S.4H2O)加速了P110SS的阳极溶解而轻微抑制了P110的溶解;大量存在的H2S(0.4%Na2S.4H2O)环境下,碳钢表面能形成保护性的产物膜,提高了对P110和P110SS腐蚀的阻抗作用;P110SS比P110明显具有更强的抗腐蚀性能;腐蚀阴极过程由活化和扩散联合控制.     

三剪统一屈服准则在柱形孔扩张问题中的应用

基于三剪统一屈服准则,通过用3条折线来描述土体的本构特征,对柱形孔扩张问题进行分析,考虑岩土材料的软化和剪胀特性,推导出柱形孔扩张问题下的应力场、应变场、扩张压力、塑性区半径的解析解。算例表明,临界扩孔压力随土的软化程度的减小而增大,在一定剪胀和软化程度下,临界扩孔压力随b的增大而增大。     

NiCr-ZrO_2复合材料的制备及其热胀性能研究

以ZrOCl2.8H2O和Ni(NO3)2.6H2O,Cr2O3,NH4HCO3为原料,采用缓冲溶液法(一种改进的共沉淀法)制备出复合氢氧化物,将其焙烧得到复合氧化物粉末,最后通过高温还原制备得到NiCr-ZrO2复合粉体材料.通过TG-DSC,XRD,激光粒度仪等现代分析技术对材料的热物性、组成、粒度分布进行测定并研究复合材料热胀系数与其成分组成之间的关系.结果表明,NiCr-ZrO2复合材料的热胀系数随其金属含量的增加而增大.     

Precipitation and stability of reversed austenite in 9Ni steel

A new method was used to analyze the factors affecting the precipitation of reversed austenite during tempering. The samples were kept at various tempering temperatures for 10 min and their length changes were recorded. Then, the precipitation of reversed austenite which led to the length reduction was shown by thermal expansion curves. The results show that the effects of process parameters on the precipitation of reversed austenite can be determined more accurately by this method than by X-ray diffraction...     

Static solution on four-region spherial cavity expansion model in a pressure sensitive medium

Spherical cavity expansion model is often used to study the mechanic characteristics of pressure sensitive mediums. The most important one we do in the paper is that we construct a four-region model with σθ≠0 in damage region,which is different from what Satapathy did before and is more reasonable. By adopting this model,different constitutive equations were constructed by different method-elastic mechanics in elastic region,damage mechanics and fracture mechanics in damage region,and macro-micro mechanics theory in plastic region. Then using Durban's self-similarity assumption,the control differential equations with boundary conditions were established,and the static numerical solution of stress field and displacement field in the three different regions of elastic,damage and plastic area were discussed respectively. Results showed that this four-region model can describe precisely the mechanic characteristics of pressure sensitive mediums under initial pressure.     

Numerical investigation on bowed blades of Iarge meridional expansion Turbine

To improve the performance of the Turbofan engine,several measures should be considered during design process.Such measures,relating to aerodynamic characteristic design,include the maximum enthalpy per stage,the shortest axial length,the minimum blade rows and the highest efficient in design and off design condition.To satisfy theses design characters,the meridian geometry of the engine will he excurvature at a high degree transition part between HP and LP turbines.The study is to investigate the effect of blade bowing on flow loss at blade tip and root of the type of turbine.Such turbine,tending towards separation,with severe secondary flow at the tip and strong radial flow at exit,was simulated by the 3D N-S solver Numerea,and there were several different stacking line bowing schemes in all.The results show that tip negative bowing and root positive bowing is able to weaken radial flow,consequently reduce the flow loss at the tip and root.     

基于wordNet的类别可拓展网页分类系统

基于文本写作常采用一个意思由多个不同写法的单词来表述,研究词义文本分类法被用来替代使用关键词分类算法以提高分类准确率.分析wordNet内Synset架构,认为一个兼顾词义以及词义间关系的词义文本分类系统可应用到网页分类中.该系统同时注意到固定的文本类别结构以及结构内不断增长的文件数目间的区别,加入了基于类别信息聚类方法的类别拓展的功能.仿真实验证明,该分类系统与现有的基于语义的分类系统相比,在分类准确度性能上能提高13%.基于类别信息类聚的文本拓展功能与采用基于相似度的类聚方法的系统相比获得了一个质量更高的新增类别.     

Experimental Study on the Expansion Uniformity of Armature

A measurement system has been developed based on high-precision printed probes in printed circuit board (PCB) and steep rising-time probe adapters,which can be applied to study the expansion uniformity of armature in a helical magnetic flux compression generator (HFCG).The influences of wall thickness and initiation position on the expansion uniformity of armature in HFCG were experimentally investigated.The results show that the armature with thinner wall thickness will easily rupture due to the high pressure of detonation products inside,the armature with larger wall thickness will easily crack due to the tensile stress on the outer surface of the wall,the influence of the end effect on the expansion uniformity can be ignored if the distance between the first group of probe and the initiation point is more than 3 times the armature diameter.