Microstructures and mechanical properties of B4C-TiB2-SiC composites fabricated by ball milling and hot pressing

B₄C-TiB₂-SiC composites were fabricated via hot pressing using ball milled B₄C, TiB₂, and SiC powder mixtures as the starting materials. The impact of ball milling on the densification behaviors, mechanical properties, and microstructures of the ceramic composites were investigated. The results showed that the refinement of the powder mixtures and the removal of the oxide impurities played an important role in the improvement of densification and properties. Moreover, the formation of the liquid phases during the sintering was deemed beneficial for densification. The typical values of relative density, hardness, bending strength, and fracture toughness of the composites reached 99.20%, 32.84?GPa, 858?MPa and 8.21?MPa?m^1/2, respectively. Crack deflection, crack bridging, crack branching, and microcracking were considered to be the potential toughening mechanisms in the composites. Furthermore, numerous nano-sized intergranular/intragranular phases and twin structures were observed in the B₄C-TiB₂-SiC composite.     

随车起重机伸缩臂截面多目标优化

为了提高某火箭炮弹药装填车随车起重机伸缩臂的结构刚度,减轻结构质量,建立了随车起重机伸缩臂参数化模型,并对伸缩臂在水平受载状态下进行仿真分析。以伸缩臂截面尺寸参数为设计变量,借助最优拉丁超立方试验设计建立样本空间,构造响应面多项式函数近似模型。在此基础上,利用NSGA-Ⅱ型遗传算法对伸缩臂自身重量、挠度进行多目标优化。优化结果表明:伸缩臂质量减轻了24.5%,减重效果明显。文中所采用的将参数化建模、有限元分析和数值寻优相结合的优化方法,可为起重机伸缩臂截面优化提供一定的参考。     

介孔分子硅剂改善茶浓缩膜结构特性应用研究

为有效提高功能性茶浓缩反渗透膜的回收效率和抗污性能,探究了3种介孔分子硅材料(MCM-41、SBA-15和MCFs)对浓缩膜面聚酰胺层聚合形成过程的结构影响。结果表明,添加质量分数0.02%经磺化预处理的MCM-41于间苯二胺水相可接枝酰氯基团,形成的聚酰胺结构层峰谷粗糙跨度仅为220 nm且交联紧致,膜抗拉伸强度增加37.8%;SBA-15和MCFs相膜面峰谷跨度达500~780 nm,横向褶皱和团聚,结构存在孔道塌陷;改性膜在3 h内对茶多酚、茶多糖、茶蛋白即可达到最大浓缩度,减少50%浓缩时间;MCM-41和SBA-15膜长时间运行的浓缩降率仅为2.8%~6.1%,48 h下降率比显示改性膜达标使用时长增加112.5%~137.5%,亲水性和抗污堵能力均大幅提升,可有效满足功能化茶浓缩精度。     

03Cr18NiMoN节镍双相不锈钢的热变形行为及热加工图

关键词：双相不锈钢； 流变曲线； 本构方程； 热加工图     

影响煤层气开发效果的地质因素再认识

地质特征认识对煤层气开发效果起着重要作用。在资源特征相差不大的情况下,发现煤层气相邻井的产量差异仍较大。排除工程因素后,通过选取8类地质参数,细致比对了保德区块低产井与邻井的参数特征,筛查出其关键因素为煤层微幅构造与顶板封盖条件,其中以微幅构造为主。据此,重新认识并划分出区块新的次生褶皱背斜单元、向斜单元和斜坡单元,获得了不同次生褶皱构造单元的开发特征。结果表明,高、低产井分布与次生褶皱背斜、向斜相关性高达92%。其中:高产井主要分布在次生褶皱背斜变化较缓、呈隆起状的“平台”,且煤层顶板以泥岩、碳质泥岩为主,封盖性较好;低产井主要分布在次生褶皱向斜,同一井台各井开发效果差异表现为从向斜条带轴部—向斜条带内—向斜条带外的煤层气井平均单井产量不断增加,到向斜轴部的距离大于向斜曲率半径73.5%的范围为主力产气区,小于向斜曲率半径40.0%范围为产水主力区。这对煤层气新井部署、生产管理、开发调整等,具有一定的指导意义。     

Disappearance and recovery of colossal permittivity in (Nb+Mn) co-doped TiO2

We investigate the effects of doping and annealing on the dielectric properties of metal ions doped TiO₂ ceramics. Colossal permittivity (CP) above 10⁴ was observed in single Nb ion doped TiO₂, which was dominated by electron transport related interfacial polarization. Moreover, the CP can be dropped to 120 when simultaneously introducing Mn ion into the sample. The disappearance of CP behaviors maybe due to the multivalence of Mn which would inhibit the reduction of Ti⁴⁺ to Ti³⁺, and thus reduce delocalized electrons. Interestingly, the CP was recovered for the (Nb+Mn) co-doped TiO₂ after post-sintering heat treatment in N₂ atmosphere. The recovery of CP in the sample after annealing can be ascribed to the semiconducting grain and the insulating grain boundary, according to impedance spectroscopy. We therefore believe that this work can help us understand the mechanism of CP from a new perspective.     

49MnVS3曲轴用非调质钢控轧控冷工艺技术研究及应用

49MnVS3非调质钢(/%:0.47C,0.39Si,0.90Mn,0.016P,0.050S,0.22Cr,0.09V,0.015Ti,0.011Al,0.02Ni)的生产流程为铁水预处理-60t顶底复吹转炉-LF处理-VD真空脱气-220 mm×300 mm坯连铸-控轧控冷。研究了控轧控冷工艺对49MnVS3非调质钢组织和性能的影响。φ110 mm轧材试验工艺参数:加热温度1150～1250℃、开轧温度1 0500℃、终轧温度850℃、轧后冷却速度70℃/min、冷却开始温度850℃和终止温度500℃。结果表明,试验炉次粒度提高高.5～1.0级,带状组织减轻轻0.5～1.5级,硬度、强度及塑韧性均有所提升,获得良好的强韧性匹配。     

基于3D打印技术复制砂浆节理的剪切试验及峰值抗剪强度模型

为进一步研究节理三维形貌特征与节理峰值抗剪强度的关系,首先采用巴西劈裂试验获取了自然劈裂岩石表面,通过三维扫描技术获取了节理面形态的高精度点云,通过逆向建模得到了自然岩石表面的立体模型,结合3D打印技术制作出了与自然岩石表面一致的PLA模具,以3D打印获得的底模通过水泥砂浆浇筑了含有自然结构面形貌的相似节理面试样。PLA模具与复制材料差异较大,复制材料在凝结过程中不易与PLA模具黏结,进而使脱模过程较为方便,不会破坏节理面。同时PLA模具可重复进行相似材料复制工作,具有可重复使用的优点。然后进行了具有5组形貌面的20个水泥砂浆节理面在4种不同法向荷载情况下的结构面剪切试验,得到了结构面剪切位移-荷载曲线。研究了结构面峰值抗剪强度、峰值位移、剪切刚度影响因素。节理经过剪切后形貌面出现不同程度的磨损,其磨损范围与等效高差分布范围基本一致,并且在等效高差为剪断破坏模式且成片的区域磨损较为严重。在新粗糙度指标基础上提出了新的峰值抗剪强度模型,经试验对比显示出新模型的有效性。在新模型基础上提出了一个简化模型。对比发现新模型简化后其计算精度较新模型有所降低但由于所需参数减小计算较为方便,新模型简化结果精度虽然有所下降但是还是比Barton公式精度高。     

Development of mobile miniature natural gas liquefiers

With increasing consumption of natural gas (NG), small NG reservoirs, such as coalbed methane and oil field associated gas, have recently drawn significant attention. Owing to their special characteristics (e.g., scattered distribution and small output), small-scale NG liquefiers are highly required. Similarly, the mixed refrigerant cycle (MRC) is suitable for small-scale liquefaction systems due to its moderate complexity and power consumption. In consideration of the above, this paper reviews the development of mobile miniature NG liquefiers in Technical Institute of Physics and Chemistry (TIPC), China. To effectively liquefy the scattered NG and overcome the drawbacks of existing technologies, three main improvements, i.e., low-pressure MRC process driven by oil-lubricated screw compressor, compact cold box with the new designed heat exchangers, and standardized equipment manufacturing and integrated process technology have been made. The development pattern of “rapid cluster application and flexible liquefaction center” has been eventually proposed. The small-scale NG liquefier developed by TIPC has reached a minimum liquefaction power consumption of about 0.35 kW·h/Nm³. It is suitable to exploit small remote gas reserves which can also be used in boil-off gas reliquefaction and distributed peak-shaving of pipe networks.     

An image encryption scheme based on precision limited chaotic system

Multimedia Tools and Applications - In recent years, various chaotic maps have been used for image encryption. However, most of these image encryption algorithms entail a lot of floating-point...