Fabrication and post heat treatment of 0.5Pb (Mg1/3Nb2/3)O3-0.5Pb(Zr0.48Ti0.52)O3 coatings by supersonic plasma spray

Pb(Mg_1/3Nb_2/3)O₃-Pb(Z_r0.48Ti_0.52)O₃ coatings were obtained by supersonic plasma spray. With subsequent heat treatment, compact structure and typical tetragonal phase were obtained, and therefore dielectric performance (ε_r ≈ 915 at ambient temperature) have been significantly improved. The reason for successfully promote the properties is attributed the elimination of defects, amorphous and pyrochlore phase. Detail analyses were conducted on the variation of defects (pores and micro-cracks) and phase (amorphous, pyrochlore) of coatings after treated at elevated temperature. With the analyses, the existence of pyrochlore phase and ZrO₂ are attributed to the incongruent melting behavior. Inhibition of grain growth is attributed to the accumulation of ZrO₂ in the grain boundary. The results also suggest the subsequent change from pseudocubic to tetragonal at elevated temperature.     

Fabrication of ice-templated tubes by rotational freezing: Microstructure,strength, and permeability

We demonstrate a facile and scalable technique, rotational freezing, to produce porous tubular ceramic supports with radially aligned porosity. The method is based on a conventional ice-templating process in a rotatory mold and demonstrated here with yttria-stabilized zirconia (YSZ). We investigated the effects of solid loading, freezing temperature, and volume of the slurry on the microstructure, strength (o-ring test and four-point bending), and air permeability. The results show that pore volume and pore size can be controlled by the solid loading and freezing temperature respectively, and overall tube thickness can be adjusted by the volume of slurry initially poured into the mold. Decreasing pore size and pore volume increases the mechanical properties but decreases the air permeability. These tubes could be particularly interesting as tubular membrane supports such as oxygen transport membranes.     

Multiple cracks on the arc-shaped interface in a semi-cylindrical magneto-electro-elastic composite with an orthotropic substrate

The present work investigates the problem of multiple cracks on the arc-shaped interface of a semi-cylindrical magneto-electro-elastic layer bonded onto an orthotropic substrate. Continuously distributed dislocation is used to simulate the anti-plane interfacial cracks. The problem is formulated as a Cauchy singular integral equation by integrating the Green’s function of an interfacial point dislocation. Both the theoretical derivation and numerical computation are verified in special cases. The effects of the interface end, crack space, layer thickness, stiffness ratio and material orthotropy are surveyed, among which the fracture behavior of the interface end deserves special attention in design.     

Anti-plane shear fracture of the interface in a cylindrical smart structure with functionally graded magnetoelectroelastic properties

The purpose of the present work is to study the fracture behavior of the arc-shaped interface in a cylindrical non-homogeneous magnetoelectroelastic structure. Fracture analysis is performed by the method of Cauchy singular integral equation. Parametric studies are conducted on the stress intensity factor, and practical guidelines are given for the optimization of fracture performance. (a) The ratio between the outer and inner radii should be at least 1.1. (b) A softer inner side plus a stiffer outer side is a good non-homogeneity design for the magnetoelectroelastic layer. (c) A soft central cylinder and a stiff outer magnetoelectroelastic layer constitute a good stiffness matching on the interface.     

铝热焊的温度场及残余应力场有限元分析

应用ANSYS软件对焊接模型进行了有限元建模,并利用单元生死技术和热-结构耦合功能仿真了焊接过程,模拟出铝热焊动态温度场和动态残余应力场。结果表明:加压的最佳时间在55~255s之间,焊接结构中最大残余应力多出现在熔合区附近,熔合区横向多为拉应力,最大值约212MPa。     

数字化部队武器装备系统整体性能试验评估指标体系构建方法研究

从数字化部队武器装备系统整体性能试验评估指标体系构建的基本问题入手，归纳总结了6种指标体系的构建思想，提出了指标体系的构建过程；针对指标体系构建过程中存在的问题，分析探讨了指标体系的优化方法，并通过实例对其方法进行了详细阐述。     

纳米压痕法测量等离子喷涂铁基涂层表面的残余应力

利用无损的绿色检测技术——纳米压痕法测量等离子喷涂铁基涂层表面的残余应力。通过对比无应力和有应力涂层的载荷-位移曲线,得出涂层表面存在残余拉应力。由于无应力和有应力涂层的压痕周围均有明显的凸起变形,目前广泛使用的Oliver法提取残余应力的特征参量——真实接触面积的公式已不适用。利用之前建立的适用于压痕周围有凸起变形的材料的真实接触面积计算公式得到无应力和有应力涂层的真实接触面积,分析两者之间的差异,最终计算出涂层表面的应力值为188 MPa,与X射线法得到的162 MPa较为符合。     

Multi-functional honeycomb ceramic materials produced from bauxite residues

Red mud is a hazardous waste produced by the Bayer process during commercial production of alumina. In this study, red mud is recycled to produce industrial honeycomb ceramic materials. The materials and processing parameters including the type and size the pore-forming agent, sintering temperature, and stripping methodology are studied. The optimal sintering temperature is determined to be 1075 °C. The bending strength, porosity, water absorption capacity, and bulk density are investigated by X-ray diffraction and scanning electron microscopy. The bending strength exceeds 32.66 MPa after addition of calcium carbonate but the porosity and water absorption capacity diminish to 28.6% and 12.6%, respectively. Incorporation of coal powders increases the porosity and water absorption capability to 36.0%, 20.24%, respectively, but the bending strength drops to 21.69 MPa.     

分布式独立驱动车辆复合转向匹配特性研究

为研究分布式独立电驱动车辆的复合转向机理,提升车辆的转向机动性、操纵稳定性,以某型8 × 8独立电驱动车辆为对象,构建整车仿真模型、分布式独立电驱动控制模型以及车辆复合转向控制模型,在几何转向的基础上,通过在驱动轮主动叠加速差转角即前馈施加车轮虚拟偏转角的方法,分析在相同轮转角状态下,几何转向模式与复合转向模式对车辆转向半径的影响。通过不同行驶工况下的动态仿真,结合车辆的横摆角度、侧向加速度、质心侧偏角等车辆稳定性特性参数,分析复合转向对于车辆操纵稳定的影响,得出分布式独立电驱动车辆复合转向匹配特性。     

PVP对石墨烯/Fe3O4复合吸波材料形貌及吸波性能的影响

目的研究分散剂PVP对Fe_3O_4在石墨烯表面分散性的影响,以获得吸波性能良好的吸波材料。方法采用溶剂热法制备石墨烯/Fe_3O_4复合吸波材料,通过扫描电子显微镜、X射线衍射分析仪、X射线光电子能谱、矢量网络分析仪等对石墨烯/Fe_3O_4复合吸波材料进行表征,并研究了PVP添加与否在石墨烯/Fe_3O_4复合吸波材料形貌及吸波性能的影响。结果添加PVP后的石墨烯/Fe_3O_4复合吸波材料与未添加PVP的相比,Fe_3O_4在石墨烯表面的团聚现象明显减少,尺寸显著减小。通过计算机模拟反射率,未添加PVP的石墨烯/Fe_3O_4复合吸波材料在匹配厚度d=2.00 mm时,在16.25 GHz处达到最大反射损耗-18.79 dB,复合材料反射损耗小于-10 dB的频带宽度可达4.1 GHz。添加PVP的复合材料在匹配厚度d=2.00 mm时,在16.25 GHz处达到最大反射损耗-25.88 dB,复合材料反射损耗小于-10 dB的频带宽度可达4.5 GHz,相比未添加PVP的复合吸波材料,反射损耗小于-10 dB的频带宽度增加0.4 GHz,最大反射损耗提高7.09 dB。结论 PVP能提高Fe_3O_4在石墨烯表面的分散性,并在石墨烯表面形成良好的导电网络,使复合材料的吸波性能明显提升。