Characteristics and formation mechanism of porosities in CFRP during laser joining of CFRP and steel

An experimental investigation on the mechanism of porosity formation during the laser joining of carbon fiber reinforced polymer (CFRP) and steel is presented. The porosity morphology and distribution were characterized by optical and scanning electron microscopy, and the thermal pyrolysis behaviors were investigated by thermal analysis and designed back-side cooling experiments. The results show that there are two types of porosities in CFRP. Porosity I only appears when the heat input is more than 77.8 J/mm. It has a smooth inner wall and distributes near the bonding interface between CFRP and steel at the central area of melted zone, which is caused by gaseous products such as CO₂, NH₃, H₂O, and hydrocarbons produced by the pyrolysis of CFRP. Porosity II can be seen under all joining conditions. It has a rough inner wall and distributes far away from the bonding interface, concentrating at the final solidification locations. Porosity II is caused by the shrinkage of melted CFRP during solidification stage.     

Effects of hydrolysis of precursor on the structures and properties of polymer-derived SiBN ceramic fibers

In this paper, polyborosilazane precursor was synthesied from HMDZ, HSiCl₃, BCl₃ and CH₃NH₂ using a multistep method. By controlling the storage conditions, parts of the polyborosilazane fibers were hydrolyzed. FT-IR, NMR, XRD, TEM and monofilament tensile strength test were employed to study the effects of hydrolysis of precursor on the structures and properties of polymer-derived SiBN ceramic fibers. FT-IR and NMR results indicate that Si-N group in PBSZ reacts with H₂O to form Si-O-Si group. After pyrolysis reaction at 1400℃, Si-O-Si group will finally transformed into highly ordered cristobalite and β-quartz, resulting in formation of the wrinkled surface of the obtained SiBN ceramic fiber. The strip-like defects on fiber surface, according to monofilament tensile strength test, had a significant effect on mechanical property of the obtained SiBN ceramic fiber and caused no increase in fiber tensile strength of hydrolytic polyborosilazane fiber before and after pyrolytic process.     

Evaluation of sorbents for thiophene removal from liquid hydrocarbons

Thiophene is a commonly occurring sulfur compound in liquid hydrocarbon streams produced in a petroleum refinery. The concentration of thiophene often needs to be reduced to very low levels for most applications. Selective adsorption of thiophene is investigated in n-heptane, 1-octene and xylenes and their mixtures. A variety of adsorbents were tested for their selectivity and adsorption capacity. Improvements in adsorption capacity were attempted based on analysis of the adsorption mechanism. Adsorption capacity of NaX zeolite was found to be highest among tested adsorbents. However, competitive adsorption from xylenes reduced adsorption capacity for thiophene from mixtures containing large concentration of xylenes. Langmuir model is applied to describe observed competitive adsorption. Selective adsorption of organic sulfur compound could be used as a polishing step in a purification scheme which allows sulfur removal from hydrocarbons at low temperature and without the use of expensive hydrogen.     

混炼胶门尼粘度的预测与控制

使用ＭＧＫＪ型密炼机混炼微机监控系统，在ＢＢ２７０型密炼机上预测混炼胶的门尼粘度值，实现了胎面胶门尼粘度值的预测。预测值与实测值的差平均为０８（相对误差１％）。借助预测门尼粘度的数学模型，对排胶点进行控制，使混炼胶门尼粘度的波动范围为－３～＋３。     

Hot deformation behavior of low carbon steel during compression at elevated temperature

Hot compression tests of low carbon steel were carried out on Gleeble-3500 system in the temperature range from 750 to 900 ℃ and in the strain rate range from 0.001 to 1.0 s-1, and the associated microstructural evolution was studied by observations with a metallographic microscope. The results show that the stress-strain curves exhibit a peak stress at critical strain, after which the fl ow stresses decrease monotonically until reaching high strains, showing a dynamic fl ow softening. The peak stress level decreases with increasing deformation temperature and decreasing strain rate, which can be represented by the Zener-Hollomon parameter Z in the hyperbolic sine equation. The fl ow stress increases with increasing strain rate and decreasing deforming temperature. The fl ow stress can be described by constitutive equation in hyperbolic sine function and can also be described by a Zener–Hollomon parameter Z. With increasing deformation temperature and decreasing strain rate, the grain size as well as the volume fraction of the recrystallized grains increase. The safe region for hot working of the alloy has been determined according to the processing map and microstructure at the true strain of 0.5, which is the deformation temperature of 840-940 ℃ and the strain rate of 0.001-1.0 s-1.     

复合溶胶–凝胶一锅法制备锂离子电池氧化亚硅/碳复合负极材料

采用复合溶胶–凝胶法结合后续热处理,制备了具有包埋结构的氧化亚硅/碳(SiO_x/C)复合负极材料。扫描电子显微镜分析结果表明:氧化亚硅纳米颗粒嵌入在无定形碳中。电化学性能测试表明:SiO_x/C复合材料具有较高的比容量、优异的循环稳定性和倍率性能。材料在0.1 A/g的电流密度下100次循环后的可逆比容量为710 m A·h/g,容量几乎无衰减;在1.6 A/g的电流密度下,可逆比容量为380 m A·h/g。优异的电化学性能是由于材料的包埋结构能有效地缓冲SiO_x充放电过程中的体积膨胀,保证材料的结构完整性和电化学循环稳定性。     

JB/T 4730-2005《承压设备无损检测》答疑--超声检测部分(Ⅲ)

35 关于焊缝的检测区宽度。JB／T4730-2005标准与原标准有何差异？ 新标准规定，检测区宽度应是焊缝自身宽度加上焊缝两侧各相当于30％T（T为母材厚度）的一段区域，此区域最小为5mm，最大为10mm。     

Analysis on quantifiable and controllable assembly technology for aeronautical thin-walled structures

Assembly affects the product's performance and reliability directly. The current assembly method based on geometric deviation quantity controlling, cannot guarantee the physical performance for complex aeronautical thin-walled structures effectively, such as assembly geometry accuracy and internal interactive stress. And assembly performance controlling is taken as the bottleneck problem that restricting the new aviation requirement of sub-millimeter assembly. In this paper, by proposing the accurate prediction and process-oriented adjustment&controlling strategies on assembly quality, construction on working mode with “quantifiable and controllable” characteristic was proposed, whose aim was to reduce the phenomenon of out-of-tolerance and deformation rebound error, and the ultimate goal is to reduce the uncertainty of assembly performance parameters. At the technical level, the academic development context and existing problems for assembling thin-walled structures were reviewed and analyzed, such as assembly process parameters optimization, assembly error transfer and accumulation, comprehensive adjustment on assembly quality, and virtual assembly simulation validation. Then the key future research trends for aeronautical structure assembly were also put forward, i.e. the force/deformation coordination among multi-type finite units for non-ideal assemblies, the dynamic construction of stiffness matrix for intermediate assemblies considering geometric nonlinearity, the adaptive balance on assembly performance driven by physical modeling and measured data, and the inverse optimization on assembly quality and parameters with intelligent data processing. This paper would lay a solid foundation for achieving the accurate assembly mode with the characteristics of “intelligent/scientific, and active/collaborative controlling on geometric shape and physical performance”, and higher assembly quality and efficiency could also be gained.     

Na3Zr2Si2PO12固态电解质研究进展

钠离子电池具有资源丰富、能量密度高等优点,使用固态电解质的固态钠电池兼具高安全性成为研究热点。固态电解质是超离子导体,是固态电池关键材料。Na₃Zr₂Si₂PO₁₂是钠超离子导体（NASICON）中最具代表性的固态电解质材料。总结了Na₃Zr₂Si₂PO₁₂材料的结构、离子传输机制及其相互关系,旨在从机理上理解Na₃Zr₂Si₂PO₁₂固态电解质中钠离子传输性能;总结了主要制备方法,指出了不同方法的优缺点;在提升离子电导率方面,对合成工艺、掺杂、界面因素进行了总结,力求归纳和探索合成高性能钠离子固态电解质的途径。     

航天器振动试验控制技术进展

航天器对恶劣动力学环境的适应能力直接关系到整个航天飞行任务的成败,振动试验控制技术是动力学环境试验的关键环节.本文分析了近年来国内外航天器振动试验设备和振动控制算法的研发动态、基本原理和关键技术达到的水平.提出了跟踪研究的基本思路,途径及建议.