Euler Critical Force Calculation for Laced Columns

The paper presents a method of solving the buckling problem of laced column as a statically indeterminate structure without analyzing determinants of high order. The flexural and torsional buckling problems of laced column are reduced to the two-point boundary value problem for a difference equation system. The value of Euler critical load is determined as a result of analyzing the fourth order determinant for column with any degree of static indeterminacy. The solution is based on the method of initial values. Stability of columns with any types of lattice (crosswise, serpentine, with batten struts); with any number of lattice panels and with variable lattice spacing can be examined by this manner. The analogy between the flexural and torsional buckling of the laced column is established. It enables one to use the same relations for consideration of both kinds of buckling. The obtained numerical results show that the Euler critical loads calculated by this method can be substantially differed from those based on the approximated Engesser’s approach. A PC program for checking stability of laced column by designer can be developed on the basis of the present method.     

Explicit local buckling analysis and design of fiber–reinforced plastic composite structural shapes

Pultruded fiber–reinforced plastic (FRP) composite structural shapes (beams and columns) are thin-walled open or closed sections consisting of assemblies of flat plates and commonly made of E-glass fiber and either polyester or vinylester resins. Due to high strength-to-stiffness ratio of composites and thin-walled sectional geometry of FRP shapes, buckling is the most likely mode of failure before material failure. In this paper, explicit analyses of local buckling of rectangular orthotropic composite plates with various unloaded edge boundary conditions (i.e., (1) rotationally restrained along both unloaded edges (RR), and (2) one rotationally restrained and the other free along the unloaded edges (RF)) and subjected to uniform in-plane axial action at simply-supported loaded edges are first presented. A variational formulation of the Ritz method is used to establish an eigenvalue problem, and explicit solutions of plate local buckling coefficients in term of the rotational restraint stiffness (k) are obtained. The two cases of rotationally restrained plates (i.e., the RR and RF plates) are further treated as discrete plates of closed and open sections, and by considering the effect of elastic restraints at the joint connections of flanges and webs, the local buckling of different FRP shapes under uniform axial compression is studied. The approximate expressions of the rotational restraint stiffness (k) for various common FRP sections are provided, and their application to sectional local buckling predictions is illustrated. The explicit local buckling formulas of rotationally restrained plates are validated with the exact transcendental solutions. The analytical predictions for local buckling of various FRP profiles based on the present discrete plate analysis and considering the elastic restraints of the flange–web connections are in excellent agreements with available experimental results and finite element eigenvalue analyses. A design guideline for local buckling prediction and related performance improvement is proposed. The present explicit formulation can be applied effectively to determine the local buckling capacities of composite plates with elastic restraints along the unloaded edges and can be further used to predict the local buckling strength of FRP shapes.     

纤维缠绕外压容器稳定性最佳铺层分析

在纤维缠绕压力容器设计中，纤维缠绕的方向及各方向纤维用量配比是关键问题。过去的研究中，这一问题一直没能得到很好地解决，特别是各方向纤维用量问题。本文在文献［１～４］的基础上，以加权因子和铺设角为参量给出了对称多层正交各向异性外压容器筒体失稳的最佳铺层理论值。得出了加权因子ｓ取最佳值的范围为０＜ｓ＜０．２５的结论。文中算例表明，按最佳取值给出的临界压力较其它情况有较大幅度的提高。     

陶瓷微球增强铝基复合材料

介绍一种以铝土矿陶瓷微球增强的铝基复合材料，具有价格低、增强物与基体合金润湿性好、界面反应几乎不存在等优点。又因其增强物为微球，有利于减小应力集中，延缓裂纹萌生与扩展，同时也提高了铸造流动性和塑性成形能力。讨论了其制造工艺、有关特性和问题。     

Compomer的摩擦磨损特性

采用Compoglass，F2000，Elan，Dyract AP4种牙科用复合体材料(Compomer)，对其玻璃颗粒含量和表面硬度进行了测量，并在球一盘往复摩擦磨损试验机上考察了它们的摩擦磨损特性。结果表明：F2000的摩擦系数最高，Elan的摩擦系数次之，Compoglass和DyractAP的摩擦系数分别为第三和第四．摩擦系数随玻璃颗粒含量的增加而增加．在同样试验条件下，低摩擦系数的DyractAP和Compoglass与高摩擦系数的F2000和Elan相比具有较好的耐磨性．磨损机理主要表现为由玻璃颗粒脆性断裂引起的玻璃颗粒脱落和磨粒磨损。     

A review of modeling approaches for oriented semi-crystalline polymers

Modeling changes in the physical properties of oriented semi-crystalline polymer films is beneficial for understanding the fundamentals associated with structure property relationships and could be used for developing new polymer films with significantly enhanced physical properties. Relating the molecular changes observed in oriented polymer films to inherent polymer characteristics provides valuable insight for the development of new polymers which exhibit enhanced physical properties upon orientation. Modeling efforts will be reviewed that have attempted to use fiber composite theory to explain the transitions seen during the orientation process.     

ISA法铜电解槽槽面水平误差的控制

本文介绍了通过采用找平装置来控制ISA法铜电解槽槽面水平误差的方法,通过现场测量及工艺操作证明是行之有效的。     

Surface Actuation of Lightweight Mirrors with Shape Memory Alloy

The ability to create lightweight mirrors that can maintain surface accuracy is a major technical challenge for future space telescopes. Processing-induced errors and surface errors due to temperature excursions and gravity sag (zero gravity in space) make it impossible to correct the surface of thin mirror face-sheets by conventional point actuators. The challenges are compounded by the requirements for mirrors to have adequate stiffness for pointing accuracy. An experimental and analytical study was conducted to explore the feasibility of correcting the shape of lightweight (≈1 kg/m2) mirrors using a “Nitinol” (nickel-titanium) shape memory alloy (SMA). Shape memory alloys are increasingly used as smart devices in aerospace applications. Their primary advantage over other smart materials (i.e., piezo-ceramics and piezo-polymers) is in their ability to undergo large strains and displacements and thus enable the development of smart mechanisms. Active shape correction is the only means of mitigating heat and zero-gravity-induced distortions in space-based optical imaging systems. The repeatability and reliability of a possible actuation system based on properties of the SMA wires were studied by testing the stress-strain and stress recovery behavior under controlled conditions. Embedded SMA wires were then used to actuate a composite beam, and the movement induced by actuation was monitored with the Moiré interferometry method.     

聚醚固体电解质锂电池放电性能研究

利用氧亚甲基连接的聚氧乙烯-聚氧丙烯多嵌段共聚物或氧亚甲基连接的聚氧乙烯多嵌段共聚物与高氯酸锂的络合物作电池的电解质,锂片作负极,几种含钒的化合物作正极,组装了全固态二次锂电池.研究了不同正极材料、不同电解质和不同温度对电池短路放电性能的影响以及电池的重复短路放电性能.研究表明,正极材料V_6O_(13)的性能优于Na_(1+x)V_3O_8;电解质(PEO)_n·LiClO_4的性能优于(PEO-PPO)_n·LiClO_4,这与它们的电导率分别为3.2×10~(-3)S·cm~(-1)和2.2×10~(-3)S·cm~(-1)是一致的.     

光伏储能用VRLA蓄电池的设计与开发

对于光伏储能用VRLA蓄电池的设计与开发,要严格按照产品的使用环境情况进行分析,有针对性地调整配方、工艺控制参数、正负极板的设计比例等,以满足光伏储能用铅酸蓄电池的要求.