Mechanical stresses in the heterosystem germanium- gallium arsenide

Mechanical stresses in thin germanium epitaxial layers deposited by vacuum deposition on monocrystalline gallium arsenide substrates have been examined. The stresses arising are attributed to two factors: the pseudomorphic character of the growth mechanism and the gradient of structural defects in the transition layer. The experimental stress dependence has been shown to be in good agreement with the theory of the dynamic properties of dislocations.     

Fatigue crack closure at positive stresses

Recently Elber proposed that fatigue cracks close at positive stress levels during constant amplitude stress cycling. To investigate this behaviour, centrally cracked 2024-T3 Aluminium alloy sheets were tested. Crack opening displacements and strains near the fracture surface were measured for a propagating fatigue crack. The experimental results confirm the presence of crack closure at significant positive stress levels during the unloading portion of the cycle.     

Mechanical stability of iron under hydrostatic stresses

A comprehensive investigation of the mechanics of iron subjected to arbitrary fluid pressure has been carried out. Apart from the classical elastic moduli (k, , and ) and conventional elastic moduli (Green and stretch moduli) computations are carried out for a family of generalised moduli of which the conventional moduli are just specific members. With the generalised moduli the mechanical stability of iron is investigated through Born criteria. It is found that classical stability, Green stability and stretch stability are all represented uniquely by the present generalised scheme. The definition of effective classical moduli under stresses enabled the amalgamation of the Born criteria of lattice stability into the single classical criteria of lattice stability of cubic crystal under hydrostatic loading environment. Computations are also carried out to investigate the coordinate and stress dependence of Young's modulus of elasticity, Poisson's ratio, mean velocity of elastic wave, and Debye temperature. Surprisingly, it is found that all these properties of solids play an important role in representing the mechanical stability of the solid. The path of uniaxial loading of iron is also investigated along with its internal energy variation on this path. This indicated the existance of stress-free fcc phase of iron on the path of uniaxial deformation at cell length a=3.6444 Å giving enthalpy of transformation (bccfcc) of 1.1 kJ/mol in good agreement with experimental results.     

Effect of cyclic stresses on the overall electrode potential of an aluminum alloy

The electrode potential of an aluminum alloy D16 was measured during corrosion-fatigue tests on notched and unnotched specimens in 3% NaCl and 5% NaOH solutions, and it was shown that cyclic stresses shift the electrode potential toward the negative values, the effect increasing with increasing stress level.     

Mechanical stresses and crack analysis of concrete under the hygrothermic effect

The hygrothermal process can change the porosity and the permeability of concrete, causing the initiation and the growth of the cracks, and thus deteriorating the integrity of the concrete structure. A numerical formulation based on the finite element method is developed to carry out the simulation of the initiation and the propagation of the cracks caused by the coupled field of thermal transfer and moisture transport. An original concept based on three-dimensional stress state of the integration points in each finite element is described. The global relative crack density is used to denote the cracking state of the entire concrete structure, which may serve as an appropriate index to evaluate the overall deterioration level of the structure.     

Mechanical stresses on products during air cargo transportation

A field study was conducted on board a Boeing 747 Combi (freight and passenger) aircraft on the route Stockholm (Arlanda) via Oslo (Gardermoen) to New York (John F. Kennedy Airport) and return to Stockholm (Arlanda). Shock and vibration, acting on the cargo, during air transportation were measured and analysed. The study encompassed all phases of the flight, including taxiing, climb, cruise during both calm and turbulent conditions, descent and approach, landing including touchdown and taxiing to apron. The field data were analysed by conventional frequency analysis and modelling techniques. In order to generalize the results, flight recorder data from the field trial and from other flights are included. Guide-lines for the development of realistic, simulation test programs for product and package design are included.     

Mechanical stresses on cargo during ground operations in air transport

Mechanical stresses from the shocks and vibrations to which air cargo is exposed during transport and handling at airports have been investigated. Field trials were carried out at Arlanda Airport, Stockholm, and John F. Kennedy Airport, New York. It was found that when products are transported in the airport area, they are exposed to much higher stresses than during actual flight. Especially severe conditions were registered during transport at John F. Kennedy Airport. Measured stresses are related to the ground and mode of driving within the airport area, as well as to location on the pallet wagon. Guidelines as regards design of realistic, simulating test programs for product and package design are reported. Future development possibilities and suggestions for further research within the area are discussed.     

Mechanical determination of internal stresses in as-quenched magnetic amorphous metallic ribbons

The layer removing method for determining the internal stress distribution through thickness in sheets has been applied to metallic glass ribbons. The internal stresses are obtained from the variation of the radius of curvature of the samples when the layers are removed. The experimental technique used is described here and the results for two ribbons, are presented. A general feature has been observed implying compressive stress near both surfaces (a strong one near the drum surface and a weak one near the air surface), and the central part under tensile stress. This is in agreement with the residual stress distribution shown by other materials after fast cooling procedures. This revised version was published online in November 2006 with corrections to the Cover Date.     

The behaviour of semiconducting rutile as the current collector in a sodium-sulphur cell

The behaviour of tantalum-doped titanium dioxide (rutile) as the current collector in a sodium-sulphur cell has been investigated. The resistivity of the material has been measured and compared with the cell impedance. The sintering characteristics, micromorphology, mechanical strength and static corrosion resistance have also been studied.     

镁离子二次电池正极"嵌入"材料研究评述

综述了迄今为止关于镁离子二次电池正极材料的研究。镁离子二次电池称得上是有望用于电动汽车的“绿色”蓄电池。它的原理与锂离子二次电池的相同；但在某些方面比锂离子二次电池更具优势。本文也对今后该领域的研究方向提出了意见。     

Aging of a polymer core composite conductor: Mechanical properties and residual stresses

Polymer core composite conductor specimens were aged in atmospheric conditions at 140 and 180 °C and then tested under four point bending. When aged up to a year at a temperature of 140 °C no detrimental effect on flexural performance of the composite was observed, as opposed to aging at 180 °C, which had a very negative effect on the properties. A finite element model was developed to characterize the residual stress in the composite on a micro scale using representative volume elements (RVE). The residual stresses developed after aging at 140 °C for a year were minimal. However, at temperatures higher than 160 °C significant increases in the stresses were observed. The effect of chemical aging on the failure process of the rods was not considered but could result in the rapid reduction in the loads at failure for the rods tested at 180 °C for up to a year.     

转移法制备顶电极在钙钛矿太阳能电池中的应用

钙钛矿太阳能电池因为其高效率、易制备和低成本等优点,近年来发展迅速。在钙钛矿器件的多层薄膜结构制备和调控中,研究者们关注最多的是钙钛矿吸光层和电荷传输层。而顶电极部分的问题,由于蒸镀Au电极作为实验室阶段标准研究方法的成功使用,而容易被人们忽略。然而,蒸镀贵金属电极的生产设备和原材料成本问题,在钙钛矿太阳能电池未来的大面积器件制备、大范围应用中将是难以避免的。为此,研究者开发了导电膜转移法、导电浆料涂布法等非蒸镀工艺,尝试解决这些问题。本综述针对这一现状,从工艺方法的角度出发,介绍包括金属、聚合物、碳等多种材料体系的顶电极的转移法应用进展,总结具有普遍性的原理、规律,讨论目前技术的缺陷、瓶颈问题和潜在的解决方案。     

直接电解法制备二氧化锰正极的研究

首次通过电解方法直接制得二氧化锰-碳电极.通过恒电流放电、XRD 衍射、差热-热重实验以及环境扫描电镜等现代实验方法研究了合成条件与放电性能的关系.结果表明,在二氧化锰-碳电极上经过420℃处理的二氧化锰具有四方结构(空间群 P42/mnm).以0.1C的电流倍率放电时放电容量达到219mAh/g.不必涂敷粘结剂,二氧化锰就可以与石墨集电极牢固的结合在一起,直接作为正极使用.     

溶剂交换制备高比表面超级电容器材料V2 O5

采用淬冷法制备V2O5溶胶,浸渍覆盖在泡沫镍上,并以低表面张力有机溶剂交换除去其自然吸附水。研究表明,所得凝胶比表面积可达36．67m^2／g。用制备的V2O5为正极,锂片为对电极,LiPF6有机溶液为电解液,组成模拟超级电容器。以电压2V计,比功率为10kW／kg,比能量达158Wh／kg,而不经过溶剂交换过程制备的电极相同比功率下比能量为106Wh／kg。     

溶剂组成对尖晶石LiMn2O4正极材料电化学性能的影响

使用恒电流充放电和粉末微电极循环伏安方法研究了尖晶石LiMn2O4正极材料在不同混合溶剂的电解质溶液中的电化学性能，结合溶剂组分和电解质溶液的理化特性,探讨了影响尖晶石LiMn2O4正极材料电化学性能的溶剂因素。研究表明，电解质溶液组分在电极导电剂表面的氧化电位是决定LiMn2O4电极在其中的电化学循环性能的重要因素。在满足一定的氧化电位的前提下，LiMn2O4初始放电容量与电解质溶液的电导率大小有关。     

TiO_2纳米管阵列电极染料敏化太阳能电池

采用电化学阳极氧化法在纯钛片表面制备了高度有序的TiO2纳米管阵列。利用SEM、XRD分别对TiO2纳米管阵列的形貌、晶型进行了表征,并通过线性扫描伏安法对N719染料敏化纳米管阵列电极的光电性能进行了研究。实验结果表明,纳米管阵列的管径和长度随着阳极氧化电压的升高和氧化时间的延长都分别相应增加。同时还发现,通过450℃热处理的TiO2纳米管阵列,具有较好的锐钛矿晶型结构,其光电转化效率为2.1%。