恶劣环境中应变测量的国内外发展综述

机器部件、构件和微电子元件,很多是在恶劣环境(包括高温、高压、低温、磁场、辐射、等离子体、腐蚀环境、高速旋转、液下等)中工作的。它们的力学破坏,对人们的安全和生产有非常不利的影响。为防止这些破坏,需要通过分析、实验和计算来改进设计、制造和检测,以提供减少破坏所必要的数据。实验力学,特别是在恶劣环境中进行力学测量,在此起了关键的作用。它提供了基本数据和检测手段,用于计算和建立破坏理论模型。本文介绍在恶劣环境中,主要在高温中,进行应变测量的国内外一些发展情况。     

Energy loss of protons in thin films of carbon,aluminium and silver

The energy loss of keV protons, in thin films of C, Al and Ag is determined by a method in which the strong energy dependence of the cross section for X-ray excitation by protons, in a material, on which the films are evaporated, is used as an indicator of the proton energy.     

Large variation in Young's modulus of carbon nanotube yarns with different diameters

Twist-spun carbon nanotube (CNT) yarns are composed of numerous CNTs and their bundles with entangled and twisted structures. In this paper, we studied the mechanical properties of CNT yarns. The individual CNT, a component of yarn, is well known to have an extremely high mechanical strength. However, CNT yarns are very flexible and relatively free to transform their shapes, showing the potential for application in the design of wearable devices. Since CNT yarns have two opposing characteristics at the same time, a wide range of Young's modulus can be achieved by simply changing the geometrical structure while using the same fabrication process. We also suggest that CNT yarns can be utilized as the base material for several applications that require different stresses in a structure, such as bioimplants or foldable devices.     

有限宽度的ZnSe/ZnTe应变超晶格中LA声子的拉曼频移(英文)

考虑到真实超晶格系统的有限宽度会造成晶格的非周期性 ,我们修正了用来决定拉曼频移峰值位置的公式中的倒格矢一项。在线性驰豫应变假设下给出了应变超晶格纵向原子间距的几何模型。在上述理论基础上计算了有限宽度的ZnSe/ZnTe应变超晶格LA声子的拉曼频移。数值计算结果同现有实验结果作了比较 ,符合很好。     

Comparative study of the band-offset ratio of conventionally strained and strain-compensated InGaAs/GaAs QW lasers

In order to achieve good high temperature laser performance, it is essential to have very deep electron wells. InGaAs system on GaAs substrate suffers from poor temperature characteristics due to the electron overflow over the rather small conduction band offset. By means of the Harrison's model, we investigate the effect of the strain compensation on band alignments of InGaAs/GaAs laser system and show that strain compensation improves the band alignments of this laser system. The use of GaAsP or InGaP barrier instead of GaAs barrier results the strain-compensated laser system having better band alignment than that of the conventionally strained InGaAs. Therefore, high temperature operation has been anticipated in these laser systems with strain compensated barriers due to better electron and hole confinement as a result of the increased band offset and a more favorable band offset ratio.     

透射式GaAs光电阴极AlGaAs窗层Al组份的X射线衍射分析

研究了AlGaAs窗层中Al组份的X射线衍射分析原理和计算方法,并给出了实例.     

Ignition of hydrogen in unsteady nonpremixed flows

The effects of unsteady strain on hydrogen (H₂) ignition in nonpremixed flows are investigated with both experimental measurements and numerical computations. A mixing layer is established in a counterflow configuration with a fuel stream containing N₂–diluted H₂ (X_H2=0.08) flowing against heated air. A reproducible ignition process is initiated by introducing atomic oxygen into the mixing layer with a pulsed ArF excimer laser, which photodissociates heated O₂ from the oxidizer stream. The temporal evolution of OH during ignition is measured by planar laser-induced fluorescence. Following the induction phase, the measured OH mole fraction increases rapidly to a super-equilibrium value that is 60% greater than the OH mole fraction in a steady diffusion flame. The peak OH mole fraction occurs at approximately 6 ms after the excimer laser pulse. To study the OH time history under transient strain, the fuel stream is pulsed at a fixed time after the initiation of ignition. The response of the ignition kernel is extremely sensitive to the time delay of the flow transient. The unsteady strain can delay the ignition time or extinguish the kernel. Comparisons between computations and experiments are made for the evolution of OH during autoignition both for steady and unsteady strain. For both steady and unsteady strain, the transient one-dimensional counterflow computations show excellent agreement with the experiment in terms of predicting ignition delays and the rate of OH accumulation during the induction period. The computations also capture the super-equilibrium OH during the transition to the formation of a steady flame, although not to the degree observed experimentally. The computations are further used to understand the influence of unsteady strain on the kernel evolution. It is found that the degree of super-equilibrium OH is sensitive to strain transients applied close to the time of thermal runaway.     

A thermo-viscoelastic model for elastomeric behaviour and its numerical application

Summary  This paper presents a model of thermo-mechanical behaviour of viscoelastic elastomers under large strain. A formulation is proposed with a generalisation to large strain of the Poynting–Thomson rheological model. A finite element formulation is then exposed taking the incompressibility constraint for mechanical equilibrium into account. On the thermomechanical coupling aspect, an algorithm of time discretisation is proposed with two time scales corresponding respectively to mechanical and thermal behaviours. Finally, an application for the simulation of a double-shearing test is presented with an analysis of parameters' influence and a comparison between numerical and experimental results. Received 22 November 2000; accepted for publication 26 June 2001     

Structural and electrical characterisation of La0.5Ca0.5MnO3 thin films grown by pulsed laser deposition

Thin films of perovskite manganite, with nominal composition La_0.5Ca_0.5MnO₃, have been prepared by pulsed laser deposition on (1 0 0) SrTiO₃, (1 0 0) LaAlO₃, (1 0 0) Si and YSZ/CeO₂-buffered (1 0 0) Si substrates. Structural and electrical characterisation was performed on the films. The magneto-transport properties of all the thin films depart from the bulk behaviour. The LCMO film grown on buffered Si shows an insulator–metallic transition around 130–150 K while the one deposited directly on Si displayed a similar behaviour under a melting field of 1 T. However, that transition is absent in the films grown on LAO and STO. We suggest that appropriate stress values induced by the substrate favour the formation of metallic percolative paths.     

Micro-experimental study for the stress effects on the interphase of composite materials

Digital speckle micro-metrology system, which is a combination of a long-focus microscope and a digital image-measuring device, is developed for studying the micro-mechanics behavior of the interphase of bimaterials. The natural texture of a specimen's surface is thought as a carrier of deformation's information and is analyzed to obtain the displacement field in each step, strain field and their real-time variation of the interphase. The resolution of the micro-metrology system is 10 nm for in-plane displacements. In this paper, the micro-metrology system is employed to investigate the micro-mechanics behavior of the interphase under thermal impulsing. The experimental results show that the interphase is the main factor affecting the mechanical characteristic of the whole composite structure.