剪切电子散斑干涉仪的实验应用

简要介绍剪切电子散斑干涉的基本原理,将标准试件在受栽后的位移和位移梯度干涉条纹,通过CCD摄取并进行处理,从干涉条纹直接获得令人满意的结果,通过实验说明该技术能够应用在各个不同的场合,将成为无损检测的有效方法.     

光栅大错位数字散斑干涉仪

本文介绍了一种新的散斑干涉仪,该仪器利用光栅作为错位元件,具有光路简单,结构紧凑,波像差小,防震要求低等特点,文中对仪器进行了详细的原理分析与介绍,并利用其测量典型试件受均布载荷下的离面位移场,进行理论值与实验结果比较,证明该仪器测量位移时具有高的精度,同时该仪器还可应用于构件的无损探伤。     

电子散斑干涉法研究铸铁的断裂特性

为研究铸铁材料的断裂过程和破坏机理,对带预制裂纹铸铁梁进行了三点弯曲加载试验,同时采用电子散斑干涉法并引入相移技术对裂纹前端的面内位移场进行了测定。通过实验得到了梁裂纹尖端附近区域的电子散斑干涉条纹图,通过图像处理得到裂纹端部变形、裂纹张开位移和中性层位置随载荷的变化曲线,并对其进行了分析。     

电子剪切散斑干涉原理的统计研究

本文从激光散斑的统计理论出发,研究了电子剪切散斑干涉术(ESSPI)的基本原理。导出了试件位移与干涉条纹的对应关系,讨论了外界干扰对条纹的影响。     

反射全息和散斑干涉结合的实验技术

一、前言在实验应力分析中,用全息干涉法得到变形,尤其是得到离面位移信息是很灵敏的,而不易获得面内位移信息。散斑法正相反,它很容易得到面内位移,而离面位移就较难得到。它的灵敏度也低于全息干涉法。在实际工作中,往往遇到既要求面内位移也要求离面位移的问题。为了保证实验精度,又不宜使用分别加载拍片的     

数字散斑相关在电致伸缩效应测量中的应用

利用数字散斑相关方法对纳米钛酸钡／聚氨酯复合材料进行了光学实验，研究了其在外加强直流电场作用下的电致伸缩应变随电压变化的规律。采用CCD及计算机处理系统，实时获取了外加高电场作用下试件表面位移场的散斑图；应用数字散斑相关方法获得了试件的应变量与外加电场强度的关系，从而得到试件的电致伸缩系数。对该方法进行了详尽的阐述，并对测量结果进行了分析。实验结果验证了数字散斑相关方法测量电致伸缩效应的可行性和有效性，为电致伸缩效应的测量提供了一个有效途径。     

用投影散斑法测量三维微位移

采用光学非接触法测量三维微位移,基于三角测量法投影数字散斑照射参考面和待测物体表面,利用数字散斑相关法原理,求解变形位移信息,实验结果表明,数字散斑相关技术在三维变形测量的有效性和可靠性,并且为三维物体形变的测量提供了新的研究思路。     

数字剪切散斑干涉技术

研究了数字剪切散斑干涉技术(DSSPI)的原理,详细讨论了剪切成像的常见方式并总结了各种方式的优缺点及适用场合,介绍了数字散斑剪切干涉技术在无损检测中的应用。     

电子散斑剪切干涉相移技术的研究

在散斑干涉技术中,待测量与干涉条纹图的相位信息直接相关,因此从干涉条纹图提取相位分布信息就显得尤为重要。文中对平移沃拉斯顿棱镜相移法进行理论分析,证明平移棱镜可以引入稳定、线性的附加相位,给出了棱镜移动和附加相位的关系。利用周边固定中心加载的圆盘进行实验。给出了实验结果,证明平移棱镜相移法可以有效地从干涉条纹中定量提取位移导数信息。     

计算机模拟技术在错位散斑干涉法中的应用

建立了电子错位散斑干涉法成像的数学模型,编制了计算机模拟软件,可以模拟不同系统设置和不同变形情况下的干涉条纹图。用该软件研究了错位量大小对条纹图的影响,得到了与经典的“位移梯度”理论不完全相符的结果。理论分析和试验结果都证明了计算机模拟的正确性,并由此提出了条纹图解释的“对点位移差”理论。本研究工作对电子错位散斑干涉无损检测系统的设计和检测结果的分析有很好的应用价值。     

DICM在发动机模态参数识别中的试验研究

基于高速摄影成像技术,利用数字图像相关方法(digital image correlation method,简称DICM),根据时间序列动态散斑相关跟踪测量原理,提出了一种用于机械结构动力学特性测试与研究的时间序列数字图像相关方法。该方法具有全场非接触,测试结构简单,测量精度高,测量位移和频率范围可调。运用该方法对柴油发动机机体在自由状态下固有频率进行了测试。采用高速CMOS摄像机及其计算机处理系统,实时获取发动机机体的振动图像,用VC编制时间序列图像相关软件,自动对序列图像进行相关运算,获得其位移-时间曲线。通过FFT频谱分析,确定了机体的固有频率。光测试验结果与电测试验结果、有限元数值计算结果基本一致。     

A new high-resolution dual-probe system for detecting and imaging thermal and plasma waves

Thermal and plasma waves have been simultaneously and independently probed by a novel differential system. This new detection system for characterising and imaging materials such as semiconductors in a noncontacting, nondestructive manner, is based on two parallel, heterodyne interferometers, which probe the specimen on a microscopic scale. These detect changes in sample reflectivity and surface displacement which are induced by a separate laser source. The optical and electronic configuration is described and results showing the measurement and imaging capabilities of the system are presented. New results indicating interference between photodisplacement and photoreflectance effects are discussed.     

Dynamic shear stress of tough-pitch copper at high strain and high strain-rate

Dynamic shear tests for the tough-pitch copper at high strain and high strain rate was performed. The Split Hopkinson Pressure Bar (SHPB) compression test system was modified to yield a shear deformation in the specimen. Hat-shaped specimens for the tough-pitch copper were adopted to generate high strain of γ=3–4 and high strain-rate of γ=10⁴/s. The dynamic analysis by ABAQUS 5.5/EXPLICIT code verified that shear zone can be localized in hat-shaped specimens. A proper impact velocity and the axial length of the shear localization region were determined through the elastic wave analysis. The displacement in a hat-shaped specimen is limited by a spacer ring which was installed between the specimen and the incident bar. The shear bands were obtained by measuring the direction of shear deformation and the width of deformed grain in the shear zone. The decrease of specimen length has been measured on the optical displacement transducer. Dynamic shear stress-strain relations in the tough-pitch copper were obtained at two strain-rates.     

A Photoelastic Method for the Study of Cage Strain in a Rolling Element Bearing

A technique has been developed by which interpretable photoelastic stress patterns can be obtained from rolling element bearing cages while operating under conditions of various speed and load. The test specimen utilized in this study was a 130 mm bore cylindrical roller bearing. A layer of bire-fringent plastic was cemented to the outboard side of the cage of the bearing by means of a reflective adhesive. This plastic material was illuminated by means of high intensity polarized light. This light passed through the birefringent plastic material, was reflected by the reflective adhesive and passed back again through the birefringent material and through another polaroid filter (analyzer). A high speed camera was located behind this second polaroid filter. High speed motion pictures were taken of the photoelastic stress patterns produced in the birefringent material as the test bearing was rotated under radial load. Photoelastic stress patterns recorded on the high speed motion picture film were analyzed and resulted in the determination of the stress distribution along a radial section of the cage.     

单边裂纹弯曲试样的转动修正方法研究

由SEB( single edged bending)试样变形几何关系,提出断裂韧度测试中用于SEB试样J积分塑性功计算的裂纹嘴张开位移V0与加载点在加载线位移VLL的弹塑性转换公式.对SEB试样进行弹塑性有限元分析表明:试样转动中心位置受材料本构关系的影响微小,仅与裂纹长度α与试样宽度W之比有关,进而提出SEB试样转动半径R(裂纹嘴初始位置到转动中心的距离)的表达式,并对公式的有效性进行验证;应用线弹性柔度公式预测裂纹长度,可以忽略试样转动效应的影响,而刚性转动对SEB试样的J积分计算有一定影响,需采用考虑转动效应的载荷与加载线位移关系曲线来获得真实的J-△α阻力曲线.     

Limit loads for the plastic bending in plane strain of cantilevers containing rectangular holes under end shear

Slip-line field solutions and upper and lower bounds are given for the plane strain plastic yielding of a rectangular section cantilever containing a rectangular hole subjected to bending with shear, the hole taking varying positions along the longitudinal axis of the cantilever. Using mild steel specimens and an etching technique, both the loads and the modes of deformation at plastic collapse are shown to well authenticate the theoretical results.     

十字形试件双向拉深试验系统建立及加载精度分析

为了研究复杂加载路径下板料塑性变形行为 ,建立了十字形试件双向拉深试验硬件与软件系统 ,实现了同轴两夹头的位移同步控制 ,位移和载荷的比例加载与非比例加载控制 ,以及根据载荷变化判断加载停止的控制等关键技术。试验验证表明 ,所建系统具有较好的准确性和可靠性 ,为进一步研究提供了试验基础。     

The effect of number of cycles on the critical transition boundary between fretting fatigue and fretting wear

The object of the present study was to investigate the influence of number of cycles on the critical amplitudes of tangential force and displacement, identifying the transition from a mixed stick-slip regime (fretting fatigue) to a gross slip regime (fretting wear) over a wide range of test conditions. Fretting experiments were conducted on three metal specimen combinations: copper/copper; stainless steel/stainless steel; copper/stainless steel. All experiments took place in air, at ambient temperature, using a crossed-cylinder geometry. Normal loads of 3.4 and 11.4 N were applied with frequencies ranging from 10 to 800 Hz. In most cases, n = 1.2×10⁴ and n = 6×10⁶ were adopted as the representative lower and higher number of cycles, respectively. At different numbers of cycles, critical amplitudes of tangential force and displacement were measured. The scars fretted under separately selected conditions were examined by scanning electron microscopy.

It was found that the critical amplitudes of both tangential force and displacement dropped with increasing number of cycles for all test combinations, but there was an upper limit above which the drop of critical transition values no longer occurred with further increases in the number of cycles. The micromorphology of fretting scars (in a mixed stick-slip regime) revealed that the stick zone has shrunk after a larger number of cycles under the conditions of constant amplitude of tangential force and displacement, and that the damage mechanisms vary for different combinations, although they are all characterized by a central stick zone surrounded by a slip annulus. It was suggested that the decrease of critical amplitudes after a larger number of cycles results from the shrinkage of the stick area, which may be a complex process related to plastic deformation, strain hardening, and the change of stress distribution on the contact surfaces.     

Inhomogeneous plastic flow investigated by X-ray absorption microtomography of an aluminium alloy containing marker particles

By combining a synchrotron X‐ray source and the microtomography technique, the displacement gradient tensor components can be measured directly throughout the volume of a metal sample containing highly absorbing marker particles to detect material flow. The present article describes application of these techniques to compression of a rectangular Al–W specimen with a central hole. The results show that the externally imposed axial displacement gradient is accommodated mainly in two 45° shear bands passing through the hole. A simple deformation analysis provides insight into shear band formation.     

Nondestructive proximate testing of plastic deformations by differential thermal EMF measurements

A method for nondestructive proximate testing of plastic deformations in metals and alloys by measuring the differential thermal emf is considered. Using an instrument that was developed for this problem, thermal emf measurements were performed on several specimens of steels of different types on which notches were made as zones of expected localization of plastic deformations. During extension of specimens, the thermal emf was measured in the plastic-deformation zone. A linear decrease in the thermal emf was observed; the maximum change occurred just before specimen fracture.