双折射材料初应力的定量研究相移等达因技术的应用

文章提出两种用相移等达因技术对存在于双折射材料内部的初始应力进行定量分析的方法，并以两种常用的双折射材料Ｐ６和Ｈｏｍａｌｉｔｅ１００为例进行了内部初应力的实验研究，给出了材料内部初应力的分布。以上研究说明双折射内部初始应力不容忽视，数字相移等达因技术是双折射材料内部初始应力进行定量分析的有力手段     

曲面拟合在平面等达因法数据处理中的应用

1 前言平面等达因法(Insodyne method)是散光法的一种发展,能得到全场的清晰条纹.与一般由片光得到的散光条纹图相比,物体的形状和条纹都不发生畸变,两幅正交方向的等达因条纹图,就是分解受力模型内各点的三个应力分量,但必须通过求导的数据处理.通常的作法,对从实验中得到的离散的等达因条纹数据,沿某一截面,用曲线拟合后再求导,以得到某一截面上的应力分量,如果需要另一方向的导数,需另外选择截面,再用曲线拟合,再求导.事实上等达因条纹级次的分布是(x,y)坐标的函数,对应的是一个曲面,在进行应力分析时,同时需要x 和y 方向的导数,因此在对实验中测得的离散数据,用     

等达因图象的自动采集与识别

文中提出了一种机机械扫描系统．小功率激光器、图象板、相移元件、微机和程序软件组成的等达因图象自动采集与处理系统，用灰度值比较的思想实现了等达因图象的跟踪采集。提出了四幅图象相移法实现等达因图象的自动识别。系统能快速、实时、精确和全自动地实现等达因图象的记录和分析。给出与物体内各点应力状态一一对应的位相图。并用来研究了其他实验方法困难的局部三维效应问题。     

平面ISODYNE法及其在复合材料力学中的应用

由J. T. Pindera提出的平面isodyne法是散光法的一种发展。具有非破坏性直接测取受力物体内部应力的特点。不需要大功率的激光器,条纹清晰,无畸变,对于平面应力问题可以得到应力分量的全部信息。在复合材料力学、断裂力学和接触问题等领域有广泛的应用前景。文章闸述了该方法的原理和技术,并应用它得到一受三点弯曲荷载的有裂纹的复合材料梁粘结层的应力分布。     

DCM 相位梯度提取技术在光力学图像信息识别中的应用

为解决相位去包裹对光力学图像处理的影响问题,本文将一种直接从数字编码傅立叶变换或相移条纹图中逐相素提取相位梯度的方法应用于光力学图像信息识别中。该方法是一个广泛应用于光纤传感器中的微分正交乘法器(DCM)的正、余弦相位检波技术。这一技术算法简单,不需计算反正切,不受相位去包裹方法标准的限制,非常适于应用在以相位梯度作为最终所需识别的信息的光力学图像处理中。本文以载波等达因条纹图应力场计算及四幅图相移等达因法求板的接触应力为例,对该技术在光力学图像信息识别中的应用进行了论证。     

双轴应力状态下正交异性动态光弹性应力——光性定律研究

基于静态下Ｈｙｅｒ和Ｌｉｕ表述的正交异性应力－光性定律，在前文中，提出了正交异性光弹性复合材料的动态应力－光性定律并证明了其在单轴应力状态下的正确性。本文旨在进一步考察在双轴应力状态下正交异性动态应力－光性定律的适用性，采用的方法是对纤维增强光弹性复合材料制作的平板模型施加冲击荷载，加载方向与材料纤维方向分别成０°、９０°及４５°角，同时进行正交异性动态光弹性实验和动态应变测量，另外，对该模型进行相应的各向异性介质时域边界元计算。把动态应变测量推算出的应力分量以及时域边界元计算出的应力分量分别代入正交异性动态应力－光性定律，得到随时间变化的双折射条纹级数历程，将其与正交异性动态光弹性实验的结果进行比较。实验及计算结果表明，在三个加载方向下，由这三种方法得到的双折射条纹级数历程均吻合良好，从而证明了前文提出的正交异性动态应力－光性定律在双轴应力状态下的正确性。     

数字光弹性法综述

将光弹性法与计算机图像处理技术相结合 ,来自动采集光弹性数据和分析应力的方法 ,称为数字光弹性法 ,与传统光弹性法相比 ,它可以进一步提高实验速度和精度。本文详细讨论了以下两个方面 :一是光弹性条纹的细化和倍增处理技术 ;二是自动确定光弹性参数的技术 ,包括相移法、傅立叶变换法、逐步载荷法、广谱分析法和RGB光弹性法等。通过对近二十年来国内外在这些方面的研究、应用和进展作了综述 ,认为采用白光的彩色域相移技术计算光弹性等倾角 ,结合采用白光源或三色光源的相移法来确定光弹性等色线级数 ,有望成为解决静态二维和三维冻结模型薄切片应力分析的最佳方法 ;另外 ,设计一种能实时和同步采集多幅条纹图的实验装置 ,通过相移法来自动获取动态光弹性数据 ,是数字动态光弹性法很有前景的发展方向     

爆炸应力场的动态云纹-光弹分析

作者首次成功地完成了爆炸加载的动态云纹-光弹混合试验,并借助于国产多火花式动态光弹性仪获得了一次爆炸加载下双折射材料中与应力波相应的云纹条纹和光弹条纹。根据云纹-光弹条纹分析了炸药爆炸产生的应力场,获得了应力场各分量随径向距离分布的规律,为定量研究爆炸应力波传播和衰减规律开创了一项新的实验技术,提供了理论分析依据。     

用散光光弹性测量Ⅰ型应力强度因子

利用散光法确定Ⅰ型应力强度因子的可行性已在一根带边裂纹的梁承受纯弯曲的情况下得到证实。可以用光弹性条纹数据米获得裂缝尖端周围奇异区内的条纹梯度的表达式。Ⅰ型应力强度因子是通过把条纹梯度与奇异区内的局部应力联系起米,然后将这些结果外推到裂缝尖端而给予确定。实验结果和解析结果表示了良好的一致性,故建议将此法应用于三维断裂力学问题。 字符: σ_(xx),σ_(yy),σ_(zz)=笛卡尔坐标中的应力分量。 σ_0=远场应力在奇异区内的效应。 x,y,z=在图1中定义的笛卡尔坐标。 γ,θ=裂纹尖端处的极坐标。 K_Ⅰ=Ⅰ型应力强度因子。 K_(Ⅰth)=Ⅰ型应力强度因子的理论值。 f_σ=散光法应力条纹系数。 (dN)/(dx)=散光条纹梯度。     

流动双折射实验

流动双折射实验周建和，周兴华，张海荣（天津大学力学系天津３０００７２）流动双折射法，是流动显示中的一种光学方法，主要用于显示低雷诺数下的剪切流动。它能形象直观地显示流场中切应力的分布和切应力的方向。通过对干涉条纹的分析处理，可对流场实现定量测量。尤其...     

Electronic techniques in isodyne stress analysis: Part 1. Basic relations

The purpose of the study was to develop electronic techniques for collecting, processing and evaluating information in experimental isodyne stress analysis. The original technique involved chemical photography recording and manual evaluation of the normal and shear isodyne functions and their derivatives, which are proportional to the stress components. One objective of the reported study was to show that it is feasible to reliably reconstruct isodyne surfaces which contain information on the internal force intensities and the components of the stress tensor. It is shown that the new technique satisfies all the theoretical conditions and constraints imposed by the theory of the analytical and optical isodynes. Thus another objective of the reported study was to demonstrate that the isodyne stress analysis allows one to obtain reliable data on the actual three-dimensional stresses in a cost-effective manner. The procedure developed to date and presented in the paper is a hybrid electronic-manual procedure. It involves electronic recording of the isodyne fields, manual determination of the isodyne orders in chosen sections, and electronic determination of the indicated and load-induced isodyne functions and of the isodyne surfaces. It is shown that the developed techniques are more reliable, accurate and cost-efficient than the traditional techniques of photomechanics. Pertinent data are illustrated by examples presented in Part 2.     

3D stress local nondestructive analysis in the middle plane of a plate

The Isodyne technique based on the scattered light scanning from a thin laser beam can be used to obtain the information inside the loaded object in the room temperature nondestructively, so it is a very powerful technique in 3D stress analysis. The problems are how to interpret the information and how to get sufficient information from the few interference fringe. Birefringence phase shift technique can distinguish the fringe orders automatically and enrich the information in 256 gray levels between maxim and minim light intensity. In the paper the Isodyne birefringence phase shift method with an oblique incidence and equilibrium equation is presented, by which the 3D stresses in the middle plane of a plate with U shape notch are separated successfully. The project supported by the National Natural Science Foundation of China under the Grant No. 1380345     

Photoelastic Stress Analysis by Use of Hybrid Technique and Fringe Phase Shifting Method

0Introduction Photoelasticityisanopticalmeasurementmethodforstressanalysis.Itcanperformwhole field measurementduetotwo dimensionalsignalprocessingoflight.Alsoitcanperformnon contact measurementbecauseoftransmissionorreflectionoflightonaspecimen.Photoelast…     

An intelligent hybrid method to automatically detect and eliminate experimental measurement errors for linear elastic deformation fields

In a previous study, to minimize or eliminate the errors and noises associated with a full-field experimental measurement and subsequent fringe analysis such as moiré interferometry, the authors derived a variational principle minimizing the experimental measurement errors. Furthemore, on the basis of this variational principle, the authors developed an intelligent hybrid method. In several test simulations, the method has demonstrated the automatic detection and elimination of randomly incorporated errors into known correct finite element displacement fields. In this study, a fringe analysis method is developed together with the two-dimensional fast Fourier transform method. Then, experimentally recorded moiré fringe patterns are analyzed by the fringe analysis method. The conventional and intelligent hybrid analyses are carried out using the analyzed fringe information as input data. The present method verifies the automatic detection of experimental errors and noises, and the simultaneous automatic elimination of those experimental errors. This method also makes it possible to obtain a fairly smooth visualization of higher order information such as the stress and strain distributions.     

二维相移逻辑云纹法—条纹图全自动处理的一种方法

本文报告的二维相移逻辑云纹法，可对二维全场条纹图，进行全自动处理。这种方法用了经典云纹的概念，运用了相移的思想，用计算机进行逻辑运算，从而获得了全场条纹图上任意点的信息，为后续的运算提供了方便。这种方法可用于若干种条纹图的处理。     

Photomechanical behavior of cellulose acetate under viscoelastoplastic deformation

To confirm the possibilities of cellulose acetate as a material for a model analysis during viscoelastoplastic deformation, the time-dependent photomechanical properties of the material were examined by means of creep tests under constant stress and recovery tests after removal of stress. Consequently, though the strain and the fringe order of cellulose acetate during creep and recovery are greatly influenced by stress and room temperature, both of them can be described simply by a power function of time, and the coefficient of each of these formulas can be represented by a function of the ratio of active stress to yield stress only. The effect of temperature is included in the formulation of the yield stress. In addition, the strain and the fringe order can be represented by the viscous-viscoelastic model proposed by Findleyet al.,^1,2 in which both of them are divided into four components: elastic, plastic, time-dependent irrecoverable viscous and time-dependent recoverable viscoelastic. The relation between viscoelastic strain and viscoelastic fringe order, and the relation between viscous strain and viscous fringe order were verified to be equivalent to that between plastic strain and plastic fringe order, all of which do not depend on stress, temperature or time. Therefore, the strain distribution of cellulose acetate under viscoelastoplastic deformation can be determined directly from the value of the fringe order measured.     

Interferometric-fiber-optic strain sensor

An interferometric-fiber-optic sensor and an efficient fringe-detection scheme are described. The fiberoptic interferometer consists of two fibers; they are labeled the reference fiber and the sensing fiber. The reference fiber is arranged in a circular pattern, whereas the sensing fiber is arranged in an ‘S’ pattern. These fibers are exposed to the same strain field and each experiences a strain-induced phase shift. A difference in the phase shift between the two fibers indicates a change in strain. The strain-induced phase difference causes the interferometrically produced fringes to shift spatially. Analysis shows that the number of fringes passing an arbitrary point on a screen (the detection point) is linearly related to the strain in the fiber. In this analysis, the strain sensor is assumed to be perfectly bonded so that the fibers experience the same strain field as the specimen. It is further assumed that the sensor covers a sufficiently small area so that the strain can be considered constant over the entire strain sensor. Also, the phase change produced by transverse strain components (with respect to the fiber) induced by the specimen is assumed negligible compared to the phase changes attributable to the axial strain components. A cantilever beam was used as a specimen. Experimentally determined strains correlated well with the strains predicted by beam theory. The fringe-detection scheme described is a high-speed fringe counter. The speed of this counter is necessary to detect vibrational phase noise which is invisible to the human eye. Two photodiodes detect the fringes, and a logic circuit counts the fringe shifts, both strain and noise induced. Since noise is random in nature, it can be averaged out. This fringe detector exhibits good sensitivity and is the key to moving the sensor from the laboratory to the field.     

Optical Metrology by Fringe Processing on Independent Windows Using a Genetic Algorithm

We present a method to retrieve the phase of a fringe pattern based on the window fringe pattern demodulation technique (WFPD). The overlapped phase similarity criterion is avoided in the proposed method, and it is substituted by a second order smoothness criterion. The fringe processing on independent windows (FPIW) method can measure physical quantities from closed and near sub-sampled fringe patterns by a simplified cost or fitness function. The fringe image is divided into a set of partially overlapping windows. In these sub-images the estimated phase is modelled as a parametric analytic-function, and its parameters are optimized using a genetic algorithm (GA). This analytic-function is used to estimate the phase in the area framed by the window. Phases from all windows are sequentially spliced to retrieve the whole phase field. A media filter is applied over the entire phase field to smooth the irregularities that appear in the junctures between windows.