光弹性—数字散斑相关混合法在光弹条纹主应力分解中的应用

光弹性法是研究结构内部应力分布问题的一个有效方法.光弹性实验中,通常可以方便地得到等色线条纹图.确定了等色线条纹级数以后,为获得平面模型中任意点的应力完全解,需要借助其它方法给出一个补充方程.本文将光弹性法与数字散斑相关法相结合,提出一种用于光弹性法分离主应力的新方法:光弹性-数字散斑相关混合法.在理论研究的基础上,设计了光弹性-数字散斑相关混合法实验系统,并通过相应的三点弯曲实验对该方法和实验系统的有效性做出分析和论证.该研究为光弹全场应力分解以及动态光弹性-数字散斑相关混合法提供了理论和实验基础.     

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     

提取等倾线的数字图象处理法

本文详细介绍了应用数字图象处理技术进行图象相除和图象相减,获取没有等色线干扰的、精确定位的和倍增信息的等倾线的全场分析方法,并作了典型验证实验,为光测弹性力学的改革提供了途径和理论依据。     

光弹性和边界元的一种混合法

本文通过光弹性实验中的等色线直接获得边界上主应力和值,並用三次样条函数对主应力和值的列表函数进行平滑,从而由边界元法计算二维物体内部的主应力和值,再与光弹性法中得到的主应力差值结合,便可分离二主应力。同时,应用本方法对圆环对径受压问题进行计算,其结果与解析解比较令人满意。     

3D打印模型在光弹性法教学中的应用研究

本文将3D打印技术引入光弹性法的教学中,解决了传统技术制作光弹模型时成型周期长、试样初始残余应力较大等问题.以圆盘为例,详细介绍了3D打印光弹模型的制备过程.基于光弹系统测量得到了对径受压模型内部的等倾线、等色线相位和条纹值.制备了含不同形状孔隙的教学模型,丰富了课堂内容.展示了数字模型设计、物理模型制备、光弹条纹图采...     

几种实体桥梁的光弹实验分析与结构评价

为探询桥梁整体结构特点,按照实验力学的相似理论,采用数控加工方法将六种典型实体结构的桥梁制成光弹性模拟试件。通过光弹性实验分析获取它们承载状况下的等色线和等倾线图,经计算机数据采集和处理后,得到模型结构的二维应力分布趋势以及应力沿桥面的变化规律。根据系统工程理论,对它们整体结构进行评价并提出局部改进建议。实验证明光弹法对桥梁结构及复杂弹性几何体承载规律的研究非常有效,是研究这一类问题的一种很好的实验仿真方法。结合理论计算和专家分析系统可以综合的进行桥梁结构方案的优选设计,为理论计算的准确合理性提供实验依据。该实验研究结果可以作为桥梁结构教学素材,为实际建桥方案的拟定提供参照。     

三向光弹性全场分析——应力连续分析法

本文提出光弹性中的一个应力连续分析法。对该方法的理论根据和适用计算公式做了分析和推导。作者提供了用光弹性“照片迭合”法拾取等色线条纹数据并结合电子计算机分析的几个实例,实践验证了这个方法的有效性.     

光弹性实验——(三)三维光弹性实验的“冻结”法

“冻结”法是当前解决三维应力分析问题比较有效的方法,在工程中已获得了广泛的应用。 “冻结”法的实验程序是:三维模型的应力“冻结”→沿需研究的截面切出薄片→将切片夹持于旋转台上,用偏光弹性仪或偏光显微镜,以平行光法或聚敛光法进行实验量测工作,获得必要的数据——等色线及等倾线→根据实验数据进行应力计算,给出工程中提出的应力分析问题。     

关于三维模型光测“冻结”法的若干问题

一、方法的简介 1.光测法 当偏振光通过受载荷作用的透明塑料模型(光测模型)时,模型各点将产生与应力状态相关联的光学干涉条纹图案——应力光图(等色线及等倾线)。用偏光弹性仪,可以定量地量测应力光图,进而对模型作全面的应力分析。若模型及作用于其上的载荷与真实结构(原型)相似,则根据相似原理,可将模型应力转换为原型应力。上述     

光弹性等差条纹级数的识别

本文根据光弹性和光干涉原理,提出了利用双波长测得的扣纹级数小数部分计算条纹全量的方法,并经计算和实验验证其正确性,它的精度取决于小数条纹部分的测量精度.本方法将为光弹性实验数据的自动采集提供了方便.     

Characteristic relations of flow birefringence

The general problems of the flow-induced birefringence in liquids have been presented and discussed in Part 1 of this paper, in which some particular responses of an aqueous solution of NGS 1828 were presented, namely, the pertinent mechanical responses and the birefringence responses in transmitted radiation. This paper presents the optical responses of NGS 1828 observed in the scattered radiation. It is shown that the scattered-light techniques can become a powerful and indispensable tool of flow-birefringence techniques, if the actual patterns of light scattering are taken into account. Proof is given that the light scattering and the related birefringence cannot be described by Rayleigh's mathematical model of scattering (Part 1, Ref. 51). The optical effects of the modulation of the primary beam and the scattered beam, called scattered primary isochromatics and scattered secondary isochromatics, are described in terms of the parameters of the system. A practical example is presented. Samples of typical recordings of light-intensity modulation by typical flow patterns are given in the form of scattered primary and secondary isochromatics and integrated isochromatics. One type of intensity modulation enables the determination of shear-strain rate at an interior point in the flow field. Using the determined shear-strain rates at the interior points, a velocity profile along the axis of symmetry of a rectangular-conduit flow was obtained. The results so obtained were satisfactory when compared with the results of direct volumetric measurement. The other type of intensity modulation reveals the nonuniform distribution of birefringence along the path of the transmitted light in the rectangular-conduit flow. The results presented in Part 1 of this paper, are complementary to the results presented below.     

An experimental investigation on isoclinic parameters in viscoelastoplastic materials under cyclic stresses

Photovisco-elastoplasticity has been developed and applied to various problems in nonlinear stress analysis as an extension of photoelasticity into nonlinear photomechanics. In photoelasticity, because stress is simply related to strain, isochromatics are proportional to either the principal stress difference or the principal strain difference and isoclinics indicate the directions of either principal stresses or principal strains separately. However, in photovisco-elastoplasticity, these optical responses are nonlinearly related to both stress and strain state simultaneously. Thus isochromatics are related nonlinearly with both the principal stress and strain differences. Isoclinics depend on the direction of principal strain as well as that of principal stress. Concerning now isoclinic parameter: according to the results of experiments performed by us for the deformation state where the directions of principal stress and strain do not coincide with one another, it has been found that isoclinic parameter moves gradually from the direction of principal stress to that of principal strain with increasing viscous deformation under constant stress. In the present research, extending our previous investigations, the behavior of isoclinic parameter has been examined experimentally under cyclic stressing, where the direction of principal stress changes alternately. In the course of an experiment, the variation of isoclinic parameter in relation to the number of cycles was measured together with the corresponding strain state on the thin-walled tubular specimen of celluloid softened by heating, subjected to combined loading conditions consisting of constant axial tension and cyclic torsion. The results obtained may be summarized as follows.

1. The cyclic-variation phase of isoclinic parameter lags behind the cyclic-variation phase of the direction of principal stress. The phase difference between these cyclic variations remains constant regardless of the number of cycles.
2. Isoclinic parameter has a value close to the direction of the principal stress within a range of a small number of cycles and decreases with an increase in the number of cycles. However, it does not approach the direction of principal strain but a value between the direction of the principal stress and that of the principal strain, with a certain constant ratio to them.

     

A simple holographic interferometer for static and dynamic photomechanics

A particular variation of holographic imaging system is described which, when used as a multiple-exposure holographic interferometer, possesses advantages for applications in static and dynamic photomechanics. Large fields of view can be obtained. Rigid-body motions produced by loading are automatically eliminated. The holograms can be recorded on medium-resolution films which have high sensitivity. Specimens manufactured with readily available materials can be used for the determination of isochromatics and isopachics. An attempt is made to describe this contribution in the background of previous developments in interferometry. Operation of the system is interpreted by showing the equivalence of the holographic interferometer to a combination of two systems presently in use in experimental stress analysis: a Fizeau interferometer and an optical spatial filter. The interpretation of isochromatics and isopachis as moiré phenomena is emphasized. Isochromatics and isopachics are presented as illustrations of the applications of the method to the solution of static-stress problems, and they are used in the solution of some not yet solved dynamic-stress problems. Whole-field static isochromatics obtained as absolute-retardation interference are shown. Also shown are whole-field dynamic isopachics.     

High-precision stress determination in photoelasticity

Stress separation is usually achieved by solving differential equations of equilibrium after parameter determination from isochromatics and isoclinics. The numerical error resulting from the stress determination is a main concern as it is always a function of parameters in discretization. To improve the accuracy of stress calculation,a novel meshless barycentric rational interpolation collocation method(BRICM) is proposed. The derivatives of the shear stress on the calculation path are determine...     

Towards RGB photoelasticity: Full-field automated photoelasticity in white light

In this paper a new full-field method for the automatic analysis of isochromatic fringes in white light is presented. The method, named RGB photoelasticity, eliminates the typical drawbacks of the classical approach to photoelasticity in white light which requires a subjective analysis of colors and an experienced analyst to acquire and interpret the results. The proposed method makes it possible to determine retardations uniquely in the range of 0–3 fringe orders. For this purpose the isochromatics are acquired by means of a color video camera and the colors are decomposed in the three primary colors (red, green and blue) and compared to those stored in a calibration array in the system. Furthermore, the influence of various spurious effects on the accuracy of the proposed method is experimentally evaluated.     

等差线和等倾线的计算机识别及绘制

在普通光弹仪上配置光电耦合二极管信号采集装置和专用程序计算机,就构成了能实时地处理光弹图象的系统。CCPD-1024成线阵排列,能同时采集模型中一个截面上的光强信号。等色线或等倾线条纹的位置由计算机从光强分布图上读出。CCPD-1024对模型扫描时,计算机记录了各个截面上的等色线和等倾线位置的信息,并据此绘制出反映全场性分布的光弹性条纹图案。     

受力光弹材料的红外辐射热像特征

在同等受力条件下,对光弹材料进行了红外热像监测和光弹性测试,在红外热图中等温区的分布与光弹图表示的应力场分布有着相当一致的对应,等温区级数与等差线级数之间存在明显的线性关系,并且拉、压应力区分别对应红外热图的降、升温区。同时发现应变率是影响受力物体红外辐射的主要因素之一。这对于将红外热像技术用于量化分析受力物体的应力场变化有着重要的现实意义。     

光弹性等倾线获取的图像处理技术

提出一种对数微分法,有效地解决了光弹性实验中等倾线的提取问题,不仅可消除平面偏振光场中等差线对等倾线的影响,而且能高精度地提取任意复杂受力模型等倾线.最后给出了等倾线提取及精度分析的两个实例,实验证明;本方法具有广阔的应用前景.     

Recording and processing of interferograms by spectral characterization of the interferometric setup

 This paper describes how the scale of experimental tints of an interferometer using a known white light source and a Wollaston prism is reproduced on a microcomputer equipped with an image processing board. Taking the spectral characteristics of the light source and the three RGB camera filters into account, it is possible to analytically express the luminous intensity of the interference fringes as a function of the path difference and to reproduce the experimentally visualized colours on the monitor. The knowledge of the interferometer colour scale allows to optimize the prism position when recording the interferograms and to process them automatically with very high accuracy. Received: 3 May 1995/Accepted: 26 January 1997     

Limitation of fourier transform photoelasticity: Influence of isoclinics

The application of the Fourier transform to photoelasticity was used in the evaluation of the retardation using a carrier system of fringes. In photoelasticity, the light intensity from the analyzer in a circular polariscope depends on both the retardation (isochromatics) and the isoclinic parameter. The theoretical analysis shows that the angle between the principal stresses in the model and in the carrier system of fringes influences the evaluation of the retardation (isochromatics), as occurs when misaligned compensators (namely, Babinet) are used. As a consequence, this method may not be applied as a full-field technique, although the error is small if the angle between the principal stresses in the model and in the carrier is less than 25 deg. Numerical simulations and experimental tests were conducted to corroborate this prediction.