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.     

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.     

光弹等差线与等倾线参数的全场检测法

本文研究了一种自动获得全场等差线级数与等倾线参数角的方法.该方法是根据“相移”思想,利用数字图像处理技术,对光弹等差线图与等倾线图进行位相检测,经过去包裹处理,确定出全场各点的等差条纹级次与主应力方向角.最后通过典型实验,考核了这种方法的正确性与处理精度。     

光弹性等倾线的同时全场显示方法

本文提出同时实时记录对应于两个或两个以上主应力方向角的等倾线方法,改变了每次只能测绘一条等倾线的传统方法,不仅极大地缩短了等倾线检测时间,而且提高了检测精度。     

T应力对光弹性条纹影响的理论分析

以裂尖弹性应力场的多参数模型为基础,研究I型、II型以及I/II混合型裂纹参数对光弹性条纹的影响. T应力的存在和符号影响着等色线条纹环的半径大小和旋转方向,对于纯I型或II型裂纹而言,条纹环的旋转角度只与T应力有关;而对于I/II混合型裂纹,条纹环旋转角度与K_{\rm I}, K_{\rm II}和T应力有关. T应力的存在使得I型裂纹在裂尖±π/3方向上出现2个各向同性点(T应力为正时),使得II型裂纹在裂尖后的裂纹面上出现1个各向同性点. 对于I/II混合型裂纹而言,当T应力为正时等倾线出现距裂尖半径不等的3个各向同性点;反之, T应力为负时在裂尖后只存在1个各向同性点,这些各向同性点分别与I型和II型裂纹情况具有相同的规律.      

Ⅰ型裂纹光弹性分析方法研究

本文对Ⅰ型裂纹,利用 Williams 裂尖场级数解,通过光弹分析,编制 FORTRAN 语言程序求解非线性方程组,从而给出了一种确定应力强度因子的方法.实例分析表明,此方法与现有方法相比,实施的条件较宽,而精度却提高了.     

单像素成像的数字光弹研究

数字光弹是光测力学中进行应力分析的重要方法,其核心是通过数字图像处理的方式确定等倾线和等差线参数并获得对应的相位图.传统的数字光弹使用面阵相机拍摄得到光弹性条纹图像,但是通常在特殊波段尤其是在非可见光波段中适用的面阵相机普遍比较昂贵、制造成本也相对较高.本文提出在数字光弹中引入一种具有低成本、高成像质量优势的成像方法—...     

新的动态光弹性主应力分离混合法研究

动态光弹性法是研究动态问题的一种重要方法,但要实现动态光弹性主应力的分离以及等倾线的获取和分离还存在较大的困难.针对动态光弹性法的主应力分离问题以及相关的试验技术展开研究,以相容方程作为动态光弹性试验的补充条件,将动态光弹性法与数值计算方法结合起来,提出一种用于动态光弹试验主应力分离的新方法:动态光弹性-数值计算混合法,研究并实现了动态光弹性试验中的等倾线的获取和分离.并选用了典型的圆盘试件进行动态光弹性试验及应力分析,对该混合法的可靠性和准确性进行了论证.     

河海大学工程力学系、工程力学研究所介绍

<正> 河海大学(原华东水利学院)工程力学系建于1960年,根据水电建设和经济发展的需要,60年代设立应用力学专业,70年代设立水工建筑力学专业,1977年设立了工程力学专业,根据系所结合体制的需要,于1982年建立工程力学研究所.工程力学系与工程力学研究所.下设理论力学、材料力学、结构力学、弹塑性力学、计算力学、实验     

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。     

Theoretical analysis and digital photoelastic measurement of circular disks subjected to partially distributed compressions

The disk in diametral compression has been quoted most frequently on developing conventional/digital photoelasticity to illustrate new theories and experimental techniques for several decades. Theoretically, the compression as a concentrated force is more conducive to analysis, but it is impossible to achieve such loading condition experimentally. The distributed compression on a finite area at rim is relatively closer to actual testing and it is complicated to seek an analytical solution. In this paper, we extend the work of Hondros to derive the full-field stress distribution of disk subjected to diametral distributed compression in an explicit functional form. The principal stress difference and principal stress orientation related to isochromatic and isoclinic fringes, respectively, are also expressed in a simple closed form. The maximum shear stress for the whole disk and the validity of using isochromatic fringes to interpret the maximum shear stress are discussed in detail. The isoclinic fringes are compared with theory, and the fringe multiplication isochromatic is compared with simulated image. All of the comparisons are in good agreement with respect to full field.     

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

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

光弹性五步彩色相移法分析初应力对等倾角的影响

通过琼斯矩阵推导出一般平面偏振场的受初应力影响的光强等式,选用有边缘效应的直边、斜边和曲边三种常见边界形状的光弹性模型,用五步彩色相移法分析了初应力对等倾角的影响,这对正确评价和执行实验技术都有着积极的作用。     

Real-time analysis of isochromatics and isoclinics using the phase-shifting method

This paper studies a new real-time phase-shifting method for the analysis of isochromatic and isoclinic parameters in photoelasticity. By rotating an analyzer at a constant rate and an output quarter-wave plate at a double rate of the analyzer and recording images by a CCD camera continuously, sequential images which brightness is integrated by sensors in a CCD camera during phase-shifting are obtained. Then, the distributions of the isochromatic and isoclinic parameters are obtained immediately and quantitatively using the proposed phase-shifting algorithm. The proposed method can be applied to high-speed inspection of optical elements or glass products. Also, it is expected that slowly varying time-dependent problems can be analyzed by the proposed method.     

Absolute determination of the isochromatic parameter by load-stepping photoelasticity

A new approach to full-field automated photoelasticity is presented in which a circular polariscope is used to enable the isochromatic phase value () to be determined unambiguously and without input of a known isochromatic value obtained using an auxiliary technique. Values of cos are obtained from light-field and dark-field images for three loads of small incremental steps. Using a relatively straight-forward procedure, ramped phase maps for are produced which can be unwrapped using conventional techniques. The resulting distribution of is then found absolutely using information provided by which is the incremental change in the isochromatic phase value between the load steps. The results obtained for disk-in-compression tests presented here in comparison with theoretical solutions demonstrate that the technique is both simple to use and very accurate. A similar approach may be adopted using three wavelengths instead of three load steps.     

2D and 3D separation of stresses using automated photoelasticity

A procedure for the separation of full-field photoelastic images for use with an automated polariscope is described. Regions of background in the image are identified thus producing the boundary of the model. The shear difference method is used to calculate the components of stress along all raster lines in the image using photoelastic parameters at the boundary points to calculate the initial values of stress. Algorithms were also used to evaluate the stress components along raster lines which did not contain boundary points. A plastic template was used to evaluate the efficiency of the boundary routine. It was found that it was able to identify edges to within approximately one pixel on screen. The complete procedure for stress separation was evaluated using a stress frozen disc in compression and a turbine slot. The values of stress found using the automated polariscope with the stress-separation procedure were found to agree well with theory and with results determined using the method of Tardy compensation and manual analysis. The automated polariscope was also used to analyze three-dimensional stress components along arbitrary lines of a 3D model. A two-model slicing regime was used to analyze a strut subjected to a vertical load. This work was compared to results obtained by Frocht and Guernsey on an identical model machined from Fosterite and subjected to a higher load. Good agreement was found between the results for points away from the region of loading. Significant differences were found near to the load point, however. A finite element analysis of the same problem suggested that this was due to the effects of plasticity.     

Design and evaluation of the poleidoscope: A novel digital polariscope

The goal of recent research in digital photoelasticity has been fast, reliable, and accurate full-field photoelastic data that will allow the technique to play a valued role in assessing material and structural integrity. A novel design for a polariscope that allows simultaneous capture of multiple images is described, and a prototype instrument is evaluated using both transmission and reflection photoelasticity. The design offers the potential for real-time data acquisition and processing of high-speed events, using a number of different approaches to digital photoelasticity. The evaluation of the instrument arranged for the phase-stepping method demonstrated that it was capable of providing results of comparable quality and accuracy to manual analysis and more conventional methods of acquiring phase-stepped images.     

光弹性测量等色线计算机数字图像色谱仿真

应用平面应力-光学定理,计算各点的光程差;应用色彩的RGB原理以及光程差和RGB之间的换算关系,将每个点的光程差换算成RGB值;利用等色线原理,采用VB编写程序,将具有相同RGB值的点按不同的色谱绘出等色线,实现了在载荷作用下光弹性测量等色线计算机数字图像色谱仿真,虚拟再现构件光弹性实验所得到的等色线。对复杂结构,特别是内部存在各种构造孔洞的构件,通过该技术可迅速获得构件全场等色线的分布,为进行结构设计和优化的光弹性实验提供了一种直观的数字化可视技术,同时为高等院校实验力学课程提供了一个虚拟的光弹性实验平台。