基于梯度的数字体图像相关方法测量物体内部变形

数字体图像相关方法通过分析两幅以体素为单位的三维体图像获得物体内部的三维变形信息.在利用数字体图像相关方法测量物体内部变形的过程中,整体素的位移场可以通过简单的空域搜索获得,因此如何计算亚体素位移是提高该方法位移测量精度的关键.介绍了一种基于空间灰度梯度的亚体素位移测量算法,并用计算机模拟生成的可精确控制位移的三维散斑...     

基于CT的数字体散斑法测量物体内部三维变形场

提出了用于测量物体内部三维变形场的数字体散斑(DVSP)法。利用计算机断层扫描(CT)、磁共振成像(MRI)、激光扫描共焦显微镜(LSCM)或光学相干断层成像术(OCT)获取具有散斑特征的物体变形前后的三维立体图像,将其分别分割成若干具有相同尺寸的子块体,对相对应的子块体进行第一步三维快速傅里叶变换,在频谱域进行数值干涉得到合成谱,对合成谱进行第二步三维快速傅里叶变换,得到含位移信息的扩展脉冲函数,通过求取峰值位置得到子块体的位移矢量,对所有变形前后相对应的子块体逐一进行上述两步三维快速傅里叶变换,就可以求出所有子块体的位移矢量,从而获得物体内部三维变形场。利用模拟生成的三维散斑体图像,通过数字实验,分析了散斑尺寸、数目、子块体尺寸、图像对比度和亮度对DVSP法精度与准确性的影响。利用DVSP法测量了红砂岩单轴压缩内部的三维应变场,由位移场及应变场分布可直观地揭示试件内部变形特征。     

基于CT的数字体散斑法测量物体内部三维变形场EI北大核心CSCD

提出了用于测量物体内部三维变形场的数字体散斑(DVSP)法。利用计算机断层扫描(CT)、磁共振成像(MRI)、激光扫描共焦显微镜(LSCM)或光学相干断层成像术(OCT)获取具有散斑特征的物体变形前后的三维立体图像,将其分别分割成若干具有相同尺寸的子块体,对相对应的子块体进行第一步三维快速傅里叶变换,在频谱域进行数值干涉得到合成谱,对合成谱进行第二步三维快速傅里叶变换,得到含位移信息的扩展脉冲函数,通过求取峰值位置得到子块体的位移矢量,对所有变形前后相对应的子块体逐一进行上述两步三维快速傅里叶变换,就可以求出所有子块体的位移矢量,从而获得物体内部三维变形场。利用模拟生成的三维散斑体图像,通过数字实验,分析了散斑尺寸、数目、子块体尺寸、图像对比度和亮度对DVSP法精度与准确性的影响。利用DVSP法测量了红砂岩单轴压缩内部的三维应变场,由位移场及应变场分布可直观地揭示试件内部变形特征。     

三维电子散斑干涉载频调制及其在柴油机上的应用

将电子散斑干涉场的三维载波调制技术应用到三维物体变形测量中.用水平方向、竖直方向及垂直试件表面的三路相干光分别照明物体，在水平和竖直方向通过控制反射镜的微小偏转引入载波，实现位移场干涉条纹的调制；利用物体的微小偏转实现离面位移场干涉条纹的调制；结合傅里叶变换法，分别解调出变形场的位相，从而实现了物体三维变形场的精确测量.将该技术应用到柴油机油泵的三维位移测量上，成功测量了油泵的三维位移场.     

运动变形表面在相干光照明下的自由空间散斑位移分布

物体表面在一束相干光照明下的空间散斑位移场分布对于分析物体表面状态及位移、变形等信息具有重要意义。本文应用散斑场的相关方法与散斑相移技术得到了物体表面位移及变形参量与自由空间衍射场散斑位移的一般关系,给出了这种一般关系的简化与分离条件,并对物体平移、转动及热加载条件下的蜂窝结构进行了实验。     

散斑照相术的三维位移正确分离方法及应用

本文针对散斑照相术中存在的三维位移分离问题进行了详细讨论.利用散斑杨氏条纹图的基本特性和物体变形的连续性提出了正确分离三维位移的方法.使得散斑照相术在三维变形测量方面得到了进一步完善.最后给出了 CMO620型车床主轴的三维热变形结果.     

基于GMA光流网络的二维变形测量数字图像相关法初值估计

提出一种利用深度学习提取散斑变形图像位移场的算法。对比几种主流光流网络模型在散斑图像上的计算精度,将全局运动聚合（GMA）光流网络引入数字图像相关法,使用光流网络模型预测的位移场作为亚像素迭代算法的初值,最后结合逆合成高斯-牛顿法计算散斑图像的亚像素位移场。结果表明,与几种主流的数字图像相关算法相比,GMA光流网络初值的计算精度和计算效率更高,适用于大变形测量,是一种兼顾计算速度和精度的变形测量算法。对木块材料进行压缩实验,结果充分显示了所提方法在散斑变形测量中的有效性。     

电子散斑干涉载频调制形貌测量方法的分析

根据电子散斑干涉载频调制测量物体形貌的基本原理,物体表面的微小偏转可引入包含物体高度信息的载波干涉条纹。将物体的偏转视为变形,对物体变形与载波干涉条纹之间的关系进行了讨论,得出了离面位移引入载波和面内位移引入含有物体高度信息相位的结论。发现利用典型电子散斑干涉系统测量物体形貌效果最好,并通过实验得到了验证。     

基于优化电子散斑光谱的三维物体测量研究

用激光光束直接照射到测试表面,再用CCD采其变形前后表面散斑颗粒干涉形成的条纹,条纹图解析为测量点的位移量和变形量,进而得到其离面位移,在优化算法的时候采用π位相技术获取另一个π相移的变形条纹图像,将面内位移与离面位移分离,为了消除零级分量,让投影光栅移动1/2个周期.通过Matlab和四步位相算法给出了三维空间模型,得出变形后物体的离面位移数据.实验仿真数据表明其能够稳定地测量物体变形场三维分量,误差较低.     

电子散斑归一化互相关法测位移

把粗糙物体表面受到相干光照明时产生的散斑场看作是一个稳态随机信号,在此基础上,本文提出了一种能做到大量程,高精度位移测量的新方法——电子散斑归一化互相关法测位移或称电子散斑照相法测位移.该法实质上是借助数字图像处理技术,通过物体位移前后二个散斑场之间的相关性来进行位移测量方法的发展.文中给出了理论分析和实验系统.实验结果表明,该法有诸如准实时,大量程(毫米级),高精度和线性可靠等优点.     

数字散斑法在局域剪切带三维变形研究中的应用

在适当的温度、应变率和预变形下,合金材料的拉伸试验中,将会出现伴随应力锯齿形跌落的雪崩式剪切变形带,即波特文-勒夏特利埃(Portevin-Le Chatelier,PLC)效应。利用高速数字摄像系统(分辨力1000 frames/s)并结合数字散斑干涉法(Digital speckle pattern interferometry,DSPI)和数字散斑相关法设计了一套光学变形测量系统,实现了拉伸试验中对试件表面三维变形的实时、精确测量。利用该光学系统对铝铜合金试件在拉伸试验中产生的跳跃传播的局域剪切带瞬态成核过程进行捕捉。通过结合数字散斑相关法得到的面内变形定量结果和数字散斑干涉法得到的表现离面变形的条纹图,再现了剪切变形带成核和传播瞬间的三维变形过程。     

时间序列动态散斑相关跟踪测量原理及其应用

在对散斑场的特性进行研究与分析的基础上,提出了时间序列动态散斑相关跟踪测量法,它弥补了一般散斑相关法不适合大变形测量的缺点,扩大了散斑相关法的应用范围.运用这种方法不仅可以测量大动态范围的面内变形,而且可以测量分析面内动态变形过程和变形速度.     

数字散斑技术在混凝土单轴压缩试验中的应用

数字散斑技术作为一种新兴的测量方法,它具有非接触、全场量测、精度高、操作简单等特点,随着计算机技术的迅猛发展,数字散斑技术得到了广泛的应用与研究。针对混凝土在外荷载作用下具有明显的非均匀变化的特征,借助传统的测量方法很难得到混凝土表面的全场变形结果的问题,结合数字散斑相关方法测量技术,开展了混凝土单轴压缩试验,拍摄了混凝土表面在单轴压缩过程中的位移与应变矢量场,为分析混凝土试件的损伤区域奠定了基础;与电测法测量结果进行了对比,其测量结果表明,这两种测量方法误差相对较小,且数字散斑技术能更早的发现混凝土表面的破坏,验证了数字散斑相关方法的准确性和可靠性。借助数字散斑技术可以更加方便准确的得到材料表面的变形场,这也将在一定程度上促进土木工程领域的发展,具有广阔的应用前景。     

Application of iteration and finite element smoothing technique for displacement and strain measurement of digital speckle correlation

In this paper, an improved method for measuring displacement in digital speckle correlation technology, which is based on an iterative and spatial-gradient algorithm, is developed. After obtaining full-field displacement, both finite element method and 2D generalized cross-validation (GCV) algorithm are adopted for smoothing the displacement field, and then the strain field can be obtained from the smoothed displacement field. The method is estimated by simulated speckle patterns and three-point bending experiment. All the results show the improved method can obtain a reasonable estimation of displacement and strain fields in digital speckle correlation method.     

The study of fractal correlation method in the displacement measurement and its application

The classical digital speckle, or digital image, correlation method of deformation measurement is based on gray level correlation between unformed and deformed digital images. The pattern of artificial random speckles and the natural textures on some object's surfaces have fractal characteristics, and their fractal dimensions represent both gray and morph information. Furthermore, the fractal dimensions are stable feature parameters of the patterns. The digitized images of the patterns are confirmed to be also fractals. By this fact, a new method of displacement measurement is developed in the paper, based on the fractal dimensions correlation. The in-plane displacement fields of a body can be acquired. In order to verify the validity of the new method, an experiment has been designed and the results have been compared with those obtained from the classical digital image correlation method. The validity of the new method is not less than that of classical method. Further discussions about the traits and the developing vista of the method are given at the end.     

Experimental study on the micromechanical behavior of a PBX simulant using SEM and digital image correlation method

The micro-scale mechanical behavior of a polymer-bonded explosive (PBX) simulant was experimentally studied using a scanning electron microscope (SEM) imaging system and digital image correlation (DIC) method. The semi-circular bend (SCB) test was chosen for the study. During the testing, a series of SEM images of the specimen was acquired in situ. The natural micro-structural features of the specimen were used as random speckle pattern for DIC analysis. The displacement and strain fields at the area of interest were obtained by DIC. The deformation and damage of PBX were analyzed. Heterogeneous strain fields demonstrated the damage evolution underneath the specimen surface and predicted possible micro-crack growth. Based on the contour plots of the correlation coefficient, the formation and extension of microscopic cracks were quantitatively analyzed.     

Assessment of speckle-pattern quality in digital image correlation based on gray intensity and speckle morphology

In digital image correlation (DIC), speckle patterns are generated on the surface of a specimen to resolve uniqueness issues. Thus, speckle patterns significantly affect the accuracy of image correlation. To assess the quality of speckle patterns, the standard deviation of gray intensities within each speckle (SDGIS) is introduced as a new metric. On the basis of the cumulative distribution of SDGIS, speckle-pattern quality measurement (ρ) is proposed, which integrates the features of gray intensity and speckle morphology. Twelve speckle patterns are generated by changing the spraying time and nozzle sizes of an airbrush because these are associated with the speckle volume fraction and speckle size, respectively. In addition, three displacement fields are used to investigate the effects of speckle patterns on the accuracy of the DIC results. For the 12 speckle images associated with the three displacement fields, the correlation results demonstrate that the proposed speckle-pattern quality measurement is inversely proportional to the averaged error of the subset method. This is statistically confirmed by evaluating the correlation coefficient and p-value. Furthermore, the error of the subset method is more affected by speckle patterns than the subset size when the subset size is sufficiently large.     

Digital ultrasonic speckle phase-shifting method

The digital ultrasonic speckle phase-shifting method (USPM), which is introduced in this paper, can be applied to the measurement of small displacement that is smaller than speckle size at the test point compared to traditional ultrasonic speckle correlation method (USCM). Using USPM, a digital ultrasonic reference signal is introduced to interfere with the ultrasonic speckle signal, which is picked up at the test point on an object surface and is referred to as the object signal. As the phase of the reference signal is shifted several times using the software and then they superimpose with the object signal respectively, the phase of the object signal can be calculated according to the intensities of the superimposed signals. If the object surface moves a small distance, the phase variation of the object speckle can be detected by the same process. As a result, the displacement of the object surface can be measured. Based on the feature of ultrasonic speckles, inner surface displacement of an object can be measured using this proposed method. In this case, the effect of outer surface roughness to the measurement accuracy of USPM is examined experimentally. The experimental results show that the measurement is successful when the displacement is smaller than half of the speckle size at the test point and the roughness parameter R_a of the outer surface of the specimen is less than about 5.47 μm.     

Volume-grating phase-shifting digital speckle pattern interferometry used for measurement of out-of-plane displacement field

A new digital speckle pattern interferometry, called volume-grating phase-shifting digital speckle pattern interferometry, is discussed in this paper. The out-of-plane displacement field of a bent plate can be quantitatively measured using volume-grating phase-shifting digital speckle pattern interferometry proposed in this paper. Theoretical and experimental results, as well as absolute errors, are given.