共查询到18条相似文献,搜索用时 436 毫秒
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数字图像相关中基于可靠变形初值估计的大变形测量 总被引:7,自引:0,他引:7
为使数字图像相关方法适用于大变形测量,提出一种变形初值估计方法.通过在变形前图像中第一个计算点附近选择三个或更多特征点并在变形后图像中选择其对应点,利用坐标对应关系获得该点可靠的变形估计值作为Newton-Rapshon方法的迭代初值.该方法可对被测物体存在任意刚体转动或大变形情况下的表面变形进行准确测量,克服了通常的基于整像素位移相关搜索再进行亚像素位移测量的数字图像相关方法在被测物面存在稍大转角或大变形情况下即不能使用的缺点.对存在相对刚体转动图像的位移场和聚丙烯泡沫塑料压缩实验的大变形进行了测量,结果充分显示本文方法的有效性. 相似文献
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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。 相似文献
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基于数字图像相关的三维刚体位移测量方法 总被引:7,自引:0,他引:7
基于三维位移测量在工程技术领域的必要性和重要性,开展了单摄像机和数字图像相关相结合的三维刚体位移测试方法的研究.基于图像位移场矢量中心和斜率与面内和离面位移的分别对应关系,采用最小二乘拟合法分离图像位移场的常量项与一次项,据此,可实现物体三维位移分量的有效分离.以针孔摄像机成像模型为基础,开展了数值模拟及硅片平移实验,发展了与三维刚体位移对应的散斑图模拟方法,验证了基于仿射变换的相关迭代法的精度和适用性.数值模拟与实验结果验证了数字图像相关方法用于实现物体三维刚体化移重构的可行性和优越性,最大测量误差为5%. 相似文献
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基于三维位移测量手段在工程技术领域的必要性和重要性,开展了基于单摄像机和数字图像相关的三维位移测试方法研究.基于图像位移场矢量中心和斜率与面内和离面位移的分别对应关系,采用Savitzky-Golay(SG)微分滤波器分离图像位移子区内的常数项与一次项,可实现物体三维位移分量的有效分离.以针孔摄像机成像模型为基础,开展了相应的数值模拟实验及悬臂梁端部受载的实验,发展了与三维线性变形对应的散斑图模拟方法,验证了基于二阶位移模式的牛顿-拉夫森迭代法的精度和适用性.数值模拟与实验结果均验证了三维位移测试方法用于实现物体三维位移重构的可行性和优越性. 相似文献
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用隔行扫描摄像机采集到的运动物体单帧变形条纹测量三维位移和速度.该方法将一帧变形条纹分成两个单场,利用傅里叶变换轮廓术重建三维面形,从单场条纹的调制度中提取二值化模板,计算质心获得亚像素匹配定位点,通过双三次插值和标定,实现了一个场周期时间内三个维度上的位移和平均速度的测量.匀速运动物体实验结果表明:被测速度的最大绝对误差为0.6 mm/s,相对误差为0.57%.该方法仅用一帧变形条纹即可测量运动物体的三维位移和速度,提高了时间分辨率和测量准确度. 相似文献
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Application of iteration and finite element smoothing technique for displacement and strain measurement of digital speckle correlation 总被引:3,自引:1,他引:3
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. 相似文献
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In the strain field measurements, especially in large strain field measurements, the correlation coefficient values obtained by the digital speckle correlation method are usually very low due to the relative pixel movement of the subset. The measuring error, therefore, is increased. A primary method, that is called compensation algorithm, is introduced for improving the correlation coefficient. A flow scheme with the compensation algorithm of our software is developed and some improved techniques for reducing the calculation time and error are discussed in the paper. After obtaining a set of displacement data with high correlation coefficient, a de-noise wavelet processing is adopted. It is obvious that the measuring accuracy of the strain field is better then before. A strain field of testing experiment is performed with this compensation technique. The correlation coefficients can increase from 0.70 to 0.99, which will be of much benefit for the improvements of the measuring accuracy. 相似文献
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Investigation of Portevin-Le Chatelier effect in 5456 Al-based alloy using digital image correlation
A variety of experimental methods have been proposed for Portevin-Le Chatelier (PLC) effect. They mainly focused on the in-plane deformation. In order to achieve the high-accuracy measurement, three-dimensional digital image correlation (3D-DIC) was employed in this work to investigate the PLC effect in 5456 Al-based alloy. The temporal and spatial evolutions of deformation in the full field of specimen surface were observed. The large deformation of localized necking was determined experimentally. The distributions of out-of-plane displacement over the loading procedure were also obtained. Furthermore, a comparison of measurement accuracy between two-dimensional digital image correlation (2D-DIC) and 3D-DIC was also performed. Due to the theoretical restriction, the measurement accuracy of 2D-DIC decreases with the increase of deformation. A maximum discrepancy of about 20% with 3D-DIC was observed in this work. Therefore, 3D-DIC is actually more essential for the high-accuracy investigation of PLC effect. 相似文献
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数字图像相关中基于位移场局部最小二乘拟合的全场应变测量 总被引:10,自引:0,他引:10
为了从含噪声的位移场中计算得到可靠的应变场,提出一种基于位移场局部最小二乘拟合的全场应变求解方法。介绍了数字图像相关方法的原理,阐述了基于位移场局部最小二乘拟合的全场应变求解方法,并讨论了计算区域边界、孔洞及裂纹附近区域等情况下的应变计算。对均匀变形和中心带圆孔的薄铝板拉伸实验的计算结果表明,该方法能有效地从原始位移场数据中提取全场应变信息。在均匀变形情况下应选择大的应变计算窗口,计算结果更逼近真值;在非均匀变形情况下,如果位移场中包含较强的噪声,则应选择较大的应变计算窗口,而位移场精度很高时可选择更小的应变计算窗口。 相似文献
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A technique to measure object shape and 3-D displacement fields in micro-scale is offered by microscopic stereo digital speckle photography. The displacement of the random features that are often present on many engineering surfaces when viewed in a microscope is measured with the system, using image correlation. In this paper the equipment, physical model and calibration routines are described. The technique can be applied for sub-mm sized objects of arbitrary shape for small deformation fields. As a verifying experiment, an in-plane rotation of a flat calibration plate is presented. The expected in-plane errors are shown to be less than 0.1 μm and the corresponding out-of-plane errors about three times larger. As a pilot experiment, micro-structural paper expansion is studied, when exposed to humidity. The scaling properties of the microscope as well as the sampling criteria and reliability of the system are discussed in detail. 相似文献
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The incremental digital image correlation (DIC) method has been applied in the past to determine strain in large deformation materials like rubber. This method is, however, prone to cumulative errors since the total displacement is determined by combining the displacements in numerous stages of the deformation. In this work, a method of mapping large strains in rubber using DIC in a single-step without the need for a series of deformation images is proposed. The reference subsets were deformed using deformation factors obtained from the fitted mean stress-axial stretch ratio curve obtained experimentally and the theoretical Poisson function. The deformed reference subsets were then correlated with the deformed image after loading. The recently developed scanner-based digital image correlation (SB-DIC) method was applied on dumbbell rubber specimens to obtain the in-plane displacement fields up to 350% axial strain. Comparison of the mean axial strains determined from the single-step SB-DIC method with those from the incremental SB-DIC method showed an average difference of 4.7%. Two rectangular rubber specimens containing circular and square holes were deformed and analysed using the proposed method. The resultant strain maps from the single-step SB-DIC method were compared with the results of finite element modeling (FEM). The comparison shows that the proposed single-step SB-DIC method can be used to map the strain distribution accurately in large deformation materials like rubber at much shorter time compared to the incremental DIC method. 相似文献