共查询到19条相似文献,搜索用时 692 毫秒
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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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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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针对一套数字全息装置只能测量离面位移这一个维度位移的局限性问题,将数字全息与数字图像相关方法相结合,利用数字全息重建的强度图像,实现了面内另外两个维度位移的测量,拓宽了一套数字全息装置的测量能力.该方法对待测物体位移前后的全息图数值重建得到两幅强度图,然后对变形前后的强度图应用数字图像相关方法得到面内两个维度位移的测量... 相似文献
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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。 相似文献
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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。 相似文献
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面内位移测量的基于梯度的数字图像相关方法 总被引:4,自引:0,他引:4
将整像素位移搜索和基于微区统计性质的亚像素位移梯度算法相结合的数字图像相关方法具有计算简单、求解效率高等优点。该方法的基本假设是变形前后的子区做刚体平移,这则与有位移梯度存在的实际情况相矛盾。首先分析了该基本假设的理论误差,在基于梯度的数字图像相关方法中,得出变形子区做刚体平移的假设和在Newton-Rapshon方法中子区均匀变形的假设所获得的变形子区中心位移在理论上为相同的结论。然后用四组实验来验证该方法在实际实验条件下的计算精度和稳定性,并在铝板试件的单向拉伸实验中,将该方法与N-R方法在有应变存在情况下的计算结果作比较,结果表明该方法计算的位移和理论位移符合得很好,但其计算速度和效率要远优越于N-R方法。 相似文献
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An improved measurement method and an automatic calibration procedure are proposed for a combined 2D Digital Image Correlation and Fringe Projection system that allows measuring in- and out-of-plane displacement maps with only one image at each deformation stage of a specimen. The proposed method increases the accuracy and range of the out-of-plane displacements by taking into account the divergences of both the projected fringes (uncollimated) and the camera (with non-zero FOV). The calibration is performed automatically by acquiring a sequence of images of a reference plane by displacing perpendicular to it the camera and fringe projector with a motorized translation stage. The acquired images are then used to obtain a fringe function for each pixel and the necessary parameters required for the correction of the in-plane displacements. Furthermore, a closed form expression is obtained that relates the out-of-plane displacements with the shifted phase at each pixel for a given experimental set-up. This expression is in good agreement with the fringe function obtained by fitting a simple 2nd order polynomial to the experimental obtained calibration data. Finally, the polynomial approach is proposed as a fringe function because it avoids the errors in the determination of the required parameters of the theoretical expression as well as some small misalignment or aberration effects. 相似文献
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本文提出一种基于双圆光栅径向剪切干涉仪的三维位移测量方法,其测量原理是径向剪切干涉仪所形成的莫尔条纹不仅由二维平面内位移决定,轴向位移会在+1和–1级莫尔条纹之间产生一个特定的相移.首先,基于标量衍射理论对双圆光栅径向剪切干涉仪的+1和–1级莫尔条纹强度分布进行推导,建立了三维位移量与莫尔条纹强度分布的精确解析关系;其次,在频谱分析的基础上,利用半圆环滤波器进行空间滤波,实现+1和–1级莫尔条纹的同时成像;然后,提出了从莫尔条纹图中定量提取三维位移的算法,并通过数值模拟进行验证;最后,实验结果验证了该方法测量平面内位移的最大绝对误差为4.8×10–3 mm,平均误差为2.0×10–4 mm,轴向位移的最大绝对误差为0.25 mm,平均误差为8.6×10–3 mm.该方法具有装置简单、测量精度高、非接触、瞬时测量等特点,可实现三维位移的同时测量. 相似文献
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U. M. Chaudhari A. R. Ganesan Chandra Shakher P. B. Godbole R. S. Sirohi 《Optics and Lasers in Engineering》1989,11(4):257-264
Digital Speckle Pattern Interferometry (DSPI) is a promising field for a wide range of applications such as measurement of displacements/deformations, contouring, nondestructive testing, etc. It has holographic sensitivity and circumvents delays in photographic processing/filtering. Speckle correlation interferometry can be made sensitive to only one of the components of in-plane displacement by illuminating the object with two beams symmetric about the viewing axis and imaging along this axis using a viction. This configuration allows measurement of in-plane displacements independent of out-of-plane displacements.
In this paper, the in-plane deformation/stress distribution has been studied for a typical bolted flange joint of a pressure vessel using two beam illumination DSPI. The information obtained can be very useful in predicting the leakage behaviour of such joints employed in pressure vessels. Experimental investigations along with theoretical predictions are presented. 相似文献
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D.C.L. Cheung R.J. Barron A.R.D. Somervell T.H. Barnes 《Optics and Lasers in Engineering》2005,43(12):1292-1304
We propose and demonstrate a novel interferometric technique for 3-D displacement measurement. The method is based on the analysis of the phase difference distribution measured when two coherent curved wavefronts originating from different locations interfere. Both the in-plane and out-of-plane displacements are found simultaneously from a single phase difference distribution. We find that our system could measure with an accuracy better than 1.5 μm for in-plane displacements and 36 μm for out-of-plane displacements over 1 mm range. This accuracy was limited by the output lens performance. Theoretical analysis reveals that sub-micron accuracy may be possible with more careful calibration. 相似文献
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A theoretical and experimental analysis is carried out showing the effect of multiple exposures on fringes in the case of three-dimensional motion of a diffuse object illuminated by a diverging beam from a laser point source. Experimental conditions are such that the speckle patterns remain fully correlated in spite of the object moving in three-dimensional space in a direction that makes an angle with the optical axis. Owing to the in-plane component of the three-dimensional displacement the point of null-speckle displacement shifts either in the direction of the in-plane component of the motion or in the opposite direction depending upon the direction of the out-of-plane displacement component. This modifies the fringe profile as compared with the case of pure out-of-plane motion. The intensity distribution at the Fresnel plane of a specklegram is investigated after filtering by a converging beam for double exposure and multiple exposures. Good agreement is found between the theoretical and experimental results. 相似文献
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A.M.R. Sousa J. Xavier J.J.L. Morais V.M.J. Filipe M. Vaz 《Optics and Lasers in Engineering》2011,49(12):1402-1412
In this paper, a digital image correlation (DIC) method coupling cross-correlation with spatio-temporal differential techniques was proposed for assessing discontinuous displacement fields. The accuracy and robustness of the algorithm was assessed on a set of numerical tests by processing computer generated speckled-pattern images. Fracture mechanical tests in mode I were considered, in which both in-plane and out-of-plane rigid-body movements were taken into account. The ability for recovering the analytical asymptotic displacement field in mode I was analysed, and stress intensity factor, crack opening displacement and crack tip location were used as quantitative parameters for validation purposes. Throughout these tests, the results obtained with the proposed method were systematically compared to the ones from Aramis DIC-2D commercial code. Globally, the results computed from both methods are in good agreement with reference values. However, due to the high spatial resolution (point-wise characteristic), a better matching of the displacements in the neighbour of discontinuities could be obtained by the proposed method. 相似文献
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In this paper, several crucial issues arising from the application of the digital image correlation (DIC) method to the measurement of heterogeneous deformation of porous solids are discussed. To handle samples with complex geometry, the performance of the two commonly employed DIC methods, namely the subset-based DIC and the finite-element based DIC methods are first evaluated and compared. A combined DIC approach and an adaptive DIC approach suitable for samples with discontinuities/holes are then proposed. Aluminum plates with circular holes subject to compressive loading are employed to evaluate the accuracy of the proposed methods. It has been found that in addition to other factors such as the number of pixels and speckle size, the orientation of the camera lens also plays an important role on the measurement accuracy. A calibration method for the adjustment of camera orientation is proposed, which leads to a good agreement between the experimentally measured displacements and finite element simulation results. Another finding of the presented work is that for relatively stiff specimens, the deformation of the loading system itself must be considered in order to obtain an accurate displacement. 相似文献