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激光错位散斑干涉测量系统 总被引:5,自引:0,他引:5
介绍了一种新的无损检测方法-激光错位散斑检测技术的工作原理、方法及其在工程上的应用。这一先进的光测技术与传统检测方法相比,具有明显的优越性。国外的应用与发展可以证明技术突破了传统的光测技术在工程应用上的瓶颈,是非常有效,先进和具有发展潜力的光测技术。 相似文献
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In order to analyze the effect of viscous medium on the deformation behavior of sheet metals in viscous pressure bulging (VPB), the entire deformation process including instability and fracture was investigated real-timely by the aid of electronic speckle pattern interferometry (ESPI). Images of speckle patterns were captured continuously to obtain fringe patterns representing the full field strain rate. Values of strain rates were calculated based on the fringe patterns. The evolution of the weak region from the initial defect to the groove until crack was also observed through the fringe patterns. The onset of diffuse and localized necking were determined qualitatively and quantitatively. Experimental results show that the deformation of sheet metals in VPB passed through five states, namely, uniform deformation, strain localization, diffuse necking, localized necking and fracture. A defect emerged in strain localization. The growth of the defect caused the diffuse necking and generated a groove. The groove expanded mainly in length direction until the localized necking occurred. Finally the specimen fractured as a result of groove deepening. The tangential adhesive stress provided by viscous medium in VPB restricted the locally larger strain of the specimen. The diffuse necking was postponed greatly. Theoretical prediction of the limit strains of sheet metals in VPB would be made based on the experimental results in further work. 相似文献
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用动电位极化和电化学阻抗等方法检测1Cr18Ni9Ti、304和316三种奥氏体不锈钢在3.5%NaCl溶液中的点蚀敏感性;用恒电位下的计时电流法结合激光电子散斑干涉技术(ESPI)实时监测这三种材料在3.5%NaCl溶液中阳极极化过程的表面动态变化及点蚀感应时间(τ)。结果表明,当电极表面发生点蚀时,激光电子散斑干涉图上会出现由点蚀产物扩散引起的亮斑。1Cr18Ni9Ti和 304不锈钢的τ值分别是1 s和9 s,316不锈钢的τ值大于50 s。由此可以判断1Cr18Ni9Ti的点蚀敏感性最大,304居中,316的点蚀敏感性最小。此结果与动电位极化和电化学阻抗等电化学方法得出的结果一致。激光电子散斑干涉技术可以做为一种实验室方法监测金属早期点蚀敏感性。 相似文献
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基于数字图像相关法搭建了一套应力测量系统,分析了散斑图质量对测量精度的影响,通过面内平移试验和平面应力状态试验验证该测量系统的准确性.结果表明,测量精度会随散斑图质量的提高有一定程度的提高.面内平移试验结果的相对误差都在3.5%以内,表明该系统具有较高的精度.平面应力状态试验的结果表明,使用该系统测量试样应力具有较高的准确度.将该测量系统应用于测量链环焊接残余应力,测量结果与使用应变片测得的结果基本一致.该应力测量系统操作简单、精度较高,可用于特定条件下代替应变片进行残余应力测量. 相似文献
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在表面组装技术(SMT)中,焊点信息数据是实现部分再流焊过程自动化基础。本文介绍了表面组装印刷电路板(SMT_PCB)图像的处理方法和SMT_PCB上焊点类型、位置信息数据的自动获取技术。本文中,SMT_PCB图像的处理包括去噪声处理、二值化和目标修饰处理。根据对SMT_PCB图像的分析,提出了SMT_PCB图像高频噪声判断模板和算子,通过采用噪声判断模板和算子先判断高频噪声再用均值滤波的方法成功地去除了高频噪声。对图像中的低频噪声,基于对图像中目标与背景灰度值特点的分析,提出了改进的差分去噪声模板。采用最大方差阈值方法得到合适的阈值对图像实现了分割。对已分割得到的二值化图像,提出了目标图像修饰算子,并对图像中的焊点图像进行了修饰。根据对处理后焊点图像特点的分析,提出以不同类型焊点为模板,通过模板匹配方法实现焊点位置数据的自动获取。 相似文献
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Electronic-speckle-pattern-interferometry (ESPI) is a sensitive interferometric imaging technique that responds to changes of surface topography caused, e.g., by pressure changes or by thermal expansion. Hidden defects are revealed by the inhomogeneity of such deformation fields. Unfortunately, field distortion may also be caused by, e.g., inhomogeneous excitation. Therefore the lockin technique has been transfered to ESPI in order to enhance its sensitivity by this kind of phase-sensitive narrow-band filtering where finally a self-normalised phase-angle image is obtained. Such an image displays features which are usually deeply hidden in noise, as will be shown on various examples. 相似文献
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ZHANG Z Y M. O. W. Richardson 《中国有色金属学报》2004,14(Z2):150-154
Barely visible impact damage (BVID) is developed when polymer matrix composites are subjected to impact loading. The damage has an adverse effect on structural integrity, and potentially leads to catastrophic failure.Thus it is important to employ a variety of advanced non-destructive testing (NDT) techniques in parallel to unambiguously determine the integrity of composite systems. This study deals with damage evaluation using visual inspection, ultrasonic C-scan, electronic speckle pattern interferometry (ESPI), electronic shearography (ES) and optical deformation and strain measurement system (ODSMS). Internal damage was introduced using an instrumented falling weight impact test (IFWIT) machine by controlling the combination of striker mass and releasing height. It was found that different NDT techniques were successfully employed to identify and visualise the impact induced internal damage. Experimental results generated from these techniques show a good agreement in damage identification and determination. The features, capabilities and limitations associated with these techniques were briefly discussed. 相似文献
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Jian Chen 《Science & Technology of Welding & Joining》2018,23(6):536-542
A novel three-dimensional (3D) digital image correlation (DIC) approach using a stereovision system was developed to measure the evolution of strain and distortion near the fusion zone during the gas tungsten arc welding process. Unlike the previously reported two-dimensional (2D) DIC approach using a single camera, the 3D DIC method was immune to the out-of-plane displacement and was capable of measuring 3D deformation. Both 2D and 3D DIC approaches in welding applications were based on the utilisation of the novel high-temperature speckle and the pulsed laser illumination plus bandpass filters. However, the speckle pattern was partially specular reflective causing issues in subset matching in the 3D approach. A new algorithm and experimental procedure was incorporated to solve this problem. 相似文献
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电子剪切散斑检测技术非常适宜复合材料的无损检测。散斑图像往往含有较大的噪声,如何对散斑图像进行降噪处理是一个非常重要的问题。小波变换是变分辨率的分析方法,用小波降噪技术处理散斑图像可以有效地降低噪声,同时能较好地保存图像细节。 相似文献
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Since cable members are the major structural components of cable bridges, they should be properly inspected for surface damage and inside defects such as corrosion and/or breakage of wires. This study introduces an efficient image-based damage detection system that can automatically identify damages to the cable surface through image processing techniques and pattern recognition. The damage detection algorithm combines image enhancement techniques with principal component analysis (PCA) algorithm. Images from three cameras attached to a cable climbing robot are wirelessly transmitted to a server computer located on a stationary cable support. To improve the overall quality of the images, this study utilizes an image enhancement method together with a noise removal technique. Next the input images are projected into PCA sub-space, the Mahalanobis square distance is used to determine the distances between the input images and sample patterns. The smallest distance is found to be a match for an input image. The proposed damage detection algorithm was verified through laboratory tests on three types of cables. Results of the tests showed that the proposed system could be used to detect damage to bridge cables. 相似文献
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介绍了基于电子错位散斑理论的应变检测技术,并采用统计光学的方法对散斑现象进行了分析,与传统光学的分析方法相比,该方法可以对电子散斑干涉行为有更深入的理解。最后提出应变检测所需要的主要数学计算方法。 相似文献
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在数字图像相关方法中,传统Newton-Raphson算法(简称N-R算法)通常采用三次样条插值算法获得散斑图亚像素位置的灰度值。而在插值算法中,Hermite插值算法具有更加良好的光滑程度。因此,为了提高传统N-R算法的计算精度,提出一种基于Hermite插值的亚像素位移求解算法。该算法应用Hermite插值函数构建散斑图亚像素位置灰度值,并应用Barron算子计算像素点的一阶灰度梯度;之后应用牛顿迭代算法进行亚像素位移求解。应用真实散斑图的数值变形实验对算法的有效性与计算精度进行了验证。实验结果表明:提出的算法有效提高了传统N-R算法的计算精度且计算稳定性较好。 相似文献
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These studies are carried out to classify the three different spangle patterns found on the galvanized steel sheets by image processing and artificial neural network. Images of 200 × 200 pixel sizes from three different spangle samples were captured using optical filter and digital camera. These images were preprocessed and Haralicks (energy, entropy, contrast and homogeneity) and Laws (LE/EL, LS/SL, LR/RL, ES/SE and SR/RS) textural parameters were calculated. Principle component analysis was carried out on the generated textural database and this database was used to train and test the artificial neural network. The artificial neural network could be able to classify the spangle pattern up to a reliable extent and the overall accuracy was 80.09% for investigated samples. The proposed methodology can be used for quantification of spangle patterns and to develop an online system for spangle classification. Matlab® 7 was used for image processing and artificial neural network studies. 相似文献
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在数字图像相关测量计算过程中,直接参与互相关计算的是散斑子图,而散斑子图质量对测量精度具有重要影响。因此,如何有效评价散斑子图质量是数字图像相关方法研究的热点问题。将信息论中用于衡量信息量的“熵”概念引入散斑子图评价,提出以图像熵为评价参数的散斑子图质量评价方法。为验证该评价参数的有效性,对采用不同方法采集的3幅不同类型散斑图进行位移测量实验。实验结果表明:位移测量精度与散斑子图熵有紧密的关系,散斑子图熵越大,位移测量精度越高。实验结果验证了图像熵可有效用于散斑子图的质量评价。 相似文献