Distortion Correction Protocol for Digital Image Correlation after Scanning Electron Microscopy: Emphasis on Long Duration and Ex-Situ Experiments
Distortion Correction Protocol for Digital Image Correlation after Scanning Electron Microscopy: Emphasis on Long Duration and Ex-Situ Experiments
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DOI：
10.1007/s11340-017-0303-1
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发表时间：
2017-07
影响因子：
2.4
通讯作者：
A. Mello;T. Book;A. Nicolas;S. E. Otto;C. Gilpin;M. Sangid
中科院分区：
文献类型：
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作者：
A. Mello;T. Book;A. Nicolas;S. E. Otto;C. Gilpin;M. Sangid
最近，扫描电子显微镜 (SEM) 已用于数字图像相关 (DIC)，因为可以以高放大倍数获取显微照片，从而提供更高的分辨率来量化应变异质性。然而，研究人员表明，由于光学图像中不存在的固有电磁畸变，SEM 图像可能会出现问题。漂移、空间扭曲和放大倍数不确定性是严重影响局部应变测量精度的主要问题。目前的工作重点是长时间的实验，这些实验的图像间隔几天或几周。我们提出了一种系统程序来减少漂移、校正空间失真并解释所采集图像对之间的放大倍数变化。此外，还讨论并选择了 SEM 参数，以提高信噪比并提高 DIC 测量的准确性。空间失真校正提高了相关值的可重复性和测量的精度。此类校正的实施是通过将经认证的网格的测量畸变梯度应用到 DIC 应变场来完成的。放大倍数调整提高了应变图的可靠性，确保测量结果与实验过程中引起的实际应变一致。我们提出了 SEM 内异位 DIC 实验的系统协议和一些基本的交叉检查程序，可用于评估参考网格的可靠性和最终应变图的精度。
Recently, scanning electron microscopy (SEM) has been used for digital image correlation (DIC), as micrographs can be acquired with high magnification, providing improved resolution to quantify strain heterogeneities. However, it has been shown by researchers that SEM images can be problematic due to inherent electromagnetic distortions that are not present in optical images. Drift, spatial distortions, and magnification uncertainties are the main issues that can seriously affect the accuracy of localized strain measurements. The present work focuses on long duration experiments, for which images are taken days or weeks apart. We have proposed a systematic procedure to reduce drift, correct spatial distortion, and account for magnification variations between pairs of acquired images. Additionally, SEM parameters are discussed and chosen to increase the signal-to-noise ratio and improve the accuracy of the DIC measurements. The spatial distortion correction increases the repeatability of the correlated values and the precision of the measurements. The implementation for this type of correction is done by applying the measured distortion gradient of a certified grid onto the DIC strain field. The magnification adjustment increases the reliability of the strain maps, ensuring the measurements are in agreement with the actual strain induced during the experiment. We have presented a systematic protocol for ex-situ DIC experiments within the SEM and some basic cross-check procedures that can be performed to evaluate the reliability of the reference grid and the precision of the final strain map.