Digital Image Correlation (DIC) is a well-established, non-contact diagnostic technique used to measure shape, displacement and strain of a solid specimen subjected to loading or deformation. However, measurements using standard DIC can have significant errors or be completely infeasible in challenging experiments, such as explosive, combustion, or fluid-structure interaction applications, where beam-steering due to index of refraction variation biases measurements or where the sample is engulfed in flames or soot. To address these challenges, we propose using X-ray imaging instead of visible light imaging for stereo-DIC, since refraction of X-rays is negligible in many situations, and X-rays can penetrate occluding material. Two methods of creating an appropriate pattern for X-ray DIC are presented, both based on adding a dense material in a random speckle pattern on top of a less-dense specimen. A standard dot-calibration target is adapted for X-ray imaging, allowing the common bundle-adjustment calibration process in commercial stereo-DIC software to be used. High-quality X-ray images with sufficient signal-to-noise ratios for DIC are obtained for aluminum specimens with thickness up to 22.2 mm, with a speckle pattern thickness of only 80 μm of tantalum. The accuracy and precision of X-ray DIC measurements are verified through simultaneous optical and X-ray stereo-DIC measurements during rigid in-plane and out-of-plane translations, where errors in the X-ray DIC displacements were approximately 2–10 μm for applied displacements up to 20 mm. Finally, a vast reduction in measurement error—5–20 times reduction of displacement error and 2–3 times reduction of strain error—is demonstrated, by comparing X-ray and optical DIC when a hot plate induced a heterogeneous index of refraction field in the air between the specimen and the imaging systems. Collectively, these results show the feasibility of using X-ray-based stereo-DIC for non-contact measurements in exacting experimental conditions, where optical DIC cannot be used.

中文翻译：

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X 射线立体数字图像相关性

数字图像相关 (DIC) 是一种成熟的非接触式诊断技术，用于测量承受载荷或变形的固体样品的形状、位移和应变。然而，使用标准 DIC 的测量可能存在重大误差或在具有挑战性的实验中完全不可行，例如爆炸、燃烧或流固耦合应用，其中由于折射率变化而导致光束转向偏差测量或样品被吞没火焰或烟灰。为了应对这些挑战，我们建议对立体 DIC 使用 X 射线成像而不是可见光成像，因为 X 射线的折射在许多情况下可以忽略不计，并且 X 射线可以穿透闭塞材料。提供了两种为 X 射线 DIC 创建适当图案的方法，两者都基于在密度较低的样品上以随机散斑图案添加致密材料。标准点校准目标适用于 X 射线成像，允许使用商业立体 DIC 软件中的常见光束调整校准过程。对于厚度达 22.2 mm 的铝试样，以及仅 80 μm 的钽散斑图案厚度，可获得具有足够 DIC 信噪比的高质量 X 射线图像。X 射线 DIC 测量的准确性和精度通过在刚性平面内和平面外平移期间同时进行光学和 X 射线立体 DIC 测量来验证，其中 X 射线 DIC 位移的误差约为 2-10 μm 适用于高达 20 mm 的应用位移。最后，当热板在空气中产生异质折射率场时，通过比较 X 射线和光学 DIC，证明了测量误差的大幅减少——位移误差减少了 5-20 倍，应变误差减少了 2-3 倍在样品和成像系统之间。总的来说，这些结果表明，在不能使用光学 DIC 的严格实验条件下，使用基于 X 射线的立体 DIC 进行非接触式测量是可行的。