The purpose of this study is to develop novel speckle pattern techniques for digital image correlation (DIC) kinematic measurements of mechanical tests at high temperatures, typically from 400 to 700°C. In this context, the speckle pattern should not only meet morphological criteria (size, density, distance) in order to improve spatial resolution, but it should also present a high contrast and resist high temperature and strain levels. To find a speckle pattern matching these specifications, a comparison was performed on six types of speckle made using different techniques. First, a computer-generated speckle pattern that meets DIC criteria was numerically designed to produce six types of speckle pattern. Next, the speckle patterns produced using these six techniques were compared in terms of speckle morphology, image quality and adherence to titanium alloy TA6V material at high temperatures. From 25 to 600°C, the speckle pattern made by the technique combining anodisation and laser engraving named M5 technique gave the best contrast (highest value of mean intensity gradient [MIG] and Shannon entropy value) and the adherence of 200% of strain measurements to the TA6V material. At 700°C, speckle image quality is considerably reduced due to oxidation of the titanium alloy, and this may not be suitable for DIC measurements. Only the speckles produced by painting in which the paint plays a protective role provide with a better speckle contrast compared with other techniques. However, these speckle patterns enable only a strain measurement of 22% by the DIC method. This article concludes with guidelines for producing a speckle pattern suitable for high-temperature mechanical tests.

中文翻译：

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应用于高达 700°C 的机械拉伸测试的二维数字图像相关应变测量的散斑图案创建方法

本研究的目的是开发用于在高温（通常为 400 至 700°C）下进行机械测试的数字图像相关 (DIC) 运动学测量的新型散斑图案技术。在这种情况下，散斑图案不仅应满足形态标准（大小、密度、距离）以提高空间分辨率，而且还应呈现高对比度并抵抗高温和应变水平。为了找到符合这些规格的散斑图案，我们对使用不同技术制作的六种散斑进行了比较。首先，符合 DIC 标准的计算机生成的散斑图案被数值设计为产生六种类型的散斑图案。接下来，在散斑形态方面比较了使用这六种技术产生的散斑图案，图像质量和高温下对钛合金 TA6V 材料的附着力。从25°C到600°C，通过阳极氧化和激光雕刻相结合的技术制成的散斑图案称为M5技术，具有最佳对比度（平均强度梯度[MIG]和香农熵值的最大值）和200％的应变测量值的遵守到TA6V材料。在 700°C 时，由于钛合金的氧化，散斑图像质量显着降低，这可能不适用于 DIC 测量。与其他技术相比，只有油漆起保护作用的绘画产生的斑点才能提供更好的斑点对比度。然而，这些散斑图案只能通过 DIC 方法进行 22% 的应变测量。