Development of Measuring System for Thermal Deformation of Heatproof Materials by Using Laser Speckle Interferometry at High Temperature

当材料将在高温气氛中使用时，材料的性能必须与高温条件相匹配。然而，现有的方法很难测量结构的热应变，因为用于应变测量的仪器本身就受温度的影响。电子散斑干涉法（ESPI）是测量面内表面位移的一种非常有用的方法。利用激光和图像处理系统，可以测量位移和应变：与传统的应变测量方法（如应变片或云纹法）不同，ESPI方法不需要特殊的表面制备或附件，可以在无接触的情况下实时测量面内位移。在这项研究中，我们讨论了使用ESPI测量物体在高温下的应变或热应变。讨论了从干涉条纹图中计算应变值的几种方法。在实验中，试样与提供加载步骤的负载传感器平行加载。标本为平板或中间有直径12mm孔的板。应变片分别在与加载方向平行的方向和垂直的方向上附着在试样上。本研究提供了一个例子，如何ESPI已被用于测量二维位移和应变分布的试样。ESPI测量的结果与应变片法在拉伸试验中获得的数据具有可比性。

When the materials will be used at a high temperature atmosphere, the properties of the material must be matched with high temperature conditions. However, it is very difficult to measure the thermal strain in structures with existing methods, because the instrument used for strain measurement is in itself influenced by temperature. Electronic speckle pattern interferometry (ESPI) is a very useful method for measuring in-plane surface displacement. Using the cw-laser and the image processing system, it is possible to measure the displacement and strain : Unlike the traditional method for strain measurement such as the strain gauge or the moire method, the ESPI method requires no special surface preparation or the attachments and can measure the in-plane displacement with no contact and in real time. In this study, we discussed the use of ESPI for the measurement of the strain or the thermal strain of the objects at high temperature. And several methods to calculate the strain value from the interference fringe pattern were also discussed. In the experiments, the specimen was loaded in parallel with a load cell which provided the loading step. The specimen was a flat plate or a plate with a 12mm-diameter hole in its center. Strain gauges were attached to the specimen both in parallel and in normal directions to the loading direction. This study provides an example of how ESPI has been used to measure the two- dimensional displacement and strain distribution in the specimen. The results measured by using the ESPI were comparable with the data which were obtained by the strain-gauge method in tensile testing.