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

当材料将在高温环境下使用时，材料的性能必须与高温条件相匹配。然而，用现有的方法测量结构中的热应变是非常困难的，因为用于应变测量的仪器本身受温度的影响。电子散斑干涉术（ESPI）是测量面内表面位移的一种非常有用的方法。使用连续激光器和图像处理系统，可以测量位移和应变：与应变片或云纹法等传统应变测量方法不同，ESPI方法不需要特殊的表面处理或附件，可以无接触和真实的实时测量面内位移。在这项研究中，我们讨论了使用电子散斑测量的应变或热应变的物体在高温下。讨论了几种从干涉条纹图中计算应变值的方法。在实验中，试样与提供加载步骤的测力传感器平行加载。试样为平板或在其中心具有12mm直径的孔的板。将应变计平行于和垂直于加载方向连接到样本上。本研究提供了一个例子，如何电子散斑已被用来测量二维位移和应变分布的标本。用电子散斑干涉仪测量的结果与用应变片法测得的拉伸试验数据相比较。

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.