Chapter 15 Investigation of Electronic Speckle Pattern Interferometry with Line Laser Scanning for Large Area Deformation Measurement Shuichi Arikawa and Yuta Ando Abstract For measuring small deformations in large structures by electronic speckle pattern interferometry (ESPI), the increase of laser power is required for providing the sufficient laser power per area. However, high-power lasers lead increasing the risk of exposure to laser, the size of the equipment and the cost. In this study, ESPI with line laser scanning is investigated for large area deformation measurements without increasing the laser power. A dual-beam interferometer for a horizontal displacement measurement which can illuminate horizontal line lasers and can scanning for vertical direction is constructed. A static in-plane deformation of an aluminum sheet specimen is measured. Speckle images for each vertical position are captured at the initial and the deformed state. Analyzed phase maps for each line show mismatch of the phases. Additionally, a method for integrating the mismatched line phase maps are investigated. Keywords Deformation Measurement • Speckle Interferometry • Line Laser • Laser Scanning • Phase Integration 15.1 Introduction For measuring surface deformations, optical or interferometric techniques are effective. Especially, electronic speckle pattern interferometry (ESPI) [1, 2] is very useful for measuring elastic deformations or thermal deformations because of the high sensitivity. When large area is measured by ESPI, a high power laser source is required to ensure the sufficient laser power per area. It is expected that a very high power laser as watt level is required for meter order of the measurement area. High power lasers more than 0.5 watt is classified class 4 as the most dangerous level. It leads requirements of safety equipment and increasing the cost. Therefore, the development of the technique for large area deformation measurement by ESPI without increasing the laser power is effective for the usefulness. In this study, ESPI with line laser scanning for large area deformation measurements are investigated. 15.2 Electronic Speckle Pattern Interferometry with Line Laser Scanning A schematic figure of a dual-beam interferometer for ESPI with line laser scanning is shown as Fig. 15.1. The line shaped interference region is made on the object surface using cylindrical lenses and can scan the object surface by moving the interferometer. Image capturing at the same scanning positions before and after the deformation are required. Additionally, an investigation of the method for integrating the line interferograms. Figure 15.2 shows a schematic of the image integration. Phase mismatches occur by environmental vibrations. Therefore, the phase correction for the image integration is necessary. In this study, phase values in overlap regions arranged between adjacent lines are compared. The line phases are then corrected and integrated. S. Arikawa ( ) •Y. Ando Department of Mechanical Engineering Informatics, School of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa, 214-8571, Japan e-mail: arikawa@meiji.ac.jp © The Society for Experimental Mechanics, Inc. 2018 L. Lamberti et al. (eds.), Advancement of Optical Methods in Experimental Mechanics, Volume 3, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-63028-1_15 93
RkJQdWJsaXNoZXIy MTMzNzEzMQ==