Digital Shearography Applied to the NDT and Strain Measurement of Structures in Civil Engineering

• Main Authors: Shan-Yuan Huang, 黃襄淵
• Other Authors: Chin-An Shao
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/50137904481969910851

碩士 === 中正理工學院 === 軍事工程研究所 === 86 === Shearography is an interferometric method which allows the whole field derivatives of surface displacement and non contacting to measure directly and needs not a special vibration isolation. Therefore, it is a tool well suited for either nondestructive testing or for strain measurement of civil engineering structures. Using shearography two states of undeformation and deformation are stored by a digital image process system. The real-time technique can be used to monitor transient deformation for nondestructive testing. The quantitative strain evaluation of fringes needs to use the phase shifting interferometry. In order to calculated the phase in the before and after deformation states, four speckle patterns are required to be recorded and processed. The relative phase change can be determined and directly related to the deformation derivatives. A major limitation of shearography is that the occurrence of rigid body motion produces a decorrelation of speckle patterns which destroys the fringe visibility. Excessive rigid body translation in digital shearography can be compensated by digitally shifting one of the speckle patterns.