Study On A Portable In Situ Three-dimensional Deformation Measurement System Using A Single-camera And Its Applications

Digital image correlation(DIC)is a non-interferometric optical metrology for full-field shape,motion and deformation measurements that was originally established in the early 1980 s.Compared with other optical interferometric techniques based on the interference of coherent light,such as holographic interferometry,speckle interferometry,and moiré interferometry,the DIC technique possesses many remarkable advantages such as the requirement for a testing environment is low,preparation of the specimen is relatively easy,simple experimental setup besides non-contact and high resolution.However,a three-dimensional digital image correlation(3D-DIC)system typically consists of two or more cameras and observes a target from multiple orientations.It is restricted by its laborious calibration process in many applications.Therefore,a stereo-DIC technique using a single-camera system would be more desirable to achieve three-dimensional deformation measurements due to its compact structure and self-calibration.The main objective of this research was to investigate the aspects of the digital image correlation techniques using a single-camera for 3D shape and deformation measurement.In this thesis,a portable in situ three-dimensional deformation measurement device(digital image correlation strain sensor(DIC-SS))was developed,which is not only used for 3D shape measurement,but also for high accuracy strain measurement as it can be attached onto the surface of the structure to remove the rigid displacement of the structure.In order to perform a long-term high accuracy strain measurement,a speckle-based self-calibration method which calibrates the single lens stereo system using the reference speckle image of the specimen instead of the calibration targets was proposed,which will make the system more convenient to be used without complicated calibration.It becomes a reality to realize in situ calibration and improve the stabilities of the system for long-term measurement.The system is used as video extensometer for non-contact,non-destructive and high-accuracy strain measurement successfully.The developed device was combined a single camera with a triangular prism mirror and two mirrors.The mirrors are utilized to convert a single camera into a stereo image system,which views a test object from two different directions and records the surface images of the test specimen on the two halves of the camera sensor,to achieve a three-dimensional measurement.The optical design and measurement procedures to obtain 3D deformation measurements of the proposed system are described in detail.The efficiency and precision of the proposed system are verified by measuring the in-plane and out-of-plane displacement of a translated plate.Moreover,a three-point bending experiment was performed on a plastic beam specimen under three points bending via an outer loading frame to determine displacements and normal strain field.The experimental results demonstrated that the proposed system can effectively and accurately measure the full-field 3D deformation and measuring accuracy have an excellent level of agreement with the multi-camera system.Due to its small size,lightweight and easy to set-up the established system demonstrates great potential in determining three-dimensional deformation measurements with the aid of a single-camera,and this system well-suited to both laboratory and field condition and will have significant application in the fields of engineering.