Measurement System For3D Deformations Based On DSPI And Its Applications

The measurement of three-dimensional deformations plays a very important role in all kinds ofindustry fields, such as aerospace, mechanical engineering, civil engineering, material science and soon. Digital speckle pattern interferometry (DSPI) is a robust modern optical measurement technique.Due to its advantages of full-field, non-contact, high precision, high detection speed and etc, DSPI iswidely used for deformation analysis, shape measurement and NDT. So far, two-dimensional DSPItechnique has been well developed. In particular, the results of DSPI can be obtained real-time andautomatically by using the high-accuracy phase extraction technique. However, three-dimensionaldeformation measurement using DSPI is not yet perfect, and there are still many problems to besolved. For example, three-dimensional displacement components are measured non-simultaneouslyand non-independently. Therefore, the research of simultaneous, independent and real-time DSPImethod and the device for three-dimensional deformation measurement can take an important place inthe fields of both science and industry.Based on reviewing the state of the research of three-dimensional deformation measurement byDSPI and analyzing the factors of the limitation of its further development, the scope of thisdissertation work is focused on the simultaneous, independent and real-time DSPI method forthree-dimensional deformation measurements. The NDT of the internal defects located in compositelaminates is also presented qualitatively. In addition, both uneven illumination correction in digitalimage correlation (DIC) and noise reduction in DSPI are investigated. The main research contents andachievements of this thesis are as follows:1. The uneven illumination of speckle patterns will influence the displacement measurementaccuracy of DIC. An uneven illumination correction method based on the morphological Top-Hattransform is hence presented for the correction of the speckle patterns. The numerical simulationexperiment is used for verifying the feasibility of the presented correction method.2. The random noise in speckle fringe pattern or wrapped phase map will influence the accuracy ofthe demodulated phase. On the basis of the existing filtering algorithm, three filtering algorithms forspeckle fringe pattern, i.e. the homomorphic filtering algorithm, Goldstein filtering algorithm, and fastdiscrete curvelet transform (FDCT) filtering algorithm, are hence adopted. The windowed Fouriertransform (WFT) filtering algorithm is also used for noise removal in wrapped phase map.3. In accordance with the theory of two-dimensional DSPI, a new three-dimensional DSPI method is proposed for simultaneous, independent and real-time measurement of three-dimensionaldeformations, as well as out-of-plane deformation and its first order derivatives.4. The high-precision equipment of three-dimensional DSPI for three-dimensional deformationmeasurement is developed. Meanwhile, the software of image grabbing for three-dimensionalmeasurement is programmed. The main functions of the software are also introduced. During theimage capturing, multiple image acquisition windows need to be monitored synchronously, andreal-time display of substracted images also needs to be carried on synchronously. Accordingly, themultithread technique and frame difference technique are introduced to solve these two matters.5. By use of the designed three-dimensional DSPI system, two-dimensional and three-dimensionaldeformations of a simple supported beam subjected to three-point bending are firstly measured.Secondly, the out-of-plane deformation and its first order derivatives of a circumferentially clampedthin plate are obtained. Thirdly, the out-of-plane deformation of a composite laminate is measured byusing the phase of difference method (PDM) and difference of phase method (DPM), respectively.Fourthly, the NDT of both low-velocity impact damage in laminates and the pre-prepared defectsinside laminates is investigated. Finally, in-plane rotation-center location of a rigid body based onDIC is investigated. Experimental results show that three-dimensional displacement components, aswell as out-of-plane deformation and its first order derivatives, can be indeed measuredsimultaneously and independently using the proposed three-dimensional DSPI method.