Study On The Electronic Speckle Pattern Interferometry Used In The Measurement Of Transient Deformations

One of the effective methods to evaluate the safety, applicability and reliability of the whole system is to measure and analyse the transient deformation of the engineering materials and structures. As a new branch of the photomechanics, electronic speckle pattern interferometry(ESPI) is often used as a whole-field, contactless, nondestructive and high-precision interferometric technique for the deformation, displacement and vibration measurement of objects with optically rough surfaces. In ESPI, the measurement of the object surface under study is acquired by analyzing the distribution of the phase change in the speckle pattern. Combining with the high-speed imaging system, ESPI is able to measure transient deformation accurately.Based on the optical statistical properties of the speckle, the high-speed ESPI used to measure the transient deformation has been fully detailed. Firstly, a high-spped temporal phase-shifting electronic speckle pattern interferometer based on Michelson interferometer is illustrated. Not only the parameters of the interferometric system, such as the phase-shifting, shear and speckle size, but also the errors of the measurement are thoroughly discussed. To overcome the drawback of the temporal phase-shifting method in the real time measurement, a(N,1) phase extraction method is adopted. Seconeldy, temporal speckle pattern interferometry(TSPI) based on the sequence of speckle patterns has been demonstrated in detail. In TSPI, the deformation field is regarded as time-varying field so that the time parameter is involved in the analysis of phase distribution. A sequence of speckle interferograms is recorded throughout the entire process of the deformation. Each pixel of the camera probes the object as an independent sensor. The phase distribution coded in the temporal intensity modulation is observed at every single pixel and extracted by the Hilbert transform based method. However, the fluctuations of the bias and modulation intensities of the interference signal may cause errors. Empirical mode ecomposition(EMD) is introduced to dispose the nonlinear and nonstationary signal to decrease the errors of the phase retrieval. By the way of computing the correlation coefficient between the original signal and each intrinsic mode function(IMF), a plenty of high frequency noiseis in the temporal interferometric signal are eliminated effectively. Thirdly, a phase analysis method, which combines temporal Hilbert transform with spatial phase unwrapping, is proposed. The wrapped phase distribution is directly determined by using Hilbert transform and triangular transform. Meanwhile, the unwrapping operation is shifted from time domain to space domain to avoid anomalous phase jumps caused by the low modulation intensity of the interferometric signal. At last, a Fourier phase filter integrated with sine-cosine filtering method is designed to cope with the noisy wrapped phase distribution maps. The continuous phase distribution is obtained by the spatial phase unwrapping based on the least square method and discrete cosine transform(DCT) and the 2D deformation field is acquired indirectly.According to the requirements of the experiment, an integrated software based on MFC is designed, which is able to control not only the measuring system based on high-speed electronic speckle interferometry but also the image acquisition and processing system. The high-speed ESPI system is set up to detect the transient deformation of a rubber plate drived by a Piezo electric transducer(PZT). The experiments reveal that temporal phase-shifting speckle pattern interferometry is suitable for the observation measurement of the transient deformation because of its characteristics and TSPI is able to realize the measurement of transient deformations not only in the whole field but also in the specified pixel.