The Technique Of NDT With Multifunctional DSPI And Its Application

In this dissertation, a multifunctional digital speckle pattern interferometry (DSPI) has been developed based on the conventional ESPI techniques. The system includes real-time sample, real-time subtraction, real-time interval, double exposure and peak store, which can be used in the measurement of in-plane displacement, out-of-plane displacement, out-of-plane displacement gradient, 3-D shape and nondestructive testing (NDT).The basic principle of digital peak store shearography is described firstly which can be used for evaluating promptly the soundness of composite and detecting the sizes, shapes and positions of the interior defects of composite. A diagnostic maps that flaws manifest as the white patches are obtained for rapid flaw detection during testing. The user can very quickly interpret the test results from this map and report on the defective areas in the test structure. The adjustable real-time interval shearography is reformed. By controlling expediently and accurately real-time interval, the technique can be used in the measurement of thermal deformation, time-dependant deformation, quasi-dynamic deformation and NDT and so on.A new technique of NDT that used a wide audio frequency sweeping in digital shearography is proposed, which can be used in NDT of the composite by exciting at or near resonant frequency of the test structure. The loading system based on this technique is designed for driving vibration of specimen. The system used the voltage-controlled waveform generator, which is developed by us and controlled by computer, that is capable of producing high accuracy sine, triangular, square waveform etc. The frequency can be selected externally from 10Hz to more than 10kHz and frequency modulation and sweeping can be accomplished using computer. The equipment has great significances in engineering.The integrative image processing technique of DSPI fringe patterns, including adjustable real-time contrast enhancement, conventional filtering, recursive filtering, wavelet filtering, edge detection and image segmentation, is firstly proposed and developed. The technique has been demonstrated to reduce effectively speckle noises and improve extremely the quality of DSPI/DSSPI (digital shearing speckle pattern interferometry) fringes in the dissertation. The nondestructive evaluation of quality of composite based on the integrative image processing technique is investigated by using the digital shearography. The quantify mistake that is caused by the amount of image shearing is corrected. The area, position and x-axes, y-axes sizes of the defect are calculated using the method. The results show that it is correct.A computer software for Windows 98 environments, which performs image sample, wide audio frequency sweeping, image processing, fringe pattern analysis and computing, is developed by using C++ Builder 5.0 language. The software is based on a VIDIO-PCI-XR image card and a PCI-9112 ADLINK advanced data acquisition card. It is very simple to manipulate and has multiple functions.At the end of the thesis, the NDT technique in the dissertation is experimentally tested. The experimental results show that we are able to evaluate promptly the quality of the composites by using the NDT technique.