Holography And Its Application In Color Digital Material Deformation Detection

With development of materials manufacturing and processing technology, new materials are widely applied in the modern engineering, meanwhile, meso-structure of material is increasingly complex, and its influence to mechanical properties of material is more and more important. So, the research of deformation and damage mechanism of material internal structure is significant to the study and application of new materials. Furthermore, material components deformation and fatigue failure have important influence on the material application. In most cases, the failure of materials performance is due to internal defects and the inappropriate selection of materials. Due to the complexity of material composition and shape, many mechanical properties, such as strength and stiffness are difficult for theoretical calculation, and usually the experimental methods for measuring are needed. Because the performance of the material components can be usually reflected by strain and stress distribution, the accurate detection method of stress deformation and stress distribution of arbitrary shape material components have important significance in materials engineering applications.Optical measurement method is one of methods to analyze material stress and deformation because of its many advantages. At present, optical measurement methods include photoelastic method, laser speckle interferometry method, moire interferometry method etc. Photoelastic method is an effective experimental method of modern material stress distribution detection, but exists in this method some problems such as stripe separation, complicate processing and so on. Holographic photoelastic method improves the detection precision and the automation degree of stripe interpretation; hence makes the application of photoelastic method more convenient and fast. But the process of hologram is more complicated, and needs record the hologram in darkroom. At present, laser speckle interferometry and moire interferometry are the main methods of displacement field (deformation) measurement, got important applications in many areas. But the measurement can only get at most two direction information.Digital holography is an important nondestructive testing method, and won widely application in many field because of the merit such as high accuracy, speed, non-contact, real-time full measurement and so on. Furthermore, we can get the phase information because of digital recording and storing of hologram. But traditional digital holography cannot get enough information for complicated vector information.In the research field of digital holography, color digital holography is a hot research issues in recent years. But there are many problems need to solve. First of all, how to accurately synthesize the three images or information of different wavelengths is the all-important problem needed to solve; In order to obtain an accurately synthesized image of different wavelength, we need to find new reconstruction algorithm for color digital hologram. Meanwhile, the zero-order image is disturbed by the object wave field information, and has serious effect of detection information of color digital holography. Therefore, another important step in color digital holography is to eliminate the zero-order.In this thesis, we try to detect the material deformation and stress distribution by using the color digital holography. In order to get high quality information, some issues about color digital holography, such as wave field reconstruction algorithm, light path optimization design and zero-order elimination are also described in this paper.Based on the results, stress detection of transparent material is presented, and displacement of rough surface is tested by use of color digital holography. The main works are included as follows:1. Algorithm of digital holography wave surface reconstruction is discussed; sampling conditions of different algorithm is selectively analyzed. The results show that, an accurate result can be got by use of angular spectrum transfer function.2. Algorithm of color digital holography is discussed. The algorithm of variable magnification is discussed; this method is more advantageous in color digital holography because the magnifier of different wavelength unified. In this paper, we discussed the recording and reconstructing of scattering object, and got the reconstruction field of scattering object.3. Accurate synthesize method of different wavelength image is discussed in this paper. And a new method about how to select the frequency filter is presented. The study shows that we can get accurate the position and size of frequency filter by refers to the S-FFT reconstructed image. Then got the color image through the reconstruction algorithm of variable magnification with same magnification.4. We discussed the frequency spectrum of hologram illuminating by spherical wave, and analyzed zero distribution. The results show that the frequency spectrum of zero-order is broadened by spherical wave, and is related to magnifier. Based on the discussion, some methods of zero-order eliminating have been studied. Zero-order image can be eliminated by adding a phase in reference beam, but two holograms are required. A good method is to get the frequency spectrum of object from hologram, then obtain the free disturb hologram from inverse fast Fourier transform. And we get the high quality reconstructed wave field without any zero-order and twin image. An improvement filter method is presented; we reconstruct the image by S-FFT method, and then select the information field, get "no disturbing hologram" by use inverse computing of diffraction, then get an image through variable magnifier algorithm. We can get the freewill information of image and let the reconstructed image full of the reconstructed field.5. Deformation measurement of transparent material is presented by use of color digital holography. We proposed a theoretical method to test stress distribution of transparent material by changing the polarizing direction of reference beam. Comparison of simulation and experimental result proved the feasibility of this method. At last, a real-time stress testing system of color holography is designed, and the testing results of displacement of scattering object is presented by use of color digital holography.