彩色数字全息及其在材料变形检测中的应用研究

【作者】 桂进斌；

【导师】 李俊昌；

【作者基本信息】 昆明理工大学 ， 材料学， 2013， 博士

【摘要】 随着材料制造与加工技术的发展,新材料在工业中获得了广泛应用,材料的细观结构越来越复杂,其对材料力学性能的影响越来越重要,对材料内部结构变形损伤机制的研究对先进材料的研究和应用具有重要意义。而且,材料构件的变形及疲劳失效对材料应用有较大的影响,材料的失效很多情况是由于材料内部缺陷及材料选择的不恰当引起的。组成构件的材料及构件形状的复杂性,使得很多材料构件的强度及刚度等力学性能理论上是较难计算得到,通常需要通过实验手段进行测量。由于材料受外力时的应变及应力分布通常能反映材料构件的性能,研究能实现对任意形状材料构件受力时变形及应力分布的准确检测的方法在材料工程应用中有重要的意义。在材料应力场分析及变形测量中,光测方法因其独有的优势而得到发展,目前主要有光弹法,激光散斑干涉法,云纹干涉法等。光弹性法是现代材料应力分布检测的一种有效的实验方法,但存在条纹分离困难、过程复杂等问题。全息光弹法提高了光弹法检测的精度及条纹判读的自动化程度,使光弹方法的应用更方便、快捷。但传统全息后期处理过程繁琐,且需要在暗室中拍摄,因此限制了其应用。对于位移场(变形)的测量,激光散斑干涉法及云纹干涉法是目前常用的方法,在很多领域获得了重要应用,但一次测量时只能得到至多两个方向的信息。数字全息技术是现代无损检测的一种重要方法,其检测精度高、速度快、非接触、可实时全场测量,且数字全息的记录、存储及再现全部采用数字化方式,容易得到相位信息,近年来在无损检测领域获得重要应用。但对于一些复杂矢量信息,传统数字全息检测信息量不足以准确获得全部的信息。在数字全息研究领域中,使用多种波长的激光照明的彩色数字全息是近几年的研究热点问题。但使用彩色数字全息进行检测应用还有很多问题需要解决,如探寻新的波面重建算法实现彩色数字全息不同波长照明下重建图像的准确合成,消除彩色数字全息重建场的零级干扰得到高质量的重建场等。基于目前对材料变形及应力检测技术的现状,本文使用彩色数字全息对材料的变形及应力分布进行检测与分析,同时对数字全息检测相关问题如彩色数字全息波面重建算法、优化的光路设计、零级干扰的消除等进行研究。然后使用彩色数字全息对透明材料应力场、变形场及散射材料三维变形进行检测研究。主要研究工作包括以下几点：1.对数字全息波面重建算法进行讨论,重点分析了不同重建算法满足采样定理的条件,结论表明,使用角谱衍射公式对数字全息波面进行重建可以得到较准确的结果。2.对彩色数字全息波面重建算法进行研究与讨论。对使用球面波为重现波的可变放大率算法进行了研究,对使用多波长激光照明的彩色数字全息来说,使用可变放大率的波面重建算法,可以较好实现不同波长全息图重建像的准确合成。论文对散射物光场的数字全息记录及再现理论进行研究,把散射物体视为基元点光源的集合,其重建场为所有点光源在重建平面的叠加,使用可变放大率算法对物光波面进行重建,可得到任意放大率的重建像。3.对彩色数字全息中不同波长记录的全息图重建像的合成方法进行了讨论,提出一种准确实现彩色数字全息不同波长物光场合成的方法。研究表明,可使用S-FFT重建像为参考,选择频谱滤波中心及滤波窗口,使用可变放大率的算法,选择合适的放大率,实现不同波长的重建像的准确重叠。4.对球面波照射后全息图的频谱进行分析,对可变放大率算法中零级干扰的形式及分布进行研究。研究表明,球面波照射后全息图零级频谱随着放大率增大而展宽。论文对各种消除零级的方法进行研究,并给出结果的比较。使用计算机控制相移,在参考光中引入任意相移,通过两幅数字全息图相减的方法实现了零级干扰的消除,扩大频谱滤波窗口的尺寸,获得较高质量的重建图像。直接对全息图进行频谱滤波处理,获得“无干扰”的全息图,并对“无干扰”全息的频谱滤波方法进行改进,通过像面滤波技术,不但可以得到高质量的重建物光场,而且可以在清晰的像平面上选择任意区域进行重建,有利于局部细节的分析与检测。5.使用彩色数字全息技术对透明材料的变形进行检测,并分析了检测的误差。理论上提出一种通过旋转参考光的偏振方向来实现透明材料应力场的数字全息检测研究的方法,并对理论公式进行计算机模拟,其结果与实验结果吻合较好,证明这种方法的可行性。然后使用这种方法对复杂开孔的构件应力分布进行了检测。设计对透明材料应力场进行实时检测的彩色数字全息检测系统。使用彩色数字全息技术,对散射物体加载时三维变形场的检测作了初步研究,实时得到了三维变形信息。更多还原

【Abstract】 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.更多还原