Electronic speckle pattern interferometry based on spatial information using only two sheets of speckle patterns

Abstract

Speckle interferometry is an important deformation measurement method for an object with a rough surface. In this paper, a novel fringe analysis method is proposed that uses a new optical system, which uses a plane wave as the reference beam of the speckle interferometer. When the optical system is employed in fringe analysis, the deformation information and the bias components of the speckle patterns are clearly separated in the frequency domain. Therefore, the deformation information can be readily extracted using a Fourier transform, which gives a pair of real and imaginary components concerning the information. The specklegram is calculated using such a pair of components, and the phase map is obtained from the specklegram. Experimental results confirmed that the resolution power of this measurement method is higher than 1/261 of the wavelength of the light source of the optical system.     

Fringe analysis method for electronic speckle pattern interferometry using only speckle patterns before and after deformation

Electronic speckle pattern interferometry is employed in many industrial fields as a useful deformation measurement method. However, two speckle patterns obtained before and after the deformation are necessary for measurement. Furthermore, at least three speckle patterns are required for high resolution measurement using ordinary fringe scanning technologies. In this paper, a novel method that can measure high speed deformations using a limited number of speckle patterns without using high speed cameras is proposed. The method enables application to dynamic deformation analysis because the method involves analysis using only two speckle patterns obtained before and after the deformation. A novel optical system that can record some spatial information into each speckle is set up for the method. In experimental results, it is confirmed that the out-of-plane deformation measurement can be precisely performed by the method and that the resolution power is almost equivalent to that of the ordinary method.     

白光频闪散斑干涉术的研究

在利用白光对振动物体进行测量时,由于白光的相干性较差,难以得到质量较好的图像,为了克服这一缺点,本文提出了一种用白光光源照明进行振动测量的新方法-白光频闪散斑干涉术.阐述了白光频闪散斑干涉术的基本原理,分析了提高图象质量的主要原因,采用了相干性较好的白光光源和合理的光路,使系统的时间相干性和空间相干性得到提高,从而提高了图像的质量.实验结果表明,该方法用于振动的测量,能给出物体在任一瞬时的振动信息,得到清晰的、高对比度的全场干涉条纹图,图像的质量得到大大提高.     

基于傅里叶变换的点衍射干涉术

在相移算法的点衍射干涉术的基础上,提出了基于傅里叶变换的点衍射干涉测量术.基于傅里叶变换的点衍射干涉测量术是一种建立在点光源衍射干涉理论基础上的测量方法,它采用傅里叶条纹分析方法来求解干涉条纹的相位分布,运用基于BFGS的拟牛顿算法进行三坐标的迭代计算,确定点光源的三维空间坐标.通过计算机模拟实验,验证了该方法在有噪声干扰的情况下,可以有效降低干扰噪声对测量的影响.     

数字散斑干涉在振动测量中的应用

在动态测试领域中,数字散斑干涉技术常用到的相位处理方法有时问平均法和空间载波相移法.空间载波相移法因其简单性和实用性,被应用于双脉冲散斑干涉测量中.     

Speckle Interferometry: A Review of the Principal Methods in Use for Experimental Mechanics Applications

Abstract:  With its nearly 40 years of existence, speckle interferometry (SI) has become a complete technique, widely used in many branches of experimental mechanics. It is thus a challenging task to try to summarise in a couple of pages its principal characteristics from both theoretical and practical points of view. Admittedly, even though this goal is not met here, it appeared worth attempting to provide the photomechanics community with a discussion of the ins and outs of the technique. The necessity of a vocabulary free of ambiguity was a prerequisite, and hence the first section is a plea for a clearer definition of the discipline. Moreover, this section offers the opportunity to re-examine the basic aspects of SI. Then, the main features of the method are briefly considered following a strengths, weaknesses, opportunities and threats (SWOT) analysis. Endowed with a lot of specific advantages, compared with other whole-field methods, SI can play an increasing role in photomechanics.     

Full‐Field Vibration Measurement by Time‐Average Speckle Interferometry and by Doppler Vibrometry – A Comparison

Abstract: Identification of dynamic material properties, non‐destructive testing and study of vibroacoustic behaviour of different structures require the use of complex, pointwise and full‐field measurements, which are capable of providing data for experimental modal analysis or model updating. Nowadays, among other techniques, optical non‐contact techniques represent the favourite choice as they do not add mass, stiffness or damping to the structure under test. When the range of vibration amplitudes allows it, most of these techniques are based on interferometric principles. Development of laser sources and detectors leads to a continuous improvement of vibration measurement techniques. However, a hard choice still has to be made between spatial resolution and temporal resolution. Another difficult choice is between space bandwidth product and energetic sensitivity of the detector. While the number of pixels of a camera is continuously increasing, the pixel size seems limited at its lower end. The paper presents a comparative study of the vibration amplitude fields as measured by two full‐field non‐contact techniques, speckle interferometry and laser Doppler vibrometry, and predicted by finite‐element model. The measurements concern the free and the forced vibrations of a thick, composite plate with free boundaries.     

Improved DSPI configuration for the inspection of components in the production line

In this paper, a digital speckle pattern interferometer configuration for the enhanced nondestructive inspection of components in the production line is presented. The setup used is adapted from the original design employed for digital speckle shearing interferometry. The theoretical principle behind the technique is outlined and its application in the detection of poor bolting in plates is demonstrated.     

Time Resolved Digital Holographic Interferometry for Investigations of Dynamical Events in Mechanical Components and Biological Tissues

Abstract:  In the first part (section 2) of the paper, a system based on digital holographic interferometry for the measurement of vibrations is presented. A high-power continuous laser (10 W) and a high-speed charge coupled device camera are used. Hundreds of holograms of an object that was subjected to dynamic deformation are recorded. The phase of the wave front is calculated from the recorded holograms by use of a two-dimensional digital Fourier-transform method. The deformation of the object is obtained from the phase. By combination of the deformations recorded at different time it is possible to reconstruct the vibration of the object. In the second part (section 3) of our paper, the holographic method is used for the measurements of the elastic properties of the bone. Samples of bone were loaded and deformed and a large number of interferograms (digital holograms) were recorded over a short period of time. In the third part (section 4) of the paper, we show how the holographic systems are adapted for performing measurements in hidden cavities.     

Identification of the Orthotropic Elastic Stiffnesses of Composites with the Virtual Fields Method: Sensitivity Study and Experimental Validation

ABSTRACT:  This paper presents the use of a sensitivity study to find the best combinations of free length and fibre angle in an unnotched Iosipescu test processed with the virtual fields method. The sensitivity to noise coefficients arising from the special virtual fields procedure are used to build up a cost function. This function is aimed at balancing out the coefficients of the different orthotropic stiffnesses so that the same confidence level can be reached on all these parameters. Then, experimental validation was performed using a speckled interferometry (ESPI) system. Full-field strains were measured and stiffnesses identified and compared between the usual 0°, 30 mm configuration and an improved 25°, 40 mm configuration. The outcome of the optimisation was confirmed by testing the same specimen several times and comparing scatter between the two configurations. This is a first promising result on the way to the design of a new test for orthotropic stiffness identification on a single specimen from full-field measurements.     

数字散斑相关方法在木材科学中的应用及展望

随着现代光电子和计算机技术的发展以及数字图像处理理论的深入，数字散斑相关方法（DSCM）迅速成为实验力学领域一种重要的测试方法。文章介绍了DSCM的基本原理，并对其在木材科学领域的应用进行了综述，包括在木材常规力学测试和木材断裂、微观力学以及复合材料力学测试等方面的应用及一些新的成果。最后根据木材材料的特点, 对DSCM在木材科学上的进一步应用提出了几点建议。     

流体温度场测量中的电子散斑干涉技术

电子散斑干涉是一种利用全电子记录和计算机图象处理系统替代传统照相干版进行测量的先进技术。本文在简要介绍其应用于流体温度场测量的理论与实验的基础上,着重描述了如何通过调整光学系统参数配置来获取最佳质量原始干涉图象的途径,并给出对比分析结果。     

Application of Double‐Focus Speckle Interferometry for Non‐Destructive Testing

Abstract: This paper deals with the application of a speckle interferometer, which works on the new operating principle of double‐focusing presented by the authors in recent studies, to the field of non‐destructive testing (NDT). Using this interferometer, the components of displacement given by holographic interferometry can be measured, but with no need for an external reference beam. The implementation of this interferometry can be indifferently carried out by adopting a Michelson or a Mach–Zender configuration. In the paper a double‐focus interferometer based on the Michelson design and sensitive to out‐of‐plane displacements was implemented and applied to a metallic specimen which simulates the deformations of a typical debonding.     

大口径高次非球面高精度面形检测方法探讨

总结了常用非球面光学元件的检验方法的分类及其特点,提出了满足大口径高次非球面的高精度检测方法的基本要求,重点分析了细光束干涉测试方法及其在大口径非球面高精度检测方面的应用．     

剪切电子散斑干涉术中消偏振效应的研究

就散射光的偏振性对剪切电子散斑干涉术中的影响进行了研究，文中给出了理论分析及实验结果，得出了消偏振效应不改变计量条纹调制度，但降低光能利用率的结论。     

聚碳酸酯拉伸应变局部化实验

采用电子散斑技术对聚碳酸酯材料拉伸过程的表面变形进行了实验研究,量化得到了试验在拉伸载荷作用下的连续变形分布,用扫描电镜(SEM)观察了断口形貌.结果表明,在粘弹性区域,沿拉伸方向产生平行的形变带,离面位移随载荷之间而增大;在屈服区域,产生应变局部化,形成800μm的剪切带,而且聚碳酸酯的断裂是由局部应力集中所致,其裂...     

测量薄膜折射率的光栅衍射干涉方法

根据光的干涉理论,讨论了条纹周期数对测量薄膜折射率不确定性的影响,推导出干涉条纹错位量与薄膜折射率和厚度的关系式。由此提出采用光栅衍射干涉测量薄膜折射率的方法和实验方案。实验表明:该方法的干涉条纹测量精度达λ/10~λ/20,薄膜折射率测量精度可达 0.01 以上。