Speckle Photography Research Articles

Displacement Measurement and Study of Surface Roughness using Laser Speckle Technique

A simple technique of speckle photography has been applied to measure small changes / deformation of the surface of laser scattering materials. Low-cost commercial charge coupled device photo camera provides the images of Laser speckle pattern with the beam splitter arrangement. A speckle pattern has been taken with the system at rest and then second image captured after the deformation was made in the surface of the material. By simple subtraction of the two images, gives information about displacement by means of correlation fringes. Binary speckles are used to study surface roughness and compared with stylus profilometer method.

PLASTIC STRAIN LOCALIZATION IN ALLOYED γ-Fe SINGLE CRYSTALS ELECTROLYTICALLY SATURATED WITH HYDROGEN

The effect of interstitial hydrogen atoms on mechanical properties and plastic strain localization patterns in tensile tested alloyed γ-Fe single crystals of austenite steel with low stacking-fault energy has been studied using a double-exposure speckle photography technique. The hydrogenation of [ 11] oriented single crystals of Fe–18Cr–12Ni–2Mo steel led to decrease in the yield stress, 1,3 times increase in plasticity (strain at break), and suppression of the neck formation in single crystals oriented for the multiple slippage. On the stress-strain curve of plastic flow measured in tension in the initial (hydrogen free) state, the transition from elasticity to developed plastic flow is followed by the stages of linear deformation hardening, and parabolic hardening. The stress-strain curve of single crystals saturated with hydrogen exhibit a small tooth and a flow trough and is followed by the stages of linear deformation hardening; parabolic hardening and prefracture. The main parameters of plastic-flow localization at various stages of the deformation hardening of crystals have been determined in single crystals of steel electrolytically saturated with hydrogen in a three-electrode electrochemical cell at controlled constant cathode potential. It is established that hydrogenation of alloyed γ-Fe specimens enhances the localization of straining, leads to significant changes in the characteristics distances between plastic shear bands and local straining zones in all scale levels.

Full-field mapping of internal strain distribution in red sandstone specimen under compression using digital volumetric speckle photography and X-ray computed tomography

It is always desirable to know the interior deformation pattern when a rock is subjected to mechanical load. Few experimental techniques exist that can represent full-field three-dimensional (3D) strain distribution inside a rock specimen. And yet it is crucial that this information is available for fully understanding the failure mechanism of rocks or other geomaterials. In this study, by using the newly developed digital volumetric speckle photography (DVSP) technique in conjunction with X-ray computed tomography (CT) and taking advantage of natural 3D speckles formed inside the rock due to material impurities and voids, we can probe the interior of a rock to map its deformation pattern under load and shed light on its failure mechanism. We apply this technique to the analysis of a red sandstone specimen under increasing uniaxial compressive load applied incrementally. The full-field 3D displacement fields are obtained in the specimen as a function of the load, from which both the volumetric and the deviatoric strain fields are calculated. Strain localization zones which lead to the eventual failure of the rock are identified. The results indicate that both shear and tension are contributing factors to the failure mechanism.

Calibration of Eddy Current Sensor Using Speckle Photography

Double exposure speckle is proposed to calibrate eddy current sensor in micro-displacement measurement for its simplicity, robustness and high resolution. The specklegram is taken as the vector of the displacement. The actual displacement of an object is calculated according to the speckle displacement on the spatial term, which is worked out according to the fringe spacing on the spectrum surface. A calibration system is proposed with proper speckle size and imaging magnification. Experiments showed that the accuracy of displacement measurement is 0.196um with an optical magnification 65.8. The calibration curve of the eddy current sensor is consistent with the result by a nanopositioning system.

Elastoplastic Invariant Relation for Deformation of Alkali-Halide Crystals

Plastic strain localization patterns in compression-strained alkali halide (NaCl, KCl, and LiF) crystals have been studied using a double-exposure speckle photography technique. The main parameters of strain localization autowaves at the linear stages of deformation hardening in alkali halide crystals have been determined. A quantitative relationship between the macroscopic parameters of plastic flow localization and microscopic parameters of strained alkali halide crystals has been established.

On slow wave process in rocks

A study was made of the general regularities of localized plasticity development in deforming rocks. The potential usefulness of speckle photography techniques in applications to problems of deformation and fracture in rocks was explored and circumscribed. The evolution of localized plasticity in rocks was addressed using wave ideas. The tests were performed for the compression samples of marble, silvinite and sandstone; the deformation occurred in these materials via different micromechanisms of plasticity. By the deformation, autowaves would form in the compression samples of rocks. The autowave propagation rates are in the range ~10−5...10−4 m/s (0.3...3 km/yr), which is close to slow motion rates observed in the earth crust after an earthquake or a rockslide. A correlation has been established between the calculated and experimental data on the time and coordinates of fracture in rocks.

Employing of Diode Lasers in Speckle Photography and Application of FFT in Measurements

The paper discusses the spectral correlation of the speckle patterns that have been produced by illuminating different surfaces with the diode laser at different tuning range of wavelengths. The diode laser could induce a shift in the wavelength value by raising the temperature of the laser cavity using a temperature controller. Young’s interference fringes could be obtained by applying the Fast Fourier transform to the spectral correlated speckle patterns, and the visibility of the interference fringes was found to be proportional to the surface roughness values of the objects of interest and the deviation in the wavelengths used in the illumination. Both the experimental and theoretical values of the standard surfaces used in the experimental work were compared. The system of the speckle photography and the diode laser as a coherent illuminating source provided good accuracy for measuring the surface roughness values greater than 1 µm. Theory, method, results, and uncertainty are presented in details.

Analysis of Various Surface Roughness Parameters of Low Modulus Aerospace Materials Using Speckle Photography

Surface roughness is a principal measure of product quality of the materials used for sophisticated applications. The present paper reports an experimental investigation of various parameters related to the surface roughness of the materials used for the aerospace applications by an inexpensive non-invasive technique known as speckle photography. Conventional non-destructive testing techniques such as X-Ray imaging, ultrasound scanning, microwave testing etc, have certain limitations on testing the surface characteristics of low modulus aerospace vehicle components. This paper explains characterization of surface roughness by analyzing certain roughness parameters such as intensity distribution, size distribution and contrast ratio of different low modulus materials used in aerospace applications. The optical setup employed for the work is simple and uses an inexpensive digital camera for grabbing the specimens under different static conditions

Systems for locally resolved measurements of physical loads in manufacturing processes

The generation of desired surface layer properties by a certain manufacturing process requires a comprehensive knowledge of the physical loads during the process and their influences on the workpiece material. This paper presents the setup and results of two in-process measurement systems, which are specifically designed to locally determine temperature and strain in several processes (in this case: grinding and deep rolling). One measuring system is based on speckle interference effects (speckle photography) detecting the deformation distribution of the workpiece surface and the other applies resistance deviation measurements of integrated thin films inside the near-surface layer to determine temperature and strain variations.

基于CT的数字体散斑法测量物体内部三维变形场

基于CT的数字体散斑法测量物体内部三维变形场

Monitoring of jute/hemp fiber hybrid laminates by nondestructive testing techniques

Abstract Damage following static indentation of jute/hemp (50 wt.% total fiber content) hybrid laminates was detected by a number of nondestructive testing (NDT) techniques, in particular, near (NIR) and short-wave (SWIR) infrared reflectography and transmittography, infrared thermography (IRT), digital speckle photography (DSP), and holographic interferometry (HI), to discover and evaluate real defects in a laminate with a complex structure. A comparative study between thermographic data acquired in the mid- (MWIR) and long-wave infrared (LWIR) spectrum bands, by pulsed (PT) and square pulse (SPT) thermography, is reported and analyzed. A thermal simulation by COMSOL® Multiphysics (COMSOL Inc., Burlington, MA, USA) to validate the heating provided is also added. The robust SOBI (SOBI-RO) algorithm, available into the ICALAB Toolbox (BSI RIKEN ABSP Lab, Hirosawa, Japan) and operating in the MATLAB® (The MathWorks, Inc., Natick, MA, USA) environment, was applied on SPT data with results comparable to the ones acquired by several thermographic techniques. Finally, segmentation operators were applied both to the NIR/SWIR transmittography images and to a characteristic principal component thermography (PCT) image (EOFs) to visualize damage in the area surrounding indentation.

Development of interior strain measurement techniques using random speckle patterns

Experimental stress analysis is a well established mechanics discipline dealing with measuring stress/strain in solids under load. Most techniques can only be applied to measuring strain of the surface. In this paper we review the development of techniques of using a random speckle patterns as a quantitative tool to mapping interior strain field of solids. After some elementary treatment of the basic principles of the speckle photography technique we describe three approaches that can probe the interior strain field of a transparent object. They are followed by a newly developed 3D strain measurement technique called digital volumetric speckle photography which can probe the interior of opaque materials as well.

Plastic Deformation Macrolocalization. Local Stresses and Fracture in Ultrafine Grain Titanium

The process of plastic deformation in ultrafine grain titanium is considered. Using the methods of speckle photography and X-ray diffractometry, the distributions of local strains and of local elastic distortions were examined for the test sample work. It is shown that the method of atomic-force microscopy can be used effectively for qualitative and quantitative assessment of ultrafine grain material structure.

Evaluating the effectiveness of correlation digital speckle photography method for non-destructive testing of rough surfaces

The work is devoted to the investigation of the process of reflection of laser beams from rough surfaces with different degrees of roughness. Based on the results of numerical experiments the applicability of the method of correlation analysis of speckle-structures for non-destructive inspection of surfaces with different parameters of roughness was evaluated. The optimal ratios between the parameters of the rough surfaces and parameters of the optical system, which provide the best efficiency of the method, were determined. It was established that in case of the increase of the number of topological charges the sensitivity of the optical system to changes of parameters of surface roughness increases.

Regularities of Macroscopic Localization of Plastic Deformation in the Stretching of a Low-Carbon Steel

The special features of plastic deformation localization in the stretching of polycrystals of low-carbon steel 08 ss after hot rolling and electrolytic saturation with hydrogen are investigated. The main types and parameters of plastic flow localization in different stages of strain hardening are determined by the method of double-exposure speckle photography.

Experimental study of plastic flow macro-scale localization process: Pattern, propagation rate, dispersion

The localization behavior of plastic flow was investigated for a range of pure metals and alloys. The localized plastic flow is regarded as an autowave process having a fixed set of features, i.e. propagation rate, wave number and dispersion law. Using the method of speckle photography, the autowave propagation rate has been determined experimentally for the stage of linear work hardening. Moreover, a dispersion relation of quadratic form and wave number dependencies of phase and group rates have been derived for localized plastic flow autowaves. A detailed quantitative comparison is made of the phase and group rates of the autowaves. This suggests that the two types of wave rates are closely related.

Regularities in localization of plastic flow upon electrolytic hydrogenation of an iron bcc-alloy

The impact of implanted hydrogen atoms on mechanical properties and characteristics of plastic-flow localization upon tensile stresses of the polycrystalline Fe-0.07 wt % C alloy is studied. Using the method of double-exposure speckle photography, we identified the main types and parameters of plastic-flow localization at different stages of strain hardening as a result of electrolytic saturation in a three-electrode electrochemical cell at a constant controlled cathodic potential.

Improved digital image correlation for in-plane displacement measurement

Electronic speckle photography (ESP) for in-plane displacement (IPD) and deformation measurements is well known with its more modern form, digital image correlation (DIC). Two speckle images of an optically rough surface before and after deformation, called reference and test images, are recorded and processed for IPD or deformation measurement of the test image with respect to the reference image. The reliability of ESP in measurements depends strongly on the postprocessing of the two images by DIC, which we have referred to as conventional DIC. In this paper, we are proposing a small but useful modification in the existing DIC methods by introducing some additional steps, which drastically improves the results obtained with the existing techniques. The modification to the conventional DIC method has been referred to as modified DIC. Computer-simulated and experimental results have been presented to validate the superiority of modified DIC over conventional DIC methods.

Discovering the Defects in Paintings Using Non-destructive Testing (NDT) Techniques and Passing Through Measurements of Deformation

The present study is focused on two topics. The former is a mathematical model useful to understand the deformation of paintings, which uses straining devices, adjustable and micrometrically controlled through a pin implanted in a hollow cylinder. Strains were analyzed by holographic interferometry (HI) technique using an appropriate frame. The latter concerns the need to improve the conservator’s knowledge about the defect’s detection and defect’s propagation in acrylic painting characterized by underdrawings and pentimenti. To accomplish this task, a sample was manufactured to clarify the several uncertainties inherent the influence of external factors on their conservation. Subsurface anomalies were also retrieved by near-infrared reflectography and transmittography techniques, using LED lamps and several narrow-band filters mounted on a CMOS camera, working at different wavelengths and in combination with UV imaging. In addition, a sponge glued on the rear side of the canvas was impregnated with a precise amount of water by means of a syringe to verify the stretcher effect by digital speckle photography (DSP) technique (using MatPIV). The same effect also affects the sharp transition of the canvas at the stretcher’s edge. In this case, the direct mechanical contact between stretcher and canvas was investigated by HI technique. Finally, advanced algorithms were successfully applied to the square pulse thermography data to detect three Mylar $$^{\textregistered }$$ inserts simulating different types of defects. These fabricated defects were also identified by optical techniques: DSP and laser speckle imaging.

2D Digital Image Correlation in strain analysis by Edge Detection And its Optimisation

Optical measurements of macroscopic parameters such as strain and displacement have evolved into a special branch of engineering called as stress analysis. Topics such as holography, speckle interferometry, speckle photography have advanced from basic stage of research to their advanced stages and are employed as solution’s to many engineering problems, however these systems suffer from stability requirements and consumes much processing time. More recently complete automated procedure for strain analysis has been proposed for computation of strain analysis are been introduced one of the most efficient technique in optical strain analysis is digital image correlation technique. This work includes implementation of two dimensional digital image correlation to aluminum plates from universal testing machine and improvise the technique by the process of edge detection