Digital Interferometry Research Articles

On the Features of Inhomogeneous Residual Stress Identification Using the Digital Speckle Interferometry and the Hole-Drilling Method

On the Features of Inhomogeneous Residual Stress Identification Using the Digital Speckle Interferometry and the Hole-Drilling Method

Application of a three-laser optical digital interferometry in a thermogravitational analysis for binary and ternary mixtures

Abstract We discuss the application of the three-laser optical digital interferometry method for the determination of transport properties such as the thermodiffusion, the molecular diffusion and the Soret coefficients by the thermogravitational column technique. The primary objective of this study is to illustrate the capabilities and limitations of the method for quantifying these properties in both binary and ternary liquid mixtures from an optical viewpoint. It is concluded that the system is highly robust for the analysis of binary mixtures, with the combination of the results obtained by the three wavelengths increasing the accuracy of the measurement. The study of ternary mixtures, on the contrary, is limited to certain types of conditions. While the accuracy of a three-laser interferometer can be improved, the method may be compromised if the optical contrast factor matrices are poorly conditioned.

Highly accurate phase unwrapping algorithm applied to comparative measurement in phase-shifting digital interferometry

Highly accurate phase unwrapping algorithm applied to comparative measurement in phase-shifting digital interferometry

Dependence of refractive index of Zamzam, bottled drinking, and distilled waters on temperature and wavelength: a simple approximation using computer simulation phase shifting digital interferometry

Dependence of refractive index of Zamzam, bottled drinking, and distilled waters on temperature and wavelength: a simple approximation using computer simulation phase shifting digital interferometry

On the features of inhomogeneous residual stress identification using the digital speckle interferometry and the hole-drilling method

A phenomenological approach to the actual problem of determining the inhomogeneous residual stress-strain state in the components of high-tech engineering systems at the stages of their design and operation is presented. The approach is based on physical and mechanical methods of measuring displacements. Current physical models describe the physical regularities of the residual states attributed to changes in the structure by the interaction of defects and dislocations in the field of micro- and meso-stresses. At the same time, there are the problems of the transition to the macrolevel, the construction of multilevel models, and the conversion of these models in engineering practice. In the framework of phenomenological approaches, in the general case, the solution of this problem requires the solution of three-dimensional inverse problems of thermoelasticity. A well-known mechanical method for determining a uniform field of residual elastic stresses recommended by ASTM E837 is described. The method proposed earlier by one of the authors for determining an inhomogeneous (in the plane) field of residual elastic stresses is discussed. A method of the three-dimensional inhomogeneous residual elastic stress-strain state determination based on the experimental determination of the displacement vector components by the method of step-by-step point hole-drilling and data of digital speckle interferometry and digital image correlation is developed. The constitutive relations for the components of the displacement vector are written in the form of Volterra integral operators. The basic operator functions are the functions of four variables, i.e., the coordinates of the cylindrical system (r, θ, z) associated with the hole, and the hole depth h. A method for verification of the basic functions is presented. The problem is reduced to the determination of three displacement functions of three variables: hole radius r, h, and z. Numerical simulation of basic functions is carried out. The obtained results are consistent with the known experimental data and calculated values of the deformation on the surface depending on the depth of the hole according to the ASTM E837 Standard.

Accurate computer simulation phase-shifting digital interferometry for measurement of the optical properties of Zamzam water in the visible spectrum Nasser A. Moustafa1,2, Hasan Assaedi2, Thamer H. Albaqami2 1Physics Department, Faculty of Science, H

Accurate computer simulation phase-shifting digital interferometry for measurement of the optical properties of Zamzam water in the visible spectrum Nasser A. Moustafa1,2, Hasan Assaedi2, Thamer H. Albaqami2 1Physics Department, Faculty of Science, H

Photoacoustic speckle pattern interferometry for detecting cracks of different sizes.

A system and method for non-destructive detection of cracks of different width and depths based on digital speckle interferometry coupled with pulsed laser excitation is introduced and tested. Based on photoacoustic effect, acoustic waves are induced onto the rear of the samples by pumping a pulsed laser beam on it. The generated mechanical wave propagates from the rear surface of the sample to the front while front surface is monitored by speckle interferometry. In order to acquire information about surface deformation, the front surface is illuminated by continuous wave laser and interference are imaged onto the camera as speckle images. After processing the produced fringe patterns, it indicates the presence and location of the cracks in qualitative way. In this study, the system and method mentioned above are validated by detecting medium density fiberboard with simulated cracks. The fringe patterns from areas with or without defects are compared and discussed. Besides, the system and method to distinguish and predict cracks sizes is proposed and validated.

Wavelength-stepping algorithm for testing the thickness and front and back surfaces of optical plates with high signal-to-noise ratio.

We propose a least-squares phase-stepping algorithm (LS-PSA) consisting of only 14 steps for high-quality optical plate testing. Optical plate testing produces an infinite number of simultaneous fringe patterns due to multiple reflections. However, because of the small reflection of common optical materials, only a few simultaneous fringes have amplitudes above the measuring noise. From these fringes, only the variations of the plate's surfaces and thicknesses are of interest. To measure these plates, one must use wavelength stepping, which corresponds to phase stepping in standard digital interferometry. The designed PSA must phase demodulate a single fringe sequence and filter out the remaining temporal fringes. In the available literature, researchers have adapted PSAs to the dimensions of particular plates. As a consequence, there are as many PSAs published as different testing plate conditions. Moreover, these PSAs are designed with too many phase steps to provide detuning robustness well above the required level. Instead, we mathematically prove that a single 14-step LS-PSA can adapt to several testing setups. As is well known, this 14-step LS-PSA has a maximum signal-to-noise ratio and the highest harmonic rejection among any other 14-step PSA. Due to optical dispersion and experimental length measuring errors, the fringes may have a slight phase detuning. Using propagation error theory, we demonstrate that measuring distances with around 1% uncertainty produces a small and acceptable detuning error for the proposed 14-step LS-PSA.

Measurement of Diffusion of Atmospheric Gases in a Liquid Perfluoro Compound by Means of an Optical Technique

We report on accurate measurements of Fickian diffusion coefficients in binary mixtures consisting of hydrofluoroether (a perfluoro compound of methoxy-nonafluorobutane or HFE-7100) with dissolved atmospheric gases CO2, N2, and O2 in the limit of an infinite dilution of the gas. We show that the use of optical digital interferometry (ODI) allows the determination of diffusion coefficients of dissolved gases with relatively small standard uncertainties for this class of experiments. In addition, we illustrate the ability of an optical approach to determine the gas concentration. We compare the capacity of four mathematical models, singly used in the literature, to obtain diffusion coefficients by applying them to the processing of a large amount of experimental data. We quantify their systematic errors and standard uncertainties. The temperature behavior of the diffusion coefficients measured in the range of 10 to 40 °C is consistent with the behavior of the same gases in other solvents available in the literature.

VISUALIZACIÓN DE PROCESOS DE MICRODILATACIÓN INDUCIDOS POR LÁSER MEDIANTE EL USO DE INTERFEROMETRÍA HOLOGRÁFICA DIGITAL

This paper presents the use of digital holography interferometry applied to the study of microdilation process. The optical setup with the use of CCD cameras allowed to obtain interferograms on different study objects, whereas a localized thermal load was induced by a 5.5 W 405 nm laser. This study was done over two samples with different thermal conductivity in order to calibrate this process. The main objective of this work was to understand the thermo-mechanical response on LED-based illumination devices due to the transition in the on-off process. The results show that these kind of lamps function under mechanical stress because of the different dilation processes of each component of the device.

Analysis of Plane Displacement of Pressure Vessels with Defects

Aiming at the problem that the internal defects of the pressure vessel are not easy to detect, the out-of-plane displacement method is used to study it. The out-of-plane displacement field of circular flat plate heads with defects is obtained by the method of elastic theory analysis and compared with the finite element method to verify the accuracy of the finite element method. Based on the finite element method, the effects of vessel material, pressure load, defect shape, and defect size on the first-order out-of-plane displacement derivative are studied. The results show that the material of the container has little effect on the out-of-plane displacement. The first derivative of out-of-plane displacement increases linearly with the increase of pressure, and this relationship will not change with the increase of pressure. With the increase of defect aspect ratio, the maximum value of the first derivative of out-of-plane displacement increases gradually. When δ ˃ 9, the defect is detectable. The research results lay a theoretical foundation for the internal defect detection of pressure vessels based on digital speckle shearing interferometry.

Concurrent optical inspection to boost characterization of plastic cortical bone under mechanical deformation.

The simultaneous surface and internal measurements from a chemically modified cortical bovine bone suffering a plastic range deformation are presented. Since the bone is an anisotropic structure, its mechanical response could be modified if its organic or inorganic phases change. The latter could result in high plastic deformations, where the interferometrical signal from an optical analysis is easily de-correlated. In this work, digital holography interferometry (DHI) and Fourier domain optical coherence tomography (FD-OCT) are used to analyze the plastic range deformation of the bone under compression. The simultaneous use of these two optical methods gives information even when one of them de-correlates. The surface results retrieved with DHI show the high anisotropy of the bone as a continuously increasing displacement field map. Meanwhile, the internal information obtained with FD-OCT records larger deformations at different depths. Due to the optical phase, it is possible to complement the measurements of these two methods during the plastic deformation.

Application of optimized 2D S-transform in digital speckle interferometry phase pattern denoising

To address the problem of a large amount of noise in the phase pattern in digital speckle pattern interferometry, which seriously affects the phase reconstruction and measurement precision, a filtering method based on optimized 2D S-transform is proposed in this paper. The optimized 2D S-transform provides high signal-to-noise ratio denoising method by adding tilt factors and translation factors to keep the Gaussian window of the appropriate size at different frequency positions. The analysis results of different frequency fringe pattern denoising show that the criteria metrics indicator signal-to-noise ratio (SNR) of the results of the proposed method can reach at least 14.5435 dB and the criteria metrics peak signal-to-noise ratio (PSNR) can reach at least 19.4555 dB, which has better precision compared with the traditional method and solves the incongruity between the smoothness of low-density fringe and the integrity of high-density fringe.

Smooth Surface Defect Detection of Metal Workpiece Based on Digital Speckle Pattern Interferometry

When the existing defect detection methods are used to detect the defects on the smooth surface of metal workpieces, there is a big difference between the detection results and the actual results, and the detection accuracy is low. Therefore, the digital speckle pattern interferometry (DSPI) technology is introduced in this paper to study the design of the detection method of smooth surface defects of the metal workpieces. In this paper, the smooth surface of metal workpiece is measured by using digital speckle interferometry. The speckle on the measurement image is processed by the Laplace algorithm, and the speckled area is automatically extracted; The defects on the smooth surface of the metal workpiece are detected and located according to the speckled area. The comparative experiments show that the detection errors of the two new detection methods are less than 0.1 µm in practical application, and the detection accuracy is high, which can realize the high-precision detection of smooth surface defects of metal workpieces.

Multi-factor fusion index assessment of digital speckle interferometry images quality under dynamic environment

When digital speckle pattern interferometry (DSPI) is applied to dynamic environmental, it is often accompanied by severe speckle de-correlation, which severely limits the application and detection accuracy of DSPI. Currently, the existing speckle image quality evaluation methods only consider the contrast of the speckle image or the morphology of speckle particles, which results in these methods unapplicable to dynamic environments. For this reason, this paper proposes a new evaluation method for laser speckle image, namely dynamic multi-factor fusion index (DMFFI), which combines evaluation of four aspects: speckle stability, speckle resolution, uniformity of gray distribution, and contrast. And then, the DMFFI method is compared with the traditional evaluation methods including mean gray gradient and second order derivative of mean gray gradient. The experimental results show that DMFFI has a better ability to evaluate the quality of laser speckle images under dynamic environment compared with the traditional evaluation methods. Finally, a comparison test under different environments is conducted, and the effects of environments on the quality of speckle images are analyzed and discussed, and a guideline for speckle image acquisition in DSPI technique is proposed, which have great significance and value for the application of DSPI technique to dynamic environment detection.

Digital holographic study of corona wind-assisted evaporation of hydrocarbon from a microliter well

The present study aims to understand the evaporation dynamics of heavy hydrocarbon liquid (cyclohexane) from a circular well cavity under the influence of corona wind. The study explores the effect of corona wind on the modification of vapor phase transport and the evaporation rate from the circular well. Particle image velocimetry is used to characterize the velocity field of the corona wind generated by a needle and plate configuration. Digital holography interferometry is used to decipher the mole fraction distribution of the vapor cloud. Circular well cavities of radius 2.0, 2.5, and 4 mm are studied. The effect of corona wind on the evaporation of different sized well cavities increases with an increase in actuation voltage. The side wall of the cavities influences the distribution of the vapor cloud due to the interaction with the incoming corona wind. More than ten times enhancement of evaporation is observed at 10 kV excitation voltage setting of the corona wind generator. The corona jet-assisted evaporation can be very useful in thin-film evaporative cooling due to its simplicity in design and superior performance.

Sign-singularity solution in single-frame speckle interferometry with vortex-phase modulation

We propose a sign-singularity solution in single-shot digital speckle interferometry based on vortex-phase modulation. The vortex phase is introduced through the reference beam as variation information by a reflective liquid crystal spatial light modulator. The sign singularity is eliminated with the help of a single spiral speckle fringe pattern. To effectively obtain the deformation phase, the measurement process is specially designed on the consideration of the modulation principle of the vortex phase, which is discussed in terms of theoretical analysis and simulation results. Experiments on out-of-plane deformation measurement reveal the feasibility of the proposed method and suggest the potential in actual dynamic measurement applications.

Transport properties of n-ethylene glycol aqueous solutions with focus on triethylene glycol-water.

Soret effect and diffusion in triethylene glycol (TEG)-water mixtures were investigated as a function of concentration at 25 °C by means of optical digital interferometry, with the use of a classical Soret cell. Diffusion D, thermal diffusion DT, and Soret ST coefficients are described for the full concentration range and an analysis is made individually for TEG-water mixture and within a series of n-ethylene glycol (n-EG) aqueous systems. All coefficients decrease with increasing the concentration of TEG and n-EG. ST shows a change of signwith concentration, and this change is directly related to the ability of the n-EG molecule to establish hydrogen bonding with water. Diffusion and thermal diffusion coefficients present a plateau behavior with increasing concentration, showing the occurrence of changes in the preferential interactions in aqueous solution with concentration and meaning that, at high TEG composition, ether oxygens can be involved in the molecular interactions.

Study on automatic measurement of deformation and application by digital single-beam speckle interferometry

The purpose of the digital single-beam speckle interferometry is to extract displacement information from gray images of the specimen surface before and after deformation, which is derived primarily from the single-beam speckle interferometry. Single-beam speckle interferometry uses optical Fourier transform to extract displacement information in the frequency domain. While digital single-beam speckle interferometry uses a computer to implement optical Fourier transform after digitizing an image to extract displacement information in the frequency domain. Four phase shift images are generated by a computer and the phase shift technology is used to obtain wrapped and unwrapped fringe patterns. Furthermore, based on the fringe patterns, the direction and magnitude of the displacement can be determined automatically. The factors that may influence measurement accuracy are investigated. To validate the reliability of this method, it is used to measure displacement near the crack tip of the cracked concrete beam.

Importance of the Higher Order Terms of the Williams series expansion: Experimental Aspects and Finite Element Simulations

The study is devoted to the multi-point Williams series expansion for the crack-tip fields in isotropic linear elastic materials and methods of estimating the coefficients of higher order terms in the power expansion. It is shown that higher order terms are very important in processing of the experimental data obtained from interference – optic methods. It is demonstrated that the accurate interpretation of the experimental data requires keeping, considering and evaluating the higher order terms of the Williams expansion. A large cohort of experiments on cracked specimens from optically sensitive materials using digital photoelasticity method was performed. The interference fringe patterns obtained show that the correct description of the stress fields in the vicinity can be given if we take into account higher order terms in the asymptotic presentation of the near crack tip fields. Two interference-optical methods were used. Digital photoelasticity method and digital holography interferometry technique are applied for determination of the coefficients of the Williams series expansion. It is shown that we can restore theoretically the stress field in the vicinity of the crack tip if at least fifteen terms in the power expansion are hold. The classical over-deterministic method is used for the evaluation of the coefficients.