Electronic Speckle Interferometry Research Articles

Deep Learning in the Phase Extraction of Electronic Speckle Pattern Interferometry

Electronic speckle pattern interferometry (ESPI) is widely used in fields such as materials science, biomedical research, surface morphology analysis, and optical component inspection because of its high measurement accuracy, broad frequency range, and ease of measurement. Phase extraction is a critical stage in ESPI. However, conventional phase extraction methods exhibit problems such as low accuracy, slow processing speed, and poor generalization. With the continuous development of deep learning in image processing, the application of deep learning in phase extraction from electronic speckle interferometry images has become a critical topic of research. This paper reviews the principles and characteristics of ESPI and comprehensively analyzes the phase extraction processes for fringe patterns and wrapped phase maps. The application, advantages, and limitations of deep learning techniques in filtering, fringe skeleton line extraction, and phase unwrapping algorithms are discussed based on the representation of measurement results. Finally, this paper provides a perspective on future trends, such as the construction of physical models for electronic speckle interferometry, improvement and optimization of deep learning models, and quantitative evaluation of phase extraction quality, in this field.

Progressive technologies of electrophysical treatment for regulation of stress-strain states of elements of welded structures

The development of industry stimulates the development of modern approaches to the optimization of welded structures. The use of pulsed electromagnetic fields, plasma currents, electrodynamic forces and their combined effects is a new trend in engineering practice to improve the mechanical characteristics of metal materials and welded joints (WJ). Treatment with a pulsed electromagnetic field (TwPEMF) is a promising direction for optimizing the stress-strain states (SSS) of welded structures made of non-ferromagnetic metal materials. Using the method of electronic speckle interferometry, the effect of TwPEMF on the SSS of specimens of circumferential WJ with a thickness of δ = 1.0 mm from aluminium AMg6 alloy was investigated. Based on the original procedure using an accelerometer, the kinetics of the action of the force P of the magnetic field pressure on the residual displacements f and SSS of the specimens during their TwPEMF were investigated. TwPEMF of WJ specimens was performed without and with the use of an additional shield made of AMg6 alloy δ = 5.0 mm. It was found that the use of a shield increases the amplitude values of force P by up to two times, which is caused by an increase in the active volume of the conductive medium. At the same time, TwPEMF without and with the use of a shield contributes to the reduction of f values by 2 and 4 times, respectively, and residual SSS by 50 and 80%. On the basis of mathematical modelling, the advantages of using electrodynamic treatment (EDT) of butt WJ δ = 3.0 mm of АMg61 (1561) alloy in the TIG welding process compared to EDT at room temperature (Tk) are substantiated. According to the results of the model verification, it was proved that EDT during TIG contributes to the formation of peak values of residual compressive stresses in the weld zone by 60% more than EDT during Tk. The use of a pulsed barrier discharge (PBD), which generates a low-temperature plasma on the surface of the metal being treated, contributes to the optimization of its structure. An increase in the hardness HV of structural 25KhGNMT steel as a result of its PBD treatment from 420 to 510 units was established, which is accompanied by the dispersion of the metal microstructure.

Estimation of TiO2 thin film shift by electronic speckle interferometry

Laser scattering from the thin film surface develops self-interference speckle images, which are treated by image processing. As a result, circular fringes are formed due to the phase differences of the two laser beams overlapping after the beams splitter in the Michelson interferometer. The speckle images are captured in double stages of the sample under test, one without loading and the other with loading. Subtracting speckle images provides the similarity of Young's fringes due to the common portions of the two images. Thus the carrier frequency is negated, and posterior spatial filtering contributes only to non-common parts such as fringes. This method shows the simple experimental setup with sufficient accuracy of fringe computation for the estimation of TiO2 thin film.

Convolutional neural network optimisation to enhance ESPI fringe visibility

The use of convolutional neuronal networks (CNN) for the treatment of interferometric fringes has been introduced in recent years. In this paper, we optimize and build a CNN model, based U-NET architecture, to maximize its performance processing electronic speckle interferometry fringes (ESPI). The proposed approach is based on quick and light trainings to select the architecture parameters (network depth and kernel sizes) to maximize the performance of the neural network improving the visibility of ESPI images. To measure the performance, the structural similarity index (SSMI) will be the lead indicator, and the need for large datasets to train neural networks, unavailable for ESPI images, forces the use of a simulated ESPI image dataset along the process. This dataset is computed using Zernike polynomials to simulate local surface deformations in the specimen under test and simulated true speckle fields for the reference and object field involved in ESPI techniques.

Study of Residual Stress Fields Using Indicating Fracture and the Method of Electron Speckle Interferometry

Study of Residual Stress Fields Using Indicating Fracture and the Method of Electron Speckle Interferometry

Convolutional neural network optimisation to enhance ESPI fringe visibility

The use of convolutional neuronal networks (CNN) for the treatment of interferometric fringes has been introduced in recent years. In this paper, we optimize and build a CNN model, based U-NET architecture, to maximize its performance processing electronic speckle interferometry fringes (ESPI).

Экспериментальное определение вибрационных характеристик рабочих лопаток турбин помехоустойчивым цифровым спекл-интерферометром

The paper notes the wide possibilities and high efficiency of vibration diagnostics of parts and assemblies of power units by the method of electronic speckle interferometry (ESI), shows the feasibility of developing and improving methods for obtaining speckle interferograms of vibrating objects. A patented by the authors' scheme of a digital speckle interferometer (DSI) for determining the dynamic parameters of products is presented. The diffuse reference wave greatly simplifies its alignment, mainly the aligned channels of propagation of interfering beams determine the resistance to mechanical and thermal disturbances, and the separate beam splitter and diffuser make it easy to optimize the optical scheme for the object under study. Speckle interferograms are obtained by speckle correlation methods and a developed method for determining the contrast of the dynamic speckle pattern. It does not impose special requirements on the parameters of the video system, does not require the use of a specialized video camera, and allows, by using a rotary platform, to organize a panoramic view of the oscillatory forms of asymmetric structures. The use of this method in combination with the proposed optical scheme provides an express analysis of products in off-bench conditions. The increased noise immunity of the installation allows the determination of the spectrum of frequencies and vibration modes (SFVM) of samples under free boundary conditions, which is rarely realized in interferometry. The paper presents examples of such speckle interferograms, the expediency of obtaining which is important in the resonance study of the elastic properties of the material and vibration resonance flaw detection. The implemented software and hardware solutions increase the resolution and visibility of the band patterns; facilitate their quantitative interpretation and the extraction of numerical information on the distribution of vibration amplitudes. The area of scientific interests and the specificity of the author's developments have determined the preferential adaptation of the proposed device with a complex of software and methodological developments for vibration testing of gas turbine engine (GTE) blades.

An Experimental Study of the Vibrational Characteristics of a Diamond Circular Blade Using Electronic Speckle-Pattern Interferometry and FEM

Abstract The compact installation and technology for determining vibration characteristics by the ESPI method has been created. The experimental determination of the dynamic characteristics of a diamond circular blade with a diameter of 203.4 mm and a thickness of 1.19 mm using real-time electronic speckle interferometry is presented. 15 mode shapes of vibration were detected in the range from 100 to 5000 Hz. The program calculation of the natural frequencies and mode shapes is carried out for three values of the clamping inner diameter (42 mm, 44 mm, 46 mm). The options for calculating a disk with a rim and without a rim are considered. It is shown that the minimum mean squared error of the calculation is achieved for the values of the diameter of the disk 46 mm, 42 mm and 44 mm for the number of nodal circles 0, 1 and 2, respectively. To verify the accuracy of the interferometer, experimental, computational and analytical studies of console steel rod 200 × 22.25 × 3.78 mm in size were carried out.

Development of prototype of electronic speckle interferometry based spirometer

The paper reports the design, construction, and calibration of the prototype of a spirometer based on electronic speckle interferometry (ESPI). The conventional ESPI setup is modified by incorporating a DNM (Diaphragm-Nozzle-Mouthpiece) module comprising a metallic diaphragm, regulated airflow channel, and a mouthpiece. The exhaled air after a deep breathe is channelled to the DNM module where the diaphragm gets deformed. From the circular fringe pattern obtained by subtracting the speckled images before and after deformation of the metallic diaphragm, the radius of curvature (R) due to deformation is calculated using the principle of Newton's rings. The value of R and peak expiratory flow rate (PEFR) from the standard spirometer reading are correlated. From the 640 observations spread over the range 100 - 500 L/min in the standard spirometer, an empirical relation is set in terms of R from the scatter plot. The ESPI spirometer (ESPIS) is validated by determining the value of R corresponding to a particular PEFR from the empirical relation and also from the standard spirometer. The PEFR calculated from ESPIS matches well with the standard spirometer reading, which suggests that the system designed and constructed can be used for biomedical applications for assessing lungs’ efficiency.

Structure, Mechanical Properties, and Stressed State of Weld Joints of the Tial(Nb, Cr, Zr) Intermetallic System

Structural features, mechanical properties, and stressed state of welded joints of the TiAl system intermetallic compound (Nb, Cr, Zr) after electron-beam welding and subsequent electron-beam local heat treatment are determined. It was shown that stresses generated immediately after welding contributed to the appearance of cold cracks in the weld. Residual stresses in welded joints were determined using the technology and compact equipment based on the method of electronic speckle interferometry created at the Paton Electric Welding Institute of the National Academy of Sciences of Ukraine. It was found that after electron-beam welding, due to rapid cooling of the weld metal, phase transformations occurred, which deteriorated its mechanical characteristics. A method was developed for the local heat treatment of a welded joint by an electron beam immediately after the end of the welding process. Parameters of the local heat treatment process can significantly reduce the cooling rate, maintaining the temperature of the welded joint for 5 min at the level of 900°C. This can significantly reduce the level of residual stresses in the weld and contribute to the formation of a favorable three-component structure: γ-phase, (γ + α2)-phase and β-phase, which increases the weld ductility. A study of mechanical properties during the compression test of the weld showed that after local heat treatment, the yield strength of the weld was improved, while the tensile strength and degree of deformation under compression increased significantly. The proposed local heat treatment is effective and economically justified, which allows to reduce residual welding stresses by 30%, thus preventing the formation of cracks in welds, as well an improving structural and mechanical characteristics.

A Device for Calibration of Electronic Speckle Pattern Interferometers

A calibration device intended for metrological assurance of instruments used to measure deformations and displacements by methods of electronic speckle interferometry and shearography is developed. The optical methods presented here may be applied to different types of materials possessing rough surfaces. The proposed device reproduces stress-strain states by means of elastic deformation of the surface of a membrane through the use of a rod and leverage. Calibration of the device is performed, its transfer characteristics are investigated, and the nonlinearity of the displacement of the surface of the membrane is estimated. Results of experiments designed to measure the stress-strain state with the use of the noncontact method of shearography are presented. The phase image produced by deformation of the membrane is described and the metrological characteristics of the calibrated device are estimated. It is shown that through the use of the present calibration device it is possible to use optical methods not only for qualitative assessment of the deformation of objects of complex shape, but also for quantitative estimation of the geometric characteristics of these objects.

Accurate and efficient extraction of fringe orientation from the poor-quality ESPI fringe pattern with a convolutional neural network.

The fringe orientation is an important feature of the electronic speckle interferometry (ESPI) fringe pattern. Accurate and efficient calculation of the fringe orientation is very important for subsequent electronic speckle processing such as skeleton extraction and image filtering. To accurately and efficiently estimate fringe orientation, we propose an effective method based on a convolutional neural network. In the proposed method, the network needs clean-noisy image pairs to train and noisy images with theoretical value to test. The aligned noise-free ESPI fringe pattern orientation fields are fairly good estimations for the corresponding noise ones. After the model training is done, the other multiple ESPI fringe patterns are fed to the trained network simultaneously; the corresponding orientation results can be obtained accurately and efficiently. The advantage of using this method to extract the orientation is that the fringe orientation information can be extracted accurately and efficiently without complicated parameter adjustment. We evaluate the performance of our method via applying our method to the computer-simulated and experimentally acquired ESPI fringe patterns and comparing the results with those of three extensively used methods.

Evaluation of thermal expansion coefficient of carbon fiber reinforced composites using electronic speckle interferometry.

An optical system for measuring the coefficient of thermal expansion (CTE) of materials has been developed based on electronic speckle interferometry. In this system, the temperature can be varied from -60°C to 180°C with a Peltier device. A specific specimen geometry and an optical arrangement based on the Michelson interferometer are proposed to measure the deformation along two orthogonal axes due to temperature changes. The advantages of the system include its high sensitivity and stability over the whole range of measurement. The experimental setup and approach for estimating the CTE was validated using an Aluminum alloy. Following this validation, the system was applied for characterizing the CTE of carbon fiber reinforced composite (CFRP) laminates. For the unidirectional fiber reinforced composites, the CTE varied with fiber orientation and exhibits anisotropic behavior. By stacking the plies with specific angles and order, the CTE of a specific CFRP was constrained to a low level with minimum variation temperature. The optical system developed in this study can be applied to CTE measurement for engineering and natural materials with high accuracy.

Effect of Low-Cycle Fatigue on Fracture Mechanics Parameters According to Speckle Interferometry

Evolution of parameters of fracture mechanics at various stages of low-cycle damage is studied. The developed approach is based on elaboration of optical interference measurements of the deformation response to a small crack length increment. Three sequential symmetrical notches simulate the fatigue crack growth process across the cumulative fatigue damage zone caused by low-cycle fatigue. The values of tangential components of displacement that are measured at several points on cut edges by electronic speckle interferometry are initial experimental information. The coefficients of stress intensity (SIC) and T strains are determined on the basis of the Williams solution. Values of opening and coefficients of stress intensity (SIC) and T strains for cracks of different length with fixed values of preloading cycles Nc equal 0, 100, 1000, 1800, 2500, and 3300 are obtained. The dependences of the parameters of fracture mechanics for cracks of the fixed length on Nc are constructed.

Comparison of Electronic Speckle Laser Interferometry Hole-Drilling and X-ray Diffraction Techniques for Determination of Residual Stresses in the Heat Treated Steels

Carburizing is widely used to improve wear resistance and fatigue life of high duty machine parts. Fatigue performance of the carburized components is greatly dependent on the residual stress state in the surface layer. The aim of this paper is to measure the depth profiles of residual stresses in the carburized steels by electronic speckle laser interferometry (ESPI) assisted hole-drilling, and to compare the results with those measured by X-ray diffraction technique. To comprehend the differences in the residual stress state, the low-C steel components were carburized, and then, tempered in the range of 180–600 $$^{\circ }$$ C. Microstructural investigations and hardness measurements were also conducted. The results obtained from both techniques gave identical results, and showed that the beneficial compressive residual stresses exist at the surface after carburizing, and their magnitudes decrease with increasing tempering temperature. It was concluded that ESPI assisted hole-drilling, with optimized drilling and stress calculation parameters, is suitable for determining the residual stress state of the carburized and tempered steels.

Application of Local Current Pulses for Determination and Control of Residual Stresses

An electrode system for inducing a high density pulsed electric current (PEC) into the material for residual stresses (RS) relaxation has been proposed. A new non-destructive technology for determination of RS using electron speckle interferometry in combination with a local PEC treatment has been developed. Application of PEC at increased power parameters was investigated for control of stressed state of welded structures used in aircraft engineering. Results of practical application of the developed technologies and equipment are presented.

Some new applications of ESPI at the mechanical tests

Some new applications of a method of electronic speckle-interferometry in two different areas of measurements are presented: dilatometry and profilometry. It is shown that at dilatometric measurements by means of a method of a speckle-interferometry carrying out of measurements on objects with a surface having a complex relief is possible. Thus the information on the field of displacements can be recorded not only from the separate points belonging to opposite sides of specially made sample, but also from an essential area of the whole surface of a three-dimensional body. As an example a thermal expansion coefficient was determined for the gypsum sample in the form of a parallelepiped on the basis of displacements measurement on its lateral surface caused by temperature changing of the sample. To increase the productivity of scanning a surface relief of a body we used a combination of a multisensory scanning of a surface with the unique method of information recording in a speckle-interferogram of real time.

Technology and Equipment for Determination of Residual Stresses in Welded Structures Based on the Application of Electron Speckle-Interferometry

The technology and equipment for determination of residual stresses in the welded structures, using electron speckle-interferometry combined with the hole-drilling method (ESPI-HD), have been described. A special new approach to the conventional method of speckle-interferometry to investigate the stress gradients over the test object surface has been added. The developed equipment has been applied for determination of residual stresses in the different structures: the gas-turbine rotor, the welded shell and the structural elements with the large grain size.

Investigation of the Deformation and Fracture of Composites with the Help of Electronic Speckle Interferometry

We develop a procedure for the experimental investigations of the deformation and fracture of specimens of coal-plastic composites. A schematic diagram of the experimental installation is presented and the results of investigations are analyzed. We also show the efficiency of electronic speckle interferometry for the detection of defects in coal-plastic composites and estimation of their critical stress-strain state.

Strain Measurements within Fibre Boards. Part II: Strain Concentrations at the Crack Tip of MDF Specimens Tested by the Wedge Splitting Method

This is the second part of an article series where the mechanical and fracture mechanical properties of medium density fiberboard (MDF) were studied. While the first part of the series focused on internal bond strength and density profiles, this article discusses the fracture mechanical properties of the core layer. Fracture properties were studied with a wedge splitting setup. The critical stress intensity factors as well as the specific fracture energies were determined. Critical stress intensity factors were calculated from maximum splitting force and two-dimensional isotropic finite elements simulations of the specimen geometry. Size and shape of micro crack zone were measured with electronic laser speckle interferometry. The process zone length was approx. 5 mm. The specific fracture energy was determined to be 45.2 ± 14.4 J/m2 and the critical stress intensity factor was 0.11 ± 0.02 MPa.