Leonid Muravsky's research while affiliated with National Academy of Sciences of Ukraine and other places

In this chapter, the authors consider the Optical Metrology and Optoacoustics techniques as a powerful and versatile tool for solving problems of nondestructive evaluation of materials and structural elements. The chapter contains a summary of all subsequent six chapters. Methods for single- and dual-wavelength two- and three-step temporal phase shifting interferometry with unknown phase shifts are described in Chap. 2. In Chap. 3, it is shown that these methods can be successfully applied to determine the surface roughness parameters of materials and to study the development of the fatigue process zone in thin metal CT-specimens under cyclic loads and the fatigue macrocrack initiation. Chapter 4 is devoted to new methods of two-step phase shifting digital speckle pattern interferometry (DSPI) and correlation DSPI, as well as to application of these techniques for studying surface deformation fields in materials and detection of surface defects in metal and composite specimens. New methods of Speckle Metrology are proposed in Chap. 5. In particular, the method for extraction the unknown phase shift between speckle interferograms using sample Pearson correlation coefficient and the method of three-frame digital speckle pattern interferometry that is used in fringe projection interferometry are described in this chapter. Chapter 6 is devoted to methods for analyzing the speckle patterns of materials surfaces. In particular, the optical-digital speckle correlation and digital image correlation methods for assessment of the stress–strain state of materials, as well as the method for detection of subsurface defects excited by ultrasonic waves are considered and analyzed. The mathematical modeling of the physical phenomena of elastic wave interaction between the crack and interfaces is considered in Chap. 7. The modeling is based on the Wiener–Hopf method, which makes it possible to find the necessary characteristics of the field with a given accuracy and provide a simple physical interpretation of their properties. Thus, combining Optical Metrology and Optoacoustics with mathematical modeling of elastic waves interacting with interface defects become the powerful tools for nondestructive testing and technical diagnostics of materials and products.KeywordOptical metrologyOptoacousticsNondestructive evaluationElastic wave interaction

This chapter discusses the temporal phase shifting interferometry methods developed at the Karpenko Physico-Mechanical Institute of the NAS of Ukraine. The two-step interferometry method with an unknown phase shift of the reference wave is analyzed. In this method, the extraction of the unknown phase shift is fulfilled using the population Pearson correlation coefficient. This method allows extraction of both 3D surface nanorelief and 3D surface macrorelief, including 3D waviness and form. However, the high error level in the retrieved phase maps induced the creation of an iterative method of two-step interferometry with the unknown phase shift. To speed up the interferograms recording and remove the reference and object waves registration, a method of three-step interferometry with unknown phase shifts is proposed. In order to expand the range of surface roughness reconstruction, the two-step dual-wavelength interferometry method (TS DWIM) was elaborated. In this method, only two pairs of interferograms are generated and each pair is differed only in an arbitrary phase shift of the reference wave. Since the method does not require phase shift calibration, it is enough to use only one arbitrary phase shift to record both pairs of interferograms. The three-frame two-wavelength interferometry method with unknown phase shifts between interferograms is similar to the TS DWIM. However, it does not require additional recording of the object and reference waves, which significantly increases its performance.KeywordPhase shifting interferometryUnknown phase shiftPearson correlation coefficientDual-wavelength interferometry

In this chapter, a two-step digital speckle pattern interferometry (DSPI) method with an unknown phase shift of a reference wave is described. The method implements the recording of two speckle fringe patterns (speckle interferograms (SIs)) before deformation of the studied surface differing in an arbitrary phase shift between the reference waves and two SIs after the surface deformation differing in the same arbitrary phase shift. In this case, the phases of the two initial SIs recorded before and after surface deformation coincide. As with the phase shifting interferometry methods considered in Chap. 2, the population Pearson correlation coefficient is used to calculate the unknown phase shift. Computer simulation and experimental verification of this method confirm its reliability to restore in-plane and out-of-plane surface displacements. Beam and sheet metal specimens, as well as composite specimens containing various defects and damages were studied by using this method performed with the help of 2D and 3D speckle interferometers. The displacement fields of the studied specimens were retrieved and the hidden defects were detected. The subtractive synchronized DSPI method for detection of subsurface defects in laminated composites is also represented in this Chapter. Subsurface defects were detected using an optical-digital speckle interferometer (ODSI) and ultrasonic excitation of the studied specimen in the frequency range from 10 to 150 kHz. Experiments performed demonstrate the ability of the ODSI to detect subsurface delaminations and disbonds in laminated composite panels.KeywordsDigital speckle pattern interferometryUnknown phase shiftSurface displacementsSubsurface defect

This chapter considers the application of the developed methods of single- and dual-wavelength phase shifting interferometry (PSI) for nondestructive evaluation of materials and structural elements. Special attention is paid to the application of PSI methods to study the fatigue life of compact tension specimens (CT-specimens) made of metals or alloys with round and U-shaped notches. The performed researches include defining the fatigue process zone (FPZ) size \(d*\), evaluating the cyclic and monotonic plasticity zones geometric parameters as well as determining the site and time of fatigue crack initiation. In order to accurate determine the dimensions of the FPZ and the parameter \(d*\) for various CT-specimens of metals and alloys, a criterion for achieving the maximum surface roughness at the FPZ boundary was proposed. Experimental verification of the proposed criterion was performed using the iterative method of two-step interferometry with an unknown phase shift. To determine the site and time of a fatigue macrocrack initiation in every pixel of the retrieved surface roughness height maps, the technique for definition of the roughness increments of the surface relief area near the notch tip during the CT-specimen fatigue was developed. The evolution of the surface roughness near the notch tip in metal and alloy CT-specimens during their fatigue was estimated by increasing the arithmetic mean roughness value \(Sa\) at each pixel of the surface roughness height maps obtained after each predetermined number of load cycles, until the appearance of a fatigue macrocrack on the surface. Results of experiments confirmed the hypothesis that the fatigue macrocracks initiation is most likely occurs within the zone \(D*\), which covers the FPZ and narrow band outside it.KeywordsNondestructive evaluationCompact tension specimenFatigue process zoneSurface roughness height map

The method of three-frame digital speckle pattern interferometry (TF DSPI) with unknown phase shifts of a reference beam is presented in this chapter. In contrast to the two-step digital speckle pattern interferometry method discussed in Chap. 4, registration of the reference and object waves intensities is removed in this method. In this regard, speckle interferograms (SIs) are recorded using the integrating-bucket technique, which increases the rate of SIs registration before and after applying loads. In this method, the sample Pearson correlation coefficient can be used for extraction the unknown phase shift between SIs. The TF DSPI method was used in fringe projection interferometry for retrieval of the surface relief. During experiment several real surface areas were restored, for example, the 3D surface shape of the diamond drill, including its form and surface roughness.KeywordDigital speckle pattern interferometrySample Pearson correlation coefficientFringe projection interferometry

The simple model of the elastic SH-plane wave scattering from the interface crack in a joint of two half-spaces is considered using the Wiener–Hopf technique. Its approximate solution is obtained for the wide crack. The study focuses on the physical features that can be used to recognize interface defects. The far scattering field for arbitrary plane wave illumination angle, including sliding and critical ones, the effects of the mutual edge waves diffraction, and the lateral wave excitation are analyzed. The approximate expressions of the stress intensity factors are obtained and establish their dependencies on the problem parameters. The elastic SH-mode diffraction from the finite interface crack in the joint of the half-space and the layer is considered. The mode transformation properties, as well as the spectral and displacement field characteristics, are analyzed. The problem of the interface crack recognition is discussed.KeywordsHalf-spacesLayerInterface crackSH-wavesWiener–Hopf technique

Study of the stress–strain state of structural materials using an optical-digital speckle correlation (ODSC) method and digital image correlation (DIC) technique are discussed in this chapter. Here, we also consider a method for detecting subsurface defects in laminated composites by analyzing dynamic speckle patterns. The developed ODSC method makes it possible to narrow the peak width and increase the signal-to-noise ratio, thereby providing a more reliable restoration of displacement and deformation fields of the studied specimens near the edges and crack tips. This method uses various architectures of the joint transform correlator (JTC) to implement a cross-correlation operation between respective subsets of two speckle patterns to generate in-plane displacement and deformation vector fields. Computer simulations and experimental studies of the displacement fields of real specimens using six JTC architectures have shown that the optical-digital implementations of the JTC with adaptive median thresholding and the JTC with ring median thresholding have the smallest surface displacements errors and demonstrate the highest robustness to output noise. On the other hand, to improve the accuracy of evaluating the stress–strain state of quasi-brittle materials near the crack tip, a method for determining the components of the stress field based on the DIC technique was developed. A new method for subsurface defects detection based on generation of dynamic speckle patterns series and the use of speckle decorrelation and speckle blurring phenomenon is described. This method allows generating light responses from subsurface defects containing in laminate composite panels. The hybrid optical-digital system with a frequency swept ultrasonic excitation implementing this method makes it possible to detect real subsurface defects in composite and metal–composite elements of aircraft structures.KeywordOptical-digital speckle correlationDigital image correlationJoint transform correlatorDynamic speckle patternsSubsurface defect