Electronic Speckle Pattern Interferometry Method Research Articles

Experimental verification of full-field accuracy in stereo-DIC based on the ESPI method.

This paper proposes a method to merge stereo-digital image correlation (DIC) and electronic speckle pattern interferometry (ESPI) data by camera calibration. The proposed method is employed to verify the accuracy of full-field out-of-plate displacements measured by stereo-DIC in a cantilever beam test. The mean absolute error and the root mean square error (RMSE) of the full-field displacement measured by four-megapixel cameras are 0.849 µm and 1.08 µm at 60 mm field of view, respectively, and the RMSE of the central area is 0.615 µm. The errors are not uniformly distributed because of the imperfect calibration. When the lenses are changed and the field of view reaches 120 mm, the RMSE is 1.48 µm with uniform distribution. These accuracies could be traced back to the laser wavelength to confirm the stereo-DIC data. The proposed method can be used not only to verify the full-field measurement accuracy of DIC but also to determine the rigid-body displacement for ESPI with a high-precision stereo-DIC. Thus, the displacement vector can be obtained. Furthermore, it can unify the coordinate of multiple ESPI systems to achieve a large range of high-precision three-dimensional deformation measurements.

Comparison Between Surface and Near-Surface Residual Stress Measurement Techniques Using a Standard Four-Point-Bend Specimen

BackgroundDetermination of near-surface residual stresses is challenging for the available measurement techniques due to their limitations. These are often either beyond reach or associated with significant uncertainties.ObjectiveThis study describes a critical comparison between three methods of surface and near-surface residual stress measurements, including x-ray diffraction (XRD) and two incremental central hole-drilling techniques one based on strain-gauge rosette and the other based on electronic speckle pattern interferometry (ESPI).MethodsThese measurements were performed on standard four-point-bend beams of steel loaded to known nominal stresses, according to the ASTM standard. These were to evaluate the sensitivity of different techniques to the variation in the nominal stress, and their associated uncertainties.ResultsThe XRD data showed very good correlations with the surface nominal stress, and with superb repeatability and small uncertainties. The results of the ESPI based hole-drilling technique were also in a good agreement with the XRD data and the expected nominal stress. However, those obtained by the strain gauge rosette based hole-drilling technique were not matching well with the data obtained by the other techniques nor with the nominal stress. This was found to be due to the generation of extensive compressive residual stress during surface preparation for strain gauge installation.ConclusionThe ESPI method is proven to be the most suitable hole-drilling technique for measuring near-surface residual stresses within distances close to the surface that are beyond the penetration depth of x-ray and below the resolution of the strain gauge rosette based hole-drilling method.

Efficient ESPI method to identify vibration characteristics of transparent films.

Electronic speckle pattern interferometry (ESPI) has been frequently used to study vibration characteristics of engineering structures. However, efficient ESPI methods for identifying the vibration characteristics of transparent membranes are rarely reported. A convenient approach to determine the resonant frequencies and the vibration modes of transparent films is proposed. A quasi-common-path ESPI (QCP-ESPI) is developed to detect out-of-plane deformation and visualize vibrational modes of a vibrating transparent diaphragm. An amplitude-modulation-based method is proposed for quick and accurate determining resonance of oscillating objects during frequency scanning. Experimental performances demonstrate the feasibility and efficiency of the QCP-ESPI and amplitude-modulation-based methods for determining the resonant frequency and vibration modes of transparent objects.

Dynamic ESPI Evaluation of Deformation and Fracture Mechanism of 7075 Aluminum Alloy.

The deformation and fracture mechanism in 7075 aluminum alloy is discussed based on a field theoretical approach. A pair of peak-aged and overaged plate specimens are prepared under the respective precipitation conditions, and their plastic deformation behaviors are visualized with two-dimensional electronic speckle pattern interferometry (ESPI). The in-plane velocity field caused by monotonic tensile loading is monitored continuously via the contour analysis method of ESPI. In the plastic regime, the peak-aged specimen exhibits a macroscopically uniform deformation behavior, while the annealed specimen exhibits non-uniform deformation characterized by a localized shear band. The occurrence of the shear band is explained by the transition of the material’s elastic resistive mechanism from the longitudinal force dominant to shear force dominant mode. The shear force is interpreted as the frictional force that drives mobile dislocations along the shear band. The dynamic behavior of the shear band is explained as representing the motion of a solitary wave. The observed decrease in the solitary wave’s velocity is accounted for by the change in the acoustic impedance with the advancement of plastic deformation.

Constructing an electronic speckle pattern interferometry system for visualizing operational deflection shapes

Electronic speckle pattern interferometry (ESPI) is an effective optical method for visualizing operational deflection shapes of vibrating objects. The time-averaged ESPI method is used to show how an object vibrates when driven sinusoidally. We describe the construction of our system, which we built using standard optical components. Such a system is appropriate for both research and educational purposes. We will discuss the lessons learned by constructing several ESPI systems.

Three-step electronic speckle pattern interferometry method with arbitrary phase shifts of reference wave

Three-step electronic speckle pattern interferometry method with arbitrary phase shifts of reference wave

Novel ESPI Measurement Prototype for Analyzing Biological Samples from Cell Culture Technique

An essential part of cell cultivation via cell culture technology is the determination and monitoring of culture parameters. Such parameters refer to the vitality or mutual mutations of the cell culture, while the actual number of living cells in each batch indicates the correct growth rate rather than stagnation or an overgrowth of the cell culture. Today such parameters are determined by applying light microscopy methods or by staining specific constituents of the cells. Commonly such methods are a stressful procedure for the studied cells. Most applied dyes are toxic over a certain period of time and thus they are used in low concentrations only when necessary. Within this work a new kind of measurement device prototype was designed to address these problems. This device is based on the Electronic Speckle Pattern Interferometry (ESPI). ESPI is an optical high-resolution method combined with a photonic analysis system capable of analyzing cellular deformations and oscillations. In this approach the combination of a greatly modified microscope together with ESPI method is presented. The apparatus allows the determination of cellular deformation (i) at very high magnifications, (ii) with high lateral resolution. Furthermore the system studies (iii) contact free, (iv) in vitro cells, in a non-invasive and non-destructive way. A co-developed cultivation system allows monitoring the culture parameters in real time minimizing the stress for the cell culture. Since no additional substances are needed, the presented prototype is automated to a large extent and can be operated by a special control-and regulation system (CRS) based on a microcontroller development board (Arduino Mega).

Investigations of the transverse vibration characteristics of piezoceramic circular plates with V-notches

This article pertains to experimental validation of the study presented in a previous paper by the same authors , in which the transverse vibration characteristics of piezoceramic circular plates with V-notches were investigated theoretically using Ritz’s method incorporating defined equivalent constants. For experimental measurement, two optical methods – amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) and laser Doppler vibrometry (LDV) – were employed to conceptualize the analytical results. The AF-ESPI method demonstrates the advantages of combining high fringe sensitivity and noise reduction, which are achieved using the time-averaged and subtraction electronic speckle pattern interferometry methods, respectively. Both vibration mode shapes and resonant frequencies of V-notched piezoceramic plates were obtained using the AF-ESPI method; in addition, the resonant frequencies were also determined quickly using the LDV method. By varying the corner angles and notch–depth ratios, various types of piezoceramic plate (V-notched, sectorial, semicircular, segmented, and sharp-notched) were used for experimental measurements. Numerical calculations were performed using the finite element method, and the results were compared with the experimental measurements and theoretical predictions. It was shown that the resonant frequencies and mode shapes obtained using the two experimental methods agreed fairly closely with the theoretical and numerical results.

The Comparisson between LBP and SQI Methods in the Surface Roughness Measurement Using ESPI Method

Surface roughness measurement using direct contact methods raises several issues, for examples stylus wear and size limitation problems. Furthermore non-contact methods are proposed to solve these problems. One of them is Electronic Speckle Pattern Interferometry (ESPI), which use Helium-Neon (He - Ne) as laser light source. A speckle pattern is produced by scattered light on the surface of the measuring object due to the interference of laser beams, and it will be captured by Charge Coupled Device (CCD) camera. Afterwards Linear Binary Pattern (LBP) and Self Quotient Image (SQI) methods are used to reduce illumination effect in the captured image. The average gray-level from the previous process will be converted into a surface roughness value by gray level to surface roughness conversion formulation. It is obtained from correlation value between gray level and a set of standard roughness. The standard roughness value range is start from 0,05 μm to 12,5 μm. It is measured from five different final machining process, which are flat lapping, grinding, horizontal milling, and vertical milling. As verification, the results of ESPI method will be compared with the result of direct contact tools using Mitutoyo Surftest 301 and 401.

The Knowledge Acquired by Using of Optical Methods by Strain Fields Investigation

These days are preferably used contactless optical methods for experimental investigation of strains and displacements, which give some information on whole investigated surface. In this contribution the optical systems working on electronic speckle pattern interferometry (ESPI) principle and digital image correlation (DIC) method are described. By using of ESPI and DIC methods the displacements and strains fields on chosen types of specimens are determined. Pros and cons of particular methods and influence of various factors on reached results accuracy are compared. There are also mentioned the possibilities of using of optical methods in application of devices on authors department.

Two approaches to the blind phase shift extraction for two-step electronic speckle pattern interferometry

A two-step electronic speckle pattern interferometry (ESPI) method with blind phase shift of a reference wave, in which the phase shift extraction is fulfilled by using both a correlation and a discrete Fourier transform (DFT) approaches, is presented here. In the correlation approach, the blind phase shift is calculated via the correlation coefficient between two similar speckle interferograms (SI) differing only by the reference wave phase shift. The DFT approach is based on the blind phase shift extraction from frequency components of SI Fourier spectra. Comparative analysis of these approaches has testified to their high performance. Moreover, it is shown that the correlation approach is more preferable for blind phase shift extraction from SIs with a rough surface than from interferograms with a smooth surface; hence, it is more convenient for ESPI than for phase-shifting interferometry. In addition, this approach provides a lesser level of systematic error of extracted phase shift in comparison with the DFT. The correlation approach was used for experimental definition of Poisson’s ratio for duralumin constructional material by the two-step ESPI method.

ESPI for the Piezoelectric Constant Measurement

This paper describes the principle of measuring small displacement of the object by using electronic speckle pattern interferometry (ESPI). The piezoelectric constant of Lead Lanthanum Zironate Titanate(PLZT) piezoelectric ceramics is determined with ESPI. Compared with other methods , this method is simpler and is operated more easily.The accuracies of ESPI and electrical method are almost at the same level, which shows that it is avalible to measure piezoelectric constant.

Micro- and macro deformation measurement by extension of correlation technique

In this work, we present the implementation of Electronic Speckle Pattern Interferometry (ESPI), Digital Speckle Photography (DSP) and Digital Image Correlation (DIC) as complementary techniques to measure in-plane micro and macro displacement. The main advantage of ESPI is its great sensitivity to small displacements (smaller than the size of the speckle). However, the contrast of fringes in this technique is severely affected by de-correlation effects when the in-plane displacement exceeds the size of the speckle. To eliminate the de-correlation effects, we use the DSP technique. It is possible to generate artificial speckles, usually bigger than those generated by means of illumination of the sample with laser light. By combining DSP and DIC the displacement field can be obtained when the ESPI method cannot be applied due to image de-correlation. The experimental results show that the combination of these techniques is useful to analyze deformations over a wider range.

DIC-Based Surface Motion Correction for ESPI Measurements

Electronic Speckle Pattern Interferometry (ESPI) provides a sensitive technique for measuring surface deformations. The technique involves comparison of the speckle phase angles within surface images measured before and after material deformation. This phase angle comparison requires that the speckle positions be consistent in all images. A lateral shift between image sets of just one pixel substantially degrades ESPI measurements, while a shift of two or more pixels typically causes complete decorrelation and compromises the measurement entirely. To prevent such rigid body motions, the specimen and the optical system must be rigidly fixed. This requirement typically impedes use of the ESPI method in applications outside laboratories or where it is necessary to remove the specimen from the optical setup between ESPI measurements. Here, Digital Image Correlation (DIC) is used to track speckle motion caused by specimen displacement between ESPI phase stepped image sets. The measured image set can then be mathematically shifted to restore the original speckle locations, thereby recorrelating the ESPI measurement. Examples are presented where ESPI measurements are successfully made with specimen shifts over 60 pixels.

Experimental and numerical investigations of vibration characteristics for parallel-type and series-type triple-layered piezoceramic bimorphs

The dynamic characteristics of parallel-type and series-type piezoelectric bimorphs are analyzed in this study. The transverse (out-of-plane) and planar (in-plane) vibrations for piezoceramic bimorphs in normal and abnormal connections are investigated experimentally by 2 noncontact optical techniques and impedance analyzer. Electronic speckle pattern interferometry (ESPI) is the major experimental technique for measuring the resonant frequency and corresponding vibration mode shape. Out-of-plane and in-plane vibrations of piezoelectric bimorphs at resonance are obtained by a self-arranged ESPI optical setup. The laser Doppler vibrometer (LDV) is a point-wise measurement technique for out-of-plane displacement and is used to determine the out-of-plane resonant frequencies. The impedance analyzer is used to measure the resonant frequencies for in-plane motions. It is noted from the experimental results that the out-of-plane modes are the dominant motion for the normal connection and only symmetric vibration mode shapes can be excited. The in-plane motions are large enough to be measured using the ESPI method for normal connections. The in-plane resonant modes are observed for parallel-type piezoelectric bimorph in parallel connections; however, the in-plane mode shapes are similar to the out-of-plane mode shapes for the series-type piezoelectric bimorph in series connection. Hence, the particle motions of the piezoelectric bimorph at resonance are essentially 3-D for the normal connection. It is interesting to note that both symmetric and asymmetric out-of-plane vibration mode shapes can be excited with large applied voltage but no in-plane motion is observed for the abnormal connection. In addition to experimental methods, numerical computations based on the finite element method are used to verify the experimental results. Good agreements of the resonant frequencies and mode shapes are obtained for experimental and numerical results.

Spatially Resolved Materials Property Data From a Uniaxial Cross-Weld Tensile Test

Application of electronic speckle pattern interferometry (ESPI) is described to measure the spatial variation in monotonic tensile stress-strain properties along “cross-weld” specimens machined from a stainless steel three-pass welded plate. The technique, which could also be done with digital image correlation, was applied to quantify how the material 0.2%, 1%, 2%, 5%, 10%, and 20% proof stress varied with distance from the center-line of the weldment for parent and weld material associated with the first and final passes. The stress-strain curves measured by the ESPI method correlated closely with stress-strain data measured using conventional test specimens. The measured results are consistent with the hypothesis that thermo-mechanical cycles associated with the welding process work harden previously deposited (single-pass) weld metal and the surrounding parent material. The stress-strain response of the heat affected zone adjacent to the first weld pass is consistent with an accumulated (equivalent monotonic) plastic strain of 6.5% and that of the first pass weld bead was consistent with an accumulated plastic strain of approximately 4% greater than the state of the final pass weld metal.

Optical investigation of diffusion of levofloxacin mesylate in agarose hydrogel

Real-time electronic speckle pattern interferometry method has been applied to study the diffusion behavior of levofloxacin mesylate (MSALVFX) in agarose hydrogel. The results show that the diffusivity of solute decreases with the increase of concentration of agarose and adapts to Kohlrausch's law. Furthermore, Amsden's model, based on the retardance effect associated with polymer chain flexibility, was employed to simulate the diffusion behavior. The consistent results suggest that the retardance effect dominates the diffusion process of MSALFVX in hydrogel; moreover, polymer chain flexibility greatly affects drug transport within the polymer matrix.

Portable electronic speckle interferometry device for the damages measurements in veneered wood artworks

Deterioration of wood artwork is often connected to mechanical material degradation that starts on microscopic scales. Insight into decay mechanisms can be obtained by monitoring surface deformation and displacement fields. This paper presents the application of Electronic Speckle Pattern Interferometry (ESPI) to detect damages of wood samples invisible into the surface. Two different damages were created on the model simulating cabinet wood panels: delaminating and worm galleries, all defects are invisible by naked eye. All optical arrangements of speckle interferometry are divided in two types of fundamentally different speckle patterns: photographic speckle patterns, which contain information only about the light wave amplitude, and holographic speckle patterns, which contain both phase and amplitude information for comparison potentialities of two approaches we present the results obtained by thermography and ESPI investigations of the wood panel under test. The fiber-optic ESPI set-up based on a He–Ne CW laser has been developed and used for studying the possibility to reveal the invisible damages and determine their locations, sizes and shapes. For this end the two digital holograms of the test object, corresponding to the non-heated and heated states of object, are captured at two video frames of the CCD camera, and then processed in a PC. The resulted fringe pattern has the information about the damages. The purpose of the work was determining the possibilities of ESPI method in revealing of different kinds of invisible damages. Our results indicate that developed variant ESPI system is well adapted to reveal the under surface damages in veneered wood samples. The set-up may be used in out-of-laboratory conditions and without severe anti-vibration preoccupations. The comparison of results obtained by developed ESPI system and thermo camera shows the higher sensitivity the ESPI system. The thermo camera does not indicate the presence of under surface damages like delaminating and worm galleries in contrast with ESPI system which is well adapted to extract information about these defects. Applying ESPI set-up we have determined the presence of different kind of damages located under surface: big delaminating and little worm galleries. The developed ESPI set-up is capable of predicting the position, shape and size of revealed damages. The results presented in this paper show that the ESPI technique is a promising tool for testing the wood artworks.

Computational modelling of thermal impact welded PEEK/steel single lap tensile specimens

In this contribution, an interfacial traction-separation-law based on elastoplasticity with Lemaitre-type-damage is applied. Related constitutive equations are decoupled with respect to a local orthonormal frame such that the stress–strain response is controlled independently in these directions. The constitutive traction-separation-law is applied to the simulation of thermal impact welded (TIW) single lap tensile specimens. The specimens consist of two steel substrates and a PEEK foil which is laid in between the joining zone. Tensile tests and electronic speckle pattern interferometry (ESPI) are consulted to verify the simulations. To provide brief background information, a short review on the manufacturing method of TIW and the method of ESPI is included. The comparisons of measurements and computations show that one-dimensional integral data given by global force–displacement-curves can be simulated sufficiently accurate. Two-dimensional data given by displacement and strain fields reveal good similarities between measurements and computations.

Use of dynamic electronic speckle pattern interferometry with the Hilbert transform method to investigate thermal expansion of a joint material

A dynamic electronic speckle pattern interferometry method is applied to investigate thermal expansion of a joint material (ceramic-stainless steel) as a practical industrial object. The speckle interference signal is considered in the temporal domain and the phase is analyzed by the Hilbert transform method. Errors caused by the bias and modulation variations over the phase values are first examined by numerical simulation. Two experiments are performed with in-plane and out-of-plane sensitive systems to study the 3D deformation field thoroughly. The deformation field showed clearly the difference between the thermal expansions of the stainless steel and ceramic. It was also revealed that the boundary of materials and its vicinity suffer very large thermal strain due to the significantly large difference in the linear coefficient of thermal expansions.