Speckle Photography Technique Research Articles

Autowave Features of Plastic Deformation by Ductile Fracture

The kinetics of fracture was examined for a wide range of metallic materials. Using speckle photography technique, displacement vector fields were recorded for the deforming sample. The deformation localization is an autowave process, which manifests macroscopic inhomogeneities from yield point to necking. This involves a changeover in the autowave types: phase autowave stationary dissipative structure propagating autowave collapse of autowave. The loading curves obtained for all studied materials have a similar autowave pattern emerging at the pre-fracture stage, no matter what is crystalline or microstructural state of material. Using experimental data on the kinetics of autowave collapse, the space-time coordinates of failure can be predicted for the object under load long before symptoms of fracture are detected visually.

Response of a circular steel plate with different weld geometries subject to impact loading

The dynamic response of clamped circular steel plates was experimentally investigated under impact loading. The experiments were performed using a high energy drop weight machine with a 5 ton drop weight, which falls from a height of 0.8 m and results in a total impact energy of 40 kJ. Target plates of 10 mm thickness and 580 mm diameter were welded in three different geometrical configurations of weld elements on the lower side. The impact process was carried out using a hemispherical punch. The force was registered by strain gages on the punch. A full dynamic strain field measurement was applied on the tension side using two high speed cameras. The evaluation of the strain field was carried out with the speckle photography technique. The effect of cracks and welding on the deformation and failure behavior was studied using pre-cracked disks and plates with welded webs, welded circular discs and also with a weld seam only. The failure of the plates was registered using the high speed cameras and from the force signal. The results are analyzed and discussed regarding the behavior of the material and component under high rate loading.

Tensile plastic strain localization in single crystals of austenite steel electrolytically saturated with hydrogen

The effect of interstitial hydrogen atoms on the mechanical properties and plastic strain localization patterns in tensile tested Fe-18Cr-12Ni-2Mo single crystals of austenite steel with low stacking-fault energy has been studied using a double-exposure speckle photography technique. 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 a controlled constant cathode potential.

Relationship between burgers vectors of dislocations and plastic strain localization patterns in compression-strained 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 inhomogeneous straining in compressed sylvinite

Spatiotemporal distributions of local components of the distortion tensor of quasi-plastic materials—saliferous rocks (sylvinite)—have been studied under active compressive straining conditions using double-exposure speckle photography techniques. The strain localization patterns are presented and the features of macroscopic strain inhomogeneity are considered for inelastic behavior of the material. Results obtained for the slow wave processes in deformed saliferous rocks are compared to analogous data available for ionic crystals.

Elaboration of speckle photography techniques for plastic flow analyses

A new method for the visualization of plastic flow localization is proposed which is based on first-order statistics of laser speckle patterns. The specific features, applicability and limitations of the proposed method are considered. The setup designed for sample testing is described. The equipment developed has space and time resolution of ∼0.03 mm and ∼1 s−1, respectively, and makes feasible the real-time investigation of plastic deformation processes. The experimental evidence obtained for plastic flow localization in commercial aluminum alloy is considered.

White-light speckle photography technique applied for free convection heat transfer problems

White light speckle photography, as its laser counterpart, measures light beam deflection through a phase object, that is a transparent medium with non uniform refractive index. As the beam deflection at the solid surface is connected to the wall-temperature gradient, a convection heat transfer coefficient can be obtained. In this work, the advantages and disadvantages of using a white light speckle photography technique are evaluated using both simulation and experimental comparison with a different optical technique, namely holographic interferometry. The simulation study is proposed to analyze the sensitivity of the technique to different data reduction algorithms. Sensitivity problems, when the working fluid is air, are considered and suggestive discussions are made to further improve the sensitivity, such as modifying the experimental setup and/or introducing an image offset. Finally, some selected experimental results and a brief discussion are presented for several free convection heat transfer problems.

Theoretical analysis for surface tilt and translation detection based on speckle photography in the Fresnel domain

The theoretical and numerical analysis in this work show that both surface tilting and translational motion can be simultaneously calculated using the speckle photographic technique by recording consecutive speckle pattern images in two different Fresnel diffraction distances. A simulation example based on the proposed scheme is given to verify the method’s validity and high accuracy of the calculated motion detection. Compared with other previous works the results show that this method is efficient and easy to implement.

Preface: phys. stat. sol. (b) 245/11

Preface: phys. stat. sol. (b) 245/11

Mapping full field deformation of auxetic foams using digital speckle photography

AbstractMeasuring strain in foam presents a number of challanges. In the case of polymeric foam, the material is so soft that a conventional strain gage is not applicable because the rigidity of gage and its associated glue is stronger than the foam itself. Transducers such as clip gage, etc. may not be suitable either because the strain field may not be uniform within the gage length. Thus it is desirable that a non‐contact and full field strain measurement technique be available. In this paper we introduce a speckle photography technique that is non‐contact and can measure the full field deformation of a foam specimen. We use the natural texture of the pattern. Digitized images of the foam specimen under different loads are “compared” using a special algorithm called CASI, to yield deformation maps of the specimen. Examples of applying this technique to testing PVC foam composites are presented in the paper. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Measuring Shape and Surface Strain of Curved Objects Using Digital Speckle Photography and Gap Effect

Abstract: We explore the validity of moiré gap equation in terms of the digital speckle photography technique and show that the equation can be adapted to measure the shape or surface strain of curved objects. Examples of the utility of this approach are demonstrated using a spherical rubber ball.

EDITORIAL

This is a special issue on ‘Digital Holography and Speckle Interferometry’. The papers of this issue were presented at the symposium on ‘Digital Holography – Exploring Possibility of Using Digital Holography for Experimental Mechanics’, organised by the authors at the ‘13th International Conference on Experimental Mechanics’ (ICEM13), Alexandroupolis, Greece, 1–6 July, 2007, chaired by Emmanuel E. Gdoutos, School of Engineering, Democritus University of Thrace, Xanthi, Greece. The call for papers of the symposium is explained in the following: “Recent progress of digital holography makes it possible to measure various mechanical and geometrical parameters accurately and quickly without film development. This technique has the potential to replace other current techniques in the near future. This session focuses on new developments and techniques of digital holography as well as their applications to various engineering problems, industrial fields and real structures. The contributions on similar techniques such as moiré, conventional holography, speckle interferometry and related techniques will also be presented in this symposium. Please join this symposium if you have interests in digital holography and related techniques.” The history of digital holographic interferometry is not so long. Schnars and Jüptner developed direct recording of Fresnel holograms with a CCD sensor in 1993. Yamaguchi and Zhang developed phase-shifting digital holography in 1997. The system is very simple, capable of whole-field analysis and high process speed. The system is similar to the system of speckle interferometry, which is widely used in the market. It is valuable to compare these techniques. This gave impetus for the publication of this special issue on ‘Digital Holography and Speckle Interferometry’. This issue contains five papers on digital holography and three papers on speckle interferometry. The first paper on the digital holography by I. Yamaguchi et al. deals with the measurement of both position and shape of an object using dual wavelengths. Yamaguchi developed the phase-shifting digital holography. In this paper they also proposed a new method to measure object shapes using both the amplitude and phase of the averaged conjugated product of complex amplitudes recorded before and after wavelength shift of a laser diode. The position determination is related to the fourth paper by M. Fujigaki et al. The second paper by G. Sheoran et al. proposes shape measurement using dual index immersion. It also proposes speckle noise reduction using 5 by 5 median filtering which is compared with the third paper. The third paper by Y. Morimoto et al. presents the effect of window size on accuracy and spatial resolution in windowed phase-shifting digital holographic interferometry. The accuracy is of the sub-nanometre level by decreasing the effect of speckle noise, though the spatial resolution becomes worse according to the number of windows. The fourth paper by M. Fujigaki et al. proposes a method to determine the reconstruction distance using the standard deviation of the intensity on the reconstructed image. It also proposes a method to obtain the orientation of the specimen. The fifth paper by Y. Zhang et al. concerns with the terahertz digital holography for the future. It provides useful applications to biology and medical sciences. The first paper on speckle interferometry by A. Moreau et al. deals with vibration measurement by time average speckle interferometry and by Doppler vibrating. The second paper by G. Kalogiannakis et al. investigates the feasibility of shearographic imaging of acoustic cross-modulation. It was motivated by the latest advances in nonlinear laser Doppler vibrometry and nonlinear ultrasonic, The third paper by F. Chiang et al. presents a new approach to 3D surface countering and surface strain measurement using speckle gap effect. Although it is not an ordinary speckle interferometry, the digital speckle photography technique applied to a flat surface is extended to 3D surface countering and strain measurement of a human heart. In addition to the above eight papers, a plenary paper of ICEM13 on ‘Three-Dimensional Displacement Analysis by Windowed Phase-Shifting Digital Holographic Interferometry’ by Y. Morimoto et al. should be mentioned. This paper extends the method of a windowed phase-shifting digital holographic interferometry mentioned in the third paper of digital holography to analyse three-dimensional displacement components in a microscope. This paper was published in the January 2008 issue of Strain. Digital holography and speckle interferometry are useful methods for measurement of whole-field displacement and strain distributions in ordinary rough surface of structures. They are superior of strain gauges, which measure point strains. Use of whole-field methods requires standardization. The symposium on ‘Digital Holography and Speckle Interferometry’ was initially organized with Dr. Satoru Yoneyama of Aoyama Gakuin University. The authors would like to acknowledge his support. Unfortunately, he could not attend the symposium because of his movement to a new position.

Features of plastic strain localization at the yield plateau in Hadfield steel single crystals

Spatiotemporal distributions of local components of the plastic distortion tensor in Hadfield steel single crystals oriented for single twinning have been studied under active tensile straining conditions using the double-exposure speckle photography technique. Features of the macroscopically inhomogeneous strain localization at the yield plateau are considered. Relations between local components of the plastic distortion tensor in the zone of strain localization are analyzed.

Non-parametric identification of the non-homogeneous stress in high strain-rate uni-axial experiments

Stress and strain homogeneity, in tested samples, is a crucial assumption during a dynamic test. Whenever this assumption is true, the conventional recovery of the mean strain and stress is valid. However, when the stress and strain fields in the sample are not homogeneous, more sophisticated treatment must be considered. Inverse problem techniques are then proposed. Nevertheless, they may yield a non-physical result. In this paper, a non-parametric solution to the problem of non-homogeneity in dynamic tests is presented. The stress field is deduced from the displacement field measured via a Digital Speckle Photography (DSP) technique and a force boundary condition.

Strain localization in compressed ZrO2(Y2O3) ceramics

Spatiotemporal distributions of local components of the distortion tensor of a nonplastic material—yttria partially stabilized tetragonal zirconia (YTZ) ceramics—have been studied under active compressive straining conditions using double-exposure speckle photography techniques. The strain localization patterns are presented and the features of macroscopic strain inhomogeneity in the elastic state of YTZ ceramics are considered.

Multiple-aperture speckle method applied to local displacement measurements

The goal of this work is to analyze the measurement capability of the modified speckle photography technique that uses different multiple aperture pupils in a multiple exposure scheme. In particular, the rotation case is considered. A point-wise analysis procedure is utilized to obtain the fringes required to access to the local displacement measurements. The proposed arrangement allows simultaneous displaying in the Fourier plane several fringes system each one associated with different rotations. We experimentally verified that the local displacement measurements can be determined with a high precision and accuracy.

Shear coupling effects on stress and strain distributions in wood subjected to transverse compression

The mechanical behaviour of a wood board subjected to transverse compression is relevant to the performance of glulam beams and solid wood structures. The wood material can be described as polar orthotropic, due to the annual ring structure and to the differences in moduli in different directions in the radial–tangential plane. Strain measurements are performed on single wood boards using a whole-field digital speckle photography technique. Finite element analysis is performed and compared with experimental data. Good agreement in terms of strain fields and apparent moduli is observed between predictions and data. The experimental data show strong variations in local strain due to the polar orthotropic behaviour of wood in this plane, and the extremely low value for shear modulus G rt as compared with the other moduli. This leads to shear coupling effects resulting in large local shear deformation and correspondingly low effective stiffness under transverse global loading.

Optical measurement techniques for high Reynolds number train investigations

This article reports on experimental aerodynamic investigations on a generic high-speed train configuration performed within two different wind tunnels. Both wind tunnels are specialized facilities for high Reynolds number investigations and offer low turbulence levels. The wind tunnels are the cryogenic wind tunnel located in Cologne (KKK) and in the high-pressure wind tunnel located in Gottingen (HDG). Both facilities are part of the German–Dutch wind tunnel association (DNW). The adaptation and application of three optical measurement techniques for such high Reynolds number investigations is described in the article. The optical methods are: Particle Image Velocimetry for the measurement of velocity fields, Background Oriented Schlieren technique for density gradient measurements, and a white light Digital Speckle Photography technique for model deformation monitoring.

Displacements measurement in a building model using the speckle photography technique

The use of reduced scale models in civil engineering has made it possible to study large structures such as buildings. Using non-destructive optical techniques such as double-exposure speckle photography, extremely valuable results can be obtained, where mathematical methods are often not very exact. This work studies the model of an eighteen-storey building in which displacements can be measured at each storey of each view. It also presents a comparison of the displacement field, which was obtained with the Finite Element Method.

Single-axis combined shearography and digital speckle photography instrument for full surface strain characterization

Full characterization of the surface strain requires the mea- surement of six displacement gradient components of the surface strain tensor. The out-of-plane displacement gradient component may be di- rectly measured using the full-field speckle interferometry technique of shearography, but to fully characterize the surface strain using shearog- raphy, a minimum of three illumination, or viewing, directions are re- quired. The image processing technique of digital speckle photography (DSP) is sensitive to in-plane displacement for normal collinear illumina- tion and viewing, with the displacement gradient components obtained by differentiation. A combination of shearography and digital speckle photography is used to perform full characterization of the surface strain using a single illumination and viewing direction. The increase in com- plexity compared with a standard single-channel shearography system lies predominantly in the additional image processing requirements. Digi- tal speckle photography image processing is performed using the optical flow field technique and the advantages of this technique compared with correlation are discussed. The design of the instrument is described and full surface strain measurements made with the system are presented.