Review of Electronic Speckle Pattern Interferometry(ESPI) for Three Dimensional Displacement Measurement

Three dimensional（3D） displacements, which can be translated further into 3D strain, are key parameters tor design, manufacturing and quality control. Using different optical setups, phase-shift methods, and algorithms, several different 3D electronic speckle pattern interferometry（ESPl） systems for displacement and strain measurements have been achieved and commercialized. This paper provides a review of the recent developments in ESPI systems for 3D displacement and strain measurement. After an overview of the fundamentals of ESP! theory, temporal phase-shift, and spatial phase-shift techniques, 3D deformation measurements by the temporal phase-shift ESPI system, which is suited well for static measurement, and by the spatial phase-shift ESPI system, which is particularly useful for dynamic measurement, are discussed. For each method, the basic theory, a brief derivation and different optical layouts are presented. The state of art application, potential and limitation of the ESPI systems are shown and demonstrated.

New speckle pattern interferometry for precise in situ deformation measurements

A new electronic speckle pattern interferometry method is proposed to realize in situ deformation measurements.The feature of the method is the combination of a high-speed camera and multiple laser Doppler vibrometers(LDVs)for synchronous measurements.The high-speed camera is used to record and select effective interferograms,while the LDVs are used to measure the rigid body displacement caused by vibrations.A series of effective interferograms with known shifted phase values are obtained to calculate the deformation phase.The experimental results show that the method performs well in measuring static and dynamic deformations with high accuracy in vibrating environments.

Measurement of out-of-plane deformation of curved objects with digital speckle pattern interferometry

Digital speckle pattern interferometry （DSPI） is a high-precision deformation t technique for planar objects. However, for curved objects, the three-dimensional （3D） shape information is needed in order to obtain correct deformation measurement in DSPI. Thus, combined shape and deformation measurement techniques of DSPI have been proposed. However, the current techniques are either complex in setup or complicated in operation. Furthermore, the operations of some techniques are too slow for real-time measurement. In this work, we propose a DSPI technique for both 3D shape and out-of-plane deformation measurement. Compared with current techniques, the proposed technique is simple in both setup and operation and is capable of fast deformation measurement. Theoretical analysis and experiments are performed. For a cylinder surface with an arch height of 9 mm, the error of out-of-plane deformation measurement is less than 0.15 μm. The effectiveness of the proposed scheme is verified.

Simultaneous 2D in-plane deformation measurement using electronic speckle pattern interferometry with double phase modulations

Electronic speckle pattern interferometry（ESPI） and digital speckle pattern interferometry are wellestablished non-contact measurement methods. They have been widely used to carry out precise deformation mapping. However, the simultaneous two-dimensional（2D） or three-dimensional（3D） deformation measurements using ESPI with phase shifting usually involve complicated and slow equipment. In this Letter, we solve these issues by proposing a modified ESPI system based on double phase modulations with only one laser and one camera. In-plane normal and shear strains are obtained with good quality. This system can also be developed to measure 3D deformation, and it has the potential to carry out faster measurements with a highspeed camera.

Measuring Vibration of Body with Speckle Interferometry

Speckle interferometry is an efficient method to analyze a vibration. In certain conditions, this technique has some outstanding advantage, and need not strict shock--proof condition, compared with the holographic method for measuring vibration. Therefore,it is suitable to analyze a vibration with a large amplitude.Real-time interferometry is a rapid and simple method for measuring vibration of a body, gives speckle pattern containing amplitude distribution of body-surface. By means of time-averaged method, the speckle pattern is recorded in Fourier transform plane, or vibration lines are seen directly with eyes, so as to analyze efficiently amplitude, phase, and model of a vibration. This paper deduces the intensity distribution function with real-time method, and gives experimental demonstration of vibration body-the vibration lines with different frequencies.

Variability on Raman Shift to Stress Coefficient of Porous Silicon

Porous silicon film is a capillary-like medium, which is able to reveal different meso-elastic modulus with porosity. During the preparation of porous silicon samples, the capillary force is a non-classic force related to the liquid evaporation which directly influences the evolution of residual stress. In this study, a non-linear relation of Raman shift to stress coefficient and the porosity is obtained from the elastic modulus measured with nano-indentation by Bellet et al. [J. Appl. Phys. 60 （1996） 3772] Dynamic capillarity during the drying process of porous silicon is investigated using micro-Raman spectroscopy, and the results reveal that the residual stress resulted from the capillarity increased rapidly. Indeed, the dynamic capillarity has a close relationship with a great deal of micro-pore structures of the porous silicon.

Experimental Investigation of Polycrystalline Material Deformation Based on a Grain Scale

We propose an experimental approach for investigation of the polycrystalline deformation behaviour at a grain scale. The technique is characterized by the joint application of micro material testing systems and the intragranular deformation analysis methods, It is attempting to map the deformation evolution at grain scale during the elastic and plastic deformations of polycrystalline specimens.

A sequence pulse counting method for shape measurement in dual-beam speckle interferometry

A temporal approach to fast shape measurement is presented.In principle,the rotational object method is used in combination with the sequence pulse counting method (SPCM) to determine the height of the object through calculating the related phase.Two specimens are tested to demonstrate the validity of the approach.One is an object covered by a Chinese character (tea) with a height variety of 0.3 mm,and the other is an object surface with a relatively large fluctuation of 3.5 mm.The experimental results are compared with mechanical measurements.An axis shifting method is also proposed to determine shapes with relatively large fluctuations.Effects of such parameters on the height measurement as incident angle of the dual light beams,tilting angle of the object,and azimuth angle of the measured point are discussed as well.

New multiplexed system for synchronous measurement of out-of-plane deformation and two orthogonal slopes

We propose a novel system for synchronous measurement of out-of-plane deformation and two orthogonal slopes using a single camera. The linearly polarized reference beam introduced by an optical fiber interferes with the unpolarized object beam to measure the out-of-plane deformation. A modified Mach–Zehnder interferometer is used to measure the two orthogonal slopes of the out-of-plane deformation. One of the object beams of the Mach–Zehnder interferometer is an unpolarized beam, and the other object beam is split into two orthogonal linearly polarized object beams by a polarizing prism. The two beams are orthogonally polarized. Hence, they will not interfere with each other. The two polarized beams respectively interfere with the unpolarized beam to simultaneously measure the two orthogonal slopes of the out-of-plane deformation. In addition, the imaging lens and apertures are respectively placed in three optical paths to independently control the carrier frequencies and shearing amounts. The effectiveness of this method can be proved by measuring two pressure-loaded circular plates.

Image processing of ESPI based on measurement the welding dynamic displacement fields

A dual-beam electronic speckle pattern interferometry (ESPI) system was adopted to get speckle patterns for the measurement of welding dynamic displacement fields. The mathematical model of this system was described, based on which methods of the ESPI pattern image processing were discussed. Gray transformation and histogram equalization were used to enhance the contrast of speckle patterns. A discrete cosine image processing method was carried out and an exponent low-pass filter was chosen to reduce multiplicative noise in speckle patterns. Speckle grain noise can be eliminated effectively after these processes.

Digital Speckle Technique Applied to Flow Visualization

Digital speckle technique uses a laser, a CCD camera, and digital processing to generate interference fringes at the television framing rate. Its most obvious advantage is that neither darkroom facilities nor photographic wet chemical processing is required. In addition, it can be used in harsh engineering environments. This paper discusses the strengths and weaknesses of three digital speckle methodologies. (1) Digital speckle pattern interferometry (DSPI) uses an optical polarization phase shifter for visualization and measurement of the density field in a flow field. (2) Digital shearing speckle interferometry (DSSI) utilizes speckle\|shearing interferometry in addition to optical polarization phase shifting. (3) Digital speckle photography (DSP) with computer reconstruction. The discussion describes the concepts, the principles and the experimental arrangements with some experimental results. The investigation shows that these three digital speckle techniques provide an excellent method for visualizing flow fields and for measuring density distributions in fluid mechanics and thermal flows.

Pitting Kinetics of 304 Stainless Steel Using ESPI Detection Technique

The electronic speckle pattern interferometer was used to in situ monitor the pitting corrosion of 304 stainless steel at anodic polarization. The pitting current and pitting current density of a single pit were obtained. The pit growth was controlled by the corrosion products diffusion. The pit morphology was observed by a scanning electron microscope. The results showed that the pit was dish shaped, and the geometric parameters and pit growth time conformed to the function of Y = A ＋ B1t ＋ B2t2 ＋ B3t3.

Shearography and its applications-a chronological review

This paper presents the activities in the field of shearography in chronological order and highlights the great potential of this holographic measurement technology.After a brief introduction,the basic theory of shearography is presented.Shear devices,phase-shift arrangements,and multiplexed shearography systems are described.Finally,the application areas where shearography has been accepted and successfully used as a tool are presented.

A DEVELOPED FULL-FIELD FEM ANALYSIS COMBINED WITH ESPI FOR THE INVESTIGATION OF DEFECT EVOLUTION IN POLYMER FILMS

A full-field finite element method （FEM） analysis combined with electronic speckle pattern interferometry （ESPI） measurement was developed to investigate defect evolution in polymer films. Different from the previous reports, which only compare the ESPI experimental and FEM simulated results at several points or lines, herein the full-field FEM results were exported, subtracted with a continuous distribution. By choosing proper parameters and number of substeps, the simulated and experimental results showed excellent correspondence. Furthermore, the displacement fields vertical to the tensional direction were also presented, and the strain field was preliminarily evaluated. The current method of combination of ESPI and FEM allows for capturing the experimental fringe maps to validate and optimize FEM results simulated, and would give a higher security to structural and mechanical analysis of polymeric materials.