Electronic Speckle Pattern Interferometry System Research Articles

Measuring thickness change of transparent plate by electronic speckle pattern interferometry and digital image correlation

The thickness change of transparent plates was measured by electronic speckle pattern interferometry (ESPI) method and digital image correlation (DIC) method. An out-of-plane ESPI system was developed based on the Michelson interferometer, and a new thickness measurement method was designed, which is on the basis of Snell's law of refraction and DIC. The main principles and experimental procedures of these two methods were presented. The thickness change of polymethyl specimens under uniaxial tensile loading were measured by the optical techniques and compared with each other. The results reveal that the data obtained with DIC method achieve better linearity than ESPI.

Residual Stress Determination Using Cross-Slitting and Dual-Axis ESPI

Hole-drilling and Electronic Speckle Pattern Interferometry (ESPI) are used to measure residual stresses in metal specimens. The slitting method is chosen as an alternative to the more commonly used hole-drilling method because it involves less material removal and leaves large areas of highly deformed material available to be measured. However the conventional single-slitting method is sensitive only to the stress component perpendicular to the slit direction, and thus has a strong directional bias. Conventional ESPI has a similar bias because it responds to surface displacements in a specific sensitivity direction. In this paper, a novel cross-slitting method with dual-axis ESPI measurements is proposed to address both directional biases. Cross-slitting is introduced as a means of releasing all in-plane stress components. The dual-axis ESPI system uses diagonal-mirror and shutter devices to provide surface displacement measurements in orthogonal in-plane directions. The combination of the cross-slit and dual-axis measurement gives isotropic sensitivity to the in-plane residual stress components. Experimental measurements are described that illustrate the capability and effectiveness of the cross-slitting/ESPI technique.

Observing Deformation and Fracture of Rock with Speckle Patterns

The high resolution technique of electronic speckle pattern interferometry (ESPI) can be very useful in determining deformation of laboratory specimens and identifying initiation of failure. The in-plane ESPI theory is described and the fringe pattern of the processed ESPI image is analyzed to determine deformation and crack opening displacement. Fringes on the ESPI image represent lines of equal intensity, which relate to surface displacement. An ESPI system was constructed and calibrated for measuring uni-directional displacements. Several types of the experiments, such as uniaxial compression and fracture testing, were conducted to demonstrate the utility of ESPI.

Determination of thickness and elastic constants of aluminum plates from full-field wavelength measurements of single-mode narrowband Lamb waves

A method based on fitting the theoretical dispersion curves of Lamb waves to experimental data is presented to determine the thickness and two independent elastic constants of aluminum plates a few millimeters thick. The waves are generated by means of the wedge method using a narrowband source, selecting the wedge angle and the acoustic frequency f so that mainly one mode is excited. A self-developed pulsed electronic speckle pattern interferometry system renders a two dimensional map of the out-of-plane acoustic displacement field at the plate surface, which allows an accurate measurement of the acoustic wavelength lambda(1). For any mode, the relation between lambda(1) and f depends on the three unknown parameters, so at least three experimental measurements (lambda(1i),f(i)) with different frequencies and/or different modes are required to calculate them. The suitability of different Lamb modes to determine each parameter when the others are known is studied, as well as the conditions that the experimental set of values must fulfill to calculate all three parameters. Numerous Lamb modes at different frequencies are generated in each plate, and a fitting is made based on the minimization of the error function, resulting in an accuracy better than 1%.

3-D ESPI법을 이용한 단점용접부의 변형률 측정

Currently knowledge of strain in welds has mainly been obtained from strain gaging method: that is directly attaching most of the material to the gage. The very few non-contact methods are still in the early stage. One of the non-contact methods is by the use of the laser that has high-level of the accuracy for the measurement, and this laser also has excellent characteristics on which many studies for its applications are focused throughout the many fields. A method of study is on the measurement of the strain caused by the characteristics of the spot welded zone which is used with 3-D ESPI system that is functionally modified through the laser ESPI(Electronic Speckle Pattern Interferometry) system. This system employed the SGCC 1.2t which are mainly used for the steel plate such as automobile, structure, building material and electronic appliances.

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.

Acquisition of full-field strain distributions on ovine fracture callus cross-sections with electronic speckle pattern interferometry

This study evaluated the feasibility of assessing continuous strain distributions on fracture callus cross-sections with an electronic speckle pattern interferometry (ESPI) system. Mid-sagittal callus cross-sections were harvested from ovine tibiae. One low stiffness (LS) specimen and one high stiffness (HS) specimen were selected to evaluate the feasibility for strain acquisition over a range of callus properties. The HS specimen was 147 times stiffer in compression than the LS specimen. ESPI captured continuous strain distributions on both specimens. Peak strain was located adjacent to cortical boundaries in the osteotomy gap. In response to 5 N compression, peak compressive strain of 5.8% in the LS specimen was over two orders of magnitude higher than peak compressive strain of 0.013% in the HS specimen. In conclusion, ESPI-based strain acquisition enables reproducible quantification of strain distributions on callus cross-sections. Such measurements may support validation of computational models and evaluation of experimental results in fracture healing research.

1239 POSTER Radiodermatitis affects more than a half of cancer patients submitted to radiotherapy, hence skin support measures mainly with urea are now widely recommended. The ESPI project

Objective: To examine the in-plane and out-of-plane response of human dentine to thermal loads in real time.Methods: An Electronic Speckle Pattern Interferometry (ESPI) system sensitive to both the in-plane and out-of-plane displacements was configured and used in conjunction with an advanced fringe processing technique. Specimens were prepared from freshly extracted lower central incisor teeth and were separately mounted on a thermal block to apply thermal loads from room temperature (25°C) to 60°C. The real time speckle patterns were acquired using a digital camera. These digital fringe patterns were subjected to further image processing to enhance the quality of fringes. The resultant images were later analyzed to study the out-of-plane and in-plane displacement gradients in the facio-lingual plane of the dentine.Results: The out-of-plane deformations were observed in the plane perpendicular to the long axis of the tooth, while the in-plane deformations occurred in the plane parallel to the long axis of the tooth.Conclusion: The ESPI analysis revealed whole-field and distinct thermal response in human dentine in-plane and out-of-plane. The cervical dentine experienced distinct and conspicuous displacement to the temperature changes.

OS12-1-3 Development of Dynamic Deformation Measurement Method using Electronic Speckle Pattern Interferometry

Electronic speckle pattern interferometry (ESPI) which is one of full-field measurement methods is technique for measuring out-of-plane and in-plane displacements of a diffusely scattering object. This paper describes a measurement method of the dynamic phenomena such as thermal deformation and creep deformation, etc. which is based on temporal phase analysis at the single pixel of the temporal speckle pattern image. The speckle pattern images are obtained by using ESPI system combined with a one-axis stage, which generated a temporal phase carrier. A Fast Fourier transform method is used to calculate the phase map and both magnitude and direction of deformation are obtained. As an application, deflections of a cantilever beam and out-of-plane deformation of a driving electronic package are measured using this method.

Elastic properties of adhesive polymers. I. Polymer films by means of electronic speckle pattern interferometry

AbstractThe elastic modulus and Poisson's ratio of seven different polymers frequently used as wood adhesives and/or matrix polymers in wood‐ and natural‐fibre‐reinforced composites, respectively, were determined by means of tensile tests. Specimen deformation during testing was measured by means of a mechanical extensometer and an electronic speckle pattern interferometry system, respectively. The results from both methods show an excellent correlation for the elastic modulus. The elastic moduli of the studied polymers cover a wide range from 0.47 GPa for polyurethane to 6.3 GPa for melamine–urea–formaldehyde, whereas Poisson's ratios show less variability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3936–3939, 2007

A Study on Measurement of Welding Residual Stress Using ESPI System

In this study, an experimental method has been studied to measure the residual stresses on a specimen with I-groove weldment. The specimens were extracted from I-groove weldment which was joined by SAW (Submerged Arc Welding) with CO2 shield gas. A FEA (Finite Element Analysis) model was developed for the estimation of the residual stresses for the specimen. Measurements were carried out using ESPI(Electronic Speckle Pattern Interferometry) system which can measure the strain distribution on the surface of specimen. The residual stresses were estimated by the value of strain measured by ESPI system. Strain gages were added to evaluate the accuracy of ESPI system. In addition, a three-dimensional FE model was used to estimate the residual stresses generated by the welding procedure. A thermal elasto-plastic analysis was performed by the FEA. The stresses measured by the experiments were compared with the results of FEA. Also, discussed are the difference and agreement between the stresses obtained by experiments and FEA, respectively.

Effect of Local Strain on Low Cycle Fatigue Measured by ESPI System

Low cycle fatigue cracks are mainly detected at discontinuous welded locations with high stresses under repeated cyclic static loads due to cargo loading and unloading. Theoretical and analytical methods have been used to estimate the local stress and strain, which affect the prediction of fatigue life, but these methods have difficulties considering stress concentration at notched locations and complicated material behavior of welded joints or heat affected zones. Electronic speckle pattern interferometry(ESPI) system is a nondestructive and non-contact measurement system, which can provide relatively accurate full field strain at critical positions such as welded zones and structurally discontinuous locations. In this study, local strain was measured by ESPI system at the welded cruciform joint, and then low cycle fatigue test was performed. Effect of local strain on low cycle fatigue life was examined by using the strain value measured by ESPI. In order to verify the relations between local strains and fatigue lives, after theoretical local strains and stresses were calculated by using Neuber’s rule, the measured local strains corresponding the experimental fatigue lives were compared with the results of Neuber’s rule and established codes of the British standard and DNV curve.

Design of Phase-shifting ESPI System for 3D Deformation Measurement

It designs the phase-shifting ESPI(electronic speckle pattern interferometry) systems for 3D deformation measurement. The first design applies common optics, single laser source and two PZTs to introduce five testing beams, in which two beams are phase-shifted. By this system, in-plane and out-plane deformation can be tested by switching the projecting beams and 3D deformation of the object can be calculated. The testing is closely dynamic. The second design applies a one to five beam-splitting fiber to simply and compact the system. In this system, the laser beam is divided into five sub-beams as the testing rays. On the heads of two sub-fibers, PZTs are attached to introduce phase-shifting. By analysis, the system error by this phase-shifting mode can be omitted. In this system, the in-plane and out-plane deformation are tested by the same switching mode as the first design, which means that the dynamic characteristic is determined by the switching speed. It describes the two designs and analyzes briefly.

Three-dimensional displacement measurement by using reversed phase-shifting electronic speckle pattern interferometry

A method for three-dimensional (3D) displacement measurement by separating out-of-plane displacement from in-plane displacement is presented. A reference beam is added to a dual-beam symmetric illumination electronic speckle pattern interferometry (ESPI) system and shared by the two illuminations. The test object is illuminated by the two object beams, respectively. Two phase maps, which include out-of-plane and in-plane displacement, can be obtained by phase-shifting techniques. In order to decrease electronic noises in the phase maps, one of the phase maps is calculated by the reversed phase-shifting method presented. By using inverse phase distribution, out-of-plane displacement can be easily separated from in-plane displacement by subtraction and can greatly decrease electronic noises. The principle of the method is presented and proved by a typical three-point bending experiment. Experimental results are offered.

Non-destructive testing with double-pulsed laser ESPI

Electronic Speckle Pattern Interferometry (ESPI) is an attractive method for non-destructive testing. There are two ESPI working modes: addition ESPI mode and subtraction ESPI mode. Overcoming the disadvantage of the subtraction ESPI mode, which strictly requires that there is no movement among the optical parts in an ESPI system, in the addition ESPI mode, the movement of a measured material is 'frozen' with a short-pulsed laser. As a result, the addition ESPI mode is believed to be feasible in adverse conditions where the subtraction ESPI mode is inapplicable. Based on the theory of double-pulsed laser ESPI, the interference fringe contrast and a simulation method are introduced in this paper. In the simulation, a compound material with a flaw is interrogated. Due to the fact that a result can only be obtained when the interference fringe passes through a special electronic filter, the filter applied to the experiment needs delicate fabrication. Its quality and central frequency influence the final interference fringe result. Therefore, a series of the filters are designed such as band-pass and high-pass filters, with a specific method applied. Subsequently, the result of the simulation for NDT with double-pulsed ESPI method is acquired and analysed.

ESPI System을 이용하여 측정한 국부 변형률이 저사이클 피로수명에 미치는 영향에 관한 연구

Low cycle fatigue cracks are mainly detected at discontinuous welded locations with high stresses under repeated cyclic static loads due to cargo leading and unloading. Theoretical and analytical methods have been used for evaluation of local stress and strain which have an effect on a prediction of fatigue life, but those have difficulties of considering stress concentration at notched location and complicated material behavior of welded joint or heat affected zone. Electronic speckle pattern interferometry(ESPI) system is nondestructive and non-contact measurement system which can get the relatively accurate full field strain at critical positions such as welded zone and structural discontinuous location. In this study, local strain was measured on welded cruciform joint by ESPI system and then low cycle fatigue test was performed. Effect of local strain on low cycle fatigue life was examined by measured values using ESPI system. Moreover, experimental fatigue life was compared with established S-N curves using theoretical local strain and stress calculated by Neuber's rule.

ESPIシステムの溶接への適用

Behavior of displacement at welded joints during welding is an important factor for reliability of the joints. But in-situ measurement of the behavior is very difficult because contact method such as strain gauge is inapplicable in high temperature. In this study, ESPI (Electronic speckle pattern interferometry) system is applied to in-situ measurement of displacement increment distribution in SUS304 steel, 9%Ni steel, and low transformation temperature welding (LTTW) material during GTA welding. Qualitative tendency of measured results agrees with numerical simulation. Expansion behavior of phase-transformation is detected in 9%Ni steel and LTTW material during cooling. Moreover ESPI system enabled measurement of displacement increment at uranami bead surface and surrounding area of molten pool. These results show that ESPI system is applicable to measurement of displacement distribution at welded joints during welding process.

An Experimental Study on Fatigue Crack Propagation under Cyclic Loading with Multiple Overloads

For many fatigue-critical parts of machines and structures, the load history under operating conditions generally involves variable amplitude loading rather than constant amplitude loading. An accurate prediction of fatigue crack propagation life under variable amplitude loading requires a thorough evaluation of the load interaction effects. In this study, fatigue tests under both constant and variable amplitude loading were carried out to investigate the overload effects on fatigue crack propagation of the notched specimens. Strain distributions around the crack tip before and after a tensile overloading were measured using the ESPI (Electronic Speckle Pattern Interferometry) system. The size of the plastic zone was determined from the measured strain distributions. The study proposes a crack propagation prediction model that incorporates the overload ratio effect. A comparative work for the overload ratio effect demonstrated that the prediction by the proposed model was in good agreement with the experimental results. The prediction of fatigue crack propagation including multiple overloads with the proposed model show also a good agreement with test results.

122 小領域におけるナノメータオーダーの振動挙動を計測可能とする光ファイバーを用いた位相変調ESPIシステムの開発(生体工学,2.学術講演)

122 小領域におけるナノメータオーダーの振動挙動を計測可能とする光ファイバーを用いた位相変調ESPIシステムの開発(生体工学,2.学術講演)

Full field and microregion deformation measurement of thin films using electronic speckle pattern interferometry and array microindentation marker method

Thin films now are widely used in micro devices and structures, such as MEMS, electronic packaging, micro sensors, and so on. Their performances highly affect the reliability of the devices. Therefore, it is important to investigate the deformation and the failure mechanism of thin films. In this paper, we present two experimental methods to measure the mechanical properties of thin films. In the first method, a double-field-of-view electronic speckle pattern interferometry system (ESPI) and an integrated deformation and load measurement system are employed, which allows in situ and real-time measurements of full-field deformations of the thin films and microforces under uniaxial tensile test. In the second method, the array microindentation markers were indented on the surface of the thin film using a nanoindenter and the microregion deformations of the tested thin films were measured. In the proposed methods, the tested thin films can be made of metals, oxide ceramics, and multi-layer composites of thickness from several tens micrometers to less than a micron, and the tensile loads from 88 μN to 15 N for the first method or up to 100 N to the second one. The underlying principle of the methods and the experimental set-ups are presented. The deformations of Au and Au/Cr multi-layer films, and the pure Ni films are measured. The performance of the methods and the testing systems are also discussed.