• Transactions of the Korean Society of Automotive Engineers
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• v.1 no.2
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• pp.125-133
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• 1993

Electronic Speckle Pattern Interferometry(ESPI) using a CW laser, a video system and image processor was applied to the rotating displacement of rigid body. ESPI require no special surface preparation or attachments and displacements between any two arbitrary points on the surface can be measured. The characteristic speckle pattern formed when imaging a scattering surface illuminated by laser light retains phase information, which can be used for interferometric measurement of surface displacement. The application of this principle to measuring in-plane displacement resolved in one direction is described, together with the novel use of television equipment to detect and process the information contained in the speckle pattern. This is faster, and more convenient and versatile than customary photographic methods.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.35-38
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• 2002

Real defects in composite structures were detected by using laser measuring system. Four types of specimens, that is, a composite laminate, a honeycomb structure, a free-edge delamination and an adhesive joint, were used to study the applicability of ESPI and Shearography to composite structures. Thermal loading method, which can easily induce the surface deformation of specimen, was used to detect defects. Experimental results show that defects in composite structures can be easily detected by ESPI and Shearography. Moreover, it shows that ESPI and Shearography can be usefully applied to the detection of defects in various kinds of composite structures.

• Nuclear Engineering and Technology
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• v.48 no.1
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• pp.259-267
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• 2016

Most manufacturing processes, including welding, create residual stresses. Residual stresses can reduce material strength and cause fractures. For estimating the reliability and aging of a welded structure, residual stresses should be evaluated as precisely as possible. Optical techniques such as holographic interferometry, electronic speckle pattern interferometry (ESPI), Moire interferometry, and shearography are noncontact means of measuring residual stresses. Among optical techniques, ESPI is typically used as a nondestructive measurement technique of in-plane displacement, such as stress and strain, and out-of-plane displacement, such as vibration and bending. In this study, ESPI was used to measure the residual stress on the welded part of butt-welded American Society for Testing and Materials (ASTM) A36 specimens with $CO_2$ welding. Four types of specimens, base metal specimen (BSP), tensile specimen including welded part (TSP), compression specimen including welded part (CSP), and annealed tensile specimen including welded part (ATSP), were tested. BSP was used to obtain the elastic modulus of a base metal. TSP and CSP were used to compare residual stresses under tensile and compressive loading conditions. ATSP was used to confirm the effect of heat treatment. Residual stresses on the welded parts of specimens were obtained from the phase map images obtained by ESPI. The results confirmed that residual stresses of welded parts can be measured by ESPI.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.120-125
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• 2007

Put Abstract text here The strain distribution measurement for wall thinned pipe bends by ESPI is presented. Defect types observed in the steel piping in the nuclear power plants (NPP) are the crack at the weld part and the wall thinning defect in the pipe bends. Especially, the wall thinning defects in the pipe bends due to the flow-accelerated corrosion (FAC) is a main type of defects observed in the carbon steel piping system. ESPI is one of the optical non-destructive testing methods and can measure the stress and the strain distribution of the object subjected by the tensile loading or the internal pressure. In this paper, the strain distribution of the wall thinned pipe bends due to the internal pressure will be measured by ESPI technique and the results are discussed. From the results, the size of the wall thinning defect can also be measured approximately.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.11
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• pp.69-74
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• 2004

This paper presents ESPI system for the measurement of thermal expansion coefficient of STS430 up to 1,00$0^{\circ}C$ . Existing methods, strain gauge and moire have the limitation of contact to object and do not supply the coefficient up to 80$0^{\circ}C$ . There needs to measure the data up to 80$0^{\circ}C$, because heat resistant materials have high melting temperature up to 1,000'E In previous studies related to thermal strain analysis, the quantitative results have not reported by ESPI at high temperature, yet. In-plane ESPI and vacuum chamber for the reduction of air turbulence and oxidation are designed for the measurement of the coefficient up to 1,00$0^{\circ}C$ and speckle correlation fringe pattern images are processed by commercial image filtering tool-smoothing, thinning and enhancement- to obtain quantitative results, which is compared with references data. The comparison shows two data are agreed within 4.1% blow $600^{\circ}C$ however, there is some difference up to $600^{\circ}C$. Also, the incremental ratio of the coefficient is changed up to 80$0^{\circ}C$ . The reason is the phase transformation of STS430 probably begins at 80$0^{\circ}C$

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.10a
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• pp.319-320
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• 2006

• Journal of Welding and Joining
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• v.20 no.2
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• pp.71-76
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• 2002

Currently knowledge of strain in welds has mainly been obtained from strain gage method; that is directly attaching the gage to the most of the material. The very flew 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. The paper is on the measurement of the strain caused by the characteristics and the temperature changes of the GTA welded zone employed with 3D ESPI system that is functionally modified through the laser ESPI system. This system may be applied the steel plate such as for the electronics, chemistry, flood instrument and electronic appliances.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.119-124
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• 2001

Currently knowledge of strain in welds has mainly been obtained form strain gaging method:; that is directly attaching most of the material to the gate. The very few non-contact method 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. The dissertation is on the measurement of the strain caused by the characteristics and the temperature changes of the TIG welded zone which is used with 3D ESPI system that is functionally modified through the laser ESPI system. This system employed the aluminum sheet-metal which are mainly used for the steel plate such as for the electronics, chemisry, food instrument and electronic appliances.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.04a
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• pp.155-161
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• 2001

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 method 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. The dissertation is on the measurement of the strain caused by the characteristics and the temperature changes of the TIG welded zone which is used with 3D ESPI system that is functionally modified through the laser ESPI system. This system employed the aluminum sheet-metal which are mainly used for the steel plate such as for the electronics, chemistry, food instrument and electronic appliances.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.10a
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• pp.267-272
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• 1993

This paper presents the performance and problems in analysis method and testing system of Electronic Speckle Pattern Interferometry (ESPI) method, in measuring two-dimensional in-plane displacement. The anyalysis result of measurement by ESPI is quite comparable to that of measurement by strain gauge method. This implieds that the method of ESPI is a very effective tool in non-contact two-dimensional in-planc strain analysis. But there is a controversal point,measurment error. This error is discussed to be affected not by ESPI method itseif, but by its analysis scheme of the interference fringe,where the first-order interpolation has been applied to the points of strain measured. In this case, it is turned out that the more errors would be occured in the large interval of fringe. so, this paper describes a computer method for drawing when the height is available only for some arbitary collection of points, the method is based on a distance-weighted, least-squares approximation technique, with the weight varying with the distance of the data points.