• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.3
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• pp.213-220
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• 2000

The method of photoelasticity allows one to obtain principal stress differences and principal stress directions in a photoelastic model. In the classical approach, the photoelastic parameters are measured manually point by point. The previous methods require much time and skill in the identification and measurement of photoelastic data. Fringe phase shifting method has been recently developed and widely used to measure and analyze fringe data in photo-mechanics. This paper presents the test results of photoelastic fringe phase shifting technique for the stress analysis of a circular disk under compression and an edge-cracked plate subjected to tensile load. The technique used here requires four phase stepped photoelastic images obtained from a circular polariscope by rotating the analyzer at $0^{\circ}$, $45^{\circ}$, $90^{\circ}$ and $135^{\circ}$. Experimental results are compared with those or FEM. Good agreement between the results can be observed. However, some error may be included if the technique is used to general direction which is not parallel to isoclinic fringe.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.10
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• pp.2577-2584
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• 1994

A method of digital image processing thechnique, which can multiply and sharpen isochromatic fringes in photoelasticity on both occasions, is developed. To test the method, photoelastic fringe patterns of a disk compressed by two diametrically opposite cocentrated loads are simulated and these patterns are processed to yield sharpened lines. The method is then aplied to measurement of residual stresses in glass bar. The procedure is proved to be capable of extraction sharpened lines accurately from photoelastic multiplied fringes, and yields good experimental results consistently and precisely.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.3
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• pp.200-206
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• 1999

This paper describes the stress analysis of a curved beam by using photoelasticity. In order to measure accurate isochromatic fringe orders at certain locations. fringes are doubled and sharpened by digital image processing. After fringe multiplication and sharpening. fringe orders can be read as a quarter order interval (N=0, 1/4, 2/4, 3/4,...). The results obtained from photoelastic experiment are compared with those calculated by using theory. Two results are agreed well even though there are some scatter bands with maximum 8 percent for the results of photoelastic measurements and theoretical calculation. Difference may be occurred due to the slight misalignment of the direction to which axial load is applied in photoelastic experiment. It is confirmed that accurate measurement of stress distribution can be possible by using the techniques of fringe multiplication and sharpening in photoelasticity.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.6
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• pp.1485-1492
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• 2015

This paper proposes a double frequency method using FTP(Fourier Transform Profilometry) in fringe projection techniques for 3D measurement systems. In fringe projection techniques, fringe pattern images are projected and captured, and then object is measured by analysing phase. PMP(Phase Measuring Profilometry) for analysing phase provides high-resolution and is robust to object's reflection and background intensities. However, the measurement range is narrow due to 2π ambiguity. In order to overcome this problem, a double frequency method is often used. This method can widen the range of measurement while maintaining the high-resolution, but the measurement time is taken about twice due to grab 2 times number of images. The proposed double frequency method using FTP requires an additional image for resolving 2π ambiguity. The proposed method effectively reduces the measurement time while maintaining the same accuracy.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.1C
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• pp.51-58
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• 2007

The purpose of this paper is to find an efficient encryption scheme for digital holograms (fringe patterns) with low encryption cost. Therefore, we introduced several encryption attempts in both hologram-domain and frequency-domain (both DCT-domain and DWT-domain) on the bases of the results from analyzing the properties of the coefficients in each domain. To effectively hide the image information, 25%, 1.5625%, and 0.0244% of the original fringe pattern need to be encrypted for hologram-domain scheme, DWT-domain scheme, and DCT-domain scheme, respectively. Consequently the DCT-domain scheme was the most efficient and it is caused by the fact that the ability for DCT to concentrate the energy of a given 2-dimensional image into a small area is the best. The encryption schemes and the analyses in this paper are expected to be used effectively on the researches on encryption and others for digital holograms.

• Journal of the Korean Society for Precision Engineering
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• v.10 no.3
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• pp.220-230
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• 1993

Photoelastic isochromatic fringes related to the difference of principal stresses have some bandwidth whose light intensities are not constant and asymmetrical in experimental images. Hence, it is difficult to measure fringe order accurately at a data point by visual observation. In this study, a method of fringe sharpening, which can extract shapened lines from both full-and half-order fringes by digital image processing, is developed. To test the method, various simple photelastic fringe patterns are simulated and their images are processed to yield sharpened lines. The method is then applied to general problems such as images of a circular disk compressed by diametrically concentrated loads and a circular cylinder sybject to internal pressure. The procedure is proved to be capable of extracting sharpened lines accurately from photoelastic isochromatic fringes.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.4
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• pp.346-351
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• 2008

• Electronics and Telecommunications Trends
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• v.27 no.6
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• pp.21-30
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• 2012

디지털 홀로그래픽 프린팅(Digital Holographic Printing: DHP)은 종래의 아날로그 방식이 아닌 디지털 기록 방식으로 이미지 또는 간섭무늬를 홀로그래픽 매질에 기록하여 정지 화상에 대한 홀로그램 상을 재생하는 홀로그래픽 기술이다. 현재 개발 중인 스테레오그램(stereogram) 기반 DHP는 수직/수평 방향의 시차(parallax)를 갖는 초다시점 영상을 매질에 촘촘히 기록하여 마치 아날로그 홀로그램과 같이 자연스럽게 3차원 상을 재현하는 기술이다. 하지만 이러한 기술은 과도기적인 성격의 기술로 향후에는 위상 정보를 포함하고 있는 홀로그램인 프린지 패턴(fringe pattern)을 직접 기록함으로써 보다 더 자연스러운 형태의 홀로그램 상을 재생할 수 있는 기술이 추가적으로 개발될 것으로 예상된다. 그러므로 본고에서는 Zebra Imaging사에서 개발한 스테레오그램 기반의 DHP 기술과 Nihon 대학이 시도한 프린지 기반의 DHP 기술 동향을 다루고자 한다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.11
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• pp.2355-2364
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• 2012

Recently, the novel loop-up table(N-LUT) method to solve the tremendous memory problem of the conventional look-up table (LUT) method as well as to increase the generation speed of hologram patterns has been proposed. But, as the resolution of an input 3-D object is enhanced, the number of object points to be calculated for generation of its hologram pattern also increases, which results in a sharp increase of the computation time. Therefore, in this paper, a new approach for fast generation of the hologram pattern of 3-D object images is proposed by using the block redundancy feature of 3-D object images and the N-LUT method. Experimental results show that in the proposed method the number of object points and the overall computation time have been reduced by 43.3 % and 47.9 %, respectively compared to those of the conventional method for the case of the $5{\times}5$ block size. These good experimental results finally confirm the feasibility of the proposed method.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.1
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• pp.27-33
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• 2012

Photoelasticity is a technique of experimental methods and has been widely used in various domains of engineering to determine the stress distribution of structures. Without complicated mathematical formulation, this technique can conveniently provide a fairly accurate whole-field stress analysis for a mechanical structure. Here, stress distribution around an inclined crack tip of finite-width plate is studied by 8-step phase-shifting method. This method is a kind of photoelastic phase-shifting techniques and can be used for the determination of the phase values of isochromatics and isoclinics. According to stress-optic law, the stress distribution could be obtained from fringe patterns. The results obtained by polariscope arrangement combined with 8-step method and ABAQUS FEM simulations are compared with each other. Good agreement between them shows that 8-step phase-shifting method is reliable and can be used for determination of stress by experiment.