The computer-aided holophotoelastic method

Brown, Gordon M.; Sullivan, J. L.

doi:10.1007/bf02410239

Cited by 45 publications

(22 citation statements)

References 22 publications

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“…Thereby, the multiple-valued fringe orders can be calculated from each normalized pattern using eq (6). Figure 3(b) shows the two fringe patterns after being normalized, adjusted and multiplied by 255.…”

Section: Digital Determination Of the Fringe Order And Resultsmentioning

confidence: 99%

A simple method for the digital determination of the photoelastic fringe order

Chen

2000

Experimental Mechanics

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ABSTRACTbA new and simple approach to the digital determination of a photoelastic fringe order using two different loads is proposed. The relationships between the intensity values of light and the isochromatic fringe orders generated from two different loads are derived. The scheme used for the automated determination of the total fringe orders of a full-field photoelastic fringe pattern is described. The usefulness of this method is demonstrated using two isochromatic fringe patterns under two different loads. Extra filters are not needed in the proposed method as in the case of the twowavelength method.KEY WORDSwPhotoelastic, two-load method, isochromatic fringe order, light field, digital determinationIn normal photoelastic analysis, half-and whole-order fringes are determined from the light-and dark-field isochromatic fringe patterns, and the fractional fringe orders are evaluated by either the Tardy method, use of a compensator, or fringe multiplication. 1 In general, the process can be very tedious and time consuming. Recent developments in photoelasticity using digital image processing techniques have made the photoelastic method more efficient and accurate. 2Approaches to the full-field digital determination of photoelastic birefringence, or fringe order, can be grouped into two categories: point-by-point analysis 3'4 using spectral contents and full-field analysis. In full-field analysis, the methods developed by Voloshin and Burger, 5 Brown and Sullivan 6 and Chen 7 are limited to half fringe orders. Patterson and Wang, 8 Sarma et al. 9 and Asundi10 developed phase-stepping algorithms to determine the phase in the modulo ~x. Unwrapping of the phase is required to obtain the total fringe order. The use of color image processing systems was reported by 11 12 Ajovalasit et al., Ramesh and Deshmukh and Hoy and Yu. 13 In these studies, the red-green-blue or hue saturation intensity values recorded by a color image processing system were used to determine the total fringe orders.Recently, Ng TM reported a method, which requires 32 isochromatic fringe patterns obtained under incremental loads, to determine the total isochromatic fringe order using Fourier transforms. Chen z5 developed a method to determine the total isochromatic fringe order from two isochro- matic fringe patterns with two different wavelengths. This method determines the full-field total fringe orders regardless of whether zero-order fringes are present. Ekman and Nurse 16 proposed a load-stepping method that enables the total isochromatic fringe order to be determined unambiguously using three incremental loads and without the input of a known fringe order obtained using an auxiliary technique. In this paper, a simple approach that uses two different loads instead of wavelengths of light is proposed to determine the total fringe order from the two isochromatic fringe patterns generated. The relationships between the intensity values of light and the fringe orders generated from two different loads are derived. Based on these relationshi...

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Section: Digital Determination Of the Fringe Order And Resultsmentioning

confidence: 99%

A simple method for the digital determination of the photoelastic fringe order

Chen

2000

Experimental Mechanics

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“…be written as (4) where I i,j (i = 0, 1, 2, 3; j = R, G, B) correspond to pixel grey levels of R-, G-and B-planes for the analyzer positions of 0, 22.5°, 45° and 67.5°, respectively. The equation for evaluating the isoclinic parameter is written as [5] (5)…”

Section: Isoclinic Parameter Estimationmentioning

confidence: 99%

“…The principal stress difference and the principal direction are presented as isochromatic and isoclinic, respectively [3]. In 1990, Brown and Sullivan [4] introduced use of polarization stepping for whole field isoclinic determination in a plane polariscope with a monochromatic light source. Petrucci [5] utilized the optical arrangement of Brown and Sullivan and replaced the monochromatic light source with a white light source.…”

Section: Introductionmentioning

confidence: 99%

Mathematical Morphology Guided Automatic Unwrapping Isoclinic Phase Map in White Light Photoelasticity

Liu¹,

Dai²

2015

Journal of the Optical Society of Korea

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By comparing the results calculated by atan() and atan2() functions, the correctly estimated region of isoclinic phase map is determined using morphological techniques. The isoclinic phase map is automatically unwrapped in the true phase range -π /2 to π /2. Demonstrations of the method on a disc and a ring under diametral compression are performed. Test results compare well with the theoretical results. Furthermore, the influences of principal stress direction and the range of isoclinic phase upon stress separation are discussed.

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“…1 Recently several methods of analyzing photoelastic fringe patterns by means of phase-measuring techniques have been presented. [2][3][4][5][6][7][8][9][10] The main problem of these techniques when they are applied to photoelasticity is that the isoclinic and isochromatic fringe patterns are completely mixed. The modulation of the isoclinic phase map depends on the isochromatics, and vice versa.…”

Section: Introductionmentioning

confidence: 99%

“…The method of Brown and Sullivan 4 can be applied only when there is half an isochromatic fringe in the field of interest; therefore the stresses must be small, the photoelastic constant of the studied material must be low, or the thickness of the sample must not be great. In general, it is difficult to obtain samples with these characteristics.…”

Section: Introductionmentioning

confidence: 99%

Phase measuring algorithm for extraction of isochromatics of photoelastic fringe patterns

Quiroga¹,

González-Cano²

1997

Appl. Opt.

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In recent years phase-measuring techniques have been applied to the problem of extracting information of photoelastic data. We present a new phase-measuring algorithm for extraction of the isochromatics of photoelastic fringe patterns. The algorithm permits the extraction of the isochromatic phase with almost no influence from the isoclinics, thus avoiding the usual problems of low-modulation areas associated with isoclinics. The isochromatic phase map obtained with this algorithm is well suited for a full separation of the stress components in a sample. The algorithm can be used with any commercial diffuse-light circular polariscope.

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The computer-aided holophotoelastic method

Cited by 45 publications

References 22 publications

A simple method for the digital determination of the photoelastic fringe order

A simple method for the digital determination of the photoelastic fringe order

Mathematical Morphology Guided Automatic Unwrapping Isoclinic Phase Map in White Light Photoelasticity

Phase measuring algorithm for extraction of isochromatics of photoelastic fringe patterns

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