Completely automated determination of two-dimensional photoelastic parameters using load stepping

Ekman, M. J.; Nurse, A. D.

doi:10.1117/1.601694

Cited by 30 publications

(18 citation statements)

References 7 publications

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“…This modulation is due to the isoclinic ambiguity such that α relative to σ 1 produces the σ 1 − σ 2 isochromatic regions and α relative to σ 2 produces the σ 2 − σ 1 isochromatic regions. The isochromatic phase may be demodulated by a load stepping method, which takes advantage of the change in δ at each point over three successive incremental loads [18,19], by an automated digital technique that identifies and corrects the ambiguous zones before analysis [20], or by unwrapping the isoclinic angle [2]. The load stepping method is not useful in an experiment that is sensitive to incremental loads as is the case with fracture.…”

Section: Photoelasticitymentioning

confidence: 98%

Phase Shifting Full-Field Interferometric Methods for Determination of In-Plane Tensorial Stress

et al. 2009

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A new method that combines phase shifting photoelasticity and transmission Coherent Gradient Sensing (CGS) is developed to determine the tensorial stress field in thin plates of photoelastic materials. A six step phase shifting photoelasticity method determines principal stress directions and the difference of principal stresses. The transmission CGS method utilizes a standard four step phase shifting method to measure the x and y first derivatives of the sum of principal stresses. These stress derivatives are numerically integrated using a weighted preconditioned conjugate gradient (PCG) algorithm, which is also used for the phase unwrapping of the photoelastic and CGS phases. With full-field measurement of the sum and difference of principal stresses, the principal stresses may be separated, followed by the Cartesian and polar coordinate stresses using the principal stress directions. The method is demonstrated for a compressed polycarbonate plate with a side V-shaped notch. The experimental stress fields compare well with theoretical stress fields derived from Williams solution for a thin plate with an angular corner.

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Section: Photoelasticitymentioning

confidence: 98%

Phase Shifting Full-Field Interferometric Methods for Determination of In-Plane Tensorial Stress

et al. 2009

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“…However, we can apply the mathematical scheme used for load stepping in Ref. 10 equivalently to a three-wavelength approach simply by changing the role of the loads and the wavelengths, thus enabling analysis of a frozen-stressed sample.…”

Section: Introductionmentioning

confidence: 99%

“…So a small amount of extra interpolation can be necessary. A related approach is so-called load stepping, 10 in which, instead of using different wavelengths, we analyze the sample by using different loads, in this way making the regions of low-modulation move to select the isoclinic parameter in a manner similar to that of the three-wavelength method. Again, many images are needed ͑nine images in Ref.…”

Section: Introductionmentioning

confidence: 99%

“…For that goal phase-measuring techniques have been applied. [1][2][3][4][5][6][7][8][9][10] For a complete isoclinic-isochromatic phase recovery many images are required ͑three or four for isoclinics and six-eight for isochromatics͒ for performing the complete analysis and separating the fringe patterns. This is a drawback in some situations: For instance, in the method of threedimensional stress analysis of Plouzenec et al, 11 it is difficult to obtain the necessary number of images to apply phase-shifting techniques; however, it is well known that, in the phase-shifting technique, the fewer the images used, the more sensitive the corresponding method is to errors such as nonsinusoidal patterns, nonlinearity in the detector, errors in the phase shifts, and background correction.…”

Section: Introductionmentioning

confidence: 99%

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Separation of isoclinics and isochromatics from photoelastic data with a regularized phase-tracking technique

Quiroga¹,

González-Cano²

2000

Appl. Opt.

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We present the application of a regularization algorithm to the processing of photoelastic fringe patterns. The method used is a modified regularized phase-tracking ͑RPT͒ algorithm applied to phase-shifted images. In particular, we present an algorithm for isoclinic-isochromatic separation that uses only five images. In the case of isoclinics the method can deal with problems associated with modulation of isochromatics and with isotropic points by means of a modified cost functional. With respect to the isochromatics the problems associated with regions of high fringe density are solved in a robust way by the unmodified RPT algorithm by use of the modulation information. The performance of the method is discussed, and experimental results are presented.

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“…Although in this paper we are dealing with 2D photoelasticity, it should be noted that 3D states of stress in transparent bodies can also be studied by this technique. 1 For the analysis of photoelastic fringe patterns, various techniques have been applied, such as phase shifting, 2 Fourier transforms, 3 spectral content analysis, 4 tricolor image analysis, 5 red-blue-green ͑RGB͒ calibration, 6,7 load stepping, 8 and regularization techniques. 9,10 One of the objectives in these techniques is the use of the smallest possible number of images.…”

Section: Introductionmentioning

confidence: 99%

Improved method for isochromatic demodulation by RGB calibration

2002

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The red-blue-green ͑RGB͒ calibration technique consists in constructing an a priori calibration table of the isochromatic retardation versus the triplet of RGB values obtained with a RGB CCD camera. In this way a lookup table ͑LUT͒ is built in which the entry is the corresponding RGB triplet and the output is the given retardation. This calibration ͑a radiometric quantity͒ depends on the geometric and chromatic parameters of the setup. Once the calibration is performed, the isochromatic retardation at a given point of the sample is computed as the one that minimizes the Euclidean distance between the measured RGB triplet and the triplets stored in the LUT. We present an enhanced RGB calibration algorithm for isochromatic fringe pattern demodulation. We have improved the standard demodulation algorithm used in RGB calibration by changing the Euclidean cost function to a regularized one in which the fidelity term corresponds to the Euclidean distance between RGB triplets; the regularizing term forces piecewise continuity for the isochromatic retardation. Additionally we have implemented a selective search in the RGB calibration LUT. We have tested the algorithm with simulated as well as real photoelastic data with good results.

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Completely automated determination of two-dimensional photoelastic parameters using load stepping

Cited by 30 publications

References 7 publications

Phase Shifting Full-Field Interferometric Methods for Determination of In-Plane Tensorial Stress

Phase Shifting Full-Field Interferometric Methods for Determination of In-Plane Tensorial Stress

Separation of isoclinics and isochromatics from photoelastic data with a regularized phase-tracking technique

Improved method for isochromatic demodulation by RGB calibration

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