Abstract

Shearography is an optical and nondestructive technique that has been largely used for damage detection in layered composite materials where delaminations and debondings are found to be among the most common flaws. Shearography detects derivative of the displacements. It is a relative measurement in which two images are recorded for different loading conditions of the sample. The applied loading induces some deformations into the sample, generating a displacement field on its surface. Thermal, acoustical, or mechanical loading are typical excitations applied in a static or dynamic way. The absolute difference between two phase maps recorded at two different loading instances produces an interference fringe pattern, which is directly correlated to the displacements produced on the material surface. In some cases, depending on the loading level and mainly on the sample geometry, interference patterns will contain fringes resulting from geometry changes. This will mask those fringes correlated to flaws introduced into the material, resulting in an image misinterpretation. This phenomenon takes place mainly when the sample has curved geometries, as in, for example, pipe or vessel surfaces. This paper presents an algorithm that uses a mathematical process to improve the visualization of flaws in shearographic images. The mathematical process is based on the calculation of the phase variation, and it is used to search for local deformations contained in the image. This algorithm highlights defect regions and eliminates fringes caused by geometry changes, providing an easier interpretation for complex shearographic images. This paper also shows the principle and the algorithm used for the process. Results, advantages, and difficulties of the method are presented and discussed by using simulated fringe maps as well as real ones.

© 2013 Optical Society of America

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References

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  1. P. E. Mix, Introduction to Nondestructive Testing, 2nd ed. (Wiley-Interscience, 2005), p. 456.
  2. J. N. Butters and J. A. Leendertz, “A double exposure technique for speckle pattern interferometry,” J. Phys. E 4, 277–279 (1971).
    [CrossRef]
  3. D. Malacara, Optical Shop Testing, 3rd ed. (Wiley, 2007).
  4. P. K. Rastogi, Optical Measurement Techniques and Applications (Artech House, 1997).
  5. P. K. Mallick, Composites Engineering Handbook (University of Michigan, 1997).
  6. T. Yoshizawa, Handbook of Optical Metrology: Principles and Applications (CRC Press, 2009).
  7. W. Steinchen and L. Yang, Digital Shearography—Theory and Application of Digital Speckle Pattern Shearing Interferometry (SPIE, 2003).
  8. K. J. Gasvik, Optical Metrology, 3rd ed. (Wiley, 2002).
  9. A. Asundi and Z. Wensen, “Fast phase-unwrapping algorithm based on a gray scale mask and flood fill,” Appl. Opt. 37, 5416–5420 (1998).
    [CrossRef]
  10. J. Fung and S. Mann, “OpenVIDIA: parallel GPU computer vision,” in Proceedings of the 13th Annual ACM International Conference on Multimedia (ACM, 2005), pp. 849–852.
  11. P. S. Hill, S. Laughlin, and G. Gardiner, “The developments in composite sleeves for permanent pipe and pipeline repair,” Aust. Pipeliner, Apr. 2008, pp. 64–66.
  12. NOV Fiber Glass Systems, Pipe Installation Handbook: Matched Tapered Bell & Spigot Joints, Jan. 2010, http://cwsfiberglass.com/docs/smithfiberglass/F6000.pdf .
  13. NOV Fiber Glass Systems, “F6301 06/12–Assembly instructions for Conical-Cylindrical (Quick-Lock®) adhesive-bonded joints,” (2012), http://www.ameron-fpg.com/?t=offshore&i=156 .
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    [CrossRef]

2010 (1)

D. P. Willemann, A. Fantin, and A. Albertazzi, “Defect assessment of bonded joints of composite tubes using shearography.” Proc. SPIE 7387, 73870J (2010).
[CrossRef]

1998 (1)

1971 (1)

J. N. Butters and J. A. Leendertz, “A double exposure technique for speckle pattern interferometry,” J. Phys. E 4, 277–279 (1971).
[CrossRef]

Albertazzi, A.

D. P. Willemann, A. Fantin, and A. Albertazzi, “Defect assessment of bonded joints of composite tubes using shearography.” Proc. SPIE 7387, 73870J (2010).
[CrossRef]

Asundi, A.

Butters, J. N.

J. N. Butters and J. A. Leendertz, “A double exposure technique for speckle pattern interferometry,” J. Phys. E 4, 277–279 (1971).
[CrossRef]

Fantin, A.

D. P. Willemann, A. Fantin, and A. Albertazzi, “Defect assessment of bonded joints of composite tubes using shearography.” Proc. SPIE 7387, 73870J (2010).
[CrossRef]

Fung, J.

J. Fung and S. Mann, “OpenVIDIA: parallel GPU computer vision,” in Proceedings of the 13th Annual ACM International Conference on Multimedia (ACM, 2005), pp. 849–852.

Gardiner, G.

P. S. Hill, S. Laughlin, and G. Gardiner, “The developments in composite sleeves for permanent pipe and pipeline repair,” Aust. Pipeliner, Apr. 2008, pp. 64–66.

Gasvik, K. J.

K. J. Gasvik, Optical Metrology, 3rd ed. (Wiley, 2002).

Hill, P. S.

P. S. Hill, S. Laughlin, and G. Gardiner, “The developments in composite sleeves for permanent pipe and pipeline repair,” Aust. Pipeliner, Apr. 2008, pp. 64–66.

Laughlin, S.

P. S. Hill, S. Laughlin, and G. Gardiner, “The developments in composite sleeves for permanent pipe and pipeline repair,” Aust. Pipeliner, Apr. 2008, pp. 64–66.

Leendertz, J. A.

J. N. Butters and J. A. Leendertz, “A double exposure technique for speckle pattern interferometry,” J. Phys. E 4, 277–279 (1971).
[CrossRef]

Malacara, D.

D. Malacara, Optical Shop Testing, 3rd ed. (Wiley, 2007).

Mallick, P. K.

P. K. Mallick, Composites Engineering Handbook (University of Michigan, 1997).

Mann, S.

J. Fung and S. Mann, “OpenVIDIA: parallel GPU computer vision,” in Proceedings of the 13th Annual ACM International Conference on Multimedia (ACM, 2005), pp. 849–852.

Mix, P. E.

P. E. Mix, Introduction to Nondestructive Testing, 2nd ed. (Wiley-Interscience, 2005), p. 456.

Rastogi, P. K.

P. K. Rastogi, Optical Measurement Techniques and Applications (Artech House, 1997).

Steinchen, W.

W. Steinchen and L. Yang, Digital Shearography—Theory and Application of Digital Speckle Pattern Shearing Interferometry (SPIE, 2003).

Wensen, Z.

Willemann, D. P.

D. P. Willemann, A. Fantin, and A. Albertazzi, “Defect assessment of bonded joints of composite tubes using shearography.” Proc. SPIE 7387, 73870J (2010).
[CrossRef]

Yang, L.

W. Steinchen and L. Yang, Digital Shearography—Theory and Application of Digital Speckle Pattern Shearing Interferometry (SPIE, 2003).

Yoshizawa, T.

T. Yoshizawa, Handbook of Optical Metrology: Principles and Applications (CRC Press, 2009).

Appl. Opt. (1)

J. Phys. E (1)

J. N. Butters and J. A. Leendertz, “A double exposure technique for speckle pattern interferometry,” J. Phys. E 4, 277–279 (1971).
[CrossRef]

Proc. SPIE (1)

D. P. Willemann, A. Fantin, and A. Albertazzi, “Defect assessment of bonded joints of composite tubes using shearography.” Proc. SPIE 7387, 73870J (2010).
[CrossRef]

Other (11)

P. E. Mix, Introduction to Nondestructive Testing, 2nd ed. (Wiley-Interscience, 2005), p. 456.

D. Malacara, Optical Shop Testing, 3rd ed. (Wiley, 2007).

P. K. Rastogi, Optical Measurement Techniques and Applications (Artech House, 1997).

P. K. Mallick, Composites Engineering Handbook (University of Michigan, 1997).

T. Yoshizawa, Handbook of Optical Metrology: Principles and Applications (CRC Press, 2009).

W. Steinchen and L. Yang, Digital Shearography—Theory and Application of Digital Speckle Pattern Shearing Interferometry (SPIE, 2003).

K. J. Gasvik, Optical Metrology, 3rd ed. (Wiley, 2002).

J. Fung and S. Mann, “OpenVIDIA: parallel GPU computer vision,” in Proceedings of the 13th Annual ACM International Conference on Multimedia (ACM, 2005), pp. 849–852.

P. S. Hill, S. Laughlin, and G. Gardiner, “The developments in composite sleeves for permanent pipe and pipeline repair,” Aust. Pipeliner, Apr. 2008, pp. 64–66.

NOV Fiber Glass Systems, Pipe Installation Handbook: Matched Tapered Bell & Spigot Joints, Jan. 2010, http://cwsfiberglass.com/docs/smithfiberglass/F6000.pdf .

NOV Fiber Glass Systems, “F6301 06/12–Assembly instructions for Conical-Cylindrical (Quick-Lock®) adhesive-bonded joints,” (2012), http://www.ameron-fpg.com/?t=offshore&i=156 .

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Figures (14)

Fig. 1.
Fig. 1.

Shearographic setup.

Fig. 2.
Fig. 2.

Shearographic inspection.

Fig. 3.
Fig. 3.

Typical shearographic pattern: (a) simulated image and (b) real image.

Fig. 4.
Fig. 4.

(a) Synthetic phase image with a butterfly pattern. (b) Pixel in the image and a set of neighboring pixels symmetrically distributed over a ROI defined by two concentric circles. The arrows show the correspondence between two pixels in the same angular position in the ROI.

Fig. 5.
Fig. 5.

(a) Phase map with an artificial defect, (b) a map of phase radial variation, and (c) phase profile of the defect region.

Fig. 6.
Fig. 6.

(a) Synthetic phase map of a regular fringe pattern. (b) Processed image.

Fig. 7.
Fig. 7.

Synthetic phase map containing two different flaws: (a) wrapped phase map and (b) phase radial variation processing using a single ROI.

Fig. 8.
Fig. 8.

Synthetic phase map containing two different flaws: (a) wrapped phase map and (b) phase radial variation processing using a two different ROIs.

Fig. 9.
Fig. 9.

Synthetic phase map of regular fringes containing a small defect.

Fig. 10.
Fig. 10.

Image processed: (a) spatial phase unwrapping algorithm, (b) phase radial variation algorithm, (c) unwrapped phase profile, and (d) phase radial variation profile.

Fig. 11.
Fig. 11.

Image processed: (a) spatial phase unwrapping algorithm, (b) phase radial variation algorithm, (c) unwrapped phase profile, and (d) phase radial variation profile.

Fig. 12.
Fig. 12.

Specimen with artificial flaws: (a) original phase map, (b) phase unwrapping map, and (c) proposed method map (contrast enhancement).

Fig. 13.
Fig. 13.

(a) Real composite sleeve, (b) common phase map obtained with shearography and pressure excitation, and (c) map obtained with the proposed method.

Fig. 14.
Fig. 14.

(a) Common map acquired with shearography in a bell and spigot composite pipe joint. (b) Map obtained with the proposed method.

Equations (2)

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Vr=i(ϕiEϕiI),
n=Rrl,

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