While defects in laminated plates are readily revealed using double-exposure shearography and holography, when an incremental vacuum pressure is applied between the exposures, the apparent defect size, measured from the boundary of the perturbed fringes, may over-estimate the actual defect size depending on the elasticity of the bond-line. In this paper, the perturbed fringes were described by a mathematical model derived from the theory of thin plates supported by a Winkler type elastic foundation which takes into consideration the elasticity of the bond-line. An iterative technique is subsequently presented for estimating the size and depth of the defect from the fringe pattern without the need to pre-determine the current elasticity of the bond-line. Laminates with a thick and highly elastic bond-line, found in foam-adhesive bonded metal laminates, and those with a thin and brittle bond-line, found in multi-layered glassflbre reinforced plastic plates, were tested. Results have shown that the defects in these laminates were accurately assessed.

1.
Erf, R. K., 1974, Holographic Nondestructive Testing, Academic Press, New York.
2.
Freedman, D., Pisani, R., Purves, R., and Adhikari, A., 1991, Statistics, W. W. Norton and Company, New York, Second Edition.
3.
Hetenyi, M., 1946, Beams on Elastic Foundation, The University of Michigan Press, Ann Arbor, MI.
4.
Hung
Y. Y.
, and
Liang
C. Y.
,
1979
, “
Image-shearing Camera for Direct Measurement of Surface Strains
,”
Applied Optics
, Vol.
18
, No.
7
, pp.
1046
1051
.
5.
Hung
Y. Y.
,
1982
, “
Shearography: A New Optical Method for Strain Measurement and Nondestructive Testing
,”
Optical Engineering
, Vol.
21
, No.
3
, pp.
391
395
.
6.
Hung
Y. Y.
,
1989
, “
Shearography: A Novel and Practical Approach for Nondestructive Inspection
,”
Journal of Nondestructive Evaluation
, Vol.
8
, No.
2
, pp.
55
67
.
7.
Rao, S. S., 1978, Optimization: Theory and Applications, Wiley Eastern Limited, New Delhi.
8.
Rubayi
N. A.
, and
Liew
S. H.
,
1989
, “
Vacuum Stressing Technique for Composite Laminates Inspection by Optical Method
,”
Experimental Techniques
, Vol.
13
, No.
3
, pp.
17
20
.
9.
Selvadurai, A. P. S., 1979, Elastic Analysis of Soil-Foundation Interaction, Developments in Geotechnical Engineering, Vol. 17, Elsevier, Amsterdam.
10.
Shang
H. M.
,
Toh
S. L.
,
Chau
F. S.
,
Tay
C. J.
, and
Tay
T. E.
,
1991
a, “
Holographic Inspection of Laminated Plates Containing Two Fully-Overlapping Identical Debonds
,”
Journal of Nondestructive Evaluation
, Vol.
10
, No.
1
, pp.
7
17
.
11.
Shang
H. M.
,
Toh
S. L.
,
Chau
F. S.
,
Shim
V. P. W.
, and
Tay
C. J.
,
1991
b, “
Locating and Sizing Disbonds in Glassfibre-reinforced Plastic Plates Using Shearography
,”
ASME JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY
, Vol.
113
, pp.
99
103
.
12.
Shang
H. M.
,
Chau
F. S.
,
Tay
C. J.
,
Toh
S. L.
, and
Tham
L. M.
,
1994
, “
A Simple Model for Sizing Unbonds in Foam-adhesive Bonded Laminates from Shearographic Fringes
,”
Composites Engineering
, Vol.
4
, No.
2
, pp.
233
245
.
13.
Vest, C. M., 1979, Holographic Interferometry, Wiley, New York.
This content is only available via PDF.
You do not currently have access to this content.