A sensitive ultrasonic technique for the quantitative nondestructive evaluation of small closed cracks is developed. The use of an oblique longitudinal wave with small angle of incidence upon the specimen surface is emphasized. Firstly, ultrasonic testing is performed with open cracks in order to predict the optimum angle of evaluation, and an empirical calibration equation is then derived for the same as a basis to deal with the analysis of closed cracks. From the measurement on real fatigue cracks, the parameters of interest, specifically the crack size and the closure stress, are determined simultaneously by analyzing the inverse problem. The method developed here is fully automated and computer-controlled. Evaluated results are found to be in good conformity with the destructive measurements, and the corresponding superiority of the method is realized, especially for tightly closed small fatigue cracks, when compared with the method using a beam of longitudinal wave incident normally and/or with a large angle.

Issue Section:
Research Papers
Topics:
Fracture (Materials), Nondestructive evaluation, Fatigue cracks, Longitudinal waves, Calibration, Computers, Inverse problems, Stress, Ultrasonic testing
1.
Buck, O., and Tittman, B. R., 1982, “The Ultrasonic Characterizations of Fatigue Cracks,” Advances in Crack Length Measurement, ed, C. J. Beevers, Engineering Material Advisory Services, Wasley, UK, pp. 413–446.
2.
Buck, O., and Skillings, B. J., 1982, “Effects of Closure on the Detection Probability of Fatigue Cracks,” Review of Progress in Quantitative Nondestructive Evaluation, eds., D. O. Thompson and D. E. Chimenti, Plenum, New York, NY, Vol. 1, pp. 349–353.
3.
Buck, O., Skillings, B. J., and Reed, L. K., 1983, “Simulation of Closure: Effects on Crack Detection Probability and Stress Distributions,” Review of Progress in Quantitative Nondestructive Evaluation, eds., D. O. Thompson and D. E. Chimenti, Plenum, New York, NY, Vol. 2A, pp. 345–352.
4.
Buck
 
O.
,
Thompson
 
R. B.
, and
Rehbein
 
D. K.
,
1984
, “
The Interaction of Ultrasound with Contacting Asperities: Applications to Crack Closure and Fatigue Crack Growth
,”
Journal of Nondestructive Evaluation
, Vol.
4
, No.
3/4
, pp.
203
–
212
.
5.
Clark
 
R.
,
Dover
 
W. D.
, and
Bond
 
L. J.
,
1987
, “
The Effect of Crack Closure on the Reliability of NDT Predictions of Crack Size
,”
NDT Intern
, Vol.
20
, No.
5
, pp.
269
–
275
.
6.
Date
 
K.
,
Shimada
 
H.
, and
Ikenaga
 
N.
,
1982
, “
Crack Height Measurement—An Evaluation of the Accuracy of Ultrasonic Timing Methods
,”
NDT Intern
, Vol.
15
, No.
6
, pp.
315
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.
7.
Golan
 
S.
,
Adler
 
L.
,
Cook
 
K. V.
,
Nanstad
 
R. K.
, and
Bolland
 
T. K.
,
1980
, “
Ultrasonic Diffraction Technique for Characterization of Fatigue Cracks
,”
Journal of Nondestructive Evaluation
, Vol.
1
, No.
1
, pp.
11
–
19
.
8.
Hudgell
 
R. J.
,
Morgan
 
L. L.
, and
Lumb
 
R. F.
,
1974
, “
Nondestructive Measurements of the Depth of Surface Breaking Cracks using Ultrasonic Rayleigh Waves
,”
British Journal of NDT
, Vol.
16
, No.
5
, pp.
144
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149
.
9.
Saka
 
M.
,
Schneider
 
E.
, and
Hoeller
 
P.
,
1989
, “
A New Approach to Detect and Size Closed Cracks by Ultrasonics
,”
Research in Nondestructive Evaluation
, Vol.
1
, No.
2
, pp.
65
–
75
.
10.
Saka
 
M.
, and
Fukuda
 
Y.
,
1991
, “
NDT of Closed Cracks by Ultrasonic Propagation Along the Crack Surface
,”
NDT & E Intern
, Vol.
24
, No.
4
, pp.
191
–
194
.
11.
Saka, M., and Abe´, H., 1994, “Sizing Closed Cracks by Ultrasonics and Analysis,” Topics in Engineering, Vol. 16, Computational and Experimental Fracture Mechanics, Developments in Japan, ed., H. Nisitani, Computational Mechanics Publications, Southampton, UK, pp. 165–185.
12.
Saka
 
M.
, and
Uchikawa
 
T.
,
1995
, “
Simplified NDE of a Closed Vertical Crack Using Ultrasonics
,”
NDT & E Intern
, Vol.
28
, No.
5
, pp.
289
–
296
.
13.
Schneider, E., Baudendistel, E., Becker, R., Dobmann, G., Gebhardt, W., Hollstein, T., Huebschen, G., Mueller, W., Pfeiffer-Vollmar, W., Walte, F., Willems, H., and Goebbels, K., 1984, “Interpretation und Bewertung schwach wechselwirkender Risse mit Hilfe zerstoerungsfreier Pruefverfahren und bruchmechanischer Analysen unter besonderer Beruecksichtigung von unter Druck stehenden Rissflaechen” (in German), Rep. No. 840108-TW, Fraunhofer-Institut fuer zerstoerungsfreie Pruefverfahren, Saarbruecken, Germany.
14.
So
 
K. K.
, and
Sinclair
 
A. N.
,
1987
, “
Size Measurement of Tightly Closed Surface Cracks by Surface Acoustic Waves
,”
Nondestructive Testing Committee
, Vol.
3
, No.
3
, pp.
67
–
74
.
15.
Tittman
 
B. R.
, and
Buck
 
O.
,
1980
, “
Fatigue Lifetime Prediction with the Aid of SAW NDE
,”
Journal of Nondestructive Evaluation
, Vol.
1
, No.
2
, pp.
123
–
136
.
16.
Walte, F., Gebhardt, W., and Hoffman, R., 1989, “NDT of Vertical Oriented Cracks by Mode Conversion with Optimized LLT Probes,” Non-Destructive Testing, Proceedings, 12th World Conference on Non-Destructive Testing, eds., J. Boogaard and G. M. van Dijk, Elsevier, Amsterdam, The Netherlands, Vol. II, pp. 1695–1701.
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