A photoelastic study of crack repair |
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Authors: | R L Hastie R Fredell J W Dally |
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Institution: | (1) Department of Engineering Mechanics, USAF Academy, 80840, CO;(2) U.S. Air Force Academy, USAF Academy, 80840, CO;(3) Department of Mechanical Engineering, University of Maryland, 20742 College Park, MD |
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Abstract: | Birefringent coatings have been employed to study the effectiveness of an adhesively bonded repair of a center-cracked tension
panel. The repair was one sided, with photoelastic coatings applied to the opposite side. Photoelastic coatings were also
applied over the patch. Analysis methods are presented to permit the stress intensity factor to be determined from the isochromatic
fringe patterns recorded from both continuous andX- andY-edged coatings. The results showed that the one-sided adhesively bonded patch reduced the stress intensity factor; however,
the repair did not markedly change the character of stress distributions. Fringe loops formed near the crack tips for both
the cracked and repaired tension panels. The primary difference was in the size of the loops. The reduction inK
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due to repair was smaller than anticipated, but even small improvements in ΔK
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markedly enhance the life of a repaired panel. The Paris power law is used to show the relation between the reduction in
ΔK
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and the improvement in the crack growth rateda/dN. Fringe patterns from the birefringent coatings applied to the patch provided a means not only to investigate the stresses
in the patch but also to detect the initiation of the local debonding of the adhesive in the neighborhood of the crack. The
birefringent coating on the patch is an approach for producing an optically “smart” repair. |
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