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Nondestructive Evaluation of Adhesively Bonded Joints by Acousto-Ultrasonic Technique and Acoustic EmissionReliable applications of adhesively bonded joints require an effective nondestructive evaluation technique for their bond strength prediction. To properly evaluate factors affecting bond strength, effects of defects such as voids and disbonds on stress distribution in the overlap region must be understood. At the same time, in order to use acousto-ultrasonic (AU) technique to evaluate bond quality, the effect of these defects on dynamic response of single lap joints must be clear. The stress distribution in a single lap joint with and without defects (void or disbond) is analyzed. A bar-Theta parameter which contains adherend and adhesive thickness and properties is introduced. It is shown for bonded joints with bar-Theta greater than 10, that a symmetric void or disbond in the middle of overlap up to the 70 percent of overlap length has negligible effect on bond strength. In contrast frequency response analyses by a finite element technique showed that the dynamic response is affected significantly by the presence of voids or disbonds. These results have direct implication in the interpretations of AU results. Through transmission attenuation and a number of AU parameters for various specimens with and without defects are evaluated. It is found that although void and disbond have similar effects on bond strength (stress distribution), they have completely different effects on wave propagation characteristics. For steel-adhesive-steel specimens with voids, the attenuation changes are related to the bond strength. However, the attenuation changes for specimens with disbond are fairly constant over a disbond range. In order to incorporate the location of defects in AU parameters, a weighting function is introduced. Using an immersion system with focused transducers, a number of AU parameters are evaluated. It is found that by incorporating weighting functions in these parameters better sensitivities (AU parameters vs. bond strength) are achieved. Acoustic emission (AE) activities of steel-adhesive-steel specimens with bar-Theta equal to 3.4 are monitored. Two different formats of energy vs. time have resulted, each corresponding to the perfect specimens or the specimens with void or disbond. The relative acoustic energy and the number of events at failure are found to be a means for predicting the bond strength.
Document ID
19990018177
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Nayeb-Hashemi, Hamid
(Northeastern Univ. Boston, MA United States)
Rossettos, J. N.
(Northeastern Univ. Boston, MA United States)
Date Acquired
August 19, 2013
Publication Date
January 1, 1997
Publication Information
Publication: Nondestructive Evaluation of Adhesively Bonded Joints
ISSN: 0730-0050
Subject Category
Quality Assurance And Reliability
Funding Number(s)
CONTRACT_GRANT: NAG3-1129
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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