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Application of pencil lead break (PLB) point source in the detection of interfacial defects in adhesive bonds.

Prathuru, Anil; Faisal, Nadimul; Steel, John; Jihan, Sha


John Steel

Sha Jihan


The presence of kissing bonds (zero-thickness disbond) along the interface of an adhesive bond is highly detrimental to its strength and longevity. The detection of these kind of defects has previously been attempted using several techniques such as ultrasonic, infrared thermography, and X-ray spectroscopy, etc. This study aims to assess the effectiveness of pencil lead break (PLB) tests as a source in detecting the defects distributed along the interface of an adhesive bond. The defects were introduced artificially using polytetrafluoroethylene (PTFE) spray along one of the interfaces of the adhesive bond fabricated with aluminium plates bonded with an epoxy adhesive. Three different interfacial defect area percentages, 0%, 25% and 40% and three adhesive layer thicknesses (i.e., 0.1mm, 0.25mm, and 0.5mm) were considered. The PLB tests were conducted, and the recorded signals were analysed to assess the variation of AE features with the defect area percentage and adhesive layer thicknesses. Different source-sensor location configurations were also considered. The 200 kHz-highpass component of the recorded signals was found to be sensitive to the presence of the interfacial defects. The duration above a chosen threshold was found to be the distinguishing factor between the different defective specimens. Of the different sensor-source configurations tried, the configurations with the PLB on the 0.5mm side were seen to be sensitive to the presence of defects.


PRATHURU, A., FAISAL, N., STEEL, J. and JIHAN, S. 2022. Application of pencil lead break (PLB) point source in the detection of interfacial defects in adhesive bonds. Journal of nondestructive evaluation [online], 41(4), article 65. Available from:

Journal Article Type Article
Acceptance Date Sep 2, 2022
Online Publication Date Sep 28, 2022
Publication Date Dec 31, 2022
Deposit Date Oct 11, 2022
Publicly Available Date Oct 11, 2022
Journal Journal of nondestructive evaluation
Print ISSN 0195-9298
Electronic ISSN 1573-4862
Publisher Springer
Peer Reviewed Peer Reviewed
Volume 41
Issue 4
Article Number 65
Keywords Metal-to-metal adhesive bonds; Acoustic emission; Pencil lead break test; Kissing bonds; Interfacial defects; Defect detection
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