TITLE:
Ultrasonic Testing Combined with Pattern Recognition for the Detection of Kissing Bonds
AUTHORS:
Jens Schuster, David Müller, Ming-Hong Chen, Quentin Govignon
KEYWORDS:
Ultrasonic Testing, Time Domain, Frequency Domain, Pattern Recognition, Bond Quality, Kissing Bond
JOURNAL NAME:
Open Journal of Composite Materials,
Vol.9 No.3,
July
10,
2019
ABSTRACT: Kissing bonds are defects in the adhesive bonds with
intimate contact of touching surface but considerably lowered shear strength.
Their detection specifically in the aerospace area is so not satisfactory.
Usually, kissing bonds are inconspicuous in ultrasonic C-scans. However, the
determination of attributes in the time domain and the frequency domain of an
ultrasound signal provides the opportunity to derive a pattern for bonded area. Deviations from the pattern found
in inconspicuous bonding areas indicate kissing bonds. The survey described
here deals with the manufacturing of adhesively joint samples that purposefully
include kissing bonds, as well as potential solutions for detecting them through ultrasonic testing combined with pattern
recognition. The properties of the epoxy-based adhesive were varied by changing
the mixing ratios between resin and hardener. Samples with a mixing ratio far
apart from the manufacturer’s recommendation with an inconspicuous appearance
in a C-scan, but low shear strength values were taken for further evaluation.
After a definition and learning phase, a 100 percent hit rate to separate good
bondings from kissing bonds could be derived in a blind test. The
discriminating feature found is due to the
frequency shift between good and kissing bonds as well as the relative amplitude of the
second peak.