Kissing bonds look perfect: no gaps, no voids, full bondline. They pass ultrasonic inspection because sound crosses the tight interface, but they hold little load. Contamination, wrong surface treatment, an expired primer or adhesive past its open time can all cause one. They are a major concern in aerospace and are why process control matters more than inspection for bonded structure.
Ultrasound came back clean but the coupon fell apart on the bench, that's a kissing bond, check the prep logs.
Kissing bonds are prevented by process control, not found by inspection, which is why bond shops log every prep step and coupon.
Also heard as
- zero-volume disbond
Related terms
Adhesive failure
A break at the interface between adhesive and part, leaving one surface clean or nearly clean.
Peel ply
A fabric layer cured onto a composite surface and torn off just before bonding to expose a clean, textured face.
Primer
A thin first coat wiped or sprayed onto a bonding surface so the adhesive grips better or the fresh prep stays clean.
Cleavage
Loading that pries a rigid joint open from one end, concentrating stress along the leading edge of the bond.