Performing bond testing and composite integrity testing can be full of unknowns easily misinterpreted by a skilled ultrasound A-Scan technician. For adhesive bonded curvature parts some luck is required.

When we say bond testing we are usually referring to delaminations and disbondments.

Some materials which bond testing can be performed on include wood-based paneling, metals, polymers, plastics, Kevlar, Graphite, and Fiberglass. Due to the nature of some materials chemicals cannot be used and the inspection is limited to dry methods.

The primary methods are Resonance, MIA (Mechanical Impedance Analysis), Pitch Catch, Standard A-Scan ultrasonics (usually with the use of a delay line) and lets not forget the TAP test.

With all of these methods the integrity of the test is strongly dependent on a good properly fabricated calibration block. The problem is what type of calibration block do you fabricate, and how do you make disbonds to properly replicate a potential disbond. For this answer you have to reference the applicable code which you are following.

Resonance method is very similar to an ultrasonic A-scan pulse echo inspection with couplant included, it is based on changes in phase and amplitude in probe resonance.
Mechanical Impedance Analysis operates without couplant and is usually spring loaded, it is based on measuring the stiffness and mass of the material under test.
Pitch-catch method is based on a dual element dry inspection. Measuring amplitude and phase changes in an acoustic wave traveling across a surface.
Tap Test method is based on taking a quarter and tapping the surface listening for a tone change or using a tap hammer specifically designed for the tap test.