Originally Posted by
slowto280
Can anyone here fill me in what defect (closure member and core-to-closure member) is being mentioned here?
In general terms, the closure member is the material that seals up the edges of the laminate/composite panel, skin, etc. The core is the material that is laminated between the skins, etc. There are various types of closure members and core materials. The defect being addressed is the lack of adhesive or the unbonding of the adhesive (voids) between the closures themselves or the core and closures.
To get a better idea look to FAA AC 43.13-1B, Chapter 5, Section 7 (link below) which describes the ultrasound process in detail and provides examples of the different types of closures and their uses. Plus it shows how to inspect them as well.
AC 43.13-1B