Forum: Interior Inspections; Pinholes

One new forum topic this week asks about NDT methods that can inspect interior components in an assembly. As usual, pinhole problems continue to be a hot topic. Three new suggestions have been offered, ranging from different surfacing materials to using Tagucchi methods to isolate the problem. In a related discussion, one reader gives suggestions for proper vacuum bagging methods. GregFillman would like to know if there is a method for inspecting closed wing cells. His company has developed a method for curing an entire wing or winglet as one part. However, they need to find a way to inspect the interior spars, or the part cannot be accepted.

More suggestions for the pinhole problem originally raised by RAHULQUEST. GregFillman suggests a calandered gel coat or surfacing film. Surfacing films are getting a lot of attention right now, so this sounds like a good lead. BEENTHEREDO2 points out that a lacquer will work, if a clear finish that shows the carbon weave isn't needed. Otherwise, a Tagucchi approach might show why some parts come out good, and that could be used to improve the others. Finally, COMPOSITEKI1 suggests focusing on the mold finish, making it as smooth and shiny as possible. After that, try to use a thinner resin.

In a related discussion, GregFillman describes the proper vacuum bagging method to remove trapped air. Debulking during layup, and the use of perforated release film and breather plies during cure, can help to remove air bubbles (of course, you need some sort of release film and breather fabric even if you don't have problems with air bubbles).