Delamination and Porosity in Composites and Adhesives Using Solid and Particulate Powdered Aerogel

Langley Research Center, Hampton, Virginia

NASA's Langley Research Center has developed a method that introduces solids and particulates — specifically aerogels — into composites or adhesives while they are being constructed. These additives survive as the structure is cured to serve as a testbed and standard. Once cured, the solid or particulate additive will behave as a delamination or porosity defect and will be indistinguishable from real delamination or porosity when inspected with popular nondestructive evaluation techniques such as ultrasound or thermography.

Diagram showing the patented aerogel process and aerogel solid.

To replicate flat delaminations/ disbonds in composites/bonded structures, solid monoliths of aerogel are fabricated to very thin tabs (>1 mm). The thin tabs are laid on a ply layer during layup of the composite at a desired ply depth and spatial location. The rest of the composite is constructed and then cured in an autoclave. After curing, the aerogel insert will completely mimic a thin air gap between the ply layers only at the area it was located. The aerogel insert will be a large acoustic impedance mismatch in the composites, meaning it will respond like a delamination in all acoustic-based measurements. And because they are very good insulators, they will also respond like a delamination in thermal-based inspections. A particulate aerogel-based method can be used to represent porosity.

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