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.
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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