Ultrasonic polar backscattering for NDE of stitched graphite-epoxy composites

The use of through-the-thickness stitching in composite structures offers new challenges for quantitative ultrasonic nondestructive examination (NDE). The polar backscatter approach is used to examine the stitches, rather than the laminae themselves, in stitched composites. By generating refracted waves which are nearly perpendicular to the stitches, maximum sensitivity may be achieved to the scattering from the stitches relative to the background fibers. The basic principles of the approach are demonstrated by examining specimens consisting of isolated fiber tows case in neat resin in order to simulate stitches. Measurements from a stitched composite are presented and discussed.<>