NDE of Thick Graphite/Epoxy Composites: Some Approaches and Problems

Composite materials are being used in many applications because they can be tailored to meet specific design requirements. Fiber and resin type, fiber orientation, layering, and thickness are deliberately used during prepreg layup or filament winding to give a composite structure specific, desirable properties. These quantities are useful design parameters, but produce attenuation of ultrasound and anisotropy in material properties, which cause difficulty in performing NDE. For example, thick, filament wound composites generally have more porosity than prepreg composites, which further increases attenuation of the ultrasonic signal. Geometric and/or viscoelastic effects cause dispersion of the wavespeed and attenuation coefficient i.e. they are frequency dependent. The general anisotropy of the composite causes the wave velocity to be a function of direction. However, some way to inspect structures made from these materials must be found if their usefulness is to be exploited