ABSTRACT
A. Purpose The purpose of nondestructive testing (NDT) is to inspect, qualify (either accept or reject), and evaluate the quality of a structure without breaking, destroying, or otherwise significantly changing the structure. NDT methods for composite materials range from simple visual inspection and coin tapping to very sophisticated techniques such as acousto-ultrasonics and shearography. Many of these techniques were originally developed for detecting flaws in metals and now, with some modifications, are also used with fiber reinforced composite materials. The modifications have been necessary to accommodate the differences in characteristics of metals and composites. For example, metals are basically isotropic and homogeneous materials, whereas composites are nonisotropic and heterogeneous. The laminated form of many composite structures creates unique internal flaws, such as delamination, that do not occur in metals. Furthermore, the processing of composite materials is not always as well controlled as that of metals. This is a source of wide variations in the quality of composite parts and increases the level of complexity in the use of NDT for composite materials.
