Ultrasonic Wave Considerations for the Development of an NDE Feature Matrix for Anisotropic Media

The problem of ultrasonic surface and bulk wave propagation in an anisotropic media and/or a composite material is addressed so that applications in Nondestructive Evaluation can be considered, emphasis in this paper being placed on bulk wave propagation. Global material property determination is considered in an inverse wave velocity computation of stiffness coefficients based on principles of anisotropic elasticity. A one-sided inspection technique based on practical considerations of a field environment is developed. The concept of a feature matrix, based on the stiffness coefficients, is then introduced as a means of both material characterization and defect analysis in composite materials. A brief discussion on a test protocol and an interpretation of the elements in the feature matrix from an NDE point of view is also presented. The conclusions of a previous theoretical investigation of wave propagation in anisotropic media are considered from an experimental point of view by way of the bulk wave technique. A result of fundamental value is that the actual propagation of quasilongitudinal waves, generated by a standard broad band pulsed transducer, is indeed well matched with the theoretical approximation obtained earlier. This approximation was based on the generalized retarded potential principle with variable energy velocity of the quasilongitudinal mode in an anisotropic medium as the substitute for the constant longitudinal velocity used in the retarded potential scheme for an isotropic medium.