Abstract:

Acousto-ultrasonics (AU) is a nondestructive testing technique for evaluating materials and structures. The name is based on the fact that principles of acoustic emission and ultrasonics are combined in this technique. Unlike conventional ultrasonics, acousto-ultrasonics is not concerned with the detection and characterization of individual flaws. Instead, it is concerned with evaluation of integrated effects of diffuse subcritical flaw populations and microstructural aberrations in composites. Porosity, fiber breaks, resin richness, poor curing, and fiber/matrix bonding are some examples of these, which in turn govern mechanical properties and durability of composite structures. These factors also influence AU signals that consequently reveal that variations in mechanical properties such as tensile strength, stiffness, toughness, etc. [A. Vary, ``Acousto-Ultrasonics,'' NDT of Fiber Reinforced Plastics Composites, Vol. 2 (Elsevier Applied Science, 1990). This paper reviews the current state of the art of this technique. Some examples on the use of AU for characterization of composites and evaluation of the adhesive bond strength of composite structures will be discussed. Finally, some of the advantages and limitations of this technique will also be discussed.