Ultrasonic Determination of the Elastic Properties of Unidirectional Composites
In recent years, extensive efforts have been made in developing ultrasonic nondestructive evaluation (NDE) methods for the characterization of the elastic properties of composite materials [1, 2]. A systematic procedure proposed by Karim, Mal and Bar-Cohen  by inverting the leaky Lamb wave (LLW) data has been found to be accurate and effective in characterizing the elastic constants of composites. However, this method can accurately determine the matrix dominated constants c22, c23, and c55 only. The fiber dominated constants, c11 and c12 can not be determined accurately, due to the fact that the Lamb wave velocity is insensitive to C11 and c12 in the range in which the dispersion data are reliable. In this paper we introduce a new technique which can determine all the material constants by analyzing the times of flight of the reflected acoustic waves in a pulsed LLW experiment. The procedure requires clear separation and identification of the reflected pulses. A generalized ray theory described in  is used to identify the modality and ray path of each arrival. The time of flight of each ray is then related to the elastic constants of the composite which are determined from these relations. The method requires access from one side of the specimen and is accurate as well as efficient.