Determination of the elastic constants of anisotropic composite materials via laser photoacoustics

Abstract

This paper presents the solution of the inverse anisotropic medium problem in which the elastic constants of an anisotropic composite material are determined from ultrasonic wave speed measurements made in nonprincipal directions of a specimen. The ultrasonic waves were generated via the point-source/point-receiver technique using a 2-ns pulsed Nd:Yag laser as a source and a 2.5-mm-diam capacitive or a 1.3-mm piezoelectric transducer as a receiver. Data were acquired during an isoangular scan of the source relative to one of the principal acoustic axes of symmetry. In each waveform, the arrivals of the quasilongitudinal and the two quasishear bulk modes were measured. The elastic constants of the material were then recovered using an optimization algorithm. Experimental results are presented for a transversely isotropic composite material. It was found that the nonlinear fit between the experimental and the recovered slowness values is excellent. Some discrepancies are observed for the two shear modes. These are shown to be related to the complexity of the detected signals.