Characterization of Thin, Fiber-reinforced Laminates by Ultrasonic Point-source/Point-receiver Techniques

Abstract

This paper reports on the results of the application of ultrasonic techniques that can be used to characterize thin structures, such as one- or two-ply, unidirectional laminates whose thicknesses are as small as 140 μm. The measurements rely on the application of the ultrasonic point-source/point-receiver technique (PS/PR) using either a pulsed laser beam operating as a dipole source or a small aperture, piezoceramic shear transducer serving as a monopole source. Detection of the signals is with a piezoceramic sensor that directly responds to the lateral or shear motions of the specimen surface. The detected time signals represent the detailed spatial and temporal characteristics of the elastic wave field. The experimental group velocity data is analyzed using a simple plane wave, plane stress model that describes the propagation of quasi-longitudinal and quasi-transverse membrane waves in the plane of the plate. Appropriate inversion procedures permit the recovery of the entire stiffness tensor of the laminates from in-situ measurements. The measurement system is also used to map out the group velocities in branches comprising the cuspidal region of the quasi-transverse group velocity curve.