A method for determination of elastic constants of a unidirectional lamina from ultrasonic bulk velocity measurements on [0/90] cross-ply composites

In this paper we introduce an inversion method to determine elastic moduli of a unidirectional lamina from ultrasonic time-delay measurements on [0/90] cross-ply composites. A lamina is a single ply (layer) of unidirectional fibers in a multiply composite plate. This method is based on a geometrical acoustic model relating the lamina properties with time-delay data for a [0/90] cross-ply composite. Interference due to multiple reflections within the laminate is assumed to be negligible. It is shown via numerical simulation that the reconstructed lamina moduli are highly accurate for composites with transversely isotropic laminae even for data containing large random scatter. For composites with orthotropic laminae, the method gives a very close approximation to the true lamina properties with reasonable accuracy. Experimental time-delay measurements in [0/90]2s cross-ply metal matrix composites (SiC/Ti–15V–3Al–3Cr–3Sn) are made in different incident planes. To avoid the effect of wave interaction within the laminate, we used the first arrival of the ultrasonic signal for time-delay measurements. From the [0/90]2s composite measurements, the elastic moduli of the lamina are determined and compared to those of a thin unidirectional composite panel measured independently by ultrasonic plate modes. The agreement between the two independent measurements is good. Utilization of measurements in the 45° plane in [0/90] composites for determination of lamina moduli is also discussed.