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 mo duli of a unidirectional lamina from ultrasonic time-delay measurement s on [0/90] cross-ply composites. A lamina is a single ply (layer) of unidirectional fibers in a multiply composite plate. This method is ba sed on a geometrical acoustic model relating the lamina properties wit h time-delay data for a [0/90] cross-ply composite. Interference due t o multiple reflections within the laminate is assumed to be negligible . It is shown via numerical simulation that the reconstructed lamina m oduli are highly accurate for composites with transversely isotropic l aminae even for data containing large random scatter. For composites w ith orthotropic laminae, the method gives a very close approximation t o the true lamina properties with reasonable accuracy. Experimental ti me-delay measurements in [0/90](2s) cross-ply metal matrix composites (SiC/Ti-15V-3Al-3Cr-3Sn) are made in different incident planes. To avo id the effect of wave interaction within the laminate, we used the fir st arrival of the ultrasonic signal for time-delay measurements. From the [0/90](2s) composite measurements, the elastic moduli of the lamin a are determined and compared to those of a thin unidirectional compos ite panel measured independently by ultrasonic plate modes. The agreem ent between the two independent measurements is good. Utilization of m easurements in the 45 degrees plane in [0/90] composites for determina tion of lamina moduli is also discussed.