Elastic Wave Transmission and Stop Band Characteristics in Unidirectional Composites

Elastic wave transmission characteristics in unidirectional fiber-reinforced composites are studied based on the two-dimensional finite element analysis. The composite is assumed to be a lay-up of a finite number of monolayers, each of which contains a single row of fibers spaced at equal distance. Influences of the stacking number and misalignment of monolayers as well as the presence of coating layer around the fibers on the wave transmission spectra are demonstrated for unidirectional SiC-fiber-reinforced Ti-alloy composites. It is shown that the transmission coefficients fall to low values in certain bands of frequency, i.e., stop bands in terminology analogous to perfectly periodic structures. This feature is found to appear more clearly for the transverse wave incidence, irrespective of the misalignment of monolayers. The stiffness reduction of the coating layer is shown to shift the stop bands to lower frequencies, which can be a useful feature for the monitoring of the fiber/matrix interfacial damage.