Anisotropy of the frequency-dependent ultrasonic attenuation in unidirectional graphite/epoxy composite material

Experimental results of the anisotropy of the frequency dependence of ultrasonic attenuation in unidirectional graphite/epoxy composite are presented. A sample with flat and parallel faces was interrogated in reflection mode with 5-MHz longitudinal and transverse wave contact transducers. The results show that for the nine waves generated (three longitudinal and six transversal) the signal loss was approximately linearly dependent on frequency over the useful bandwidth of the measurement system. Thus, a least-squares line fit to the data divided by the total propagation length in the sample provided the slope of attenuation. The slope of attenuation for longitudinal waves propagating parallel to the fibers was substantially less than those with propagation perpendicular to the fibers. In contrast, for transverse waves, the slopes of attenuation associated with either propagation or polarization parallel to the fibers were larger than those corresponding to both polarization and propagation perpendicular to the fibers