(The) ultrasonic velocity and attenuation measurements in carbon fiber reinforced plastics

Abstract

The velocities and attenuation of the longitudinal and shear waves propagating in various directions to the fiber axis were measured as function of the fiber volume fraction of carbon/epoxy composites over the range of frequencies, 1-12 MHZ, using pulse-echo method. The frequency dependence of the velocity showed that the dispersive effects appeared in wave propagations. Dispersive effects were more pronounced for waves propagating along the fiber direction than normal to it. The attenuation of waves decreased with the volume fraction of fibers. In addition to it, the linear dependence of the attenuation with the frequency showed that the attenuation of ultrasonic waves in the composites was mostly caused by the epoxy matrix. The ln w dependence of the longitudinal phase velocity obtained from the Kramers-Kronig relationship implied that the contribution of the epoxy matrix in the dispersion of the wave was great.