A Relationship between Frequency Dependent Ultrasonic Attenuation and Porosity in Composite Laminates
The detrimental effects of porosity on material strength are well known. The work of Hsu, Rose, and Adler[l] provides a means of estimating the volume fraction of pores and the average pore radius in isotropic elastic media from the value of frequency at which the attenuation coefficient becomes frequency independent and the magnitude of the attenuation coefficient at that plateau. Quantitative results for the isotropic case depend on numerical factors obtained by Gubernatis et al.  which are functions of the ratio of the transverse to longitudinal sound velocities, i.e., on the Poisson ratio. Mobley et al.  have tested these theories by making measurments of attenuation covering a frequency range that extended well into the frequency independent plateau. The experimental results of these investigators suggest that the theoretical results obtained by Rose et al. are qualitatively correct even though some of the features of wave propagation in layered, anisotropic media are not explicitly incorporated into the scattering model.