Elastic Wave Propagation in a Porous Laminated Composite

An analysis is presented for linear elastic wave propagation normal to the laminations of a periodically laminated porous composite. The porosity is randomly distributed throughout one constituent and is composed of small spherical voids. This type of porosity is called randomly periodic and produces Rayleigh scattering where the wavelength of the incident wave is much larger than the void diameter. Porosity also reduces the wave speed in a constituent and thereby affects geometric dispersion. A DISSIPATIVE EQUATION OF MOTION IS DEVELOPED FOR POROUS MATERIAL THAT INCLUDES A POROSITY-DEPENDENT WAVE SPEED AND A SCATTERING TERM THAT PROVIDES SPATIAL ATTENUATION. This equation is then used for a constituent of a composite, and a dispersion relation and pulse solution are obtained to determine the significance of porosity in a laminated composite. It is concluded that Rayleigh scattering produces a small damping effect in far-field pulse shapes and small-void porosity can be adequately simulated with an effective wave speed. (Author-PL)