Growth and decay of acceleration waves in non-associative elastic-plastic fluid-saturated porous media

modes under which acceleration waves can propagate in elastic-plastic fluid-saturated porous media have been obtained in Loret and Harireche [J. Mech. Phys. Solids 39, 569-606 (1991)]. The implications of the existence of complex wave-speeds are analyzed here. First, like elastic mixtures, elastic-plastic mixtures with an associative flow rule may be characterized by a positive and finite decay coefficient : acceleration waves propagate with an amplitude that either strictly decreases or remains constant. Moreover, the range of variation of the decay coefficient is the same as for elastic mixtures. In contrast, when the squares of the wave-speeds are real, nonassociative flow rules may give rise to negative and/or unbounded decay coefficients. When the squares of the wave-speeds are complex, the so-called flutter phenomenon, the decay coel&ient is found to be positive and tin&e. The analytical derivations require the material state on the wave front to be constant; on the other hand, the analysis is valid independently of the compressibilities of the solid and fluid constituents. 0 1997 Elsevier Science Ltd