Influence of buried objects on the dynamic nonlinearity of inhomogeneous materials

Abstract

Donskoy et al. [J. Acoust. Soc. Am. 111, 2705–2714 (2002)] and Korman et al. [J. Acoust. Soc. Am. 116, 3354–3369 (2004)] have shown that the nearby presence of compliant buried objects results in a significant nonlinear response in the spectrum of surface vibration induced by acoustic excitation. The latter have suggested that there is a strong connection with the inherent Nonlinear Mesoscopic Elasticity (NME) of inhomogeneous materials. Laboratory experiments are reported that investigate the comparative NME of granular and fibrous materials and the variation observed between several states of a single material (sand) subject to high sound pressure levels in the frequency range 100 Hz to 2 kHz. Fiberglass and gravel are shown to have strong inherent nonlinearity whereas wet compacted sand has relatively little. In both two-tone and single tone experiments, it is shown that, the presence of buried objects may enhance or reduce the inherent NME of the embedding medium. In cases where the NME is enhanced, compliant buried objects have a greater effect than relatively stiff objects. [Work supported by DSTL, UK.]