Abstract

Bistability and Nonlinear Contact "Memory" in Acoustic Wave-Crack Interaction in Solids

B.A.Korshak, I.Yu.Solodov (Department of Acoustics, Faculty of Physics, Moscow State University, Moscow, Russia)

e-mail: solodov@acs465a.phys.msu.su

It has been shown [1] that a scenario for nonlinear oscillations of a non-bonded contact strongly depends on the driving force amplitude. At low input, the contact nonlinearity suggests a deterministic topic of the higher harmonic generation and it changes to stochastic (subharmonics, instabilities and chaotic nonlinear oscillations) for the higher input. The present paper demonstrates that both of the above families of the nonlinear effects can be observed in acoustic wave interaction with realistic cracked defects and are accompanied by the bistability and storage phenomena in the latter case. In the experiment, we used a reflection mode of the surface acoustic waves in YZ-LiNbO3 substrate to probe the crack nonlinearity. An evident bistability in the amplitude behavior brings down the thresholds for both sub- and superharmonics so that the nonlinear state of the crack does not fully recover after the wave impact. For the subharmonics, the ratio (storage time/read-in time) is found to be about 10-20, while it increases up to several hundreds for the higher harmonic case. The absolute value of the "memory" time in the latter case exceeds 4 hours for a 25-s read-in. A physical mechanism of the acoustic wave impact on the crack is shown to be associated with the heating of the crack area by the wave and subsequent slow relaxation of the thermally induced microstrain within the fractured defect. [1]. E. Ballad, B.A. Korshak, N. Krohn, I.Yu. Solodov and G. Busse, Local nonlinear and parametric effects for non-bonded contacts in solids, Book of abstracts 16 ISNA, 2002, Moscow, Russia

Section : 3