Abstract

Local Nonlinear and Parametric Effects for Non-Bonded Contacts in Solids

E.M.Ballad, B.A.Korshak, I.Yu.Solodov (Department of Acoustics, Faculty of Physics, Moscow State University, Moscow, Russia); N.Krohn, G.Busse (Institute for Polymer Testing and Polymer Science (IKP), Nondestructive Testing (ZFP), University of Stuttgart, Stuttgart, Germany)

e-mail: balade@mail.ru

A strongly nonlinear behavior of a closed non-bonded contact area in solids for a harmonic drive is associated with two major mechanisms: the lack of symmetry for compression-extension deformations across the interface ("clapping" mechanism) and the nonlinearity of "slide-and-stick" forces between the surfaces in contact (hysteresis mechanism). A phenomenological approach developed for the above mechanisms reveals their inherently distinctive nonlinear manifestations caused by different contact stiffness variation in time domain. An asymmetrical temporal distribution provides the stiffness changes at the fundamental frequency in the case of "clapping", while an obvious odd stress-strain relationship in a hysteresis loop leads to doubling of the stiffness modulation frequency. As a result, one can expect both odd and even harmonics in the former case and only odd harmonic contribution to the hysteresis driven nonlinear sprectra. A specific sinc-type higher harmonic amplitude distribution and non-monotonic dynamic characteristics may be a common feature due to a similar "pulse" mode of stiffness variation. For the double frequency modulation of the contact stiffness, one can expect parametric contribution to the higher harmonics only, whereas the "clapping" mechanism promotes fractional subharmonic oscillations, development of instabilities and dynamic chaos. A number of experiments have been performed in our two laboratories to study the properties of the nonlinear contacts in a wide frequency range using simulated non-bonded interfaces as well as various materials with real fractured defects. The results to be presented illustrate peculiar characteristics of the conventional nonlinear effects as well as new parametric manifestations in nonlinear acoustic wave phenomena.

Section : 3