V. Yu. Zaitsev
Inst. of Appl. Phys., 46 Uljanova str., Nizhny Novgorod 603600, Russia
Acoustical properties of built-of-contact systems are rather interesting both from the viewpoint of general physical acoustics and applied problems. Such structures can often demonstrate rather unusual acoustic properties (in this sense they are similar to such a popular object in acoustics as bubbly liquid). On the other hand, built-of-contact systems correspond to real physical structures, e.g., grainy media and rough contacting interfaces. Manifestations of their structural changes in linear and nonlinear acoustic properties are important for the creation of new methods of acoustical diagnostics. The results of numerical simulation of nonlinear harmonic generation under the action of an external sinusoidal drive in a model built-of-contact system with different initial compression is presented. The model has allowed experimental explanation of observed ``unusual'' nonlinear elastic properties of real grainy materials, which cannot be explained by known theoretical models, which do not take into account nonideality of packing, i.e., the presence of intergrain contacts with significantly different initial compression. It was revealed that higher-order elastic parameters are much more sensitive to the material structure changes than the liner modulus. This fact is rather encouraging for the creation of new nonlinear acoustic structure diagnostics methods.