Abstract:

The enormously high nonlinear response of solids with cracks to an acoustic excitation makes nonlinear methods possible for nondestructive testing (NDT). Among the problems to be solved are the mechanisms of such nonlinear responses and the development of NDT methods. Results of an experimental study of nonlinear effects for elastic waves in metal rods with cracklike defects and their dependence on the type of contacts in the cracks are given. Unlike earlier works concerned mainly with longitudinal and flexural waves in solids, the present experiment shows that a high degree of nonlinearity is found for torsional waves as well. The crack was modeled by cutting a rod and tightly filling a crack with metal plates. Two types of contact were studied: dry and lubricated contacts. Modulation of high-frequency torsional waves (20 kHz and 22.8 kHz) in a rod by low-frequency flexural vibrations was studied. Flexural vibrations were excited in two ways: with a shock and with the help of a vibrator. Amplitude modulation was observed only in a rod with a crack, the level of this modulation drastically decreasing in the presence of liquid lubricant. [Work supported by RFBR, Russia---Grant No. 97-02-17524---and by INCAS, Nizhny Novgorod, Russia.]