Modulation of torsional waves in a rod with a crack

Results of experiments concerning nonlinear effects for elastic waves in metal rods with the crack-type defects are presented. The dependence of the nonlinear effect on the contact type is discussed. The crack has been modeled by cutting a rod and tightly filling the crack with metal plates. Two types of contact have been studied: a dry contact and a contact with lubricant. The modulation of high-frequency torsional waves (20 and 22.8 kHz) in the rod under the effect of low-frequency flexural vibrations has been investigated. Flexural vibrations have been excited by a shock and by a vibrator. The modulation of high-frequency torsional waves under the effect of low-frequency vibrations has been observed only in the rod with a crack. The level of modulation drastically decreases in the presence of liquid lubricant.