Self-action of the acoustical wave in glass with cracks

Abstract

The recently developed nonlinear acoustic method for nondestructive testing uses the modulation of sound by vibrations. However, there are many other nonlinear acoustic effects that could also be used for nondestructive testing. These effects include: amplitude-dependent internal friction, high-amplitude vibration shifting the resonance frequency, generation of higher harmonics, and others. These effects were observed in a glass rod that was fractured by an intensive laser beam, while a similar unfractured glass rod did not exhibit them. The resonance acoustical field in the glass rod was excited on the frequency about 4 kHz and the strain in this field was up to 10−5. Some of the observed effects varied in time, which suggests a change in the crack contact surfaces due to the acoustical field. A theoretical model of acoustic propagation in cracked media to explain the observed nonlinear behaviors is discussed. [This work is supported by the United States Industry Coalition, with the US DOE Contract W-7405-ENG-36, through the University of California.]