Abstract

Modulation Acoustic Method of Crack Location

V.Kazakov (Institute of Applied Physics of RAS, Nizhny Novgorod, Russia); P.A.Johnson (Los Alamos National Laboratory, Los Alamos, NM, USA)

e-mail: kazak@appl.sci-nnov.ru

Nonlinear wave modulation spectroscopy (NWMS) was recently introduced as a new tool in NDE. This technique employs the nonlinear interaction of ultrasound and vibration in the presence of defects. Vibration changes the contact area within a defect effectively modulating an ultrasonic wave sensing the defect. A new method for locating defects or cracks in a material, presented in this paper, is based on the modulation of ultrasonic pulses by vibration. The CW vibration induces modulation of the signal reflected from cracks. Measurements of the spatial distribution of the modulation level are the basis of nonlinear acoustic imaging. Experimental verification of the method has been conducted in steel plates containing a circular hole and a fatigue crack. The high-frequency (carrier) impulse was about 3 MHz, and the modulating vibration frequency was 5--15 Hz. This technique images a crack very well while a hole was not detected. High space resolution allows the observation of increasing nonlinear reflection near the crack tips. A new method of space resolution employing highly time resolved pulses, suggested by Professor Zverev, is applied for improvement of NWMS.

Section : 3