Crack location using nonlinear means applying modulation of ultrasonic pulses by cw vibration

Abstract

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. NWMS has high sensitivity to the presence of cracks and can be a very good tool for a ‘‘pass–fail’’ test but cannot provide the crack location. 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. As the location of damage is the next important issue in NWMS, this work represents an important step. [This work was partially supported by International Science Technical Center, Grant No. 1369.]