Nonlinear Time Reversal Focusing and Detection of Fatigue Crack

Abstract

This paper presents an experimental study on the detection and location of nonlinear scattering source due to the presence of fatigue crack in a laboratory specimen. The proposed technique is based on a combination of nonlinear elastic wave spectroscopy(NEWS) and time reversal(TR) focusing approach. In order to focus on the nonlinear scattering position due to the fatigue crack, we employed only one transmitting transducer and one receiving transducer, taking advantage of long duration of reception signal that includes multiple linear scattering such as mode conversion and boundary reflections. NEWS technique was then used as a pre-treatment of TR for spatial focusing of reemitted second harmonic signal. The robustness of this approach was demonstrated on a cracked specimen and the nonlinear TR focusing behavior is observed on the crack interface from which the second harmonic signal was originated.

Time reversal focusing of elastic waves in plates for an educational demonstration

“…The reverberation in a measured impulse can be exploited as a virtual array of sources during the time reversal focusing process. TR has been used to locate and characterize defects and cracks in mechanical parts, [13][14][15][16][17][18][19][20][21][22][23][24][25][26] communicate signals along pipes, 27 and in seismology to locate the epicenter of earthquakes 28 and geophysical tremor. 29 One method of achieving time reversal focusing, sometimes termed reciprocal time reversal, obtains an impulse response between locations A and B in a sample or medium.…”