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Crack detection on beams by time-frequency analysis of transient flexural waves

Apostoloudi A., Douka E., Hadjileontiadis L. J., Rekanos I. T., Trochidis A.

Archives of Acoustics

2007

Vol. 32, No. 4

941--954

A method for crack detection in beams by time-frequency analysis of flexural waves is described. Two different time-frequency representations, namely the continuous wavelet transform and the smoothed pseudo-Wigner distribution are employed. Simulated and measured exural waves in a cracked beam are analysed and both the location and size of the crack are accurately determined. The location of the crack is estimated using the arrival time of reflected waves with different group velocities. The ratio of the reflected wave energy to the incident wave one is calculated and used as an indicator of the crack size. Wave experiments in a slender brass beam are in good agreement with predictions verifying the effciency of the method. In view of the results obtained, the advantages and shortcomings of the time-frequency representations employed are presented and discussed.

Acoustic emission from a dislocation kink accelerated by an external force

Douka E., Polyzos B., Trochidis A.

Archives of Acoustics

2005

Vol. 30, No. 2

247-253

The emission of elastic waves from a dislocation kink accelerated by a constant external force is presented. The dynamics of the dislocation kink interacting with longitudinal acoustic waves is described by a sine-Gordon--d'Alembert system, i.e. a sine-Gordon equation nonlinearly coupled with the d'Alembert wave equation. Within the framework of this model, the evolution of velocity of the dislocation kink altered by the applied force is determined, allowing for mechanical couplings. The total energy radiated from the dislocation kink and its spectral composition is calculated numerically and analytically. Computer simulations are presented, which graphically illustrate the analytical considerations and model the acoustic radiation.