Time-resolved modal decomposition based on the Linear Prediction Method-Applied for crack detection

A nondestructive technique for testing and monitoring structures is presented, this uses guided waves to avoid a long scanning process. In contrast to other techniques that use guided waves this method can be applied to any structure made of a material that can be dispersive, strongly attenuating, and anisotropic, without the need of special adaptation. This is demonstrated on beams made of aluminum and wood. The propagating waves are reflected at any acoustic discontinuity, for example, by cracks and defects. In strongly attenuating materials such as wood, it is necessary to work with low frequencies, but due to the correspondingly long wavelength, the incident and reflected (from defects and boundaries) waves superimpose. The presented new signal processing technique allows the determination of the wave modes and their propagation direction very accurately in the time domain. Incident and reflected waves can easily be distinguished by the propagation direction. Since the wave mode is known from signal processing the right group velocity is applied for an accurate calculation of the defect location.