Dynamic behavior of a zero-group velocity guided mode in rail structures.

Important characteristics of a zero-group velocity (ZGV) mode in a standard rail are investigated through numerical simulation and experiment. First, the semi-analytical finite element analysis is implemented to compute dispersion curves for the rail structure and the first ZGV point is identified. Backward waves are identified through opposing senses of group and phase velocities.

Air-coupled ultrasonic diffuse-wave techniques to evaluate distributed cracking damage in concrete.

In this study, we investigated the suitability of applying air-coupled ultrasonic diffuse-wave techniques to concrete structures for the evaluation of arbitrarily distributed micro-cracking damage. Air-coupled test results were compared with those obtained using a conventional full-contact measurement system. Three different micro-cracking damage levels were simulated by embedding varying amounts of low-stiffness polypropylene fibers in concrete samples.

Extracting non-propagating oscillatory fields in concrete to detect distributed cracking.

Work to detect and locate distributed subsurface cracks in concrete by extracting non-propagating oscillatory fields is presented. The medium of interest is concrete, but the approach also applies to other types of inhomogeneous media. The theoretical basis of the work is first presented through a one-dimensional point-scatterer model that considers the wavefield set up by multiple distinct scatterers.

Surface-Wave Based Model for Estimation of Discontinuity Depth in Concrete.

In this paper, we propose an accurate and practical model for the estimation of surface-breaking discontinuity (i.e., crack) depth in concrete through quantitative characterization of surface-wave transmission across the discontinuity.