Influence of Surface Roughness on Guided Waves in Plates

摘要

This report covers fundamental research performed on the effect of surfaceroughness on ultrasonic guided waves in plates. The effort reported here consists both of experiments and calculations. The measurements exploit guided waves generated in either immersion or with contact coupling. Samples have included aluminum prepared by indenting or sandblasting. The sandblasted specimens have been independently profiled to determine rms roughness. A simple model calculation is also described which, using analytical methods only, has led to a successful approximate theoretical description of guided wave attenuation caused by scattering from randomly rough surfaces. The model takes advantage of the Kirchhoff approximation, in which the rough surface wave interaction is assumed to be restricted to the signal phase. This phase screen method is applied to guided plate waves through Auld's transverse resonance approach to derive a dispersion relation of the rough waveguide. This calculation is generalized to fluid immersed plates having only a single rough surface either on the same or opposite side of the plate as the ultrasonic transducers. Detailed comparisons between the results of the experimental study and predictions of the model calculations show good agreement, generally demonstrating the utility of the theoretical approach over a reasonably wide range of variation of the experimental parameters.