Feature Based Studies on Guided Ultrasonic Wave Modes for Anomaly Estimation in Composite Structures
This paper reports some of the recent studies on the utilization of surface waves and plate waves resonances for a quantative estimation of anomalies such as porosity, fiber volume fraction changes, fiber mis-orientation, hydro-thermal degradation in fiber reinforced composite materials. Models describing anomalies within an arbitrary layup of fiber reinforced composite laminates are coupled to generalized wave propagation models for plate waves and surface waves in such structures thus providing useful NDE tools. A feature based approach was also adopted here, for the analysis of the wave mechanics interaction with anomalies.
In the case of Plate wave resonance, the critical frequency values (minimas) were found to provide new features which provide additional sensitivity (when compared to traditional methods) to subtle anomalies such as porosity. Careful experiments were shown to support theoretical predictions. The new features were tested on a wide range of specimens with programmed anomalies.
The surface waves were successfully generated on composite structures using a novel line source wedge transducer (due to Snell’s law limitations, the regular angle shoes were not found practical). Features from the azimuthal velocity variations are useful to isolate specific anomaly influence from the often occuring velocity changes due to anisotropy and inhomogenieties.
KeywordsSurface Wave Line Source Fiber Fraction Warp Yarn Porosity Content
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