Measuring predictability in ultrasonic signals: an application to scattering material characterization

A Nonlinear Method for Characterizing Discrete Defects in Thick Multilayer Composites

Discrete defects in thick composites are difficult to detect for the small size and the structure noise that appears in multilayer composites. In this paper, a nonlinear method, called recurrence analysis, has been used for characterizing discrete defects in thick section Carbon Fiber Reinforced Polymer (CFRP) with complex lay-up. A 10 mm thick CFRP specimen with nearly zero porosity was selected, and blind holes with different diameters were artificially constructed in the specimen. The second half of the backscattered signal was analyzed by recurrence analysis for areas with or without a defect. The recurrence plot (RP) visualized the chaotic behavior of the ultrasonic pulse, and the statistical results of recurrence quantification analysis (RQA) characterized the instability of the signal and the effect of defects. The results show that the RQA variable differences are related to the size of blind holes, which give a probable detection of discrete geometric changes in thick multilayer composites.

A model of blind zone for in situ monitoring the solid/liquid interface using ultrasonic wave

To in situ monitor a solid/liquid interface to control metal qualities, the paper analysis blind models of the ultrasonic propagation in the solidifying molten metal with a solid/liquid interface in the Bridgman type furnace, and a mathematical calculation model of blind zone with different source locations and surface concavities is built. The study points out that the blind zone I is caused by ray bending in the interface edge, and the blind zone II is caused by totally reflection which is related with initial ray angle, critical refraction angle of solid/liquid media. A serial of simulation experiments are operated on the base of the model, and numerical computation results coincide with model calculated results very well. Therefore, receiver should locate beyond these blind zones in the right boundary to obtain time of flight data which is used to reconstruct the solid/liquid interface.