The presentation will show that thermographic NDT, which has long been associated with the detection of sub-surface in-plane faults in composites or coatings, also has great potential to compete with DPI and MPI for the detection of cracks in metallic components. Work on three thermographic NDE techniques that have been developed to locate and image cracks in metallic components will be reviewed. These techniques are: thermosonics (sonic IR, ultrasonically stimulated thermography); laser spot thermographic imaging and pulsed eddy current stimulated (induction) thermography. The three techniques will be explained and examples will be given of their performance in imaging well characterised cracks. Factors concerning the practical and reliable implementation of the techniques will be discussed.
Abstract. In this chapter we report on the application of the pulsed eddy current thermography inspection technique to the detection and quantification of defects in a variety of materials. After introducing the appropriate modelling and simulation techniques an overview of a typical PEC thermography system setup is provided. Applications of the system for defect detection in nickel alloys, composite materials and ferritic materials including multiple complex cracking in rail-tracks are discussed.
There is increasing demand for accurate characterization of the in vivo behavior of microbubble agents used for ultrasound imaging and therapy. This study examines bubble-vessel interaction, in particular the propagation of disturbances along the vessel wall. Finite element simulations of a 3 μm radius microbubble suspended in a viscous liquid and enclosed in a 4 μm radius elastic vessel were performed, and the results compared with existing analytical results for wave propagation in elastic liquid-filled tubes. The vessel wall was shown to have a significant effect upon the amplitude of bubble oscillation and hence acoustic radiation from it, as well as distension of the vessel wall. It was found that the most important factor was the ratio of the excitation frequency to the natural "ring" frequency of the vessel which in turn depends upon its dimensions and mechanical properties. As this ratio increases, the motion of the vessel wall becomes increasingly localized to the site of the bubble. It was also shown that the validity of the results obtained using the applied model of vessel elasticity is limited to frequencies below the ring frequency, and this should be taken into account in the development of protocols for ultrasound safety and/or therapeutic procedures.
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