Development and Applications of Laser-ultrasonic Testing in Nuclear Industry
A laser-based maintenance system, which includes the las er-ultrasonic testing as a non-destructive testing technology, the laser-peening as a surface stress imp rovement technology and the laser welding as a repair technology, for the in-service maintenance of n uclear reactor internal components is presented. Regarding the laser-ultrasonic testing, surface acoustic wave generated and detected by lasers is used to detect surface-breaking cracks. As the benefits of broad -ban feature of the laser-ultrasonics, this method allows to detect very small cracks having the depth of les s than 0.1mm. Also, a frequency response analysis technique of the surface acoustic wave, which propagates through the crack, is developed to size the depth of the crack. The error of this depth measurement thod is estimated at less than 0.2 mm through a series of experiments using stress corrosion cracki ng. A part of the laser-based maintenance system has been already applied to the actual maintenance works in Japanese nuclear power plants . The developed system and its operation are presented. Finally, m ore recent work to detect and visualize small defects on the weld bead by using leakly-Rayleigh waves is introduced.
Looking at sound: optoacoustics with all-optical ultrasound detection
Originally developed for diagnostic ultrasound imaging, piezoelectric transducers are the most widespread technology employed in optoacoustic (photoacoustic) signal detection. However, the detection requirements of optoacoustic sensing and imaging differ from those of conventional ultrasonography and lead to specifications not sufficiently addressed by piezoelectric detectors. Consequently, interest has shifted to utilizing entirely optical methods for measuring optoacoustic waves. All-optical sound detectors yield a higher signal-to-noise ratio per unit area than piezoelectric detectors and feature wide detection bandwidths that may be more appropriate for optoacoustic applications, enabling several biomedical or industrial applications. Additionally, optical sensing of sound is less sensitive to electromagnetic noise, making it appropriate for a greater spectrum of environments. In this review, we categorize different methods of optical ultrasound detection and discuss key technology trends geared towards the development of all-optical optoacoustic systems. We also review application areas that are enabled by all-optical sound detectors, including interventional imaging, non-contact measurements, magnetoacoustics, and non-destructive testing.Optical sensors: Ultra-sharp views of ultrasoundOptoacoustic systems that use laser-induced ultrasound waves to reveal the 3D interiors of biological and man-made materials can find wider applications with optical sensors. Georg Wissmeyer from the Technische Universität München in Germany and colleagues review how high-bandwidth optical components are replacing conventional piezoelectric and capacitive sound detectors. One approach, which measures the phase of a probe beam as it reacts to ultrasound-driven changes in refractive index, can capture the entire acoustic field moving through a medium in a single snapshot. Another strategy employs micro-resonators to miniaturize interferometric sound sensors onto the tips of optical fibers for challenging intravascular imaging, such as during stent implantation. Because all-optical sensors are relatively insensitive to electromagnetic noise, they can be deployed in industrial environments for non-destructive testing of material defects.
ULTRASONIC ELASTIC WAVE MODEL STUDIES
The scattering of ultrasonic waves forms the basis for many NDE techniques. Numerical models are shown to provide insight into a range of Rayleigh wave/surface feature interactions for which there is no adequate analytical theory. Results are obtained with the ‘USWAPS’ computer programs for slots and troughs and compared with those from laboratory experiments. The range of features which can be studied is extended with the development of models based on a general curvilinear grid for smooth sided troughs. The results obtained have potential application in ultrasonic NDE as well as both seismology/geophysics and SAW Electronics.