Acoustic Emission Testing (AE)

Jeff's Hideaway

Wave Based Acoustic Emission (Modal AE)

Traditional AE only uses some of the features of the AE signals due to the limitations of the sensors and data capturing and analysis capabilities. Modal acoustic emission is a relatively new nondestructive testing (NDT) method which represents the latest development in the field of acoustic emission, including wide band high sensitivity sensors that can capture the entire waveform and fast data acquisition and waveform analysis. Modal AE determines the location of acoustic emission sources in plates, rods, shells, and other thin-walled materials using the shape of the wave mode.

Extensional and Flexural Wave

Technology

The wide band stress wave that is emitted from the fracture will propagate in the material in particular modes. These modes have a characteristic shape and frequency content. The extensional and flexural modes will arrive first and are easily identified. The software can then discriminate actual fracture events from extraneous noise and perform accurate location algorithms.

History
Knowledge of the modal nature of wave motion in finite or bounded structures has a long history, but its application to acoustic emission is relatively recent. Modal AE was first applied to composite material laboratory specimens where it was shown that transverse matrix cracks produce a definite wave mode which can easily be measured and counted. Modern modal AE testing was stimulated by the introduction of the first modal AE instrument, the Fracture Wave Detector, by Digital Wave in 1992. Modal AE is now a rapidly growing subject of study at universities and research laboratories worldwide and testing in the aerospace industry.

Applications

Modal acoustic emission (AE) can be applied to laboratory specimens or large production structures with no change in the testing procedure or analysis. This method has been used successfully to detect and locate cracking in both compact test specimens as well as in pressure vessels (spheres, bullets, multi-layer, towers), aboveground storage tanks (AST's), and in composites (FRP Fiberglass Reinforced Plastics). Modal AE allows the researcher to determine the type of failure (e.g., fiber bundle breakage or matrix cracking) occurring in the vessels, based on the frequency content and wave mode shape detected.

Acoustic Emission Sensors on sphere

Digital Wave web site

Digital Wave performs aboveground storage tank (AST) leak detection using procedures based on passive acoustic measurements (API 322) which have been field proven to find leaks. A SONAR beamforming algorithm maps the sound intensity across the floor of the tank from each event. Noise from condensation, floating roof supports, wind blown particles or rain are eliminated due to their non-coherent nature, while coherent leak signals will be displayed much like on a radar screen, occurring over and over at the same position. Peak sound intensities are then plotted as a function of tank bottom location to identify leak sources. If your leak is actively making noise, we will detect and locate the leak to within 1% of the tank diameter. The results of the examination are presented in a clear, easy to read map showing the locations of any leaks.

My email is jeffh(-at-)digitalwavecorp.com.

Some interesting wave sites.

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