Tomography Techniques for Acoustic Emission Monitoring

The acoustic emission (AE) technique represents a structural health monitoring approach that uses AE events caused by crack formation and growth in a structure under external load to monitor its structural integrity. Besides pure counting (AE activity), localization as well as moment tensor inversion are well known variants of AE analysis. In this paper a new imaging technique is presented that uses AE events as sources for ultrasonic travel time tomography. For that purpose the localization algorithm is iteratively combined with an appropriate tomography algorithm. In addition to visualizing the volume of the specimen in terms of source positions, the resulting new imaging technique provides a locally varying wave speed distribution. Moreover, the finally determined sources can be used to image the reflection properties by applying synthetic aperture focusing techniques (SAFT). The new imaging method was developed, tested, and validated by using extensive numerical simulations based on the elastodynamic finite integration technique (EFIT). Examples of application in the field of concrete testing and guided wave monitoring of plate-like structures are presented.