Finite element modeling of conical acoustic emission sensors and corresponding experiments

Mass-backed piezoelectric conical sensor elements are investigated by modeling and corresponding experiments for their response to pencil lead breaks on an aluminum plate. For the experiment and modeling investigation, the plate is chosen large enough to avoid interference of the detected signal by edge reflections within a time frame of 150 μs. Signals from conical elements with varying cone angle are investigated. For simulation of the sensor signals an approach using multi-scale finite element modeling with coupled partial differential equations is presented. The simulation approach takes into account the signal excitation by pencil lead fracture, formation of Lamb waves, signal propagation and the details of the detection process. This process includes piezoelectric conversion and the influences of the complex impedance of the attached cables and circuitry. Experimental signals and simulated signals are compared as a function of the tip diameter of conical sensor elements. Using the presented method the absolute sensor response can be predicted for arbitrary propagation media and geometries like plates or rods, as well as for alternate sensor geometries.