Virtual Sensors for SHM using Isogeometric Piezoelectric Finite Elements

Guided waves like Lamb waves can be excited and received easily by PZT patches attached on plates and plate-like structures. They propagate over large areas with small attenuation and interact with structural discontinuities such as impacts. Therefore, this principle can be used for impact detection and localization. The wave propagation can be very complex due to reflections, refractions or mode conversions. A simulation of the exact wave behavior in complex components poses a hard challenge due to non-exactly known material parameters and high requirements on computing power. Furthermore, simulations have to be validated with experiments. At the German Aerospace Center an imaging technique for guided wave investigations was developed. Here, a combination of bonded actuators for wave excitation and air coupled ultrasonic scanning technique is used for wave propagation investigations. The measurement data contains all information of wave interaction with the real structure and can be used for different imaging methods like B-Scans or video animations of wave propagation. The measurement data can also be used for advanced tasks like virtual sensors. In this technique measured displacements of the structure surface are used as stimulation of a virtual sensor which can be designed by software and positioned within available data field. For the calculation of sensor signals an isogeometric finite element model is used. The virtually bonded layer of the virtual piezoceramic sensor interpolates with non-uniform rational B-Splines (NURBS) the measured nodal data for each time step. This interpolation corresponds to a displacement boundary condition and is used to calculate the electrical potential at the free surface of the sensor. Isogeometric finite elements have, due to their higher polynomial approach, a better convergence and the elements can be distorted. Therefore, they allow better results with less numerical effort than standard FEM applications