Structural Health Monitoring Using Lamb Waves

Abstract

In opposite to longitudinal waves which are used for local testing with high resolution, Lamb waves can penetrate large areas of components. However, for a given frequency at least two modes – one symmetric and one antisymmetric – are generated. These modes are dispersive, which means that their velocities are frequency-depending. For the damage detection it is important to select the optimal wave mode and to know the propagation and the interaction with defects. Therefore research fields are: sensors, excitation, onding/embedding of sensors, excitation, propagation, interaction with defects, signal processing and signal evaluation. Our research topics are visualisation of the Lamb wave propagation and its interaction with damages, as well as analysis of the correlation between progressing damage types and active Lamb wave signals. The ultrasonic imaging technique has been adapted for the visualisation of Lamb waves. DLR is involved in the EU-project AISHA (Aircraft integrated structural health assessment) together with METALogic (coordinator, SME), Katholieke Unversiteit Leuven – MTM, CEDRAT Technologies Eurocopter France, Riga Technical University, Fundacion Centro de Tecnologias Aeronauticas, TGA (SME) and ASCO. This paper presents results about the interaction between Lamb waves and damage types caused by impacts and Lamb waves in CFRP- sandwich components with honeycomb cores.