Analysis Method for Guided Wave Propagation Direction in Anisotropic Structures

Abstract

Guided waves, such as Lamb waves, enable a Structural Health Monitoring (SHM) of modern composite structures. However, due to the complex wave propagation different scanning and imaging methods were developed in the past. They enable a better understanding of the wave interaction with complex structures. Beyond video animations of the wave propagation advanced analysis methods are possible. A promising application is the virtual design and optimization of sensors and sensor networks based on acquired measurements. In this technique a piezoelectric transducer is used for guided wave excitation in a specimen. An air-coupled ultrasonic sensor is moved across the specimen surface. For every scanning point the received signal is recorded. After this, a compensation of the wave radiation through the air gap combined with a model of the investigated specimen is used to reconstruct its dynamic surface deformation. The deformation is applied to a numerical model of a virtual sensor which delivers the response signal. In this way an optimal dimensioning of sensors in number, position, form and material properties can be developed for SHM sensor networks. Applications like this require knowledge of the propagation direction of every guided wave mode within a wave field. The actuator position cannot be used exclusively because mode conversion may occur on any position. This paper presents a method for propagation direction evaluation based on acquired measurement data. In combination with a mechanical model of the structure anisotropic propagation is utilised for accuracy improvement. The results are calculated in the time domain and contain a specific time window for any identified wave mode. The presented method can be used for advanced applications of guided wave analysis.