Visualisation of guided wave propagation by ultrasonic imaging methods

Structural health monitoring (SHM) with Lamb waves (LWs) principally enables an in-service damage detection of large aircraft components without time-consuming scanning. Piezoelectric elements can be effectively used as senders and receivers for LWs. However, the complex interaction between defects and Lamb waves – especially for composites, the presence of two wave modes in minimum and its dispersive behaviour and reflections from all structure elements contribute to receiver signals which are very difficult to predict and to evaluate. Ulltrasonic imaging technique (UIT) can also be used for the visualisation of LW propagation in composites especially using air-coupled techniques. Out of the recorded full-wave data calculations of Lamb wave A-, B-, C- and D-scans and video animations can be carried out. Examples of visualisation in composites such as monolithic specimens, a stringer stiffened laminate and a sandwich tail boom which impressively show the Lamb wave propagation and also their interaction with defects.