Visualisation of guided wave propagation by ultrasonic imaging methods

Abstract

-Composite materials are more and more used for primary structures in aerospace components. Examples are the new aeroplanes Boeing 787 and the Airbus A350 which are mostly produced out of composites. In order to take advantage of the specific properties of composites the complexity of the structures increases more and more. On the other hand the costs for inspection after fabrication and especially in service have to decrease. Cost effective NDT-methods have to be implemented. This paper presents the possibilities of guided waves inspection techniques for complex composite components. Guided waves such as Lamb waves can be easily excitated and received by applied piezo-elements and penetrate large areas so that complex structures in principle can be inspected (SHM). However, for each frequency in minimum two different wave modes exist so that the responses are difficult to evaluate. The Lamb wave research is carried out within the EU project AISHA. The ultrasonic imaging technique is successfully used for the visualisation of the Lamb wave propagation. This combination between SHM and ultrasonic technique provides the optimisation of the sensor and actuator placement and also an interesting method for in-field inspection of air aerospace components. The coupling of the scanning receiver transducer can be carried out with water split coupling as well as with air (non contact).

Robust and Adaptive Signal Segmentation for Structural Monitoring Using Autonomous Agents

“…The two-dimensional recording of the wave propagation and interaction of guided waves can be performed by using laser vibrometry [9], [10] or an airborne ultrasonic testing technique [11]. In order to be able to excite guided waves, an actuator, usually made of piezo-ceramic materials, must be applied to the structure.…”

“…In order to be able to excite guided waves, an actuator, usually made of piezo-ceramic materials, must be applied to the structure. By adjusting the geometry of the actuator [11] or its electrode configuration [8], the amplitudes of individual modes can be amplified or attenuated to emphasize specific wave interaction. The identification of damages is made by wave interactions, such as reflection, scattering, mode conversion and wave number changes, in wave propagation.…”

Quantitative characterization of interface delamination in composite T-joint using couplant-free Lamb wave methods

“…Non-contact excitation and reception of Lamb waves using either laser ultrasonics or air-coupled transducers are being increasingly used. In early works, visualization of propagating Lamb waves across the impact damages using a scanning laser-Doppler vibrometry 28 and air-coupled ultrasonic transducers 29,30 was proposed to image the scattered out-ofplane Lamb wave field in plate-like structures. In recent work, Hillger et al 31,32 presented an application more directly related to the present paper.…”

“…5–11 In more recent works, Hillger et al . 29,30 presented a Lamb wave–based inspection using a unique transduction combination of fixed PZT’s and air-coupled transducer as an receiver. Group of PZT transducers serving as transmitters were glued on to a section of a Tail-boom structure to excite Lamb waves.…”