The paper presents the application of ultrasonic guided waves for fatigue crack detection in metallic structures. The study involves a simple fatigue test performed to introduce a crack into an aluminium plate. Lamb waves generated by a low-profile, surface-bonded piezoceramic transducer are sensed using a tri-axis, multi-position scanning laser vibrometer. The results demonstrate the potential of laser vibrometry for simple, rapid and robust detection of fatigue cracks in metallic structures. The method could be used in quality inspection and in-service maintenance of metallic structures in aerospace, civil and mechanical engineering industries.

Lamb waves have shown great potential for structural health monitoring. The technique is based on guided ultrasonic waves introduced into a structure at one point and sensed at a different location. Damage in a structure is identified by a change in the output signal. However, previous studies show that even simple structural configurations can lead to complex response signals. Therefore a knowledge and understanding of wave propagation can ease the interpretation of damage detection results. This paper reports an application of the local interaction simulation approach for Lamb wave propagation modelling in metallic structures. The focus of the analysis is on two-dimensional wave interactions with slot-type defects. The method shows the potential for complex modelling of acousto-ultrasonic waves in damage detection applications.

Lamb waves have great potential for structural damage detection in many engineering areas. However, the method requires some experience when complex structures are monitored. Deciding the optimal positions of transducers is one of the most important problems. Sensor location studies can be investigated using a number of signal processing techniques. This paper applies wave propagation modelling for the analysis of sensor positions in Lamb wave based damage detection. The problem is investigated using the local interaction simulation approach for Lamb wave propagation modelling in an aluminium plate with a rectangular damage slot and a fatigue crack. The study demonstrates that sensor location is important for clarity and physical understanding of propagating wave packages, good signal-to-noise ratio and reliable damage detection. All these elements can be investigated using numerical simulations.