Instantaneous crack detection under varying temperature and static loading conditions

On the basis of guided wave propagation in plate-like structures, the authors' group previously developed a reference-free crack detection technique. The previous technique requires the placement of two pairs of collocated lead zirconate titanate (PZT) transducers on the top and bottom surfaces of a structure. However, as access to both surfaces can be limited for some structural systems, such as aircraft and pipelines, an improved reference-free crack detection technique is developed in this study to overcome this limitation. The major advancements of the proposed reference-free technique over the previous one are (1) reformulation of the reference-free technique considering energy distribution among Lamb wave modes to overcome the limitations of the previous time domain approach, (2) extension to allow the use of various input waveforms including broadband chirp signals and narrowband toneburst signals, and (3) newly designed PZT transducers for single surface installation and better ruggedness. Numerical simulations and experimental tests on aluminum plates are performed to investigate the performance of the proposed technique. In particular, its robustness to varying temperature and external loading is experimentally tested. Copyright (C) 2010 John Wiley & Sons, Ltd.