Phased array for guided waves and crack detection for airframe structures

Linear phased arrays approach is proposed in comb configuration to excite guided wave modes either with a toneburst or a spike-pulse on relatively thin airframe skin and lap joint structures. In a first instance, it is shown that, through time-delay adjustments, the generated guided modes could be selected independently of the type of excitation and exhibit unidirectionality. Then, tests to detect crack-like defects at the faying surface between the lower skin and the upper skin/doubler assembly were performed by selecting appropriate guided waves modes. These modes were launched from outside the hidden area to interrogate the interested rivets, their respective received RF signals including indications and reflections from the defects. For each guided wave test, a single line of data was collected by moving the probe along the inspected line of rivets. Signals are presented in color-coded two-dimensional C-scan format. For defect separation and characterization, images are then averaged and reconstructed using a synthetic focusing technique.