The crack detection and evaluation by elastic wave propagation in open hole structures for aerospace application

The rectangular plate made of aluminum alloy with a relatively large circular hole in the geometrical center of the structure is subjected to uniform tension. This loading causes that in the vicinity of a hole a process of crack formation is triggered. The crack is detected and evaluated with the use of elastic wave propagation method. The piezoelectric activator is located directly on the edge of the hole and the rest of sensors are placed at an equal distance from the activator. The crack is detected by comparison of the reference, obtained for the intact plate, and the actual signal (pitch-catch measurement). The appropriate damage magnitude measurement is proposed. Moreover, the system, which works without knowledge of an intact structure, is also discussed. In order to estimate and visualize the length of a crack, the advanced diagnostic imaging is introduced. The applied method is based on a visualization of sensing paths with an assigned value of correlation coefficients, computed for reference and actual signals. The effectiveness of the described system is verified with the use of numerical simulation and experimental test. The theoretical analysis is carried out with the use of the finite element method. The computations are performed for several assumed lengths of cracks. The obtained theoretical results, as well as the experimental analysis, confirm the fact that the crack can be detected at an early stage of formation. Moreover, a relatively good agreement between the real crack lengths and the ones obtained with the use of the proposed method is observed in the numerical analysis as well as in the experiment.