A study on crack detection using eigenfrequency test data

In this paper, a simple and easy nondestructive evaluation procedure is presented for identifying a crack, the location and size of the crack, in a one-dimensional beam-type structure using the natural frequency data. The first procedure is to find the lowest four natural frequencies of the cracked structure by F.E.M. Then, the approximate crack location is obtained by Armon’s Rank-ordering method that uses the above four natural frequencies. Second, by applying the result of the crack position range, an appropriate F.E.M. model is adopted and the crack size is determined by F.E.M. Finally, the actual crack location can be identified by Gudmundson’s equation using the determined crack size and the aforementioned natural frequencies. The application and accuracy of the proposed procedure can be demonstrated by means of an example of the detection of a crack on the cantilever beam which was tested and studied by Rizos PF, Aspragathos N, Dimarogonas AD. Journal of sound and vibration 1990; 138 (3): 381-388.