Crack identification in a cross-stiffened plate system using the root mean square of time domain responses

Abstract

On-line identification of cracks occurring in large structures has attracted the attention of many researchers. Identification becomes difficult when there is no easy access available for investigators to employ conventional nondestructive evaluation techniques. In this paper, a scheme is presented for identifying the crack location and its extent using vibration response. Numerical studies were carried out on a 1/20th-scale model of the side shell of the structure of a ship. The first natural frequency of the numerical model was 584.3 Hz. The numerical and physical models were excited by a random force having a dominant spectral frequency of 2 Hz. Cracks under investigation occurred at the connection between a horizontal and bulkheads and at the intersection between horizontals and a web frame. A scheme using the root mean square of vibration response is presented for identifying cracks occurring in the flange and web of the horizontal. It is demonstrated that the scheme can identify the crack location and size.Key words: side shell of a ship model, pre-resonance excitation regime, vibration-based monitoring.