A Time and Frequency Domain On-line Crack Identification of Stiffened Plate Panels

摘要

This paper describes a methodology for on-line crack identification of a stiffened plate structure. The methodology is based on the measured/computed root mean square (rms) amplitude response obtained from random vibration testing and analysis. The random excitation force simulated the excitation force exerted on the structure due to the modeled wave spectrum (with a dominant frequency of 2 Hz). The fundamental frequency of the structure was 584.3 Hz (flexural-torsional frequency of the main stiffener), whereas the first bending frequency of the stiffened plate system was 1136.7 Hz. The basic idea is that when a crack is present in a structure, the computed/measured rms amplitude of response would change; and by monitoring the rms responses at several locations for several crack cases, the crack location and extent could be identified. A one-twentieth scale model, of a stiffened side shell panel of a tanker ship structure, was tested in the experimental study; a specimen was tested for different crack development scenarios. Since the methodology does not require the measurement of the excitation forces, the measured structural responses were normalized by the computed rms response amplitude [computed for the excitation frequency range (0 to 5 Hz)]. Results of testing carried out on the model and analysis of test results for predicting various damage cases are reported.