Random decrement technique for damage identification of stiffened plates

Most of the damage in ship structures occurs in the side shell, especially in the connection between the longitudinal and transverse members. The purpose of this study is to apply the random decrement technique for identifying the damage in the longitudinal using a combination of experimental and numerical studies. The side shell was modeled as a stiffened plate that consists of a plate, a longitudinal and a T-section transverse member. An experimental study using modal testing technique was carried out to measure the acceleration frequency response function and the random acceleration response of an undamaged model as well as a model with progressive damage. The damage was made with a hacksaw at the longitudinal near the transverse member. The random response time history for each crack length was analyzed using the random decrement technique to obtain its random decrement signature. Furthermore, a finite element model was developed by applying the SISO (single-input single-output) procedure to analyze the acceleration frequency response functions and the acceleration free vibration responses of the undamaged and damaged stiffened plates. The results were then compared to those of the experimental ones. From the random decrement signatures and free vibration responses, their sensitivity to the induced cracks of various lengths was correlated.