Large welded structures, including ships and offshore structures, are normally in operation under cyclic fatigue loadings. These structures include many geometric as well as material discontinuities due to weld joints, and the fatigue strength at these hot spots is of critical importance for the structural performance. In the past, various Non-Destructive Evaluation (NDE) techniques have been developed to detect fatigue cracks and to estimate their location and size. However, important limitations of most of the existing NDE methods are that they are off-line; the normal operation of the structure has to be interrupted and the device often has to be disassembled. In this context, a new impedance-based structural health monitoring system employing piezoceramic transducers is developed with a special interest in applying the technique for welded structural members in ship and offshore structures. In particular, the impedance-based structural health monitoring technique that employs the coupling effect of piezoceramic (PZT) materials and structures is investigated. Moreover, a preliminary study of using fiber Bragg grating (FBG) type optical fiber sensors for the stress measurement of a typical weld structure is investigated. The final goal is to extend the fiber optic sensor technique for the global and local stress measurements of ship or offshore structures.
