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Online damage detection and structural health monitoring (SHM) of aerospace structures are having great scientific and economical importance, since maintenance costs can be considerably reduced by introducing condition-based structural maintenance instead of time-linked preventive maintenance. Active structural health monitoring using guided wave modes is gaining importance after the introduction of lightweight piezoelectric wafer transducers (PWTs) since the mass penalty associated with these systems is considerably less. Multiple research papers are generated worldwide on the use of guided Lamb wave modes for active defect detection in thin platelike structures. Since so many civil and aerospace structures are cylindrical in shape, studies on the use of guided wave modes for SHM of cylindrical shells are gaining importance. Studies on the use of guided wave modes for SHM of cylindrical shells and pipes are done by a few authors by pulse echo method. In this chapter, the methods to generate different guided wave modes in metallic isotropic cylindrical shells, dispersion characteristics of wave modes in cylindrical shells, their interaction with defects, etc., are studied. Moreover, the structural health monitoring of cylindrical shells using the time reversibility concept adopted from guided Lamb wave mode is also studied. Numerical modelling of propagation of guided wave modes in plates and cylindrical shells is done using finite element methods, and comparisons are made. Experimental evaluation on the propagation of guided waves in cylindrical shells is carried out. Dispersion characteristics of guided wave modes in cylindrical shells and the signature of guided wave modes for different defects are studied by numerical modelling and experiments. A tomography scheme is worked out which can predict the presence of defects and its propagation, which can be used for condition-based structural maintenance of aerospace structures. A comparison between the numerical modelling and experimental studies is done, and damage indices based on time-reversed reconstruction are generated. |
