DAMAGE DETECTION IN CIRCULAR CYLINDRICAL SHELLS BY FREQUENCY SENSITIVITIES AND MODE SHAPES

The damage location assurance criterion (DLAC) is extended to locate and assess damage in a circular cylindrical shell based on natural frequency sensitivities and mode shape deviations. Frequency sensitivities obtained from a defect-free finite element model are applied to calculate the theoretical frequency changes. The axial position of the damage can be easily obtained by comparing the theoretical and measured frequency changes due to damage. For the shell is axis-symmetric, additional information of mode shapes is introduced to locate the exact damage position. The damage extent can be estimated by the first order approximation method. The feasibility and practicality of the damage detection scheme are evaluated by locating and sizing damage for several damage scenarios in the free-free, simple-supports and free-clamped shells, respectively. Simulation results show that the proposed detection scheme can well locate the single or multiple positions of damage. It is also observed that damage extent can be estimated within a relatively small error. The robustness of the proposed method in the presence of measurement errors is demonstrated.