Structural integrity inspection using dynamic responses

Structural Health Monitoring is of vital importance in today's industry. This thesis will present a model-independent method of detecting damage in structures. A scanning laser vibrometer is used as a quick and accurate means of obtaining the dynamic response of structures. The natural frequencies and mode shapes thus obtained are compared to analytical and numerical results and are shown to be in close conformance. A numerical solution is obtained using an in-house finite element code developed in Matlab. Further, the experimental data is processed using a Boundary Effect Detection (BED) method to pinpoint the location of defects. This method uses a sliding-window least-squares curve fitting technique and the concept of boundary and central solutions to locate defects. Defects are characterized by the existence of additional boundary solutions at points other than the structural boundaries. Numerical simulation is performed on a clamped-clamed beam to study the detection of defects close to structural boundaries. Experiments are conducted on a beam with a fatigue crack, a cantilevered beam with 4 cracks and 2 internal holes, a hollow aluminum pipe with damage on its rear surface and an aircraft wing panel with a damage located in the vicinity of a machined feature. Results show that the experimental and numerical dynamic characteristics match closely and that the BED method is capable of accurately predicting the location of defects.