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A Local Sensor Configuration for Multiscale Damage Detection in an Aluminum Beam Alloy Structure with a Loose Bolt Joint



In this work we present the results of a basic experimental research effort to detect local damage over a spectrum of natural space and time scales of impulsebased interrogation free waves-and-vibrations in a physical aluminum alloy beam structure with a damaged bolts-based local joint. The joint is considered healthy if all its bolts are tightened to the level of the design recommended torque load. We use three mono-axial sensors in a local three dimensional arrangement and a modal hammer to mine rich information on the dynamics in the form of collocated axial, lateral and transverse acceleration signals. The mutually perpendicular collocated databases are analyzed in terms of their proper orthogonal decomposition (POD) modes. We find that the dominant POD modal shape-in all three directions-of the healthy structure changes when one of the bolts is left loose. This change is quantified as a distributed damage index which turns out to possess localized behavior near the loose bolt and the nodal points of the POD modal shape. It is found that the lateral collocated acceleration database is much more sensitive to the loose bolt kind of damage than the axial and the transverse collocated databases are.

doi: 10.12783/SHM2015/65

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