Effect Of Axial Load On Admittance Signatures Of A Beam With Clamped Boundaries

In recent years, the drawbacks of conventional non-destructive testing methods for civil structures have gradually revealed as the construction techniques developing. Health monitoring system based on smart material holds evident advantages over the conventional methods, providing reliable, cost-efficient and real-time monitoring, amongst which the electro-mechanical impedance(EMI) method arouses general attention of many researchers due to its sensitivity in detecting damage.Practical structures are inevitably suffered from loads which can affect the admittance signatures measured using the EMI method. In this thesis, to investigate the effect caused by axial load applied on host structures, a series of theoretical, numerical, experimental and compensation studies are conducted.The admittance expression of an aluminum beam under varying axial load with both of its boundaries clamped is derived. Theoretically, the resonant peaks caused by the transversal vibration move rightward or leftward respectively with the increase of tensile or compressive load, while ones caused by the extensional vibration modes are not affected.Experiments to investigate the effect of axial loads on the admittance signature are conducted. It can be found that the resonant peaks caused by both the transversal and axial vibration move rightwards. However, the resonant peaks caused by the axial vibration move less while the differences of the measured resonant peaks and their theoretical values are nearly the same. In addition, the effect of the enhancement of the boundary constraints on the admittance signature is much larger than that of the compressive load, and all of the resonant peaks move rightwards. The index RMSD(root-mean-square deviation) of the experimental data is calculated. Comparing the RMSD index of different experimantal data, it can be found that the axial loads on the structure bring considerable variation to the RMSD index, which may lead to the misjudgement of the health condition of the main structures.