Study On Properties Of Guided Waves Excited By D₃₆ Type Wafers On Pipes

The pipe structure is widely used in civil engineering, mechanical engineering andaerospace engineering. The structural damage of pipe structures could lead to seriouseconomic losses and casualties. The damage detection and health monitoring for pipestructures can insure their safety, integrity and durability. The damage detection methodbased on ultrasonic guided wave has been proven its availability. The horizontal shear(SH) wave has more advantages since it is non-dispersive and there is no modeconversion while reflecting on the boundary. This thesis studies mainly on theproperties of guided waves excited by d36type piezoelectric wafer. The contents of thisthesis are as following:Guided wave theory for pipe is reviewed at first, including the dispersion equationsand curves for axisymmetric and non-axisymmetric wave modes and circumferentialwave modes. The displacement responses of guided waves are analyzed underasymmetric excitation. The materials properties of d36type piezoelectric wafers and thecharacteristics of guided waves excited by this wafer in plate are also introduced.Secondly, the d36piezoelectric wafer would excite the torsional wave as well as theflexural wave and longitudinal wave together, which results in the additional complexityof the guided waves propagating in pipe. Therefore, finite element simulation isemployed to explore the characteristics of guided waves exciting and receiving by d36type wafer in pipe. Different wafer configurations are used to understand thecharacteristics of all wave modes.Finally, the experiment of exciting and receiving of guided waves using d36piezoelectric wafers are implemented in an aluminum pipe. Under asymmetric andsymmetric excitation, the characteristics of guided waves, the tuning frequencyproperties and the distribution in circumference are investigated mainly. The differencebetween boundaries reflection and direct receiving methods are comparedexperimentally.