On Structural Damping Characteristics in the Electro-Mechanical Impedance Method

The electro-mechanical impedance method is a useful tool for structural health assessment in a broad range of applications. In the past, the electro-mechanical impedance method was utilized for assessment of metallic aerospace structures. However, advancements in materials engineering have led to the emergence of composite materials as the preferred choice for many aerospace applications. Limited work exists on application of the electro-mechanical impedance method to composite materials. To evaluate the behavioral differences between metallic and composite materials, a study into the impedance response of one dimensional beam structures with surface-bonded thin piezoelectric wafer sensors was conducted. Euler-Bernoulli beam theory is incorporated in the development of an analytical solution, along with viscous and strain-rate damping models, to evaluate the interaction between the piezoelectric wafer and the resulting bending moment and axial force in the beam. Modeling results were compared to experimental observations. Experimentally obtained damping characteristics were utilized to update analytical and numerical electro-mechanical impedance models. The sensitivity of the electromechanical impedance method to detect damage at various distances from a piezoelectric sensor was evaluated in composite and metallic materials using beams of different lengths. Using the results from these studies and evaluation of the effects of attenuation and structural geometry suggestions for structural evaluation using the electro-mechanical impedance method are presented.