Electromechanical Impedance Based Structural Health Monitoring During a Dynamic Event

Structural health monitoring (SHM) is a relatively new field with many applications in static and dynamic structures. The capability to develop SHM systems to operate in the microsecond timescale during highly dynamic events has been a focus with applications from mining to aerospace industries. One of the potential solutions is creating an impedance measurement system using the electromechanical impedance (EMI) method. EMI measurements have traditionally been performed using an impedance analyzer such as the HP-4194A, however, these systems are inadequate due to their slow measuring speeds. Other methods of measuring impedance have been developed which offer a dramatic decrease in the time of measurement and other benefits such as decreased size and cost. In this study, a previously developed test stand at the Dynamic and Smart Systems Laboratory at Tennessee Technological University was utilized to investigate the ability of the EMI method to monitor a dynamic event caused by an impact of a pneumatically actuated striker bar against a beam bonded with a piezoelectric disk. The dynamic response of the beam and impedance during the impact are studied experimentally, and a finite element model of the experiment is studied to better understand the propagation of elastic waves at different impact velocities. Preliminary results indicate a change in impedance at impact , but further research is necessary to determine if this change is due to the change in boundary conditions (added mass of the projectile) or simply a result of the impact waves in the system because of the impact