Apr 05 2018

Ekramul Ehite defends his MS thesis

Ekramul Ehite¬†successfully defended his Masters of Science degree in Mechanical Engineering entitled “Experimental Investigation of Electromechanical Impedance-Based Structural Health Monitoring in Highly Dynamic Environments” on April 4, 2018. ¬†Congratulations Ehite!


Structural Health Monitoring (SHM) is a damage detection strategy widely used for monitoring the state of engineering structures. The Electromechanical Impedance (EMI) method utilizing piezoelectric (PZT) materials is one of the most common techniques for applying SHM. Contemporary SHM technologies for characterization and assessment of in-service structures are suitable for detecting incipient damage in slowly changing structures on the order of seconds to minutes. There is a growing need to advance this technology for structures operating in highly dynamic environments (e.g. shock, blast, high-velocity impact, hypersonic flight, etc.) to enable microsecond to millisecond detection.

In this study, the application of the EMI method for continuous monitoring of changes of state in dynamic environments is investigated. A modular impact-based experimental system (MIES) is designed, which creates a dynamic event in the form of a collision between a pneumatically actuated moving striker bar and an instrumented static incident bar at different impact velocities. The parameters of the system including the impact velocity, incident bar boundary conditions, and the striker bar dimensions and material are made user-configurable. The velocity of the striker is measured by a photoelectric sensor-based measurement system. The incident bar is instrumented with a single PZT transducer, and the PZT is excited using both single-tone and multi-tonal excitation signals. The impedance of the PZT is measured by an EMI-based impedance measurement system. The velocity data is used to verify the capability of the system to generate customized, repeatable impact events. The impedance data using single-tone excitation signals at different impact velocities show that the impact causes a significant change in the PZT impedance signature, resulting from a corresponding change in the dynamic system state of the incident bar. The impedance data using multi-tonal excitation signals show a similar change in the PZT impedance signature, while allowing multiple frequencies to be monitored simultaneously, thereby providing more information about the system without increasing the measurement time. The overall results indicate that the experimental system can be potentially used for continuous evaluation of system state in highly dynamic environments by combining it with a rapid data acquisition and processing system capable of operating in the microsecond to millisecond scale.