9. Electromechanical Impedance Method for Applications in Boundary Condition Replication

One of the most challenging parts of modeling structural dynamics is realistically replicating boundary conditions from either a theoretical or experimental perspective. In a finite element model, the mechanical impedance of bolted joints in an assembly can be modeled, as a first step, as an equivalent spring-damper connection. For relatively simple systems, the parameters of such an approximation are updated such that the dynamic characteristics of the model match with the jointed structure. When the assembled structure is in an operational environment, joints are one of the first components of the assembly to change their dynamic characteristics. As a result, identifying a change in their dynamics and further keeping track of the changes is burdensome. Additionally, if a change is detected, it is equally difficult to modify the structure to its previous state without exhaustive testing.

To address some of these issues, the present work leverages coupled electro-mechanical impedance-based techniques to monitor the jointed boundary conditions. In this technique, the mechanical impedance of the assembly is indirectly tracked by measuring the electrical impedance of the attached piezoelectric (PZT) system. In the present study, a PZT patch is bonded to the Box Assembly with a Removable Component (BARC) test structure with ten dry bolt connections. First, a baseline electro-mechanical measurement of the ideal assembly is determined and then the torque of the connecting bolts is then slightly altered. As a result, the dynamic properties of the BARC structure along with electrical impedance response of the PZT changes. The feasibility of tracking these changes and determining the modifications necessary to bring the system to its previous dynamic state is the focus of this work.