Austin Scheyer successfully defended his Masters of Science degree in Mechanical Engineering entitled “An Investigation into the Feasibility of Embedding Piezoelectric Sensors in Additive Manufactured Structures for Impedance Based Structural Health Monitoring” on June 25, 2015. Congratulations Austin!
Abstract:
Embedding sensors within additive manufactured (AM) structures gives the ability to develop smart structures capable of monitoring the mechanical health of a system. AM provides an opportunity to embed sensors within a structure during the manufacturing process. One major limitation of AM technology is the ability to verify the geometric and material properties of fabricated structures. Over the past several years, the electromechanical impedance (EMI) method for structural health monitoring (SHM) has been proven to be an effective method for sensing damage in structures. The EMI method utilizes the coupling between the electrical and mechanical properties present in piezoelectric transducers to detect a change in the dynamic response of a structure. A piezoelectric device, usually a lead zirconate titanate (PZT) ceramic wafer, is bonded to a structure and the electrical impedance is measured across a range of frequencies. A change in the electrical impedance is directly correlated to changes made to the mechanical condition of the structure. In this work, the EMI method is employed on piezoelectric transducers embedded within AM structures to evaluate the feasibility of performing SHM as well as detecting manufacturing errors. The fused deposition modeling (FDM) method is used to print specimens from polylactic acid (PLA) with an embedded monolithic piezoelectric ceramic disc for this feasibility study. The specimen is mounted as a cantilever while impedance measurements are taken using an HP 4194A impedance analyzer. After taking a baseline measurement of the healthy specimen, the Root Mean Square Deviation (RMSD) method is utilized as a metric for quantifying changes to the system. Both destructive and non-destructive damage is simulated in specimens by adding a tip mass and drilling a hole near the free end of the cantilever, respectively. The SHM method proved to be successful at detecting both destructive and non destructive damage. Manufacturing errors are simulated using a reduced infill percentage and internal voids to change the internal structure of specimens. The manufacturing errors proved to be more difficult to detect due to variation between responses from different specimens, though this method was still successful in detecting the manufacturing errors. ANSYS is used to model both free and embedded PZTs to simulate piezoelectric materials under various conditions. Free PZTs are modeled in both 2D and 3D simulations. Embedded PZT models with no damage and both non-destructive and destructive damage are simulated in 3D. ANSYS proved to be highly accurate when modeling a free PZT in both 2D and 3D models. The embedded PZT models with no damage and destructive damage showed promising results, though it had a frequency shift with respect to the experimental data. The simulation of non-destructive damage also showed promising shifted results, though in some areas it was slightly erratic.