Dynamic Electromechanical Fracture of Ferroelectric Ceramics: A Full-Field Approach to Crack Tip Energetics

Colorado School Of Mines, Golden CO

Investigators

Abstract

This project will perform experiments under impact-type loading conditions on two of the most widely used ferroelectric ceramics, in order to further develop dynamic ferroelectric fracture theory. Ferroelectric ceramics have widespread use in advanced technological applications and are considered smart materials due to their ability to provide an electrical signal when given a mechanical load. By exploiting this unique electromechanical effect, these materials can function as sensors and actuators, and are found in a broad spectrum of industrial and civil systems including: transportation fuel injectors, structural health monitoring devices, rocket engines and microvalves, to name a few. One of the main issues with these materials is that they are brittle, and are susceptible to failure from cracking, or fracture. While there is a great deal of theory to help describe how these materials may fracture under well-known loading conditions, very little experimental data and fracture analysis exists that explore ferroelectric ceramic fracture under impact-type loading conditions. The newly gained knowledge will help engineers and designers understand how these smart materials break under complex dynamic loading conditions, which will in turn be used to exploit the smart electromechanical effect to mitigate damage, and consequently increase robustness and functionality in real applications. The faculty member will also host an experimental mechanics learning experience at Drexel's Introduce a Girl to Engineering Day and train undergraduate research scholars. The goal of this research is to determine the anisotropic, dynamic electromechanical response of ferroelectric ceramics under transient, mixed-mode loading conditions using full-field experimental measurement techniques. This goal will be achieved emphasizing experimental investigation, supported by existing dynamic fracture and piezoelectric field theory, finite element modeling and microscopy. Impact fracture experiments will be conducted on poled and unpoled, doped and undoped lead zicronate titanate (PZT), and barium titanate (BaTiO3) with varying electrical and mechanical boundary conditions. Full-field deformation measurements during tests from high-speed imaging will be used to extend a hybrid experimental-computational analysis that extracts relevant crack tip energetics to include coupled electromechanical response and explore meaningful fracture criterion for these unique electromechanical materials. To date, the theoretical fundamentals of linear piezoelectric fracture mechanics have been successfully established, as have important analytical aspects of electromechanical crack tip fields and the role of electric crack face boundary conditions. At the same time, no body of dynamic fracture experiments is available to corroborate with the existing theory and challenge the physical basis (or lack thereof) of the analytical assumptions. The outcome of the experiments and analysis in this work will fill that existing knowledge gap.