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

本项目将对两种应用最广泛的铁电陶瓷进行冲击型加载条件下的实验，以进一步发展铁电动态断裂理论。铁电陶瓷在先进的技术应用中有着广泛的应用，并且由于它们在给定机械负载时能够提供电信号而被认为是智能材料。通过利用这种独特的机电效应，这些材料可以作为传感器和执行器，并在广泛的工业和民用系统中被发现，包括：运输燃料喷射器，结构健康监测装置，火箭发动机和微阀，仅举几例。这些材料的一个主要问题是它们很脆，容易破裂或断裂。虽然有大量的理论来帮助描述这些材料如何在已知的加载条件下断裂，但很少有实验数据和断裂分析来探索铁电陶瓷在冲击型加载条件下的断裂。新获得的知识将帮助工程师和设计师了解这些智能材料在复杂的动态加载条件下是如何断裂的，这将反过来用于利用智能机电效应来减轻损伤，从而提高实际应用中的鲁棒性和功能。该教员还将在Drexel的“介绍女孩到工程日”上主持实验力学学习体验，并培训本科生研究学者。本研究的目的是利用全场实验测量技术确定铁电陶瓷在瞬态混合模式加载条件下的各向异性动态机电响应。这一目标将在现有的动态断裂和压电场理论、有限元建模和显微镜的支持下，通过加强实验研究来实现。在不同的电学和力学边界条件下，对极性和未极性、掺杂和未掺杂的钛酸锌铅（PZT）和钛酸钡（BaTiO3）进行冲击断裂实验。高速成像测试期间的全场变形测量将用于扩展混合实验-计算分析，提取相关的裂纹尖端能量，包括耦合机电响应，并探索这些独特机电材料的有意义的断裂准则。迄今为止，线性压电断裂力学的理论基础已经成功建立，机电裂纹尖端场和电裂纹面边界条件作用的重要分析方面也已经建立。同时，没有大量的动态裂缝实验来证实现有的理论，并挑战分析假设的物理基础（或缺乏物理基础）。这项工作的实验和分析的结果将填补现有的知识空白。

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.