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式加载条件下的实验，以进一步发展动态铁电断裂理论。铁电陶瓷在先进的技术应用中有着广泛的应用，由于其在机械载荷作用下能够提供电信号，因此被认为是智能材料。通过利用这种独特的机电效应，这些材料可以用作传感器和执行器，并在工业和民用系统中广泛存在，其中包括：运输燃料喷射器、结构健康监测设备、火箭发动机和微阀等。这些材料的主要问题之一是它们很脆，很容易因开裂或断裂而失效。虽然有大量的理论来帮助描述这些材料在众所周知的加载条件下如何断裂，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，这反过来将被用于利用智能机电效应来减轻损伤，从而增加实际应用中的健壮性和功能性。这位教师还将在德雷克塞尔的工程介绍日主持一次实验力学学习体验，并培训本科生研究奖学金。这项研究的目标是使用全场实验测量技术来确定铁电陶瓷在瞬变、混合模式加载条件下的各向异性动态机电响应。这一目标将以实验研究为重点，以现有的动态断裂和压电场理论、有限元建模和显微技术为支持。对极化和未极化、掺杂和未掺杂的钛酸铅(PZT)和钛酸钡(BaTiO_3)在不同的电学和机械边界条件下进行了冲击断裂实验。高速成像测试期间的全场变形测量将被用于扩展混合实验-计算分析，该分析提取相关的裂纹尖端能量以包括耦合的机电响应，并探索这些独特的机电材料的有意义的断裂准则。到目前为止，已经成功地建立了线性压电断裂力学的理论基础，以及机电裂纹尖端场的重要分析方面和电裂纹面边界条件的作用。同时，没有大量的动态断裂实验可以证实现有的理论，并挑战分析假设的物理基础(或缺乏物理基础)。这项工作中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.