EAGER: Development of an Experimental Methodology to Probe Crack Tip Chemistry and Electrochemistry

在美国，基础设施老化的问题越来越受到关注，这些应用中使用的金属，包括铝和钢，必须承受苛刻的机械载荷和腐蚀性环境条件。当机械载荷存在于腐蚀性环境中时，会发生被称为环境辅助开裂（EAC）的现象。 EAC是由于机械应力和外部腐蚀环境的有害相互作用而发生的材料降解，导致在低于预期的应力水平下产生裂纹，并且裂纹生长速度快于预期。检查损坏的常规安全检查是维护成本的一个组成部分，如果组件故障和寿命预测模型通过包括EAC的影响来提高准确性，则可以降低维护成本。EARLY概念探索性研究基金（EAGER）支持开发一种实验技术，可以直接探测和改变增长裂纹内的环境条件，提供一种工具来生成增强寿命预测模型所需的数据和知识。环境辅助开裂（EAC）通过裂纹尖端附近的腐蚀和机械过程发生。 因此，裂纹尖端条件的知识是至关重要的，以了解驱动EAC的机制。在大范围的材料系统和外部环境的裂纹环境的实验验证已经完成。该奖项下的工作将开发一种实验方法，用于探测和/或改变不断增长的EAC裂纹内的化学和电化学（pH值和电化学电位）条件，以实现短期和长期的研究计划，直接探测裂纹尖端条件，并了解广泛的合金和散装环境条件下的EAC机制。为此，研究小组将重新设计腐蚀疲劳断裂力学试样，使其具有小孔（直径为1 mm或更小），用于插入能够测量pH值和电化学电位的微电极或用于提取或注入电解质进行化学分析的管道。

Ever growing attention is being given to the issue of aging infrastructure in the United States, and metals utilized in these applications, including aluminum and steel, must withstand demanding mechanical loads and corrosive environmental conditions. When mechanical loads are present with a corrosive environment, a phenomenon referred to as environment assisted cracking (EAC) can occur. EAC is material degradation that occurs because of the deleterious interaction of mechanical stresses and an external corrosive environment causing crack initiation at stress levels lower than expected and crack growth faster than expected. Routine safety inspections to check for damage are a component of maintenance cost that could be reduced if component failure and life prediction models increased accuracy by including the effects of EAC. This EArly-concept Grant for Exploratory Research (EAGER) award supports the development of an experimental technique that can directly probe and alter the environmental conditions within a growing crack, providing a tool to generate the data and knowledge necessary to enhance life prediction models.Environment Assisted Cracking (EAC) occurs via corrosion and mechanical processes localized near the crack tip. Therefore, knowledge of crack tip conditions is vital to understanding the mechanism driving EAC. Little experimental verification of the crack environment over a wide range of material systems and external environments has been done. The work under this award will develop an experimental methodology for probing and/or altering both the chemical and electrochemical (pH and electrochemical potential) conditions within a growing EAC crack to enable both short-term and long-term research initiatives that directly probe crack tip conditions and understand EAC mechanisms in a wide range of alloy and bulk environment conditions. To do this, the research team will re-design a corrosion fatigue fracture mechanics specimen to have small holes (1 mm or less in diameter) used to insert micro-electrodes capable of measuring pH and electrochemical potential or tubing to extract or inject electrolyte for chemical analysis.